Лако-красочные материалы — производство

Some of the terms are defined in DIN 16920 [24] and EN 923 [132].

Adherent: a body that is or is intended to be bonded to another body.

Adhesion: state in which two surfaces are held together by interfacial bonds.

Adhesive application: the application and distribution of an adhesive over the surface to be joined.

Adhesive coat: adhesive layer applied to an adherent.

Appearance of separated surfaces: surfaces formed in the event of failure of an adhesive joint; they provide information on the reason for the failure. Distinctions can be drawn visually between: [1] [2] [3]

4) Insufficient coalescence: separation of two adhesive layers at the interface, for

example, in the case of contact adhesives

5) Rupture of the surface layer of an adherent, breakage of the adherent (material

failure)

In many cases, several types of failure occur together.

Assembly time: interval between application of adhesive to the adherents and the initiation by heat and/or pressure of the setting process in the assembled joint.

Application weight, spread of adhesive, coverage: quantity of adhesive applied per unit area of a surface. A distinction is drawn between wet application (including solvent or dispersant) and dry application (100 % adhesive). Each type of adhesive has tech­nically and economically an optimal application weight. In principle, rough and porous substrates (paper, fabrics) require more adhesive than smooth surfaces (glass, metals, films) to obtain whole-surface wetting and bonding. Application weights range from 1 g/m2 (for example, for bonding films) to several 100 g/m2, depending on the sub­strate, the method of application, and the type of adhesive.

Bond layer thickness: the thickness of the set layer of adhesive in millimeters. It may be influenced by the application weight and the fixing pressure. In general, a thin (< 0.001 mm) and uniform bond layer leads to the highest bond strengths.

Bond line: adhesive layer in a bonded joint.

Bond strength: force necessary to bring an adhesive joint to the point of failure in or near the plane of the bond line.

Closed assembly time: interval between assembly of the adhesive joint and the initiation by heat and/or pressure of the setting process in the assembled joint.

Cohesion: state in which the particles of a single substance are held together by primary or secondary valence forces.

Cold flow: deformation of an adhesive layer (or film) at room temperature without external applied load.

Creep: slow inelastic deformation of an adhesive layer under load following initial instantaneous elastic or rapid deformation.

Curing: the setting of an adhesive by chemical reaction (polymerization, polycon­densation, polyaddition).

Heat resistance: the maximum temperature that a set adhesive in a joint is capable of withstanding. It depends upon the nature and intensity of the load and must be determined in each individual case.

Initial tack: the ability of a setting adhesive to hold two substrates together imme­diately after they have been joined. At this stage of the bonding process, strength is determined largely by rheological properties and depends on the cohesion of the unset adhesive. In the case of hot-melt adhesives, the analogous term “hot tack” is used, and this property is determined by the viscosity of the unsolidified melt. The transitions between the use of the terms initial tack and tack are fluent.

Minimum film-forming temperature: the temperature at which an emulsion-based adhesive just no longer dries to form a clear, homogeneous film.

Open assembly time, open time: interval between adhesive application to the adherents and assembly of the adhesive joint. The expression “open time” also is used occasionally for the period of time that elapses in a machine between application of the adhesive and bonding.

Primers: (mixtures of) substances that are applied before the adhesive to one or both of the surfaces to be joined, for improving adhesion and/or durability of the bond.

Setting: process by which an adhesive develops its cohesive strength and hence the physical and chemical properties of its bond.

Setting rate: the increase in strength in the bond line per unit time. It depends upon the setting mechanism and temperature and also may be influenced by the substrate (absorbency), bond layer thickness, etc. The setting rate generally is not constant and decreases toward the end of the setting time.

Setting time: time between joining of the adherents and the setting of the adhesive. It varies from a few seconds to several days, depending on the type of adhesive.

Shear strength: force per unit surface area necessary to bring an adhesive joint to the point of failure by means of shear forces.

Shelf life, storage life: time of storage under stated conditions during which an adhesive can be expected to retain its working properties. Appropriate storage generally is understood to mean that the adhesives are stored in clean, hermetically sealed containers and in cool, dry, well-ventilated rooms. Shelf life is largely dependent upon temperature. Aqueous and in some cases even solvent-containing systems have a tendency for skin formation, separation, and an increase in viscosity, particularly when stored for long periods at relatively high temperatures. They also can be spoiled by
microbial attack. Wide fluctuations in temperature (freeze/thaw) lead to coagulation. Shelf lives of less than 12 months generally are indicated on the packing. Manu­facturer’s instructions should always be followed.

Tack: property of a material that enables it to form a bond immediately on contact with another surface, which can be an adherent or another layer of adhesive. High tack is particularly important in the case of pressure-sensitive adhesives (tapes, labels), for which it is even measured. Tack is generally difficult to measure in setting adhesives.

Thixotropy: decrease in apparent viscosity under shear stress, followed by a gradual recovery when the stress is removed. Thixotropic behavior allows pasty adhesives, for example, to be spread readily and applied in relatively thick layers, in some cases even on vertical surfaces, without running or flowing out of the gap before bonding because the adhesive loses its fluidity immediately after application.

Viscosity: property of a material to increasingly resist deformation with increasing rate of deformation. This property is quantitatively defined as dynamic viscosity or coefficient of viscosity and is often used synonymously with apparent viscosity. The viscosity of adhesives is primarily determined by means of rotational or throughflow viscometers (DIN cup, Ford cup, Zahn cup). Adhesives generally show non-Newtonian behavior, fn addition to temperature, any expression of viscosity must also refer to the measuring instrument and measurement parameters (rotating spindle, rate of shear, nozzle diameter).

Working life, pot life: period of time during which a multicomponent adhesive can be used after mixing the components. The pot life of a given system depends primarily on the initial temperature of the mixture and on the quantity used (a high temperature and large quantities result in shorter application times), although it also depends on the mixing conditions (with or without cooling, type of stirrer used), on the ratio of surface area to volume of the mixing vessel, and on the method used for end-point deter­mination. Moisture-curing single-component adhesives also can have a working life, which begins with the contact of atmospheric moisture with the adhesive and which, apart from temperature, is largely dependent upon the existing humidity and upon the degree of moisture uptake during stirring operations.

Standards: comparisons of ASTM, MIL, GB, ISO, and DIN standards can be found in [25] and [26].

Legal Regulations. In view of the formulation of adhesives, particularly the solvent content, their manufacture, packaging, storage, transportation, and application are governed by a large number of regulations, which concern generally goods containing inflammable, explosive, or physiologically harmful constituents. Clean-water and clean — air regulations also must be observed.