GB1592358A

GB1592358A - Bookbinding

Info

Publication number: GB1592358A
Application number: GB50503/76A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1977-12-01
Filing date: 1977-12-01
Publication date: 1981-07-08

Description

(54) BOOKBINDING (71) We, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V., a company organised under the laws of the Netherlands, of 30 Carel van Bylandtlaan, The Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a process for bookbinding and to books made using said process.

The existing bookbinding techniques are still to a high extent based on procedures which have been known for centuries and which comprise an elaborate series of operations. The pages are printed on large sheets, which are cut and folded to the desired size and arranged to form a series of stacks, known as signatures. These are enclosed by means of end sheets, which are attached to the first and last signature of the book, whereupon all signatures are fixed by being sewn individually and to each other. The back edge of the thus obtained bundle is deformed so as to assume a convex curvature and fixed in this position by the application of an adhesive layer, whereby also a strip of fabric and usually a strip of paper is bonded to the back edge to provide the required strength. After subsequent trimming operations the bound book is provided with a hard cover.

This conventional technique is inefficient, not so much as a result of its discontinuous nature, but in particular by the fact that the sewing step takes a relatively long time as compared with the other steps, thus retarding the entire bookbinding process. Therefore, procedures were developed in which the sewing operation is abandoned. Instead, binding of the signatures is accomplished by means of emulsion adhesives or hot melt adhesives. In particular the latter are most useful, as they solidify quickly, which allows fast bond formation. This is essential if it is wished to keep up with the high speed of the trimming operation mentioned before, which is capable of handling some 5,000 to 10,000 books per hour.

The invention is in particular concerned with a process for bookbinding, wherein the pages are joined together by means of a hot melt adhesive.

As mentioned above, there are bookbinding techniques in which the sewing operation is replaced by a bonding operation using an adhesive. There are, however, also bookbinding techniques which have never comprised a sewing step, such as those methods applied to make paper-backed books. Herein, the pages are present in the form of loose sheets instead of signatures. The sheets are clamped together, provided with a layer of adhesive at their back edge and usually wrapped in a cover which integrally forms the front and back covers and the spine of the book and is bonded by the same adhesive layer that holds the pages together.

Whether a bookbinding process without a sewing step is applied to make hard-covered or paper-backed books, in either case certain requirements have to be met. These requirements are related to the conditions regarding the application of the adhesive, the performance of the latter and the properties of the books made.

To obtain optimal results the adhesive must have good adhesion to the paper and the material of the cover and it must be capable of rapid wetting and easy penetration between the edges of the paper sheets or signatures to form the book.

Depending on the application technique used, special requirements have to be met as regards the melt viscosity of the adhesive and its stability at the application temperature. The surface of the solidified adhesive after the bond has been formed should not be tacky at room temperature, to prevent that those parts of the adhesive that remain exposed collect dirt or cause books which are stacked to stick to each other. Further, the bond obtained should be strong enough to last during normal usage. The latter can be judged by the force which has to be exerted to pull out individual pages, while also the spine must meet certain performance demands. An undesirable feature is warm flow, i.e. the tendency of the spine of the book to flow apart under stress as, for example, the reader folds the book back to back for a period of time.This characteristic becomes especially troublesome in hot, humid atmospheric conditions. Another undesirable property is cold crack, which results from brittleness of the spine and causes the latter to break as the book is opened too far, so that the book falls apart.

Bookbinding techniques without a sewing step have hitherto been characterized by an unsatisfactory behaviour in one or more of the aspects mentioned above. For example, books bound by means of polyvinyl acetate based hot melt adhesives show poor warm flow and cold crack properties. Hot melt adhesives based on ethylene vinyl acetate copolymers, which have been used since the 1960's, exhibit various adhesion problems, while the books made using such adhesives have a spine which combines sufficient strength with too high stiffness or satisfactory flexibility with too low strength.

An improvement was proposed in Patent Specification 1,219,394, describing a bokbind- ing process which comprises the use of an adhesive composition based on a tflermopiastlc elastomeric three-block copolymer, one or more tackifying resins, one or more stabilizers and optionally one or more diluents such as low molecular weight polyolefins, fats, oils and waxes.

Said three-block copolymer comprises two terminal non-elastomeric polymer blocks and a non-terminal elastomeric polymer block. The tackifying resins are compatible with the non-terminal polymer block and incompatible with the terminal polymer block.

A disadvantage of this process has been found to be that such adhesives show a high tack, making it difficult to convert them into granules or pellets and, once they are in this forum, to prevent them from clogging together.

Applicants have discovered a bookbinding process, in which the difficulties so far encoun tered are avoided and the various processing and performance requirements are substantially met, while books of good quality are manufactured.

Accordingly, the present invention is concerned with a process for bookbinding, wherein the pages in the form of signatures or loose sheets are joined together by means of a hot melt adhesive, which process comprises the following steps: (1) clamping the pages together; 2 applying to the edges at one side of the clamped pages a molten layer of a hot melt adhesive composition comprising a blend of (a) a thermoplastic block copolymer having terminal non-elastomeric polymer blocks and at least one non-terminal elastomeric polymer block, (b) at least one resin compatible with the terminal non-elastomeric polymer block, (c) at least one resin compatible with the non-terminal elastomeric polymer block, and (d) at least one wax;; 3 optionally applying a cover to said layer while the latter is still in a molten state; 4 allowing said layer to solidify.

Clamping of the signatures or sheets to be bound may be carried out by any suitable means, which holds the signatures or sheets firmly together as close as possible to the edge to be provided with adhesive and at least for as long a period of time as is needed for the adhesive to fully solidify.

A hot melt adhesive composition used in accordance with the present invention may be applied by means of any technique suitable to the bookbinding industry. An example of a simple and yet effective method is to hold the clamped signatures or sheets in a vertical position with the edges to be bonded downwards, and to pass them over a dip roll rotating in an open bath containing the molten adhesive.

Block copolymers suitable for the process of the invention are linear, branched or star shaped block copolymers, but preferred are those having the general formula A-B-A, wherein both A's are similar or dissimilar polymer blocks of a mono-alkenyl substituted aromatic hydrocarbon such as styrene, and B is a polymer block of a conjugated diene hydrocarbon such as butadiene or isoprene, each block A having a weight average molecular weight in the range of from 5,000 to 50,000, and the block B having a weight average molecular weight in the range of from 40,000 to 500,000. The amount of polymer blocks A is in the range of from 10 to 65 No w of the total block copolymer. The block copolymer may also be subjected to a hydrogenation treatment which leaves the polymer blocks A unaffected, but by which all olefinic double bonds or part thereof present in polymer block B are saturated.

Compatibility of resins with either a terminal or a non-terminal block of the block copolymer is determined by a film clarity test. It is known that a film made from a blend of two or more compatible components is substantially clear, whereas incompatibility manifests itself by an obvious opacity due to the presence of a separate disperse phase. It is also known that mutual compatibility of two or more substances not only depends on their chemical and phvsical nature, but also on the ratio in which they are mixed.

Therefore, a resin is for the purpose of the invention compatible with a terminal polymer block of a block copolymer, if a film clarity test shows the resin to be compatible with a homopolymer of the same sort and molecular weight as the terminal polymer block, when resin and homopolymer are mixed in the same ratio as the resin/terminal polymer block ratio in the block copolymer will be. A similar criterion can be adopted for compatibility between a resm and a non-terminal polymer block.

In practice, however, a resin can usually be regarded as being compatible with a terminal polymer block, if it is compatible with polystyrene having a molecular weight between 8,000 and 15,000 in a resin to styrene ratio of about 7. Likewise, a resin can usually be regarded as being compatible with a non-terminal polymer block, if it is compatible with polybutadiene having a molecular weight between 40,000 and 100,000 in a resin to butadiene ratio of about 2.

Consequently, to assess terminal-block compatibility a film from a blend of polystyrene having a molecular weight between 8,000 and 15,000 and an about 7 times as high amount of resin is cast from a solution in, e.g., toluene. The formation of a clear film indicates the presence of a compatible resin. In a similar way the non-terminal-block compatibility of a resin is assessed from a film cast from a solution in, e.g., toluene of a blend of polybutadiene having a molecular weight between 40,000 and 100,000 and an about twice as high amount of resin.

Terminal-block compatible resins serve to provide high tensile strength. Suitable representatives of this kind of resins have a softening point above 100"C as determined according to ASTM E28-67. Examples are coumarone-indene resins, alpha-methyl styrene polymers or copolymers, e.g. with styrene or vinyl toluene, and polyindene resins. They are preferably incorporated in an amount between 75 and 200 phr.

Non-terminal-61Ock compatible resins are incorporated for their tackifying effect, i.e. to provide the initial adhesion between adhesive and substrate. Suitable representatives are found among alpha- and beta-pinene resins, polyhydric esters of natural or modified rosins, synthetic polyterpenes, and aliphatic petroleum hydrocarbon resins. They are preferably incorporated in an amount between 5 and 150 phr.

The incorporation of wax, preferably a petroleum wax such as paraffin wax, provides the low viscosity level required for the process of the invention. A similar effect could also be obtained by using a plasticizing oil, as is customary in the art, but this would cause the surface of the adhesive layer to retain a certain degree of stickiness after solidification. This is undesirable for reasons already set out above. Nevertheless, not too high an amount of oil is permissible without giving rise to problems. Apart from the paraffin wax already mentioned, examples of suitable waxes are other petroleum waxes such as microcrystalline wax, natural waxes from vegetable or animal origin, and synthetic hydrocarbon waxes. Wax is preferably used in amounts of from 5 to 150 phr.

To prevent degradation during preparation and application of the adhesive and to give good ageing resistance in end use it is highly recommendable to incorporate a stabilizer in the formulation. Examples of suitable stabilizers are: zinc dibutyl dithiocarbamate, polyalkyl phosphite, pentaerythritol-tetrakis[3-(3 5 '-di-tert-butyl-4' -hydroxyphenyl) propionate], a blend of dilaurylthiodipropionate and 1,3,5-trimethyl -2,4,6-tris(3,5 -di-tert-butyl-4-hydroxybenzyl) benzene, a blend of 2-mercaptobenzimidazole and sym-di-beta- naphthyl-p-phenylenediamine.

Optimal additives other than the oil already mentioned may be incorporated. Examples are fillers and colourants such as talc, clay, titanium dioxide etc.

The preparation of the hot melt adhesive composition is carried out in such a way that the various ingredients are thoroughly mixed into a homogeneous blend in the shortest possible time at the lowest possible temperature. In principle hot melt adhesives can be prepared in any mixing equipment in which the blend can be heated. Because of the distinct differences in melt viscosity between the various components, however, mixing in low shear mixers takes a relatively long time, which is inefficient and increases the risk of degradation. Optimum mixing is achieved at a reasonable high viscosity so as to provide for sufficient shear. The best mixers for this purpose are of the Z or Sigma blade type.

A good mixing technique comprises the following procedure. The mixer is heated to 1200C and blanketed with an inert gas such as nitrogen. 50 phr of the resin having the lowest melting point and all stabilizer are charged to the mixer and melted, which takes about 5 minutes. The block copolymer is added and the mass is homogenized, which takes about 20 minutes, during which the temperature rises to about 140"C. Then the remaining resin is added and after 10 minutes the wax and any other ingredients. After again 10 minutes the mixture is discharged from the mixer. Thus, in totally about 45 minutes an adhesive composition is prepared, the temperature of which is about 135-140"C.

The invention is illustrated by the examples described below.

EXAMPLES 1-3 The compositions used for the Examples were prepared as follows. A Z-blade mixer was heated to 1 200C and blanketed with a nitrogen atmosphere. 50 phr non-terminal-block compatible resin and all stabilizer were brought into the mixer and melted together, which took 5 minutes. All block copolymer was added and as soon as a homogeneous mixture was obtained, which occurred after a total time of 25 minutes, the remaining non-terminal-block compatible resin was added (only in Example 3), followed by the terminal-block compatible resin. At this time the temperature had risen to 135-140"C. Finally, after another 10 minutes, the paraffin wax was incorporated. After 10 minutes again, the resulting mixture was dumped from the mixer, extruded into strands, cooled in a water bath and cut into granules.

For the manufacture of books the adhesive composition was melted and applied at a temperature of 140, 160 or 1800C from a dip roll onto about 100 paper sheets clamped together. On solidification of the adhesive a book was obtained with a spine of about 10 cm length and 5 mm width.

The Table gives the composition of block copolymer based adhesives, their processing and product properties and a property of the book obtained at different adhesive application temperatures. The latter property, related to the strength of the bond between the pages on the one hand and the spine on the other, is determined by the page pull test, carried out on a book built up from individual sheets and having a 10 cm long 5 mm wide spine, which test indicates the force per cm of spind length required to pull at a speed of 30 cm/min one page out of the book, which is folded back to back.

In addition to the examples illustrating the invention the Table includes an adhesive formulation, referred to as Example A, which is not covered by the invention and is given for comparison.

Table Example 1 2 3 A Composition, parts by wt: Blockcopolymer(1) 100 100 100 100 Aromatic hydrocarbon resin (2) 100 100 100 Glycerol ester of per hydrogenated rosin (3) 50 - 100 100 Hydrogenated rosin (4) - 50 - Paraffin wax (softening point58-60"C) 100 100 100 100 Stabilizer (5) 5 5 5 5 Softening point (ASTM E28-67),"C 88 90.5 77 Melt viscosity at:: 1600C,poise 88 66 46 140"C, poise 166 138 94 1200C,poise 556 428 238 Hardness (Shore A) 76 73 64 Tensile stress/strain 300%modulus,MN/m2 1.9 1.9 1.6 500% modulus, " 2.2 2.2 2.0 1.7 700 % modulus, " 2.4 2.0 1.7 Yield stress, " 3.7 3.5 3.7 Ultimate stress, " 5.5 5.6 4.7 Elongation at break, % 910 920 950 Page pull test applied at 140"C, N/cm 2.6 2.9 4.6 " " 160 C, " 3.4 3.0 3.5 "1800C, " 3.2 4.3 8.1 (1) Styrene-butadiene-styrene block copolymer, block molecular weights 12,000-56,000 12,000 2 "Hercules" A140 ex Hercules (terminal-block-compatible resin) 3 Foral 85 ex Hercules (non-terminal-block-compatible resin) 4) "Staybelite" Resin ex Hercules (non-terminal-block-compatible resin) (5) Zinc dibutyl dithiocarbamate. ("HERCULES" and "STAYBELITE" are Registered Trade Marks).

In addition to the tests referred to in the above Table the ready books were subjected to a simple low-temperature performance test by bending them open at - 18 0C. All books withstood this treatment without showing any cracking.

Not all properties given are equally important, but their suitability for the process of the invention is especially proven by the page pull test results, which are on a highly satisfactory level, as well as yield stress and ultimate stress, which are obtained with adhesive compositions showing not too high viscosity figures at the application temperatures used. In this respect, in particular the results from Example 3 are excellent, wherein the viscosity stays well below 100 poises already at 1400C, while at an application temperature of 1800C a page pull result of more than 8 N/cm is obtained.

As regards the comparative Example A, it was found that the adhesive having this composition exhibited such a high tack that it proved impossible to convert it into granules or pellets. Consequently, no further properties were determined using this formulation.

WHAT WE CLAIM IS:- 1. A process for bookbinding, wherein the pages in the form of signatures or loose sheets are joined together by means of a hot melt adhesive, which process comprises the following steps: (1) clamping the pages together; (2) applying to the edges at one side of the clamped pages a molten layer of a hot melt adhesive composition comprising a blend of (a) a thermoplastic block copolymer having terminal non-elastomeric polymer blocks

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Table Example 1 2 3 A Composition, parts by wt: Blockcopolymer(1) 100 100 100 100 Aromatic hydrocarbon resin (2) 100 100 100 Glycerol ester of per hydrogenated rosin (3) 50 - 100 100 Hydrogenated rosin (4) - 50 - Paraffin wax (softening point58-60"C) 100 100 100 100 Stabilizer (5) 5 5 5 5 Softening point (ASTM E28-67),"C 88 90.5 77 Melt viscosity at:: 1600C,poise 88 66 46 140"C, poise 166 138 94 1200C,poise 556 428 238 Hardness (Shore A) 76 73 64 Tensile stress/strain 300%modulus,MN/m2 1.9 1.9 1.6 500% modulus, " 2.2 2.2 2.0 1.7

700 % modulus, " 2.4 2.0 1.7 Yield stress, " 3.7 3.5 3.7 Ultimate stress, " 5.5 5.6 4.7 Elongation at break, % 910 920 950 Page pull test applied at 140"C, N/cm 2.6 2.9 4.6 " " 160 C, " 3.4 3.0 3.5 "1800C, " 3.2 4.3 8.1 (1) Styrene-butadiene-styrene block copolymer, block molecular weights 12,000-56,000 12,000 2 "Hercules" A140 ex Hercules (terminal-block-compatible resin)

3 Foral 85 ex Hercules (non-terminal-block-compatible resin) 4) "Staybelite" Resin ex Hercules (non-terminal-block-compatible resin) (5) Zinc dibutyl dithiocarbamate. ("HERCULES" and "STAYBELITE" are Registered Trade Marks).

In addition to the tests referred to in the above Table the ready books were subjected to a simple low-temperature performance test by bending them open at - 18 0C. All books withstood this treatment without showing any cracking.

Not all properties given are equally important, but their suitability for the process of the invention is especially proven by the page pull test results, which are on a highly satisfactory level, as well as yield stress and ultimate stress, which are obtained with adhesive compositions showing not too high viscosity figures at the application temperatures used. In this respect, in particular the results from Example 3 are excellent, wherein the viscosity stays well below 100 poises already at 1400C, while at an application temperature of 1800C a page pull result of more than 8 N/cm is obtained.

As regards the comparative Example A, it was found that the adhesive having this composition exhibited such a high tack that it proved impossible to convert it into granules or pellets. Consequently, no further properties were determined using this formulation.

WHAT WE CLAIM IS:- 1. A process for bookbinding, wherein the pages in the form of signatures or loose sheets are joined together by means of a hot melt adhesive, which process comprises the following steps: (1) clamping the pages together; (2) applying to the edges at one side of the clamped pages a molten layer of a hot melt adhesive composition comprising a blend of (a) a thermoplastic block copolymer having terminal non-elastomeric polymer blocks

and at least one non-terminal elastomeric polymer block, (b) at least one resin compatible with the terminal non-elastomeric polymer block, c) at least one resin compatible with the non-terminal elastomeric polymer block, and d) at least one wax; 3 optionally applying a cover to said layer while the latter is still in a molten state; 4 allowing said layer to solidify.
2. A process as claimed in claim 1, in which said thermoplastic block copolymer has the general formula A-B-A, wherein both A's are similar or dissimilar polymer blocks of a mono-alkenyl substituted aromatic hydrocarbon and B is a polymer block of a conjugated diene hydrocarbon, each block A having a weight average molecular weight in the range of from 5,000 to 50,000, and the block B having a weight average molecular weight in the range of from 40,000 to 500,000, the amount of polymer blocks A being in the range of from 10 to 65 Sow of the total block copolymer.
3. A process as claimed in claim 2, in which said block copolymer has the configuration polystyrene-polybutadiene-polystyrene or polystyrene-polyisoprene-polystyrene.
4. A process as claimed in any one of claims 1-3, in which said terminal-block-compatible resin is, as established by a method as hereinbefore described, compatible with polystyrene having a molecular weight between 8,000 and 15,000 in a resin to styrene ratio of about 7.
5. A process as claimed in any one of claims 1-4, in which said non-terminal-blockcompatible resin is, as established by a method as hereinbefore described, compatible with polybutadiene having a molecular weight between 40,000 and 100,000 in a resin to butadiene ratio of about 2.
6. A process as claimed in any one of claims 1-5, in which a terminal-block-compatible resin is applied, having a softening point above 100"C as determined according to ASTM E 28-67.
7. A process as claimed in any one of claims 1-6, in which terminal-block-compatible resin is applied in an amount between 75 and 200 phr.
8. A process as claimed in any one of claims 1-7, in which non-terminal-block-compatible resin is applied in an amount between 5 and 150 phr.
9. A process as claimed in any one of claims 1-8, in which wax is applied in an amount between 5 and 150 phr.
10. A process as claimed in any one of claims 1-9, in which a stabilizer is applied.
11. A process as claimed in any one of claims 1-10, in which the preparation of the adhesive composition comprises mixing of the components in high shear mixing equipment.
12. A process as claimed in claim 1, substantially as hereinbefore described, with special reference to the Examples.
13. Books made using a process as claimed in any one of claims 1-12.