Agitating – Rubber or heavy plastic working – Stirrer is through-pass screw conveyor
Reexamination Certificate
1997-07-24
2001-04-24
Teskin, Fred (Department: 1713)
Agitating
Rubber or heavy plastic working
Stirrer is through-pass screw conveyor
C366S088000, C366S142000, C366S291000, C366S301000, C366S319000, C425S203000, C425S378100, C528S501000
Reexamination Certificate
active
06220745
ABSTRACT:
BACKGROUND OF THE INVENTION
(1). Field of the Invention
The present invention relates to a method of removing liquids from water containing resin of high melting point over 200° C., and more particularly to a monitoring system for removing liquids from the high melting point resin by melt-kneading in a co-rotating twin screw extruder for removing the water component with extrusion, and method and apparatus as well as molding thereof.
(2). Background Information
Generally, resin materials produced in a polymer manufacturing process of thermoplastic resins or ground materials produced in a recycling process of the waste plastic products (hereinafter simply referred to as resin materials) contain a relatively large quantity of liquid so that a liquid removing process is required to remove the water component at the end of each process.
Hitherto, in a manufacturing process of ABS (acrylonitrile butadiene styrene) resins for example, a flow drying oven and the like have conveniently been used. ABS latex manufactured by an emulsion polymerization may be obtained as a slurry which contains a large quantity of liquid after coagulation and water washing. As a method of removing liquids, the slurry is supplied into a centrifugal dehydroextruder for obtaining a water containing powder or a wet cake containing water in the range of 30%-40%. The water containing powder is dried until the water content reaches 1% by heat energy using a drying pipe and a flow drying oven to avoid compounding by an extruder in the final process, a vent-up and a blowing phenomenon in a granulation process.
In the drying process, the approximately 30%-4% water component of the powder or cake is vaporized by consuming large quantities of heat energy and time. The powder of lower water content in almost dried state is associated with a risk of dust explosion so that the device as a whole needs to be isolated from oxygen with a hot nitrogen gas and a larger scale of the facility.
A resin material of approximately 1% water content is supplied to a co-rotating twin screw extruder for the ultimate dryness followed by compounding and granulating.
For a scale down version of the device, a method of removing liquids by means of a co-rotating twin screw extruder has been proposed. A water removing system of this type generally comprises a squeeze process and a vaporization process.
In the liquid removing method of the squeeze type as illustrated in
FIG. 9
, for example, a co-rotating twin screw extruder
10
is mounted with a co-rotating twin screw
14
in a barrel
12
and provided with a material feeding section (or port)
16
to which is supplied a mixture of a water containing powder
30
a
, a pellet
30
b
and a process adjuvant
30
c
of the resin material
30
from which liquids are previously removed by a centrifugal hydroextruder
32
. It is proposed to provide such structure so that the resin material within the mixture is squeezed at the liquid removing screw portion (not shown) of the screw
14
so that the resin material is mold-extruded as a solid from a delivery (outlet)
18
.
ABS water containing powder
30
a
of water content of 30%-40% reduced by the centrifugal hydroextruder
32
is supplied to the material feeding section
16
at the uppermost stream of the co-rotating twin screw extruder
10
together with other materials such as SAN (styrene and acrylonitrile copolymer) pellet
30
b
and the process adjuvant
30
c
. The material supplied to the material feeding section
16
is conveyed effectively to the lower stream without retention by the twin screw
14
having a self-cleaning finction. The material being conveyed is squeezed by a liquid removing screw portion
24
comprising a kneading block and a reverse-flighted screw provided in the twin screw
14
, whereby the material is elastically or plastically deformed for reduction of the specific volume of the material so that the water component in the material is removed as a liquid.
The liquid separated flows in reverse through the screw channel against the upper stream of the liquid removing screw portion
24
along a pressure gradient directing from a maximum pressure point of the liquid removing screw portion to the material feeding section
16
and is discharged from a delivery
20
(water removing screen) provided between the upper stream of the liquid removing screw
24
and the material feeding section
16
. At this section, approximately 30%-90% of the entire water component in the resin material is separated and discharged, and approximately 10%-70% of the remaining water component is separated and vaporized through vent holes
22
a
,
22
b
and
22
c
of the vent portion provided at the lower stream of the liquid removing screw, and is finally vaporized through the vent hole
22
c
and the resin is extruded from the delivery
18
.
According to the liquid removing method of the aforementioned type, a certain quantity of water is removed from the resin material in the form of liquid without vaporization so that water vaporization energy effectiveness may be improved. Since the wet material is used, a risk of dust explosion may be avoided without any particular device for sealing oxygen with minimized scale of a facility. Further, in accordance with the liquid removing method of this type, continuation of the manufacturing process, simplification of the multi-stage processes and drastic rationalization of the manufacturing process may be achieved.
In the liquid removing method of the squeeze process as proposed in
FIG. 10
, for example, a method of removing the liquid is similar to the aforementioned system but a method of discharging the liquid is different. Namely, in the former method of the squeeze process, a separated liquid is flowed in reverse and discharged from the liquid removing screen located in the upper stream of the liquid removing screw portion. In the process shown in
FIG. 10
, however, to separate and evaporate water the liquid removing portion
34
is provided with a discharge port
35
at a portion where the resin material is compressed and with a vent staffer means
36
to prevent a material from flowing out the discharge port. Other structures are the same as those of the liquid removing method as hereinbefore described.
The liquid removing method free of water reverse flow may expand the operational conditions and this method is well tolerated to a recycling process of the waste plastics.
Further, another liquid removing method of the vaporization process has been proposed as illustrated in
FIG. 11
where SAN pellet and water containing ABS powder are supplied into the twin extruder
10
from different places.
Namely, to remove the liquid SAN (styrene and acrylonitrile copolymer), a pellet
30
b
is supplied to the extruder
10
for quick melting, to which preheated water containing ABS powder
30
a
with the process adjuvant are added by means of a side feeder
37
having a preheating means in the middle portion of the extruder. Thus, the water component is steamed by an enthalpy of the molten SAN so that the separated and vaporized steam is discharged from the vent holes
22
a
,
22
b
and
22
c
of the vent portion
22
.
Accordingly, in the liquid removing method of the type as hereinbefore described, the wet material is also used to avoid any risk of the dust explosion without necessitating any facility to isolate oxygen and to minimize an arrangement. A residual monomer value obtained after devolatilization from the vent hole
22
c
is better than that of the liquid removing method of the squeeze process as hereinbefore described and the liquid removing method of this type is well tolerated in the case where a material of two components, for example, containing ABS diluted by SAN is adopted.
In the aforementioned conventional liquid removing method of the squeeze process, however, a melting point, a glass transition point or a heat distortion temperature is extremely high as compared with a boiling point of water, and when liquid is removed from the solid resin material of more than 10% water content by means
Ishibashi Junya
Kobayashi Akiyoshi
McGuireWoods LLP
Teskin Fred
Toshiba Machine Co. Ltd.
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