Cold-Seal Adhesives

US Patent 4,902,370 Synthetic based cold seal adhesives. Feb 20 1990. 

Cold-seal adhesives are members of a general category sometimes termed coadhesive substances that have a great tendency to stick to themselves, but often not to much else. Cold-seal adhesives are typically based on natural rubber, which has been applied in a latex (suspension in water) form. One major application is in plastic packaging for chocolate candy. The seal between the two parts of the wrap can then be activated with pressure, as an alternative to heat-sealing, which is problematic with the low-melting temperature candy. 

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. 

ExxonMobil OPPalyte films are coated, pearlescent white, opaque OPP films, with a proprietary core providing excellent opacity, good machinability, excellent flavor and aroma barrier properties, good oxygen barrier properties, excellent stiffness and flex resistance, excellent print performance, strong cold seal adhesion, and good bond strength. 

Shear strength modulus curves of cold seal adhesives [94]. 

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. 

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. 

Coatings are an alternative means of adding properties which are not present in the base material improved barrier, heat or cold sealing, improved appearance, adhesion, etc. 

Achieved by aqueous, solvent, hot melt, etc., adhesives or self-adhesives, cold seal materials. Solder is a metallic adhesive system. Solvent bonding is a chemical adhesive system. 

Natural rubber adhesive, or latex, is used in self-seal applications, where it makes use of its unique ability to bond only to itself with pressure. Applications include selfseal envelopes, press-to-seal cases, and cold-seal candy wraps. Natural rubber latex is also used in adhesives for lamination of polyethylene film to paper, such as in multiwall hags. 

Cold seal release films are most commonly used as the outside web or film of a multiweb packaging structure. The release film is a clear web that is reverse printed and adhesive laminated to an iimer web, such as an opaque film or a metallized film. " ... 

Sealants (sealing materials) and compounds (filling materials) are thickflowing pastes which solidify in the cold. They are prepared by mixing low-molecular silicone elastomers with mineral ingredients. Sealants and compounds are supplemented with special catalysts which help them to solidify in the cold. Before using sealants or compounds, the surface of the product is sometimes covered with a sub-layer to improve adhesion. 

Copolymers of PE with vinylacetate, acrylic acid ester and methacrylic acid increase the heat sealability, adhesion to other materials and seal strength and they improve the polymer s cold resistance and transparency. EVA in the form of shrink films are well suited for meat packaging because of their relatively high gas permeabilities. 

When removed from refrigerated storage, the adhesive must be brought to its application temperature, usually room temperature. The containers should remain closed until they are at temperature. A material is most vulnerable to moisture collection when it is removed from cold storage and the package or container is not properly sealed. Moisture condenses on the adhesive and quickly reduces its capabilities. Containers that are not completely used when originally opened, should be sealed immediately after use to prevent loss of volatile ingredients or contamination from moisture in the air. Equipment used to remove the contents from the containers, such as spatulas, flasks, and cups, should be cleaned between each use. 

Other differences, both in kind and degree, combine to make the thermosetting resins as a class useful in many industrial applications for which the thermoplastics are chemically unsuited. The thermosetting epoxy resins possess a number of unusually valuable properties immediately amenable to use in the formulation of adhesives, sealing liquids, cold solders, castings, laminates, and coatings. The more important of these properties include ... 

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