Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-12-26
2002-10-29
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S134000, C264S235800, C264S288800, C264S290200, C428S314200, C428S314400
Reexamination Certificate
active
06472445
ABSTRACT:
The present invention relates to a porous film used for moisture-permeable and waterproofing sheets for a roof and a wall. Specifically, the present invention relates to a film which is excellent in a heat adhesive property with a nonwoven fabric and which is provided with a weatherability in addition to a moisture permeability and a waterproofing property.
A sheet obtained by sticking a polyolefin base porous film to other reinforcing porous materials has so far been widely used as a waterproofing and moisture-permeable material which is used in a gas-permeable layer method for a wall and a roof. Required to a moisture-permeable film used for such use are not only a strength and a durability in construction in addition to the functions of water-proofing and moisture permeability but also a low production cost.
Accordingly, the above porous film is usually laminated on one face or both faces thereof with a reinforcing porous material such as a nonwoven fabric to elevate a strength and a durability. Sticking with a hot melt adhesive and heat fusion are usually used for the laminating method. In particular, used in many cases from a view-point of a profitability is a method in which fused on the above porous film is a nonwoven fabric comprising a polyethylene (hereinafter referred to as PE) fiber or a polypropylene (hereinafter referred to as PP) fiber, for example, a span bond, which is produced by a heat fusion method. In order to achieve such object, a porous film having a good heat fusibility with a nonwoven fabric has to be obtained, and the film is usually composed of a resin of the same series as a non-woven fabric. PP base resins are usually used in many cases. The PP base resin called here is a general term of a polymer or a polymer mixture comprising 50 wt % or more of a propylene component.
Further, it is investigated to reduce a film thickness of the porous film and expedite a film-forming speed thereof as means for reducing the production cost.
It has so far been tried to use a blend of a PP resin and low density polyethyrene as a resin for a PP base porous film to thereby improve the heat adhesive property (Japanese Patent Publication No. 48141/1989). In this process, however, though the laminate strength is revealed, the film itself is increased in a thickness and can not be thinned.
Further, it is proposed to thermally stick a PP-made reticulate fiber as a reinforcing substance to a film obtained by adding a lubricant to a PP-made resin and an inorganic filler to obtain a composition, extruding the composition and monoaxially stretching the extruded matter at a high magnification (Japanese Patent Application Laid-Open No. 248043/1993). However, the above reinforcing substance has a low melting point and therefore does not necessarily have a sufficiently high heat adhesive property with a PP resin film.
When a nonwoven fabric such as a PP span bond is thermally stuck to a polyolefin base porous film which is monoaxially stretched in a thickness of 20 to 50 &mgr;m for the purpose of obtaining a thin film, a suitable tear strength is required to the film, and if the tear strength is weak, the film is torn in laminating in a certain case. Accordingly, it has been considered difficult to use a thin film of, for example, 50 &mgr;m or less for the use described above.
Further, also proposed as a method for producing a porous film is a method in which a film discharged from a T-die is received at a draft ratio of 20 to 1000 and then monoaxially stretched (Japanese Patent Application Laid-Open No. 335043/1992). However, when obtaining a thin film having a thickness of, for example, 20 to 50 &mgr;m, the more the draft ratio is increased, the more the draw resonance is liable to be caused, and therefore the purpose of forming a film at a high speed has not necessarily been sufficiently achieved.
With respect to a PE base porous film among the polyolefin base porous films blended with inorganic fillers in large quantities, it is proposed to improve the moldability by blending with other resins and adding the third component. However, a technique for producing a PP base porous film having a small film thickness at a high speed has not so far been published at all.
Accordingly, a technique for producing at high speed, a porous film which is a thin film having an even thickness using a PP resin for a matrix and which has a gas permeability and a moisture permeability and is excellent in a weatherability and a tear strength has been desired.
The present inventors have considered that it shall be insufficient for achieving the technique described above only to investigate a production technique therefor and that a technique for solving the following subjects (1) and (2) regarding a resin to be used has to be found:
(1) to find a filler-added resin composition making it possible to evenly discharge a non-stretched film in drawing at a high speed of 20 m/minute or more, preferably 30 m/minute or more and capable of providing a film which does not cause draw resonance and has a thickness reduced to a degree of 20 to 60 &mgr;m, preferably 20 to 50 &mgr;m by stretching and which is excellent in a tear strength, and
(2) to find a resin capable of providing a film which has a thickness reduced to 20 to 60 &mgr;m, preferably 20 to 50 &mgr;m by stretching at least by 1.3 time in terms of an area magnification, a water vapor transmission rate of 1000 to 3000 g/m
2
24 h and a tear strength of 50 mN (milli-Newton) or more in an orientation direction (stretching direction) and which is excellent in a heat adhesive property with a PP nonwoven fabric.
Intensive investigations made by the present inventors in order to solve the problems described above have resulted in finding that capable of solving the problems described above is a composition prepared by adding calcium carbonate as an inorganic filler to a resin blend comprising a specific ethylene-propylene block copolymer, low density polyethylene and an ethylene-vinyl acetate copolymer in specific proportions.
Thus, provided according to the present invention is a porous film comprising a composition comprising:
(1) 100 parts by weight of a polypropylene base resin blend comprising 100 parts by weight of an ethylene-propylene block copolymer having a maximum peak temperature (Tm) of 140° C. ≦Tm ≦165° C. which is given by differential scanning calorimetry (DSC), 3 to 40 parts by weight of low density polyethylene and 3 to 40 parts by weight of an ethylene-vinyl acetate copolymer and
(2) 100 to 200 parts by weight of calcium carbonate, wherein the porous film has a thickness of preferably 20 to 60 &mgr;m, a tear strength of 50 mN or more in an aligning direction and a water vapor transmission rate of 1000 to 3000 g/m
2
24 h.
This porous film can be produced by melt-extruding the composition comprising:
(1) 100 parts by weight of the polypropylene base resin blend comprising 100 parts by weight of an ethylene-propylene block copolymer having a maximum peak temperature (Tm) of 140° C. ≦Tm ≦165° C. which is given by differential scanning calorimetry (DSC), 3 to 40 parts by weight of the low density polyethylene and 3 to 40 parts by weight of the ethylene-vinyl acetate copolymer and
(2) 100 to 200 parts by weight of calcium carbonate, cooling and then stretching the extruded matter, preferably by melt-extruding it by a T-die method, receiving it at a draft ratio of 2 to 30 and a non-stretched film-forming speed of 20 m/minute or more, cooling it by an air chamber method or an air knife method and then stretching it at least by 1.3 time in terms of an area magnification in a monoaxial or biaxial direction. In the present specification, this porous film and a production process therefor are called the first embodiment of the present invention.
The porous film according to the first embodiment of the present invention not only has a moisture permeability (gas permeability) and a water-proofing property but also has a suitable strength and a good heat adhesive property with a nonwoven fabric and is excellent in a productivity. Accordi
Osaki Daisuke
Takahashi Yoshinori
Foelak Morton
Tokuyama Corporation
Wenderoth , Lind & Ponack, L.L.P.
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