New Era manufactures a wide variety of web coating equipment, including gravure, offset gravure, differential offset gravure, slot die, reverse roll, knife over roll (KOR), dip and squeeze, mayer rod, spray, slide and five roll coaters to name a few. Every coater we build is purpose designed for our customers’ exact process conditions. Our coater designs range from standard construction with manual adjustment for process parameters, to fully automatic, closed loop systems controlled real time by online thickness gauging systems. These closed loop systems can control coater pump speeds, roll speeds and gap profiles utilizing servo positioned gap controls. New Era fabricates coater machinery for water based, solvent and hot melt processes and we have the ability to trial most coatings on our pilot line. Please see below for a brief description of common coater types that New Era manufactures:
Gravure coating and its many variants offer a coating method which delivers a pre-metered amount of coating solution to the substrate. In direct gravure coating an engraved roll is used to control the amount of coating that is delivered to the web. This engraved roll (often referred to as the gravure or applicator roll) typically features a steel or ceramic surface into which a cell pattern is engraved. Coating is introduced to the surface of the engraved roll either via a pan that the roll is partially submersed in or by an enclosed applicator head that holds the coating against the roll. Once the coating is introduced to the rotating roll’s surface, a blade is used to wipe off any excess. As the roll continues to rotate the coating is introduced to the web at a nip point formed between the engraved roll and a rubber covered backing roll, with both rolls rotating in the same direction and at the same speed as the web. The coating is transferred to the web by the nip force between the rolls. The size and shape of the cells are the primary factor in determining the amount of coating that is delivered to the web. However, other factors such as the rubber thickness and hardness, doctor blade construction, angle and pressure, coating viscosity, web properties and surface and operating speed also affecting the coating laydown. Under a given set of operating parameters the coating application rate of a direct gravure coater is highly repeatable.
A variation of direct gravure coating is reverse gravure coating, where the gravure roll rotates opposite the web. The coating is split between that which is transferred to the web and that which remains in the gravure roll’s cells. Unlike direct gravure, where it is important to wipe the surface of the gravure roll clean, light doctor blade pressure is often used in this method so that coating stays on the surface of the gravure roll (as well as in the cells). In addition to the factors mentioned for direct gravure coating, the laydown rate for reverse gravure coating is affected by the gap between the rolls and the speed of the gravure roll. The speeds and coating thicknesses are similar to those shown above for direct gravure coating. However, it is typical that the coating viscosity is slightly higher (0.01 – 2 Pa.s). The gravure is easy to operate, is fairly low maintenance, has a good speed range, handles a fairly wide viscosity range and gives highly repeatable coating rates.
Offset gravure coating is a variation of the previously described gravure coating where an intermediate roll is used to transfer the coating from the gravure roll to the web. This intermediate roll, which is often referred to as an “offset” roll, is rubber covered and is located between the gravure roll and the backing roll, which now features a hard surface such as chrome plated steel, with the web passing through the nip formed between the offset roll and the backing roll. The previously described features and hardware associate with the gravure roll for direct gravure coating still apply. The size and shape of the engraved roll’s cells are the primary way of determining how much coating is delivered to the offset roll, which typically runs at the same speed as the gravure roll, with one roll turning clockwise and the other counter clockwise. The speed ratio of the offset roll to the web as well as their relative direction with respect to each other greatly affects the amount of coating applied to the web. The offset gravure coater has a good speed range, handles a fairly wide viscosity range and is good for changing coating laydown rates.
Slot Die Coaters
Slot die coating enables even distribution of a pre-metered coating to be applied to a substrate. In many cases a slot die can increase production speeds and improve coat weight control. The slot die is used in conjunction with a rubber or precision steel backing roll to apply coating to the substrate. Our precision die positioners can allow for a wide array of flexibility with regard to die setup, including die to roll gap, die angle of attack adjustment as well as die position with relation to the backing roll. A slot die can be used to apply coating directly to a supported or unsupported substrate, to a transfer roll or in a curtain configuration. Slot dies can be used when coating aqueous, solvent based and hot melt coatings and can apply coatings from a range of 1 micron thick (wet) up to 50 mils. In conjunction with the solution delivery system, slot dies can be used for patch coating. In addition to patch coating, shims can be used to allow for lane coating. With a wide viscosity and speed range, excellent temperature control and coating thickness accuracy, slot die coaters are an extremely effective coating method for many processes.
Reverse Roll Coaters
A reverse roll coater is a multi-roll coater that uses a series of rolls to pre-meter and apply a coating to the web. A typical reverse roll coater features three rolls, all rotating in the same direction. In a nip fed reverse roll coater the coating is puddled in the gap formed between the metering and applicator roll, both of which are of precision steel construction. A layer of coating forms on the surface of the applicator roll as it rotates away from the coating puddle. The thickness of this layer is determined by the gap between the metering and applicator rolls, as the coating passes between them. As the coating continues to rotate about the applicator roll it is wiped onto the web, which is traveling in the opposite direction on the rubber covered backing roll. A variation of this design is a pan fed reverse roll coater. In this arrangement, the coating resides in a pan in which the applicator roll is partially submersed. As the applicator roll rotates, it picks the coating up out of the pan, passes it through the gap formed with the metering roll and then delivers it to the web at the backing roll. This arrangement is particularly useful with coatings near the lower end of the viscosity range where holding them in the nip between the rolls would be difficult. The amount of coating that is delivered to the web is controlled by the gap between the metering and applicator roll as well as the relative speed of the applicator roll and web speed. The greater the gap, the thicker the layer of coating. The greater the speed of the applicator roll, the more coating that is delivered to the web. The reverse roll coater has wide coating thickness and viscosity ranges and is good for changing coating laydown rates.
Transfer Roll Coaters
Transfer roll coaters are typically used for applying thin coating layers, particularly as required for 100% solid coatings. These coaters typically use 4, 5 or 6 rolls, with each consecutive roll running in the opposite direction of the previous one. The rolls in the stack alternate from rubber covered to steel surface rolls (typically chrome plated). The web is supported by the last roll in the series, which is referred to as the backing roll and runs at web speed. The web passes between the backing roll and the next to last roll, referred to as the applicator roll, which also typically runs at web speed. The coating is typically placed in the gap between the first two rolls, with the first roll, referred to as the metering roll and the second roll both rotating away from the coating puddle. Each roll from the metering roll through the applicator roll runs faster than the previous one, with the coating continuing to be reduced in thickness by the combination of the gap between the rolls and the increase in speed. The coating is transferred from the applicator roll to the web as it passes through the gap with the backing roll. The transfer roll coater has a very good speed range and has fairly wide coating thickness and viscosity ranges.
For added flexibility, most coater types that we manufacture can be designed as modular coaters, allowing multiple coating methods in the same station, or cartridge coaters, enabling quick change of coating heads for offline cleaning and setup. The degree of flexibility on these designs is up to the customer, but these portable coaters can be completely removed from the web line, or in other cases, utilize common base frames where commonality of components between coating methods is desired. These designs are available with varying degrees of sophistication, with the more advanced models featuring completely tool-less module changes.
Knife Over Coaters
Knife over roll coaters utilize a precision ground knife blade loaded against precision gap adjustment assemblies to form a gap between the coating knife and backing roll which is typically a precision steel roll. One area where knife over roll coaters are extremely useful is in processes where total product thickness uniformity is of great importance. The reason for this is regardless of the substrate uniformity, the precision gap between the coating knife and the backing roll will result in a total product thickness which is extremely uniform. This is in contrast to pre-metered coating applicators which will provide a uniform coating thickness, but depending on the base substrate may result in a finished product with thickness irregularities. Coating is generally fed into a coating hopper or backup board complete with adjustable edge dams to set the coating width. The feed head and or a coating distribution method within the coating in the hopper are important depending on the coating to help prevent coating defects and thickness variations. Knife over roll coaters are ideal for high viscosity coatings as well as applications with high coat weights.
Hot Melt Coaters
Many of the coating methods described elsewhere in this section can also be built to apply hot melt coatings. Hot melt coatings are applied to the substrate at elevated temperatures and bond to the web material. These coatings, typically delivered to the coater at temperature, can be applied via hot melt slot die, smooth roll, hot melt gravure or knife over roll and knife over table coating application methods. After coating, they are typically cooled or cured prior to further processing. Special care needs to be given to the type of release coatings on downstream rolls which will contact the face side of the coating. These coaters can be run at a wide range of speeds and coating thicknesses.
There are many other coater configurations that have been developed to meet a wide variety of coating applications. Many of these are either hybrids, variations or combinations of the previously described coaters. One such example is a dip and squeeze coater which in its simplest form is similar in design to the kiss coater except that the web passes beneath the roll where it is dipped into the coating being held in the pan, then through a set of squeeze rollers. Like the kiss coater, it is typical that a metering device/system such as a mayer rod, notch bar or smoothing bar follows the application of the coating. Another example is a coater that uses a die to feed a coating to the surface of an applicator roll, which then transfers the coating to the web. Still another example is commonly referred to as a Levelon Coater which can be considered a combination of kiss and reverse roll coating, where the coating is applied to the web by a kiss roll and is then metered off as the web passes between a backing roll and a reverse running metering roll.