JPS6137103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to metal products coated with polyolefin, and more specifically, the present invention relates to metal products coated with polyolefin. This invention relates to polyolefin-coated metal products.

Polyolefins, especially polyethylene and polypropylene, are resins that are inexpensive and available in large quantities and have excellent properties such as water resistance, chemical resistance, and electrical insulation, and are non-toxic and highly processable, but they are non-polar. Therefore, it has poor adhesion to other materials, and it is particularly difficult to coat metal materials. Therefore, when manufacturing polyolefin-coated metal products,
A method has been used in which an adhesive resin different from polyolefin is used as a primer and the polyolefin is applied thereon to cover the metal, but at present, a fully satisfactory product has not been obtained.

For example, ethylene-vinyl acetate copolymer and ethylene-acrylic acid ester copolymer have poor water resistance, and have the disadvantage that adhesion strength decreases when water enters the end surface of the coating, and peeling spreads over the entire surface. Also, although polyurethane has good adhesion to metals, it has poor adhesion to polyolefins, and cannot be used as a primer at all.

The present invention has been made in view of the above-mentioned conventional drawbacks of polyolefin-coated metal products, and an object of the present invention is to provide polyolefin-coated metal products with excellent water resistance by using a primer that has good adhesion to metal and polyolefin. The gist of the invention is to provide a polyolefin obtained by applying a ply composition containing hydroxypolyolefin, polyisocyanate, and zinc powder to a metal surface, baking and drying the surface, and then coating the metal surface with polyolefin. Exists in coated metal products.

The hydroxy polyolefin in the present invention refers to a polyolefin having two or more hydroxyl groups in one molecule, preferably one hydroxyl group at both ends, and generally has two or more hydroxyl groups in one molecule, preferably both. It is obtained by adding hydrogen to a hydroxydiene polymer having one hydroxyl group at each end.

However, the addition of hydrogen here refers not only to cases where the double bonds in the hydrocarbon chains constituting the hydroxydiene polymer are completely hydrogenated, but also to cases where only a small portion of the double bonds remain. It also includes.

Hydroxydiene polymers can be synthesized by various methods. For example, it can be easily obtained by polymerizing a conjugated diene monomer together with other radically polymerizable monomers as necessary using hydrogen peroxide or an azobisisonitrile initiator having a hydroxyl group. The conjugated diene monomers used here include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-butadiene,
- Examples include dimethylbutadiene. Examples of other radically polymerizable monomers include styrene, acrylic monomers, vinyl pyridine, etc. These are used within a range where the content in the copolymer with the conjugated diene monomer is less than 50% by weight. From the viewpoint of compatibility with polyolefin, it is preferably used in an amount of 20% by weight or less.

A more preferable method is to react a living diene polymer with an epoxy compound such as a halogenoalkylene oxide, and then to react with a protonic acid. and a method of adding an aldehyde to a diene-based living polymer. Polybutadiene is preferably used as the living polymer in either case.

Nickel,
Cobalt, rhodium, etc. may be mentioned, and these may be used alone or in an appropriate mixture, or in an alloy system.

If the molecular weight of the hydroxypolyolefin used in the present invention is too large, it will be dispersed in a solvent together with polyisocyanate, etc., resulting in poor dispersibility and heat meltability in a solvent when used as a primer, and if it is too small, it will not dissolve in the cured primer composition. The number average molecular weight is generally set to be in the range of 500 to 5000, and is more preferably
It is said to be between 1000 and 4000.

The polyisocyanate in the present invention refers to an isocyanate compound having two or more isocyanate groups in the molecule, which is used as a curing agent that reacts with the hydroxypolyolefin to promote crosslinking. Specific examples include ordinary isocyanates such as diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, and triphenylmethane-P,P',P''-triisocyanate, as well as blocked isocyanates that have almost no reaction activity at room temperature. Diisocyanates such as diphenylmethane diisocyanate and tolylene diisocyanate are particularly preferably used.

In the present invention, the above-mentioned hydroxypolyolefin, the above-mentioned polyisocyanate, and metal zinc powder described below are used as essential components of the primer composition, and the content of polyisocyanate in the composition is determined by the equivalent of the isocyanate group to the hydroxyl group of the hydroxypolyolefin. The ratio is between 0.5 and 1.5, preferably
It is adjusted to be 0.8 to 1.2. If this ratio is less than 0.5, curing will be insufficient and the strength of the primer will be weak; if this ratio is more than 1.5, the pot life will be short and handling will be troublesome, or the cured product will become too hard and its adhesion to polyolefin will decrease.

As the metal zinc powder contained in the primer composition, those commonly used in zinc-rich primers having a particle size of about 100μ or less, preferably about 50μ or less are suitably used, and if the amount is too small, the corrosion protection by zinc The effect will not be sufficiently expressed, and if it is too much, the final film obtained will become brittle.
Approximately per 100 parts by weight of hydroxy polyolefin
It is said to be about 400 to 1500 parts by weight.

Furthermore, zinc oxide, zinc hydroxide, aluminum compounds, etc. may be mixed in advance in the metal zinc powder as long as they do not impede the anticorrosion effect.

The above hydroxy polyolefin, polyisocyanate and zinc powder may contain carbon black, calcium carbonate, titanium dioxide chalk,
Fillers and colorants such as clay and silica, antioxidants,
Additives such as ultraviolet absorbers and catalysts such as peroxides are added to form a primer composition, and the composition is used as a primer by being dispersed in an appropriate solvent such as xylene, toluene, methyl ethyl ketone, etc.

If it is necessary to particularly increase the cohesive force of the primer layer obtained by drying, it is preferable to add 5 to 50 parts by weight of carbon black to 100 parts by weight of the hydroxypolyolefin. In addition, when it is desired to increase the heat resistance of the primer layer, it is preferable to use a hindered phenol type, phosphate ester type, organic sulfur type antioxidant, etc. alone or in combination in an amount of 0.01 to 5% by weight in the primer composition. is preferably added in an amount of 0.1 to 2% by weight.

The primer is applied to the metal surface by dipping, spraying, brushing, etc., and then baked and dried. Conditions such as baking drying temperature and time are appropriately determined depending on the type and amount of hydroxypolyolefin and polyisocyanate, but industrially it is usually
The temperature is approximately 220°C for 5 to 15 minutes. The thickness of the primer after drying is preferably about 10 to 100 microns, regardless of the type of polyolefin coated afterwards.

Specific examples of the polyolefin used in the present invention include polyethylene, polypropylene, polybutene and the like, as well as maleic anhydride-modified adhesive polyethylene (trade name: Admer). Examples of methods for coating the metal surface with polyolefin via the primer include powder coating methods, methods for heat-pressing a molded resin sheet, and methods for coating by heating and shrinking a molded resin tube. From the viewpoint of adhesive properties, a method of heat-melting adhesion is preferred, and among these methods, a powder coating method is preferred from the viewpoint of forming a thin polyolefin layer.

Further, as the powder coating method, a fluidized dip coating method, an electrostatic dip coating method, an electrostatic spray coating method, etc. can be appropriately used depending on the shape of the metal, the purpose of the coated article, productivity, etc.

In the present invention, metal materials to which anti-corrosion coating treatment is applied include iron, aluminum, copper, tin, zinc,
Examples include lead and alloys containing these, and various shapes such as a tube, a rod, a wire, a plate, and the like can be adopted as the shape. Therefore, the present invention is particularly suitable for use in steel pipes whose inner surfaces are coated with polyolefin.

Part of the reason why the polyolefin-coated metal products of the present invention have excellent adhesion, particularly so-called secondary adhesion in the presence of moisture over a long period of time, is due to the primer composition used in the present invention containing hydroxyl in the primer layer. A unique polyurethane is formed as a reaction product of polyolefin and polyisocyanate. In addition to polyurethane's inherent high adhesion to metals, the hydrophobic moieties introduced into the primer layer by hydroxypolyolefin make polyolefin It is presumed that this is because it is well compatible with the material and exhibits excellent adhesive properties over a long period of time.

Furthermore, by introducing the zinc powder in the primer composition used in the present invention into the primer layer, the zinc has a lower tendency to ionize than the base metal, etc., which has a lower tendency to ionize, so that the zinc powder is introduced into the primer layer. This is presumed to be because it exhibits an electrochemical protective effect in its presence.

The polyolefin-coated metal product of the present invention is constructed as described above, and includes hydroxypolyolefin,
Since it is obtained using a primer containing polyisocyanate and zinc powder, it has excellent properties such as adhesiveness and water resistance required for anticorrosive coating of metals.

Examples of the present invention are shown below.

Example 1 The inner surface of a steel pipe with a nominal diameter of 20 m/m was subjected to grid blasting. Next, a primer composition containing 100 parts by weight of a hydroxypolyolefin with a molecular weight of 2800 obtained by adding hydrogen to hydroxypolybutadiene, 12 parts by weight of diphenylmethane diisocyanate, and 450 parts by weight of zinc powder with an average particle size of 10 μm was prepared. A primer obtained by dissolving hydroxyl polyolefin (hydroxyl group equivalent ratio 1.1) in 300 parts by weight of xylene was applied to the inner surface of the steel pipe using an airless spray gun, and baked and dried at 200° C. for 10 minutes. Primer dry film thickness is 30μ
It was hot. Next, this steel pipe is heated to 220°C in the air, and a mixed fluid of powdered low-density polyethylene with a Melton Index of 10 g/10 min is passed through the inner surface of the steel pipe for about 10 minutes to melt and bond the pipe, and a film is formed on the inner wall. thick contract
A 650μ polyethylene film was formed. The primary adhesion strength of this steel pipe at 25°C was 7.2 kg/cm when measured by the 180° peeling method with a width of 10 m/m. In addition, when measuring secondary adhesion, the steel pipe was cut to a length of 100 m/m, immersed in 3% saline solution at 50°C for 90 days, and then the peeling of the film from the end surface was observed. There was no peeling at all, and no rust was observed anywhere other than the cut portion (edge).

Example 2 A steel plate was degreased, pickled, and then treated with zinc phosphate. Next, 10 parts by weight of the same hydroxypolyolefin used in Example 1, 500 parts by weight of the same zinc powder used in Example 1, 12 parts by weight of tolylene diisocyanate, and dilaurylthiodipropionate as an antioxidant. Primer composition containing 0.1 part by weight and 0.1 part by weight of a hindered phenol compound (equivalent ratio of isocyanate groups of polyisocyanate to hydroxyl groups of hydroxy polyolefin)
A primer obtained by dispersing 1.1) in 350 parts by weight of xylene was applied to the above steel plate using an airless spray gun, and then baked and dried at 180°C for 10 minutes to form a primer layer with an average dry film thickness of 50μ. . Next, this steel plate was preheated at a temperature of 230°C in an electric furnace, fluidized immersed in low-density polyethylene powder with a melt index of 10 g/10 minutes, and then returned to the furnace and heated at 230°C for 5 minutes. Melt adhesion was carried out. The thickness of the polyethylene film obtained was 800μ. The primary adhesion strength of this steel plate is 10m/m wide.
It was 8.7 to 9.0 kg/cm by 180° peeling method. When measuring secondary adhesion, we made numerous cuts in the steel plate and immersed it in 3% saline solution at 50°C for 90 days.
There was no peeling of the film at all, and no rust occurred anywhere other than the notched areas.

Comparative Example 1 After grid blasting the inner surface of a steel pipe with a nominal diameter of 20 m/m, the same polyethylene powder used in Example 1 was used in Example 1 without using a primer.
It was melted and bonded to the inner surface of the steel pipe using the same method as above. The average thickness of the dried film was 665μ. Adhesion was measured in the same manner as in Example 1. Primary adhesion strength is 4.3Kg/
cm, and after being immersed in salt water, the coating on the steel pipe had peeled off over a distance of 25 m/m from the cut area, and rust had developed in that area.

Comparative Example 2 A steel pipe with a nominal diameter of 20 m/m was washed with sulfuric acid to completely remove scale, and then treated with zinc phosphate.

Next, steel pipes are placed in air without using any primer.
The tube was heated to 220° C., and then a polyethylene resin film was formed on the inner surface of the steel tube in the same manner as in Example 1.

The average thickness of the dried film was 620μ, and the adhesion was then measured in the same manner as in Example 1. The primary adhesion was 3.9 Kg/cm, and after immersing the steel pipe in the saline solution, the coating peeled off over a distance of 12 m/m from the notch, and rust had developed in that area.

Comparative Example 3 The inner surface of a steel pipe with a nominal diameter of 20 m/m was subjected to grid blasting, ethylene-vinyl acetate copolymer powder was applied, and then heated and melted to form a primer layer with a thickness of 30 μm.

Next, a film thickness of 800 mm was applied to the inner surface of the steel pipe in the same manner as in Example 1.
A polyethylene film of μ was formed, and the adhesion was measured in the same manner as in Example 1. Primary adhesion is 6.8
Kg/cm, and after being immersed in the saline solution, the coating on the steel pipe had peeled off over a distance of 50 m/m from the notch, and rust had developed in that area.

Claims (1)

[Scope of Claims] 1. A polyolefin obtained by applying a primer composition containing a hydroxypolyolefin, a polyisocyanate, and a zinc powder to a metal surface, baking it and drying it, and then coating the metal surface with a polyolefin. Coated metal products. 2. The metal product according to item 1, wherein the primer composition contains about 400 to 1500 parts by weight of zinc powder per 100 parts by weight of hydroxypolyolefin. 3. The metal product according to item 1 or 2, wherein the hydroxypolyolefin has a number average molecular weight of about 500 to 5,000. 4 Items 1 to 3 in which the equivalent ratio of the isocyanate group of the polyisocyanate to the hydroxyl group of the hydroxy polyolefin is 0.5 to 1.5 in the primer composition.
Metal products described in any one of the above items. 5 The film thickness of the primer composition after baking and drying is approximately 10
The metal product according to any one of Items 1 to 4, which has a particle size of ~100μ. 6. The metal product according to any one of items 1 to 5, which is coated with polyolefin by heating and melting. 7. The metal product according to item 6, which is powder coated using powdered polyolefin.