Heat activated adhesive

Figure 52 Employment of a heat-activated adhesive to fix the crown in a protective helmet...

Today, instead of the Japanese rice past method, I am using the vacuum hot table (2) with a heat-activated adhesive, which is also harmless and reversible. I am stressing here the use of the vacuum hot table in the treatment of textiles as it is a fairly recent technique for us. The vacuum hot table was designed for painting conservators and used by them in re-lining old paintings. The first published account I know of in the use of this table for textiles is by Sheila Landi (3) of the Victoria and Albert Museum in London. Another reference is by Kathryn Scott... 

There are three typical differentiating characteristics for heat-activated adhesives ... 

Beilstein Handbook Reference) AI3-00515 BRN 1889288 CCRIS 6190 DCHP Dicyclohexyl 1,2-benzenedicarboxylate Dicyclohexyl phthalate EINECS 201-545-9 Ergoplast FDC HF 191 Howflex CP HSDB 5246 KP 201 NSC 6101 Phthalic acid, dicyclohexyl ester Unimoll 66. A plasticizer for nitrocellulose, ethylcellulose, chlorinated rubber, PVAc, PVC, and other polymers. Used in formulation of delayed tack heat sealable coatings, it Is a heat activated plasticizer for heat seal applications such as food wrappers/labels, pharmaceutical labels and other applications where delayed heat activated adhesive is required used in manufacture of printing ink formulations for paper, vinyl, textiles, and other substrates. Solid mp = 66° d = 1.383 insoluble in H2O, soluble in EtOH, Et20, CHCI3, Bayer AG Lancaster Synthesis Co. Miles Inc. Morflex Unitex. 

Uses Vinyl acetate copolymer for heat-activated adhesive coatings on paper, cardboard, nitrocellulose-coated aluminum foil, etc., and for nitrocellulose lacquers... 

Uses Flexible resin for heat-activated adhesive coatings, lacquers Trade Names Containing Vinnapas B100/20 VLE... 

Adhesives may also be classified by the way they are applied or cured. Hence, anaerobic adhesives are adhesives that set only in the absence of air, for instance, when confined between plates or sheets. A contact adhesive is one that is apparently dry to the touch but will adhere to itself instantaneously on contact (also called contact bond adhesive and dry bond adhesive). A heat-activated adhesive is a dry adhesive film that is made tacky or fluid by application of heat or heat and pressure to the assembly. A pressure-sensitive adhesive is a viscoelastic material that in solvent-free form remains permanently tacky. Such materials will adhere instantaneously to most solid surfaces with the application of very slight pressure. Room-temperature setting adhesives are those that set in the temperature range of 20-30°C. These are usually two-component adhesives that must be mixed before application. A solvent adhesive is an adhesive that has a volatile organic liquid as a vehicle and sets or becomes tacky after the solvent has evaporated. A solvent-activated adhesive is a dry adhesive film that is rendered tacky just before use by applicafion of a solvent. 

Adhesives can set or cure by carrier (solvent or water) evaporation, chemical reaction, or thermal activation. Chemically reactive adhesives solidify primarily by a chemical reaction of one or more components in the adhesive formulation. It should be noted that solvent welding cementing processes or solvent-borne adhesives are in disfavor due to environmental, safety, and health concerns and regulations. As a result, waterborne adhesives and heat-activated adhesives are replacing solvent-based adhesives in many applications. 

Conventional thermal welding Welding is a thermal process requiring melting of fabric materials. A separate heat-activated adhesive material can also be used. Heating is achieved by direct contact of the fabric with a heated-tool surface or hot air. Fully or partially synthetic fabrics (woven and nonwoven) with thermoplastic components that are chemically and physically compatible when fused together. 

Thermoplastic adhesives can be apphed as a molten liquid to encapsulate the fabric and then harden by cooling. These heat-activated adhesives generate joint strength almost instantly after cooling. The most common sources of heating include hot air or heated... 

The major uses of heat-activated adhesives are in applications where fast production speed and reduced environmental hazards from solvent or liquid waste have significant importance. The primary strengths and weaknesses of heat-activated adhesives compared to other forms of adhesives are listed in Table 13.8. 

Seam-sealing tape is the most recognized form of heat-activated adhesive. This is applied in film form, and heat is used to activate or liquefy the polymer. On cooling of the seam under pressure, the adhesive goes from a molten liquid to a cohesive solid, and a strong bond is formed. 

Chemical types of heat-activated adhesives include polyolefin, polyamide, polyester, PU, and styrene butadiene copolymers. These are described in Table 13.9. There are copolymer variants of each type, allowing a wide range of applications and performance properties. 

A product can be applied as a molten liquid which cools, so forming a solid. Heat-activated adhesives in laminating systems are of this type. 

Heat-activated adhesive A heat-activated adhesive is a dry film that is made tacky by heat applied to the assembly. For example, BEVA is heat activated above 68 °C. 

NeoRez R-1400 is an aliphatic polyester urethane polymer dispersion developed for heat-activated adhesive formulation. NeoRez R-1400 offers the combined properties of low temperature activation, good early green strength, and high temperature resistance when crosslinked with poly-dispersible isocyanate. 

Low softening point resins have the reverse effect, namely to lower the tensile strength at elevated temperatures, to cause the tack in heat activated adhesives to develop at lower temperatures, and to reduce the temperature at which the formulation can be handled as a hot-melt. 

The trend in new hot melt adhesives will be to develop more specific adhesives. Thus, the number and range of adhesives should increase. An example of a specialized adhesive is the development of a film heat-activated adhesive. The adhesive film may be 5 20 mils thick and can be cut to a variety of shapes for application. The adhesive is then activated by heat or other means such as radio frequency vibration. 

Uniplex 250 is a beat activated plasticizer used in heat seal applications such as food wrappers, food labels, pharmaceutical labels and other applications where a delayed heat activated adhesive is required. 

Film adhesives They resemble hot melts and heat-activated adhesives in the sense that heat is used for activation with a subsequent cure schedule, which may include additional heat application under pressure. They may contain lightweight fabrics, nylon, polyester, glass mats in the form of carrier cloth. Thus, the adhesive thickness may be controlled uniformly. Epoxies, phenolics, nitrile-elastomers, polyamides, PVC, polyvinyl butyl, ethylene-carbolic acid copolymers are available in film form with or without carrier cloths. 

Single-component epoxy resins contain dicyandiamide as latent hardeners, which become effective at high temperatures - usually above 150°C. As such, they belong to the class of heat-activated adhesives. They are available in viscous or paste forms, and those of even higher viscosities are available as films on release paper. 

Labels used for blow molding are typically constructed of paper or polymer film and require a heat-activated adhesive for adhesion purposes. The adhesive can be applied either during co-extrusion when the film is being produced, or at final conversion of the label. During the latter, the adhesive is applied to the reverse side of the label facestock and activated by heat while the label is in the mold. The use of corona discharge treatment on polymer film labels is advised and usually sufficient at a minimum level of 38-40 dynes/cm. Bonding takes place when the adhesive is activated by heat and expansion within the mold. 

Delayed-tack adhesives require activation often by moisture, heat/pressure, or contact. Stamps and envelopes are two examples of moisture activation. A common example of heat-activated adhesive is the one applied to wood edge tapes (veneers). These tapes are used to cover the raw edges of plywood in applications such as shelving. A heated iron is used to press the wood tape against the edge to which it is being apphed. The heat activates the adhesive, which becomes tacky and bonds to the wood edge. 

Microencapsulation is a method for separating an activating solvent or a reactive catalyst from the adhesive base. The materials, whether solid or liquid, are packaged in very small microscopic capsules. When adhesion is desired, the encapsulated solvent is released by breaking the capsules by heat or pressure, and a tacky adhesive with instant grab is produced. In addition to solvents, small quantities of plasticizers or tackifiers may be contained in the capsules. The capsules are made of gelatin and are insoluble in water and neutral to the solvents. Heat-activated adhesives are another form of... 

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