 |
Description  |
|
|
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 performances of low resilience, high vibration absorption and high durability.
DISCLOSURE OF THE INVENTION
The present inventors have conducted an extensive study to solve the above problem and as a result have found that a flexible polyurethane foam produced by reacting a polyoxyalkylene polyol comprising both a polyoxyalkylene polyol having a
specific structure produced by means of a double metal cyanide complex catalyst and a polyoxyalkylene polyol produced by means of an alkali metal catalyst in a specific ratio, or a fine polymer particle-dispersed polyol using such a polyoxyalkylene
polyol as the base polyol, with a specific polyisocyanate compound, satisfies all performances of low resilience, high vibration absorption and high durability, as is different from conventional highly elastic flexible polyurethane foams. The present
invention has been accomplished on the basis of this finding.
Namely, the present invention provides a process for producing a flexible polyurethane foam, which comprises reacting the following polyoxyalkylene polyol (C) and the following polyisocyanate compound in the presence of a catalyst and a blowing
agent to produce a flexible polyurethane foam having a resonance frequency of at most 3.7 Hz, a resonance ratio of at most 3.5 and an impact resilience of at most 70%: Polyoxyalkylene polyol (C): a polyoxyalkylene polyol which contains from 0.5 to 45
mass % of a random addition structure of ethylene oxide and an alkylene oxide having a carbon number of at least 3 in its structure and which further contains from 95 to 50 mass % of the following polyoxyalkylene polyol (A) and from 5 to 50 mass % of the
following polyoxyalkylene polyol (B); Polyoxyalkylene polyol (A): a polyoxyalkylene polyol produced by ring opening polymerization of a cyclic ether by means of an alkali metal catalyst; Polyoxyalkylene polyol (B): a polyoxyalkylene polyol produced by
ring opening polymerization of a cyclic ether by means of a double metal cyanide complex at least partially as a polymerization catalyst; Polyisocyanate compound: a polyisocyanate compound containing from 0 to 50 mass % in total of a diphenylmethane
diisocyanate and/or a polymethylenepolyphenyl isocyanate.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the polyoxyalkylene polyol (C) is a fine polymer particle-dispersed polyol.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the content of the fine polymer particles dispersed in the polyoxyalkylene polyol (C) is from 3 to 50 mass %.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the polyoxyalkylene polyol (A) has from 2 to 6 functional groups and a hydroxyl value of from 10 to 45 mgKOH/g.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the polyoxyalkylene polyol (B) has an unsaturation value of at most 0.04 meq/g, from 2 to 6 functional groups and a hydroxyl
value of from 16 to 45 mgKOH/g, and has from 10 to 60 mass % of a random addition structure of ethylene oxide and propylene oxide in its structure.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the polyoxyalkylene polyol (C) has an unsaturation value of at most 0.09 meq/g, from 2 to 6 functional groups and a hydroxyl
value of from 10 to 45 mgKOH/g.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the total content of oxyethylene groups in the structure of the polyoxyalkylene polyol (C) is from 3 to 80 mass %.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the core density of the flexible polyurethane foam is at most 55 kg/m.sup.3.
Further, the present invention provides the above-mentioned process for producing a flexible polyurethane foam, wherein the blowing agent is at least one member selected from water and an inert gas.
BEST MODE FOR CARRYING OUT THE INVENTION
The polyoxyalkylene polyol (C) to be used in the present invention contains both a polyoxyalkylene polyol (A) and a polyoxyalkylene polyol (B). The polyoxyalkylene polyol (A) is a polyoxyalkylene polyol produced by ring opening polymerization of
a cyclic ether by means of an alkali metal catalyst. The polyoxyalkylene polyol (B) is a polyoxyalkylene polyol produced by ring opening polymerization of a cyclic ether at least partially by means of a double metal cyanide complex catalyst. The
polyoxyalkylene polyol (A) and the polyoxyalkylene polyol (B) may, respectively, be one type or a mixture of two or more types.
As the above cyclic ether, an alkylene oxide having at least two carbon atoms, is preferred. Specifically, ethylene oxide, propylene oxide, 1,2-epoxybutane or 2,3-epoxybutane, may, for example, be mentioned. Particularly preferred is a combined
use of ethylene oxide and at least one member selected from propylene oxide 1,2-epoxybutane and 2,3-epoxybutane, and more preferred is a combined use of ethylene oxide and propylene oxide.
The polyoxyalkylene polyol (C), i.e. at least one of the polyoxyalkylene polyol (A) and the polyoxyalkylene polyol (B), contains oxyethylene groups in the structure (in the molecule or at the terminal thereof). It is particularly preferred to
contain oxyethylene groups at the molecular terminals. A polyoxyalkylene polyol containing oxyethylene groups in its structure may be produced by mixing ethylene oxide and an alkylene oxide having at least three carbon atoms sequentially or at once to a
polyvalent initiator for ring opening polymerization. Particularly, a polyoxyalkylene polyol containing oxyethylene groups at the molecular terminals can be produced by the above-mentioned ring opening polymerization, followed further by ring opening
polymerization of ethylene oxide. An average content of oxyethylene groups in the structure of the polyoxyalkylene polyol (C) i.e. in the structures of the polyoxyalkylene polyol (A) and the polyoxyalkylene polyol (B), is preferably at least 3 mass %,
particularly preferably at least 5 mass %. Further, the upper limit is preferably at most 80 mass %, particularly preferably at most 70 mass %.
Further, the polyoxyalkylene polyol (C) of the present invention, i.e. at least one of the polyoxyalkylene polyol (A) and the polyoxyalkylene polyol (B), contains a random addition structure of ethylene oxide and an alkylene oxide having a carbon
number of at least 3. The average content of the random addition structure of ethylene oxide and an alkylene oxide having a carbon number of at least 3, in the structure of the polyoxyalkylene polyol (C), i.e. in the structures of the polyoxyalkylene
polyol (A) and the polyoxyalkylene polyol (B), is from 0.5 to 45 mass %, preferably from 0.5 to 40 mass %, particularly preferably from 1 to 35 mass %. Further, the alkylene oxide having a carbon number of at least 3 is preferably propylene oxide.
Particularly, the content of the above random addition structure in the structure of the polyoxyalkylene polyol (B) is preferably from 10 to 60 mass %, more preferably from 10 to 50 mass %, particularly preferably from 10 to 40 mass %.
In a broad sense, the random addition structure means the structure of a polyoxyalkylene polyol obtained by mixing ethylene oxide and an alkylene oxide having a carbon number of at least 3 in a predetermined ratio, followed by introducing the
mixture into a reactor and subjecting it to ring opening polymerization. In the obtained random addition structure, fine block structures of oxyethylene groups and oxyalkylene groups having a carbon number of at least 3, are also contained. The mixing
ratio of ethylene oxide to the alkylene oxide having a carbon number of at least 3 (mass ratio: ethylene oxide/alkylene oxide having a carbon number of at least 3) may theoretically be within a range of from 1/99 to 99/1. However, from the difference in
the reactivity between them at the time of ring opening polymerization, it is preferably within a range of from 1/99 to 80/20.
As the polyvalent initiator to be used for the polyoxyalkylene polyol (A) and the polyoxyalkylene polyol (B), a polyhydric alcohol, a polyhydric phenol, a polyamine or an alkanolamine, may, for example, be mentioned. The number of active
hydrogen of the initiator is preferably from 2 to 6. In the present invention, the number of hydroxyl groups in the polyoxyalkylene polyol means the number of active hydrogen in the initiator.
Specific examples of the polyvalent initiator include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, glycerol, sorbitol, trimethylolpropane, pentaerythritol, diglycerol,
dextrose, sucrose, bisphenol A, ethylene diamine, aminoethylpiperazine and a polyoxyalkylene polyol having a low molecular weight obtained by adding a small amount of an alkylene oxide thereto. These initiators may be used alone or in combination as a
mixture of two or more of them. A particularly preferred polyvalent initiator is polyhydric alcohol.
The alkali metal catalyst to be used for the production of the polyoxyalkylene polyol (A) in the present invention, may, for example, be sodium metal, potassium metal or cesium metal; an alkali metal alkoxide such as sodium methoxide, sodium
ethoxide, sodium propoxide, potassium methoxide, potassium ethoxide, potassium propoxide, cesium methoxide, cesium ethoxide or cesium propoxide; an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide or cesium hydroxide; or an alkali
metal carbonate such as sodium carbonate, potassium carbonate or cesium carbonate. The hydroxyl value of the polyoxyalkylene polyol (A) is preferably at most 100 mgKOH/g, particularly preferably from 20 to 60 mgKOH/g.
In the present invention, the double metal cyanide complex to be used as a catalyst for the production of the polyoxyalkylene polyol (B) having a low unsaturation value, is preferably a complex containing zinc hexacyanocobaltate as the main
component, more preferably its ether and/or alcohol complex. As the composition, the ones which are described in JP-B-46-27250, may substantially be employed. The ether may, for example, be preferably ethylene glycol dimethyl ether (glyme), diethylene
glycol dimethyl ether (diglyme), ethylene glycol mono-tert-butyl ether (METB), ethylene glycol mono-tert-pentyl ether (METP), diethylene glycol mono-tert-butyl ether (DETB) or tripropylene glycol monomethyl ether (TPME). The alcohol is preferably
tert-butyl alcohol as disclosed in JP-A-4-145123. Further, the above complex may have a mixture of the ether and the alcohol as a ligand.
At the time of producing the polyoxyalkylene polyol (B), if the polymerization initiator (the initiator) is of a low molecular weight, there will be a problem that the reaction of the cyclic ether is very slow, and a method disclosed in
JP-A-4-59825 is effective wherein a polyoxyalkylene polyol having propylene oxide preliminarily addition polymerized, is used as its polymerization initiator. The polyoxyalkylene polyol which can be used as the polymerization initiator, includes one
having a random addition structure of propylene oxide and ethylene oxide.
The hydroxyl value of the polyoxyalkylene polyol (B) is preferably at most 100 mgKOH/g. Further, from the relation between the viscosity and the mechanical properties (particularly the elongation property) of the resulting urethane foam, it is
more preferably from 16 to 45 mgKOH/g, particularly preferably from 25 to 40 mgKOH/g. The unsaturation value of the polyoxyalkylene polyol (B) is preferably at most 0.04 meq/g, particularly preferably at most 0.03 meq/g. It is also preferred to use two
or more types in combination so that the polyoxyalkylene polyol (B) will substantially have an unsaturation value of at most 0.04 meq/g, from 2 to 6 functional groups and a hydroxyl value of from 16 to 45 mgKOH/g. The mixing ratio of the polyoxyalkylene
polyol (A) to the polyoxyalkylene polyol (B) is such that the mass ratio ((A)/(B)) is within a range of from 95/5 to 50/50, preferably within a range of from 95/5 to 70/30, particularly preferably within a range of from 90/10 to 80/20.
In the present invention, as the polyoxyalkylene polyol (C), a fine polymer particle-dispersed polyol using the polyoxyalkylene polyol (C) as the base polyol, may be used. Further, it is possible to obtain a polyoxyalkylene polyol (C) having
fine polymer particles stably dispersed, by preparing a fine polymer particle-dispersed polyol using the polyoxyalkylene polyol (A) as the base polyol and then mixing it with the polyoxyalkylene polyol (B). Further, likewise, it is possible to obtain a
polyoxyalkylene polyol (C) having fine polymer particles stably dispersed by preparing a fine polymer particle-dispersed polyol using the polyoxyalkylene polyol (B) as the base polyol and then mixing it with the polyoxyalkylene polyol (A).
The fine polymer particle-dispersed polyol is a dispersion system where fine polymer particles (dispersoid) are stably dispersed in a polyoxyalkylene polyol as the base polyol (dispersing medium). The polymer for the fine polymer particles, may,
for example, be an addition polymerization type polymer or a polycondensation type polymer. Specific examples include an addition polymerization type polymer such as a homopolymer or copolymer of acrylonitrile, styrene, methacrylate, acrylate or another
vinyl monomer; and a polycondensation type polymer such as polyester, polyurea, polyurethane or melamine. By the presence of such fine polymer particles, the hydroxyl value of the entire fine polymer particle-dispersed polyol tends to be usually lower
than the hydroxyl value of the matrix polyol.
The content of the fine polymer particles in the polyoxyalkylene polyol is preferably at most 50 mass %. The amount of the fine polymer particles is not required to be particularly large, and if it is too large, there is no particular
disadvantage other than the economical one. In many cases, it is preferably from 3 to 50 mass %, particularly preferably from 3 to 35 mass %. The presence of the fine polymer particles in the polyoxyalkylene polyol is effective for the improvement of
the hardness, air permeability and other physical properties of the foam. Further, in the calculation of the mass of the polyoxyalkylene polyol, the mass of the fine polymer particles is not included.
The above polyoxyalkylene polyol (C) may be used in combination with a high molecular weight polyamine having at least two primary or secondary amino groups or a high molecular weight compound having at least one primary or secondary amino group
and at least one hydroxyl group, as another high molecular weight active hydrogen compound.
Such another high molecular weight active hydrogen compound has a molecular weight of at least 400, particularly at least 800, per functional group, and the number of functional groups per one molecule is preferably from 2 to 8. Further, the
molecular weight per functional group is preferably at most 5000.
Such another high molecular weight active hydrogen compound may, for example, be a compound obtained by converting some or all of hydroxyl groups of the above-mentioned polyoxyalkylene polyol, to amino groups, or a compound obtained by
hydrolyzing and converting to an amino group the isocyanate group of a prepolymer h | | |
