JPS6012112B2 - Polyolefin coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyolefin coating method, and more specifically, the present invention relates to a method for coating polyolefin, and more specifically, by using a special primer, it has excellent properties such as adhesiveness and water resistance, especially when metal is used as the object to be coated. The present invention relates to a coating method for easily obtaining coated polyolefin 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. Poor adhesion to materials
In particular, it has been extremely 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 a polyolefin is applied thereon to cover the metal, but at present, a fully satisfactory product has not been obtained. That is, for example, ethylene-pinyl acetate copolymer and ethylene-acrylic acid ester copolymer have poor water resistance, and have the disadvantage that adhesion strength decreases due to water seepage from the end surface of the coating, and peeling spreads over the entire surface. Although polyurethane has good adhesion to adherends such as metals, it has poor adhesion to polyolefins and cannot be put to practical use as a primer. In view of the above-mentioned conventional drawbacks in the polyolefin coating method, the present invention provides a polyolefin coating that makes it possible to easily obtain a polyolefin-coated article with excellent water resistance by using a primer that has good adhesion to the object to be coated and the polyolefin. The purpose of this work was to provide a method for coating polyolefins, the gist of which is that after applying a primer containing a reaction product of hydroxypolyolefin and polyisocyanate as a main component to the surface of an object to be coated, , a polyolefin coating method characterized by coating a polyolefin.

The hydroxy polyolefin in the present invention has 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 at both ends. It is obtained by adding hydrogen to a hydroxyl-based polymer each having one hydroxyl group.

However, the addition of hydrogen here refers not only to cases where the double bonds in the hydrocarbon chains constituting the hydroxygene polymer are completely hydrogenated, but also to cases where only a small portion of the double bonds remain. It also includes. Hydroxygen polymers can be synthesized by various methods.

For example, it can be easily obtained by polymerizing a conjugated gene monomer together with other radically polymerizable monomers as necessary using hydrogen peroxide or an azobisisonitrile initiator having a hydroxyl group. Examples of the conjugated diene monomer used here include 1,3-butadiene, isoprene, 1,3-bentadiene, and 2,3-dimethylbutadiene. Other radically polymerizable monomers
Examples include styrene, acrylic monomers, vinyl pyridine, etc., and these are used within a range where the content in the copolymer with the conjugated diene monomer is less than 50% by weight, and the compatibility with the polyolefin to be coated is determined. From this point of view, it is preferably used in a range of 2% by weight or less. A more preferred method since it is possible to obtain a hydroxydiene-based polymer having one hydroxyl group at each end is to react a gen-based IJ ping polymer with an eboxy compound such as a halogenoalkylene oxide, and then react with a brotonic 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 and the like can be used as catalysts for adding hydrogen to the hydroxygene polymer obtained in this way, 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 dissolve in a solvent together with the polyisocyanate compound, resulting in poor solubility in solvents and heat meltability when used as a primer. The number average molecular weight is generally in the range of 500 to 5,000, more preferably 1,000 to 4,000, since the number of urethane bonds is relatively large and gelation tends to occur, resulting in poor adhesion. 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 block isocyanate, which has almost no reaction activity at room temperature, such as diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, and triphenylmethane-P,P',P''-triisocyanate. Examples include cyanates.The amount of polyisocyanate to be used is such that when the above-mentioned hydroxypolyolefin and polyisocyanate compound are charged, the equivalent ratio of the isocyanate groups of the polyisocyanate to the hydroxyl groups of the hydroxypolyolefin is 0.5 to 1.
The ratio is preferably adjusted to 0.8 to 1.2. If this ratio is less than 0.5, the 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 difficult, and the hard material will be too hard and will not bond with polyolefin. Adhesion is reduced. The above hydroxy polyolefin and the above polyisocyanate are usually dissolved in an appropriate solvent such as xylene, toluene, methyl ethyl ketone, etc. and used as a primer. Additives such as fillers, colorants, antioxidants, ultraviolet absorbers, and catalysts such as peroxides may be added.

If it is particularly necessary to increase the cohesive force of the dried primer layer, it is preferable to add carbon black to the primer in an amount of 5 to 5% by weight. In addition, especially when it is necessary to increase the heat resistance of the primer layer to about 250 to 300°C, use of an antioxidant such as a hindered phenol type, a phosphate ester type, or an organic sulfur type antioxidant alone or in combination can be used to improve the heat resistance of the above-mentioned reactant. 0.01-5 per 100 parts by weight
It is recommended to add 0.1 to 2 parts by weight, preferably 0.1 to 2 parts by weight. Thereafter, the primer is applied to the surface of the object to be coated, such as metal, by dipping, spraying, brushing, etc., and phosphorized and dried at an appropriate temperature.

Conditions such as temperature and time for phosphorization drying are appropriately determined depending on the type and amount of hydroxypolyolefin and polyisocyanate, but are usually 170-230 pm for 5-15 minutes. In some cases, the primer composition containing the above-mentioned hydroxypolyolefin and polyisocyanate as main components may be applied to the coated object in powder form and then heated, or the above-mentioned powdered primer composition may be applied to the object to be coated which has been heated to a high temperature in advance. Objects may also be attached. Specific examples of the polyolefin used in the present invention include polyethylene, polypropylene, polybutene, and other adhesive polyethylenes modified with hydrophilic maleic acid (trade name: Admer).

Examples of methods for coating objects with polyolefin include powder coating, heat-pressing a molded resin sheet, and heating-shrinking a molded resin tube. A powder coating method is preferable because it can form a coating. Further, as the powder coating method, a fluidized coating method, a static coating method, a static spray coating method, etc. can be used as appropriate. The object to be coated used in the present invention includes metal materials such as iron, aluminum, copper, tin, zinc, lead, etc. and alloys containing these, as well as reinforced plastics and glass, and the shape thereof is a tube. , rods, wires, plates, and other various shapes may be adopted.

Therefore, the present invention is particularly suitable for manufacturing steel pipes whose inner surfaces are coated with polyolefin. The reason why the method of the present invention provides a polyolefin coating with excellent adhesion to the object to be coated, especially the so-called secondary adhesion in the presence of moisture over a long period of time, is because the primer used in the present invention is composed of hydroxypolyolefin and polyolefin. The main component is a unique polyurethane, which is a reaction product with socyanate. This is presumed to be because the hydrophobic moiety introduced into the primer by the hydroxy polyolefin is well compatible with the polyolefin and exhibits excellent adhesive properties over a long period of time.

The method for coating polyolefin of the present invention is configured as described above, and uses a primer whose main component is a reaction product of hydroxy polyolefin and polyisocyanate.
According to the method of the present invention, a polyolefin coating with excellent properties such as adhesiveness, water resistance, chemical resistance, and electrical insulation properties can be easily obtained.

Examples of the present invention are shown below.

Example 1 A steel pipe with a nominal diameter of 15 mm and a total length of 550 mm was pickled with sulfuric acid to completely remove scale, and then treated with zinc phosphate (4 mm).
(Yu/me) was applied.

Next, hydroxy polyolefin lk with a molecular weight of 2000
9. A primer was obtained by dissolving 120 g of diphenylmethane diisocyanate (hereinafter referred to as MDI) in 2 ml of xylene.

The equivalent ratio of isocyanate groups to hydroxyl groups in the primer was 1.1. Pour this primer into the above-mentioned rotating steel pipe and leave it at an angle of 45° and 10° at 180°C.
It took a few minutes to harden. The average dry film thickness of the primer at this time was about 20 peaks. Next, hold this steel pipe in the air for 25 minutes.
A mixed fluid of low density polyethylene powder with a melt index of 10°/1° and air was passed through the inner surface of the steel pipe to form a polyethylene lining film with a thickness of about 950 mm on the inner wall of the steel pipe.

The primary adhesion force of this convex steel pipe at 25 qo was 8.5 kg/c by the 180 o peeling method. 50q of this steel pipe
The adhesion of the lining film after being immersed in water for 210 days was the same as before immersion, and no peeling of the lining film was observed at the end interface (cut portion) of the steel pipe. Examples 2 to 4 Primers obtained by dissolving hydroxypolyolefin lk9 having the number average molecular weight shown in Table 1 and skin D in the amount shown in Table 1 in 5 xylene (equivalent ratio of isocyanate groups to hydroxyl groups 1. 1) was sprayed onto a pickled steel plate, and 17
It was dried with a vacuum cleaner.

The average dry film thickness at this time was about 50 mm. Next, this steel plate was heated to 200℃, and the melt index was 10/1.
A low-density polyethylene powder having a thickness of 0.0 mm was powder coated in substantially the same manner as in Example 1 to form a film having a thickness of 900 mm to 0.0 mm.

Table 1 shows the primary adhesion strength of these steel plates, which were measured in the same manner as in Example 1. Table 1 Also, after these steel plates were immersed in 50°C hot water for 210 days, the adhesion of the Linisog film remained the same as before immersion, and the lining film peeled off at the end interface (cut section) of the steel pipe. was not recognized at all.

Example 5 The inner surface of a steel pipe with a nominal diameter of 20 mm was grit blasted, and 100 parts by weight of hydroxypolyolefin and MDI12
Primer obtained by dissolving parts by weight in 300 parts by weight of xylene (equivalence ratio of isocyanate groups to hydroxyl groups is 1.1)
was applied to the inner surface of the above-mentioned chisel pipe J using a spray gun, and 20
Phosphorizing and drying was performed at 000 for 10 minutes.

The dry film thickness of the primer was 30 peaks. Next, the same polyethylene powder as used in Example 1 was applied to the inner surface of the steel pipe, and then heated and melted and bonded at 22,000°C for 10 minutes to obtain a polyethylene inner-coated steel pipe with a total film thickness of 0. The primary adhesion strength of this steel pipe measured using the same method as in Example 1 was 7.
．． 5k9/It was an enemy.

In addition, when measuring secondary adhesion, the steel pipe was cut to a length of 100 skins/skin, immersed in 50 pieces of 3% saline for 90 days, and then measured while the film was being peeled off from the end surface. 0～
It was / skin of 1. Comparative Example 1 A steel pipe with a nominal diameter of 15 m and a total length of 550 m was pickled with sulfuric acid to completely remove scale, and then treated with subsalt phosphate (4
In the evening, I went to

Next, the steel pipe was placed in the air for 2 hours without any primer application.
5,000 ℃, and thereafter a polyethylene resin film was formed in the same manner as in Example 1.

The primary adhesion strength of this steel pipe was measured using the same method as in Example 1.
It showed 0 kg/arc. Place this steel pipe in 50 gallons of hot water for 2 hours.
The secondary adhesion of the lining film after being immersed for 10 days was 0 to 1.5 kg/arc using the same 180° peeling method, and the damage at the end interface of the steel pipe was significant. That is, hot water penetrated into the adhesive surface between the inner wall of the steel pipe and the polyethylene lining film at the cut portion, and the occurrence of red rust was observed. Comparative Example 2 Molecular weight 2 instead of the hydroxy polyolefin of Example 1
A polyethylene-coated steel pipe was obtained in the same manner as in Example 1 except that a primer obtained using ethylene glycol polymer No. 000 was used.

The primary adhesion strength of the steel pipe measured in the same manner as in Example 1 was 0.
5-1.0k9/skin, secondary adhesion after soaking in warm water is 0
．． It was less than 5 kg/Sakaki. Comparative Example 3 After grit blasting the inner surface of a steel pipe of a kite with a nominal diameter of 20 mm and adhering ethylene monoacetate pinyl copolymer powder,
A primer layer having a thickness of 30 cm was formed by heating and melting and bonding.

Next, the same polyethylene powder as used in Example 1 was adhered to the inner surface of the steel pipe, and heat-melted and bonded at 220 mm for 10 minutes to obtain a polyethylene inner surface coated steel pipe with a total film thickness of about 850 mm.

Claims (1)

[Scope of Claims] 1. A polyolefin characterized in that when coating the polyolefin, a primer whose main component is a reaction product of hydroxypolyolefin and polyisocyanate is applied to the surface of the object to be coated, and then the polyolefin is coated. coating method. 2. The coating method according to item 1, wherein the object to be coated is metal. 3 The number average molecular weight of hydroxy polyolefin is approximately 50
0 to 5000, the coating method according to item 1 or 2. 4. The coating method according to any one of items 1 to 3, wherein the primer has a film thickness of about 10 to 100 μm. 5. The coating method according to any one of items 1 to 4, which comprises powder coating using powdered polyolefin.