JP2006117750A - Method for producing polyurethane foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently producing polyurethane foam having a fine uniform cell structure, high mechanical strength and little difference in the mechanical strength among the sites without causing curing of a raw material in a stirring mixer (a mixing head). <P>SOLUTION: The method for producing the polyurethane foam by a mechanical froth method involves a process for stirring and mixing a polyol mixture containing a polyol and a catalyst with an isocyanate component in the absence of an inert gas in a premixer (A) to prepare a urethane-forming liquid composition, feeding the obtained liquid composition and the inert gas to a stirring mixer (B), mechanically mixing the liquid composition in an inert gas atmosphere to prepare a froth-shaped raw material wherein the inert gas is finely dispersed in the liquid composition, and extruding the froth-shaped raw material from the stirring mixer (B). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a polyurethane foam, and more particularly to a method for producing a polyurethane foam capable of efficiently producing a polyurethane foam having a fine and uniform cell structure.

As a method for producing a polyurethane foam, there is known a mechanical floss method in which urethane-forming components (polyol and isocyanate) are foamed by stirring and mixing in an inert gas atmosphere (see, for example, Patent Document 1).
The mechanical froth method is advantageous in that the molding operation is simpler than the chemical foaming (water foaming) method, and a foam having no deterioration in physical properties due to urea groups can be obtained.

In the mechanical flossing method, a polyol mixture containing a polyol and a catalyst, an isocyanate component, and an inert gas (air) are supplied into a stirring mixer (mixing head), and the polyol mixture is mixed in an inert gas atmosphere. By mechanically stirring the isocyanate component with a stirring rotor, the “mixing of the polyol mixture and the isocyanate component” and the “dispersion of the inert gas” proceed simultaneously to prepare a floss-like raw material, which is then added from the stirring mixer. The polyurethane foam is obtained by discharging, pouring into a mold or the like and curing.
Here, it is necessary for the polyurethane foam to have fine and uniform cells (bubbles caused by inert gas).
JP 2001-89547 A

Therefore, in order to simultaneously proceed the mixing of the two liquids (the polyol mixture and the isocyanate component) and the dispersion of the inert gas, it is necessary to set the rotational speed of the stirring rotor to be considerably high (for example, about 1800 rpm).
However, when the rotational speed of the stirring rotor increases, there is a problem that the shear heat generated during stirring increases and the urethanization reaction proceeds and the raw material is cured in the stirring mixer.

Here, in order to avoid the problem of curing in the stirring mixer, it is also conceivable to set the rotation speed of stirring low (for example, about 150 rpm).
However, if the number of revolutions of stirring is set low, the polyol mixture and isocyanate component cannot be sufficiently mixed, resulting in a long curing time for the resulting froth-like raw material and difficult dispersion of the inert gas. As a result, the mechanical strength of the formed polyurethane foam is lowered, and the variation in mechanical strength depending on the part is also increased. Furthermore, in the formed polyurethane foam, the cells cannot be sufficiently miniaturized and uniform.

It is also conceivable to reduce the content of the catalyst in the polyol mixture in order to avoid the problem of curing in the stirring mixer.
However, if the content of the catalyst is reduced, the curing time of the obtained froth-like raw material becomes extremely long, and the production efficiency is lowered, which is not practical. Moreover, the mechanical strength of the formed polyurethane foam is lowered, and the variation in mechanical strength depending on the part is also increased. Furthermore, in the formed polyurethane foam, the cells cannot be sufficiently miniaturized and uniform.

  The present invention has been made based on the circumstances as described above, and the object thereof is to prevent the raw material from being hardened in a stirring mixer (mixing head), to have a fine and uniform cell structure, An object of the present invention is to provide a method capable of efficiently producing a polyurethane foam having high mechanical strength and less variation in mechanical strength depending on the part.

  The production method of the present invention is a method of producing a polyurethane foam by a mechanical froth method, and in a premixer (A), a polyol mixture containing a polyol and a catalyst and an isocyanate component are mixed with an inert gas. In the presence, a urethane-forming liquid composition is prepared by stirring and mixing, and the obtained liquid composition and an inert gas are supplied to the stirring mixer (B). In the stirring mixer (B) Then, the liquid composition is mechanically stirred under an inert gas atmosphere to prepare a floss-like raw material in which the inert gas is finely dispersed in the liquid composition. The method includes a step of discharging from (B).

  In the production method of the present invention, two or more stirring mixers (B) are connected, and the liquid composition is mechanically stirred in an inert gas atmosphere in the first stirring mixer (B). To prepare a froth-like raw material in which an inert gas is finely dispersed in the liquid composition, and the atmosphere of the inert gas in the stirring mixer (B) after the second stirring mixer (B) It is preferable to further include a step of further mechanically stirring the froth-shaped raw material.

According to the production method of the present invention, the raw material is not cured in the stirring mixer (B), has a fine and uniform cell structure, has high mechanical strength, and has little variation in mechanical strength depending on the part. A polyurethane foam can be produced efficiently.
That is, in the premixer (A), the polyol mixture and the isocyanate component are stirred and mixed in the absence of an inert gas, whereby a uniform liquid composition is obtained.
And the dispersion | distribution operation (mechanical stirring with a stirring mixer (B)) of such an inert gas to such a liquid composition (uniform liquid mixture) is compared with the dispersion | distribution operation performed simultaneously with mixing operation of two liquids. Can be carried out at a low rotational speed (for example, about 500 rpm) (the inert gas can be sufficiently finely dispersed), and therefore the shear heat generated during stirring is also low, so urethane in the stirring mixer (B) The reaction does not occur and the raw material is not cured in the stirring mixer (B).
Furthermore, the dispersion operation of the inert gas in the liquid composition (homogeneous mixed solution) is finer (for example, the average particle size is 100 μm or less) and uniform than the dispersion operation performed simultaneously with the mixing operation of the two liquids. A cell structure with a variation (for example, within ± 40 μm) can be formed.

Hereinafter, the present invention will be described in detail.
In the production method of the present invention, the mixing operation of the urethane-forming components (stirring and mixing by the premixer (A)) is different from the stirring operation of the inert gas (mechanical stirring by the stirring and mixing device (B)). It is characterized in that it is implemented separately by the device.

<Stirring and mixing by premixer (A)>
In the production method of the present invention, first, in the premixer (A), a polyol mixture and an isocyanate component are stirred and mixed in the absence of an inert gas to prepare a urethane-forming liquid composition.

FIG. 1 is an explanatory diagram showing a schematic configuration of an example of a premixer (A) used in the present invention.
In FIG. 1, 11 is a casing, 12 is a head block, 13 is a mixing chamber, 14 is a stirring rotor, 15 is a rotating shaft thereof, 16 is a first nozzle, 17 is a second nozzle, and 18 is a raw material discharge port. .
A spiral groove 19 is formed on the outer peripheral surface of the stirring rotor 14. The shape of the outer peripheral surface of the stirring rotor 14 is not particularly limited as long as it improves the stirring efficiency. For example, the entire outer peripheral surface may be formed in an uneven shape.
The capacity of the mixing chamber 13 of the premixer (A) is, for example, 10 to 450 cm ³ .

Mixing of the polyol mixture and the isocyanate component is performed in a mixing chamber 13 partitioned by the casing 12. Specifically, the polyol mixture is supplied from the first nozzle 16, the isocyanate component is supplied from the second nozzle 17, and both are stirred and mixed by rotating the stirring rotor 14.
This mixing operation is performed in the absence of an inert gas. Thereby, even if it is a comparatively low rotation speed (for example, 200-1000 rpm), both can be equalized efficiently. Here, the rotation speed of the stirring rotor 14 is preferably 200 rpm or more, and more preferably 200 to 900 rpm.
When the rotational speed is less than 200 rpm, the polyol mixture and the isocyanate component cannot be sufficiently uniformed.

The stirring and mixing time (raw material residence time) by the premixer (A) is, for example, 0.5 to 10 seconds.
By stirring and mixing with the premixer (A), a urethane-forming liquid composition in which the polyol mixture and the isocyanate component are uniformly mixed is obtained.

<Mechanical stirring by the stirring mixer (B) (Menical floss method)>
The liquid composition thus obtained is supplied to an agitating mixer (B) together with an inert gas. In the agitating mixer (B), the liquid composition (polyol mixture and isocyanate is added under an inert gas atmosphere. Mechanically agitate the mixture).

FIG. 2 is an explanatory diagram showing a schematic configuration of an example of a stirring mixer (B) used in the present invention.
In FIG. 2, 21 is a cylindrical casing, 22 is a mixing chamber, 23 is a stirring rotor, 24 is a rotating shaft thereof, 25 is a raw material supply nozzle, 26 is a gas supply nozzle, and 27 is a raw material discharge port.

  The casing 21 has a double pipe structure (jacket structure) of an outer pipe 211 and an inner pipe 212, and a refrigerant (water) flow path 213 is partitioned by the outer pipe 211 and the inner pipe 212. Reference numeral 214 is a refrigerant inflow nozzle, and 215 is a refrigerant outflow nozzle.

Pins 28 are planted on the outer peripheral surface of the agitating rotor 23 at regular intervals in the length direction of the rotating shaft 24 and extending radially outward from the rotating shaft 24.
On the other hand, on the inner peripheral surface of the casing 21 (inner tube 212), pins 29 are planted along the length direction at regular intervals (same intervals as the pins 28) and extending inward. ing. As shown in FIG. 2, the pin 28 of the stirring rotor 23 and the pin 29 of the casing 21 are alternately provided, whereby an efficient stirring operation (giving a shearing force) can be performed.
The volume of the mixing chamber 22 of the stirring mixer (B) is, for example, 200 to 3000 cm ³ .

As a method of mechanically stirring the liquid composition in an inert gas atmosphere, the liquid composition discharged from the raw material discharge port (18) of the premixer (A) is supplied to the raw material supply of the stirring mixer (B). The liquid composition is mechanically stirred in an inert gas atmosphere by supplying the inert gas (air) from the gas supply nozzle 26 and rotating the stirring rotor 23 while supplying the mixing chamber 22 from the nozzle 25. . At this time, the refrigerant is passed through the flow path 213 to cool the contents in the mixing chamber 22.
Here, the ratio of the liquid composition supplied to the mixing chamber 22 of the stirring mixer (B) and the inert gas is preferably 1: 9 to 1: 0.01 by volume ratio.

Moreover, as rotation speed of the stirring rotor 23, it is set as 200-1500 rpm normally, Preferably it is set as 300-600 rpm.
When the rotational speed is less than 200 rpm, it is difficult to finely disperse the inert gas in the liquid composition. On the other hand, when stirring is performed at a high rotational speed exceeding 1500 rpm, the shear heat generated during stirring is also increased, and the urethanization reaction may proceed.

  In the present invention, the inert gas can be finely dispersed even at a relatively low rotational speed (for example, about 500 rpm), and is generated by performing mechanical stirring at such a low rotational speed. There is no problem that the shearing heat is lowered and the raw material is cured in the stirring mixer by the progress of the urethanization reaction.

By the mechanical stirring of the liquid composition in the atmosphere of the inert gas by the stirring mixer (B), a froth-like raw material in which the inert gas is finely dispersed in the liquid composition is prepared.
The obtained floss-like raw material is discharged from the raw material discharge port 27 and injected into a mold or the like, and is cured in the mold to obtain a molded product made of polyurethane foam.
Here, the stirring time (raw material residence time) by the stirring mixer (B) is, for example, 30 to 90 seconds.
Further, the amount of the floss-like raw material discharged from the raw material discharge port 27 is set to 400 to 5000 cm ³ / min).
The curing time in the mold is not particularly limited, but is preferably within 30 minutes from the viewpoint of production efficiency.

<Other embodiments>
In the present invention, two or more stirring mixers (B) are connected, and in the first stirring mixer (B), the liquid composition obtained in the premixer (A) is treated with an inert gas. To prepare a froth-like raw material in which an inert gas is finely dispersed in the liquid composition by mechanical stirring under the atmosphere of the second stirring mixer (B) and the subsequent stirring mixer (B) Inside, the floss-like raw material can be further mechanically stirred in an inert gas atmosphere.

  For example, two stirring mixers (B) are prepared, the raw material supply nozzle of the first stirring mixer (B) is connected to the raw material discharge port of the preliminary mixer (A), and the first stirring mixer ( By connecting the raw material discharge port of B) and the raw material supply nozzle of the second stirring mixer (B), the floss-like raw material obtained by the first stirring mixer (B) is converted into the second stirring mixer. It transfers to (B) and further mechanical stirring (mechanical flossing operation) of the said froth-shaped raw material is performed in a 2nd stirring mixer (B). Thereby, further refinement | miniaturization and uniformity of the cell structure of the polyurethane foam obtained can be achieved.

The polyurethane foam obtained by the production method of the present invention is a polyurethane foam obtained by a conventionally known mechanical floss method (a polyurethane foam obtained by simultaneously mixing a polyol mixture and an isocyanate component and dispersing an inert gas). A cell structure having a smaller cell diameter (for example, an average particle diameter of 100 μm or less, particularly 80 μm or less) and a small variation in cell diameter (for example, variation within ± 40 μm, particularly within ± 20 μm) can be formed.
And the polyurethane foam which has such a fine and uniform cell structure has high mechanical strength, and also the variation in the mechanical strength by a site | part becomes small.

<Polyol mixture>
The “polyol mixture” used in the production method of the present invention contains a polyol and a catalyst as essential components.

  Examples of the polyol constituting the polyol mixture include polyether polyol, polyester polyol, polycarbonate polyol, polyolefin polyol, acrylic polyol, and low molecular polyol (chain extender).

In particular, it is preferable to use in combination at least one polyol selected from the following (1) and (2) and at least one low-molecular polyol selected from the following (3).
(1) A polyether polyol having an average functional group number of 2.0 to 4.0 and a number average molecular weight of 600 to 10,000.
(2) Polyester polyol having an average functional group number of 2.0 to 4.0 and a number average molecular weight of 600 to 10,000.
(3) A low molecular polyol having 2 to 4 functional groups and a molecular weight of 600 or less.

As the polyether polyol of the above (1), poly (oxyethylene) polyol, poly (oxypropylene) polyol, poly (oxytetramethylene) polyol having a nominal average functional group number of 2.0 to 4.0; 2 to 4 A compound produced by adding a cyclic ether to a compound having an active hydrogen as an initiator.
Examples of the “compound having 2 to 4 active hydrogens” used for the production of the polyether polyol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 2,2-dimethyl-1,3. -Propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, trimethylene glycol, triethylene glycol, tetramethylene glycol, Low molecular weight diols such as hexamethylene glycol, decamethylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, bisphenol A; low molecular weight triols such as glycerin, hexanetriol, trimethylolpropane; pentaerythritol Low molecular weight polyols such as ethylene; aliphatic diamines such as ethylene diamine and propylene diamine; aromatic diamines such as phenylene diamine, tolylene diamine and xylylene diamine diphenylmethane diamine; aromatic amines such as aniline; monoethanol amine, diethanol amine, tri Examples thereof include low molecular amino alcohols such as ethanolamine; tetramethylolcyclohexane; methyl glucoside and the like. These can be used alone or in combination of two or more.
Examples of the “cyclic ether” used for the production of the polyether polyol include ethylene oxide, propylene oxide, butylene oxide, trimethylene oxide, tetrahydrofuran and the like.

As the polyester polyol of (2) above, a compound having two or more hydroxyl groups (polyhydric alcohol) and a compound having two or more carboxyl groups (polybasic acid) are reacted by a known method. Mention may be made of what is produced.
Examples of the “compound having two or more hydroxyl groups (polyhydric alcohol)” used for the production of the polyester polyol include the low molecular weight diol and the low molecular weight triol. These may be used alone or in combination of two or more. Can be used in combination.
Examples of the “compound having two or more carboxyl groups (polybasic acid)” used for the production of polyester polyol include adipic acid, malonic acid, succinic acid, tartaric acid, pimelic acid, sebacic acid, oxalic acid, phthalic acid, Terephthalic acid, isophthalic acid, phthalic anhydride, azelaic acid, trimellitic acid, curtaconic acid, α-hydromuconic acid, β-hydromuconic acid, α-butyl-α-ethylglutaric acid, α, β-diethylsuccinic acid, Hemimellitic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylmethanedicarboxylic acid, 4,4 ′ -Diphenylsulfone dicarboxylic acid, 4,4'-diphenylisopropylidenedicarboxylic acid, 1,2- Examples thereof include phenoxyethane-4 ′, 4 ″ -dicarboxylic acid, anthracene dicarboxylic acid, 2,5-pyridinedicarboxylic acid, diphenylketone dicarboxylic acid, and the like. These may be used alone or in combination of two or more. it can.

The average number of functional groups of the polyols (1) and (2) is 2.0 to 4.0, preferably 2.0 to 3.0.
When the average functional group number of the polyol is less than 2.0, the obtained polyurethane foam does not have high mechanical strength (tensile strength / tear strength). On the other hand, when the average functional group number of the polyol exceeds 4.0, the resulting polyurethane foam does not have a high elastic force (elongation) and exhibits brittleness.

The number average molecular weights of the polyols (1) and (2) are 600 to 10,000, preferably 1,000 to 5,000.
When the number average molecular weight of the polyol is less than 600, the obtained polyurethane foam does not have a high elastic force (tensile strength / elongation). On the other hand, when the number average molecular weight of the polyol exceeds 10,000, the resulting polyurethane foam has high mechanical strength (tensile strength / tear strength) and good compression characteristics (for example, low compression set). Not.

As the low molecular polyol of the above (3), low molecular weight diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, Examples thereof include low molecular weight triols such as glycerin, trimethylolpropane, trimethylolethane, and hexanetriol, and low molecular weight tetraols such as diglycerin.
By using a low molecular polyol in combination, high mechanical strength can be imparted to the resulting polyurethane foam.

  Examples of the “catalyst” constituting the polyol mixture include dibutyltin dilaurate, dioctyltin dilaurate, triethylenediamine (TEDA), tetramethylhexamethylenediamine (TMHMDA), pentamethyldiethylenetriamine (PMDETA), dimethylcyclohexylamine (DMCHA), bisdimethyl Aminoethyl ether (BDMAEA), N-methylimidazole, trimethylaminoethylpiperazine, tripropylamine, triethylamine, N-methylmorpholine, dibutyltin diacetate, tin compounds such as dibutyltin dilaurate, metal complex compounds such as acetylacetone metal salt, reaction Type amine catalyst [for example, dimethylethanolamine (DMEA), N, N, N′-trimethylaminoethylethanol May be mentioned amine, N, N-dimethylaminoethoxy ethanol] and the like.

The polyol mixture may contain components other than the polyol and the catalyst.
Examples of such optional components include foam stabilizers, colorants (pigments / dyes), antioxidants and ultraviolet absorbers.

<Isocyanate component>
As the isocyanate component used in the production method of the present invention, diphenylmethane diisocyanate (MDI), phenylene diisocyanate, 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI) ), Etc., aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate (HDI), alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated TDI, and hydrogenated MDI, obtained by reacting isocyanate and polyol. NCO group-terminated prepolymers can be used, and these can be used alone or in combination of two or more.

  Among these, it is preferable to use an NCO group-terminated prepolymer obtained by reacting an MDI-based isocyanate and a polyol (hereinafter also referred to as “MDI-based NCO group-terminated prepolymer”).

The MDI-based NCO group-terminated prepolymer constituting the urethane-forming composition is obtained by reacting an MDI-based isocyanate and a polyol.
Here, “MDI-based isocyanate” includes MDI (binuclear) and polymeric MDI (polynuclear more than trinuclear).

The ratio of MDI and polymeric MDI used to obtain the MDI-based NCO group-terminated prepolymer is preferably 30 to 100: 70 to 0, and more preferably 40 to 100: 60 to 0.
The MDI used includes isomers of 4,4′-MDI, 2,4′-MDI and 2,2′-MDI, but the ratio of 4,4′-MDI is 70% or more. Is preferred.

  Examples of the polyol used for obtaining the MDI-based NCO group-terminated prepolymer include dihydric alcohols such as polyether glycol, polyester diol, and polycarbonate diol.

  The “polyether glycol” used to obtain the MDI-based NCO group-terminated prepolymer includes polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), polyoxytetramethylene glycol (PTMG); cyclic ether ( For example, ethylene oxide, propylene oxide, trimethylene oxide, tetrahydrofuran) can be converted into an aliphatic diol (eg, ethylene glycol, 1,3-butanediol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,2-propylene glycol, 1 , 3-propylene glycol) as an initiator, polyether polyols produced by ring-opening polymerization can be exemplified, and these can be used alone or in combination of two or more. Kill.

  The “polyester diol” used to obtain the MDI-based NCO group-terminated prepolymer includes poly (ethylene adipate) diol, poly (propylene adipate) diol, poly (ethylene-propylene adipate) diol, poly (butylene adipate) diol, Poly (hexamethylene adipate) diol; copolyester diol produced by polycondensation of ethylene glycol, propylene glycol, adipic acid [eg poly (tetramethylene-ethylene adipate) diol, poly (1,4-butylene-propylene) Adipate) diol, and poly (1,4-butylene-ethylene-propyleneadipate) diol]; caprolactone and / or dicarboxylic acid (eg succinic acid, malonic acid, pimeli, among others) Acid, sebacic acid and suberic acid), a polyester diol produced by polycondensation of low molecular weight diol can be exemplified, which may be used alone or in combination of two or more kinds.

Examples of the “polycarbonate diol” used to obtain an MDI-based NCO group-terminated prepolymer include those obtained by reacting a low molecular weight carbonate with a low molecular weight diol (dealcoholization polycondensation reaction). 1 type (s) or 2 or more types can be used in combination.
Examples of the low molecular weight carbonate used to obtain the polycarbonate diol include dialkyl carbonate (for example, diethyl carbonate), dialkylene carbonate (for example, diethylene carbonate), and diphenyl carbonate.

  The MDI-based NCO group-terminated prepolymer can be prepared by mixing an MDI-based isocyanate and a polyol and heating the mixture to cause a urethanization reaction.

The NCO content of the MDI-based NCO group-terminated prepolymer is preferably 3 to 34% by mass, and more preferably 4 to 16% by mass.
When the NCO content is less than 3% by mass, the viscosity of the prepolymer becomes too high, and the mixing property with the polyol becomes inferior, resulting in a decrease in production efficiency.
On the other hand, when the NCO content exceeds 34% by mass, the storage stability of the prepolymer may be deteriorated.

The average number of functional groups of the MDI-based NCO group-terminated prepolymer is preferably 2.0 to 3.5, and more preferably 2.0 to 2.5.
When the average number of functional groups is less than 2.0, the resulting polyurethane foam does not have good compression characteristics and high mechanical strength.
On the other hand, if the average number of functional groups exceeds 3.5, gelation tends to occur and the stability is poor.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

<Preparation Example 1 (Preparation of polyol mixture)>
85.0 parts by mass of a poly (oxytetramethylene) polyol having a nominal average functional group number of 2,000, a number average molecular weight of 2,000, and a poly (oxypropylene) polyol having a nominal average functional group number of 3, a number average molecular weight of 3,000. Mixing 10.0 parts by weight, 5.0 parts by weight of 1,4-butanediol, 1.0 parts by weight of a modified silicone foam stabilizer, and 0.02 parts by weight of a tin-based catalyst (DOTDL) Thus, a polyol mixture was obtained.

<Preparation Example 2 (Preparation of polyol mixture)>
A polyol mixture was obtained in the same manner as in Preparation Example 1, except that the amount of tin-based catalyst (DOTDL) used was changed to 0.002 parts by mass.

<Synthesis Example 1 (Synthesis of NCO group-terminated prepolymer)>
MDI (mixture of isomers consisting of 2,2′-MDI and 2,4′-MDI is contained in a proportion of 1% by mass or less in a reaction vessel having a capacity of 1000 mL equipped with a stirrer, a cooling tube, a nitrogen introduction tube and a thermometer 100.0 parts by mass of diphenylmethane diisocyanate containing 4,4′-MDI at a ratio of 99% by mass or more, and a poly (oxytetramethylene) polyol having a nominal average functional group number = 2, a number average molecular weight = 2,000 166.2 parts by mass were charged and stirred at 80 ° C. for 4 hours for urethanization reaction to obtain an NCO group-terminated prepolymer having an NCO content of 10.0% by mass.

<Example 1>
The polyol mixture obtained in Preparation Example 1 and the NCO group-terminated prepolymer (isocyanate component) obtained in Synthesis Example 1 were mixed in the molar ratio of the latter isocyanate group to the former hydroxyl group ([NCO] / [OH]). Is supplied to the premixer (A) (mixing chamber capacity = 15 cm ³ ) configured as shown in FIG. 1 at a rate of 1.05, and the stirring rotor is set at 600 rpm in the absence of inert gas. The mixture was stirred and mixed with each other to prepare a urethane-forming liquid composition that was a uniform mixed solution (residence time of raw material in the mixing chamber (actual value) = 3 seconds).

The liquid composition thus obtained has the structure shown in FIG. 2 and is a mixing chamber (capacity = 450 cm ³ ) of the stirring mixer (B) connected to the premixer (A). , While supplying 0.67 parts by volume of dry air (inert gas) to one part by volume of the liquid composition to the mixing chamber and rotating the stirring rotor at 500 rpm while cooling with cold water Thus, the liquid composition was mechanically stirred in an inert gas atmosphere, thereby preparing a floss-like raw material in which the inert gas was finely dispersed in the liquid composition (the raw material in the mixing chamber). Dwell time (actual value) = 60 seconds). The obtained froth-like raw material is discharged from the stirring mixer (B) (discharge amount = 833 cm ³ / min), poured into a mold (260 mm × 220 mm × 30 mm) under normal pressure, and after sealing, the mold is 110 By leaving it in an oven at 0 ° C. for 30 minutes, the injected floss-like raw material was cured to form a polyurethane foam, which was taken out of the mold.

<Example 2>
The stirring mixer (B) connected to the premixer (A) (this is referred to as “first stirring mixer (B1)”), and the stirring mixer (B) (this is referred to as “first stirring mixer (B1)”). No. 2 stirring mixer (B2)), the rotation speed of the stirring rotor of the first stirring mixer (B1) is 400 rpm, and the rotation speed of the stirring rotor of the second stirring mixer (B2) is A urethane-forming liquid composition was prepared in the same manner as in Example 1 except that the speed was 600 rpm, a floss-like raw material was prepared, a polyurethane foam was formed, and this was taken out from the mold.

<Comparative Example 1>
Using a stirring mixer (B) having two raw material supply nozzles, the polyol mixture obtained in Preparation Example 1 and the NCO group-terminated prepolymer (isocyanate component) obtained in Synthesis Example 1 were mixed in a molar ratio ( [NCO] / [OH]) is supplied to the mixing chamber of the stirring mixer (B) from different nozzles without stirring and mixing by the premixer (A) at a ratio of 1.05, By supplying dry air (inert gas) to the mixing chamber and cooling with cold water, the stirring rotor is rotated at 1800 rpm to stir and mix the polyol mixture and the isocyanate component in an inert gas atmosphere. As a result, the raw material was cured in the mixing chamber, and the floss-like raw material could not be discharged.

<Comparative example 2>
A froth-shaped raw material was prepared by stirring and mixing a polyol mixture and an isocyanate component in an inert gas atmosphere in the same manner as in Comparative Example 1 except that the rotation speed of the stirring rotor was changed to 150 rpm. Is discharged from the stirring mixer (B) (discharge amount = 833 cm ³ / min), poured into a mold (260 mm × 220 mm × 30 mm) under normal pressure, and after sealing, the mold is placed in an oven at 110 ° C. By leaving it for a minute, the injected floss-like raw material was cured to form a polyurethane foam, which was taken out of the mold.

<Comparative Example 3>
Instead of the polyol mixture obtained in Preparation Example 1, the polyol mixture obtained in Preparation Example 2 was used, and the rotation speed of the stirring rotor was changed to 500 rpm (molar ratio ([NCO] / [OH]) Except for 1.05), a floss-like raw material was prepared by stirring and mixing a polyol mixture and an isocyanate component in an inert gas atmosphere in the same manner as in Comparative Example 1, and this was mixed with a stirring mixer (B). (Discharge amount = 833 cm ³ / min), injected into a mold (260 mm × 220 mm × 30 mm) under normal pressure, and after sealing, the mold was left in an oven at 110 ° C. It took 720 minutes to stand until the injected froth-shaped raw material was cured. The resulting polyurethane foam was removed from the mold.

  For each of the polyurethane foams obtained in Examples 1-2 and Comparative Examples 2-3, the following items were measured and evaluated. The results are shown in Table 1 below.

(1) Average cell diameter [average value (D _av )]:
By cutting an arbitrary part of the foam and measuring the diameter of a cell existing within a sampling range of area = 2 cm ² at each of the five cut surfaces selected without deviation, the average cell diameter at each cut surface ( D ₁ , D ₂ , D ₃ , D ₄ , D ₅ ) were calculated, and the average value (D _av ) [D _av = (D ₁ + D ₂ + D ₃ + D ₄ + D ₅ ) / 5] was calculated. .

(2) Cell diameter variation:
The difference between the maximum value (D _max ) and the minimum value (D _min ) of all the cell diameters (measurement range = 2 cm ² × 5 = 10 cm ² ) measured in (1) above (D _av ) ( _{Dmax- Dav} ) and ( _{Dmin- Dav} ) were determined.

(3) Density:
The measurement was performed according to JIS Z 8807.

(4) Hardness:
Based on JIS K 6253, the hardness (JIS-A hardness) by a durometer (type A) was measured.

(5) Tensile strength and elongation (average value and variation):
A test piece (dumbbell No. 3) prepared by sampling from five selected parts without bias was subjected to a tensile test at a tensile speed of 500 mm / min in accordance with JIS K 6251, and measured tensile strength and elongation data ( Based on n = 5), respective average values and variations [(maximum value−average value) / average value and (minimum value−average value) / average value] were determined.

(6) Tear strength (average value and variation):
Test specimens (B-type dumbbells) prepared by sampling from five selected parts without bias were subjected to a tear test at a tensile speed of 200 mm / min in accordance with JIS K 6252, and the average value and variation of tear strength [(Maximum value−average value) / average value and (minimum value−average value) / average value] were determined.

  The above results are shown in Table 1 below.

According to the production method of the present invention, it is possible to efficiently produce a polyurethane foam having a fine and uniform cell structure, high mechanical strength, and little variation in mechanical strength depending on the site.
The polyurethane foam obtained by the production method of the present invention is used in the building materials field (vibration isolation materials, seismic isolation materials, packing, etc.), the railway material field (vibration isolation materials, shock absorbers, etc.), and the vehicle field (impact absorbers, etc.). It can be used in various fields such as rubber substitutes (lightweight elastomers, etc.), cosmetics (puffs, etc.), roll materials (OA rolls, etc.), sanitary products (toilet seats, etc.).

It is explanatory drawing which shows schematic structure of an example of the premixer (A) used by this invention. It is explanatory drawing which shows schematic structure of an example of the stirring mixer (B) used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Casing 12 Head block 13 Mixing chamber 14 Stirring rotor 15 Rotating shaft 16 1st nozzle 17 2nd nozzle 18 Raw material discharge port 19 Spiral groove 21 Casing 211 Outer pipe 212 Inner pipe 213 Refrigerant flow path 214 Refrigerant inflow nozzle 215 Refrigerant outflow nozzle 22 Mixing chamber 23 Stirring rotor 24 Rotating shaft 25 Raw material supply nozzle 26 Gas supply nozzle 27 Raw material discharge port 28 Stirring rotor pin 29 Casing pin

Claims (2)

A method for producing a polyurethane foam by a mechanical floss method,
In the premixer (A), a polyol mixture containing a polyol and a catalyst and an isocyanate component are stirred and mixed in the absence of an inert gas to prepare a urethane-forming liquid composition,
By supplying the obtained liquid composition and an inert gas to the stirring mixer (B) and mechanically stirring the liquid composition in an atmosphere of the inert gas in the stirring mixer (B). Preparing a froth-like raw material in which an inert gas is finely dispersed in the liquid composition,
A method for producing a polyurethane foam, comprising a step of discharging the floss-like raw material from a stirring mixer (B). Two or more stirring mixers (B) are connected, and the liquid composition is mechanically stirred in an inert gas atmosphere in the first stirring mixer (B). A froth-like raw material in which an inert gas is finely dispersed is prepared, and the froth-like raw material is placed in an inert gas atmosphere in the stirring mixer (B) after the second stirring mixer (B). Furthermore, the manufacturing method of the polyurethane foam of Claim 1 including the process of stirring mechanically.

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