Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-11-19
2002-06-11
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S092000, C521S097000, C521S098000, C264S045300, C442S327000
Reexamination Certificate
active
06403666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polyolefin porous film and a production process for the same. More specifically, the present invention relates to a polyolefin porous film in which calcium carbonate particles are used as an inorganic filler for making the film porous and a production process for the same.
2. Description of the Prior Art
There has so far been known a method in which a film obtained by melting and molding a polyolefin composition in which an inorganic filler is dispersed is subjected to stretching treatment to cause interfacial peeling between the above inorganic filler and polyolefin to thereby produce a polyolefin porous film. The polyolefin porous film obtained by such method has good gas permeability and moisture permeability, but on the other hand, it has liquid non-permeability, so that it is effectively used for back sheets for a sanitary napkin and a paper diaper, medical or sanitary materials such as a disposable type operation gown, and other various materials such as clothes for rainy weather and industrial materials.
It is known that various inorganic particles are used as the inorganic filler used for a production process for such polyolefin porous film. Among them, calcium carbonate particles have good dispersibility and are liable to cause interfacial peeling from polyolefin, so that the homogeneous porous structure can be formed. In addition, they are relatively inexpensive and therefore advantageously used.
However, calcium carbonate is such a strongly basic compound that the pH of the aqueous suspension exceeds 9. A porous film which is produced using such calcium carbonate particles as described above stimulates the skin in uses where it contacts human bodies in many cases, so that it has been limited in use in a certain case. In particular, a sanitary napkin is used while contacting directly the skin, and therefore it exerts a large influence and has had a problem in use for a back sheet. Accordingly, a porous film using particles of neutral compounds such as barium sulfate and the like has to be used for such uses, but the above barium sulfate particles are slightly inferior in properties such as dispersibility as compared with those of calcium carbonate particles and in addition thereto, they are expensive, so that they are only a little far from being satisfactory.
Described in Japanese Patent Application Laid-Open No. 28644/1978 is a polyolefin-stretched composition obtained by stretching a composition comprising an active filler obtained by covering the surface of an inorganic filler with a polymerizable organic monomer having an ethylenically double bond and polyolefin at a temperature which is lower by 5 to 30° C. than the melting point of the polyolefin. Further, given therein are acrylic acid as the example of the preceding polymerizable organic monomer having an ethylenically double bond and calcium carbonate and various compounds as the examples of the inorganic filler described above. However, an object of such techniques is to obtain molded articles having a small width such as monofilaments and tapes having an excellent mechanical strength, and it is not intended to produce a porous film. In addition thereto, the stretching temperature is set at such high temperature as described above for the purpose of obtaining the high strength. When a sheet-shaped article is stretched at such high temperature, it is difficult to cause interfacial peeling between an inorganic filler and polyolefin, so that a porous film having good properties can not be produced.
Under such circumstances as described above, it is desired in this industry to develop a polyolefin base porous film which is produced using calcium carbonate and has a low stimulation to skin.
Accordingly, an object of the present invention is to provide such polyolefin base porous film as described above.
SUMMARY OF THE INVENTION
Intensive researches continued by the present inventors have resulted in successfully developing a polyolefin base porous film which meets the object described above.
Thus, according to the present invention, provided is a polyolefin base porous film characterized by comprising a polyolefin composition in which calcium carbonate particles are dispersed and having a pH of a leached solution with water which falls in the vicinity of neutrality.
Such polyolefin base porous film is obtained by using calcium carbonate particles subjected to surface treatment with chain carboxylic acid having 3 to 6 carbon atoms as the calcium carbonate particles according to the preferred embodiment of the present invention. Hence, according to the present invention, provided is the preceding polyolefin base porous film produced by using the calcium carbonate particles as subjected to surface treatment in such manner as described above.
According to the present invention, further provided as well is a production process for the preceding polyolefin base porous film, comprising the steps of molding a polyolefin composition in which calcium carbonate particles subjected to surface treatment with chain carboxylic acid having 3 to 6 carbon atoms are dispersed into a sheet and then stretching it at least in a uniaxial direction.
DETAILED DESCRIPTION OF THE INVENTION
Though the polyolefin base porous film of the present invention is a polyolefin base porous film obtained by stretching a polyolefin composition in which calcium carbonate particles are dispersed to thereby make it porous, the pH of a leached solution with water falls in the vicinity of neutrality, wherein a pH of the leached solution with water is obtained by measuring a pH of a leached solution obtained by dipping 10 g of the polyolefin base porous film in 100 ml of water at a temperature of 25° C. for 5 minutes. The pH may be determined by any method. Usually, it is determined by a method in which 25 ml of a leached solution is sampled and three drops of a phenolphthalein reagent solution are added thereto to observe whether or not the solution presents a crimson color and in which another 25 ml of the leached solution is sampled and one drop of a Methyl Orange reagent solution is added thereto to observe whether or not the solution presents a red color.
In the present invention, the pH of the leached solution which falls in the vicinity of neutrality means a pH falling in a range where in the preceding measurement of pH, a crimson color is not presented by addition of a phenolphthalein reagent solution and in which a red color is not presented by addition of a Methyl Orange reagent solution reagent solution. This corresponds to a pH falling in a range of 4.4 to 8.3.
The method for determining a pH of a leached solution with water is based on an acid and alkali test described in a sanitary product disposal standard notified (on May 24, 1966) as the Welfare Ministry notification No. 285 in Japan.
The polyolefin base porous film of the present invention having such properties can be: obtained by using the calcium carbonate particles subjected to surface treatment with chain carboxylic acid having 3 to 6 carbon atoms. In this case, both of heavy calcium carbonate particles and heavy calcium carbonate particles can be used for the calcium carbonate particles subjected to the surface treatment described above without limitations. They have usually an average particle diameter of 0.1 to 50 &mgr;m, preferably 0.5 to 10 &mgr;m. If the calcium carbonate particles have an average particle diameter larger than 50 &mgr;m, the maximum pore diameter revealed on the film after stretching tends to grow larger to reduce a minuteness of the pore. On the other hand, if the average particle diameter is smaller than 0.1 &mgr;m, the molding property of the film becomes inferior due to the inferior dispersion or uneven stretching is caused, so that the homogeneous porous film tends to be unobtainable.
The chain carboxylic acid reacted onto the surface of the calcium carbonate particles described above has 3 to 6 carbon atoms. When the surface of the calcium carbonate particles is tre
Enokuchi Masaji
Nakayama Nobuhiko
Cooney Jr. John M.
Tokuyama Corporation
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