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pressure sensitive adhesive, English name: pressure sensitive adhesives (abbreviation: PSA), its bonding process is very sensitive to pressure so-called pressure sensitive type, pressure sensitive adhesive is generally not directly used in the adhesive, pressure sensitive adhesive is made through a variety of materials pressure sensitive adhesive products (adhesive tape and adhesive label).

Pressure-sensitive adhesive is a kind of viscoelastic body which has both the viscous property of liquid and the elastic property of solid. This kind of viscoelastic body has the influence factors and properties of both the contact process and the failure process of bonding.

Pressure-sensitive adhesive classification:

1. Classification of the main components of the press-sensitive adhesive

① Elastic type pressure-sensitive adhesive

The elastomer used for this kind of pressure-sensitive adhesive was originally natural rubber, and then gradually expanded to a variety of synthetic rubber and thermoplastic elastomer. According to the elastomer used, this kind of pressure-sensitive adhesive can be further divided into natural rubber pressure-sensitive adhesive, synthetic rubber pressure-sensitive adhesive, and thermoplastic elastomer pressure-sensitive adhesive.

• Natural rubber pressure-sensitive adhesive

This is a kind of rubber pressure sensitive adhesive developed the earliest and the output is still large up to now. They are natural rubber elastomer as the main body, with viscosifying resin, softener, antioxidant, makeup filler and crosslinking (curing) agent and other additives complex mixture, because natural rubber has high cohesion strength and elasticity, and can be well miscible with many viscosifying resin, get high viscosity and good wetness to the adhesive material, So natural rubber is a kind of ideal pressure sensitive adhesive body material. Its main disadvantages are the existence of unsaturated double bonds in the molecule, poor light resistance and oxygen aging performance. However, its weatherability and heat resistance can be improved by cross-linking and using antioxidant. Almost all kinds of pressure sensitive adhesive products can be made with natural rubber pressure sensitive adhesive.

• Thermoplastic elastomer pressure sensitive adhesive

Thermoplastic elastomers represented by styrene-butadiene-styrene block copolymer (SBS) and styrene-isopentadiene-styrene block copolymer (SIS) are the main raw materials for manufacturing hot melt pressure-sensitive adhesives. Hot-melt pressure-sensitive adhesive does not use solvents, does not produce environmental pollution, high production efficiency, in today’s society for energy saving and elimination of environmental pollution is increasing, the importance of this kind of pressure sensitive adhesive is also increasing.

② Resin pressure-sensitive adhesive

This kind of pressure sensitive adhesive used resin polyacrylate, polyurethane, polyvinyl chloride, polyethylene ether and so on. Among them, polyacrylate is the most used, and its yield has surpassed that of natural rubber pressure sensitive adhesive.

• Acrylic pressure sensitive adhesive

Acrylate copolymer obtained by copolymerization of various acrylate monomers is one of the most important resin pressure sensitive adhesives. Compared with the rubber type pressure sensitive adhesive, they have many advantages: colorless and transparent appearance and good weather resistance; Generally do not need to use adhesive resin, softener and antioxidant additives can get good pressure sensitive bonding properties, so the formula is simple; By using copolymerization and crosslinking, pressure sensitive adhesives can be prepared to meet different performance requirements. Therefore, in the past 20 years, this kind of pressure sensitive adhesive has developed very rapidly, and has replaced the dominant position of natural rubber pressure sensitive adhesive.

• Silicone and other resin type pressure sensitive adhesives

The pressure sensitive adhesive composed of organic silicone resin and organic silicone rubber has excellent high temperature resistance and aging resistance. It is a kind of more important special pressure sensitive adhesive. Its main use is to manufacture a variety of high-grade pressure sensitive adhesive products.

Polyvinyl ether is a kind of resin pressure sensitive adhesive developed earlier, but its importance has been gradually replaced by acrylate pressure sensitive adhesive.

In addition, ethylene. Vinyl acetate copolymer (EVA), polyurethane, polyester, PVC and other resins can also be prepared into a variety of pressure sensitive adhesives.

2. Press the form classification of sensitive glue

Pressure sensitive adhesive can be divided into solvent pressure sensitive adhesive, aqueous pressure sensitive adhesive, emulsion pressure-sensitive adhesive, hot melt pressure sensitive adhesive and calendering pressure sensitive adhesive five types.

Emulsion, solvent – based and hot – melt pressure – sensitive adhesives are dominant.

3. Press whether the main polymer of the sensitive adhesive is cross-linked

Pressure sensitive adhesives can be divided into crosslinked and non-crosslinked pressure sensitive adhesives. Crosslinked pressure sensitive adhesive can be divided into heating crosslinking type, room temperature crosslinking type, optical crosslinking type, etc. Crosslinked pressure sensitive adhesive has good bonding strength, especially suitable for making permanent pressure sensitive labels.

Bonding mechanism of pressure sensitive adhesive

There is no chemical reaction between the pressure sensitive adhesive and the substrate, so the bonding force between the pressure sensitive adhesive and the substrate is mainly achieved by the intermolecular force between the polymer and the substrate (namely, van der Waals force).

However, the van der Waals force is a short-range force whose force decays rapidly with the sixth power of distance. In order to obtain high strength bonding interface, close contact at the molecular level should be established at the interface, and the molecular spacing should generally be less than 0.5 nm.

However, the solid surface is usually unable to reach the level of 1 nm, which means that the pressure sensitive adhesive needs to have sufficient wettability to spread on the substrate surface, to fill the peak and valley, to promote the two adhesive surfaces to increase the contact area through the adhesive, and to reach the short distance below 0.5 nm of molecular force. So as to achieve a strong adhesive relay.

The relationship between the application performance and the physical performance of the structure

In the use of pressure sensitive adhesive, the main performance includes adhesion and deviscosity, usually evaluated by the following indicators: initial viscosity, holding viscosity, peeling strength and failure mode.

3.1 Initial viscosity

Initial viscosity refers to the adhesion produced in a very short time after pressure sensitive adhesive is subjected to pressure. Good initial adhesion requires strong activity of the adhesive chain segment and good wettability of the substrate. Under small external pressure, it can quickly wet the rough surface of the substrate and reach the molecular level contact, so that countless intermolecular forces can produce sufficient bonding strength.

On the contrary, the bond hysteresis of the polymer with poor chain segment activity is weakened, and the initial viscosity is lower.

From the perspective of dynamics, the pressure sensitive adhesive must produce liquid-like flow under the external pressure of low frequency (about 0.01Hz) to improve the contact area on the rough surface of the substrate, thus improving the bond strength. Therefore, only when the energy storage modulus of the polymer is low, the initial viscosity will be generated.

3.2 Stickiness

Stickiness refers to the ability of a pressure-sensitive adhesive to resist persistent shear creep damage after sticking to an object.

In daily use, you will find that the double-sided adhesive tape of the bonding material will automatically fall off after a long time, and adhesive marks will remain on the surface of the bonded material, which means that the failure mode of the adhesive tape is mainly manifested as the cohesive damage of the pressure sensitive adhesive, which indirectly indicates that the adhesive property of the adhesive tape is mainly determined by the cohesive strength of the pressure sensitive adhesive.

Therefore, increasing the energy storage modulus of polymer at low frequency (frequency of load action) can improve the stickiness of pressure-sensitive adhesive.

3.3 Peeling strength

Peel strength refers to the force required for the adhesive layer to peel off from a standard substrate at a constant rate and Angle, mainly reflecting the size of the adhesion force between the pressure sensitive adhesive and the surface of the adhesive.

Some researchers have found that the peel strength of all pressure-sensitive adhesives is proportional to the ratio of (frequency 435 Hz) to (frequency 1 Hz). It is believed that the mass of pressure-sensitive adhesives can be described by the size (25 ℃) and glass transition temperature at 0.1 and 100 Hz, where the frequency 0.1 Hz corresponds to the formation of cementation. And 100 Hz corresponds to desviscosification. A good pressure sensitive adhesive is lower at low frequencies, indicating that cementation is easy to form, and higher at high frequencies, indicating that it has better resistance to stripping.

3.4 Failure Mode

Failure mode, pressure sensitive adhesive failure mainly has two forms: interface failure and adhesive layer failure. The interface failure is caused by the poor “viscosity” of the substrate, mainly depends on the adhesion strength between the adhesive and the substrate, and the adhesive layer failure is mainly caused by the low cohesion strength of the adhesive itself.

In general, what is expected to happen when stripping is interface failure (no residual glue will be left), and should try to avoid adhesive layer failure (cohesive failure), so when considering the stripping strength, it is often necessary to consider the change of failure mode of pressure sensitive adhesive.

In recent years, the demand for pressure sensitive adhesive has maintained a fast growth rate, especially the development of high-performance special pressure sensitive adhesive is particularly rapid, its production and sales continue to rise sharply, has become the world’s highest sales of pressure sensitive adhesive varieties. Silicone pressure sensitive adhesive has higher chemical resistance, temperature resistance and dielectric properties than other organic pressure sensitive adhesive.

It has the highest temperature resistance (up to 300℃ for short-term use) and the widest temperature range (-75 ~ 260℃) in all pressure sensitive adhesive. It can be widely used in the production of electrical and electronic adhesive tapes and other products requiring temperature resistance. In addition, silicone pressure sensitive adhesive can withstand the cold and hot multiple cycles, which is incomparable to other pressure sensitive adhesive.

With the increasing market competition, people have put forward higher requirements for other properties of silicone pressure-sensitive adhesive. For example, in automotive, building window film and other fields, the demand for silicone pressure-sensitive adhesive with higher peeling strength (>1000g/inch) has been put forward.

However, at present, the low peeling strength of many pressure sensitive adhesive cannot meet this demand. In view of the existing organosilicone pressure sensitive adhesive is mainly composed of polysiloxane elastomer, viscid MQ silicone resin, catalyst, additives, and the key to improve the peeling strength is mainly viscid MQ silicone resin. Therefore, the invention modifies MQ silicone resin in order to obtain an organosilicone pressure sensitive adhesive with improved peeling strength.

As a professional acrylic pressure sensitive adhesive supplier, Smprotectivefilm is committed to solving the glue problems encountered by customers due to different production equipment and processes.

Compared with traditional solvent-based pressure sensitive adhesive, our emulsion pressure sensitive adhesive has the advantages of environmental protection, safety and easy operation. Using deionized water instead of traditional solvent reduces the pollution to the environment and is an ideal environmental protection product.

By adjusting the proportion of curing agent, pressure sensitive adhesive with different adhesive force can be obtained to meet the needs of different applications. Suitable for a variety of materials, transparent after drying.

Transdermal medicated patch, also known as “plaster”, is a kind of external use of traditional Chinese medicine. It is made of vegetable oil or animal oil and boiled into a gelatinous substance. It is applied on the side of cloth, paper or skin and can be pasted on the affected area for a long time, mainly used for treating boils and relieving swelling and pain. Black plaster has the effect of reducing swelling, removing poison, relieving pain and promoting blood circulation.

It is an important part of traditional chinese medicine, western medicine and orthopedics, and is widely used in clinic. The medicine in the plaster is directly pasted on the body surface acupoints, the property through the fur from the surface into the subcutaneous tissue, on the one hand, the relative advantage of the concentration of the drug in the local, on the other hand, through the operation of the meridians, direct to the disease of the zang fu organ disorder of Qi disorder, play the drug “return to the meridian” and functional effect, so as to give full play to the maximum systemic pharmacological effect.

However, in addition to damaging nerve, blood vessel, muscle and other tissues and intestinal reactions, traditional injection and oral therapy is not easy for patients to accept, and these methods are easy to make drugs through the whole body’s blood circulation and intestinal damage, and few drugs actually reach the local area of the disease, so the amount of drugs used is very large, and the targeted effect is poor. The external treatment of plaster completely solves this problem.

The drug acts directly on the affected area, making the efficacy several times higher, and is not easy to produce drug resistance. Nowadays, most drugs are taken orally, and the market of percutaneous patches drug release fast, high cost, poor effect, low cure rate, obvious side effects. Pressure sensitive adhesive is the key material of transdermal drug delivery patch. It is usually dissolved in organic solvent before coating, which has the problems of environmental pollution and high energy consumption. The rapid development of emulsion pressure sensitive adhesive in recent years is also limited by slow drying speed, emulsifier migration and other problems. Hot melt pressure sensitive adhesive is thermoplastic polymer as the main body of the pressure sensitive adhesive, in the molten state coating, do not need to use organic solvents.

It has the advantages of low pollution, fast coating speed and so on. It is widely used in packaging, medical and health. It has been found that hot melt pressure sensitive adhesive has good compatibility with lipophilic drugs and fast release speed, so it is expected to be the material of this kind of drug patch.

In recent years, for smart phones, liquid crystal displays, vehicle components as the representative of the electronic equipment, not only requires high performance, but also requires space saving, energy saving. In this society, electrical and electronic components are becoming smaller and smaller, and the assembly process is becoming more complicated and difficult. In recent years, technologies that can selectively and collectively transfer such micro-refined components and components have been developed.

Transferring the technology, called Micro Printing (Micro-Transfer-Printing) technology, is the use of adhesion of disposable picking up subtle parts of the elastomer, causing them to Transfer the adhesion strength of the desired place.

As the pressure-sensitive bonding material used in this purpose, organosilicon elastomers are known, and a large number of heating and curing types of solvent-free organosilicon system pressure-sensitive adhesives have been proposed. However, in the case of the heating and curing type of silicone pressure-sensitive adhesive, energy is required due to the heating process, in addition, the heating and cooling of the material takes a lot of time. In order to eliminate such a process, the development of organosilicone resin which can be cured in a short time by using ultraviolet light has been carried out. However, due to the adhesive strength of organosilicon raw material itself, there are some problems such as insufficient cohesive force and limited components and components that can be used.

Therefore, in terms of materials, it is desirable to have UV-curable pressure-sensitive bonded silicone materials that can also be applied to components and components that are not lifted and have stronger adhesion. However, if the adhesion is simply increased, it is easy to incur cohesive failure when the pressure-sensitive adhesive is removed from the transfer, and there is a problem of the pressure-sensitive adhesive remaining in the transferred components and components. Therefore, there is a strong desire to develop materials that can be cured by ultraviolet light, that can be adjusted from weak adhesion to strong adhesion according to the member, and that, although they have strong adhesion, do not cohesively break when stripped.

The existing pressure-sensitive tape cannot meet the environmental requirements of high temperatures and humidity.

In recent years, with the development of the national economy and scientific and technological level, the adhesive has become an indispensable new material in the development of high and new technology and has been widely used in various sectors of the national economy and related fields of daily life. With the development of China’s industry, the application field of adhesives has been expanding, from mainly used in wood processing, clothing, light industry, construction, and packaging industries to new energy, machinery manufacturing, aerospace, electronic and electrical appliances, transportation, environmental protection and energy saving, medical and health and many other fields, has become an indispensable important chemical product in the national economy and people’s life. Adhesive tape is a specific structure of pressure sensitive adhesive and a variety of thin materials. It is one of the tools often used to fix parts in daily life and work.

According to its function, it can be divided into high temperature tape, double-sided tape, conductive tape, special tape, pressure sensitive tape and die cutting tape. With the thinning and globalization of electronic products, electronic products demand more and more adhesive tape, and more and more strict, adhesive tape in electronic products increasingly prominent importance.

At the same time, the tape also put forward more physical requirements, such as enhanced universality, not only to metal, PET and other easily adhesive surface bond stability, but also to PE, PP or PC with glass fiber adhesive strong; It should meet the needs of temperate and tropical environments as well as cold regions such as the north and Europe. With the opening of the global market, the export of many electronic products increases, resulting in more and more electronic products need to meet the requirements of high temperature and humidity environment, but the adhesive tape in the existing technology can not meet these environmental requirements.