Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1999-07-21
2003-07-29
Troung, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S271000, C428S441000, C428S442000
Reexamination Certificate
active
06600008
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a novel aliphatic polyester film.
In the first aspect, the present invention relates to an aliphatic polyester film having a desirable handling property, transparency, and adhesiveness, which is particularly suitable for packaging applications.
In the second aspect, the present invention relates to an aliphatic polyester film having a desirable suitability for processes such as printing and laminating processes, which is an important property of a packaging film for use with fresh food, processed food, drugs, medical devices, electronics, or the like, and also having a desirable heat seal strength after being made into a bag.
In the third aspect, the present invention relates to a novel aliphatic polyester film having a desirable suitability for processes such as printing and laminating processes.
In the fourth aspect, the present invention relates to a gas barrier film and, more particularly, to a gas barrier film which has desirable transparency, flexibility, running property during the film processing (i.e., the capability of smoothly running through the film-forming machine), and gas barrier property after the film has run through a film processing machine while being in contact with a part thereof. These are important properties required in a packaging film for use with fresh food, processed food, drugs, medical devices, electronics, or the like.
2. Description of the Related Art
Conventionally, various plastic materials such as a polyolefin (e.g., polyethylene, polypropylene), an aromatic polyester (e.g., polyethylene terephthalate), and a polyamide (e.g., nylon 6) have been used in packaging films for packaging various items such as food. Used packaging films are supposed to be collected, and either incinerated or buried underground. However, such collection requires a lot of effort. Therefore, as we know, some used packaging films are in fact left uncollected, creating various problems such as environmental pollution. When used films are incinerated, an excessively large heat is often generated which significantly damages the furnace, while the incineration requires a large amount of fuel and thus a high cost. When buried underground, on the other hand, used films, which are not biodegradable, remain in the soil on a semipermanent basis. In view of the current situations as described above, there is an increasing demand for a general purpose packaging film which has a desirable biodegradability.
In order to provide a biodegradability to a polyethylene, or the like, various methods have been derived in the art in which a component having a biodegradability, e.g., starch, is blended with the film. Moreover, a method of providing a photo-degradability, and a method of blending a polyethylene provided with a photo-degradability and a starch component having a biodegradability, have been devised in the art. These methods have attracted public attention as methods which may possibly solve the above-described problems. With such methods, however, while the starch component having a biodegradability is degraded by microorganism, polymer components other than the starch are not degraded, thereby failing to completely solve the above-described problems.
Thus, along with the increasing public concern for environmental protection, there has been a demand for a plastic product which, when disposed in the natural environment, degrades or disappears over time without adversely affecting the natural environment.
In order to provide a complete solution to the above-described problems, various biodegradable polymer materials in which the polymer itself has a biodegradability have been devised in the art. Particularly, various polylactic acid materials have been actively developed in the art because a polylactic acid easily degrades when disposed in the natural environment. For example, a polylactic acid film is naturally hydrolized in the soil and then degraded by microorganisms into an environmentally harmless substance. For example, a polylactic acid film has been used in medical molded products (Japanese Publication for Opposition No. 41-2734, Japanese Publication for Opposition No. 63-68155, etc.), as well as in basic materials of other general-purpose disposable materials which are biodegradable.
Particularly, a biaxially drawn aliphatic polyester film is expected to be used in a wide variety of applications such as general packaging materials, because it has a transparency, a biodegradability, as well as mechanical properties comparable to those of commonly used films.
For example, Japanese Laid-Open Publication No. 7-207041 describes a biodegradable film having a practically acceptable strength and thermal dimensional stability, which is made of a polylactic acid-based polymer, and in which the degree of plane orientation &Dgr;p is about 3.0×10
−9
or more, and (&Dgr;Hm-&Dgr;Hc) is about 20 J/g or more, which is the difference between the amount of crystallization melting heat &Dgr;Hm resulting when heating the film and the amount of crystallization heat &Dgr;Hc resulting from the crystallization during the heating.
However, these films have the following problems.
The first problem is as follows. Generally, a film is required to have a take-up property during a film-forming process, and a slipperiness during use. When the slipperiness is insufficient, the handling property during film production and film processing deteriorates. Due to the low slipperiness, the tension on the film increases while the film is running in contact with a guide roll, or the like, resulting in a frictional flaw on the film surface, thereby lowering the running property. Japanese Laid-Open Publication Nos. 8-34913 and 9-278997 disclose methods for improving the slipperiness and thus the handling property of a film. The improvement is provided by adding, to a film, an organic slip additive such as a fatty acid ester-based slip additive, a fatty acid-based slip additive, a fatty acid amide-based slip additive, as well as an inorganic minute particle anti-blocking agent such as silica and calcium carbonate.
However, when used in a packaging bag, a polylactic acid film needs to be laminated by a heat seal with a sealant film such as a polyolefin. With the addition of the organic slip additive as described in Japanese Laid-Open Publication Nos. 8-34913 and 9-278997 to a polylactic acid film in order to improve the handling property, the running property is improved, but the adhesion strength between the polylactic acid film and a sealant is reduced. Then, it is difficult to use such a film as a packaging bag because of the insufficient adhesion.
Thus, it has ben difficult to improve the process suitability such as the printing process suitability or the handling property, which is required for a package film, while also improving the adhesiveness at the heat seal portion after the film is made into a bag, by the addition of only the above-described slip additive or the anti-blocking agent.
The second problem is as follows. The above-described polylactic acid-based film has been developed while preferentially improving the degradability in the natural environment. Consequently, the desirable properties inherent to an aliphatic polyester have not been sufficiently retained. In other words, the orientation and the crystallization of the film, as well as the strength and the thermal dimensional stability, have not been sufficient, because of the preferential improvement in the biodegradability thereof.
It has been found that, when used as a packaging film for fresh food, processed food, drugs, medical devices, electronics, or the like, such a film may experience a change in dimension or wrinkling in processes such as a printing process or a laminating process which are required for a packaging film.
The third problem is as follows. A polylactic acid film has a relatively high gas permeability. Thus, when a polylactic acid film is used in a food packaging material, there is a vital problem of shortening
Kobayashi Hisato
Mori Keiji
Oda Naonobu
Okudaira Tadashi
Kenyon & Kenyon
Toyo Boseki Kabushiki Kaisha
Troung Duc
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