Adhesive-sealed packages

Strip packages represent an alternative form of packaging for unit-dose medication. Strips can be produced from single- or multiple-ply laminated materials provided the two inner plies can be sealed by heat or pressure (e.g., cold self-adhesive seals). Materials can range from relatively permeable plies to those that incorporate a foil ply of sufficient thickness and effectiveness of seal so that an individual hermetic seal is produced for each dosage. Strip packages are produced at lower speeds and occupy greater volume than blisters. 

Low density poly(ethylene) (LDPE) may have unsatisfactory heat seal properties, as they often do not provide sufficient adhesion between the sealing layers to result in a good adhesive seal for a package. Efforts to improve the heat seal characteristics of LDPE by blending them with other materials, such as ethylene copolymers with methacrylic acid or acrylic acid, have not had universal success. 

In dry-heat sterilization, the parts are exposed for 2-3 hours at 165°C-170 °C. Dry-heat exposure is the least effective sterilization method and most likely to degrade materials and electronic devices. Although adhesives may have been cured at 165 °C prior to hermetic packaging, the additional temperature exposure within the sealed package can result in further outgassing of moisture and corrosive volatiles causing electrical failures. Outgassing is worse if the adhesive had been cured at a temperature below 165 °C. 

Differential scanning calorimetry directly measures the heat flow to a sample as a function of temperature. A sample of the material weighing 5 to 10 g is placed on a sample pan and heated in a time- and temperature-controlled manner. The temperature usually is increased linearly at a predetermined rate. DSC is used to determine specific heats (Fig. 10-11), glass transition temperatures (Fig. 10-12), melting points (Fig. 10-13) and melting profiles, percent crystallinity, degree of cure, purity, thermal properties of heat-seal packaging and hot-melt adhesives, effectiveness of plasticizers, effects of additives and fillers (Fig. 10-14), and thermal history. 

Applications - film, flexible piping, hot-melt adhesives, membranes, packaging, seals, shoe soles, wire cable ... 

Many tablet medications intended for unit dose applications are protected by the familiar blister packs, an example of which is shown in Figure 10-26. These are typically manufactured with laminated materials that consist of a transparent polymer, an aluminum foil, and an interfacial adhesive. There are many variations of this construction. The transparent polymer layer is first dimpled with a heated die to produce the tablet cavities. The web material, consisting of the aluminum foil and adhesive, is thermally bonded under pressure to the perimeter of the cavities after the tablet is inserted. This is a continuous process in which the line speed, compression force, and temperature must be controlled to assure a hermetically sealed package. 

These are immiscible with P-l-B. Low concentrations of HDPE nucleated and changed the crystallinity of P-1-B [78]. Blends with LDPE or EVA were coextruded to form heat-seal adhesives for packaging these could be reopened easily because the incompatible polymers provided low peel strength [101]. 

Other considerations include the delivery form and packaging, which allow the differentiation of solid from liquid adhesives. Liquid adhesives are stored in sealed packaging, containers, barrels, or tanks at room temperature between 18°C and 25°C. Homogeneous... 

Additionally, it is a basic condition during adhesive storage to keep the adhesive in its original sealed packaging before use, as far as possible, even if humidity does not always appear to influence the adhesive shelf life. 

Some flexible packaging is fabricated by converters into bags and pouches. Bag material is either small monolayer or large multiwall with paper as a principal substrate. Pouches are small and made from laminations. Bags usually contain a heat-sealed or adhesive-bonded seam mnning the length of the unit and a cross-seam bonded in the same fashion. 

Applications. Preformed bags are opened by the packager, filled with food product, and closed by adhesive, heat-sealing, clipping, stitching,... 

The primary non-woven applications for hot melts are in disposable articles such as diapers and sanitary napkins (see Fig. 22). These articles are made by high speed processes and are immediately packaged in sealed plastic bags, thus they are prime candidates for hot melt use. The applications are broken down into three categories, requiring three different types of adhesives construction, elastic attachment, and garment attachment. 

Case and carton sealing is a high volume application for hot melt adhesives. Typical formulas use 20-30% wax, 25-40% polymer, and 35-55% tackifier resin. The basic requirements for packaging adhesives will be described followed by formulating guidelines for specific market areas. The focus of this discussion will be on EVA and EnBA-based systems, which are the most common. 

Activation by a metal surface also takes place in the commercially important anaerobic adhesives. These one-part adhesives are stable in the package, but cure quickly in an oxygen-free environment such as a tightly controlled bond line. Important applications include thread-locking, sealing, retaining, and some structural bonding [111]. A representative model formulation has recently been described [112] (Fig. 3). 

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