Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-06-22
2001-05-22
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C264S045100, C264S048000, C264S051000, C264S101000, C264S102000, C264S257000, C264S294000, C521S051000
Reexamination Certificate
active
06235806
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an open-celled rigid polyurethane foam and a method for producing the same. It also relates to a thermal insulation material or a vacuum insulation material comprising the open-celled rigid polyurethane foam as a component, which can be used as a thermal insulation panel or a thermal insulation material for profile shapes of high quality in various applications such as freezing and refrigerating equipment, freezers, refrigerated vehicles, freezing containers, transportation and storage of LNG and LPG, storage containers, pipe covers, housing panels and the like.
DESCRIPTION OF THE PRIOR ART
Recently, aiming at protection of the ozone layer and prevention of the global warming for global environmental protection, there have eagerly been sought use of less or no flons and energy saving in various production fields, and hence substitution of some materials has been desired. Among such materials, thermal insulation materials including rigid polyurethane foams have been one of the targets of such material substitution.
Therefore, various kinds of technologies have been proposed in the thermal insulation material production field. For example, as a technology for realizing no use of flons, there have been known production methods using water as a blowing agent. Further, aiming at energy saving, there have been proposed, for example, vacuum insulation panel structures prepared by filling a bag composed of a gas barrier metal-plastic laminate film with a core material for maintaining a predetermined shape, for example, inorganic powder or an open-celled body, and sealing the bag under reduced pressure.
Under the circumstance described above, because rigid polyurethane foams comprising open cells have a light weight and exhibit high performance, they are attracting much attention as thermal insulation materials for freezing and refrigerating equipment, in particular, as a core material of the aforementioned vacuum insulation panels, which can contribute to the prevention of global warming.
For example, Japanese Patent Examined Publication No. 63-61589, Japanese Patent Unexamined Publication No. 6-213561, a seminar report of Japan Thermophysical Property Study Group [Nippon Netsu-bussei Kenkyu-kai] (Jun. 30, 1989) and the like proposed to obtain high performance vacuum insulation materials with an open-celled rigid polyurethane foam foamed with water as a core material by using finer cell size or controlling the shape of the cells in the foams.
By the way, most of open-celled rigid polyurethane foams used as the core material in the aforementioned conventional vacuum insulation panels are produced by the double-conveyer method utilizing the so-called rigid slab foam or continuous panel molding, or by compression molding.
However, rigid polyurethane foams obtained by these methods would have a surface layer, called skin layer, in which open cells are not formed. Therefore, open-celled rigid polyurethane foams must currently be obtained by removing such a skin layer. In addition, the volume of the skin layer removed in the aforementioned method reaches as much as 50% of the total volume. The resulting waste is harmful to the protection of global environment, at the same time, reduces productivity, and increase the material cost per unit volume of the foams. Moreover, open-celled rigid polyurethane foams obtained as described above are limited in their shape, lack surface smoothness, and do not have a sufficient mechanical strength depending on the intended use.
On the other hand, a baking treatment for removing gases released from open-celled rigid polyurethane foams has generally been performed by using a circulating hot air oven. However, even after such a baking treatment, gases are released for a long period of time. Therefore, use of a getter agent for adsorbing the gases is essential when the open-celled rigid polyurethane foams are used for thermal insulation materials, especially for vacuum insulation materials. This also leads to reduction of productivity and considerable increase of the product cost, which obstruct wide use of these products.
Water has of course been used as a blowing agent in the production of all of the aforementioned conventional open-celled rigid polyurethane foams for no use of flons. However, such production method reduces the mechanical strength of foams upon foam molding and increases friability (brittleness of foam), and therefore molded foams of high quality have not currently been obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the aforementioned problems and to provide an open-celled rigid polyurethane foam which can be used without removing a skin layer therefrom, can reduce the material cost per unit volume of the foam, and is excellent in the surface smoothness, because of its unique structure, and a method for producing an open-celled rigid polyurethane foam having such a unique structure, and to further provide a thermal insulation material which does not result waste upon production, and affords good appearance and high reliability when used for products such as freezing and refrigerating equipment by using the aforementioned open-celled rigid polyurethane foam, and a method for producing a vacuum insulation material using the aforementioned open-celled rigid polyurethane foam.
The inventors have conducted diligent studies in order to solve the aforementioned problems and, as a result, found that a foam exhibiting a remarkably high open cell content throughout the foam as a whole can be obtained even the skin layer is remained as it is by adjusting a formulating ratio of a polyol component and isocyanate component in a material for rigid polyurethane foam to a certain specific range. Thus, the present invention has been accomplished.
That is, the present invention provides an open-celled rigid polyurethane foam produced by foam molding of foaming components comprising a polyol component, an isocyanate component and a blowing agent, wherein the foam has an open cell content of not less than 99% in a state that a skin layer is left on the foam.
The specific examples of the open-celled rigid polyurethane foam of the present invention include an open-celled rigid polyurethane foam having the aforementioned characteristics, wherein a surface layer of the foam constituting a portion of 0.5 mm thickness from the surface toward the inside of the foam has a density of about 0.9-1.5 times as high as that of a core portion constituting a portion of the foam other than the surface layer, and both of the surface layer and the core portion has an open cell content of not less than 99%.
According to the present invention, there is also provided a method for producing the aforementioned open-celled rigid polyurethane foam of the present invention, which comprises a step of foam molding foaming components containing a polyol component, an isocyanate component and a blowing agent, wherein a content ratio of the polyol component and the isocyanate component is about 0.55-0.95 in terms of equivalent ratio of NCO/OH.
As the blowing agent used for the method for producing the open-celled rigid polyurethane foam of the present invention, water is exemplified as a preferred one. As a specific example of the means for performing the foam molding in the production method of the present invention, a molding process including the following steps (A)-(C) can be mentioned:
(A) a step of mixing foaming components and allowing them to foam freely,
(B) the first compression step of compressing the freely rising foam which is freely rising in the step (A) before its gel time, and
(C) the second compression step of further compressing the compressed foam obtained in the step (B) before its rise time.
As a specific example of the method of compressing in the steps (B) and (C) in the aforementioned molding process including the steps (A)-(C), the method includes the following steps (B) and (C) can be mentioned:
(B) the first compression step of compressing the freely rising foam which is
Hayashi Masato
Hosaka Junnichi
Naka Reishi
Ohga Michihiro
Cooney Jr. John M.
Kilpatrick & Stockton LLP
Nisshinbo Industries Inc.
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