Running cohesive on Flexo
HANDLING AND USE:
GRAVURE OR FLEXO APPLICATIONS
1. APPLICATION EQUIPMENT MAKE-READY
Cohesive applications should be made from the last applicator station on the pressor laminator. This especially critical for flexo applications due to the minimal drying capacity available between applicators.
All other applicator station make-readies should be performed prior to the Cohesives station make-ready. Cohesives are sensitive to both loss of ammonia and to shear upon idling.
Cover as tightly as possibly the applicator pan and pump (if a recirculating system is used) as well as any drums that contain cohesive.
All pumps used in the transfer of liquid cohesive must be of low shear type. Air actuated drum pumps, parastolic tubing pumps or Graco No. 205460 or 205637 pumps are recommended. Best method of transfer is a demand, gravity feed set-up.
2. EQUIPMENT IDLING OR SHUTDOWN
Dry Cohesive film does not redisperse as do common solvent based inks and coatings, therefore, it is essential that the gravure cylinder, fountain and/or anilox rolls remain rotating at all times when Cohesive is in the pan or fountain.
During prolonged idling or shutdown (5 minutes or longer) the doctor blade on gravure or blade doctored flexo should be backed off to allow flooding of the applicator rolls to reduce shear and prevent drying – in of the etched or engraved cells.
3. ON-SITE MODIFICATIONS TO COHESIVES
In general, it is not recommended that any modifications be-made to the as-received Cohesive formulations. Experience has shown that Cohesive machine and perform best when used unmodified by the converter. There are circumstances, however, when slight modifications may be necessary or desirable. Typical of these types of modifications are:
pH Adjustment: It is recommended that the pH of Cohesive be monitored with a pH meter (not pH papers) particularly after prolonged periods of idling or other exposure to air. In the unlikely event that the pH has dropped to the point where ammonia addition is required (below pH 9.0) do the following:
Add ammonia water made from non-detergent/29.4%, 26 degrees Baume’ Ammonia. The ammonia should be slowly added to the Cohesive with appropriate mixing. pH should be measured frequently so as to not add more ammonia water than is necessary to bring the pH up to 9 .0 – 10.0.
Reduction of Solids:
If it is absolutely necessary to reduce the solids of the as-received Cohesive to achieve the desired coating weight or to adjust the viscosity for equipment considerations; cool tap water, preferably containing a small amount of non- detergent ammonia, may be added to any of the Cohesives. It is strongly recommended that the pH be monitored during dilution to be sure it does not drop below 9 .0. (We strongly recommend against dilution of Cohesives; rather, we recommend equipment changes if at all possible).
Excessive Foaming:
Cohesives should not foam excessively, as they are specifically formulated to control foaming. However, if excessive foaming should occur, empty and discard the foamed material. Add fresh Cohesive to the applicator after adding 1/4 to 1/2 pint of defoamer (Rhodiline 675 from Rhodia) to a 430 lb. drum or an appropriate amount to yield a 0.1% solution. Dilute appropriate amount of defoamer with an equal volume of warm tap water. Add to Cohesive and stir well.
Tinting of Cohesives:
Some converters tint Cohesives prior to use in pattern applications to aid in registering the pattern with the printing. Food, Drug and Cosmetic dyes(FD&C Dyes) may be used for tinting Cohesives. (FD&C dyes must be usd in food end use applications). FD&C No. 1 Blue and FD&C No. 5 Yellow. are suitable and are available from:
Allied Chemical Corporation
Sterling Drug
Specialty Chemicals Div., Diamond Shamrock Co
The dyes are purchased as dry powders and can be added to Cohesives as follows:
Dissolve 5 parts of dye to 100 parts of warm water. Stir well and add to Cohesive while agitating.
4. OVERPRINT VARNISH OR LACQUER REQUIREMENTS
Some substrates, whether or not they are surface printed, require an overprint varnish or lacquer on the opposite side from the Cohesive coating to avoid blocking within the roll.
Tests should be conducted with the specific substrate to be used prior to machine coating trials to determine the need for and type of varnish or lacquer necessary. In general, reco end a polyamide resin based overprint coating. The following coating has been shown to be effective in avoiding Cohesive blocking:
Cattie Adhesive # 8005
Running cohesive on Flexo
Recommend that the customer discuss requirements for an overprint coating with his current ink supplier and submit any candidate coatings to our lab for evaluation.
5. DRYING OF COHESIVES
Coalescing and complete drying of Cohesive coatings is required for maximum adhesive strength to the substrate, maximum cohesive seal strengths and for maximum uniformity from roll to roll. Complete drying also reduces blocking tendencies. Several simple observations can be made to assist in evaluating the degree of drying they are:
Coating surface should fee1 dry, not wet, to the touch. The coating will feel tacky but should not easily rub off the substrate.
There should be no ammonia odor to a freshly dried sample.
There should b no acetic acid (vinegar) odor to freshly dried samples.
Experience has shown that optimal drying is obtained when: using a gas fired high air velocity oven. The oven has two zones, the first zone at a lower temperature than the second zone. The air movement in the oven is very turbulent and the air balance is 90% fresh air and 10% recirculated air.
Low velocity air ovens heated by steam, electricity or infra-red energy may be used, but will sharply limit web speeds.
Air velocity and turbulence are more important than the maximum temperature capabilities of the oven.
Maximum oven temperature are limited only by the substrate being coated. Experience has shown that the Nip-Welds will not be damaged by oven temperatures no ally encountered in converting operations.
Typical oven temperatures seen in practice range from 185 degrees Fahrenheit to 400 degrees Fahrenheit. Cohesive coated on glassine are typically dried at 250 degrees Fahrenheit to 285 degrees Fahrenheit at speeds in excess of 400 feet per minute.
CAUTION: When Cohesive are coated on plastic films, the chill rolls used to-cool the web before winding-up should be maintained at a temperature above the dew point. Condensate on freshly coated Cohesive may result in blocking. Chill Roll temperatures should be maintained at a level that will, _when combined with web speed, give a web temperature of 90 to 100 degrees Fahrenheit at the wind-up.
6. Machine clean up
Clean-up of the machine applicator station used to apply Cohesive is relatively simple and easy if the following steps are followed:
At the end of the run, when the machine is shut down, keep the Cohesive applicator station idling and back-off any doctor blades or flexo plate cylinders.
In addition Drain applicator pan or fountain into either the reservoir sump or directly into a waste container. Pump the reservoir sump (if used) into a waste container.
NOTE: We do not recommend the re-use of Cohesives as they have been subjected to shear and to loss of ammonia during the application process.
NOTE: Cohesives are a non-hazardous waste and may be disposed of in compliance with local regulations covering such materials.
If storage of used Cohesive is desired, recommend that a separate, clean container be used, not the original container. A separate container eliminates the potential for contamination of fresh Cohesive by the used material.
With the drained application station idling, immediately flush the entire station with cool tap water. Also, Ammoniated water may also be used but is not necessary.
Wipe down rolls, cylinders, plates, pans or fountains with a wet rag as the station is being flushed. Lastly, a soft bristle brush may also be used if desired.
DO NOT USE ANY ORGANIC SOLVENTS FOR CLEAN-UP Solvents will cause the Cohesive to coalesce and “gum up” the equipment. Then Partially dried Cohesive should be allowed to dry completely and then removed by peeling or rubbing. Again, do not use organic solvents.
Running cohesive on Flexo- this method of application uses a rubber plate, called a flexo plate, which has the desired pattern raised on its surface.
Need more information? To speak with a technical representative about your application, and to request samples or pricing, please call 800-249-0337 or email us at [email protected]