JPS6249303B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for manufacturing a heat insulating tube having excellent heat resistance and heat insulation properties.

Conventionally, a heat insulating pipe is a product in which a heat insulating layer made of polyethylene foam having an expansion ratio of about 2 to 3 times is formed on the outside of a metal pipe. However, in recent years, energy saving has become essential, and the outside of the metal tube is coated with cross-linked polyethylene or rubber foam with a high expansion ratio as a heat insulating layer with low heat dissipation loss. In the case of coating, the manufacturing process is extremely complicated and costs are high.

Furthermore, as a conventional method for producing polypropylene foam, there is a method of directly extruding polypropylene using a volatile solvent, but when this method is applied to the production of heat-insulating pipes having a polypropylene foam heat-insulating layer, it has the following drawbacks. . With this method, highly expanded polypropylene foam can be produced, but with polypropylene homopolymer, the temperature must be kept as low as several tens of degrees below the melting point (for example, about 130 degrees Celsius), and moreover, the temperature must be kept at a severe temperature of 2 to 3 degrees Celsius. Requires control. As a result, when the polymer is extruded to the outside of the metal tube when used for manufacturing the above-mentioned heat-insulating tube, it is easily affected by cooling from the metal tube, and good foam extrusion cannot be achieved.

In addition, since the conventional method uses polypropylene homopolymer as mentioned above, CCl ₂ F− is used as a blowing agent.
Only certain foaming agents that are liquid at room temperature and pressure, such as CClF ₂ , can be used, and as a result, the foam structure shrinks after foaming, making it impossible to use conventional methods for manufacturing insulated pipes. It is something.

Furthermore, when this method is used, there is a risk that the surface will crack or crack when the bending process is performed.

The present invention has been made as a result of intensive research aimed at improving these drawbacks, and as a result has discovered a method for manufacturing an insulated tube that has excellent heat resistance and heat insulation properties, is easy to process, and is low cost. That is, in the method of the present invention, 100 parts by weight of a mixed polymer consisting of 60 to 90% by weight of an ethylene-propylene block copolymer containing 1 to 15% of ethylene and 40 to 10% by weight of plastic or rubber are added with 0.1 to 10 parts by weight of a cell nucleating agent. A composition to which a volatile solvent mainly consisting of one or more selected from CCl ₃ F, CClF ₂ -CClF ₂ and CCl ₂ F ₂ is added as a foaming agent is extruded to the outside of a metal tube. It is characterized by heating and foaming.

According to the method of the present invention, by using the mixed polymer as described above, the extrusion operation can be facilitated and the operation can be carried out stably for a long time.The reasons for this are thought to be as follows. That is, the optimal polymer elasticity for foaming plastics is usually a shear modulus of 2×10 ⁶ to 5×10 ⁶ dyn/cm ^{2 .}
It is said that The foaming mechanism that foams a polymer with a volatile solvent swells the polymer in an extruder with a solvent, extrudes it from an extruder die at a temperature below its melting point, and further uses the latent heat of vaporization of the solvent to cool it and foam it all at once. However, it is thought that during this time it will be in a state where it has an elastic modulus suitable for foaming with the above numerical value.

When using solvents, conventionally polymers were used.
The temperature must be 140°C or lower, and the appropriate temperature range is extremely narrow, such as ±2°C, but in the method of the present invention, the polymer can be foamed to a sufficiently high degree even within a range of about 10°C below its melting point. The appropriate temperature range is as wide as ±6°C.

The reason why a volatile gas can be used as a blowing agent at room temperature and pressure in the method of the present invention is considered to be as follows. In other words, in the conventional method, the polymer must be kept at an extremely low temperature, and a solvent with a high latent heat of vaporization must be used as a liquid at room temperature and pressure, but in the method of the present invention, the polymer has a high temperature near its melting point. A gaseous solvent can be used at room temperature and pressure because it can cause foaming.

In addition, in the method of the present invention, the heat insulating layer after foaming does not undergo any shrinkage and can have a smooth and beautiful surface.

Note that the heat insulating tube obtained by the method of the present invention does not exhibit any cracks even if it is bent.

Next, in the method of the present invention, as a mixed polymer
The reason for using an ethylene-propylene copolymer containing MI 0.1-40 and ethylene 1-15% is that the melt modulus during extrusion is 2 x 10 ⁶ - 5 as mentioned above.
This is because it is 10 ⁶ dyn/cm ² and has excellent heat resistance. Therefore, the polymer can be easily extruded without requiring severe restrictions on extrusion conditions. The reason why plastics and rubbers that can be mixed with this copolymer are blended is to impart appropriate flexibility to the copolymer. That is, in the method of the present invention, since extrusion foaming is carried out at a low temperature, there is a risk that the foam will become brittle, but this brittleness can be improved by adding plastic or rubber as described above.

Examples of this rubber include ethylene-propylene rubber, polyisobutylene, cis 1.4 polybutadiene, butyl rubber and plastics such as polybutene-1, low, medium and high density polyethylene, ethylene-vinyl acetate copolymer, ethylene-α olefin (propylene). copolymers, etc. In particular, ethylene-propylene rubber containing a propylene component of 10 to 60% by weight, preferably 20 to 50% by weight is preferred.

The amount of plastic rubber added should be 10 to 40% by weight.
The reason for this limitation is that if it is less than 10% by weight, the brittleness of the foam cannot be improved, and if it exceeds 40% by weight, suitable viscoelasticity cannot be obtained and the bubbles will burst, resulting in a foam with a high magnification. I can't.

Nucleating agents used in the method of the present invention include finely powdered silica, calcium carbonate, clay, boric acid, tartaric acid, etc., and finely powdered silica is particularly preferred.

The amount added was limited to 0.1 to 10 parts by weight, especially 0.5 to 40 parts by weight, because if it was less than 0.1 part by weight, it would not be possible to obtain a foam with fine cells; This is because if it exceeds the limit, the foam becomes brittle.

Further, as a blowing agent used in the method of the present invention,
The reason for limiting CCl ₃ F, CClF ₂ -CClF ₂ and CCl ₂ F ₂ is that when the foam obtained with this foaming agent is used as a heat insulating layer of a heat insulating pipe, wrinkles, shrinkage, etc. will not occur in the heat insulating layer. It's for a reason.

The blowing agent can be press-fitted into the polymer by using a vent-type screw and press-fitting it into the vent part from the middle of the cylinder.

Further, pigments, various fillers, heat retardants, antioxidants, copper damage inhibitors, ultraviolet inhibitors, etc. may be added to these.

According to the method of the present invention, a composition prepared by adding a nucleating agent and a foaming agent to the above-mentioned mixed polymer is extruded to the outside of a metal tube through a conventional process, and the mixture is heated and foamed.

Next, examples of the method of the present invention will be described.

Example 1 80% by weight of ethylene-propylene block copolymer (ethylene component: 4%, MI 0.7) and 20% by weight of ethylene propylene rubber (propylene component: 26% by weight)
A mixed polymer consisting of 100 parts by weight of finely powdered silica
After supplying 10 parts by weight to an extruder with a vent tap of 65 mmφ and melting and kneading, CCl ₂ F ₂ 6 was added to the belt section of the extruder.
A weight part was press-fitted and dissolved in the polymer, and the above composition was extruded and foamed at 158°C on the outside of a 15.88φ copper pipe passing through the crosshead to form a heat insulating layer to obtain a heat insulating copper pipe.

In the thus obtained heat-insulating copper tube, the bubble diameter of the heat-insulating layer was small, and its density was 0.08 g/m ² .

Example 2 CCl ₂ F ₂ and CCl ₃ F as volatile blowing agents at 1:1
A heat-insulating copper tube was obtained in the same manner as in Example 1 except that 10 parts by weight of the mixture in Example 1 was used.

The insulation layer of this insulated copper pipe is fine and the density is
It was 0.042g/ ^m2 .

As detailed above, the method of the present invention has excellent heat resistance and heat insulation properties, and is extremely useful for hot water supply and space heating.

Claims (1)

[Claims] 1 100 parts by weight of a mixed polymer consisting of 60 to 90% by weight of an ethylene-propylene block copolymer containing 1 to 15% of ethylene and 40 to 10% by weight of plastic or rubber, and 0.1 to 10 parts by weight of a cell nucleating agent. and CCl ₃ F, CClF ₂ −CClF ₂ , CCl ₂ F ₂ as blowing agents.
1. A method for producing a heat insulating tube, which comprises extruding and foaming a composition containing one or more volatile solvents selected from the following to the outside of a metal tube.