Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-06-08
2002-09-10
Koslow, C. Melissa (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C525S095000, C428S035700
Reexamination Certificate
active
06447858
ABSTRACT:
TECHNICAL FIELD
The present invention relates to multilayered pipes, in particular, multilayered pipes for hot water circulation used for central heating or central floor heating facilities using hot water circulation, the multilayered pipes for hot water circulation having a thermoplastic resin composition (C) layer containing 50 to 99% by weight of ethylene-vinyl alcohol copolymer (A) and 1 to 50% by weight of multilayered polymer particles (B).
BACKGROUND ART
Conventionally, for floor heating by hot water circulation, pipes for hot water circulation made of metal have been commonly used. In many cases, pipes for hot water circulation are buried in concrete at the time of construction and installed under the floor, and therefore once the pipe is installed, subsequent repair work is very difficult, and usually a durability of about 50 years is required. Under such severe conditions, it is preferable to use plastic pipes, which are inexpensive compared with metal pipes and whose material is not corroded. Examples of such plastic pipe material include polyethylene, polypropylene, and polybutene.
However, when such plastic pipes are used in a floor heating system that employs a hot water circulation, metal portions of the heat exchanger, pump, or the like are corroded by oxygen. It seemed that this corrosion occurs because oxygen in the air passes through plastic pipe walls, permeates into hot water circulating in the pipe and is dissolved therein. Therefore, multilayered polyethylene pipes having aluminum as an intermediate layer were developed. However, the aluminum layer may crack, which seems to be caused by temperature changes, so that the corrosion due to oxygen is not prevented.
As a countermeasure for that, various multilayered pipes formed of a plastic resin having excellent oxygen gas barrier properties and polyethylene have been studied. Among them, it has been confirmed that multilayered pipes employing ethylene-vinyl alcohol copolymer (hereinafter, referred to as EVOH) have the best oxygen barrier properties and mechanical strength, and nowadays EVOH based multilayered plastic pipes are widely used as pipes for hot water circulation. For example, Japanese Laid-Open Patent Publication No. 61-140691 describes pipes for hot water circulation including an EVOH layer as an intermediate layer, and Japanese Laid-Open Patent Publication No. 2-74341 describes pipes for hot water circulation having an EVOH layer as the outermost layer. However, for both of them, anti-crack properties are not always sufficient.
It is believed that the insufficient anti-crack properties stem from the rigidity of EVOH. In other words, EVOH has the problem that the EVOH itself is a very rigid resin compared with ordinary plastic resins although EVOH has excellent oxygen barrier properties and mechanical strength (impact resistance) as described above. In order to improve the rigidity of EVOH, various studies have been conducted. For example, Japanese Laid-Open Patent Publication No. 10-24505 describes a multilayered structure that is used for a fuel container, in which the structure comprises a resin composition layer having excellent gas barrier properties and impact resistance and that is formed of an EVOH resin and resin fine particles having a core-shell structure. Furthermore, Japanese Laid-Open Patent Publication No. 7-331020 describes a resin composition having excellent flexibility that comprises EVOH and multilayered polymer particles including a polymer that contains epoxy groups.
However, these studies have been conducted only from the viewpoint of imparting flexibility and impact resistance to a molded product, such as a film and a tank having gas barrier properties, and studies to improve characteristics of EVOH regarding rigidity have not been conducted from the viewpoint of improving the anti-crack properties. The impact resistance shown in such prior art is the ability to withstand stress applied instantly from the outside of a pipe. On the other hand, the anti-crack properties referred to in the present invention are the ability to withstand stress applied not instantly but slowly, in general, from the inside of a pipe, in particular, the ability to withstand tensile stress. Therefore, in order to satisfy the anti-crack properties, the molded product requires a performance that is different from the performance that satisfies the above-mentioned impact resistance.
Furthermore, in the pipes for hot water circulation containing EVOH as that of the present invention, impact from the outside of the pipe such as drop impact or collision generally is not likely to happen, so that the anti-crack properties are evidently more important than the impact resistance. In other words, in general, cracks may occur in an EVOH layer when the pipe for hot water circulation is bent slowly with a special tool, as it is required. Furthermore, when two pipes for hot water circulation are connected with a plastic or a metal connector, it is necessary first to enlarge the diameter of one end of the pipes slowly with a special tool for enlargement in several discrete operations. In this case, a large crack may occur in the EVOH layer. Therefore, the anti-crack properties of pipes for hot water circulation are different properties from impact resistance, and are important properties.
Japanese Laid-Open Patent Publication No. 10-230555 describes that a multilayered pipe comprising a resin composition layer having excellent flexibility is used for a pipe for hot water circulation, in which the resin composition layer comprises an EVOH resin and an ethylene-(meth)acrylic acid resin. In this multilayered pipe, no cracks occur in the EVOH layer when the temperature at which the pipe is deformed is at room temperature level (about 20° C.). However, since pipes for hot water circulation are used generally in cold areas, the anti-crack properties are not necessarily sufficient at work, especially in an environment where the air outside temperature is very low (e.g., −15° C.), as has been made clear by the case described below.
In order to improve the anti-crack properties at low temperatures, it was attempted to improve the EVOH layer by adding a flexible polymer. However, the following was found when a multilayered pipe having a resin composition containing EVOH and flexible polymer as the outermost layer was produced. With certain types of flexible polymer blended, the EVOH resin may be deposited on a lip portion of an extrusion die and the deposit on the lip portion of the die is sometimes attached to the surface of the pipe, which degrades the commercial value of the pipe as a finished product, (which will described in examples and comparative examples later). Therefore, there has been no successful attempt to improve the pipe for hot water circulation from the viewpoint of improving the anti-crack properties, and at present, no pipes for hot water circulation having an EVOH based resin composition layer having excellent anti-crack properties and excellent gas barrier properties are available.
Thus, there is a great demand for development of pipes for hot water circulation comprising an EVOH based resin composition layer having oxygen barrier properties and excellent anti-crack properties, in particular, anti-crack properties at low temperatures.
DISCLOSURE OF INVENTION
It is an object of the present invention to solve the above problem. The present invention provides a multilayered pipe for hot water circulation having excellent oxygen barrier properties and anti-crack properties, in particular, anti-crack properties at low temperatures.
More specifically, the present invention is directed to a multilayered pipe for hot water circulation including a thermoplastic resin composition (C) layer comprising 50 to 99% by weight of an ethylene-vinyl alcohol copolymer (A) and 1 to 50% by weight of multilayered polymer particles (B).
In a preferred embodiment, the multilayered polymer particles (B) have a hard layer as an outermost layer and a rubber layer in an inner portion.
In a preferred embodiment, a polym
Shimo Hiroyuki
Yamashita Takashi
Koslow C. Melissa
Kuraray Co. Ltd.
Manlove Shalie
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