Heat-activated film

The heat-activated films are also used for back injection with polyurethanes, PET, copolyamides, TPE and polyolefins. The films exercise a barrier function for the flowable injection molding material. With composite films, the results are plastic... 

A particular adhesive group used for high heat-resistant bonding is the single-component reactive adhesive, as a combination of phenolic resin and nitrile rubber, in the form of heat activated films (HAF). These contain latent hardeners for the phenolic resins, which are activated at a temperature of approximately more than 120°C. The advantages include clean and precise handling. 

Heat-activated films (HAF) can be stored for 12—18 months under dry conditions at room temperature, depending on the type of phenolic resins present in the system. For special applications, such as in the electronic industry, clean room environment and subsequent dust-proof packaging and storage are necessary. 

Thermoplastic urethane adhesives may be processed into an adhesive film. I,amination of two substrates can, in theory, be done immediately, but the film is often extruded onto one substrate, covered by a release liner, and allowed to cool. Crystallization follows to create a non-tacky film that may be cut into specific shapes. The release liner is then removed, and the shaped adhesive can be heat-activated on one substrate, using infrared lamps. The second substrate is then nipped under pressure, followed by a cooling press to speed crystallization. Once the backbone has crystallized, the bond should be strong. 

The results obtained in above experiments confirm the removal of chemisorbed particles in the process of immersion of the film with preliminary chemisorbed radicals in a liquid acetone. Note that at low pressures of acetone, the CHa-radicals absorbed on ZnO film could be removed only by heating the film to the temperature of 200 - 250°C. Moreover, if the film with adsorbed radicals is immersed in a nonpolar liquid (hexane, benzene, dioxane), or vapours of such a liquid are condensed on the surface of the film, then the effect of removal of chemisorbed radicals does not take place, as is seen from the absence of variation of electric conductivity of the ZnO film after it is immersed in liquid and methyl radicals are adsorbed anew onto its surface. We explain the null effect in this case by suggesting that the radicals adsorbed on the surface of the ZnO film in the first experiment remained intact after immersion in a nonpolar liquid and blocked all surface activity of the adsorbent (zinc oxide). 

In laser-assisted thermal CVD by gas-phase heating, the laser is used to vibrationally excite the gas (e.g., SiH4) and active film precursors (e.g., SiH2). The modeling of these processes revolves around the transport phenomena that control the access of the film precursors to the surface, as exemplified by the finite-element analysis by Patnaik and Brown of amorphous silicon deposition (228). 

A new approach was proposed for making effective helmets which could replace the former British army steel helmet. Essentially the new helmet used modified phenolic resins reinforced with nylon, and the crown cap inside was thermoformed from polyethylene. Formerly the crown cap was attached to the steel by rivets—not an appropriate method for fixing polyethylene to reinforced plastics. Instead a method was developed with a hot-melt adhesive based on ethylene-vinyl acetate copolymers cast as film on release paper. For assembly, the cast film is cut in advance to match the intricate shape required and activated by heat to bond under light pressure subsequently, a further heat activation is employed to fix the crown cap in place (Figure 52 illustrates this). 

MS polymers Phenol-formaldehyde resins Polyimides Acrylates and epoxides, radiation-crosslinkable Rubber adhesives, crosslinking Adhesive films, heat activating Activation temperature variable... 

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. 

Other techniques have been used for the fabrication of thin-film metal-oxide gas sensors. At NIST in the USA, Cavicchi et al. (1995) and Semancik et al. (2001) produced gas sensors by chemical vapor deposition (CVD). By applying a current and thus heating the hotplate, sensing films could be deposited locally (i.e. only on heated active areas) using an adequate organ-ometaUic precursor. SnOj and ZnO films were obtained with tetramethyltin and diethylzinc in an oxygen atmosphere. They were deposited onto different seed layers, which played a significant role in terms of gas selectivity. 

Variety of forms Rubber-based adhesives can be supplied to the user in solvent or water-based formulations, as a solid hot melt or a soft tacky extrusion, as a tape (reinforced or not, single or double-sided), as a film, and even pre-applied to a surface for later solvent or heat activation. Products can be single or multiple component, depending on the application requirements. 

Uses Adhesive for PVC and other films, and in nonblocking coating applies. Features Waterborne high performance heat-activating good tens, str., heat and water resist., flexibility in low VOC systems ability to heat seal at relatively low temps. 

This is also true for PBT, as is shown by the study of as-extruded and heat-treated films of Feldman et al. [210]. The maximum values obtained for modulus and strength, 238 G Nm and 1.51 G Nm " respectively, are considerably lower than the largest fiber values, see Table 3. A study of the temperature and strain rate dependence of the deformation behaviour of these films revealed the onset of a structural reorganization near 300 °C, while the stress activation volume characterizing the activated rate process of the yield stress increased considerably above 200 °C [172]. 

Table 4.9 Heat-Activated Systems (One-Part, May be Solid Film)...

An example of a 100% solid, non-flammable, heat-activated hot-melt adhesive recommended for structural bonding of aluminum, steel, copper, brass, titanium, fabric, and some plastics is 3M Company s Scotch -Weld Thermoplastic Adhesive Film 4060. Strength data are shown in Table 5.5. " Bonding using this clear, amber, unsupported film adhesive takes place rapidly. The speed of bonding is hmited only by the heat-up time required to reach the optimum bonding temperature of 149°C at a pressure sufficient to maintain contact between the surfaces to be bonded. The adhesive... 

Film adhesives may be used only on flat surfaces or simple curves. Application requires a relatively high degree of cure to ensure non-wrinkfing and removal of separator sheets. Characteristics of available film adhesives vary widely, depending on the type of adhesives used. Film adhesives are supplied in both unsupported and supported types. The carrier for supported films is generally fibrous fabric or mat. Film adhesives are supplied in heat-activated, pressure-sensitive, or solvent-activated forms. 

Adhesive, heat activated n. A dry adhesive film that is rendered tacky or fluid by application of heat or heat and pressure to the assembly. 

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. 

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. 

The main growth area for adhesives is in heat-activated tapes or films, where there is substantial overlap with thermal-welding processes. Thermal bonding is increasingly used at the expense of adhesive bonding for the following reasons ... 

Fabrics may be 100% synthetic or blends with up to 40% natural fibres content. For nonsynthetic fabrics or blends with more than 40% natural fibre content, heat-activated materials (thermoplastic adhesive films or fabric coatings) are placed between two pieces of fabric. The material must have uniform thickness, yam density, tightness of weave, elasticity of the substrate, and style of knit which are the factors that can influence the welding ability. The various fabrics that can be joined by ultrasonic welding are shown in Table 13.15. 

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. 

For bonding with heat activation, the sole is activated by IR irradiation or rapid flash activation the activation time may be 2-6 s, and a surface temperature 55-80 °C can be reached. During the process it is the adhesive film that is heated, rather than the sole, which remains cooler. This ensures a more rapid development of bond strength. Soft soles that tend to deform when hot can be bonded at room temperature or with adhesives that have a low activation temperature. 

Adhesive, Heat Activated n A dry adhesive film that is... 

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