Double-sided tape is a roll of adhesive tape made of paper, cloth, or plastic film as the base material, with elastomeric pressure-sensitive or resin-type pressure-sensitive adhesive evenly coated on the above base material. It comprises three parts: base material, adhesive, and release paper (film).

1.Coating method

1.1 Transfer coating: After the release paper is dried in the oven, it is laminated with the laminate material to transfer the glue to the laminate material. It is suitable for double-sided tapes, single-sided label tapes, and foam substrate tapes.

Features:

The film thickness is uniform, and the total thickness of the tape depends on the thickness deviation of the laminate material;

The finished tape or process needs to be peeled off;

The maximum oven temperature can be controlled to 120°C when using release paper.

1.2 Direct coating: The adhesive is directly coated on the substrate and rolled up, also known as back-coiling. Suitable for packaging tapes and removable tapes.

Features:

The adhesive can easily penetrate the interior of the substrate and has good adhesion;

The total thickness of the tape is consistent. When the material has deviations, the thickness of the adhesive layer changes in the opposite direction;

The drying speed and temperature depend on the type of substrate.

2.Drying process and principle

Drying refers to the process of applying adhesive to the substrate and volatilizing the water and solvent in the adhesive at a certain speed to obtain a dry film. The drying process is an important part of the production of tapes and has a great impact on product quality. During the drying process, heat and substances are changing at the same time. The initial drying stage is mainly the continuous transfer of heat from the air into the adhesive, which causes the solvent to diffuse from the inside of the adhesive layer to the surface and reach a saturated state on the surface. This period is called constant rate drying.

The speed of the substance’s movement depends on the amount of heat transferred to the adhesive. After the solvent vaporizes on the surface, the drying enters the rate reduction stage. The surface temperature of the adhesive rises in a short time and enters a higher-temperature oven. The bottom solvent gradually diffuses outward through the surface film. If the initial temperature is too high and the surface film hardens prematurely, it will affect the volatilization of the internal solvent vapor. When the temperature is higher than the boiling point of the solvent, the solvent gas in the adhesive layer will expand and foaming will occur, which will eventually affect the cohesive strength of the adhesive layer. Therefore, it is required to monitor the adhesive surface for foaming. At the same time, confirm whether the smell of the glue is too heavy. On the other hand, check whether the thickness of the glue layer is normal and whether the drying effect is sufficient.

Excessive residual solvent will cause the initial adhesion of the tape to be large, and the performance of the tape will change easily after aging. At the same time, it will increase the peeling property of the release paper. For use, the excessive solvent will affect the adherend or printed layer with poor solvent resistance. The heavy smell during use will affect the working environment. The residual solvent content of the P120 series of gold finger tapes produced by our company is about 1.5%. The drying effect of the adhesive mainly depends on the transfer of heat. To achieve sufficient heat supply, the circulation of hot air in the oven must be guaranteed, so it is necessary to regularly check and clean the filter of the oven in time.

3.Winding

The design of the winding part needs to consider tension control. The tension of the substrate changes with the winding diameter during winding, showing a gradual downward trend. Generally, the slope is used to adjust to reduce the downward trend of tension. It can overcome the problem of air entry when winding is too loose and the problem of winding when too tight. The winding part is designed with a special drive device and a pressing device. When producing double-sided tape and PE protective film tape with single-layer release paper, if air is drawn in, it will cause pattern marks on the surface of the adhesive layer. If there are bubble marks on the appearance of the protective film tape, it will limit the application range of the product (products with high appearance requirements cannot be used). The air drawn in by the double-sided tape (moisture in the air) will cause the product’s adhesive performance to decrease (especially when the air humidity is too high), so it is best to use a pressing shaft to eliminate air when winding.

4.Double-sided tape peeling method

When the second process of double-sided tape is produced, it is transferred to the first process product after being coated with release paper (construction paper) and then peeled off. To achieve the smoothness of the adhesive surface and prevent lateral wrinkles, it is necessary to consider which paper-passing route is more reasonable. When the pliability of the first process surface is relatively small or the adhesive layer is thin and easy to deform, when peeling in the direction of the engineering paper, especially when the winding tension is too large, the adhesive layer is easily pulled up and enters the air, so it is more reasonable to peel in the direction of the tape, and reducing the winding tension can improve the problem of the adhesive layer being pulled up. For example, in the production of foam double-sided tape, to avoid wrinkles in the engineering paper, the method of peeling the tape downward in advance can also be adopted. However, it is easier to control the general double-sided tape to peel in the direction of the engineering paper.

5.Methods to improve the adhesion between adhesive and substrate

The above figure shows the adhesion between adhesive and substrate, reflecting the adhesion between adhesive and substrate. It is ideal for peeling force A and peeling force B to be greater than C, especially for re-peelable (low-viscosity protective film) tapes. If A value is smaller than B or C, adhesive residue will remain on the adherend after peeling.

To meet the requirement that peeling force A is greater than peeling force B, the following methods can be considered:

Primer treatment;

Corona treatment. Plastics generally have low surface energy and are inert, with poor wettability. After treatment, the surface energy can be increased to improve adhesion and printing. After corona discharge, the surface molecules of the material are destroyed, turning into a polar state, and the surface tension increases. The treatment effect depends on the discharge power and the operating speed.

Points to note:

1.Conductive materials cannot be treated;

2.The surface tension of the original material needs to be tested before treatment, and the changes after treatment must be confirmed;

3.The treatment discharge power cannot be too large, and the material may be broken down when the material is thin;

4.Static electricity should be eliminated immediately during treatment to avoid damaging the back material.

5.The treatment effect will gradually decrease with the increase in storage time, and the surface tension must be confirmed before processing.

6.When transferring, the material surface is heated by a heating shaft, or the material is preheated before bonding;

7.Increase the final oven temperature to increase the colloid temperature or increase the bonding metal shaft temperature.