Proper Storage Extends Plate Life
Proper storage of AVantage® liquid photopolymer plates will extend plate life and provide faster turnaround on orders that are refills of previously run jobs. Converters dread finding plates that have degraded in storage. Here are a few steps for cleaning flexo plates that will minimize plate degradation and extend plate life:
- Clean Plates: Plates should be thoroughly cleaned after each press run. Residual ink deposits on printing plates foster cracking and surface tack. Plates with dried ink are harder to clean and perform poorly during the next press run. Liquid photopolymers should be cleaned immediately after use with detergent and water or a similar plate wash solution and a soft bristle brush, lint-free rags, or an automatic plate wash machine. Do not use a solution with a temperature in excess of 140°F. Plates should be completely dry before storage – leftover cleaner or ink can deteriorate the photopolymer surface.
- Light: Photopolymer plates cure in the presence of light, typically in ultraviolet (UV) light such as direct sunlight, or in standard light sources including warehouse lights (unfiltered mercury vapor lamps and metal halide lamps), fluorescent, and incandescent light. If a plate sits in front of a window or other light source for an extended period, eventual damage may occur. Store plates after cleaning in a cool, dry place away from any light source. Plates stored on cylinders should be wrapped with an opaque material such as black polyethylene film.
- Heat: Prolonged heat exposure can affect a plate’s physical properties. Heat accelerates UV light degradation and increases the likelihood of ozone cracking, tack, and shrinkage. Plates should be kept preferably in a cool, dry storage area. Generally, the best temperature range for plate storage is 70°F – 100°F with a relative humidity of 60- 80%. Most photopolymer like printing plates should not be affected by higher storage temperatures (up to 120°F) and higher humidity (up to 90% RH). Good air circulation in the plate storage area will help maintain more consistent temperature and humidity conditions for the plates.Pre-mounted plates can be stored on a hanging rack or stood on edge to maintain their in-the-round, curved position. Placing the plate back into the shipping box will help to protect it from possible damage. If an in-the-round plate is stored flat, the plate may buckle and separate from the mounting material, thus damaging it beyond repair.
Liquid Photopolymer Plate Processing Room Specifications
Processing photopolymer plates requires a dust-free environment, similar to other photographic processes such as film development. The ideal room has a low level of environmental pollutants such as dust and chemical vapors. The technology required for this is common and relatively inexpensive, and the benefits realized in production and material savings will far outweigh the costs.
For your health and comfort, make sure your plate processing room is properly ventilated to allow fresh air into the room. Also, be sure to follow the safety recommendations given in the instructions, labels, and Material Safety Data Sheets.
- Room Layout – Your plate processing room should be designed for easy cleaning (dusting, mopping, etc). Ideally, the room does not allow for through traffic, and entrances and exits should connect to low dust environments. Furniture should produce a minimum of particles and be easy to clean.
- Lighting – Use lighting fixtures that eliminate or minimize dust collection. Cover any light sources (exposed windows, fluorescent lamps, etc.) with UV filters. These clear plastic films are extremely effective and last for many years. The cost of UV filters is easily recouped by the money and time saved by having to replace a set of mounted plates.
- Temperature – The ideal temperature is between 70° and 75°F (21 and 24°C). The ability to control temperature is important.
- Humidity – Ideal relative humidity is between 55 and 65 percent.
- Ceilings – Drywall ceilings with a smooth finish work best. Drop ceilings made from dust-free, non-flaking panels may also be used.
- Walls – Walls should be painted with a smooth, low-glare finish. Avoid walls with ledges, chair rails, or panels that collect dust.
- Floors – Floors may be solvent-resistant tile or epoxy-sealed concrete that can be mopped for easy cleanup. Rubber floor mats may also be used.
- Airflow – Room design should include multiple air ducts (ceiling inputs and cold air returns) with a high-efficiency filtration filter.
Plate Cleaning Solution for Water Based Inks
When a good photopolymer plate cleaning solution is needed to clean a plate of dried water-based inks while on press, the following steps are recommended. These steps can also be used after a press run to clean a plate before it is stored for future usage. This solution can be mixed in-house and used where needed.
The formula for this solution is composed of three ingredients. The first ingredient is isopropyl alcohol that will liquify the dried ink very quickly. The second ingredient is cleaning ammonia that puts the ink back into solution. The last ingredient is water which acts as the flushing vehicle for the cleanup. Rags can be used to blot up the ink being cleaned off. DO NOT RUB THE PLATE, IT MAY CAUSE PLATE DAMAGE.
Once the plate area has been cleaned it can be reused. If the plate is being cleaned for storage, it should be rinsed with water then dried before storage.
Industrial Ammonia Solution
Example: 1 oz.
Example: 2 oz.
Example: 7 oz.
This solution can then be put into a hand spray bottle and used to clean dirty, dried-up ink on a printing plate surface.
Safety: Protective gloves and safety glasses should be worn during all plate cleaning activities.
Proper Handling of Resins
The safety hazards associated with using chemicals and liquid photopolymer resins can be minimized by following the recommendations in the MSDS literature and utilizing the proper Personal Protective Equipment (PPE).
Eye and skin irritation and/or allergic skin sensitization is still possible when working with liquid photopolymers photopolymers, detergents, and processing solutions.
Employers should be aware that some workers may be more sensitive than others and have allergic effects to either the photopolymer resins or processing chemicals, thus may require individualized precautions.
Safe Work Practices: Implementation of some general guidelines for good industrial hygiene and safe work practices is advised when using the chemicals and liquid photopolymer resins.
Skin Protection: Skin contact is best avoided by wearing protective gloves. Disposable gloves work very well. Seamless and vinyl gloves also offer good protection for short usage as long as they are cleaned between reusing. It must be understood gloves do not last forever and should be replaced when necessary. Clean hands are important so not to spread chemicals to other body parts. Hands should be washed after removing gloves and especially before leaving the plate room area.
Clothing: Contaminated clothing should be removed and laundered before reuse. If cleaned at home, these clothes should be washed separate to prevent any cross contamination. If irritation occurs despite following this guideline, the incident should be reported promptly to medical or first aid personnel.
Eye Protection: Because the eyes can be easily irritated or damaged, special care needs to be taken to prevent chemicals from splashing into someone’s eyes. Safety glasses should be worn at all times when using the chemicals or liquid photopolymer resins.
AVantage® photopolymer resins are processed using UV light exposure units. Exposure to the eyes by UV light can cause photokeratitis. Symptoms include increased tears and a feeling of pain likened to having sand in the eyes. UV protective glasses should be worn during testing and maintenance of the UV light source.
Inhalation: Areas in which the AVantage® photopolymers and chemicals are being used should be adequately ventilated. Inhalation can occur from exposure to dust, mist, fumes, and/or vapors. Such exposure must be kept below the levels as prescribed by the Occupational Safety and Health Administration (OSHA). See the OSHA venting requirements for their standards.
Ingestion: Food and drink should never be stored, prepared, or consumed in areas where they may be exposed to any industrial processing chemicals.
Good Housecleaning: Maintain good housekeeping practices throughout the plant. Eliminate handling problems and abuses, plus carelessness in the work area. Clean spills right away and using the proper PPE. A clean operation will prevent chemical exposures.
Summary: AVantage® chemicals and liquid photopolymer resins should be given the same consideration that other industrial chemicals are given. MSDS literature should be reviewed and followed prior to chemical usage. Safe work practices and operation should always be used. Waste chemicals should be disposed of properly in accordance with local, state and federal regulations. Specific information on handling and disposal can be found in the product’s MSDS sheets.
Feed and Bleed Set-up
Proper set-up of the Feed and Bleed system on small (3048) and large (5280) systems will ensure high quality plate washouts without changing the bath every 15 plates. Bath life is not forever so the washout unit should be cleaned, recharged, and checked every two weeks to ensure the system is operating correctly.
Feed and Bleed Setup:
The starting bath should be charged into the bath. If not sure please reference Tech Tip on washout bath formulation for your sized washout unit.
The Feed and Bleed requires four or five additions to the bath on each wash cycle. There is water, detergent, defoamer, and developer. If AVenhance is being used it is pumped in along with the other chemicals.
Feed and Bleed amounts to washout bath size:
Note: AVenhance also acts as a defoamer, so be aware that the suggested amount of defoamer can be reduced, possibly as much as 50%.
AVenhance is a chemical detack component added directly into the washout unit to help generate a completely tack-free photopolymer printing plate. This additive is used with AVantage® photopolymers 32C and 32MLR resins. AVenhance can effect how much foam is produced in the bath, so be aware that the typical amount of defoamer can be reduced, possibly by as much as 50%. When using AVehance, germicidal treatment is not to be used.
Usage amounts: The amount of AVenhance used in a bath is dependent upon the total plate surface to be tack-free. An I-Plate type corrugated plate will require less AVenhance than conventional corrugated plates. The size of the washout unit being used will also determine the required amount of AVenhance. The last factor is if the washout bath has a feed-and-bleed operation.
- Regular Bath, Conventional or I-Plate – 3048 @ 70 gallons – ½ gal. AVenhance.
- Regular Bath, Conventional or I-Plate – 5280 @ 150 gallons – 1 gal. AVenhance.
Washout Cycle Time: The recommended washout temperature for 32C and 32MLR is 110°-120°F for a period of 10-15 minutes.
Bath Life: Each bath should last for 15-20 plates depending upon the amount of resin being washed out after reclaiming. Generally, small plates that are 3048 in size will washout about 1.5 lbs of liquid resin. The larger 5280 plate will have roughly
4.5 lbs of resin on it after reclaiming. An I-Plate may have 3 to 3.5 lbs on its surface after reclaim. Your amount can be determined by weighing a plate before and after the washout phase. This will tell you the resin washout amount per plate. Knowing this is very useful to set the start-up bath with the required chemicals needed and estimating the plates per bath volume.
Plate Set-up Formula
All photopolymer resins shrink slightly when exposed and cured during the plate making process. The AVantage® line of liquid polymers is no different.
To set the proper shim pack, the resin shrinkage rate must be accounted for in the set-up. First and foremost is the target plate thickness desired. Next is the film thickness being used to make the printing plate. There are many different types of film being used these days to produce printing plates. There is the old standard silver film at 4 mil and 7 mil thickness. The new AVSTAR printed film sold by Anderson & Vreeland, Inc. is available in 5.5 mil and 8 mil film bases. The system uses a piece of cover film to protect the negative and seal it to the lower glass. The cover film is generally 0.7 mil thick.
The following equation will set the shim pack to make the desired plate requirements using AVantage® resins:
- 67 mil + 1 + 1.5 + 4 mil silver = 73 mil
- 67 mil + 1 + 1.5 + 5.5 printed film = 75 mil
- 250 mil + 1 + 5 + 7 mil silver = 263 mil
- 250 mil + 1 + 5 + 8 mil printed film = 264 mil
Note: Plate exposure times will be different for silver film and printed film because printed film has a UV coated layer to generate the density needed with the ink coating to prevent the UV from coming through the dark black areas of the negative.
Washout Bath Formulations
The AVantage® washout bath formulation ensures the removal of any remaining unreacted resin to yield a quality photopolymer printing plate. As with any formulation, proper processing of the printing plate is very important to ensure the quality finished plate. The separate components of the AVantage® washout bath are all liquids that are easy to dispense and good for many plate washes.
Below is the recommended bath formula for different sizes of washout units. The washout bath and chemical set-up amounts are based on a fixed bath water volume. The washout water volume should be determined for an exact bath formulation.
Defoamer amounts can vary dependent on the condition of the local water hardness.
ALWAYS MIX YOUR DETERGENT / DEVELOPER BEFORE ADDING DEFOAMER.
Procedure: First mix the DETERGENT before dispensing the desired amount and adding it to the bath. Next add the recommended DEVELOPER to the bath. Lastly, pour out the DEFOAMER volume and add it to the bath. Ensure the washout temperature is set correctly. Run one cycle to mix the chemicals in the bath and then check for possible excessive FOAM. More DEFOAMER can always be added, in small portions – 8 ounces at a time.
Temperature: The temperature setting for the bath will vary dependent on the resin product being used. Check with your local Technical Representative for recommendations.
Changing of the Bath: The typical bath life depends upon the type of copy, plate thickness, reclaimed, and thus the amount of liquid resin left on the plate. Maintain a log of plates washed to find your general usage results. A typical bath should last between 12-18 plates. Washout time cycle is generally 10-15 minutes.
Exposure Unit Glass Cleaning
The upper and lower frame glasses have a matte finish to ensure a proper seal of the cover film to the lower glass and contact seal of the substrate to the upper glass. Over time, the matte finish can become contaminated with dust, cleaning agents, tack rag residue, and even resin. These contaminates will fill-in the matte finish causing the glass to turn clear. Once the matte finish is gone, air will be prevented from escaping. This may result in a poor lower vacuum seal between the cover film and the negative being used. It may also result in a poor upper vacuum seal. When this occurs plates may have dime size low spots, or a Zebra pattern can also occur. To correct these problems the upper and lower glasses need to be thoroughly cleaned. The following procedure is recommended for cleaning both glasses:
Materials Needed: Lint-free towels, soft scrub solution or powder, sponge with Scotch-Brite on one side, protective gloves, safety glasses, two buckets of clean warm water, glass cleaner, and alcohol.
Exposure Unit Glass Cleaning Process:
1. Open the upper frame on the machine.
2. Turn the unit off at the main power supply.
3. Cover the lower frame area to prevent spills and easy clean up.
4. While wearing gloves and safety glasses, spray the glass with the glass cleaner. Next using the sponge soaked in warm water, apply the soft scrub solution to the Scotch-Brite surface. Using small circular rotations apply the cleaning solution to the glass surface and clean the whole surface of the glass. Rinse the sponge in separate, warm water bucket to prevent a redeposit of polymer on glass. If the glass is really dirty you may need to repeat cleaning the whole surface again.
5. After cleaning, take a lint-free towel and wipe down the glass surface removing the residue cleaning solution. Once rinsed, repeat cleaning the glass with glass cleaner using a lint-free towel. Finally, use some alcohol soaked into the lint-free towel and repeat cleaning the glass surface.
6. Once the glass dries it should have a matte look to it again. If not repeat steps #1-5 again.
7. When cleaning the lower glass the process is the same except the vacuum lines are covered with masking tape to prevent liquids from getting into the vacuum system.
8. If this fails to achieve a clean upper and lower glass, contact your local Anderson and Vreeland Technical Service Representative. A&V’s trained personnel can perform an additional procedure referred to as “lapping”. This is done with a special tool that cleans the crevasses of the glass where resin may be trapped and not accessible without the specially designed glass tool and cleaning compounds.
Safety: Please read and follow the safety recommendations for the products listed under “Materials Needed” before proceeding to clean the glasses.
Lamp Output on Exposure Units
Lamp intensity in exposure units is critical in the production of an AVantage® photo- polymer printing plate. Low intensity lamps will affect the quality of the plate being made and the finishing steps during processing. The life of a lamp is dependent upon a variety of factors including the type of exposure unit being used, the type of lamp, operational temperature, the number of cycles run, total hours of all cycles, and the surface of the bulb being cleaned. Lamp output depends upon the type of glass in the exposure unit; smaller units have Pyrex glass while large systems have soda-lime glass.
High output UV lamps at 350 nm can be used in the upper and lower frame sections. The output range of these lamps varies from 3.0 – 6.5 mW/cm2 in the upper frame area. The lower glass lamp range varies from 4.0 – 6.5 mW/cm2. Higher intensity 370 nm lamps are used in special units where the bulb position has been lowered, with an output intensity of 4.0 – 8.0 mW/cm2.
Large exposure systems are built using soda-lime glass. This type of glass absorbs UV light, and the lamps are farther away from the glass surface. The upper frame area uses 350 nm lamps. The lower frame uses high intensity 370 nm lamps. UV lamp intensity varies from 2.0 +/- 0.5 mW/cm2 in the upper frame area. Replace these bulbs when they reach less than 1.2 units. Lower frame lamp intensity varies from 4.0 +/- .5 mW/cm2. These lamps need to be replaced when they reach 2.5 units or less.
The Post-X unit for all systems uses a special, reflective, high intensity bulb at 370 nm. The output of this lamp is 20.0 +/- 1.0 mW/cm2. These lamps should be replaced once they fall below 10.0 mW/cm2.
Periodic cleaning of lamps on a quarterly basis will improve lamp intensity and performance. Take precautionary measures by wearing protective gloves and safety glasses. Remove dust build up from lamps using a lint-free towel and Windex® or a similar cleaning solution.
Periodic cleaning of the exposure unit’s upper and lower frame glasses will also improve performance. Refer to AVantage® TechTip #9 for complete instructions.
Post Exposure Conditions
The post exposure step is very critical for producing tack-free AVantage® photo- polymer printing plates. The quantity of post exposure salt, lamp intensity, post exposure time, and a clean post exposure bath, plus the frequency of bath changes all will impact the quality of the finished plate. Recommendations are provided below for the proper salt concentration and time of post exposure.
Concentration of Post-X Salt Bath:
1 lb per day
2.5 lbs per day
3.5 lbs per day
Per day rates are quoted because the bath should be clean and clear for the best Post-X results. Once the bath turns cloudy it will filter the UV light during Post-X. Changing the Post-X bath daily is recommended.
Mixing: Pre-dissolve the Post-X salt in water using a one or two gallon container then pour the solution into the Post-X bath water. The Post-X bath water level should be deep enough to completely cover the plate.
Lamps: New lamps will range from 15-20 mW/cm2 when measured with a UV light meter. After a short “burn-in” period the intensity will level off to around 15-18 mW/cm2. Bulbs should be replaced once the intensity falls to 7 mW/cm2. Bulb life is dependent upon the hours they are used. Under typical production conditions bulbs should last 1 year.
Exposure Times: The correct Post-X exposure time is dependent upon lamp intensity.
The following is the recommended guideline:
9.0 mW/cm2 or higher
8.0 – 9.0 mW/cm2
7.0 – 8.0 mW/cm2
Resin Reclaim Guidelines
The ability to reclaim and reuse the liquid photopolymer resin differentiates the product from sheet plates and in many cases creates a very attractive financial advantage for the customer.
Equipment and procedures for the collection and handling of the liquid photopolymer reclaim resin may vary from one place to another. With careful handling, resin reclaim can produce high-quality printing plates with some basic guidelines being observed.
Collection: The photopolymer resin must be protected from UV light. Thus, all collection containers should be opaque and the room illuminated with yellow or UV filtered lights in the room.
Filtration: The reclaimed liquid resin needs to be filtered to remove any gels, solid pieces of resin or foreign matter. The filter should be in a position that is easy to access. It could be either in-line or at the mouth of the collection container. Filtering with cheesecloth, aluminum, or stainless steel using 100-200 mesh is recommended. The filter should be cleaned once a week.
Overflow resin can be collected from the overflow tray too. It must also be screened and then can be mixed with the reclaim resin.
Mixing: If the reclaim is being used straight to a bucket system the resin needs to be aerated before use and mixed with virgin resin.
The tank mixture is easy to complete. The reclaim resin can be mixed 3 to 1 (3 virgin resin to 1 reclaim) and then blended in the tank. Always add resin at the end of the day, pouring reclaim in first followed by equal amounts of virgin resin. Let the systems mixer or blender run all night to thoroughly blend the resin to ensure it’s homogeneous. It should be practiced to add reclaim resin and virgin resin daily to avoid build-up large volumes of reclaim resin.
Safety: Use proper Personal Protective Equipment (PPE), gloves, and safety glasses when handling the liquid resin from the reclaimer to the storage tank.
AVantage® Resins and Silver Film Material
Specifications and recommendations for using silver film are detailed here to obtain optimum quality reproduction when using AVantage® photopolymer resins.
- Base film for plates should be clear or a light matte surface. It should be smooth and free of handling defects such as nicks and dings. A heavy matte material may diffuse the UV light too much and fill reverses.
- Using a transmission densitometer to determine the measurement, the optical density in the clear area of the negative should be 0.05 or less. The black area of the negative should be 4.0+ to avoid reduction in etch deep of the character or midtone screens and shadows. The image should be right reading, requiring the emulsion side up on the negative (bronze plate production requires wrong reading negative so the final product will be right
- Negative thicknesses are 4.0 mil and 7.0 mil. The film can be clear or matte format. Clear film is recommended to ensure quality reproduction of the negative. Do not mix negative thicknesses on a liquid exposure unit because the resulting plate will note the 3.0 mil difference in the film.
- A one-piece negative is recommended for platemaking. Overlapping, stripping, or taping negatives together may cause a plate tolerance problem.
- A high-contrast negative is needed in order to properly expose the photopolymer resin, reproducing the desired dot or screen without halos or fringes. The UV light will transmit through the character area for quality reproduction with quality structure support.
- Using an exposure control guide will help monitor the plate quality on a daily basis.