Liquid adhesives, specifications

Most moisture-curing liquid adhesives utilize poly(oxypropylene) (PPG) polyols, as shown above. These raw materials produce among the lowest-viscosity prepolymers but may not have sufficient modulus at higher temperatures for some applications. A certain percentage of polyester polyols may also be utilized to boost performance, but these may cause a large increase in viscosity, and so they are more often used in conjunction with polyether polyols to provide a high-performance adhesive with workable viscosities. Poly(butadiene) polyols may be utilized for specific adhesion characteristics. 

Silk screen application is often used when the adhesive has to be applied to specific controlled areas. The liquid adhesive is forced through pores in a cloth or screen. It is possible to coat only selected areas by masking parts of the screen so that adhesive does not pass through in the unwanted areas. Adhesives generally must be specifically formulated for silk screen processing. Very low-viscosity adhesives, with flow characteristics similar to those of coatings, are best for silk screening operations. 

D 1580 Specification for Liquid Adhesives for Automatic Machine Labeling of... 

D 1874 Specification for Water- or Solvent-Soluble Liquid Adhesives for Automatic... 

Preforms, tape, or film adhesives, unlike the paste or liquid adhesives, are already in the solid state. They may be thermoplastic or thermosetting but, in both cases, may be purchased as sheets of various thicknesses and cut to size to accommodate specific device or part sizes. In using preforms, the electronics assembler avoids problems associated with the storage, handUng, and dispensing of liquid adhesives. Parts such as leadframes, lids, and substrates may also be purchased with pre-attached preforms, a convenience to the user, who then avoids having to cut and handle individual preforms. Most parts can also be stored for up to one year in ambient conditions without affecting their properties. 

Fuks [59] directed attention to the dependence of the adhesion on the period of contact between the particles and the surface on settling in the liquid. At the initial instant the adhesion of the particles is a minimum (Fig. IV.3), but with increasing contact time adhesion becomes stronger, the rise ceasing some 60-90 min after the particle first came into contact with the surface. This phenomenon has become known as aging. Fuks [59] studied the effect of contact time on adhesion specifically for the case of the liquid settling of particles. 

Case I—Consider an interfacial area of Icm is separated so as to create a liquid surface of specific surface free energy Tlv ergs/cm, and a solid surface covered with an adsorbed monolayer of liquid in equilibrium with the vapor of the liquid of specific surface free energy Tsv ergs/cm. In this process Icm of the interfacial area disappears and the thermodynamic work of adhesion is given by... 

D-1874. Specification for Water- or Solvent-Soluble Liquid Adhesives for Automatic Machine Sealing of Top Flaps of Fiberboard Shipping Cases. For non-pressure-sensitive adhesives. 

When used by private individuals, liquid adhesive residues are usually collected in the hazardous waste collection boxes, but are also often disposed of with the rest of the household waste. The amounts involved here are, however, small. For industrial and commercial users, disposal must be carried out in accordance with the so-called waste code numbers (to be found on the safety data sheets), which determine how the waste is disposed. Adhesive residues are normally disposed of as landfill or incinerated. Regarding the latter, specific contamination of the air by the incineration plants is not expected. The energy used in the manufacture of the adhesives can be partially recovered here. 

In industry, residues of cured adhesives and also non-cross-linked and liquid adhesives occur as waste. The former, as solid materials are either directly passed on as waste for disposal, or are preferably passed on for recycling. In the least favorable environmental scenario, they are disposed of as landfill. They are, however, usually recycled, either via composting or for energy recovery via incineration. Depending on how they have been treated, liquid adhesives are discharged with the wastewater and are either directly passed to a treatment plant or, if necessary, passed to a treatment plant after undergoing a specific pretreatment. There they are biodegraded or removed. 

W. quantifies the specific, discrete interactions that exist between a wetting liquid and a substrate. These interactions may be Van der Waals, acid-base, or covalent. The reversible work of adhesion is the product of the areal density of these interaction sites (or attachment points) and the energy per attachment point ... 

The surface energy of silicones, the liquid nature of the silicone polymers, the mechanical properties of the filled networks, the relative insensitivity to temperature variations from well below zero to very high, and the inherent or added reactivity towards specific substrates, are among the properties that have contributed to the success of silicone materials as adhesives, sealants, coatings, encapsulants, etc. 

The field of composite liquids has not received much attention outside the industries associated with specific liquid products (e.g., the petroleum industiy). In areas such as lubrication, the United States has clear technological leadership. The situation is less clear for liquid crystals and adhesives, where there is greater competition from Europe and Japan. 

The work of adhesion measures the degree of attraction between the two phases. For the specific case where A is a solid (S) and B is a liquid (L), ya becomes the solid surface energy, ys, Yb become the liquid surface tension, yl, and Young s equation, Eq. (2.72),... 

These applications are a domain that is shared by UV and EB processes, because both can directly convert reactive liquids into solids almost instantly. There are specific areas where EB irradiation is more suitable than the UV curing process. In general, these include applications where thick layers of coatings or adhesives are applied. Other instances are coatings with high levels of inorganic pigments or fillers, which usually cannot be cured by UV radiation because of their opacity. As pointed... 

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