Adhesives sealants, viscosity

Electronics, electrotechnical industry Additives to mineral oils Adhesives, sealants Viscosity regulators, dispersants Aromatic HRs Maleinized or imidized polyisobutene A promising domain of importance [4201... 

Butyl mbber, a copolymer of isobutjiene with 0.5—2.5% isoprene to make vulcanization possible, is the most important commercial polymer made by cationic polymerization (see Elastomers, synthetic-butyl rubber). The polymerization is initiated by water in conjunction with AlCl and carried out at low temperature (—90 to —100° C) to prevent chain transfer that limits the molecular weight (1). Another important commercial appHcation of cationic polymerization is the manufacture of polybutenes, low molecular weight copolymers of isobutylene and a smaller amount of other butenes (1) used in adhesives, sealants, lubricants, viscosity improvers, etc. 

Polyisobutylene is produced ia a range of mol wts, and has found a host of uses. The low mol wt Hquid polybutenes have appHcations as adhesives, sealants, coatings, lubricants, and plasticizers, and for the impregnation of electrical cables (7). Moderate mol wt polyisobutylene was one of the first viscosity-iadex modifiers for lubricants (8). High mol wt polyisobutylene is used to make uncured mbbery compounds, and as an impact additive for thermoplastics. 

The viscosity of nonflowable products is determined by an extrusion test. A Semco 440 nozzle or its equivalent is attached to a standard adhesive/sealant cartridge filled with the material to be tested. The cartridge is then placed in an air-operated sealant gun set for a pressure of 90 to 95 psi. The weight of material that is extruded in 10 s is measured, and the extrusion rate is reported in grams per minute (g/min). Care must be taken to clear trapped air from the cartridge and nozzle. 

Sealants are divided into groups according to the generic names of polymer base. The main groups include polyurethanes, silicones, acrylics, polysulfide and others (PVC, polybutylene, styrene-butadiene-styrene copolymers, polychloroprene, and several others). The amount of solvent used in sealants is controlled by the standards which previously divided sealants into two groups these below 10% VOC and those above. Recently, a provision was made to include water-based acrylics and the limit of VOC for class A sealants was increased to 20%. Polyurethane sealants and structural adhesives can be made without solvent (the first solvent-free polyurethane sealant was made in 1994). Solvents are added to reduce sealant viscosity and to aid in the manufacture of polymer. Typical solvents used are mineral spirits, toluene, and xylene. A small amount of solvent is emitted from curatives... 

Thermoplastic rubber is a relatively new class of polymer. It has the solubility and thermoplasticity of polystyrene, while at ambient temperatures it has the toughness and resilience of vulcanized natural rubber or polybutadiene. These rubbers are actually block copolymers. The simplest form consists of a rubbery mid-block with two plastic end blocks (A-B-A), as shown in Figure 5.7. Examples of commercial products are Kraton and Solprene . These materials are often compounded with plasticizers to decrease hardness and modulus, eliminate drawing, enhance pressure-sensitive tack, improve low-temperature flexibility, reduce melt and solution viscosity, decrease cohesive strength or increase plasticity if desired, and substantially lower material costs. Low levels of thermoplastic rubbers are sometimes added to other rubber adhesives. These materials are used as components in the following applications PSAs, hot-melt adhesives, heat-activated-assembly adhesives, contact adhesives, reactive contact adhesives, building construction adhesives, sealants, and binders. Two common varieties of thermoplastic rubber adhesives are styrene-butadiene-styrene (S-B-S) and styrene-isoprene-styrene (S-I-S). ... 

ASTM D1337 provides a method for determining the shelf life of liqnid polymeric systems (e.g., resin, coating, adhesive, sealant). The changes in consistency (viscosity) of the product or an end property (bond strength) are measured after various storage periods at a specified temperature. 

In all cases, Saret 633 increased adhesion to oily and clean steel relative to the control. The failure mode was predominantly cohesive with the Saret 633 in all sealant formulations. The sealant viscosity for each formulation was approximately 1500 MPa. No attempt was made to optimise the cure conditions or the formulations for performance. 

Appiications adhesives, caulks, fibers, inks, oil modifiers, processing aids, sealants, viscosity modifiers, wax substitutes ... 

Principal styrenic TPE markets are molded shoe soles and other footwear extruded flhn/sheet and wire/cable covering pressure-sensitive adhesives (PSA) and hot-melt adhesives and viscosity index (VI) improver additives in lube oils, resin modifiers, and asphalt modifiers. They are also popular as grips (bike handles), kitchen utensils, clear medical products, and personal care productsAdhesives and sealants are the largest single market. Styrenic TPEs are useful in adhesive compositions in web coatings. ... 

There are a wide range of viscosities - from thick pastes, to very thin liquids. Some are thixotropic. The very high viscosity versions are used as adhesive/sealants. 

Manufecturers Comments High viscosity, flexible adhesive/sealant. Cure accelerated by increasing temperature and humidity. Paintable. 100% solids. Very good sag resistance. 

Manutocturers Comments High viscosity adhesive/sealant Cure Manuf urers Comments Very good adhesion to many plastics and ... 

With the exception of a few products designed to be poured (for potting or casting), viscosities are normally high to allow use as adhesive/sealants. 

Many technical characteristics or test methods are similar for adhesives and sealants, for instance, viscosity, specific gravity, shear strength. But the test methods usually differ because sealants have different properties and different functions from adhesives sealants must usually fill a large gap (several mm), they must remain flexible and much softer in order to accept movements, while adhesives must provide a stronger and harder bond. 

Plastisol usage for automotive sealants is typically 10-20 pounds (4.5-9 kg) per vehicle. The plasticizer levels may vary over a range from 50 to 200 phr likewise, the filler types and concentration vary widely, ranging from 30 to 600 phr. A typical formulation may start with 100 parts PVC copolymer, 100 phr DINP, 100 phr CaCOs, plus adhesion promoters, viscosity control agents. 

The cylindrical-type sealing process for strip packaging does not usually have a cooling cycle or quench surface, hence any pull on the seal ply will tend to weaken the seal while the sealant is still pliable. Therefore, it is desirable that the sealant have good hot tack or a high melt viscosity at processing temperatures. Hot tack is generally accepted to mean the adhesion quality of the sealant from the moment it leaves the seal head and the time it returns to its set or permanent condition. 

Fissure sealants are clear, low-viscosity, photocurable liquids, based on a mixture of fefrafunctional and difuncfional mefhacrylafes. Other dental photocurable materials are cements, adhesives, and denture base resins. " ... 

Adhesives and Sealants. Dominated by copolymers, adhesives and sealants remain somewhat of a specialty market. These polymers usually contain high copolymer content and low viscosity, and often require blending with oilier compounds prior to final application. Their uses are numerous, e.g., as seals for bottled drinks, as tie layers between incompatible polymers, or as automotive adhesives... 

The analogous large-volume series ZSK MEGAvolume with 8.7 Nm/cm3, a diameter ratio of 1.8, and screw speeds of up to 1800 rpm is used for compounds with a high solid matter content, such as those often found in the chemical/food/pharmaceutical industries. The maximum speeds of up to 1800 rpm are used mainly for low-viscosity products, such as pressure-sensitive adhesives and silicon sealants because they provide better elastomer and filler dispersion. Other processes often require large volume only and operate at very moderate speeds of 100 to 600 rpm to protect the product or for direct extrusion into films, sheets, or profiles. 

Aliphatic amines Convenience Room temperature cure, fast elevated-temperature cure Low viscosity Low formulation cost Moderate chemical resistance Critical mix ratios Strong skin irritant High vapor pressure Short working life, exothermic Poor bond strength above 80°C Rigid, poor peel and impact properties Adhesives and sealants Casting and encapsulation Coatings... 

Control of Viscosity. To ensure that adhesives and sealants function well during their application and end use, the formulator must be able to control the flow properties of the product. The challenge that faces the formulator is that the adhesive or sealant may need different flow characteristics at different times. For example, adhesives must flow readily so that they can be evenly applied to a substrate and wet out the surface. Yet, there should not be an excess of penetration into porous substrates, nor should the adhesive run or bleed to create a starved joint. Certain adhesives and sealants must be capable of convenient flow application by trowel or extrusion, but they must also exhibit sag and slump resistance, once applied. Therefore, the flow properties, or rheology, of the material must fit the desired method of application. 

Adhesive and sealant manufacturers employ rheological additives for thickening and to prevent sag of their products. In practice, rheological additives may provide benefits in addition to viscosity or flow control. When properly formulated into adhesives and sealants, rheological additives can... 

Control of Thixotropy. Often the adhesive application will require that the product be fluid for mixing and application, but it must not flow or sag once applied. For example, ASTM C920 defines a nonsag sealant as one that permits application in joints on vertical surfaces without sagging or slumping. This property is called thixotropy. Thixotropic materials, such as tomato catsup, toothpaste, etc., undergo a decrease in viscosity when subject to shearing. 

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