Flexible polyurethane foam

Details Flexible polyurethane foam Flexible polyurethane foam

1997-04-30

2001-10-16

Sergent, Rabon (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S110000, C521S117000, C521S128000, C521S137000, C521S163000, C521S160000

Reexamination Certificate

active

06303669

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a flexible polyurethane foam (hereinafter referred to as “flexible foam”) which can hardly be hydrolyzed and shows a small drop of tensile strength, etc. even after exposure to ozone. The present invention also relates to a flexible foam which exhibits further improvements in physical properties such as tensile strength and elongation, suffers little deterioration due to ultraviolet rays, etc., and has a proper air permeability, a good formability and an excellent waterproofness. The present invention further relates to a speaker edge made of a flexible foam excellent in these various properties. The flexible foam of the present invention can find wide application, e.g., speaker edge as well as soundproofing material for hard disc apparatus, damping material, roll and sealant for toner cartridge in various printers, etc.
BACKGROUND OF THE INVENTION
Flexible foams are divided into two groups, i.e., foam comprising a polyester polyol (hereinafter referred to as “polyester foam”) and foam comprising a polyether polyol (hereinafter referred to as “polyether foam”). The characteristics of these foams are drastically affected by the polyol used. Thus, these foams essentially differ in mechanical and chemical properties depending on the molecular structure of polyol, the intramolecular cohesive force of foam, etc.
The polyester foam has small cells, an excellent appearance and a great tensile strength and elongation. With respect to elongation after compression molding in particular, the polyester foam is very superior to the polyether foam. The polyester foam is also excellent in oil resistance and solvent resistance and chemically stable. Further, the polyester foam exhibits good heat resistance and weather resistance. However, the polyester foam has a great disadvantage that it shows a strength drop due to hydrolysis of ester bond attributed to polyester polyol used for the production of foam. The inhibition of hydrolysis will be hereinafter referred to as “resistance to wet heat aging”. The polyester foam is further disadvantageous in that it suffers a relatively great hysteresis loss and thus is not suitable for use as cushioning material.
On the other hand, the polyether foam is very superior to the polyester foam with respect to hydrolysis. The polyether foam is also excellent in flexibility, restorability, etc. However, the polyether foam is inferior to the polyester foam with respect to oil resistance, solvent resistance, etc. Further, a polyether foam having a very low air permeability can be hardly obtained. Moreover, the polyether foam exhibits a small tensile strength and elongation. In particular, the polyether foam shows a great drop of strength and elongation after compression molding. Further, the polyether foam is considerably inferior to the polyester foam with respect to resistance to ozone deterioration. At present, therefore, the polyether foam yields to the polyester foam in many practical uses despite its advantage that it can be hardly hydrolyzed and exhibits an excellent resistance to wet heat aging. The inhibition of ozone deterioration will be hereinafter referred to as “resistance to ozone deterioration”. Further, the polyether foam is inferior to the polyester foam with respect to resistance to deterioration by ultraviolet ray, etc. (The inhibition of deterioration by ultraviolet ray, etc. will be hereinafter referred to as “weather resistance”.)
The flexible foam is essentially porous. Even when compressed under heating, the flexible foam cannot be provided with desired waterproofness regardless of whether it is of ester or ether type. In order to solve the problem of waterproofness, the following approaches have been proposed.
(i) A method which comprises providing a waterproof film on the surface of the flexible foam
(ii) A method which comprises impregnating the flexible foam with an emulsion of a fluororesin, and then drying the flexible foam to remove water therefrom, thereby rendering the flexible foam water-repellent
However, the method (i) is disadvantageous in that it is difficult to form a homogeneous water-impermeable film on the surface of a flexible foam having numerous micropores. Further, as the material constituting the film there is often used a low heat-resistance material. A film formed of such a material can soften and melt to destruction when compressed under heating. Moreover, this method adds to cost. On the other hand, the method (ii) is disadvantageous in that it is considerably difficult to uniformly impregnate a flexible foam having the low air permeability with an emulsion of a fluororesin to enhance its waterproofness. Even if such a flexible foam can be uniformly impregnated with an emulsion of a fluororesin, it is difficult to completely remove water content from the foam, making it easy to render the waterproofness heterogeneous. Further, such an emulsion of a fluororesin is very expensive. Thus, the resulting foam, too, is very expensive.
It has been attempted to develop a foam having advantages of polyester foam and polyether foam in combination by the combined use of a polyester polyol and a polyether polyol. However, the two general-purpose polyols are poorly compatible with each other. Thus, the two polyols cannot be uniformly mixed and hence suffer phase separation that makes it impossible to provide a normal foam unless the mixing proportion of the polyester polyol is at least 50% by weight, particularly at least 80% by weight. The incorporation of a large amount of the polyester polyol makes it impossible to provide a foam well-balanced in physical properties. For the details of disadvantages caused by the mixing of a polyether polyol and a polyester polyol, reference can be made to Iwata, “Handbook of Polyurethane Resin”, Nikkan Kogyo Shinbunsha, 1987, page 160. It is reported in this reference that the mixing of a slight amount of a polyether polyol in a polyester polyol during the preparation of a flexible polyurethane foam makes it impossible to obtain a normal cell, having a delicate effect on the cell conditions. Thus, when the foregoing two types of polyols are used in admixture to prepare a flexible urethane foam, the foam stability of which is important because its expansion rate is high, the resulting foam have cracks or voids. In some extreme cases, the foam can be destroyed, giving troubles in the production line.
It has been attempted to enhance the properties of a foam by the use of a polyether polyol having an ester bond incorporated therein. Further, a method which comprises using a special polyol such as phosphorus-containing polyester polyol in combination with a specific foam stabilizer and a method which comprises using a hydroxyl-terminated prepolymer or isocyanate-terminated prepolymer have been proposed. In a technical field of connecting a foam to a surface layer made of a polyvinyl chloride or the like by molding, the combined use of a specific polyester polyol and a polyether polyol has been proposed.
However, these proposed methods are conducted in restricted fields such as filter foam free of cell membrane (JP-B-52-35077 (the term “JP-B” as used herein means an “examined Japanese patent publication”), JP-A-55-27315 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), etc.) and semirigid foam (JP-B-3-26694, JP-A-62-148516, etc.). These proposed methods are not put into practical use in the technical field of ordinary flexible foam. The preparation of the foregoing specific polyester polyol comprising a polyether polyol having an ester bond incorporated therein requires a complicated procedure. Thus, the resulting polyester polyol is expensive. If such a polyester polyol is used singly, the properties of the resulting foam cannot be widely varied. Further, the concentration of ester groups which can be incorporated into the foam is too low to provide a sufficient enhancement in the physical properties of the foam. U.S. Pat. No. 4,374,935 discloses that a mixture of a specific polyester polyol

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