Film/coating properties hardness

In the electronics industry, gold is used as fine wires or thin film coatings and frequendy in the form of alloys to economize on gold consumption and to impart properties such as hardness. Gold has properties that satisfy specific requirements not achievable with less expensive metals (see Electrical connectors Electronics coatings Thin films). 

The maximum recommended film thickness is 25 p.m. At greater thicknesses, volatiles from the curing reaction, mainly water and some formaldehyde and phenol, can cause defects. These coatings have excellent electrical insulation properties, ie, up to 20 V/p.m, because of low moisture absorption and low conductance. The coatings are hard with low flexibiUty, depending on curing conditions and film thickness. 

Tablet properties Tablet properties such as hardness, shape, and intaglia-tion (if required) are important to obtain a good film-coated tablet. The tablet needs to be hard enough to withstand the coating process. If tablet attrition occurs, the tablets will have a rough surface appearance. For tablet shape, a round tablet will be easier to coat than tablets will multiple sides or edges because of the uniformity of the surface. For intagli-ated tablets, the intagliation style and depth should be developed to prevent fill-in or chipping of the intagliation.

Ethyl cellulose (EC) is a water-insoluble cellulose ether. It is produced by reaction of alkali cellulose with ethylene chloride. It has film-forming and thermoplastic properties. As a plastic, it can be processed by extrusion and injections. It is hard, stiff and with good resistance to impact. It is soluble in the molten state with other thermoplastics. As for its film-forming properties, it is used in the formulation of varnishes, inks and glues. It forms removable coatings. 

The properties given in Table 84 for povidone are also useful in the film-coating of tablets and hard gelatin capsules [281]. 

One quality control application of near-IR spectroscopy is the nondestructive determination of tablet hardness. Near-IR prediction of tablet hardness has been used and investigated by Drennen for a number of years. In 1991, the first publication of the near-IR technique for this application appeared [26]. Ciurczak and Drennen published similar results in 1992 [60] and Drennen and Lodder in 1993 [61]. Results of a study presented at the 1994 annual meeting of the American Association of Pharmaceutical Scientists were published in a 1995 paper [62]. In that paper, Kirsch and Drennen identified the utility of the technique in the determination of multiple film-coated tablet properties, including tablet hardness. In a review paper regarding the use of near-IR in the analysis of solid dosage forms, Kirsch and Drennen discussed the historical aspects of near-IR prediction of tablet hardness [27]. 

Acrylated melamines have properties which make them suitable for use in OV curable coatings. Properties can be varied by adjusting the combined acrylamide content and the inclusion of other modifiers. Formulation viscosities are satisfactory for normal application methods, and films cure to a high degree of hardness at practical irradiation levels. Benefits demonstrated include improved tape and scratch adhesion, abrasion resistance, color, and Q-U-V durability. 

Increasing relative molecular mass of the binder in the polymer film improves properties such as elasticity, hardness, and impact deformation, but also leads to higher solution viscosity of the binder. While the usefulness of a coating is enhanced by good mechanical film properties, low viscosity combined with low solvent content are also desirable for ease of application and for environmental reasons. Therefore, a compromise is necessary. 

The mechanical properties of biomaterial thin films depend strongly on factors such as the deposition process and the microstmcture of the deposited film. Accurate techniques are needed to measure the properties of these films because their properties such as hardness and Young s modulus can be different from the equivalent bulk material and the underlying substrate on which they are deposited. It is essential to have tools such as scratching and nanoindentation available for the characterization of sub micron coating properties. 

Determination of properties of film coated tablets was demonstrated by Kirsch and Drennen [73] in 1995. Here, the thickness of an ethylcellulose coating, T50 (50% dissolution time), and the hardness of the tablet were determined from NIR spectra measured on grating based and acousto-optic tunable filter (AOTF) specfiometers. While the performance of the grating based spectrometer was superior, the AOTF was demonstrated to perform adequately for most pharmaceutical applications and had the advantage of substantially shorter measurement times. This demonstration of the capacity for rapid tablet analysis was a critical step towards the implementation of such systems in an in-line tablet analysis system. 

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