GB2245277A

GB2245277A - Plastic tubes, their production and use

Info

Publication number: GB2245277A
Application number: GB9111217A
Authority: GB
Inventors: Tatuhiko Mukawa
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1990-05-30
Filing date: 1991-05-24
Publication date: 1992-01-02
Also published as: GB9111217D0; DE4117028A1; JPH0434290A; DE4117028C2

Abstract

A plastic tube is made of polyamide and acrylonitrile rubber polymer, the latter being elastomeric. The plastic has a network structure comprising normal chains and side chains (1) of repeating amide units and either elastomer (2) present in spaces (3) formed in the network structure in the case of a blended polymer or attached to said chains in the case of copolymerised polymer. Such tubes may be used to connect motor vehicle parts requiring flexible but durable tubing. <IMAGE>

Description

- 1 1 1 PLASTIC TUBES, THEIR PRODUCTION AND USE The present invention

relates to plastic tubes, methods for their production and their uses in, e.g. pipes and hoses for connecting various elements, devices, equipment and the like. A tube made of rubber or soft resin is generally used for connecting various devices in a motor vehicle.

Japanese Utility Model Application Laid-Open 5951291 discloses a tube for connection to a steel pipe. On an outer wall of the steel pipe, an annular projection is provided to engage an annular groove formed in an inner wall of the tube.

The tube is required to be free of rust, inexpensive, easy to work on, and to have sufficient strength, high heat resistance and stability. However, none of the materials so far proposed satisfies all of these requirements.

For example, some synthetic rubber tubes may be suitable for connection to such devices, but inferior in heat resistance so that use of such rubber tubes is limited in motor vehicles. Furthermore, there are problems such as reduction in plasticity, oxidation and polymer deterioration.

In order to solve such problems, tubes made from resin softened by mixing in a plasticizer have been used in some cases. The plastic tube thus manufactured is advantageous in that the tube can be directly connected to devices such as a solenoid operated valve. However, the plastic tube is so expensive that wide usage is limited. Therefore, rubber hoses have been used in conjunction with such tubes for connecting devices as may require connection within a motor vehicle.

An object of the present invention is to provide a less expensive plastic tube which is adaptable, has desirable heat resistance and which can be directly connected to such devices as mentioned above.

According to the present invention, there is provided a plastic tube made of polyamide polymer which has a network structure comprising normal chains and side chains of repeating amide units, and which further comprises elastomer, such as an acrylonitrile rubber.

The term elastomer will be familiar to those in the art as embracing synthetic polymers with rubber-like characteristics.

In an aspect of the invention, the elastomer is located in spaces present in the network structure.

In the method aspects of the present invention there is also provided a method of making a plastic tube as defined above comprising blending elastomer monomer or polymer in an amount of 30%-60% by weight, based on the weight of polyamide in the end product, with polyamide monomer to provide a polymerisable composition, polymerising the composition and forming the polymerised composition into a tube.

In order that the invention may be illustrated and readily carried into effect, embodiments thereof will now be described and illustrated for example only, with reference to the accompanying drawings, wherein:

Fig. 1 is a schematic diagram showing a molecular model of polyamide plastics material which has been blended with elastomer polymer; Fig. 2 is a schematic diagram showing a molecular model of polyamide plastics material which has been copolymerized with elastomer monomer; and Fig. 3 is a diagram showing piping for a solenoid operated valve to which plastic tubes of the present invention have been fitted.

Polyamide plastics material, such as polyamide resin is a typical synthetic resin having high heat resistance. For example, 11-polyamide and 12-polyamide have excellent heat resistance and stability even at temperatures in excess of 120C. In the present invention, in order to improve flexibility, the polyamide component is blended with or copolymerized by polymer mainly or essentially comprising monomer units of elastomer such as acrylonitrile rubber.

Referring to Fig. 1, the polyamide polymer blended with acrylonitrile polymer has a three dimensional network structure comprising normal chains and side chains of amide monomer units. Elastomer 2 is enclosed in spaces 3 in the network. When an external force is applied to the polymer end product, the elastomer monomer units 2 can move within the space 3, thereby allowing the polyamide product to deform.

Copolymer of polyamide and acrylonitrile has a structure schematically shown in Fig. 2. The elastomeric polymer component 2 is trapped in a part of the polyamide polymer chain 1 which forms the three-dimensional network structure. With application of external force, the elastomer 2 can be deformed, thus providing sufficient flexibility.

In either case, the structural frame is formed of the polyamide component whereby the plastic has a high heat resistance and a sufficient strength, thereby largely preventing the structure from deforming. Moreover, by blending or copolymerizing with elastomer, the molecular chains of amide monomer units can slip or otherwise move such that flexibility is improved.

In order to provide sufficient strength and flexibility, for the uses mentioned herein it is highly desirable to maintain the amount of elastomer polymer to be in a range of 30% to 60% by weight based on the amount of the polyamide polymer in the end product. If the elastomer polymer is present in an amount of less than 30%, a hard polyamide plastics material with low flexibility is produced. On the other hand, when the amount of elastomer polymer exceeds 60%, the network structure is not sufficiently crosslinked whereby the end product is of poor strength and durability.

Examples of the polyamide plastics material manufacturing method are now described. EXAMPLE 1 Acrylonitrile rubber polymer in an amount of 40% by weight, based on the weight of the product polyamide, is added to a water suspension of w- aminoundecanoic acid to prepare the polymerisable composition. Phosphoric acid as a catalyst is added. After dehydration, the composition is polymerized at 25C and a pressure of 10kg/cm2. The polymer obtained contains a small quantity of monomer and has a melting point of 225C. The polymer is maintained in a molten state and formed into a tube by an extruder.

The produced tube has, at 23C, physical properties such as tensile strength of 750kgf/cm2, elongation of 65%, modulus of elasticity of 31000kgf/cm2, shearing force of 500kgf/cm2, flexural rigidity of 980kgf/cm2 and compression 2 strength for 1% deformation of 210kgf/cm.

The plastic tube is applied to the piping of a solenoid operated valve shown in Fig. 3. A solenoid operated valve 11 having a solenoid and a valve body therein is attached to a bracket 12 which is securely mounted on a vehicle body by a screw 13. An inlet pipe 14 and an outlet pipe 15 of the plastic tube are connected to the solenoid operated valve 11 through joints Ila and llb, respectively. When the solenoid of the valve 11 is energized, the valve body is actuated to communicate the pipes 14 and 15 with each other so that a fluid such as air flows through the inlet pipe 14, the solenoid operated valve 11 and the outlet pipe 15.

Tubes of hard resin have been employed as the pipes 14 and 15 in a conventional piping, but with rubber hoses between the joints Ila and llb and pipes. As distinct from such arrangements, the polyamide polymer tubes of the present invention can have excellent strength and sufficient flexibility compared to rubber, so that pipes 14 and 15 formed according to the present invention can be directly connected to joints Ila and llb of the solenoid operated valve 11.

W tl Even though the inner diameter of the pipes 14 and 15 may be slightly smaller than the outer diameter of the joints Ila and Ilb, the pipes 14 and 15 can be elastically expanded, allowing the pipes to be attached to the joints. Thus the pipes 14 and 15 can be hermetically connected to the solenoid operated valve 11. EXAMPLE 2 Phosphoric acid is added to a water suspension of lauric lactam, and acrylonitrile rubber monomer, in an amount of 40% by weight based on the amount of polyamide product, is further added to provide the polymerisable composition. Diisocyanate as a cross-linking agent was further added to the composition. The polyamide polymer product was cast into a tube of a predetermine dimension. The cross-linking conditions were polymerisation at a temperature of 250C and a pressure of l0kg/cm2.

The physical properties of the manufactured tube at 23C are tensile strength of 730kgf/cm2, elongation of 60%, modulus of elasticity of 29000kgf/cm2, shearing force of 470kgf/cm2, flexural rigidity of 880kg/cm2 and compression strength for 1% deformation of 190kgf/cm2.

The tube can also be directly connected to joints l1a. and Ilb of the solenoid operated valve 11 as the tube manufactured in Example 1. The pipes and joints were sufficiently hermetically sealed so that fluid did not leak even after use for 1000 hours at 100C.

The tube thus manufactured can also be applied to air hose, oil hose, various gaskets, fuel hose and others.

From the foregoing it will be understood that the present invention embraces within its scope flexible tube made of polyamide plastics material which has been blended or copolymerized with acrylonitrile rubber polymer or monomer, respectively. Thus the plastic tube can have better heat resistance, strength and flexibility so that even thin tubes can be readily directly connected to joints. Hence the auxiliary rubber hose which is necessary in connecting conventional plastic tubes is obviated thereby decreasing manufacturing cost and the number of elements. Tubes made according to the invention will remain free of rust so that hermetically sealed connections can be maintained for a long period of time.

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Claims

1. A plastic tube made of polyamide polymer which has a network structure comprising normal chains and side chains of repeating amide units, and which further comprises elastomer.

2. A plastic tube according to claim 1, wherein the elastomer is present as a blended polymer in spaces formed in the network structure.

3. A plastic tube according to claim 1, wherein the elastomer is present as a copolymerised polymer, being attached to the chains of repeating amide units.

4. A tube as claimed in any one of claims 1 to 3, wherein the elastomer is acrylonitrile rubber.

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5. A tube as claimed in any one of claims I to 4, wherein the polyamide comprises 11-polyamide and/or 12polyamide.

6. A tube as claimed in any one of claims I to 5, wherein the polyamide is derived from w-aminoundecanoic acid and/or lauric lactam and is optionally cross-linked.

7. A method of making a plastic tube as defined in any preceding claim comprising: rt blending acrylonitrile rubber polymer ij( an amount of 30% to 60% by weight, based on the weight of polyamide in the end product, with monomer capable of polymerisation to form polyamide to provide a polymerisable composition, polymerising the composition and forming the polymer product into a tube.

8. A method of making a plastic tube as defined in any 1 1 one of claims I to 6 comprising:

copolymerizing acrylonitrile monomer in an amount of 30% to 60% by weight, based on the weight of polyamide in the end product with monomer capable of polymerisation to form polyamide to provide a polymerisable composition, and polymerising the composition and forming the polymer product into a tube.

9. A method of making a plastic tube as claimed in claim 7 or 8, substantially as herein described and/or illustrated in either example.

10. A plastic tube as claimed in any one of claims I to 6, substantially as herein described and/or illustrated in either example.

11. Use of a plastic tube as claimed in any one of claims 1 to 6 or 10, in forming connections to a motor vehicle part such as a solenoid valve.

Published 1991 at The Patent Office, Concept Houre. Cardiff Road. Newport. Gwent NP9 111H. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwmfelinfach, Cross Keys. Newport. NP1 7HZ. Printed by Multiplex techniques ltd. St Mary Cray Kent.

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