Composition and Formulation of Rubber Pressure-Sensitive Adhesives

Rubber type pressure sensitive adhesive is made of natural rubber or synthetic rubber with appropriate tackifying resins, softeners, antioxidants, fillers, crosslinking agents, solvents, etc. Rubber is the main component, which imparts sufficient cohesive strength to the pressure sensitive adhesive. The tackifying resin provides a certain degree of adhesiveness to the pressure sensitive adhesive. The softening agent is used to reduce the bulk viscosity of the pressure sensitive adhesive and improve the initial tack at low temperatures. Rubber-based pressure-sensitive adhesives can be made into solvent-based, water-emulsified, and solvent-free (mainly calendered) and other forms. Among them, solvent-based rubber-based pressure-sensitive adhesives are still used more often and are more important.

Rubber pressure-sensitive adhesive composition and formula

First, rubber elastomer

Rubber elastomer is the main component of rubber-based pressure-sensitive adhesive. Its main function is to impart necessary film-forming properties, cohesive strength, and elasticity components in viscoelasticity. Actually used as a rubber elastomer are natural rubber and partially synthetic rubber such as natural rubber, styrene-butadiene rubber, polyisobutylene, butyl rubber, cis-1,4-polyisoprene rubber, butadiene rubber, and the like and their Reclaimed rubber, natural rubber latex, styrene-butadiene latex, etc.

The average molecular weight of natural rubber is high and has a certain degree of crystallinity, and the cohesive strength is high. The pressure-sensitive adhesive obtained has a good tack force. Natural rubber has low glass transition temperature and good elasticity over a wide temperature range (-70~1300C). Therefore, the pressure-sensitive adhesive made is soft, elastic, and has good low temperature performance. The polarity of natural rubber is small and easy to work with. The non-polar tackifying resin is miscible, and the surface pressure of the pressure-sensitive adhesive made is low, and it is easy to wet the solid surface. Therefore, the initial tackiness and adhesiveness are relatively good. It is the most ideal elasticity of rubber for making pressure-sensitive adhesives. body. As the natural rubber molecules contain a large number of unsaturated double bonds, the weathering resistance is poor, and oil and organic solvents are poor.

Styrene butadiene rubber and tackifier resin compatibility is not as good as natural rubber, adhesive properties and natural rubber, butyl benzene rubber resistance to aging, low water absorption, low oil resistance, oil resistance, plasticizer resistance, low prices Therefore, it is often mixed with natural rubber or used alone to prepare a pressure-sensitive adhesive with good water resistance, aging resistance, and oil resistance.

Butyl rubber retains the advantages of polyisocyanate, but it has double bonds in the molecule and can be vulcanized and crosslinked. In addition, halogenated butyl rubber and partially sulfurized butyl rubber can also be used to formulate pressure-sensitive adhesives. However, due to the fact that its three major pressure-sensitive adhesive properties (initial adhesion, adhesive force, and cohesion) are difficult to achieve a high level of balance, Can not be used as a universal pressure sensitive adhesive, can only be used to manufacture metal protection and anti-corrosion pressure sensitive adhesive products.

Second, tackifying resin

Tackifying resin is an important component of the pressure sensitive adhesive. Its role is to give the necessary initial viscosity and adhesive force of the pressure sensitive adhesive. Research shows that when the tackifying resin exceeds a certain amount, it forms a two-phase dispersion system with the rubber. Rubber is a continuous phase, giving the pressure sensitive adhesive a sufficient cohesive strength; a tackifying resin and a small amount of a low molecular rubber are the dispersed phases, forming a very thin viscous layer at the adhesive interface, viscous flow can occur directly in the external force, and the wetted be Sticking the surface increases the initial tack force. When the tackifier resin and the rubber are used properly, the tackifier resin can be well dispersed in the rubber phase. At this time, the initial tack force reaches a maximum, and the performance is best. If the amount of the resin is too large, a sharp phase change takes place and the resin When the phase changes to the continuous phase and the rubber phase changes to the dispersed phase, the adhesive layer loses its initial tack force (adhesive force produced after the adhesive is adhered to the adherend for an instant (0.2 to 10 seconds or 5 to 10 minutes)).

The two-phase morphological point of view does not satisfactorily prove that the initial viscosity varies with the nature of the viscosity-enhancing lipid consumption. It was explained from the perspective of polymer viscoelasticity that the dissolution of the resin makes the rubber phase independent of the phase separation. The decrease in viscosity is the main reason for the increase in initial viscosity. With the increase in the use of resin, the apparent viscosity of the system decreases, and the initial tack force increases. The lower the softening point of the resin, the lower the minimum viscosity value reached, and the higher the initial tack, the greater the amount of resin needed to reach the lowest viscosity. The addition of a tackifying resin reduces the elastic modulus of the pressure sensitive adhesive, changes the viscoelasticity, increases the viscosity, and increases the initial tack, which is the scientific, more thorough explanation of the nature of the tackifying effect.

The tackifying effect mainly refers to the effect of the tackifier resin added on the pressure-sensitive adhesive performance of the adhesive, ie, the initial tackiness, the 1800C peel strength and the tack force, and the balance relationship between them. The better the three physical properties, the better the tackifying effect.

Third, softener

Softeners, also known as plasticizers or viscosity modifiers, can reduce the bulk viscosity of the pressure sensitive adhesive, improve the wetting of the adhered surface, and increase the initial tack, especially at low temperatures. With the increase of the amount of softener, the initial tack force increases first and then decreases, the holding tack force decreases significantly, and the 1800C peel strength also decreases.

Commonly used softeners are oils and fats, including mineral oils and vegetable oils, such as transformer oils, petrolatum, naphthenic oils, lanolin, stearic acid, () sesame oil, glycerin, liquid paraffin, and the like. The mineral oil softening effect is good and cheap, the naphthenic oil has good comprehensive performance and is used in many ways, such as liquid rubber and resin, such as low molecular weight polyisobutylene, polybutene, liquid polyisoprene, depolymerized rubber. , liquid terpene resin, liquid Coumarone resin, etc. Because the relative molecular mass is larger than that of oils and fats, its softening effect is relatively small, but it has a certain viscosity-increasing effect. Synthetic plasticizers, such as dibutyl phthalate, dioctyl phthalate, tricresyl phosphate, etc., have good compatibility with rubber, softening effect, and colorless and transparent, especially suitable for the manufacture of light-colored Transparent pressure sensitive adhesive products.

IV. Antioxidants

Natural rubber, styrene-butadiene rubber, rosin, and terpene resins in rubber-based pressure-sensitive adhesives all contain double bonds, and they degrade or crosslink under light, heat, oxygen, etc., resulting in significant aging phenomena, making pressure-sensitive adhesives. The layer is gradually brittle, losing its elasticity and tackiness, and its performance is degraded so that it cannot be used. Therefore, an appropriate anti-aging agent must be added. Commonly used antioxidants are 264, antioxidants D, antioxidants MB UV absorbers. It must be noted that some anti-aging agents are contaminating (such as anti-aging agent D), and some anti-aging agents have vulcanization promoting effects (such as MB). The amount of anti-aging agent is generally 0.5 to 2.0 parts by mass.

V. Filler

In order to reduce costs, improve performance and coloring, etc., certain pigment fillers are sometimes added. Some inorganic salts and metal oxides or hydroxides, such as calcium carbonate, silicates, talc, barium sulfate, are commonly used. Lithopone, zinc oxide, titanium dioxide, aluminum hydroxide, starch, etc. The use of pigment fillers can generally increase the cohesion of pressure-sensitive adhesives more or less, but at the same time it will reduce the initial adhesion and release force. The use of pigment fillers must pay attention to particle size, shape, water content, acidity and specific surface to pressure-sensitive Adhesive effect.