Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-10-08
2003-11-25
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...
C521S124000, C521S125000, C521S130000, C521S131000, C521S133000
Reexamination Certificate
active
06653362
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a flexible polyurethane foam having low resilience, high vibration absorption and high durability, whereby the impact resilience, and the resonance frequency and the resonance ratio measured by the methods in accordance with the vibration test methods of the cushion property test methods for automobile seats as stipulated in automobile standards JASO B407-87, are controlled to be within the optimum ranges.
BACKGROUND ART
An automobile seat is basically constituted by a pad made of a flexible polyurethane foam, a spring and a frame material. As a flexible polyurethane foam at the earlier stage, a foam produced by a hot curing method, was used and employed in combination with a spring material. Here, the hot cure foam was prepared by using, as a polyoxyalkylene polyol, one having a relatively low molecular weight, usually at a level of a molecular weight of 3000, and since the reaction was relatively slow, the mold was heated from outside to complete the reaction, whereby relatively intense heating was required, and this is the reason for the naming of “hot cure”. Along with an increase of deep foam seats having springs omitted since a few years ago, it has become important to improve the performance of flexible polyurethane seat pads. Particularly, in order to improve the riding comfortableness of seat cushions, it is desired to improve impact resilience, durability and vibration characteristics. With respect to the vibration characteristics, the relation between the car body vibration and human is not uniform, but it has been said to be effective for the improvement of the riding comfortableness to take large damping in a frequency region particularly sensitive to human (which is said to be for example from 4 to 8 Hz or from 6 to 20 Hz).
In order to improve such characteristics, it is considered to be effective to produce a seat cushion by means of a polyoxyalkylene polyol having a molecular weight higher than the conventional ones, and on this basis, a cold cure foam has been developed. The cold cure foam is produced by a method wherein usually one having a molecular weight of at least about 4500 is used, and since the reactivity is relatively high, external heating of the mold is not required as in the case of a hot cure foam, whereby the energy consumption is small. Further, the cold cure foam is referred to also as a HR foam, since it has high resilience similar to a foam rubber.
Usually, a polyoxyalkylene polyol to be used as a starting material for a polyurethane, is produced by ring opening polymerization of an alkylene oxide such as propylene oxide using a polyhydric alcohol as an initiator and employing a sodium type catalyst such as sodium hydroxide or a potassium type catalyst such as potassium hydroxide. In this method, a monool having an unsaturated bond (an unsaturated monool) will be formed as a by-product, and the amount of this unsaturated monool to be formed, increases with an increase of the molecular weight of the polyoxyalkylene polyol (a decrease of the hydroxyl value). With a polyoxyalkylene polyol having a hydroxyl value of about 56 mgKOH/g which is widely used as a starting material for flexible polyurethane foams, the presence of such an unsaturated monool was not a problematic amount. However, with a polyoxyalkylene polyol having a low hydroxyl value having the molecular weight increased, the presence of this unsaturated monool may sometimes be problematic. For example, with a polyoxyalkylene polyol having a hydroxyl value of about 34 mgKOH/g, the unsaturation value will be usually at least 0.1 meq/g. If an elastic foam is produced by means of a polyoxyalkylene polyol having a high total unsaturation value, there will be a problem such as decrease in the hardness, the decrease in the impact resilience, deterioration of the compression set or decrease in the curing property at the time of forming a foam. Further, even if it is attempted to produce a polyoxyalkylene polyol having a low hydroxyl value by means of a sodium type catalyst or a potassium type catalyst, the total unsaturation value tends to be remarkably high, such being practically inacceptable.
Further, in order to improve the above-mentioned characteristics, a method is known to produce a flexible polyurethane foam having high elasticity by means of a polyoxyalkylene polyol having a low total unsaturation value. For example, such is disclosed in JP-A-3-14812 and JP-A-3-128914 i.e. publications of applications by the present applicants. Further, highly elastic flexible polyurethane foams using polyoxyalkylene polyols produced by suing cesium hydroxide as a catalyst, are disclosed in JP-A-9-263621, JP-A-9-59340, JP-A-10-251508, JP-A-7-309924, JP-A-7-330843, and JP-A-8-208800. Further, JP-A-11-60721, JP-A-11-106500 and JP-A-11-140154 disclose that similar effects can be obtained also with a highly elastic flexible polyurethane foam using a polyoxyalkylene polyol produced by using a phosphazenium compound as a catalyst.
However, in recent years, it has been found that with highly elastic flexible polyurethane foams produced by using polyoxyalkylene polyols having low total unsaturation value, the impact resilience is extremely high (from 71 to 90%), and the transmissibility in the vicinity of the resonance frequency of the foams is extremely high, and accordingly, suppression of pushing up feeling or the supporting property for a passenger during driving tends to be inadequate. To solve such a problem, JP-A-11-60676 discloses an invention designed to solve the above problem by reducing the impact resilience of the foams and increasing the value of hysteresis loss to a proper level, by a combination of a polyoxyalkylene polyol produced by using cesium hydroxide as a catalyst with a polyoxyalkylene polyol having a relatively low molecular weight and a hydroxyl value of from 90 to 300 mgKOH/g. However, this literature gives no specific data relating to improvement of the vibration characteristics, which will be an index for driving comfortableness. Further, the hysteresis loss value of the foam disclosed in this literature is relatively large at a level of from 25 to 35%, and such a foam is disadvantageous from the viewpoint of the durability.
On the other hand, JP-A-9-176270 discloses an invention relating to a latex-like flexible polyurethane foam having a relatively small impact resilience, by a combination of a fine polymer particle-dispersed polyol with a hydrophilic polyol, but there is no disclosure relating to the vibration characteristics or durability of this foam. Further, JP-A-9-52932 discloses a method for producing a flexible polyurethane foam using from 2 to 70% of a polyoxyalkylene polyol having ethylene oxide in its molecule, but there is no disclosure relating to the unsaturation value of the polyoxyalkylene polyol, or the vibration characteristics or durability of the foam thereby produced. Likewise, a method for producing a flexible polyurethane foam using a polyoxyalkylene polyol prepared by using a double metal cyanide complex, is disclosed in U.S. Pat. Nos. 5,700,847, 5,668,191, 5,605,939 and 5,648,559, but there is no disclosure relating to the above problem. On the other hand, as a flexible polyurethane foam usually having low transmissibility in the vicinity of the resonance point (usually a resonance ratio of at most 4.0), a hot cure foam is known, and the details of the vibration characteristics are disclosed, for example, on page 199 in Polyurethane Resin Handbook, complied by Keiji Iwata. However, with a hot cure foam, the resonance point is usually within a frequency range sensitive to human (from 4 to 8 Hz), whereby the performance for riding comfortableness has been inadequate. Namely, by the above-mentioned prior art, it has been difficult to produce a flexible polyurethane foam which satisfies all performances of low resilience, high vibration absorption and high durability.
It is an object of the present invention to produce a flexible polyurethane foam which satisfies the respective per
Horie Akio
Sasaki Takayuki
Sugiyama Kayoko
Takeyasu Hiromitsu
Toyota Yoshinori
Asahi Glass Company Limited
Cooney Jr. John M.
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