Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-01-31
2004-03-09
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S313000, C524S423000, C524S425000, C524S427000
Reexamination Certificate
active
06703439
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyolefin film, a polyolefin resin composition which is the starting material of the polyolefin film, and a porous film prepared by stretching the polyolefin film. Specifically, it relates to a polyolefin film excellent in balance of tensile strength, tensile elongation at break, and the like, a polyolefin resin composition which is the starting material of the polyolefin film, and a porous film prepared by stretching the polyolefin film and having an excellent vapor permeability.
BACKGROUND OF THE INVENTION
A number of processes for producing porous films have hitherto been proposed wherein films are made of polyolefin resin compositions containing a polyolefin resin, an inorganic filler, and various oils and waxes, the resulting films are stretched at least in a uniaxial direction so that interfacial stripping is allowed to occur between the filler and the resin, thus to produce voids. These porous films contain therein a number of minute voids and therefore, have high vapor permeability, but liquid is not allowed to permeate the films. On the basis of this nature, the films are used for a wide variety of purposes including sanitary materials such as a throwaway paper diaper, building materials, reflective films, and galvanic cell separators.
When a porous film is used as a material for the throwaway diaper, the film needs to be flexible. Therefore, the porous film used as a material for the diaper is exclusively polyethylene. However, the film has the disadvantage of having insufficient strength although it has excellent flexibility. For example, Japanese Patent Publication No. 35734/1993 proposes a porous film where a resin composition containing a straight-chain low-density polyethylene consisting of a copolymer of ethylene and &agr;-olefin, an inorganic filler, and a particular oil are used. However, the porous film has the disadvantage of having low strength, although it has good gas permeability and flexibility.
Furthermore, in recent years, the manufacturers of the paper diapers themselves carry out stretching or the formation of porosity from the precursors of porous films in a stretching step incorporated into a process for manufacturing the diapers according to a method such as texture processing or gear stretch. The precursors of the porous films in particular are expected to have good balance in strength, elongation, and flexibility.
SUMMARY OF THE INVENTION
The invention aims at providing a polyolefin film balanced in characteristics such as strength, flexibility, and elongation in a high level, providing a porous film prepared from the polyolefin film and exhibiting an excellent vapor permeability, and providing a polyolefin resin composition suitably used as the starting material of the film.
As a result of intensive studies to solve the aforesaid problems, the present inventors have found that in the production of a polyolefin film, a resin composition comprising polyolefin resins containing particular amounts of polyethylene resin and polypropylene, and an inorganic filler provides a polyolefin film balanced in characteristics such as strength, flexibility, and elongation in a high level and in addition, that a porous film prepared by stretching the polyolefin film has an excellent vapor permeability, thus having accomplished this invention.
That is, the first invention of the invention is a polyolefin resin composition comprising 25 to 70 weight percent of polyolefin resin and 75 to 30 weight percent of an inorganic filler wherein the polyolefin resin contains 40 to 80 weight percent of polyethylene resin and 60 to 20 weight percent of polypropylene, and the polyethylene resin contains 60 to 98 weight percent of a linear low-density polyethylene and 40 to 2 weight percent of a branched low-density polyethylene.
The second invention of the invention is a polyolefin film made of the aforesaid polyolefin resin composition. The polyolefin film herein means a film before undergoing ordinary stretching. That is, the film is the precursory film of a porous film. The third invention of the invention is a porous film prepared by stretching the aforesaid polyolefin film.
The feature of the invention consists in a resin composition comprising 25 to 70 weight percent of polyolefin resin and 75 to 30 weight percent of an inorganic filler wherein the polyolefin resin is a mixed resin comprising 40 to 80 weight percent of polyethylene resin and 60 to 20 weight percent of polypropylene resin, and the polyethylene resin contains 60 to 98 weight percent of a linear low-density polyethylene and 40 to 2 weight percent of a branched low-density polyethylene.
The polyolefin resin composition of the invention is suitably used as the starting material of a polyolefin film balanced in characteristics such as strength, flexibility, and elongation in a high level. Therefore, the polyolefin film of the invention has excellent characteristics as described above. The porous film exhibiting excellent vapor permeability is easily prepared by stretching the polyolefin film of the invention. Accordingly, the polyolefin resin composition, polyolefin film, and porous film of the invention are very useful in the fields of sanitary materials such as a throwaway paper diaper, building materials, reflective films, and galvanic cell separators.
DETAILED DESCRIPTION OF THE INVENTION
The invention is illustrated in detail below. The polyolefin resin composition of the invention is prepared by adding 75 to 30 weight percent of an inorganic filler to 25 to 70 weight percent of polyolefin resin and mixing. In preferred composition, the ratio of the inorganic filler to the polyolefin resin falls in the range of 70 to 40 weight percent to 30 to 60 weight percent. Composition outside the aforesaid ratio is unsuitable for the starting material for the porous film. When the inorganic filler is not greater than 30 weight percent, adjacent mutual voids produced by interfacial stripping between the polyolefin resin and inorganic filler are difficult to joint together. Exceeding 75 weight percent resulting in decreasing elongation in stretching to make stretching difficult.
The polyolefin resin used in the invention is a mixture of polyethylene resin and polypropylene. The ratio of both components is 60 to 20 weight percent of polypropylene to 40 to 80 weight of polyethylene resin. When the polyethylene resin exceeds 80 weight percent, the resulting film fails to have sufficient strength. On the other hand, the polyethylene resin not greater than 40 weight percent causes deterioration in flexibility and elongation.
In the invention, the polyethylene used is a low-density polyethylene. In view of the flexibility of the resulting film and uniformity of thickness thereof after stretching, the polyethylene resin is preferably a resin containing 60 to 98 weight percent of a linear low-density polyethylene and 40 to 2 weight percent of a branched low-density polyethylene. The polyethylene resin preferably has a density of 0.890 to 0.940 g/cm
3
and a melt index of 0.1 to 30 g/10 min.
The polypropylene is a propylene homopolymer or a copolymer of propylene and other &agr;-olefin, and preferably has a density of 0.90 to 0.94 g/cm
3
and a melt index of 0.1 to 30 g/10 min.
Examples of the inorganic filler include calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, aluminum hydroxide, zinc oxide, magnesium oxide, titanium oxide, silica, and talc. Of these, calcium carbonate and barium sulfate are preferred. The average particle size of the inorganic filler is preferably 20 &mgr;m or less, more preferably 10 &mgr;m or less, and most preferably from 0.5 &mgr;m to 5 &mgr;m.
In order to improve dispersibility to resin, it is preferable that the inorganic filler is subjected to a surface treatment. Preferred surface treatments are those with which the surface of the filler can be covered to make the surface hydrophobic. Examples thereof include higher fatty acids such as stearic acid and lauric acid and the metal salts of these.
Wang Mindiaw
Yano Shigeru
Burns Doane , Swecker, Mathis LLP
Mitsui Chemicals Inc.
Rajguru U. K.
Seidleck James J.
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