Note: Descriptions are shown in the official language in which they were submitted.
WO 95/02649 PCT/GB94/01496
1
ADHESION PROCESS
THIS INVENTION relates to an adhesion process. More
particularly it relates to a process of bonding articles
together with an adhesive comprising a biodegradable
polymer.
It is known to coat paper with polyhydroxyalkanoic
acids (PHA), for example polymers of hydroxybutyric acid
{PHB) and copolymers with hydroxyvaleric acid (PHBV) both
as latex and as dry solid, preferably as dry powder. The
coating is biodegradable but is non-adhesive.
We have now found that articles may be stuck
together using PHA as an adhesive under cold application
conditions and setting it with both articles in contact
with one another under pressure and preferably with heat.
The adhesive is biodegradable. The adhesive is believed
to set by crystallisation.
Thus, according to the present invention there is
provided a process of bonding two or more articles
together using an adhesive composition comprising at
least one polyhydroxyalkanoate (PHA) wherein the PHA is
placed between the articles to be bonded and the articles
are subjected to pressure to set the adhesive, optionally
at elevated temperature.
The PHA is especially one capable of a relatively
high level of crystallinity, for example over 30~,
especially 50-90~, in the absence of plasticiser.
Suitably it is or includes at least one microbiologically
produced polyester having units of formula I:
- O - Cm Hn - CO - I
where m is in the range 1-13 and n is 2m or (if m is at
least 2) 2m-2. Typically Cm Hn contains 2-5 carbon atoms
e.f
WO 95/02649 PCT/GB94/01496
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in the polymer chain and the remainder (if any) in a side
chain. In very suitable polyesters n is 2m and there are
preferably units with m = 3 and m = 4 copolymerised ~
together and with respectively a C1 and Cz side chain on
the carbon next to oxygen in the chain. The polymer may
be homopolymer, especially a polyhydroxybutyrate (PHB),
or a copolymer, especially a copolymer of hydroxybutyric
acid and hydroxyvaleric acid (HV) containing preferably
4-30 mold of m=4 units. Thus, particular polyesters
contain a preponderance of m = 3 units, especially with
70 - 98 mol ~ of such units, the balance (if any) being
units in which m = 4. The molecular weight of the PHA
is preferably over 50000, especially over 100000, up to
eg 2 x 106.
The PHA may be a blend of two or more copolymers
differing in the value of m. A particular example
contains
(a) PHA consisting essentially of Formula I units in
which 2-5 mol ~ of units have m = 4, the rest m = 3;
and
(b) PHA consisting essentially of Formula I units in
which 5-30 mold of units have m = 4, the rest m = 3.
In each such PHA there are preferably side chains as
above mentioned. The proportions in such a blend are
preferably such as give an average m = 4 content in the
range 4 - 30, more preferably 10-28, mol ~.
In each such PHA having units with m = 3 and m = 4
there may be very small, typically fractional, '
percentages of units having higher values of m.
Typically the composition contains microbiologically
produced PHA to the extent of over 50, especially over
WO 95/02649 PCT/GB94/01496
3
80,~ w/w.
The PHA is preferably a fermentation product,
especially of a microbiological process in which a
microorganism lays down PHA during normal growth or is
caused to do so by cultivation in the absence of one or
more nutrients necessary for cell multiplication. The
microorganism may be wild or mutated or may have had the
necessary genetic material introduced into it.
Alternatively the necessary genetic material may be
harboured by a eukariote, to effect the microbiological
process.
Examples of suitable microbiological processes are
the following:
for Formula I material with m = 3 or m = partly 3, partly
4 . EP-A-69497 (Alcaliaenes eutrophus);
for Formula I material with m = 3: US 4101533
eutrophus H-16), EP-A-144017 ($s latus);
for Formula I material with m = 7-13: EP-A-0392687
(various Pseudomonas sp.).
The PHA can be extracted from the fermentation
product cells by means of an organic solvent, or the
cellular protein material may be decomposed leaving small
granules of polymer for example of which less than 10~
have diameters greater than 1 micrometres. For
specialised end uses the cellular protein may be partly
or wholly allowed to remain with the PHA, but preferably
subjected to cell breakage.
Alternately, the PHB or PHBV can be a product of
synthetic chemistry (Bloembergen and Holden,
Macromolecules 1989, 22, p1656-1663. Bloembergen,
Holden, Bluhm, Hamer and Marchessault, Macromolecules
WO 95/02649 PCT/GB94/01496
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1989, 22, p1663-1669).
The PHA may contain one or more nucleants, for
example, boron nitride.
The PHA may optionally contain a variety of
additives making it suitable for a range of applications.
Such additives include tackifiers, waxes, plasticisers,
stabilizers or antioxidants and compatible thermoplastic
polymers. It is an advantage of the invention that good
results can be obtained in the absence of tackifier.
The adhesive composition preferably contains 20 to
99~ by weight of PHB or the copolymer PHBV, particularly
50 to 95~, especially 50 to 90~.
If a tackifier is present, the composition
preferably contains 5 to 80~ w/w thereof. Examples of
suitable tackifiers include rosin and rosin derivatives,
terpene phenolics and pure phenolic resins; and more
specifically, gum rosin, wood rosin, tall oil rosin,
distilled rosin, hydrogenated rosin, dimerized rosin,
polymerised rosin, glycerol-, or pentaerythritol- esters
of natural and modified rosins, such as for example wood
rosin, the glycerol- or pentaerythritol- ester of
hydrogenated rosin, the phenolic-modified pentaerythritol
ester of rosin, phenolic modified terpene resins and
hydrogenated derivatives thereof, and thermoplastic alkyl
phenolic resins such as those described in USP 4,073,776
and USP 4,023,826.
A combination of two or more of the above mentioned
tackifers may be used if suitable.
If a wax diluent is present, the composition
preferably comprises 1 to 30~ w/w thereof. Suitable
examples are 12-hydroxystearamide wax, hydrogenated
~~.fi6~~.~ v
WO 95/02649 PCT/GB94/01496
castor oil, oxidized synthetic waxes and polyethylene
oxide.
If a stabilizer is present the composition
preferably contains 0.1-4~ w/w thereof. Suitable
5 examples are high molecular weight phenols and
multifunctional phenols such as sulphur and phosphorus-
containing phenols, for example, 1,3,5-trimethyl-2,4,6-
tris-(3,5-di-tert-butyl-4-hydroxy-benzyl)benzene;
pentaerythritol 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-tert-butylphenol; 6-(4-hydroxyphenoxy)-2,4-bis(n-
octyl-thio)-1,3,5-triazine; di-n-octadecyl- 3,5 di-tert-
butyl-4-hydroxybenzylphosphonate; 2-(n-octyl-thio)-
ethy13,5-di-tert-butyl-4-hydroxy-benzoate; and sorbitol
hexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate.
If a plasticiser is present, the ratio thereof to
PHA may be up to 40 phr w/w and the range 5-20 especially
6-12, phr w/w is generally suitable.
Examples of suitable plasticisers are high-boiling
esters of polybasic acids, such as phthalates,
isophthalates, citrates, fumarates, glutarates,
phosphates or phosphates. The esterified radicals may be
for example C1 - C1z alkyl, aryl, aralkyl or aralkyl.
Particular examples are dialkyl, for example dioctyl,
phthalates, and dialkylalkylene oxide glutarates high-
. boiling esters and partial esters of polyhydric alcohols,
especially glycols, polyglycols and glycerol. The acid-
derived radical of the ester typically contains 2-10
carbon atoms. Examples are triacetin, diacetin and
WO 95/02649 PCT/GB94/01496
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glycerol dibenzoate and aromatic sulphonamides such as
paratoluenesulphonamide
Particular examples of such plasticisers are esters
of polyhydric alcohols, for example glyceryl esters of C1
- C4 carboxylic acids, especially Estaflex (Tradename).
Generally it is preferred that the plasticiser should be
biodegradable.
Additional optional additives include colorants such
as titanium dioxide, and fillers such as talc and clay.
These may be present in small amounts usually 0-20~,
preferably 5 to 20~.
Particularly preferred PHA adhesive compositions
comprise 50-95~ PHA, 0-20~ of plasticiser, 0-1~ of
nucleant, 0-20~ of tackifier, 0-4~ of stabiliser or
antioxidant, 0-10~ of wax diluent, and 0-20~ of a
colorant and/or filler.
PHA adhesive formulations can be, for example,
granules, dry powder or preferably latex suspensions. In
such formulations the PHA is in particulate form before
the setting treatment. The adhesive layer may be at
least partly discontinuous after the setting treatment.
Granules may be formed by a normal extrusion process,
using for example, a single or twin screw extruder in
which the PHA powder is melted and passed through a die
before cutting into granules.
' Amorphous PHA tends to crystallise with time and it
may be supplied as an aqueous suspension or latex, in
which the average particle size is from 0.1 ~.un to 2.0 dun
and preferably from 1.0 ~zm to 2.0 um.
Suitable latices can be produced in known processes
for producing PHA, particularly polymers of
s
W0 95/02649 PCT/GB94/01496
7
hydroxybutyric acid and copolymers thereof with
hydroxyvaleric acid, in which microorganisms are grown
under conditions such that they accumulate PHA and are
then treated to break their cellular structure and to
release particles of PHA into an aqueous suspension.
This can be accomplished for example by heat treatment
and/or digestion with enzymes. Organic matter other than
PHA is preferably largely removed, for example by
separating the PHA from the liquid, preferably in the
presence of a surfactant.
The PHA may be resuspended in water to provide a
suitable latex for use as an adhesive. Suitable latices
and methods of their production are described in European
Patent 145,233. Those containing peptidoglycan as the
major non-PHA cell material may be used. The pepti-
doglycan is believed to be present as a layer surrounding
the substantially amorphous PHA particles. It need not
be completely removed as it tends to isolate the
particles from surrounding materials which may induce
crystallisation. The latex may be stabilised with a
surfactant.
The process of the present invention may be carried
out without heating if a latex is used. If powder or
granules are used heating is usually necessary. The
adhesive composition is placed between the two articles
i.n the cold state, preferably at a temperature from 15°C
to 50°C, especially 15°C to 35°C. Then the articles are
subjected to pressure and optionally a heat treatment to
set the adhesive. Typically the pressure is applied in
the range 500 to 2000 and up to 10000 psig (34.5 to 690
bar), especially 500 to 8000 psig (34.5 to 550 bar) for
~~.~1G
WO 95/02649 PCT/GB94/01496
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setting at the "cold" temperatures mentioned above.
Typically the heat treatment if used is in the range 120
to 190, especially 130 to 190,°C: pressures up to 2000
prig (138 bar) are then usually sufficient.
The adhesives of the present invention are useful
for a wide range of applications. Of particular interest
are sealing operations for example, in packaging and
carton sealing, in sanitary napkins, disposable baby
napkins and hospital equipment, etc. The adhesives are
useful for disposable articles in which at least one
flexible film material is bonded to at least one tissue,
non-woven, polyolefin or other flexible polymeric film
substrate. Alternately, the adhesive may bond elastic to
polyethylene, polypropylene or a non-woven substrate.
The adhesive composition when set does not
necessarily have to provide a permanent or strong bond in
order to satisfy the requirements of a particular bonded
article. In some cases it may be advantageous for the
bond to be weak enough to enable the articles to be
peeled apart. The adhesive layer contains PHA typically
at 0.1 to 10.0 g/dm2.
Latex suspensions may be used in the absence of
nucleants, tackifiers, stabilisers, antioxidants,
plasticisers, colorants and fillers if desired.
The following examples illustrate the invention but
do not in anyway limit the scope of the invention.
Latex susraension preparation
A sample of fermentation broth from a culture producing
PHBV (ll~mol HV) was heat shocked to break open the cells
and treated with a proteolytic enzyme followed by a water
wash regime as described in EP-A-145 233. At this stage
~~~~~J
WO 95/02649 PCT/GB94/01496
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in the preparation a sample of latex suspension was taken
for use in the present invention. The molecular weight
of the PHBV in the latex suspension was 527,000.
Granule preparation
PHBV dry powder (24~mo1 HV) prepared by methods known in
the art (available from ZENECA Bioproducts, PO Box 2,
Belasis Avenue, Billingham, Cleveland, TS23 1YN, UK) was
used to prepare PHBV granules (24~mo1 HV) containing 10
phr triacetin and 1 phr boron nitride. The granules were
prepared by extrusion at a die temperature of 155°C
(maximum). The molecular weight of the PHBV in the
granules was 294,500.
N~~terials Specification
Paper = 76.02 g/m2
Aluminium Foil = 33.81 g/m2
PHB-Film = 72.94 g/m2
Card = 340 to 550 g/m2
gamble pret~aration
Latex suspension adhesive (no heat treatment)
Strips (l0cm x 2cm) of a range of materials were cut.
Latex solution (40~ w/w of PHA; 1m1) was pipetted on to
the first test material. A second test material was
overlaid on the first with a 5 cm overlap and then the
combined test sample was put between two pieces of
MELINEX (trade mark) film and placed between two plates
in a press at room temperature (20°C). The plates were
adjusted until they touched the test sample and then
pressure was applied to 5 tonnes (490 bar) and held for 1
minute. The pressure was released and the sample removed
from the plates. The samples were cut into 2 cm wide
strips.
WO 95/02649 PCT/GB94/01496
,~~atex suspension adhesive - Cheat treatment)
Strips of a range of materials to be tested were cut into
20cm x 9 cm strips. Latex suspension (1m1) was pipetted ,
on to an area in the centre of the first strip of test
5 material with a 5 cm overlap. The second strip of test
material was overlaid on top of the first strip of test
material. Then the combined test sample was put between
two pieces of "MELINEX" (trade mark) film and placed
between two plates in a press. The press temperature was
10 set to either 190°C or 134°C. Pressure was applied to 5
tonnes (109 bar) and held for 1 minute. The sample was
removed quickly and allowed to cool. When completely
cold the samples were cut into 2cm wide strips.
~r rnn P adhesive (heat treatment)
Strips (20cm x 9cm ) of the materials to be tested were
cut. One piece of test material was laid on a press with
"MELINEX" (trade mark) film between it and the plate.
Between 1.5g and 1.8g of granules were placed in the
intended 5 cm overlap area and the second test material
was laid on top of the first test material. "MELINEX"
(trade mark) film was placed between the second test
material and the second plate. The plates with the test
sample between were transferred to a press at 190°C or
134°C. The pressure was increased to 5 tonnes (109 bar)
and held for 1 minute at 190°C or 45 seconds at 134°C.
The sample was then removed from the press and cooled. ,,
When completely cool the samples were cut into 2cm wide
strips.
P~ test for adhesive strength
All the samples were tested for the strength of the
adhesive bond using an Instron 11220 mechanical test
WO 95/02649 PCT/GB94101496
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machine at a 90 degree peel angle, speed 10 mm per minute
and at a temperature of 23°C. The bond strength is
presented according to the following scale:
Gic (Niri ~)
'VERY POOR less than 1
POOR between 1 and 10
LOW between 10 and 100
GOOD between 100 and 500
VERY GOOD over 500
in which Gic (Niri2) is (force - width) x (1-cos Q) where Q
is the peel angle. The results are presented in Table 1.
'FABLE 1
SPEC IMEN ADHESIVE TEMP BOND
TYPE C
BASE TOP
STRENGTH
PAPER PAPER LATEX 20 LOW
PAPER PAPER LATEX 190 GOOD
PAPER A1-FOIL LATEX 20 POOR
PAPER A1-FOIL LATEX 190 POOR
PAPER PHB-FILM LATEX 134 GOOD
CARD PAPER LATEX 20 POOR
CARD PAPER LATEX 190 GOOD
A1-FOIL A1-FOIL LATEX 190 LOW
PHB-FILM PHB-FILM LATEX 20 POOR
PHB-FILM PHB-FILM LATEX 134 v GOOD
CARD PHB-FILM LATEX 20 POOR
WO 95/02649 PCT/GB94/01496
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CARD PHB-FILM LATEX 134 GOOD
CARD CARD LATEX 20 V POOR
CARD CARD LATEX 190 GOOD
PAPER PAPER GRANULE 190 GOOD
PAPER PAPER GRANULE 134 GOOD
PAPER Al-FOIL GRANULE 134 POOR
PAPER PHB-FILM GRANULE 134 GOOD
CARD PAPER GRANULE 134 GOOD
A1-FOIL A1-FOIL GRANULE 190 POOR
A1-FOIL A1-FOIL GRANULE 134 POOR
Al-FOIL PHB-FILM GRANULE 134 POOR
CARD A1-FOIL GRANULE 134 POOR
CARD PHB-FILM GRANULE 134 GOOD
CARD CARD GRANULE 190 GOOD
CARD CARD GRANULE 134 GOOD
93SKM14S/MS - 5 July 1994
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