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FLEXO Magazine : October 2009
48 FLEXO OCTOBER 2009 www.flexography.org • Liquid photopolymer platemakers are essentially a miniature manufacturing plant. • With bagged photopolymer, one side of the bag acts as a film negative. • The lack of a coating unit reduces the capital invest- ment to 30 percent that of a conventional liquid photopolymer platemaker. The advantages of liquid photopolymer plates have been well known for years. However, the high cost of such devices creates a barrier to entry. The reason for this high price is that the machine is essentially a miniature manu- facturing plant of photopolymer plates. The equipment must have a coater, a spreader, the prepared base film and a layer that allows air to escape. Special attention has to be given to the evenness of a plate and to avoid the formation of bubbles on or inside the plate. Liquid photopolymer is a high-viscosity material that is very sticky right before it is cured and hardened. Therefore, the coating and spreading process is very slow. In addition, if bubbles do occur, they are not easy to remove. It can take between one and two hours to make a full plate, which means that only four plates can be made in most working shifts. All of these downsides are common knowledge for those familiar with liquid photopolymer technology. But a new type of liquid photopolymer platemaking based out of Taiwan claimed to get around many of the pitfalls. It's a bagged liquid photopolymer. The manufacturer touts several benefits: Sharper image. By using one side of the bag as a film negative, the photopolymer-in-a-bag creates a clearer image area as a result of its close contact to the plate material. Solid plates all have a "slip coat layer on the top to help air escape from between the negative film and photosensitive resin during exposure. As a result, the photopolymer is not in direct contact with the negative film. The same is true of conventional liquid plates. Less stock. Users can reduce stock by using the photo- polymer-in-a-bag. All that is required is the 18kg (40lbs) liquid resin. This requirement does not change, regardless of the thickness, width and length of the plates required. Instead, these can be all determined by the gauge and bag size. No bubbles. Bubbles are always an important issue for liquid photopolymer platemaking. By using a bag, bubbles can be reduced by standing the bag in a vertical position and heating up the resin. Alternatively, it can be pre-prepared before exposure to let any bubbles out in advance before the platemaking, rather than during exposure with a blower or removing by hand. Water washout. Bagged photopolymer, like conventional liquid plates, can be washed out with water, which saves about 20 to 30 percent of plate costs compared to solvent wash plates. Cheaper equipment. Because of the innovative design of the bagged photopolymer, the exposure can be simple, using only back-to-back vacuum frames. As such, the exposure unit also has a simple design, without any coating unit attached, so the capital investment cost can be reduced to only 30 per- cent of a conventional liquid resin platemaking machine. Cost reduction. This new liquid photopolymer features no bubbles, a wide latitude, good ink transfer, high resilience, abrasion resistance, fine resolution, tack-free, excellent shoul- der support for long runs and low production costs. It is only 30 to 50 percent the cost of making a solvent washout plate. Time saving. As the bag is pre-filled without bubbles, there is no need for coating, spreading, waiting and bubble removal. For a 3.94mm plate, the total processing time is about 32 min- utes. This includes exposure (back exposure for 50 seconds, film exposure for 45 seconds), washout (150 seconds), post- exposure (150 seconds), anti-tack treatment (300 seconds) and drying (20 minutes). A conventional liquid machine could take between 90 and 120 minutes, while a solid plate would take lon- ger time than it, even without the exposure and washout time. Immediate printing. After the plate is processed, it can be mounted on a cylinder immediately. Because no solvent is used, there is no swelling of the image area, and no need to wait overnight until the plate is stabilized completely for good registration. In the Bag! A New Liquid Photopolymer Plate Show Promise TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009