JPH0139452B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for coating a zinc surface of galvanized steel or the like with a synthetic resin. Traditionally, metals such as steel have been coated with synthetic resin sheets or plates with adhesives for rust prevention and surface protection. Methods using hot-melt adhesives are being developed. however,
For zinc surfaces such as galvanized steel, conventional hot-melt adhesives have low adhesive strength, and furthermore, immersion in hot water causes the adhesive strength to drop significantly and cause the synthetic resin coating to peel off. The present invention aims to solve the above-mentioned problems, and its gist is that sulfur and/or thiurams, thiazoles, dithioacids, etc. A method for bonding a synthetic resin layer to a zinc surface using a hot-melt adhesive whose main component is a composition containing 0.1 to 10 parts by weight of a salt-based vulcanization accelerator. This is a synthetic resin coating method. The present invention is further particularly useful for manufacturing metal tubes having a zinc surface on the inner surface and lining the inner surface with a thermally expandable synthetic resin tube. In other words, in such lined metal pipes, during the cooling process, such as when hot water is passed through and then cooled, the inner synthetic resin pipe tends to become larger than the steel pipe and shrink in diameter, so there is a gap between the inner synthetic resin pipe and the steel pipe. Due to peel stress, a complex load is applied to the adhesive.
For this reason, in applications where hot water passes through, if there is a weak point at the interface with the zinc surface, the adhesive will not be able to fully demonstrate its performance, and the inner surface may bulge due to peeling at the interface, or synthetic resin pipes may be damaged due to impact. However, if the method of the present invention is used to manufacture synthetic resin-lined steel pipes that are used under such harsh conditions, the problem of bulges and cracks will not occur. You can get the product you want. In the present invention, a polyolefin copolymerized with an unsaturated aliphatic carboxylic acid or its anhydride (hereinafter referred to as "acid-containing polyolefin") has good adhesion to metals even when used alone, but in addition to sulfur or vulcanized polyolefin. By adding an accelerator, the adhesion to galvanized surfaces could be improved. The unsaturated aliphatic carboxylic acids to be copolymerized with the polyolefin used in the present invention include acrylic acid, methacrylic acid, crotonic acid, vinyl acetic acid, maleic acid,
These include fumaric acid, itaconic acid, mesaconic acid, citraconic acid, etc., and the unsaturated aliphatic carboxylic acid anhydrides include maleic anhydride, itaconic anhydride, citraconic anhydride, etc., and these can be used singly or in combination. is 0.1-30.0% by weight, preferably 1.0-20
Copolymerization or graft copolymerization within a range of % by weight. Polyolefins include polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, ethylene -4 methyl-1
Ethylene, propylene, 1 such as pentene copolymer
- Homopolymers and copolymers of butene, 4-methyl-1-pentene, etc., and ethylene-vinyl acetate copolymers containing these olefins as main components,
These include ethylene vinyl chloride copolymer, ethylene/glycidyl methacrylate copolymer, ethylene/ethyl acrylate copolymer, saponified ethylene vinyl acetate copolymer, and the like. Among these, ethylene/acrylic acid copolymer, ionomer, acrylic acid-modified polyethylene, maleic anhydride-modified polyethylene, maleic acid-modified polyethylene, maleic anhydride-modified ethylene-vinyl acetate copolymer, etc. can be suitably used. In the adhesive composition of the present invention, sulfur or a vulcanization accelerator is added to 100 parts by weight of acid-containing polyethylene.
It is necessary to add 0.1 to 10 parts by weight. If it is less than 0.1 part by weight, the adhesion to galvanized steel pipes will be insufficient, and if it exceeds 10 parts by weight, the improvement in adhesion will reach a plateau and undesirable phenomena such as blistering will occur. Examples of vulcanization accelerators include thiurams such as tetramethylthiuram disulfide and tetrabutylthiuram disulfide, thiazoles such as 2-mercaptobenzothiazole and dibenzothiazole disulfide, Zn diethyldithiocarbamate, and Zn-di-n- It can be selected from dithioate salts such as butyldithiocarbamate. In addition to the above, the adhesive components include rosin,
Tackifier resins such as terpenes, hydrocarbons, and phenols, fillers such as calcium carbonate, talc, and clay, rubber components, elastomer components, various waxes, plasticizers, antioxidants, and the like may be added. In order to adhere the synthetic resin layer to the zinc surface using the above adhesive, the adhesive is melted and applied to the synthetic resin layer surface and/or the zinc surface in advance, or a film-like adhesive is sandwiched. For example, the synthetic resin layer and the zinc layer may be superimposed via the adhesive layer, and the adhesive may be melted by heating to be bonded. Furthermore, in order to manufacture a synthetic resin-lined metal tube according to the present invention, the following steps may be taken. Thermally expandable synthetic resin pipes are mainly made by extruding synthetic resin such as polyvinyl chloride or polypropylene into a tubular shape, and then stretching it in the axial direction at a temperature above the softening point and below the melting point of the synthetic resin. It is possible to use a material that has been reduced in diameter and immediately quenched to give it thermal expansion properties. It is preferable to provide the hot-melt adhesive layer on the outer circumferential surface of the synthetic resin pipe in advance to form a laminated pipe for lining, since it is easy to apply the adhesive layer.For this purpose, the composition is applied to the synthetic resin using an extruder using a crosshead die. The adhesive can be melt coated by extruding it into an annular shape on the outside of the pipe, or extruding it into a band and wrapping it around a synthetic resin pipe, or by forming an adhesive into a flat film and wrapping it around a synthetic resin pipe. can. In order to line the above-mentioned lining laminated tube inside a metal tube, insert the lining laminated tube into the metal tube whose inner surface has been cleaned in advance, and use a method such as a gas burner or hot air blowing from the outside of the metal tube to open one end of the tube to the other end. By heating successively from the end or center to both ends, or by passing heated fluid through the inside of the lining laminated tube, the lining laminated tube is expanded and the adhesive is melted and bonded at the same time. It is. When lining galvanized steel pipes using conventional hot-melt adhesives, complicated pre-treatments such as treating the inner surface of the steel pipes with zinc phosphate were required in advance. According to this method, sufficient practical strength can be obtained by polishing with a wire brush to remove white rust, impurities, and oil and fat. Furthermore, the adhesion strength may be further improved by providing an intermediate layer with good adhesiveness between the heat-expandable synthetic resin pipe and the hot-melt adhesive composition. For example, when a polyvinyl chloride resin pipe is used as a thermally expandable synthetic resin pipe, the intermediate layer may contain a tackifier such as a rosin resin or a terpene resin, and ethylene in addition to the acid-containing polyolefin, which is the main component of the adhesive. A compound containing a polyolefin elastomer such as a -1-butene copolymer can be used. Since the present invention has the structure described above, it is possible to apply a strong synthetic resin coating that is highly resistant to hot water without performing complicated pretreatment on the zinc surface. Synthetic resin lined metal pipes, which are obtained by coating the inner surface of the metal pipe with synthetic resin, do not blister on the inner surface of the synthetic resin pipe even under harsh conditions such as passing through hot water, and do not crack due to impact. This is an extremely superior synthetic resin coating method for zinc surfaces. Hereinafter, it will be explained in more detail with reference to Examples. In the following example, a synthetic resin-coated metal pipe will be explained. Example 1 100 parts by weight of ethylene-acrylic acid copolymer (melt index 2.0, acrylic acid content 6.5% by weight) was used as the acid-containing polyolefin, and sulfur or additives as shown in Experiment Nos. 1 to 4 of Table 1 were used. An adhesive composition containing 1 part by weight of a sulfur accelerator, 100 parts by weight of the same ethylene-acrylic acid copolymer, 100 parts by weight of ethylene-1-butene copolymer elastomer (melt index 2.0), and terpene phenol resin. An intermediate layer composition containing 30 parts by weight (softening temperature: 150°C) was prepared. Next, the intermediate layer composition was applied to the outer surface of the heat-expandable polyvinyl chloride pipe, and the adhesive composition was applied to the inner surface thereof by coextrusion coating using a crosshead die to obtain a synthetic resin pipe for lining. .
The middle layer has an average thickness of 50μ, and the adhesive layer has an average thickness of
It was 25μ. . Insert the obtained synthetic resin pipe for lining into a galvanized steel pipe (for water supply, size 50A, length 5500mm) and use a gas burner to turn the steel pipe surface from one end to the other until the steel pipe surface reaches 140℃. Heat it like this,
I lined it. The inner surface of the steel pipe was previously cleaned with a wire brush. Next, the heat resistance of the thus obtained lined metal tube was evaluated by the following method, and the results are shown in Table 1. Length from any location of the lining metal pipe
Cut a 1000mm sample and place it in 80℃ hot water for 2 hours at 20℃.
The test was repeated for 60 cycles, each cycle consisting of immersion in water for 2 hours. Observe the inner surface of this sample with the naked eye, and if it does not bulge, it is considered good.
marked something as defective. After that, five test pieces with a width of 20 mm were cut out from the sample at uniform intervals for measuring adhesive strength, and JWWAK-116 method (Japan Water Works Association standard) was used.
The punch-out strength based on the above was measured at 20° C. and was defined as the residual adhesive strength (Kg/cm ² ). In addition, an additional 1,000 pieces of lining metal tube were cut from the sample for repeated testing.
A mm sample was cut out, and the punching strength was measured in the same manner as above to determine the initial adhesive strength.

[Table] Example 2 As acid-containing polyolefin, 100 parts by weight of the same ethylene-acrylic acid copolymer as in Example 1, sulfur in the amounts shown in Experiment Nos. 5 to 9 in Table 2, and ethylene-1-butene were added. An adhesive composition containing 50 parts by weight of a polymer elastomer (melt index 2.0) and 30 parts by weight of α-pinenephenol with a softening temperature of 150°C was directly applied to the same polyvinyl chloride pipe as in Example 1 using a crosshead die. A laminated pipe for lining was obtained by extrusion coating. This laminated pipe was lined with a galvanized steel pipe in exactly the same manner as in Example 1, and the heat resistance was evaluated in exactly the same manner as in Example 1. The results are shown in Table 2. For comparison, Experiment No. 10 shows a tube lined in the same manner as in Example 1 using a laminated tube for lining coated with a commercially available solvent-based adhesive (chloroprene-phenolic type).

[Table] As shown in Table 2, in Experiment No. 5 where the amount of sulfur added was less than 0.2 parts by weight, the initial adhesive strength was 30.1 kg/
^cm2 , but after repeated tests, the residual strength became extremely small at 2.1Kg/ ^cm2 , and a bulge occurred on the inner surface of the synthetic resin tube due to peeling. On the other hand, Experiments Nos. 6 to 9 of the present invention exhibited superior residual strength even compared to Experiment No. 10, which used a conventional solvent-based adhesive, and had a good appearance. Note that if more than 10 parts by weight of sulfur was added, it would blow out onto the surface and would not be of practical use. Example 3 As acid-containing polyethylene, 100 parts by weight of maleic anhydride-modified ethylene-vinyl acetate copolymer (melt index 2.0), 1 part by weight of sulfur, ethylene-vinyl acetate copolymer (melt index 2.0),
Using an adhesive composition containing 50 parts by weight of a 1-butene copolymer elastomer (melt index 2.0) and 30 parts by weight of α-pinene phenol (softening temperature 150°C), zinc coating was carried out in exactly the same manner as in Example 2. When the heat resistance was evaluated in the same manner as in Example 1 by lining a steel pipe, the initial adhesive strength was 29.2 kg/
cm ² , residual adhesive strength was excellent at 14.1 Kg/cm ² , and the appearance was also good.

Claims (1)

[Claims] 1 100 parts by weight of polyolefin copolymerized with unsaturated aliphatic carboxylic acid or its anhydride, mixed with 0.1 to 10 parts by weight of sulfur and/or thiurams, thiazole type, dithioate type vulcanization accelerator. 1. A method of coating a zinc surface with a synthetic resin, the method comprising adhering a synthetic resin layer to the zinc surface using a hot-melt adhesive containing a composition as a main component.