Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2002-03-29
2004-04-13
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S304400, C428S317900, C428S318400
Reexamination Certificate
active
06720067
ABSTRACT:
The present invention relates to a porous film used for moisture-permeable and waterproofing sheets for a roof and a wall, a production process therefor and a laminate sheet comprising the above porous film and a polyolefin base nonwoven fabric. More specifically, the present invention relates to a porous film which is excellent in a heat adhesive property to a polyolefin base nonwoven fabric and which has not only a moisture permeability and a waterproofing property but also a weatherability and a heat resistance and a laminate sheet produced using the above porous film.
A polyolefin base porous film has so far been widely used as a waterproofing and moisture-permeable material which is used in a so-called air-permerable layer method for a wall and a roof. A strength and a durability as well as the functions of waterproofing and moisture permeablity are required to a moisture-permeable film used for such use in construction, and it is required as well to be inexpensive.
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, whereby it is attempted to elevate the strength and the durability. Heat fusion or sticking with a hot melt adhesive is usually used for the laminating method. In particular, used in many cases from a viewpoint 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 obtain a good laminate, a porous film having a good heat fusibility with a nonwoven fabric has to be used, and therefore the film comprising a resin of the same series as a nonwoven fabric, usually a PP base resin is used in many cases. In this connection, the PP resin is a general term of an olefin polymer or an olefin polymer mixture comprising 50 wt % or more of a propylene component.
Further, it is investigated to reduce a film thickness of a polyolefin base porous film and expedite a film-forming speed thereof as means for reducing the production cost. PE base resin porous films out of polyolefin base porous films blended with a large amount of inorganic fillers are proposed to be improved in a moldability by blending with other resins and adding the third components. However, a technique for producing a PP base resin porous film having a small film thickness at a high rate has scarcely been present.
Accordingly, there has been desired a technique for forming a PP base porous film at a high rate, which has excellent appearance, air permerable-moisture permeable property and durability and a high tear strength and which has a thin and even film thickness.
When laminate sheets comprising a PP base porous film and a nonwoven fabric are used for building materials such as house wrapping and roofing, they are left standing in an outside place where they are exposed directly to sunshine before construction, whereby they are likely to be deteriorated. Further, the performances such as a waterproofing property are reduced with the passage of time after construction in a certain case by heat conduction from sunshine and heaters. Under such circumstances, in a law related to an acceleration in quality security in houses which is enforced in April, 2000, guaranty for 10 years is requested to materials such as laminate sheets which are used outside as construction materials. In order to provide laminate sheets which can meet this requirement, a weatherability-heat resistance test is imposed to the above sheets in the industrial field where house-related materials are produced. It is judged in this test whether or not laminate sheets irradiated with a UV ray and then subjected to heat treatment have performances as a moisture permeable-water proofing sheet, and the above sheets are evaluated as having a moisture permeable-water proofing property if they show a water resistance of some fixed level.
Included is another problem that a laminate sheet produced by sticking a PP base porous film having a large heat shrinkage together with a polyolefin base nonwoven fabric by heat fusion causes deformation (curl and the like) by heat shrinking, so that the above film has to be subjected to heat shrinkage-reducing treatment by preliminary heating before sticking, which has inevitably resulted in increasing the treating cost. Further, a porous film subjected to such heat shrinkage-reducing treatment is reduced in a length, and therefore there has been involved therein the problem that an extra raw material cost is required in order to make up for a reduction thereof.
Proposed as a publicly known example of a porous film for construction materials such as house wrapping which is improved in a weatherability is, for example, a porous film obtained by monoaxially or biaxially drawing a composition comprising a PE base resin, an inorganic filler and a UV absorber (Japanese Patent Application Laid-Open No. 277414/1997). However, both of this porous film and a laminate sheet produced by laminating it on a polyolefin base nonwoven fabric do not show a satisfactory weatherability and has a problem as well on a strength.
Accordingly, an object of the present invention is to develop a PP base porous film which can be produced at a high rate and is excellent in a film appearance, a tear strength and performances as a construction material and which has a low heat shrinkage and shows sufficiently high moisture permeability and weatherability-heat resistance when it is laminated on a polyolefin base nonwoven fabric to form a sheet. Intensive investigations repeated by the present inventors have resulted in finding that the intended PP base porous film can be obtained by molding into a sheet, a resin composition comprising a resin blend comprising an ethylene-propylene block copolymer, a low density PE and an ethylene-vinyl acetate copolymer in a specific proportion; calcium carbonate as an inorganic filler; titanium oxide covered on a surface thereof with silica and/or alumina as a weatherability-heat resistance improver; a specific light stabilizer; and a specific antioxidant, then drawing it, subjecting it to heat treatment at a prescribed temperature and preferably taking it at a specific heat treatment draw ratio (ratio of a cooling roll speed to a heat treatment roll speed).
Thus, provided according to the present invention is a porous film comprising a resin composition comprising:
(a) 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 a low density polyethylene and 3 to 40 parts by weight of an ethylene-vinyl acetate copolymer,
(b) calcium carbonate,
(c) titanium dioxide coated on a surface thereof with silica and/or alumina,
(d) a hindered amine light stabilizer having a molecular weight of 1500 to 4500,
(e) an ethyl ester phosphorous acid or biphenylene phosphonite antioxidant, and
(f) a hindered phenol antioxidant,
wherein the above resin composition comprises 100 to 200 parts by weight of (b), 0.5 to 20 parts by weight of (c), 0.2 to 10 parts by weight of (d), 0.03 to 3 parts by weight of (e) and 0.05 to 3 parts by weight of (f) each per 100 parts by weight of (a).
Further, provided according to the present invention is a production process for the porous film described above comprising the steps of:
molding the resin composition comprising the components (a) to (f) described above into a sheet and drawing it,
then subjecting it to heat treatment at a temperature (T) satisfying the following equation (1):
Tc−
30
≦T<Tc
(1)
(wherein Tc represents a crystallizing temperature of the raw material resin composition, and T represents a heat treatment roll temperature), and
then taking it at a heat treatment draw ratio (R2/R1) satisfying the following equation (2):
Osaki Daisuke
Takahashi Yoshinori
Chang Victor S
Tokuyama Corporation
Wenderoth , Lind & Ponack, L.L.P.
Zirker Daniel
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