Updated August 25, 2025
What Are Roll Coaters?
Roll coaters are machines used to quickly and evenly apply liquids such as paints, oils, coatings, or adhesives to a substrate. Roll coaters can be simple or highly specialized and complex depending on the application and the setup. In industrial applications, roll coaters can be used with numerous materials like paper, wood, metal, and plastic.
Adhesive Roll Coaters
In particular, roll coaters are commonly used to apply hot melt or cold glue adhesives to a variety of substrates. Both hot and cold roll coaters allow you to evenly apply adhesives to flat-rolled goods using dipped or spray-on techniques. Depending on the type of hot melt roll coater you use, you can save a lot of time and reduce costs.
How Roll Coaters Work
Rolls coaters are used to evenly apply a material onto a substrate. The specific parameters and roll coating setup will depend on the exact application. Often, there is an application roll that distributes the coating onto the substrate as it travels across a conveyor belt.
The exact amount of the coating that is applied to the substrate will depend on the characteristics of the roller and the substrate. A blade or another roller is used to control the thickness of the coating. Roll coaters can be fine-tuned to meet whatever specifications the job requires. Fine-tuning allows tolerances to within thousandths of an inch, depending on the requirements.
The process of roll coating involves transferring a layer of coating from the surface of the rollers to the surface of the substrate. During application, the coating will split in a process known as film splitting, as part of it remains on the roller and the other part is applied to the substrate.
Roll Coater Coverings
Most coating rolls have some kind of covering that offers various resistance properties. Three of the most common types are:
#1 - Nitrile
Nitrile is a Food and Drug Administration (FDA) approved synthetic rubber coating used in the food and pharmaceutical industries. The roller core is preferably made from stainless steel to help minimize further possible contamination.
#2 - Ethylene Propylene Diene Monomer (EPDM)
EPDM synthetic rubber has excellent resistance to heat and chemicals. Manufacturers save costs by simply applying a coat, then grinding it down to the correct tolerance of the roll coating machine.
#3 - High-Release Silicone
Silicone offers excellent heat resistance and provides high release. These silicone coatings are used when applying adhesive to plastic film or paper. High-release silicone costs more than other types.
The Five Most Common Types of Roll Coaters
The five most common types of coaters used for adhesives are the gravure, die, reverse roll, flex bar, and rod.
Gravure
The gravure coater has an engraved gravure roll with a pattern that determines the exact amount of adhesive delivered. An applicator - a pressurized head or a pan, for example - applies the adhesive to the roll.
Die Coaters
A die coater pumps adhesive through a die and transfers it to the web, supported by the backup roller. The coat weight determines the speed of the pump. Die coaters are used in label production.
Reverse Roll
Reverse roll coaters have an applicator roll, a rubber-coated backup roll, and a metering roll. The substrate and adhesive are fed in opposite directions.
Flex Bar
In a flex bar coater, the applicator roll picks up the adhesive coating from a pan and meters it between the flex bar gap and the applicator. Flex bar coaters often apply tape.
Rod
The rod coater has a rod, a pump, a multi-chambered pan, and an applicator roll. The coating flows into the center part of the multi-chambered pan at a constant rate. The overflow spills into the other two pans. The overflow will pick up and wash out any debris that might drop into the center pan adhesive liquid. The applicator picks up the adhesive from the center pan, transfers it to the web, and continues to the rod. The rod's size determines the film thickness before it is applied to the substrate.
Gravure, die, and reverse roll work best for hot melt. All work well for solvent- or water-based adhesives.
Selecting an Adhesive Roll Coater
Choosing the right adhesive coater is imperative to getting the best results. When selecting a glue roll coater for your business, you should consider the following factors:
#1 - Type of Adhesive
The type of adhesive used specifically affects the materials used for the rollers and the reservoirs. The materials used in the construction of the machine can impact the way the adhesives react, either degrading the adhesive to a certain extent or fouling the machinery.
Hot melts, for example, need the machine or rollers to heat the melt before applying it to the product or material.
#2 - The Thickness of the Substrate
To configure the feed roll correctly, you must ensure the substrate comes into full contact with the coating roller so the film of adhesive will be consistent, but you do not want the coating to transfer to the feed rolls. If you have flexible substrates, like thin plastic film or paper, then you want a roll coater that uses a pressure roller or a dual feed system. Thicker substrates, such as wood, require a soft-faced roll coater system to ensure the entire surface is coated evenly.
#3 - Full Coat or Partial Coat
Depending on what part of the substrate you want coated - the entire surface, an edge, or a pattern - determine the type of roll coater machine to purchase. In addition to roll coaters that apply adhesive to the entire sheet or piece of substrate, some roll coating machines allow you to set a pattern while others only coat the edge.
#4 - Width of the Substrate
Your adhesive roll coater machine should be at least two inches wider than the surface you coat. This allows the entire surface to receive a full coat of adhesive, even when loaded crookedly.
#5 - Top or Bottom Coating and Handling
Which side of your substrate gets coated first also impacts your roll coater selection. Remember that after the material exits the machine, you must process it further, whether you are boxing, stacking, or sealing.
Coating the top portion first makes the substrate easier to handle, especially if it is going directly onto a conveyor belt to go to the next part of the process. The least expensive machines usually coat the bottom surface, making it necessary for someone to handle the substrate immediately once it leaves the machine. Glue contamination is always a concern, especially in sensitive environments like the food and beverage industry.
#6 - Cleanup
Use an adhesive roll coater that disassembles and cleans easily. Some need cleanup more often than others, depending on how continuously they are used. Some of the maintenance features to look for when choosing a roll coater include easily removable tanks, separate wash tanks, removable rollers, and a wash-down system for the rollers and tanks.
Adhesive Roll Coaters
Once you have a better idea of the type of roll coater you need, the next step is finding the specific product. Our team highlights a few cold glue and hot melt roll coaters that may work for your application.
Cold Glue Roll Coaters
Tabletop Cold Glue Roll Coater- This roll coater is designed for water-based adhesives and will apply glue from half an inch up to 36 inches. It is easy to clean and does not require tools for disassembly or reassembly.
Vera Cold Series Roll Coater- This cold glue roll coater is made of stainless steel and can have a roller size from 7 inches to 61 inches wide. Designed with versatility in mind, the roller can easily be placed at either the top or the bottom.
Hot Melt Roll Coaters
High Volume Tabletop Hot Melt Roll Coater- This roll coater comes in standard 6-inch, 12-inch, and 18-inch sizes, but you can order a custom size up to 50 inches. The reservoir holds up to a pound of adhesive per roll inch. Its simple start and heat-up procedure allows you to start using it almost as soon as you turn it on.
Hot Melt Top or Bottom Roll Coater- This versatile machine allows you to use it as either a hot melt roll coater or a top coater. It comes with a Teflon conveyor belt and a wide range of sizes. It can also accommodate just about any type of material.
Extra Large Industrial Roll Coater- For wide-area coverage, this roll coater could be for you. It can apply adhesive to substrates up to six feet and has a synchronized dual roller for consistent coverage. Customization is also available to ensure this product can meet your needs.
Troubleshooting Roller Coating Issues
Even when using a quality adhesive roll coater, issues can still arise during the roller coating process. The cause of each problem varies and can be hard to troubleshoot if you are not sure what you are doing. To help, our team of hot melt experts is sharing a few of the most common roll coating issues as well as how to fix them.
Cratering
Roll coating cratering - or pitting - happens when bubbles form in the adhesive and then break, creating concave depressions in the film surface. Fisheye cratering is when silicone compounds create small craters in the substrate. Sometimes cratering can reach all the way to the surface of the material.
Cause: Oil, grease, and sometimes dirt on the substrate surface
Solution: Prime the surface prior to applying the adhesive or use a higher-quality adhesive
Crawling
Roll coater crawling happens when the liquid adhesive can't completely cover the substrate due to low surface energy. The adhesive can't fully wet the material and consequently, pulls back. This forms droplets and leaves some portions of the substrate without glue.
Cause: Low surface energy substrate
Solution: Raise the surface energy of the substrate by removing oils and other contaminants, or use adhesives specifically manufactured for low surface energy substrates
Foam
Foam may already be present in an adhesive before using the roll coater. If you use gravure coating, the gravure process could also force the formation of foam.
Cause: Air enters the adhesive
Solution: Prevent air from entering the adhesive before use, and minimize the use of surfactants or substances that reduce surface tension in the adhesive
Orange Peel
Orange peel is rough, irregular patches throughout the surface of the adhesive.
Cause: The binder doesn't flow evenly across the substrate's surface
Solution: Use an adhesive with a different viscosity
Delamination
Delamination is the separation of the coating from the substrate or from other layers of the coating system.
Cause: The surface is not clean, or the adhesive is not compatible with the substrate
Solution: Clean the surface of the substrate thoroughly and check the manufacturer's guidelines to ensure compatibility between the material and the adhesive
Roll Coater Maintenance
Do not forget about performing regular maintenance on your roll coater machine. You can leave most hot melts or liquids that don't dry, like oils, on a machine, but you must clean out most other types of glue from the machine. Liquid rollers can clog, or chemicals can coagulate and foul the interior workings. For larger roll coaters, you can use an acid flush procedure to thoroughly clean all parts.
Need Help?
If you have any questions about next steps or what is right for your specific needs, feel free to contact us. With over fifty years in the adhesives industry, we have a team of hot melt experts who are happy to answer your questions.
