JPS6040378B2 - coated metal pipe - Google Patents

Description

[Detailed description of the invention] The present invention relates to coated metal tubes.

More specifically, it is a coated metal tube in which a coating made of a specific thermoplastic crystalline polyethylene terephthalate polymer is adhered to the outer surface of the metal tube, and is highly corrosion resistant and has excellent adhesion of the coating, making it easy to bend. The object of the present invention is to provide a coated metal tube with good workability that does not cause peeling or breakage of the coating even when subjected to processing such as pressing. Melted polyethylene terephthalate resin, especially the third component
By coating the metal tube with a polymer or polymer mixture containing ~30 mol% and quickly cooling it to a temperature below the secondary transition point, it is possible to achieve excellent bending that cannot be achieved with conventional metal tubes coated with polyvinyl chloride or polyethylene. It is known that a coated metal tube having workability such as pressability can be obtained.

However, this coated metal tube is still not satisfactory in terms of workability, and even if it is subjected to somewhat severe processing, problems such as peeling of the coating may occur. The present inventors set out to provide a coated metal tube with superior workability than a polyethylene terephthalate resin coating, and assumed that the terminal carboxyl group is related to the adhesion of the coating.

Theoretically, all terminals of polyethylene terephthalate resin are CH20, but in reality, terminal carboxyl groups are generated due to thermal decomposition or side reactions caused by the atmosphere. The amount of terminal carboxyl groups produced varies depending on the temperature, time, catalyst, melt molding conditions, etc. during polymerization. Generally, terminal carboxyl groups are considered to have an adverse effect on the properties of the polymer, so polymerization is carried out under conditions that minimize the formation of terminal carboxyl groups, and melt molding is carried out. The terminal carboxyl groups of polyethylene terephthalate polymers, which are mass-produced for fibers and films, are about 5 to 20 equivalents/1 pita, and copolymers that can lower the polymerization temperature are produced with lower amounts of terminal carboxyl groups. can. However, the present inventors have discovered that a polyethylene terephthalate-based resin-coated metal tube with improved workability can be obtained by regulating the amount of terminal carboxyl groups when adhering to metal, and have arrived at the present invention. That is, the present invention consists of a metal tube and a coating of a thermoplastic crystalline polyethylene terephthalate polymer that adheres to the outer surface of the metal tube, and the polyethylene terephthalate polymer has a content of 15 to 100 equivalents/ The outer surface of the metal tube is coated with a crystalline polyethylene terephthalate polymer, which has a terminal carboxyl group of 100% and has a secondary transition point higher than 5000, and the coating is in a substantially amorphous state. It is a coated metal tube. Examples of the metal tube used in the present invention include tubes made of iron, aluminum, copper, or alloys containing these metals.

The thermoplastic crystalline polyethylene terephthalate-based polymer used for the coating is a polymer mainly composed of polyethylene terephthalate, and preferably contains copolymerizable estel constituent units other than ethylene terephthalate, such as ethylene isophthalate, neoventilate, etc. It is a copolymer or polymer polymer containing 5 to 25 mol%, particularly 5 to 20 mol%, of units such as luterephthalate. These polymers generally contain about 1 to 3 mol % of a diethylene glycol component due to side reactions during polymerization. These polymers have an intrinsic viscosity of at least 0.5, derived from a value measured at 3500 in orthochlorophenol, and 0.55
~0.9 is preferred. If the amount of copolymerization is small or the intrinsic viscosity is high, the workability during adhesion coating will be reduced, and if the amount of copolymerization is too large or the intrinsic viscosity is low, the workability of the coated metal tube will be reduced, which is not preferable. The polyethylene terephthalate-based polymer needs to have a terminal carboxyl group of 15 to 100 equivalents/1 pitch, preferably 20 to 70 equivalents/1 pitch, more preferably It is 25 to 50 equivalents/1 pita. The terminal carboxyl group plays an important role in the adhesion between the polyethylene terephthalate polymer and the metal. That is, if the amount of terminal carboxyl groups is less than 15 equivalents/1 pita when adhering to metal, sufficient adhesion cannot be obtained and peeling of the coating is likely to occur during processing of the coated metal tube. In addition, if the terminal carboxyl group exceeds 100 equivalents/1 quantity, cracks may easily occur in the coating during processing. ) Yamacho day.・'"
- By cooling the phthalate polymer from a molten state to a temperature below the second-order transition point within the crystallization derivative time according to the method described in Kogyo Kagaku Zasshi No. 69, page 406, it is brought into a substantially amorphous state, i.e. , the crystallinity can be in a state ranging from amorphous to a low crystallinity of about several percent. When the secondary transition point is high, amorphous polymers have poor deformability such as stretchability, so bending,
The coating is damaged during severe deformation such as press working.

For this purpose, a substantially amorphous coating made of a crystalline polymer with good stretchability is used. And crystalline (amorphous state is 15
The degree of crystallinity reached when held at 0oo for 3 hours) is at least 10% or more, preferably 20% or more, and the elongation in an amorphous state is at least 50% or more, preferably 80%.
It is desirable to use the above polymers. The degree of crystallinity is determined by the density method according to a conventional method. If it cannot be measured using the density method, it is determined using an X-ray method or the like and converted to the density method value. Various additives may be added to the polymers used in the coating, such as pigments, dyes, metal powder matting agents, retardants, fillers, stabilizers and some amount of other polymers. The coating of the metal tube is preferably carried out by a melting method.

For example, using an extruder equipped with a crosshead die, a thermoplastic crystalline polyethylene terephthalate polymer is melt-extruded into a cylindrical shape, and the surface is polished to a diameter of about 150 mm.
A metal tube preheated to ~3000°, preferably 180~280° is inserted, fusion coated, and cooled to a temperature below the secondary transition point within the crystallization induction time. If the thickness of the coating is too thin, the coating is likely to be torn during actual use or due to scratches during processing. Furthermore, if the thickness of the coating is too large, it will be difficult to achieve a substantially amorphous state during coating. Therefore, the thickness of the film is 50 to 500 microns, and it is a dark Washiyama, Z. nL mountain and day mountain rhZ group・i
In addition, the coated metal pipe of the present invention, which has a draft of, for example, 1 to 3 bases or higher, is tough, has a high secondary transition point, and has good film resistance, heat resistance, cold resistance, and chemical resistance. A crystalline polyethylene terephthalate polymer coating with low water absorption tightly adheres to the outer surface of the metal tube, resulting in excellent insect resistance, a luxurious and beautiful appearance, and moderate surface hardness. Not only can it be used as a straight pipe, but also,
Because it has excellent workability that can withstand deformation such as bending and pressing, it can be widely used in almost any field where metal pipes are used, including indoor and outdoor furniture, architecture, electrical appliances, and miscellaneous goods. The present invention will be explained below by giving examples. Example 1 A polyethylene terephthalate copolymer prepared by polymerizing 10 mol% of isophthalic acid with different terminal carboxyl groups was placed on a steel pipe with a circular cross section, having an outer diameter of 15.9 mm and a wall thickness of 1.2 mm with a polished outer surface. was coated by melt extrusion and cooled under conditions that did not cause crystallization to obtain a coated steel pipe with a substantially amorphous coating of 200 microns thick.

The polymer forming the film has an intrinsic viscosity of 0.60 to 0.62,
The secondary transition point was 6500, and the crystallinity was 36%. These polymers NO. 1 to 6 were produced by a transesterification method from dimethyl terephthalate (9 parts by weight), dimethyl isophthalate (1 part by weight), and ethylene glycol (75 parts by weight), and the polycondensation temperatures were 270, 275, and 28, respectively.
The numbers were 0.28 and 290.2960. Thirty coated steel pipes each having different amounts of terminal carboxyl groups in the polymer forming the coating were crushed into a fan flat with a press material. Table 1 shows the appearance of the processed pipe obtained. No. outside the scope of the present invention. 1.No. 6 has a very large number of defective pieces. Table 1 Terminal 000 days Appearance of processed pipe coating (equivalent weight/106 days) (Number of defects out of 30) Repair 1 9
9-piece peeling repair 2 22 2-piece peeling repair 3 32 No abnormality repair 4 53 1-piece crack repair 5 81 4-piece crack repair 6 119 13-piece crack Example 2 Outer diameter 15.9 mm Wall thickness 1.2 mm circular cross section A polyethylene terephthalate copolymer made by copolymerizing 10 mol% of neobentyl glycol component, which was heated to 27,000 ℃ and passed through a crosshead die attached to an extruder, and melted and extruded from the crosshead die at 27,000 ℃. The mixture was cooled by pouring water coated by fusion (intrinsic viscosity: 0.6 ft, secondary transition point: 0, crystallinity: 32%, terminal carboxyl group content: 21 equivalents/1 bit).

Claims (1)

[Claims] 1. Consisting of a metal tube and a thermoplastic crystalline polyethylene terephthalate polymer coating adhered to the outer surface of the metal tube, the polyethylene terephthalate polymer has a
It has a terminal carboxyl group of 100 equivalents/10^6g,
1. A coated metal tube, the outer surface of which is coated with a crystalline polyethylene terephthalate polymer, which has a secondary dislocation point higher than 50° C. and is substantially amorphous.