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Development prospect

The pressure sensitive adhesive industry has been monopolized by international giants and multinational companies for a long time. Many domestic industries need high-end pressure sensitive adhesive products that rely on imports or joint ventures. Since the 1990s, domestic enterprises, scientific research institutes, and other enterprises and institutions gradually began to enter the independent research and development of products in this field. After years of technological accumulation, they have gradually obtained independent intellectual property rights in high-performance organic silicone, acrylic glue, anaerobic glue, epoxy resin glue and polyurethane glue, and other products, and their products are mainly aimed at replacing imports.

In the whole domestic pressure sensitive adhesive industry, there are more than 30 enterprises with independent research and development ability and a certain production scale [1], that own their own brands, and take pressure-sensitive adhesive products as their main business. Therefore, the domestic pressure sensitive adhesive has formed a comprehensive product structure and leading technology of multinational companies. Domestic enterprises focus on the segmentation of the field, and rapid growth, closely follows the competition pattern of foreign competitors, and the overall industry diversification is high.

Pressure sensitive adhesive is the high-end area of the adhesive industry, the requirements of enterprise research and development ability, product technology level, and sales channels are very high. After ten years of rapid growth, the growth of pressure sensitive adhesives has slowed down in recent years. The existing production capacity is excessive and the market competition is fierce, but the application field is constantly being developed, and the annual growth is still in double digits. The output of pressure sensitive adhesive has gradually increased in the past five years.

With the development and application of various new synthesis and curing methods, the performance of pressure sensitive adhesive has been greatly improved. At the same time, in order to meet the requirements of various applications, further development of its application field, but also developed many pressure sensitive adhesives with special functions and uses. The increasing demand for pressure sensitive adhesives in many industries further deepens the research on pressure sensitive adhesive, and the research and development of new pressure sensitive adhesives will be paid more and more attention to by people. In the future, pressure sensitive adhesive will be more environmentally friendly, more convenient, and in a higher performance direction.

What are the initial adhesion and peeling force of pressure sensitive adhesive?

Initial Tack force T (Tack), also called fast tack force, refers to the anti-separation ability shown when PSA products and adhesive are quickly separated immediately after contact with very light pressure.

Adhesion A refers to the ability of adhesion to the PSA product and surface to resist interfacial separation by adhesion at appropriate pressure and time. C(cohesion) refers to the strength of the adhesive layer itself; Adhesive base force K (keying) refers to the adhesion between the adhesive and the substrate, or between the adhesive and the substrate and the substrate.

A good PSA must satisfy the balance of four adhesion properties, that is, T<A<C<K. This is because A must be greater than T, otherwise, PSA is not pressure-sensitive; C must be greater than A, otherwise, the adhesive layer will be destroyed when the tape is removed, resulting in adhesive pollution, sticky surface, wire drawing, and other defects; C must be less than K, otherwise the adhesive layer will be separated from the substrate.

The peeling force of the pressure-sensitive adhesive (the peeling force between the adhesive tape and the adhesive surface) < the cohesion of the adhesive (the force between the molecules of the pressure-sensitive adhesive) < the adhesive base force (the adhesion between the adhesive and the substrate). Such a pressure sensitive adhesive in the process of use will not have the phenomenon of degumming.

Flame retardant polymer mixed with acrylic polymer imparts flame retardant to the acrylic polymer. Generally speaking, the flame-retardant polymer is mixed with an acrylic polymer to produce a uniform composition. They are not only transparent but also elastic, wear-resistant, and self – extinguishing.

Flame retardant polymer

The commonly used allyl chloride oligomer flame retardant pressure sensitive adhesive is to add a chloride of allyl chloride oligomer to the acrylic ester. Ionized by irradiation to induce polymerization. Another common polymer-based flame retardant is vinyl chloride -2- ethylhexyl acrylate copolymer. This flame retardant is actually a copolymer of vinyl chloride and 2-ethylhexyl acrylate, in which the latter content is generally 3% to 5% of the total. This copolymer is mixed with the copolymer of MMA homopolymer or alkyl acrylate mixture to obtain a transparent, self-extinguishing uniform thermoplastic component. In practical application, a small amount of organophosphate ester can be added to increase the flame retardant effect and plasticity.

Polyacetylene benzene polymer

Polyacetylene benzene polymer is a new type of polymer flame retardant explored in recent years. Because a benzene ring containing 3 or more acetylene compounds itself is easy to polymer, the thermosetting resin can also form a copolymer with other monomers. These polymers can be cracked into carbon at high temperatures in the air, and the carbon layer formed is resistant to high temperatures and oxidation. It is predicted that these polymeric-derived carbon-carbon complexes have the potential to withstand extremely high temperatures (1000℃,1500℃, or even 2000℃) in oxidizing environments, and have the potential to be used as ablative materials in re-entry equipment for rocket missile systems and spacecraft.

This polymer is mixed with acrylates to give the acrylates excellent flame retardancy.

Linear siloxane-acetylene polymer

Linear siloxane-acetylene polymer in the field of flame retardant materials is very important, this is because the siloxane group has good thermal and oxidative stability and hydrophobicity, and the diacetylene group can carry out thermal reaction or photochemical reaction and form a toughness of conjugate network crosslinked polymer, Therefore, the resin formed by mixing this polymer with acrylates has excellent thermal oxidation stability and flame retardant.

Chemical flame retardants refer to flame retardants with clear chemical composition and small dosages, and some can indeed have a chemical reaction with polymer. Although the dosage of this kind of flame retardant is small, their efficiency is generally high, and the number of varieties is large, which has the role of similar polymer chemical additives, and they are divided into halogenated flame retardants and halogen-free flame retardants.

(1) The halogen-containing pressure sensitive adhesive widely used at present has excellent flame retardancy.

Organic halide produces active halogen groups in the gas phase, which can effectively change the thermal oxidation process of polymers. The HX released by the decomposition of flame retardants interacts with the H and OH free radicals produced by polymer degradation so that the concentration of free radicals is reduced, thus delaying or terminating the combustion chain reaction.

(2) Chemical flame retardants——halogen-free flame retardants include phosphorous flame retardants, nitrogen flame retardants, antimony flame retardants, boron flame retardants, silicon flame retardants, and smoke suppressors.

1. Phosphorous flame retardant: phosphorous flame retardant is added to the polymer pressure sensitive adhesive when heated, it will decompose into polyphosphate, polyphosphate is a stable compound that is not volatile, forming an isolation layer on the surface of the combustion material. In addition, the dehydration of poly meta phosphate promotes carbonization, so that the surface of the carbonized film, so as plays a flame-retardant role. The main products of inorganic flame retardants containing phosphorus are red phosphorus flame retardant, microcapsule red phosphorus flame retardant, ammonium phosphate, ammonium polyphosphate, and so on. Organophosphorus flame retardants include phosphate ester, phosphonic acid and phosphonate ester, phosphonic oxygen compound, cyclic phosphate ester, phosphorus-containing diols, and polyols. Red phosphorus is easy to hygroscopic hydrolysis, releases toxic phosphine, and industrial products need to be stabilized and coated.
   With the increase in the amount of halogen-free flame retardant materials, the amount of red phosphorus flame retardant (microencapsulated red phosphorus flame retardant) is also increasing, and its flame retardant effect is better than that of phosphate esters. Phosphorous flame retardants also have some disadvantages, such as a large amount of smoke, high toxicity, easy hydrolysis, and poor thermal stability. Therefore, phosphorous flame retardants need to be further studied and improved.
2. Nitrogenous flame retardant: in the decomposition process to form ammonia and other non-combustible gas, dilution and dilution of flammable gas or covered in pressure sensitive adhesive surface and flame retardant. Mainly melamine and its salt, guanidine salt. It has no halogen and low smoke, which is conducive to environmental protection. However, the flame retardant efficiency is generally not high when used alone, and a large amount is required, which often leads to problems in the processing and mechanical properties of the polymer. It is often used in combination with other flame retardant systems (such as phosphorus or halogen).
3. Antimony-containing flame retardant: mainly antimony trioxide (SbO) and antimony pentoxide (Sbs), in the flame retardant application, is mainly used with halogen flame retardant, as a synergistic agent.
4. Boron containing flame retardant: mainly as a synergistic agent of the flame retardant system to use, through melting and then covering in the surface, so that oxygen can not contact with the combustion surface, the further oxidation of the carbon layer has a protective effect. Zinc borate is the most commonly used flame retardant containing boron, its cost is low, and has a synergistic effect with a variety of flame retardants.
5. Silicon-containing flame retardants: The addition of silicon-containing compounds can promote the combustion of carbon in the solid phase, and can capture active free radicals in the gas phase, which is generally considered to be environmentally friendly additives. It mainly includes silicate, polymer nano-layered silicate, and other inorganic silicon as well as linear silane, siloxane, and another organosilicon.
6. Smoke suppressant: the smoke and gas generated when the polymer combustion is the main culprit of death, adding a smoke suppressant can reduce the amount of smoke. The main smoke suppressants available now are zinc borate, alumina trihydrate, molybdenum compound (molybdenum dioxide, ammonium molybdate) and its complex, magnesium-zinc complex, ferrocene, ammonium polyphosphate, tin compounds, etc.

It is not an easy task to assume the role of safety guard against fire. Flame retardants must have excellent skills.

Combustion requires three main elements — combustibles, combustibles (oxygen), and ignition sources.

The process of combustion is divided into heating, decomposition, fire, combustion, and spread. If any of these elements are removed, or if the burning process is controlled to the initial stage of heating and decomposition, the fire can be effectively avoided.

Different types of flame retardants have their own tricks for stopping the flame from burning.

Some prevent combustible materials from producing combustible gases by absorbing heat; Some form a dense covering layer on the surface of fuel to isolate the contact between fuel and oxygen; Some capture the free radicals involved in the combustion reaction, so as to inhibit the free radical chain reaction. Others dilute oxygen by producing a non-flammable gas, thus slowing the rate of combustion.

Inorganic flame retardant Al(OH)3

Inorganic flame retardant Al(OH)3 will decompose when it is heated to 200℃ and give off crystalline water, which evaporates into water vapor when heated. This series of processes absorbs a large amount of heat, reducing the temperature of the material surface and the flame zone, and slowing down the thermal cracking reaction. In addition, the water vapor produced by the crystallizing water also reduces the oxygen concentration, further inhibiting the spread of the fire.

Phosphorous flame retardant

When heated, phosphorous flame retardants turn into a more stable cross-linked solid material or carbonized layer, which acts like a solid armor to wrap the fuel, preventing both further pyrolysis of the material and the escape of the decomposed flammable gas inside the material to continue burning.

Bromine flame retardant

The evaporation temperature of bromine flame retardants is the same or similar to the decomposition temperature of polymer materials. When the polymer materials are decomposed by heat, bromine flame retardants will also volatilize and enter the gas phase combustion zone at the same time as the thermal decomposition products. Flame retardants can quickly capture free radicals in the gas phase combustion zone, inhibit free radical chain reaction, prevent flame propagation, and finally slow down the combustion reaction until termination.

In short, each flame retardant has its own secret.

With the increase of the demand for acrylic pressure sensitive adhesive, more and more attention will be paid to its flame retardant research, with characteristics, new, high efficiency, environmental protection of flame retardant and flame retardant system as the focus of research. The research on green flame retardant additives should focus on the development of new environment-friendly low-smoke, low-toxicity halogen-free products, the use of non-toxic and harmless raw materials, solvents, and catalysts in the production process, the use of environment-friendly chemical reactions.

• Halogen-based flame retardants will eventually be replaced by new, high-efficiency, low smoke, low toxicity, halogen-free products. Because of their excellent flame-retardant properties, physical properties, non-toxic and pollution-free, the carboniferous and carboniferous promoting flame retardants and inorganic polymer nanocomposites will be the focus of research and development.
• Phosphorous flame retardants and inorganic hydroxides will be further studied in the fields of microencapsulation technology, super refinement technology, surface modification technology, and synergistic effect between various flame retardants.

Development of bulk flame retardant acrylate pressure sensitive adhesive

More and more attention will be paid to the development of bulk flame retardant acrylate pressure sensitive adhesive by adding flame retardant groups. The composite technology of flame retardants is also one of the essential ways to achieve high-efficiency flame retardants. The synergistic effect produced by the composite use of organic flame retardants and inorganic flame retardants will be the resistance reaction (protection of amino group), nitration reaction, acid hydrolysis reaction, reduction reaction, and neutralization reaction of synthetic materials to get the ideal target product 3.3’4.4 ‘-tetromino diphenyl ether, the melting point of 152.8℃; There is only one sharp single peak in DSC map, which has high purity. There was an obvious triple amino absorption peak in the FT-IR map.

Therefore, it is certain that the resultant product is 3.3’,4.4 ‘-tetromino diphenyl ether. TADE and terephthalic acid can be polymerized in the system of polyphosphoric acid and P2Os to obtain high molecular weight polybenzimidazole resin, which can be used to manufacture PBI films, adhesives, coatings, and composite materials, especially in the field of fuel cell film production which has been rising in recent years.