JPH023708B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polyethylene composite sheets. Specifically, the present invention relates to a polyethylene composite sheet for metal coating. Traditionally, metal materials, especially metal pipes,
In order to prevent corrosion and protect the surface, coating with synthetic resin is performed. Polyethylene, which has excellent weather resistance and flexibility, is preferably used as such a synthetic resin. The anticorrosion layer and the outer protective layer of such a metal tube are each independent as separate layers, and are coated on the metal tube in the form of a composite sheet. When joining such anti-corrosion layers and metal pipes coated with protective layers, it is common practice to peel off and remove only the protective layer corresponding to the joint portion from the anti-corrosion layer, and then attach a joining tool to the removed portion. It is. When joining such metal pipes, especially when joining is done manually by workers during on-site construction, the outermost protective layer does not peel off inadvertently from the anti-corrosion layer under normal conditions. It is desired that the material be easily peeled off when an external force is applied. However, it is relatively difficult to control the adhesive strength between the anticorrosion layer and the protective layer, and therefore adhesive substances (hereinafter referred to as adhesives) such as low molecular weight polyethylene or low molecular weight polybutene are used between the anticorrosion layer and the protective layer. The current situation is that there is a However, such a method not only complicates the manufacturing process of the anti-corrosion treated pipe, but also makes handling inconvenient as the adhesive is exposed on the surface when the outermost protective layer is peeled off. Since dust and the like are likely to adhere to the surface, there is a risk that the air-tightness of the joint portion of the metal pipes using the joint tool may not be maintained. The present inventors have solved these drawbacks of the conventional technology, and when joining metal pipes, especially when joining is done manually by workers in on-site construction, the outermost protective layer peels off from the anti-corrosion layer in an elastic state. In order to provide a composite sheet for metal coating that can be easily peeled off when an external force is applied for peeling, without causing any inconvenience due to the use of an adhesive, we have made extensive studies and arrived at the present invention. Ivy. That is, the gist of the present invention is that polyethylene ()
In contrast, it is a composite sheet consisting of a molded layer made of a composition containing 0.1 to 30% by weight of polypropylene and a molded layer of polyethylene (), and the fluidity index (MI) of polyethylene () and the fluidity index (MFI) of polypropylene are and a polyethylene composite sheet in which the relationship with the blending ratio P of polypropylene is 0.5≦MFI/MI×P≦25. The present invention will be explained in more detail below. The polyethylene used in the present invention is an ethylene homopolymer produced by a high-pressure method or a medium-low pressure method, or a copolymer containing ethylene as the main component and other α-olefins such as propylene or 1-butene, or an ethylene and copolymers of vinyl acetate, acrylic acid, etc. Furthermore, mixtures of two or more of these can also be used. Polyethylene () and () are selected from the polyethylenes mentioned above, and both may or may not be the same. Examples of polypropylene include propylene homopolymers, random copolymers or block copolymers of propylene containing propylene as a main component, and α-olefins such as ethylene and 1-butene. In addition, heat stabilizers, ultraviolet inhibitors, carbon black, pigments, or fillers such as talc, calcium carbonate, and silica may be added to these polyethylenes and polypropylenes as required. The present invention is a composite sheet comprising a molded layer made of a composition in which polypropylene is mixed with polyethylene (2), and a molded layer of polyethylene (2). Therefore, the blending amount of polypropylene to polyethylene () varies depending on the ratio of MI of polyethylene to MFI of polypropylene, MFI/MI, or the desired adhesive strength, but it is 0.1 to 30.
Weight%. If this amount is less than 0.1% by weight, good peelability cannot be obtained, and if it exceeds 30% by weight, the excellent weather resistance of polyethylene
Physical properties such as flexibility are impaired. The present invention is a composite sheet as described above, and further has a fluidity index (MI) of polyethylene ().
The fluidity index (MFI) of polypropylene and the blending fraction P (weight fraction) of polypropylene are 0.5≦
Good releasability cannot be obtained unless the relationship is MFI/MI×P≦25, preferably 1≦MFI/MI×P≦15. In other words, if it is less than 0.5, the adhesive strength is strong and the peelability is poor;
If it exceeds 25, the adhesive strength becomes too weak. A mixed composition of polyethylene and polypropylene can be obtained by various conventionally known methods. For example, mixing in powder or pellet form, or melt-mixing polyethylene and polypropylene in a roll, Banbury mixer, extruder, etc., can be used. Also,
It is also possible to use a mixture of a powdered or pelleted composition prepared by melt-mixing a part of polyethylene and a part of polypropylene in advance and polyethylene in powdered or pelleted form. Various known methods can be employed as a method for manufacturing the composite sheet of the present invention. For example, on a polyethylene sheet extruded by a T-die,
A method in which layers made of polyethylene and polypropylene extruded by other T dies are superimposed, or polyethylene and a composition made of polyethylene and polypropylene are simultaneously extruded from two extruders into the same die, and both are superimposed within the die. A method of forming a composite sheet of two layers can be used. The present invention will be explained below using Examples, but the present invention is not limited by the Examples unless the gist thereof is exceeded. Example 1 Polypropylene (Novatek-P 4500J, MFI) was used as polyethylene (Novatek-P 4500J, MFI
=9, produced by Mitsubishi Chemical Industries, Ltd.) pellets in a ratio of 95:5 (wt%) was extruded from a 30 mmφ extruder into a two-layer sheet molding die, and on the other hand, polyethylene () was mixed with polyethylene (). By extruding the same polyethylene from a 50 mmφ extruder into the die, a two-layer sheet with a thickness of 4 mm (sheet thickness of the single polyethylene portion: 2 mm, sheet thickness of the composition consisting of polyethylene and polypropylene: 2 mm) was formed. . At this time, the resin temperature for both is 230℃.
It was hot. After the formed sheet was cooled to room temperature, a sheet of 10 mm width x 200 mm length was cut out, and a 90° peel test was performed using a conventional method to measure the adhesive strength between a layer made of polyethylene alone and a layer made of a mixture of polyethylene and polypropylene. It was measured by
The results are shown in Table-1. Furthermore, similar sheets were manually peeled off, and those that could be easily peeled off were marked as ○, and those that could not be peeled off were marked as x. The results are also listed in Table 1 as releasability. Examples 2 and 3 Composite sheets were obtained in exactly the same manner as in Example 1, except that the grade of polypropylene was changed to those shown in Table 1, and the adhesive strength and peelability were evaluated. The results are shown in Table-1. Comparative Example 1 A composite sheet was obtained in exactly the same manner as in Example 1, except that the grade of polypropylene was changed to that shown in Table 1 so that the relationship of MFI/MI×P was outside the scope of the present invention, and Adhesive strength and peelability were evaluated. The results are shown in Table-1. Examples 4 to 7 Composite sheets were obtained in exactly the same manner as in Example 1, except that the grade of polypropylene was changed to that shown in Table 2, and the mixing composition (wt%) with polyethylene () was changed, respectively. Furthermore, adhesive strength and peelability were evaluated. The results are shown in Table-2. Examples 8 to 10 Composite sheets were obtained in exactly the same manner as in Example 1, except that the mixed compositions of polyethylene (2) and polypropylene were changed, and the adhesive strength and peelability were evaluated. The results are shown in Table-3.

【table】

【table】

[Table] As is clear from Tables 1, 2 and 3, the composite sheet of the present invention can keep the interlayer adhesive strength relatively low, and therefore when applied to metal pipe coatings. In addition, the peeling operation necessary for joining the pipes can be carried out extremely easily, which is of great practical advantage.

Claims (1)

[Scope of Claims] 1. A composite sheet consisting of a molded layer made of a composition in which 0.1 to 30% by weight of polypropylene is mixed with polyethylene () and a molded layer of polyethylene (), which has a flow index ( The relationship between MI), flow index of polypropylene (MFI), and blending ratio of polypropylene (P) is
A polyethylene composite sheet where 0.5≦MFI/MI×P≦25.