Rubber-based adhesives: compounding

Natural rubber (NR) is the base polymer for many Rubber-based adhesives. This article is designed to supplement with specific information the more general treatment given in Rubber-based adhesives compounding and Rubber-based adhesives typical characteristics. 

Some typical rubber adhesive formulations are given in Rubber-based adhesives compounding. Specific formulations for NR can be found in the references below. 

Most Rubber-based adhesives may be cured by a sulphur-based vulcanizing system (see Rubber-based adhesives compounding), however, as mentioned in Polychloroprene rubber adhesives applications and properties, CR adhesives are cross-linked by various reactions involving the labile chlorine atoms in the repeat unit. This is reflected in the additives used, as discussed below. ... 

Compared with other adhesives systems, the formulation of the rubber-based adhesives is very complex considerable training and practical experience is necessary before they can be successfully formulated (see Rubber-based adhesives compounding). The properties of the elastomeric adhesives depend on both the chemical type and particular grade of the natural or synthetic elastomer and on the modifying additives that may be incorporated into the adhesive formulation (tackifiers, reinforcing resins, fillers, plasticizers, curing agents, etc.). 

As discussed in other articles (see Rubber-based adhesives, and Rubber-based adhesives compounding, it is clear that the chemical nature and molecular weight of the rubber will largely determine the properties of the adhesive. However, there are some common characteristics of most of rubber-based adhesives, which are treated here. 

Rubber tyre cord adhesion W J VAN OOlJ Adhesion to brass-coated steel Rubber-based adhesives J M MARTfN MARTInEZ General introduction Rubber-based adhesives compounding J M MARTIN MARTfNEZ Formulations, etc. 

Rubber-based adhesives compounding J M MARXfN MARXINEZ Formulations, etc. 

MIL-A-8576 MIL-A-9117 MIL-A-12850 MIL-C-14064 MIL-C-15705 MIL-C-18255 MIL-C-18969 MIL-C-23092 MIL-C-27315 MIL-C-27725 MIL-C-5539 MIL-C-7438 Adhesive, Acrylic Monomer Base Synthetic Elastomeric Sealant Natural Liquid Rubber Cement Grinding Disk Cement Caulking Compound Caulking Compound with Synthetic Rubber Base Caulking Compound—Watertight Exterior Hull Seams of Vessels Cement, Natural Rubber Coating Systems, Elastomeric Coating, Corrosion, Preventative, Air Fuel Tanks Natural Rubber Cement Core Material, Aluminum, for Sandwich Construction... 

Virtually all rubber materials, and plastic materials, can be made into an adhesive or sealant compound. This is because many elastomers begin as monomers dispersed in water or solvent and are polymerized in situ. Latex products can remain so, while solid elastomers that are extracted from either water or solvent systems can be solvated with an appropriate organic solvent system. In addition, most solid elastomers exhibit thermal flow characteristics which can make them suitable for hot-melt formulations. And since there are many different rubber polymer families, it stands to reason that there will be many different rubber-based adhesives to identify and describe. Some, however, have... 

Surprisingly, using an acrylate-based adhesive (A 7275, Beiersdorf), the crosslinkers containing aromatic compounds did not show the expected increase in release force values with a higher content of organic compounds (Fig. 2). This was confirmed in various measurements in which the SiH/vinyl ratio as well as the type of adhesive and the method of sticking (inline or offline) were modified. When a rubber-based adhesive (RP 51, Raflatec) was stuck onto the coated surfaces, an increase in the release force values was also observed in case of C2, whereas the other crosslinkers showed approximately the same release force values for all compositions. 

Nitrile rubber, also known as nitrile-butadiene rubber (NBR), is a copolymer of acrylonitrile and butadiene (Fig. 1). As a base polymer for Rubber-based adhesives, it provides a number of specialized properties, which supplement those summarized in the article Rubber-based adhesives typical characteristics. NBR adhesives comprise a range of materials that may differ in proportion of comonomer or may be compounded with other resins. NBR adhesives are characterized by high oil and plasticizer resistance, excellent heat resistance and high adhesion to metallic substrates. 

The curing of CR adhesives is different from that for most rubber-based adhesives as it involves the labile chlorine atoms. This is reflected in the compounding ingredients. The most common room curing agent is zinc oxide, but isocyanates are also very common. Further discussion is given in Polychloroprene rubber adhesives modifiers and additives. 

Some rubber-based adhesives need vulcanization to produce adequate ultimate strength, and the adhesion is mainly due to chemical interactions at the interface. Other rubber-based adhesives (see Contact adhesives) do not necessarily need vulcanization but need adequate compounding to produce the adhesive joints, mainly with porous substrates. In this case, the mechanism of diffusion dominates their adhesion properties. See Diffusion theory of adhesion and Polymer diffusion reptation and interdigitation. 

The difference between plasticizers and tackifiers is somewhat arbitrary and the effect of this difference is described below in the section on Physical Properties. Plasticizers are typically lower in molecular weight and melting or softening point than are tackifiers. Hydrocarbon oils including aromatic, naphthenic, and paraffinic are commonly used with rubber-based adhesives. Phthalates, such as dioctyl phthalate or dibutyl phthalate, are more typically used in small amounts with acrylics. Since plasticizers are usually low molecular weight compounds, there is often more latitude in the chemical types that will be compatible with the base pol5mier because of the contribution from entropy of mixing. 

Carbon Black (Queen, 1978) - Carbon black is the most widely used filler for reinforcing rubber compounds and, as such, is used in the manufacture of black rubber based adhesives and sealants. Carbon black reinforcing fillers and pigments are made by the incomplete combustion of organic hydrocarbons under controlled conditions. 

The concept of rubber reversion protection by using biscitraconimidomethylbenzene, trade name Perkalink 900, is discussed. The advantages of using this chemical in NR based adhesion compounds was examined. The effects of its use on adhesion to textiles, cure characteristics physical, mechanical and thermal properties are discussed. 14 refs. 

Styrene-butadiene-styrene (SBS) rubbers are either pure or oil-modified block copolymers. They are most suitable as performance modifiers in blends with thermoplastics or as a base rubber for adhesive, sealant, or coating formulations. SBS compoimds are formulations containing block copolymer rubber and other suitable ingredients. These compounds have a wide range of properties and provide the benefits of rubberiness and easy processing on standard thermoplastic processing equipment. 

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