1. Field of the Invention
2. Description of the Prior Art
A conventional container, in consideration of a cost and a purpose, is generally a paper-made or plastics-made container, such as a paper-made or plastics-made cup, bowl, and dish, or a filling container made of this material, such as a packaging container, a heat preservation container, and a lunch box. An existing paper-made container is provided with a single layer that cannot preserve and insulate heat. The container may be provided with two layers with a partition, the cost is, however, extremely high and the cost efficiency is not satisfying since the container is designed for one-time usage.
For heat insulation purpose, the existing paper-made cup is held with an additional plastic cup supporter. However, the addition of the plastic cup supporter is in conflict to the original design intention of the one-time-usage paper-made cup since the cup supporter has to be recycled and stored after the paper-made cup is thrown.
On the other hand, a heat insulation container composed of foamed material is provided to solve the previous problems. A conventional foamed container is manufactured by the process that the paper sheet is foamed before modeled to a container. However, the foamed paper sheet has a large volume and is difficult to be stacked. Also, a cutting machine is unable to cut the foamed paper sheet into desired shape due to the soft foamed layer. Moreover, stacked foamed paper sheets are unable to be fed into machines due to the large friction of the foamed layer, so that the yield rate is low.
Besides, some conventional foamed containers have a plurality of deficiencies. Patent publication US 2002/0182347 showed that the foaming layer composed of 60-90% by weight the microcapsules of foaming agent and 10-40% by weight the binder, and that the paper sheet is foamed before shaped into a container so that the problems mentioned above occur. That is, the microcapsules are much more than the binder. It results that the foaming layer may flake off in powder. Also, microcapsules are quite closed to each other and don't have enough space to expand. Moreover, a plurality of adjacent microcapsules may integrate into a larger capsule to form a rough surface. Thus, the process disclosed in US 2002/0182347 is impossible to be introduced in practice.
Another application of foamed paper sheet is shown in U.S. Pat. No. 5,498,860. '860 disclosed a card with a braille portion which is selectively protruded. “The binder of the braille portion is softened, and the microcapsules are foamed at the same time”. However, the process is not suitable for manufacturing a container. When the softening point of the binder is the same with the foaming point of the microcapsules, the microcapsules are unable to be rearranged before foaming so that the foamed surface is rough. In addition, a preferred ratio of the binder and the microcapsules for heat insulation is not provided here. More specifically, a foamed braille portion of a card must have different composition from that of a heat insulation container due to the different purposes.
WO 03/104338 discloses that the foam coating comprising 1-99.9% or preferably 8-80% by weight of binder and preferably 5-25% by weight of the unexpanded. However, the binder is softened and the heat expandable particles are foamed at the same time. WO 03/104338 does not disclose step(s) for redistributing the heat expandable particles which are dried and cannot flow itself under only the effect of gravity without external force.