JPS5839663B2 - polyester coated metal tube - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing polyester coated metal tubes.

More specifically, the present invention covers the surface of a metal tube with a polyethylene terephthalate polymer extruded by a melt extrusion method, and then cools it so that the crystallinity of the coating layer is 10% or less. The present invention relates to a method for producing a polyester-coated metal tube that is coated with a coating that is highly workable.

Polyethylene terephthalate has good crystallinity and is manufactured in large quantities into fibers, films, etc. because of its excellent mechanical properties when stretched and oriented.

Although L or L has excellent properties, undrawn products are brittle due to their crystallinity, and are used for purposes such as melt extrusion coating to prevent corrosion of metal pipes, as is done with polyethylene. Currently, it is not used as it is considered inappropriate.

The present inventors have found that when a metal tube is coated with polyethylene terephthalate copolymerized with polyethylene terephthalate, particularly neopentyl glycol, etc. by a melt extrusion method and the coating is made into a coating with a low degree of crystallinity, the adhesion to the metal is improved. The present invention was achieved based on the finding that a polyester-coated metal tube having extremely good properties and excellent properties can be obtained, and that the coated metal tube has particularly good workability.

That is, the present invention provides a polyester-coated metal characterized in that the surface of a metal tube is coated with a polyethylene terephthalate polymer extruded by a melt extrusion method, and then cooled so that the crystallinity of the coating layer becomes 10% or less. Method of manufacturing tubes.

The polyethylene terephthalate polymer referred to in the present invention is a thermoplastic polymer mainly composed of polyethylene terephthalate,
These include polyethylene terephthalate copolymers and mixtures thereof.

Among these, polyethylene terephthalate copolymers containing a copolymer component of 5 mol % or more and less than 25 mol □, especially 8 to 20 mol % of a neopentyl glycol component, because those with low crystallinity are easily obtained by melt extrusion. Preferably, those containing

If the copolymerization component exceeds 30 mol %, the secondary transition point will be significantly lowered and the material will become soft, which is not preferable.

Polyethylene terephthalate polymers contain various additives such as pigments, dyes, metal powders, matting agents, flame retardants, antioxidants, UV stabilizers, antistatic agents, fillers, reinforcing agents and other polymers. It is possible to add some amount of.

In the present invention, first, a polyethylene terephthalate polymer is melt-extruded by a known method to coat a metal tube having a circular, square or irregular cross section.

For example, a polyethylene terephthalate polymer can be extruded into a cylindrical shape from an extruder equipped with a cross rad die, and a metal pipe such as a steel pipe or aluminum pipe can be fed into the extruder using a pushing device to coat the extruder.

The coated metal tube is taken off by a taking off device.

In the case of polyethylene terephthalate, since it is highly crystalline, when the coating diameter is allowed to cool, the crystallinity of the coating film exceeds 10%.

Therefore, in order to obtain a coating with a low degree of crystallinity, it is necessary to rapidly cool the coating by water cooling or the like immediately after the molten coating.

In this respect, copolymers are more suitable for obtaining coatings with low crystallinity.

If the crystallinity of the coating film is higher than 10%, the adhesion with the metal will be lost and other properties will deteriorate, so the crystallinity of the coating film must be 10% or less.

The thus obtained cladding tube can be freely subjected to processing such as bending, pressing, and drilling.

Metal tubes are required to have such workability in many applications, and the coated metal tube of the present invention satisfies this requirement.

The crystallinity is completely amorphous and the density is 1.33, io.

Assuming that the density when % crystallized is 1.455, it can be calculated from the measured density according to a conventional method.

When the film contains additives such as inorganic substances, the degree of crystallinity is determined by the X-ray method, and the degree of crystallinity by the density method is determined from the correlation between the value of the X-ray method and the value of the density method.

The polyester-coated metal pipe produced by the method of the present invention has excellent corrosion resistance because it is coated with polyethylene terephthalate polymer, which has excellent properties such as strong chemical resistance and weather resistance. It has good adhesion and excellent workability, and the coating will not be damaged even if the coated metal tube is bent at an acute angle, for example.

Therefore, the polyester-coated metal tube obtained by the method of the present invention can be used in a wide range of applications, such as furniture and building materials.

The present invention will be further explained below with reference to Examples.

Example 1 and Comparative Example 1 Polyethylene terephthalate pellets with an intrinsic viscosity of 0.65 are melt-extruded into a cylinder shape from an extruder equipped with a rad die to a cylinder at a temperature of 270 to 290°C, and extruded to 250°C using a pushing device. A heated 13mm diameter steel pipe is fed into this.

It was quenched by pouring cold water at about 10° C. and taken off to obtain a coated steel pipe.

The thickness of the coating on this coated steel pipe was 200μ, and the crystallinity of the coating was 7%.

On the other hand, for comparison, the same procedure as above was carried out except that the steel pipe was taken out and allowed to cool without being rapidly cooled with cold water.

The thickness of the coating on the obtained coated steel pipe was 200μ, and the crystallinity of the coating was 25%.

When a diagonal peeling test was conducted using these coated steel pipes, it was found that the one with a crystallinity of 7% (the one of Example 1) had good adhesion between the coating and the steel pipe and did not peel off, but the coated steel pipe with a crystallinity of 25% did not peel off.
The sample (comparative example 1) had poor adhesion and was easily peeled off.

In addition, the film with a crystallinity of 7% was not damaged even when crushed with a press, but the film with a crystallinity of 25% peeled off and was damaged when crushed with a press.

Example 2 A polyethylene terephthalate copolymer pellet with an intrinsic viscosity of 0.67 copolymerized with 15 mol% neopentyl glycol was melt-extruded into a cylindrical shape at a cylinder temperature of 270 to 280°C from an extruder equipped with a cross-layer die. An aluminum tube with a diameter of 18 mm was sent in, cooled with cold air at about 5 degrees Celsius, and then taken out.

The resulting cladding had a crystallinity of 8% and a thickness of 120%.
It was μ.

The adhesion between the coating and the aluminum tube was extremely good, and the coating did not peel or tear even when the coated aluminum tube was bent at an acute angle.

Claims (1)

[Scope of Claims] 1. A polyester characterized in that the surface of a metal tube is coated with a polyethylene terephthalate polymer extruded by a melt extrusion method, and then cooled so that the crystallinity of the coating layer is 10% or less. Method for manufacturing coated metal pipes. 2 Polyethylene terephthalate polymer is 5 mol%
2. The method for producing a polyester-coated metal tube according to claim 1, which is a polyethylene terephthalate copolymer containing less than 25 mol% of neopentyl glycol as a copolymerization component.