Coater Diagrams

Before you begin your next coating project, knowing what type of equipment you have and understanding a little bit about how your coater works are helpful. Recognizing your coating equipment style is essential for working with ACC Coatings because we design and manufacture a coating technology specifically for your equipment.

Whether you purchased specially manufactured coating equipment or you use a makeshift coater setup created in-house, coaters fundamentally align with one of the following styles:

• Roll coater (traditional or nip style)
• Dip/squeegee coater
• Offset or “kiss” coater
• Spray-style coater

This page discusses the various styles so you can identify the type you have as closely as possible. We also offer some pros and cons of each coating type to help you decide what style to purchase when you need new equipment.

The roll coater can be configured horizontally or vertically. The coating is flooded into the nip between the “doctor roll” and the “applicator roll.” The applicator roll is commonly made of rubber, nitrile, urethane or EPDM. The applicator roll has a recommended surface roughness value of 15 – 20 Ra. The applicator roll recommended durometer (hardness) is 50A – 80A.

The impression between the two applicator rolls or the applicator roll and the backing roll applies a thin, uniform layer of coating. A higher impression (smaller gap) typically applies less coating, while a lower impression (larger gap) lays down more coating. The impression depends on the durometer and the roughness of the rolls.

PROS

• The roll coating process allows you to apply a thin layer of coating
  • Capable of applying high solids/high-viscosity solutions
• Can apply on one side or both sides of sheet
  • Cost-effective
  • Utilize two types of coatings simultaneously (e.g., an anti-fog on one side and a silicone coating on the other)
• Usually has a covered sump to keep coating from contamination and evaporation    

CONS

• When not driven, the applicator/doctor rolls can slip, causing unwanted patterning or inconsistent application
• Damage or wear to applicator rolls can be very apparent on the sheet

The sheet is usually submerged or flooded with coating and then “squeegeed” off by metering rolls. A higher impression (smaller gap) reduces the amount of coating applied. A lower impression (larger gap) lays down more coating. The impression is dependent on the durometer (hardness) and roughness of the rolls.

The squeegee roll recommended roughness value is 15 ­­­–­ 20 Ra. The recommended durometer is between 50A and 80A.

PROS

• Features a simplistic coating mechanism
• Applies coating across the entire web
• Coats both sides of the sheet simultaneously
• The coating is constantly agitated           

CONS

• Usually, coating can be applied only to both sides of the sheet; cannot isolate one side
• Overapplication is common, even with adequate squeegee rolls
• Sump usually necessitates large volumes of coating
• Coating in the sump is exposed to contamination and evaporation

This coater is similar to the traditional roll coater except that it lacks a backing roll to create an impression; instead, the impression comes solely from the tension of the sheet. The impression between the doctor roll and applicator roll helps determine the amount of coating applied.

The applicator roll recommended roughness value is 15 –­ 20 Ra. The recommended durometer is 50A – 80A.

PROS

• Able to apply thin layer of coating
• Can apply on one side or both sides of sheet
  • Cost-effective
  • Utilizes two types of coatings simultaneously (e.g., an anti-fog on one side and a silicone coating on the opposite side)

CONS

• The coating is not metered off by the impression of a backing roll
• Maintaining a uniform or consistent coating application is difficult
• Any variation in web tension or sheet thickness can cause issues

The coating is sprayed or atomized onto the sheet with the use of nozzles or rotary spray discs. Sometimes the coating is metered off utilizing a smoothing roll, but this is not typical. The speed of the line, the nozzle opening size, the pressure and nozzle placement dictate how much coating is applied.

PROS

• No applicator rolls to wear out over time
• Can apply to one or both sides of the sheet           

CONS

• The high sheer from atomization often causes foaming
• The spray coating process can be messy, raising issues around safety hazards
• Creating a uniform layer of coating is very difficult without a smoothing roll