Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-09-07
2003-08-19
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S908000, C412S004000, C412S006000, C412S008000, C412S900000
Reexamination Certificate
active
06607629
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an adhesive system based on at least one adhesive for a one-step or multi-step perfect binding process and to a process for the perfect binding of brochures, books, catalogues, writing pads and similar printed articles using this process.
2. Discussion of the Related Art
Perfect binding has long been successfully used for the rapid and economic production of books, catalogues, writing pads and brochures. In perfect binding processes, the function of the adhesive is, on the one hand, to hold the individual pages together along one edge, on the other hand, to affix a cover or a liner around the inner book.
Optimal bonding of the individual pages is achieved if the individual page edges can be thoroughly wetted by the adhesive, for which purpose low-viscosity adhesives (for example hotmelt adhesives or dispersion adhesives) are generally preferred.
However, the pickup of the covers generally requires products of higher viscosity because the covers partly consist of papers with very high weights per unit area which are very bulky and can only be safely picked up providing the adhesive has a certain initial tackiness.
If only one adhesive can be used (one-shot process), the viscosity has to be selected so that adequate page edge adhesion and safe pickup of the liner are guaranteed. Since these two requirements cannot always be satisfied by a single adhesive, the idea of introducing the so-called two-shot process was adopted at an early stage. In the two-shot process, two different adhesives are used one after the other. In a first step, the inner book is very thinly coated with a dispersion or a hotmelt adhesive, preferably in a layer thickness of less than 0.2 mm. Where a dispersion is used, the adhesive can be dried in a matter of seconds in the machine, for example using an infrared dryer. The second adhesive is then applied in a second step. Depending on the system, the second adhesive is a dispersion adhesive at room temperature or a hotmelt adhesive at temperatures of 120 to 200° C. In the two-shot process, the low-viscosity adhesive is responsible for page adhesion in step 1 while the high-viscosity dispersion adhesive or hotmelt adhesive is responsible for the strength of the inner book in step 2.
One example of a two-shot process is described in WO 85/04669. In this process, a water-based coupling agent is used as the first adhesive while a hotmelt adhesive is used as the second adhesive, the hotmelt adhesive containing a segmented monoalkylene/vinyl acetate copolymer and the water-based coupling agent containing an aqueous rubber latex emulsion. Accordingly, in this process, a non-reactive low-viscosity adhesive is initially applied in the form of a dispersion while the hotmelt adhesive is applied after drying of this layer, as described above.
Reactive systems are used both in one-shot processes, for example in the form of reactive polyurethane hotmelt adhesives, and in two-shot processes, for example in the form of a two-component reactive dispersion and a hotmelt.
EP-A 0 568 803 relates to a book binding process in which a water-based coupling agent and a hotmelt adhesive are successively applied to the spine of an inner book, the coupling adhesive being an aqueous dispersion of a polymeric adhesive resin and an isocyanate hardener. In this two-shot process, therefore, a two-component reactive dispersion is applied first, the hotmelt adhesive being applied after this dispersion has dried.
The disadvantage of the process known from EP-A 0 568 803 is that the polymer to be crosslinked always has to react with another substance in one of the two reaction steps. Accordingly, systems of the type in question either require special application systems to avoid premature crosslinking before application (when the second component is water, for example moisture from the air) or have only a limited pot life (in the case of two-component systems where chemical components are mixed).
BRIEF SUMMARY OF THE INVENTION
The problem addressed by the present invention was to provide an improved adhesive system for a one-step or multi-step perfect binding process for book binding which, in particular, would be easier to handle.
An adhesive system of the type in question is obtained through the presence of at least one photoinitiator so that a low molecular weight component can be hardened by a radical or cationic reaction induced by electromagnetic radiation, for example by UV radiation or more powerful electromagnetic radiation. In addition, known reactive groups, for example NCO groups, may also be present bound either to the same molecules which are capable of the radiation-induced reaction or to different molecules.
Accordingly, the present invention relates to an adhesive system for a one-step or multi-step perfect binding process for book binding, characterized in that it contains at least one photoinitiator and at least one adhesive A which is capable of a radiation-induced reaction.
DETAILED DESCRIPTION OF THE INVENTION
The adhesive systems differs in its composition according to whether it is used in a one-shot process or in a two-shot process.
In the one-shot process, the adhesive system comprises as the adhesive A a radiation-crosslinkable adhesive of a low-viscosity crosslinkable mixture of monomers and/or polymers which has a viscosity of 0.1 to 20 and preferably 0.1 to 10 Pas at the application temperature and which additionally contains at least one photoinitiator.
In the two-shot process, the adhesive system according to the invention comprises the adhesive A, namely a low-viscosity radiation-crosslinkable adhesive (for example solventless or solvent-containing systems or a dispersion) which has a viscosity at the application temperature of 100 to 10,000 mPas and preferably in the range from 100 to 1,000 mPas and which additionally contains at least one photoinitiator, and the adhesive B which has a viscosity at the application temperature of 1,000 to 20,000 mPas and preferably in the range from 5,000 to 10,000 mPas.
Apart from the practically non-existent pot life, the advantage of this system is that there is no need to keep to any mixing ratios and no special applicators are required. This provides for simple production on an industrial scale.
In the context of the present invention, a “multi-step perfect binding process” is understood to be a perfect binding process comprising at least two application steps, the two-shot process being preferred.
A “radiation-induced reaction” is understood to be a radical or cationic reaction in which the molecular weight is increased. Accordingly, adhesive A is based on solventless or solvent-containing mixtures in the form of solutions or aqueous dispersions of, preferably, acrylate monomers and/or acrylate-modified polymers and/or aliphatic epoxy monomers and/or epoxy-modified polymers.
In cases where the molecular weight is increased by a radical reaction, the functional group is quite generally an olefinically unsaturated double bond. According to the invention, olefinically unsaturated double bonds as present, for example, in derivatives of acrylic acid or styrene are preferred. Derivatives of acrylic acid, for example acrylates and methacrylates containing 1 to 16 and preferably 1 to 4 carbon atoms in the alcohol component, are particularly suitable and preferred for the purposes of the invention.
Adhesive A according to the invention preferably contains at least one polymer with a molecular weight of at least 800 as the radically reactive component. Suitable reactive components are any of the polymeric compounds typically used in adhesives, for example polyvinyl acetate, polyvinylidene chloride, polyacrylates, polyesters, polyethers, polycarbonates, polyacetals, polyurethanes, polyolefins or rubber polymers, such as nitrile, chloroprene, isoprene or styrene/butadiene rubber, providing they contain at least one functional group polymerizable by exposure to UV light or to electron beams and optionally at least one functional group capable of reacting w
Aftergut Jeff H.
Haran John T.
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Ortiz Daniel S.
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