Medical patch gels with custom coating technology

Employees at Des Moines, Iowa-based Katecho Inc. manufacture hydrogel-based pads for use with a variety of medical devices, which include single-use, sticky pads used with monitoring electrodes – such as electroencephalogram (EEG) and electrocardiogram (EKG) devices – and wound dressings for treating first-response injuries.

Producing the company’s latest hydrogel pad required a unique, custom solution to control gel thickness and subsequent shrinkage and to introduce a supporting scrim between a top and bottom liner. Multiple trials and tweaks were needed to achieve the desired specifications. Even then, producing a wound roll of gel had its own set of challenges.

Not your common coating

Katecho has engineered more than 30 different hydrogels – water-based mixtures with gel-like consistency – most formulated to meet requirements of special applications and medical devices. Others are designed for use as first-response wound dressings.

Katecho wanted to double web widths to 23", all while maintaining a tight-tolerance coating thickness run-to-run of 0.001". The process required:

• Application of hydrogel solution to Mylar web
• Non-woven scrim web application to provide structure to the gel
• Hydrogel curing
• Web cooling
• Polyethylene web top liner application
• Slitting, winding into manageable rolls

Founder Lorne Scharnberg knew this could only be achieved with a highly engineered, custom coating machine, and he found the solution with Faustel, a Germantown, Wisconsin-based original equipment manufacturer (OEM) of custom coating, laminating, and winding machinery.

Engineering the perfect process, however, was anything but simple or conventional.

Faustel employees built the coating line in their plant, but testing and refining was done at Katecho. Once installed and tested, the real production challenges surfaced.

Unconventional coater

When applied to the base web, hydrogel shrinks in width and increases in thickness. This starts from the edges of the laydown and works its way inward until the scrim is introduced. Support from the scrim halts this undesirable process. Consequently, coating thickness must be varied across the width to accommodate the gel’s physical changes. A conventional coater would not work.

“Hydrogel material clearly presented a coating challenge. After examining how it changed through the curing process, we determined the ideal coating method was a custom slot die that could be adjusted for casting variable thicknesses at the outer edges,” says Sam Gely Jr., the Faustel project engineer who spearheaded the machine development and subsequent modifications.

Once the equipment was installed, Gely began trial runs, making adjustments onsite to achieve the ideal casting – a slightly wider coating that was 0.008" thinner at the outer edges. This countered the undesirable characteristics, and the results were within customer specs.

The structural scrim material was added next. Running the scrim web had its own handling challenges, Gely notes.

“Too much tension would stretch this nonwoven mesh-type material, causing it to neck down, which narrows the operating window for a tension range,” Gely explains.

The answer: lower-range-tension load cells. With tension cells applied, the tension zone could operate at the high-resolution control of 1.2 lb to 1.3 lb. In addition, operators could adjust the tension to a fraction of a pound via a touch-screen control.

Such processes do not allow for high-speed production. Running at 450ipm was acceptable in achieving the exact quality output Katecho wanted. Lower speeds, however, affected the web guiding – used with each of the three unwinds, before the laminator, and on the rewinder.

The loop response between the edge detectors and the web guides was thrown off, causing the web to oscillate. The systems needed to be dialed down. AccuWeb Inc., a Madison, Wisconsin-based web guide OEM, provided the original web guiding systems. Engineers responded by developing response parameters that could be adjusted using the Micro 1000 controller. Infrared-type edge detectors also proved effective in sensing the edge of the porous scrim web.

The cure

Once cast with an embedded scrim web, wet hydrogel is cured using a series of UV lamps. Bethel, Connecticut-based Electro-Lite Corp. provided UV curing stations with four lanes the length of the web with 13 lamps per lane.

Each bank has 400W UV bulbs to cure specific hydrogel chemistries. Bulbs operate either full-on or in stand-by mode during non-production times. A sensor runs the length of each UV lane, making sure each is generating the desired amount of UV energy.

Katecho Production Director Chris Gunsaulus says, “Ultimately, the desired state of hydrogel curing is achieved through control of the web speed. The entire UV curing section stretches 12ft, and that adds a significant amount of heat to the entire web.”

Because of this, operators perform tests and trials to establish ideal parameters.

The cool down

Following curing, the web needs to be cooled from the UV lights and the heat generated by the hydrogel as it cures. Winding is the next step.

“Too high web temps can negatively impact the poly film liners, causing them to distort, resulting in deformation of the wound rolls,” Gely notes.

A custom-engineered cooling plate recirculates cooled liquid through embedded coils, removing heat from the web as it slides over the plate for first-stage cooling. Following the cooling section, the final top poly liner is laminated to the coated web. The web then travels across a large heat transfer roll, often called a chill roll, to remove more heat prior to final winding.

To conserve floor space, Faustel placed the unit’s unwinder and rewinder at floor level and elevated the coating and cooling sections.

Winding a gel roll

The original machine was designed to continuously wind single rolls. A turret in the rewind section rotates a new core into winding position as the active roll reaches its target size. Most continuous winding operations use a knife-driven system to cut the web during transfer, however that wasn’t practical on the hydrogel line due to low web tensions. Instead, during web transfer, a cutting knife traverses quickly across the web, making the clean cut. The cut web is then applied to the new core where double-sided tape has already been applied.

Not long after startup of the new equipment, Katecho wanted to add a slitting section to wind three separate rolls. The low web speed prevented the use of conventional shear-type slitting systems, but a crush-cut system from Camas, Washington-based Tidland Corp. worked. A blunt-edge knife rides over the web, pinching the web apart as it is pressed against an anvil plate underneath.

Gunsualus notes other challenges in minding gel-coated web.

“Too much web material with not enough tension in the wound roll would cause the roll to deform under its own weight. It could also deform more easily during handling once off the machine. As a result, the winding tension window was very narrow,” Gunsualus says.

Wound roll sizes are typically limited to 250ft, depending upon customer specifications.

The wrap up

To remove the heavy rolls from the winder, Katecho engineers added a custom pneumatic manipulator from Positech Corp. in Laurens, Iowa. The unit’s arm positively locks onto the rewind shaft so operators can safely transfer finished rolls onto the manipulator arm. The manipulator then positions rolls vertically or horizontally for protective wrapping, palletizing, or transfer to another converting operation.

Some of Katecho’s hydrogel rolls are shipped to customers who perform additional converting. Other customers look to Katecho to fully convert, package, ship, and inventory ready-to-use product. None of the finished products carry the Katecho name.

As far as Scharnberg is concerned, “It’s all just part of running a first-class operation.”

AccuWeb Inc.
www.accuweb.com

Faustel
www.faustel.com

Katecho Inc.
www.katecho.com

Positech Corp.
www.positech.com

Tidland Corp.
www.maxcessintl.com/tidland