# US 4,397,797 A · Method for extrusion coating of a pipe with a foamed cover layer having three integrally formed cellular sub-layers

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- Number: US 4,397,797 A
- Document ID: US4397797A
- Status: Granted
- Kind: A
- Application number: 06/172,422
- Filed: 1980-07-25
- Granted: 1983-08-09
- Earliest claimed: 1979-07-31
- Assignees: Furukawa Electric Co., Ltd.; Furukawa Metals Co., Ltd.
- Inventors: Akio Nojiri; Toshio Koreeda; Masao Horiguch
- Web page: https://patentgrep.com/patent/US4397797A

## CPC

- C08J 9/34: Chemical features in the manufacture of articles consisting of a foamed macromolecular core and a macromolecular surface layer having a higher density than the core
- B29C 44/22: consisting of at least two parts of chemically or physically different materials, e.g. having different densities
- B29C 44/322: {the preformed parts being elongated inserts, e.g. cables}
- C08J 9/00: Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof (mechanical aspects of shaping of plastics or substances in a plastic state for the production of porous or cellular articles B29C)
- F16L 59/04: Arrangements using dry fillers, e.g. using slag wool
- F16L 59/14: Arrangements for the insulation of pipes or pipe systems (F16L59/02 - F16L59/12 take precedence)
- C08J 2323/10: Homopolymers or copolymers of propene
- Y10S 138/09: Cellular
- Y10T 428/1376: Foam or porous material containing
- Y10T 428/249961: With gradual property change within a component
- Y10T 428/249977: Specified thickness of void-containing component [absolute or relative], numerical cell dimension or density
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00)
- F16L: PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A method for manufacturing a heat insulating pipe having a foamed insulating layer around the outer surface of said pipe. The foamed insulating layer has an expansion ratio of at least 4. It has three integral sub-layers, said sub-layers including a cellular middle foamed sub-layer which is integral with a cellular inner foamed sub-layer and a cellular outer foamed sub-layer, said inner and outer sub-layer being on opposite sides of said middle sub-layer, said cellular inner foamed sub-layer being the innermost sub-layer with respect to said pipe and surrounding the outer surface of said pipe. The cells of said inner and outer sub-layers are smaller than the cells of said middle cellular sub-layer, the ratio .mu..sub.1 /.mu..sub.2 of the cell dimensions of said cellular middle sub-layer are between 0.3 and 0.9, wherein .mu..sub.1 is the average cell dimension measured in the radial direction of said pipe and .mu..sub.2 is the average cell dimension measured in the axial direction of said pipe. The method for producing said 3 sub-layered foamed insulating layer comprises passing a pipe heated to a temperature of between 60.degree. C. and 120.degree. C. through the nipple of a cross-head die and simultaneously extruding a mixture of a propylene-ethylene block polymer having an ethylene content of between 1 and 20% by weight and a Melt Index of between 0.1 and 4 together with a foaming agent over the outer surface of said pipe to cause said mixture to expand and form said 3 sub-layered foamed insulating layer on said pipe, the relationship between the overall thickness t of the 3 sub-layered foamed insulating layer, the expansion ratio M of the 3 sub-layered foamed insulating layer, and the die-nipple distance d of a cross-head die being ##EQU1## wherein K=0.75 to 0.20.

## Claims

### Claim 1

A method for manufacturing a heat insulating pipe comprising a pipe having a foamed insulating layer around the outer surface of said pipe,
said foamed insulating layer having an expansion ratio of at least 4 and comprising three integrally formed sub-layers, said sub-layers including a cellular middle foamed sub-layer which is integral with a cellular inner foamed sub-layer and a cellular outer foamed sub-layer, said inner and outer sub-layer being on opposite sides of said middle sub-layer, said cellular inner foamed sub-layer being the innermost sub-layer with respect to said pipe and surrounding the outer surface of said pipe,
the cells of said inner and outer cellular sub-layers being smaller than the cells of said middle cellular sub-layer, the ratio .mu..sub.1 /.mu..sub.2 of the cell dimensions of said cellular middle sub-layer being between 0.3 and 0.9, wherein .mu..sub.1 is the average cell dimension measured in the radial direction of said pipe and .mu..sub.2 is the average cell dimension measured in the axial direction of said pipe;
the method for producing said 3 sub-layered foamed insulating layer comprising:
passing a pipe heated to a temperature of between 60.degree. C. and 120.degree. C. through the nipple of a cross-head die and simultaneously extruding a mixture of a propylene-ethylene block polymer having an ethylene content of between 1 and 20% by weight and a Melt Index of between 0.1 and 4 together with a foaming agent over the outer surface of said pipe to cause said mixture to expand and form said 3 sub-layered foamed insulating layer on said pipe,
the relationship between the overall thickness t of the 3 sub-layered foamed insulating layer, the expansion ratio M of the 3 sub-layered foamed insulating layer, and the die-nipple distance d of the cross-head die being ##EQU3## wherein K=0.75 to 0.20.

### Claim 2 (depends on 1)

The method of claim 1 wherein K is 0.3-0.4.

### Claim 3 (depends on 1, 2)

The method of claim 1 or 2 wherein said propylene-ethylene block copolymer is a powder having a Melt Index of 0.1-2 and an ethylene content of 7-20%.

### Claim 4 (depends on 3)

The method of claim 3 wherein said propylene-ethylene block copolymer has admixed therewith up to 40% by weight of an ethylene-propylene rubber.

### Claim 5 (depends on 1, 2)

The method of claim 1 or 2 wherein said propylene-ethylene block copolymer has admixed therewith up to 40% by weight of an ethylene-propylene rubber.

### Claim 6 (depends on 1)

The method of claim 1 wherein said foaming agent has a decomposition temperature of between 120.degree. and 170.degree. C.

### Claim 7 (depends on 4)

The method of claim 4 wherein said foaming agent has a decomposition temperature of between 120.degree. and 170.degree. C.

### Claim 8 (depends on 1, 2)

The method of claim 1 or 2 wherein said pipe is a copper pipe which has been precoated with resin.

### Claim 9 (depends on 6)

The method of claim 6 wherein said pipe is a copper pipe which has been precoated with resin applied from an aqueous resin-containing emulsion or an aqueous-containing solution and then baked.

### Claim 10 (depends on 1)

The method of claim 1 wherein said middle sub-layer comprises 40-90% of the total thickness of said formed insulated layer.