Function/Description

With knife systems, the coating paste is applicated onto the carrier or the substrate with a knife. Depending on the counterpiece to the knife, roller knives and air knives are distinguished. The knife bar of modern coating plant is equipped with several coating knives and is turnable according to the socalled revolver principle. This facilitates a quick change of the knives, especially of the roller and the air knife. All application systems are equipped with either manually or powered adjustable side scrapers.

In some cases, the side scrapers are completed to a closed paste basin with a front plate, which is necessary especially when low-viscous coating pastes are concerned. Depending on the thickness of the coat to be applicated, on the way of the knife´s configuration and the viscosity of the paste, knives of different profiles are used.

With knives, the thickness of the coat is defined by:

• Distance between knife and substrate
• Kind of the substrate to be coated
• Kind and form of the knives
• Angle of the knife
• Position of the knife
• Viscosity of the paste
• Speed of the web

For air knives it is especially the web tension that influences the thickness of the coat.

Function/Description

In case of the engraved roller system, also called kiss coating system, the carrier material is led through between two rollers. From a dipping basin, the application roller passes the paste onto the substrate. The coating paste quantity is determined by the design or the raster of the applicating roller.

The surplus paste on the applicating roller is scraped off by a knife. A a lacquering unit can be integrated directly into the coating machine or as a separate coating system. Coating layers of between 2 and 10 µm can be applicated by the lacquering process.

In most cases, acrylic or PU- varnishes are applicated. The application of e.g thin varnish layers onto already coated material is mostly being done with engraved roller systems.

Examples

Function/Description

The application of the coating raw material by a die system is another alternative. A die is a closed application system, consisting of a die chamber, into which the coating raw material is pumped. For each coating raw material, the design of the die is evaluated regarding the raw material´s flow behavior. This guarantees the raw material´s even outflow out of the die lips.
A special micro pump feeds highly precise meterings of the coating material to the die. The coating weight can be precisely defined by the speed of the pump. Also the die lips and the speed of the web influence the coating weight.

The advantages of the die system are:

• a closed system, advantageous for the processing of solvent-based systems and with regard to the cleanness of the application
• depending on the viscosity of the raw material, very thin layers of under 5 µm can be realised, but layer thicknesses of up to 300 µm are also possible
• realisation of intermitting coatings
• the coating can be realised either with a contact of the die to the substrate, but also contactless.

The use of the die technology grows constantly, as the application of coating materials needs to become increasingly precise.

Examples

Function/Description

The difference between a standard die system and the Curtain-Coating System is, that there is no contact between the die and the web while the coating raw material is applicated.

After flowing out of the die, the coating film falls like a curtain onto the substrate that moves through below the die. The advantage of the contacless coating is a more even and, depending on the viscosity of the coating material, much thinner coating film

Examples

Function /Description

In a foulard, the coating or impregating of the substrate is realised by dipping it completely. Depending on the viscosity of the coating raw material and on the substrate´s structure, the coating compound either attaches superficially to the substrate or it permeates completely through it. Thus, the texture of the substrate and the coating viscosity mainly define the application weight.

After the dipping, the surplus coating amount is squeezed off or scraped off. This can be realised between two rollers, the so-called squeezing rollers or by cleaning knives. Exemplary applications are: The impregnation of an open-structured substrate before the coating process or the complete dipping of glass fibres or glass non-wovens (for the production of circuit boards). In this case, the surplus coating raw material is evenly scraped off by bilateral polished rollers.

Examples

Function/Description

This system is called "Reverse Roll Coater" because the applicating roller moves in the opposite direction to the web´s moving direction. Principally, this system consists of three roller that are either arranged vertically align or in an S-shape. The coating raw material is placed between the two upper rollers and is kept in the roller gap by double-sided limitating knives.

The coating weight is determined by the distance between the upper metering roller and the application roller, but also by varying the roller´s speed. The lower roller that guides the material mostly is a rubber roller. The coating roller transmits the plastic film on it in counter direction onto the substrate. Each roller is powered separately. By default, the speed of each roller can be varied by approximately 50%. The rotating direction of the upper roller can also be adjusted to the counter direction.

Because of the various possible settings, the application can be defined optionally by the gap distance, the rotational speed of the rollers and the relative roller speed to each other. Also the thickness of the coating layer can be influenced by changing the relative speed of the rollers to each other and the relative speed between the applicating roller and the substrate. The Reverse-Roll-Coater is used for the processing of pastes with a low viscosity and a good flow behavior. Dilatant pastes, which means coating raw materials the viscosity of which increases proportionally to high shearing forces, as well as highly viscous pastes cannot be processed because of the high shearing forces that appear. However, very thin applications can be realised with this technology.

Examples

Function/Description

The coating system called Kisscoater for materials with a low or medium viscosity which has been used as application system for quite a long time now, has been advanced by COATEMA. Basically, the system consists of an application roller and two guiding rollers.

The system offers the user a multitude of adustment possibilities. The control of the coating unit can be influenced by the positioning of the guiding rollers and the web tension as well as by the proportion of the application roller´s speed to the plant speed. The positioning of the guiding rollers determines the contact angle between the applicating roller and the substrate. Here, a variation between a large wrap angle and the application of the coating raw material into the substrate and al small wrap angle and a linear contact between the substrate and the application roller.

With the linear contact, the coating raw material is only applicated onto the substrate´s surface. Apart from the adjustment of the contact angle between the application roller and the substrate, the quantity of coating raw material is determined by the speed of the application roller. Here, a higher speed in relation to the substrate´s speed entails a higher coating weight.

Examples

Function/Description

A 2 roller system is comparable to an engraved roller system. The difference lies in the structure of the roller. With the engraved roller, a structured roller is used to applicate the coating raw material, where as in case of a simple 2 roller system, a chrome-plated, polished roller is used.

The coordination of the coating raw material with the application of an unstructured roller is important. This technology is used when very thin layers have to be applicated.

Examples

Function/Description

In case of the 5 roller system, 5 rollers are collocated in horizontal direction to each other. By the highly precise distance of the rollers as well as by the absolute and relative rotating speed of the individual rollers to each other, the thickness of the coating film that is applicated through the first roller gap, flattens out increasingly. This is how coating films with a layer thickness of under 1 µm can be achieved.

Examples

Function/Description

The definition chamber knife or case knife means semi-or completely closed roller application systems. But in general, the coating paste is not fed to the application roller by dipping, but from chambers placed either in front of the application roller or from above. A closed or open paste basin which is placed in front of or on the applciation roller, guarantees a controlled feeding of the coating raw material.

The closed system facilitates the processing of volatile coating raw materials and is thus interesting for many technical purposes. With the case knife, the front and the rear side of the attached paste basin are each constructed as knives. These knives facilitate a pre- metering of the coating paste. The applicating roller may be a chrome-plated, polished roller or an engraved roller with a special design. The sideways limiters of the case attachment are latterally adjustable and can be used for an application across the whole width of the substrate. A lamellar desing can be achieved by using several limiters. The rotating direction and speed of the application roller are adjustable.

By the variable setting of the coating system described, diverse effects can be achieved when applicating the coating paste onto the substrate or rather the carrier. When highly viscous coating raw materials are concerned, the applicating roller is mostly used in the reverse operation to realise the greasing of the paste onto the substrate. Generally, the combination of roller and knife application guarantee an even and exact coat.

Examples