U.S. patent application number 09/986776 was filed with the patent office on 2003-05-08 for silane-grafted materials for solid and foam applications.
This patent application is currently assigned to Sentinel Products Corp., a New York corporation. Invention is credited to Bambara, John D., Hurley, Robert F., Kozma, Matthew L..
Application Number | 20030087976 09/986776 |
Document ID | / |
Family ID | 25014980 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030087976 |
Kind Code |
A1 |
Bambara, John D. ; et
al. |
May 8, 2003 |
Silane-grafted materials for solid and foam applications
Abstract
New cross-linked polymeric foam compositions, and methods for
making the same, are provided. The new compositions utilize novel
cross-linked polyolefin copolymers and show improvements in
strength, toughness, flexibility, heat resistance and heat-sealing
temperature ranges as compared to conventional low density
polyethylene compositions. The new compositions also show
processing improvements over linear low density polyethylene. The
novel polyolefins, which are essentially linear, comprise ethylene
polymerized with at least one alpha-unsaturated C3 to C20 olefinic
comonomer, and optionally at least one C3 to C20 polyene, and
exhibit, in an uncross-linked sense, a resin density in the range
of about 0.86 g/cm.sup.3 to about 0.96 g/cm.sup.3, a melt index in
the range of about 0.5 dg/min to about 100 dg/min, a molecular
weight distribution in the range of from about 1.5 to about 3.5,
and a composition distribution breadth index greater than about 45
percent. The polyolefins are silane-grafted to enhance the physical
properties and processability of the resins. Slow silane-grafted
materials exhibit enhanced physical and processing properties.
Inventors: |
Bambara, John D.;
(Osterville, MA) ; Kozma, Matthew L.; (Osterville,
MA) ; Hurley, Robert F.; (Centerville, MA) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Assignee: |
Sentinel Products Corp., a New York
corporation
|
Family ID: |
25014980 |
Appl. No.: |
09/986776 |
Filed: |
November 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09986776 |
Nov 9, 2001 |
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09557261 |
Apr 24, 2000 |
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6316512 |
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09557261 |
Apr 24, 2000 |
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09270583 |
Mar 16, 1999 |
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6103775 |
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09270583 |
Mar 16, 1999 |
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08749740 |
Nov 15, 1996 |
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5883144 |
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08749740 |
Nov 15, 1996 |
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08308801 |
Sep 19, 1994 |
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Current U.S.
Class: |
521/144 ;
264/232; 264/239; 264/45.7; 264/45.9; 521/79; 521/82; 525/191;
525/63; 525/64; 525/70 |
Current CPC
Class: |
C08L 23/0869 20130101;
C08L 23/28 20130101; C08J 2323/02 20130101; C08J 9/04 20130101;
C08L 23/16 20130101; C08J 2323/16 20130101; C08L 83/04 20130101;
C08J 9/0061 20130101; C08L 2312/08 20130101; C08F 255/08 20130101;
C08J 2451/00 20130101; C08L 23/10 20130101; C08L 23/04 20130101;
C08L 2205/03 20130101; C08L 2205/02 20130101; C08F 8/00 20130101;
C08J 2423/00 20130101; C08L 51/085 20130101; C08L 2205/035
20130101; C08L 51/06 20130101; C08J 2351/00 20130101; C08L 23/0815
20130101; C08F 255/02 20130101; C08L 2314/06 20130101; C08J 9/103
20130101; C08J 2201/03 20130101; C08L 23/08 20130101; C08L 2312/00
20130101; C08L 23/06 20130101; C08F 255/00 20130101; C08L 23/0853
20130101; C08J 2425/00 20130101; C08L 91/00 20130101; C08L 23/04
20130101; C08L 83/00 20130101; C08L 23/0815 20130101; C08L 2666/24
20130101; C08L 23/0815 20130101; C08L 2666/02 20130101; C08L
23/0853 20130101; C08L 2666/02 20130101; C08L 23/0853 20130101;
C08L 2666/24 20130101; C08L 23/0853 20130101; C08L 2666/06
20130101; C08L 23/10 20130101; C08L 83/00 20130101; C08L 23/16
20130101; C08L 2666/02 20130101; C08L 51/06 20130101; C08L 2666/24
20130101; C08L 51/06 20130101; C08L 2666/02 20130101; C08L 51/06
20130101; C08L 2666/06 20130101; C08L 51/085 20130101; C08L 2666/04
20130101; C08F 8/00 20130101; C08F 210/02 20130101; C08L 23/06
20130101; C08L 2666/02 20130101; C08L 23/0815 20130101; C08L
2666/06 20130101; C08L 23/10 20130101; C08L 2666/24 20130101; C08F
255/00 20130101; C08F 222/06 20130101; C08L 23/10 20130101; C08L
2666/06 20130101; C08L 23/16 20130101; C08L 2666/06 20130101; C08L
51/06 20130101; C08L 2666/04 20130101; C08L 23/06 20130101; C08L
2666/06 20130101; C08F 255/00 20130101; C08F 230/085 20200201 |
Class at
Publication: |
521/144 ; 521/79;
521/82; 525/63; 525/64; 525/70; 525/191; 264/45.7; 264/45.9;
264/232; 264/239 |
International
Class: |
C08F 210/00 |
Claims
What is claimed is:
1. A polyolefin article comprising a silane-grafted single-site
initiated olefin copolymer resin having a silane-graft content of
up to 6 percent, the silane including a hydrolyzable group.
2. The polyolefin article of claim 1, comprising a partially
cross-linked polyolefin blend, the polyolefin blend including the
single-site initiated olefin copolymer resin.
3. The polyolefin article of claim 1, wherein the single-site
initiated olefin copolymer resin is a polyethylene, a copolymer of
ethylene and a C3-C20 alpha-olefin, a polypropylene, or a copolymer
of ethylene, a C3-C20 alpha-olefin and a C4-C20 diene.
4. The polyolefin article of claim 1, wherein the article has a gel
content of between 10 and 100 percent.
5. The polyolefin article of claim 1, wherein the single-site
initiated olefin copolymer resin contains between about 0.1 and 2
percent silane-graft.
6. The polyolefin article of claim 1, wherein the silane includes a
vinyl silane having 2 or 3 hydrolyzable groups.
7. The polyolefin article of claim 1, wherein the hydrolyzable
group is an alkoxy groups.
8. The polyolefin article of claim 5, wherein the polymer blend
further comprises a copolymer including ethylene and propylene, an
ethylene-propylene-diene terpolymer, an ethylene-vinyl acetate
copolymer, an ethylene-maleic anhydride copolymer, an
ethylene-ethyl acetate copolymer, a low density polyethylene, a
linear low density polyethylene, a medium density polyethylene, a
high density polyethylene, or a polypropylene.
9. The polyolefin article of claim 8, wherein the polyolefin blend
is partially silane-grafted.
10. The polyolefin article of claim 1, further comprising maleic
anhydride.
11. The polyolefin article of claim 1, wherein the article is
foamed.
12. The polyolefin article of claim 11, further comprising a cell
nucleating agent and a gas exchange additive.
13. The polyolefin article of claim 11, wherein the foamed
polyolefin blend is in the form of a sheet, plank, laminated plank,
bead, or extruded profile.
14. The polyolefin article of claim 11, wherein the foamed
polyolefin blend has an average foam density between 1.0 and 50
pounds per cubic foot.
15. The polyolefin article of claim 1, wherein the silane comprises
an alkyl trialkoxy silane, where the alkyl is a C1 to C20 group and
the alkoxy is a C1 to C10 group.
16. The polymer article of claim 11, wherein the foamed article is
a closed cell foam.
17. The polymer article of claim 11, wherein the foamed article is
an open cell foam.
18. A method of making a polymer article comprising the steps of:
providing a mixture including silane-grafted single-site initiated
olefin copolymer resin, the silane including a hydrolyzable group;
and cross-linking the polymer mixture.
19. The method of claim 18, wherein the mixture is a silane
cross-linkable polymer blend.
20. The method of claim 18, wherein the providing step includes the
step of blending the single-site initiated olefin copolymer resin
with a copolymer including ethylene and propylene, an
ethylene-propylene-diene terpolymer, an ethylene-vinyl acetate
copolymer, an ethylene-maleic anhydride copolymer, an
ethylene-ethyl acetate copolymer, a low density polyethylene, a
linear low density polyethylene, a medium density polyethylene, a
high density polyethylene, or a polypropylene.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. Ser.
No. 08/749,740, filed Nov. 15, 1996, which is a
continuation-in-part of co-pending U.S. Ser. No. 08/308,801, filed
Sep. 19, 1994.
BACKGROUND OF THE INVENTION
[0002] The invention relates to the silane-grafting of polyolefin
materials to enhance the properties of the materials.
[0003] Current art for the production of cross-linked polyolefin
foam structures involves the use of conventional high-pressure
reactor-produced, low density polyethylene (LDPE). LDPE is
comprised of a wide-ranging distribution of branch lengths, best
characterized as "long- but variable-chain branching", and a
molecular weight distribution (Mw/Mn) which is generally greater
than about 3.5. LDPE resin densities, which directly relate to the
resulting bulk property stiffness, typically range between 0.915 g
cm.sup.-3 to about 0.930 g cm.sup.-3, thus limiting the degree of
mechanical flexibility in foam structures thereof since the lower
limit of secant moduli for LDPE is about 20 ksi. While
processability of LDPE is quite good, the physical properties, in
particular the tensile strength, low-temperature flexibility and
toughness, are less than would be obtained from a linear low
density polyethylene (LLDPE), due in part to the substantially
non-linear nature of LDPE and the profusion of "long-chain
branches."
[0004] Conventional linear low density polyethylene (LLDPE)
exhibits physical properties which are superior to that of LDPE at
about the same range of resin densities, but show somewhat higher
secant moduli and are difficult to process, resulting in foams with
poor cell structure and higher than desired foam structure
densities. LLDPE resins, produced by conventional Ziegler
transition metal catalysts in the copolymerization of ethylene with
one or more alpha-unsaturated monomers, exhibit considerably
narrower molecular weight distributions than LDPE, higher molecular
weights, and typically only about 15-20 "short-chain branches" per
1000 carbon atoms. Melt-processing in general, and foam processing
in particular, are greatly enhanced by the ability of the resin to
"shear-thin" or demonstrate a strong, inverse dependency of melt
viscosity toward shear rate. "Shear thinning" increases with the
degree of branching, which is exemplified in the relative
shear-insensitivity of LLDPE and particularly HDPE and resulting
foam processing difficulty. Commercially-available LLDPE resins
with densities below about 0.910 g/cc are unavailable, thus further
limiting the flexibility of foam structures thereof.
[0005] Very low density polyethylene (VLDPE) is a special subset of
LLDPE wherein an even greater number of "short-chain branches" (ca.
30-50 per 1000 carbon atoms) are effected by appropriate level of
comonomer to result in much lower resin densities than LLDPE, e.g.
0.88 g cm.sup.-3 to 0.91 g cm.sup.-3. These materials thus exhibit
greater flexibility than LLDPE. However, generally with
conventional linear polyolefins, the greater the number of
"short-chain branches," the lower the resulting resin density, but
also the shorter the length of the molecular backbone. The presence
of shorter molecular backbones, with greater comonomer content
therein, prematurely leads to a phenomena known as "melt fracture,"
which is manifested as the onset of perturbations at the surface of
an extrudate with increasing shear rate, resulting in loss of
control of the quality of such profiled, extrudable materials.
[0006] Certain other undesirable structural features accompany
efforts to increase "short-chain branching" while employing
conventional linear polyethylene technology, such as an increase in
the non-uniformity of the distribution of branches on the molecular
backbone. Additionally, conventional linear polyethylene technology
leads to a distribution of molecular weights, with a greater
propensity of incorporation of the alpha-unsaturated comonomer into
the lower molecular weight fractions, thereby leading to melt
fracture. Also, as a result of this non-uniformity of molecular
weights and distribution of comonomeric species within and among
the distribution thereof, linear polyolefins exhibit less than
optimal performance in various parametric standards such as
toughness, particularly at low temperatures, and stability of
extrusion, particularly at high rates.
[0007] Many of the above noted deficiencies in the foamable
polyolefin art could be satisfied through the use of a linear
olefinic resin which is essentially free of "long-chain branches",
and which has a molecular weight that is sufficiently high to
preclude melt-fracture, a narrow molecular weight distribution, a
considerable melt-viscosity/shear rate sensitivity and a full range
of resin densities. Such a linear polyolefin would exhibit the
preferred balance of physical properties, would exhibit good
toughness and processability, and would be available in a range of
resin flexibilities. It is thus an object of this invention to
provide a linear olefinic resin which possesses these
characteristics.
[0008] Various catalysts are known to the art of polyolefin foams.
"Metallocenes" are one class of highly active olefin catalysts,
well known in the art of preparation of polyethylene and copolymers
of ethylene and alpha-unsaturated olefin monomers. U.S. Pat. No.
4,937,299 (Ewen et al.) teaches that the structure of the
metallocene catalyst includes an alumoxane which is formed when
water reacts with trialkyl aluminum with the release of methane,
which complexes therein with the metallocene compound to form the
active catalyst. These catalysts, particularly those based on group
IV B transition metals such as zirconium, titanium and hafnium,
show extremely high activity in ethylene polymerization.
[0009] Metallocene catalysts have great versatility in that, by
manipulation of process conditions such as catalyst composition and
reactor conditions, they can be made to provide polyolefins with
controlled molecular weights from as low as about 200 to about 1
million or higher. Exemplary of the latter case is ultra-high
molecular weight linear polyethylene. At the same time, the
molecular weight distribution of the polymers thereof can be
controlled from extremely narrow to extremely broad, i.e. from less
than 2 to greater than 8.
[0010] Metallocene catalysts are particularly advantageous in the
preparation of copolymers of ethylene and one or more
alpha-unsaturated olefin comonomers to provide highly random
distributions of comonomer within each and every molecular
backbone, while separately controlling the average molecular weight
as well as the distribution of molecular weights about the average.
It is thus an object of the present invention to use the
versatility of metallocene catalysts to produce linear olefinic
resins having the aforementioned properties.
[0011] These and other objects are realized by the present
invention, as disclosed herein.
SUMMARY OF THE INVENTION
[0012] In one aspect, the invention features a polyolefin article
including a silane-grafted essentially linear olefin copolymer
resin having a silane-graft content of up to 6 percent, more
preferably 0.1 to 2 percent. The essentially linear olefin
copolymer resin has a density between about 0.86 and about 0.96 g
cm.sup.-3, a molecular weight distribution between about 1.5 and
about 3.5, a melt index in the range of about 0.5 dg/min to about
100 dg/min, and a composition distribution breadth index greater
than about 45 percent. In preferred embodiments, the essentially
linear olefin copolymer resin is a polyethylene, a copolymer of
ethylene and a C3-C20 alpha-olefin, a polypropylene, or a copolymer
of ethylene, a C3-C20 alpha-olefin and a C4-C20 diene. The silane
includes a vinyl silane having a C2 to C10 alkoxy group. In
preferred embodiments, the silane includes a vinyl silane having 2
or 3 hydrolyzable groups. Preferably, the hydrolyzable groups are
C2-C10 alkoxy groups. Most preferably, the silane includes vinyl
triethoxysilane. In foamed polyolefin articles, the silane includes
a vinyl silane having a C1 to C10 alkoxy group.
[0013] In preferred embodiments, the article includes a partially
cross-linked polyolefin blend which includes the essentially linear
olefin copolymer resin. Preferably, the article has a gel content
of between 10 and 100 percent. The polymer blend can include
between about 5 and 95 weight percent of the essentially linear
olefin copolymer resin.
[0014] In preferred embodiments, the polymer blend includes a
copolymer including ethylene and propylene, an
ethylene-propylene-diene monomer terpolymer, an ethylene-vinyl
acetate copolymer, an ethylene-maleic anhydride copolymer, an
ethylene-ethyl acetate copolymer, a low density polyethylene, a
linear low density polyethylene, a medium density polyethylene, a
high density polyethylene, or a polypropylene. The polyolefin blend
can be partially silane-grafted.
[0015] In preferred embodiments, the silane can further include an
alkyl trialkoxy silane, where the alkyl is a C1 to C20 group and
the alkoxy is a C1 to C10 group.
[0016] In preferred embodiments, the article is foamed. The foamed
article can including a cell nucleating agent and a gas exchange
additive. Preferably, the foamed polyolefin blend is in the form of
a sheet, plank, laminated plank, bead, or extruded profile. The
preferred foam has an average foam density between 1.0 and 50
pounds per cubic foot. The foam can be a closed cell foam or an
open cell foam.
[0017] In another aspect, the invention features a method of making
a polymer article including the steps of providing a mixture
including silane-grafted essentially linear olefin copolymer resin
and a foaming agent and cross-linking the polymer mixture, where
the silane includes a vinyl silane having a C2 to C10 alkoxy
group.
[0018] In preferred embodiments, the method includes the step of
silane-grafting a portion of the mixture.
[0019] In other preferred embodiments, the method includes the step
of expanding the polymer blend to form a foam. The polymer blend
can be cross-linked prior to the expanding step. Alternatively, the
cross-linking can occur after the expanding step. The cross-linking
can occur by exposing the polymer mixture to moisture, reacting the
polymer blend with a peroxide, or, at times, both.
[0020] In preferred embodiments, the mixture is extruded.
[0021] In other preferred embodiments, the expanding step includes
compression molding the polymer mixture at increased temperature
and pressure. The compression molding can include the steps of
pressing the polymer mixture using a high tonnage press at a
temperature of between 275 and 320.degree. F. and a pressure of
between 250 and 2500 psi for between 20 and 90 minutes followed by
heating the polymer mixture at a temperature between 300 and
380.degree. F.
[0022] In other preferred embodiments, the method includes applying
a coating to the polymer article.
[0023] According to one embodiment of the present invention, there
is provided a method of producing a foamed, cross-linked structure
comprising the steps of: (a) providing a polymeric composition
which is composed of at least 5% and up to 100% of a polyolefin
copolymer, wherein said copolymer is produced from ethylene and one
or more alpha-unsaturated ethylenic monomers, and is substantially
free of "long-chain branching"; (b) inducing the cross-linking
reaction; and (c) expanding the composition. In this embodiment,
the polyolefin copolymer comprises a polymer selected from the
group of ethylene polymerized with at least one comonomer selected
from the group consisting of at least one alpha-unsaturated C3 to
C20 comonomer and optionally at least one C3 to C20 polyene, has a
resin density in the range of about 0.86 g cm.sup.-3 to about 0.96
g cm.sup.-3, a melt index in the range of about 0.5 dg/min to about
100 dg/min, a molecular weight distribution in the range of from
about 1.5 to about 3.5, and a composition distribution breadth
index greater than about 45 percent.
[0024] According to another embodiment of the present invention,
there is provided a method of producing a foamed, cross-linked
structure comprising the steps of: (a) providing a polymeric
composition which comprises at least 5% and up to 100% of a
polyolefin copolymer, wherein said copolymer is produced from
ethylene and one or more alpha-unsaturated ethylenic monomers and
is substantially free of branch lengths exceeding 20 carbon atoms;
(b) inducing the cross-linking reaction; and (c) expanding the
composition.
[0025] The expansion of the composition may be accomplished by use
of a decomposable foaming agent, or by use of a
physically-expanding, volatile foaming agent. The cross-linking may
be effected by reacting the foam composition with a silane
cross-linking agent, which may be subsequently combined with other
polymeric resins, and then effecting the cross-linking by exposing
the mixture to moisture, possibly with the use of a suitable
silanol condensation catalyst.
[0026] In other embodiments, the cross-linking of the polymeric
composition is effected by free-radical initiators, or by
irradiation.
[0027] In the preferred embodiment, the cross-linked foam
structures exhibit 70% or greater closed-cells, and densities
greater than about 0.7 lb/cu.ft. but less than about 22
lb/cu.ft.
[0028] Polyolefinic foams can be produced either through the use of
physical or chemical foaming agents.
[0029] The present invention also contemplates the addition of
other resins, particulate and fibrous fillers, antioxidants,
ultra-violet and thermal stabilizers, pigments and colorants,
cell-growth nucleants such as talc, cell-structure stabilizers such
as fatty acids or amides, property-modifiers, processing aids,
additives, catalysts to accelerate cross-linking and other
reactions, and other materials which will be obvious to one skilled
in the art.
[0030] A slow silane is a silane cross-linking agent that
hydrolyzes (i.e., cross-links) more slowly than VTMOS. It can take
a longer time to cure a slow silane-grafted material than a VTMOS
grafted material.
[0031] The invention can have one or more of the following
advantages. The enhancement in the properties of slow
silane-grafted polyolefinic materials prepared by the methods of
the invention can be demonstrated by, for example, improvement in
the cross-linking behavior of the polymers, improvement in the
processing characteristics of the foam materials, and improvement
in the surface bonding. properties of the polymer materials.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a graph depicting the cross-linking rate, as
indicated by an increase in torque in the mixer over time, of an
essentially linear olefin copolymer grafted with VTMOS at
163.degree. C.
[0033] FIG. 2 is a graph depicting the cross-linking rate, as
indicated by an increase in torque in the mixer over time, of an
essentially linear olefin copolymer grafted with VTEOS at
163.degree. C.
[0034] FIG. 3 is a graph depicting the cross-linking rate, as
indicated by an increase in torque in the mixer over time, of an
essentially linear olefin copolymer grafted with a mixture of VTEOS
and 9116 at 163.degree. C.
DETAILED DESCRIPTION
[0035] Foaming requires that polyolefins be capable of being
expanded and strong enough to sustain and contain gases in a
homogeneous group of cells (bubbles). Cross-linking of polyolefins
makes it possible to use previously unsuitable polyolefins in
foaming applications. The previously unsuitable polyolefins
included, but were not limited to, many types and grades of LDPE,
LLDPE, VLDPE, HDPE, EVA, PP, EVOH, EPDM, EPR, and blends thereof.
Cross-linking of polyolefinic materials can be effected through
several known methods including: (1) use of free radicals provided
through the use of organic peroxides or electron beam irradiation;
(2) sulfur cross-linking in standard EPDM (rubber) curing; (3) and
moisture curing of silane-grafted materials. The cross-linking
methods can be combined in a co-cure system or can be used
individually to make the polymer compositions foamable.
[0036] The cross-linking of the polyolefinic materials aids in the
formation of desirable foams and also leads to the improvement of
the ultimate physical properties of the materials. The level of
cross-linking in the material can be related to the physical
properties of the foam. The silane-grafting cross-linking mechanism
is particularly advantageous because it provides a change in the
polymer rheology by producing a new polymer structure having
improved physical properties.
[0037] Silane-grafting can be used to enhance the properties of
polymeric materials in all current types of polyolefinic foams
produced such as, for example, physically blown continuous sheet
materials, physically blown block (bun) materials, chemically blown
continuous sheet materials, and chemically blown block (bun)
materials. The foamed materials can be made by continuous extrusion
methods or by a batch mixing processes with subsequent
calendaring.
[0038] Silane-grafting cross-linking technology provides for the
grafting of a polyolefinic polymer with a hydrolyzable silane that
is subsequently hydrolyzed to form cross-links between grafted
polymer chains. The cross-linking can take place before or after
expanding the material as a foam. Although previous silane-grafted
polyolefins required the presence of a catalyst to have effective
cross-linking, the catalyst is no longer required in systems that
use VTEOS as the hydrolyzable silane. In particular, the
cross-links are formed during and after expanding the foam in the
present systems. By adjusting the levels of cross-linking and the
chemical nature of the hydrolyzable groups, the rates of
cross-linking and foaming can be controlled in order to provide
foams having enhanced physical properties.
[0039] The present invention is a unique class of cross-linked,
polyolefin foam compositions which, by virtue of the catalyst
technology and methods utilized in their preparation from monomeric
alpha-olefins, manifest a molecular structure that greatly
facilitates processing and exhibits superior physical properties
for cellular articles made therefrom.
[0040] There are a number of structural variables in polyolefin
copolymers which effect both the processing characteristics as well
as the ultimate physical properties of the polymer, and which thus
directly influence the processing and ultimate properties of
cross-linked compositions thereof. Two of the most important are
the uniformity of molecular weight and the uniformity of
distribution of comonomers within each, and among all, of the
polymeric molecular backbones.
[0041] The uniformity of both molecular weight and comonomer
distributions influences the toughness of polymeric materials and
articles made therefrom, particularly at low temperatures.
Likewise, these factors also influence the stability of melt
processability, particularly at high shear rates, as well as the
level and balance of other physical properties achievable in
articles formed thereof. Additionally, the type and amount of
comonomer employed along with ethylene in the polymerization, the
average molecular weight, melt index and specific gravity all
effect the properties of the subject polyolefin copolymer. The
intrinsic properties of the subject polyolefin copolymers along
with the relative amount of the copolymers and type and amount of
additional polymeric resins are a major factor contributing toward
the superiority of the compositions.
[0042] Polyolefin resins of this invention possess a narrow
molecular weight distribution and are "essentially linear,"
although they contain the desired level of uniformly distributed,
highly controlled "short-chain branching". As a result of this
combination, the resins exhibit a strength and toughness
approaching that of linear low density polyethylenes, but have
processability similar to high pressure, reactor produced low
density polyethylene. These "essentially linear" polyolefin resins
are characterized by a resin density in the range of about 0.86 g
cm.sup.-3 to about 0.96 g cm.sup.-3, a melt index in the range of
about 0.5 dg/min to about 100 dg/min, a molecular weight
distribution in the range of from about 1.5 to about 3.5, and a
composition distribution breadth index greater than about 45
percent.
[0043] As used throughout this disclosure, the term "linear
polyolefin" refers to an olefin polymer lacking "long-chain
branching," as exemplified by the conventionally produced linear
low density polyethylene or linear high density polyethylene
polymers made using Ziegler polymerization processes and disclosed,
for example, in U.S. Pat. Nos. 4,076,698 and 3,645,992. The term
does not refer to high pressure, reactor produced branched
polyethylenes, or to copolymers of ethylene and vinyl acetate,
vinyl alcohol, ethyl acrylate, methyl acrylate, acrylic acid, or
the like which are made using high-pressure technology and which
are known to have numerous long-chain branches.
[0044] As used throughout this disclosure, the term "essentially
linear" refers to a "linear polymer" with a molecular backbone
which is virtually absent of "long-chain branching," to the extent
that less than about 0.01 "long-chain branches" per one-thousand
carbon atoms are manifested thereof. Similarly, as used throughout
this disclosure, the phrase "substantially free from long-chain
branching" refers to a "linear polymer" with a molecular backbone
with less than about 0.01 "long-chain branches" per one-thousand
carbon atoms manifested thereof.
[0045] As used throughout this disclosure, the term "long chain
branching" refers to a molecular branch of a molecular backbone of
at least 6 carbon atoms, above which the length cannot be
distinguished using 13C nuclear magnetic resonance (NMR)
spectroscopy. The long chain branch can be as long as about the
same length as the molecular backbone. Methods of quantifying long
chain branching by use of 13C NMR spectroscopy were described by
Randall (Rev. Macromol. Chem. Phys., C29 (2&3), p.
285-297).
[0046] As used throughout this disclosure, the term "short-chain
branching" is defined as a molecular branch of a molecular backbone
of less than 6 carbon atoms which, as described above, would be
distinguishable by 13C NMR spectroscopic methods.
[0047] As used throughout this disclosure, the term "copolymer"
refers to material resulting from the polymerization of two or more
monomeric species, and specifically encompasses terpolymers (e.g.,
materials resulting from the polymerization of three or more
monomeric species), sesquipolymers, and greater combinations of
monomeric species thereof.
[0048] The densities, or specific gravities, of the resins herein
disclosed were measured using ASTM D-792 methods, except that they
were additionally conditioned by holding them for 48 hours at
ambient temperature (23.degree. C.) prior to the density
measurements. The essentially linear polyolefin resins disclosed in
this invention are generally characterized by a resin density in
the range of about 0.86 g cm.sup.-3 to about 0.96 g cm.sup.-3,
preferably of about 0.86 g cm.sup.-3 to about 0.91 g cm.sup.-3.
[0049] The "Melt Index" (MI) is a measurement of processability
under low shear rate conditions, in accordance with ASTM D-1238
Condition E (190.degree. C./2.16 kg) For the essentially linear
polyolefins disclosed in this invention, the MI is generally in the
range of about 0.2 dg/min to about 100 dg/min. Preferably, the MI
is in the range of about 1 dg/min to about 10 dg/min, and most
preferably in the range of about 2 dg/min to about 8 dg/min.
[0050] The molecular weight distribution (MWD or Mw/Mn) is a
parameter determined by use of gel permeation chromatography with
multiple mixed-porosity columns, comparing elution volumes of the
unknown to those of narrow MWD polystyrene standards. The
correspondence is accomplished by using the appropriate
Mark-Houwink coefficients for the polystyrene standard and the
polyethylene unknown, with procedures as described by Williams and
Word in Journal of Polymer Science, Polymer Letters, Vol. 6, (621)
1968, incorporated herein by reference.
[0051] The Composition Distribution Breadth Index (CDBI) is a
measurement of the uniformity of distribution of comonomer to the
copolymer molecules, and is determined by the technique of
Temperature Rising Elution Fractionation (TREF), as described in,
for example, Wild et. al., J. Poly. Sci., Poly. Phys. Phys. Ed.,
Vol. 20, p. 441 (1982). This attribute relates to polymer
crystallizability, optical properties, toughness and many other
important performance characteristics of compositions of the
present art. For example, a polyolefin resin of high density with a
high CDBI would crystallize less readily than another with a lower
CDBI but equal comonomer content and other characteristics,
enhancing toughness in objects of the present invention. The
benefits to the discovery of the subject invention that--accrue
through the specific use of essentially linear polyolefin
copolymers of narrow composition distribution are elucidated later
in the examples.
[0052] As used herein, the CDBI is defined as the weight percent of
the copolymer molecules having a comonomer content within 50% (i.e.
+/-50%) of the median total molar comonomer content. Unless
otherwise indicated, terms such as "comonomer content," "average
comonomer content" and the like refer to the bulk comonomer content
of the indicated interpolymer blend, blend component or fraction on
a molar basis. For reference, the CDBI of linear poly(ethylene),
which is absent of comonomer, is defined to be 100%. CDBI
determination clearly distinguishes the low density polyolefins of
this art, which show narrow composition distribution as assessed by
CDBI values generally above 70%, from very low density polyolefin
copolymers produced by conventional linear catalyst technology,
which have a broad composition distribution as assessed by CDBI
values generally less than 55%. The CDBI of the essentially linear
polyolefin copolymers disclosed in this invention is generally
about 45% or higher. Preferably, the CDBI is about 50% or higher.
More preferably, the CDBI is about 60% or higher, and most
preferably, about 70% or higher.
[0053] The "essentially linear" polyolefin copolymers of the
present invention are preferably produced through the use of
metallocene catalysts in accordance with any suitable
polymerization process, including gas phase polymerization, slurry
polymerization, and high pressure polymerization. However, the
methods of the present invention are not restricted to the use of
metallocene catalysts. Preferably, the "essentially linear"
polyolefins used in the foam compositions of the present invention
are produced by gas-phase polymerization. Gas phase polymerization
processes generally utilize super-atmospheric pressures and
temperatures in the range of about 50.degree. C. to about
120.degree. C. Such polymerization can be performed in a stirred or
fluidized bed of catalyst and product particles in a pressurized
vessel adapted to facilitate the separation of product particles
from unreacted gases therein. Maintenance of temperature may be
accomplished by circulation of ethylene, comonomer, hydrogen or
inert gas such as nitrogen. Triethylaluminum may be added as needed
as a scavenger of water, oxygen, and other undesirable impurities.
Polymer produced thereof may be withdrawn continuously or
semi-continuously at a rate necessary to maintain a constant
product inventory in the reactor.
[0054] Subsequent to polymerization and deactivation of the
catalyst, the product copolymer may be recovered by any suitable
means. In commercial practice, the polymeric product can be
recovered directly from the gas phase reactor, freed of residual
monomer with a nitrogen purge, and used without further
deactivation or catalyst removal.
[0055] The essentially linear polyolefin copolymers of the present
invention may also be produced using a high pressure process by
polymerizing ethylene in combination with the other desired
monomers in the presence of the metallocene alumoxane catalyst
system. Critical to this method is that the polymerization
temperature be above 120.degree. C., but below the decomposition
temperature of the product, and that the polymerization pressure be
above about 500 kg/cm.sup.2. In certain instances wherein the
molecular weight of the product must be controlled, any of the
suitable techniques known in the art for control of molecular
weight, such as the use of hydrogen or reactor temperature, may be
employed to effect such control therein.
[0056] The essentially linear olefinic copolymers of the present
invention are preferably derived from ethylene polymerized with at
least one comonomer selected from the group consisting of at least
one alpha-unsaturated C3 to C20 olefin comonomer, and optionally
one or more C3 to C20 polyene. The types of comonomers selected to
produce the essentially linear polymer utilized in the present
invention will depend upon economics and the desired end-use of the
resultant cross-linked foam structure.
[0057] Generally, the alpha-unsaturated olefin comonomers suitable
for use in the present invention contain in the range of about 3 to
about 20 carbon atoms. Preferably, the alpha-unsaturated olefins
contain in the range of about 3 to about 16 carbon atoms, and most
preferably in the range of about 3 to about 8 carbon atoms.
Illustrative, non-limiting examples of such alpha-unsaturated
olefin comonomers used as copolymers with ethylene include
propylene, isobutylene, 1-butene, 1-hexene, 3-methyl-1-pentene,
4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, styrene, halo-
or alkyl-substituted styrene, tetrafluoroethylene, vinyl
cyclohexene, vinyl-benzocyclobutane and the like.
[0058] Generally, the polyenes used in the present invention
contain about 3 to about 20 carbon atoms. Preferably, the polyenes
contain about 4 to about 20 carbon atoms, and most preferably about
4 to about 15 carbon atoms. Preferably, the polyene is a
straight-chain, branched chain or cyclic hydrocarbon diene having
from about 3 to about 20 carbon atoms, more preferably from about 4
to about 15 carbon atoms, and most preferably from about 6 to about
15 carbon atoms. It is also preferred that the diene is
non-conjugated. Illustrative non-limiting examples of such dienes
include 1,3-butadiene, 1,4-hexadiene, 1,6-octadiene,
5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene,
3,7-dimethyl-1,7-octadiene, 5-ethylidene-2-norbornene and
-dicyclopentadiene. Especially preferred is 1,4-hexadiene.
[0059] Preferably, the polymeric foam composition of the present
invention will comprise either ethylene/alpha-unsaturated olefin
copolymers or ethylene/alpha-unsaturated olefin/diene terpolymers.
Most preferably, the essentially linear copolymer will be
ethylene/1-butene or ethylene/1-hexene.
[0060] The comonomer content of the olefin copolymers utilized in
the present invention is typically in the range of about 1 percent
to about 32 percent (based on the total moles of monomer),
preferably in the range of about 2 percent to about 26 percent, and
most preferably in the range of about 6 percent to about 25
percent.
[0061] The preferred essentially linear olefin copolymers used in
making the products of the present invention are produced
commercially by Exxon Chemical Company, Baytown, Texas, under the
tradename Exact , and include Exact , and include Exact.TM. 3022,
Exact.TM. 3024, Exact.TM. 3025, Exact.TM. 3027, Exact.TM. 3028,
Exact.TM. 3031, Exact.TM. 3034, Exact.TM. 3035, Exact.TM. 3037,
Exact.TM. 4003, Exact.TM. 4024, Exact.TM. 4041, Exact.TM. 4049,
Exact.TM. 4050, Exact.TM. 4051, Exact.TM. 5008, and Exact.TM. 8002.
Other essentially linear olefin copolymers are available
commercially from Dow Plastics, Midland, Mich. (or DuPont/Dow),
under the tradenames Engage.TM. and Affinity.TM., and include
CL8001, CL8002, EG8100, EG8150, PL1840, PL1845 (or DuPont/Dow
8445), EG8200, EG8180, GF1550, KC8852, FW1650, PL1880, HF1030,
PT1409, CL8003, and D8130 (or XU583-00-01). Most preferably, the
essentially linear olefin copolymers are selected from the group
consisting of Exact.TM. 3024, Exact.TM. 3031, Exact.TM. 4049,
PL1845, EG8200, and EG8180. However, one skilled in the art will
appreciate that other resins satisfying the requirements of an
absence of long-chain branching, the range of molecular weight
distributions, the range of composition distribution breadth
indices, the range of resin densities, and the range of melt flow
indices, are also available and may be used without departing from
the scope of the invention.
[0062] While the aforementioned essentially linear olefin
copolymers are most preferable as the compositions of this
invention, the addition of other polymers or resins to the
composition, either prior or subsequent to grafting or
cross-linking, can result in certain advantages in the economic,
physical and handling characteristics of the cellular articles made
in accordance with this invention. Examples of the polymers and
resins which may be advantageously added include low density
polyethylene, high density polyethylene, linear low density
polyethylene, medium density polyethylene, polypropylene, ethylene
propylene rubber, ethylene propylene diene monomer terpolymer,
polystyrene, polyvinyl chloride, polyamides, polacrylics,
cellulosics, polyesters, and polyhalocarbons. Copolymers of
ethylene with propylene, isobutene, butene, hexene, octene, vinyl
acetate, vinyl chloride, vinyl propionate, vinyl isobutyrate, vinyl
alcohol, allyl alcohol, allyl acetate, allyl acetone, allyl
benzene, allyl ether, ethyl acrylate, methyl acrylate, methyl
methacrylate, acrylic acid, and methacrylic acid may also be used.
Various polymers and resins which find wide application in
peroxide-cured or vulcanized rubber articles may also be added,
such as polychloroprene, polybutadiene, polyisoprene,
poly(isobutylene), nitrile-butadiene rubber, styrene-butadiene
rubber, chlorinated polyethylene, chlorosulfonated polyethylene,
epichlorohydrin rubber, polyacrylates, and butyl or halo-butyl
rubbers. Other resins are also possible, as will be apparent to one
skilled in the art, including blends of the above materials. Any or
all of the--additional polymers or resins may be advantageously
grafted or cross-linked, in concert or separately, within the scope
of the object of this invention.
[0063] Preferred resins, to be added to the object copolymer of
this invention, include polypropylene, other essentially linear
olefin copolymers, low density polyethylene (LDPE), high density
polyethylene (HDPE), linear low density polyethylene (LLDPE),
ethylene-propylene rubber, ethylene-propylene-diene monomer
terpolymer (EPDM), polystyrene, polyvinylchloride (PVC),
polyamides, polyacrylates, celluloses, polyesters, polyhalocarbons,
and copolymers of ethylene with propylene, isobutene, butene,
hexene, octene, vinyl acetate, vinyl chloride, vinyl propionate,
vinyl isobutyrate, vinyl alcohol, allyl alcohol, allyl acetate,
allyl acetone, allyl benzene, allyl ether, ethyl acrylate, methyl
acrylate, acrylic acid, or methacrylic acid. The polymer blends can
also include rubber materials such as polychloroprene,
polybutadiene, polyisoprene, polyisobutylene, nitrile-butadiene
rubber, styrene-butadiene rubber, chlorinated polyethylene,
chlorosulfonated polyethylene, epichlorohydrin rubber,
polyacrylates, butyl rubber, or halobutyl rubber. The rubber
material can be peroxide-cured or vulcanized. Preferred resins
include single-site initiated polyolefins, LDPE, LLDPE,
polypropylene, polystyrene, or ethylene copolymers such as
ethylene-vinyl acetate copolymer (EVA), or ethylene-ethyl acrylate
copolymer (EEA).
[0064] The preferred level of the essentially linear polyolefin
copolymer, as a percentage of total polymeric resin, preferably
ranges from about 5% to about 100%, more preferably from about 10%
to about 60%, and most preferably from about 10% to about 40%.
[0065] The silane-grafted material can further include EPDM resins
or essentially linear EPDM (i.e., prepared with a metallocene
catalyst). The silane-grafted EPDM resins can be cross-linked by
the slow silane mechanism or the co-cure system. When foamed, the
silane-grafted resins that include an EPDM resin do not need to
include oil to produce a soft foam.
[0066] The slow silane-grafted materials include essentially linear
polyolefin resins (i.e., essentially linear olefin copolymers). The
slow silane-grafted materials can be nearly 100% essentially linear
olefin resins, or blends of the essentially linear polyolefin
resins with other materials such EPDM, PP, EVA, EMA, EEA, or other
related resins. The slow silane-grafted materials preferably have
silane contents above about 0.6 percent. At these levels of silane,
the faster silanes (i.e., VTMOS), could not be extruded without
experiencing processing complications due to a reaction in the
grafting line or extruder. The slow silane can be mixed or extruded
without detrimental cross-linking reactions in the mixer or
extruder that would render it unusable for foaming.
[0067] The composition can also include polypropylene resins. The
preferred polypropylene resins are Rexene Rexflex FPO D1700CS6, a
flexible polypropylene, and Himont PP 632. Polymer blends including
about 20 to 80 percent polypropylene with an essentially linear
polyethylene resin have improved temperature stability.
Silane-grafted materials that include a flexible polypropylene with
the essentially linear polyolefin resin can be processed to yield a
flexible material instead of a rigid, board-like material that is
typical of polypropylene-containing materials. The higher grafting
levels in the slow silane-grafted materials can make the polymer
combinations more compatible for blending with higher temperature
resistant polypropylene resins than previous silane-grafted
materials.
[0068] The slow silane-grafted material avoids previous
difficulties that were encountered in foaming materials that
cross-linked too rapidly, such as materials that include EPDM or
EPR resins. These materials have a tendency to cross-link too
rapidly under ordinary conditions which causes damage to the
material during expansion which can include, for example, cracking,
forming voids or rounded corners, and incomplete expansion.
[0069] Slow silane-grafted materials that include polypropylene and
soft essentially linear polyethylene resins or ethylene vinyl
acetate resins (EVA) can be used to produce thin gauge foams (e.g.,
0.020" to 1/8" thick) for use as foam adhesive backed tapes which
exhibit high thermal stabilities. A lower cost silane-grafted
polypropylene blend based foam can suitably replace higher cost
acrylic foam tapes having high temperature stabilities due
equivalent performance at a lower cost. By including an EVA resin,
lower density and thinner materials can be obtained that have the
performance characteristics of non-EVA containing thicker gauge
materials.
[0070] The cross-linking of the compositions useful in the practice
of the present invention is preferably accomplished by the use of
chemical cross-linking agents or high-energy radiation. Suitable
methods of chemical cross-linking include the use of decomposable,
free-radical generating species, or the use of silane-grafting,
wherein the molecular backbone of the constituents of said
composition are chemically reacted with a subsequently
cross-linkable chemical species. In the latter case, the cross-link
is appropriately effected by the use of warm, moist conditions
subsequent to the grafting step, optionally with a suitable
catalyst. Combinations of methods of cross-linking may be utilized
to facilitate the degree of control and achieve the desired level
of cross-linking.
[0071] Representative chemical cross-linking agents which are
usefully employed herein include the organic peroxides, azido and
vinyl functional silanes, multifunctional vinyl monomers,
organo-titanates, organo-zirconates and p-quinone dioximes. The
chemical cross-linking agent may be advantageously selected by
reference to the processing temperature and permissible time at the
desired event of said cross-linking reaction. That is to say, by
selecting a chemical cross-linking agent which exhibits a half-life
of between one minute and 60 minutes at the preferred temperature
of the cross-linking event, the rate of cross-linking may be
expeditiously induced with the required degree of control. The
processing temperature and permissible time of the cross-linking
event are often dictated by material handling requirements, for
example proper conveyance of the composition through an extruder at
reasonable rates thereof.
[0072] Suitable chemical cross-linking agents for the compositions
of this invention include, but are not limited to, organic
peroxides, preferably alkyl and aralkyl peroxides. Examples of such
peroxides include:
[0073] dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,
1,1-di-(t-butylperoxy)-cyclohexane, 2,2'-bis(t-butylperoxy)
diisopropylbenzene, 4,4'-bis(t-butylperoxy)butylvalerate,
t-butyl-perbenzoate, t-butylperterephthalate, and t-butyl peroxide.
Most preferably, the cross-linking agent is dicumyl peroxide
(Dicup) or 2,2'-bis(t-butylperoxy) diisopropylbenzene (Vulcup).
[0074] Chemically-cross-linked compositions are improved upon with
the addition of multi-functional monomeric species, often referred
to as "coagents." Illustrative, but non-limiting, examples of
coagents suitable for use in chemical cross-linking in accordance
with the present invention include di- and tri-allyl cyanurates and
isocyanurates, alkyl di- and tri- acrylates and methacrylates,
zinc-based dimethacrylates and diacrylates, and 1,2-polybutadiene
resins.
[0075] The compositions used in compression molding are constrained
by processing conditions. In particular, the higher temperatures
are required to decompose certain organic peroxides to cross-link
the polymers, such as Vulcup (2,2'-bis(tert-butylperoxy)
diisopropylbenzene). The slow silane-grafted materials permit the
use of high temperature activated organic peroxides (e.g., Vulcup)
as the cross-linking peroxide for producing the thick (e.g., 1" to
4" thick) cross section compression molded foam materials by using
a silane co-cure system. The high temperature activated organic
peroxides such as Vulcup help eliminate unpleasant odors from the
foamed materials due to chemical residuals of other peroxides in
the materials. Without the use of the silane co-cure system, Vulcup
could not be used as the cross-linking peroxide due to activation
and half life temperature requirements in the primary step for
cross-linking and foaming. The co-cure system makes it feasible to
use Vulcup to reduce residual odor in the material.
[0076] Included in the cross-linking agents that may be used with
the present invention are the azido-functional silanes of the
general formula RR'SiY.sub.2, in which R represents an
azido-functional radical attached to silicon through a
silicon-to-carbon bond and composed of carbon, hydrogen, optionally
sulfur and oxygen; each Y represents a hydrolyzable organic
radical; and R' represents a monovalent hydrocarbon radical or a
hydrolyzable organic radical.
[0077] Azido-silane compounds graft onto an oletinic polymer though
a nitrene insertion reaction. Cross-linking develops through
hydrolysis of the silanes to silanols followed by condensation of
silanols to siloxanes. The condensation of silanols to siloxanes is
catalyzed by certain metal soap catalysts such as dibutyl tin
dilaurate or butyl tin maleate and the like. Suitable
azido-functional silanes include the trialkoxysilanes such as
2-(trimethoxylsilyl) ethyl phenyl sulfonyl azide and
(triethoxysilyl) hexyl sulfonyl azide.
[0078] Other suitable silane cross-linking agents useful in the
practice of the present invention include vinyl functional alkoxy
silanes such as vinyl trimethoxy silane and vinyl triethoxy silane.
These silane cross-linking agents may be represented by the general
formula RR'SiY.sub.2 in which R represents a vinyl functional
radical attached to silicon through a silicon-carbon bond and
composed of carbon, hydrogen, and optionally oxygen or nitrogen,
each Y represents a hydrolyzable organic radical, and R' represents
a hydrocarbon radical or Y.
[0079] Usually, free-radical initiating species, such as the
organic peroxides described above, are incorporated along with the
vinyl alkoxy silane to perform hydrogen extraction from the
polymeric molecular backbone, whereupon the vinyl-functional silane
may react and graft thereto. For reference, U.S. Pat. No. 3,646,155
presents further examples of such silanes. Subsequently, the
grafted polymeric composition may be exposed to moisture to effect
silanolysis condensation reactions therein to cross-link multiples
of pendant silane grafts. Preferably, the composition contains a
suitable condensation catalyst, and further is preferably shaped
and formed into the desired profile or shape prior to contact with
moisture. Most preferably, the silane cross-linking agent is vinyl
trimethoxy silane (VTMOS), grafted on to the polymer backbone by
the free-radical reaction which is initiated by
2,2'-bis(t-butylperoxy) diisopropylbenzene. The most preferred
silanol condensation catalyst is dibutyl tin dilaurate, which
greatly facilitates the cross-linking of pendent silane groups in
the presence of moisture, preferably in hot water.
[0080] Methods of effecting the moisture induced cross-linking by
condensation of silane grafts are widely disclosed in the art.
Aside from the obvious exposure to hot water, preferably at a
temperature above the softening point of the composition, hydrated
inorganic compounds such as gypsum or other water-solvable or
water-absorbing species may be incorporated into the composition
which, upon heating the composition above the hydration-liberation
temperature, advantageously release moisture to effect the
condensation or silane pendent groups. Alternatively, moisture may
be introduced directly into continuous melt-processing equipment,
such as an extruder, either alone or in combination with one of the
components of the composition, preferably at a downstream feeding
port, optionally in combination with a physically expanding foaming
agent. For example, U.S. Pat. No. 4,058,583 (Glander) discloses the
injection of moist inert gasses, such as nitrogen, into a
downstream port of a profile extruder, to both effect the expansion
of silane-grafted compositions and the condensation of the
silanes.
[0081] It is possible to cross-link a polyolefinic material that
includes a single or multiple component silane-grafted material by
hydrolysis. The silane-grafts can be a vinyl silane (e.g., VTEOS or
other vinyl trialkoxy silane having C2 to C10 alkoxy groups) or a
mixture of hydrolyzable silanes, one of which is VTEOS.
Silane-grafts that include VTEOS allow for a higher level of
cross-linking in the polyolefin material than was previously
attainable for producing acceptable foams. The silane-graft can be
a single slow silane, preferably VTEOS, or it can be a combination
of VTEOS with an alkyl trialkoxy silanes having a C1 to C20 alkyl
group and C1 to C10 alkoxy groups, such as the Dynasil 9116, which
is hexadecyl trimethoxy silane available from Huls, Germany.
[0082] The use of slow silane-grafted material allows silane
cross-linking to occur simultaneously with or subsequent to
expanding the foam. For example, when the silane graft was only
VTMOS, the cross-linking reactions occurred prior to foaming. By
including VTEOS in the silane graft mixture, it is possible to
control reaction rates (i.e., cross-linking and foaming rates) to
produce materials with excellent physical properties. Due to the
high reactivity rate of VTMOS, silane cross-linking levels in
compositions grafted with VTMOS were limited to an average of about
0.4% and a maximum of about 0.6% due to processing difficulties. By
using slower reacting silanes, such VTEOS or combinations of VTEOS
with 9116, higher levels of silane grafting can be used to provide
greater cross-linking in later processing steps while maintaining
cross-linking uniformity throughout the foamed material. The slow
silane graft, either alone or in combination with co-curing, leads
to more uniform in density, cell structure, and physical properties
in the foams, particularly for foams having thicker cross sections
than prepared previously. The slow silane graft enhanced the
ability to control uniformity in thick and thin cross sections of
foams. The gain in uniformity by using VTEOS is preferential to the
less uniform cross-linking obtained through the cross section of
the foamed material that can occur when the silane graft is VTMOS.
The non-uniformity has been observed in compression molded foamed
materials (bun) and continuously foamed materials (extruded).
[0083] Typically the silane cross-linked polymer industry has
focussed on faster processing cycles utilizing catalysts to affect
rapid cross-linking of polyolefins (i.e., in wire and cable
applications as described, for example, in Spenadel et al. U.S.
Pat. No. 5,246,783). By utilizing a much slower cross-linking
mechanism, higher silane levels can be obtained for cross-linking
while maintaining the feasibility to produce foam, even low density
foams. The slow silane-grafted materials permit producing articles
such as wire and cable, profile extrusions, sheet extrusions, and
sheet molding without requiring complete cross-linking until later
in the process or after processing of material is complete to
provide improvement in physical properties. In addition, high rate
uncontrolled reactions are not acceptable in most foaming
applications. In foaming, a controlled level of cross-linking is
desirable and must be such that polymer rheology is controlled to
yield sufficient melt strength in the process at the appropriate
time to contain gas expansion forming a cellular structure.
[0084] By using large amounts of slow silanes relative to fast
silanes, it is possible to essentially control the relative rates
of cross-linking and foaming reactions. In this way, it is possible
to the control of reaction rates during foaming, for example, by
using long alkyl chain, high molecular weight silanes (such as
Dynasil 9116) at levels from 1%-70% of the silane graft mixture.
The delay of silane cross-linking step can be achieved by grafting
mixtures of VTEOS and 9116.
[0085] It is possible to change the timing of the silane mechanism
for cross-linking from prior to foaming to cross-linking
simultaneously with foaming. It is also to partially cross-link the
material, such that some cross-linking occurs to provide sufficient
melt strength to allow foaming, but remainder of the cross-linking
takes place after the material has been expanded into a foam. This
approach leads to enhancement of physical properties of the
foam.
[0086] The slow silane-grafted materials are sufficiently
cross-linked to permit oven expansion without thermal quenching.
The material remains at higher temperatures for longer periods of
time, thus allowing residual volatile components to evaporate and
otherwise be eliminated from the foamed material.
[0087] In compression molding, press or molding cycle time can be
decreased due in part to the increased thermostability of the
material.
[0088] Cold (i.e., room temperature) compounded slow silane-grafted
material can be used in compression molding operations, therefore
permitting pre-formed solid sheets of material to be shipped for
later expansion at distant locations. This results in an economic
benefit since the materials do not occupy increased volumes when
transported. In addition, the pre-formed solid sheets can be
extruded and calendared as individual sheets that can be layered
(plied) to give structures having particular desired thickness. The
plied structure can be cured and expanded in a press or a free
expansion oven at a later time or remote location.
[0089] The densities of the materials obtained from the slow
silane-grafted materials can range from foams of about 1 pcf up to
solid materials. The high cross-linking levels that can be achieved
correspond to gel contents of between 40 and 100 percent.
[0090] The slow silane-grafted materials can withstand long
expansion cycles while maintaining dimensional stability and
resisting overcuring, which can make the material brittle, and
formation of voids, blisters, cracks, or splits. For example, the
slow silane-grafted materials can withstand up to two hours of
secondary expansion to promote complete curing at elevated
temperatures between 320.degree. F. and 400.degree. F. The
temperature stability depends, in part, on the level of
cross-linking in the material.
[0091] The slow silane-grafted materials can have higher cross-link
densities than previously described silane-grafted polyolefin
foams. The higher cross-link densities lead to improved material
properties, such as compression set, for example. The grafted
material can be blended with other non-grafted polyolefin resins to
decrease the overall cost of the materials without completely
compromising the physical properties of the materials, although the
physical properties are less than the 100% grafted material when
blended. By slowing down the rate of cross-linking in the slow
silane-grafted material, other polymers that are ordinarily
incompatible with higher cross-linking levels can be blended with
the silane-grafted material.
[0092] For moisture-cured polyolefin systems wherein long-term
moisture stability is essential, U.S. Pat. No. 4,837,272 (Kelley)
discloses methods of subsequently reacting the silane-grafted
compositions with organo titanates to result in relatively
moisture-stable adducts which readily cross-link in the presence of
atmospheric moisture, even in absence of silanol condensation
catalysts, to form the cross-linked structures.
[0093] Suitable methods for cross-linking olefinic compositions
with high-energy, ionizing radiation involve the use of equipment
which generates electrons, X-rays, Beta-rays or Gamma-rays.
"Ionizing radiation" denotes electromagnetic waves or charged
particles having the ability to interact directly or indirectly
with a substance and consequently ionizing the substance. "High
energy" is used to denote the relatively high potential of such
radiation, necessary to uniformly and sufficiently penetrate the
articles of the composition of this invention.
[0094] The most preferred method for cross-linking olefinic
compositions through exposure to ionizing radiation is through the
use of an electron-beam radiation source. The use of electron-beam
radiation cross-linking results in fine cell structure and good
surface quality, due in large part to the completion of
cross-linking prior to the initiation of the expansion process
step. Disadvantages of this method include the high cost of the
equipment and the infeasibility of utilizing this method in a
continuous manufacture of foam, since a single electron-beam source
will only be economically supported by many continuous extrusion
lines. Furthermore, certain polymers are susceptible to
preferential chain scission or degradation instead of undergoing
the desired cross-linking reaction.
[0095] Exposure of the compositions of the present invention to
ionizing radiation may be accomplished at dosages in the range of
about 0.1 to 40 Megarads, and preferably, at about 1 to 20
Megarads. U.S. Pat. No. 4,203,815 (Noda) discloses methods of
exposing compositions to both high and low-energy ionizing
radiation to effect improvements in surface quality, strength and
subsequent heat-sealing or embossing processes. The amount of
cross-linking may be appropriately controlled by the dosage of
ionizing radiation, with preference dictated by the requirements of
the ultimate application of the composition of this invention.
Optionally, coagents as described above may be incorporated into
radiation-cross-linked compositions with advantageous results
toward cure speed and uniformity of cross-linking.
[0096] More than one cross-linking mechanism can take place in the
materials. By using slow silane-grafted polymers, a
co-cross-linking mechanism (i.e., a co-cure or dual cure system)
can be used to make a foam with enhanced properties. The
polyolefinic materials can be combined with silane-grafted
materials and an organic peroxide. By regulating levels and types
of organic peroxide relative to silane levels, the relative rates
of the steps of the co-cure can be varied to permit foaming of the
polymer materials. The resulting materials have high cross-link
levels and thus have improved physical properties.
[0097] Also, by adjusting the levels and types of cross-linking
agent, it is possible to cross-link the material partially or
completely before, during, or after expanding the material to make
a foam. By adjusting the rates of the different cross-linking
reactions, it is possible to achieve the desired levels of
cross-linking without applying water, steam, the addition of water
liberating materials, or some other outside source of moisture in a
separate processing step. The delay of cross-linking can permit
processing steps, such as, for example, laminating, thermoforming,
molding, to take place prior to the final cross-linking step. Thus,
by selecting cross-linking agents that cross-link under different
conditions, the cross-linking and foaming operations can take place
in a single or two step process.
[0098] Regardless of the method of cross-linking used, acceptable
foamed articles may only be obtained by utilization of
cross-linking over certain ranges of cross-linking density or
level. Excessive cross-linking prior to foaming will render the
foam composition too inelastic, resulting in less than optimal
expansion and greater than optimal density for a given level of
foaming agent. For processes which invoke cross-linking subsequent
to expansion, excessive cross-linking would be economically
inefficient. Less than optimal cross-linking may be detrimental to
certain physical properties, such as compression set properties or
thermal resistance.
[0099] One parameter for quantifying the degree of cross-linking is
the "gel content" of the composition. The term "gel content," as
used in this disclosure, is intended to describe the weight percent
of an insoluble portion of the cross-linked product (on a dried
basis) remaining after about 50 mg of a sample of the cross-linked
product has been immersed in 25 ml of molecular-sieve dried xylene
for 24 hours at 120.degree. C. Process conditions should be
utilized when providing for a cross-linked foam structure such that
the resulting gel content is preferably in the range of about 5% to
about 95%, more preferably in the range of about 10% to about 90%,
and most preferably in the range of about 15% to about 85%.
[0100] The expanding medium, or foaming agents, useful in the
practice of the present invention may be normally gaseous, liquid
or solid compounds or elements, or mixtures thereof. In a general
sense, these foaming agents may be characterized as either
physically-expanding or chemically decomposing. Of the physically
expanding foaming agents, the term "normally gaseous" is intended
to mean that the expanding medium employed is a gas at the
temperatures and pressures encountered during the preparation of
the foamable compound, and that this medium may be introduced
either in the gaseous or liquid state as convenience would
dictate.
[0101] Included among the normally gaseous and liquid foaming
agents are the halogen derivatives of methane and ethane, such as
methyl fluoride, methyl chloride, difluoromethane, methylene
chloride, perfluoromethane, trichloromethane,
difluoro-chloromethane, dichlorofluoromethane,
dichlorodifluoromethane (CFC-12), trifluorochloromethane,
trichloromonofluoromethane (CFC-11), ethyl fluoride, ethyl
chloride, 2,2,2-trifluoro-1,1-dichloroethane (HCFC-123),
1,1,1-trichloroethane, difluoro-tetrachloroethane,
1,1-dichloro-1-fluoroethane (HCFC-141b),
1,1-difluoro-1-chloroethane (HCFC-142b), dichloro-tetrafluoroethane
(CFC-114), chlorotrifluoroethane, trichlorotrifluoroethane
(CFC-113), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124),
1,1-difluoroethane (HFC-152a), 1,1, 1-trifluoroethane (HFC-143a),
1,1,1,2-tetrafluoroethane (HFC-134a), perfluoroethane,
pentafluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane,
perfluoropropane, dichloropropane, difluoropropane,
chloroheptafluoropropane, dichlorohexafluoropropane,
perfluorobutane, perfluorocyclobutane, sulfur-hexafluoride, and
mixtures thereof. Other normally gaseous and liquid foaming agents
that may be employed are hydrocarbons and other organic compounds
such as acetylene, ammonia, butadiene, butane, butene, isobutane,
isobutylene, dimethylamine, propane, dimethylpropane, ethane,
ethylamine, methane, monomethylamine, trimethylamine, pentane,
cyclopentane, hexane, propane, propylene, alcohols, ethers,
ketones, and the like. Inert gases and compounds, such as nitrogen,
argon, neon or helium, can be used as foaming agents with
satisfactory results. A physical foaming agent can be used to
produce foam directly out of the extrusion die. The composition can
optionally include chemical foaming agents for further
expansion.
[0102] Solid, chemically decomposable foaming agents, which
decompose at elevated temperatures to form gasses, can be used to
expand the compositions of the invention. In general, the
decomposable foaming agent will have a decomposition temperature
(with the resulting liberation of gaseous material) from
130.degree. C. to 350.degree. C. Representative chemical foaming
agents include azodicarbonamide, p,p'-oxybis (benzene) sulfonyl
hydrazide, p-toluene sulfonyl hydrazide, p-toluene sulfonyl
semicarbazide, 5-phenyltetrazole, ethyl-5-phenyltetrazole,
dinitroso pentamethylenetetramine, and other azo, N-nitroso,
carbonate and sulfonyl hydrazides as well as various
acid/bicarbonate compounds which decompose when heated.
[0103] The slow silane-grafted materials can be foamed with
chemical foaming agents, physical foaming agents, or combinations
thereof. Materials with relatively high silane contents (high
cross-link levels) can also be foamed. Higher density foams can be
prepared, not only by varying the level of foaming agent added, but
by the addition of fillers at contents that are difficult to
incorporate without the assistance of the silane cross-linking and
coupling mechanism.
[0104] The controlled cross-linking of the slow silane-grafted
material permits better utilization of foaming agent in bun
processes. Better utilization of the foaming agent provides for a
reduction in fogging, as tested using the GM 9305 01/92 or ASTM
D-523-94 protocols.
[0105] The preferred volatile liquid foaming agents include
isobutane, difluoroethane or blends of the two. For decomposable
solid foaming agents, azodicarbonamide is preferred, while for
inert gasses, carbon dioxide is preferred.
[0106] The art of producing cross-linked foam structures is well
known, especially for polyolefin compositions. The foam structure
of the present invention may take any physical configuration known
in the art, such as sheet, plank, other regular or irregular
extruded profile, and regular or irregular molded bun stock.
Exemplary of other useful forms of foamed or foamable objects known
in the art include expandable or foamable particles, moldable foam
particles, or beads, and articles formed by expansion and/or
consolidation and fusing of such particles. Such foamable article
or particle compositions may be cross-linked prior to expansion,
such as for the process of free-radical initiated chemical
cross-linking or ionizing radiation, or subsequent to expansion.
Cross-linking subsequent to expansion may be effected by exposure
to chemical cross-linking agents or radiation or, when
silane-grafted polymers are used, exposure to moisture optionally
with a suitable silanolysis catalyst.
[0107] The slow silane provides the flexibility to cross-link
partially or completely before a molding or expanding step.
Alternatively, the cross-linking can occur simultaneously with or
after the molding or expanding step. The silane-grafted polymer
materials can be used to produce a foam which can be thermoformed
and cross-linked in a subsequent step.
[0108] Slow silane-grafted materials can be used in molding
processes to expand a particular form in mold from compound
containing blowing agents and mixtures of cross-linking agents
including slow silane grafts. The physical form of the slow
silane-grafted materials prior to expansion can be in the shape of,
for example, pellets, granules, chips, powder, fragments, or other
small particulates which can enter small crevice areas of the mold.
In this process, the foaming and cross-linking step can take place
completely in the mold. Prior to the use of the slow silane-grafted
materials, either the use of "faster" silanes alone or in
conjunction with a peroxide did not permit the successful foaming
and cross-linking in a mold cavity. Materials attempted would not
bond together, nor successfully fill the entire mold, nor produce a
smooth surface or skin of acceptable appearance. Alternatively, the
molding process can occur in two steps. Here also, it was the use
of the slow silane made it possible to delay cross-linking
sufficiently to permit expansion of the material into the entire
mold cavity. The "slow" silane-grafted material had sufficient time
to foam into difficult to fill cracks and crevices without being so
cross-linked as to prevent material flow. Also, there was
sufficient delay in the cross-linking mechanism so as to permit the
knitting together of particles or fragments of compounded material
while foaming to fill the cavity. This delay also helped to improve
the smoothness of the surface and skin. The molding process can be
used to mold products such as, for example, automotive bumpers,
packaging, footwear from the slow silane-grafted materials.
[0109] The silane-grafted materials can be used in injection
molding, compression molding, transfer molding, or other types of
molding operations.
[0110] Because of the controlled cross-linking capabilities that
are obtained by using a slow silane graft, the silane-grafted
materials can be used in other processes including, for example,
rotational molding, slush molding, injection molding, the
manufacture of solid sheet materials, the manufacture of cast
films, and profile extrusions.
[0111] The slow silane-grafted material can be a thermoset foam or
solid material. The thermoset materials can be fully cross-linked
material to set their form.
[0112] Illustrative, but non-limiting, of methods of combining the
various ingredients of the foamable composition include
melt-blending, diffusion-limited imbibition, liquid-mixing, and the
like, optionally with prior pulverization or other particle-size
reduction of any or all ingredients. Melt-blending may be
accomplished in a batchwise or continuous process, and is
preferably carried out with temperature control. Furthermore, many
suitable devices for melt-blending are known to the art, including
those with single and multiple Archimedean-screw conveying barrels,
high-shear "Banbury" type mixers, and other internal mixers. The
object of such blending or mixing, by means and conditions which
are appropriate to the physical processing characteristics of the
components, is to provide therein a uniform mixture. One or more
components may be introduced in a step-wise fashion, either later
during an existing mixing operation, during a subsequent mixing
operation or, as would be the case with an extruder, at one or more
downstream locations into the barrel.
[0113] Expandable or foamable particles will have a foaming agent
incorporated therein, such as a decomposable or physically
expandable chemical blowing agent, so as to effect the expansion in
a mold upon exposure of the composition to the appropriate
conditions of heat and, optionally, the sudden release of
pressure.
[0114] One preferred method of providing a sheet object of this
invention involves silane-grafting, subsequent extrusion of a
melt-blended profile, moisture-induced cross-linking of the
profile, and finally oven-expansion of the profile. In the first
step, a portion of the polymeric resins of the foam composition,
which contains at least a portion of the essentially linear olefin
copolymer of this disclosure, is melt-blended with a 20:1 mixture
of vinyl trialkoxy silane and dicumyl peroxide in an extruder to
effect the grafting of vinyl silane onto the polymers. This
composition is extruded out of a multiple-strand die face, is
chilled in water, and is then pelletized. In a subsequent step, the
silane-grafted composition, along with ungrafted polymeric resins,
chemically decomposable foaming agents, colorants, pigments,
dibutyl tin dilaurate silanolysis catalyst, and, optionally,
antioxidants and stabilizers, are melt-blended and extruded out of
a sheet die and then passed through a three-roll stack to shape the
profile to the correct gauge. The unexpanded sheet is then passed
through a hot-water tank for sufficient time to effect the
cross-linking, and is then passed through a gas-fired, hot-air oven
to effect the decomposition of the foaming agent and expansion.
[0115] In another preferred method, the extruded profile from the
above method, prior to exposure to hot water, is multiple-stacked
and consolidated in a press within a suitable mold at a temperature
below the decomposition of the foaming agent. Subsequently, it is
exposed to hot water for sufficient time so as to effect the
cross-linking via the silanolysis reaction. Optionally, at this
point the resulting preform is again placed into a high-pressure
press within a suitable mold to initiate the foaming agent
decomposition. Finally, the partially expanded preform is fully
expanded within a hot-air forced-convection oven.
[0116] In an alternate procedure, a "Banbury" type mixer is used to
fuse a mixture of the grafted composition and other ungrafted
resins and components. The fused mixture is then molded into a
preform, cross-linked by exposure to hot water, and then expanded
as described above.
[0117] In yet another preferred method, a silane-grafted
composition is melt-blended with a physically-expanding foaming
agent such as isobutane, additional ungrafted polymeric resins,
dibutyl tin dilaurate silanolysis catalyst, nucleants such as talc,
and optionally antioxidants and stabilizers in a single-screw
extruder. Optionally, a twin-screw extruder may be utilized. This
composition is extruded out of a coat-hanger die whereupon the
foaming agent expands and a fully-expanded foam sheet or plank
results thereof. The net-shape sheet, plank, or board is the placed
in humid storage for sufficient time to effect the
cross-linking.
[0118] When a slow silane cross-linking agent is used, a chilling
step after foaming is optional. Avoiding the chilling step is
preferred since it maximizes utility of chemical blowing agents.
Under conditions where foamed polyolefinic materials have
previously been chilled to stop continuing reactions or to solidify
the material in a fixed geometry (i.e., rectangular solid bun), the
hot material can continue to co-cure and cross-link further while
slowly cooling to room temperature. This impacts processing
economics by permitting an energy savings by not requiring a
cooling system (i.e., cooling water) to chill the foamed
material.
[0119] Physically foamed materials can be prepared in a single
stage extrusion operation with subsequent final or complete
cross-linking of the foamed extrudate. Slow silane-grafted
materials having high graft levels can be used in extrusion coating
applications.
[0120] The slow silane-grafted polyolefinic materials can be
cross-linked, optionally with a peroxide co-cure, to produce an
open cell foam articles. Prior to the use of the slow silane
system, polyolefinic materials other than EVA could not be
cross-linked and foamed to produce and acceptable open cell foam.
Utilizing the slow silane system, the rates of reaction for the
cross-linking mechanism are controlled to permit regulation of the
foaming reaction in order to produce open cell material. If a
co-cure is used, a variety and combination of organic peroxides
commonly used in the industry can be used to further cross-link the
polymers. The controlled reaction rates described above allow for
the use of single site catalyzed polyolefin resin at 100% or blends
with other polyolefinic materials to make an open cell foams which
can replace EVA, urethane, PVC, or other types of open cell
foams.
[0121] The change in cross-linking rate upon changing the chemical
nature of the silane graft is indicated in FIGS. 1-3. The graphs
indicate the relative rates of reaction at 163.degree. C. of
essentially linear olefin copolymers (i.e., Engage 8200) grafted
with VTMOS (0.4%), VTEOS (1.3%), and a mixture of VTEOS and 9116
(95/5, 1.3%). A small amount of processing aid (3%) was added in
each case. In FIGS. 1-3, the lower plotted line on the chart record
is a plot of the cross-linking rate, as indicated by an increase in
torque in the mixer over time. Points "B" (at .about.3.0 minute in
FIG. 1) indicate the time at which the cross-linking reaction is
induced by the addition of a moisture liberating additive. The
points "R" and "X" indicate the times of completing the
cross-linking reactions. The time to reach the maximum
cross-linking level, "X", increases as slower silanes (or blends)
are used. The slope of the curve visibly indicates the slower
reaction rates for the VTEOS (FIG. 2) and the VTEOS/9116 (95/5)
(FIG. 3) grafted materials relative to the "fast" silane-grafted
material (VTMOS; FIG. 1).
[0122] Some of the advantages in being able to use polyolefinic
silane-grafted materials, in particular those of the metallocene
type in producing an open cell foam include, but are not limited
to: (a) no toxic residues are present in the foam, permitting their
use in medical applications, for example; (b) no other residuals
ordinarily found in urethane, PVC, and EVA, any of which can be
skin irritating, are present; and (c) there are no EVA residuals to
interfere with active additives (e.g., nerve gas deactivating
chemicals. In the metallocene resin based open cell foam, there are
no unwanted materials to be removed from the foamed material (and,
therefore, no requirement to remove such materials in separate
processing steps), since the polyolefin is essentially inert to the
activity of the nerve gas deactivating chemicals. The minimization
of additives can provide material and economic savings. The open
cell foams can be used, for example, as air or water filtering
media without imparting possible allergenic or potentially toxic
(or otherwise hazardous materials) into a downstream flow of air or
water.
[0123] Several additives, as are known to the art, may be added to
the compositions of the present invention without departing from
the scope of the invention. Specifically contemplated is the
addition of materials which are relevant toward cross-linked foam
structure compositional development and production, such as
particulate and fibrous fillers to reinforce, strengthen or modify
the Theological properties of the foam composition. Also
contemplated is the addition of antioxidants (e.g., hindered
phenolics such as Irganox 1010, phosphates such as Irgafos 168, or
polymerized trimethyl-dihydroquinoline such as Agerite AK, Resin D
or Flectol H), ultra-violet and thermal stabilizers, pigments or
colorants, cell-growth nucleants such as talc and the like,
cell-structure stabilizers such as fatty-acids, -esters (e.g.
glycerol monostearate) or -amides, property-modifiers, processing
aids, additives, catalysts to accelerate cross-linking or other
reactions, and blends of two or more of the aforementioned
materials.
[0124] It is possible to include different levels of additional
catalysts in the mixture of materials, such as catalyst commonly
added to increase the rate of cross-linking between grafted
polyolefins. The slow silane-grafts materials allow for the
reduction or omission of hydrolysis catalysts from the
cross-linking system to provide foam materials with a high
cross-link density by adjusting reactivities of the components. The
omission of the additive can improve the shelf life of the
material.
[0125] Other functional additives, such as maleic anhydride, can be
included in the materials to improve bonding characteristics (e.g.,
for laminating or coating) and the ability of the foamed materials
to hold fillers. It is possible to use more additives and fillers
in compositions containing the slow silane-grafted materials.
[0126] The high levels of silane cross-linking agent lead to the
enhancement of surface properties of polyolefinic materials. The
high levels of cross-linking do not interfere with the adhesion of
silane-grafted cross-linked materials to similar materials, and
provide for improved bonding between the silane-grafted foams and
other materials to produce laminate structures. There is also an
improvement of surface properties provided by the enhancement of
bonding between polyolefinic materials and applied liquid coatings
(i.e., polymeric, aqueous suspensions, or solvent-carried
suspensions). The enhanced surface properties of the materials
allow coating of polyolefinic materials that were previously unable
to be coated.
[0127] Slow silane-grafted materials can be used effectively in
wire and cable formulations, both in solid and foamed form, to
enhance physical properties utilizing high cross-link levels. The
high levels of cross-linking can enhance process stability,
providing performance characteristics similar to thermoset
materials. The solid or foamed slow silane-grafted materials can
also be used in water pipe and sewage pipe formulations.
[0128] Table IA is a non-limiting tabulation of certain parametric
characteristics of some essentially linear polyolefin copolymers
which are suitable for use with the present invention. The
materials in Table IA are commercially available and are produced
by the Exxon Chemical Company at its facility in Baytown, Tex.:
1TABLE IA Melt Den- Co- Con- Product Index sity monomer tent Mw
Designation (dg/min) (g/cc) Type (%) CBDI Mn Exact 4041 3.0 0.878
1-butene 23.5 NA 2.0 .+-. 0.2 Exact 5008 10 0.865 1-butene 31.6 NA
2.0 .+-. 0.2 Exact 4028 10 0.880 1-butene 23.1 NA 2.0 .+-. 0.2
Exact 4017 4.0 0.885 1-butene 20.2 NA 2.0 .+-. 0.2 Exact 4024 4.5
0.905 1-butene 11.2 83.7 2.0 .+-. 0.2 Exact 3025 1.2 0.910 1-butene
9.6 >83 2.0 .+-. 0.2 Exact 3012 4.5 0.910 1-hexene 10.4 88.2 2.0
.+-. 0.2 Exact 3011 3.5 0.910 1-hexene 11.1 92.0 2.0 .+-. 0.2 Exact
3030 2.25 0.905 1-hexene 12.9 92.2 2.0 .+-. 0.2 Exact 3031 3.5
0.900 1-hexene 15.4 >88 2.0 .+-. 0.2 Notes: NA = Not Applicable,
polymer is too soluble to determine by TREF.
[0129] The following examples are illustrative of certain features
of the present invention, and are not intended to be limiting.
[0130] Examples 1-7 illustrate the continuous extrusion process of
the present invention.
EXAMPLE 1
[0131] A silane-grafted composition, consisting primarily of a
resin of the present invention along with polyethylene/ethyl
acrylate (EEA) as a softener, was prepared at the rate of about 30
lb/hr using a 60 mm diameter, 24:1 L/D, single-screw extruder
maintained at approximately 200.degree. C. A mixture of organic
peroxide and VTMOS was metered directly into the feed throat of the
extruder. The grafted composition was passed out of a multi-strand
die head through a water-cooling trough, and chopped into pellets
with a granulator. The composition of the pellets consisted of:
2 pbw Material 90 Exact 4041, Exxon Chemical Co. 10 DPDA 6182
(0.930 g/cm.sup.3, 1.5 MI), polyethylene/ethyl acrylate, 15% ethyl
acrylate content, Union Carbide Corp. 0.4 #CV4917, Vinyl trimethoxy
silane, Huls America, Inc. 0.02 Vulcup-R, 2,2'-(tert-butylperoxy)
diisopropylbenzene, Hercules Chemical Co.
[0132] The pellicular grafted composition was admixed with
additional pellicular components in a 5 gallon drum tumbler,
metered into a 2.5" diameter, 24:1 L/D single-screw extruder
maintained at approximately 125.degree. C. and fitted with a 14"
wide coat-hanger die head, and passed through a 24" wide three-roll
stack to form an unexpanded sheet, 9" wide.times.0.069" thick, of
the following composition:
3 pbw Material 78.9 Exact 4041/DPDA 6182 graft, from above 3.3
DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in LDPE (0.92
g/cm.sup.3, 2.0 MI), Union Carbide Corp. 11.6 40% concentrate of
Bayer ADC/F azodicarbonamide in EEA-6182 3.9 20% zinc stearate, 30%
zinc oxide concentrate in high-pressure LDPE (7-8 MI) 2.3 White
color concentrate, 50% titanium dioxide in high-pressure LDPE (7-8
MI)
[0133] The sheet was exposed to 190.degree. F. and 95% relative
humidity for 80 minutes to effect the silanolysis cross-linking.
Subsequently, the sheet was passed through a
thermostatically-controlled foaming oven with infrared heaters to
maintain a surface temperature of 670.degree. F., but with
supplementary makeup air at 730.degree. F., whereupon the
cross-linked composition expanded to a width of 20".times.0.150"
thickness. The resulting density was 6 pcf, with additional
properties as shown in Table I.
COMPARATIVE EXAMPLE 1A
[0134] A silane-grafted, pellicular composition, comprising a
mixture of LDPE and LLDPE, was prepared at the rate of about 400
lb/hr using a 4" diameter, 44:1 L/D, single-screw extruder
maintained at approximately 200.degree. C. A mixture of organic
peroxide and vinyl trimethoxy silane was metered directly into the
feed throat of the extruder. The grafted composition was passed out
of a multi-strand die head and through a water-cooling trough, and
was chopped into pellets with a granulator. The composition
consisted of:
4 pbw Material 67 LF-0219A, LDPE (0.919 g/cm.sup.3, 2.0 MI),
Novacor Chemical Co. 33 ETS 9078, LLDPE (0.910 g/cm.sup.3, 2.5 MI),
Union Carbide Corp. 0.4 #CV4917, Vinyl trimethoxy silane, Huls
America, Inc. 0.02 Vulcup-R, 2,2'-bis(tert-butylperoxy) diisopropyl
benzene, Hercules Chemical Co.
[0135] The pellicular grafted composition was admixed with
additional pellicular components in a 200 gallon ribbon blender.
The mixture was metered into a 6" diameter, 24:1 L/D single-screw
extruder maintained at approximately 125.degree. C. and fitted with
a 30" wide coat-hanger die head, and passed through a 52" wide
three-roll stack to form an unexpanded sheet of the following
composition:
5 pbw Material 67.5 LF-0219A/ETS 9078 graft, from above 11.2
LF-0219A, LDPE (0.919 g/cm.sup.3, 2.0 MI), Novacor Chemical Co. 3.5
DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in LDPE (0.92
g/cm.sup.3, 2.0 MI), Union Carbide Corp. 9.8 40% concentrate of
Bayer ADC/F azodicarbonamide in LDPE (0.919 g/cm.sup.3, 2.0 MI) 6.0
20% zinc stearate, 30% zinc oxide concentrate in high-pressure LDPE
(7-8 MI) 2.0 White color concentrate, 50% titanium dioxide in high
pressure LDPE (7-8 MI)
[0136] As described above, the sheet was exposed to 190.degree. F.
moisture to effect the silanolysis cross-linking then passed
through a thermostatically-controlled foaming oven. The resulting
density was 6 pcf, with comparative properties as shown in Table I.
The object cross-linked foam structure of Example 1, containing the
essentially linear olefin copolymer of this invention, exhibited
superior tensile strength, elongation, compression set and a finer
cell size, in comparison to the LLDPE/LDPE foam article of this
example.
EXAMPLE 2
[0137] This example illustrates the preparation of a 2 pcf density
foam structure in accordance with the method of the present
invention.
[0138] The essentially linear olefin copolymer silane-grafted
composition of Example 1 was admixed with additional pellicular
components, extruded on a sheet line with coat-hanger die and
three-roll stack as described in Example 1, and slit down into a
continuous sheet 5" wide and 0.070" thick and having the following
composition:
6 pbw Material 56.7 Exact 4041/DPDA 6182 graft, from Example 1,
above. 3.6 DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in
LDPE (0.92 g/cm.sup.3, 2.0 MI), Union Carbide Corp. 33.2 40%
concentrate of Bayer ADC/F azodicarbonamide in EEA-6182 4.0 20%
zinc stearate, 30% zinc oxide concentrate in high-pressure LDPE
(7-8 MI) 2.5 White color concentrate, 50% titanium dioxide in high
pressure LDPE (7-8 MI)
[0139] The sheet was then exposed to 200.degree. F./95% relative
humidity for 60 minutes to effect the silanol condensation and
cross-linking. Subsequently, the sheet was passed through a
thermostatically-controlled foaming oven with infrared heaters to
maintain a surface temperature of 680.degree. F., but with
supplementary makeup air at 750.degree. F., whereupon the sheet
expanded to a width of 20".times.0.365" thickness. The resulting
density was 2.2 pcf, with additional properties as shown in Table
I.
COMPARATIVE EXAMPLE 2A
[0140] A silane-grafted, pellicular composition was prepared using
the same equipment and methods as described in Example 1A, but with
a mixture of LDPE and LLDPE, according to the following
composition:
7 pbw Material 80 LF-0219A, LDPE(0.919 g/cm.sup.3, 2.0 MI), Novacor
Chemical Co. 20 ETS 9078, LLDPE(0.910 g/cm.sup.3, 2.5 MI), Union
Carbide Corp. 0.4 #CV4917, Vinyl trimethoxy silane, Huls America,
Inc. 0.02 Vulcup-R, 2,2'-bis(tert-butylperoxy) diisopropyl benzene,
Hercules Chemical Co.
[0141] The pellicular grafted composition was admixed with
additional pellicular components and extruded on a sheet line with
coat-hanger die and three-roll stack, as described in Example 1A,
to give an extrudate of the following composition:
8 pbw Material 56.7 LF-0219A/ETS 9078 graft, from above 3.6
DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in LDPE(0.92
g/cm.sup.3, 2.0 MI), Union Carbide Corp. 33.2 40% concentrate of
Bayer ADC/F azodicarbonamide in LDPE (0.919 g/cm.sup.3, 2.0 MI) 4.0
20% zinc stearate, 30% zinc oxide concentrate in high pressure LDPE
(7-8 MI) 2.5 White color concentrate, 50% titanium dioxide in high
pressure LDPE (7-8 MI)
[0142] As described in Example 1A, the sheet was exposed to
190.degree. F. moisture to effect the silanolysis cross-linking,
and then passed through a thermostatically-controlled foaming oven.
The resulting density was 2 pcf, with comparative properties as
shown in Table I. The object cross-linked foam structure of Example
2, containing the essentially linear olefin copolymer of this
invention, exhibited superior tensile strength and elongation, and
a finer cell size in comparison to the LLDPE/LDPE foam article of
this example.
EXAMPLE 3
[0143] This example illustrates the preparation of a 3 pcf density
foam structure in accordance with the method of the present
invention.
[0144] The essentially linear olefin copolymer silane-grafted
composition of Example 1 was admixed with additional pellicular
components and extruded on a sheet line with coat-hanger die and
three-roll stack, as described in Example 1, and slit down into a
continuous sheet 5" wide and 0.070" thick and having the following
composition:
9 pbw Material 68.1 Exact 4041/DPDA 6182 graft, from Example 1,
above 3.4 DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in
LDPE(0.92 g/cm.sup.3, 2.0 MI), Union Carbide Corp. 22.3 40%
concentrate of Bayer ADC/F azodicarbonamide in EEA-6182 3.7 20%
zinc stearate/30% zinc oxide concentrate in high pressure LDPE (7-8
MI) 2.5 White color concentrate, 50% titanium dioxide in high
pressure LDPE (7-8 MI)
[0145] As described in Example 1, the sheet was exposed to
150.degree. F. and 95% relative humidity for 18 hours to effect the
silanolysis cross-linking. Subsequently, the sheet was passed
through a thermostatically-controlled foaming oven with infrared
heaters to maintain a surface temperature of 700.degree. F., but
with supplementary makeup air at 750.degree. F., whereupon the
cross-linked sheet expanded to a width of 16.5".times.0.350"
thickness. The resulting density was 3.0 pcf, with additional
properties as shown in Table I.
COMPARATIVE EXAMPLE 3A
[0146] A silane-grafted, pellicular composition was prepared using
the same equipment and methods as described in Example 1A, but with
a mixture of LDPE and LLDPE, according to the following
composition:
10 pbw Material 67 LF-0219A, LDPE (0.919 g/cm.sup.3, 2.0 MI),
Novacor Chemical Co. 33 ETS 9078, LLDPE(0.910 g/cm.sup.3, 2.5 MI),
Union Carbide Corp. 0.4 #CV4917, Vinyl trimethoxy silane, Huls
America, Inc. 0.02 Vulcup-R, 2,2'-bis(tert-butylperoxy) diisopropyl
benzene, Hercules Chemical Co.
[0147] The pellicular grafted composition was admixed with
additional pellicular components and extruded on a sheet line with
coat-hanger die and three-roll stack, as described in Example 1A,
to give an extrudate with the following composition:
11 pbw Material 59.6 LF-0219A/ETS 9078 graft, from above 9.0
LF-0219A, LDPE(O.919 g/cm.sup.3, 2.0 MI), Novacor Chemical Co. 3.5
DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in LDPE(O.92
g/cm.sup.3, 2.0 MI), Union Carbide Corp. 22.3 40% concentrate of
Bayer ADC/F azodicarbonamide in LDPE (0.919 g/cm.sup.3, 2.0 MI) 4.1
20% zinc stearate, 30% zinc oxide concentrate in high-pressure LDPE
(7-8 MI) 2.5 White color concentrate, 50% titanium dioxide in high
pressure LDPE (7-8 MI)
[0148] As described in Example 1A, the sheet was exposed to
190.degree. F. moisture to effect the silanolysis cross-linking,
and then passed through a thermostatically-controlled foaming oven.
The resulting density was 3 pcf, with comparative properties as
shown in Table I. The object cross-linked foam structure of Example
3, containing the essentially linear olefin copolymer of this
invention, exhibited superior tensile strength, elongation,
compression set and a finer cell size, in comparison to the
LLDPE/LDPE foam article of this example.
EXAMPLE 4
[0149] This example illustrates the preparation of a 4 pcf density
foam structure in accordance with the method of the present
invention.
[0150] A silane-grafted, pellicular composition was prepared using
the same equipment and methods as described in Example 1, and
consisting primarily of a resin of the present invention along with
polyethylene/ethyl acrylate (EEA) as a softener and a minor amount
of a fluoroelastomer processing aid concentrate designated as SAX
7401. The composition consisted of the following ingredients:
12 pbw Material 85 Exact 4041, Exxon Chemical Co. 10 DPDA 6182
(0.930 g/cm.sup.3, 1.5 MI), polyethylene/ethyl acrylate, 15% ethyl
acrylate content, Union Carbide Corp. 5 SAX 7401, fluoroelastomer
processing aid, Dupont Chemical Co. 0.4 #CV4917, Vinyl trimethoxy
silane, Huls America, Inc. 0.02 Vulcup-R, 2,
21-bis(tert-butylperoxy) diisopropyl benzene, Hercules Chemical
Co.
[0151] The essentially linear olefin copolymer silane-grafted
composition from above was admixed with additional pellicular
components and extruded on a sheet line with coat-hanger die and
three-roll stack, as described in Example 1, and slit down into a
sheet of 8" width.times.0.041" thick, to give an extrudate of the
following composition:
13 pbw Material 72.0 Exact 4041/DPDA 6182/SAX 7401 graft, from
above 3.5 DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in
LDPE (0.92 g/cm.sup.3, 2.0 MI), Union Carbide Corp. 18.5 40%
concentrate of Bayer ADC/F azodicarbonamide in EEA 6182 4.0 20%
zinc stearate, 30% zinc oxide concentrate in high pressure LDPE
(7-8 MI) 2.0 Black color concentrate, 45% carbon black in
high-pressure LDPE (7-8 MI)
[0152] As described in Example 1, the sheet was exposed to
150.degree. F. and 95% relative humidity for 16 hours to effect the
silanolysis cross-linking. Subsequently, the sheet was passed
through a thermostatically-controlled foaming oven with infrared
heaters to maintain a surface temperature of 700.degree. F., but
with supplementary makeup air at 750.degree. F., whereupon the
cross-linked sheet expanded to a width of 21".times.0.150"
thickness. The resulting density was 4.1 pcf, with additional
properties as shown in Table I.
COMPARATIVE EXAMPLE 4A
[0153] A silane-grafted, pellicular composition was prepared using
the same equipment and methods as described in Example 1A, but with
a mixture of LDPE and LLDPE, according to the following
composition:
14 pbw Material 67 LF-0219A, LDPE (0.919 g/cm.sup.3, 2.0 MI),
Novacor Chemical Co. 33 ETS 9078, LLDPE (0.910 g/cm.sup.3, 2.5 MI),
Union Carbide Corp. 0.4 #CV4917, Vinyl trimethoxy silane, Huls
America, Inc. 0.02 Vulcup-R, 2, 2'-bis(tert-butylperoxy)
diisopropyl benzene, Hercules Chemical Co.
[0154] The pellicular grafted composition was admixed with
additional pellicular components and extruded on a sheet line with
coat-hanger die and three-roll stack, as described in Example 1A,
to give an extrudate of the following composition:
15 pbw Material 73.1 LF-0219A/ETS 9078 graft, from above 3.5
DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in LDPE (0.92
g/cm.sup.3, 2.0 MI), Union Carbide Corp. 15.2 40% concentrate of
Bayer ADC/F azodicarbonamide in LDPE (0.919 g/cm.sup.3, 2.0 MI) 6.0
20% zinc stearate, 30% zinc oxide concentrate in high pressure LDPE
(7-8 MI) 2.0 Black color concentrate, 45% carbon black in high
pressure LDPE (7-8 MI)
[0155] As described in Example 1A, the sheet was exposed to
190.degree. F. moisture to effect the silanolysis cross-linking,
and then passed through a thermostatically-controlled foaming oven.
The resulting density was 4 pcf, with comparative properties as
shown in Table I. The object cross-linked foam structure of Example
4, containing the essentially linear olefin copolymer of this
invention, exhibited superior tensile strength, elongation, and a
finer cell size, in comparison to the LLDPE/LDPE foam article of
this example.
EXAMPLE 5
[0156] This example illustrates the process dependency of the foam
properties of materials made in accordance with the present
invention.
[0157] Samples of the extruded and calendared sheet from Example 4
were stacked to a combined thickness of 0.75", placed into a mold
and pressed for 67 minutes in a 200 Ton compression-molding press
with platens thermostatically controlled at 300.degree. F. The
pressure was released, the press opened and the molded bun
partially expanded in response to the decrease in pressure.
Cross-linking was induced only by the effect of the residual
moisture in the composition at the time of compression-molding. The
resulting density was 3.2 pcf, with additional properties as shown
in Table I. This object exhibited superior tensile strength,
elongation, compression set and a finer cell size, in comparison to
the 3 pcf density LLDPE/LDPE foam article of Example 3A. In
comparison to the foam structure of Example 3, which was also a 3
pcf object of the present invention, certain properties were
superior, indicating that foam properties of the present discovery
are somewhat process dependent.
EXAMPLE 6
[0158] This example illustrates the preparation of a 3 pcf density
foam structure based on polypropylene and the essentially linear
olefin polymers of this invention.
[0159] A silane-grafted, pellicular composition was prepared using
the same equipment and methods as described in Example 1, but at a
temperature of 220.degree. C., consisting primarily of a 3 MI
polypropylene along with a 3 MI resin of the present invention,
according to the following composition:
16 pbw Material 70 Exact 4017, Exxon Chemical Co. 30 Escorene PD
9272 (0.89 g/cm.sup.3, 3.1 MI), polypropylene, Exxon Chemical Co.
0.5 #CV4917, Vinyl trimethoxy silane, Huls America, Inc. 0.025
Vulcup-R, 2, 2'-bis(tert-butylperoxy) diisopropyl benzene, Hercules
Chemical Co.
[0160] The essentially linear olefin copolymer silane-grafted
composition from above was admixed with additional pellicular
components, extruded on a sheet line with coat-hanger die and
three-roll stack as described in Example 1, and slit down into a
sheet 711 wide and 0.052" thick, to give a material of the
following composition:
17 pbw Material 72.0 Exact 4017/EscoreneTM PD 9272 graft, from
above 3.6 DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in
LDPE (0.92 g/cm.sup.3, 2.0 MI), Union Carbide Corp. 23.8 40%
concentrate of Bayer ADC/F azodicarbonamide in Exact 4041
[0161] As described in Example 1, the sheet was exposed to
150.degree. F. and 95% relative humidity for 32 hours to effect the
silanolysis cross-linking. Subsequently, the sheet was passed
through a thermostatically-controlled foaming oven with infrared
heaters to maintain a surface temperature of 700.degree. F., but
with supplementary makeup air at 750.degree. F., whereupon the
cross-linked composition expanded to a width of 20" and a thickness
of 0.190". The resulting density was 2.8 pcf, with additional
properties as shown in Table I. Shown for comparison and reference
therein is a competitive organic peroxide cross-linked foam product
of 3 pcf density.
EXAMPLE 7
[0162] In this example, a 4 pcf density foam structure is prepared
based on a silane-grafted composition of primarily LDPE along with
a minor amount of the essentially linear olefin polymers of this
invention.
[0163] A silane-grafted, pellicular composition was prepared using
the same equipment and methods as described in Example 1, according
to the following composition:
18 pbw Material 30 Exact 4041, Exxon Chemical Co. 70 LF-0219A, LDPE
(0.919 g/cm.sup.3, 2.0 MI), Novacor Chemical Co. 0.4 #CV4917, Vinyl
trimethoxy silane, Huls America, Inc. 0.02 Vulcup-R, 2,
2'-bis(tert-butylperoxy) diisopropyl benzene, Hercules Chemical
Co.
[0164] The silane-grafted composition containing the essentially
linear olefin copolymer from above was admixed with additional
pellicular components, extruded on a sheet line with coat-hanger
die and three-roll stack as described in Example 1, and slit down
into a sheet of 8" width and 0.041" thickness. The resulting sheet
had the following composition:
19 pbw Material 72.0 Exact 4017/Escorene PD 9272 graft, from above
3.5 DFDA-1173 NT, 1% dibutyl tin dilaurate concentrate in LDPE
(0.92 g/cm.sup.3, 2.0 MI), Union Carbide Corp. 18.5 40% concentrate
of Bayer ADC/F azodicarbonamide in EEA 6182 4.0 20% zinc stearate,
30% zinc oxide concentrate in high pressure LDPE (7-8 MI) 2.0 Black
color concentrate, 45% carbon black in high pressure LDPE (7-8
MI)
[0165] As described in Example 1, the sheet was exposed to
150.degree. F. and 95% relative humidity for 16 hours to effect the
silanolysis cross-linking. Subsequently, the sheet was passed
through a thermostatically-controlled foaming oven with infrared
heaters to maintain a surface temperature of 700.degree. F., but
with supplementary makeup air at 750.degree. F., whereupon the
cross-linked composition expanded to a width of 21".times.0.150"
thickness. The resulting density was 4.1 pcf, with additional
properties as shown in Table I. Shown for comparison and reference
therein is a competitive radiation cross-linked foam product of 4
pcf density, demonstrating the superiority of the object of this
discovery toward the properties of tensile strength and
elongation.
[0166] Examples 8-14 illustrate the preparation of articles through
the use of compression-molding.
EXAMPLE 8
[0167] This example demonstrates the use of the essentially linear
olefin copolymers to produce a press cured foam bun, using both
chemical cross-linking (organic peroxide) as well as
silane-grafting followed by exposure to moist heat to effect the
silanol condensation and thus cross-linking. Process conditions,
cross-linking sequencing, and expansion procedures were adjusted to
optimize the preparation of the cross-linked foam structure of this
art for the particular selection of method of cross-linking.
[0168] In this example, an organic peroxide cross-linking system
was utilized with the olefin copolymer object of this invention by
methods commonly employed for the production of cross-linked LDPE
molded foam buns. The composition utilized comprised:
20 pbw Material 100 Exact 4041, Exxon Chemical Co. 10
Azodicarbonamide, 10 micron particle size 0.25 Kadox 911C, zinc
oxide, Zinc Corp. of America 0.5 dicumyl peroxide, 99% active
[0169] The composition was mixed in an internal, high shear
"Banbury" type mixer by fusing the mixture at approximately
240.degree. F., which is below the decomposition temperature of the
foaming agent. The resulting admixture was calendared and shaped
into a preform so as to fill a 1.25" deep, rectangular mold cavity.
The mold with preform therein was then held in a 200 ton
compression molding press for 55 minutes at 305.degree. F.
Following release from the press, the resulting bun was further
heated in a hot air oven for 40 minutes at 330.degree. F. The
resulting density was 2 pcf, with additional properties as shown in
Table II. Internal voids and a tendency to over-cross-link and
under-expand, symptomatic of LLDPE response similarly cured, were
observed herein.
EXAMPLE 9
[0170] In this example, the olefin copolymer object of this
invention was silane-grafted by methods described in Example 1
according to the following composition:
21 pbw Material 100 Exact 4041, Exxon Chemical Co. 0.4 #CV4910,
Vinyl triethoxy silane, Huls America, Inc. 0.02 Vulcup-R, 2,
2'-bis(tert-butylperoxy) diisopropyl benzene, Hercules Chemical
Co.
[0171] Utilizing the above silane-grafted composition, the
following was mixed in an internal, high shear "Banbury" type mixer
by fusing the mixture at approximately 240.degree. F., which is
below the decomposition temperature of the foaming agent:
22 pbw Material 100 Exact 4041/VTEOS-grafted resin, from above 14
Azodicarbonamide, 10 micron particle size 0.3 Kadox 911C, zinc
oxide, Zinc Corp. of America 6.0 DFDA-1173 NT, 1% dibutyl tin
dilaurate concentrate in LDPE (0.92 g/cm.sup.3, 2.0 MI), Union
Carbide Corp.
[0172] The resulting admixture was calendared and shaped into a
preform so as to fill a 1.251" deep, rectangular mold cavity. The
preform was then exposed to 95% relative humidity conditions for
sufficient time so as to effect the cross-linking. The preform was
placed into the mold, and held in a 200 ton compression molding
press for 75 minutes at 290.degree. F. Following release from the
press, the resulting bun was further heated in a hot air oven for
40 minutes at 330.degree. F. The resulting density was 2 pcf, with
additional properties as shown in Table II.
EXAMPLE 10
[0173] Herein, the silane-grafted and cross-linked preform of
Example 9 was expanded without the pressing operation, i.e. "freely
expanded", in an oven for 60 minutes at 330.degree. F. The
resulting density was 2.7 pcf, with additional properties as shown
in Table II.
EXAMPLE 11
[0174] In this example, an organic peroxide cross-linking system
was utilized with the olefin copolymer object of this invention in
a blended composition with ethylene vinyl acetate (EVA), ethylene
methyl acrylate (EMA) and ethylene/propylene diene monomer
terpolymer (EPDM), comprising:
23 pbw Material 30 Exact 4041, Exxon Chemical Co. 5 AT-1070, EVA,
9% vinyl acetate content, AT Plastics, Inc. 30 AT-1710, EVA, 17%
vinyl acetate content, AT Plastics, Inc. 30 XV 53-04, EMA, 15%
methyl acrylate content, 0.7 MI, Exxon Chemical Company 5 Nordel
1440, EPDM, 45 Mooney viscosity, 55% ethylene content, 5% diene
content, Dupont, Inc. 10 Azodicarbonamide, 10 micron particle size
0.11 Kadox 911C, zinc oxide, Zinc Corp. of America 0.9 dicumyl
peroxide, 99% active 0.05 Irganox 1010, antioxidant, Ciba Geigy
Corp.
[0175] The composition was mixed as described in Example 8 and
similarly calendared and shaped. The mold with preform therein was
then held in a 200 ton compression molding press for 60 minutes at
290.degree. F. Following release from the press, the resulting bun
was further heated in a hot air oven for 60 minutes at 330.degree.
F. The resulting density was 1.5 pcf, with additional properties as
shown in Table II.
EXAMPLE 12
[0176] In this example, an organic peroxide cross-linking system
was utilized with a lower specific gravity version of the olefin
copolymer object of this invention in a blended composition with
ethylene vinyl acetate (EVA) and ethylene/propylene diene monomer
terpolymer (EPDM), comprising:
24 pbw Material 50 Exact 5008, Exxon Chemical Co. 10 AT-2306, EVA,
23% vinyl acetate content, AT Plastics, Inc. 30 AT-2803-A, EVA,
289., vinyl acetate content, AT Plastics, Inc. 10 Nordel 1440,
EPDM, 45 Mooney viscosity, 55% ethylene content, 5% diene content,
Dupont, Inc. 14 Azodicarbonamide, 10 micron particle size 0.2 Kadox
911C, zinc oxide, Zinc Corp. of America 1.0 dicumyl peroxide, 99%
active 0.5 Irganox 1010, antioxidant, Ciba Geigy Corp. 0.6 Silicone
oil 0.4 Coagent 20 Calcium Carbonate
[0177] The composition was mixed as described in Example 8 and
similarly calendared and shaped. The mold with preform therein was
then held in a 200 ton compression molding press for 60 minutes at
290.degree. F. Following release from the press, the resulting bun
was further heated in a hot air oven for 60 minutes at 330.degree.
F. The resulting density was 2 pcf, with additional properties as
shown in Table II.
COMPARATIVE EXAMPLE 13
[0178] In this example, an organic peroxide cross-linking system
was utilized with LDPE, by methods commonly employed for the
production of cross-linked LDPE molded foam buns. The composition
comprised the following ingredients:
25 pbw Material 100 Dowlex 510, LDPE (0.919 g/cm.sup.3, 2.0 MI),
Dow Chemical Co. 14.4 Azodicarbonamide, 10 micron particle size
0.25 Kadox 911C, zinc oxide, Zinc Corp. of America 0.52 dicumyl
peroxide, 99% active 0.53 Paraffinic oil
[0179] The composition was mixed as described in Example 8 and
similarly calendared and shaped. The mold with preform therein was
then held in a 200 ton compression molding press for 40 minutes at
310.degree. F. Following release from the press, the resulting bun
was further heated in a hot air oven for 25 minutes at 320.degree.
F. The resulting density was 2 pcf, with additional properties as
shown in Table II.
COMPARATIVE EXAMPLE 14
[0180] Herein, an organic peroxide cross-linking system was
utilized with EVA, by methods commonly employed for the production
of cross-linked EVA molded foam buns. The composition comprised the
following ingredients:
26 pbw Material 100 Dowlex 510, LDPE (0.919 g/cm.sup.3, 2.0 MI),
Dow Chemical Co. 14.4 Azodicarbonamide, 10 micron particle size
0.25 Kadox 911C, zinc oxide, Zinc Corp. of America 0.52 dicumyl
peroxide, 99% active 0.53 Paraffinic oil
[0181] The composition was mixed at a fusion temperature of
225.degree. F. as described in Example 8 and similarly calendared
and shaped. The mold with preform therein was then held in a 200
ton compression molding press for 40 minutes at 295.degree. F.
Following release from the press, the resulting bun was further
heated in a hot air oven for 25 minutes at 320.degree. F. The
resulting density was 2.1 pcf, with additional properties as shown
in Table II.
27TABLE I COMPARATIVE PROPERTIES OF CONTINUOUS PROCESS EXAMPLES
Example Example Example Example Example 1 1A Example 2 2A Example 3
3A Example 4 4A Density (pcf) 6 6 2.2 2 3 3 4.1 4 Tensile 235 154
77 40 113 53 132 91 Strength (psi) Elongation (%) 562 350 474 235
533 360 475 345 Tear Strength 29.3 38 11.6 11.6 18.1 14.5 22.3 26.5
(pli) Compression 10.9 17 3.3 4.9 4.6 5.1 5.7 8.9 Resistance (psi)
at 25% Compression 9 15 32.8 30 17.6 25 20 20 Set, 50% (%) compr.
Cell Size Mode 0.1 0.3 0.2 0.4 0.2 0.4 0.2 0.3 (mm) Thermal
Stability (%) Shrinkage 3 hours @ 250.degree. F. 4 PCF Radiation XL
Foam Example 5 Example 5 3 PCF Voltek Free Press Example XLPE
(Volara Expanded Expanded Example 6 3A TORAY Example 7 #4A) Density
(pcf) 4.1 3.2 2.8 3 3 4.1 4 Tensile 132 116 94 53 132 108 Strength
(psi) Elongation (%) 475 460 405 360 124 475 162 Tear Strength 22.3
17.6 14.5 235 22.3 20 (pli) Compression 5.7 5 5.1 5.7 10 Resistance
(psi) at 25% Compression 20 14.5 25 20 16 Set, 50% (%) compr. Cell
Size Mode 0.2 0.15 0.4 0.2 ND (mm.) Thermal 31.3 1.9 Stability (%)
Shrinkage 3 hours @ 250.degree. F.
[0182]
28TABLE II COMPARATIVE PROPERTIES OF MOLDED BUN COMPARATIVE
EXAMPLES Formulation 8 9 10 11 12 13 14 Density (pcf) 2 2.09 2.66
1.5 2.0 2.06 2.1 Tensile Strength ND 55 ND 35 75 50 61 (psi)
Ultimate Elongation ND 440 ND 280 260 180 370 (%) 25% CD, (psi) ND
3.4 ND 2.3 2.3 10 5.1 50% CS, (%) ND 30 ND 35 35 20 16 Cell Size
Mode (mm) Collapsed.sup.a 0.5.sup.b 1.0.sup.b 0.1 0.2 0.14 0.15
.sup.apoor quality foam .sup.bwith some 1.5 mm cells
EXAMPLE 15
[0183] A chemically blown block (bun) material that exhibited
enhanced bonding properties was prepared by using a co-cure system
of silane and peroxide to cross-link a polyolefinic material while
foaming in a two step process. Example 15 contained silane-grafted
resin and Example 15A was not silane-grafted. The material had the
following composition:
29 Formulation Example 15 Example 15A Component PHR PHR Engage 8200
1% graft VTEOS 100 0 Engage 8200 0 65 LDPE 0 35 Dibutyl tin
dilaurate 0.03 0 Zinc oxide 0.2 0.2 Azodicarbonamide 13.3 13.75
Parafinic process oil 0.3 0.2 Dicumyl peroxide 0.2 0.9 Anti-oxidant
0 0.5
[0184] As described in previous Examples, a VLDPE essentially
linear polyolefin resin was grafted with VTEOS in a laboratory
extruder at approximately 375.degree. F. Following the extrusion
reaction, the grafted resin was cooled and pelletized. The cooled,
grafted and pelletized resin was compounded with additional
ingredients, including a blowing agent, activators, anti-oxidants,
additional peroxide cross-linking agent, and dispersant aids as
indicated in the above formulation. All ingredients were
incorporated into the grafted resin on a two roll mill set at
approximately 250.degree. F. Mixing was accomplished by sequential
addition of portions of the materials into the polymer. The fluxed
and fused polymer was banded on the heated mill roll surface as is
customary in mixing in this operation when there is no availability
of an internal high intensity batch mixer. At the completion of the
mixing operation, the hot compounded material was sheeted off the
mill at approximately 3/8" thickness.
[0185] While still hot, the pre-formed material was then layered
(plied up) into a 1.25".times.6".times.6" preheated rectangular
flat mold cavity. The mold with compound was then immediately
placed between heated hydraulic press platens. The hydraulic press
was closed and the cure/expansion cycle was begun. The material was
heated under approximately 900 psi for 50 minutes at 300.degree. F.
At the end of the cycle the material was removed from the heated
press platens as a removed hot, partially cured and partially
foamed material and placed directly into a hot air oven for further
curing. The semi-cured and foamed bun was further cured for
approximately 40 minutes at approximately 320.degree. F. The
resulting expanded material was a white, fine celled foam with
acceptable appearance and acceptable physical properties.
[0186] The foam was allowed to cool and age prior to skiving for
physical property testing.
[0187] The sample was also evaluated to assess the effect of the
use of grafted resin on bonding a vinyl dip solution to the foam
surface. Both Example 15 (made with the silane-grafted essentially
linear polyolefin resin) and Example 15A (made with the ungrafted
essentially linear polyolefin resin) were dipped into a PVC/organic
solvent coating solution. The first coating was allowed to dry
overnight. After air drying, both samples were again dipped into
the PVC solution to increase the thickness of the coating. The
second coating was also allowed to dry overnight.
[0188] An assessment was made of the bonding of the dip coating to
each of the samples. The silane-grafted material had improved
surface bonding to the vinyl dip solution. There was more of a foam
tear with the silane-grafted resin based foam than with the
ungrafted resin based foam when the dip coating was peeled off. The
foam tearing in Example 15 indicates that the bond between the dip
coating and the foam is greater than the strength of the foam
itself. The physical properties of Examples 15 and 15A are
summarized in Table III.
30 TABLE III Example Example Property 15 15A Density (pcf) 2.17 2.5
Tensile (psi) 56 58 Elongation (%) 360 345 25% Compression 2.6 3.1
Deflection (psi) 50% Compression 9.2 9.5 Deflection (psi) 50%
Compression 37 27 Set (%) (ASTM-3575) 50% Compression 74 58 Set (%)
(ASTM-1056) Tear Die C (pli) 5.6 8.9 Durometer Shore 00 30 43 Cell
size average (mm) 0.16 0.24 Cell size min. (mm) 0.05 0.05 Cell size
max. (mm) 0.37 0.05 Dip bonding foam tears residual dip on foam,
dip peels off
EXAMPLES 16-18
[0189] A chemically blown bun material was produced by a
silane-graft cross-linking mechanism only. The polymer resin was
grafted with VTEOS and the compositions are prepared with and
without adding the cross-linking catalyst dibutyl tin dilaurate.
Both materials produced foams with acceptable properties. There is
greater flexibility achieved in foam production with slow silane
mechanism. This Example illustrates the affects of higher levels of
cross-linking on physical properties of the foams and the
attributes of a co-cure system utilizing both silane and peroxide
cross-linking mechanisms.
[0190] The grafted resin was prepared as described in the previous
Examples. In each Example, the grafted resin was compounded with
other ingredients described in Example 15 according to the
following formulations:
31 Example Example Example Example Formulation 16 17 18 17A
Component PHR PHR PHR PHR Engage 8200 1.6% 100 0 0 0 VTEOS Engage
8200 1.95% 0 100 0 100 VTEOS Engage 8200 2.5% 0 0 100 0 VTEOS
Dibutyl tin dilaurate 0.025 0.025 0.025 0 Zinc oxide 0.2 0.2 0.2
0.2 Azodicarbonamide 14 14 14 14 Parafinic process oil 10 10 10 0
Dicumyl peroxide 0.8 0.8 0.8 0 Anti-oxidant 1 1 1 0
[0191] In each test case, the hot compounded materials were
expanded in a press as described in Example 15. The catalyst free
material (Example 17A) was heated for 60 minutes with other
conditions the same. At the end of the second heating step, the
completely foamed material was removed from the oven and cooled
with water to room temperature. The resultant foam samples were
uniform, fine celled materials. The materials were submitted for
physical property testing, the results of which are summarized in
Table IV.
32TABLE IV Example Example Example Example Property 16 17 18 17A
Density (pcf) 2.16 2.25 2.21 2.05 Tensile (psi) 33.7 39 45 34
Elongation (%) 410 347 254 633 25% Compression 2.7 2.8 2.9 2.5
Deflection (psi) 50% Compression 9.1 9.3 9.2 8.7 Deflection (psi)
50% Compression 32.5 33.7 36.5 46 Set (%) (ASTM-3575) 50%
Compression 67.3 64.8 70.2 89 Set (%) (ASTM-1056) Tear Die C (pli)
4.4 4.8 5.7 4.5 Durometer Shore 00 33 34 34.8 40 Cell size average
(mm) 0.3 0.2 0.2 0.2 Cell size min. (mm) 0.05 0.05 0.05 0.05 Cell
size max. (mm) 0.4 0.4 0.4 0.5
EXAMPLE 19
[0192] A slow silane-grafted essentially linear polyolefin resin
was used to produce a non-EVA open cell bun material. The
VTEOS-grafted VLDPE resin was grafted as described above and was
compounded with other ingredients as described above in Example 15
to give a material having the following formulation:
33 Formulation Example 19 Component PHR Engage 8200 1% VTEOS 100
Dibutyl tin dilaurate 0.5 Zinc oxide 0.5 Azodicarbonamide 16
Calcium carbonate 15 Dicumyl peroxide 0.2
[0193] Multiple sheets were plied up into a pre-form for molding in
a 1".times.7".times.10" high pressure hydraulic press mold while
still hot. The mold containing the hot compound was put between
heated high pressure hydraulic press platens under pressure for 25
minutes at 275.degree. F. at 500 psi. The mold was released and the
resulting material was removed from the hydraulic press mold and
inserted into a lower pressure mold cavity of the expected final
dimensions of 3".times.18".times.24". The material was allowed to
complete cross-linking and expansion in the lower pressure mold
cavity for 90 minutes at 330.degree. F. The mold cavity and foamed
material therein was cooled with water to room temperature. The
expanded material was removed from the mold, yielding a medium fine
open cell type of foam having the physical properties summarized in
Table V.
34 TABLE V Example 19 Property Top Middle Density (pcf) 2.3 1.82
Tensile (psi) 19.2 23.1 Elongation (%) 354 284 25% Compression
Deflection (psi) 0 0.33 50% Compression Deflection (psi) 0.33 0.65
50% Compression Set (%) (ASTM-3575) 3.13 3.61 50% Compression Set
(%) (ASTM-1056) 5.42 9.35 Tear Die C (pli) 7.3 6.05 Durometer Shore
00 15 18 Cell size average (mm) 0.6 0.48 Cell size min. (mm) 0.05
0.07 Cell size max. (mm) 0.6 1.29
EXAMPLE 20
[0194] This example demonstrates the use of a co-cure system of
slow silane-graft cross-linking and Vulcup peroxide cross-linking
to produce a cross-linked polyolefinic foam with low or no odor in
comparison to materials made with odor causing peroxides such as
Dicup. The silane-grafted resins and compounded formulations were
prepared as described in Example 15 according to the following
formulation:
35 Formulation Example 20 Component PHR Engage 8200 1.95% VTEOS 100
Dibutyl tin dilaurate 0.25 Zinc oxide 0.2 Azodicarbonamide 14
Vulcup 100% active 0.4 Anti-oxidant 1
[0195] The material was then plied up to fit into a
1.25".times.6".times.6" mold cavity.
[0196] The composition was expanded as described in Example 15,
however, the second heat treatment (at 320.degree. F.) lasted about
60 minutes. The resulting expanded material was a white, fine
celled foam that was allowed to cool and age prior to skiving for
physical property testing (Table VI).
36 TABLE VI Property Example 20 Density (pcf) 2.06 Tensile (psi) 58
Elongation (%) 333 25% Compression Deflection (psi) 3.03 50%
Compression Deflection (psi) 9.8 50% Compression Set (%)
(ASTM-3575) 35 50% Compression Set (%) (ASTM-1056) 68 Tear Die C
(pli) 5.2 Durometer Shore 00 31 Cell size average (mm) 0.2 Cell
size min. (mm) 0.05 Cell size max. (mm) 0.7
EXAMPLES 21-26
[0197] Silane-grafted essentially linear polyolefin resins can be
blended with polypropylene to produce a continuous sheet foam
material with improved heat resistant properties. In these
Examples, six silane-grafted polyolefin blends were prepared with
the formulations listed in Table VII by the methods described in
Examples above:
37TABLE VII Component Ex. 21 Ex. 22 Ex. 23 Ex. 24 Ex. 25 Ex. 26
Engage 8200 75 75 75 75 75 75 Engage 8445 22 22 22 22 22 22
Processing 3 3 3 3 3 3 Aid.sup.1 Silane.sup.2 VTMOS VTMOS VTMOS
VTEOS VTEOS VTEOS Silane 0.37 1.00 1.90 1.00 1.50 2.00
content.sup.3 Note 1. The processing aid concentrate was SAX 7401,
fluoroelastomer processing aid, Dupont Chemical Co. Note 2. 20
parts silane to 1 part Vulcup R peroxide were combined for
grafting. Note 3. Silane content is noted in parts per hundred
parts resin blend.
[0198] Each of the silane-grafted resins was blended into the
following formulation (parts by weight):
38 Component Formulation (parts by weight) Grafted resin from Table
VII 0.795 Catalyst Compound.sup.1 0.010 Foaming Agent
Compound.sup.2 0.130 Zinc Activator Compound.sup.3 0.040 Titanium
Oxide Compound.sup.4 0.025 Note 1. 98% LDPE, 1% Irganox 1010 AO, 1%
dibutyl tin dilaurate. Note 2. 60% EVA resin, 40% azodicarbonamide.
Note 3. 70% LDPE, 10% zinc oxide, 20% zinc stearate. Note 4. 50%
LDPE, 50% titanium dioxide.
[0199] Each of the materials were blended and extruded using a 2.5
inch diameter 24:1 L:D single screw extruder and a 14 inch sheet
die. The melt temperature and residence time were controlled to
prevent premature foaming of the sheet. The resulting unfoamed
sheet was cross-linked by exposure to warm moist air as described
below, and foamed by passing through a vertical foaming chamber
where the sheet was rapidly heated to 400-450.degree. C., causing
the foaming agent to decompose to form a foam of fine cell
structure. The physical properties are summarized in Table
VIII.
39TABLE VIII Property.sup.1 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Ex. 25 Ex.
26 Density (pcf) 4.8 5.3 no 5.2 5.6 6.5 Tensile (psi) 123 88 foam
119 139 200 Elongation (%) 658 450 622 519 417 Tear Die C (pli) 16
16 16 19 23 25% Compression 5.6 5.5 5.8 6.1 9.1 Deflection (psi)
50% Compression Deflection (psi) 15.4 16.3 15.2 16.1 21.7 50%
Compression Set (%) 16 12 13 9 5 Durometer Shore 00 65 60 63 64 66
Cell size average (mm) 0.25 0.3 0.3 0.3 0.2 Thickness (inches)
0.101 0.110 0.085 0.095 0.117 Note 1. Properties were measured
according to ASTM D-3575, with the exception of cell size average
which was measured optically.
[0200] Examples 21, 22, and 23 had increasing levels of VTMOS
silane. Examples 22 and 23 used a 50/50 blend of grafted resin with
Engage 8200. Efforts to increase the concentration of grafted resin
resulted in poor quality foam due to inability of the matrix to
expand because the cross-linking level was too high at the time of
foaming. Even at that concentration, the matrix for Example 23
could not be expanded without severe blistering, which is caused by
over cross-linking. The compression set was reduced from 16 to 12
percent when silane level was increased from 0.37 to 1.0.
[0201] Examples 24, 25, and 26 were produced with increasing levels
of VTEOS. Higher levels of VTEOS were attainable because the
cross-linking level can be controlled for ideal foaming, and the
material can continue to cross-link after foaming, yielding higher
physical properties relative to the VTMOS foams.
[0202] Compression set can be used as an indicator of cross-linking
level in the materials. In general, the higher the level of
cross-linking, the lower the compression set. Low compression set
is desirable in load bearing applications such as shoe parts,
packaging, and industrial gasketing. At the highest attainable
VTMOS level, compression set is 12 percent. Due to the ability to
add twice as much VTEOS in the slow silane system, a material
having a compression set of 5 percent was obtained at the expense
of a higher density, 6.5 vs. 5, due to the tighter cross-linking
network that restricted foam expansion. Tensile strength and cell
size were also dramatically improved. Higher tensile strength and
lower elongation are further indications of higher cross-linking
levels in the slow silane materials.
EXAMPLE 27
[0203] The slow silane-grafted polyolefinic resin can be used to
produce a 5 pcf continuous sheet foam material with improved
physical properties. A slow silane-grafted polyolefin resin was
prepared using the following formulation according to the Examples
described above:
40 Component Example 27 Engage 8200 97 Processing Aid.sup.1 3
Silane.sup.2 VTEOS Silane content.sup.3 1.60 Note 1. The processing
aid concentrate was SAX 7401, fluoroelastomer processing aid,
Dupont Chemical Co. Note 2. 20 parts silane to 1 part Vulcup R
peroxide were combined. Note 3. Silane content in parts per hundred
parts resin blend.
[0204] The grafted resin was incorporated into the compound
formulation:
41 Component Formulation (parts by weight) Grafted resin 0.795
Catalyst Compound.sup.1 0.010 Foaming Agent Compound.sup.2 0.130
Zinc Activator Compound.sup.3 0.040 Titanium Oxide Compound.sup.4
0.025 Note 1. 98% LDPE, 1% Irganox 1010 AO, 1% dibutyl tin
dilaurate. Note 2. 60% EVA resin, 40% azodicarbonamide. Note 3. 70%
LDPE, 10% zinc oxide, 20% zinc stearate. Note 4. 50% LDPE, 50%
titanium dioxide.
[0205] The material was extruded as described in Examples 21-26.
Samples were exposed to processing conditions for expansion into
foams as shown in Table IX.
42TABLE IX Cross-linking Wet Bulb Post Expansion Wet Bulb Exam-
time at Temperature Time at 150.degree. F. Temperature ple
150.degree. F. (hours) (minimum) (hours) (minimum) 27A 3
145.degree. F. 0 145.degree. F. 27B 6 145.degree. F. 0 145.degree.
F. 27C 9 145.degree. F. 0 145.degree. F. 27D 16.5 145.degree. F. 0
145.degree. F. 27E 3 145.degree. F. 66 145.degree. F.
[0206] The Example foams 27A-E were tested. The physical properties
are summarized in Table X. Table X.
43TABLE X Property.sup.1 Ex. 27A Ex. 27B Ex. 27C Ex. 27D Ex. 27E
Density (pcf) 5.4 5.1 5.5 6 5.5 Tensile (psi) 121 116 143 171 114
Elongation (%) 628 610 576 542 602 Tear Die C (pli) 16 14 17 20 14
25% Compression 5.1 4.7 5.5 6 13.5 Deflection (psi) 50% Compression
15.5 14.9 16.3 16.8 16.4 Deflection (psi) 50% Compression Set 21 20
10 7 32 (%) Durometer Shore 00 59 55 59 61 60 Cell size average
(mm) 0.30 0.30 0.3 0.25 0.3 Thickness (inches) 0.100 0.089 0.113
0.108 0.101 Note 1. Properties were measured according to ASTM
D-3575, with the exception of cell size average which was measured
optically.
[0207] This Example shows the effect of increased cross-linking
time on the properties of the finished foam. Increasing
cross-linking time incrementally from 3 to 16.5 hours produces an
increase in physical properties, notably compression set and
tensile strength. In this case, attempts to cross-link the material
after foaming by exposure to 150.degree. F. for 66 hours produced
lowered physical properties. This is probably attributable to
deterioration of the polymer rather than low cross-linking levels
in the material.
EXAMPLES 28-30
[0208] In these Examples, 100% essentially linear polyolefin resin
is used to produce an extruded sheet utilizing a slow silane
continuous cure/foaming system. Two silane-grafted resin blends
were prepared with the following formulations, as described in
previous Examples (Table XI).
44 TABLE XI Example Example Example Component 28 29 30 (blank)
Engage 8200 97 97 97 Processing Aid.sup.1 3 3 3 Silane.sup.2 VTEOS
VTEOS 0 Silane content.sup.3 1.30 2.00 0.00 Note 1. The processing
aid concentrate was SAX 7401, fluoroelastomer processing aid,
Dupont Chemical Co. Note 2. 20 parts silane to 1 part Vulcup R
peroxide were combined. Note 3. Silane content in parts per hundred
parts resin blend.
[0209] Each of the resins were then blended according to the
following formulation:
45 Component Formulation (parts by weight) Resin from Table XI
0.920 Catalyst Compound.sup.1 0.005 Foaming Agent Compound.sup.2
0.010 Zinc Activator Compound.sup.3 0.040 Titanium Oxide
Compound.sup.4 0.025 Note 1. 98% LDPE, 1% Irganox 1010 AO, 1%
dibutyl tin dilaurate. Note 2. 60% EVA resin, 40% azodicarbonamide.
Note 3. 70% LDPE, 10% zinc oxide, 20% zinc stearate. Note 4. 50%
LDPE, 50% titanium dioxide.
[0210] The compounds above were extruded using the extruder of
Example 21 at a melt temperature of 400.degree. F., which caused
the foaming agent to decompose in the extruder, resulting in foam
being extruded from the die. The foam was cooled and rolled. The
foams had properties described in the following table:
46 Example Example Example Property.sup.1 28 29 30 (blank) Density
(pcf) 29 33 34 Tensile (psi) 479 520 344 Elongation (%) 703 665 640
Tear Die C (pli) 72 80 81 25% Compression Deflection (psi) 58 60 54
50% Compression Deflection (psi) 216 243 211 Durometer Shore 00 85
86 84 Cell size average (mm) 0.40 0.30 0.25 Thickness (inches)
0.054 0.055 0.054 Note 1. Properties were measured according to
ASTM D-3575, with the exception of cell size average which was
measured optically.
[0211] Grafting VTECS improved the tensile strength from 344 with
0% VTEOS, to 479 with 1.3% and 520 with 2% VTEOS. Cell size is
reduced significantly. Attempts to duplicate these results with a
fast silane (VTMOS) were unsuccessful since there was premature
cross-linking in the die which caused unacceptable gels and
irregular sheet forms. Hardness was not effected.
EXAMPLE 31
[0212] The slow silane-grafted materials (VTEOS or other slower
silane grafts) have a wider processing window and allows. for
higher cross-linking levels in the finished product. In this
example, a sheet of the following formulation was produced:
47 Grafted resin of Example 23 0.965 Catalyst Compound.sup.1 0.010
Titanium Oxide Compound.sup.2 0.025 Note 1. 98% LDPE, 1% Irganox
1010 AO, 1% dibutyl tin dilaurate. Note 2. 50% LDPE, 50% titanium
dioxide.
[0213] The compound was extruded using the extruder of Example 21
with a melt temperature of 300.degree. F. The resulting sheet
cross-linked in the machine prior to extrusion and causing gels to
form in the sheet. The sheet was of unacceptable quality for
commercial applications.
[0214] The compound was modified using the grafted resin of Example
29 (Engage 8200/Processing Aid:97/3.times.2% VTEOS blend listed in
Table XI) in place of the grafted resin of Example 23, listed in
Table VII. The formulation was extruded and produced a smooth
sheet. The tensile strength and elongation could not be determined
because the material stretched beyond the limits of the tensile
testing machine. The ultimate elongation of the material was in
excess of 900% and tensile strength was in excess of 1000 psi.
EXAMPLES 32-33
[0215] These Examples employ a VTEOS silane-grafted essentially
linear olefin copolymer and a blended VTEOS/9116 silane-grafted
essentially linear olefin copolymer. The materials were
cross-linked and expanded to produce cross-linked polyolefinic
foams.
[0216] The grafted resins were prepared as described in Example 15.
In each Example, the grafted resin was compounded with other
ingredients described in Example 15 according to the following
formulations:
48 Formulation Example 32 Example 33 Component PHR PHR Engage 8200
2% VTEOS graft 100 0 Engage 8200 2% 95/5 VTEOS/9116 graft 0 100
Dibutyl tin dilaurate 0.025 0.025 Zinc oxide 0.2 0.2
Azodicarbonamide 14 14 Paraffinic process oil 10 10 Dicumyl
peroxide 0.8 0.8 Anti-oxidant 1 1
[0217] In each test case, the hot compounded materials were
expanded in a press as described in Example 15, except that the
semi-cured and foamed buns were cured for approximately 50 minutes
at approximately 320.degree. F. The resulting foam samples were
uniform, fine celled materials. The materials were submitted for
physical property testing, the results of which are summarized in
Table IV.
49 TABLE XII Property Example 32 Example 33 Density (pcf) 2.25 2.28
Tensile (psi) 39 37 Elongation (%) 347 404 25% Compression 2.8 3.1
Deflection (psi) 50% Compression 9.3 9.8 Deflection (psi) 50%
Compression 33 34 Set (%) (ASTM-3575) 50% Compression 64 66 Set (%)
(ASTM-1056) Tear Die C (pli) 4.7 4.5 Split Tear 3.5 4.3 Durometer
Shore 00 34 35 Cell size average (mm) 0.2 0.2 Cell size min. (mm)
0.05 0.05 Cell size max. (mm) 0.4 0.45
[0218] The physical property testing results were very similar. One
significant difference was noted in the improved elongation
characteristics of the foam produced with the blend of VTEOS/9116
silane. Another observed difference was the greater processing
window indicated in the slower VTEOS/9116 blend material verses the
VTEOS alone, as discussed in Example 31.
* * * * *