Buschman Creates Five Powerful New Coating Calcu... Buschman Introduces Drawdown Boards for Laborato... Buschman Introduces New Metering Rod Installatio...
The Advantages of Smaller Metering Rods: Balanci... How to Monitor and Measure Metering Rod Service ... How to Use Masking Film to Control Dry Areas of ... More…

3 Reasons to Control Pre-Coat Flood in Metering Rod Coating

Written by Ross DeFelice

A little-known secret to defect-free rod coating is often directly linked to the pre-coat flood volume before the rod.

Metering rod coating is essentially removing excess coating by doctoring off the surplus. Whether using an applicator roll, spray, fountain, dip tank, or slot die, controlling the pre-coat volume before the metering rod is essential and often overlooked or neglected over time. Too often in rod coating users turn to mechanical and/or chemical Band-Aids, when what is actually required is to monitor, minimize and control the pre-coat flood volume before the rod.

Consider this: How much are you asking of the rod to remove: 200%, 400%, 600% perhaps 1000% of target volume? Who controls this? Who decides what’s best?

See diagram below:

Customers often ask about ideal pre-coat volume. The answer is not always uniform for all coating applications. We customarily suggest a good starting point of 400% pre-coat flood over final rod volume, though this is just a starting point and converters often need to adjust up or down to meet their application specific coating operation.

Why is pre-coat flood volume important?

  1. Let’s start with the obvious: Not enough pre-coat flood will starve the substrate. You need enough pre-coat volume to ensure even wetting without starvation streaks and striations. (Wetting is when the comb lines in the coating on the substrate disappear.)
  2. Excess pre-coat volume can cause other coating defects. The more you ask the rod to remove, the higher the risk for unwanted defects:
    1. If the coating is shear sensitive, varying degrees of viscosity can hinder efforts. Viscosity that’s too high risks failure to wet out before the coating dries.
    2. The problem is often exacerbated when coating onto non-absorbent substrates such as films and foils, which are unforgiving and often reveal apparent defects.
    3. Keeping the rod from hydroplaning is essential to maintaining control throughout the rod coating application. This is more apparent in high viscosity >600cps. If the rod rises from the substrate, the rod ceases to be volumetric and becomes hydrodynamic. When this occurs, the ability to change rods and forecast incremental increases or decreases based on thread size fails.
  3. Applying a narrow volume pre-coat flood range increases control and decreases the “corduroy” effect, which is a harmonic frequency effect found more so in lightweight films. It is patternistic and can traverse 4-10 threads or wires. The problem is often misunderstood and many users turn to dual rods to eliminate the corduroy pattern. However, in our experience, when the pre-coat volume is minimized, the harmonic corduroy pattern often is eliminated.

If instrumentation controls to pre-coat flood are limited, visually inspect the run off. In most applications, the desired run off is similar to a heavy rain or drizzle effect. If the coating coming off the rod looks like a solid curtain (think Niagara Falls) without a break, you may be expecting too much of the rod.  Once you have located the ideal narrow range for the pre-coat flood volume write it into your operational methods sheets to keep the application within that range.

Buschman has helped many of our customers identify, locate, and adapt to the range that is right for a particular application. We also have engineered a variety of customer-specific threaded rods to optimize customer-specific rod applications. We can help you run an engineering experiment on your rod coater to determine the best pre-coat flood range for your application.

To minimize potential problems, pursue methods to control the pre-coat flood before the rod. You’ll be glad you did.

Looking for more information about metering rods, rod holders, or coatings?

Ask us! Buschman's experts are here to help. Contact us with your questions.

Testimonials

Buschman Delivers Consistent Quality

“It’s all about the quality of the rod we’re using to meter the product onto the paper. Without the proper rod application, your coating isn’t going to lay properly. Buschman has a quality product that performs the way it’s supposed to and they get it to us when we need it. They consistently meet all our expectations.”

Coated Products Manager
International Packaging Paper Producer

Trusted for Superior Quality & Service

“The number one reason we work with Buschman is the product quality. The second reason is service. If we are running low on product, they’ll turn the world upside down to get us what we need. Buschman delivers product performance and customer service.”

Coated Products Manager
Prominent Packaging Paper Producer in Northern US

The Supplier of Choice for Coating Rods

“The quality of Buschman’s products is excellent. In the ten years we’ve been purchasing coating rods from them, we’ve had maybe two or three issues and they are minor issues. For the number of coating rods we purchase, that’s incredible. Their quality has been so high and they work so well with us that we don’t even consider looking at other vendors for our coating rod needs.”

Purchasing Manager
Leading Packaging Paper Producer in Southern US

Top Ratings for Quality Products & Service

“Since we’ve opened the doors here, we’ve worked and had a great partnership with Buschman. They are a very highly reputable company and we’re proof of that as a happy customer. We have a lot of trust and faith in Buschman, so we just give them gold stars.”

Production Manager
Large Multinational Packaging Paper Plant

Consistent Quality

“Consistent quality is the number one requirement for me and that’s what Buschman delivers.”

Senior Manager
Multinational Paper Mill in Australia

Quality, Performance & Responsiveness

“Buschman’s service is outstanding. You don’t find that anymore. If we need something custom tweaked through Buschman, they’re more than willing to sit down with us and do so. They have quality, performance, and great delivery time and they’re very responsive to our needs. They go above and beyond. They’re first class.”

Coating Manager
Leading U.S. Packaging Paper Plant

Going Above & Beyond for Customers

“We’ve used Buschman for well over ten years. Buschman goes above and beyond: The quality of materials, the finished goods, the on-time deliveries. They go out of their way to get us the product we need.”

Coating Manager
Large Converter in Northern US