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subject: Tablet Presses In Pharmaceutical Industries [print this page]

Dry granulation processes create granules by light compaction of the

powder blend under low pressures. The compacts so-formed are broken up

gently to produce granules (agglomerates). This process is often used

when the product to be granulated is sensitive to moisture and heat.

Dry granulation can be conducted on a Rotary tablet press using slugging

tooling or on a roll press called a roller compactor. Dry granulation

equipment offers a wide range of pressures to attain proper

densification and granule formation. Dry granulation is simpler than

wet granulation, therefore the cost is reduced. However, dry

granulation often produces a higher percentage of fine granules, which

can compromise the quality or create yield problems for the tablet. Dry

granulation requires drugs or excipients with cohesive properties, and

a 'dry binder' may need to be added to the formulation to facilitate

the formation of granules.

After granulation, a final lubrication step is used to ensure that the

tableting blend does not stick to the equipment during the tableting

process Pharmaceutical Industries . This usually involves low shear blending of the granules with

a powdered lubricant, such as magnesium stearate or stearic

acid.Whatever process is used to make the tableting blend, the process

of making a tablet by powder compaction is very similar. First, the

powder is filled into the die from above. The mass of powder is

determined by the position of the lower punch in the die, the

cross-sectional area of the die, and the powder density. At this stage,

adjustments to the tablet weight are normally made by repositioning the

lower punch. After die filling, the upper punch is lowered into the die

and the powder is uniaxially compressed to a porosity of between 5 and

20%. The compression can take place in one or two stages (main

compression, and, sometimes, pre-compression or tamping) and for

commercial production occurs very fast (50050 msec per tablet).

Finally, the upper punch is pulled up and out of the die

(decompression), and the tablet is ejected from the die by lifting the

lower punch until its upper surface is flush with the top face of the

die. This process is simply repeated many times to manufacture multiple

tablets.

Common problems encountered during Rotary tablet press manufacturer operations include:

* poor (low) weight uniformity, usually caused by uneven powder flow into the die

* poor (low) content uniformity, caused by uneven distribution of the API in the tableting blend

* sticking of the powder blend to the tablet tooling, due to

inadequate lubrication, worn or dirty tooling, and sub-optimal material

properties

* capping, lamination or chipping. Such mechanical failure is due

to improper formulation design or faulty equipment operation.

Tablet formulations are designed and tested using a laboratory machine

called a Tablet Compaction Simulator or Powder Compaction Simulator.

This is a computer controlled device that can measure the punch

positions, punch pressures, friction forces, die wall pressures, and

sometimes the tablet internal temperature during the compaction event.

Numerous experiments with small quantities of different mixtures can be

performed to optimise a formulation. Mathematically corrected punch

motions can be programmed to simulate any type and model of production

tablet press. Initial quantities of active pharmaceutical ingredients

are very expensive to produce, and using a Compaction Simulator reduces

the amount of powder required for product development.

Tablet presses, also called Rotary tablet press machines , range from small,

inexpensive bench-top models that make one tablet at a time

(single-station presses), with only around a half-ton pressure, to

large, computerized, industrial models (multi-station rotary presses)

that can make hundreds of thousands to millions of tablets an hour with

much greater pressure. The tablet press is an essential piece of

machinery for any pharmaceutical and nutraceutical manufacturer. Common

manufacturers of tablet presses include Fette, Korsch, Kikusui, Manesty

and Courtoy. Tablet presses must allow the operator to adjust the

position of the lower and upper punches accurately, so that the tablet

weight, thickness and density can each be controlled. This is achieved

using a series of cams, rollers, and/or tracks that act on the tablet

tooling (punches). Mechanical systems are also incorporated for die

filling, and for ejecting and removing the tablets from the press after

compression. Pharmaceutical tablet presses are required to be easy to

clean and quick to reconfigure with different tooling, because they are

usually used to manufacture many different products.

Many tablets today are coated after being pressed. Although

sugar-coating was popular in the past, the process has many drawbacks.

Modern tablet coatings are polymer and polysaccharide based, with

plasticizers and pigments included. Tablet coatings must be stable and

strong enough to survive the handling of the tablet, must not make

tablets stick together during the coating process, and must follow the

fine contours of embossed characters or logos on tablets. Coatings are

necessary for tablets that have an unpleasant taste, and a smoother

finish makes large Albendazole tablets easier to swallow. Tablet coatings are also

useful to extend the shelf-life of components that are sensitive to

moisture or oxidation. Opaque materials like titanium dioxide can

protect light-sensitive actives from photodegradation[citation needed].

Special coatings (for example with pearlescent effects) can enhance

brand recognition.

If the active ingredient of a tablet is sensitive to acid, or is

irritant to the stomach lining, an enteric coating can be used, which

is resistant to stomach acid, and dissolves in the less acidic area of

the intestines. Enteric coatings are also used for medicines that can

be negatively affected by taking a long time to reach the small

intestine, where they are absorbed. Coatings are often chosen to

control the rate of dissolution of the drug in the gastrointestinal

tract. Some drugs will be absorbed better at different points in the

digestive system. If the highest percentage of absorption of a drug

takes place in the stomach, a coating that dissolves quickly and easily

in acid will be selected. If the rate of absorption is best in the

large intestine or colon, then a coating that is acid resistant and

dissolves slowly would be used to ensure it reached that point before

dispersing. The area of the gastrointestinal tract with the best

absorption for any particular drug is usually determined by clinical

trials.

It is sometimes necessary to split tablets into halves or quarters.

Tablets are easier to break accurately if scored, but there are devices

called pill-splitters which cut unscored and scored tablets. Rotary tablet press

with special coatings (for example enteric coatings or

controlled-release coatings) should not be broken before use, as this

will expose the tablet core to the digestive juices, short-circuiting

the intended delayed-release effect.

source:townhall|rotary tablet press

by: wenjun

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