The present invention relates to a flexible polyurethane foam, its production method and a material system for its production.
In recent years, along with progress in an automobile industry, not only improvement in performance of an automobile but also a high degree of vehicle interior and improvement in interior comfort have been desired, and development of a flexible polyurethane foam for seat (hereinafter referred to as a flexible foam) having more excellent cushioning properties has been strongly desired in view of improvement in comfort to sit on and comfort to ride in.
Heretofore, as a seat cushion, a combination of metal springs and a pad material comprising a flexible foam has been used widely. However, in recent years, a seat for an automobile so-called full-foam type, wherein a flexible foam itself is made to have spring properties so that metal springs are not used, tends to be employed, with a demand for cost saving, weight saving, etc. The full-foam type seat tends to be thick since no metal spring is used together, and properties of the flexible foam are factors which greatly contribute to comfort to sit on and comfort to ride in of the seat. Namely, importance has been given to static characteristics and dynamic characteristics as indices of comfort to sit on and comfort to ride in, in development of a flexible foam. Particularly among the static characteristics, control of the feeling of support at the initial stage of sitting and the feeling of bottom out at the terminal stage of sitting are important.
When a person actually sits on a seat equipped with a pad material made of a flexible foam, the flexible foam is compressed and indented, and the position of e.g. the bottom falls to a certain height. As a method of measuring the static characteristics (static seat feeling), a load test in accordance with a performance test method of a pad material for a seat for an automobile in JASO (Japanese Automobile Standards Organization) B408-89, wherein a deflection is measured to obtain a load-deflection loop, is used. In FIG. 2 is shown a load-deflection loop of a conventional flexible foam. In the load-deflection loop, the value of the tangent of the tangent line at the pressing side (upper side in FIG. 2) at each load is the static spring constant. Namely, when the static spring constant is high, the curve has a steep slope and when the static spring constant is low, the curve has a gentle slope.
The load-deflection loop of a flexible foam usually rises quickly at the initial stage of application of the load, then gently increases at the inflection point 1 and with further application of the load, it rapidly increases at the inflection point 2. A flexible foam excellent in the feeling of support is considered to be such a flexible foam that the curve steeply rises at the initial stage of application of the load, and the static spring constant is high from the starting point to the vicinity of the inflection point 1. Further, a flexible foam which provides no feeling of bottom out and provides favorable comfort to sit on, is considered to be such a flexible foam that the static spring constant is low even in the high load region after the inflection point 2. Adjustment of hardness of the flexible foam has conventionally been carried out to obtain the feeling of support, however, in such a case, the static spring constant in the high load region tends to be high, and the feeling of bottom out can not be overcome.
Generally, a full-foam type flexible foam for seat provides a small deflection in the high load region as the static characteristics, it provides the feeling of bottom out, and the comfort to sit on tends to deteriorate, as compared with the foam for seat in combination with metal springs. In order to overcome such problems, a method has been known to make the foam thick or to increase the density to make the deflection large, however, problems of increase in cost and increase in the seat weight can not be overcome.
JP-A-11-322875 proposes a method of adding a specific fluorine type surfactant to a material for production of a polyurethane foam composed mainly of a polyol and an isocyanate component so as to increase the deflection. However, there are such problems that the feeling of support is insufficient, the fluorine type surfactant itself is expensive, thus increasing the cost, and the surface tension of the surfactant is low, whereby the inside of a mold at the time of foam production may be polluted.
Further, JP-A-5-320304 proposes a method for producing a polyurethane foam, which comprises reacting a polyol component comprising a polyol, a catalyst, a blowing agent and other additives, with a polyisocyanate component, wherein a specific bifunctional secondary amine is added, to produce a foam which provides a small slope of the pressing side curve at 75% deflection as a characteristic to evaluate the feeling of bottom out, which provides no feeling of bottom out, and which has a well balance among softness, degree of falling and vibrating property. However, the feeling of support is insufficient, and durability particularly heat and humid permanent compression set is insufficient.
Namely, such a flexible foam is not present that the static spring constant is high in the low load region, the feeling of support and rigidity are satisfied, and further, the static spring constant is low in the high load region, the deflection is large and the feeling of bottom out is overcome.
Under these circumstances, it is an object of the present invention to provide a flexible foam for an automobile seat, with which the feeling of bottom out is overcome, the feeling of support is favorable, and the comfort to sit on is significantly improved, and which has favorable vibrating property and durability, and a method for producing said foam and a material system for production of said foam.
The present inventors have conducted extensive studies to overcome the above problems and as a result, they have found a foam which exhibits a load-deflection loop which satisfies characteristic conditions in a load test of the flexible foam or in a load test of its core portion, and found that a foam having such a characteristic load-deflection loop significantly improves the comfort to sit on as the static seat feeling, when an automobile seat is molded (see FIG. 1). A foam which satisfies such conditions has such characteristics that the deflection is small at the initial stage of application of the load, the feeling of support is sufficient, and after that region, the rate of change of the static spring constant is small, and the curve gently increases. Namely, it is estimated that at the initial stage of sitting, the feeling of support is sufficient, whereby the foam is excellent in body weight support, and after a person sits on the foam, it is well bent, whereby the body weight is softly supported, and accordingly the feeling of bottom out is overcome, and the comfort to sit on becomes favorable.
Namely, the present invention provides a flexible polyurethane foam, wherein in a load (N)-deflection (mm) loop obtained by a load test of the flexible polyurethane foam, the X value as calculated from the formula (1) is at most 4.2:
X=(static spring constant at a load of 883N)/(static spring constant at a load of 98N)xe2x80x83xe2x80x83(1)
The present invention further provides a flexible polyurethane foam, wherein in a load (N)-deflection (mm) loop obtained by a load test of a core portion of the flexible polyurethane foam, the Y value as calculated from the formula (2) is at most 1.8:
Y=(static spring constant at a load of 127.4N)/(static spring constant at a load of 19.6Nxe2x80x83xe2x80x83(2)
The present invention further provides a method for producing the above flexible polyurethane foam, which comprises reacting a polyol having from 5 to 85 mass % of an oxyethylene/oxypropylene random chain, the oxyethylene group content in the random chain being from 3 to 40 mass % and the content of the terminal oxyethylene block chain being from 3 to 40 mass %, and having a hydroxyl value of from 10 to 56 mgKOH/g and a degree of unsaturation of at most 0.04 meq/g, with a polyisocyanate in the presence of a blowing agent and a catalyst.
Still further, the present invention provides a material system for production of the above flexible polyurethane foam, which comprises a polyol system liquid containing a polyol having from 5 to 85 mass % of an oxyethylene/oxypropylene random chain, the oxyethylene group content in the random chain being from 3 to 40 mass % and the content of the terminal oxyethylene block chain being from 3 to 40 mass %, and having a hydroxyl value of from 10 to 56 mgKOH/g and a degree of unsaturation of at most 0.04 meq/g, and a polyisocyanate.