Product should be stored in a low humidity, moderate temperature environment away from strong UV light sources. In addition, care should be taken to ensure product is stored in a way that it will not be exposed to dripping liquids including pipe condensation or leaking oils. Appropriate humidity levels are below 50% RH. Appropriate temperature levels are between 66°F and 82°F. Storage conditions should not be confused with conditions on press as these will be different.
It is best to store product in a vertical position and not on its side. The only exception to this is when product is stored on shafts or rods that can extend through the product’s inner sleeve. When this approach is used it is preferred that the shaft or rod be at least 2.5” in diameter to avoid excessive load on the product’s inner sleeve.
In order to achieve maximum bond strength between plates, tapes and sleeves it is critical to adhere to proper cleaning and mounting techniques. Ensuring that the mating surfaces are free from contaminants is very important. Contaminants include moisture, oils, dust, dirt and prior adhesives from tapes or edge seals.
Both the print sleeve and the back of the printing plate should be cleaned using 100% isopropyl alcohol applied to a new, lint free cloth or other product that will not leave behind residual particles. Stronger chemicals such as MEK, acetone or other acetates can be used to remove stubborn contaminants. However, they should always be followed with cleaning with a new cloth having 100% isopropyl alcohol in order to remove the film residue that can result with the use of these other chemicals.
Once the sleeve and plate are cleaned, one should avoid touching the cleaned surface with unprotected hands as this can result in new contamination. It is best to wait 15 minutes before applying the tape to the sleeve or the plate to the tape in order to be sure the cleaning liquids have evaporated. Failure to do so can result in air bubbles under the plate or tape due to the cleaning liquids becoming trapped under the plate and becoming gaseous after the product is exposed to heat.
If plates will remain mounted to sleeves for an extended period of time (such as repeated print runs over several weeks) it is desirable to use a stronger tape product than one might use otherwise to avoid plate lifting or buckling. This is particularly true for small diameter sleeves (below 5”) and thicker plates (over .045” thick).
Perhaps the most important issue towards extending print sleeve life and performance relates to cutting techniques on the print sleeve surface. Excessive force used in cutting sleeves will result in a damaged sleeve surface and can lead to poor tape adhesion, air bubbles under the plate and out-of-registration conditions.
Two factors are important when considering proper cutting techniques. These are the force applied and the sharpness of the cutting tool. These two factors are closely related. If low forces are applied then a sharper cutting tool can be used. Conversely, if high forces are applied then a duller cutting surface should be used. Ideally, plates and tapes would not be cut on sleeves at all. While not always possible, this can be achieved by cutting tapes and plates on a glass surface and transferring them to the sleeve after cutting is complete. Another approach that protects the sleeve is to lay a metal or plastic ruler onto the sleeve and cutting the tape or plate while it is supported on this protective surface.
If it is not possible to cut tapes and plates while off the sleeves or personnel are not inclined to use metal or plastic rulers, then other techniques are available for accomplishing this task. The first approach is to use a rotary knife which resembles a pizza cutter. The circular design of this style knife distributes the sharp cutting surface over a larger surface area, thus greatly reducing the force on the sleeve. OLFA is a company that offers such a knife.
Another approach is to use traditional box cutter style knives with curved points. However, perhaps the best approach is to take traditional box cutter style knives and create a short (approximately 1/16” long) flat surface by sanding away the point using 120-grit sandpaper. This provides a smooth, dull surface that rides on the surface of the sleeve while providing a sharp edge to cut the tape or plate.
If over the course of time raised edges begin to occur due to excessive cutting, these edges can be removed by lightly sanding the surface. However, care should be exercised in doing so to avoid changing the thickness of the sleeve which can lead to print registration or print quality issues.
Mounting / Demounting
Use of proper bridge and sleeve mounting techniques are critically important towards maximizing product life and achieving proper print quality. Failure to do so can result in damaged product and/or dimensional discrepancies such as excessive TIR (Total Indicator Reading) which is essentially an out of round condition.
Bridge mandrels or print sleeves should be mounted on base mandrels (metallic or non-metallic) that are free from burrs, nicks or scratches to avoid damaging the inner sleeve of these products and ensure the product slides freely onto the supporting base. If print sleeves are being mounted to bridge mandrels then the bridge is the base and should be free of such defects. If a defect is detected on a steel base mandrel then it should be removed using appropriate methods such as through the use of sand paper or a fine file. As always, great care should be used when sanding or filing on any precision surface.
Air supply to the base mandrel should be such that it provides from 80 psi to 100 psi (5.4 to 7 bars) of air pressure at no less than 0.42 cubic feet per second (12 liters per second). Sleeves less than .065” thick can be easily mounted with air pressure as low as 50 psi. However, thicker sleeves will require higher air pressure.
Factors that can easily compromise these needed conditions include 1) diminished air flow and/or pressure due to excessive losses from air requirements on other equipment 2) air lines or fittings that are too small to allow flow and 3) blocked air holes in base mandrels or bridges mandrels.
Perhaps the most important direction when mounting or demounting bridges and sleeves is to ensure they are mounted in a manner that they are parallel to the surface onto which they are being mounted. When bridges or sleeves are “cocked”, meaning, they are held at an angle to the mounting surface, then the operator needs to wiggle the product up and down or side to side in order to get it to reach a point where it can slide freely. This action will produce radial forces that travel through the thickness of the product and can lead to an out of round condition also know as excessive TIR. In reality, some up and down or side to side motion is required to mount product because it is difficult to achieve a perfectly parallel mounting conditions without the use of automated or mechanized equipment. However, care should be taken to keep these actions to a minimum and, ideally, never exceed an angle of three degrees as referenced to the base mandrel.
Once the product is mounted over the leading air holes on the base mandrel, it is helpful to pause a few seconds to let the air pressure build under the inner sleeve of the product. Once the air pressure is fully established the product can then be slid onto the base mandrel in one smooth motion.
If the base mandrel has a pin, the operator should ensure the notch on the product and the pin on the base mandrel are in line before mounting the product to the base mandrel. Further, the operator should avoid applying excessive force to the product when mounting to the base mandrel to avoid damage to the pin or notch. If the bridge mandrel has the bayonet, TruLoc™ design then care should be taken to rotate the bridge mandrel in the clockwise direction after the bridge has traveled the full distance of the base mandrel and the notch is engaged with the pin. Once the bridge mandrel is in place the operator should check to ensure that air is flowing through the holes in the bridge.
When demounting bridges or sleeves proper removal is also critical to avoid TIR issues. The main point is to remove the product with one continuous motion. When an operator stops before demounting is complete, particularly if the product has less than 15% remaining on the base mandrel, the operator is inclined to rock the product up and down or side to side to remove it due to a loss of air pressure under the product. This can result in excessive radial loads to the product and lead to TIR outages. If the product becomes stuck during demounting due to insufficient force during demounting, it is better to remount the product by carefully pushing the product onto the base mandrel again and attempting to demount a second time.
If the product being removed is a bridge mandrel having the TruLoc™, bayonet notch it is very important that the operator rotate the bridge mandrel in a counter-clockwise direction to disengage the bayonet notch from the pin. Failure to do so can lead to the operator to believe the bridge is stuck which can cause him/her to resort to excessive force for bridge removal thus leading to bridge mandrel damage.
At times product can become stuck on a base mandrel. This can occur due to ink reaching the interface between the product and the base mandrel. It can also occur if air pressure or air volume becomes reduced for a variety of reasons. In these instances, product demounting with human hands alone may not be possible. Nonetheless, extreme care should be used when attempting to remove product using foreign objects such as hammers or mallets. Product should never be directly struck with a hammer, mallet or other hard object. A soft wood or plastic block should always be used as a barrier between the product and the striking device. This will reduce the maximum contact load and distribute the load more evenly across the face of the product. The supporting block should always be placed on the face of the product and never on the outer, round surface.
Initial strikes to the supporting block should start with low levels of force to minimize the shock load applied to the stuck product. It should be noted that every attempt should be made to restore air pressure and/or volume to proper levels before attempting to remove a product with force other than human hands. Failure to do so can result in damage to the product. If it appears excessive loads have been applied to the product ends as evidence by cracking or flaring then measurements should be taken to ensure product is still in specification before the product is returned to the press operation.
Xymid’s bridges and sleeves are made of a combination of materials, the variety of which will depend upon the thickness of the product and the performance requirements. These materials include thermoplastic and thermoset resins which have certain temperature limitations. In order to maintain dimensional stability and construction integrity it is important that product not be exposed to excessive temperatures for extended periods of time. Any material response to thermal exposure will depend on the maximum temperature and the duration of the exposure. In general, product should not be allowed to reach temperatures in excess of 150°F (65°C). It is preferred that product not reach temperatures between 135°F (57°C) and 150°F (65°C) for more than thirty minutes. If exposed to these temperatures then product should be supported on a mandrel. Excessive temperature exposure can occur if a dryer on a press is allowed to blow onto a sleeve or bridge without any substrate running over the surface. Bubbling of the urethane outer surface has been observed when sleeves are exposed to temperatures up to 180°F (82°C) for as little as two minutes. This occurs due to the outer layer heating more quickly than the inner layers, thus expanding at a faster rate. Once this occurs the product is typically damaged beyond repair.