Filled resin compositions containing atactic polypropylene

Filled thermoplastic compositions have a lower melt index than do the virgin resins, leading to problems in molding. The melt index of the filled resin can be raised by the addition of 3-12 wt.% atactic polypropylene.

BACKGROUND OF THE INVENTION 
This invention relates to resin compositions. More particularly, it relates 
to filled resin compositions containing atactic polypropylene. 
Filled resin compositions are well known in the resin industry. "Filling" 
resin with an organic or inorganic filler is an accepted method of 
"stretching" the available supply of a particular resin or of producing a 
resin composition at a lower cost per unit. Whittington's "Dictionary of 
Plastics" (Technomic Publishing Co., Stamford, CT., 1968) discusses 
fillers. 
The preparation of a mixture of isotactic and atactic polypropylenes is 
disclosed in U.S. Pat. No. 3,640,921. Other U.S. patents, such as U.S. 
Pat. Nos. 2,927,047; 2,956,042; 3,220,966; 3,261,889; 3,370,106; and 
3,375,303 are typical of the prior art concerning the use of atactic 
polypropylene with other resins. 
Filling a resin, such as low density polyethylene, with a filler, such as 
limestone or calcium carbonate, results in a composition that typically 
has a melt index lower than the melt index of the virgin resin. Thus, even 
though filled resins may have certain economic advantages, one of the main 
disadvantages arises during the extrusion of these resins. The melt index 
of the filled resin is lower than that of the virgin resin, the amount of 
lowering depending on the percentage of filler in the finished resin 
composition. Materials with a lowered melt index require special attention 
during extrusion. One method of raising the melt index of such a finished 
filled resin is to raise the extruder temperature, but this can result in 
thermal decomposition or some associated degradation, of the resin, thus 
giving an inferior product. 
SUMMARY OF THE INVENTION 
Our invention overcomes this major disadvantage, in that the composition 
that we claim has a melt index almost equal to that of the virgin resin 
used. 
Our filled thermoplastic resin composition contains atactic polypropylene 
and comprises 
(A) A MAJOR AMOUNT OF A FILLED RESIN COMPRISING 
(1) a basic resin selected from the group consisting of polyethylene, 
polypropylene, polystyrene, polybutylene, copolymers of vinyl acetate and 
ethylene, and acrylic resins, and 
(2) a filler selected from the group consisting of organic fillers and 
inorganic fillers, and, 
(B) A MINOR AMOUNT OF ATACTIC POLYPROPYLENE. 
DETAILED DESCRIPTION OF THE INVENTION 
The resins used as the bases for the filled compositions can be any of the 
typical thermoplastic resins. These thermoplastic resins include 
polyethylene, polypropylene (isotactic), polybutylene, polystyrene, vinyl 
acetate-ethylene copolymers, and acrylic resins. In the finished 
composition, these resins may contain such additives as coloring pigments, 
antioxidants, mold release agents, etc., but, typically, the total amount 
of such additives is usually small enough so that the melt index of the 
resultant composition is not greatly different from that of the virgin 
resin. However, as noted above, when a filler is added, depending on the 
percentage of filler in the finished composition, the melt index is 
lowered. 
The fillers used in such compositions are organic and inorganic in nature. 
The chemical and physical properties of the various fillers are well known 
in the trade and need not be discussed here. Examples of organic fillers 
are wood flour, cellulose, lignin, keratin, soybean meal, cherry pit 
flour, starch and peanut shells. Examples of inorganic fillers are calcium 
carbonate (limestone), wollastonite, silica, gypsum, mica, fly ash, clay, 
and talc. The relative ratio of resin to filler, in a filled resin, can 
vary from about 19 to 1, meaning that the wt.% resin in a filled resin can 
vary from about 95 to about 50. 
As mentioned above, atactic polypropylene can be prepared in various ways 
and separated from the isotactic form. The atactic form is amorphous and 
the isotactic is crystalline--the atactic polypropylene is the desired 
component for this invention. It is desirable that the atactic 
polypropylene used have at least 98 wt.% of the atactic form, with a 
maximum of 2 wt.% of the isotactic form present. A commercially-available 
grade of atactic polypropylene, such as Polytac, from Crowley Chemical 
Co., New York, New York, contains about 98% atactic form. 
To improve the melt index of a filled resin composition, we have found that 
the addition of from 3 to about 12 wt.% atactic polypropylene, based on 
the total wt. of the finished filled composition (and excluding the 
above-mentioned additives such as pigments, antioxidants, etc.) is the 
desired range. A preferred range is from about 5 to about 10 wt.%. The 
exact percentage to be added to the filled composition depends on the 
loading of the filler in the filled resin composition, the type of filler 
used, and the improvement in melt index desired. If not enough atactic 
polypropylene is added, the melt index of the filled composition shows 
only a slight improvement. On the other hand, if too much atactic 
polypropylene is added, the resultant composition becomes tacky, with the 
resultant disadvantages attached thereto. 
Various procedures can be used in preparing the finished resin composition 
of the invention. For example, the filler, along with other additives, can 
be mixed with the virgin resin on a Banbury or a 2-roll mill, with the 
atactic polypropylene being mixed in a separate step. Or, the filler, the 
resin, and the atactic polypropylene can be mixed in one step. Such 
procedures are well known in the resin industry and need not be discussed 
here.

The examples below will show how the addition of atactic polypropylene to a 
filled resin composition improves the melt index of the composition. 
EXAMPLE 1 
______________________________________ 
Ingredients (parts) 
(a) (b) (c) (d) (e) 
______________________________________ 
CaCO.sub.3 -- 10 10 10 10 
(Camel Carb - 
H.T. Campbell & Sons Corp.) 
Atactic Polypropylene 
-- -- 2 4 6 
(Polytac 500 - 
Crowley Chemical Co.) 
Polyethylene (low 40 30 28 26 24 
density ) - (EM 447 - 
Cities Service Co.) 
Melt Index (STM-1238) 
20.5 14.8 21.6 29.9 50.2 
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In this example, the filled resin had a loading of 25% (based on the 
finished composition that was tested), and the wt.% of atactic PP added 
varied from 5 to 15 (based on the finished composition). The use of about 
5 wt.% atactic PP restored the melt index of the filled composition to 
approximately that of the virgin resin. The use of 15 wt.% atactic PP not 
only resulted in a high MI but also gave a tacky composition. 
EXAMPLE 2 
______________________________________ 
Ingredient (parts) 
(a) (b9 (c) (d) 
______________________________________ 
CaCO.sub.3 -- 20 20 20 
(Camel Carb) 
Atactic PP -- -- 2 4 
(Polytac 500) 
PE (low density) 
40 20 18 16 
(EM 447) 
Melt index 20.5 8.2 14.1 21.4 
______________________________________ 
In this example, the loading was 50 wt.%, and the addition of 10 wt.% of 
atactic PP to the filled composition gave a melt index close to that of 
the virgin resin. 
EXAMPLE 3 
______________________________________ 
Ingredient (parts) 
(a) (c) (c) (d) (e) 
______________________________________ 
Clay ("Dixie" clay - 10 10 10 10 
hard kaolin - 
R.T. Vanderbilt Co.) 
Atactic PP -- -- 2 4 6 
(Polytac 500) 
PE (low density) 
40 30 28 26 24 
(EM 447) 
Melt Index 20.5 11.4 15.4 27.6 35.1 
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Here, at a 25 wt.% loading of clay, the addition of 5 wt.% atactic PP 
almost restored the melt index of the filled resin to the value of the 
virgin resin, while the addition of 10 wt.% atactic PP gave a filled 
composition with a larger melt index value. 
Additional tests, using polybutylene, PVA copolymers, and methyl 
methacrylate, with cellulose, gypsum, and fly ash as fillers, and using 5 
and 10 wt.% atactic polypropylene, give similar restoration of melt index 
to that of the virgin resin. 
While the present invention has been described with reference to particular 
embodiments, it will be appreciated by those skilled in the art that 
various changes and modifications can be made without departing from the 
scope of the invention as set forth.