In the hot-melt adhesive industry, petroleum resin is gradually replacing natural rosin and terpene resin at home and abroad to meet the requirements of packaging products, pressure-sensitive tapes and other disposable products. It is an inevitable trend for petroleum resin to replace rosin and terpene resin as hot melt adhesive.
What is petroleum resin?
Petroleum resin is a kind of low molecular polymer obtained by cationic polymerization with C5 and C9 fractions as raw materials, which can be roughly divided into C5 aliphatic petroleum resin with C5 fraction as raw material, C9 aromatic petroleum resin with C9 fraction as raw material, C5-C9 copolyester petroleum resin with C5 and C9 fraction as raw material, and dicyclopentadiene (DCPD) grease There are five kinds of cyclo petroleum resin and hydrotreated petroleum resin.
Properties of petroleum resin
The softening point of petroleum resin is generally 80-140 ℃, the relative density is 0.970-0.975, the relative molecular weight is less than 2 × 103, insoluble in water, easily soluble in organic solvents, with the characteristics of low acid value, good adhesion, water resistance and chemical resistance, as well as good regulation of viscosity and thermal stability. Therefore, petroleum resin can completely replace rosin resin and terpene resin for hot-melt adhesive and pressure-sensitive adhesive to improve the wettability and adhesion. The emergence of petroleum resin also solves the problems of limited sources, poor thermal stability, expensive price and easy aging of natural rosin and terpene resin, and the performance of rosin resin modified hot melt adhesive can be achieved by using petroleum resin with mass fraction of 60%.
Performance index of petroleum resin for hot melt adhesive
In the preparation of hot-melt adhesive and pressure-sensitive adhesive, only the matrix resin has the bonding force when it melts at a certain temperature. Once the temperature drops, the bonding will decline or even lose the bonding ability. Adding petroleum resin into the elastomer can not only improve the viscosity and wettability of the hot melt adhesive, improve the surface contact effect and characteristic adhesion performance, and obtain the ideal balance between the viscosity, cohesive strength and interface strength, but also increase the glass transition temperature of the mixture and the heat resistance temperature of the hot melt adhesive by adjusting the rheological property of the adhesive, so as to expand the heat resistance of the hot melt adhesive Use environment. As the amorphous petroleum resin polymerized from mono olefin and Bi olefin with complex components has no fixed melting point, the global softening point of the resin becomes an important factor to determine the performance of the resin, and other physical properties of the petroleum resin such as chromaticity, compatibility, melt viscosity, acid value and iodine value are also important factors to determine the application field of the petroleum resin. The indexes of petroleum resin used in hot melt adhesive industry are shown in the table below. In addition to the above basic requirements, the petroleum resin for hot-melt adhesive and pressure-sensitive adhesive should also have the characteristics of good thermal stability, high shear strength, fast curing speed, uniform and stable dispersion of filler, and strong wettability. There are many preparation methods of petroleum resin for hot-melt adhesive and pressure-sensitive adhesive abroad, and various modifiers are used. Styrene and its derivatives, terpene, pinene, maleic anhydride and C9 fraction with complex components are all used for the preparation of tackifying resin.
Influence of compatibility
The compatibility between petroleum resin and elastomer is an important factor affecting the bond strength of hot melt adhesive. The adhesive resin and elastomer with good compatibility can reduce the amount of energy storage membrane of the colloid, and make the colloid fully adhere to the adherend under certain stress; if they are not compatible, the amount of energy storage membrane of the colloid will increase, which will reduce the adhesion between the colloid and the adherend. The compatibility between tackifying resin and polymer matrix is a physical quantity related to their polarity and relative molecular weight of resin. For example, aromatic polystyrene (PS) is not compatible with natural rubber, but with aromatic styrene butadiene rubber; polyethylene cyclohexane (pvch) with average molecular weight of 650 is very compatible with natural rubber, but pvch with relative molecular weight of 1800 is not compatible with natural rubber. In the preparation of hot-melt adhesive, if the compatibility between the petroleum resin and the elastomer is very poor or incompatible, increasing the petroleum resin in the system will easily cause the initial adhesion strength, the adhesion strength and the 180 ° peel strength of the pressure-sensitive adhesive to decrease at the same time, and the petroleum resin can not play a role in increasing the viscosity. The relationship between the properties of petroleum resin and the properties of hot melt adhesive is as follows:
Discussion on compatibility
Different kinds of petroleum resins, because of their different molecular structures, have good viscosity only when they are compatible with corresponding elastomers. In general, C9 petroleum resin prepared by cationic catalytic polymerization or thermal polymerization has high softening point and strong polarity, and has poor compatibility with natural rubber, styrene isoprene styrene block copolymers (SIS) and other elastomers with conjugated diene structure, so it is not suitable to be used as viscosity enhancer of these rubber adhesives, but it is not suitable for SBS and benzene Ethylene butadiene rubber (SBR) has good compatibility and can be used as a tackifier for this kind of elastomer. From the general compatibility range of elastomer and petroleum resin, it is better to choose C9 petroleum resin and C5-C9 Copolymerized Petroleum Resin as viscosity enhancer with SBS and SBR as elastomers, SIS as elastomer, C5 petroleum resin and C5-C9 copolymerized resin as viscosity enhancer. The details are shown in the table below.
Softening point effect
The softening point of petroleum resin is generally determined by the relative molecular weight of the resin and the structure of the resin, which is about 40-50 ℃ higher than its glass transition temperature Tg. The larger the relative molecular weight is, the higher the ring structure proportion is, the higher the softening point of petroleum resin is. The softening point of petroleum resin has a great influence on the adhesive strength of hot melt adhesive. The higher the softening point of the resin, the stronger the cohesive strength of the resin, the higher the adhesive holding strength, the higher the service temperature of the hot melt adhesive, and the wider the application range. Therefore, the softening point of tackifier is required to be as high as possible in use, but too high softening point may improve the melt viscosity of resin, reduce the wetting ability of hot-melt adhesive, but it is not conducive to the bonding of hot-melt adhesive. If the melt viscosity is reduced by increasing the sizing temperature of hot melt adhesive, it is easy to cause the thermal degradation of the matrix resin and reduce the service life of hot melt adhesive. The softening point of petroleum resin is generally between 80 ℃ and 130 ℃. In addition, the softening point of petroleum resin has a great influence on the curing speed and sizing speed of hot melt adhesive. Too high softening point is also easy to cause the hardening and crusting of hot melt adhesive.
Effect of melting viscosity and thermal stability
The melting viscosity of petroleum resin is often determined by its molecular weight, molecular weight distribution and structural characteristics. At high shear rate, the viscosity of monodisperse or narrow molecular weight distribution polymer is higher than that of wide distribution polymer; at the same injection and extrusion processing conditions, the fluidity of wide molecular weight distribution polymer is better than that of narrow distribution polymer.
The hot-melt adhesive with low melting viscosity can spread well on the base material, increase the contact area between the hot-melt adhesive and the base material, improve the infiltration degree of the hot-melt adhesive on the adherend, which is conducive to the improvement of the interface strength between the hot-melt adhesive and the adherend; however, the low melting viscosity may cause the settlement of the filler in the hot-melt adhesive system, resulting in the uneven distribution of the material composition, On the other hand, it may lead to the decrease of cohesive strength of hot melt adhesive which is not conducive to bonding. The melting viscosity of petroleum resin should be 150-250 MPa.
expectation
At present, the world petroleum resin is developing in the direction of light color, specialization, multi-purpose and electron beam curing. Due to historical conditions and other reasons, China's tackifier resin has been dominated by rosin resin and terpene resin for a long time, while the development of petroleum resin is slow, and the main quality indicators such as compatibility and softening point are still far behind the same kind of products in foreign countries. High softening point, low color weather resistant resin, copolymerized resin, modified DCPD resin and colorless hydrogenated petroleum resin have been imported 。
In the aspect of C5 petroleum resin modification, we should make great efforts to develop new modifiers to prepare C5 petroleum resin with lower brilliance, higher softening point and wider application range; increase the distillation degree of C9 fraction and improve the chromaticity of C9 petroleum resin to obtain C9 and C5-C9 petroleum resin with high quality and low price, so as to meet the increasing demand of petroleum resin for hot-melt adhesive and pressure-sensitive adhesive in China.
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China building materials Suzhou non Mining Institute waterproof material design and Research Institute is an institution specialized in the research, design and development of new building waterproof, plugging and grouting materials. It has 13 invention patents, more than 50 industry standards and specifications, more than 30 science and technology progress awards of ministry, province and city, more than 100 waterproof monographs, more than 80 enterprise standard drawings, and prevention publications The director of the Institute is Professor Shen Chunlin, a famous waterproof expert who enjoys the special allowance of the State Council. The technical personnel with senior titles in the Institute account for more than 80%.