JP7759745B2 - Polyurethane foam, polyol composition, and method for producing polyurethane foam - Google Patents

Description

The present invention relates to a polyurethane foam with good thermal conductivity, a polyol composition, and a method for producing a polyurethane foam.

Traditionally, polyurethane foam has been used as a vibration-damping and soundproofing material in office equipment and electrical appliances. For example, polyurethane foam is placed inside or on the exterior of the housing of PC hard disk drives and electric motors in electric vehicles to improve vibration-damping and soundproofing. Furthermore, because hard disk drives and electric motors can become very hot due to heat generation during operation, polyurethane foam is required to have good thermal conductivity in order to dissipate heat to the outside.

One method for imparting thermal conductivity to polyurethane foam is to blend a thermally conductive filler such as graphite into the polyurethane foam raw material.
Another method for producing polyurethane foam involves pouring (injecting) a foamed urethane resin raw material containing magnetic particles bonded to the surface of thermally conductive particles with a binder into the cavity of a foaming mold, and then foaming the resin while applying a magnetic field so that the magnetic flux density within the cavity is approximately uniform (Patent Document 1).

Patent No. 5829279

However, depending on the type of thermally conductive filler, acidic substances may leak from the thermally conductive filler during stirring and mixing of polyurethane foam raw materials containing the thermally conductive filler, causing the polyurethane foam raw materials to become acidic. As a result, the polyurethane foam raw materials may experience a decrease in reactivity (deactivation), making it impossible to obtain a polyurethane foam with a good foaming state.
The present invention has been made in view of the above points, and an object of the present invention is to provide a thermally conductive polyurethane foam that is in a good foamed state.

The first aspect is a polyurethane foam obtained from a polyurethane foam raw material containing a polyol composition containing a polyol and a thermally conductive filler, and a polyisocyanate, characterized in that the thermally conductive filler is a combination of a carbon-based filler and a metal-based filler.

The second aspect is the first aspect, characterized in that the content of the carbon-based filler is 20 to 100 parts by weight per 80 parts by weight of the polyol, and the content of the metal-based filler is 10 to 50 parts by weight per 80 parts by weight of the polyol.

The third aspect is characterized in that, in the first or second aspect, the polyol composition contains a monool.

The fourth aspect is a polyol composition containing a polyol and a thermally conductive filler, characterized in that the thermally conductive filler is a carbon-based filler selected from flake graphite and expanded graphite, in combination with a metal-based filler.

The fifth aspect is a method for producing polyurethane foam, which comprises stirring the polyol composition of the fourth aspect, mixing it with polyisocyanate, and foaming it.

In the present invention, the carbon-based filler contained in the polyol composition is selected from flake graphite and expanded graphite, which makes it less likely to experience a decrease in reaction activity (deactivation) and allows for the production of a thermally conductive polyurethane foam with a good foaming state.

1 is a table showing the formulations and raw material properties of polyurethane foam raw materials in Examples 1, 2, 3, and 4 and Comparative Examples 1 and 2, and the results of measuring the physical properties of molded products molded with a mold. 1 is a table showing the results of measuring the raw material properties and the physical properties of the polyurethane foams obtained by varying the circulation time using a low-pressure injector for Example 1 and Comparative Example 1.

The following describes an embodiment of the present invention. The polyurethane foam of the present invention is obtained from a polyurethane foam raw material containing a polyol composition containing a polyol and a thermally conductive filler, and a polyisocyanate.

The polyol may be a polyhydric alcohol or a polyol to which an alkylene oxide such as ethylene oxide (EO) or propylene oxide (PO) has been added. Polyols used for polyurethane foams can be used. For example, polyether polyols, polyester polyols, polyether ester polyols, etc. may be used, and one or more of these may be used.

Examples of polyether polyols include polyether polyols obtained by adding alkylene oxides such as ethylene oxide (EO) and propylene oxide (PO) to polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, glycerin, pentaerythritol, trimethylolpropane, sorbitol, and sucrose.

Examples of polyester polyols include polyester polyols obtained by polycondensation of an aliphatic carboxylic acid such as malonic acid, succinic acid, or adipic acid, or an aromatic carboxylic acid such as phthalic acid, and an aliphatic glycol such as ethylene glycol, diethylene glycol, or propylene glycol.
Examples of polyetherester polyols include those obtained by reacting the above-mentioned polyether polyols with polybasic acids to form polyesters, and those having both polyether and polyester segments in one molecule.

It is preferable to use one or more polyols with a hydroxyl value (OHV) of 10 to 280 mg KOH/g, a functionality of 2 to 4, and a weight-average molecular weight of 800 to 10,000 (more preferably 2,000 to 7,000).

The thermally conductive filler is a combination of a carbon-based filler and a metal-based filler.
Examples of the carbon-based filler include conductive carbon compounds such as graphite and graphene, such as plate-like graphite, flake graphite, granular graphite, irregularly shaped graphite, crushed graphite, flaky graphite, and expanded graphite. More preferably, one or more selected from flake graphite, flaky graphite, and expanded graphite are used.
Flake graphite is composed of many overlapping plate-shaped (graphene) structures with hexagonal crystals.
On the other hand, expanded graphite can be obtained by chemically treating graphite such as flake graphite with sulfuric acid or the like to obtain expandable graphite, which can then be expanded by heat treatment and then refined.

The carbonaceous filler preferably has the average particle size (D50) shown in (1) below or the particle size distribution shown in (2).
(1) Preferred range of average particle size (D50) The average particle size (D50) is preferably 30 μm or more, more preferably 40 μm or more, even more preferably 90 μm or more, and even more preferably 150 μm or more. On the other hand, the upper limit is preferably 400 μm or less, and more preferably less than 300 μm.

(2) Preferred range by sieve The particle classification was measured in accordance with "JIS K0069 Sieving test method for chemical products."
The sieve residue is determined by stacking multiple sieves on a tray, with the sieve with the largest openings on top, and inserting the sample into the top sieve to perform a sieving test.The mass of the sample above and below each sieve is then measured to determine the sieve residue.
The sieve residue corresponding to the particle size range is determined, and the sieve residue is determined in descending order of particle size.
Specifically, the sieves are stacked on a tray with the smaller mesh size at the bottom and the larger mesh size at the top. Next, the sample is placed on the top sieve and the lid is placed on it. After that, the sieve is vibrated with a vibrator and sieved. After sieving is complete, the mass of the over-sieved and under-sieved particles at each sieve is measured to determine the sieve residue (particle size distribution).

After determining the sieve residue in descending order of particle size range, the sieve residues are integrated to determine the integrated percentage corresponding to each sieve opening.
The sieve opening corresponding to a cumulative distribution of 50 wt % (particle diameter of cumulative distribution 50 wt %) is treated as the average particle diameter, for example, the average particle diameter (D50).
That is, sieves with a plurality of openings were prepared, and attention was paid to a sieve opening corresponding to 50 wt% or more of the cumulative distribution (particle diameter of 50 wt% or more of the cumulative distribution) and a sieve opening coarser than that sieve (particle diameter of less than 50 wt% of the cumulative distribution). That is, the cumulative distribution 50 wt% particle diameter corresponding to the average particle diameter corresponds to a size between the particle diameter of 50 wt% or more of the cumulative distribution and the particle diameter of less than 50 wt% of the cumulative distribution. Therefore, the cumulative distribution 50 wt% particle diameter corresponding to the average particle diameter exists in the particle diameter range from 50 wt% or more of the cumulative distribution to less than 50 wt% of the cumulative distribution.
The particle size at 50 wt % cumulative distribution, which corresponds to the average particle size of the carbon-based filler, is preferably in the following range.
Of the sieves with multiple openings, the smaller sieve opening has a particle size (opening) corresponding to a cumulative distribution of 50 wt % or more of preferably 45 μm or more, more preferably 90 μm or more, and even more preferably 180 μm or more.
On the other hand, among sieves with multiple openings, the opening of the larger sieve is preferably 500 μm or less, more preferably 355 μm or less, and even more preferably 300 μm, in terms of particle size (opening) corresponding to an integrated distribution of less than 50 wt %.

If the carbon-based filler has the average particle size (D50) shown in (1) above or the particle size distribution shown in (2), the carbon-based filler is densely dispersed within the polyurethane foam, thereby enabling the thermal conductivity to be further increased.
The content of the carbon-based filler is 20 to 100 parts by weight, more preferably 30 to 100 parts by weight, and even more preferably 50 to 100 parts by weight, per 80 parts by weight of the polyol. If the amount of carbon-based filler is too small, the thermal conductivity of the polyurethane foam will be low, and conversely, if it is too large, the foaming of the polyurethane foam will be poor.

Examples of metal-based fillers include conductive metal powders obtained by finely grinding various metals, various ferrites such as soft magnetic ferrite, metal oxides such as zinc oxide, titanium oxide, aluminum oxide, magnesium oxide, and silicon oxide, metal nitrides such as boron nitride, aluminum nitride, and silicon nitride, metal carbides such as silicon carbide, and metal carbonates such as magnesium carbonate.
More preferred examples include alumina, magnesium oxide, metallic silicon, boron nitride, etc. These may be used alone or in combination.
The particle size of the metal filler is preferably 5 to 25 μm.
The content of the metal filler is 10 to 50 parts by weight, more preferably 15 to 30 parts by weight, per 80 parts by weight of polyol. If the amount of metal filler is too small, the thermal conductivity of the polyurethane foam will be low, and conversely, if it is too large, the foaming of the polyurethane foam will be poor.

The polyol composition contains a catalyst and a blowing agent.
The catalyst may be any known catalyst for polyurethane foams. Examples include amine catalysts such as triethylamine, triethylenediamine, diethanolamine, dimethylaminomorpholine, N-ethylmorpholine, and tetramethylguanidine; tin catalysts such as stannous octoate and dibutyltin dilaurate; and metal catalysts (also called organometallic catalysts) such as phenylmercury propionate and lead octenate. The amount of catalyst is preferably about 0.5 to 2.0 parts by weight per 80 parts by weight of polyol.

In terms of mixing the raw materials, it is preferable to use water as the blowing agent. The amount of blowing agent (water) is preferably 0.5 to 2.0 parts by weight per 80 parts by weight of polyol. If the amount of blowing agent (water) is less than 0.5 parts by weight, the mixing and reactivity of the raw materials will be poor, making molding defects more likely. On the other hand, if it exceeds 2.0 parts by weight, the amount of foaming gas will increase, causing cracks inside the polyurethane foam and reducing thermal conductivity.

Preferred components contained in the polyol composition include a monool and a dispersant.
The monool is a monohydric alcohol having a hydroxyl value (OHV) of 10 to 50 mgKOH/g and a weight average molecular weight of 300 to 3500, more preferably 400 to 1000, and can be used singly or in combination.
The amount of monool to be blended is preferably 5 to 20 parts by weight per 80 parts by weight of polyol.
By blending a monol in the polyol composition, an increase in viscosity of the polyurethane foam raw material due to the blending of the thermally conductive filler can be suppressed, and poor stirring and mixing of the polyurethane foam raw material can be made less likely to occur.

Examples of dispersants include urethane-based dispersants, polyethyleneimine-based dispersants, polyoxyethylene alkyl ether-based dispersants, polyoxyethylene glycol diester-based dispersants, and sorbitan aliphatic ester-based dispersants. The dispersants may be used alone or in combination. When a dispersant is used, it is preferably used in an amount of about 1.0 to 3.0 parts by weight per 80 parts by weight of the polyol.
By incorporating a dispersant into the polyol composition, an increase in viscosity of the polyurethane foam raw material due to the incorporation of the thermally conductive filler can be suppressed, and poor stirring and mixing of the polyurethane foam raw material can be made less likely to occur.

The polyol composition may contain other additives such as a foam stabilizer, a foam opener, a colorant, and a flame retardant.
As the foam stabilizer, any foam stabilizer known for polyurethane foams can be used, including, for example, silicone-based foam stabilizers, fluorine-based foam stabilizers, and known surfactants.

Examples of the cell breaker include hydrocarbon-based, ester-based, and silicone-based agents, and two or more of these may be used in combination.
Examples of hydrocarbon-based cell openers include oils such as polybutene. Examples of ester-based cell openers include dimer acid diesters. Examples of silicone-based cell openers include cyclopentasiloxane.

As the colorant, a colorant such as a carbon pigment can be used depending on the intended use of the polyurethane foam.
The flame retardant may be a powder flame retardant such as a phosphorus-based flame retardant or ammonium polyphosphate, or a liquid flame retardant such as a phosphate ester-based flame retardant, and either one or both may be used in combination.

Polyisocyanates that can be used include aliphatic or aromatic polyisocyanates containing two or more isocyanate groups, mixtures of these, and modified polyisocyanates obtained by modifying these. Examples of aliphatic polyisocyanates include hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexamethane diisocyanate. Examples of aromatic polyisocyanates include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate, xylylene diisocyanate, and polymeric MDI (crude MDI). Prepolymers can also be used.

The isocyanate index (INDEX) is preferably 75 to 120. The isocyanate index is calculated as follows: [(isocyanate equivalents in polyurethane foam raw materials / active hydrogen equivalents in polyurethane foam raw materials) x 100].

Polyurethane foam is produced by stirring a polyol composition, mixing it with polyisocyanate, and foaming it. One type of equipment used in the production of polyurethane foam is an injection machine. In an injection machine, liquid A, which contains the polyol composition, is circulated and stirred separately from liquid B, which contains polyisocyanate. During foaming, liquid A and B are supplied to a mixing head, mixed, and then discharged from the nozzle of the mixing head to produce foam. There are two types of injection machines: high-pressure injection machines, which mix liquid A and B supplied to a mixing head by colliding them under high pressure, and low-pressure injection machines, which mechanically mix liquid A and B supplied to a mixing head using a stirring blade or similar.

When producing polyurethane foam molded into a specified shape, a mold foam molding method is preferred, in which a polyol composition is stirred and mixed with polyisocyanate to form a polyurethane foam raw material, which is then poured (injected) into a mold, foamed, and then the mold is opened and the molded product is removed. The mold cavity is shaped to the product shape appropriate for the intended use of the polyurethane foam.

The density (JIS K 7222) of the polyurethane foam of the present invention is preferably about 0.20 to 1.20 g/cm ³ for a molded foamed article.

The thermal conductivity of the polyurethane foam of the present invention (measured using a QTM500 measuring instrument manufactured by Kyoto Electronics Manufacturing Co., Ltd., which measures thermal conductivity using the hot wire method) is preferably 0.10 W/m·K or more for molded foamed articles.

The polyurethane foams of Examples 1, 2, 3, and 4 and Comparative Examples 1 and 2 were produced using the open foaming method using the following raw materials, and the raw material properties and the physical properties of the molded products were measured and confirmed.

Polyol: Polyether polyol, Mw 5000, hydroxyl value 34 mg KOH/g, functionality 3, product number: Sannix FA-703, Sanyo Chemical Industries, Ltd. Catalyst: product number: DABCO 33LSI, EVONIK Co., Ltd. Foam stabilizer: Silicone foam stabilizer, product number: B8738LF2, EVONIK Co., Ltd. Foam breaker: Dimer acid diester, product number: ADDITIVE T, Hitachi Chemical Polymer Co., Ltd. Foaming agent: Water

Expanded graphite (meaning expandable graphite; the same applies hereinafter): average particle size (D50) 300 μm, product number: SYZR502FP, Sanyo Trading Co., Ltd. Flake graphite: particle size (mesh opening) corresponding to a cumulative distribution of 50 wt% or more is 180 μm, particle size (mesh opening) corresponding to a cumulative distribution of less than 50 wt% is 300 μm, and the particle size range corresponding to a cumulative distribution of 50 wt% is 180 μm or more and 300 μm. Product code: CRC-80N, Higashi Nippon Carbon Co., Ltd. Expanded graphite 1, average particle size (D50) 200 μm, product code: AED-200, Fuji Graphite Industries Co., Ltd. Expanded graphite 2, average particle size (D50) 100 μm, product code: AED-100, Fuji Graphite Industries Co., Ltd. Metallic silicon, average particle size 20 μm, product code: #200, Kinseimatec Co., Ltd. Monool: polyoxyethylene polyoxypropylene butyl ether , hydroxyl value 42 mg KOH/g, functionality 1, product code: Newpol 50HB-400, Sanyo Chemical Industries, Ltd. Dispersant: salt of unsaturated polyaminoamide and low molecular weight polyester acid, product code: ANTI-TERRA-U100, BYK Corporation
Polyisocyanate 1 : Crude MDI, NCO%=31.5%, Product Code: Lupranate M5S, BASFINOAC Polyurethanes Co., Ltd. Polyisocyanate 2: Prepolymer MDI, NCO%=27%, Product Code: M249, Sumika Covestro Urethane Co., Ltd.

Examples 1, 2, 3, and 4 and Comparative Examples 1 and 2 will be described.
A polyurethane foam raw material was prepared according to the formulation shown in FIG. 1, and the raw material deactivation and viscosity of the liquid A were measured as raw material properties.
The deactivation of raw materials was determined by measuring the pH of Solution A before and after 15 minutes of stirring in a lab mixer in accordance with JIS K 1557-5:2007, and by visually observing the foaming state of a polyurethane foam raw material prepared by mixing polyisocyanate with Solution A after 15 minutes of stirring. The lab mixer used had a rotating blade diameter of 80 mm and a rotation speed of 2000 rpm.

The viscosity of Liquid A was measured at 20°C, 30°C, and 40°C using a B-type viscometer (TVB-15, manufactured by Toki Sangyo Co., Ltd.).

Furthermore, after mixing the liquid A and polyisocyanate in the formulation shown in Figure 1 in a lab mixer, they were poured into a 150 x 400 x 10 mm (t) or 150 x 100 x 10 mm (t) mold and foamed to form polyurethane foam. The mixing time for liquid A and polyisocyanate here was set to 10 seconds, which is shorter than the mixing time used to measure raw material deactivation, minimizing changes in the pH of liquid A. This also made foam molding possible for comparative examples 1 and 2.

Regarding polyurethane foam, the physical properties of the molded products were investigated, including density, thermal conductivity, and thermal conductivity.
The density (g/cm ³ ) was measured in accordance with JIS K 7222.
The thermal conductivity (W/m·K) was measured using a measuring instrument (QTM500, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) that measures thermal conductivity using a hot wire method.
The thermal conductivity was calculated as thermal conductivity/density [(W/m·K)/(g/cm ³ )].

Example 1
Example 1 is an example in which flake graphite was used as the carbon-based filler, and contained 80 parts by weight of polyol, 0.50 parts by weight of catalyst, 0.20 parts by weight of foam stabilizer, 0.75 parts by weight of foaming agent, 60 parts by weight of flake graphite, 15 parts by weight of metallic silicon, 20 parts by weight of monool, and 1.5 parts by weight of dispersant.

In Example 1, the pH of Solution A was 8.98 before stirring and 8.93 after stirring, and there was almost no change in pH (acidification) between before and after stirring. In addition, there was no curing failure of the polyurethane foam, and foam molding was possible.
The viscosity (mPa·s) of Solution A was 12,000 at 20°C, 8,900 at 30°C, and 4,200 at 40°C.
The polyurethane foam had a density (g/cm ³ ) of 0.48, a thermal conductivity (W/m·K) of 0.34, and a thermal conductivity [(W/m·K)/(g/cm ³ )] of 0.71.
As described above, in Example 1, there is almost no change in pH before and after stirring of Solution A (almost no acidification), and the foam can be well foamed and molded, and the composition has good thermal conductivity.

Example 2
In Example 2, the flake graphite in Example 1 was increased from 60 parts by weight to 70 parts by weight, the metallic silicon (silicon) from 15 parts by weight to 18 parts by weight, and the foaming agent from 0.75 parts by weight to 1.40 parts by weight.

Regarding the raw material properties of Example 2, the pH of Solution A was 8.94 before stirring and 8.92 after stirring, and there was almost no change in the pH of Solution A before and after stirring (acidification), and the pH value was the same as in Example 1. In addition, there was no poor curing of the polyurethane foam, and foam molding was possible.
The viscosity (mPa·s) of Solution A was 16,000 at 20°C, 9,300 at 30°C, and 4,600 at 40°C.
The polyurethane foam had a density (g/cm ³ ) of 0.24, a thermal conductivity (W/m·K) of 0.13, and a thermal conductivity [(W/m·K)/(g/cm ³ )] of 0.54.
As described above, in Example 2, there is almost no change in pH before and after stirring of Solution A (almost no acidification), and the foam can be well foamed and molded, and the composition has good thermal conductivity.

Example 3
Example 3 is an example in which expanded graphite was used as the carbon-based filler, and contained 100 parts by weight of polyol, 0.70 parts by weight of catalyst, 1.00 part by weight of foam stabilizer, 10 parts by weight of cell opener, 0.70 parts by weight of foaming agent, 37 parts by weight of expanded graphite 1, and 45 parts by weight of metallic silicon.

Regarding the raw material properties of Example 3, the pH and viscosity of Solution A were not measured, but the polyurethane foam did not have poor curing properties and could be foam-molded.
The polyurethane foam had a density (g/cm ³ ) of 0.89, a thermal conductivity (W/m·K) of 1.44, and a thermal conductivity [(W/m·K)/(g/cm ³ )] of 1.62.
As described above, in Example 3, foam molding can be performed well and the material has good thermal conductivity.

Example 4
Example 4 is an example in which expanded graphite was used as the carbon-based filler, and contained 100 parts by weight of polyol, 0.70 parts by weight of catalyst, 1.00 part by weight of foam stabilizer, 10 parts by weight of cell opener, 0.70 parts by weight of foaming agent, 25 parts by weight of expanded graphite 2, and 30 parts by weight of metallic silicon.

Regarding the raw material properties of Example 4, the pH and viscosity of Solution A were not measured, but the polyurethane foam did not have poor curing properties and could be foam-molded.
The polyurethane foam had a density (g/cm ³ ) of 0.73, a thermal conductivity (W/m·K) of 0.75, and a thermal conductivity [(W/m·K)/(g/cm ³ )] of 1.03.
As described above, in Example 4, foam molding can be carried out satisfactorily and the material has good thermal conductivity.

Comparative Example 1
Comparative Example 1 is an example in which the flake graphite of Example 1 was replaced with 100 parts by weight of expanded graphite, 25 parts by weight of metallic silicon, and 3.0 parts by weight of dispersant, and the other components were the same as those of Example 1.
The raw material properties of Comparative Example 1 were such that the pH of Solution A was 9.40 before stirring and 5.43 after stirring, and the pH value of Solution A dropped significantly and became acidic after 15 minutes of stirring. In addition, the polyurethane foam cured poorly, making foam molding impossible.
The viscosity (mPa·s) of Solution A was 20,000 at 20°C, 9,300 at 30°C, and 4,900 at 40°C.
The polyurethane foam had a density (g/cm ³ ) of 0.51, a thermal conductivity (W/m·K) of 0.32, and a thermal conductivity [(W/m·K)/(g/cm ³ )] of 0.63. In Comparative Example 1, the thermal conductivity decreased despite the fact that the blending amount of the thermally conductive filler was increased compared to Example 1.
As described above, in Comparative Example 1, the pH value of Solution A was significantly decreased (acidified) due to stirring, and the raw material was deactivated.

Comparative Example 2
Comparative Example 2 is an example in which 100 parts by weight of expanded graphite was blended in place of the flake graphite of Example 2, 25 parts by weight of metallic silicon, and 1.70 parts by weight of a foaming agent, and the other components were the same as those of Example 2.
In Comparative Example 2, the pH of Solution A was 9.21 before stirring and 5.56 after stirring, and the pH value of Solution A dropped significantly after 15 minutes of stirring, becoming acidic. In addition, the polyurethane foam cured poorly, making it impossible to perform foam molding.
The viscosity (mPa·s) of Solution A was 21,000 at 20°C, 13,000 at 30°C, and 7,400 at 40°C.
The polyurethane foam had a density (g/cm ³ ) of 0.24, a thermal conductivity (W/m·K) of 0.10, and a thermal conductivity [(W/m·K)/(g/cm ³ )] of 0.42. In Comparative Example 2, the amount of thermally conductive filler was increased compared to Example 2, but the thermal conductivity decreased.
As described above, in Comparative Example 2, the pH value of Solution A was significantly decreased (acidified) due to stirring, and the raw material was deactivated.

At manufacturing sites, Liquid A is stored in an injector and circulated, and when foaming is required, Liquid A and Liquid B (polyisocyanate) are supplied to a mixing head, mixed, and then ejected from a nozzle. Liquid A is then circulated again until the next foaming time, which significantly impacts the deactivation of the raw materials in Liquid A and increases its viscosity.

So, for liquid A in Example 1 and Comparative Example 1, we circulated them within a syringe and measured the raw material properties depending on the circulation time within the syringe. We also mixed liquid A with liquid B, discharged it into an open-topped container, and measured the physical properties of the foamed (opened) polyurethane foam molded product. The pH and viscosity of liquid A were measured by removing only liquid A from the syringe during viscosity measurement. The syringe used was a low-pressure syringe manufactured by Nippon Sosei Kogyo Co., Ltd. The measurement results are shown in Figure 2.

Example 1
In Example 1, the pH, viscosity (20°C), whether or not there was poor curing, whether or not the product could be molded, and the density (g/cm ³ ), thermal conductivity (W/m·K), and thermal conductivity [(W/m·K)/(g/cm ³ )] of the molded product were measured at circulation times of 0, 60, and 180 minutes.

In Example 1, during a circulation time of 0 to 180 minutes, the pH value of Solution A was 8.92 to 8.94, the viscosity (mPa·s) was 13,000 to 54,000, there was no curing failure, and molding was possible, and the polyurethane foam had a density (g/cm ³ ) of 0.48, a thermal conductivity (W/m·K) of 0.33 to 0.41, and a thermal conductivity [(W/m·K)/(g/cm ³ )] of 0.69 to 0.85.

In Example 1, the pH value of Liquid A remained almost unchanged between 8.92 and 8.94 when the circulation time was between 0 and 180 minutes, resulting in no deactivation of the raw materials, favorable foam molding, and good thermal conductivity.

Comparative Example 1
In Comparative Example 1, the pH, viscosity (20°C), whether or not there was poor curing, whether or not it could be molded, and the density (g/cm ³ ), thermal conductivity (W/m·K), and thermal conductivity [(W/m·K)/(g/cm ³ )] of the molded product were measured at circulation times of 0, 5, 10, 20, and 60 minutes.

In Comparative Example 1, the pH value of Solution A significantly decreased (acidified) from 8.52 at 0 minute circulation time to 3.84 at 60 minutes circulation time, and the viscosity (mPa s) significantly increased from 27,000 at 0 minute circulation time to 88,000 at 60 minutes circulation time.
In addition, in Comparative Example 1, when the circulation time was 0 minutes, there was no curing failure and molding was possible, and the polyurethane foam density (g/cm ³ ) was 0.48, the thermal conductivity (W/m·K) was 0.31, and the thermal conductivity [(W/m·K)/(g/cm ³ )] was 0.65. However, when the circulation time was 5 minutes or more, there was curing failure and molding was not possible, and therefore the density, thermal conductivity, and thermal conductivity could not be measured.

As such, in Comparative Example 1, polyurethane foam could be molded when the circulation time was 0 minutes, but when the circulation time was 5 minutes or more, raw material deactivation occurred and good foam molding was not possible. In actual manufacturing sites, raw materials are circulated even during the foaming (discharge) timing, so good foam molding products cannot be produced with the raw materials of Comparative Example 1.

Thus, the present invention provides a thermally conductive polyurethane foam in a good foamed state.
The present invention is not limited to the above-described embodiment, and can be modified within the scope of the invention.

Claims (4)

A polyurethane foam obtained from a polyurethane foam raw material containing a polyol composition containing a polyol and a thermally conductive filler, and a polyisocyanate,
As the thermally conductive filler, a carbon-based filler selected from flake graphite and expanded graphite is used in combination with metal silicon,
the content of the carbon-based filler is 20 to 100 parts by weight relative to 80 parts by weight of the polyol;
The content of the metallic silicon is 10 to 50 parts by weight per 80 parts by weight of the polyol . 2. The polyurethane foam according to claim 1, wherein the polyol composition comprises a monool. A polyol composition comprising a polyol and a thermally conductive filler,
As the thermally conductive filler, a carbon-based filler selected from flake graphite and expanded graphite is used in combination with metal silicon,
the content of the carbon-based filler is 20 to 100 parts by weight relative to 80 parts by weight of the polyol;
The polyol composition , wherein the content of the metal silicon is 10 to 50 parts by weight relative to 80 parts by weight of the polyol . A method for producing a polyurethane foam, comprising stirring the polyol composition according to claim 3 , mixing with a polyisocyanate, and foaming the mixture.