JPH0223755B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to lead pipes, particularly plastic-coated lead pipes that are heat-fused coated with plastic and have improved corrosion resistance. Used for piping. (Conventional technology) Lead pipes are defined as lead pipes (JIS
H4311) Classified as lead pipes for water supply (JIS H4312) and hard lead pipes (JIS H4313), and are widely used for chemical industry, general use, and gas use, respectively. These lead pipes have already been used for many years, and their usefulness is being reconsidered today, but some defects have also surfaced. For example, as a tap water lead pipe, the lead pipe itself based on the above standards is often buried directly in concrete or mortar, which is an alkaline substance, or in acidic or alkaline soil, and is used as piping.
Since metallic lead is a so-called amphoteric substance, it undergoes chemical corrosion under such alkaline or acidic conditions. Lead pipes can also be corroded by soluble chlorides near the coast, and sometimes electrically corroded by so-called stray currents leaking into the ground from railroad tracks or electrical equipment. On the other hand, lead pipes have easy bendability, making piping and connection work easy, but their low surface hardness makes them susceptible to damage from external factors. In order to suppress these defects, the surface of the lead pipe is thoroughly degreased and cleaned, and then coated with polyethylene resin by extrusion. As a result of the development of adhesive plastics, adhesive plastic coatings have begun to replace the polyethylene resins mentioned above. However, the adhesive strength of these adhesive plastics to lead materials is extremely low when compared with the adhesive strength to other metal materials such as aluminum, steel, copper, etc.; The adhesive strength by the method is about 0.7-2.0Kg/cm.
Therefore, due to the low adhesive strength, when such plastic-coated lead pipes buried underground are bent due to changes in earth pressure or vibrations caused by frequent vehicle traffic, or due to earthquakes, etc. There was a defect that caused peeling at the interface between the lead pipe and the plastic layer when the lead pipe was bent during burying work, or when it was exposed to temperature changes underground after being buried. The reason why the adhesive strength of adhesive plastics to lead materials shows such a low value as mentioned above is that when coating lead pipes, the lead pipes are first degreased and cleaned, and then the lead pipes are preheated to a temperature of 150 to 250°C in the atmosphere. Thereafter, an adhesive plastic coating is applied to the preheated lead pipe using an extrusion method, but an oxide film is formed on the surface of the lead pipe due to the preheating process, and this oxide film has extremely poor adhesion to the lead metal in the base lead pipe. This is thought to be due to stability. Therefore, even if adhesive plastic is used as a coating material, it is not only impossible to improve the adhesion to the lead pipe, but also the preheating treatment described above generates discolored (yellowish) oxides on the inner wall of the lead pipe, which may damage the product. On the other hand, it has been found that if the preheating temperature is set low to prevent the formation of this oxide, the adhesion of the adhesive plastic to the lead pipe will be further reduced. As a way to avoid and overcome these defects, a composition in which asphalt is blended with an adhesive resin such as ethylene-vinyl acetate copolymer, styrene-butadiene copolymer, or low-molecular-weight propylene-ethylene copolymer is used as a metal material. It has been proposed to melt-coat pipes (including lead pipes) (Japanese Unexamined Patent Publication No. 112819/1982), and another method is to modify the surface of the lead pipes by soldering and then coat them with adhesive sulfur-containing plastics. Melting coating has been proposed (Japanese Patent Publication No. 54-3177). (Problems to be Solved by the Invention) Melt extrusion is generally used to coat lead pipes with anticorrosive plastic, and in order to ensure that the plastic film formed in this case adheres closely to the lead pipe, As mentioned above, the lead pipe is 150 ~
It is necessary to heat the pipe to 250°C, and the oxide film that forms on the lead pipe due to this preheating prevents sufficient bonding between the lead pipe and the plastic layer. In other words, even if the plastic material used for coating is improved to improve its adhesion to metal lead, an oxide film will be formed as long as preheating is required when coating lead pipes, and this oxide film and the base will The essential problem with plastic-coated lead pipes is that good adhesion between the lead pipe and plastic cannot be achieved unless the adhesion with the lead pipe itself is improved. In order to solve this essential problem, it is sufficient to preheat the lead pipes and subsequently melt-coat the plastics in a non-oxidizing atmosphere, but such oxidation prevention measures not only require additional equipment but also require manufacturing time. This is not desirable in terms of industrial production because it complicates the process and increases costs. On the other hand, Japanese Patent Application Laid-Open No. 1983-1999, which was introduced in relation to the conventional technology,
The coating material in the coated metal pipe disclosed in Publication No. 112819 has relatively high fluidity, and therefore has difficulty in handling during construction. On the other hand, in the coated lead pipe disclosed in the above-mentioned Japanese Patent Publication No. 54-3177, the entire length of the lead pipe is pretreated by solder plating, which has the drawback of increasing the number of steps and increasing costs. Therefore, the present invention relates to a plastic-coated lead pipe that is coated with a heat-melted coating of plastic, such as an adhesive plastic, and the lead pipe is preheated during coating, but this preheating treatment also does not affect the coating plastic. There is no decrease in adhesive strength or adhesion to the lead pipe, and there is no need to select a material with high fluidity as the coating plastic, and there is no need to pre-modify the surface of the lead pipe. The object of the present invention is to completely avoid and overcome the above-mentioned deficiencies in the prior art. (Means for solving the problems and problems) The present invention basically aims to solve the above problems and problems by modifying the lead pipe itself so that it is coated with a plastic material. can be,
Specifically, the present invention provides a plastic-coated lead pipe characterized in that the lead pipe contains 0.003 to 0.025% by weight of aluminum. In the plastic-coated lead pipe according to the present invention, the lower and upper limits of the aluminum content of the base lead pipe are not absolute critical values, but if they are below the lower limit, it is due to the preheating treatment of the lead pipe prior to coating with the plastic material. This is because the upper limit corresponds to the maximum amount of aluminum that lead can contain at room temperature. The plastic that is the coating material in the plastic-coated lead pipe according to the present invention is a so-called adhesive plastic, which has a carboxyl group in the main chain or side chain, a carboxyl-derived group, a urea group, a hydroxyl group,
Polymers having polar groups such as epoxy groups are preferred, and examples of these polymers include ethylene-acrylic acid copolymers, ethylene-ethyl acrylate-acrylic acid copolymers, and ethylene-methyl acrylate-acrylic acid copolymers. Copolymer, ethylene-methacrylic acid copolymer and its metal salt, ethylene-glycidyl acrylate copolymer, ethylene-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate-vinyl acetate copolymer, ethylene-vinyl acetate Examples include copolymers and hydrolysates thereof. Among these polymers, Himilan (Mitsui Polymer Co., Ltd.) is an ionomer resin made by graft polymerizing polyolefins such as ethylene-acrylic acid copolymer, polyethylene, and polypropylene with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and maleic acid. chemical standard), Admar adhesive resin (trademark of Mitsui Petrochemicals), Bond Fast adhesive resin (trademark of Sumitomo Chemical), maleic anhydride grafted polyethylene, etc. are commercially available, so from the viewpoint of availability. suitable. These plastic materials can be used alone or in combination. The thickness of the plastic layer in the plastic-coated lead pipe according to the present invention is suitably about 0.1 to 10% of the diameter of the lead pipe. (Operations and Effects) In the plastic-coated lead pipe according to the present invention, the base lead pipe contains 0.003 to 0.025% by weight of aluminum.
Even if it is preheated for a long time in the temperature range of 150 to 300 degrees Celsius, the inner and outer surfaces of this lead pipe remain silvery white and do not change color. Of course, it is thought that an oxide film is formed due to such preheating treatment, but in this case, the plastic coating layer applied to the aluminum-containing lead pipe is the same as the plastic coating layer applied to the conventional lead pipe. It shows significantly better adhesion than that of It is not clear what mechanism of action is responsible for this improvement in adhesion of the plastic coating layer, but the oxide film formed when preheating aluminum-containing lead pipes is similar to that when preheating conventional lead pipes. It is assumed that this is because this oxide film exhibits good adhesion to the base aluminum-containing lead pipe itself as well as to the covering plastic material. be done. In the plastic-coated lead pipe according to the present invention, the adhesive strength of the plastic coating layer to the lead pipe is sufficiently high and corresponds to the adhesive strength to aluminum, steel, and copper, and therefore the plastic layer does not peel off even when bent. Therefore, the plastic-coated lead pipe according to the present invention has the advantage of being significantly superior in durability when compared with conventional coated lead pipes of this type. Moreover, the only way to achieve this effect is to add a small amount of aluminum, which is an inexpensive raw material, to the manufacturing of the base lead pipe, and then cover this aluminum-containing lead pipe with a plastic material. Since there are no extra steps involved in this process, there is no increase in costs, and rather the additional effect of being able to manufacture economically can be obtained. (Test Examples and Manufacturing Examples) Next, preliminary tests conducted to confirm adhesive strength and manufacturing examples of plastic-coated lead pipes according to the present invention will be described. Test example (a) Preparation of metal sample pieces Place predetermined amounts of lead metal (JIS H2106, lead content of 99.95% by weight or more) and electrical aluminum wire (aluminum content of 99.90% by weight or more) into a graphite crucible, and then After sufficiently covering the material with carbon powder, both metal materials were melted by high-frequency induction heating, and the mixture was cast into a mold kept at about 350°C and cooled to form a plate material of 150 x 30 x 15 mm. The front and back surfaces of this plate were cut to a depth of about 2 to 3 mm, and then cold rolled into a plate with a thickness of 1.5 mm. (b) Preheating treatment of metal sample pieces The metal sample pieces obtained by the method described in section a above were heat treated under various conditions, and the presence or absence of discoloration in the sample pieces was visually observed. (c) Preheat treatment results and discussion The results were as shown in Table 1 below. As is clear from this table, lead materials that contain a certain amount of aluminum exhibit a white silver color without any discoloration even after preheating treatment, and that if the aluminum content is less than the specified amount, the oxidation resistance decreases. It was found that discoloration occurred.

[Table] (d) Preparation of composite sample by joining preheated metal piece and plastic material Preheated metal sample piece and 0.5 mm thick adhesive plastic plate (ionomer resin manufactured by Mitsui Polychemicals - Mark) - thickness between
A composite in which the sample metal piece and the plastic material were bonded was prepared by processing for 3 minutes at a pressure of 5 kg/cm ² under various preheating temperature conditions with a 0.2 mm mask spacer interposed, and then rapidly cooled. A composite sample was obtained. (e) Peel test of composite samples Each composite sample was set in a T-type peel tester to measure adhesive strength. (f) Peeling test results and design The results were as shown in Table 2 below. From this table, sample 1a is a composite of lead material and plastic material containing a specified amount of aluminum.
~4a (corresponding to those using metal sample pieces of sample numbers 1 to 4 as the base)
Reference sample 7, which is a composite of aluminum and copper plates
-9, whereas control samples 5a and 6a (sample number 5
It was found that the samples (corresponding to those in which the metal sample pieces of No. 6 and 6 were used as the substrate) could not provide sufficient adhesive strength.

【table】

[Table] Production example 1 Melted lead-aluminum alloy (contains 0.1% by weight of Al) held at 600°C and molten lead (contains 99.95% by weight or more of Pb, JIS H2106) held at 400°C
The aluminum content was adjusted to 0.01% by weight by stirring thoroughly while pouring it into the container, and the resulting melt was injected into the container section of a hydraulic lead pipe extrusion molding machine.
After cooling and solidifying, it was extruded as an aluminum-containing lead pipe with an outer diameter of 29 mm and an inner diameter of 20 mm, and was wound up using a winder while cooling. The rolled aluminum-containing lead pipe is heated to approximately 50 to 60℃.
The material is first heated, sent out using a lead pipe delivery device, and passed through a tri-clean tank to completely clean its surface.
A straightening machine straightens the bend in the pipe.
This aluminum-containing lead pipe is then heated with a heater (gas infrared heater or gas flame) to a temperature of about 100 to 300
℃, preferably 150 to 230℃, and passed through the extrusion die of a plastics extrusion molding machine to coat with adhesive plastic (Mitsui Petrochemical's "Admer LF300" (trademark)) to a thickness of 0.5 mm. After that, it was cooled with water, dried, and then rolled up into a fixed length using a winding machine to make a product. This product was cut into rings with a width of 10 mm and the adhesion strength of the coating plastic layer to the aluminum-containing lead pipe was examined using a T-type peel tester, and it was found to be 4 to 5 kg/cm. In addition, when a lead pipe made only from lead metal (JIS H2106) and no aluminum is treated in the same manner as above and coated with adhesive plastic, the adhesive strength is 1 to 2 kg/cm. It was hot. Production example 2 Melted lead-aluminum alloy (contains 0.5% by weight of Al) held at 900°C is converted into molten lead (contains 99.95% by weight or more of Pb, JIS H2106) held at 380°C
The aluminum content in the mixed melt was adjusted to 0.02% by weight by thoroughly stirring the mixed melt. This aluminum-containing lead melt is injected into the container of a hydraulic lead pipe extrusion molding machine, cooled and solidified, and an aluminum-containing lead pipe is manufactured in the same manner as in Production Example 1. It was coated and made into a product. The adhesive strength of the plastic layer in this product was examined in the same manner as in Production Example 1 and was found to be 4 to 5 kg/cm.

Claims (1)

[Claims] 1. A lead pipe coated with heat-fused plastic, characterized in that the lead pipe contains 0.003 to 0.025% by weight of aluminum,
Plastic-coated lead pipe.