Pressure sensitive adhesive, refers to a kind of adhesive which can be bonded instantly under a little pressure. Pressure sensitive adhesives are generally divided into three types: solvent activation type, heating type and pressure sensitive type, among which the pressure sensitive type is the most convenient and develops rapidly.
I. Classification of pressure sensitive adhesives.
Pressure sensitive adhesive can be divided into rubber pressure sensitive adhesive and resin pressure sensitive adhesive according to the type of adhesive.
1. Rubber pressure sensitive adhesive.
Rubber pressure sensitive adhesive with rubber as adhesive, adding tackifier, filler, antioxidant and so on. According to the type of rubber, it can be divided into natural rubber, polyisobutene rubber, styrene-butadiene rubber pressure sensitive rubber and so on.
2. Resin pressure sensitive adhesive.
The adhesive of resin pressure sensitive adhesive is synthetic resin, which has homopolymer resin and copolymer resin. Usually, the composition also includes tackifier, softener, filler and antioxidant. According to the type of resin can be divided into polyolefin, chlorine vinegar copolymer, acrylic resin, silicone and fluorine resin pressure sensitive adhesive and so on.
II. Composition of pressure sensitive adhesive.
1. Sticky material.
The adhesive of pressure-sensitive adhesive is rubber or synthetic resin, its function is to give the adhesive layer enough cohesion strength and adhesion, the dosage is 30%-50%.
Tackifier has rosin and its derivatives, petroleum resin and so on, its function is to increase the adhesive layer adhesion. The dosage is 20%-40%.
The plasticizer used is a plasticizer for general plastic processing, and its function is to increase the fast viscosity of the adhesive layer. Its dosage is 0-10%.
General rubber, plastic antioxidant are available, the role is to improve the service life, the dosage is 0-2%.
The filler used is general plastic filler, the function is to improve the cohesion strength of the adhesive layer, reduce the cost, the dosage is 0-40%. In addition, for some pressure-sensitive adhesives, viscosity regulators, curing agents and solvents need to be added.
III. Common types of pressure-sensitive adhesives.
At present, there are three main types of pressure-sensitive adhesives: rubber pressure-sensitive adhesive, acrylate pressure-sensitive adhesive and silicone pressure-sensitive adhesive.
1. Rubber pressure sensitive adhesive.
Rubber pressure sensitive adhesive is a kind of pressure sensitive rubber which is widely used at present. There are natural rubber, synthetic rubber and recycled rubber.
The pressure sensitive adhesive with natural rubber as adhesive has good compatibility, pressure sensitivity and creep resistance, but the aging resistance is poor and the hardness changes greatly.
The pressure sensitive adhesive with synthetic rubber as adhesive has good heat resistance and durability, but the bonding strength is poor.
Recycled rubber as adhesive, recycled rubber that can only usually use natural rubber. For the pressure sensitive adhesive with natural rubber as adhesive, natural rubber can be mixed with synthetic rubber, partially vulcanized and crosslinked, grafted or modified by adding appropriate reinforcement filler. These methods can improve the aging resistance of the adhesive layer and increase the service life of the adhesive.
2. Acrylate pressure sensitive adhesive.
The adhesive of acrylate pressure sensitive adhesive is the copolymer of acrylate and other ethylene monomers. The comonomer is divided into main monomer, secondary monomer and functional monomer. The main monomer has butyl acrylate and so on, the function is to provide toughness and adhesion. The secondary monomers are methyl methacrylate and styrene, which are hard monomers and can provide rigidity and cohesion strength. Functional monomers are monomers containing other functional groups, such as ethyl methacrylate, which can play a cross-linking role in the process of polymerization and further improve adhesion, cohesion and heat creep resistance. This scientific monomer combination can make the copolymer itself have the basic properties of pressure-sensitive adhesive, so acrylic pressure-sensitive adhesive is almost one-component.
Acrylic pressure sensitive adhesive has excellent weather resistance and heat resistance, good oil resistance, transparent adhesive layer and no phase separation and migration phenomenon. Because a variety of polar groups can be introduced through copolymerization, the secondary valence force between molecules can be increased, so it has large bonding strength and cohesion strength.
3. Silicone pressure sensitive adhesive.
Silicone pressure sensitive adhesive is made of silicone rubber and silicone resin. Silicone rubber is the basic component of pressure sensitive adhesive and silicone resin is used as tackifier. The properties of pressure sensitive adhesive change with the change of the ratio of them.
When selecting raw materials, silicone resin is usually required to have an active end group at the end. Commonly used are methyl silicone resin, methyl phenyl silicone resin, phenyl vinyl silicone resin. They all have good thermal stability, and silicone pressure sensitive adhesive has outstanding advantages in bonding properties.
IV. Composition of pressure sensitive adhesive tape.
Pressure-sensitive adhesive tape is generally made into a ribbon drum, there are one-sided adhesive, double-sided adhesive and adhesive film three forms.
One-sided glue is coated on the front of the substrate after the bottom coating, and then coated with pressure-sensitive adhesive, and the reverse side is coated with the back treatment agent, then the drum can be applied.
Double-sided adhesive tape and one-sided adhesive film do not need back treatment agent, but need a layer of isolation paper on one surface.
Bottom coating agent, also known as bottom treatment agent, bottom glue. Coating the bottom coating between the pressure sensitive adhesive and the substrate can enhance the adhesion of the pressure sensitive adhesive to the substrate and prevent degumming.
The back treatment agent is a layer coated on the back of the single side adhesive tape substrate, which can act as an interlayer isolation when the adhesive tape is rolled into a circle.
For double-sided adhesive tape, label, adhesive paper, adhesive film, etc., its pressure-sensitive adhesive surface should be covered with a layer of isolation paper.
V. Adhesion characteristics of pressure sensitive adhesive.
The pressure sensitivity of pressure sensitive adhesive is the manifestation of its adhesion characteristics, which are composed of four elements: fast adhesion, cohesion and adhesion.
Fast adhesion usually refers to the initial viscosity, which is a kind of interfacial peeling force when the adhesive tape and the adhesive are separated immediately after contact with the lightest pressure and the fastest speed, and it is also the ability of viscosity and pressure-sensitive adhesive to infiltrate the adhesive.
Adhesive force refers to the peeling force between the adhesive tape and the surface of the adhesive after proper bonding, and its size determines the adhesion of the adhesive tape.
Cohesion is the cohesion strength of adhesive layer, which is related to intermolecular force, intermolecular bond, molecular size and intermolecular arrangement.
The adhesive force is the adhesive force between the pressure sensitive adhesive and the substrate.
Generally speaking, the relationship between the four forces is fast adhesive force < cohesive force.