JPS6023026B2 - plastic coated metal products - Google Patents

Description

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

Conventionally, various metal products including an undercoat layer and a plastic layer have been known, such as plastic-coated steel pipes and vinyl chloride-laminated steel plates.
In particular, the former is widely used, for example, in buried pipelines for transporting gas, oil, etc., and involves coating the surface of the steel pipe with thermoplastic plastic such as polyethylene or polypropylene to prevent corrosion after burial. is commonly practiced.

At that time, adhesives such as modified polyethylene, ethylene-vinyl acetate copolymer, asphalt, petroleum resin, etc. are used to bring the thermoplastic plastic coating layer into close contact with the surface of the steel pipe and prevent moisture from penetrating. A so-called undercoat layer such as an adhesive is applied to the surface of the steel pipe. That is, plastic-coated steel pipes are usually coated with two layers: an undercoat layer of adhesive or pressure-sensitive adhesive, and a thermoplastic plastic layer.

After a plastic-coated steel pipe having such a structure is buried as a pipeline, for example, cathodic protection is usually used in combination to further ensure corrosion protection.

The magnetic insulation resistance of the plastic coating layer of ordinary plastic-coated steel pipes is extremely high and remains constant for a long period of time. It is recognized that it exhibits a performance of ○/me level, so this alone is sufficient for corrosion protection. However, it is practically difficult to ensure that the plastic coating layer is completely free from damage during transportation or construction of plastic-coated metal pipes, so cathodic protection is used in combination to prevent corrosion from progressing from the bowl. -ing The electrolytic protection has a corrosion protection potential of -1 of the steel pipe.
．． 0y (Cu/CuS04 electrode comparison), the required current is set in consideration of the actual insulation resistance of the coating.

Even if there is a reduction in the plastic coating layer and the steel pipe is exposed, electrical corrosion protection is provided, but on the other hand, if the adhesion between the plastic coating layer and the steel pipe is very weak or the potential is excessive. In this case, the undercoat layer around the eaves will gradually peel off, and the plastic layer and steel pipe will no longer be in close contact with each other. This phenomenon is generally referred to as "cathode exfoliation".
It is called. However, the worse the cathode peeling resistance, the larger the diameter of the part that peels off in the same circle around the original shape. If the plastic coating layer becomes distorted and holes are formed, exposing the surface of the steel pipe and polarizing it as a cathode, the following phenomena may occur due to the presence of corrosive aqueous or electrolyte solutions in the buried soil. Be looked at.

1 Generation of hydrogen gas by reduction of hydrogen ions (11 left day 2 ↑) 2 Alkalinization by cathodic polarization (4011/2020 → OH-) As a result of the combined effects of these series of phenomena, The adhesive strength of the undercoat layer decreases, and peeling occurs between the plastic coating layer and the steel pipe surface.

In order to solve the above-mentioned problems, conventionally, before applying an undercoat layer such as an adhesive or a pressure-sensitive adhesive, a primer paint such as a Fe/lepoxy type or a Tarepoxy type is applied to the surface of the steel pipe in advance, and then the A method of coating with an undercoat layer and further coating with polyethylene or the like is known.

Also known is a method in which a steel pipe is subjected to a blast treatment or pickling treatment, and then subjected to a base treatment such as a phosphate treatment or a chromic acid treatment, and then coated with an undercoat layer and polyethylene.

All of the above methods have some effect on cathode peeling resistance.

However, it becomes complicated due to the addition of one processing step, and
The former method requires equipment such as painting equipment and exhaust treatment equipment during application, while the latter method requires wastewater treatment equipment, both of which avoid an increase in manufacturing costs.
A similar problem occurred in a pinyl chloride laminated steel plate having a structure in which an adhesive is used as an undercoat layer and a vinyl chloride sheet is pressure-bonded thereon.

'The present invention aims to eliminate the drawbacks of the prior art as described above, and provides a plastic-coated metal product that does not require any special process or treatment equipment during production and has excellent performance such as cathode peeling resistance. This is what we are trying to provide.

That is, the present invention provides a plastic-coated metal product consisting of an undercoat layer and a plastic layer thereon,
A compound that has an oxidizing effect on the undercoat layer.
The present invention relates to a plastic-coated metal product characterized in that it contains at least one of an oxyacid salt, an internal metal lead, or an acid salt thereof or a salt thereof. As a result of various studies, the inventors of the present invention found that a specific substance was used to effectively prevent cathode peeling without impairing the role of the undercoat layer that exists between the steel surface and the thermoplastic layer. They have discovered that it is sufficient to incorporate it into the undercoat layer, and have arrived at the present invention.

As mentioned above, when the steel surface is polarized by the cathode, hydrogen gas generation and alkalization phenomena are observed on the exposed steel surface.As a means to prevent or suppress these phenomena, for example, '1' Increasing overvoltage, ■ Preventing hydrogen generation using compounds with oxidizing properties,
'31 Neutralization of alkali with oxyacid salts, etc. can be considered.

In order to increase the hydrogen overpressure on the steel surface of the suppressing or preventing means, it is sufficient to adsorb or precipitate metal ions with a high hydrogen overvoltage on the steel surface. The most effective are metallic lead and its oxides or salts, such as metallic lead, lead zinc oxide, lead monoxide, lead dioxide, lead mother circle, lead cyanamide, calcium leadate, basic lead sulfate, and base. lead chromate, etc. are exposed.

In addition, any compound that can be easily reduced at the cathode is effective as the compound that has the oxidizing effect described in (2) above, but in order to maintain its oxidizing effect over a long period of time, chromium, molybdenum, tungsten, manganese, etc. oxides or oxyacid salts thereof are more preferred. Examples of the oxide or oxyacid include chromium trioxide, molybdenum trioxide, tungsten trioxide, manganese dioxide, strontium chromate, calcium chromate, zinc chromate,
Zinc molybdate, calcium molybdate, potassium molybdate, zinc tungstate, calcium tungstate, magnesium tungstate, chromate, etc. are listed.

Furthermore, the neutralizing effect of the alkali by the above-mentioned 3L oxy-acid salts traps and immobilizes OH- ions generated by cathodic polarization, suppressing the increase in pH value. If you fist it, Zn3 (P04) 20 H-
→Zn(OH)20 becomes 0 reed-.

In addition to the above-mentioned chromium oxide and its oxyacid salts, compounds having the above-mentioned neutralizing effect include salts obtained from oxyacids such as phosphoric acid, boric acid, and sulfuric acid and metals such as zinc, lead, aluminum, and tin. There is, specifically. For example, zinc phosphate, lead orthophosphate, lead pyrophosphate, lead metaphosphate, aluminum phosphate, tin orisophosphate, tin pyrophosphate, tin oxyphosphate, zinc tetraborate, zinc metaborate, lead metaborate, lead tetraborate. , lead sulfate, lead(II) sulfate, etc.
Although methods for suppressing abnormal phenomena in cathodic polarization and materials used therefor have been exemplified above, these methods do not occur uniformly as explained above.

Naturally, it is assumed that there are complex mutual phenomena or effects.
Therefore, it is possible to use not only one kind of the above compound but also two or more kinds of compounds in combination. As mentioned above, various compounds having an oxidizing effect, oxyacid salts, metallic lead, its oxides, or its salts are suitable for use in the present invention, but particularly preferably chromium, molybdenum, and tungsten are used as compounds having an oxidizing effect. Oxygen acid salts include phosphoric acid, boric acid,
It is a salt obtained from chromic acid, sulfuric acid, and zinc, lead, and aluminum.Metal lead, its oxide, or its salt includes lead metal, lead zinc oxide, lead monoxide, lead dioxide, lead oxide, lead white, Lead cyanamide, calcium leadate, and basic lead sulfate are exposed. Next, the undercoat such as a pressure-sensitive adhesive or adhesive as used in the present invention is, for example, (i) ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, styrene-isoprene block copolymer, styrene-butylene copolymer, etc. Polymers such as Genb block copolymer, polyisobutylene, isobutylene-isoprene rubber, petroleum resin, terbenfer/-ol resin, styrene-olefin copolymer, terbene polymer, terbene resin, hydrogenated carbon iris sheath resin, Mixtures with rosins such as gum rosin, wood rosin, tall oil, rosin, modified rosins, tackifier resins such as diterbene resins, coumarindane resins, xylene resins, and, if necessary, blown asphalt, straight asphalt, etc., paraffin wax, Hot-melt adhesives made by mixing waxes such as low molecular weight polyethylene, plastic substances such as paraffinic mineral oil, naphthenic mineral oil, etc., or (ii) synthetic rubbers such as polyisobutylene, isoprene-isobutylene rubber (butyl rubber), etc. extrusion-type pressure-sensitive adhesives whose main components are so-called modified polyethylenes such as ethylene-pinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and maleated products thereof.

However, in the present invention, the pressure-sensitive adhesive or adhesive is not particularly limited. In the present invention, at least one of the compounds having an oxidizing effect, oxyacid salts, metal lead powder, etc. is contained in the undercoat such as the pressure-sensitive adhesive or adhesive, preferably in an amount of 0.1 to 5% by weight, and further Preferably 2~
3% by weight and mixed uniformly.

When the content is less than 0.1% by weight, there is almost no resistance to cathode peeling, and conversely, when the content is less than 5% by weight,
Exceeding this is not preferable because it significantly reduces the adhesive strength of the undercoat.

The content of the oxidizing compound, oxyacid salt, metal lead powder, etc. may vary somewhat depending on the type of undercoat.

For example, in a synthetic rubber adhesive whose main component is polyisobutylene, isoprene-isobutylene rubber, etc., it may be contained up to 5% by weight, but in a modified polyethylene adhesive, the melt index is around 5. When the content is as small as , it is preferable to limit the content to 2% by weight or less. The undercoat thus obtained is applied to the metal surface by conventional methods. The product is then coated with a thermoplastic such as polyethylene to obtain a coated metal product with excellent cathode peeling resistance. As mentioned above, the present invention does not require any special measures for environmental conservation such as special coating equipment or wastewater treatment equipment, and also does not impair the characteristics of the conventional undercoat layer (cathode peeling resistance). The industrial value of this method is extremely high because it produces very superior coated metal products.

The details of the present invention will be explained below with reference to Examples.

"Part" or "%" indicates "part by weight" or "% by weight".
Example 1 External diameter 609.6, rust removed by blasting in advance
After preheating the side steel pipe to 18 mm with a burner, apply an adhesive consisting of 95% ethylene-ethyl acrylate copolymer (melt index 7, density 0.93) and 5% zinc chromate to a thickness of about 200 mm. The target was extrusion coating.

Next, low density polyethylene (melt index 0.3
A plastic-coated metal product of the present invention was obtained by extrusion coating the plastic-coated metal product with a density of 0.93i and containing 2.5% carbon black to a thickness of approximately 3 skins. A test piece is cut from this coated steel pipe, and according to the test method of ASTM-G8-72, a hole of a predetermined diameter is made in advance until it reaches the steel pipe, and then it is immersed in an electrolyte solution.A test piece is applied to the cathode and peeled off after a predetermined period of time. Find the radius. In addition, the test piece was left under an atmospheric condition of 20°C, and when the temperature of the test piece stabilized to the specified temperature, two parallel lines were cut into the polyethylene coating layer to reach the steel pipe base in one direction. One end of the strip-shaped polyethylene coating was attached to a spring scale, and it was
A peel test was conducted at an angle of 100 degrees to measure the peel strength. still,
For comparison, a test was also conducted on a coated steel pipe manufactured under the same conditions as described above using an adhesive obtained by removing zinc chromate from the above-mentioned drumming agent. Example 2 A plastic coated product was obtained in the same manner as in Example 1 using an adhesive consisting of 80% of the same ethylene-ethyl acrylate copolymer and 20% of metallic lead powder.

Example 3 A plastic coated article was obtained in the same manner as in Example 1 using an adhesive consisting of 95% of the same ethylene-ethyl acrylate copolymer and 5% of zinc phosphate.

Example 4 A plastic-coated metal product was obtained in the same manner as in Example 1 using an adhesive consisting of 99% of the same ethylene-ethyl acrylate copolymer and 1% of molybdenum trioxide.

Example 5 Isobutylene, isoprene rubber [Essobutyl 265;
Manufactured by Esso Chemical ■Product name: 10 Ikarito, tackifier resin [EC
R-110 wave: Esso Chemical ■Product name] A composition consisting of 5 cornerstone parts, polybdenum (Nisseki Polybdenum HV-300 manufactured by Nippon Petrochemical Company name) 2 anchor parts (hereinafter referred to as butyl rubber mixture) 50% and cyanamide lead. An adhesive consisting of 50%
The surface of a steel pipe with an outer diameter of 609.6 mm, which has been blasted to remove rust and preheated to 15 mm with a burner, is coated with a target thickness of 300 mm, and then low-density polyethylene (melt index 0.3 , density 0.935, carbon black content 2.5) was extrusion coated to a target thickness of 3 skins.

A test piece was cut from this coated steel pipe and subjected to a 180 degree beer peel test and a cathode peel test between the adhesive and the coated polyethylene using the same machine, and the peel radius after the test was determined. still,
For comparison, a test was also conducted on a coated steel pipe manufactured under the same conditions using an adhesive with cyanamide lead removed from the adhesive described above, and the results are also shown in Table 2. Example 6 Same butyl rubber mixture as Example 5 70%, zinc chromate 30%
A plastic coated product was obtained analogously to Example 5 using an adhesive consisting of %.

Example 7 Same as Example 5 butyl rubber mixture 80%, white lead 20%
A plastic coated product was obtained in the same manner as in Example 5 using an adhesive consisting of:

Example 8 A plastic coated product was obtained in the same manner as in Example 5 using an adhesive consisting of 95% of the same butyl rubber mixture and 5% of zinc tungstate.

Example 9 Styrene-butadiene block copolymer [Tuffrene A: trade name manufactured by Asahi Kasei Corporation] 25 parts, tackifying resin [Estel Gum H: trade name manufactured by Arakawa Hayashi Ibaku ■] 2
Anchorage, composition consisting of 55 parts of straight asphalt 80/1OQ (hereinafter referred to as asphalt mixture) 95
%, and 5% aluminum phosphate, was treated with plastic to remove rust, and heated to 100% with a burner.
``Thickness 3 on the surface of a steel pipe with an outer diameter of 609.6 that has been preheated to 0.
The film was flow-coated with a target thickness of 0.00 mm, and then extrusion coated with low-density polyethylene (same as in Example 1) with a target thickness of 3 ribs.

A test piece was cut from this coated steel pipe and subjected to a 180 degree beer peel test and a cathode peel test between the adhesive and the coated polyethylene in the same manner as described above, and the peel radius after the test was determined. In addition, similar to the above, comparative tests using only asphalt mixtures were also conducted and are shown in Table 3. Example 10 Same asphalt mixture as Example 9 80%, metallic lead 2
A plastic coated product was obtained in the same manner as in Example 9 above using an adhesive consisting of 0%.

Example 11 A plastic-coated product was obtained in the same manner as in Example 9 using an adhesive consisting of 85% of the same asphalt mixture and 15% of lead phosphate.

Example 12 A plastic coated product was obtained in the same manner as in Example 9 using an adhesive consisting of 95% of the same asphalt mixture and 5% of zinc tetraborate.

Table 1 Formulation and test results Table 2 Formulation and test results Table 3 Formulation and test results As is clear from the results in Tables 1 to 3 above, the coated metal products of the present invention have excellent cathodic peel resistance and peel strength. It showed remarkable effects in this respect.

Claims (1)

[Scope of Claims] 1. A plastic-coated metal product consisting of an undercoat layer and a plastic layer, in which the undercoat layer contains at least one of a compound having an oxidizing effect, an oxyacid, metal lead, its oxide, or its salt. A plastic-coated metal product characterized by containing: 2. A patent characterized in that the undercoat layer contains 0.1 to 50% by weight of at least one of the oxidizing compounds, oxyacid salts, metallic lead, oxides thereof, or salts thereof. A plastic-coated metal product according to claim 1. 3. Claim 1, wherein the compound having an oxidizing effect is at least one of oxides of chromium, molybdenum, and tungsten, or oxyacids thereof.
A plastic-coated metal product according to item 1 or 2. 4. The plastic-coated metal according to claim 1 or 2, wherein the oxyacid is at least one salt obtained from phosphoric acid, boric acid, chromic acid, sulfuric acid, and zinc, lead, or aluminum. product. 5 The metal lead, its oxide, or its salt is metal lead, lead zinc oxide, lead monoxide, lead dioxide, red lead, lead white, cyanamide lead, calcium lead acid, basic lead sulfate, and basic lead chromate. A plastic-coated metal product according to claim 1 or 2, which is at least one of: 6. A plastic-coated metal product according to claim 1, wherein the undercoat layer is a pressure-sensitive adhesive or an adhesive. 7. The plastic-coated metal product according to claim 1, wherein the plastic-coated metal product is a plastic-coated steel pipe.