Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1996-12-23
2002-03-26
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S205000, C523S209000, C523S216000, C524S425000, C524S440000, C524S443000
Reexamination Certificate
active
06362252
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to extender-filled thermoplastic compositions. More particularly, the invention relates to a polymer composition, such as a thermoplast, that can be highly loaded with low cost fillers and that can be used for manufacturing articles of high flexibility, strength, and adhesive properties suitable for many critical applications.
DESCRIPTION OF THE PRIOR ART
In the last decades, the number of thermoplastic materials have increased not so much through development of new polymers, but rather through modification of existing ones. By blending two or more different polymers, and/or by adding modifiers and fillers it becomes possible to modify such properties of articles produced from the aforementioned polymer compositions as strength, resistance to UV, resistance to oxidation, shrinkage, electrical conductivity, adhesive properties, and cost. For example, some inexpensive extender filler can increase the strength of the polymeric products and decrease their cost. All too often, however, while the targeted properties improve, some other properties deteriorate beyond the level acceptable for the given application.
It is a widely known fact that high density polyethylene and polypropylene, the materials which are easy to extrude and mold, have high shrinkage, from 2.5 to 5%, and a large coefficient of linear thermal expansion. The coefficient of linear expansion for polypropylene between 0 and 100° C. is from 1×10
−4
/° C. to 2.5×10
−4
/° C., and for polypropylene at 20° C. is 1.1×10
−4
/° C. That makes these materials less applicable for products which require high dimensional accuracy. However, it is also known that filling of polymers usually reduces their shrinkage and the coefficient of thermal expansion.
The filler material may be in the form of particles, flakes, fibers, etc. In the context of the present invention, the word “particle” means any particulate element such as a sawdust particle, a finely cut fiber, a flake of mica, etc.
The importance of fillers in the plastic industry is to some degree reflected by the fact that production of fillers has been growing at a faster pace than that of plastics in general. Inexpensive extenders having substantially microsphere-like particles, such as calcium carbonate, reground post-industrial and post-consumer plastics (hereinafter referred to either as “used plastics” or “recycled plastics”), are commonly used as polymer fillers. Extrapolating from the statistics for 1967 to 1985 (provided by Kiln and Co.), the current total annual US use of extender fillers could be above 2,000,000 tons. Other sources have higher estimates.
U.S. Pat. No. 3,830,776 of August 1974, issued to Carlson and Banks, discloses a method for separating particulate fractions from fly ash for use as a filler for epoxy. The compositions formed by this method have high crush resistance and strength, but are relatively rigid.
U.S. Pat. No. 4,294,750, issued to Klingaman and Ehrenreich in October 1980, discloses a method for separating filler particles from coal-burning power plants' fly ash for use in a nylon-based composition. These pyroplastoid particles are ellipsoidal in shape and, by weight, at least 90% of them are less than 25 &mgr;m in size.
In 1986, Electric Power Research Institute (EPRI) in Palo Alto, Calif., published a study (EPRI CS4765, Project 2422-11), Evaluation of Plastic Filler Applications for Leached Fly Ash. The study looked into the commercial potentials of acid-leached fly ash from coal-burning power stations. Their conclusion was that the leached fly ash has a potential as a filler for polymeric compositions. They also concluded that the higher the ash content in a polypropylene or nylon composition, the more drastically the elasticity of the composition drops. That deficiency explains why such an inexpensive and widely available extender, such as fly ash is not widely used in the polymer industry. Instead, much of the fly ash, a plentiful byproduct of power generation, is currently disposed of in landfills at a considerable expense to coal-burning power stations.
U.S. Pat. No. 5,308,693 of May 1994, issued to Ryle et al, relates to Unstretched Synthetic Papers and Methods of Producing Same and discloses a non-stretched synthetic paper having 10 to 25 wt. % diatomaceous earth-filled and high density polyethylene-based compositions. Synthetic paper is increasingly being used in countries where wood is expensive. Since synthetic paper does not produce dust or tear easily, it has additional value for the high speed printing industry. Despite the advantages of synthetic paper, its cost is still too high to compete with wood-pulp paper in countries having abundant wood resources.
To improve the bond between a filler and the rest of the polymer composition, various so-called “coupling agents” are empirically selected, and fillers are treated with them either prior to being mixed into the composition, or during in-line compounding. For example, it is known that treatment of fine-grain fillers with silicone hydrates (Si
n
H
2n+2
) maximizes the hydrophobicity and optimizes the electrical properties of filled polymer compositions; it is known that preliminary treatment of a filler with the hydrates of Si or Ti will improve the impact strength, thermal resistance, water stability, and strain-stress properties of filled compositions.
Atactic polypropylene has been known to increase the levels of loading compositions with carbon black and flame retardants (see U.S. Pat. No. 4,425,262 of January 1984). Atactic polypropylene has also been used as a thermally-removable binding agent for ceramics (see U.S. Pat. No. 5,256,609 of October 1993, issued to Dolhert). This invention relates to the clean burning green ceramic tape cast system using atactic polypropylene binder. However, such compositions are not suitable for molding into rigid components that maintain some flexibility.
While the extender fillers increase the modulus of elasticity of a composition, they drastically reduce its elongation at rupture. For any product which incorporates flexing elements or which has to withstand even occasional surface impacts, such as containers, furniture, instrument housings, automotive oil pans, bumpers and body panels, this reduced elongation is detrimental. Thus, for all practical purposes these filled polymers cannot be effectively used for items requiring stretching or bending properties.
Table 1 shows the change of some properties for a selected group of polymer compositions loaded 30 to 40 wt. % (percentage in weight) with various substantially microspheric fillers.
TABLE 1
Modulus
of
Tensile
Elonga-
Amount
Elasticity
strength
tion
of Filler
(bending)
at yield
at yield
Polymer & Filler
wt. %
MPa
MPa
%
Polypropylene
0
931
23
93%
Filled Polypropylene
Talc
40 wt. %
2,617
22
8%
CaCO
3
40 wt. %
1,939
18
12%
Glass Microspheres
40 wt. %
1,497
14
43%
Cenospheres
40 wt. %
1,731
16
33%
Polyamide 6,6
0
2,335
72
58%
Filled Polyamide 6,6
Talc
40 wt. %
5,265
73
1.6%
CaCO
3
40 wt. %
4,411
75
1.9%
Glass Microspheres
30 wt. %
3,008
56
12%
Cenospheres
40 wt. %
4,227
65
1.9%
Polyvinylchloride
0
2,525
51
32%
Filled Polyvinylchloride
Talc
40 wt. %
5,954
44
1.8%
CaCO
3
40 wt. %
4,609
42
2.3%
Glass Microspheres
40 wt. %
3,853
29
30%
Cenospheres
40 wt. %
4,160
27
22%
High Density Polyethylene
0
*
*
*
Filled High Density
Polyethylene
CaCO
3
(sold as PE-3CC-3
33 wt. %
172
9
—
by Washington Penn)
CaCO
3
(sold as RTP-740
40 wt. %
1,379
17
11%
by RTP)
*Data unknown to the author.
The data given in Table 1 are typical; highly extender-filled compositions have low relative elongation and do not have high tensile strength. The actual data related to filled polypropylene, polyamide 6,6, and polyvinylchloride are taken from
Plastics Compound,
1986, v. 9, no. 7, pp. 12-18. The actual data about calcium
Cain Edward J.
Zborovsky I.
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