JPS6351085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer tubular structure suitable for use indoors, particularly for water supply and drainage pipes installed through a plurality of connected compartments. Specifically, the outer peripheral surface of a synthetic resin pipe, such as a hard vinyl chloride pipe, is coated with a hydraulic inorganic material to provide fire resistance, thereby creating a multilayer tubular structure that can prevent the spread of fire to other compartments in the event of a fire. It relates to a manufacturing method.

Conventionally, hard vinyl chloride pipes have been widely used as water supply and drainage pipes for buildings because they are easy to construct and are inexpensive. However, if hard vinyl chloride pipes are used as is, they are flammable and can be dangerous in the event of a fire. It was not suitable for water supply and drainage purposes because it could cause the fire to spread to neighboring rooms or upper floors, or emit toxic gases, increasing damage.

On the other hand, metal pipes are also used because they are fire-resistant and strong, but they are heavy, difficult to cut, etc., and usually expensive, and they are also susceptible to rust and limescale buildup on the inside. This has the disadvantage that water flow rate is reduced and dew condensation occurs on the outer surface of the pipe.

Therefore, a multilayer pipe has been proposed that combines an inner pipe made of a synthetic resin pipe such as a hard PVC pipe and a fire-resistant outer pipe made of an inorganic material such as cement. It has become rapidly popular in recent years due to its excellent prevention performance.

However, the technically difficult problem in constructing this type of multilayer pipe is that the inner pipe is a synthetic resin pipe with a significantly large thermal expansion, and the outer pipe is made of an inorganic material with a relatively small thermal expansion. This technology prevents the inner tube from thermally expanding and compressing the outer layer tube when water flows down, thereby preventing harmful cracks from occurring in the outer layer tube.

The simplest method for this is to provide a certain amount of space between the inner tube and the outer tube. Specifically, it is possible to combine the outer layer tube and inner tube, which are each precisely manufactured separately. Alternatively, a method has been used in which a synthetic resin foam sheet is wrapped around the outer periphery of the inner tube to form a rear outer layer tube, but these methods also have various problems. That is, as described above, the method of separately manufacturing and inserting the inner tube and the outer layer tube is not only complicated in terms of manufacturing process, but is actually impossible when there are branches such as T tubes and Y tubes. On the other hand, the method of wrapping a synthetic resin foam sheet in advance makes it difficult to wrap the sheet uniformly around the inner tube due to the elasticity peculiar to the synthetic resin foam sheet, so The hydraulic material for forming the outer layer tube flows between the wound layers of the sheet, making it difficult to achieve the intended purpose. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing a multilayer pipe that improves the drawbacks of the conventional multilayer pipe manufacturing technology. As a result of intensive research in accordance with these objectives, the present inventors have developed a material that changes in volume upon absorption and desorption of water, or a thin layer such as paper, film, or cloth whose main component is swollen in water. The material is wrapped around the outer circumferential surface of a synthetic resin inner tube and then dried to form a thin layer on the outer surface of the inner tube. When the kneaded material is coated and molded and cured and dried, the thin layered material that had absorbed water from the kneaded material and swelled and increased in volume dehydrates and dries and returns to the thin layered material with almost the original thickness. It was discovered that a void of the desired thickness was created between the tubes, and the outer layer tube could withstand thermal stress such as when hot water of 90°C or higher flows down, leading to the completion of the present invention.

Examples of the material of the water-swellable thin layer body that changes its volume upon absorption and desorption of water in the present invention are as follows.

i.e. starch, starch derivatives, CMC, MC, HEC,
Water-soluble cellulose derivatives such as HPC, tannin, lignin, alginic acid and gum arabic, proteins such as gelatin and casein, polyvinyl alcohol, polyethylene oxide, polypropylene oxide, polyacrylic acid, polymethacrylic acid, water-soluble polyester, polyepoxy compounds, and ketones. Formaldehyde resin, polyvinylpyrrolidone, polyamine, polyelectrolyte, urea formaldehyde resin, melamine formaldehyde resin, phenol formaldehyde resin, etc. Of course, it will be clear from the following description that the structure of the present invention is not limited to the materials exemplified in any way. It is also possible to use a mixture of the above-mentioned substances to form a paper, film, or cloth-like thin layer, or to partially use a material that does not swell with water.

The hydraulic inorganic materials used in the present invention include, for example, Portland cement, silica cement, blast furnace cement, flyash cement, alumina cement, various ettringite cements, and various types of gypsum. Asbestos, rock wool, glass fiber, wood wool, synthetic fiber,
It is also effective to add natural fibers, steel fibers, copper wire, mica, perlite, vermiculite, synthetic vermiculite, volcanic rock, silica sand, aluminum hydroxide, calcium carbonate, calcium silicate, and the like.

In the present invention, the effect of wrapping a paper, film, or cloth-like thin layer made of a material that changes volume during water absorption and desorption and swelling with water around the outer surface of the synthetic resin inner tube and then drying it is as follows: In addition to the fact that the layer can be easily formed on a hydrophobic surface such as a synthetic resin pipe and can be formed with good adhesion, this thin layer absorbs water, swells, and gels when coated with a water-kneaded material of hydraulic inorganic material. The volume increases and the thickness of the layer increases, and the hydraulic inorganic material maintains its gel state until it hardens and forms a structure. The gel releases water and forms a certain gap between the outer tube and the inner tube. Therefore, the mounting thickness of the paper, film, or cloth-like thin layer used in the present invention is determined by selecting the thickness of one sheet or the number of stacked sheets, taking into consideration the relationship between the desired voids and the degree of swelling of the thin layer. do it.

After sprinkling the paper, film, or cloth-like thin layer swollen in water on the outer peripheral surface of the synthetic resin pipe, it is dried to form a thin layer. As a method for coating and molding with a kneaded material, for example, a resin pipe having the above-mentioned thin layer body is set in advance in a formwork that can be divided into upper and lower parts, and the above-mentioned water is poured into the gap between the mold and the synthetic resin pipe. A method of casting a kneaded material of a hard inorganic material, a method of extruding a kneaded material of the material to form a coating layer around a synthetic resin pipe having the thin layer body, and a method of molding a sheet-like material of a kneaded material of the material as described above. Examples include a method of wrapping one or more layers around the outer circumference of a treated synthetic resin pipe.

The curing method for the hydraulic inorganic material may be either room temperature curing or heating curing, and it is preferable to hold it in a humid air condition during this period. Next, it is dried, preferably air drying. The multilayer tubular structure manufactured by the present invention, with or without branch pipes, has a gap formed between the inner pipe and the outer pipe, so that it is coated by thermal stress when high temperature fluid passes through the pipe. Not only does it not have any negative effect on the layer, but in the case of straight pipes, the positional relationship between the inner and outer pipes can be easily changed during construction, and the inner pipe can be removed.

It should be noted that it is not always necessary to form the voids according to the present invention over the entire surface of the inner tube, but it is also effective to provide the voids only partially, for example, at the end of the outer layer tube. Therefore, the desired effect can be achieved even if the thin layer is provided only partially.

The present invention will be explained in more detail below with reference to Examples.

Example 1 A 60 μm thick polyvinyl alcohol film soaked in water and swollen was wrapped around the outer circumferential surface of a hard vinyl chloride pipe (outer diameter 114 mm, inner diameter 107 mm, length 2100 mm), and the inside was air-dried. on top of the tube
A kneaded product with the following composition was coated on cheesecloth (material: vinylon) to a constant thickness and wrapped three times,
It was placed on two horizontally installed parallel metal rolls rotating in the same direction and pressed while rotating to approximate a perfect circle. The thickness of the coating layer at that time was 9 mm. After leaving this item at room temperature for 30 minutes, 50℃80%RH
The sample was placed in a curing chamber and maintained for 5 hours. After 3 weeks of air-drying, this product was connected to the multilayer tubular structure of the comparative example described below using a joint, and hot water at 90°C was poured at 20/min.
After that, the lower end was closed and the water was kept full for 10 minutes. No abnormalities were observed in the coating layer during or after this test, and it was confirmed that the stress caused by thermal expansion of the inner tube was sufficiently absorbed.

Kneaded product composition (parts by weight) Ordinary Portland cement 45 Alkali-resistant glass fiber chopped strands
0.5 Chrysotile asbestos 4.5 Silica sand 9 Light aggregate (perlite) 6 Thickener (methylcellulose) 0.1 Water 35 When the cut surface of the multilayer pipe was continuously observed until it was air-dried, it was found that it swelled with water. The thickened polyvinyl alcohol film remains as it is while the curing reaction of the hydraulic coating layer progresses to form the outer tube, and as it dries, this swollen gelled layer loses water again and contracts, forming a layer on the inner surface of the outer tube. A phenomenon was observed in which the film adhered in the form of a thin film close to the original thickness, and voids were formed on the outer surface of the inner tube. It is believed that the voids formed by drying the swollen layer, which has increased in volume by absorbing water, provide the multilayer tubular structure according to the present invention with a thermal stress absorbing function.

Example 2 Paper made of 20% pulp and 80% CMC fiber (120
g/m ² ) wetted with water to swell, rolled up in two layers, dried, and placed into a hollow internal mold made of chloroprene rubber to match the diameter and length of the desired multilayer tubular structure. Both ends are fixed using holders, and from the injection hole at the bottom of the form, a water mixture, namely 60 parts by weight of Portland cement, 12 parts by weight of silica powder, 3 parts by weight of an expanding admixture (quicklime), and a lightweight aggregate (perlite) is added. 5 parts by weight of chrysotile asbestos, 20 parts by weight of chrysotile asbestos, and 0.1 part by weight of a thickener (methylcellulose) were blended in advance, then an appropriate amount of water was added and kneaded.The water kneaded material was press-fitted and filled, and then placed in a curing chamber at 50°C. The temperature was then raised to 5 hours. After cooling naturally, remove the mold.
After 3 weeks of air-drying, this product was connected to the multilayer tubular structure obtained in Example 1, and the same hot water flow test as in Example 1 was conducted. During and after this test, no abnormalities were observed in the outer tube of the coating layer.

Comparative Example 1 A long length of multilayer tubular structure was produced using the same process and operation as in Examples 1 and 2, except that the operation of wrapping the film or paper on the outer peripheral surface of the hard vinyl chloride tube in Examples 1 and 2 was omitted. Manufactured straight pipes and joints.

After 3 weeks of air-drying, this product was subjected to the same hot water flow test as in Example 1, and a plurality of cracks were found in the outer layer of both the long straight pipe and the joint of the multilayer tubular structure.

Claims (1)

[Claims] 1. Prior to coating the outer circumferential surface of the synthetic resin inner tube with a kneaded material whose main components are a hydraulic inorganic material and water, paper, film, or cloth whose volume changes when water is absorbed and desorbed is applied to the outer circumferential surface of the inner tube. 1. A method for producing a multilayer tubular structure, which comprises wrapping a material swollen with water, drying it to form a thin layer, and curing, curing, and drying it after the coating.