JPH07186325A - Straight-chain low density polyethylene adhesive - Google Patents

Abstract

PURPOSE:To obtain straight-chain low density polyethylene adhesive capable of developing strong stable coating adhesion in short time even at low adhesion bond temperature. CONSTITUTION:An polyethylene adhesive used as an adhesive intermediate layer of polyolefin coated steel is adopted. The adhesive is constituted as follows; 1, straight-chain low density polythylene by copolymerization of ethylene and 1-butene; 2, ratio of 1-butene/ethylene is 7-10wt.%; 3, one or two maleic anhydrides are grafted to one molecule of polyethylene; 4, a weight-average molecular weight obtained by a GPC method is 95000-130000; 5, Mw/Mn is 6 or under.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin adhesive used as an adhesive intermediate layer when a polyolefin resin is laminated on a steel material to produce a polyolefin-coated steel material.

More specifically, it relates to a linear low-density polyethylene adhesive having a strong and stable adhesive force in a short time even at a low adhesive temperature.

[0003]

2. Description of the Related Art Polyolefin-coated steel materials are used not only as line pipes for transporting fluids such as crude oil and natural gas, but also as civil engineering materials for revetment work and marine structures such as jetties and breakwaters. More recently, it has been widely used both in Japan and abroad as an energy transportation pipe in the field of district heating and cooling.

The greatest feature of polyolefin coated steel is
In addition to the relatively cheap coating material used, it is chemically stable, so coating with an appropriate film thickness of about several millimeters will result in a long term of 40 to 50 years under various practical environments. Being able to withstand use. Therefore, the cost required for the maintenance of the steel material can be kept low.

Because of its chemical stability, this polyolefin coating material does not adhere to steel by itself.

In order to overcome this, a polyolefin-coated steel material is generally manufactured by the following method.

That is, the scale is removed by pickling treatment, blasting treatment, etc., and after the base treatment is carried out by using chromate, phosphate, silane coupling agent, etc., the steel surface heated to an appropriate temperature is reacted. A primer layer of curable epoxy resin is provided, and a polyolefin resin adhesive layer is formed on the primer layer by an extrusion method or a powder coating method. Further, a polyolefin material such as low-density polyethylene, high-density polyethylene, or polypropylene is formed as a single layer. Lamination is performed by a layer extrusion method, a two-layer extrusion method with a polyolefin resin adhesive, a sheet attachment method, or the like.

The polyolefin-coated steel material coated in this manner is finally cooled to a temperature near room temperature by water cooling or the like.

Regarding the polyolefin-based resin adhesive used in the above-mentioned manufacturing process, the Japanese Patent Laid-Open No. 49-59187 has been used for a long time, and the Japanese Patent Laid-Open No. 4-2 has been newly used.
Various materials have been provided up to Japanese Patent No. 88383.

The basic idea common to these polyolefin adhesives is that a polymer compound having a polyolefin as a basic skeleton is grafted with an acid derivative such as maleic anhydride within a range of approximately 0.01 to 10% by weight. It is modified by polymerization to give it adhesive properties.

[0011] On the other hand, some attempts have been made to give polyolefin adhesives various characteristics. For example, JP-A-61
-89276, Polyolefin-maleic anhydride-vinyl acetate copolymer, JP-A-61-136559, polyolefin-maleic anhydride-styrene copolymer, JP-A-61-138679, polyolefin-maleic anhydride An acid-methyl methacrylate copolymer or the like is a multi-component copolymer.

[0012] On the other hand, there are two types of acid derivative-modified polyolefin and unmodified polyolefin disclosed in JP-A-2-58586.
Component mixture, three-component mixture of ethylene-propylene copolymer, modified propylene and ethylene homopolymer described in JP-A-2-3479, and further JP-A-59-68319.
A mixture of high-density polyethylene and linear low-density polyethylene as disclosed in Japanese Patent Publication No.
It is a multi-component mixture.

[0013]

As described above, many excellent polyolefin adhesives have been already provided.
When these were applied to an actual production line, there were some inconveniences in any of them, and none was satisfactory.

For example, when the ternary copolymerized polyolefin-based adhesive of JP-A-61-89276 described above is applied to a steel pipe coating line, although it certainly exhibits a strong adhesive force, the line It had to be slowed down and was not suitable for actual production.

Next, 2 of JP-A-59-68319
When the component mixed polyolefin adhesive was applied to the steel pipe coating line, it showed a strong adhesive force under high temperature conditions, but only low adhesive force was obtained as the adhesive time was extended under low temperature conditions. .

The above problems are dominated by factors such as the size of the steel material, the thickness of the polyolefin anticorrosion layer, the manufacturing speed, and the like, at which the temperature of the interface between the primer layer and the polyolefin-based adhesive layer is entangled with each other in the actual manufacturing line. This is because it is extremely difficult to artificially and accurately control the change in interface temperature over time.

An object of the present invention is to provide a polyolefin-based adhesive capable of exhibiting a strong adhesive force in a short time even at a low adhesive temperature.

[0018]

In order to solve the above-mentioned problems, the present inventors have found that the modified amount of an acid derivative, the molecular weight and molecular weight distribution of a polyolefin adhesive, and the molecular weight of a polyolefin polymer as a raw material. As a result of diligent study on the structure, it was found that a proper combination of these can develop a strong adhesive force in a short time without introducing a special molecular structure into the polyolefin-based adhesive or forming a complex multi-component system. Found and arrived at the present invention.

That is, the gist of the present invention is that
In a polyolefin resin adhesive used as an adhesive intermediate layer of a polyolefin-coated steel material obtained by laminating various polyolefin resins on a steel material, a straight chain synthesized by copolymerizing 1-butene with ethylene at a ratio of 7 to 10% by weight. 1 to 2 molecules of low-density polyethylene are grafted and modified with 1 to 2 maleic anhydride, and the weight average molecular weight determined by gel permeation chromatography (GPC method) is 95,000 to 130000. A linear low-density polyethylene adhesive characterized by having a number average molecular weight ratio (Mw / Mn) of 6 or less.

[0020]

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

The adhesiveness of polyolefin adhesives is often discussed in relation to the physical properties such as density and melt viscosity, but these physical properties are essentially governed by the molecular weight, molecular weight distribution, and molecular structure of polyolefin. Should be. Further, as far as the phenomenon of adhesion is concerned, the kind and amount of the adhesive functional group also influence.

By the way, the adhesion between the primer and the polyolefin-based adhesive has heretofore been based on the intermolecular interaction at the interface. It is a pure chemical reaction between the existing hydroxyl groups and the functional groups of the polyolefin adhesive, and it was found that there is a clear relationship between the number of covalent bonds generated and the adhesive force.

From the above, maleic anhydride is most desirable as the adhesive functional group because it is highly reactive with the hydroxyl group and does not form a low molecular weight compound as a by-product in the adhesive formation process.

Based on the above idea, in the process of reaching the present invention, the modified amount of maleic anhydride as an adhesive functional group,
The linear low-density polyethylene adhesive synthesized by changing the average molecular weight, Mw / Mn (that is, molecular weight distribution), the copolymerization ratio of the comonomer constituting the raw material polyolefin, and the type was used for the study.

The evaluation test piece was prepared by applying a powder of the above-mentioned various linear low-density polyethylene adhesives to a uniform thickness of about 0.2 mm on a steel plate coated with an epoxy primer and cured to give a predetermined thickness. The linear low-density polyethylene adhesive was held at a temperature until it started to melt, and then a polyolefin resin sheet was fused on the upper layer at the same temperature, held for an arbitrary time, and then rapidly cooled.

For the epoxy primer layer, Epicoat 828 manufactured by Yuka Shell Epoxy Co.
What was cured at 60 ° C. for 5 minutes was used, and low-density polyethylene was used as the polyolefin resin sheet.

Next, the adhesive strength of the obtained laminated plate was measured. The adhesive strength was evaluated by using the so-called peel strength according to the measuring method described in DIN30670 or the like.

The adhesive force is generally low at the initial stage of adhesion, but increases with the adhering time, and eventually does not increase even if the adhering time is lengthened.

Therefore, a time zone showing a constant adhesive force irrespective of the adhesive time was defined as an adhesive force stable region, and the adhesive force in the adhesive force stable region was evaluated.

The adhesive strength was determined to be 15 kg / cm or more at a bonding temperature of 140 to 200 ° C. as a good criterion.
The required adhesion time was the time from the start of adhesion to the time at which the stable adhesive strength was reached.

It was judged that this time is suitable for actual production when the adhesion temperature is within 2 minutes at 200 ° C. and within 5 minutes at 170 ° C.

The results of the above examination are shown in Tables 1-5.

First, Table 1 shows the influence of the modified amount of maleic anhydride.

When the modified amount of maleic anhydride is less than 1 per 1 molecule of linear low-density polyethylene, the adhesive strength is relatively good, but the required adhesive time is long.

When the amount of modification is 1 to 2, the adhesive force is high and stable regardless of the adhesive temperature, and the required adhesive time is shortened.

Further, when the amount of modification exceeds 2, the required adhesive time is further shortened, but the adhesive strength is lowered. In particular, when the bonding temperature is low, the adhesive strength is significantly reduced.

The reason for this is that if the amount of modification is excessive,
Since the linear low-density polyethylene adhesive molecule becomes oriented on the primer surface at multiple points, entanglement with adjacent free linear low-density polyethylene adhesive molecule is less likely to occur, resulting in It is considered that that part became a mechanically weak layer.

Next, Table 2 shows the influence of the molecular weight of the linear low-density polyethylene adhesive.

When the molecular weight is small, the linear low-density polyethylene adhesive layer itself has low mechanical strength, and therefore high adhesive strength cannot be obtained even if the adhesive temperature is raised.

However, when the molecular weight becomes large, high adhesive strength can be obtained by raising the adhesive temperature.

However, if the molecular weight is large, the segmental motion of the linear low-density polyethylene adhesive, which is indispensable for the formation of adhesion, is hindered, so that the orientation of the maleic anhydride group on the primer surface is difficult to occur and the required adhesion is required. It takes a long time and is not suitable for actual production.

This tendency is more remarkable as the bonding temperature is lower. Therefore, a suitable molecular weight range is 950
The range is from 00 to 130,000, but for example, in the case of a linear low density polyethylene obtained by copolymerizing 10% by weight of 1-butene with ethylene as in this example, 12,000 is obtained.
A molecular weight of about 0 to 125,000 is desirable.

Next, Table 3 shows the influence of the polymerization ratio of 1-butene in a linear low-density polyethylene adhesive which is a copolymer of ethylene and 1-butene.

The linear low-density polyethylene adhesive obtained by copolymerizing 1-butene in an amount of 12% by weight or more has a low adhesive force and a long adhesive time.

On the contrary, when the polymerization ratio of 1-butene is lowered to about 3% by weight, the adhesive time is dramatically shortened but the adhesive strength is lowered.

When the polymerization ratio of 1-butene is about 7% by weight, high adhesive strength can be obtained even when the molecular weight is about 95,000.
Bonding time is also shortened. Therefore, the most suitable polymerization ratio of 1-butene is 7 to 10% by weight.

Next, Table 4 shows the influence of the type of comonomer copolymerized with ethylene in the linear low-density polyethylene adhesive.

In the linear low-density polyethylene adhesive obtained by copolymerizing 1-hexene and 1-octene instead of 1-butene, an effective improvement for improving the adhesive force and shortening the required adhesive time is not obtained. Not only are they not found, but they tend to reduce the adhesion.

That is, the basic skeleton of the linear low-density polyethylene adhesive is most preferably ethylene and 1-butene copolymer.

Finally, Table 5 shows the effect of Mw / Mn of the linear low density polyethylene adhesive. What is Mw / Mn?
It is a measure of the breadth of the molecular weight distribution, and the larger this value is, the wider the molecular weight distribution is.

When Mw / Mn becomes large, the required adhesion time becomes short, which is convenient for actual production, but the adhesive strength is remarkably reduced and it becomes unsuitable for actual production.

Thus, in order for the adhesive force and the adhesive time to be suitable for actual production at the same time, there is an appropriate range for Mw / Mn, which is preferably 6 or less, and when it exceeds 6, the adhesive force is suitable for actual production. Absent.

It is considered that this is because the low-molecular weight component preferentially contributes in the process of forming an adhesive, and therefore exhibits adhesiveness as if a low-molecular weight adhesive was used.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

[0058]

[Table 5]

[0059]

[Table 6]

[0060]

[Table 7]

[0061]

EFFECTS OF THE INVENTION By using the linear low-density polyethylene adhesive of the present invention, for example, in a polyolefin-coated steel material, it is possible to make the coating strong and stable in a short time even at a low bonding temperature.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Harada 20-1 Shintomi, Futtsu-shi Nippon Steel Co., Ltd. Technical Development Division (72) Inventor Kenmasa Yusaba 20-1 Shintomi, Futtsu Nippon Steel Co., Ltd. Technology Development Headquarters (72) Inventor Hirotaka Sato 1 Kimitsu, Kimitsu-shi Kimitsu, Nippon Steel Corporation Kimitsu Steel Works (72) Inventor, Shinichi Kimitsu, Kimitsu, Japan In-house (72) Inventor Masaharu Ito 3-10 Shiodori, Kurashiki City, Okayama Prefecture Mitsubishi Kasei Co., Ltd. Mizushima Plant

Claims (1)

[Claims] 1. A polyolefin resin adhesive for use as an adhesive intermediate layer of a polyolefin-coated steel material, which is obtained by laminating a polyolefin resin on a steel material, wherein:
1 to 2 molecules of linear low-density polyethylene synthesized by copolymerizing butene at a ratio of 7 to 10% by weight, and 1 to 2 maleic anhydride grafted and modified, gel permeation chromatography (GPC Method), the weight average molecular weight is 95,000 to 130000, and the ratio (M) of the weight average molecular weight (Mw) to the number average molecular weight (Mn).
A linear low-density polyethylene adhesive characterized in that w / Mn) is 6 or less.