1. Preparation

New belts must be cleaned thoroughly in order to remove any talc, unpolymerized material or machine oil that may be adhering to their surface. A belt should first be cleaned with a chlorinated solvent and then 2-3 times with a surfactant. Before coating an old belt, it is important that all paste is removed.

To improve the affinity between the belt and Newdine, the belt should be polished once with 300-400 mesh sandpaper. Polishing with sandpaper is extremely simple, areas with a mirror-like surface simply being polished lightly once or twice to produce a roughened surface without damaging the belt. Be sure not to polish the belt too hard. It is very important that the belt is prepared correctly.

2. Applying Newdine

1) Intermittent drive belts

With an intermittent drive, a conventional applicator is not an effective way of applying the adhesive because when the belt is stopped, resin applied previously will dissolve due to the solvent in the newly applied adhesive. A Series, however, can be applied with an applicator easily. The method outlined here is for screens that are attached to machines. Polyester gauze (120 mesh) is spread over the screen and the adhesive is applied to the inside of an area framed by cellophane tape or adhesive paper tape as shown in Fig. 9.

Fig. 9

Without fixing the frame and with one operator on either side of the belt, the end of the frame labeled A in the diagram is lifted towards A' as the squeegee moves from A to B. This is reversed when the squeegee is moved from B to A. When resin is reapplied to a part of the belt that has already had resin applied, the screen may be damaged due to the resin's adhesion and so the operation should be carried out quickly following the motion of the squeegee.

If the width of the coating of table adhesive is wider than the cloth that is to be set on the belt, the coating may adhere to the gauze of the frame when the print is squeegeed and this can lead to the gauze tearing when lifted. This means that the width to which table adhesive is applied must match the width of the substrate.

This problem can be addressed by methods such as applying cellophane tape to the gauze of the screen.

Fig. 10

2) Continuous drive belts

When using a machine with a continuous drive belt, the doctor blade is placed against the upper surface of the belt, and the adhesive is applied while the belt is fed at a speed of 5-8m/min. Be sure that Newdine does not spill around either end of the doctor blade and spread over a width wider than that of the substrate. In order to adjust the width of application, the doctor blade should be set as in Fig. 11 with vertical movement being posible.

Fig. 11

When applying Newdine to a rotary screen printing machine, because the endless belt of a rotary screen printing machine is shorter than that of an auto-screen printing machine, the surface which has been applied with Newdine diluted with solvent may hit the surface of the guide roll before the diluting solvent evaporates. This may result in the Newdine coating wrapping around the guidance roll or being damaged by the applicator squeegee. Thus, when applying Newdine to a rotary machine, use a type of Newdine that has a hard surface and a low adhesive strength without diluting it with solvent and apply it with the doctor blade when the belt is in motion.

Fig. 12

3) Points to note during application and operations

In order to achieve a good print, it is essential that the surface of the Newdine is perfectly flat and smooth. To achieve this, table adhesive must be applied evenly. Factors during application that are important in attaining an even surface include the ingredients of the adhesive and its consistency (viscosity).

Here we will touch on these problems and discuss what is important in ensuring that the surface of the applied adhesive is flat and smooth. These points should be remembered during the application of Newdine.

In ensuring that the surface of the applied adhesive is smooth and flat, the first important point is the viscosity of the adhesive. Experimental results show that if the viscosity of the adhesive is too high when it is applied it will not flow well and will be difficult to apply. In addition, as the solvent evaporates, sometimes the surface of the resin becomes uneven due to the appearance of ridges. While problems of this sort are relatively limited with Newdine, they can be more pronounced with table adhesives of other manufacturers. If a large amount of adhesive is added at one time while making the film, solvent contained in the resin will not be able to evaporate easily and this may cause the surface of the resin to rise.

The optimum viscosity for application differs according to the type of adhesive resin. In the case of Newdine, a viscosity of around 70 cps is ideal.

If the viscosity of the adhesive is too high, it can be adjusted through the addition of a thinner.

When applying table adhesive to the print blanket of auto screen machines, sometimes when the mesh is lifted, threads of adhesive will be produced between the coating of adhesive and the mesh, causing pockmarks on the surface of the resin. This problem is more pronounced when applying more adhesive over adhesive that has already been applied.

Solvent in newly applied adhesive dissolves the resin of the film that has already been applied, and this causes it to be pulled into threads when the gauze is raised. Since these threads of resin are hollow, if cut, the outside rings will remain raised from the surface of the blanket forming pockmarks.

In order to prevent these pockmarks occurring, pay attention to the following:

1. Make sure that the viscosity of the adhesive is not too high.
2. Application of the adhesive (and the raising of the mesh) should be conducted quickly.
3. Do not use gauze with too fine a mesh. If the mesh is too fine, resin from which solvent has evaporated will be left on its surface. This will lead to the production of threads of resin when it comes into contact with resin on the printing blanket.
4. During operations, the mesh should occasionally be cleaned with solvent.

In addition, ensure that no drops of solvent fall onto the surface of the adhesive resin that has already been applied to the print blanket. Resin will be dissolved anywhere a drop falls, creating a slight depression. Even if adhesive is reapplied over the entire surface, these depressions will still remain. Special care must be taken to ensure that the surface of the resin is not damaged in this way.

3. Specialized Equipment

Since Newdine is not a water-based adhesive, the table must be completely dry before any substrate is fixed to its surface. In addition, the belt should be heated to room temperature or above. The belt is washed as shown in the right of Fig. 13, and moved with the guide roll. Since the guide roll and the belt come into contact, the guide roll must be completely covered with nylon taffeta to prevent resin from adhering to it. (This is not necessary for guide rolls that have been treated with Teflon.)

The belt is heated by the preheater at K in Fig. 13. A preheater incorporating infrared irradiation or blowing with hot air will achieve good results. For woven fabrics such as nylon taffeta that tend to lift off, heating and drying of the belt during printing with additional drying of the belt between screens will ensure good results.

Fig. 13

4. Changing the width of the substrate

In order to engage in operations with a different substrate, the area to which Newdine is applied must be adjusted to suit the width of the new substrate.

The width of a coating of Newdine can be altered with the methods outlined below.

1. Reducing the width

When a substrate is fixed to Newdine that was prepared for a wider fabric, the Newdine which extends beyond the width of the fabric will come into direct contact with the mesh of the screen, thus affecting the lowering and raising of the screen. In this case, apply a harder type of the same series of Newdine (TH, K2H, J2H, ASH) to the protruding areas with a brush or a doctor. (Dilute with an organic solvent during application if necessary.)

2. Extending the width

When a substrate is fixed to Newdine that was prepared for a narrower fabric, the sides of the fabric will extend beyond the Newdine coating and have nothing to adhere to.

A. For the printing of a thick substrate After adjusting its adhesive strength, apply Newdine with a brush or a doctor. (Dilute with an organic solvent if necessary.)

B. For the printing of a thin substrate Do not use method A because it will result in obvious resin marks on the surface of the printed substrate. The best method is to remove all the Newdine and then apply a new coating of adhesive for the width of the new fabric.

5. Removing Newdine

While Newdine of the series T, K and J can be removed with an organic solvent, this is not recommended because of low efficiency and the risks to health as outlined above. We use a remover that readily emulsifies the adhesive in water.

Method:

1. 1. Set a piece of cotton cloth or any other material which will readily absorb the solution (this cloth should be slightly wider than the width of the Newdine coating to be removed and around 2m long) on top of the belt in two or three places as denoted by A in Fig. 14.

Fig. 14

2. Turn the belt on with a low speed of around 3m/min (continuous or intermittent.)
3. Soak the cloth with remover solution.
4. Rinse thoroughly with water at position B as shown in Fig. 15.

Fig. 15

5. Add more remover solution to the cloth as the stripping process proceeds.

With this method, all the Newdine can be removed after 2 or 3 revolutions.

Remover Solutions

1. For Newdine of the series T, K or J, use Remover FK.
2. Three types of belt are currently in use.
   1). Buna rubber
   2). Neoprene
   3). Nitrile rubber

For belts of nitrile rubber, use Remover CL diluted with an equal amount of triclene or trichloroethane instead of Remover FK

3. For A Series, use Remover A conc diluted with 3-5 times as much water.