Low-resilience flexible polyurethane foam and process for producing the same

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TECHNICAL FIELD

The present invention relates to a low resilience flexible polyurethane foam using a high-molecular weight polyol having a low hydroxyl value, and a process for producing the same.

BACKGROUND ART

Heretofore, a flexible polyurethane foam (hereinafter referred to as a flexible foam) having a low impact resilence, namely, of low resilence is used as a shock-absorbing body, a sound-absorbing body or a vibration-absorbing body. Further, it is known that when such a foam is used for a cushion material of a chair or for a mattress, body pressure distribution becomes uniform, whereby fatigue feeling and a decubitus can be relieved. For example, a flexible foam of low resilence as disclosed in JP-A-11-286566 is known.

The above document discloses a flexible foam of low resilence, which can be obtained by reacting a urethane foam composition comprising a polyol (a), a polyisocyanate (b), a catalyst (c) and a blowing agent (d), and which has at least one glass transition point within each of a temperature range of from -70.degree. C. to -20.degree. C. and a temperature range of from 0.degree. C. to 60.degree. C., such that when the above glass transition point is represented by a peak value of tan .delta. obtained by measurement of the dynamic viscoelasticity at a frequency of 10 Hz, the peak value of tan .delta. within the temperature range of from -70.degree. C. to -20.degree. C. is at least 0.15 and the peak value of tan .delta. within the temperature range of from 0.degree. C. to 60.degree. C. is at least 0.3.

In this prior art, in order to obtain a flexible foam of low resilence, which is excellent in low resilence at room temperature and shows little increase of hardness at a low temperature, a polyol (a-1) having an average number of functional groups of from 1.5 to 4.5 and a hydroxyl value of from 20 to 70 mgKOH/g and a polyol (a-2) having an average number of functional groups of from 1.5 to 4.5 and a hydroxyl value of from 140 to 300 mgKOH/g are used as the polyol (a), and from 32 to 80 wt % of (a-1) and from 20 to 68 wt % of (a-2) are blended for use. Thus, a flexible foam having at least one glass transition point within each of a temperature range of from -70.degree. C. to -20.degree. C., preferably from -50.degree. C. to -25.degree. C., and a temperature range of from 0.degree. C. to 60.degree. C., preferably from 30.degree. C. to 55.degree. C., is formed.

However, in a method for blending at least two kinds of specific polyols having different hydroxyl values to form a flexible foam as in the above prior art, there was a problem that a hardness change due to a temperature change could not be sufficiently controlled. Further, in recent years, a level of durability required for a flexible foam has been raised. And further, it has been desired to further lower the impact resilience (in Examples of the above document, the impact resilience is somewhat high at a level of from 5 to 18%) to develop a low-resilience where the impact resilience is approximately 0.

The resilience (the impact resilience) of an urethane foam can be usually reduced by blending a plasticizer in a flexible foam, and by adding a proper amount of the plasticizer, a flexible foam having a certain degree of desirable low resilience can be obtained. However, in use, there is a possibility that the added plasticizer is volatilized and absorbed in a human body, and thus, a substance harmful to a human body can not be used. Further, a plasticizer was likely to elute during washing of the foam, whereby it was difficult to maintain the low-resilience of the foam after it was washed repeatedly.

The present invention has been made under these circumstances, and it is an object of the present invention to provide a flexible polyurethane foam, which is excellent in durability, and whereby an excellent low-resilience is obtainable without using a plasticizer, and the hardness change due to a temperature change is little, and a process for producing the same.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, the present invention provides the following flexible polyurethane foam and a process for producing the flexible polyurethane foam.

(I) A flexible polyurethane foam characterized by having a core impact resilience of at most 30% and a glass transition point of from -80.degree. C. to -60.degree. C. Here, the flexible polyurethane foam preferably has a hard segment content of at most 40 mass %

(II) A process for producing a flexible polyurethane foam, which comprises reacting a polyol with a polyisocyanate compo