Title: Wax for hot melt adhesive applications
Abstract: Waxes prepared from hydrogenated plant oils, such as palm and soybean, are used as substitutes for petroleum derived waxes in hot-melt adhesive compositions. Unlike petroleum-derived or synthetic waxes, adhesive compositions comprising these waxes, which are obtained from naturally derived, renewable resources, achieve adhesion performance similar to conventional adhesives containing petroleum-derived waxes. The inventive waxes have a low iodine value (between 2-5), and melting points between approximately 120-165 degrees F. (Mettler Drop Point). These waxes comprise a triglyceride whose fatty acids are predominantly stearic acid (C18). The naturally derived waxes are used as an alternative to petroleum and synthetically derived waxes in the manufacture of adhesives used to bond paper, wood, glass, plastic and metal in a variety of manufacturing operations.
Patent Number: 6,890,982 Issued on 05/10/2005 to Borsinger, et al.
| Inventors:
|
Borsinger; Gregory (Chatham, NJ);
Hassan; Aziz (Sugarland, TX)
|
| Assignee:
|
Marcus Oil and Chemical-Corp. (Houston, TX)
|
| Appl. No.:
|
166959 |
| Filed:
|
June 11, 2002 |
| Current U.S. Class: |
524/277; 524/272; 524/274; 524/275 |
| Intern'l Class: |
C08L 091/06 |
| Field of Search: |
524/272,274,275,277,177
|
References Cited [Referenced By]
U.S. Patent Documents
| 3474055 | Oct., 1969 | Dooley.
| |
| 3573240 | Mar., 1971 | Flanagan.
| |
| 4081415 | Mar., 1978 | Matubara et al.
| |
| 4394915 | Jul., 1983 | Nelson.
| |
| 4792495 | Dec., 1988 | Taniguchi et al.
| |
| 5120781 | Jun., 1992 | Johnson, Jr.
| |
| 5177133 | Jan., 1993 | Peck et al.
| |
| 5326413 | Jul., 1994 | Esemplare et al.
| |
| 5371135 | Dec., 1994 | Suzuki.
| |
| 5574084 | Nov., 1996 | Peacock.
| |
| 6022947 | Feb., 2000 | Frihart et al.
| |
| 2003/0152707 | Aug., 2003 | Hassan et al.
| |
Other References
Notification of Transmittal of the International Search Report, mailed May 19, 2003.
International Search Report—PCT/US 03/00218.
|
Primary Examiner: Szekely; Peter
Attorney, Agent or Firm: Adams; Thomas L.
Claims
1. A hot-melt adhesive composition, the adhesive composition comprising:
(a) from about 25% to about 35% by weight of a thermoplastic copolymer consisting
essentially of an ethylene containing copolymer, the copolymer being selected from
the group consisting of an ethylene copolymer, an ethylene vinyl acetate copolymer,
and copolymers and terpolymers thereof,
the copolymer having a vinyl acetate content from about 18% to about 28%, the
copolymer having a melt viscosity of from about 100,000-about 600,000 cP at 302
degrees F.;
(b) from about 15% to about 40% by weight of a tackifier resin, the tackifier
resin being characterized by having an acid number of from about 3 to about 10;
(c ) from about 15 -about 35% by weight of a wax derived from a hydrogenated
vegetable oil (a vegetable derived wax), the wax being characterized by having
a melt viscosity of from about 50 to about 70 SUS at 210 degrees F., and a Mettler
drop point of from about 130 degrees to about 170 degrees F.; and
(d) the adhesive composition being characterized by having a DSC melt point of
from about 50 degrees C. to about 80 degrees C., and a melt viscosity of from about
1000-about 5000 cps at 350 degrees F., the adhesive composition being capable of
binding a fibrous cellulosic article to an article selected from the group consisting
of a fibrous cellulosic article, wood, metal, glass and plastic.
2. The adhesive as described in claim 1, wherein the vegetable derived wax is
selected from the group consisting of soybean, corn, cottonseed, rape, canola,
sunflower, palm, palm kernel, coconut, crambe, linseed and peanut wax.
3. The composition as described in claim 2, wherein the vegetable derived wax
is derived from soybean.
4. The composition as described in claim 2, wherein the vegetable derived wax
is derived from palm.
5. The adhesive as described in claim 2, wherein the adhesive composition is
further characterized by having a DSC melting point which is preferably from about
53 degrees to about 58 degrees C.
6. The adhesive as described in claim 2, wherein the wax more preferably comprises
from about 25%-about 35% by weight of the composition.
7. The adhesive as described in claim 6, wherein the wax most preferably comprises
from about 30%-about 35% by weight of the composition.
8. The adhesive as described in claim 2, wherein the copolymer preferably comprises
from about 30% to about 35% by weight of the composition.
9. The adhesive as described in claim 1, wherein the fibrous cellulosic article
is chosen from the group consisting of corrugated paper, kraft paper, linerboard
and paper.
10. The adhesive as described in claim 9, further comprising one or more compounds
chosen from the group consisting of stabilizers, plasticizers, fillers, antioxidants,
preservatives, synergists, dyes, pigments, and waxes.
11. A hot-melt adhesive composition, the adhesive composition comprising:
(a) from about 25% to about 35% by weight of a thermoplastic copolymer selected
from the group consisting of a copolymer consisting essentially of an ethylene
containing copolymer or a copolymer consisting essentially of an ethylene vinyl
acetate ("EVA") copolymer, ethylene acrylic acid copolymers, ethylene ethyl acrylate
copolymers; ethylene methacrylic acid copolymers; ethylene/vinyl acetate/acid terpolymers,
polymers derived from ethylene, polyamides, polyethylene, polyester, and polypropylene;
(b) from about 15% to about 40% by weight of a tackifier resin, the tackifier
selected from the group consisting of a rosin ester, a hydrogenated rosin, a high
acid number rosin, and a maleic modified rosin and wherein the tackifler resin
is characterized by having an acid number of about 3 to about 10;
c) from about 15-about 35% by weight of a wax derived from a hydrogenated vegetable
oil (a vegetable derived wax), the wax being characterized by having a melt viscosity
of from about 50 to about 70 SUS at 210 degrees F., and a Mettler drop point of
from about 130 degrees to about 170 degrees F.; and
(d) the adhesive composition being characterized by having a DSC melt point of
from about 50 degrees C. to about 80 degrees C., a melt viscosity of from about
1000-about 5000 cps at 350 degrees F., the adhesive composition being capable of
binding a fibrous cellulosic article to an article selected from the group consisting
of a fibrous cellulosic article, wood, metal, glass and plastic.
12. The adhesive as described in claim 11, wherein the preferred copolymer is
a copolymer consisting essentially of an ethylene containing copolymer selected
from the group consisting of an ethylene vinyl acetate polymer; and copolymers
and terpolymers thereof.
13. The adhesive as described in claim 12, wherein the ethylene vinyl acetate
copolymer is characterized by having a vinyl acetate content of from about 18%
to 28%, the copolymer having a melt viscosity of from about 100,000-about 600,000
cP at 302 degrees F.
14. The adhesive as described in claim 12, wherein the vegetable derived wax
is selected from the group consisting of soybean, corn, cottonseed, rape, canola,
sunflower, palm, palm kernel, coconut, crambe, linseed and peanut wax.
15. The composition as described in claim 14, wherein the vegetable derived wax
is derived from soybean.
16. The composition as described in claim 14, wherein the vegetable derived wax
is derived from palm.
17. The adhesive as described in claim 14, wherein the adhesive composition is
further characterized by having a DSC melting point which is preferably from about
53 degrees to about 58 degrees C.
18. The adhesive as described in claim 17, wherein the wax more preferably comprises
from about 25%-about 35 % by weight of the composition.
19. The adhesive as described in claim 18, wherein the wax most preferably comprises
from about 30%-about 35 % by weight of the composition.
20. The adhesive as described in claim 17, wherein the copolymer preferably comprises
from about 30% to about 35 % by weight of the composition.
21. A composition for application to an article intended to be bonded to another
article, the composition consisting essentially of a polymer, tackifler and a wax
derived from a hydrogenated vegetable oil (a vegetable-derived wax),
the polymer comprising from about 30% to about 35% by weight of the composition,
the polymer being a thermoplastic copolymer consisting essentially of an ethylene
containing copolymer, the copolymer being selected from the group consisting of
an ethylene copolymer, an ethylene vinyl acetate copolymer, and copolymers and
terpolymers thereof, the copolymer having a vinyl acetate content of from about
18%, the polymer having a melt viscosity of about 105,000 cp at 302 degrees F.;
the tackifier comprising from about 30% to about 35% by weight of the composition,
the tackifier being characterized by having an acid number of from about 3 to about
10; and the wax comprising from about 30% to about 35% by weight of the composition,
the wax comprising a triglyceride having a melting point between 136-160 degrees
F, the triglyceride being characterized by having an iodine value of between 2
and 5, the composition being characterized by a viscosity of between 10 to 200
cps at 140 degrees F., wherein the triglyceride comprises a fatty acid, the fatty
acid being stearic acid.
22. The composition as described in claim 21, wherein the vegetable derived wax
is derived from soybean.
23. The composition as described in claim 21, wherein the vegetable derived wax
is derived from palm.
24. A composition for application to an article intended to be bonded to another
article, the composition consisting essentially of a polymer resin, tackifier and
a wax derived from a hydrogenated vegetable oil (a vegetable-derived wax,
a. the polymer resin comprising from about 30% to about 35% by weight of the
composition, the polymer being a thermoplastic copolymer consisting essentially
of an ethylene containing copolymer, the copolymer selected from the group consisting
of an ethylene copolymer an ethylene vinyl acetate copolymer; and copolymers and
terpolymers thereof, the ethylene vinyl acetate copolymer having a vinyl acetate
content of 28%, the polymer having a melt viscosity of about 580,000 cp at 302
degrees F.;
b. the tackifier comprising from about 30% to about 35% by weight of the composition,
the tackifier being characterized by having an acid number of from about 3 to about
10; and
c. the wax comprising from about 30% to about 35% by weight of the composition,
the wax comprising a triglyceride having a melting point between 136-160 degrees
F, the triglyceride being characterized by having an iodine value of between 2
and 5, the composition being characterized by a viscosity of between 10 to 200
cps at 140 degrees F., wherein the triglyceride comprises a fatty acid, the fatty
acid being stearic acid.
25. The composition as described in claim 24, wherein the vegetable derived wax
is derived from soybean.
26. The composition as described in claim 24, wherein the vegetable derived wax
is derived from palm.
Description
FIELD OF THE INVENTION
The present invention is a vegetable wax comprising triglycerides with a melting
point of from about 50-70 degree C. Particularly, the present invention is used
as an additive in hot met adhesive compositions, which are used in bonding articles
such as those made from fibrous cellulosic materials, plastic, wood, metal and
the like. The adhesive compositions comprise a high molecular weight, ethylene
vinyl acetate copolymer with greater than about 18 weight percent vinyl acetate
("VA") and having a melt index greater than about 0.5. Because the waxes of the
present invention have melting points that are lower than the melting points of
many waxes traditionally used in hot melt adhesives, the compositions of the present
invention have melting points which are towards the low end of the melting point
spectrum of hot melt adhesives. This can be advantageous from a safety and handling perspective.
BACKGROUND OF THE INVENTION
Hot melt adhesives are versatile in industrial applications such as bonding articles,
for example, cardboard boxes, plastics parts, bookbinding and furniture manufacturing.
Hot melt adhesives generally comprise 100% solids, and, in commercial applications,
are typically used at temperatures at about 350 degrees F. These materials do not
generate volatile compounds during the task of bonding, which is particularly advantageous
in high-speed packaging operations where there is little time for drying an adhesive
that contains solvent. The lack of volatile emissions is also an advantage over
adhesives containing organic solvents, because the emission organic solvents, many
of which are known to be toxic and may have an adverse effect when released into
the environment, may pose environmental and health concerns.
Hot melt adhesive compositions are typically thermoplastic materials that are
heated to a molten state for their application to cardboard or corrugated cartons,
boxes, plastics and other items that need to be sealed or to be adhered to. For
example. after application of the molten adhesive to a substrate such as paper
(or similar cellulosic fibrous article), a second item that needs to be bonded
to the substrate is placed in contact with the molten hot melt adhesive. As the
molten adhesive cools and solidifies, a bond is formed between the substrate and
the second item that has utility in many areas of commerce including consumer and
industrial packaging.
The time a hot melt adhesive takes to solidify to a point where it can no longer
bond with the intended article is called the ‘open time’.
The time required for the adhesive to cool to the point where it has enough strength
to form a bond is the ‘set speed’. Set speed is an important parameter
for applications such as high speed packaging lines, where bonding needs to occur
rapidly to avoid poorly sealed or unsealed boxes from exiting the packaging line
and having to be rejected, for example, in applications where items such as consumer
packaged goods are being sealed.
Hot melt adhesives are generally composed of three components: (1) a polymer
resin; (2) a tackifier; and (3) a wax. The polymer provides the formulation with
its strength and adhesive characteristics. The polymer in the formulations generally
range from 25 to 50% by weight of the formulation.
The tackifier allows the polymer to be more adhesive by improving wetting during
the application. Tackifying agents are added to give tack to the adhesive and also
to lower viscosity. Tack is required in most adhesive formulations to allow for
proper joining of articles prior to the hot melt adhesive solidifying.
The wax reduces the overall viscosity of the adhesive, thereby allowing it to
liquefy. The wax also controls the open time and set speed of the system. In the
present invention, the use of a wax having a low but relatively sharp melting point
leads to a hot melt adhesive composition which liquefies at a temperature lower
than that of commercially available hot melt adhesives, but still retains good
set speed characteristics.
The ratio of polymer to tackifier to wax is generally specific to a particular
application's need. In general, the percent wax is minimized and added in sufficient
quantities to achieve desired viscosity and set speeds. The level of wax is generally
in the range of 15 to 35% by weight of the formulation. The waxes employed in most
hot melt adhesive compositions are waxes which are derived from petroleum, such
as the paraffins and microcrystalline waxes.
Depending upon the specific application desired, various other components,
such as plasticizers, are used in the formulation of hot melt adhesives. Plasticizers
reduce the overall viscosity of the adhesive and promote flexibility and wetting.
Typical types of plasticizers used are phthalates, glycolates, polybutenes, and
mineral oil. See "Adhesive Bonding", Chap. 8 Hot-melt Adhesives, by Thomas Flanagan,
at p. 8-3, published by MacMillan.
In formulating adhesives all the ingredients should be compatible, so the formulation
does not separate in the molten storage tank. Separation would result in the inability
to apply the adhesive and also poor adhesive performance. The closer the solubility
parameters of the different components are to each other, the greater the compatibility.
See "Some Factors Affecting the Solubility of Polymers", by P. A. Small, J. Appl.
Chem., 3, February 1953 (which teaches how to predict solubility parameters).
The cloud point temperature is the temperature at which a component begins to
solidify or "cloud up" as it cools from a clear liquid phase to the solid phase.
For example, for waxes, the cloud point is usually close to the melting point of
the wax. Compatibility is related to cloud point temperature, where generally,
the lower the cloud point temperature, the greater the compatibility. See "Adhesives
and Coatings Manual" by National Distillers and Chemical Corporation (1983).
Most hot melt adhesive formulations utilize polymer resins having a low vinyl
acetate content due to its lower cost relative to high vinyl acetate content polymers.
Low vinyl acetate polymers are relatively non polar and can be formulated with
other relatively non-polar tackifiers and waxes to yield compatible formulations.
The commonly used waxes are non polar and can be formulated into compatible adhesives
with low vinyl acetate containing polymer; these waxes include various grades of
paraffin wax.
Higher vinyl acetate content polymer resins (>18% Vinyl acetate) are
also used in hot melt adhesive formulations. The higher vinyl acetate content results
in a stronger ionic bond to polar substrates such as paper, thereby creating a
stronger adhesive. Vinyl groups are also known to modify polymer physical properties,
making the composition more pliable and thereby increasing its adhesion performance,
as known to those skilled in the art. The use of higher vinyl acetate content polymers
requires formulating using more polar waxes and tackifiers to maintain formulation
compatibility. These more polar waxes are generally more expensive than paraffin
wax and the selection and supply of these more polar waxes is limited. Fischer-Tropsch
("FT") waxes are often used with higher vinyl acetate content polymer due to their
better compatibility. From a supply standpoint however, Fischer-Tropsch waxes are
not produced in the Americas. The two largest suppliers of FT waxes are Sasol from
South Africa and Shell Oil from Malaysia; supplies of FT waxes are thus potentially
subject to supply interruptions caused by world events.
Large oil companies such as Shell Oil, ExxonMobil and other oil refiners supply
petroleum waxes used in these applications. Most of this wax is derived in the
process of refining lube oil where the wax is separated from the lube oil stock
and refined into various fractions of wax including paraffins, and microcrystalline
waxes. Formulators such as Astor Wax, IGI and Moore & Munger also supply wax for
these applications that is resold as is from the oil companies, and/or formulated
and repackaged to meet the specific needs of customers.
A wax that is to be used in hot melt adhesives must have a relatively sharp melt
point to yield an adhesive with a short ‘set speed’ and controllable
open time. The melt point is another property in addition to compatibility. The
wax must also allow for a reduction of overall adhesive viscosity to allow for
the proper application or coating of the hot melt adhesive on the intended substrate.
Generally, hot melt adhesive formulations are heated to 300-350 degrees F. prior
to application in order to reduce viscosity. The wax must be stable at these temperatures
to allow for extended periods as a molten product prior to application. It is well
known to those versed in the art that stabilizers such as antioxidant (for example,
hindered phenols) and free radical scavenger (such as, but not limited to, butylated
hydroxy toluene "BHT", butylated hydroxyanisole "BHA", and Irganox 1010, supplied
by Ciba Corp.) compounds can be added to the adhesive compound to further enhance
thermal stability.
Synthetic ethylene vinyl acetate ("EVA") waxes have been developed and
are commercially available for use with high vinyl acetate content polymer in adhesive
formulations. Low molecular weight ethylene vinyl acetate waxes such as AC 400
(available from Honeywell); EVA1 (BASF); and MC400, available through Marcus Oil
and Chemical, are examples of such commercially available materials. These waxes,
however, are not widely used because of their relatively high cost to manufacture
and resulting high selling price. These waxes also have relatively poor set speed
characteristics when incorporated into adhesive formulations due to their low crystallinity
and a lack of a sharp melting point.
Various attempts to utilize alternatives to imported and/or petroleum derived
waxes have been reported (U.S. Pat. No. 4,749,739, U.S. Pat. No. 4,396,673 and
U.S. Pat. No. 4,388,138; these patents are incorporated by reference herein).
For example, Foster, et al. (U.S. Pat. No. 4,749,739) discloses incorporation
of a synthetic polyethylene wax, hydrocarbon tackifier and amorphous propylene
polymer to create a low viscosity hot melt adhesive.
Ball, et al. (U.S. Pat. Nos. 4,396,673 and 4,388,138) mentions use of vegetable
wax in combination with an isocyanate binder as a release agent in the manufacture
of particleboard.
Mehaffy, et al (U.S. Pat. No. 6,117,945) highlights the need for low application
temperature (between 200 to 300 degrees F.) hot melt adhesives and suggests a styrene,
alpha-methylstyrene and/or vinyltoluene polymer combined with ethylene vinyl acetate
polymer and paraffin wax.
The prior art thus illustrates the use of petroleum-derived waxes and synthetic
waxes for formulating hot melt adhesive compounds. There are no mentions of vegetable
derived triglyceride waxes for use in hot melt adhesive formulations, yet there
is a recognized and long-felt need to find alternatives to products such as petroleum
waxes that are derived from scarce and limited natural resources. There is also
a recognized and long-felt need to use materials in hot melt adhesives that are
considered safe to humans because of the adhesives' use in the manufacture of containers
used to transport and store foodstuffs. There is also a recognized and long-felt
need to use materials in hot melt adhesives that are naturally derived and can
be easily recycled back into the environment without long-term adverse effects;
corrugated cartons having wax-based coatings and adhesives, for example, are known
to be difficult to recycle. Therefore, there is a need for employing a wax, which
has similar properties of petroleum derived or synthetic waxes used in hot melt
adhesive formulations. Due the large volume of waxes consumed in these applications
it is also preferred that the compositions be readily available. From both a supply
and a natural resource viewpoint, it is preferred that the compositions be obtained
from a source that preferably is renewable, such as from plant extracts.
There is a need for a wax that is compatible with high vinyl acetate content
polymer resins, has a sharp melting point, low viscosity, does not adversely affect
adhesion and is thermally stable. It is also desirable to have a wax that does
not have to be imported, and produced at a cost which is competitive with that
of the paraffin and microcrystalline waxes. Given that the world's petroleum supply
is finite, and dwindling, it is also desirable to have a wax that can be obtained
from a renewable source, such as plants, rather than being petroleum based. Further,
because hot melt adhesives are frequently used in food packaging applications,
it is also desirable for the wax to have food grade properties for safety. The
waxes of the present invention meet the rigorous requirements for this and other applications.
The present invention is a natural wax for use in hot melt adhesive formulations.
The product is a commercially available high triglyceride wax derived from the
processing of natural oil containing commodities such as soybeans, palm and other
crops from which oil can be obtained. Hydrogenated vegetable oils are widely used
in the food industry. Products of the present invention are highly hydrogenated
to minimize un-saturation. Although commercially available, these materials are
not widely produced or used due to their limited applications in the food industries.
The materials are processed and supplied by Archer Daniels Midland (Decatur Ill.)
designated by their product number 86-197-0, Cargill Incorporated (Wayzata,
Minn.) designated by their product number 800mrcs0000u and other sources under
a generic name ‘hydrogenated soybean oil’. Palm oil wax was supplied
by Custom Shortenings & Oils (Richmond, Va.) and was designated as their product
Master Chef Stable Flake-P.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a composition that can be
incorporated into hot melt adhesive formulations.
Another object of the present invention is to provide an adhesive composition
which can be subsequently applied to articles such as paper, paperboard and the
like to bond them for use in consumer and other packaged goods applications.
It is an object of the present invention to provide a composition that can be
incorporated into hot melt adhesive formulations as a substitute for petroleum-derived
waxes currently used in such formulations.
Another object of the present invention is to provide a composition that
when incorporated into hot melt adhesive formulations, is compatible with the other
components of the formulations.
Still another object of the present invention is to provide a composition which
when formulated into a hot melt adhesive, and which adhesive is applied to an article
for the purpose of bonding that article to another article, the adhesive has adhesive
performance characteristics similar to that of a conventional hot melt adhesive
formulation prepared utilizing petroleum-derived wax.
Yet another object of the present invention is to provide a composition which
can be derived from a renewable resource in place of non-renewable petroleum based compositions.
Still another object of the present invention is to provide a composition which
can be derived from a renewable resource and which can be economically produced.
Another object of the present invention is to provide a composition for use
in hot melt adhesives and for paper coating and have properties that are generally
regarded as safe by the Food and Drug Administration.
The present inventors have unexpectedly discovered that highly hydrogenated oils
such as palm and soybean can be converted into a wax that can be used effectively
as substitutes for conventional petroleum and synthetic waxes in the formulation
of hot melt adhesive compounds.
The present invention comprises a highly hydrogenated vegetable oil (derived
from sources such as palm, soybean, corn or others) that has wax-like properties
and can be formulated using conventional means with other components in the manufacture
of hot melt adhesive compounds, to produce adhesive compositions which have adhesive
characteristics similar to adhesive formulations containing petroleum derived wax.
The inventive waxes consists essentially of a hydrogenated oil that comprises >90%
triglyceride, and whose fatty acid components have a range of carbon numbers, with
stearic acid (C
18), being the most predominant (>50%). The wax
compositions have a low iodine value (between 2-5), and melting points between
approximately 120-165 degrees F. (Mettler Drop Point). The wax compositions of
the present invention can also be used as an additive (as a coating) in the manufacture
of wax coated boxes, which can then be recycled more readily than boxes prepared
using conventional waxes.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG. 1 is a flow chart illustrating a process for the manufacture of hydrogenated oils.
FIG. 2 illustrates the open time parameter of adhesive of adhesive formulations
of the present invention.
FIG. 3 illustrates the viscosity of adhesive formulations of the present invention.
FIG. 4 compares the adhesive properties of the present invention with a control
hot melt adhesive, using the Shear Adhesion Failure Test ("SAFT").
FIG. 5 illustrates the melting points of adhesive formulations of the present
invention, as determined by Differential Scanning Calorimetry.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a wax composition, derived from compounds of plant origin,
which can be used as an alternative to petroleum derived wax in formulating hot
melt adhesives that are subsequently used to bond articles, yet which composition
yields adhesive properties similar to adhesives containing petroleum derived waxes.
As known in the art, triglycerides are fatty acid esters of glycerol. As used
herein, the term "free fatty acid" will refer to a fatty acid that is not covalently
bound through an ester linkage to glycerol. Additionally, as used herein, the term
"fatty acid component" will be used to describe a fatty acid that is covalently
bound through an ester linkage to glycerol.
Naturally occurring carboxylic acids ("fatty acids") and their derivatives,
most commonly the glyceryl derivatives in which all three hydroxy groups of the
glycerol molecule are esterified with a carboxylic acid, are used commercially.
The carboxylic acids may be saturated or unsaturated. The tri-substituted glycerols
(triglycerides, also referred to as triacylglycerols) are major components of most
animal and plant fats, oils and waxes. When all three hydroxy groups of a glycerol
molecule have been esterified with the same fatty acid, it is referred to as a
monoacid triglyceride. Whether one refers to triglycerides as "waxes," "fats,"
or "oils" depends upon the chain lengths of the esterified acids and their degree
of saturation or unsaturation as well as the ambient temperature at which the characterization
is made. Generally, the greater the degree of saturation and the longer the chain
length of the esterified acids, the higher will be the melting point of the triglyceride.
Naturally occurring and synthetic waxes are extensively used in a wide
cross-section of industries including the food preparation, pharmaceutical, cosmetic,
and personal hygiene industries. The term wax is used to denote a broad class of
organic ester and waxy compounds, which span a variety of chemical structures and
display a broad range of melting temperatures. Often the same compound may be referred
to as either a "wax," "fat" or an "oil" depending on the ambient temperature. By
whatever name it is called, the choice of a wax for a particular application is
often determined by whether it is a liquid or solid at the temperature of the product
with which it is to be used. Frequently it is necessary to extensively purify and
chemically modify a wax to make it useful for a given purpose. Despite such efforts
at modification, many of the physical characteristics of waxes still prevent them
from being used successfully or demand that extensive, and oftentimes, expensive,
additional treatments be undertaken to render them commercially useable.
Many commercially utilized triglycerides and free fatty acids are obtained preferably
from plant sources, including soybean, cottonseed, corn, sunflower, canola and
palm oils. The triglycerides are used after normal refining processing by methods
known in the art. For example, plant triglycerides may be obtained by solvent extraction
of plant biomass using aliphatic solvents. Subsequent additional purification may
involve distillation, fractional crystallization, degumming, bleaching and steam
stripping. The triglycerides obtained are partially or fully hydrogenated. Furthermore,
fatty acids may be obtained by hydrolysis of natural triglycerides (e.g., alkaline
hydrolysis followed by purification methods known in the art, including distillation
and steam stripping) or by synthesis from petrochemical fatty alcohols. The free
fatty acids and triglycerides may further be obtained from commercial sources,
including Cargill, Archer Daniels Midland, Central Soya and other suppliers.
In the present invention. the free fatty acids and fatty acid components of the
triglycerides are preferably saturated, and have various chain lengths. The free
fatty acids and fatty acid components of the triglycerides may be unsaturated,
provided that the coating composition will be a solid at the temperature at which
the coating is used. The properties of the free fatty acid/triglyceride mixture,
such as melting point, varies as a function of the chain length and degree of saturation
of the free fatty acids and the fatty acid components of the triglycerides. For
example, as the degree of saturation decreases, the melting point decreases. Similarly,
as the chain length of the fatty acids decreases, the melting point decreases.
Preferred free fatty acids are saturated fatty acids, such as palmitic acid, and
other saturated fatty acids having longer carbon chain lengths, such as arachidic
acid and behenic acid. Stearic acid is further preferred.
The iodine value ("I.V."), also referred to as the iodine number, is a measure
of the degree of saturation or unsaturation of a compound. The iodine value measures
the amount of iodine absorbed in a given time by a compound or mixture. When used
in reference to an unsaturated material, such as a vegetable oil, the IV is thus
a measure of the unsaturation, or the number of double bonds, of that compound
or mixture.
Vegetable oils or animal fats can be synthetically hydrogenated, using
methods known to those skilled in the art, to have low or very low iodine values.
Fats naturally composed primarily of saturated triglycerides (such as palm oil
or fractionated fats) can be used alone or in blend formulations with adhesives/laminants
to achieve an enhanced water tolerance for composite materials (U.S. Pat. No. 6,277,310).
The major components of plant oils are triacylglycerols.
Saturated triglycerides having a low iodine value (a range of iodine values
of about 0-70 with 0-30 preferred) may be produced by hydrogenation of a commercial
oil, such as oils of soybean, soy stearine, stearine, corn, cottonseed, rape, canola,
sunflower, palm, palm kernel, coconut, crambe, linseed, peanut, fish and tall oil;
or fats, such as animal fats, including lard and tallow, and blends thereof. These
oils may also be produced from genetically engineered plants to obtain low IV oil
with a high percentage of fatty acids.
Fats are commonly fractionated by a process known as "winterization", wherein
the mixture is chilled for a period of time which is long enough to allow the harder
fractions of the fats to crystallize. This chilling is followed by filtration,
with the harder fractions being retained on a filter cake. These harder fractions
have a lower iodine value and, therefore, a melting point that is higher than the
melting point of the fat from which it has been separated. Hence, winterization
can be used as a source for lower IV fats.
The winterization process is generally used to fractionate animal fats, and can
thus produce a variety of animal fat fractions, having differing iodine values
and consequently, differing chemical properties. These fractions can be blended
with fatty acids and free fatty acids obtained from other sources, such as plant
or vegetable extracts referred to above, and these blends can also be used in the
present invention.
The present invention performs best with a hydrogenated triglyceride where the
iodine value is close to zero thereby rendering the triglyceride more thermally
stable. The triglycerides can be chosen from those having an iodine value of between
0-30, but a triglyceride having an iodine value of between 2-5 is preferred.
Adhesives generally comprise a wax, a tackifying agent and a polymeric
resin. When an adhesive is applied to a substrate, such as, for example only, paper
or other cellulose based products, and the substrates joined to each other, the
adhesive serves to bond the substrates together. Hot melt adhesives are routinely
used in the manufacture of corrugated cartons, boxes and the like. They are also
used in diverse areas, such as bookbinding; sealing the ends of paper bags; furniture
manufacturing; and adhering other articles, such as glass, metals and various plastics,
including attaching paper labels to plastic containers. Additional uses of hot-melt
adhesives include, but are not limited to, carpet seam sealing tape, lamination,
product assembly, nonwoven construction, and potting and encapsulation compounds.
For the manufacture of corrugated cartons, especially those used for shipping refrigerated
or frozen foods, or for shipping foods packed in ice, hot melt adhesives are generally
selected because of their ability to maintain a strong bond under the difficult
conditions, such as stress and shock in handling, high humidity and variations
in the environmental temperature. The wax component of adhesives affects properties
such as its setting speed and thermal stability.
Prior art hot-melt adhesive compositions generally utilize waxes derived from
petroleum products, and include the paraffins and microcrystalline waxes described
previously Oxidized polyethylene waxes, also derived from petroleum products, may
be used. Additionally, Fischer-Tropsch waxes can be utilized, but they are not
preferred because of their having to be imported and their generally higher cost
compared to the petroleum-derived waxes.
The ratio of polymer to tackifier to wax is generally specific to a particular
application's need. In general, the percent wax is minimized and added in sufficient
quantities to achieve desired viscosity and set speeds. The level of wax is generally
in the range of approximately 15% to approximately 75% by weight of the formulation.
The waxes employed in most hot melt adhesive compositions are waxes which are derived
from petroleum, such as the paraffins and microcrystalline waxes. Preferably, the
level of wax in the formulation is in the range of approximately 25%-approximately
35% by weight of the formulation. More preferably, the level of wax in the formulations
of the present invention is in the range of approximately 3-%-approximately 35%
by weight of the formulation.
The tackifier allows the polymer to be more adhesive by improving wetting during
the application. Tackifying agents are added to give tack to the adhesive and also
to lower viscosity. Tack is required in most adhesive formulations to allow for
proper joining of articles prior to the hot melt adhesive solidifying. Effective
tackifiers include: glycerol and pentaerythritol esters of natural and chemically
modified rosins; naturally occurring and chemically modified resins, such as wood
rosin, gum rosin, tall oil rosin, distilled rosin, and rosins modified by processes
such as polymerization, hydrogenation, maleation and dimerization; polyterpene
resins; modified terpene resins, such as chlorinated terphenyl resins and phenolic-modified
terpene resins; and aliphatic petroleum hydrocarbon resins, such as those resulting
from polymerization of olefin and diolefin monomers
Tackifiers added to hot-melt adhesives can be characterized by parameters
such as their softening points, specific gravities, or by acid number. A tackifier
can be selected from among the variety of tackifiers, as described above but not
limited thereto, and from tackifiers characterized by a range of acid numbers,
such as acid numbers between 3 and 100, more preferably between 3 and 25, and most
preferably a tackifier having an acid number between 3-10. The tackifier can be
used in amounts ranging from approximately 2% by weight to approximately 70% by
weight. The tackifier is preferably used in amounts between approximately 15% by
weight to approximately 40% by weight, and more preferably in amounts ranging from
approximately 30% to approximately 35% by weight in the present invention. is typically
necessary in preferred compositions.
In the composition of the present invention, a preferred tackifying agent is
FORAL®
85 (Hercules, now available from Eastman). This agent is a hydrogenated glycerol
ester, with a softening point between 80-88 degrees C., and characterized by having
a specific gravity of 1.07 at 25 degrees, C., and an acid number ranging from 3-10
(Table 3).
The copolymer can be selected from one or more reagents, such as copolymers of
ethylene; or copolymers of ethylene and vinyl acetate (ethylene-vinyl acetate,
"EVA"). The copolymer can be chosen from the group consisting of, but not limited
to, ethylene acrylic acid copolymers, ethylene ethyl acrylate copolymers; ethylene
methacrylic acid copolymers; ethylene vinyl acetate terpolymers and other copolymers
derived from ethylene, such as polyamides, polyethylene, polyesters, and polypropylenes;
natural or synthetic rubbers, including styrene-isoprene and styrene-butadiene
random and block copolymers, polyvinyl acetate and vinyl acetate/unsaturated carboxylic
acid copolymers, polyvinyl acetals, polyurethanes and ethyl cellulose.
In the present invention, the copolymer is selected from the ULTRATHENE®
(trademark of Equistar Chemicals, Houston Tex.) group of polymers. The ULTRATHENE®s
are described as ethylene vinylacetate copolymers, whose relevant properties are
listed in Table 3. ULTRATHENE® UE 612-04 comprises 18% vinyl acetate, and
ULTRATHENE® UE 646-04 comprises 28% vinyl acetate. The copolymer is used in
the adhesive compositions of the present invention in concentrations ranging from
approximately 5% by weight to approximately 50% by weight of the composition. The
coolymer can more preferably be used at concentrations ranging from about 25% to
about 35% by weight of the composition, and is most preferably employed at concentrations
from about 30% to about 35% by weight of the composition (Table 4).
The adhesives of the present invention preferably also contain a number of additional
components, such as a stabilizer, plasticizer, filler or antioxidant. Among the
applicable stabilizers or antioxidants which can be included in the adhesive composition
of the present invention are high molecular weight hindered phenols and multifunctional
phenols, such as sulfur-containing and phosphorous-containing phenols. Hindered
phenols, known to those skilled in the art, may be described as phenolic compounds,
which also contain sterically bulky radicals in close proximity to the phenolic
hydroxyl group. Specifically, tertiary butyl groups generally are substituted onto
the benzene ring in at least one of the ortho positions relative to the phenolic
hydroxyl 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. It is this hindrance that provides the stabilizing
properties of these phenolic compounds.
Representative hindered phenols include; but are not limited to:
2,4,6-trialkylated monohydroxy phenols; 1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-benzene;
pentaerythritol tetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate, commercially
available under the trademark IRGANOX® 1010; n-octadecyl-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate;
4,4′-methylenebis (4-methyl-6-tert-butyl-phenol); 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;
2-(n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxy-benzoate; di-n-octadecyl 3,5-di-tert-butyl-4-hydroxy-benzylphosphonate;
and sorbitol hexa[3,3,5-di-tert-butyl-4-hydroxy-phenyl)-propionate.
Antioxidants include, but are not limited to, butylated hydroxy anisole
("BHA") or butylated hydroxy toluene ("BHT") which may also be utilized to render
the formulation more thermally stable These stabilizers and antioxidants are added
in amounts ranging approximately 0.01% to approximately 5% by weight of the formulation.
The performance of these antioxidants may be further enhanced by utilizing known
synergists in conjunction with the antioxidants. Some of these known synergists
are, for example, thiodipropionate esters and phosphates. Chelating agents and
metal deactivators, may also be used. Examples of these compounds include ethylenediaminetetraacetic
acid ("EDTA"), and more preferably, its salts, and disalicylalpropylenediimne.
Distearylthiodipropionate is particularly useful. When added to the adhesive composition,
these stabilizers, if used, are generally present in amounts of about 0.1 to about
1.5 weight percent, and more preferably in the range of about 0.25 to about 1.0
weight percent.
The present invention also contemplates the addition of a polymeric additive
to the adhesive. The polymeric additive can be selected from the group consisting
of ethylene methyl acrylate polymers containing 10 to 28 weight percent by weight
methyl acrylate; ethylene acrylic acid copolymers having an acid number of 25 to
150; polyethylene; polypropylene; poly(butene-1-co-ethylene) polymers and low molecular
weight and/or low melt index ethylene n-butyl acrylate copolymers. When such a
polymeric additive is added, it is present in amounts up to about 15 weight percent
by weight of composition.
Depending on the contemplated end uses of the adhesive composition, other
additives such as plasticizers, pigments and dyestuffs that are conventionally
added to hot-melt adhesives may be included. In addition, small amounts of additional
(secondary) tackifiers and/or waxes such as microcrystalline waxes, hydrogenated
castor oil and vinyl acetate modified synthetic waxes may also be incorporated
in minor amounts, i.e., up to about 10 weight percent by weight, into the formulations
of the present invention. A plasticizer may be used in lieu of, or in combination
with, the secondary tackifier to modify viscosity and improve the tack properties
of the adhesive composition.
A dispersant can also be added to these compositions. The dispersant can be a
chemical,
which may, by itself, cause the composition to be dispersed from the surface to
which it has been applied, for example, under aqueous conditions. The dispersant
may also be an agent which when chemically modified, causes the composition to
be dispersed from the surface to which it has been applied. As known to those skilled
in the art, examples of these dispersants include surfactants, emulsifying agents,
and various cationic, anionic or nonionic dispersants. Compounds such as amines,
amides and their derivatives are examples of cationic dispersants. Soaps, acids,
esters and alcohols are among the known anionic dispersants. The addition of a
dispersant may affect the recyclability of products to which a hot-melt adhesive
may been applied.
The surfactants can be chosen from a variety of known surface-active agents.
These can include nonionic compounds such as ethoxylates available from commercial
suppliers. Examples include alcohol ethoxylates, alkylamine ethoxylates, alkylphenol
ethyoxylates, octylphenol ethoxylates and the like. Other surfactants, such as
a number of fatty acid esters may be employed; for example, but not limited to,
glycerol esters, polyethyleneglycol esters and sorbitan esters.
The present invention is a natural wax for use in hot melt adhesive formulations.
The product is a commercially available high triglyceride wax derived from the
processing of natural oil-containing commodities such as soybeans, palm and other
crops from which oil can be obtained. The waxes used in the present invention are
a palm oil wax and a soybean wax, prepared from hydrogenated oil. The materials
are processed and supplied by Archer Daniels Midland (Decatur Ill.) designated
by their product number 86-197-0; Cargill Incorporated (Wayzata, Minn.) designated
by their product number 800mrcs0000u; and other sources under a generic name ‘hydrogenated
soybean oil’. Palm oil wax was supplied by Custom Shortenings & Oils (Richmond,
Va.) and was designated as their product Master Chef Stable Flake-P. The soybean
was is also distributed by Marcus Oil and Chemical Corp., Houston, Tex. under the
designation Marcus Nat 155; these waxes can also be used as food additives.
Generally, the vegetable-derived waxes that can be employed in the present
invention have melting points that are in the range of between about 130 degrees
F. to about 180 degrees F.
The properties of the two waxes are summarized in Tables 1 and 2, where it can
be seen that these waxes have IV's of between 5 and 2, respectively.
The soybean oil wax has a melting point, as measured by Mettler Drop Point, of
between 155-160 degrees F., while that of the palm oil wax is between 136-142 degrees F.
These waxes are further characterized by having a viscosity of between 10-200
cps at a temperature of 210 degrees F.,
Each wax comprises 98% triglyceride by weight with trace amounts of fatty acids.
The triglyceride can be saponified through the addition of a base such as KOH to
yield a saponification value. Saponification values will vary depending mainly
upon the chain length of the fatty acids, which is a function of the source from
which the vegetable wax was derived. For the hydrogenated soy and palm waxes used
in the present invention, the saponification (SAP) value is in the range of 180-200
mg KOH/g.
When the waxes were analyzed for their fatty acid content using known methods
of Gas Liquid Chromatography ("GLC"), the soybean wax was found to comprise between
82-94% stearic acid (C
18:0) and between 3-14% palmitic acid (C
16:0).
By comparison, the palm oil wax comprises approximately 55% stearic acid (C
18:0),
39.5% palmitic acid (C
16:0), 1.1% myristic acid (C
14:0) and
approximately 1.0% oleic acid (C
18:1).
The adhesive compositions of the present invention can be utilized for adhering
corrugated carton members to each other, for adhering paper and other items manufactured
from cellulosic fibers, for use in furniture manufacturing, plastics manufacturing,
and adhesion of paper substrates to items such as other paper items, corrugated
materials, kraft paper and the like, linerboard, glass and plastic items
Although the present invention has been described with a certain degree
of particularity, it is to be understood that the examples below are merely for
purposes of illustrating the present invention, the scope of the present invention
intended to be defined by the claims.
PREPARATION OF EXAMPLES
Example 1
Preparation and Evaluation of Adhesive Formulations
For the purpose of illustrating the invention, evaluations were conducted to
determine the performance of wax material versus a ‘control’ petroleum
derived microcrystalline wax in standard hot melt EVA formulations.
The following materials were used to make the EVA adhesive formulations.
- 1. EVA resin with 18% VA content, ULTRATHENE® 612-04 made by Equistar
Chemical, LP.
- 2. EVA resin with 28% VA content, ULTRATHENE® 646-04 made by Equistar
Chemicals, LP.
- 3. Rosin Ester tackifier, FORAL® 85 made by Hercules.
- 4. Microcrystalline Controll Wax, 1251/7 supplied by Frank B. Ross Co.
- 5. Thermal stabilizer IRGANOX® 1010 made by Ciba-Geigy.
The compositions of the formulations used are in Table 4; the ingredients were
added on a weight basis, and were designated as either "High VA" (indicating the
use of the 28% EVA content resin), or "Low VA" (indicating the use of the 18% EVA
content resin). Ingredients were blended in a quart can heated by a glass-heating
mantle. Tackifier resin and Anti-oxidant were added into the can and allowed to
heat for 10 minutes. Mixing was started at a moderate rate of speed while the EVA
was slowly added over 25 minutes. While mixing continued the wax was slowly added
over a 15-minute period into the adhesive. The adhesive was allowed to mix an additional
15 minutes to assure uniformity. The final adhesive temperature was 350-360 degrees F.
Example 2
Compatibility Testing of Waxes with Adhesive Formulation Components
To determine whether the waxes were compatible with the other components of the
hot melt adhesive formulations, 25 grams of adhesive were placed into a 4-ounce
glass jar. The jar was placed in an oven at 350 degrees F. and the adhesive examined
visually every half hour for 2 hours for evidence of phasing or incompatibility.
The results showed that after 2 hours at 350 degrees F., the adhesive formulations
were crystal clear and uniform in appearance, indicating that the soy and palm
waxes were compatible with the other components of the adhesive formulations, in
formulations having high and low VA content.
Example 3
Adhesive Properties of the Inventive Formulations
To evaluate the adhesive properties of the inventive formulations, the hot melt
formulations were coated onto 56# basis weight paper typically used in the manufacture
of cardboard boxes. The formulations were coated at both 5 and 10 mil thickness.
Coatings were made using a wet film applicator (Bird type) with a 5 or 10
mil gap. The adhesive composition, the 4 inch wide applicator and sheets of ½
inch thick plate glass were placed into an oven for equilibration. After the appropriate
time interval, the glass was removed from the oven and strips of the 56# basis
weight paper, were placed onto the glass. A volume of the specific coating was
placed at one end of the paper, the applicator applied to the paper and the hot
molten adhesive drawn by hand to coat the paper. Equivalent coating weights were
calculated as 73 g/1000 square feet for the 5 mil coating, and 146 g/1000 square
feet for the 10 mil coating.
Example 3A
Open Time
Open time evaluations were conducted on the adhesive formulations according
to the ASTM D-4497 test procedure. For this evaluation, a 10 mil thick layer of
each formulation is coated onto 56# basis weight paper, and 1×4 inch strips
