Acrylate pressure sensitive adhesive formula analysis, acrylic pressure sensitive adhesive detection method

 Pressure-sensitive adhesive (pressure sensitive adhesive, PSA), as the name suggests, is a pressure-sensitive adhesive, is a kind of adhesive without solvent, heat or other means, only practical adhesive strength, usually processed into adhesive tape, labels and a variety of sheet products for application.

 

Pressure-sensitive adhesive (pressure sensitive adhesive, PSA), as the name suggests, is a pressure-sensitive adhesive, is a kind of adhesive without solvent, heat or other means, only practical adhesive strength, usually processed into adhesive tape, labels and a variety of sheet products for application.

Due to its inherent advantages, pressure-sensitive adhesive has been widely used in daily life, medical and health care, building materials, automobile, electronics, aerospace and so on. Pressure-sensitive adhesive is divided into five categories according to the main body, among which acrylate pressure-sensitive adhesive has become the largest adhesive type due to its simple composition, high transparency, excellent weather resistance, low toxicity or non-toxic characteristics, and its output accounts for about 40% in the world market. Acrylate pressure sensitive adhesive can be divided into solvent type, emulsion type and light curing type. Acrylate pressure sensitive adhesive can be applied because of non-toxic or low toxicity in food and medical fields.

 

 

Classification of the acrylate pressure-sensitive adhesive

Solvent type polyacrylate pressure sensitive adhesive: acrylate monomers in organic solvents, the commonly used organic solvents are ethyl acetate and toluene. This kind of pressure-sensitive adhesive has the advantages of large initial viscosity, good wettability and fast drying speed than the emulsion type, but due to the addition of organic solvents and the need for retreatment of organic solvents, its problems in environmental protection and energy consumption are increasingly prominent.

Emulsion-type polyacrylate pressure-sensitive adhesive: a certain proportion of acrylate monomer can evenly disperse the acrylic ester copolymer in the water phase in the form of latex particles through the emulsion polymerization reaction. Compared with solvent type, emulsion pressure sensitive adhesive has the advantages of low cost and environmental protection; but its poor water resistance, slow drying speed and poor wetting to low energy surface.

Hot melt polyacrylate pressure sensitive adhesive: hot melt pressure sensitive adhesive is made of polyacrylate elastomer as the main component, with the corresponding adhesive resin mixed evenly, and then coated in the molten state, showing the pressure sensitive viscosity after cooling. It has the advantages of no organic solvent, no pollution, simple formula and easy operation. However, because of its low cohesion strength and high melting viscosity at high temperature, it is only used in special occasions.

Radiation type polyacrylate pressure sensitive adhesive: Radiation curing refers to the polymerization or crosslinking caused by absorbing radiation energy under radiation irradiation. According to the different radiation energy, it is divided into ultraviolet light curing (200-400nm) and electron beam curing (100 keV-5 MeV). Photocuring pressure sensitive adhesive has many advantages: short curing time, high efficiency, available at room temperature, low energy consumption, no organic solvent, green environmental protection; but also limited light penetration, strong radiation damage to the substrate.

 

 

 

Formula analysis of acrylate pressure-sensitive adhesive

Acrylic acid pressure sensitive gel acrylate copolymer generally with the vitrification temperature (Tg) low (methyl) acrylate long chain alkyl ester (soft monomer) as the main monomer component, with a certain amount of Tg higher (methyl) acrylate or other ene monomer (hard monomer) and a small number of functional monomer by polymerization reaction.

The more commonly used soft monomer in industry are isocectyl acrylate (EHA), butyl acrylate (n-BA), ethyl acrylate (EA) and so on. The carbon chain of the hard monomer is short and the Tg is generally high, and the molecular chain of the polymer is more rigid, which provides the cohesin strength for the pressure-sensitive adhesive. Commonly used such monomers include vinyl acetate, (methyl) methyl acrylate, (methyl) ethyl acrylate and styrene, etc.

Functional monomer refers to ene monomers with one or several functional groups such as carboxyl, hydroxyl, epoxy, amine, amide groups and can be copolylated with soft and hard monomers. The existence of active groups can not only improve the adhesion properties of pressure-sensitive adhesive to various substrate, but also provide cross-linking point. By cross-linking or external cross-linking agent cross-linking, the creep resistance and cohesion strength of pressure-sensitive adhesive can be greatly improved, and the heat resistance and aging resistance can also be greatly improved. Commonly used functional monomers are acrylic acid, (methyl) hydroxyl ethyl acrylate, (methyl) hydroxypropyl acrylate, N-hydroxymethacrylamide, maleic anhydride, etc.

Initigger: Acrylate monomer is easy to polymerize, initiator, light, heat or radiation can cause polymerization, but in industrial production rarely use light or heat, mainly peroxides and azo initiators to cause polymerization. Common photoinitiators are 1-hydroxycyclohexyl phenylketone (184), methyl benzoate (MBF), common thermal initiators are benzoyl peroxide (BPO), ditert-butyl peroxide isopropyl benzene (BIPB), etc.

Cross-linker agent: the relative molecular weight of the polymer has a significant impact on the performance of solvent-based acrylate pressure sensitive adhesive, that is, to obtain good pressure sensitive adhesive performance, the relative molecular weight of the polymer must be improved. However, if the relative molecular mass of the polymer is too large, the heat generated in the glue liquid during the polymerization process is not easy to lose, which is easy to cause explosion. On the other hand, the viscosity of adhesive will also increase, thus affecting the coating performance of pressure sensitive adhesive. Common cross-linking agents include acetylacetone aluminum (external crosslinker), HDDA, TMPTA, and TPGDA (internal crosslinker), etc.

Bonded resin: usually, acrylic ester pressure sensitive adhesive do not need to add adhesive resin, the adhesive properties can be controlled by adjusting the type and dosage of monomer, but sometimes in order to broaden its properties, especially for low surface materials (such as PP, PE, etc.) bonding, or in order to reduce the cost of pressure sensitive adhesive, can also add acrylic ester pressure sensitive adhesive resin.

For solvent-type acrylate pressure sensitive adhesive, the adhesive resin can be directly dissolved in a suitable solvent, the representative products are rosin and its derivatives, hydrocarbon resin, terpene resin, phenolic resin and silicone resin, etc. However, because the adhesive resin itself is an oligomer, improving the initial adhesion also affects the cohesion of the pressure-sensitive adhesive.

Therefore, when choosing the adhesive resin, we must consider the softening point, molecular weight and the compatibility between the adhesive resin and the acrylic ester polymer, but also consider adding the appropriate amount, in order to obtain a good adhesive effect.

 

Detection method of acrylate pressure-sensitive adhesive

Acrylate pressure sensitive adhesive is obtained by radical co-polymermerization of acrylic monomer, which has many prominent characteristics. However, no matter which type of acrylic pressure sensitive adhesive still has urgent problems to be solved, and the performance still needs to be optimized in the future. The methods are:

1. Crosslinking modified acrylic pressure-sensitive adhesive:

The crosslinking modification can have an impact on the mechanical properties of polypolymer including the bonding properties, among which the most important effect on acrylate polymer is to increase the creep resistance of PSA. In addition, it can also improve the high temperature resistance, water resistance, oxidation resistance and tensile resistance of PSA.

2. Silica-modified resin:

The modified product, with good adhesion, low temperature flexibility, high temperature resistance, solvent resistance, water resistance and air permeability, is considered as the high-grade products in adhesives.

3. Nanoparticle modification:

The modification methods mainly include in-situ emulsion polymerization method and blending method. The heat resistance, tensile strength, bonding strength, impact resistance, aging resistance, corrosion resistance and coating properties of the PSA of modified by nanoparticles were significantly improved.

4. Other modification methods:

The methods of reactive emulsifier, adhesive resin modification, epoxy resin modification, polyurethane modification, organic fluorine modification, emulsion interpenetration polymer network modification, soap-free emulsion polymerization, core and shell structure modification designed by particles, and multiple polymer composite modification were introduced.