JP4850574B2 - Method for producing foamed polyurethane - Google Patents

Description

  The present invention relates to a method for producing foamed polyurethane.

Conventionally, polyurethane has been used in various industrial applications (such as shock absorbers, vibration damping materials, seal members, surface protection members for automobiles). In recent years, foamed polyurethane (hereinafter referred to as “foamed polyurethane”) has been used for the above-mentioned applications, and various foaming techniques have been reported (Patent Document 1). . However, such foamed polyurethane is required to be further improved in terms of strength, vibration damping, shock absorption, heat insulation and the like. And about these characteristics, it is thought that refinement | miniaturization of the bubble diameter in foaming polyurethane and the increase in a bubble number density (increase in the number of bubbles per unit volume) are required.
JP 2002-201301 A

  Then, an object of this invention is to provide the manufacturing method of the polyurethane foam which implement | achieves refinement | miniaturization of a bubble diameter and an increase in a bubble number density.

  In order to achieve the above object, the method for producing a foamed polyurethane according to the present invention comprises foaming polyurethane by dissolving bubbles in a composition containing a polyurethane resin under pressure and then generating bubbles in the composition under reduced pressure. In which the composition further contains hydrophobic silica.

  The foamed polyurethane of the present invention is a foamed polyurethane containing a polyurethane resin and silica, wherein the silica is hydrophobic silica, and is a foamed polyurethane obtained by the method for producing a foamed polyurethane of the present invention. is there.

  According to the method for producing foamed polyurethane of the present invention, by using hydrophobic silica in combination with polyurethane resin, it has a finer cell diameter and a higher cell number density than conventional foamed polyurethane ( A polyurethane foam having a large number of bubbles per volume) can be obtained. Since the foamed polyurethane of the present invention has such a fine bubble diameter and high density of bubbles, for example, it can exhibit the effects of high strength, vibration damping, shock absorption and heat insulation. Is possible. The reason why a foamed polyurethane having fine and high-density cells can be obtained by the combined use of hydrophobic silica and polyurethane resin is not clear, but generally, polyurethane resin is composed of fine hard segments and soft segments. It is thought that it contributes to the refinement of the bubbles, and further, the hydrophobic silica serves as a nucleating agent for the bubbles and contributes to the improvement of the bubble number density.

<Hydrophobic silica>
The hydrophobic silica used in the present invention is not particularly limited as long as it exhibits hydrophobicity. In the method for producing foamed polyurethane of the present invention, by using hydrophobic silica as described above, for example, compared to a foam obtained by a production method having the same composition and treatment conditions other than hydrophobic silica, The bubble diameter can be further reduced, and the number of bubbles per unit volume can be increased even if the volume content of the bubbles is the same.

  The silica is not particularly limited, and conventionally known silica can be used. The silica may be natural or synthetic, and may be crystalline silica or amorphous silica. The method for synthesizing silica is not particularly limited, and examples thereof include a high heat method, a dissolved solid method, and a wet chemical method. The high heat method is, for example, a method in which fine silicate particles are generated at a high temperature of 1,000 ° C. or higher, and so-called fumed silica is obtained. As the wet chemical method, for example, by reacting sodium silicate and mineral acid, water in the gel is replaced with an organic solvent to form an organosol, which is subjected to pressure and heat treatment in an autoclave, or sodium silicate and A method of reacting a mineral acid with a salt in an aqueous solution can be mentioned. Among these, synthetic silica is preferable from the viewpoint of safety to the human body, and as a manufacturing method thereof, high-temperature silica is preferable from the viewpoint of particle size control.

  Untreated silica usually exhibits hydrophilicity because silanol groups are distributed on the surface thereof, but hydrophobic silica can be prepared by applying a hydrophobic treatment. The method for the hydrophobic treatment is not particularly limited, and examples thereof include treatment with a coupling agent. Examples of the coupling agent include a titanium coupling agent and a silane coupling agent. Specifically, those that react with hydroxyl groups on the silica surface can be used, and examples thereof include alkyl alkoxysilanes, amino group-containing alkoxysilanes, vinyl group-containing alkoxysilanes, methacryloxy group-containing alkoxysilanes, and the like. The alkoxy group of these coupling agents may be substituted with a chlorine atom. These coupling agents may be used alone or in combination of two or more. The amount of the coupling agent to be treated with respect to 100 parts by weight of silica is preferably 0.01 to 20 parts by weight.

  In the present invention, as a method for treating silica with a coupling agent, various methods known as ordinary coupling agent treatment methods can be employed. For example, as a wet method, a method in which the coupling agent is dissolved in a solvent and silica is mixed and then the solvent is removed. As a dry method, a method in which the coupling agent and silica are dry-mixed with a mixer, or Examples of the vapor phase method include a method of performing a surface treatment with a silane coupling agent and an inert gas at a high temperature, and a method of performing a surface treatment by further introducing water vapor depending on the type of the coupling agent. Alternatively, after treatment with a coupling agent, or simultaneously with treatment with a coupling agent, it may be hydrophobized with a hydrophobization solvent. Preferred examples of the hydrophobization solvent include dimethyldichlorosilane, hexamethylsilazane, aminosilane, alkylsilane, octamethyltetracyclosiloxane, and the like. Among them, hexamethylsilazane is preferred because it can increase the hydrophobicity indicating the degree of hydrophobicity. Is particularly preferred.

The hydrophobicity of the treated hydrophobic silica can be determined by the methanol precipitation test shown below. First, 10.000 g to 10.100 g of ion-exchanged water is weighed in a sample bottle (recorded amount is recorded), and 0.020 g of silica to be evaluated is precisely weighed and put into the ion-exchanged water at 25 ° C. Then, while sufficiently stirring the ion-exchanged water, methanol (special grade, manufactured by Wako Pure Chemical Industries, Ltd.) was dropped therein, and when the silica was not suspended and completely dispersed, the dropping was terminated. Record the amount. The hydrophobicity can be calculated by substituting these results into the following equation. For example, since a hydrophilic substance is easily soluble in water and a hydrophobic substance is easily soluble in methanol, it can be determined that the higher the value, the higher the hydrophobic silica.
Hydrophobicity = [A / (A + B)] × 100
A: Amount of methanol used (g)
B: Amount of ion-exchanged water used (g)

  The hydrophobicity of the hydrophobic silica is not particularly limited, but is preferably 10 to 100, more preferably 20 to 100, and still more preferably 30 to 100. In addition, the hydrophobicity of hydrophobic silica can be adjusted by increasing / decreasing the usage-amount of the silane coupling agent used for a process, for example.

  The shape of the hydrophobic silica is not particularly limited, but is preferably a particle. In consideration of the function as a nucleating agent in the production of a foam, the particle size is preferably relatively small from the viewpoint of increasing the number of additions per unit weight. Moreover, since the apparent particle diameter becomes conversely large due to aggregation of the hydrophobic silica particles, and it can be sufficiently suppressed that the hydrophobic silica particles do not function effectively as a nucleating agent, a particle diameter that does not cause aggregation is preferable. As a specific example, the lower limit of the average particle diameter of the primary particles of the hydrophobic silica is preferably 1 nm or more, more preferably 5 nm or more, still more preferably 10 nm or more, and the upper limit thereof is preferably 10,000 nm or less, more preferably 100 nm. Hereinafter, it is more preferably 50 nm or less. Therefore. The range of the average particle diameter of the primary particles is preferably 1 to 10000 nm, more preferably 5 to 10000 nm, still more preferably 10 to 100 nm, and particularly preferably 10 to 50 nm.

  The average particle diameter of primary particles can be measured by the following method. First, an enlarged photograph of hydrophobic silica is taken with a scanning electron microscope (field emission electron microscope, trade name S-4000; manufactured by Hitachi, Ltd.). And 100 primary particles are selected from the primary particle itself or secondary aggregated primary particle aggregate from the enlarged photograph, and the diameter in the major axis direction and the minor axis direction of each primary particle are measured. The average particle diameter of each primary particle is calculated from those results, and can be obtained by arithmetic average from these calculated values and the magnification of the enlarged photograph. The diameter in the major axis direction means the longest length in the axial direction of each selected primary particle of the enlarged photograph, and the diameter in the minor axis direction means the shortest length in the axial direction in each primary particle. Means.

<Polyurethane resin>
The polyurethane resin used in the present invention is not particularly limited, and examples thereof include conventionally known polyurethane resins having a urethane bond (—NH—COO—), a urea bond, a burette bond, an allophanate bond, and the like in the molecule. Among them, thermoplastic polyurethane (TPU) is preferable from the viewpoint of melt kneading with silica and ease of extrusion and processing. A thermoplastic polyurethane resin has thermoplasticity because it has few crosslinked structures. The method for preparing such a polyurethane resin is not limited in any way, and a compound having an active hydrogen (hereinafter referred to as “compound A”) and an isocyanate group (—N═C═O) (hereinafter referred to as “compound B”). Can be obtained by a conventionally known method. Examples of the thermoplastic polyurethane resin include polyester urethane and polyether urethane. Among these, polyester urethane is preferable from the viewpoint of fine foaming. The polyester-based urethane uses a raw material containing 50% by weight or more of a polyester polyol as the compound A. The thermoplastic polyurethane resin can be obtained by selecting the types and amounts of Compound A and Compound B.

The active hydrogen of the compound A is not particularly limited, and examples thereof include active hydrogen such as a hydroxyl group (—OH) and an amino group (for example, —N (R) H, —NH ₂ ). The compound A is not particularly limited, but a foamed polyurethane having excellent strength, vibration damping properties, shock absorption properties, heat insulation properties, and the like can be obtained. Therefore, the compound A has two or more active hydrogens in one molecule and has a number average molecular weight. Of less than 400 (preferably, 150 or less) (hereinafter referred to as “compound A-1”), two or more active hydrogens in one molecule, and a number average molecular weight of 400 or more and less than 20,000 ( Preferably, the compound (hereinafter referred to as “Compound A-2”) of 800 or more and less than 10,000 is preferable.

  Examples of the compound A-1 include a crosslinking agent, a chain extender, and the like, and specific examples include ethylene glycol, propylene glycol, and 1,4-butanediol, Those oligomers (polytetramethylene glycol (PTMG) etc.) etc. are mention | raise | lifted. On the other hand, examples of the compound A-2 include polyols such as polyester polyols, polycarbonate polyols, and polyether polyols. Among them, polyester polyols and polycarbonate polyols that are polyols containing polar groups such as carbonyl groups are preferable. Polyols are preferred. Such a polyol can further improve the affinity with a high-pressure gas or a supercritical fluid in a foaming process described later. Compound A may further contain other reaction components and additives as long as the reaction with compound B is not hindered.

  The compound B is not particularly limited as long as it is a compound having an isocyanate group, but so-called isocyanate can be used, and examples thereof include diphenylmethane diisocyanate (MDI), tolylene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

  Specific product names include “Elastollan” manufactured by BASF Japan, “Bandex” manufactured by DIC Bayer Polymer, “Edform” manufactured by Kao, and the like.

  In the method for producing a foamed polyurethane according to the present invention, the type of the polyurethane resin is not limited at all. However, by selecting the type of the polyurethane resin, not only the above-described effects due to the use of the hydrophobic silica but also the foamed polyurethane can be obtained. Characteristics can be changed. That is, when a foamed polyurethane is produced by the production method of the present invention with the same type of hydrophobic silica, composition other than the polyurethane resin, processing conditions, etc., for example, a polyurethane resin having a polyester polyol as compound A is used. Thus, the bubble diameter can be made smaller than that of the polyurethane resin containing the polyether polyol as the compound A, and the number of bubbles contained per unit volume can be increased even if the volume content of the bubbles is the same. be able to. From this point, it is preferable to use 50% by weight or more of the polyester polyol in the compound A.

<Polyurethane resin composition>
The polyurethane resin composition used as the raw material for the foamed polyurethane is a mixture containing the polyurethane resin and the hydrophobic silica. The foamed polyurethane of the present invention can be produced by subjecting this to a foaming treatment described later.

  The content of the polyurethane resin in the composition is not particularly limited, but is preferably 60% by weight or more, more preferably 80% by weight or more from the viewpoint of maintaining the properties specific to the polyurethane resin. In addition, the amount of hydrophobic silica in the composition is preferably 0.1 to 50 parts by weight with respect to 100 parts by weight of the polyurethane resin, and a foamed polyurethane having further excellent vibration damping properties, shock absorption properties and heat insulation properties can be obtained. More preferably, it is 0.3-40 weight part, More preferably, it is 0.5-20 weight part.

  This polyurethane resin composition is preferably melt-kneaded with a polyurethane resin and hydrophobic silica using a twin screw extruder or the like prior to the foaming treatment described below. In addition to polyurethane resin and hydrophobic silica, this polyurethane resin composition includes plasticizers, activators, antistatic agents, antifogging agents, antioxidants, weathering agents, colorants, organic or inorganic fillers, etc. The additive may be included.

<Method for producing foamed polyurethane>
In the method for producing a foamed polyurethane according to the present invention, the polyurethane resin composition to be foamed may contain the hydrophobic silica, and other processes and conditions are not limited. For example, a method of manufacturing a polyurethane resin after previously mixing a polyurethane raw material and silica, a method of mixing silica after manufacturing a polyurethane resin, and the like can be mentioned. An example of the production method of the present invention will be given below, but the present invention is not limited to this.

  First, a polyurethane resin composition as described above is prepared, pelletized, and molded into a desired shape by an injection molding machine or the like. And after melt | dissolving gas in this shape | molded polyurethane resin composition under pressure, it is pressure-reduced and a foam (foaming polyurethane) can be obtained by generating a bubble from the said composition. Thus, when the composition is placed under pressure, the gas is dissolved in the composition. Further, when the composition is further put under reduced pressure, the gas dissolved in the composition is generated again to generate bubbles, whereby the form of the composition becomes foamed. Here, under reduced pressure is a pressure that is lower than the pressure at which a gas is dissolved under pressure and at which the dissolved gas is generated again. For example, the reduced pressure includes normal pressure.

  The pressure condition under pressure is not particularly limited and can be appropriately determined according to the type and temperature of the gas. In particular, since the affinity between the gas species (gas species) and the polyurethane resin can be improved, the gas is supercritical. It is preferable to be in a state. As a specific example, a range of 1 to 40 MPa is preferable. The “supercritical state” generally means a state where the pressure is equal to or higher than the critical pressure and the temperature is equal to or higher than the critical temperature. The supercritical state is a subordinate concept under pressure.

  The gas species is not particularly limited, but carbon dioxide and nitrogen are preferred, and carbon dioxide is particularly preferred because of its high affinity (diffusion rate) to the polyurethane resin. When the gas species is carbon dioxide, if the pressure condition is not less than the critical pressure of carbon dioxide (7.38 MPa) and the temperature condition is not less than the critical temperature (31.1 ° C.), it becomes a supercritical state. preferable. More specifically, the temperature of carbon dioxide is preferably 40 to 180 ° C. and the pressure is preferably 7.38 to 40 MPa, more preferably 80 to 170 ° C. and the pressure is 10 to 30 MPa. When the gaseous species is nitrogen gas, the critical pressure is 3.40 MPa and the critical temperature is −147 ° C., specifically, the temperature range is −140 ° C. to 180 ° C., and the pressure range is 3. 4-30 MPa is preferable.

  In the production method of the present invention, the combined use of hydrophobic silica and polyurethane resin makes it possible to make the foam diameter of the foamed polyurethane smaller and to increase the number of bubbles per unit volume. The method for controlling the cell diameter of the obtained polyurethane foam and the number of cells is not particularly limited, but can be performed as described below.

(Polyurethane polyurethane of the present invention)
The foamed polyurethane of the present invention is characterized by containing a polyurethane resin and hydrophobic silica, and can be obtained, for example, by the production method as described above. Since the foamed polyurethane of the present invention is produced using hydrophobic silica as described above, it is a production method (so-called conventional method) having the same composition and treatment conditions except that the hydrophobic silica is not used. Compared to the obtained foam, the bubble diameter is smaller, and even if the volume content of bubbles is the same, the number of bubbles contained per unit volume is larger. For this reason, according to the polyurethane foam of this invention, the following remarkable effects are also realizable. That is, the foamed polyurethane of the present invention is more suppressed in strength reduction and has higher shock absorption and vibration damping properties than conventional non-foamed polyurethane and foamed polyurethane having relatively larger cells than the present invention. It is understood that For this reason, it is useful as an impact absorbing member or a damping member. In addition, it is lighter because it contains more bubbles, and because the bubbles are very fine and the shape is almost spherical, it exhibits optical properties and heat insulation performance that could not be realized with conventional polyurethane foam. Is also possible. In the foamed polyurethane of the present invention, “bubbles” are also referred to as “cells” in the technical field. The foam is usually composed of air bubbles that are hollow and a diaphragm that partitions them, but the air bubbles in the present invention may be only air bubbles that are completely partitioned by the film, or air bubbles in which a plurality of air bubbles communicate with each other. May be included.

  The average cell diameter of the cells in the foamed polyurethane of the present invention is not particularly limited, but is preferably 1.5 μm or less, more preferably, since effects such as strength, vibration damping properties, shock absorption properties and heat insulation properties can be expected. It is 1 μm or less, more preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. In addition, the foamed polyurethane with fine bubbles as in the present invention, for example, a foamed polyurethane having an average cell diameter of 200 nm or less can pass light, and therefore, it is excellent in transparency. Applicable. In addition, since the foamed polyurethane of this invention can form a fine bubble diameter easily compared with the conventional method with the manufacturing method as mentioned above, it is also possible to implement | achieve the above bubble diameter.

  The average bubble diameter can be measured by the following method. First, an enlarged photo of polyurethane foam is taken with a scanning electron microscope (field emission electron microscope, trade name S-4000; manufactured by Hitachi, Ltd.). Then, 100 bubbles are selected from the enlarged photograph, and the diameter in the major axis direction and the diameter in the minor axis direction are measured. From the results, the average diameter of each bubble is calculated, and the average bubble diameter can be obtained by arithmetic average from these calculated values and the magnification of the enlarged photograph. The major axis diameter means the longest axial length of each selected bubble in the enlarged photograph, and the minor axis diameter means the shortest axial length of each bubble. means. The bubble diameter can be reduced by increasing the hydrophobicity of the silica, and the number of bubbles can be increased by increasing the number of silica as the nucleating agent.

The volume content of the bubbles in the polyurethane foam of the present invention is preferably 1% or more, more preferably 5% or more, and still more preferably, since effects such as strength, vibration damping, shock absorption and heat insulation can be expected. Is 10% or more, particularly preferably 15% or more. The upper limit is not particularly limited, but is preferably 100% or less, more preferably 50% or less , and further preferably 30% or less . This volume content can be measured by the following method.

A sample of a polyurethane resin composition before foaming treatment and a foamed polyurethane after foaming treatment having the same composition is used. First, after measuring the weight of each sample, the volume which increases by immersing each said sample in water is measured. These results are substituted into the following formula (1) to determine the density (g / cm ³ ) of each sample. Furthermore, these results are substituted into the following formula (2) to calculate the volume content of bubbles.
Density = weight / increased volume (1)
Bubble volume content (%) = [1- (ρf / ρp)] × 100 (2)
ρf: density of foam after foaming treatment
ρp: density of the sheet before foaming

The bubble number density is preferably 1 × 10 ¹⁰ / cm ³ or more, more preferably 1 × 10 ¹¹ / cm ³ , since effects such as strength, vibration damping, shock absorption, and heat insulation can be expected. cm ³ or more, more preferably 1 × 10 ¹² pieces / cm ³ or more, particularly preferably 1 × 10 ¹³ pieces / cm ³ or more. This bubble number density is calculated by the following method.

The cell number density is an index representing how many cells are contained per 1 cm ^{3 of} polyurethane foam. This is calculated from the density of the polyurethane resin composition before the foaming treatment and the density and average cell diameter of the foamed polyurethane after the foaming treatment. This calculation method is described in NanoLetts. 2001; 1: 503.
Bubble number density (pieces / cm ³ ) = (X / 100) / [(4/3) π × [(d / 2) × 10 ⁻⁴ ] ³ ]
X: Gas volume content (%)
d: Average bubble diameter (μm)

The storage elastic modulus (for example, the frequency of 10 Hz, 25 ° C.) of the polyurethane foam of the present invention is preferably 1 × 10 ⁸ to 1 since effects such as strength, vibration damping, shock absorption and heat insulation can be expected. It is * 10 < ⁹ > Pa, More preferably, it is 5 * 10 < ⁸ > -1 * 10 < ⁹ > Pa. This storage elastic modulus is measured by the following method.

  About foaming polyurethane, using a dynamic viscoelasticity measuring apparatus (product name DVA-250, manufactured by IT Measurement Control Co., Ltd.), a temperature range of −20 ° C. to 180 ° C. under a condition of a frequency of 10 Hz and a heating rate of 2 ° C./min. Measure the storage modulus.

  The foamed polyurethane of the present invention is excellent in strength, vibration damping properties, shock absorption properties and heat insulation properties, and therefore can be suitably used for applications such as heat insulation films and protective films.

  As the polyurethane resin, a thermoplastic polyurethane A (manufactured by BASF Japan, trade name: Elastollan C74D; ester urethane) was previously allowed to stand in a dry air atmosphere at 100 ° C. for 15 hours and dried.

  As fillers such as hydrophobic silica, those shown in the following table were used as they were. The fillers a to e are products already treated with the following surface treatment agent. As for g, an ion exchange-treated product was purchased.

(Hydrophobicity: methanol precipitation test)
The hydrophobicity of the filler was measured by the methanol precipitation test shown below. First, 10.000 g to 10.100 g of ion-exchanged water is weighed in a sample bottle (recorded amount is recorded), and 0.020 g of silica to be evaluated is precisely weighed and put into the ion-exchanged water. Then, while sufficiently stirring this, methanol (special grade, manufactured by Wako Pure Chemical Industries, Ltd.) was dropped into this, and when the silica was completely dispersed without floating, the dropping was terminated and the amount of the dropped methanol was recorded. did. The hydrophobicity was determined by substituting these results into the following equation. In addition, it can be judged that it is a silica with high hydrophobicity, so that the value of hydrophobicity is large.
Hydrophobicity = [A / (A + B)] × 100
A: Amount of methanol used (g)
B: Amount of ion-exchanged water used (g)

  Each thermoplastic polyurethane and each filler were mixed with a twin-screw extruder (trade name HK-25D (41D), manufactured by Parker Corporation, screw diameter φ25, screw rotation speed 200 rpm, pelletizer so as to have the composition shown in Table 2 below. The mixture was kneaded using a speed of 8 m / min L / D = 41 and a set temperature of 220 ° C. to form a pellet. Thereafter, the pellets were injected into a mold (120 mm × 60 mm × 2 mm, set temperature 25 ° C.) using an injection molding machine (trade name F-40, manufactured by Crockner Co., Ltd., cylinder temperature 220 ° C.). After taking out from the mold, it was left in a dry air atmosphere at 120 ° C. for 3 hours to prepare a thermoplastic urethane sheet.

The obtained sheet was put into an autoclave having an internal volume of 1000 cm ³ and impregnated with carbon dioxide in a supercritical state for 6 hours under the conditions of a predetermined temperature (temperature shown in Table 3 below) and 20 MPa. Then, foaming was performed by releasing the pressure in the autoclave at a pressure release rate of 2 MPa / second to obtain a foam. The characteristic results for these foams are shown in Table 3 below. In Table 3 below, Examples 1 to 7 are sheet Nos. To which hydrophobic silica was added. 1 to 7 is a foamed body, and Comparative Example 1 is a sheet No. 7, Comparative Example 2 is a sheet no. No. 8 foam, Comparative Example 3 is a sheet No. 1 with hydrophilic silica added as a filler. No. 9 foam, Comparative Example 4 is a sheet No. with montmorillonite added as a filler. 10 foams. In Comparative Example 5, a sheet was produced and a foam was produced using the sheet in the same manner as described above except that PMMA (polymethyl methacrylate) was used as the resin and no filler was used. In Comparative Example 6, a sheet and a foam using the sheet were prepared in the same manner as described above except that PC (polycarbonate) was used as the resin and no filler was used.

(1) Storage elastic modulus Using a dynamic viscoelasticity measuring apparatus (product name DVA-250, manufactured by IT Measurement Control Co., Ltd.) The storage elastic modulus in the temperature region was measured. The results at 25 ° C. are shown in Table 3 below.

(2) Average cell diameter The foam is sliced, a photograph of its fractured section is taken, and the photograph is subjected to image processing using a scanning electron microscope (trade name S-4000, manufactured by Hitachi, Ltd.), as described above. Thus, the average bubble diameter was determined.

(3) Bubble volume content (%)
A thermoplastic urethane sheet before foaming treatment having the same composition and a foam after foaming treatment were used as samples. After measuring the weight of each sample, the volume which increases by immersing each said sample in water was measured. These results were substituted into the following formula (1) to determine the density (g / cm ³ ) of each sample. Furthermore, these results were substituted into the following formula (2) to calculate the volume content of bubbles.
Density = weight / increased volume (1)
Bubble volume content (%) = [1- (ρf / ρp)] × 100 (2)
ρf: density of foam after foaming treatment
ρp: density of the sheet before foaming

(4) Bubble number density (pieces / cm ³ )
This is an index representing how many bubbles are contained per 1 cm ^{3 of} foam. This is calculated from the density of the sheet before the foaming treatment, the density of the foam after the foaming treatment, and the average cell diameter. In this calculation method, the bubble number density was calculated from the following equation using bubbles as spheres.
Bubble number density (pieces / cm ³ ) = (X / 100) / [(4/3) π × [(d / 2) × 10 ⁻⁴ ] ³ ]
X: Gas volume content (%)
d: Average bubble diameter (μm)

(5) Tensile property deterioration rate A tensile test was performed using AUTOGRAPH AGS-500G manufactured by Shimadzu Corporation. The foam after the foaming treatment was punched with a No. 2 dumbbell to prepare a punched sample, and the test was performed at a pulling speed of 500 mm / min. The ratio of the breaking strength obtained in the test is shown as a reduction rate (%).

(6) Bending resistance The obtained foam was used as a sample, this was folded in two, and the presence or absence of cracks was visually evaluated. The case where a crack occurred was marked as x, and the case where no crack occurred was marked as o.

  As shown in Table 3, Comparative Example 1 without foaming, Comparative Example 2 with no silica added, Comparative Example 3 with hydrophilic silica, Comparative Example 4 with montmorillonite instead of silica, and other resins used As compared with Comparative Examples 5 and 6, the foamed polyurethane of each Example using hydrophobic silica had a result that the average cell diameter was extremely small and the cell number density (the number of cells per volume) was large. . For this reason, the rate of decrease in tensile properties could be reduced, and the bending resistance was excellent. Further, by comparing Examples 1 to 7 and Comparative Examples 2 and 3 using the same thermoplastic polyurethane, by changing the hydrophobicity (hydrophobicity) of the silica used, the average cell diameter and the cell It can be seen that the number density can be adjusted as appropriate. Furthermore, the following can be seen by comparing the examples. Examples 1 to 3 are the result of the addition of hydrophobic silica being the same and the hydrophobicity of silica being different, but comparison of these shows that the higher the hydrophobicity, the higher the bubble number density. Examples 3 to 5 are the results of the same type of surface treatment agent for silane and different filler particle sizes (hydrophobicity and foaming temperature are almost the same). It can be seen that the smaller the diameter, the higher the bubble number density. In particular, according to the conditions of Example 7, an excellent foam having an extremely high cell number density could be obtained.

  As described above, according to the method for producing a foamed polyurethane of the present invention, the use of hydrophobic silica in combination with the polyurethane resin has a finer bubble diameter than the foamed polyurethane according to the conventional method, and the bubbles. A foamed polyurethane having a high number density (a large number of bubbles per volume) can be obtained. And since the foamed polyurethane of the present invention has such a fine bubble diameter and high density of bubbles, it can exhibit the effects of high strength, vibration damping, shock absorption and heat insulation. is there. Although the reason why a foamed polyurethane having fine and high-density cells can be obtained by the combined use of hydrophobic silica and polyurethane resin is not clear, polyurethane resin contributes to the miniaturization of cells, and hydrophobic silica is a cell nucleating agent. Thus, it is considered that it contributes to the improvement of the bubble number density.

Claims (6)

A method for producing foamed polyurethane by dissolving a gas in a polyurethane resin composition containing a polyurethane resin under a pressure of 1 to 40 MPa, and then generating bubbles in the composition under a reduced pressure, the composition comprising: And a method for producing foamed polyurethane, further comprising hydrophobic silica.   The production of foamed polyurethane according to claim 1, wherein the addition ratio of the hydrophobic silica is in the range of 0.1 to 50 parts by weight with respect to 100 parts by weight of the polyurethane resin.   The manufacturing method of the polyurethane foam of Claim 1 or 2 whose said polyurethane resin is polyester-type urethane.   The manufacturing method of the polyurethane foam as described in any one of Claims 1-3 whose said hydrophobic silica is the fumed silica hydrophobized. The foamed polyurethane obtained by the production method according to any one of claims 1 to 4, wherein the average cell diameter is 1.5 µm or less and the volume content of the gas is 1% or more . The foamed polyurethane according to claim 5 , wherein the storage elastic modulus is 1 × 10 ⁸ to 1 × 10 ⁹ Pa under conditions of a measurement temperature of 25 ° C. and a measurement frequency of 10 Hz.