Rigid polyurethane foam

Abstract

To reduce the thermal conductivity of a rigid polyurethane foam compared to traditional levels.SOLUTION: A rigid polyurethane foam comprises an urethane resin containing a constituent unit derived from a polyol and a constituent unit derived from an isocyanate, a foaming agent, and fine particles, wherein the fine particles have a surface layer, and the surface layer has a hydrophobic group and a hydrophilic group.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rigid polyurethane foam that can be used, for example, as a heat insulating material for refrigerators.

Background Art

[0002] In rigid polyurethane foam, if the cells become too large, the thermal conductivity increases. Therefore, in order to keep the thermal conductivity low, it is necessary to suppress excessive cell growth. Therefore, in order to make the rigid polyurethane foam have a lower thermal conductivity, as described in Patent Document 1 or 2, hollow fine particles made of aluminosilicate or hollow fine particles made of hydrophobic silica are incorporated into the rigid polyurethane foam, and it is considered that these fine particles physically suppress the growth of the cells when the rigid polyurethane foam foams.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the rigid polyurethane foam described in Patent Documents 1 and 2, in order to exhibit the effect of reducing the thermal conductivity, it is necessary to relatively increase the content of the fine particles to at least 3% by weight or more.

[0005] However, when the inventors studied, when trying to produce a rigid polyurethane foam using hollow fine particles made of aluminosilicate as described in Patent Document 1, if an amount of fine particles for achieving the above-described effect was to be contained in the polyol premix which is a material of the rigid polyurethane foam, since the fine particles themselves are hydrophilic, after a lapse of time from mixing, hydrophobic components (for example, cyclopentane etc. contained in the polyol premix as a foaming agent) which had been dissolved or dispersed in the polyol premix would separate, and it was found that there was a problem that the foaming ratio of the rigid polyurethane foam would decrease.

[0006] Also, even when trying to produce a rigid polyurethane foam using hydrophobic fine particles as described in Patent Document 2, if an amount of hydrophobic fine particles necessary for achieving the above-described effect was to be contained in the polyol premix which is a material of the rigid polyurethane foam, in this case as well, after a lapse of time from mixing, the fine particles would separate from the polyol premix and it would be difficult to uniformly disperse the fine particles, and as a result, it was found that the growth of bubbles could not be efficiently suppressed.

[0007] The present invention has been made in view of such problems, and a main object thereof is to provide a rigid polyurethane foam having a lower thermal conductivity than conventional ones while maintaining a sufficient foaming ratio.

Means for Solving the Problems

[0008] That is, the rigid polyurethane foam according to the present invention is as follows. [1] A rigid polyurethane foam containing a urethane resin containing a structural unit derived from a polyol and a structural unit derived from an isocyanate, a foaming agent, and fine particles, wherein the fine particles have a surface layer, and the surface layer has a hydrophobic group and a hydrophilic group. [2] The surface layer is formed by a modifying group chemically bonded to the surface of the fine particles, The modifying group is derived from a surface treating agent having a hydrophobic group and a hydrophilic group in one molecule, the rigid polyurethane foam according to [1]. [3] The hydrophilic group is an amino group or a hydroxyl group, the rigid polyurethane foam according to [1] or [2]. [4] The hydrophobic group is a linear alkyl group having 1 to 10 carbon atoms, the rigid polyurethane foam according to any one of [1] to [3]. [5] The fine particles contain an inorganic material, the rigid polyurethane foam according to any one of [1] to [4]. [6] The fine particles are hollow particles or porous particles, the rigid polyurethane foam according to any one of [1] to [5]. [7] The content of the fine particles with respect to the whole rigid polyurethane foam is 0.01% by volume or more and 0.5% by volume or less, the rigid polyurethane foam according to any one of [1] to [6]. [8] The content of the fine particles with respect to the whole rigid polyurethane foam is 0.1% by weight or more and 1.5% by weight or less, the rigid polyurethane foam according to any one of [1] to [7]. [9] The average particle diameter of the fine particles is 0.03 μm or more and 20 μm or less, the rigid polyurethane foam according to any one of [1] to [7].

[10] The bulk density of the fine particles is 200 kg / m 3 or less, the rigid polyurethane foam according to any one of [1] to [9].

[11] A polyol premix containing a polyether polyol and / or a polyester polyol, a foaming agent, and fine particles, and an isocyanate, and a method for producing a rigid polyurethane foam, characterized in that the fine particles have a surface layer, and the surface layer has a hydrophobic group and a hydrophilic group.

[12] The method for producing a rigid polyurethane foam according to

[11] , wherein the viscosity of the polyol premix is 500 mPa·s or more and 2000 mPa·s or less.

Advantages of the Invention

[0009] According to the present invention, the thermal conductivity of the rigid polyurethane foam can be further reduced compared to the prior art.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. <Configuration of the Rigid Polyurethane Foam According to this Embodiment> The rigid polyurethane foam according to this embodiment is formed by foam curing to form a large number of cells, more preferably closed cells, inside. The density of the entire rigid polyurethane foam is 30 kg / m 3 or more and 45 kg / m 3It is preferably the following, 32 kg / m 3 or more and 40 kg / m 3 or less. More preferably, it is 32 kg / m 3 or more and 38 kg / m 3 or less.

[0012] The rigid polyurethane foam contains a urethane resin composed of a structural unit derived from a polyol and a structural unit derived from an isocyanate, a foaming agent that forms the aforementioned bubbles, and fine particles. Note that the rigid polyurethane foam is a urethane foam that has lost its resilience and cushioning properties after curing, and is often used for heat insulation applications.

[0013] Examples of the polyol include polyether polyol and / or polyester polyol. It is preferable that the structural unit derived from the polyol contains a structural unit derived from an aromatic amine compound having 4 to 6 functional groups and to which both ethylene oxide and propylene oxide are added (also referred to as the first structural unit). Specific examples of the first structural unit include, for example, 2,3-toluenediamine, 2,4-toluenediamine, 2,6-toluenediamine, etc. The content of the first structural unit is preferably in the range of 65% by mass or more and 99% by mass or less when the total of the structural units derived from the polyol is 100% by mass.

[0014] The structural unit derived from the polyol may further contain a structural unit derived from an aliphatic non - amine compound having 2 to 4 functional groups and to which ethylene oxide is added (also referred to as the second structural unit). Specific examples of the second structural unit include, for example, ethylene glycol, propylene glycol, glycerin, pentaerythritol, and the like. In this case, the content of the second structural unit is preferably in the range of 1% by mass or more and 10% by mass or less when the total of the structural units derived from the polyol is 100% by mass. By containing the structural unit derived from the non - aromatic amine compound in the above - mentioned range in the structural unit derived from the polyol, steric hindrance due to the aromatic ring can be suppressed, and the strength of the bubble film can be improved. As a result, the bubbles can be made finer and high gas barrier properties can be imparted, so it is considered that the thermal conductivity of the particulate - containing rigid polyurethane foam can be further reduced.

[0015] The structural unit derived from the polyol may contain the above - mentioned first structural unit and a structural unit derived from an aromatic dicarboxylic acid having 2 to 4 functional groups and to which a diol is added (also referred to as the third structural unit). Specific examples of the aromatic dicarboxylic acid constituting the third structural unit include phthalic anhydride, terephthalic acid, and the like. Examples of the diol include diethylene glycol, 1,4 - butanediol, 1,3 - propanediol, 3 - methyl - 1,5 - pentanediol, and the like. In this case, when the total of the structural units derived from the polyol is 100% by mass, it is preferable to contain the first structural unit in the range of 65% by mass or more and 99% by mass or less, and it is preferable to contain the third structural unit in the range of 1% by mass or more and 10% by mass or less. By the structural unit derived from the polyol containing the first structural unit and the third structural unit, the aromatic rings of these structural units stack on each other, and the strength of the bubble film can be further improved. As a result, the bubbles can be made finer and high gas barrier properties can be imparted, so it is considered that the thermal conductivity of the particulate - containing rigid polyurethane foam can be further reduced. Note that the names of the above-mentioned first structural unit, second structural unit, and third structural unit are for convenience, and do not have any special meaning such as necessarily containing the first structural unit or the second structural unit as a prerequisite when containing the third structural unit, etc.

[0016] As the isocyanate, those conventionally used in rigid polyurethane foams can be widely used, but it is preferable to use polymeric MDI.

[0017] As the foaming agent, any foaming agent can be used as long as it is used in the production of rigid polyurethane foams. For example, it is particularly preferable to use an organic solvent with a relatively low boiling point as the foaming agent. Specifically, it is preferable to use a foaming agent with a boiling point of 55°C or lower, and particularly preferably a foaming agent with a boiling point of 50°C or lower. In this embodiment, cyclopentane is used as an example of such a foaming agent.

[0018] The rigid polyurethane foam according to this embodiment may further contain additives such as a catalyst and a foam stabilizer (binder) in addition to the above-mentioned components.

[0019] Examples of the catalyst include a resinification catalyst, a foaming catalyst, and a trimerization catalyst. If these catalysts contain a tertiary amine, it is preferable because a polyurethane foam that takes environmental considerations as much as possible can be obtained while suppressing the production cost.

[0020] As the foam stabilizer, those conventionally used in rigid polyurethane foams can be widely used, but it is particularly preferable to use a silicone-based foam stabilizer.

[0021] As shown in FIG. 1, the fine particles contained in the rigid polyurethane foam according to this embodiment include an air layer (core), a spherical or polygonal shell, and a surface layer formed so as to cover the surface of the shell.

[0022] The shell is preferably made of an inorganic material excellent in strength and heat resistance, and examples thereof include hollow particles, porous particles, aerogels, xerogels, etc. made of oxides such as silica and alumina.

[0023] The surface layer has both a hydrophobic group and a hydrophilic group. The surface layer is, for example, a modifying group fixed to the above-described shell via a chemical bond such as a covalent bond, and is formed by a modifying group having both a hydrophobic group and a hydrophilic group.

[0024] The modifying group is not particularly limited as long as it has one or more hydrophobic groups and one or more hydrophilic groups. However, as shown in FIG. 2, a bonding group for chemically bonding the shell and the modifying group, a hydrophobic group, and a hydrophilic group are preferably linearly bonded in this order from the side closer to the shell. Furthermore, after the bonding group, the hydrophobic group, and the hydrophilic group are arranged from the side closer to the shell, a structure in which there is further a hydrophobic group or a structure in which pairs of hydrophobic groups and hydrophilic groups are repeated may also be acceptable. The surface layer may be composed of only one type of the above-described modifying group, or may contain two or more types of the above-described modifying groups.

[0025] The bonding group is not particularly limited as long as it can chemically bond the shell and the modifying group. For example, when the shell is silica, a silane compound such as trimethoxysilane may be used. Examples of the hydrophobic group include linear or cyclic hydrocarbon groups having 1 to 10 carbon atoms such as an ethyl group, a methyl group, and a propyl group. The hydrophilic group preferably has an amino group or a hydroxyl group. In one modification group derived from the surface treatment agent, one or more of the hydrophobic groups described above may be included, or one or more hydrophilic groups may be included. Further, when a plurality of types of hydrophobic groups and / or hydrophilic groups are included in one modification group, as long as there is a bonding group first and then the hydrophobic groups and hydrophilic groups are arranged alternately, they may be arranged in any order and in any number.

[0026] The surface layer as described above can be formed, for example, by surface-treating the shell using a surface treatment agent such as a silane coupling agent having both a hydrophobic group and a hydrophilic group in one molecule. More specifically, the surface layer may be formed by chemically bonding the surface of the shell and the surface treatment agent to each other by a covalent bond or the like so that a large number of the modification groups are arranged to cover the surface of the shell. When the surface treatment agent is linear, the modification group derived from the surface treatment agent is arranged to extend outward from the surface of the shell.

[0027] From the viewpoint of minimizing the thermal conductivity of the rigid polyurethane foam, it is preferable that the thermal conductivity of the fine particles is lower than that of the urethane resin. The thermal conductivity of the fine particles is preferably, for example, 50 mW / m·K or less, more preferably 30 mW / m·K or less, and particularly preferably 20 mW / m·K or less.

[0028] The bulk density of the fine particles is preferably 200 kg / m 3 or less, and more preferably 150 kg / m 3 or less. If the bulk density of the fine particles is 200 kg / m 3 or less, the viscosity of the polyol mix does not become too high, and the generation of the voids described above can be more suppressed, which is preferable. Since the heat insulation performance of the rigid polyurethane foam improves as the bulk density of the fine particles decreases, the smaller the bulk density of the fine particles, the better. The bulk density can be obtained by unit conversion from the bulk density (g / ml) determined by gently placing 100 g of the particulate powder into a graduated cylinder, leveling the upper surface, and reading the bulk volume V0 (unit: ml).

[0029] The average particle diameter of the fine particles is preferably 0.03 μm or more and 20 μm or less. If the average particle diameter of the fine particles is 0.03 μm or more, the effect of suppressing the growth of bubbles due to the presence of the fine particles can be sufficiently exerted, which is preferable. Further, if the average particle diameter of the fine particles is 20 μm or less, the number of fine particles contained in the rigid polyurethane foam can be sufficiently ensured, and the effect of suppressing the growth of bubbles can be sufficiently exerted, which is preferable. The average particle diameter of the fine particles can be measured by observation with a scanning electron microscope.

[0030] The shape of the fine particles may be any of spherical, ellipsoidal, other geometric shapes, irregular shapes, etc., but spherical or ellipsoidal shapes are preferable. It is more preferable that the shape coefficient, which is the quotient obtained by dividing the sum of the aspect ratio (the value obtained by dividing the major axis length by the minor axis length) and the concavity-convexity coefficient (the value obtained by dividing the cross-sectional area in the plane including the major axis and the minor axis by the square of the outer peripheral length) by 2, is 120 or less.

[0031] In the rigid polyurethane foam according to the present embodiment, the content of the fine particles is preferably 0.01% by volume or more and 1.0% by volume or less, and more preferably 0.05% or more and 0.5% by volume or less, when the total volume of the rigid polyurethane foam is 100% by volume.

[0032] By setting the content of the fine particles to 0.01% by volume or more, the number of particles per bubble can be 1 or more, so that the bubbles can be surely refined. Further, by setting the content of the fine particles to 1.0% by volume or less, an increase in the viscosity of the polyol mix, which is a material of the rigid polyurethane foam before foaming and curing containing polyol or the like, can be suppressed, and an increase in the thermal conductivity due to large bubbles generated in the urethane foam not escaping and forming voids can be suppressed. In addition, the viscosity of the polyol premix can be adjusted not only as described above but also by the types of polyol mix and isocyanate used, etc. For example, it is preferably 500 mPa·s or more and 2000 mPa·s or less.

[0033] <Method for producing rigid polyurethane foam according to this embodiment> The rigid polyurethane foam according to this embodiment can be produced, for example, by the following procedures and steps. First, a mixed solution containing polyether polyol and / or polyester polyol is prepared. This mixed solution and the fine particles are mixed at normal temperature and under atmospheric release, and then a blowing agent is added and mixed in a sealed space at 20°C to 25°C to adjust the polyol premix.

[0034] After adding isocyanate to the polyol premix and stirring, the mixed solution is poured into an appropriate mold and freely foamed at an appropriate temperature to produce a rigid polyurethane foam.

[0035] The polyol premix may further contain a foam auxiliary agent. When the foam auxiliary agent is contained, the content of the foam auxiliary agent in the polyol premix is preferably 0.5% by mass or more and 2.0% by mass or less. The foam auxiliary agent is not particularly limited, but it is preferable to use water from the viewpoint of achieving both high reaction efficiency and low cost.

[0036] <Effect according to this embodiment> According to the rigid polyurethane foam according to this embodiment, since the fine particles are provided with a surface layer having a hydrophobic group and a hydrophilic group, even when the fine particles are contained in the polyol premix, the balance between hydrophilicity and hydrophobicity in the polyol premix is not disrupted, and it is possible to suppress the separation of hydrophobic components and fine particles. As a result, as shown in Figure 3, the size of the bubbles can be made small and uniform throughout the entire rigid polyurethane foam.

[0037] In addition, if the number of hydrophilic groups contained in the surface layer is large, the formation of chemical bonds forming the urethane resin can be further promoted, thereby promoting the curing of the urethane resin. Therefore, the urethane resin can be cured before the bubbles become too large, and the growth of the bubbles can be more effectively suppressed.

[0038] The hydrophilic groups contained in the above-described modifying groups can directly form chemical bonds via urethane bonds or urea bonds with the urethane resin constituting the urethane resin. Therefore, fine particles having a lower thermal conductivity than the urethane resin are incorporated into the urethane skeleton forming the urethane resin, and as shown in FIG. 4, the heat that has been transmitted along the urethane skeleton of the conventional urethane resin can be made difficult to transmit.

[0039] Since the surface layer is formed by a linear modifying group in which a hydrophobic group and a hydrophilic group appear in this order from the side closer to the shell, and further a modifying group having a structure in which a hydrophobic group and a hydrophilic group repeatedly appear, the hydrophilic groups contained in these modifying groups can easily access the polyol or isocyanate, and the fine particles can be easily incorporated into the urethane skeleton.

[0040] According to the particulate-containing rigid polyurethane foam according to the present embodiment, since the fine particles are contained in the particulate-containing rigid polyurethane foam after foaming and curing at a ratio of 0.05% by volume or more and 0.35% by volume or less in 100% by volume, it is possible to avoid the number of fine particles contained per volume of the rigid polyurethane foam becoming extremely large or small. Even when the type of the fine particles changes, the required number of fine particles for refining the bubbles is present in the particulate-containing rigid polyurethane foam, and the growth of the bubbles during foaming can be suppressed.

[0041] The particulate-containing rigid polyurethane foam according to this embodiment can be used for various applications as a heat insulating material. Since it has a sufficiently low thermal conductivity and the manufacturing cost can be suppressed within an appropriate range, it can be suitably used, for example, as a heat insulating material for household appliances such as refrigerators.

[0042] Since the particulate-containing rigid polyurethane foam has a lower thermal conductivity than conventional ones, it is possible to exhibit the same heat insulating performance as conventional ones even with a smaller thickness than before. Further, as a result, when used as a heat insulating material between the outer box and the inner box of a refrigerator, the thickness of the heat insulating layer between the outer box and the inner box can be reduced, and the volume inside the inner box (refrigerating compartment) can be made larger than before.

[0043] The present invention is not limited to the above-described embodiments, and various modifications and combinations of embodiments may be made as long as they do not contravene the gist of the present invention.

Examples

[0044] Hereinafter, the present invention will be described in more detail based on specific examples. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0045] First, mixed liquids as described in Table 1 or Table 2 below were prepared respectively. In this example and comparative examples, the viscosity of the polyol premix measured at 20 °C using TVC-10 manufactured by Toki Sangyo Co., Ltd. was 950 mPa·s in all cases. The above mixture adjusted to a liquid temperature of 25 °C was stirred with a hand mixer at 5000 rpm for 4 seconds. Then, it was poured into a wooden box of 300 mm × 300 mm × 30 mm whose temperature was adjusted to 42 °C to 44 °C and allowed to freely foam to produce the rigid polyurethane foams of the example and comparative examples. Table 1 shows the content of the component containing particulates in the whole rigid polyurethane foam in weight %, and Table 2 shows the content of particulates in the whole rigid polyurethane foam after foaming in volume % for the examples and comparative examples shown in Table 1.

[0046]

Table 1

[0047]

Table 2

[0048] Next, the performance of these examples and comparative examples was evaluated by the methods shown below, and the results are shown in Table 3. Also, the micrographs of each example and comparative example are shown in Figures 5 and 6. <Measurement of thermal conductivity> For each of the particulate-containing rigid polyurethane foams and the particulate-free rigid polyurethane foams of the examples and comparative examples after foaming and curing, a rigid polyurethane foam with dimensions of 300 mm × 300 mm × 30 mm in thickness was measured for its thermal conductivity at an average temperature of 20°C using a NETZSCH steady-state thermal conductivity measuring device (HFM436).

[0049] <Measurement of bubble size> Using a Keyence digital microscope VHX-5000, the bubble diameters of 10 arbitrary bubbles within the observation field of view were measured, and the bubble size (D50) was calculated from the average value thereof.

[0050] <Measurement of the density of the entire particulate rigid polyurethane foam> The weight of a rigid polyurethane foam with dimensions of 300 mm × 300 mm × 30 mm in thickness was measured using an electronic balance, and the density of the entire foam was calculated from the volume of the entire rigid polyurethane foam.

[0051]

Table 3

[0052] From the results of the examples and comparative examples shown in these Table 3, Figure 5, and Figure 6, as shown in Examples 1 to 9, when the surface layer of the fine particles contained in the rigid polyurethane foam has both a hydrophobic group and a hydrophilic group, phase separation does not occur at the stage of adjusting the polyol premix, and a rigid polyurethane foam having a sufficient foaming ratio can be obtained, and the thermal conductivity can be made smaller compared to the case where no fine particles are added. On the other hand, as shown in Comparative Examples 10 to 13, when the surface layer of the fine particles contained in the rigid polyurethane foam is hydrophobic, even when the content is 0.14% by weight, the hydrophobic fine particles are separated from the polyol premix, and instead of the effect of reducing the thermal conductivity by containing the fine particles, the thermal conductivity becomes larger than that in Comparative Example 14 where no fine particles were added. Further, in Comparative Examples 11 to 13 where the surface of the fine particles is hydrophilic, the thermal conductivity can be reduced because the polyol premix is foamed and cured immediately after mixing. However, when the polyol premixes of these Comparative Examples 11 to 13 are allowed to stand for 10 hours or more in the same manner as in mass production, the hydrophobic foaming agent is separated from the polyol premix, resulting in an insufficient foaming ratio.

Claims

1. A rigid polyurethane foam containing a urethane resin containing a structural unit derived from a polyol and a structural unit derived from an isocyanate, a foaming agent, and fine particles, wherein the fine particles have a surface layer, and the surface layer has a hydrophobic group and a hydrophilic group. A rigid polyurethane foam characterized by this.

2. The surface layer is formed by a modifying group chemically bonded to the surface of the fine particles, The rigid polyurethane foam according to claim 1, wherein the modifying group is derived from a surface treatment agent having a hydrophobic group and a hydrophilic group in one molecule.

3. The rigid polyurethane foam according to claim 1, wherein the hydrophilic group is an amino group or a hydroxyl group.

4. The rigid polyurethane foam according to claim 1, wherein the hydrophobic group is a linear alkyl group having 1 to 10 carbon atoms.

5. The rigid polyurethane foam according to claim 1, wherein the fine particles contain an inorganic material.

6. The rigid polyurethane foam according to claim 1, wherein the fine particles are hollow particles or porous particles.

7. The rigid polyurethane foam according to claim 1, wherein the content of the fine particles with respect to the entire rigid polyurethane foam is 0.01% by volume or more and 0.5% by volume or less.

8. The rigid polyurethane foam according to claim 1, wherein the content of the fine particles with respect to the entire rigid polyurethane foam is 0.1% by weight or more and 1.5% by weight or less.

9. The rigid polyurethane foam according to claim 1, wherein the average particle diameter of the fine particles is 0.03 μm or more and 20 μm or less.

10. The bulk density of the microparticles is 200 kg / m ３ The rigid polyurethane foam according to claim 1, wherein the bulk density is 200 kg / m or less.

11. A polyol premix containing a polyether polyol and / or a polyester polyol, a foaming agent, and fine particles, A method for producing a rigid polyurethane foam by mixing an isocyanate, wherein the fine particles have a surface layer, and the surface layer has a hydrophobic group and a hydrophilic group. A method for producing a rigid polyurethane foam characterized by this.

12. The method for producing a rigid polyurethane foam according to claim 11, wherein the viscosity of the polyol premix is 500 mPa·s or more and 2000 mPa·s or less.

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