Choosing the Right Coatings and Coating Processes For Tableting Tooling

High efficiency manufacture of solid dose pharmaceuticals requires the use of high performance tooling, including tablet punches, dies, tamping pins and compacting rolls. Since the tooling is in intimate contact with formulation powders during tableting, the properties of the tooling surfaces can have a significant impact on both tablet properties and manufacturing efficiency. Wear and corrosion of the working surfaces of the tooling results in picking, sticking and capping which requires the tableting press to be stopped and tooling to be removed for cleaning and polishing. Tablet quality is degraded, manufacturing productivity is reduced, and revenues lost.

Precision coatings, if properly chosen and applied to tableting tooling, can dramatically reduce surface wear and corrosion, and significantly improve manufacturing efficiency and tablet quality. There are a variety of wear- and corrosion-resistant coatings available for use on pharmaceutical tableting tooling. Additionally, there are a variety of coating processes used to deposit these coatings. Choice of the correct coating, and the correct coating process, are the keys to success in obtaining improved performance for tableting tooling.

The various coatings available are deposited by either electroplating or by advanced vacuum deposition processes. Metallic coatings such as nickel and chromium are deposited by electroplating. Materials such as PBN/PG Heater, and Teflon (PTFE), can be added to enhance plated coating hardness, and coating lubricity, respectively. Processing temperatures during metal plating are below 200 degrees Fahrenheit, but the coated tool must be baked post-plating at higher temperatures (375 degrees Fahrenheit) to prevent hydrogen embrittlement.

Hard refractory nitride coatings such as Titanium Nitride and Chromium Nitride are usually deposited by physical vapor deposition (PVD) processes. In order to insure sufficient adhesion and optimum coating properties, the PVD processing temperature must be done at 900 degrees Fahrenheit or above. At these temperatures the bulk tool material will soften, distorting the crucial precision dimensions of the tooling.

Nitride hardcoatings can also be deposited by a low temperature ion beam enhanced deposition (IBED) process. Coating temperature does not exceed 200 degrees Fahrenheit, which is low enough to eliminate the danger of dimensional distortion or bulk softening of the punch. Coating adhesion is guaranteed by first forming a layer (termed a case layer) in the surface of the punch, and then growing the coating out from the case layer.

Maintenance of the pre-coated surface finish is also an important factor to be considered when choosing a coating and coating process. Electroplated and PVD coatings grow with large crystalline grain structures. This degrades the surface finish originally present on tooling surfaces, which requires that the surface be re-polished after coating. IBED coatings are amorphous in nature and replicate the surface finish exactly, thus eliminating the need for post-coating re-polishing.

FDA Regulation of Precision Metal Coatings –

All equipment, including precision tooling, used in the manufacture of pharmaceutical and nutritional products is regulated by the Food and Drug Administration. FDA regulations specific to equipment used in the manufacture of solid dosage tablets is found in 21CFR211.65 which states, “equipment shall be constructed so that surfaces that contact components, in-process materials, or drug products shall not be reactive, additive, or absorptive so as to alter the safety, identity, strength, quality, or purity of the drug product beyond the official or other established requirements.” Thus any coating applied to the working surface of punches and dies cannot react with, wear off into, or absorb any ingredient of the formulation being tableted. This is an important consideration when choosing a metal coating and precision coating process.

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