JPS6116619B2 - - 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, and more specifically, metal products coated with polyolefin, which are obtained using a special primer composition and have excellent properties necessary for corrosion prevention of metals, such as adhesion and water resistance. This invention relates to polyolefin-coated metal products.

Polyolefins, especially polyethylene and polypropylene, 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. It has poor adhesion to other materials, and it is particularly difficult to coat metal materials. For this reason, conventional methods for manufacturing polyolefin-coated metal products have been to use an adhesive resin different from polyolefin as a primer, and then coat the metal with polyolefin on top of the primer, but there is no method that is fully satisfactory. The current situation is that it has not been obtained.

For example, ethylene-vinyl acetate copolymer and ethylene-acrylic acid ester copolymer have poor water resistance, and the adhesive strength decreases when water enters the end surface of the coating, causing peeling to spread over the entire surface. Furthermore, although epoxy resin has good adhesion to metals, it has poor adhesion to polyolefins, and has not yet been able to withstand practical use as a primer.

The present invention was made in view of the above-mentioned conventional drawbacks of polyolefin-coated metal products, and aims to provide polyolefin-coated metal products with excellent water resistance by using a primer that has good adhesion to metal and polyolefin. The gist is that a primer composition containing an epoxy group-containing polymer obtained by reacting a hydroxydiene polymer or its hydride with epihalohydrin and a curing agent is applied to a metal surface and baked and dried. The present invention relates to a polyolefin-coated metal product characterized in that a polyolefin is coated on a primer layer.

The hydroxydiene polymer in the present invention refers to a diene polymer having two or more hydroxyl groups in one molecule, preferably one hydroxyl group at both ends, and the hydride refers to a hydroxydiene polymer having two or more hydroxyl groups in one molecule, preferably one hydroxyl group at both ends. This includes not only cases where the double bonds in the hydrocarbon chains constituting the system polymer are completely hydrogenated, but also cases where some double bonds remain.

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, if necessary, using hydrogen peroxide or an azopisisonitrile initiator having a hydroxyl group. The conjugated diene monomers used here include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-butadiene,
-dimethylbutadiene, etc. 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.

In addition, a more preferable method since it is possible to obtain a hydroxydiene polymer having one hydroxyl group at both ends is to react a living diene polymer with an epoxy compound such as a halogenated alkylene oxide, and then to react with a proton-based polymer. Examples include a method of treating with an acid and a method of adding an aldehyde to a living diene polymer, and polybutadiene is preferably used as the living polymer in either case.

Catalysts for hydrogenating the hydroxydiene polymer thus obtained include nickel, cobalt, rhodium, etc., and these may be used alone or in appropriate mixtures or in alloys.

Other methods for producing hydrides of hydroxydiene polymers include a method in which a copolymer of α-olefin and a diene monomer is subjected to ozonolysis treatment and then reduced.

Specific examples of epihalohydrin used in the present invention include epichlorohydrin, epipromohydrin, α-methylepichlorohydrin, etc., and epichlorohydrin is particularly frequently used.

The reaction product of the hydroxydiene polymer or its hydride and epihalohydrin is usually obtained by reacting the raw materials in a hydrocarbon solvent in the presence of various catalysts. Specific examples of solvents include toluene, xylene, benzene, hexane, heptane, and mixtures thereof. Specific examples of catalysts include alkaline catalysts such as caustic soda,
In addition to acid catalysts such as hydrochloric acid and acetic acid, more preferred examples include poron trifluoride, its ether complex, and titanium halide. If an acid catalyst is used first, it is not possible to introduce epoxy groups in a one-stage reaction, so it is necessary to carry out a further reaction in the presence of an alkali after the first stage reaction, but such a two-stage method is generally better. It is easier to quantitatively introduce epoxy groups than a one-step method that uses an alkali catalyst first.

If the molecular weight of the thus obtained epoxy group-containing polymer is too large, it will be dissolved or dispersed in a solvent together with a curing agent, resulting in poor dissolution, dispersibility, and heat meltability in a solvent when used as a primer, and if it is too small, it will gel. This tends to result in poor adhesion, so
Generally, the number average molecular weight is in the range of 500 to 5000,
More preferably it is 1000-4000.

As the curing agent in the present invention, compounds having an atomic group capable of reacting with the above-mentioned epoxy group-containing polymer to form a polymer with a network crosslinked structure are widely used, and are generally polycarboxylic acids, their anhydrides, polyamines, and melamine. Acid anhydrides are often used because they are easy to handle.

Examples of acid anhydrides include phthalic anhydride, maleic anhydride, methyl- ^Δ4 -tetrahydrophthalic anhydride, pimelic acid, etc.; examples of polyamines include primary aliphatic amines such as triethylenetetramine, metaphenylenediamine, etc. A primary aromatic amine or the like is used. Furthermore, depending on the case, low molecular weight polyamides such as dicyandiamide, high molecular weight polyamides such as polyamide resins, halides such as carboxylic acid chlorides, polyisocyanates, etc. may also be used. Any of the above curing agents may be used in combination as appropriate.

The equivalent ratio of the epoxy group in the epoxy group-containing polymer to the atomic group capable of crosslinking with the epoxy group in the curing agent in the primer composition is usually from 0.7 to
2 is preferably adjusted to 0.8 to 1.2.
If this ratio is greater than 2, curing is generally insufficient;
This is because if it is smaller than 0.7, the pot life will be short and handling will be troublesome, and the cured product will become too hard and the adhesiveness with the polyolefin will decrease. However, when using a self-condensing type curing agent such as melamine, it is preferable to use a slightly larger amount of the curing agent than the above range. The equivalent weight of the atomic group capable of crosslinking with the above epoxy group in the curing agent is calculated based on the functionality, that is, the number of potential bonds exhibited during polymer formation. contains 4 active hydrogen atoms in one molecule, so 1 mole thereof is considered to be 4 equivalents, and 1 mole of phthalic anhydride is considered to be 2 equivalents.

The above epoxy group-containing polymer and curing agent may include carbon black, calcium carbonate,
Additives such as fillers and colorants such as titanium dioxide, chalk, clay, and silica, antioxidants, ultraviolet absorbers, and catalysts such as peroxides are added to form a primer composition. It is used as a primer after being dissolved or dispersed in an appropriate solvent such as xylene, toluene, methyl ethyl ketone, etc.

If it is particularly necessary to increase the cohesive force of the primer layer obtained by baking and drying, it is preferable to add 5 to 50 parts by weight of carbon black to 100 parts by weight of the epoxy group-containing polymer. In addition, when it is particularly necessary to increase the heat resistance of the primer layer, use of a hindered phenol-based, phosphoric ester-based, or organic sulfur-based antioxidant, alone or in combination, is added in the amount of 0.01 to 5% in the primer composition. Weight% preferably 0.1
It is preferred to add an amount of ~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 the epoxy group-containing polymer and curing agent, but industrially it is usually 5 to 50 degrees at about 170 to 220℃.
It is said to be 15 minutes. The thickness of the dried primer layer is preferably about 5 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 adhesive polyethylene modified with maleic anhydride (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, etc., and sums 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.

The reason why the polyolefin-coated metal products of the present invention has excellent adhesion, especially so-called secondary adhesion in the presence of moisture over a long period of time, is because the primer composition used in the present invention contains hydroxydiene-based A polymer produced by a ring-opening reaction of the epoxy group of a unique epoxy group-containing polymer obtained by reacting a polymer or its hydride with epihalohydrin (more specifically, a polymer with a glycidyl ether group at the end or middle part). In addition to the fact that reaction polymers with epoxy groups inherently have high adhesion to metals, hydroxydiene-based polymers or their hydrides It is presumed that this is because the hydrophobic moiety introduced into the primer layer is well compatible with the polyolefin and exhibits excellent adhesion over a long period of time.

The polyolefin-coated metal product of the present invention is constructed as described above, and includes a primer composition containing an epoxy group-containing polymer obtained by reacting a hydroxydiene polymer or its hydride with epihalohydrin and a curing agent. Since the polyolefin is coated on the baked and dried primer layer, it has excellent adhesive properties, water resistance, and other properties required for anticorrosion coatings on metals.

Examples of the present invention are shown below.

Example 1 600g of hydroxypributadiene with a number average molecular weight of 2800 and a hydroxyl value of 47 was dissolved in dehydrated toluene, and the resulting solution was heated at 100°C in an argon stream.
11.1g of ether complex of boron trifluoride
was added, and then 120 g of purified epichlorohydrin was added and the reaction was carried out with stirring for 1 hour. The resulting reaction mixture was allowed to cool, and 50% aqueous sodium hydroxide solution 2 was added at 30°C, followed by stirring for 1 hour. The toluene layer was extracted, washed with water, neutralized with carbon dioxide gas, further washed with water, the toluene was distilled off, and purified by reprecipitation with methanol. The epoxy equivalent of the obtained polymer A is
It was 1400.

On the other hand, a steel pipe with a nominal diameter of 15 m/m and a total length of 5500 mm was pickled to completely remove scale, and then treated with zinc phosphate (4.2 g/m ² ). Next, 100 g of the above epoxy group-containing diene polymer A and methyl-Δ
⁴ - 6.0 g of tetrahydrophthalic anhydride and 200 g of solvent
The primer obtained by dissolving the primer was applied to the inner surface of the steel pipe using a spray gun and dried at 180°C for 10 minutes. The average thickness of the primer layer at this time was 30μ. After that, this steel pipe was preheated to 200℃ in air, and a mixed fluid of low density polyethylene powder and air with a melt index of 10 g/10 min was passed through the inner surface of the steel pipe for about 10 minutes to melt and bond it, resulting in a film thickness of 900°C on the inner wall surface of the pipe. ~
A 1000μ polyethylene coating was formed.

The primary adhesion of this steel pipe coating at 25℃ is 10
It showed 8.5Kg/cm when peeled at 180℃ with a width of m/m. When measuring secondary adhesion, this steel pipe was cut into appropriate lengths and immersed in warm water at 50°C for 210 days.
The adhesion was the same as before dipping, and no peeling of the coating from the end face of the steel pipe was observed.

Example 2 An epoxy group was added to 60 g of hydroxypolybutadiene hydride (iodine value 0.5) obtained by adding hydrogen to hydroxypolybutadiene having a number average molecular weight of 2800 and a hydroxyl value of 47 in the same manner as in Example 1. By introducing epoxy groups, an epoxy group-containing polymer B was obtained. Add 100g of this polymer B and 7.0g of methylmelamine hardener to 200g of xylene.
The primer obtained by dissolving the primer was applied to the pickled steel plate surface and dried at 180°C for 10 minutes. The average thickness of the primer layer was 60μ. Next, this steel plate was preheated to 220°C on a hot plate, and Example 1
The same polyethylene was powder coated to form a film with a thickness of 500μ. The primary adhesion strength of this steel plate coating is
It was 8.0 to 8.5 kg/cm by 180° peeling method with a width of 10 m/m. In addition, the secondary adhesion after immersion in 50°C warm water was the same as before immersion, and no peeling of the film was observed from the incisions made before immersion.

Comparative Example 1 A steel pipe with a nominal diameter of 15 m/m was pickled, treated with zinc phosphate, and ethylene-vinyl acetate copolymer powder was adhered to the inner surface of the steel pipe, and then heated and melted to form a primer with a film thickness of 150 μm. formed a layer.

Next, a film thickness was applied to the inner surface of the steel pipe in the same manner as in Example 1.
A polyethylene film having a thickness of 900 to 1000 μm was formed, and the adhesion was measured in the same manner as in Example 1. The primary adhesion is 6.0Kg/cm, and the adhesion after soaking in hot water is 0.
~2Kg/cm, and the coating was peeled off over a distance of 30m/m from the end of the steel pipe, and rust had developed in that area.

Comparative Example 2 Containing 80 parts by weight of an epoxy group-containing polymer having an internal urethane bond (manufactured by Mitsui Toatsu Co., Ltd., Epokey 803) and 20 parts by weight of a butylated melamine-based curing agent (manufactured by Mitsui Toatsu Co., Ltd., Yuban 20SE) A primer composition was applied to the pickled steel plate surface, a primer layer was formed in the same manner as in Example 2, and polyethylene was powder coated to obtain a polyethylene-coated steel plate.

When the adhesive strength was measured in the same manner as in Example 2, the primary adhesive strength was 0.5 to 1.0 Kg/cm. Further, after immersion in hot water, the film peeled off from the notch made before immersion to other areas, and rust developed in those areas.

Claims (1)

[Scope of Claims] 1. A primer composition containing an epoxy group-containing polymer obtained by reacting a hydroxydiene polymer or its hydride with epihalohydrin and a curing agent is applied to a metal surface and baked and dried. A polyolefin-coated metal product characterized in that a polyolefin is coated on a primer layer. 2. The metal product according to item 1, wherein the curing agent is at least one of polyhydric carboxylic acids, their anhydrides, and polyamines. 3 The number average molecular weight of the epoxy group-containing polymer is approximately
500 to 5000, the metal product according to item 1 or 2. 4. Any one of Items 1 to 3, wherein the equivalent ratio of the epoxy group in the epoxy group-containing polymer to the atomic group capable of crosslinking with the epoxy group in the curing agent in the primer composition is 0.7 to 2. Metal products listed. 5. The metal product according to any one of items 1 to 4, wherein the primer layer has a thickness of about 5 to 100 μm. 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.