Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1996-12-17
2002-07-09
Robinson, Ellis (Department: 1772)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C428S035700, C524S284000, C525S437000, C525S444000
Reexamination Certificate
active
06417294
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART
1. Field of the Invention
The present invention relates to a preparation process of a simultaneously transparent and crystallized formed item which comprises an aliphatic polyester and one or more transparent nucleating agent ingredients selected from the group consisting of aliphatic carboxylic acid amide, aliphatic carboxylic acid salt, aliphatic alcohol and aliphatic carboxylic acid ester; and a formed item prepared by the process.
2. Related Art
Recently, general purpose plastics have led to public issues after use. Disposal of waste plastics increases the amount of refuse. Additionally, these plastics are scarcely degraded in the natural environment and thus semipermanently remain under ground even after burial disposal. Further, abandoned plastics have caused problems such as an adverse effect on the beautiful scenery and impairment of living environment for marine organisms.
On the other hand, thermoplastic and degradable polymers which include polyhydroxycarboxylic acid such as polylactic acid and aliphatic polyester such as polybutylene succinate, a polycondensation product of aliphatic polyhydric alcohol and aliphatic polycarboxylic acid, have been developed as countermeasures for these problems.
These polymers can completely decompose in an animal body within a few months to one year. Further, these polymers begin to degrade within a few weeks in a humid environment such as in soil or in sea water and disappear after an year to several years. The final decomposition products of these plastics are lactic acid, carbon dioxide and water which are nontoxic to a human body. Such characteristic of the plastics has now received attention as medical materials and a substitute for general-purpose resins.
On the other hand, in recent years, the demand for transparent plastic films has increased and their uses are making rapid progress accompanied by dramatical development of technology in the field of electronics, mechatronics, optoelectronics and laser which include optical communications, CD, CD-ROM, CD-R, LD, DVD and magneto-optic recording, liquid crystal, optic, office automation (OA) and factory automation.
Specific examples of uses include an overhead projector film, printing plate film, tracing film, food wrapping film and agricultural film.
Practical examples of high-performance uses include, for example, an electrically conductive transparent film such as a screen touch panel for computer input, thermal reflection film, liquid crystal display film, polarizing film for liquid crystal display, and printed circuit board (PCB).
Conventionally, glass, acrylates (polymethyl methacrylate (PMMA), polycarbonate (PC) and other less flexible and rigid resins have been used for these uses. However, recently, it has been inclined also in these uses to require replacement with a transparent film having excellent flexibility, processability and thermal resistance.
A polyethylene terephthalate (PET) film can conform to a portion of such substitution demand. However, PET leads to problems, for example, in uses which require degradability.
In view of such background, a transparent film which has transparency, thermal resistance (crystallinity), and degradability in combination is anticipated to have great significance in the technical field of the transparent film.
Next, degradable and thermoplastic polymers such as polylactic acid, copolymer of lactic acid with other hydroxycarboxylic acid, and copolymer of lactic acid with aliphatic polyhydric alcohol and aliphatic polycarboxylic acid are aliphatic polyester comprising lactic acid as structural units. Processed items of these degradable polymers include, for example, a bottle and other molded articles having a three-dimensional shape, unstretched films and sheets having two-dimensional shape and unstretched filaments and yarns having a one-dimensional shape. Immediately after processing, these processed items are usually amorphous and almost absent from crystals which have a size equal to or larger than the wavelength of light beams and result in light scattering. Consequently, these items are transparent.
However, these transparent processed items are usually inferior in thermal resistance due to the amorphous state. For example, amorphous polylactic acid containers are excellent in transparency and poor in thermal resistance, and thus cannot be used for hot water or a microwave oven. As a result, the uses of these transparent items have been restricted.
Accordingly, crystallinity is increased in order to improve thermal resistance by charging polymer to the mold maintained in the neighborhood of crystallization temperature in the processing or by heat-treating (annealing) the amorphous formed item after processing. Such procedures usually accelerate rapid growth of crystals, for example, crystals (for example, spherulites) which have a size equal to or larger than the wavelength of light beams and result in light scattering, crystals grow-up to the size larger than the wavelength of visible light, and the processed items thus obtained become opaque.
Crystalline aliphatic polyester such as polybutylene succinate usually crystallize and become opaque immediately after forming due to presence of crystals which have a size equal to or larger than the wavelength of light beams and scatter the light.
Thus, conventional technique has been difficult like antinomy to simultaneously provide transparency and crystallinity for formed items of aliphatic polyester.
On the other hand, it has been known in the technical field of general-purpose resin to control growth of the crystals and simultaneously provide transparency and crystallinity for the formed items by addition of a transparent nucleating agent (clarifying crystallization nuclei). The transparent nucleating agent is said, concerning the crystal, to have inhibiting action of excess growth in [size], increasing action in [numbers] and accelerating action in [crystallization velocity].
Specific examples thereof include, for example, a technique for providing polypropylene resin formed items with transparency by addition of a sorbitol derivative to polypropylene resin, or a process for adding fine powder of aromatic polyester comprising terephthalic acid and resorcinol as major structural units in order to accelerate crystallization velocity of polyethylene terephthalate.
However, in the technical field of aliphatic polyester, techniques involving crystals have not yet been known to inhibit excess growth in [size], increase in [numbers], accelerate in [crystallization velocity], and thus provide molded items with transparency and crystallinity at the same time.
[Action Mechanism of the Transparent Nucleating Agent]
The transparency emerging mechanism of transparent nucleating agent in the processed items of crystallinity resin is not so clearly known. Further, the invention is not confined by specific mechanism or hypothesis.
However, the mechanism for developing transparency by the transparent nucleating agent in the crystalline resin formed items can also be illustrated by the following models.
1) A model of crystalline resin formed items without addition of a transparent nucleating agent
When a resin formed item is crystallized without addition of a transparent nucleating agent, a small number of crystal nuclei provides a basis of crystal growth as compared with the case of adding the transparent nucleating agent. Thus a relatively small number of crystals are generated and each crystal grows to a giant size. That is, on the basis of a unit volume, a relatively small number of large crystals is formed even under equal crystallinity as compared with the case of adding the transparent nucleating agent. As a result, the crystals having a size equal to or larger than the wavelength of visible light are formed, scatter visible light, and inhibit straight propagation thereof. Consequently, formed items of crystalline resin become opaque in the absence of the transparent nucleat
Ajioka Masanobu
Kawaguchi Tatsuya
Kitahara Yasuhiro
Nakata Tomoyuki
Obuchi Shoji
Burns Doane Swecker & Mathis L.L.P.
Mitsui Chemicals Inc.
Nolan Sandra M.
Robinson Ellis
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