Note: Descriptions are shown in the official language in which they were submitted.
WO94/10257 2 ~ 2 ~ PCT/US93/08913
POLYLACTID~ CONTAINI~G HOT M~T AD~8IVE
R~CR~POUND OF THE INVENTION
Hot melt adhesives are used commercially for a wide
variety of applications. The major advantage of hot melt
adhesive systems is the lack of a carrier fluid which
eliminates the need for drying the adhesive film once it
is applied to the substrate. This elimination of the
drying step overcomes hazards associated with solvent
usage and also allows for faster production line speeds
and lower transportation costs. Depending on the desired
use, the degree of tack of the hot melt adhesives may be
varied over a wide range to produce adhesives varying
from pressure sensitive to non-pressure sensitive in
character. Non-pressure sensitive are used, for example,
in bookbinding, bag ending, case and carton sealing.
Pressure sensitive hot melts are used in many
applications, and particularly in disposables such as
diapers, sanitary products and the like, where room
temperature tack and long open time are required.
Hot melt adhesives have historically been based on
petroleum derived polymers such as polyethylene,
ethylene-vinyl acetate, styrenic block copolymers, and
polypropylene to name a few. These compositions are
further tackified, plasticized, and reinforced with a
variety of resins, oils and waxes which are derived from
both petroleum and naturally occurring feedstocks such as
wood, gum and tall oil rosin and terpenes. These classic
compositions suffer from the cyclical price cycles common
to all oil derived materials, and also are generally very
resistant to degradation once the articles employing them
are disposed of.
The present invention stems from the growing
movement away from petroleum derived raw materials to
SUB~ 11~ ~JTE SHEET
W O 94/10257 PC~r/US93/08913
3t ~
those derived from renewable, natural resources and as
part of an effort to utilize raw materials which have
demonstrated some level of degradation. The present
invention utilizes a class of naturally occurring or
synthetically produced thermoplastic, biodegradable
copolymers derived from a non-petroleum feedstock as the
base polymer. Such compositions advance the state of the
art of hot melt adhesives by alleviating the dependence
on petroleum based materials and by allowing for the
development of hot melt adhesives which either degrade
naturally after coming in contact with the soil or which
can be composted.
8UMMARY OF TRE INVENT~ON
It has been discovered that hot melt adhesive
compositions suitable for a variety of applications are
obtained by use of polylactide (i.e., the bimolecular
cyclic
ester of lactic acid) or copolymers with other lactones
such as glycolide and caprolactone, tackifiers, and
optionally, waxes and/or plasticizers. The adhesives may
be formulated using conventional additives and may vary
from pressure sensitive to non-pressure sensitive in
character depending upon the desired application.
In its broadest aspect, the present invention is
directed to hot melt adhesive compositions comprising 20
to 98% by weight of a polylactide homo- or copolymer
where the copolymer contains at least 20 molar percent of
the lactide component (1 or d or d,l or meso or mixtures
thereof) 2 to 80% by weight of a polar tackifier having
a Ring and Ball softening point (as described by ASTM E-
26) greater than about 60~C; o to 50% by weight of a
plasticizer; 0 to 30% by weight of a wax diluent and 0-3%
by weight of a stabilizer.
It will be recognized that the general formulations
described above can be adapted to include a wide variety
of hot melt adhesive compositions, the more precise
formulations of which will vary depending upon the
SUB~ JTE SHEET
3 ~ 4 ~ ~
~ specific end use, the knowledge of which is readily
available to those skilled in the particular art.
Thus, in general, pressure sensitive adhesives can
be prepared using 20 to 70~ by weight of the polylactide
homo- or copolymer, 10 to 60% of a tackifying resin, 10
to 50% plasticizer and 0 to 3% of a stabilizer.
Preferred pressure sensitive adhesives are prepared using
30 to 60~ of the polylactide homo- or copolymer; 20 to
50~ of a tackifying resin, preferably a terpene phenolic
resin; and 20 to 30~ of a plasticizer, preferably Pycal
TM
94, d phenyl ether of poly(ethylene glycol) from ICI; or
Hercolyn D, a methyl ester of hydrogenated rosin from
Hercules. Lower levels of plasticizer may also be
employed to produce adhesives useful for various end uses
such as in construction adhesives for disposable products
where some initial degree of tack is needed but no
residual pressure sensitive properties are required.
In general, non-pressure sensitive adhesives can be
prepared using 20-98% by weight of the polylactide homo-
or copolymer, 2-80~ tackifying resin, 0-30~ of a wax-like
diluent, 0-30% plasticizer and 0 to 3% of a stabilizer.
Preferred non-pressure sensitive adhesives are prepared
using 30-80% of the polylactide homo- or copolymer; 10-
40% tackifying resin, preferably terpene-phenolic resins
or rosin derivatives; 0-25% of a plasticizer, preferably
the phenyl ether of poly(ethylene glycol) or the methyl
ester of hydrogenated wood rosin; and 0-20% of a wax-like
diluent, preferably hydrogenated castor oil (also known
as castor wax) or 12-hydroxystearamide.
Additionally, polymers other than the polylactide
may be incorporated into the hot melt adhesives at levels
less than about 20~ by weight. Representative
formulations and applications are discussed hereinbelow
and illustrated by the examples, however, these should
not be construed as limiting the invention.
DET~ILED DESCRIPTION OF THE lNV~N'llON
The major component of the adhesive of the
A invention, present in an amount of 20 to 98% by weight of
CA 02l26849 l998-06-02
the adhesive, comprises a homo- or copolymer of polylactide
containing at least 20 molar percent of the lactide comonomer.
The general structure of the polylactide is shown below:
~ o
=Cf~
~o C
n
Suitable polymers for use herein have a number average molecular
weight (Mn) within the range of 10,000 to 200,000.
While poly(d,1-lactide) and the meso- are essentially
amorphous, poly(l-lactide) and poly(d-lactide) is crystaIline in
nature and has a crystalline melting point of 186~C depending on
its molecular weight and stereopurity. The polymers may be
prepared by ring-opening polymerization of the bimolecular cyclic
ester of lactic acid with acid or base catalysts such as PbO,
SnCl2, SnCl4, ZnCl2, SbFs, Sb2O3, or triethylamine using solution,
precipitation or melt processes. Alternatively, they may be
obtained commercially from Henley Chemicals, Inc. under the
Resomer~ tradename; from Poly Sciences Inc. or from Ecological
Chemical Products Company (EcoChem).
In addition to homopolymers of poly(l-lactide), poly(d, l-
lactide), and poly(meso-lactide) suitable polymers for use herein
may also be prepared by copolymerization with other lactones such
as glycolide or caprolactone. Thus, poly(d, 1-lactide-co-
glycolide) polymers containing equimolar amounts of the lactide
and glycolide components are available from Henley Chemicals as
Resomer RG502 , 503 , 504 , 505 and 506 and are suitable for
use herein. In addition, poly(d, l-lactide-co-glycolide)
polymers known as Resomer RG752TM, 755TM and 756TM containing 75
of the lactide component as well as the
; ~ 4~
TM
Resomer 858 polymer which contains 8S~ lactide are also
suitable.
The tackifying resins useful in the adhesive
compositions are generally polar in nature and have a
Ring and Ball softening point greater than 60~C and
include rosin and rosin derivatives, terpene phenolics,
pure phenolic resins, 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 and pentaerythritol esters of natural and
modified rosins, such, for example as the glycerol ester
of pale, wood rosin, the glycerol ester of hydrogenated
rosin, the glycerol ester of polymerized rosin, the
pentaerythritol ester of hydrogenated rosin, and the
phenolic-modified pentaerythritol ester of rosin; (3)
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; (4)
thermoplastic alkyl phenolic resins such as those
described in U.S. Patent Nos. 4,073,776 and 4,023,826.
Mixtures of two or more of the above described tackifying
resins, as well as blends of the above resins with small
amounts of (e.g., less than about 10% of the adhesive)
less compatible resins may be utilized for some
formulations. While the tackifier may comprise up to
about 80% of the adhesive, it is generally used in
amounts of 10 to 60% by weight.
Depending on the end-use application, and
- particularly for uses requiring pressure sensitive
properties, various compatible plasticizing or extending
oils may also be present in the composition. Preferred
compatible plasticizers include phthalate plasticizers
such as dioctyl phthalate; liquid pclyesters such as
Dynacol 720 from Huls; benzoate plasticizers such as l,4-
6 212684~
cyclohexane dimethanol dibenzoate (e.g., Benzoflex 352available commercially from Velsicol); phosphate
plasticizer such as t-butylphenyl diphenyl phosphate
(e.g., Santicizer lS4 available commercially from
Monsanto); poly(ethylene glycols) and derivatives thereof
such as the phenyl ether of poly(ethylene glycol) (e.g.,
Pycal 94 available commercially from ICI) as well as
liquid rosin derivatives having Ring and Ball melting
points below about 60~C such as the methyl ester of
hydrogenated rosin (e.g., Hercolyn D from Hercules); as
well as vegetable and animal oils such as glyceryl esters
of fatty acids and polymerization products thereof.
Other applications conventionally employing
adhesives based on these polylactide polymers may require
the use of wax diluents in order to reduce the melt
viscosity or cohesive characteristics of the hot melt
adhesive compositions without appreciably decreasing
their adhesive bonding characteristics. These waxes are
often used in adhesives which do not exhibit pressure
sensitive properties.
Suitable waxes include 12-hydroxystearamide wax,
hydrogenated castor oil, oxidized synthetic waxes,
poly(ethylene oxide) having a weight average molecular
weight above about 1000 and functionalized synthetic
waxes such as carbonyl containing Escomer H101 from
Exxon.
It should be recognized that some adhesive
formulations described herein may contain both wax and
plasticizer components so that the presence of one or the
other is not mutually exclusive.
Among the applicable stabilizers or antioxidants
which may be included herein are high molecular weight
hindered phenols and multifunctional phenols such as
sulfur and phosphorous-containing phenols.
Representative hindered phenols include: 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-
~,~
WO94/10257 ~ 1 2 ~ ~9 PCT/US93/08913
tert-butyl-4-hydroxyphenyl) propionate; 4,4'-methylene-
bis (2,6-di-tert-butylphenol); 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-hydroxy-benzylphosr~onate;
2-(n-octyl-thio)-ethyl 3,5-di-tert-butyl-4-
hydroxybenzoate; and sorbitol hexa[3-(3,5-di-tert-butyl-
4-hydroxyphenyl)propionate]. If used, the stabilizer is
present in levels of about 0.1 to 3% by weight.
Optional additives may be incorporated into the hot
melt compositions in order to modify certain properties
thereof. Among these additives may be included colorants
such as titanium dioxide; and fillers such as talc and
clay, etc. There may also be present in the adhesive
small amounts (e.g., less than about 20% by weight, and
preferably 5 to 20% by weight) of certain thermoplastic
polymers such as ethylene vinyl acetate, ethylene acrylic
acid, ethylene methyl acrylate and ethylene n-butyl
acrylate copolymers containing about 12 to 50% vinyl
acetate as well as caprolactone polymers. These polymers
are employed in order to impart flexibility, toughness
and strength. Alternatively and in particular, it may be
desirable to incorporate into the hot melt adhesive up to
20% by weight of certain hydrophilic polymers such as
poly(vinyl alcohol), hydroxyethyl cellulose, starch,
modified starch, poly(vinyl methyl ether), poly(ethylene
oxide), or poly(hydroxy butyrate/hydroxy valerate) which
will function to increase the water sensitivity of the
adhesives which may be desired for some applications.
These hot melt adhesive compositions may be
formulated using techniques known in the art. An
exemplary procedure involves placing approximately 40% of
the total tackifying resin concentration with all the
polymer, wax, plasticizers and stabilizers in a jacketed
mixing kettle, preferably in a jacketed heavy duty mixer,
which is equipped with rotors and thereupon raising the
temperature to a range of from up to about 190~C. After
the resin has melted, the temperature is lowered to 150~
SUB~ 111 ~JTE SHEEr
WO94/10257 PCT/US93/08913
4 ~ 8
to 165~C. Mixing and heating are continued until a
smooth, homogeneous mass is obtained whereupon the
remainder of the tackifying resin is thoroughly and
uniformly admixed therewith.
sThe adhesives disclosed herein may be employed in a
wide variety of uses as are known in the art. The
adhesives described herein may be effectively utilized in
a variety of packaging and carton sealing applications.
The non-pressure sensitive adhesives may also be used to
bind a plurality of sheets in a wide range of bookbinding
operations. They may also be used for laminating tissue
and/or screen-reinforced tissue layers such as are used
in individual or roll use applications as in wipers,
paper towels, toilet tissue and other consumer or
industrial end uses. When formulated with plasticizers,
the resultant adhesives may be used in the assembly or
construction of various disposable applications
including, but not limited to, sanitary napkins,
disposable diapers, hospital gowns, bed pads and the
like. In particular, adhesives are useful for the
assembly of disposable articles using multi-line
construction t~chniques wherein at least one flexible
film substrate is bonded to at least one tissue, non-
woven, polyolefin or other flexible polymeric film
substrate. In addition, the adhesives may be useful in
the bonding of elastic to polyethylene, polypropylene or
non-woven substrate so as, for example, to impart
elongation resistant gathers thereto. The adhesive may
also be utilized in less demanding disposable
construction applications such as for end or perimeter
sealing.
In the following illustrative examples all parts are
given by weight and all temperatures in degrees Celsius
unless otherwise noted.
35EXAMPLE I
In preparing the following samples, a heavy duty
mixer which had been heated to 190~C and which was
equipped with a stirring paddle was charged with 40% of
SUB~ 111 IJTE SHEET
the tackifying resin, and/or diluent. After melting of
the resins, stirring was then initiated whereupon the
polylactide was added slowly at 190~C over a one-half
hour period after which the temperature was lowered to
170~C. Heating and stirring were continued until a
homogeneous mass was obtained whereupon the remainder of
the tackifying resin and/or diluent was admixed
therewith. The samples were tested using the
following procedures:
Viscosity measurements were determined after 30
minutes using a 8rookfield viscometer (Spindle 27) at
350~F. ~'
The adhesive was also subjected to Peel/Shear
testing such as is conventionally required in the
pac~aging industry. Peel Temperature Test: A bead of
test adhesive approximately 1/8 inch in diameter is
applied at 325~F to 350~F with a glass rod onto 60
pound/ream kraft paper. A second sheet of the same paper
is superimposed on the first sheet within 2 seconds and
pressed thereto to form a kraft-to-kraft bond. The
bonded sheets are then cut perpendicular to the adhesive
line into 1 inch wide strips. Duplicate bonded specimens
are placed in an oven with one free end of the specimen
attached to a fixed support and a 100 gram load suspended
from the other sheet at the same end of the bond. The
oven temperature is then increased in 10~F increments at
15 minute intervals. The temperature at which bond
delamination occurred is specified as the peel
temperature.
Shear Temperature Test: Samples are prepared as in
peel temperature test but separate sheets of Kraft at
opposite ends of the bonded specimen are suspended and
weighted to stress the bond in a shear mode. The
temperature of the oven is increased as in peel test
until failure occurs.
Adhesion Test: A molten bead of hot melt at 325~F
tc 3S0~F was drawn across the middle (widthwise) of a L"
x 3" strip of Kraft paper. A second strip of Kraft paper
... .
' 0 ~ 7~ 4 ~
~ was then immediately superimposed upon the first and a 50
gram weight placed on top of the construction. The Kraft
to Kraft bonds were then aged 24 hours at either room
temperature (RT or 70~F) or at 40~F. After aging, the
samples were stressed by hand at the temperature of
storage in a goo peel mode. The presence or absence of
fiber tear was then noted.
The compositions and the results of the testing are
shown in Table I.
10TABLE I
1 2 3 4 5 6 7 Poly(1-
lactide)
Poly(l-21.518.015.015.0 17.015.0 15.0 ----
lactide)
Hercolyn D7.5 9.0 9.0 6.010.09.0 9.0 ----
TM
PEG-2001.0 3.0 ---- ---- ---- ---- ---- ----
Pycal 94 ---- ---- 3.0 6.0 3.0 3.0 3.0 ----
Nirez 30~M ____ 3
Super ---- ---- ---- ---- ---- 3.0 ---- ----
Fluidity TM
Hylon VII
40% VA, ------- --------~~--~ ~----~ ~--~~ 3.0 -------- -------
EVA
Compat- Yes Yes Yes Yes Yes Yes Yeq ----
ibility
DSC
Tg NtT N/T N/T -- 75~C
Tm 47~C 32~C 161~ 159~ 162~ 4~C 31~C 186~C
169~ 160~ C C C 161~ 162~ ---
Viscosity C .C 400 NJT 250 C C ---
(cpg) Q N/T 23580 N/T 100 N/T N/T ___
350~F N/T 120>200 N/T >200 120~ 120~ ---
Peel N/T >200F.T. N/T F.T. >200 >200 ---
(~F) N/T F.T. F.T. N/T F.T. o 0
Shear N/T F.T. F. T . F . T .
(~F) F.T. F.T.
Adhesion
(Kraft)
RT (40~)
Hercolyn D - methyl ester of hydrogenated rosin from Herculeq
PEG-200 - polyethylene glycol from Union Car~ide
Pycal 94 - phenyl ether of polyethylene glycol from ICI
Nirez 300 - terpene- phenolic resin from Arizona Chemical
N/T - not tested
Super Fluidity Hylon VII - modified starch propionate
The test resu]ts presented above show the adhesives
45 to be particularly suitable for pac~aging applications
11 2,~
~ such as case and carton sealing due to its low viscosity,
good fiber tear and acceptable peel and shear values.
Similar performance results would be expected ~rom
the use of comparable amounts of poly(d,l-lactide) or
copolymers thereof, however, due to the more amorphous
nature of the poly(d,l-lactide) the later polymers would
be particularly suitable for hot melt pressure sensitive
applications.
Another series of hot melt adhesives were formulated
and tested as described above. In this series, the
adhesives were also tested for thermal stability by
storing at 3S0~F for 72 hours and then noting the
appearance of the adhesive.
The compositions and test results are shown in Table
II.
TABLE II
8 9 lo
Poly(l- 25.0 25.0 25.0
lactide)
Hercolyn D --- 15.0 15.0
Pycal 94 15.0 --- ---
Nirez 300 10.0 --- 10.0
Foral NCTM ___ 10.0 -__
Irganox lOlOTM 0.1 0.1 0.1
Viscosity ~ 335 cps 470 cps 4125 cps
350~F 100 >80~F 140
Peel >200 150 >200
Shear F.T. F.T. F.T.
Adhesion RT F.T. F.T F.T
40~F
Thermal None Yes None
Stability None None None
(72 Brown Black Light
hours/350~F) None Yes Brown
Skin None None None
3S Gel 15 cps --- None
Color 175 cps
Separation
Char
Final
4~ Viscosity @
350~F
.
12
-- Foral NC is a calcium salt of rosin from Hercules
Irganox 1010 is a hindered phenol antioxidant from Ciba
Geigy
The results presented in Table II indicate that
samples 8 and 10 have acceptable thermal stability for
most applications. It is also to be noted that the
thermal stability may be even further improved by pre-
drying of the polylactide polymer since the polymer picks
up moisture when stored as a raw material.
The results also show that sample 10 would be
particularly suitable for industrial bag applications
where high heat resistance and relatively higher
viscosity are required. Sample 8 shows particular use
for case and carton sealing. Sample 9, while not having
as high a degree of heat resistance, would nonetheless be
suitable for less stringent heat resistant applications
such as bottle labelling.
Although preferred embodiments of the invention have been
described herein, it will be understood by those skilled in the art
that variations may be made thereto without departing from the spirit
of the invention or the scope of the appended claims.
