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
1999-10-28
2001-11-20
Cain, Edward J. (Department: 1714)
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...
C524S425000, C524S427000
Reexamination Certificate
active
06319975
ABSTRACT:
TECHNICAL FIELD
The present invention relates, in general, to a composition for an air permeable film and, more particularly, to a composition which can be molded into an air-permeable film with superior processability, tensile strength and permeability. Also, the present invention is concerned with a method for producing such a film.
PRIOR ART
Many methods for producing air permeable or porous films are disclosed. Of them, the following process is known as being the most economically favorable and now commercialized: a mixture of a polyolefin resin and an inorganic filler is formed into a film which is then mono- or bi-axially drawn to subject the resin and the filler to interfacial separation, thus forming fine pores.
Prior arts directed to the production of air permeable films taking advantage of inorganic fillers can be found in many patents. For example, European Pat. Laid-Open Publication Nos. 66,672, 307,116, 456,142 and 779,325 (which are referred to as “first patent group” for convenience, hereinafter) disclose third materials, such as aliphatic acids, which are used, along with polyolefin and inorganic fillers, to make film smoother, or compositions with which the unbalance in physical properties between the machine direction and the transverse direction of a film can be solved. Leading to the first patent group, the third additives play an important role in mixing and dispersing a large quantity of inorganic fillers during extrusion and in producing uniform drawn films upon processing. Belonging to a second patent group, European Pat. Laid-Open Publication No. 232,060 discloses an after-treatment process, such as embossing, which can control the mechanical strength of air permeable films while U.S. Pat. No. 4,777,073 teaches a technique for increasing permeability and improving tear strength.
The prior arts of the first patent group are economically unfavorable due to the expensive third additives. In addition, they are poor in the compatibility with polyolefin, giving rise to a decrease in the tensile strength of the films. Further, after films are formed, the additives are released into the surfaces of the films during storage. Pertaining to after-treatment processes by which the physical properties of films can be controlled, the prior arts of the second patent group have a disadvantage of being limited in controlling physical properties of films as compared with the modification of film compositions.
The above conventional techniques paid much attention to additives and after-treatment processes, but not to the resin compositions which form the matrix of the films. The recent tendency has been directed to the productivity improvement of films in order to achieve high-speed film production. However, the compositions now commercially available are poor in processability because calcium carbonate is incorporated at an amount of as much as at least 50% into polyolefin. To obtain desired permeability, calcium carbonate must be incorporated at an amount of more than 55% or the films must be excessively drawn. Therefore, the conventional prior arts find difficulty in overcoming the unbalance in physical properties.
DISCLOSURE OF THE INVENTION
With the background in mind, the present invention has an object of providing a composition for an air-permeable film superior in processability and permeability.
It is another object of the present invention to provide a method for producing an air-permeable film using such a composition.
The present invention is characterized in that a variety of appropriate binder resins are employed to sufficiently express their own advantageous functions and to lower the content of the inorganic filler used. In this regard, a polyethylene resin with a wide molecular distribution is used to ameliorate processability when molding a film. A polypropylene resin is also used to control the softness, machine direction tensile strength, and thermal adhesiveness to propylene non-woven fabrics of a film. With the aim of improving the close adherence to a drawing roll upon drawing the film and of making it easy to conduct the interfacial separation from the inorganic filler, a polyolefin with a high melt index (MI) and an ethylene-propylene copolymer are contained in the composition. In cooperation, these polymers have advantages of assuring high permeability even at a low draw ratio, minimizing the unbalance in physical properties between the machine direction and the transverse direction of the drawn film, improving the tensile strength of the film, and preventing the physical property degradation due to the inorganic filler. Consequently, the air-permeable film is significantly improved in permeability and processability and has balanced physical properties between the machine direction and the transverse direction.
In accordance with one aspect of the present invention, there is provided a composition for an air-permeable film, comprising: 30 to 100 weight parts of a linear, low density polyethylene resin which ranges, in molecular weight distribution, from 5 to 20; 1 to 100 weight parts of a polypropylene resin; 1 to 30 weight parts of an ethylene-propylene copolymer; 1 to 30 weight parts of a polyolefin resin which has a melt index of 12 or higher; and 50 to 200 weight parts of an inorganic filler based on 100 weight parts of the total resins.
In accordance with another aspect of the present invention, there is provided a method for producing an air-permeable film, in which a composition comprising 30 to 100 weight parts of a linear, low density polyethylene resin which ranges, in molecular weight distribution, from 5 to 20, 1 to 100 weight parts of a polypropylene resin, 1 to 30 weight parts of an ethylene-propylene copolymer, 1 to 30 weight parts of a polyolefin resin which has a melt index of 12 or higher, and 50 to 200 weight parts of an inorganic filler based on 100 weight parts of the total resins, is mono-axially drawn by 1.5 to 3 times, whereby the air-permeable film can be provided with superior processability and permeability.
BEST MODES FOR CARRYING OUT THE INVENTION
In the present invention, there is used a linear, low density polyethylene resin which has an MI of 0.5 to 5 g/10 min as measured according to ASTM D 1238, and a density of 0.915 to 0.935 with a molecular weight distribution ranging from 5 to 20. For example, a molecular weight distribution less than 5 causes an extrusion surging phenomenon when producing films at high speeds, making the film thickness poor in uniformity. On the other hand, when the molecular weight distribution exceeds 20, the physical properties of the film are degraded. The linear, low density polyethylene resin is used at an amount of 30 to 100 weight parts when a polypropylene resin is present at an amount of 1 to 100 weight parts, an ethylene-propylene copolymer at an amount of 1 to 30 weight parts, and a polyolefin resin which has a melt index of 12 or higher at an amount of 1 to 30 weight parts. For example, if the linear, low density polyethylene resin is used at an amount less than 30 weight parts, the film is poor in tensile strength and elongation. On the other hand, the use of the linear, low density polyethylene resin at an amount of more than 100 weight parts causes an extrusion surging phenomenon upon high-speed production.
With the aim of controlling the tensile strength and soft physical properties of a film, or ameliorating the thermal adhesiveness to a polypropylene non-woven fabric, a polypropylene resin is used at an amount of 1 to 100 weight parts when the linear, low density polyethylene resin is present at an amount of 30 to 100 weight parts. An amount less than 1 weight part does not show an addition effect. On the other hand, when using the polypropylene resin at an amount more than 100 weight parts, the soft sense of touch is depreciated. The polypropylene resin useful in the present invention has an MI of 1 to 10 and is selected from the group consisting of homo polypropylene, random polypropylene, impact polypropylene, and mixture thereof.
As for the ethylene-propylene copoly
Jo Byoung Cheon
Kim Tae Joon
Kim Young Wook
Lee Young Keun
Abelman ,Frayne & Schwab
Cain Edward J.
SK Corporation
Wyrozebski Katarzyna
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