Sealing adhesives

In the adhesives area, thermoplastic, fatty polyamides are used in hot-melt and heat-seal adhesives for leather, paper, plastic and metal. Blends of EDA- and DETA-based polyamides are suggested for use in metal can seam sealants with improved toughness (234) pressure sensitive adhesives have been formulated with DETA-based polyamides (235) and anionic and cationic suspensoid adhesives are used as heat-seal coatings in paper converting (236). PIP and certain PIP derivatives are used with EDA in some appHcations (237). 

Although the primary function of sealants is to seal, adhesion promoters are often added, which allows them to adhere to the adjoining base materials. It is therefore sometimes difficult to distinguish between an adhesive and a sealant. For example, structural silicone adhesives are used in the building construction industry owing to their sealing, adhesive, elastomeric properties, and their resistance to harsh environmental conditions [67,70,77]. 

Isobutylene is more reactive than n-butene and has several industrial uses. It undergoes dimerization and trimerization reactions when heated in the presence of sulfuric acid. Isobutylene dimer and trimers are use for alkylation. Polymerization of isobutene produces polyisobutenes. Polyisobutenes tend to be soft and tacky, and do not set completely when used. This makes polyisobutenes ideal for caulking, sealing, adhesive, and lubricant applications. Butyl rubber is a co-polymer of isobutylene and isoprene containing 98% isobutene and 2% isoprene. 

It has been found that in the development of EVA polymers for heat seal applications by emulsion polymerization that the concentration of vinyl acetate and ethylene in the polymer is not solely responsible for its use as a heat seal adhesive (2). 

For packages incorporating heat seal adhesives, the attributes of integrity have a direct relationship with the process parameters, process equipment, and packaging materials. Visual inspections are very suitable for production in-process controls of quality assurance. 

Polymers Unsaturated fatty-acid chains offer opportunities for polymerisation that can be exploited to develop uses in surface coatings and plastics manufacturing. Polyunsaturated fatty acids can be dimerised to produce feedstocks for polyamide resin (nylon) production. Work is also ongoing to develop polyurethanes from vegetable oils through manipulation of functionality in the fatty-acid chains, to produce both rigid foams and elastomers with applications in seals, adhesives and moulded flexible parts (see Chapter 5 for more information). 

Poly(vinyl alcohol) may also be added if water resistance is required. Another formulation that does not require cooking to develop its adhesive characteristic is based on the cold, caustic conversion of an acid-modified starch (75 fluidity) (fi). Clay filler may be added to any case or carton sealing adhesive if the board being glued is too porous. 

The adhesive may be solvent or water-based, hot-melt, coldseal or heatseal and pressure sensitive or chemically reactive. So the solidification process may occur via drying of water or solvent-based adhesives, by cooling of hot-melt and heat-seal adhesives, or by curing of chemically-reactive systems. With two notable exceptions - self-adhesive labels used on items of fruit or vegetables, and heat-sealable layers on packaging films - adhesives are in general not intended to touch the packaged food directly. 

US Patent 4,902,370 Synthetic based cold seal adhesives. Feb 20 1990. 

The process time is determined by the technical parameters heatup, application, and cooling It is very short compared to the process times of reactive adhesives. Processing is done with so-called sticks, spreadable powders, extrusions, nets, or films. Hotmelt adhesives in the form of films in particular are among the heat-activated or heat seal adhesives. In film and textile composites the term used is laminate adhesives. 

In the latter case, the hot-melt adhesives are applied in the form of films (also perforated for moisture exchange) as heat-sealing adhesives. The film is put between the two webs to be bonded and is then melted in heating presses or by means of an iron. The melt penetrates the tissue and, after cooling, forms a firm bond, thus stiffening the tissue. 

Adhesive films Consisting of two-component reactive adhesives applied to a nonadhesive substrate for transport and storage purposes that is removed prior to processing. Curing occurs via chemical reaction under application of heat and pressure. Adhesive films are also commercially available as physically setting films, see heat-sealing adhesive. 

Heat-sealing adhesive A hot-melt adhesive applied to the adherends as solid adhesive layer, which melts under heat/pressure and joins the adherends after cooling. 

Micromid. [Unitm Camp] Waterborne polyamide dispersions for laminating adhesives, heat seal adhesives for pkg., release coatings. 

In the paper industry, acrylate dispersions are used for clear, greaseproof coatings, as binders for clay coatings, and as heat-sealing adhesives. 

Self-sealing shingles- Shingles containing factory-applied strips or spots of self-sealing adhesive. 

Envelope front seal adhesives are made from solutions of dextrins in water. They require high solid contents, usually 60 to 70%. Which of the two dextrin types (white or yellow) would be more suitable as adhesives for envelope seals ... 

Cold-seal adhesives are members of a general category sometimes termed coadhesive substances that have a great tendency to stick to themselves, but often not to much else. Cold-seal adhesives are typically based on natural rubber, which has been applied in a latex (suspension in water) form. One major application is in plastic packaging for chocolate candy. The seal between the two parts of the wrap can then be activated with pressure, as an alternative to heat-sealing, which is problematic with the low-melting temperature candy. 

Adhesive lamination can also be done as a part of a printing press operation, if the press is properly equipped. This is the way many OPP/ink/adhesive/OPP/cold seal type structures are made. In this case the laminating station, with its secondary unwind and nip rolls, is inserted in line with the press. An additional printing station following the laminating section applies the cold seal adhesive. 

ExxonMobil OPPalyte films are coated, pearlescent white, opaque OPP films, with a proprietary core providing excellent opacity, good machinability, excellent flavor and aroma barrier properties, good oxygen barrier properties, excellent stiffness and flex resistance, excellent print performance, strong cold seal adhesion, and good bond strength. 

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