Stock material or miscellaneous articles – Web or sheet containing structurally defined element or...
Reexamination Certificate
2002-09-11
2003-12-02
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
C528S298000, C528S308000, C528S361000, C428S402000
Reexamination Certificate
active
06656578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aromatic liquid crystalline polyester which is excellent in film molding property (film forming property) and is suitable for a film and a method for producing the same.
2. Description of the Related Art
Recently, films produced from various polymers are essential in daily life. For example, there have been developed a variety of films such as high strength films, high elasticity films, oxygen barrier films, conductive films, heat-resistant films, light shielding films and the like. Among other, oxygen barrier films or water vapor barrier films are widely used in our life as wrapping materials irrespective of industrial use or private use.
Conventionally, there have been developed, in this filed, stretched films of polyolefins such as polyethylene, polypropylene and the like, stretched films of polyethylene terephthalate (hereinafter, abbreviated as PET), polyvinylidene chloride (hereinafter, abbreviated as PVDC) films, saponified ethylene-vinyl acetate copolymer (hereinafter, abbreviated as EVOH) films and the like, and they are used as mono-layer or two or more multi-layer films depending on the object and use.
Multi-layer is often essential for maintaining gas barrier properties, and one of factors for raising production cost. Recently, in food wrapping field such as retort pouch and the like, wrapping treatment tends to be conducted at higher temperature for shorter time for effective sterilizing treatment and wrapping materials having high heat-resistance are required. Nowadays, PET films on which silica, alumina or the like is vapor-deposited and the like have been developed, however, problems remain regarding separation and burning of refuse to be solved in the future. Polyethylene naphthalate (hereinafter, abbreviated as PEN)-based wrapping materials (vessels) having improved heat-resistance of a PET film and oxygen barrier property have been developed, however, this gas barrier properties is insufficient for high gas barrier (oxygen permeability: 1 cc/m
2
·24 hr·1 atm or less) use (for example, Japanese Patent Application Laid-Open (JP-A) Nos. 8-113631 and 8-92467).
Further, in the case of EVOH excellent in oxygen barrier property and poor in water vapor barrier property, polyolefin or the like excellent in water vapor barrier property is laminated to form a multi-layer film for imparting excellent water vapor barrier property to EVOH, however, problems still remains in heat-resistance.
In these fields, film resin materials excellent in water vapor barrier property and simultaneously excellent in oxygen barrier property (high gas barrier material) are desired for realizing low cost and heat-resistance in view of distribution at ordinary temperature in the future. As the material having oxygen barrier property and water vapor barrier property, liquid crystalline polymers, particularly, a thermotropic liquid crystal polyester (hereinafter, sometimes abbreviated as LCP) is noticed, and film forming from this polyester has been investigated. For example, there are reported films made of a liquid crystalline copolyester composed of PET/p-hydroxybenzoic acid (hereinafter, sometimes abbreviated as POB) having an aliphatic chain in the main chain (Japanese Patent Application Publication (JP-B) No. 8-2974) or made of a semi-aromatic liquid crystalline polyester (JP-B No. 6-53383), and films made of a wholly aromatic liquid crystalline polyester (JP-A Nos. 7-323506 and 7-251438), and the like. However, in these investigations, it is difficult to form thin films since molecular orientation occurs in flow direction (MD) which is characteristic of LCP and anisotropy in mechanical strength occurs against the transverse direction (TD), therefore, it is difficult to obtain a practical LCP-based thin film having a thickness of 50 &mgr;m or less.
Wholly aromatic LCPs often have a processing temperature of over 300° C., and heat-resistant wholly aromatic liquid crystalline polyesters having a temperature of deflection under load (TDUL) of over 250° C. sometimes require a further higher processing temperature of 350° C. or more, therefore, an expensive process machine having specific specification is necessary.
As film forming methods from a wholly aromatic polyester which forms an optically anisotropic melted material in melting, an blown film forming method and a film forming method using a T die method are disclosed, for example, in JP-B Nos. 62-58378 and 63-33450 and the like. However, any of these methods needs a processing temperature of 340° C. or more, and the processing temperature is still required to be improved.
For obtaining aromatic liquid crystalline polyesters, there are known a suspension polymerization method, interfacial polymerization method, solution polymerization method, bulk melt polymerization method and the like, however, the former three methods have problems regarding post-treatments, for example, removal of solvents, washing of a polymer and drain load. Though bulk polymerization is preferable in economical point of view, the equilibrium constant of polycondensation reaction of a polyester is lower as compared with a polyamide, therefore, for progressing the polycondensation reaction, it is necessary to adopt a method for removing by-products by raising the reaction temperature or conducting the reaction under reduced pressure.
In the polymerization combined with a reduced pressure polymerization process, when the molecular weight is increased to show desired melt tension, in view of melt viscosity at polymer discharging, problems sometimes occur such as the difficulty of successive discharging of polymers or the contamination by retained polymers heat-treated at a high temperature in the polymerization vessel or at the discharging portion.
In case of aromatic liquid crystalline polyesters having comparatively low melt viscosity, the reaction is often conducted at a reduced pressure in later stage, and it is difficult to obtain a resin polymerized into high molecular weight in a stable state, thus discharging method has been proposed. (JP-A No. 8-192421).
Further, compounds having low boiling point produced in polymerization and unreacted raw materials remain in an aromatic liquid crystalline polyester, evaporate in molding to pollute environments, gradually migrate from the molder article to destruct product mechanism, and when foaming occurs in blown film forming, it disturbs formation of bubble and makes film formation difficult.
The present inventors have disclosed, for producing a heat-resistant polyester, a method in which a polyester is melt-polycondensed then taken out in a molten state (JP-A No. 2-69517) and a method for producing an aromatic polyester by combining this method and solid phase polymerization (JP-A No. 2-69518).
A wholly aromatic liquid crystalline polyester which has a sufficient molecular weight for manifesting suitable mechanical strength and can be molded at a lower temperature (320° C. or lower) is disclosed in JP-B No. 63-3888 and a semi-aromatic liquid crystalline polyester is disclosed in JP-A No. 61-102234 and the like. As film forming methods using this, a method for forming blown film at high shear rate is described in JP-A No. 2-3430, a film forming method using a ring die and the like is described in U.S. Pat. No. 4,975,312 and WO 9015706. Any of them discloses a method for relaxing anisotropy specific to a liquid polyester by a special molding method. In view of cost performance, decrease in thickness of 25 &mgr;m or less, preferably 15 &mgr;m or less is required, since an expensive monomer, 6-hydroxy-2-naphtoic acid is used. JP-A No. 2-3430 describes that melt strength measured under constant conditions as one of technical factors revealing important indication in blow molding film formation at a high shear rate, and exemplifies a film having a thickness of 16 &mgr;m to 22 &mgr;m. However, there still remains a problem to produce a thin thickness film.
The object of the present invention is to provide a process for producing an aro
Akiyoshi Kazunori
Moriyama Shino
Ohbe Yoshitaka
Acquah Samuel A.
Sughrue & Mion, PLLC
Sumitomo Chemical Company Limited
LandOfFree
Process for producing aromatic liquid crystalline polyester... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing aromatic liquid crystalline polyester..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing aromatic liquid crystalline polyester... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3161928