U.S. patent application number 10/082604 was filed with the patent office on 2002-09-05 for plastic logs.
Invention is credited to Kelley, Patrick W..
Application Number | 20020122941 10/082604 |
Document ID | / |
Family ID | 26767657 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020122941 |
Kind Code |
A1 |
Kelley, Patrick W. |
September 5, 2002 |
Plastic logs
Abstract
Plastic logs having a smooth, textured, glossy surface with a
nominal diameter greater than 2 inches and a flexural modulus at
40.degree. F. of at least 70,000 psi. Thermoplastic material
comprising such logs is preferably substantially polyolefin and
other plastic materials having a higher melt temperature, e.g. a
melt temperature at least 20.degree. C. higher than the melt
temperature of the polyolefin component. Such logs are produced by
extrusion through a circular die to a heat transfer medium Such
extruded logs are especially useful for durable fencing.
Inventors: |
Kelley, Patrick W.;
(Saylorsburg, PA) |
Correspondence
Address: |
Thomas E. Kelley
P.O. Box 300
East Burke
VT
05832
US
|
Family ID: |
26767657 |
Appl. No.: |
10/082604 |
Filed: |
February 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60272743 |
Mar 2, 2001 |
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Current U.S.
Class: |
428/401 |
Current CPC
Class: |
B29C 48/09 20190201;
B29C 48/175 20190201; B29C 48/911 20190201; Y10T 428/298 20150115;
B29C 48/13 20190201; B29K 2023/06 20130101; B29L 2031/06 20130101;
B29K 2067/00 20130101; Y02W 30/62 20150501; B29K 2023/12 20130101;
B29C 48/10 20190201; B29L 2031/73 20130101; B29B 17/0042
20130101 |
Class at
Publication: |
428/401 |
International
Class: |
D02G 003/00 |
Claims
What is claimed is:
1. A plastic log having an average diameter greater than 2 inches,
a flexural modulus at 40.degree. F. of at least 70,000 psi and a
diameter deviation in the range of 2 to 60%.
2. A log of claim comprising at least 80% of thermoplastic
material.
3. A log of claim 2 wherein said thermoplastic material comprises
at least one polyolefin selected from the group consisting of
polyethylene and polypropylene.
4. A log of claim 3 further comprising at least one other polymeric
material having a melt temperature at least 20.degree. C. higher
than the melt temperature of said polyolefin.
5. A plastic log having deviations in diameter simulating a natural
wood log comprising at least 80% polypropylene and having an
average diameter greater than 2 inches, a flexural modulus at
40.degree. F. of at least 90,000 psi and a diameter deviation
defined by the algorithm ((D-d)/D).times.100 in the range of 2 to
60%, where D is the maximum diameter and d is the minimum
diameter.
6. A method of producing a plastic, cylindrical log comprising
extruding through a circular die a plastic material to form a
cylindrical mass with a molten surface and cooling said molten
surface with an air stream from an annular nozzle proximate to said
die.
7. A method of claim 6 wherein said shape is further cooled by
contacting with an aqueous fluid.
8. A method of claim 7 wherein said shape is further cooled by
natural air convention around a supported length of log.
9. A method of claim 8 further comprising pulling said shape from
said die.
Description
[0001] Disclosed herein are plastic logs which are useful for
landscaping and methods of making such logs, e.g. from recycled
plastic materials.
BACKGROUND OF THE INVENTION
[0002] Highly segregated and homogenous, scrap plastic can be
recycled as molding resin. Mixed plastic typically have a variety
of properties, e.g. variable melt temperatures and low values of
mechanical properties, that make them difficult to process into
useful articles.
[0003] Despite the difficulties U.S. Pat. No. 5,916,932 discloses
the processing of recycled curbside plastic tailings materials into
composite building materials composed of an extruded mixture of
high density polyethylene and a thermoplastic coated fiber material
such as fiberglass. The plastic tailings is a mixture of recycled
plastic with polyethylene terephthalate (PET) soda bottles and high
density polyethylene (HDPE) milk and water bottles removed. The
plastic tailings typically comprised 90.2% HDPE, 4.5% PET, 3.2%
polyvinyl chloride (PVC), 0.5% polypropylene (PP) and 1.6% other
plastic. The plastic tailings was mixed with glass fiber and
extruded into a mold and water cooled for 3 hours providing a
shaped composite useful for railroad tie applications.
[0004] An object of this invention is to provide a convenient
method for recycling plastic into a log shapes for use as
fencing.
SUMMARY OF THIS INVENTION
[0005] This invention provides plastic logs in sizes useful for
fence applications, e.g. having an average diameter greater than 2
inches, preferably at least about 3 inches. Such logs are
characterized by a fiexural modulus at 40.degree. F. of at least
100,000 psi. Such logs are further characterized by a diameter
deviation which provides a log-like appearance. In preferred
aspects the logs of this invention have a smooth and/or glossy
surface, e.g. similar to the texture of barkless logs.
[0006] Logs of this invention preferably comprise a substantial
amount of recycled thermoplastic material, e.g. at least about 80%
thermoplastic material. Preferred aspects of this invention provide
plastic logs substantially comprising polyolefin selected from the
group consisting of polyethylene (e.g. HDPE) and polypropylene
(PP). The composition of such polyolefin logs can preferably
farther comprise at least one other polymeric material having a
melt temperature higher than the polyolefin material, e.g. at least
about 20.degree. C. higher than the melt temperature of the
polyolefin.
[0007] In other aspects of the invention plastic logs can
substantially comprise other tough plastics such as ABS and other
styrenic polymers, polycarbonates, acrylics, PET and nylons.
[0008] This invention also provides methods of producing a plastic,
cylindrical log by extruding a plastic material through a circular
die to form a cylindrical mass with a molten surface and cooling
the molten surface with an air stream The air stream preferably
flows from an annular nozzle proximate to said die.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 serves to illustrate an embodiment of heat transfer
of an extruded log shape.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0010] As used herein the term "log" means a nominally cylindrical,
extruded shape which can be cut into useful lengths.
[0011] As used herein the term "average diameter" is determined
from the average of four measurements of log diameter at 45.degree.
increments at a cross sectioned cut of a log.
[0012] The logs of this invention preferably have a visible
deviation in diameter to simulate a natural wood log. Such diameter
deviation is be expressed as the percent difference between the
minimum diameter (d) and the maximum diameter (D) by the following
formula:
Diameter deviation=((D-d)/D).times.100
[0013] Such diameter deviation is at least 2% and less than 60%,
more preferably at least 4% and less than 40%, even more preferably
in the range of 5 to 25%.
[0014] As used herein the term "flexural modulus" means a measure
of resistance to bending and is determined by measuring the
deflection (D) resulting from a load (W) on the center span of a
length (L) of log of average radius (r). Flexural modulus, E, is
determined from the formula
E=(W/D)(L.sup.3/12.pi.r.sup.4)
[0015] The logs of this invention preferably have a flexural
modulus of at least 70,000 pounds per square inch (psi) at
40.degree. F., more preferably at least 90,000 psi even more
preferably at least 110,000 psi.
[0016] The logs of this invention are fabricated from recycled
plastic materials, e.g. industrial or household waste. A preferred
composition comprises a substantial amount of polyolefin, e.g.
preferably at least 80% polyolefin, more preferably at least 90%
polyolefin, and selected from the group consisting of polypropylene
and the polyethylenes and mixtures thereof Useful polyethylenes
include high density polyethylene (HDPE), low density polyethylene
(LDPE) and linear low density polyethylene (LLDPE). The composition
can comprise other plastic materials which typically have a higher
melting temperature than polyolefin such as PET and PVC. Such other
components may be present in blends of polyolefin from industrial
scrap, e.g. of polymer blends or alloys. Alternatively, such other
components may be present in recycled household plastic scrap. The
composition can also comprise other materials commonly found in
plastics, e.g. reinforcing fillers and fibers such as glass fiber
and high melt temperature fibers. While other filler materials such
as wood chips can be used, it is preferred for many applications to
keep readily biodegradable materials to a minimum to enhance the
durability of the logs.
[0017] Scrap plastic for recycle is preferably shredded and dried
to remove moisture which can vaporize in extruders causing
cavitation. Useful drying methods include passing the plastic
through a fluidizing bed of low relative humidity air to extract
typically surface moisture from the scrap plastic. In general it is
not necessary to remove dried "soil", e.g. residual contents such
as food, beverages or cleaners from the plastic. Even with drying
some moisture is likely to enter the extruder. Venting practices
well known in the extruder art can be employed to remove vaporized
moisture from the extruder.
[0018] Mixed scrap plastics are preferably blended to provide a
composition range requiring minimal adjustments, e.g. in extruder
operating temperatures. In preferred embodiments useful
compositions include at least 80% polyolefin and the extruder
conditions are adjusted for processing a substantially polyolefin
composition. It is also preferred to provide a color concentrate to
provide natural wood colors to the extruded shape. Desirable colors
include shades of browns, yellows and grays to simulate aged
wood.
[0019] Shredded plastic scrap and color concentrate are fed to a
extruder to provide a molten mass at about the melt temperature of
the polyolefin component The extrudate is preferably a composite
comprising a matrix of molten polyolefin with dispersed particles
of higher melting plastic. The extrudate is forced through a
circular die to form the log shape. Due to the phenomena of die
swell it is useful to employ an extended die with an progressively
increasing diameter to minimize swell after the molten mass has
left the confinement of the die. It is generally preferred to cool
the surface of the extruded shape as uniformly and rapidly as
possible using a heat transfer fluid directed from an annular
source place close to the die. Useful heat transfer fluids include
air and water. Air, e.g. cooled air is a preferred heat transfer
fluid which can put a smooth, glossy skin on a log without unduly
or inadvertently chilling the die. With reference to FIG. 1 there
is shown an embodiment of a heat transfer fluid nozzle I for
directing a cooling fluid 2, e.g. gas or liquid, to the surface of
an extruded shape 3. A nozzle lip 4 directs the fluid away from the
face of an expanding circular die 5. After initial heat transfer
for forming a skin, supplemental heat transfer can be effected by
spray nozzles 6 directing a cooling liquid 7 to the log. Surface
deformation at the die to provide a natural texture on the surface
is believed to result from a combination of irregular shrinkage and
mass migration in the short zone from the edge of the die until a
rigid skin is formed by heat transfer. Such natural texture imparts
a log like character to an otherwise cylindrical shape.
[0020] Because long lengths of extruded log are preferred and
because of slow heat transfer into the bulk of the extruded shape
it is useful to extruded in a horizontal direction supporting the
shape on rollers or other conveyer system as close to the die as
possible to minimize distortion from gravity induced sag. Because
of the bulk of the log and slow heat transfer it is useful to
effect heat transfer by immersion in a heat transfer liquid such as
water as the shape is being carried from the die. Immersion can be
effected by shower or bath. Moreover, because there is little
compressive strength in the molten mass exiting the die, it is
useful to carry the shape from the die at a constant speed, e.g. at
about the speed of extrusion, to minimize cross sectional
distortion. In one preferred embodiment the extruded shape is
pulled at faster than the linear speed of extrusion to provide an
extruded shape with reduced cross section as compared to the die;
such reduced crosssectioned extruded shapes, e.g. not more than 3.5
inches in average diameter, are especially useful for fence rails.
In another preferred embodiment the extruded shape is pulled at
slower than the linear speed of extrusion to provide am extruded
shape with enlarged cross section as compared to the die; such
enlarged cross-sectioned extruded shapes, e.g. not less than 3.5
inches in average diameter, are especially useful for fence posts.
Pulling of the extruded shape can be effected by friction contact
with a moving surface.
[0021] Cooling is desirable to stabilize the extruded shape. The
extruded shape is preferably conveyed in a heat transfer fluid
until the outer layers are sufficiently cool to maintain a desired
log shape. Logs can be cut from a moving, cooling shape into
desired lengths, e.g. 8 to 10 feet is a useful length for fence
rails and 5 to 7 feet is a useful length for fence posts. Rail
slots in posts can be cut by power saws or mortising drills.
Tapered rail ends can be cut by power saw.
[0022] The following example illustrates one embodiment of the
invention.
EXAMPLE 1
[0023] Plastic scrap consisting essentially of HDPE and PET is
shredded, dried and fed to an extruder feed hopper with a brown
color concentrate. The extruder heaters are set to bring the
plastic mass to a temperatures of 200.degree. C. as it is fed
through an expanding circular die having an exit diameter of 3.5
inches. An annular air nozzle is set adjacent to die face to blow
cold air along the surface of the extruded shape in the direction
of extrudate motion. The extruded shape is supported by a roller
conveyor from a distance of about 2 inches from the annular air
nozzle through 5 feet of a water shower.
[0024] Logs with an average diameter of 3.5 inches were cut in 9
foot lengths and stored on racks to permit air convection cooling
of residual heat.
[0025] A log produced in this example was supported at an 8 foot
span and loaded by an 85 pound weight at mid span. The log
deflection was 1.625 inches. Flexural modulus was determined to be
about 132,000 psi.
* * * * *