Case sealing adhesives

The tops and bottoms of corrugated boxes are closed with case sealing adhesive. Although liquid glues and hot melts are preferred, carton adhesives are used, sometimes with added caustic. Carton sealing involves bonding the bottom and top flaps of folded paper boxes. A... 

Case seal adhesive Very fast, nonwarp Canary dextrin borated white dextrin resin 40-50 ... 

Case sealing adhesives based on EVA resins are often a blend of several ingredients. A typical formulation is listed in Table 7. 

Poly(vinyl alcohol) may also be added if water resistance is required. Another formulation that does not require cooking to develop its adhesive characteristic is based on the cold, caustic conversion of an acid-modified starch (75 fluidity) (fi). Clay filler may be added to any case or carton sealing adhesive if the board being glued is too porous. 

In the latter case, the hot-melt adhesives are applied in the form of films (also perforated for moisture exchange) as heat-sealing adhesives. The film is put between the two webs to be bonded and is then melted in heating presses or by means of an iron. The melt penetrates the tissue and, after cooling, forms a firm bond, thus stiffening the tissue. 

Adhesive lamination can also be done as a part of a printing press operation, if the press is properly equipped. This is the way many OPP/ink/adhesive/OPP/cold seal type structures are made. In this case the laminating station, with its secondary unwind and nip rolls, is inserted in line with the press. An additional printing station following the laminating section applies the cold seal adhesive. 

A new technological development for hot melts is their application by robotics (87). Robotics have been used to apply hot melts to structural components, e. g. , fiberglas-reinforced components. In one case, structural adhesives are applied at 480 F (249 C) with a specially designed hot-melt dispenser and gun marketed by Monsanto Co. Robotics have also been used to apply hot-melts to make PSA s. Robotics are useful in applying hot-melts to gaskets and seals. In general, robotics provide higher productivity, improved quality, and reduced cost. 

Permanent attachments such as footrings, headrings, neckrings or marking plates should be inspected to make sure they are in place and firmly attached. The area of attachment to the cylinder should be checked for possible entry of moisture to the cylinder surfaces that cannot be seen. In the case of adhesive attachments, any evidence of a break in the seal is cause for removal of the attachment. The use of a dull probing tool is recommended. Attachments made of plastic also must be checked carefully for gouges or splits, which would require their removal. When the cylinder bears a removable attachment such as a removable boot (footring), the attachment must be removed for visual inspection. 

Heat-sealing adhesives are applied to the materials to be sealed in the form of solutions, emulsions, or, preferably, in melt or powder form. The solvent-free layer is intended to be nontacky and only to melt and to wet the adherent under the action of heat during sealing. Solidification takes place after cooling. In many cases, sealing is carried out on a coating-to-coating basis. 

A special case of bonding is the heat-sealing of previously applied heat-seal adhesives. Such coatings are converted by heat into a tacky state and bonded by the application of pressure. Thermal activation is carried out by heated sealing bars or plates, hot air, and sometimes by IR radiation. 

High-frequency welding is used for special applications, in which cases the necessary heat is generated by the interaction of high-frequency radiation with the dipole moment of the pre-applied heat-seal adhesive itself... 

Fast tack, rigid films, low viscosity, and very good adhesion are obtained from this combination. High speed case sealing and fiber foil cans are some uses. 

A representative hot melt adhesive formulation based on a low molecular weight polyethylene resin would be composed of the materials shown in Table 8. A low density polyethylene based hot melt adhesive for case sealing might contain the formulation shown in Table 9. 

These compounds primary function is to seal out air, dust, or water in order to reduce corrosion or improve comfort. In many cases they may also function as holding adhesives. Their low strength generally precludes their use in structural applications. Typical sealing adhesives are listed in Table 3. 

One of the most widely used polymers in the formulation of hot-melt adhesives is the copolymer of ethylene and vinyl acetate (EVA). For example, such copolymers containing abut 28 to 33% vinyl acetate are widely used as the basis of hot-melt adhesives for bookbinding. They not only bond the individual pages of a paperback book together but they also attach the cover. For such an application the adhesive must have excellent flexibility, toughness and fatigue resistance, and these properties need to be maintained from about -20 to 60 °C. EVA hot-melts are also used for carton and case sealing, carpet applications and in many other industries. 

For example, tackified ethylene-vinyl acetate hot-melts are mostly used in the manufacture of exterior grade plywood, where water resistance is required, as well as in other general woodbonding applications. They are also used in book binding, carton and case sealing, shoe manufacture, carpet seaming, as well as pressure-sensitive adhesives. 

The alkoxy silicone often showed a strength of 1.4 N/mm for many of the plastics tested but in this case the adhesive has failed cohesively. A silicone adhesive is often used where sealing might be the main priority of the adhesive rather than structural strength. 

Nonfood hydroxyethyl starch applications are in the paper industry for surface sizing and coating, as quality enhancer for pigmented papers, as wet-end additives in textiles for warp sizing as an adhesive component for bag pastes, case sealing and enveloping materials. Hydroxypropyl starches with higher DS are used routinely in pharmacy as a blood plasma extender. 

Vapors emitted from the materials of closed storage and exhibit cases have been a frequent source of pollution problems. Oak wood, which in the past was often used for the constmction of such cases, emits a significant amount of organic acid vapors, including formic and acetic acids, which have caused corrosion of metal objects, as well as shell and mineral specimens in natural history collections. Plywood and particle board, especially those with a urea—formaldehyde adhesive, similarly often emit appreciable amounts of corrosive vapors. Sealing of these materials has proven to be not sufficiently rehable to prevent the problem, and generally thek use for these purposes is not considered acceptable practice. 

Another way to determine durabHity is to find successfuHy sealed, existing field instaHations. Sealant manufacturers often have case histories of successful instaHations. Adhesion performance can vary widely with sealant type, substrate type, and cleaning method. Eor this reason, it is important to understand the sealant s sensitivity to cleaning practices. Often with difficult-to-adhere substrates, a primer is used. Sealant manufacturers can provide recommendations as to which substrates require primers, what type of primers should be used, and how they should be appHed. 

Tlie most common ceU case and cover materials are nylon and st) T enic (ABS). After inserting the ceU element, with cov er attached, into the ceU case, cover and case are cemented. For nylon, a most satisfactory adlieswe is phenol For styrene copoltyiiers, either a solvent seal or an ultrasonic seal is effective (see Adhesives). 

Covers for the battery designs in Figures 1 and 2 are typically molded from materials identical to that of the respective case, and vent plugs are frequentiy made of molded polypropylene. Other combinations are possible, eg, containers molded of polyethylene or polypropylene may be mated with covers of high impact mbber for use in industrial batteries. After the cover is fitted over the terminal post, it is sealed onto the case. The cover is heat bonded to the case, if it is plastic it is sealed with an epoxy resin or other adhesive, if it is vulcanized mbber. Vent caps are usually inserted into the cover s acid fiU holes to faciHtate water addition and safety vent gasses, except for nonaccessible maintenance-free or recombinant batteries. In nonaccessible batteries, the vent is fabricated as part of the cover. 

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. 

The adhesive was developed for application to seal food containers with alumina foils and to seal glass plates. In this case, the vinyl polymerization step can be carried out by UV light radiation through the already mounted glass plates with a photoactive radical initiator to cure the viscous adhesive material. Another application of this material is the development of diffusion barrier containing protective coatings on medieval stained glasses (31). 

Hot melt adhesives based on poly(3HB-co-3HV) have also been described [119]. Hot melts are commonly used in bookbinding, bag ending and case and carton sealing and are mostly based on synthetic materials such as polyethylene, polypropylene ethylene-vinyl acetate and styrene block copolymers [119]. Hot melts based on PHAs alleviate the dependence on petroleum based materials and allow the development of biodegradable alternatives based on natural raw materials. 

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