Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
Calcium carbonate is a commonly used filler for
rigid polyviryl chloride (PVC) compounds used in making
various products such as pipes. While not commonly used,
5calcium carbonate has also been used as a filler in PVC
siding.
PVC products intended for exterior use require
protection from ultraviolet (UV) radiation to avoid
excessive fading and chal~ing. While some products are
10made with a separate outer layer or protective coating
adapted to provide such protection, it is erequently
desired to provide such protection against weathering by
incorporating one or more UV absorbers in the PVC
composition itself.
15Unfortunately UV stabilized, while PVC products
such as those used for building panels are subject to some
yellowing of the product; particularly during the initial
stages of exposure. Such yellowing can be reduced by
incorporating additional amounts o UV absorber. UV
20absorbers are, however, expensive and it is desirable to
use a minimum amount of UV absorber consistent with desired
resistance to weathering.
SUMMAR P THE INVENTION
25It is an object of the invention to provide an
improved PVC composition suitable for making white, rigid
PVC products such as building panels.
It has now been found that calcium carbonate may be
used successfully as a filler in white P~C compositions,
including building panels such as siding, provided finely
ground amorphous calcium carbonate is used and the
individual particles of calcium carbonate are-coated with
calcium of a higher fatty acid. More specifically, the
invention contemplates a white PVC composition comprising:
a) PVC;
b) between about 2 and about 50 pounds per
hundred pounds of PVC resin (PHR) of finely
divided amorphous calcium carbonate filler
having an average particle size between about
0.1 and about 1.0 micron with at least about
90% of such calcium carbonate particles used
having a maximum ~particle size of not more
than about 2 microns, the individual particles
of such filler being coated with calcium salt
of a higher fatty acid; and
c) an effective amount of a UV absorber.
In a preferred embodiment, stearic acid is utilized
so that the resulting calcium carbonate filler particles
are coated with calcium stearate. Preferred embodiments
also include the use of TiO2 as both a pigment and as a UV
absorber. The invention also contemplates rigid building
panels such as PVC siding comprising the composition of the
invention.
DETAIL~D DESCRIPTIQN OF THE INVENTION
As mentioned above, the composition of the
invention comprises white PVC, finely divided amorphous
calcium carbonate coated with calcium salt of a higher
fatty acid and a W absorber.
PVC suitable for use in compositions and rigid
building panels of the invention includes any of the
conventional PVC materials generally considered suitable
for use in the manufacture of rigid PVC products. These
include, for instance, materials such as polyvinyl chloride
itself, poly vinylidene chloride, copolymers thereof, post
chlorinated polyvinyl chlorides, mixtures of polyvinyl
chlorides with chlorinated polyethylenes or
acrylonitriles, butadiene/styre-ne copolymers, etc. PVC
material for use in the invention usually has a weight
average molecùlar weight between about 30,000 and about
200,000 more usually between about 50,000 and about
100, 000 .
It is generally preferred that the PVC used in the
products of the invention be at least about 80 wt~ vinyl
chloride polymer with from 0 to about 20 wt% of one or more
of the other monomers or copolymers mentioned being
present.
Suitable coated calcium carbonate filler is based
upon finely divided amorphous calcium carbonate such as
chalk. The use of more crystalline forms of calcium
carbonate such as marble does not appear to provide the
unexpected advantages found when coated particles of
amorphous calcium carbonate are used. Finely ground
amorphous calcium carbonate having an average particle
diameter between about 0.1 and about 1.0 microns with a
maximum particle size for at least about 90~ of the
particles of not more than about 2 microns is required.
The individual particles of amorphous calcium
carbonate are coated with the calcium salt of a higher
fatty acid, i.e., a fatty acid having at least 12 carbon
atoms in the molecule. Stearic acid is a preferred fatty
acid for use in preparing the product of the invention.
The calcium salt coating may be obtained in a conventional
manner by mixing the fatty acid with the calcium carbonate
particles, preferably at temperatures between about 60 and
about 200C so that the fatty acid reacts with the surface
of the calcium carbonate to form on the carbonate particles
an adherent coating of calcium salt. Such coating
substantially covers the individual particles, although it
should be understood that in some instances some of the
fatty acid may also be present on the surface of the
carbonate particles. Coated calcium carbonate ~iller used
in products of the invention is well known for other uses
such as in the manufacture of PVC products which do not
contain UV absorbers. Such filler is available, for
instance, under the trade name Omyalite 90T. Coated
calcium carbonate filler as d scribed herein is used in
products of the invention in amounts broadly ranging
between about 2 an~ about 50 PHR. For exterior
applications such as siding, where weatherability is a
problem, amounts between about 5 and about 35 PHR, more
especially between about 5 and about 12 PHR are preferred.
--4--
It is preferred that the total of calcium salt of
higher fatty acid present as coating on the calcium
carbonate particles and any unreacted higher fatty acid be
present in products of the invention in amounts not
exceeding about 3 P~R. Excessive amounts o higher fatty
acid or salts thereof can result in overlubrication,
whereby impact, strength and homogeniety o t~se finished
product is adversely affected.
As mentioned above, PVC products such as siding,
intended for exterior use require the incorporation of W
absorbers in the PVC composition if excessive fading or
chalking due to weathering is to be avoided. UV absorbers
may be any of the materials commonly sold for such purpose,
including for instance benzotriazoles, ben~ophenoner and
substituted acrylonitriles. Alternatively, additional
TiO2 may be incorporat~ed into the PVC composition so that
the Tio2 functions as a UV a~\sorber as well as a ~hite
pigment. TiO2 when used as a pigment is normally used in
amounts between about 1 and about 3 PHR. When additional
TiO2 is incorporated for the purpose of providing UV
protection as well as normal pigmentation, the amount of
TiO2 used is normally between about 5 and about 2S PHR.
Other UV absorbers, when used, are normally used in amounts
between about 0.1 and about 5 PHR.
The titanium dioxide used as a pigment or as a UV
absorber in the products of the invention may be any
titanium dioxide normally used as white pigme~station in
rigid PVC products. The rutile form of TiO2 is considered
most satisactory since its relatively higher refractive
index and reflectivity and opacity is desirable.
However, for economy it is possible to use up to about 40
wt% based on TiO2 of the anatase form. Excessive amounts
of anatase are undesirable because of the recognized
in~eriority of anatase relative to rutile in regard to
weathering characteristics of the finished product. This
is especially significant in the production of PVC building
panels, such as siding, intended for exterior use.
In addition to the basic ingredients of PVC, coated
calcium carbonate particles and TiO2 described above, the
products of the invention may contain other ingredients
normally used in rigid PVC products such as stabilizers,
processing aids, lubricants, impact modifiers, additional
fillers, etc. Such other ingredients, when used,
frequently are used in amounts totaling between about lO
and about 40 PHR. Conventional plasticizers such as
dioctyl phthalate, dihexyl phthalate, phthalate esters,
etc. may also be included in the! products of the invention.
Depending on the particular physical properties desired,
ot~er ingredients used, etc., plasticizer may be included
in compositions of the invention in amounts up to about 30
PHR.
Rigid PVC compositions of the invention may be
manufactured in any suitable conventional manner, such as
to powder or pellet extrusion, calendering, thermoforming,
etc., it being understood that suitable methods for
manufacturing rigid PVC products such as pipes, siding,
etc. are well known in the art and do not constitute a part
of this invention~ While manufacturing methods are not a
:, .
7~
part of the invention, it should also be understood that
the particular manufacturing technique selected may effect
the desirable formulation of the product of the invention
within the broad limits given above.
The followiny examples illustrate preferred
embodiments and advantages of the invention, but are not
intended to limit the scope of the invention. In exàmples,
yellowing of the various samples tested was measured after
six months exposure. This particular time interval was
selected because white PVC siding pigmented with TiO2
characteristically yellows to the maximum degree in about
this time at the location where these tests were carried
out. Following initial yellowing, chalking usually occurs
followed by further yellowing. The yellowing is normally
at its worst, i.e. most yellow, about 3-9 months after
initial exposure depending upon the climatic conditions to
which the siding is exposed.
EXAMPLE I
To evaluate the effectiveness of various forms of
calcium carbonate filler in reducing yellowing of white PVC
siding, a number of siding samples were prepared from
filled compounds formulated as described herein and exposed
in a southerly direction at an angle of about 45 in
northern New Jersey for a period of six months. The
various calc um carbonate filled PVC compounds lrom which
the siding panels tested were produced were formulated and
extruded in a conventional manner using screw extruders and
the siding panels were produced by conventional extrusion
--7--
6~3
techniquesO The method of manufacture was in all cases
substantially identical. The only difference in the
various panels tested was the type of calcium carbonate
filler used. For these tests the formulation used
comprised, in addition to the calcium carbonate filler, the
following ingredients:
Ingredient Parts by Weight
PVC Homopolymer (I.V. 0.90) lO0
Tin Stabilizer 1.6
Acrylic Impact Modifier 7.0
Process Aid 1.5
~ax 0.95
Calcium stearate 2.00
TiO2 (semi-rutile) 14.00
.
Calcium carbonate particles were in each instance
used in the formulation testedl in an amount of lO PHR.
Calcium carbonate particles used in forming siding samples
A-F, for which test results are reported below, were as
follows:
Sample A was a control sample in which no calcium
carbonate filler was used.
Sample B used calcium carbonate particles wet
ground to an average particle size of 2.5 microns from
amorphous chalk with the maximum particle size being about
lO microns (i.e. at least 90% of the particles were no
larger than lO microns in size). These calcium carbonate
particles were coated with calcium stearate.
79~
Sample C incorporated calcium carbonate particles
obtained by wet grinding marble to an average particle si~è
of 0.7 microns with a maximum particle size of 2 microns.
These particles also were coated with calcium stearate.
Sample D incorporated amorphous calcium carbonate
particles wet ground to an average particles size of 0.7
microns with a maximum particle size of about 2 microns.
These particles were coated with calcium stearate.
` Sample E incorporated calcium carbonate particles
ground from a relatively crystalline calcium carbonate to
an average particle size of 0.7 microns with a maximum
particle diameter of about 2 microns. These particles were
not coated with calcium stearate.
Sample F incorporated c:alcium carbonate particles
formed by precipitation and having particle si%e diameters
between 0.1 and 0.35 micron. These particles were not
coated with calcium stearate.
Table I below shows the results obtained when the
samples of siding described above were first exposed
immediately after manufacture and after six months'
exposure under the conditions described above. In Table I,
values are reported for both "Hunter Color Ll' (a
conventional test in which the L value measures lightness
with an L value of 100 being perfectly white) and the "b"
value (another conventional test in which the b value
indicates degree of yellowing with increasing yellowing
causing positive changes in b value).
_g_
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U~ _~ ~D ~
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From Table I it can be seen that the control sample
A containing no calcium carbonate filler has a delta b
(representing the difference between the b value measured
immediately after manufacture and that measured after six
months' exposure) of 0.7. By contrast sample D, the only
sample tested which was formulated in accordance ~ith the
invention, had a delta b after six months' of only 0.1.
Other samples tested, none of which were formulated in
accordance with the invention, had delta b values after six
months ranging from 0.6 to 0.9. It is thus apparent that
both the uncoated calcium carbonate filler and the coated
calcium carbonate filler in which crystalline calcium
carbonate was used were of essentially no help in improving
the yellowing characteristics of the finished siding. Even
the coated amorphous calcium carbonate having an average
particle size of 2.5 microns (~3ample B) was unsatisfactory
in this respect. Only the siding sample formulated in
accordance with the invention, i.e., containing very fine
ground amorphous calcium carbonate particles coated with
calcium stearate, provided this unexpected advantage.
EXAMPLE II
This example illustrates the effectiveness of the
finely divided amorphous calcium carbonate ~iller required
by the invention in reducing yellowing of white PVC siding
exposed in a southerly direction at an angle c~f about 45
degrees in Arizona for a period of nine months.
s~
The siding panels tested were produced in the same manner
described above in Example I. The control sample was
produced from the same formulation used in producing the
- control Sample A of Example I, while the remaining samples
tested in this example were produced using various amounts
of the same coated calcium carbonate particles utilized in
Sample D of Example I. The composition of the samples
tested in this example and changes in b values of the
samples tested after six and nine months are reported in
Table II below.
-12-
~L~
- CCl~
a~ ~ o o o o
. ~, JJ
aJ a~
~U
~a
~o
.,,
U~ o o o
. ~ . .
H C ~11~ t~
~ ~a
~ ~ . ~ .
O ~ ~ o ~ a
~ C~ ~
C)
aJ
Eit~ ~ H ~)
1~1
U~
t~
It can be seen that Examples H, I and J which
contain varying amounts of coated calcium carbonate filler
according to the invention exhibit substantially less
~ difference in b values than did the control Sample G which
did not contain the coated calcium carbonate filler. The
substantially larger differences in b value in Example II
versus those reported in Example I were due to the fact
that the test panels for Example II were exposed in Arizona
rather than New Jersey and were therefore subjected to
considerably greater amounts of solar radiation.
EXAMPLE III
This example demonstrates the usefulness of the
invention when chlorinated polyethylene (CPE) impact
modifier is used. Such impact modifier is known to cause
yellowing of PVC products to the extent that more expensive
ac~rylic impact modifiers have in the past normally been
used for PVC products intended for exterior use. As shown
in ~he example, white PVC products of the invention may
include ingredients such as CPE which normally promote
yellowness upon prolonged exposure of the product to the
sun. For this evaluation four compounds identified below
as compounds K,L, M & N were tested according to the
procedure outlined in Example I, Compounds K and M had the
following compositions.
-14-
Compound K Compound
Ingredient (PHR) (PHR)
PVC Homopolymer
(0.9 I.V.) 100 100
Tin Stabilizer 1.6 1.6
CPE 10.0 15.0
Process Aids 1.5 1.5
Calcium Stearate 2.0 2.0
Wax 0.95 0 95
i2 7.0 7 0
10Compound L was identical witb compound K except for
the addition of 20 PHR of the coated calcium carbonate of
Sample D of Example I and compound N was identical with
compound M except for the addit:ion of 35 PHR of the coated
calcium carbonate of Sample D of Example I. When formed
15into test panels and evaluat~ed for changes in b value
according to procedures outlines in Example I, the
following results were obtained.
Sample: R L M N
Difference in
value after 6 2.2 1.11 2.58 1.24
mos. exposure
