Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1994-11-02
1996-06-11
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264 50, 264 53, 521 54, 521 79, 521139, 521146, 521148, 525316, 525901, C08J 914, C08J 916
Patent
active
055256392
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved expanded foamed bead of a rubber-modified styrene polymer. More particularly, the present invention is concerned with an expanded foamed bead of a rubber-modified styrene polymer, comprising a plurality of closed cells defined by cell walls which constitute a matrix for the bead. Each of the cell walls comprises two surfaces separated by a distance equal to the thickness of the cell wall. The matrix comprises: (a) a continuous styrene polymer phase; and (b) a rubber phase dispersed in said continuous styrene polymer phase (a), wherein the rubber phase comprises a plurality of substantially flat, butadiene polymer rubber particles each having at least one styrene polymer particle occluded therein; wherein the flat rubber particles are arranged in a specific lamellar configuration along the thickness of the cell wall. The expanded foamed bead of a rubber-modified styrene polymer of the present invention is excellent in its ability to retain a foaming agent gas within the closed cells, and can advantageously be employed for producing, for example, packaging materials and cushioning materials or packings which are improved in resistance to breakage, such as cracking.
2. Discussion of Related Art
Expanded foamed beads of a styrene polymer are molded into various shaped products. During the molding, the expanded foamed beads are further foamed (or expanded) to give an ultimate foamed, molded product. The obtained foamed, molded products are widely employed as, for example, packaging materials and cushioning materials or packings. However, foamed, molded products produced from conventional expanded foamed beads of a styrene polymer are insufficient in resistance to breakage, such as cracking. Therefore, for example, when a foamed, molded product produced from conventional expanded foamed beads of a styrene polymer is used as a cushioning material in packaging an article having a relatively large weight and the packaged article is transported, there is a danger that when the packaged article sustains a jolt or impact during the transportation, the cushioning material suffers cracking. When the packaged article further repeatedly sustains an impact after the cracking of the cushioning material, it is likely that the article is damaged. The cracking of a cushioning material can be prevented by increasing the thickness of the cushioning material. However, when the thickness of a cushioning material to be used in packaging an article is increased, the volume of the resultant package becomes inevitably disadvantageously increased, so that the efficiency of the transportation is lowered.
In order to solve the above problems, it has been proposed to produce an expanded foamed bead from a styrene polymer having a butadiene polymer added thereto, i.e., a rubber-modified styrene polymer.
Unexamined Japanese Patent Application Laid-Open Specification No. 56-67344 discloses an expanded foamed bead of a styrene polymer having non-oriented rubber particles dispersed therein. In the above Japanese Patent document, a foamed, molded product produced from the expanded foamed beads of a rubber-modified styrene polymer disclosed therein is described to have an improved impact strength. However, since the rubber particles dispersed in the styrene polymer are of a non-oriented type, it is difficult for the rubber particles to change in conformity with the formation of cells during the expansion of the rubber-modified styrene polymer. Therefore, during the expansion of the rubber-modified styrene polymer, the rubber particles are likely to be disadvantageously exposed on the surfaces of cell walls or protrude into the cells, thereby adversely influencing the cells. Especially when a highly expanded foamed bead is produced, in which the thickness of cell walls is very small, the exposed or protruding rubber particles are likely to damage the cell walls, so that the retention of a foaming agent gas in the cells is unsatisfactory.
Unexamined
REFERENCES:
patent: 4594363 (1986-06-01), Blankenship et al.
patent: 4880842 (1989-11-01), Kowalski et al.
patent: 4970241 (1990-11-01), Kowalski et al.
patent: 5229209 (1993-07-01), Gharapetian et al.
patent: 5369135 (1994-11-01), Campbell et al.
Keneko Masamichi
Kiba Isao
Asahi Kasei Kogyo Kabushiki Kaisha
Foelak Morton
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