1. The adhesive mechanism

Since fabric setting involves a certain type of adhesive, before we can embark upon a discussion of fabric setting, it is important that we first understand what adhesion is.

Adhesion is the result of forces between molecules when two materials come into contact. These forces (intermolecular force) are thought to consist of two types: 1) chemical bonding forces, that is, forces arising from covalent bonds, ionic bonds, coordinate bonds and metallic bonds (primary bonding forces); and 2) van der Waal's forces (secondary bonding forces). Primary bonding forces are much stronger than secondary bonding forces.

Table adhesives that temporarily fix fabrics for printing through Van der Waal's forces must meet the following requirements:

1. The fabric is securely fastened to the printing table during printing.
   
2. Adhesive does not remain attached to the fabric after printing.

Fig. 1 shows a cross-section displaying how table adhesives function. In the diagram, fabric (F) has been set over table adhesive (R) that been applied to the surface of a printing table (T).

van der Waal's forces include:

1. An orientation effect that reserves the equilibrium between the adhesive and the substrate.
   
2. An induction effect in which nonpolar molecules polarize due to the charge of other molecules.
   
3. A dispersion effect in which two nonpolar molecules attract each other through temporary dipoles produced by their relative structures.

Forces arising from these three are commonly called cohesive forces. Cohesive forces include those between molecules of the same type and those between molecules of different types. In Fig. 1, the forces F-F, R-R, and T-T are cohesive forces between molecules of the same type, and the forces T-R and R-F are cohesive forces between molecules of different types. Fabric setting places certain demands on the forces R-R, T-R and R-F.

As mentioned previously, the goal of fabric setting is the temporary fastening of the substrate for the purpose of printing. Since the substrate must be peeled off the printing table after printing, the force between the table adhesive and the substrate (R-F) must be smaller than the force between the adhesive and the printing table (T-R). If the reverse is true, the table adhesive will adhere to the substrate. Thus it is important to maintain the following relationships during fabric setting:

2. Important points in fabric setting

1) Area of adhesion

In order to achieve a high level of adhesion, it is important to maximize the area of contact between the substrate and the table adhesive. When, for example, table adhesive is directly applied to a wooden printing table (most adhesives can penetrate wood), the table adhesive forms an uneven film as shown in Fig. 2. Since the area of contact between the table adhesive and the substrate is limited to the raised sections, the area of adhesion is extremely small and the adhesive strength is relatively weak. Measures must be taken to ensure the surface is smooth in order to increase the area of adhesion.

2) Application pressure

The force applied when the substrate is fixed to the table adhesive is called here the application pressure.

Increasing the application pressure increases the area of adhesion because the adhesive enters the substrate more effectively. This increases the friction and the cohesive force between molecules of different types. Thus, it is important to use as high an application pressure as possible.

3)Temperature

Since table adhesives of synthetic resin are thermoplastic, the strength of adhesion varies according to the temperature. Thus it is important to consider the temperature before blending the table adhesive.

4) Quantity

If an insufficient quantity of table adhesive is applied, the desired adhesive strength will not be achieved. For the first film, the adhesive should be applied through 5 or 6 separate operations so that it exceeds 200g/m². At this point, one must be careful to limit the amount of adhesive that is added during a single application, otherwise the film may break as shown in Fig. 3, causing solvent (containing resin) from under the surface to attach itself to the substrate. Thus, the adhesive should be applied a little at a time in repeated operations between which the resin is allowed to dry.