Note: Descriptions are shown in the official language in which they were submitted.
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13369~0
. I
-~ TOUGHENED HOT MELT ADHESIVE
` COMPOSITION FOR BOOK HINGE JOINT
,
The present invention is directed to toughened pressure sensitive hot
--~ melt adhesives used to form the hinge joint of a flexible covered bcok.
~-
~-; 5Flexible or soft covered books are generally formed by ooating a
layer of hot melt adhesive on the secured edge of a series of printed
. ~ .
stocks or signatures to form a book block to which a paper backing or
other suitable cover is applied to fonm the spine of the bcok. While this
process produces the primary bonding of the book block to the cover, a
,..~
secondary bond is often formed at the hinge or joint of the cover. This
bond is produced by applying a small amount of adhesive to the outer sheet
.
of each side of the bcok block immediately adjacent to the hinge area.
~-~ This hinge joint formation is actually carried out in two separate steps
with the adhesive being applied to the book block before the cover is
~,:-,.
~ 15 affixed and the joint then being formed by application of pressure to the
~,
bcok cover at some point "downline" in the manufacturing operation. The
-~ purpose of this adhesive application is to conceal the binding adhesive
,`!'~ '. and also to reinforce the binding and to prevent the book from falling
apart relatively easily when grasped only by the flexible cover.
20The adhesives used for this application must possess a variety of
.~
~ properties, specifically they must possess low viscosity (i.e., about 500
.~ .~i
-~i to 5000 cps at 350F) for easy application, strong agressive tack at the
.
13369~0
point of formation of the hinge bond, gocd adhesion to difficult cover
stocks and resistance to creep or cold flow both at room temperature and
under elevated temperature conditions. Heretofore the adhesives used have
generally been either the non-pressure sensitive hot melt adhesives used
in the bcok binding operation or emulsion adhesives. Both types of
adhesives suffer from the common deficiency of their relatively short open
time i.e., the time during which a bond may be found. This lack of open
time creates a serious problem in the automated book binding process where
interruptions, slow downs or even shut downs of the manufacturing line
~- 10 result in loss of agressive tack properties with the subsequent need to
. .
~ discard large quantities of partially completed products. Another problem
,.
f` resulting from the finite open time of the adhesives of the prior art is
; ,~
`- the high rejection rate due to poorly formed joints caused by the
relatively high coating weights which must be applied in order to assure
, ,
the presenoe of the needed residual agressive tack at the time the hinge
joint is formed, particularly when slow machine speeds are involved.
~,
~ Additional rejects are created with finite open time pro~ucts, when
. , .
~ appropriate thin coating weights are used for high production speeds, but
,. ,
when machine slows down or stops because of some other interruption in the
- ~ 20 binding line the thin ooating weight causes solidification prior to bond
,, .
formation and therefore no bond can be formed.
. We have now found that pressure sensitive hot melt adhesive
oompositions prepared adhesives which comprise a substantially radial
styrene-butadiene block oopolymer, the copolymer having a styrene content
. .,, ~.,
^-l 25 greater than about 35% by weight, a modulus at 300% elongation of at least
" ~
4.5 MPa and a solution viscosity less than about 1000 cps are particularly
- useful in the fonmation of hinge joints for flexible bcoks.
~ 3 - 13369~0
-
Thus, the present invention is directed to a process for the
- formation of hinge joints on bound book blocks comprising the steps of
applying a molten film of a hot melt pressure sensitive adhesive to the
, .
outer sheet of each side of the book block on an area immediately adjacent
the bound edges and for a length substantially coterminus with the bound
i-, .
edges; applying a cover thereto; and exerting pressure on the book cover
. . .
~- in the area of the pressure sensitive hot melt film; wherein the pressure
;-ii; sensitive hot melt adhesive comprises:
~. ~
`-i a) 10 to 40% by weight of a substantially radial styrene-butadiene
~ ,.
~-~ l0 block copolymer, the copolymer having a styrene content greater than
`: ~
about 35% by weight, a modulus at 300% elongation of at least 4.5 MPa
and a solution viscosity less than about 1000 cps;
b) 20 to 65% by weight of a compatible tackifying resin;
~.*,
~-r' C) 0~1 to 4% by weight stabilizer;
:~.
-¢~ 15 d) the remainder (to 100%) comprising a plasticizing oil.
The block copolymers useful herein are comprised of styrene and
butadiene blocks arranged in a substantially radial configuration and
contain at least 35%, and generally up to about 50%, by weight of the
~- styrene moiety. Of greater significance however, the copolymers selected
.,
should exhibit a modulus at 300% elongation of at least about 4.5 MPa and
a solution viscosity less than about 1000 cps (25% in toluene at 23C
.
-~ using a Brookfield viscometer). These copolymers may be prepared using
$ :73
~; methods taught, for example, in U.S. Pat. Nos. 3,239,478; 3,427,269;
3,700,633; 3,753,936 and 3,932,327. Alternatively they are available from
Shell Chemical Co. under the trademark Kraton DX1122 (37% styrene, modulus
..~
of 4.8 MPa, viscosity 670 cps) and from Eni Chem Americas (Agip USA Inc.)
~~-i as Europrene SOL T 162LW/1 (40% styrene, modulus of 5.0 MPa, viscosity 750
~''
. .~ .
- 1336950
cps) or SOl T 162 LW/2 (40% styrene, modulus of 4.6 MPa, viscosity (640
~I cps). While the optimum amounts of the copolymer used in the adhesive
- will vary depending on the end use application, the copolymer will
,j.
generally be present in the adhesive formulation at levels of 10 to 40% by
weight, preferably 15 to 25% by weight.
.~
~- The tackifying resins useful in the adhesive compositions can be
hydrocarbon resins, hydrogenated hydrocarbon resins, synthetic
. ~
- polyterpenes, rosin esters, natural polyterpenes, and the like. More
.;
- particularly, the useful tackifying resins include any compatible resins
or mixtures thereof such as (1) natural and modified rosins such, for
~.,
example, as gum rosin, wood rosin, tall oil rosin, distilled rosin,
hydrogenated rosin, dimerized rosin, and polymerized rosin; (2) glycerol
i~- and pentaerythritol esters of natural and modified rosins, such, for
,
~-,~ example as the glycerol ester of pale, wood rosin, the glycerol ester of
..
~ 15 hydrogenated rosin, the glycerol ester of polymerized rosin, the
,.~
pentaerythritol ester of hydrogenated rosin, and the phenolic-modified
pentaerythritol ester of rosin; (3) copolymers and terpolymers of natured
terpenes, e.g. styrene/terpene and alpha methyl styrene/terpene; (4)
~=~ polyterpene resins having a softening point, as determined by ASTM method
-- ,.
E28-58T, of from 80 to 150C; the latter polyterpene resins generally
resulting from the polymerization of terpene hydrocarbons, such as the
-~ bicyclic monoterpene known as pinene, in the presence of Friedel-Crafts
- - catalysts at moderately low temperatures; also included are the
hydrogenated polyterpene resins; (5) phenolic modified terpene resins and
hydrogenated derivatives thereof such, for example, as the resin product
~ ... .
~ resulting from the condensation, in an acidic medium, of a bicyclic
,, . ~
" terpene and a phenol; (6) aliphatic petroleum hydrocarbon resins having a
~ .. .
:
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1336950
Ball and Ring softening point of from 70 to 135C.; the latter resins
resulting from the polymerization of monomers consisting of primarily of
.
olefins and diolefins; also included are the hydrogenated aliphatic
petroleum hydrocarbon resins; (7) aromatic petroleum hydrocarbon resins
and the hydrogenated derivatives thereof; and (8) alicyclic petroleum
~- hydrocarbon resins and the hydrogenated derivatives thereof. Mixtures of
two or more of the above described tackifying resins may be required for
some formulations. The tackifier is used in amounts of 20 to 65% by
-~ weight.
-~ 10 The remainder (up to about 60% by weight) of the hot melt adhesive
comprises at least one oil diluent. Suitable plasticizing or extending
. ~
oils include not only the usual plasticizing oils but also olefin
oligomers and low molecular weight polymers as well as vegetable and
animal oil and their derivatives. The petroleum derived oils which may be
` 15 employed are relatively high boiling materials containing only a minor
..,.,~
proportion of aromatic hydrocarbons (preferably less than 30% and, more
particularly, less than 15% by weight of the oil). Alternatively, the oil
may be totally non-aromatic. The oligomers may be polypropylenes,
;`"J polybutenes, hydrogenated polyisoprene, hydrogenated polybutadiene, or the
. ~
-- 20 like having average molecular weights between 350 and 10,000. Among the
,. . _.
applicable stabilizers or antioxidants included herein are high molecular
weight hindered phenols and multifunctional phenols such as sulfur and
~ . ~
phosphorous-containing phenols. Hindered phenols are well known to those
... .
skilled in the art and may be characterized as phenolic compounds which
also contain sterically bulky radicals in close proximity to the phenolic
. - ~
~- hydroxyl group thereof. In particular, tertiary butyl groups generally
,:
are substituted onto the benzene ring in at least one of the ortho
1336950
positions relative to the phenolic hydroxy group. The presence of these
sterically bulky substituted radicals in the vicinity of the hydroxyl
; group serves to retard its stretching frequency and, correspondingly, its
~. "
reactivity; this steric hindrance thus providing the phenolic compound
` ~ 5 with its stabilizing properties. Representative hindered phenols include:
'r~-~ !
, ~1
~-; 1,3,5-trimethyl 2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl)benzene;
~ .
r,~ pentaerythrityl tetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;
n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenol)-propionate; 4,4'-
methylenebis (2,6-tert-butylphenol); 4,4'-thiobis (6-tert-butyl-o-cresol);
.~,
2,6-di-tertbutylphenol; 6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5-
'
triazine; di-n-octadecyl 3,5-di-tert-butyl-4-hydroxy-benzylphosphonate;
2-(n-octylthio)ethyl 3,5-di-tert-butyl - 4-hydroxy-benzoate; and sorbitol
hexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate]. The stabilizer is
~-~, present in amounts of 0.1 to 4% by weight, preferably less than about 2%.
r, 15 Optional additives may be incorporated into the hot melt compositions
~- in order to modify oe rtain properties thereof. Among these additives may
be included colorants such as titanium dioxide; and fillers such as talc
. .,
~ and clay, etc. as well as minor amounts (e.g. less than about 5%) of a
~i:
~ petroleum derived wax.
=~ 20 These hot melt adhesive compositions may be formulated using
techniques known in the art. An ex~ ry procedure involves placing
.; approximately half of the total tackifying resin ooncentration in a
,~
jacketed mixing kettle, preferably in a jacketed heavy duty mixer of the
Baker-Perkins or Day type, which is equipped with rotors and thereupon
raising the temperature to a range of from 250 to 350F., the precise
,, ~,
`,t~,,,~. temperature utilized depending on the melting point of the particular
~ tackifying resins. When the resin has melted, stirring is initiated and
.
, . ~.
1336950
~ the block polymer and stabilizer are added together with any optional
additives whose presence may be desired, the addition of the latter
....
components being extended over a prolonged period in order to avoid the
,,,
formation of lumps. Mixing and heating are oontinued until a smooth,
S homogeneous mass is obtained whereupon the remainder of the tackifying
.-r'' resin and the oil are thoroughly and uniformly admixed therewith. The
resultant hot melt adhesives are generally produced with an oil in bulk
-j form and packaged in release coated tube or boxes.
~-~ In the following illustrative examples all parts are given by weight
and all temperatures in degrees Celsius unless otherwise noted.
EXAMPLE I
The following example illustrates the preparation of adhesives of the
invention in formulations suitable for use in the bookbinding industry as
discussed above.
In preparing the following samples, a heavy duty mixer which had been
heated to 150C and which was equipped with a stirring paddle was charged
with half of the tackifying resin. After melting of the resins, stirring
was then initiated whereupon the block copolymers and the antioxidants
~ were added slowly. Heating and stirring were continued until a
-~; 20 hamogeneous mass was obtained whereupon the remainder of the tackifying-.
resin and the oil were ~m;xed therewith. The molten mixture was then
poured into a siliconized paper tube and cooled to room temperature.
-- Adhesives were prepared from the materials and amounts shown in Table
I using the general procedure described above. Viscosity measurements
~ .
; 25 were determined using a Brookfield viscometer (Spindle 27) at 325F. The
.,-i
. ~ ~ .
. .
',.' '`,
- 8 - 1336950
adhesives were subjected to the following tests to determine the heat
resistance of the adhesive under a constant load and static stress and
elevated temperature.
s~ The adhesive was heated to 320F and a lamination of kraft paper was
made using heated rollers. The adhesive thickness was 50 mil and the
~, bonds having an adhesive area of one square inch. The bonds were aged
~ overnight at 72F and 50% RH. The peel mode samples were then hung in a:. .
105F oven using 300 gram/inch weights. The time at which the bond failed
~; was noted as was the mode of failure.
The tensile strength of the hot melt adhesive was determined on
samples cast from the hot melts and molded in silicone rubber molds into
-~ the shape of dog bones . After cooling, the dog bone shaped specimens
. --i
were removed from the mold and tested using an Instron Tensile Tester.
The force required to start to stretch the specimen is recorded as the
~- 15 "tensile yield", the foroe required to break the specimen as "tensile
-~ break". This procedure also provides a measurement of percent elongation,
which is the percentage stretch of the hot melt sample at the point of
rupture in obtaining the ultimate tensile strength.
.
. .
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1336950
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1~ - 1 336950
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- 11 - 13~6950
The testing results of Samples 1-8 show significantly higher ultimate
tensile strength of the adhesives of the present invention when contrasted
with presently commercially utilized adhesive ccmpositions containing
similar amounts of raw materials.
Sample 9 shows that it is possible to use less polymer to obtain a
- lower visoosity adhesive without sacrifi oe of tensile strength. (Compare
-~ to Sample 11 prepared with 15 parts Stereon). Note however the product did
suffer with respect to Kraft/Kraft adhesive and hen oe would not be readily
~- useful for certain end use applications where stringent heat resistance
values are required.
`~ Samples 12, 13 and 14 show results similar to those of Sample 9,
~ additionally overcoming the deficiency of Sample 9 with respect to heat
- resistance by use of a different tackifier system.
''-! Sample 17 shows a further formulation according to the invention using
a different tackifying system. Note, in particular, the high heat
resistanoe value.
Samples 18 through 26 again show the improved heat resistance and
..,
~ ultimate tensile strength achieved using adhesive compositions of the
~;
~ invention as contrasted to conventionally employed Stereon containing
- 20 adhesive systems with Samples 24, 25 and 26, also showing that lower levels
~,
~ of the Kraton D1122X may be used to obtain lower viscosity products without
:
-~` sacrifice to the tensile strength.
.. ...
- All of samples 1-22, on testing, gave entirely cohesive modes of
failure in the Kraft to Kraft heat resistance test, i.e., adhesive residue
` 25 was observed on both substrates after bond failure.
!
~.,
- 12 - 13369SO
_
The resultant a &esives may be used to form the hinge joint using
methods conventional in the book binding art and without limitation to the
particular binding method employed. Thus the bcok block may be bound by
; . .
any of the usual procedures, including, but not limited to, perfect
-5 binding with hot melt adhesive, burst binding with emulsion adhesive and
~.,
then with hot melt adhesive; sewn and glued off with emulsion adhesive; or
,... ..
;~~perfect or burst bound with emulsion adhesive. The hinge joint may be
.. ~
formed on any book, construction, i.e., a flexible or soft cover book or a
.i
bcok block wi=hich will eventually be hard bound or case bound bcok, but
~;~10 wherein a hinge joint is formed between the book block and the combined
end sheets. In general, regardless of the method of construction, a film
of a non-pressure sensitive adhesive is ooated on the secured edges of the
i ' ~ .
j`-book block; then a molten film of the hot melt pressure sensitive adhesive
. ..
~described previously is coated on the outer sheet of each side of the book
.,
r-ti~15 block on an area immediately adjacent the secured edges and for a length
k.~substantially coterminus therewith; the flexible cover is applied to the
first film while the latter is still in the uncured state and pressure is
exerted on the book oover in the area of the pressure sensitive hot melt
~:film to form the hinge joint. Alternatively, the hinge or joint hot melt
-~;20 may be applied in appropriate lines to the flexible cover as the oover is
fed on the binder to next to the bcok block.
, .i ~,
-; .
. . .
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