Lidding materials
The lidding material act as the base or main structural component upon which the final blister package is built. Selection for lidding material should consider the size, shape, weight of the product, and the style of the package to be produced. Lidding materials range in caliper or thickness from 0.36 to 0.76 mm (0.46–0.61 mm is the most popular range). The surface of the lidding material must be compatible with the heat-seal coating process. Clay coatings are added to the lidding material to enhance printing.

Lidding material can be clear plastic, but in pharmaceutical packaging it is either plain or printed 1-mil foil (for push-through blister types) or paper/foil or paper/PET/foil laminations (for child-resistant peel–push types). The lidding material must guarantee a WVTR that is at least as low as that of the forming films, and it must be suitable for the type of opening appropriate to the package (e.g., push-through or peel-off).

Comparison of Lidding Material
Lidding Material Price per Unit Area Weight*
0.8-mil Aluminum, hard, push-through601
0.8-mil Aluminum, hard, heat seal-coated, side-printed, push through611.25
1-mil Aluminum, soft, child resistant761.15
45 g(m-2)/1-mil Paper/aluminum, peel-off1211.55
45 g(m-2)/0.48-mil Paper/PET/aluminum, peel off-push through1422.00

*Where 1 represents the price per unit area of 0.8-mil, hard, push-through aluminum

Types of lidding materials.

There are several type of lidding material :
1. Hard aluminum
2. Soft aluminum
3. Paper/aluminum
4. Paper/PET/aluminum

Hard aluminum The foil usually has a thickness of 0.8 mil. There are endeavors, however, to reduce the thickness of this foil to 0.6 mil. The hardness of the aluminum facilitates push-through opening. The print primer side features printed design and the side with the heat-sealing coating also can be printed.
The heat-sealing primer ensures optimum adhesion of the heat-sealing coating to the aluminum foil. The heat-sealing coating can then be matched to the formed films. If the heat-sealing primers are colored, applying the heat-sealing coating over the primer can protect the packaged product from coming in contact with the pigments. If additional printing is required on the side of the heat-sealing coating, the only alternative is to apply two coats of the coating. This technique is necessary because the printing inks must be located between the heat-sealing primer and the actual heat-sealing coating.

Soft aluminum (1 mil) frequently is used for child-resistant push-through foils. With the exception of the type of aluminum used, the structure of this lidding material corresponds to that of hard aluminum (0.8 mil). The softness and thickness of this type of aluminum help prevent children from pushing tablets through it. This material also is supplied with a perforation along the sealed seams so that it can not be peeled off the formed film in one piece.

Paper/aluminum. In combinations of paper and aluminum, the weight of the paper amounts to 40–50 g/m2 . The thickness of the aluminum typically is 0.28–0.48 pm, but in the United States it has a thickness of 0.6–1 mil. The reason for this difference lies in the fact that this lidding material is used in Europe for child-resistant push-through packages, so the aluminum foil must be relatively thin. In the United States, this type of material is used as a peel-off foil, so the foil must be relatively thick for effective peeling. Because printing is applied to the side with the paper, no print primer is required. Virtually all of the previous comments regarding heat-sealing coating apply to combinations of paper and aluminum.

Paper/PET/aluminum. Lidding material made of a paper/PET/aluminum laminate is often called peel off–push through foil. The concept is to first peel off the paper/PET laminate from the aluminum and then to push the tablet through the aluminum.

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