Introduction

Platens, Pallets, Shirtboards, Printing Tables, whatever you call them – they are the most important production accessory responsible for your product quality. Whether you are printing with the most expensive automatic on the market or the least expensive manual press, without a good pallet you can forget about doing quality prints. Pallets must be extremely flat & rigid, heat resistant and free of any surface defect in order to facilitate a high quality print. If any of these characteristics are not realized to there full capacity, the result is an obviously flawed print.

I'm sure that many of you remember as warmly as I do how we did things in the mid 70's-AKA ‘The Good ‘Ole Days'. Flashing was done maybe once and required a dwell time that would reduce production rates by 30-50%. This being because of the limited number of stations available and the low power infrared emitters that we used then. I also remember using film developer and fix and cutting Rubylith to produce the artwork. I once exposed an entire box of film when I was 14 and my father hit the roof! – I had to work it off catching and folding. There were no fax machines or e-mail and the time it took to acquire an order, produce and approve artwork, and then produce the finished product was probably an average of 5 times as long as today's average. Artwork gets e-mailed instead of courier, computer generated onto film instead of cutting ruby and the rest of it. Everything's been streamlined and improved.

No one can possibly argue that our industry has made enormous advancements in both the quality of work and the time it takes to produce a finished piece. Advancements in flashing, screen tensions, inks, and of course machine technology has driven our industry to realizing both greater profits and greater respect. The purpose of this article is to discuss the upsides and downsides of material choices of pallets and how these choices can be evaluated for you shops needs.

How would you like to have a jumbo platen that's as light as a feather, ultra-rigid, perfectly flat, and can be left underneath a flash cure indefinitely? And, how about all of this for basically what your used to spending now? Well, you can't. At least yet anyway.

What are Pallets

Pallets are essentially jigs, which allow your press to change print areas, shirt sizes, substrate types, and to accomplish specialty applications such as printing on socks and sleeves. The use of the term jig here is quite appropriate. As a manufacturer of parts and accessories, we ourselves are continuously designing and implementing new jigs that may help and improve our production. Our jigs, like your pallets, have a useable life span mostly determined by materials quality and usage. Printing Pallets come in different sizes, shapes, and materials. All three of these characteristics must be considered when making the best choice for your production needs.

•  Important Characteristics of a Pallet

•  Whether using a manual or an automatic or any pallet shape, size, or material – your pallet must be flat.

•  Pallets must be very rigid and flex resistant

•  Pallets surface must be free of any dents, scratches, or any aberration

•  If using a flash, pallet material must be flash compatible.

Advances in Screen Printing Production and their effects on Pallets

Before discussing the best material for your application it's necessary to first look at the comparative history of printing pallets to other attributes of the printing process.

•  Advances and Changes in Flashing – There is no other area of production advancement which has had as much impact on printing pallets as flashing. Through the years, we have all seen a tremendous increase in the amount of flashing being implemented during production. As well, the temperatures that are now used are significantly higher.

But even more important for our discussion than temperature is the term ‘power density'. Power Density is simply the flash wattage divided by the flash area. It's actually this flash specification which has increased the greatest. Many of you may recall the older hydraulic oval shaped machines and the OEM built flash cures for it. The Power Density of those units were/ is approximately 15-watts/ sq. inch. Today's quartz flash cure units are typically in the range 30-45 watts/ sq. inch & higher Additionally, the infrared units are significantly higher also. That is to say that today we are using two to three times as much flashing power per flash as we were 5 to 10 years ago. While at the same time using 2,3 and even 4 flashes where we were previously using none or one.

The effects of this advancement on printing pallets – Herein lies the largest detriment to the life of your pallet. With these higher power densities, the amount of heat imparted to the pallet itself has increased with the same ratio. That is to say, we're heating our pallets to temperatures never before attained in half the time by using higher powered multiple flashes. Then, we keep them hot for 4 times as long as we used to, basically never let them cool down. Guess what – there's no known cost compatible material that will last indefinitely. Please note the wording used there, cost compatible. Could you cost justify spending 3 to 4 times as much for some of the space age exotic materials? How about a 16” x 22” pallet for $400?If you're willing to spend this, then we do have materials that tested better than the Solid or Honeycomb Aluminum. The environment is just too brutal. Even the heat shields on the outside of the space shuttles have to be continuously replaced because of the heat degradation.

Advances in Screen Tension – Another advance made in our industry that greatly effects the contribution of your pallet to your print quality is the ever-increasing screen tensions. In short, the tighter the tension of your screens, the more prevalent pallet surface aberrations become in the print. While only a few years ago, a low-tension screen would easily conform to any contour, that is not the case today.

Advances in Pallet Materials – Generally speaking, there has been only one significant material addition for use as a pallet and one advancement. That material is honeycomb and that advancement is discussed in more detail below. However this material itself has limitations. It has been the experience and observation of this author that honeycomb Aluminum as used for a printing pallet requires a thickness of no less than 3/8”. The thicker the honeycomb aluminum laminate the stronger and more heat resistant it becomes. At thickness of less than 3/8” it has been observed that the material exhibits an unacceptably high level of degradation. Our company only offers a ½” and a ¾” Honeycomb laminate in our material selections for the reasons stated.

Pallet Paper – If you haven't heard of this material by now than you've either just entered the wonderful world of screen-printing or you just need to read this publication more often. Pallet paper is essentially very wide masking tape sold in various widths such as 18”. After covering the pallet surface with it, your pallet gets protected from several harsh elements and affords you a reduction in clean up time. It's an up-front expense which is easily cost justified.

These advances were developed for one reason and one reason only, to increase production quality and rates. While in the past it was typical to see a multi-flash job with a noticeable dwell delay, it's now common for the production rates of a job with multiple flash units to be comparable to those jobs with no flashes. Additionally, this speed is being accomplished using screens many times the previous tension with artwork of greater resolution and complexity.

•  Current Materials Available on Market

Soft Top Rubber – This material is actually a covering for your pallet and not considered a pallet material. It's important to reference this material here because it can be applied to any of the other mentioned materials.

The 1/8” thick, heat resistant rubber provides an excellent printing surface across the board. (No-Pun) This surface offers many advantages. Slight inaccuracies in the alignment of the printing planes are absorbed by this surface while providing an improved ink shear & penetration.

This material is designed to withstand very high flashing temperatures. However, if left under a flash cure unit, the rubber starts to smoke and then melt and burn as shown here.

The addition of rubber to your pallet has upsides and downsides. First the downsides, it costs money and eventually requires replacement. The upsides are numerous. The rubber normalizes any inaccuracies in the trueness of your printing planes and of material thickness tolerance of the pallet. That is, we're all aware that especially on our automatic, it's vitally important for the pallets, frames, and squeegee stroke plane to be as parallel as possible. That's the reason for leveling heads to pallets. Regarding material thickness tolerances, man made layers of material such as aluminum, double sided tape, glue, rubber – they all have manufacturers stated tolerance ranges. Any slight inaccuracy on your press will be normalized with the use of a soft material under the substrate. Other benefits as noted by this author and other screen printers would be reduced pinholes, increased mesh life & better substrate penetration.

The addition of Soft Top Rubber does increase the thermal reticence of your pallet. That is – it does holds the heat in and pallets with rubber will stay warm longer than a pallet without rubber. Heating these materials separately resulted in no significant difference in thermal emission rates between the two. The change in emission rates, or time to cool down, is caused by the creation of thermal reflections at the contact surfaces of the laminate material. This of course has pros and cons in and of itself. Pallets that stay warm require less flash time, but the spray tack adhesive on the pallets degrades more quickly.

Melamine Clad MDF – This is the most common material used for the manufacturing of pallets for manual presses. Specifically, it's a wood composite material known as Medium Density Fiberboard, which has a top and sometimes bottom piece of white Melamine material laminated to it. The melamine is a kitchen countertop-like material, which is very smooth and flat. The upside of this material is the cost. The downside of this material is its durability. This material is good for very limited production but its level of degradation is very high when used with flash cures.

Solid Aluminum with and without Soft Top Rubber – This is the most recommended and widely used material configuration today. For quality, durability, and price nothing compares. The choice of aluminum is very important, as there are many different grades available. Through experience we have found that there is no substitute for the best materials. We experimented with less expensive grades of aluminum for a short while many years ago, but quickly found that the quality differences between the various grades of materials were extensive.

Absolutely, the most durable surface. The aluminum should be the best available and manufactured for flatness. With or without rubber, the surface easily withstands trauma, and can be refinished if necessary.

Solid Aluminum can handle the heat of a flash better than any other cost class of material that this author is familiar with. Its upside is durability and its biggest detriment is the weight. Solid Aluminum is the heaviest of the materials available today. For applications requiring large format pallets, it's often recommended that honeycomb be used instead of the solid material recognizing the obvious trade of durability for less weight and machine load.

Quite a number of printers are very comfortable printing without rubber on their solid aluminum pallets. Theoretically, this is the optimum printing surface.

Honeycomb Aluminum with and without rubber. The only significant advancement in material choices for the last 10 years has been honeycomb aluminum. Brought to us by designers & suppliers to the aviation industry, it's a three layer laminated material manufactured using two thin sheets of aluminum and a core referred to as honeycomb. This core material is what makes the overall laminate advantageous for some applications.

Cross Sectional View of HoneyComb core material. This core material is what makes the overall laminate advantageous for some applications. Viewed from above, the core looks like a beehive.

	A Larger Cell size in the core will reduce weight, however it also decreases the amount of glue line.

Another downside is, it's become much more expensive for our use in the last year. This is basic supply and demand. The relatively small number of U.S. companies that manufacture the core honeycomb material are extremely busy because of recent aviation contracts, a robust economy and the generally increasing popularity of this material. Whereas, last year a pallet made of solid aluminum was basically the same price as honeycomb, that is not the case at the present time.

The ability of Honeycomb Aluminum to withstand repeated flashing is tremendous. Honeycomb handles the heat. But, only up to a point. It's still a laminate made with heat degradable epoxy. While the density of Honeycomb is so much less than that of its solid counterpart it's logical to assume that less heat energy is retained by the material. Testing has found this not to be the case. In fact, it was found that the Honeycomb material actually took longer to cool down than the solid. We can attribute this to the laminate nature of the material. Again we see evidence of thermal reflections caused by changes in thermal conductivity between the layers. Adding Rubber to the surface resulted in even greater thermal retainance, thus holding the heat in even longer.

Other Materials – Our company has experimented with various materials such as Dupont's Corian TM , Allied Signals-Granite Clad Composites, and a few others. They all looked great at first, but after a few weeks or even hours in our environment they degraded to useless or did not meet other logistical requirements. Other materials are on the horizon however and we are continuously tracking material advancements that might improve on the pallets that you use.

Summary

The point of all this is for you and your company personnel to understand the current status of pallet materials research and the proper care and evaluation of your most important printing accessory. Your pallets will make and break the quality of your product. If you flash them, you have a finite number of prints on each one. A good analogy for all of you racing fans – If your favorite driver keeps his gas pedal all the way on the floor, all of the time, than his chances of crashing increase and he'll certainly wear out his tires and other parts prematurely. A good driver knows how to pick his equipment and pace himself and his machinery for optimum performance.

The facts are – flashing technology has advanced faster than pallet material advancements. This has resulted in the ability of your flashing jobs to be produced with almost the same production rates as a simple 1-color job. All this is great except for one thing. If your going to take brand new pallets, with freshly applied non-cured adhesive and run wide open like that, you will be reducing the life-span of your pallets. This is of course a trade off. If you do the math, it turns out that you'll still cost justify killing your pallets for the increased production.

Does and Don'ts of Pallets

Do use the best pallet material for the job.

Do use Pallet Paper.

Don't soak your pallets in cleaning agents.

Don't over-flash them.

Do-Praise them occasionally for a job well done.

Our company is currently testing and evaluating the latest and greatest materials available on the market. Many of these do look promising, but so far – nothing competes for cost and performance like the ones available today and listed here. You'll be sure to hear about any major developments either from us or from your friends.

The very best of luck to all of you during this very busy & promising season in our industry.