Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2001-10-31
2004-07-27
Yoon, Tae H. (Department: 1714)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S307300, C428S312200, C428S319900, C264S288800
Reexamination Certificate
active
06767622
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel porous polyolefin film and to a process for producing same. More particularly, the present invention relates to a porous polyolefin film suitable for use in various medical or sanitary supplies, in particular, such as back-sheets for disposable diapers, which is excellent in vapor-permeability and liquid-imparmeability, good see-through property by virtue of light transmission, and high tear strength, a process for producing the film and an intended use thereof.
BACKGROUND ART
From the past, porous polyolefin films having a number of small holes resulting from an inorganic filler are produced by stretching an unstretched film of polyolefin incorporated with the inorganic filler.
These porous polyolefin films are, however, opaque throughout the films and poor in see-through property due to low light transmission so that it is hard to confirm the color and the state of an article existing on the opposite surface of the film.
In a disposable diaper using the aforesaid porous polyolefin film as back-sheet, for example, the state of excreted urine or excreta could not be visibly confirmed so that a problem arose in delayed time of exchanging for a new diaper.
Accordingly, a device for enhancing light transmission of the film has been made for the application where the see-through property is demanded as in back-sheet for disposable diapers.
For example, there is proposed a porous polyolefin film provided with partial see-through property by subjecting a porous polyolefin film to an embossing treatment and fusing the resin in microporous portions to collapse voids (Japanese Laid-open Patent Appln. No. Hei. 5-168660), etc. In such porous films, mechanically formed portions higher in light transmission exist locally, through which portions it is at any rate possible to observe the opposite surface.
TECHNICAL SUBJECT OF THE INVENTION
However, porous polyolefin films of a non-homogeneous series obtained according to the embossing method, which contain non-porous portions or low porous portions and porous portions in mixed state, are poor in see-through property in the porous portions so that degradation of the moisture permeability is obliged to take place for sufficiently enhancing the see-through property of the whole film. For this reason, the light transmission of a porous polyolefin film obtained according to embossing was generally at most about 60%.
A porous polyolefin film possessing coarse embossed portions varies the ratio of the non-(or lower-)porous portions to the porous portions, thus forming difference in the physical properties of the film, such as moisture-permeability.
As a countermeasure for the aforementioned, a means for extremely minimizing the interval of embossed portions is thinkable in the embossing treatment. As a result of see-through property in the embossed portions being equalized by the adjacent porous portions by minimizing the intervals of the embossed portions, however, there may be the case wherein the see-through property is degraded.
In case the porous polyolefin film is used as a back-sheet or the like, on the other hand, a high degree of tear strength is also required lest the sheet should be broken on the use. However, the porous polyolefin film wherein the non-homogeneous portions having been formed by the aforesaid embossing still leaves room for improvement in this point.
Accordingly, it is an object of the present invention to provide a porous polyolefin film possessing sufficient moisture-permeability, high light transmission and high tear strength in spite of being uniformly made porous throughout the film.
DISCLOSURE OF THE INVENTION
As a result of extensive research for solving such problem, the present inventors has succeeded in development of a porous polyolefin film capable of achieving all of the aforesaid objects by producing a porous polyolefin film with a resin composition incorporated with an inorganic filler together with a wax of polyolefin series.
In accordance with the present invention, there is provided a porous polyolefin film which comprises a polyolefin containing an inorganic filler and a wax of polyolefin series, the film being provided with micropores originated from the inorganic filler, a water vapor transmission rate of at least 1000 g/m
2
·24 hours, a light transmission of at least 65%, and a tear strength of at least 0.6 N, and the film having a uniform moisture-permeability throughout.
In accordance with the present invention, there is also provided, as a preferable process for producing the porous polyolefin film, a process for producing a porous polyolefin film which comprises stretching an unstretched polyolefin film having a resin composition of 100 parts by weight of polyolefin, 50-150 parts by weight of an inorganic filler having a 50% median diameter of at least 2 &mgr;m but less than 7 &mgr;m measured according to the light-scattering method, and 2-20 parts by weight of a wax of polyolefin series in at least uniaxial direction at an area magnification of 1.1-1.5 times,
In accordance with the present invention, there is further provided a composite porous polyolefin film composed of the porous polyolefin film and a non-woven fabric of polyolefin series as well as a back-sheet for disposable diapers which comprises the above porous polyolefin film or the above composite porous polyolefin film.
BEST MODE FOR CARRYING OUT THE INVENTION
The porous polyolefin film of the present invention comprises polyolefin containing an inorganic filler and a wax of polyolefin series.
As a material for the inorganic filler, any of the known inorganic fillers used heretofore for producing porous polyolefin film may be employed without any limitation. Mentioned, for example, are calcium carbonate, gypsum, calcium sulfite, calcium phosphate, magnesium carbonate, silicic acid hydrate, silicic anhydride, soda lime, sodium chloride, barium sulfate, talc, clay, various kinds of cement, volcanic ash, shirasu, titanium oxide, iron oxides, carbon black, various kinds of metal powder, and organic metal salts containing inorganic substances or mainly inorganic substances. Among these exemplified, calcium carbonate is especially preferred.
As described in detail hereinafter, the inorganic filler functions synergestically with the wax to increase light transmission due to micropores based thereon and to improve see-through property so that the filler having a 50% median diameter measured according to the light-scattering method (referred to hereinafter simply as “the median diameter”) of at least 2 &mgr;m but less than 7 &mgr;m, especially 2.5-5.5 &mgr;m is preferably used.
No limitation exists in the polyolefin in the porous polyolefin film of the present invention. However, illustrative of the representative one are homopolymers of &agr;-olefins such as polyethylene, polypropylene, polybutene-1, and poly-(methylpentene), copolymers of &agr;-olefins with other copolymerizable monomers, and a mixture of these polymers. No particular limitation exists in the monomers copolymerizable with the &agr;-olefin and known monomers can be employed, but &agr;-olefins having 2-8 carbon atoms are generally preferable.
Among the aforesaid polyolefins, polyethylene, polypropylene, propylene-ethylene copolymer, and a linear low density polyethylene produced according to the intermediate or low pressure method are preferable. In particular, a linear low density polyethylene preferable as it affords good flexibility.
The aforesaid polyolefin constitutes a skeleton of the porous polyolefin film and so preferably has a melt flow rate of 1-30 g/10 minutes, preferably 0.5-10 g/10 minutes for fully exhibiting the strength such as tear strength mentioned hereinafter.
In the present invention, the wax of polyolefin series is important, as it functions synergestically together with the inorganic filler added to imparts a high degree of light transmission to the porous polyolefin film. Further, the wax of polyolefin series is preferable in the point of workability such as extrusion or of non-odor.
The wax of
Hada Kazuyuki
Takahashi Yoshinori
Tokuyama Corporation
Westerman Hattori Daniels & Adrian LLP
Yoon Tae H.
LandOfFree
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