JPS5838298B2 - Polyester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing polyester coated metal rods.

More specifically, it relates to a method for manufacturing a coated metal bar by covering a metal bar with a polymethylene terephthalate heat-shrinkable tube to provide a fusion coating. A polyester-coated metal rod is obtained.

BACKGROUND ART Conventionally, in order to prevent corrosion of a metal rod-shaped object, such as a metal tube, it has been practiced to melt-extrude a polymer such as polyethylene or vinyl chloride to coat the metal tube, or to coat the metal tube.

However, these resin-clad tubes or painted tubes lack workability such as bending and caulking, and there is a demand for resin-clad tubes with excellent workability.

Polymethylene terephthalate has good crystallinity and is produced in large quantities into fibers, films, etc. because of its excellent mechanical properties when crystallized by stretching and orientation.

However, due to its crystallinity, the undrawn product is brittle and has not been used at all for the purpose of melt-coating metal pipes to prevent corrosion, as is done with polyethylene, for example.

The present inventors have found that by covering a metal tube with a heat-shrinkable polymethylene terephthalate tube and heating it to form a shrink coating and fusion, cooling the tube to prevent crystallization will improve the adhesion between the coating and the metal. The present invention was completed based on the discovery that the material has extremely good properties and can be freely processed such as bending, caulking, and drilling.

According to the present invention, it is surprising that a coated metal rod with excellent workability, which has not been seen in metal rods coated with conventional polymers such as polyethylene or hynyl chloride, can be obtained from a polymethylene terephthalate polymer. That's true.

That is, in the present invention, a heat-shrinkable tube made of one kind of polymer or a mixture of two or more kinds of polymers of polymethylene terephthalate and polymethylene terephthalate copolymer is placed over a metal rod, and the tube is passed through a heating zone at a constant speed. This is a method for manufacturing a polyester-coated metal rod, which is characterized in that the polyester-coated metal bar is cooled so that the crystallinity of the coating becomes 20% or less after sequential fusion treatment.

The heat-shrinkable tube used in the present invention is made of a polymethylene terephthalate polymer, that is, one of polymethylene terephthalate and polymethylene terephthalate copolymers.
It is preferably made of a variety of polymers or a mixture of two or more of these polymers, and contains 5 to 30 mol% of a copolymer component.

Therefore, the polymethylene terephthalate referred to in the present invention is a thermoplastic polymer such as polyethylene terephthalate or polypropylene terephthalate, and the polymethylene terephthalate copolymer is an acid component such as isophthalic acid or neopentyl glycol added to the polymethylene terephthalate. Suitable are polymers containing a diol component such as, for example, as a copolymer component, up to an extent not exceeding 35 mol% of the copolymer.

A heat-shrinkable tube is usually obtained by forming the above-mentioned polymethylene terephthalate polymer into a tubular body using an extruder, and stretching the tubular body in at least one direction, preferably in two directions.

The heat-shrinkable tube preferably has a thickness of about 50 to 200 microns, and has a practical secondary transition point of 50° C. or higher for the final product.

Furthermore, it is preferable that the heat-shrinkable tube has an inner circumference approximately 1.03 to 1.1 times larger than the outer circumference of the metal rod, from the viewpoint of operation when covering the metal rod or the appearance of the final product.

As a heat-shrinkable tube, in the manufacturing process of the tube or the manufacturing process of polymethylene terephcrate polymer,
Various additives such as pigments, dyes, metal powders, matting agents,
Those made by adding lubricants, flame retardants, glass powder, reinforcing materials, antioxidants, ultraviolet stabilizers, and some amount of other polymers may also be used.

The metal rod-shaped body referred to in the present invention is a metal tube or metal rod made of iron, stainless steel, aluminum, copper, brass, etc., and has a circular, elliptical, polygonal, or irregular cross section, or is uniform. Any shape that can be tightly covered by covering with a heat-shrinkable tube and heating may be used.

The heat-shrinkable tube is attached to the metal surface by passing the metal rod-shaped body covered with the heat-shrinkable tube through a heated region using various known means such as electric heating, infrared heating, and high-frequency induction heating at a constant speed. Fuse the coating.

For example, when using a cylindrical electric heating furnace, the temperature in the heating zone should in principle be above the melting point of the heat-shrinkable tube, but for efficient operation it is desirable that the temperature in the heating zone be 300°C or above. Also, if the temperature is too high, it is likely that the polymer will decompose, so it is not desirable to exceed 800°C.

Heat-shrinkable metal on a metal rod? It is also possible to cover the metal rod with a heat-shrinkable tube and pass it through a high-temperature heating area to achieve shrinkage and fusion. The fusion process may also be performed through.

In the fusion process, it is necessary to pass a metal rod covered with a heat-shrinkable tube at a constant speed through the heating zone and perform a sequential fusion process to uniformly and continuously fuse the metal rods one after another. Otherwise, problems such as air bubbles being introduced and the coating being torn may occur.

The heating operation can be carried out by providing one or more heating zones.

The crystallinity of the coated metal bar body subjected to fusion treatment is 2.
It is necessary to cool to 0% or less, preferably 15% or less.

If the crystallinity of the coating exceeds 20%, the adhesion to the metal will be lost, making it impossible to obtain a coated rod with good workability.

For example, in many cases where polymethylene terephthalate heat-shrinkable tubes are used, the crystallinity of the film exceeds 20% if left to cool after fusion treatment, so it is necessary to rapidly cool the tube by water cooling or other means immediately after fusion treatment. be.

The degree of crystallinity can be calculated from the measured density according to a conventional method, assuming that the density of a completely unfinished product is 1.33 and the density of 100% crystallization is 1455.

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

The polyester-coated metal rod manufactured by the method of the present invention has a coating made of a tough polymethylene terephthalate polymer that is highly resistant to chemicals and weather, and has excellent corrosion resistance, and has excellent adhesion between the coating and the metal. It has excellent properties in that the coating will not peel off or be damaged even if the rod-shaped body is bent at an acute angle or subjected to caulking or drilling.

Therefore, the polyester-coated metal bar produced by the method of the present invention is useful in a wide range of fields such as furniture, building materials, and conduits.

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

Example 1 A heat-shrinkable tube with a folded diameter of 22 mm and a wall thickness of 75 microns made of polyethylene terephthalate copolymer (secondary transition point 63°C) copolymerized with 10 mol% neopentyl glycol was made into a steel tube with an outer diameter of 13 mm. Cover, inner diameter 5.5 cTL, length 40 CrIl, furnace atmosphere temperature 4. Immediately after sequential fusion treatment was carried out by passing through a cylindrical electric furnace at 0 0°C at a constant rate of 40 cr/'L/min, cold water was poured to rapidly cool the material, resulting in a substantially amorphous state (crystallinity 7). %) of polyester copolymer resin was firmly and uniformly fused and coated on the outer surface.

This cladding tube was bent at a right angle and caulked with a vise, but no damage or peeling of the coating was observed.

On the other hand, for comparison, a cladding tube with a crystallinity of 25% was obtained by air cooling after the fusion treatment.

When this cladding tube was bent at a right angle, the coating was damaged and peeled off.

Claims (1)

[Claims] 1 A heat-shrinkable tube made of one kind of polymer or a mixture of two or more kinds of polymers of polymethylene terephthalate and polymethylene terephthalate copolymer is placed over a metal rod, and successively fused by passing through a heating zone at a constant speed. A method for producing a polyester-coated metal bar, which comprises cooling the coating so that the degree of crystallinity of the coating is 20% or less after the treatment.