Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-04-28
2001-04-24
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S082000, C521S084100
Reexamination Certificate
active
06221924
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is a 371 of PCT/JP98/03860 filed Aug. 28, 1998, the disclosure of which is incorporated herein by reference.
1. Technical Field
The present invention relates to a biodegradable cellulose acetate foam and to a process for its production. More particularly, the present invention relates to a biodegradable cellulose acetate foam which is suitable for various purposes including heat insulating materials, cushioning materials, food packaging materials, etc. and to a production process by which the foam can be stably obtained.
2. Background Art
Many types of different foams have been produced from synthetic resins in the past, and they have been employed in a wide range of fields including heat insulating materials, cushioning materials, food packaging materials and so forth. In recent years there has been a yearly trend toward increased demand for these synthetic resin foams, which has led to an increased volume of waste year by year, adding to environmental and pollution problems that have been the focus of much attention. However, various efforts have been made toward recycled utilization of discarded synthetic resin foams on a public scale, and with the numerous mounting issues including preventing production of noxious gases by burning disposal and preventing degeneration of heat incinerators by high heat, there is a strong demand for the development of foams which can be easily discarded and disposed of.
In order to meet this demand, various foams have been proposed wherein these synthetic resins (such as polystyrene) are replaced with biodegradable resins. For example, in Japanese Unexamined Patent Publication No. 6-136168, Japanese Examined Patent Publication No. 5-65536, Japanese Unexamined Patent Publication No. 6-335919, Japanese Unexamined Patent Publication No. 8-151469, Japanese Unexamined Patent Publication No. 8-59892, etc. there are disclosed processes for obtaining biodegradable foam molded products comprising starch as the main material. Also, Japanese Unexamined Patent Publication No. 6-15753 discloses a process whereby foam beads comprising pulp as the main material are loaded into a mold and fused together to obtain a molded product. Japanese Unexamined Patent Publication No. 5-320405 discloses a process using foamable woody resin particles prepared by adding a foaming agent to non-solution type chemically modified wood to obtain a molded product mainly by in-mold shaping. Japanese Unexamined Patent Publication No. 6-32928 discloses a process for obtaining a foam sheet from a foamable woody resin prepared by impregnating a non-solution chemically modified wood with a foaming agent, in order to prepare vessel-shaped molded products. Also, Japanese Unexamined Patent Publication No. 8-3357 discloses a process of loading at least a biodegradable resin comprising an acetate or a compound which contains one together with substantial moisture as the starting materials, and after heating and pressurization, suddenly releasing the pressure to make a foam and then molding it into the desired shape with a mold. The foam molded products obtained by these processes, however, have unstable mechanical properties (tensile strength, rupture strength, compressive strength, etc.), hardness and rigidity, and are therefore not always suitable for use as heat insulating materials or cushioning materials.
DISCLOSURE OF INVENTION
The present invention has been accomplished in light of the aforementioned problems of the prior art, and its object is to provide a biodegradable cellulose acetate foam with excellent mechanical properties, and with stable and suitable hardness and rigidity to thus facilitate shaping of various molded products for heat insulating materials, cushioning materials, food packaging materials and the like, as well as a process for its production.
By using cellulose acetate as a biodegradable material in an attempt to overcome the aforementioned problems, the present inventors have found that the object described above can be achieved by producing foams imparted with specific foam properties.
Thus, according to the present invention there is provided a biodegradable cellulose acetate foam with a foam cell size of 0.001-0.8 mm and an apparent density of 0.01-0.27 g/cm
3
.
The present invention further provides a process for producing a biodegradable cellulose acetate foam, which comprises combining a mixed starting material (D) comprising (A) cellulose acetate, (B) a plasticizer and (C) a foam nucleating agent with a weight ratio of (A):(B):(C) of (100):(0-80):(2-50) with water (E) as the foaming agent at a weight ratio of 2-100 with respect to (D), and after melting the mixture (F) at a temperature of 150-250° C., dispensing it at a temperature of 120-220° C. and then extruding it at a shear rate of 1000-20,000 sec
−1
.
REFERENCES:
patent: 4376752 (1983-03-01), Nuckolls et al.
patent: 657 060 (1965-04-01), None
patent: 4-142344 (1992-05-01), None
patent: 6-335919 (1994-12-01), None
patent: 8-59892 (1996-03-01), None
patent: 8-151469 (1996-06-01), None
patent: 10-100264 (1998-04-01), None
Matsui Michikage
Mori Hiroyuki
Nakanishi Motoyasu
Yoshida Makoto
Nutter Nathan M.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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