JPH08259917A - Modified polyethylene adhesive and steel stock coated with polyolefin resin - Google Patents

Abstract

PURPOSE: To make it possible to develop firm adhesion of a coating, by using as an adhesive a modified polyethylene comprising a specified linear low-density polyethylene grafted with a cyclic unsaturated carboxylic acid anhydride. CONSTITUTION: In producing a steel stock coated with a polyolefin resin by extrusion coating to laminate a polyolefin resin through an adhesive on a steel stock, the adhesive used comprises a modified polyethylene which is obtained by copolymerizing ethylene with more than 7wt.% to at most 10wt.% 1-butene in the presence of a Ziegler catalyst to give a linear low-density polyethylene and grafting this polyethylene with 1 to 2 molecules of a cyclic unsaturated carboxylic acid anhydride for one molecule of the polyethylene and which has a weight-average molecular weight (Mw) of above 130,000 to at most 160,000, a number-average molecular weight (Mn) of 23,000 to 31,500 and a molecular weight distribution (Mw/Mn) of at most 6. The use of this adhesive can give higher peel strength than with other modified polyethylene adhesive.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a modified polyethylene adhesive used as an adhesive intermediate layer in the case of laminating a polyolefin resin on a steel material to produce a polyolefin-coated steel material, and a modified polyethylene adhesive through the modified polyethylene adhesive. The present invention relates to a polyolefin resin-coated steel material formed by laminating resins.

[0002]

BACKGROUND OF THE INVENTION Polyolefin-coated steel has been used for a long time as a line pipe for transporting fluids such as crude oil and natural gas. Newly, it is widely used both in Japan and abroad as an energy transportation pipe in the field of district heating and cooling.

[0003] This polyolefin coating material does not adhere to steel by itself because of its chemical stability. In order to overcome this and obtain a strong coating adhesion, the polyolefin coated steel material generally has the following coating structure.

That is, as shown in FIG. 2, a surface treatment layer 2 made of chromate, phosphate, silane coupling agent, etc. is provided on the surface of the steel material 1 from which scale has been removed by pickling, blasting, etc. Is provided with a primer layer 3 of epoxy resin or the like, a modified polyethylene adhesive layer 4 is provided thereon, and a polyolefin resin layer 5 of polyethylene, polypropylene or the like is further laminated thereon.

The present inventors have already invented a modified polyethylene adhesive based on the method of applying a modified polyolefin adhesive by an electrostatic powder coating method, and a polyolefin-coated steel material using the same. Patent applications were filed as No. 346897 and Japanese Patent Application No. 5-346898.

In these inventions, the electrostatic powder coating method is premised as a method for laminating the modified polyethylene adhesive, so that not only the adhesive force but also the upper limit of the adhesive time is regarded as an important factor. It is, so to speak, an average adhesive that obtains a relatively high adhesive force in a short adhesive time.

In the electrostatic powder coating method, first, the powder of the modified polyethylene adhesive is laminated and the powder layer is melted by the heat held by the steel material. Then, the outer cover is coated with the polyolefin resin and cooled.

If the powder layer of the modified polyethylene adhesive is not sufficiently melted, it will be cooled before it is sufficiently adhered, so that high adhesion cannot be obtained. Melting of the modified polyethylene adhesive is essential in powder coating processes. Therefore, the bonding time is limited to a limited range from the equipment side of the coating line laminated by the electrostatic powder coating method.

[0009]

However, as a method for laminating the modified polyethylene adhesive, there is an extrusion coating method in addition to the above electrostatic powder coating method.

In this extrusion coating method, since the modified polyethylene adhesive which has been sufficiently melted is laminated in advance, the adhesion starts simultaneously with the lamination. Therefore, unlike the electrostatic powder coating, the process of melting is not required, and the restriction of the bonding time is relaxed accordingly.

In view of the above problems, the present invention is premised on a method of laminating a modified polyethylene adhesive by an extrusion coating method, and a modified polyolefin adhesive capable of exhibiting a high adhesive force, and a polyolefin coating in which the adhesive is applied to an intermediate layer. Providing steel materials.

[0012]

Means for Solving the Problems As a result of detailed investigations for obtaining a high adhesive force, the present inventors have found that the strength of the adhesive force is one molecule of modified polyethylene adhesive in addition to the covalent bond amount generated at the adhesive interface. It was shown that the tensile breaking strength and tensile modulus of elasticity and the melt viscosity of the modified polyethylene adhesive have a great influence. The inventors have found that these various factors largely depend on the average molecular weight of the modified polyethylene adhesive, and have arrived at the present invention.

That is, according to the first aspect of the present invention, when a polyolefin resin is laminated by an extrusion coating method via an adhesive to produce a polyolefin resin-coated steel material, the adhesive is
(1) A linear low-density polyethylene obtained by copolymerizing more than 7% by weight and less than 10% by weight with respect to ethylene of 1-butene using a Ziegler type catalyst, and (2) the linear low density thereof. It is one in which a cyclic unsaturated carboxylic acid anhydride is grafted in a range of 1 to 2 per molecule of polyethylene, and (3) a linear low-density polyethylene after grafting a cyclic unsaturated carboxylic acid anhydride Weight average molecular weight (M
w) is more than 130000 and 160000 or less,
A modified polyethylene adhesive having a number average molecular weight (Mn) of 23000 or more and 31500 or less and a molecular weight distribution (Mw / Mn) of 6 or less.

A second aspect of the present invention is a polyolefin resin-coated steel material, characterized in that a polyolefin resin is laminated via the modified polyethylene adhesive according to the first aspect of the present invention.

[0015]

In the present invention, linear low density polyethylene obtained by copolymerizing ethylene and 1-butene using a Ziegler type catalyst is used as the raw material of the modified polyethylene adhesive.

Instead of 1-butene, propylene, 1-
When using hexene, 1-octene, etc., high adhesive strength cannot be obtained. Further, the copolymerization ratio of 1-butene to ethylene is preferably in the range of more than 7% by weight and 10% by weight or less.

Cyclic unsaturated carboxylic acid anhydride is grafted within a range of 1 to 2 per molecule of the linear low-density polyethylene. When the amount of modification of the cyclic unsaturated carboxylic acid anhydride is less than 1, good adhesion can be obtained, but the time required for adhesion becomes long, and when it exceeds 2, high adhesion cannot be obtained.

If an unsaturated carboxylic acid is used instead of the cyclic unsaturated carboxylic acid anhydride, high adhesive strength cannot be obtained. Even if it is an unsaturated carboxylic acid anhydride, if it is a chain compound, the dispersion of the adhesive force becomes large. Among the cyclic unsaturated carboxylic acid anhydrides, 5-membered or 6-membered ring compounds are desirable, and maleic anhydride is particularly desirable.

The molecular weight of the modified polyethylene adhesive is such that the weight average molecular weight (Mw) and number average molecular weight (Mn) measured by gel permeation chromatography are over 130,000 to 160,000 and 2300, respectively.
It is desirable that the molecular weight distribution (Mw / Mn), which is a ratio of these, is 0 or more and 31500 or less, and 6 or less. If it is out of this range, high adhesion cannot be obtained.

[0020]

EXAMPLES The present invention will be described in detail below based on examples.

As Example 1, a steel plate having a length of 150 mm, a width of 50 mm and a thickness of 4.5 mm was first used to perform an adhesiveness evaluation test. The evaluation test piece was created by the following procedure.

A laminated sheet was prepared by bonding a modified polyethylene adhesive sheet having a thickness of about 0.2 mm and a polyolefin resin sheet having a thickness of about 3 mm. The modified polyethylene adhesive used here is 10% by weight based on ethylene.
Is a linear low-density polyethylene obtained by copolymerizing 1-butene of 1 to 1 molecule of the linear low-density polyethylene,
Maleic anhydride is grafted at a ratio of 1 to 2. As the polyolefin resin, low density polyethylene was used.

This laminated sheet and a steel plate coated with an epoxy primer were held on a hot plate set at a predetermined temperature for 7 minutes. Epoxy coat 828 manufactured by Yuka Shell Epoxy Co., Ltd. was used as the epoxy primer, and a heterocyclic amine compound was used as the curing agent. Next, the molten laminated sheet was attached to the primer-coated surface of the steel sheet, held for a predetermined time as it was, and then rapidly cooled.

Next, the coating adhesive strength of the polyolefin laminated steel sheet thus obtained was measured. Adhesive strength was measured with a peeling width of 2 cm and at room temperature according to DIN306.
The peel strength measuring method described in 70 etc. was followed.
Then, the measured value is converted per 1 cm of peeling width,
evaluated.

Although the adhesive strength is generally low at the initial stage of adhesion, it increases with the adhering time, and eventually does not increase even if the adhering time is lengthened. Therefore, the time zone that shows a constant adhesive force regardless of the adhesive time is defined as the adhesive force stable region, and the adhesive force in the adhesive force stable region is evaluated. And 20 kg / cm or more was made into the favorable adhesive force.

FIG. 1 shows the adhesive strength of the test pieces produced at the interface temperatures of the steel sheet and the laminated sheet of 170 ° C. and 200 ° C., respectively. In the figure, ○ indicates a peel strength of 20 kg /
Less than cm, ● represents a peel strength of 20 kg / cm or more, Mw represents a weight average molecular weight, and Mn represents a number average molecular weight.

From this figure, the modified polyethylene adhesive has a weight average molecular weight (Mw) of 130000 to 1600.
00, number average molecular weight (Mn) is 23,000 to 31,500
It was found that in the range where the molecular weight distribution (Mw / Mn) is 6 or less, an adhesive force of 20 kg / cm or more can be obtained.

Next, the same study was conducted using a modified polyethylene adhesive having a 1-butene copolymerization ratio of 7% by weight. In this case, the weight average molecular weight is 95,000 to 12
When the number average molecular weight was 20,000 and the number average molecular weight was in the range of 22,000 to 25,000, the adhesive strength showed a maximum value. However, the value was less than 20 kg / cm, and when the molecular weight was out of this range, the adhesive force was further significantly reduced. Therefore, a modified polyethylene adhesive having a 1-butene copolymerization ratio of 7% by weight or less cannot provide good adhesive strength.

Next, as Example 2, the polyolefin-coated metal pipe shown in FIG. 2 was manufactured by further using the modified polyethylene adhesives of the present invention and comparative examples described above.

First, as the metal pipe 1 whose surface was adjusted by blasting, a steel pipe having an outer diameter of 16 inches and a plate thickness of 0.2 inches was used. These steel pipes were subjected to chromate treatment as a base treatment. The obtained chromate layer 2 had 200 to 400 mg of chromium deposited per mm ^{2 in} terms of metallic chromium.

Then, the epoxy resin of Epicoat 828 manufactured by Yuka Shell Epoxy Co. and the heterocyclic diamine compound are stoichiometrically mixed at a ratio of 1: 0.8, and the mixture is atomized to 1
It was applied to the surface of a steel pipe heated to 55 to 160 ° C. so as to have a thickness of 0.05 mm, and sufficiently cured by the heat held by the steel pipe to form the epoxy primer layer 3.

The modified polyethylene adhesive and the low density polyethylene are coated thereon by a two-layer T-die coextrusion coating method at a temperature of 225 to 230 ° C. to simultaneously form the modified polyethylene adhesive layer 4 and the polyolefin resin layer 5. Formed. At this time, the interface between the steel pipe and the coating was 180 to 185 ° C.

Then, the coated steel pipe was cooled to room temperature by water cooling. The modified polyethylene adhesive layer 4 has a thickness of about 0.2 mm, and the polyolefin resin layer 5 has a thickness of about 3 m.
It was m.

In all of the above coating steps, the metal tube 1
The transport speed was 1.5 m / min. Then, the adhesive force between the epoxy primer layer 3 of the various coated steel materials and the modified polyethylene adhesive layer 4 obtained was investigated. The evaluation of adhesive strength is
The peel strength was measured according to the measuring method described in DIN30670.

In general, when a metal tube is coated with polyolefin, the peel strength is improved by about 5 kg / cm as compared with the case where a corresponding flat plate is coated. Therefore, a peel strength of 25 kg / cm or more was used as a good criterion. Table 1 shows the survey results.

[0036]

[Table 1]

As is clear from Table 1, when the modified polyethylene adhesive of the present invention is used, higher peel strength can be obtained as compared with the modified polyethylene adhesive outside the scope of the present invention.

[0038]

As described above, by laminating the modified polyethylene adhesive of the present invention on an epoxy primer or the like by the extrusion coating method, strong coating adhesiveness can be exhibited. Further, in the production of a polyolefin-coated steel material, by laminating a polyolefin resin with the modified polyethylene adhesive of the present invention as an intermediate layer, it is possible to obtain a polyolefin-coated steel material having a strong coating adhesive property, such as crude oil and natural gas. It is possible to provide mechanically and chemically stable coated steel materials as line pipes, offshore structures, and energy transportation piping.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a molecular weight range of a modified polyethylene adhesive of the present invention.

FIG. 2 is a drawing showing a coating configuration of a polyolefin-coated metal tube according to an embodiment of the present invention.

[Explanation of symbols]

 1 Metal Tube 2 Chromate Layer 3 Epoxy Primer Layer 4 Modified Polyethylene Adhesive Layer 5 Polyolefin Resin Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Harada 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technical Development Division

Claims (2)

[Claims] 1. When manufacturing a polyolefin resin-coated steel material by laminating a polyolefin resin through an adhesive by an extrusion coating method, the adhesive is (1) 10 wt% with respect to ethylene exceeding 7 wt%. % Of 1-butene is copolymerized using a Ziegler type catalyst, and is a linear low-density polyethylene (2) The linear low-density polyethylene 1
A cyclic unsaturated carboxylic acid anhydride is grafted to the molecule in a range of 1 to 2, and (3) a weight average of linear low-density polyethylene after grafting the cyclic unsaturated carboxylic acid anhydride. The molecular weight (Mw) exceeds 130000 and is 16000 or less, and the number average molecular weight (Mn) is 2
3,000 or more and 31500 or less, molecular weight distribution (M
A modified polyethylene adhesive characterized in that w / Mn) is 6 or less. 2. A polyolefin resin-coated steel material, which is obtained by laminating a polyolefin resin through the modified polyethylene adhesive according to claim 1.