Note: Descriptions are shown in the official language in which they were submitted.
2164376
A POLYlVIERlC COMPOSITION IN PELLET FOR~I
Field Of The Invention
This invention relates to a polymeric composition in pellet form comprising a high
5 molecular weight block copolymer having the general configuration A-B-A, and a molecular `
weight greater than about 200,000. Specifically, it relates to a hot melt composition in pellet
form having special properties especially suited for molding.
Background Of The Invention
Hot melt pressure sensitive compositions have been used widely in the adhesive
industry due to their ability to adhere to a wide variety of substrates. Block copolymers are the
preferred polymer base due to their good heat stability, high cohesive strength, and
compatibility with a wide range of tackifiers and plasticizers. A primary property of a hot melt
pressure sensitive composition is that it remains tacky at room temperature and can be adhered
to substrates when it has completely cooled from its molten state.
Applications requiring this property include labeling. Paper, polyethylene,
polypropylene or other such substrates may be coated with the hot melt pressure sensitive
adhesive, covered with release liner, and then shipped for later applications of labels, such as
those used on various containers, books, magazines, or envelopes just to name a few.
The fact that pressure sensitive hot melt compositions remain tacky at room --
temperature has precluded their use in a variety of other applications such as molding. One
such application is the formation of articles by injection molding. Injection molding is used to
form various articles such as shoe soles, drum pads, therapeutic hand exercising grips, shock
absorbers, acoustical insulators, chair pads and so on.
The tackiness of these hot melt pressure sensitive compositions also makes them
difficult to handle. They may adhere to skin, clothing, application equipment, floors and so on.
This is undesirable. Many packaging methods therefore, have been devised to avoid the
problems encountered in the handling of these hot melt pressure sensitive compositions. Such
methods include supplying them in pellet and pillow forms as disclosed by German Pat. 22 48
046. Slats or chicklets, blocks and cakes are also disclosed.
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French Pat. No. 2,544,654 published October 26, 1984 discloses forming a tackless hot
melt by adding the molten hot melt to a mold which contains a preformed support layer having
a transfer film which is compatible with the hot me}t.
U.S. Pat. Nos. 4,748,796 issued June 12, 1988 and 4,755,24S issued July S, 1988
5 disclose forming a protective coating for an adhesive material by electrostatically coating a
mold or cavity with a powder screen and then pouring hot melt into the mold.
French Pat. No. 2,601,616 published October 22, 1988 discloses forming blocks of hot
melt pressure sensitive adhesive by casting the adhesive into molds precoated by spraying with
a film of non self-sticking hot melt material.
Gerrnan Pat. Nos. DE 31 38 222, DE 32 34 065 and DE 36 25 358 teach coating or
wrapping a formed hot melt block with various types of film.
U.S. Pat. No. S,257,491 to Rouyer et al. teaches a method of packaging a hot melt
adhesive composition with a film wherein the adhesive composition is flowable at the time of
packaging. It also discloses packaging adhesive compositions after solidifying or even
15 coextruding the adhesive .with the packaging material. The packaging material does not
interfere with the properties of the adhesive composition during application.
U.S. Pat. No. 5,373,682 to Hatfield et al. issued December 20, 1994 teaches a method
for packaging hot melt adhesive compositions by directly pouring or purnping the molten
adhesive into a cylindrical plastic tube being in contact ~vith a heat sink. The adhesive package
20 is provided in a readily handeable, cartridge forrn which may be produced in a continuous line
operation. The adhesive is fused to some extent with the film and in turn allows some mixing
and compatibilizing of the film, improving the opportunity for more complete mixing.
U.S. Pat. No. 4,645,537 and 4,576,835 to Garderlier et al. disclose an aqueous release
agent for hot melt pressure sensitive adhesives and a method for applying the same to hot melt
25 pressure sensitive adhesives. It was desired in Gardenier that the antiadhesive or nontacky
surface be temporary. The pressure sensitive adhesive of Gardenier show no substantial
difference in physical characteristics before and after addition of the release agent.
U.S. Pat. No. to Durbin et al. discloses the interfacial polymerization of one polymer
onto a second polymer to provide a non-tacky, non-porous outer coating or shell to prevent
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blocking and water entrapment. This teaches using condensation polymers to forrn a protective
coating on the polymer, but have no permanent effect on the surface tack of the polymers, and
therefore can be used in pressure sensitive hot melt adhesives.
U.S. Pat. No. 3,723,03S discloses a machine and an improved method of packaging a
5 hot melt adhesive. This produces an er.d product known as pillows in the industry. These
pillows can be coextruded with a non-tacky polymer such as polyethylene for producing
pressure sensitive adhesives that are non-tacky at room ternperature. This coextrusion coating
prevents the pillows from blocking together in a solid mass at room temperature.This as well as other packaging methods discussed above produce hot melt adhesives in
10 non-tacky packages. However, once the coextruded pillows, as well as others are melted for
use on an application line, the hot melt composition returns to being tacky again.
The key to all of the above methods, is that the packaging film or detackifying means
are compatible with the adhesive so as to not change the resu~ting physical characteristic of the
adhesive. Thus, the adhesive remains tacky at room temperature after the adhesive and its
15 package have been melted together.
The present invention is novel and different from all of the above disclosures in that it
utilizes a pelletizing aid to change the physical characteristics of the hot melt pressure sensitive
compositions to allow for their use in other applications such as injection molding. The
compositions can be used to produce non-tacky articles by injection molding. The present
20 invention therefore allows the use of pressure sensitive hot melt compositions in applications
other than adhesives.
Summary Of The Inven~ion
The present invention discloses a polymeric composition in pellet forrn comprising:
I. From about 97 par~s to about 99.9 parts by weight of a tacky hot melt
composltlon comprislng:
a) from about 2.0 to about 20 percent by weight of a high molecular weight block
copolymer having the general configuration A-B-A and a molecular weight
greater than about 200,000;
b) up to about 30 percent by weight of at least one compatible block copolymer;
and
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c) from about 20 to about 98 percent by weight of a compatible viscosity modifier;
and
II. from about 0.1 to about 3.0 percent by weight of a pelletizing aid.
These resultant compositions are further characterized by a viscosity of greater than
about 500 cps at 1 77C, specific gravity of greater than about 0.8, and Mettler Softening Points
of greater than about 90C. The pellets thus formed are soft, non-blocking, substantially
without surface tack, and exhibit an elastic rebound, as characteriæd by G' (elastic or storage
modules) measurements. These pellets are suitable for use in molding, especially injection
molding. Any molded products produced therefrom also retain the substantially surface tack
free properties.
The pellets can be made into any convenient sizes. Preferably, the pellets are
substantially spherical, with sizes ranging from about 1/8 to about 3/8 inch (3mm to 10mm)
in diarneter for easy handling. The pellets can also be ellipsoidal and cylindrical. The
preferred dimensions for these shapes can range from about 3mm by 10mm to about 10mm by
20mm. While the rest of the composition deterrnines the overall bulk properties of the pellets
and articles molded therefrom, the pelletizing aid determines the surface properties of not only
the pellets, but the articles made from such pellets.
The present invention further discloses articles molded from polymeric compositions in
pellet form comprising:
a) a tacky hot melt composition comprising;
1 ) at least one high moiecular weight triblock copolymer of the general
configuration A-B-A; and
2) a plasticizer; and
b) a pelletizing aid,
25 wherein said pelletizing aid substantially surrounds the tacky composition such that the molded
articles are soft, non-blocking and substantially without surface tack. Optionally, other
polymers such as diblock or other triblocks can be added.
Injection molded articles produced from such compositions can include shoe soles,
drum pads, toys, therapeutic hand exercising grips, shock absorbers, acoustical insulators,
`-- 216437~
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synthetic skin, masks, chair pads and so on. These compositions have potential for use in any
article that can be injection molded, and is not limited to injection molded articles.
The present invention also discloses an under-water pelletizing process, utilizing a
pelletizing aid to produce pellets that are substantially free of surface tack, soft and non-
5 blocking. The process varies slightly for each product depending on the plasticizer loading,and comprises the steps of:
a) blending the hot melt components to form a substantially homogenious hot melt mixture;
b) forcing said substantially homogeneous hot melt mixture through a die for
forming substantially homogeneous hot melt ribbons and forming resultant
pellets therefrom;
c) solidifying said pellets by use of a cooling medium;
d) applying said pelletizing aid.
Detailed Descriptions
The polymeric composition of the present invention comprises a high molecular weight
triblock copolymer. This copolymer presents in amounts of about 2 to about 20 percent by
weight, preferably from about S to about 20 percent by weight, ar d is a subst~ntially linear A-
B-A block copolymer having a molecular weight in excess of about 200,000 as measured by
Gel Permeation Chromatography, with values reported relative to polystyrene standards,
wherein said A block can be polystyrene and said B block can be ethylene-butylene, ethylene-
propylene, or mixtures thereof. Polymers of this type, such as Kraton G- 1651, are of
substantially h~gher molecular weight than conventional S-EB-S block copolymers generally
used in the hot melt adhesive industry.
A compatible A-B-A triblock copolymer, A-B diblock copolymer, and A-B-A-B-A-B
multiblock copolymer, radial block copolymer, and grafted versions of such copolymers can
also be present and include Shell Chemical's TKG-IOI and RP-6912, and A-B-A block
copolymers as disclosed in Collins et al., U.S. Pat. No. 4,136,699 or available under the
tradename of Kraton G- 1650 commercially available from Shell Corporation. Smallconceht-ations of less than about 4 percent of Kraton G- 1651 may also be blended with other
polymers such as EVA and EMA as well as crystalline and amorphous polyolefins if onc
21~4376
desires to reduce the viscosity and improve processability of the composition and/or increase
the tack for some applications.
The plasticizer is broadly defined as a typically organic composition that can be added
to thermoplastics, rubbers, and other resins to improve extrudability, flexibility, workability or
5 stretchability and is chosen in such a way that the resultant softness and tack-free
characteristics of both the pellets and the subsequently produced articles are met. Fluid or
liquid plasticizers are preferred. Such fluid ingredient may be provided as a liquid resin, a
liquid elastomer, or any other material which flows at ambient temperatures and is compatible
with the block copolymer.
The plasticizers useful herein are those selected from the group consisting of mineral or
petroleum based hydrocarbon oils, polybutene, liquid tackifying resins, liquid elastomers, or
functionalized oils such as glyceryl trihydroxyoleate or other fatty oils. The oils used are
primarily hydrocarbon oils and are low in aromatic content and are paraffinic or naphthelnic in
character. The oils are preferably low in volatility, are transparent, or have minim~l color and
15 odor. The use of plasticizers in this invention also contemplates the use of olefin oligomers,
low molecular weight polymers, vegetable oils and their derivatives and similar plasticizing
liquids. These plasticizers are useful in amounts up to about 98 percent by weight, preferably
up to about 90 percent.
The pelletizing aid is selected from the group consisting of polyethylene, modified
20 polyethylene, polyamide or steararnide waxes. Many other waxes or other pelletizing aids not
on this list could also be useful provided the resultant softness and tack-free properties are met.
The pelletizing aid is capable of substantially surrounding the pellet and the surface of the
articles formed remained non-tacky. Preferred waxes are Acrawax CTM stearamide wax
available from Lonza, Inc. in Fairlawn, NJ, Castor hydroxy waxes and ParicinTM hydroxyamide
25 waxes available from Caschem in Bayonne, NJ, Neptune 968T~ available from Shamrock
Technologies in Newark, NJ, Shamrock S-395 rM polyethylene wax available from Shamrock
Technologies in Newark, NJ, Hoechst Wax PED 1217~ modified polyethylene available from
Hoechst Celanese in Somerville, NJ. More preferably, these pelletizing aids are polyethylene
waxes and come in powder form.
216~376
The pellelizing aid is present in small amounts compared to the total hot melt
composition. It is present from about 0.1 to about 3 percent by weight, preferably from about
0.1 to about I percent by weight. This amount is substantially less or comparable to the
packaging film of prior art packaging methods.
S As discussed above, the pellets thus formed are soR, non-blocking, substantially
without surface tack and exhibit an elastic rebound. rhis last characteristic can be measured by
the elastic or storage modulus (G'). The higher the modulus, the more likely for the material to
go back to its original shape. Depending on the applications, the preferred amounts of the
triblock copolymers used can vary. At lower loadings of the high molecular weight triblock
copolymer, the pellets forrned resemble gels. They possess some elastic rebound, but tend to
retain same physical property over a wide-temperature range, or over a long time frame. These
pellets are desirable for making articles such as Santa Claus' bellies. At higher loadings of this
copolymer, the pellets formed have high elastic modulus and hence, tend to return to their
original shape faster. They are more suited for producing articles such as drum pads.
Compatible polymers or copolymers discussed above can also be added to modify the
properties of the pellets. These are generally of low molecular weight, and pellets made with
an amount of the high molecular weight triblock copolymer tend to have more rebound than
those made with the same amount of a blend of this copolymer and the low molecular weight
compatible polymer or copolymer. These compatible polymers or copolymers are thus added
for customizing the final applications or uses.
These pellets are suitable for use in molding, especially injection molding. Thecomposition suitable for such processes comprises:
a) a tacky hot melt composition comprising;
I) at least one high molecular weight triblock copolymer of the general
configuration A-B-A; and
2) a plasticiær; and
b) a pelletizing aid;
wherein said pelletizing aid substantially surrounds the tacky composition such that the molded
articles are soft, non-blocking and substantially without surface tack. Optionally, other-
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polymers such as diblock or other triblocks can be added. Preferably, the tacky hot melt
composition comprises from about 97 to 99.9 percent by weight of the article, more preferably
from about 99 to 99.9 percent by weight.
Any molded articles produced therefrom also retain the substantially surface tack-free
5 properties and rebound. Such articles can include drum pads useful as acoustical pads for
vibration damping, disc players, ear phones, percussion surfaces on electronic drum kits and so
on; soles, shoe insoles, in-line skate soles and so on; pads for use in athletic gear such as
mouth pads, protective guards, encapsulants for other solid protective pads and so on; bicycle
seats, gloves, bicycle shorts and so on; medical equipments such as pads for wheel chairs,
10 donut-shaped pads for seats and so on; furniture pads such as mattress pads, chair pads and so
on; special effects articles such as body parts, Santa Claus belly, and others that are useful in
movies. Unlike the prior art, the pelletizing aid used herein blooms to the surface during the
molding process, such that it substantially completely surrounds the tacky composition below
and produces ar~icles substantially free of surface tack when cooled. Tl~s is surprising
15 because the amount of pelletizing aid used in the formu~ation is small, and according to prior
art teachings, should not substantially interfere with the properties of the bulk composition, nor
should it change the surface properties.
The present invention further discloses a method for making such pellets. The
manufacturing process can vary slightly for each product depending on the plasticizer
20 loading. The current process requires multiple passes through a co-rotating twin screw with
the product being pelletized at the end of each pass and then refed into the extruder for
the further addition of plasticizer. The 90 percent plasticizer materials require three passes,
while lower plasticizer loadings may only require two passes. It is important to note that the
materials are pelletized with the pelletizing aid after both passes. llle concentration of the
25 pelletizing aid in the water can range from about 0.1 percent to about 3 percent by weight,
preferably about 0.1 to about lwt percent based on anticipated production rate for each pass. A
specific, preferred manufacturing process comprises:
a) blending the hot melt components to form a substantially homogeneous hot melt mixture;
_- 2164376
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b) forcing said substantially homogeneous hot melt mixture through a die having a
series of voids in a circular pattern to form a series of substantially
homogeneous hot melt ribbons;
c) further forcing said homogeneous hot melt ribbons past rotating blades in
substantially parallel position to said die, cutting said substantially
homogeneous hot melt ribbons to forrn resultant pellets;
d) substantially solidifying said pellets by use of a liquid cooling mediurn said
liquid cooling medium containing a pelletizing aid, being circulated past said
die and rotating blades on the side where said substantially homogeneous hot
melt ribbons emerge;
e) transporting said hot melt pellets to a drying area;
f) substantially removing liquid from said hot melt pellets by blowing.
As depicted above, the pelletizing aid is present in the cooling medium. It can also be
added to the hot melt composition prior to blending or during the pelletizing steps by co-
feeding a solution of pelletizing aid with the hot melt composition.
It is well known in the art that stabili~ers or antioxidants can also be used in the
compositions to protect against heat or light induced degradation. These compounds are added
to the compositions in small arnounts, are inert, and therefore have no effect on the other
physical properties of the compositions. Other compounds that could be added that also do not
effect physical properties are pigments for color, fluorescing agents, and any compounds that
mask odor. Additives such as these are known to one of skill in the art.
This invention is further illustrated by the following non-limiting examples.
F~amples
Test Methods
1. Melt Viscosities
The melt viscosities of the hot melt adhesives were deterrnined on a Brookfield
Thennosel Viscometer Model DV-II+. The viscosities are reported in centipoise.
(rnPascc)
30 2. S~ecific GraYitY
-- ~16437b
The specific gravity was determined using test method ASTM D792 with isopropyl
alcohol as the liquid.
3. Mettler SoRenin~ Point
The Mettler softening points are deterrnined using test method ASTM D3461.
5 4. nyn~rnic Temperatllre Steps
Storage modulus (G') and Tg were determined using a Rheometrics Scientific Dynamic
Mechanical Spectrometer Model #RDS7700. The parallel plates used had a 25 mm
diameter and a 1.502 mm gap. The instrument was set to a frequency of 10 rads/sec
and temperature sweep was performed from 180C to -50C.
10 5. Rloom Gelometer
Rigidity of the samples was determined using a Precision Bloom Gelometer CatalogNo. 68705.
E~amples 1~:
The following adhesive formulations are provided for illustrative purposes only.These examples illustrate the physical properties achieved with these types of hot melt
compositions but there are many more compositions with differing physical characteristics.
These compositions are listed in Table 1.
The dynamic properties (G') were measured as described above and are shown in figure
20 1. The higher the G' value, the more elastic character, and hence t'ne higher tendency to
return to its original shape. These were also tested for other properties and the measurements
are shown in Table 2.
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Table I
Composition By Weight Percent
F~ample 1 ~ ~ 4
Kraton G1651 10.0 5.0 7.0 7.0
Kraton G1650 -- 5.0 12.0 17.0
Kaydol Oil 89.5 89.5 80.0 75.0
* Antioxidant 0.1 0.1 1.0 o.5
** W Absorber 0.4 0.4 -- o.5
*** Pigment -- Minute Amount Minute Arnount
About 0.1% Shamrock S-395 Pelletizing aid was added to each of the compositions.* Either Irganox 1076 antioxidant or Irganox 1010 antioxid~nt or a blend of the two may be used.
** A blend of approximately half Tinuvin 770 and half Tinuvin 328 was u~ed.
*** Minute arnounts of either Sudan Blue 670, Sudan Orange 220, or Sudan Yellow 146 or blends
thereof may be used.
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Table 2
Physical Characteristics
E~ample 1 2 3 4
Method Used
Specific ASTM D792 0.86 0.85 0.86 0.86
Gravity
Density (#/gal) " 7.1 7.1 7.1 7.2
Viscosity ,~ 143,250 cp 1,700 cp
325 F
Viscosity ~ 21,625 cp 770 cp
3S0F
Viscosity ,~ 4,350 cp 190 cp
375F
Viscosity ~ 1,060 cp 60 cp
400F
Mettler ASTM D3461 282.8 + 2.9 255.8 _ 0.3
SoRening Pt
~)
G' at 300F RDS - Parallel 2.64E+04 3.29E+03 4.24E+03 4.18E+04
Plates
G' at 200F Frequency =1 4.76E+04 1.97E+04 5.1 IE+04 2.1 lE+05
O rad/s
G' at 77F Initial Temp = 4.27E+04 3.12E+04 1.71E+05 5.14E+05
356F
Tg (upper) - " 97.9 (208.2) 104.9 (220.8)
C (F)
Tg(lower)- " -58.1 (-72.6) -SS.S (-67.9) -54.3 (-65.7) -56.9 (-70.4)
C ~F)
