U.S. patent application number 10/842925 was filed with the patent office on 2005-11-17 for white polyolefin compositions having reduced die drool.
Invention is credited to Lee, Chun D..
Application Number | 20050256239 10/842925 |
Document ID | / |
Family ID | 34969699 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050256239 |
Kind Code |
A1 |
Lee, Chun D. |
November 17, 2005 |
White polyolefin compositions having reduced die drool
Abstract
Filled polyolefin compositions suitable for use in
extrusion/coextrusion processes which reduce die drool are
provided. More particularly, the compositions are white or opaque
compositions comprising a polyolefin, whitening or opacifying
inorganic filler and a mercaptobenzimidazole compound.
Inventors: |
Lee, Chun D.; (Cincinnati,
OH) |
Correspondence
Address: |
William A. Heidrich
Equistar Chemicals, LP
11530 Northlake Drive
Cincinnati
OH
45249
US
|
Family ID: |
34969699 |
Appl. No.: |
10/842925 |
Filed: |
May 11, 2004 |
Current U.S.
Class: |
524/425 ;
524/451; 524/492 |
Current CPC
Class: |
C08K 5/378 20130101;
C08L 23/04 20130101; C08L 23/10 20130101; C08L 23/10 20130101; C08L
23/06 20130101; C08K 5/378 20130101; C08L 23/04 20130101; C08L
2666/06 20130101; C08L 2205/02 20130101; C08L 23/02 20130101; C08L
81/00 20130101; C08L 81/00 20130101; C08L 23/06 20130101 |
Class at
Publication: |
524/425 ;
524/492; 524/451 |
International
Class: |
C08K 003/34; C08K
003/26 |
Claims
I claim:
1. A polyolefin composition comprising: (a) 40 to 98.5 weight
percent, based on the weight of the composition, polyolefin resin
selected from the group consisting of ethylene homopolymers,
ethylene copolymers, propylene homopolymers and propylene
copolymers, said polyolefin having a melt index from 0.5 to 50 g/10
min; (b) 1.5 to 60 weight percent, based on the weight of the
composition, whitening/opacifying inorganic filler; and (c) 0.01 to
1 weight percent, based on the weight of the composition,
mercaptobenzimidazole compound of the formula 6where A is hydrogen
or zinc, R is a C.sub.1-4 alkyl group, n is 0 to 4 and x is 1 or
2.
2. The composition of claim 1 wherein (b) is selected from the
group consisting of titanium dioxide, calcium carbonate, barium
sulfate, silica, silica dioxide, talc, mica and kaolin.
3. The composition of claim 1 wherein R is methyl and n is 0 or
1.
4. The composition of claim 1 comprising 45 to 97.5 weight percent
(a), 2.5 to 55 weight percent (b) and 0.05 to 0.5 weight percent
(c).
5. The composition of claim 4 wherein (b) is titanium dioxide and
(c) is selected from the group consisting of
2-mercaptotolylimidazole, 2-mercaptobenzimidazole,
zinc-2-mercaptobenzimidazole and zinc 2-mercaptotolylimidazole.
6. The composition of claim 5 wherein (a) is low density
polyethylene or linear low density polyethylene having densities
from 0.915 to 0.930 g/cm.sup.3.
7. The composition of claim 6 wherein the titanium dioxide has an
average particle size from 0.1 to 10 microns.
8. The composition of claim 4 wherein (b) is calcium carbonate and
(c) is selected from the group consisting of
2-mercaptotolylimidazole, 2-mercaptobenzimidazole,
zinc-2-mercaptobenzimidazole and zinc 2-mercaptotolylimidazole.
9. The composition of claim 8 wherein (a) is low density
polyethylene or linear low density polyethylene having densities
from 0.915 to 0.930 g/cm.sup.3.
10. The composition of claim 9 wherein the calcium carbonate has an
average particle size from 0.1 to 10 microns.
11. The composition of claim 1 which additionally contains 0.1 to 1
weight percent, based on the weight of the composition, processing
aid.
12. The composition of claim 11 wherein the processing aid is a
fatty acid metal soap.
13. The composition of claim 12 wherein the processing aid is
aluminum stearate.
14. The composition of claim 1 which additionally contains 0.1 to 1
weight percent, based on the weight of the composition, hindered
phenol stabilizer.
15. The composition of claim 14 wherein the hindered phenol
stabilizer is selected from the groups consisting of
4,4'-methylenebis(2,6-di-t-butylph- enol), tetrakis [methylene
(3,5-di-t-butyl-4-hydroxyhydrocinnamate)methane-
,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)-benzene,
1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-s-triazine
2,4,6(1H,3H,5H)trione,
N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propany- l]-hydrazine
and octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to white polyolefin compositions
useful in extrusion processes which exhibit reduced die lip
build-up during extrusion. More particularly, the compositions
contain a polyolefin, a whitening or opacifying filler and a die
drool-reducing amount of mercaptobenzimidazole compound
[0003] 2. Brief Description of the Prior Art
[0004] Inorganic fillers are commonly incorporated in polyolefin
resins for a variety of purposes. For example, inorganic fillers
may be employed to reduce cost, impart flame retardancy, improve
modulus or toughness, impart opacity, impart
printability/writeability, impart ultraviolet (UV) resistance and
the like. The amount and type of polyolefin used and inorganic
filler incorporated can vary widely depending on the intended
end-use application.
[0005] Whitening or opacifying inorganic fillers, such as titanium
dioxide and calcium carbonate, are widely used in the production of
white or opaque polyolefin packaging films. Films of this type may
be used individually or incorporated as one of the layers in a
coextruded multi-layer film construction. White films are commonly
employed where a white background for printing is desired and to
protect packaged foods which are sensitive to light exposure.
[0006] The problems associated with the high-speed extrusion of
filled polyolefins and subsequent forming operations are well
documented. For example, U.S. Pat. No. 5,277,970 describes the
tendency of opaque, vacuole-containing films to develop
undesirable, stripe-like markings of varying intensity in the
longitudinal direction when processed on high-speed automatic
packaging machines and discloses multi-layered white film resistant
to the development of such marking.
[0007] The presence of inorganic fillers is also known to
contribute to undesirable die lip build-up during
extrusion/coextrusion of the film. Dip lip build-up, also referred
to as die drool, die drip or plate out, is the undesirable
accumulation of polymer on the open face of the die. Die lip
build-up can change the geometry of the die exit and cause surface
roughness. Also, the built-up material can periodically break free
and cause localized surface defects. If die drool is excessive it
may require periodic shut down to clean dies and/or it may require
operating at reduced line speeds. A discussion of the problems
associated with die lip build-up and the various factors which
contribute to this phenomenon and a review of common methods
suggested to minimize or eliminate die lip build-up problems is
provided in a paper presented by J D. Gander and A. J. Giacomin,
SPE ANTEC, Indianapolis (May 1996), pages 1113-1117.
[0008] One approach to reducing die drool is the use of additives
that function as processing aids/lubricants for the polyolefin.
Fluoropolymer additives have been widely used for this purpose.
There is a continuing need to provide new and improved white,
filled polyolefin compositions which exhibit reduced die lip
build-up upon extrusion. It would be particularly desirable if
these compositions utilized readily available and low cost
additives.
[0009] Benzimidazole compounds have been used as stabilizers for
polyolefins to prevent degradation caused by oxidative, thermal and
ultraviolet exposure. For example, U.S. Pat. No. 3,218,276
discloses polypropylene fiber-forming compositions protected
against thermal and ultraviolet degradation containing 0.2 to 2
percent C.sub.3-20 alkyl-substituted benzimidazole. U.S. Pat. No.
2,997,456 teaches the use of metallic mercaptobenzimidazole
compounds as stabilizers for polymers of 1-olefins, primarily
polypropylene, to protect against molecular degradation under
conditions of elevated temperature and/or mechanical working. Zinc
mercaptobenzimidaole is specifically mentioned.
[0010] Combinations of hindered phenols with various zinc salts of
mercapto compounds to stabilize crosslinkable polyolefin insulation
compositions is taught in U.S. Pat. Nos. 4,260,661; 4,693,9837;
4,797,323 and 4,824,883. For example, combinations of IRGANOX 1010
with the zinc salts of 2-mercaptobenzimidazole and
2-mercaptotoylimidazole are disclosed.
[0011] Other references which disclose benzimidazole stabilizers
for crosslinkable elastomeric polymeric materials include U.S. Pat.
Nos. 4,459,380; 4,808,643 and 5,196,462.
[0012] U.S. Pat. No. 6,197,852 discloses the use of
mercaptobenzimidazole compounds for carbon black-filled
concentrates having improved resistance to thermo-oxidative
degradation and improved dispersion of carbon black.
SUMMARY
[0013] It is an object of the present invention to provide
polyolefin compositions suitable for use in extrusion processes
which exhibit reduced die drool. It is a further object to provide
white or opaque polyolefin extrusion compositions having reduced
die lip build-up.
[0014] The improved compositions of the invention, which can
include both concentrates and let-down resins produced therefrom,
comprise 40 to 98.5 weight percent, based on the weight of the
composition, polyolefin resin selected from the group consisting of
ethylene homopolymers, ethylene copolymers, propylene homopolymers
and propylene copolymers, said polyolefin having a melt index from
0.5 to 50 g/10 min; 1.5 to 60 weight percent, based on the weight
of the composition, whitening/opacifying inorganic filler; and 0.01
to 1 weight percent, based on the weight of the composition,
mercaptobenzimidazole compound of the formula 1
[0015] where A is hydrogen or zinc, R is a C.sub.1-4 alkyl group, n
is 0 to 4 and x is 1 or 2.
[0016] The mercaptobenzimidazole compound is preferably
2-mercaptotolylimidazole, 2-mercaptobenzimidazole,
zinc-2-mercaptobenzimidazole or zinc 2-mercaptotolyl-imidazole.
Useful whitening/opacifying inorganic fillers include titanium
dioxide, calcium carbonate, barium sulfate, silica, silica dioxide,
talc, mica and kaolin.
[0017] Compositions containing titanium, dioxide and calcium
carbonate fillers, especially those wherein the average particle
size of the filler is in the range 0.1 to 10 microns, are
particularly useful.
[0018] Especially useful extrusion compositions contain 45 to 97.5
weight percent low density polyethylene resin or linear low density
polyethylene resin, 2.5 to 55 weight percent filler and 0.05 to 0.5
weight percent mercaptobenzimidazole compound. It is even more
advantageous if these compositions contain 0.1 to 1 weight percent
processing aid and/or 0.1 to 1 weight percent hindered phenol
stabilizer.
DETAILED DESCRIPTION
[0019] The present invention relates to white polyolefin
compositions having reduced die drool. As used herein the term
white polyolefin compositions refers to compositions which are
white or opaque. The degree of whiteness/opacity can vary depending
on the type and amount of the inorganic filler incorporated in the
polyolefin.
[0020] The compositions in their broadest terms are comprised of a
polyolefin capable of being extruded, an inorganic filler capable
of imparting the desired degree of whiteness/opacity and a die
drool-reducing amount of mercaptobenzimidazole compound.
Optionally, one or more additional additives commonly used in
extrusion compositions, such as stabilizers and processing aids,
may be included in the composition.
[0021] Conventional polyolefin resins suitable for use in extrusion
processes are employed for the invention. These include ethylene
homopolymers and copolymers, propylene homopolymers and copolymers
and mixtures thereof having melt indexes (MIs) in the range from
about 0.5 to 50 g/10 min determined in accordance with ASTM D
1238-01, condition 190/2.16. It is particularly advantageous to use
polyolefins having MIs from about 2 to 40 g/10 min.
[0022] Useful ethylene homopolymers and copolymers within the
specified MI range are available from commercial sources and
include low density polyethylene (LDPE), linear low density
polyethylene (LLDPE), medium density polyethylene (MDPE) and high
density polyethylene (HDPE). Copolymers contain minor amounts of
C.sub.3-8 .alpha.-olefin comonomers such as propylene, butene-1,
hexene-1 and octene-1; however, copolymers of ethylene with
comonomers having functional groups such as vinyl carboxylates,
alkyl acrylates and alkyl methacrylates may also be used.
Ethylene-vinyl acetate and ethylene-n-butyl acrylate copolymers are
highly useful copolymers as are copolymers of ethylene with
butene-1 and hexene-1.
[0023] Densities of the ethylene homopolymers and copolymers can be
as high as 0.965 g/cm.sup.3 but are most advantageously from 0.910
to 0.950 g/cm.sup.3. With highly filled compositions, such as when
concentrates or masterbatches are prepared, LDPEs and LLDPEs having
densities from 0.915 to 0.930 g/cm.sup.3 are highly useful. LDPEs
having densities from 0.915 to 0.925 are particularly advantageous
for formulating highly filled compositions in view of their ready
processability and the ease of incorporating the high filler
loadings. Densities recited herein are determined in accordance
with ASTM D 1505.
[0024] Useful propylene polymers include polypropylene (PP), i.e.,
propylene homopolymer, random copolymers of propylene with ethylene
or a C.sub.4-6 .alpha.-olefin and impact propylene-ethylene
copolymers which can include thermoplastic polyolefins (TPOs) and
thermoplastic polyolefin elastomers (TPOEs). The impact copolymers
can be either reactor-made intimate mixtures of polypropylene and
ethylene-propylene copolymer or conventional blends obtained by
physically mixing the polypropylene and ethylene-propylene
copolymer components.
[0025] The polyolefin resin(s) will constitute 40 to 98.5 weight
percent (wt. %) and, more preferably, from 45 to 97.5 wt. % of the
total composition. The filler, which can be any inorganic filler
capable of imparting the desired degree of whiteness or opacity to
the finished product, comprises 1.5 to 60 wt. % and, more
preferably, 2.5 to 55 wt. % of the total composition.
[0026] Inorganic fillers which can be used include any of the
filler materials known to be useful for whitening/opacifying
purposes. By way of illustration, these can include titanium
dioxide, calcium carbonate, barium sulfate, silica, silica dioxide,
talc, mica, kaolin and the like.
[0027] In one highly useful embodiment of the invention the
inorganic filler is titanium dioxide (TiO.sub.2) which can be of
either the anatase or rutile form. Due to its superior opacity, the
rutile form is preferably employed. The titanium dioxide may be
surface treated, i.e., coated in accordance with known procedures.
For example, the titanium dioxide particles may be coated with
organic compounds or inorganic oxides where specific applications
dictate. In another highly useful embodiment, the inorganic filler
is calcium carbonate.
[0028] Average particle size of the inorganic filler will typically
range from about 0.05 up to about 50 microns. While smaller
particle size fillers provide a greater whitening/opacifying effect
and better performance, they are typically harder to disperse.
White compositions wherein the whitening/opacifying filler,
particularly TiO.sub.2 or calcium carbonate, has a particle size in
the range 0.1 to 10 microns are particularly useful.
[0029] A mercaptobenzimidazole compound is included in the
formulation with the polyolefin base resin and inorganic filler in
order to achieve the reduced die lip buildup with the compositions
of the invention. Useful mercaptobenzimidazole compounds for the
invention correspond to the following formula 2
[0030] where A is hydrogen or zinc, R is a C.sub.1-4 alkyl group, n
is 0 to 4 and x is 1 or 2. Preferably, R is methyl and n is 0 or 1.
Preferred mercaptobenzimidazole compounds include
2-mercaptotolylimidazole (MTI), 2-mercaptobenzimidazole (MBI),
zinc-2-mercaptobenzimidazole (ZMBI) and zinc
2-mercaptotolylimidazole (ZMTI). Whereas mercaptobenzimidazoles of
the above types have been used as stabilizers for crosslink able
polymers and as an adjuvant to facilitate dispersion of carbon
black in carbon black concentrates they have not been utilized in
white/opaque formulations to reduce die drool.
[0031] The mercaptobenzimidazole compound is used in an amount from
0.01 to 1 wt. %, based on the total composition. In a highly useful
embodiment compositions exhibiting significantly reduced die lip
build-up contain from 0.05 to 0.5 wt. % of the
mercaptobenzimidazole compound. The amount of mercaptobenzimidazole
compound required to effectively reduce die drool will depend on
the particular polyolefin and inorganic filler used and the
relative percentages of each, the type and the amount of other
resins/additives included in the formulation, the particular
application involved and processing/operating conditions employed.
As a general rule, however, all other things being equal, die lip
build-up increases as the amount of filler is increased.
Accordingly, it may be advantageous to use higher levels of the
mercaptobenzimidazole compound and include other optional
processing aids when formulating highly filled white
compositions.
[0032] In one embodiment of the invention compositions useful for
extrusion coating photographic papers will contain 85-90% LDPE,
10-15% TiO.sub.2 and 0.05-0.5% mercaptobenzimidazole compound. In
another useful embodiment, compositions useful as extrusion
coatings for Kraft papers and the like contain 90-95% LDPE, 5-10%
calcium carbonate and 0.05-0.5% mercaptobenzimidazole compound.
[0033] Conventional additives may be included in the composition in
accordance with known formulation procedures. These additives can
include antioxidants, light and heat stabilizers, processing aids,
nucleating agents, flame retarding agents, metal deactivators and
the like. Additives of this type are known in the art and are
generally used at relatively low levels, i.e., not exceeding 2% on
a combined basis. Since mercaptobenzimidazole compounds are known
to impart antioxidative properties, incorporation of additional
antioxidants and stabilizers may not be necessary except for the
most rigorous applications and/or processing conditions.
[0034] In one highly useful embodiment of the invention 0.1 to 1
wt. % of a hindered phenol stabilizer is included in the
formulation. Useful hindered phenols used will contain one or more
substituted phenyl groups of the formula 3
[0035] where R is a C.sub.1-4 alkyl group and, most preferably, a
tertiary butyl group. Where more than one,
3,5-dialkyl-4-hydroxyphenyl group is present, they will be joined
through a linking group and the resulting compounds will correspond
to the formula 4
[0036] where n is an integer from 2 to 4 and L represents the
linking group.
[0037] Representative linking groups can include: 5
[0038] It is especially advantageous when the above-identified
linking moieties are substituted with
3,5-di-t-butyl-4-hydroxyphenyl groups. Representative hindered
phenol compounds of the above types include:
[0039] 4,4'-methylenebis(2,6-di-t-butylphenol);
[0040] tetrakis[methylene
(3,5-di-t-butyl-4-hydroxyhydrocinnamate)methane;
[0041]
1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)-benzene;
[0042] 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-s-triazine 2,4,6
(1H,3H,5H)trione;
[0043]
N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propanyl]-hydrazine;
and
[0044] octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate.
[0045] All of the foregoing materials are commercially available.
Tetrakis[methylene (3,5-di-t-butyl-4-hydroxyhydrocinamate)]methane
and octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate are
particularly useful hindered phenols which can be used in
conjunction with the mercaptobenzimidazole compound for the
compositions of the invention.
[0046] In another highly useful embodiment, 0.1 to 1 wt. % of a
processing aid is included in the formulation. Conventional
processing aids such as fatty acids, fatty acid metal soaps, fatty
acid amides, long chain aliphatic amides, fatty acid esters,
silicone oils, natural and synthetic hydrocarbon waxes, low
molecular weight polyethylene waxes, low molecular weight aliphatic
resins and combinations thereof can be used for this purpose.
Compositions wherein a fatty acid metal soap, such as calcium
stearate or aluminum stearate, is employed in combination with the
mercaptobenzimidazole compound are particularly advantageous.
[0047] To prepare the compositions, all of the ingredients can be
dry blended and used as such or, as is more typically the case,
melt blended prior to use. This latter procedure insures intimate
mixing of the filler, mercaptobenzimidazole compound and any
optional additives prior to extrusion since many extrusion
operations do not utilize extruders having sufficient mixing zones
to insure homogeneity of the extrudate. Mixers capable of imparting
high shear, such as Banbury mixers, twin screw extruders or the
like, can be used to accomplish the melt blending. Another useful
approach in preparing the compositions is to prepare a concentrate
or masterbatch of the base resin or another readily processible
polyolefin resin which contains the inorganic filler,
mercaptobenzimidazole compound and any optional ingredients and
then to "let down" the concentrate in the base resin during the
melt blending operation to produce the final formulation.
[0048] The compositions of the invention can be utilized in any
operation where a white-filled polyolefin is extruded through a
single die opening, such as a slit or circular die, or multiple die
opening. While they are particularly effective in reducing die lip
build-up in film extrusion and coextrusion processes they can also
be advantageously utilized for extrusion coating, wire and cable
coating, blow molding, film blowing, fiber spinning and the like.
Reduced die drool is also observed when a concentrate is processed
and extruded, such as when the concentrate is pelletized using a
strand cutter.
[0049] The following examples illustrate the invention more fully.
Unless otherwise indicated, all parts and percentages reported in
the examples are on a weight basis.
[0050] All compositions were prepared by first preparing a
concentrate. Concentrates were prepared using a Farrel OOC Banbury
mixer having a capacity of 2400 cc. All of the ingredients were
dry-blended and the preheated (35.degree. C.) chamber of the
Banbury filled with the mixture. A pressure of 40 psi was then
applied with mixing (125 rpm). When flux was achieved, i.e., the
temperature of the mixture in the chamber reached approximately
132.degree. C. (usually about 40-50 seconds), the ram was raised
for 15 seconds and any material collected in the throat of the
mixer scraped into the mixing chamber. Pressure was reapplied and
mixing continued for at least 3 minutes or until the temperature
reached 171.degree. C. The melt was then pelletized at 182.degree.
C. using a 2.25 inch single screw extruder (L/D=23; 10 rpm)
connected to an underwater pelletizer. The concentrates were then
let-down into the appropriate amount of the polyolefin resin in
order to obtain the extrusion composition.
EXAMPLE 1
[0051] A white composition suitable for extrusion coating and
coextrusion was prepared in accordance with the invention. The
composition was comprised as follows:
1 50% LDPE (MI 5.6 g/10 min; density, 0.923 g/cm.sup.3) 25% LDPE
(MI 9 g/10 min; density, 0.923 g/cm.sup.3) 24.7% TiO.sub.2 (Rutile;
average particle size 0.2 microns) 0.2% Aluminum Stearate (AlSt)
0.1% Zinc 2-mercaptotolylimidazole (ZMTI)
[0052] The composition was prepared by letting down one part of a
concentrate prepared as described above and containing 50%
TiO.sub.2, 49.4% of the 9 MI LDPE, 0.4% AliSt and 0.2% ZMTI into
one part of the 5.6 MI LDPE.
[0053] To evaluate die lip build-up the composition was then
extruded at 235.degree. C. using a Haake twin screw equipped with a
11/2 inch slit die with 40 mil opening. The extruder was operated
at 150 rpm. As the extrusion proceeded, the die lip was examined
after one hour and at 30 minute intervals thereafter and the width
of the amount of drool accumulated on the lip of the die measured.
The amount of accumulated die drool was then reported as a
percentage of the overall die width. Die drool results obtained for
the white composition prepared above were as follows:
2 60 minutes 5% build-up 90 minutes 15% build-up 120 minutes 30%
build-up 150 minutes 40% build-up 180 minutes 45% build-up
COMPARATIVE EXAMPLE 2
[0054] To demonstrate the significance of the above results a
comparative formulation was prepared and evaluated. The comparative
formulation was identical in all respects to that of Example 1
except that the ZMTI was omitted and replaced with 0.1% of a
hindered phenol antioxidant (Irganox 1010)--a conventional
stabilizer additive commonly used in filled polyolefin compositions
All of the procedures used to prepare and evaluate the comparative
composition were identical to that described for Example 1. Die lip
build-up results obtained for the comparative composition were
markedly inferior to those obtained with the composition of the
invention as evidenced by the following test results.
3 60 minutes 40% build-up 90 minutes 80% build-up 120 minutes 90%
build-up 150 minutes 95% build-up
EXAMPLES 3 AND 4 AND COMPARATIVE EXAMPLE 5
[0055] Following the procedure described for the preparation of
white concentrates, the following compositions were prepared.
4 Example 3 Example 4 Comparative Example 5 LDPE 50 50 50 TiO.sub.2
49.3 49.3 49.3 AlSt 0.3 0.3 0.3 ZMTI 0.2 -- -- MTI -- 0.2 --
Irganox 1010 -- -- 0.2
[0056] The LDPE used had an MI of 9 g/10 min and density of 0.923
g/cm.sup.3. Rather than letting the concentrates down into
additional resin, the concentrates were evaluated directly for die
lip build-up during extrusion. Extrusion of highly filled
compositions is considered to be a more rigorous test and
considerably shortens the time required for testing. Die lip
build-up results obtained for the above white concentrates were as
follows:
5 Percentage Die Lip Build-up Extrusion Time Example 3 Example 4
Comparative Example 5 5 minutes 25 30 80 10 minutes 30 45 90 20
minutes 45 50 95 40 minutes 50 50 98
[0057] The marked reduction in die drool obtained with the white
compositions of the invention is apparent from the above
results.
EXAMPLE 6
[0058] When a mercaptobenzimidazole compound is employed in
conjunction with a hindered phenol compound, comparable reductions
in die drool are possible. For example, using 0.2% of a mixture
comprised of equal parts of ZMTI and Irganox 1010 in a concentrate
containing 50% LDPE, 49.3% TiO.sub.2 and 0.3% AlSt gives results
comparable to those of Examples 3 and 4.
* * * * *