JPS6130892B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing lightweight, robust thermoplastic pipes and tubes, and to products made by the method. Polyvinyl chloride (PVC) and fused acrylonitrile
Thermoplastic pipes made of hard plastics such as butadiene-styrene (ABS) are commercially available in large quantities for use in water supply pipes, sanitary pipes and rain gutters, as well as other applications. One major advantage of thermoplastic pipe is that it is light compared to other pipes it replaces, and another advantage is that it is easy to fabricate into fluidic devices. While the structural integrity of thermoplastic pipe is good for many applications, improvements are desired for other applications.

Over the past 20 years, thermoplastic pipes containing blowing agents have gained acceptance in many industries;
The use of foamed thermoplastics for many pipe applications is limited by the problem of fluid leakage in foamed thermoplastic pipes or by expensive and inadequate methods for making leak-tight pipes.

The preferred pipe for many applications is a smooth-surfaced, fluid-impermeable pipe that is thick enough to provide good structural integrity, but is sufficiently lightweight and has the advantage of being easy to manufacture plastic pipe. It is. The present invention relates to a simple, inexpensive and novel method for manufacturing such pipes and to pipes made by such a method.

The pipe made by the method of the present invention is a lightweight, strong pipe having a hard thermoplastic exterior and interior and a foamed thermoplastic interior. The outer and inner surfaces as well as the foamed interior are preferably of the same thermoplastic material. However, the foamed interior may be a different plastic so long as it blends with the plastic used for the exterior and interior surfaces.

The pipe is made by extruding multiple layers of thermoplastic material. The extruded outer and inner layers are made of a rigid plastic and include the exterior and interior of the pipe, and the extruded middle layer is preferably made of the same foamed plastic as the outer and inner layers.

The thermoplastic used to make the pipe may be ABS, PVC, phenylene oxide polymer, polycarbonate, polyethylene, polypropylene, polystyrene, polybutylene, or combinations thereof. The center layer of the foamed thermoplastic contains a chemical blowing agent that is incorporated into the plastic before it is loaded into the extruder. Preferred blowing agents are sodium bicarbonate and citric acid, azodicarbonamide, and N-nitroso compounds. Modern Plastics Encyclopedia
Encyclopedia) 1975-1976, pages 127-129, show other chemical blowing agents that can be used to make foamed thermoplastic materials.

The apparatus used to carry out the method of the invention comprises a plurality of, preferably a single die, connected to a single die having a plurality of passages for receiving and molding the plastic discharged by the extruder. Equipped with two extruders.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a tool or die, generally designated by the reference numeral 10, used to carry out the method of the present invention is shown. Tool 10 includes a mounting member 11, a die plate 12 and a forming die 13. The mounting member 11 comprises a housing 11' having openings 14 and 15 which are respectively fitted to the discharge ends of two screw extruders (not shown). An inlet plate 16 is provided in housing 11' and includes an aperture 17 and a diverter plug or mandrel 18.
A plurality of passageways 19 communicate with openings 17 and 14.

Opening 15 in housing 11' communicates with passage 21, which communicates with passages 22 and 23. Passage 23 communicates with a manifold 24 which communicates with a passage 25 provided in flow restriction device 26 . The passage 22 is formed by a hole in the housing 11' and a hole in the nozzle element 22'. Restriction 26' is defined by the inner surface of flow restrictor 26 and the outer surface of nozzle 22.

Die plate 12 includes a mandrel or spreader 27 and a die orifice 28. The forming die includes a tubular passage 29 and is heated or cooled by a fluid passage connected to a conventional heat exchanger (not shown).

When using the tool 10 to carry out the method of the present invention for forming the pipe 32 of FIG. The thermoplastic material which has been heated to a melting temperature in
through the manifold 24 and thence into the passageway 2
5, through the restriction 25', through the die orifice 28 and through the tubular passage 29 of the forming die 29 to form the outer surface of the flow pipe 32. At the same time, another portion of the thermoplastic material flows from channel 21 through channel 22, by spreader 27, through die orifice 28 and channel 29 of forming die 13 to form the inner surface of the pipe.

At the same time, foamable thermoplastic material is discharged from the extruder into opening 14 and passage 17.
, past the diverter plug 18 , through the passage 19 , through the restriction 26 ′ and thence through the center of the orifice 28 and through the passage 29 of the forming die 13 to form the inner core of the pipe 32 .

A preferred embodiment of the invention includes a hard inner layer or inner surface 33, 34 of ABS and an inflated interior 35.
The manufacture of a pipe 32 made of a grafted polymer of acrylonitrile-butadiene-styrene ABS having the following properties. Approximately 204℃ without foaming agent
The molten ABS at a temperature of (400〓) enters the opening 15 under pressure from the extruder and passes through the passages 22 and 23 and their communicating passages, through the die orifice 28 and the forming orifice 29 and into the pipe 32. Inner and outer surfaces 33 and 34 are formed, respectively. ABS is a product that is in pellet form and prepared by polymerizing 30 (by weight) of polybutadiene to 25 (by weight) acrylonitrile and 45 (by weight) styrene. same
A batch of ABS is the decomposition temperature of azodicarbonamide (approximately 196.1℃~204.4℃ (385〓~400℃)
〓)) A foamable mixture is made by mixing 3/100 of azodicarbonamide in its portion at a lower temperature. The mixed foamable ABS mixture is pelletized and loaded into an extruder where it is heated to approximately 204.4°C.
It is gradually heated to a temperature of (400〓). At this temperature, the mixture melts and the azodicarbonamide decomposes. However, the mixture is not completely foamed due to the inherent pressure within the extruder.
The molten foamable ABS enters the opening 14 of the fitting 11 and passes, still under pressure, through the opening 17, the opening or passageway 19, the restriction 26' and the center of the die orifice 28, and the inner layer 35 of the pipe 32.
form. When the simultaneously extruded stiff and foamable ABS leaves the die orifice 28, it enters the passage 29 of the forming die where it can be foamed.
The ABS foams due to the reduction in pressure, thus forming a pipe 32 with a rigid inner surface 33 and outer surface 34 and a foamed interior 35.

Although the preferred embodiment of the invention has been described for the manufacture of ABS pipe with a foamed interior, the invention
Other thermoplastic materials such as polymers, polycarbonate, polystyrene, polypropylene, polystyrene and polybutylene are also applicable. The foamed interior can be made of one thermoplastic material and the inner and outer surfaces can be made of another thermoplastic material.

Azodicarbonamide was used in the preferred embodiment to foam the internal ABS layer of the pipe. However, other chemical blowing agents may be used. Modern Plastics Encyclopedia 1975-1976, pages 127-129, shows the use of azodicarbonamide as a blowing agent as well as other chemical blowing agents suitable for carrying out the invention.

Although a special tool 10 is shown as one means for carrying out the invention, other tools may be used, as well as other feeding devices to the apertures 14 and 15.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an extrusion die used to make a pipe, and FIG. 2 is a cross-sectional view of a pipe made by the method of the present invention. 10: Tool, 11: Mounting member, 12: Die plate, 13: Molding die, 14, 15: Opening, 1
8: Mandrel, 19: Passage, 21, 22, 2
3: Passage, 24: Manifold, 25: Passage, 2
6: Flow restriction device, 33: Inner surface, 34: Outer surface, 3
5: Inside.

Claims (1)

Claims: 1. Dense inner and outer surfaces and a foamed inner layer by extruding thermoplastic material through a plurality of radially spaced passages 19, 22, 23 of the pipe forming tool 10. A method of manufacturing a thermoplastic pipe 32 having a blowing agent-free heated molten thermoplastic material from an extruder communicating with said two passages 22, 23 to form said inner and outer surfaces. injecting into said two passages and heated molten thermoplastic material containing a chemical blowing agent from another extruder communicating with another passage 19 to form said foamed inner layer. spreading the heated molten thermoplastic material flowing through one of the passageways 22 by a spreader 27 to form a uniform inner surface, and containing the blowing agent. extruding the thermoplastic material containing the thermoplastic material and the chemical blowing agent from the passages 19, 22, 23 into the passage 29 of the forming die of the pipe forming tool without heating the thermoplastic material; A method of manufacturing a thermoplastic pipe, comprising: inflating and adhering a thermoplastic material containing said chemical blowing agent to said inner and outer surfaces under reduced pressure. 2. The method of manufacturing a thermoplastic pipe according to claim 1, wherein the thermoplastic material and the thermoplastic material containing a chemical blowing agent are grafted polymers of acrylonitrile, styrene, and butadiene.