Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1985-12-04
1988-03-01
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524271, 525 80, C08J 5100, C08L 3102
Patent
active
047286881
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an improved method of perfect binding using hot melt adhesives and to a novel adhesive system for use in such a method.
Perfect binding is the term used to describe a method of book binding in which the sheets making up a book are stacked in order to form a so-called signature which is then held in a clamp while adhesive is applied to the edge or spine to be bound whereafter a cover sheet or strip is brought into contact with the spine before the adhesive sets.
Perfect binding originally was used as a cheap and rapid binding method for so-called paperback or pocket books. However, it is now used for binding magazines, catalogues, directories, etc and even for binding signatures for case-bound books. For convenience the single term "books" is thus used hereinafter to refer to books, magazines, catalogues, etc. Particularly rapid and efficient perfect binding has been made possible by the use of hot melt adhesives which are solid at ambient temperatures and which after application in molten form at elevated temperatures, generally about 150.degree.-180.degree. C., cool and set rapidly, generally within about 20 seconds. Using such adhesives the bound books can be removed from their clamps to be trimmed much more rapidly than where a water-based adhesive is used as that must first be allowed to dry.
The polymer-based hot melt adhesives however do not penetrate the book spines as well as water-based adhesives and where a stronger binding is required it is known to precede the application of the hot melt adhesive by the application of a water-based primer, generally an aqueous adhesive emulsion of a polymer such as polyvinyl acetate (PVA) or vinyl acetate-ethylene copolymer (VAE). This so called "two-shot" adhesive system lengthens the time required for binding as at least partial drying of the primer must be permitted before application of the hot-melt adhesive but the penetration of the water based adhesive results in a stronger binding than is achieved with the so-called "one-shot" system where only the hot-melt adhesive is used.
The one-shot system is nevertheless still more widely used than the two-shot system, the latter in general being adopted only where the binding needs to conform to rigorous standards such as is the case for example with books with world wide distribution which have to withstand extremes of high and low temperatures.
Thus at low temperature, one-shot perfect bound books are liable to cold crack where the book cracks or splits along the spine, and at high temperatures they are liable to cold flow under stress where the individual pages "creep" out of the adhesive binding. This is termed "cold" flow because it occurs at temperatures cooler than the softening temperature of the hot melt adhesive.
Several hot melt adhesives have been used in two-shot perfect binding but in recent years the preferred hot melt adhesives for such systems have been based on the aromatic monovinyl - conjugated diene block copolymers (hereinafter AMCD) available from Shell Chemical Co. under the trade Mark Kraton. The use of AMCD based hot melt adhesives in perfect binding is disclosed in U.K. Pat. No. 1219394 of National Starch and Chemical Corporation.
Before the AMCD adhesive system of U.K. Pat. No. 1219394, ethylene vinyl acetate (EVA) copolymer based hot melt adhesives, which are still widely used in one-shot binding, had been used in two-shot binding. However, as acknowledged in U.K. Pat. No. 1219394, EVA two-shot binding was unsatisfactory in that books produced thereby were found to exhibit relatively poor cold crack and cold flow properties and also to exhibit poor adhesion between the primer and the hot melt adhesive. The poor adhesion at the primer-hot melt interface is thought to be due at least in part to the inability of the EVA to absorb moisture and bind to incompletely dried primer. Attempts to improve the binding by using as a primer an adhesive based on VAE rather than PVA to provide improved compatibility with EVA were only marginally successful and did not produce
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Thomas George C.
Tizzard Richard E.
Mulcahy Peter D.
Schofer Joseph L.
Swift Adhesives Limited
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