JP2014055606A - Vacuum heat insulation material - Google Patents
Vacuum heat insulation material Download PDFInfo
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- JP2014055606A JP2014055606A JP2012199530A JP2012199530A JP2014055606A JP 2014055606 A JP2014055606 A JP 2014055606A JP 2012199530 A JP2012199530 A JP 2012199530A JP 2012199530 A JP2012199530 A JP 2012199530A JP 2014055606 A JP2014055606 A JP 2014055606A
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- 239000012774 insulation material Substances 0.000 title abstract 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 103
- 239000002245 particle Substances 0.000 claims abstract description 89
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 64
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 53
- 238000012856 packing Methods 0.000 claims abstract description 24
- 238000007789 sealing Methods 0.000 claims abstract description 23
- 238000010521 absorption reaction Methods 0.000 claims abstract description 16
- 238000002156 mixing Methods 0.000 claims abstract description 14
- 239000010439 graphite Substances 0.000 claims abstract description 13
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 13
- 238000010079 rubber tapping Methods 0.000 claims abstract description 11
- 125000001183 hydrocarbyl group Chemical group 0.000 claims abstract 6
- 239000011810 insulating material Substances 0.000 claims description 59
- 238000010438 heat treatment Methods 0.000 claims description 22
- 239000000377 silicon dioxide Substances 0.000 claims description 17
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 238000012545 processing Methods 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 4
- 150000002430 hydrocarbons Chemical group 0.000 description 38
- 238000012546 transfer Methods 0.000 description 35
- 238000009413 insulation Methods 0.000 description 22
- 230000000694 effects Effects 0.000 description 18
- 239000007787 solid Substances 0.000 description 16
- 239000011162 core material Substances 0.000 description 12
- 238000012360 testing method Methods 0.000 description 11
- 239000006229 carbon black Substances 0.000 description 9
- 230000005855 radiation Effects 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- -1 for example Substances 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 239000011164 primary particle Substances 0.000 description 3
- 230000001629 suppression Effects 0.000 description 3
- 238000000862 absorption spectrum Methods 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 238000003763 carbonization Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 238000002834 transmittance Methods 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 239000004952 Polyamide Substances 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- 229920001328 Polyvinylidene chloride Polymers 0.000 description 1
- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000008033 biological extinction Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000007771 core particle Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000000280 densification Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 239000003574 free electron Substances 0.000 description 1
- 229910021485 fumed silica Inorganic materials 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229920006280 packaging film Polymers 0.000 description 1
- 239000012785 packaging film Substances 0.000 description 1
- 229920002647 polyamide Polymers 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 239000005033 polyvinylidene chloride Substances 0.000 description 1
- 238000003908 quality control method Methods 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
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Abstract
Description
本発明は、真空断熱材に関する。 The present invention relates to a vacuum heat insulating material.
従来から、各種温冷機器や住宅などにおいて、内外の熱伝達を遮断する断熱材が使用されている。ここで、伝熱機構には、大きく分けて固体伝熱、気体伝熱、及び輻射伝熱とがあり、望ましくはこれら全てに対応することで、断熱性を向上できることが一般的に知られている。そこで、固体伝熱に対する断熱性に優れる粒子と輻射伝熱を抑制する粒子とを混合分散し、非通気性の封止フィルムで真空封止することで気体伝熱にも対応した、真空断熱材の開発が進められている。当該真空断熱材では、断熱性の高い粒子として一般的にシリカ粒子が使用され、輻射伝熱を抑制する粒子として炭素粒子が使用されることが多い。 2. Description of the Related Art Conventionally, heat insulating materials that block heat transfer inside and outside have been used in various types of heating and cooling equipment and houses. Here, the heat transfer mechanism is roughly divided into solid heat transfer, gas heat transfer, and radiant heat transfer, and it is generally known that it is possible to improve the heat insulation property by desirably dealing with all of them. Yes. Therefore, vacuum heat insulating material that supports gas heat transfer by mixing and dispersing particles with excellent heat insulation for solid heat transfer and particles that suppress radiant heat transfer, and vacuum-sealing with a non-breathable sealing film Development is underway. In the vacuum heat insulating material, silica particles are generally used as particles having high heat insulating properties, and carbon particles are often used as particles for suppressing radiant heat transfer.
このような真空断熱材としては、例えば特許文献１がある。特許文献１では、シリカ粒子の粒径や炭素粒子の種類又は比表面積を改良することで、真空断熱材の向上を図っている。具体的には、平均一次粒子径が５０ｎｍ以下のヒュームドシリカ粒子に、黒鉛化炭素（グラファイト）粒子又は比表面積１００〜３００ｍｍ2／ｇのカーボンブラック粒子を１〜１０重量％混合している。
As such a vacuum heat insulating material, there exists
特許文献１では、シリカ粒子に関してはその平均一次粒子径を調整することで断熱性の向上を図っている。しかしながら、シリカ粒子の性状（特に表面性状）も断熱性に大きく影響する。したがって、特許文献１のようにシリカ粒子の平均一次粒子径を調整（改良）するだけでは、断熱性の向上には限界がある。
In
そこで、本発明は上記課題を解決するものであって、シリカ粒子の表面性状を改良することで断熱性が向上された、真空断熱材を提供することを目的とする。 Then, this invention solves the said subject, and it aims at providing the vacuum heat insulating material by which the heat insulation was improved by improving the surface property of a silica particle.
そのための手段として、本発明は次の手段を採る。
（１）多孔質シリカ粒子と、炭素粒子とを混合し、非通気性の封止フィルムによって真空封止してなる真空断熱材であって、前記多孔質シリカ粒子は、表面に炭化水素基を有する多孔質シリカ粒子であって、熱処理により前記炭化水素基の存在量が低減されていることを特徴とする、真空断熱材。
（２）前記熱処理を３５０〜５５０℃の範囲で行う、（１）に記載の真空断熱材。
（３）前記多孔質シリカ粒子は、タッピング嵩密度が０．１ｇ／ｃｍ３以下であり、且つパッキング密度が０．１２５ｇ／ｃｍ３以下である、（１）または（２）に記載の真空断熱材。
（４）前記炭素粒子がグラファイト粒子である、（１）ないし（３）のいずれかに記載の真空断熱材。
（５）前記炭素粒子の混合量が２．５〜１２．５重量％である、（１）ないし（４）のいずれかに記載の真空断熱材。
（６）前記炭素粒子の平均粒子径が２０μｍ以下である、（１）ないし（５）のいずれかに記載の真空断熱材。
（７）赤外線吸収係数が１１０ｍ２／ｋｇ以上である、（１）ないし（６）のいずれかに記載の真空断熱材。
（８）多孔質シリカ粒子と、炭素粒子とを混合し、非通気性の封止フィルムによって真空封止する真空断熱材の製造方法であって、前記多孔質シリカ粒子は表面に炭化水素基を有する多孔質シリカ粒子であって、前記炭素粒子と混合する前に、予め熱処理により前記炭化水素基の存在量を低減する工程を有することを特徴とする、真空断熱材の製造方法。
（９）前記熱処理を３５０〜５５０℃の範囲で行う、（８）に記載の真空断熱材の製造方法。
For this purpose, the present invention adopts the following means.
(1) A vacuum heat insulating material obtained by mixing porous silica particles and carbon particles and vacuum-sealing with a non-breathable sealing film, wherein the porous silica particles have hydrocarbon groups on the surface. A vacuum heat insulating material comprising porous silica particles, wherein the abundance of the hydrocarbon group is reduced by heat treatment.
(2) The vacuum heat insulating material according to (1), wherein the heat treatment is performed in a range of 350 to 550 ° C.
(3) The porous silica particles are a tapping bulk density of 0.1 g / cm 3 or less, and packing density of 0.125 g / cm 3 or less, vacuum insulation according to (1) or (2) Wood.
(4) The vacuum heat insulating material according to any one of (1) to (3), wherein the carbon particles are graphite particles.
(5) The vacuum heat insulating material according to any one of (1) to (4), wherein a mixing amount of the carbon particles is 2.5 to 12.5% by weight.
(6) The vacuum heat insulating material according to any one of (1) to (5), wherein an average particle diameter of the carbon particles is 20 μm or less.
(7) The vacuum heat insulating material according to any one of (1) to (6), wherein the infrared absorption coefficient is 110 m 2 / kg or more.
(8) A method for producing a vacuum heat insulating material in which porous silica particles and carbon particles are mixed and vacuum-sealed with a non-breathable sealing film, wherein the porous silica particles have hydrocarbon groups on the surface. A method for producing a vacuum heat insulating material, comprising: a step of reducing the abundance of the hydrocarbon group by heat treatment before mixing with the carbon particles.
(9) The manufacturing method of the vacuum heat insulating material as described in (8) which performs the said heat processing in the range of 350-550 degreeC.
なお、本発明において多孔質シリカ粒子のタッピング嵩密度とは、ＪＩＳＲ １６２８に従って測定される嵩密度である。具体的には、一定容積の容器に多孔質シリカ粒子を充填し、十分に緻密化するまで数百回タッピングを繰り返す。そして、重量変化が０．３％以下に収まったところで、そのときの多孔質シリカ粒子の重量と体積から求められる密度である。 In the present invention, the tapping bulk density of the porous silica particles is a bulk density measured according to JIS R 1628. Specifically, the porous silica particles are filled in a fixed volume container, and the tapping is repeated several hundred times until it is sufficiently densified. When the weight change is within 0.3%, the density is obtained from the weight and volume of the porous silica particles at that time.
また、パッキング密度とは、封止フィルム内に一定重量の芯材粒子を充填し、内部を真空とした際の大気圧で加圧された状態における重量と体積から求められる密度である。 The packing density is a density determined from the weight and volume in a state where core particles of a constant weight are filled in the sealing film and the interior is evacuated and pressurized at atmospheric pressure.
また、本発明において数値範囲を示す「○○〜××」とは、特に明記しない限り「○○以上××以下」を意味する。 In the present invention, “OO to XX” indicating a numerical range means “XX or more and XX or less” unless otherwise specified.
本発明では、シリカ粒子として内部に多数の空隙を有する多孔質シリカ粒子を使用しているので、非多孔質なシリカ粒子を使用した場合よりもシリカ粒子そのものによる断熱性を向上することができる。ところで、表面に炭化水素基（例えばＣＨ３基）を有する多孔質シリカ粒子は基本的に疎水性であって、当該炭化水素基の存在により空気中の水分が吸着し難い。これにより、真空断熱材を真空封止する際の真空引きに要する時間が短縮され、生産性を向上できる。また、同じ真空引き時間であれば、真空度を向上することができる。しかしながら、この表面炭化水素基の存在は熱伝導に影響を及ぼし、当該表面炭化水素基が単純に固体伝熱のパスを増やす要因となる。また、表面炭化水素基の存在により多孔質シリカ粒子間の摩擦が低減されるため、粒子の流動性が高くなる。この場合、真空封止時の充填状態が過度によくなってパッキング密度が高くなることで、熱伝導率が増大してしまう。そこで、本発明では、多孔質シリカ粒子の表面炭化水素基を低減していることで、上記のような問題を解決でき、熱伝導率の低減すなわち断熱性の向上に有効となる。 In this invention, since the porous silica particle which has many space | gap inside is used as a silica particle, the heat insulation by the silica particle itself can be improved rather than the case where a non-porous silica particle is used. By the way, porous silica particles having a hydrocarbon group (for example, CH 3 group) on the surface are basically hydrophobic, and moisture in the air is difficult to adsorb due to the presence of the hydrocarbon group. Thereby, the time required for evacuation at the time of vacuum-sealing a vacuum heat insulating material is shortened, and productivity can be improved. In addition, the degree of vacuum can be improved with the same evacuation time. However, the presence of the surface hydrocarbon group affects heat conduction, and the surface hydrocarbon group simply increases the path of solid heat transfer. Further, since the friction between the porous silica particles is reduced due to the presence of the surface hydrocarbon group, the fluidity of the particles becomes high. In this case, the state of filling at the time of vacuum sealing is excessively improved and the packing density is increased, thereby increasing the thermal conductivity. Therefore, in the present invention, since the surface hydrocarbon groups of the porous silica particles are reduced, the above-described problems can be solved, which is effective in reducing the thermal conductivity, that is, improving the heat insulation.
多孔質シリカ粒子を３５０〜５５０℃の範囲で熱処理すれば、的確に断熱性を向上することができる。また、多孔質シリカ粒子のタッピング嵩密度が０．１ｇ／ｃｍ３以下と小さく、且つパッキング密度も０．１２５ｇ／ｃｍ３以下と小さければ、真空断熱材中の固体成分が少なく空隙率が大きくなる。これにより、固体伝熱に対する断熱性が向上する。 If the porous silica particles are heat-treated in the range of 350 to 550 ° C., the heat insulating properties can be improved accurately. Also, small tapped bulk density of the porous silica particles and 0.1 g / cm 3 or less, and the smaller the packing density 0.125 g / cm 3 or less, the solid component porosity increases less in the vacuum heat insulating material . Thereby, the heat insulation with respect to solid heat transfer improves.
炭素粒子としてグラファイトを配合していれば、カーボンブラックを配合した場合よりも輻射伝熱の抑制効果が大きく、真空断熱材の断熱性をより向上できる。ここで、輻射伝熱は固体振動による熱放射であり、その主体は波長が赤外線領域の熱放射である。したがって、赤外線吸収係数が１１０ｍ２／ｋｇ以上と大きければ、輻射伝熱の主体をなす赤外線領域の放射の吸収能も大きくなることで輻射伝熱が的確に抑制され、断熱性がより向上する。 If graphite is blended as carbon particles, the effect of suppressing radiant heat transfer is greater than when carbon black is blended, and the heat insulation of the vacuum heat insulating material can be further improved. Here, radiant heat transfer is heat radiation by solid vibration, and its main component is heat radiation having a wavelength in the infrared region. Therefore, if the infrared absorption coefficient is as large as 110 m 2 / kg or more, the radiation absorption capability in the infrared region, which is the main component of the radiant heat transfer, is increased, so that the radiant heat transfer is accurately suppressed and the heat insulation is further improved.
以下、本発明について詳しく説明する。本発明の真空断熱材は、多孔質シリカ粒子と炭素粒子との混合粒子を芯材とし、当該芯材を非通気性の封止フィルムによって真空封止してなる。 The present invention will be described in detail below. The vacuum heat insulating material of the present invention comprises a mixed particle of porous silica particles and carbon particles as a core material, and the core material is vacuum sealed with a non-breathable sealing film.
シリカ粒子としては、多孔質シリカ粒子を使用する。真空封止した際はシリカ粒子同士ないしシリカ粒子と炭素粒子との接触は避けられず、この粒子接触により固体伝熱（熱伝導）の経路が形成され得るが、多孔質シリカ粒子であれば、非多孔質シリカ粒子を使用した場合よりも固体伝熱に対する断熱性が向上する。多孔質シリカ粒子の気孔率は９０％以上が好ましい。気孔率が低いと、ポーラス構造による断熱性の向上効果が得られ難くなるためである。 As silica particles, porous silica particles are used. When vacuum sealed, contact between silica particles or between silica particles and carbon particles is unavoidable, and a solid heat transfer (heat conduction) path can be formed by this particle contact, but if porous silica particles, The heat insulation against solid heat transfer is improved as compared with the case of using non-porous silica particles. The porosity of the porous silica particles is preferably 90% or more. This is because if the porosity is low, it is difficult to obtain the effect of improving the heat insulation by the porous structure.
また、表面に炭化水素基（ＣＨ３基）を有する多孔質シリカ粒子が好ましい。多孔質シリカ粒子の中には本来的に炭化水素基を有しないものもあるが、このような多孔質シリカ粒子は親水性なので、空気中の水分を吸着し易い傾向がある。そのため、断熱材を真空封止する際の所要時間が長くなったり、真空度が向上し難い傾向がある。一方、表面に炭化水素基を有する多孔質シリカ粒子であれば、断熱材を真空封止する際に空気中の水分が吸着され難いので真空効率が向上し、真空断熱材の断熱性を向上することができる。 The porous silica particles having a surface to a hydrocarbon group (CH 3 groups) are preferred. Some porous silica particles do not inherently have a hydrocarbon group, but since such porous silica particles are hydrophilic, they tend to adsorb moisture in the air. Therefore, the time required for vacuum-sealing the heat insulating material tends to be long, and the degree of vacuum tends to be difficult to improve. On the other hand, if the porous silica particles have hydrocarbon groups on the surface, moisture in the air is hardly adsorbed when the heat insulating material is vacuum-sealed, so that the vacuum efficiency is improved and the heat insulating property of the vacuum heat insulating material is improved. be able to.
但し、表面炭化水素基の存在量はできるだけ少ないことが好ましい。表面炭化水素基の存在量が少ないほど固体伝熱を減らすことができ、真空断熱材の断熱性が向上する。また、表面炭化水素基の存在量を適切に減らすことで多孔質シリカ粒子間の流動性を下げて真空封止後のパッキング密度を下げ、断熱性を向上できる。表面炭化水素基の低減量の目安としては、表面炭化水素基の存在量の指針となる炭化水素基由来の炭素量が、５重量％以下となる程度まで低減することが好ましく、３重量％以下となる程度まで低減することがより好ましい。但し、表面炭化水素を完全に除去することは現実的に困難であり、また表面炭化水素基が存在する上記効果が得られなくなるので、表面炭化水素基由来の炭素量の下限は０重量％を超えていることが好ましい。より好ましくは０．１重量％以上であり、さらに好ましくは０．５重量％以上である。 However, the amount of surface hydrocarbon groups is preferably as small as possible. The smaller the amount of surface hydrocarbon groups, the more solid heat transfer can be reduced and the heat insulation of the vacuum heat insulating material is improved. In addition, by appropriately reducing the amount of surface hydrocarbon groups, the fluidity between the porous silica particles can be lowered, the packing density after vacuum sealing can be lowered, and the heat insulation can be improved. As a measure of the amount of surface hydrocarbon groups to be reduced, it is preferable to reduce the amount of carbon derived from hydrocarbon groups, which serves as a guide for the amount of surface hydrocarbon groups, to 5 wt% or less, preferably 3 wt% or less. It is more preferable to reduce to such an extent. However, it is practically difficult to completely remove surface hydrocarbons, and the above effect due to the presence of surface hydrocarbon groups cannot be obtained, so the lower limit of the amount of carbon derived from surface hydrocarbon groups is 0% by weight. It is preferable to exceed. More preferably, it is 0.1 weight% or more, More preferably, it is 0.5 weight% or more.
表面炭化水素基の存在量は、多孔質シリカ粒子を熱処理することで低減できる。熱処理温度は３５０〜５５０℃、好ましくは３７０〜５３０℃、より好ましくは４００〜５００℃とする。多孔質シリカ粒子の熱処理温度が３５０℃未満では、有効に表面炭化水素基の存在量を低減できない。一方、熱処理温度が５５０℃を超えると、多孔質シリカ粒子の焼結収縮により密度が増加する。これにより、パッキング密度も増大することで、真空断熱材の断熱性が低下してしまう。熱処理は、電気炉等によって行えばよい。また、熱処理は酸素存在下で行う。酸素存在下で熱処理することで、表面炭化水素基が酸素と反応して低減するからである。不活性雰囲気下で熱処理すると、表面炭化水素基の炭素化が進行するだけなので、断熱性向上効果が損なわれる。 The amount of surface hydrocarbon groups can be reduced by heat-treating the porous silica particles. The heat treatment temperature is 350 to 550 ° C, preferably 370 to 530 ° C, more preferably 400 to 500 ° C. When the heat treatment temperature of the porous silica particles is less than 350 ° C., the amount of surface hydrocarbon groups cannot be effectively reduced. On the other hand, when the heat treatment temperature exceeds 550 ° C., the density increases due to sintering shrinkage of the porous silica particles. Thereby, the packing density also increases, and the heat insulating property of the vacuum heat insulating material is lowered. The heat treatment may be performed with an electric furnace or the like. The heat treatment is performed in the presence of oxygen. This is because heat treatment in the presence of oxygen reduces surface hydrocarbon groups by reacting with oxygen. When the heat treatment is performed in an inert atmosphere, the carbonization of the surface hydrocarbon group only proceeds, so that the effect of improving heat insulation is impaired.
多孔質シリカ粒子は、できるだけ微細であることが好ましい。微細な多孔質シリカ粒子であることでタッピング嵩密度及びパッキング密度を低減できるため、炭素粒子添加による断熱性の改善効果が向上して真空断熱材の熱伝導率を相乗的に低く抑えられるからである。そこで、多孔質シリカ粒子のタッピング嵩密度が、少なくとも０．１ｇ／ｃｍ３以下、好ましくは０．０８ｇ／ｃｍ３以下となる程度の微細な多孔質シリカ粒子を使用する。また、多孔質シリカ粒子のみを芯材とした場合のパッキング密度が、少なくとも０．１２５ｇ／ｃｍ３以下、好ましくは０．１１０ｇ／ｃｍ３以下となる程度の微細な多孔質シリカ粒子を使用する。多孔質シリカ粒子のタッピング嵩密度が０．１ｇ／ｃｍ３より大きかったり、若しくはパッキング密度が０．１２５ｇ／ｃｍ３より大きいと、真空断熱材において優れた断熱性を得られ難い。 The porous silica particles are preferably as fine as possible. Since the tapping bulk density and packing density can be reduced by using fine porous silica particles, the effect of improving the heat insulation by adding carbon particles is improved and the thermal conductivity of the vacuum heat insulating material can be kept low synergistically. is there. Therefore, fine porous silica particles having a tapping bulk density of the porous silica particles of at least 0.1 g / cm 3 or less, preferably 0.08 g / cm 3 or less are used. Further, the packing density in the case where only the porous silica particles as a core material is at least 0.125 g / cm 3 or less, preferably using a fine porous silica particles to the extent that the 0.110 g / cm 3 or less. Large or tapped bulk density of the porous silica particles is from 0.1 g / cm 3, or a packing density of greater than 0.125 g / cm 3, it is difficult to obtain excellent thermal insulation in the vacuum thermal insulating material.
炭素粒子は、真空断熱材において輻射伝熱を抑制するために混合される。その混合量は、多孔質シリカ粒子と炭素粒子との合計重量基準で、２．５〜１２．５重量％、好ましくは４〜１０重量％、より好ましくは５〜７．５重量％とする。炭素粒子の混合量が２．５重量％未満では、輻射伝熱の抑制効果を的確に得られない。一方、１２．５重量％を超えると、本来炭素粒子は比較的熱伝導率の高い材料なので、輻射伝熱の抑制効果よりも、炭素粒子を混合したことによる固体伝熱性が大きくなってしまい、結果として真空断熱材の断熱性が低下してしまう。 Carbon particles are mixed to suppress radiant heat transfer in the vacuum heat insulating material. The mixing amount is 2.5 to 12.5% by weight, preferably 4 to 10% by weight, more preferably 5 to 7.5% by weight, based on the total weight of the porous silica particles and the carbon particles. If the mixing amount of the carbon particles is less than 2.5% by weight, the effect of suppressing radiant heat transfer cannot be obtained accurately. On the other hand, if it exceeds 12.5% by weight, the carbon particles are inherently a material having a relatively high thermal conductivity, so that the solid heat transfer by mixing the carbon particles becomes larger than the effect of suppressing the radiant heat transfer, As a result, the heat insulating property of the vacuum heat insulating material is lowered.
また、炭素粒子もできるだけ微細であることが好ましいため、平均粒子径は２０μｍ以下、好ましくは１５μｍ以下、より好ましくは１０μｍ以下、さらに好ましくは６μｍ以下とする。炭素粒子の粒子径が大きいと、芯材となる混合粒子中において固体伝熱性の高い連続領域（１個の炭素粒子）が長くなり固体伝熱の経路が形成されやすくなるため、真空断熱材の熱伝導率が大きくなってしまう。 In addition, since the carbon particles are preferably as fine as possible, the average particle size is 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 6 μm or less. If the particle size of the carbon particles is large, a continuous region (one carbon particle) with high solid heat transfer becomes longer in the mixed particles as the core material, and a solid heat transfer path is easily formed. Thermal conductivity will increase.
炭素粒子であれば、例えばカーボンブラック等でもある程度の輻射伝熱抑制効果を期待できるが、中でもグラファイト粒子が好ましい。グラファイトは、非晶質の炭素やカーボンブラックなど他の炭素粒子よりも層状構造が規則的に構成されており、自由電子が多く光の吸収係数が高いため、他の炭素粒子よりも輻射伝熱の抑制効果が高いからである。 In the case of carbon particles, for example, carbon black or the like can be expected to have a certain degree of radiation heat transfer suppression effect, but among these, graphite particles are preferable. Graphite has a regular layered structure compared to other carbon particles such as amorphous carbon and carbon black, and has many free electrons and a high light absorption coefficient. This is because the suppression effect is high.
封止フィルムは、非通気性である限りその材料は特に限定されない。例えば、ポリエチレンテレフタレート等のポリエステル、ポリアミド、ポリビニルアルコール、ポリエチレン、ポリプロピレン、ポリ塩化ビニリデンなどからなる包装フィルムを使用できる。なお、封止フィルムは、断熱性やガスバリヤ性等を向上させるために、アルミニウム等からなる金属ラミネート層を有することが好ましい。 The material of the sealing film is not particularly limited as long as it is non-breathable. For example, a packaging film made of polyester such as polyethylene terephthalate, polyamide, polyvinyl alcohol, polyethylene, polypropylene, polyvinylidene chloride, or the like can be used. In addition, it is preferable that the sealing film has a metal laminate layer made of aluminum or the like in order to improve heat insulating properties, gas barrier properties, and the like.
真空断熱材は、多孔質シリカ粒子と炭素粒子とを所定の割合で混合分散させたものを芯材として封止フィルムに充填し、十分に真空引きできたところで封止フィルムの開口を熱溶着等によって封止することで得られる。このとき、多孔質シリカ粒子は、炭素粒子と混合する前に、上述のごとく予め熱処理することで表面炭化水素基の存在量を低減しておく。真空圧力は、５〜２０Ｐａ程度とすればよい。 The vacuum heat insulating material is a mixture of porous silica particles and carbon particles mixed at a predetermined ratio and filled into the sealing film as a core material, and when the vacuum is fully evacuated, the opening of the sealing film is thermally welded, etc. It is obtained by sealing with. At this time, the porous silica particles are preliminarily heat-treated as described above before being mixed with the carbon particles to reduce the amount of surface hydrocarbon groups. The vacuum pressure may be about 5 to 20 Pa.
真空封止後の真空断熱材全体のパッキング密度（芯材に炭素粒子も含む場合の密度）は、０．１３８ｇ／ｃｍ３以下が好ましく、０．１２０ｇ／ｃｍ３以下がより好ましい。真空断熱材のパッキング密度が低いことで、内部の空隙量が多く固体伝熱の経路が少ないこととなり、断熱性が向上する。また、真空断熱材の赤外線吸収係数は１１０ｍ２／ｋｇ以上であることが好ましい。赤外線吸収係数が大きいほど、輻射伝熱の抑制効果が大きいからである。 Vacuum heat insulator overall packing density after vacuum seal (density when the core material including carbon particles) is preferably 0.138 g / cm 3 or less, 0.120 g / cm 3 or less is more preferable. Since the packing density of the vacuum heat insulating material is low, the amount of voids in the interior is large and the path of solid heat transfer is small, and the heat insulation is improved. Moreover, it is preferable that the infrared absorption coefficient of a vacuum heat insulating material is 110 m < 2 > / kg or more. This is because the greater the infrared absorption coefficient, the greater the effect of suppressing radiant heat transfer.
以下、本発明の具体的な実施例について説明するが、これに限られず本発明の要旨を逸脱しない範囲で種々の変更が可能であることは言うまでもない。 Specific examples of the present invention will be described below, but it is needless to say that various modifications are possible without departing from the scope of the present invention.
＜試験１＞
先ず、多孔質シリカ粒子のタッピング嵩密度及びパッキング密度の影響について評価した。多孔質シリカ粒子としては、９０％以上の気孔率をもち、タッピング嵩密度が約０．０８〜０．１１ｇ／ｃｍ３の範囲でそれぞれ異なる（表１参照）４種類の多孔質シリカ粒子（試料１〜４）を使用した。この試料１〜４の各多孔質シリカ粒子５０ｇを芯材として、アルミニウムラミネート層を有する昭和電工製の封止フィルムによって真空圧力１０Ｐａにまで減圧した状態で真空封止して、縦２００ｍｍ×横２００ｍｍ×高さ１０ｍｍの真空断熱材を作製し、そのパッキング密度を測定した。その結果を表１に示す。
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First, the influence of the tapping bulk density and packing density of the porous silica particles was evaluated. As the porous silica particles, four types of porous silica particles (samples) having a porosity of 90% or more and different in tapping bulk density in the range of about 0.08 to 0.11 g / cm 3 (see Table 1). 1-4) were used. Using each porous silica particle 50g of
次いで、上記試料１〜４の各多孔質シリカ粒子に、炭素粒子を５重量％の割合で均一に分散するまで十分に撹拌混合した混合粒子５０ｇを芯材として、上記と同様にして真空断熱材を作製し、そのパッキング密度も測定した。その結果も表１に示す。なお、炭素粒子としては、平均粒子径５μｍのグラファイト（ＳＥＣカーボン社製のＳＧＰ−５）を使用した。
Next, a vacuum heat insulating material in the same manner as described above, using as a core 50 g of mixed particles obtained by sufficiently stirring and mixing carbon particles in each porous silica particle of
続いて、炭素粒子の混合量を種々変更した（図１の横軸参照）混合粒子５０ｇを芯材として、上記と同様にして作製した真空断熱材の熱伝導率（Thermal conductivity）を測定した。その結果を図１に示す。なお、熱伝導率の測定には、保護熱板法（ＧＨＰ：GuardedHot Plate法）を用いた。具体的には、ホットプレート高温部３０℃の上下に真空断熱材２枚をセットして、その外側に低温部２０℃を設けて定常状態とする。その定常熱流を保つためにホットプレートに供給される熱量（電力）をもとに、熱伝導率の絶対値を求めることができる。
Subsequently, the thermal conductivity of the vacuum heat insulating material produced in the same manner as described above was measured using 50 g of mixed particles with various amounts of carbon particles mixed (see the horizontal axis in FIG. 1) as a core material. The result is shown in FIG. In addition, the protection hot plate method (GHP: GuardedHot Plate method) was used for the measurement of thermal conductivity. Specifically, two vacuum heat insulating materials are set above and below the hot plate high temperature portion 30 ° C., and the
図１及び表１の結果から明らかなように、多孔質シリカ粒子のタッピング嵩密度及びパッキング密度が小さいほど熱伝導率が低くなる傾向が確認された。 As is clear from the results of FIG. 1 and Table 1, it was confirmed that the thermal conductivity tends to be lower as the tapping bulk density and packing density of the porous silica particles are smaller.
＜試験２＞
次に、多孔質シリカ粒子の表面炭化水素基の存在量に基づく断熱性の影響について評価した。多孔質シリカ粒子としては、上記試験１で使用した試料４を使用した。そして、多孔質シリカ粒子を、酸化性雰囲気（酸素ガス雰囲気）で３５０℃、４５０℃、５５０℃、７５０℃、及び不活性雰囲気（窒素ガス雰囲気）で７５０℃の各条件でそれぞれ熱処理した。なお、熱処理は、真空ガス置換が可能な電気炉により行い、昇温速度２００℃／時間として、各熱処理温度において１０時間保持した。また、多孔質シリカ粒子の表面炭化水素基の存在量を低減できていることを確認するために、代表的なサンプルとして熱処理前および４５０℃にて熱処理した多孔質シリカ粒子について炭化水素基由来の炭素量を測定したところ、前者は６．９重量％、後者は２．１重量％であった。表面炭化水素基由来の炭素量は、酸素気流中燃焼−赤外線吸収法によって測定した。
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Next, the influence of heat insulation based on the amount of surface hydrocarbon groups in the porous silica particles was evaluated. As the porous silica particles, the
当該各熱処理多孔質シリカ粒子及び未処理多孔質シリカ粒子に、それぞれ上記試験１と同じ炭素粒子を２．５〜１２．５重量％の範囲で混合量を種々変更した（図２参照）混合粒子５０ｇを芯材とし、試験１と同様にして作製した真空断熱材の熱伝導率を、試験１と同様に測定した。その結果を図２に示す。また、炭素粒子の混合量を７．５重量％とした場合の、真空断熱材のパッキング密度も測定した。その結果を図３に示す。
Each heat-treated porous silica particle and untreated porous silica particle were mixed in various amounts in the range of 2.5 to 12.5% by weight of the same carbon particles as in
図２の結果から明らかなように、酸素存在雰囲気において３５０〜５５０℃で熱処理することで表面炭化水素基が的確に低減され、真空断熱材の熱伝導率が向上することが確認された。中でも、熱処理温度４５０℃、炭素粒子含有量７．５重量％の真空断熱材は、熱伝導率が２．８７ｍＷ／ｍＫと最も低かった。一方、酸素存在雰囲気でも７５０℃にて熱処理した場合や、不活性雰囲気において熱処理した場合は、熱伝導率の低減効果は殆ど得られなかった。これは、多孔質シリカ粒子の焼結収縮による高密度化や表面炭化水素基の炭素化が原因と考えられる。 As is clear from the results of FIG. 2, it was confirmed that the surface hydrocarbon groups were accurately reduced by heat treatment at 350 to 550 ° C. in an oxygen-existing atmosphere, and the thermal conductivity of the vacuum heat insulating material was improved. Among them, the vacuum heat insulating material having a heat treatment temperature of 450 ° C. and a carbon particle content of 7.5% by weight had the lowest thermal conductivity of 2.87 mW / mK. On the other hand, when heat treatment was performed at 750 ° C. even in an oxygen-existing atmosphere, or when heat treatment was performed in an inert atmosphere, the effect of reducing thermal conductivity was hardly obtained. This is considered to be caused by densification due to sintering shrinkage of porous silica particles and carbonization of surface hydrocarbon groups.
この表面炭化水素基の低減によって熱伝導率を低減できるという結果は、２つの効果によるものである。一つは、表面炭化水素基が固体伝導の経路となっており、それを低減した効果である。もう一つは、図３の結果から明らかなように、表面炭化水素基の低減によりパッキング密度を低減できた効果によるものである。これは、炭化水素基が多孔質シリカ粒子表面に存在することで、粒子間の摩擦係数が低減され流動性が向上してパッキング密度が増大する傾向があるが、表面炭化水素基を減らすことで多孔質シリカ粒子の流動性も低下し、パッキング密度を有意に下げることができたと考えられる。しかし、パッキング密度を下げると、固体伝熱が低下する反面、輻射伝熱が増加する傾向があるが、この問題は輻射伝熱抑制効果のある炭素粒子を混合することにより解決できる。 The result that the thermal conductivity can be reduced by the reduction of the surface hydrocarbon groups is due to two effects. One is the effect of reducing the surface hydrocarbon group as a solid conduction path. The other is due to the effect of reducing the packing density by reducing the surface hydrocarbon groups, as is apparent from the results of FIG. This is because the presence of hydrocarbon groups on the surface of the porous silica particles tends to reduce the friction coefficient between the particles and improve the fluidity and increase the packing density, but by reducing the surface hydrocarbon groups. It is considered that the fluidity of the porous silica particles also decreased, and the packing density could be significantly reduced. However, when the packing density is lowered, the solid heat transfer is reduced, but the radiant heat transfer tends to increase. However, this problem can be solved by mixing carbon particles having an effect of suppressing the radiant heat transfer.
＜試験３＞
そこで、炭素粒子の種類の違いによる断熱性への影響を評価した。上記試験２において最も熱伝導率の低かった真空断熱材（熱処理温度４５０℃、炭素粒子７．５重量％）に対して、炭素粒子をカーボンブラック（東海カーボン製、＃８５００）に代えた以外は同様にして真空断熱材を作製した。その熱伝導率を測定したところ、熱伝導率は３．７９ｍＷ／ｍＫであり、炭素粒子としてグラファイトを使用した場合（熱伝導率２．８７ｍＷ／ｍＫ）よりも熱伝導率低減効果は低かった。この熱伝導率の低減効果の違いは、炭素粒子の種類により輻射伝熱抑制の効果が異なるためと推察される。したがって、輻射伝熱抑制効果を定量的に反映するパラメータを決定することで、真空断熱材における性能保証・品質管理に有効な指標として活用できる。
<
Then, the influence on the heat insulation by the difference in the kind of carbon particle was evaluated. Except that the carbon particles were replaced with carbon black (# 8500, manufactured by Tokai Carbon Co., Ltd.) with respect to the vacuum heat insulating material (heat treatment temperature 450 ° C., carbon particles 7.5% by weight) having the lowest thermal conductivity in
そこで、輻射伝熱の抑制効果を示すパラメータとして、赤外吸収係数を評価した。まず、赤外分光光度計により、上記試験３で使用した芯材粒子（多孔質シリカ粒子＋グラファイト：試料５、及び多孔質シリカ粒子＋カーボンブラック：試料６）の赤外吸収率を測定した。また、参考として、上記試験２で使用した不活性雰囲気熱処理の多孔質シリカ粒子（試料７）と、未処理多孔質シリカ粒子（試料８）の赤外吸収率も測定した。このときの周波数範囲は３７０〜７８００ｃｍ-１であり、波長範囲は１．２８〜２７μｍである。赤外域での透過率の高いＫＢｒ板の間に試料５〜８の粒子を挟み、赤外透過率を測定して吸収率に換算した。この赤外吸収率をそれぞれの粒子の密度で割った吸収係数（Specific Extinction）の波長依存性を図４に示す。
Therefore, the infrared absorption coefficient was evaluated as a parameter indicating the effect of suppressing radiant heat transfer. First, the infrared absorptivity of the core material particles (porous silica particles + graphite:
図４の結果において、波長の短い近赤外領域ではカーボンブラック（試料６）の吸収係数が高いものの、抑えるべき３０℃付近の温度に対する輻射スペクトルのピーク付近よりも長波長領域ではグラファイト（試料５）の吸収係数が高くなるという結果を得た。さらに、試料５〜８の赤外吸収率スペクトルに対して、ロッセランド（Rosseland）平均の演算処理を加えることで、輻射伝熱λｒの下記計算式（１）におけるロッセランド吸収係数Ｋｓを密度で割った値を求め、当該値を本発明における「赤外線吸収係数」とした。その結果を表２に示す。なお、下記計算式（１）において、ｎは屈折率、σはステファンボルツマン定数、Ｔは温度、ρ’は相対密度、ρｓは固体密度である。また、参考試料７，８を芯材として上記試験２と同様にして作製した真空断熱材の熱伝導率も測定した。その結果も表２に示す。
In the result of FIG. 4, although the absorption coefficient of carbon black (sample 6) is high in the near-infrared region where the wavelength is short, graphite (sample 5) is used in the longer wavelength region than the vicinity of the peak of the radiation spectrum with respect to a temperature near 30 ° C. to be suppressed. ), The absorption coefficient is high. Further, with respect to the infrared absorption spectrum of the sample 5-8, the addition of arithmetic processing Rosserando (Rosseland) average, divided by Rosserando absorption coefficient Ks in the following equation of radiative heat transfer lambda r (1) at a density The value was determined and used as the “infrared absorption coefficient” in the present invention. The results are shown in Table 2. In the following calculation formula (1), n is a refractive index, σ is a Stefan-Boltzmann constant, T is a temperature, ρ ′ is a relative density, and ρ s is a solid density. Moreover, the thermal conductivity of the vacuum heat insulating material produced by using the
表２の結果からも明らかなように、炭素粒子としてグラファイトを使用した方が、カーボンブラックを使用した場合よりも赤外線吸収係数が高く、熱伝導率は低かった。これにより、グラファイトの方がカーボンブラックよりも輻射伝熱抑制効果が高いことが確認された。また、優れた断熱性を備える真空断熱材とするには、赤外線吸収係数が１１０ｍ２／ｋｇ以上であることが好ましいことも確認された。
As is clear from the results in Table 2, the infrared absorption coefficient was higher and the thermal conductivity was lower when graphite was used as the carbon particles than when carbon black was used. As a result, it was confirmed that graphite had a higher effect of suppressing radiant heat transfer than carbon black. It was also confirmed that an infrared absorption coefficient of 110 m 2 / kg or more is preferable for a vacuum heat insulating material having excellent heat insulating properties.
Claims (9)
前記多孔質シリカ粒子は、表面に炭化水素基を有する多孔質シリカ粒子であって、熱処理により前記炭化水素基の存在量が低減されていることを特徴とする、真空断熱材 A porous heat insulating material obtained by mixing porous silica particles and carbon particles and vacuum-sealing with a non-breathable sealing film,
The porous silica particle is a porous silica particle having a hydrocarbon group on its surface, wherein the abundance of the hydrocarbon group is reduced by heat treatment,
前記多孔質シリカ粒子は表面に炭化水素基を有する多孔質シリカ粒子であって、前記炭素粒子と混合する前に、予め熱処理により前記炭化水素基の存在量を低減する工程を有することを特徴とする、真空断熱材の製造方法。 A method for producing a vacuum heat insulating material, in which porous silica particles and carbon particles are mixed and vacuum-sealed with a non-breathable sealing film,
The porous silica particle is a porous silica particle having a hydrocarbon group on its surface, and has a step of reducing the abundance of the hydrocarbon group by heat treatment in advance before mixing with the carbon particle. A method for manufacturing a vacuum heat insulating material.
The manufacturing method of the vacuum heat insulating material of Claim 8 which performs the said heat processing in 350-550 degreeC.
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