CA2381628A1 - Use of a uv-reactive, humidity-cross-linking pu hot-melt-type adhesive - Google Patents

Abstract

The aim of the invention is to simplify the production of books with rounded book blocks. According to the invention, a UV-reactive hot-melt-type adhesiv e on the basis of a humidity-cross-linking polyurethane is used for the in-lin e binding of book blocks after the adhesive has been applied. The adhesives to be used contain olefinically unsaturated double bonds, such as present in th e derivatives of acrylic acid or styrene for instance, and NCO groups. The processing conditions for the binding have to be chosen in such a way that said conditions result in characteristics in the following areas when a corresponding adhesive film is used: expansion > 100 %, yield stress > 0.5 N/mm2 and preferably tearing strength > 1N/mm2.

Description

Use of a UV-Reactive, Humidity-Cross-linking PU Hot-melt-Type Adhesive This invention relates to the use of a UV-reactive hotmelt adhesive based on a moisture-crosslinking polyurethane for the glueing off and perfect binding of book blocs.
The dimensional stability of a back spine during the use, storage and transportation of the book depends to a large extent on the profile of the bloc spine that was given to the bloc during production. It may be straight or rounded. The rounded spine is the most appropriate. Rounding of the glued-off book achieves the following:
a) the slope of the signature in the region of the rounding is uniformly displaced, b) the strength of the binding of the signature in the bloc is increased, c) better conditions are created for the opening of the book and d) the shape of the spine is better retained during the use of the book.
The same applies to books made by perfect binding. When books with rounded spines and an elastic paper spine insert of the cover are opened, the end sheets and case folds are not subjected to such severe stressing as they are in books with a straight spine and a stiff spine insert.
Accordingly, high-quality back spines are preferably rounded.
To this end, the glued-off or perfect-bound book blocs are fed by hand one or several at a time or are guided on a conveyor belt into the cutting position. Standing on the front cut, the cut book bloc is directly delivered by hand from automatic 3-knife trimmers to the rounding and pressing machine via a conveyor belt, bar chains or a buggy independently of the bloc feeder or the line speed. In the process, the book bloc is first pre-rounded by shaping elements and a shaping rail and then round-drawn by grooved rollers. The bloc is then taken up by two pressing jaws in the region of the fold and pressed off by a shaping block. The rounded and pressed-off bloc is either guided to a delivery station or is directly transferred to the following machine.
The quality of rounding and pressing off is critically determined inter alia by the binding process and by the properties of the adhesive film.
Various adhesive systems are used for the perfect binding of printing products such as, for example, books, catalogs, etc.
Adhesive dispersions, for example based on plasticized vinyl acetate polymers which also impart favorable properties in the long term, such as high bond strengths, high resistance to mineral oil and heat resistance, have been known for some time. Accordingly, these adhesives are used both for high-quality printing products and for low-level binding, for example pocket books of various kinds. Disadvantages of these adhesives are their poor flexibility at low temperatures and the fact that the adhesive layer has to be dried before further processing, such as rounding of the book bloc.
Accordingly, drying lines have to be provided for in-line production which not only is expensive on machinery and space and involves high energy costs, it is also a limiting factor so far as speed is concerned.
Hotmelt adhesives (hotmelts) are another class of adhesives. For example, formulations based on ethylene/vinyl acetate copolymers (EVA) are used as hotmelts. Advantages over dispersions are generally the faster setting rates. This allows the production of large numbers in short times. Disadvantages in relation to dispersions are poorer bond strengths and mineral oil resistances and lower resistance to heat and ageing.
Accordingly, EVA-based hotmelts tend not to be used for high-quality productions, but instead for the mass production of telephone directories, magazines, catalogs, etc. or pocket books. These are generally not rounded, but have flat spines. If they are rounded, this is done in the described manner.
Another class of hotmelt adhesives which can be used for high-quality perfect binding is based on reactive, moisture-crosslinking polyurethanes. Bond strengths, mineral oil resistance and heat resistance are clearly better than those of EVA-based hotmelts. So far as low-temperature flexibility is concerned, polyurethane adhesives are superior both to EVA-based hotmelts and to dispersion-based adhesives. Their disadvantage lies in the poor setting rate through chemical crosslinking of conventional systems. Accordingly, the printed product can only be used or further processed at the earliest after several hours but more generally after several days.
All these adhesive systems are also used for the glueing-off of thread-bound printed products which are then rounded.
WO 98/40225 describes adhesive systems for a one-step or multi-step process for the perfect binding of publications. In order to increase strength, a radically and/or cationically reacting photosensitive adhesive is proposed for the perfect binding of books. It may be used in a one-shot or two-shot process. Typical hotmelt adhesives and dispersion-based adhesives may be used as the second adhesive. The photoreactive adhesive A is a low-viscosity crosslinkable mixture of a monomer and/or a polymer which has a viscosity at the application temperature of 0.1 to 20 Pas. The optional hotmelt adhesive B is based on polyamides, polyurethanes and, in particular, on copolymers of ethylenically unsaturated monomers. The document in question also describes a process for the perfect binding of brochures, catalogues, books, writing pads and similar printed articles by a one-step or multi-step perfect binding process in which the book bloc is first coated with a low-viscosity crosslinkable adhesive A in a film thickness of less than 0.2 mm and, after the adhesive A has set, is finally coated with the adhesive B, the polymer film A additionally containing at least one photoinitiator. Besides the UV-reactive groups, the adhesive A may also contain free NCO groups. There is no specific reference to the use of this adhesive system for rounding book spines.

It has now been found that some of these adhesive systems are eminently suitable for the rounding of book blocs after binding (in-line rounding).
Accordingly, the present invention relates to the use of UV-reactive hotmelt adhesives based on moisture-reactive polyurethanes in the in-line rounding of book blocs (directly after binding). The hotmelt adhesives in question have two curing mechanisms (dual cure hotmelts). Early strength and hence the further processability of the book bloc are achieved through an increase in molecular weight by exposure to light, particularly UV light.
The final properties are then established by a crosslinking reaction with (atmospheric) moisture. The chemical basis of these products is described in WO 98/40225 to which reference is specifically made. Accordingly, hotmelt adhesives of a reactive component, a photoinitiator and optionally additives are suitable for the stated purpose.
The reactive adhesive quite generally contains olefinically unsaturated double bonds and NCO groups. 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.
The adhesive to be used in accordance with 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 nitrite, 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 with a compound containing at least one acidic hydrogen atom, for example an NCO group.
However, polyacrylates, polyesters or polyurethanes are preferably used as reactive component in the adhesives according to the invention because the polymers mentioned make is particularly easy to attach the functional groups required in accordance with the invention to the polymer molecule.
The polymers suitable for use as reactive component in accordance with the invention can be produced particularly easily from a basic polymer containing at least two isocyanate-reactive functional groups, preferably OH groups, in the polymer molecule. The required functional group can be attached particularly easily to this basic polymer by reaction with a polyisocyanate or a suitably functionalized monoisocyanate.
One example of a suitable basic polymer is a polymer selected from the group consisting of polyesters, polyethers, polycarbonates or polyacetals with a molecular weight (M~) of at least about 200 or mixtures of two or more such polymers which contain terminal OH groups.
Polyesters suitable for use in accordance with the invention as the basic polymer for producing the reactive component may be obtained in known manner by polycondensation of acid and alcohol components, more particularly by polycondensation of a polycarboxylic acid or a mixture of two or more polycarboxylic acids and a polyol or a mixture of two or more polyols.
Polycarboxylic acids suitable in accordance with the present invention for the production of the basic polymer may be based on an aliphatic, cycloaliphatic, araliphatic, aromatic or heterocvclic aarent compound and, besides the at least two carboxylic acid groups, may optionally contain one or more substituents which do not react in the course of a polycondensation reaction, for example halogen atoms or olefinically unsaturated double bonds. The free carboxylic acids may even be replaced by their anhydrides (where they exist) or esters with C~_5 monoalcohols or mixtures of two or more thereof for the polycondensation reaction. Suitable polycarboxylic acids are, for example, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, glutaric acid, glutaric anhydride, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylene tetrahydro-phthalic anhydride, glutaric anhydride, malefic acid, malefic anhydride, fumaric acid, dimer fatty acids or trimer fatty acids or mixtures of two or more thereof. Small quantities of monofunctional fatty acids may optionally be present in the reaction mixture.
Various polyols may be used as the diols for producing a polyester or polycarbonate suitable for use as the basic polymer. Examples of such polyols are aliphatic polyols containing 2 to 4 OH groups per molecule.
The OH groups may be both primary and secondary OH groups. Suitable aliphatic polyols include, for example, ethylene glycol, propane-1,2-diol, propane-1,3-diol, butane-1,4-diol, butane-1,3-diol, butane-2,3-diol, butene-1,4-diol, butine-1,4-diol, pentane-1,5-diol, and the isomeric pentanediols, pentenediols or pentinediols or mixtures of two or more thereof, hexane-1,6-diol and the isomeric hexanediols, hexenediols or hexinediols or mixtures of two or more thereof, heptane-1,7-diol and the isomeric heptane, heptene or heptinediols, octane-1,8-diol and the isomeric octane, octene or octinediols and higher homologs or isomers of the compounds mentioned, which are obtained in known manner from a step-by-step extension of the carbon chain by one CH2 group at a time or by introducing branches into the carbon chain, or mixtures of two or more thereof. Other suitable polyols are alcohols of relatively high functionality such as, for example, glycerol, trimethylol propane, pentaerythritol or sugar alcohols, such as sorbitol or glucose, and oligomeric ethers of the substances mentioned either as such or in the form of a mixture of two or more of the compounds mentioned with one another, for example polyglycerol with a degree of polymerization of about 2 to about 4. In the alcohols of relatively high functionality, one or more OH groups may be esterified with monobasic carboxylic acids containing 1 to about 20 carbon atoms, with the proviso that, on average, at least two OH groups remain intact. The higher alcohols mentioned may be used in pure form or, where possible, in the form of the technical mixtures obtainable in the course of their synthesis.
The reaction products of low molecular weight polyfunctional alcohols with alkylene oxides, so-called polyether polyols, may also be used as the polyol component for producing the basic polymers. Polyether polyols, which are to be used for the production of polyesters suitable as the basic polymers, are preferably obtained by reaction of polyols with alkylene oxides. The alkylene oxides preferably contain 2 to about 4 carbon atoms. Suitable polyether polyols are, for example, the reaction products of ethylene glycol, propylene glycol, the isomeric butanediols or hexanediols, as mentioned above, or mixtures of two or more thereof with ethylene oxide, propylene oxide or butylene oxide or mixtures of two or more thereof. Other suitable polyether polyols are products of the reaction of polyfunctional alcohols, such as glycerol, trimethylol ethane or trimethylol propane, pentaerythritol or sugar alcohols or mixtures of two or more thereof, with the alkylene oxides mentioned to form polyether polyols.
Polyether polyols with a molecular weight (M~) of about 100 to 3,000 and preferably in the range from about 200 to about 2,000 obtainable from the reactions mentioned are particularly suitable. The polyether polyols mentioned may be reacted with the polycarboxylic acids mentioned above in a polycondensation reaction to form the polyesters suitable for use as the basic polymers.
Polyether polyols formed, for example, as described above are also suitable as OH-terminated basic polymers. Polyether polyols are normally obtained by reacting a starting compound containing at least two reactive hydrogen atoms with alkylene or arylene oxides, for example ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrin or mixtures of two or more thereof. Suitable starting compounds are, for example, water, ethylene glycol, 1,2- or 1,3-propylene glycol, 1,4- or 1,3-butylene glycol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-hydroxymethyl cyclohexane, 2-methylpropane-1,3-diol, glycerol, trimethylol propane, hexane-1,2,6-triol, butane-1,2,4-triol, trimethylol ethane, pentaerythritol, mannitol, sorbitol, methyl glycosides, sugars, phenol, isononyl phenol, resorcinol, hydroquinone, 1,2,2- or 1,1,2-tris-(hydroxyphenyl)-ethane, ammonia, methyl amine, ethylenediamine, tetra- or hexamethylenediamine, triethanolamine, aniline, phenylene-diamine, 2,4- and 2,6-diaminotoluene and polyphenyl polymethylene polyamines which can be obtained by condensing aniline with formaldehyde.
Polyether polyols modified by vinyl polymers are also suitable for use as the basic polymer. Products such as these can be obtained, for example, by polymerizing styrene or acrylonitrile or a mixture thereof in the presence of polyethers.
A polyether polyol particularly suitable in accordance with the invention for use as the basic polymer is polypropylene glycol with a molecular weight of about 300 to about 1,500.
Polyacetals are also suitable for use as the basic polymer or as the polyol component for producing the basic polymer. Polyacetals are understood to be compounds obtainable by reacting glycols, for example diethylene glycol or hexanediol, with formaldehyde. Polyacetals suitable for the purposes of the invention may also be obtained by polymerizing cyclic acetals.
Polycarbonates are also suitable for use as the basic polymer or as the polyol used for producing the basic polymer. Polycarbonates may be obtained, for example, by reacting the polyols mentioned above, more particularly diols, such as propylene glycol, butane-1,4-diol or hexane-1,6-diol, diethylene glycol, triethylene glycol or tetraethylene glycol or mixtures of two or more thereof, with diaryl carbonates, for example diphenyl carbonate or phosgene.
OH-functional polyacrylates are also suitable as the basic polymer or as the polyol component used for producing the basic polymer. OH-functional polyacrylates may be obtained, for example, by polymerizing ethylenically unsaturated monomers bearing OH groups. Such monomers are obtainable, for example, by esterification of ethylenically unsaturated carboxylic acids and difunctional alcohols, the alcohol generally being present in only a slight excess. Ethylenically unsaturated carboxylic acids suitable for this purpose are, for example, acrylic acid, methacrylic acid, crotonic acid or malefic acid. Corresponding OH-functional esters are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxy-propyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropyl methacrylate or mixtures of two or more thereof.
If the molecular weight of the basic polymer is too low for use as a reactive component, it may be increased, for example, by chain extension.
To this end, the OH-terminated basic polymer is initially reacted with a polyfunctional compound, preferably a difunctional compound (functionality related to the terminal OH groups). Accordingly, in the context of the invention, particularly suitable polyfunctional compounds are polyepoxides, more especially diepoxides, or preferably polyisocyanates, more especially diisocyanates. Diisocyanates are particularly preferred for the purposes of the invention. The stoichiometric ratios between basic polymer and polyfunctional compound required for obtaining a certain increase in molecular weight are known to the expert. In general, however, an excess of basic polymer will be present during the chain-extending reaction to obtain an increase in the length of the chain, the chain-extended basic polymers formed again being terminated by OH groups.
In order to be suitable for use as a reactive component, the OH-terminated, optionally chain-extended basic polymers mentioned above must be provided with at least one functional group polymerizable by exposure to UV light or to electron beams and optionally with at least one functional group polymerizable by reaction with a compound containing at least one acidic hydrogen atom.
To this end, the basic polymers are preferably reacted with a compound which is polyfunctional and preferably difunctional in relation to the terminal OH groups. Suitable polyfunctional compounds for the purposes of the invention are the polyfunctional compounds already usable for chain extension, more especially polyepoxides, particularly diepoxides, but preferably polyisocyanates, especially diisocyanates. Diisocyanates are particularly preferred for the purposes of the present invention.
Suitable polyfunctional polyisocyanates which are suitable for reaction with the basic polymers contain on average two to at most about four isocyanate groups. Examples of suitable isocyanates are 1,5-naphthalene diisocyanate, 4,4'-diphenyl methane diisocyanate (MD/), hydrogenated MDI
(dicyclohexyl methane diisocyanate, H~2-MDI), xylylene diisocyanate (XD/), tetramethyl xylylene diisocyanate (TMXDI), 4,4'-diphenyl dimethyl methane diisocyanate and di- and tetraalkyl diphenyl methane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and 2,6-toluene diisocyanate (TD/) and mixtures thereof, more particularly a mixture containing about 20% of 2,4- and 80% by weight of 2,6-toluene diisocyanate, 1-methyl-2,4-diisocyanatocyclohexane, 1,6-diisocyanato-2,2,4-trimethyl hexane, 1,6-diisocyanato-2,4,4-trimethyl hexane, 1-isocyanatoethyl-3-isocyanato-1,5,5-trimethyl cyclohexane (/PD/), chlorinated and brominated diisocyanates, phosphorus-containing diisocyanates, 4,4'-diisocyanatophenyl perfluoroethane, tetramethoxy-butane-1,4-diisocyanate, 1,4-butane diisocyanate, 1,6-hexane diisocyanate (HD/), cyclohexane-1,4-diisocyanate, ethylene diisocyanate, phthalic acid-bis-isocyanatoethyl ester; polyisocyanates containing reactive halogen atoms, such as 1-chloromethylphenyl-2,4-diisocyanate, 1-bromomethylphenyl-2,6-diisocyanate, 3,3-bis-chloromethylether-4,4'-diphenyl diisocyanate. Sulfur-containing polyisocyanates obtainable, for example, by reacting 2 moles of hexamethylene diisocyanate with 1 mole of thiodiglycol or dihydroxydihexyl sulfide are also suitable. Other diisocyanates are trimethyl hexamethylene diisocyanates, 1,4-diisocyanatobutane, 1,2-diisocyanatododecane and dimer fatty acid diisocyanates. Triisocyanatoisocyanurates may be obtained by trimeriz-ation of diisocyanates at elevated temperature, for example at around 200°C, and/or in the presence of a catalyst, for example an amine, and may also be used for the purposes of the present invention. According to the invention, the polyisocyanates mentioned may be used either individually or in the form of a mixture of two or more of the polyisocyanates mentioned. A single polyisocyanate or a mixture of two or three polyisocyanates is preferably used for the purposes of the present invention. Preferred polyisocyanates used either individually or in admixture are HDI, MDI or TDI, for example a mixture of MDI and TDI.
The basic polymer is preferably reacted with the polyfunctional compound, preferably with the diisocyanate, in a ratio of 1:>2, the excess of polyfunctional compound being, for example, just large enough to avoid chain extension of the basic polymer, although only small quantities of unreacted polyfunctional compound are present in the reactive component.
A procedure such as this can be of advantage in particular where a diisocyanate is used as the polyfunctional compound. A polymer terminated by two functional groups which can be polymerized by reaction with a compound containing at least on acidic hydrogen atom is obtained in this way.
In order to obtain a polymer suitable for use as a reactive component from a polymer such as this, the polymer is preferably reacted with a compound which contains both a functional group polymerizable by exposure to UV light or to electron beams and a functional group suitable for reaction with the terminal functional group of the polymer. Hydroxyalkyl acrylates or methacrylates, i.e. reaction products of acrylic acid or methacrylic acid with difunctional alcohols, are particularly suitable for this purpose. Hydroxyacrylates or methacrylates particularly suitable for use in accordance with the present invention are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropyl methacrylate or mixtures of two or more thereof.
Polymers suitable for use as the reactive component may also be obtained, for example, in several steps. In a first step, the OH-terminated basic polymer is reacted with a compound which contains both a functional group polymerizable by exposure to UV light or to electron beams and a functional group capable of reacting with the terminal OH group of the basic polymer. One example of such a compound is styrene isocyanate. Other such compounds may be obtained, for example, by reacting a substantially equimolar quantity of a hydroxyalkyl acrylate or methacrylate with a diisocyanate. After reaction of a substantially equimolar quantity of the basic polymer (optionally adapted by chain extension to the molecular weight required for use in component A) with such a compound in a second step, a polymer terminated both by an OH group and by a functional group polymerizable by exposure to UV light or to electron beams is formed. If this polymer is reacted, for example, with a diisocyanate, a polymer suitable for use as the reactive component is obtained.
The two steps mentioned above may also be combined by reacting a basic polymer, a diisocyanate (or optionally another polyfunctional compound in the context of the foregoing observations) and a compound containing both a functional group polymerizable by exposure to UV light or to electron beams and a functional group capable of reacting with the terminal OH group of the basic polymer with one another in a suitable molar ratio so that the percentages of the two types of functional groups in the polymer mixture obtainable by such a reaction vary between >0% and <100% (based on functional groups). Favorable results can be obtained, for example, if around 1 to around 50%, preferably around 5 to around 30%
and, more preferably, around 8 to around 15% of the functional groups present as terminal groups in the polymer are functional groups polymerizable by exposure to UV light or to electron beams.
Typical NCO contents for polymers suitable for use as the reactive component are about 2.5% by weight to about 7% by weight and, more particularly, about 3.5% by weight to about 5% by weight.
The reactive component used in accordance with the present invention may consist of only one of the described polymers, although it may advantageously represent a mixture of two or more of the polymers mentioned. For example, it is of advantage to use a mixture of one or more polyester polyols and one or more polyether polyols as the basic polymer.
The various basic polymers may differ, for example, in their molecular weights (M~) or in their chemical compositions or in both.
In one preferred embodiment of the invention, around 20 to around 40% by weight of polyester polyols and around 20 to around 60% by weight of polyether polyols, based on component A as a whole, are used as the basic polymers for producing the reactive component. In another preferred embodiment, at least two different polyether polyols, more particularly a mixture of a polyether polyol with a molecular weight of about 800 to about 1,500 and a polyether polyol with a molecular weight of about 300 to about 700, are used in addition to a polyester polyol as the basic polymer.
To produce the reactive component, the individual basic polymers may be provided with functional groups and optionally chain-extended, as described above, so that they are directly suitable for use as the reactive component. In one preferred embodiment of the invention, however, a mixture of OH-functional basic polymers is initially reacted with a suitable quantity of polyisocyanates and then - in a suitable molar ratio - with compounds which contain both a functional group polymerizable by exposure to UV light or to electron beams and a functional group capable of reacting with the terminal OH group of the basic polymer.
In another embodiment, at least one compound with a molecular weight of about 100 to about 8,000 which contains at least two functional groups polymerizable by exposure to UV light or to electron beams may also be used as the reactive component.
Accordingly, acrylates or methacrylates with a functionality of two or more are particularly suitable as the reactive component. Acrylates or methacrylates such as these include, for example, esters of acrylic acid or methacrylic acid with aromatic, aliphatic or cycloaliphatic polyols or acrylate esters of polyether alcohols.
Various polyols may be used as the polyols for producing suitable reactive acrylate or methacrylate esters of the type in question. Examples of such polyols are aliphatic polyols containing 2 to 4 OH groups per molecule and 2 to about 40 carbon atoms. The OH arouos may be hnth primary and secondary OH groups. Suitable aliphatic polyols include, for example, ethylene glycol, propane-1,2-diol, propane-1,3-diol, butane-1,4-diol, butane-1,3-diol, butane-2,3-diol, butene-1,4-diol, butine-1,4-diol, pentane-1,5-diol and the isomeric pentanediols, pentenediols or pentinediols or mixtures of two or more thereof, hexane-1,6-diol and the isomeric hexanediols, hexenediols or hexinediols or mixtures of two or more thereof, heptane-1,7-diol and the isomeric heptane, heptene or heptinediols, octane-1,8-diol and the isomeric octane, octene or octinediols and higher homologs or isomers of the compounds mentioned, which may be obtained in known manner by step-bv-step extension of the hydrocarbon chain by one CH2 group at a time or by introducing branches into the carbon chain, or mixtures of two or more thereof.
Other suitable polyols are higher alcohols, such as for example glycerol, trimethylol propane, pentaerythritol or sugar alcohols, such as sorbitol or glucose, and oligomeric ethers of the substances mentioned either as such or in the form of mixtures of two or more of the compounds mentioned with one another, for example polyglycerol with a degree of polymerization of about 2 to about 4. In the case of the higher alcohols, one or more OH groups may be esterified with monobasic carboxylic acids containing 1 to about 20 carbon atoms, with the proviso that, on average, at least two OH groups remain intact. The higher alcohols mentioned may be used in pure form or, where possible, in the form of the technical mixtures obtainable in the course of their synthesis.
In addition, reaction products of low molecular weight, polyfunctional alcohols with alkylene oxides, so-called polyether polyols, may be used as polyol component for the production of the acrylate or methacrylate esters.
Polyether polyols which are intended to be used for the production of polyesters suitable as basic polymers are preferably obtained by reaction of polyols with alkylene oxides. The alkylene oxides preferably contain 2 to about 4 carbon atoms. Suitable polyether polyols are, for example, the reaction products of ethylene glycol, propylene glycol, the isomeric butanediols or hexanediols, as mentioned above, or mixtures of two or more thereof with ethylene oxide, propylene oxide or butylene oxide or mixtures of two or more thereof. Products of the reaction of polyfunctional alcohols, such as glycerol, trimethylol ethane or trimethylol propane, pentaerythritol or sugar alcohols, or mixtures of two or more thereof with the alkylene oxides mentioned to form polyether polyols are also suitable.
The polyether polyols with a molecular weight (M~) of about 100 to about 2,000, preferably in the range from about 150 to about 1,500 and more preferably in the range from about 150 to about 800 obtainable from the reactions mentioned are particularly suitable.

Acrylate esters of aliphatic diols containing 2 to about 40 carbon atoms include, for example, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylol propane tri(meth)acrylate, penta-erythritol tetra(meth)acrylate and (meth)acrylate esters of sorbitol and other sugar alcohols. These (meth)acrylate esters of aliphatic or cycloaliphatic diols may be modified with an aliphatic ester or an alkylene oxide. The acrylates modified by an aliphatic ester comprise, for example, neopentyl glycol hydroxypivalate di(meth)acrylate, caprolactone-modified neopentyl glycol hydroxypivalate di(meth)acrylates and the like. The alkylene oxide-modified acrylate compounds include, for example, ethylene oxide-modified neopentyl glycol di(meth)acrylates, propylene oxide-modified neopentyl glycol di(meth)acrylates, ethylene oxide-modified 1,6-hexanediol di(meth)-acrylates or propylene oxide-modified hexane-1,6-diol di(meth)acrylates or mixtures of two or more thereof.
Acrylate monomers based on polyether polyols comprise, for example, neopentyl glycol-modified trimethylol propane di(meth)acrylates, polyethylene glycol di(meth)acrylates, polypropylene glycol di(meth)-acrylates and the like. Trifunctional and higher acrylate monomers comprise, for example, trimethylol propane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa{meth)acrylate, caprolactone modified dipentaerythritol hexa(meth)acrylate, pentaerythritol tetra(meth) acrylate, tris[(meth)acryloxyethyl)-isocyanurate, caprolactone-modified tris[(meth)acryloxyethyl]-isocyanurates or trimethylol propane tetra(meth) acrylate or mixtures of two or more thereof.
Of the above-mentioned difunctional, trifunctional or higher acrylate monomers which may be used in accordance with the invention as the reactive component, tripropylene glycol diacrylate, neopentyl glycol propoxylate di(meth)acrylate, trimethylol propane tri(meth)acrylate and pentaerythritol triacrylate are preferred.

The adhesives to be used in accordance with the invention contain the reactive components in a quantity of about 10 to about 99.9% by weight and preferably in a quantity of about 15 to about 99% by weight.
The molar ratios between the basic polymer and the compound containing both a functional group polymerizable by exposure to UV light or to electron beams and a functional group capable of reacting with the terminal functional group of the polymer may vary within wide limits during the reaction. In general, a larger number of functional groups polymerizable by exposure to UV light or to electron beams in the reactive component leads to an adhesive bond of relatively high strength whereas a larger number of functional groups capable of reacting with a compound containing at least one acidic hydrogen atom leads to greater ultimate strength.
If, for example, the basic polymer is reacted with the compound containing both a functional group polymerizable by exposure to UV light or to electron beams and a functional group capable of reacting with the terminal functional group of the polymer in a molar ratio of about 1:1, each polymer molecule in the resulting polymer mixture contains on average both a functional group polymerizable by exposure to UV light or to electron beams and a functional group capable of reacting with a compound containing at least one acidic hydrogen atom. The percentages of the two types of functional groups in the polymer mixture obtainable by such a reaction can be varied accordingly between greater than 0 and greater than 100% (based on functional groups in the context of the present invention).
Good results can be obtained, for example, if about 100 to about 10%, preferably about 1 to about 50% and, more preferably, about 8 to about 15% of the functional groups present as terminal groups in the polymer are functional groups polymerizable by exposure to UV light or to electron beams.
Compounds and mixtures of compounds which are capable of initiating the radical polymerization of olefinically unsaturated double bonds on exposure to light with a wavelength of about 260 to about 480 nm are used as a photoinitiator, more especially for the radical reaction. In principle, any commercially available photoinitiators which are compatible with the adhesive according to the invention, i.e. which form at least substantially homogeneous mixtures, may be used for the purposes of the present invention.
Commercially available photoinitiators such as these are, for example, any Norrish-type I fragmenting substances, for example benzophenone, camphor quinone, Quantacure (a product of International Bio-Synthetics), Kayacure MBP (a product of Nippon Kayaku), Esacure BO
(a product of Fratelli Lamberti), Trigonal 14 (a product of Akzo), photoinitiators of the Irgacure~, Darocure~ or Speedcure~ series (products of Ciba Geigy), Darocure~ 1173 and/or Fi-4 (made by the Eastman Company). Of these, Irgacure~ 651, Irgacure~ 369, Irgacure~
184, Irgacure~ 907, Irgacure~ 1850, Irgacure~ 1173 (Darocure~ 1173), Irgacure~ 1116, Speedcure~ EDB, Speedcure~ ITX, Irgacure~ 784 or Irgacure~ 2959 or mixtures of two or more thereof are particularly suitable.
Photoinitiators from the following group are preferred: benzoin and benzoin derivatives, phenyl hydroxyalkanone types and thioxanthone types.
A photoinitiator with a molecular weight of more than about 200 is at least partly used in one preferred embodiment of the invention.
Commercially available photoinitiators which meet this requirement are, for example, Irgacure~ 651, Irgacure~ 369, Irgacure~ 907, Irgacure~ 784, Speedcure~ EDB and Speedcure~ ITX.
However, photoinitiators which meet the above-stated requirement in regard to their molecular weight can also be obtained by reacting a low molecular weight photoinitiator containing an isocyanate-reactive functional group, for example an amino group or an OH group, with a high molecular weight compound containing at least one isocyanate group (polymer-bound photoinitiators). Compounds containing more than one photoinitiator molecule, for example two, three or more photoinitiator molecules, are preferably used as the photoinitiator. Compounds such as these can be obtained, for example, by reacting a polyfunctional alcohol containing two or more OH groups with suitable diisocyanates or triisocyanates and photo-initiators containing a suitable isocyanate-reactive functional group.
Suitable polyfunctional alcohols are any of the polyfunctional alcohols mentioned above, but especially neopentyl glycol, glycerol, trimethylol propane, pentaerythritol and alkoxylation products thereof with C2.~ alkylene oxides. Other suitable and, according to the invention, particularly preferred polyfunctional alcohols are the reaction products of trihydric alcohols with caprolactone, for example the reaction product of trimethylol propane with caprolactone (Capa 305, a product of Interox, Cheshire, UK; molecular weight (M~) = 540).
Another preferred embodiment of the present invention i~
characterized by the use of a photoinitiator obtainable by reacting an at least trihydric alcohol with caprolactone to form a polycaprolactone containing at least three OH groups with a molecular weight of about 300 to about 900 and then linking the polycaprolactone to 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methylpropan-1-one by means of a compound containing at least two isocyanate groups.
Suitable compounds containing at least two isocyanate groups, more particularly suitable diisocyanates, for reaction with the polyols mentioned are, for example, any of the diisocyanates mentioned in the present specification. However, the 2,4-isomer and the 2,6-isomer of toluene diisocyanate are particularly preferred, the isomers being used either in their pure form or in the form of a mixture.
Suitable photoinitiators for producing the polymer-bound photoiniti-ators are any photoinitiators which contain an isocyanate-reactive func-tional group. 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methylpropan-1-one (Irgacure~ 2959), which has one primary OH group, is particularly preferred for the purposes of the present invention.
The photoinitiators may also be prepared by using a small quantity of photoinitiator molecules reactive to isocyanate groups in the production of the adhesive A. In this way, the photoinitiator is attached to a molecule of the adhesive.
The photoinitiator may also be attached to a polymer chain of the adhesive A by adding the photoinitiator containing a corresponding functional group to the adhesive in monomeric form and then reacting it with a corresponding polymeric component of the adhesive A, for example during storage of the adhesive.
It is also possible to provide the photoinitiator with a functional group polymerizable by exposure to UV light or to electron beams, in which case the functional group polymerizable by exposure to UV light or to electron beams can be attached to the photoinitiator, for example by reaction of the photoinitiator with an unsaturated carboxylic acid. Suitable unsaturated carboxylic acids are, for example, acrylic acid and methacrylic acid. The reaction products of Irgacure~ 2959 with acrylic acid or methacrylic acid are particularly suitable for the purposes of the invention.
Accordingly, a compound which contains both a photoinitiator and a functional group polymerizable by exposure to UV light or to electron beams may be used as the photoinitiator.
The adhesive to be used in accordance with the invention contains the photoinitiator in a quantity of up to about 25% by weight, based on the adhesive A as a whole, the lower limit being at around 0.01 % by weight.
Based on the individual photoinitiator molecule itself (irrespective of whether it is covalently bonded to another compound), the percentage content in the adhesive should be at least about 0.01 % by weight to about 10% by weight, preferably in the range from about 0.5 to about 5% by weight and more preferably in the range from about 1 to about 3% by weight, based on the adhesive as a whole.
In addition, coinitiators or photosensitizers, for example acetophenone, benzophenone and fluorescin and derivatives thereof, may also be used.
The adhesive may optionally contain additives which may make up as much as about 49% by weight of the adhesive as a whole. Additives which may be used in accordance with the present invention include, for example, plasticizers, stabilizers, antioxidants, dyes or fillers.
The plasticizers used are, for example, plasticizers based on phthalic acid, more especially dialkyl phthalates, preferred plasticizers being phthalic acid esters which have been esterified with a linear alkanol containing about 6 to about 12 carbon atoms. Dioctyl phthalate is particularly preferred. Other suitable plasticizers are benzoate plasticizers, for example sucrose benzoate, diethylene glycol dibenzoate and/or diethylene glycol benzoate, in which around 50 to around 95% of all the hydroxyl groups have been esterified, phosphate plasticizers, for example t-butyl phenyl diphenyl phosphate, polyethylene glycols and derivatives thereof, for example diphenyl ethers of polyethylene glycol), liquid resin derivatives, for example the methyl ester of hydrogenated resin, vegetable and animal oils, for example glycerol esters of fatty acids and polymerization products thereof.
The stabilizers or antioxidants suitable for use as additives in accordance with the present invention include phenols, sterically hindered phenols of high molecular weight (M~), polyfunctional phenols, sulfur- and phosphorus-containing phenols or amines. Phenols suitable for use as additives in accordance with the invention are, for example, hydroquinone, hydroquinone methyl ether, 2,3-(di-tert.butyl)-hydroquinone, 1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert.butyl-4-hydroxybenzyl)-benzene; pentaerythritol tetra-kis-3-(3,5-ditert.butyl-4-hydroxyphenyl)-propionate; n-octadecyl-3,5-ditert.-butyl-4-hydroxyphenyl)-propionate; 4,4-methylene-bis-(2,6-di-tert.butylphe-nol); 4,4-thiobis-(6-tert.butyl-o-cresol); 2,6-di-tert.butylphenol; 6-(4-hydroxy-phenoxy)-2,4-bis-(n-octylthio)-1,3,5-triazine; di-n-octadecyl-3,5-di-tert.butyl-4-hydroxybenzyl phosphonates; 2-(n-octylthio)-ethyl-3,5-ditert.butyl-4-hydroxybenzoate; and sorbitol hexa[3-(3,5-ditert.butyl-4-hydroxyphenyl)-propionate]; and p-hydroxydiphenylamine or N,N'-diphenylenediamine or phenothiazine.
Other additives may be incorporated in the adhesive A in order to vary certain properties. These other additives include, for example, dyes, such as titanium dioxide, fillers, such as talcum, clay and the like. The adhesives to be used in accordance with the invention may optionally contain small quantities of thermoplastic polymers, for example ethylene/vinyl acetate (EVA), ethylenelacrylic acid, ethylene/methacrylate and ethylene/n-butyl acrylate copolymers which optionally impart additional flexibility, toughness and strength to the adhesive. Certain hydrophilic polymers may also be added, including for example polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl methyl ether, polyethylene oxide, polyvinyl pyrrolidone, polyethyl oxazolines or starch or cellulose esters, more particularly the acetates with a degree of substitution of less than 2.5. These hydrophilic polymers increase the wettability of the adhesives for example.
The development of strength and elasticity in these hotmelt adhesives is designed in such a way that the book bloc can be rounded immediately after binding, i.e. without any delay through drying or reaction of the NCO groups. The conditions to be maintained for this purpose should be determined in advance with the aid of adhesive films. Important parameters (to DIN 53455) and their ranges are:
1. yield stress around < 0.5, preferably 1 to 5 N/mm2.
2. elongation > 100, preferably > 200 and more particularly 300 to 600%.

3. ultimate tensile strength > 1, preferably > 2 and more particularly > 3 NImm2.
The yield stress and elongation ranges and preferably the ultimate tensile strength range should be adhered to.
Round book spines are advantageously produced as follows:
As generally known, the hotmelt adhesive is applied to the pre-prepared (milled and optionally grooved) spine either by wheel or by nozzle. The adhesive film thickness is ca. 0.05 to 1 mm, more particularly 0.1 to 0.5 mm and above all 0.2 to 0.4 mm.
The book bloc clamped in the clamps of the perfect binder then passes through a UV station, i.e. is exposed to UV light. This exposure to high-energy radiation produces an increase in molecular weight which, in addition to the increase in cohesion by cooling of the hotmelt, brings about a distinct increase in cohesion to such an extent that the above-mentioned ranges can be adhered to. As a result of the increase in molecular weight, the book bloc can then be directly forwarded to a book making line where it is cut in-line and rounded under known conditions. The rounded book bloc is then optionally cased in a hard cover. Depending on atmospheric humidity and paper moisture, the isocyanate groups of the polyurethane react off over the next 24 to 72 hours at the latest so that the cohesion of the rounded adhesive film is further increased.
This further reaction leads to excellent stability of the rounding which other systems cannot achieve and to excellent performance properties of the books bound with polyurethane adhesives, such as for example resistance to mineral oil, heat resistance, resistance to ageing, etc.

Claims (5)

24

1. The use of a UV-reactive hotmelt adhesive based on a moisture-crosslinking polyurethane in the in-line rounding of book blocs.

2. The use claimed in claim 1, characterized by a hotmelt adhesive which contains both olefinically unsaturated double bonds, more particularly of acrylic acid derivatives, and NCO groups.

3. The use claimed in claim 1, characterized by process conditions before rounding which provide the corresponding adhesive films with the following properties to DIN 53455:
- elongation > 100%, - yield stress > 0.5 N/mm2 and preferably - ultimate tensile strength > 1 N/mm2

4. A process for the production of book blocs with a round spine comprising the following steps:
1. applying a hotmelt adhesive as claimed in claim 1 or 2 to the spine in a film thickness of ca. 0.05 to 1 mm, 2. exposing the hotmelt adhesive to radiation to an extent which corresponds to the process conditions defined in claim 3 and 3. forwarding the treated book bloc directly to a book making line where it is cut in-line and rounded under known conditions.

5. A process as claimed in claim 4, characterized by exposure to UV
radiation.