Method of preparing polyurethane foam and polyurethane foam

Abstract

The present invention relates to a method for manufacturing polyurethane foam and a polyurethane foam manufactured thereby. According to the present invention, a polyurethane foam with improved thermal insulation performance is provided.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing polyurethane foam and polyurethane foam. Background Technology

[0002] Generally, polyurethane foam is known as a material with excellent thermal insulation properties among organic and inorganic insulation materials, and it is primarily used as an insulation material for refrigerators, refrigerated containers, and cold storage warehouses where high insulation performance is required.

[0003] In particular, to apply polyurethane foam insulation to the storage tanks or fuel tanks of LNG carriers, it is essential to reduce the Boil-Off Rate (BOR) to maximize the remaining LNG volume.

[0004] Since heat transfer in polyurethane foam is largely driven by gas conduction, reducing gas heat transfer is a critical factor. Accordingly, conventional technology has attempted to improve the thermal conductivity of polyurethane foam by modifying the blowing agent. Although the currently used HFC-245fa blowing agent exhibits the lowest thermal conductivity in the cryogenic range among existing polyurethane foam blowing agents, its high Global Warming Potential (GWP) makes it highly likely that its use will be restricted due to environmental concerns.

[0005] Meanwhile, the thermal insulation performance of polyurethane foam improves due to the Knudsen effect as the cell size decreases. The reason pores enlarge during polyurethane foam foaming is that the cells continuously grow or fuse due to cell wall destruction caused by insufficient elongation viscosity—that is, resistance to tensile deformation occurring in the foam's cell walls. Therefore, conventional technology has proposed the following techniques to improve elongation viscosity. First, a technique involving the introduction of solid additives (fillers) was proposed, but there were problems such as the additives not being evenly dispersed or the viscosity rising rapidly. Second, a technique involving mixing two or more polymers was proposed; however, when using raw materials other than urethane, it was necessary to control the reaction, and there was a concern that the compressive strength and thermal conductivity of the polyurethane foam might decrease. Third, a technique for controlling the degree of crystallization was proposed, but there was a problem in that urethane raw materials cannot crystallize.

[0006] Accordingly, there is a need to develop a polyurethane foam with excellent thermal insulation performance that does not cause environmental problems, eliminates concerns about rapid viscosity increase, and allows the use of existing processes. Prior art literature

[0007] Republic of Korea Published Patent Application No. 10-2019-0124593 The problem to be solved

[0008] The objective of the present invention is to provide a method for manufacturing a polyurethane foam capable of producing a polyurethane foam having improved thermal insulation performance. means of solving the problem

[0009] According to one aspect of the present invention, a method for manufacturing a polyurethane foam is provided, comprising the steps of: (S1) synthesizing a multi-arm linear polymer by reacting a branched monomeric polyol, a first isocyanate, and a linear polyol; and (S2) mixing the multi-arm linear polymer, a second isocyanate, and a linear polyol to foam.

[0010] According to one aspect of the present invention, a polyurethane foam manufactured by the polyurethane foam manufacturing method is provided. Effects of the invention

[0011] According to the present invention, a polyurethane foam with improved thermal insulation performance by reducing the cell size of the polyurethane foam and a method for manufacturing the same are provided. Brief explanation of the drawing

[0012] FIG. 1 is a diagram showing the structure of a 3-branched linear polymer and a 4-branched linear polymer according to one embodiment of the present invention. FIG. 2 is a diagram showing the FT-IR (infrared spectroscopy) analysis results of a multi-branched linear polymer according to one embodiment of the present invention. FIGS. 3(a) and FIGS. 3(b) are drawings showing the NMR analysis results of a multi-branched linear polymer according to one embodiment of the present invention. Figure 4 is a diagram showing the GPC analysis results of a multi-branched linear polymer according to one embodiment of the present invention. FIG. 5 is a diagram showing the results of observing a polyurethane foam according to one embodiment of the present invention using a scanning electron microscope (SEM). FIG. 6 is a diagram showing the results of measuring the compressive strength of a polyurethane foam according to one embodiment of the present invention. Specific details for implementing the invention

[0013] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0014] In storage tanks or fuel tanks of LNG carriers, a higher thermal conductivity of the insulation leads to an increase in the Boil-off Rate (BOR) due to LNG vaporization, resulting in significant economic losses. Therefore, reducing the thermal conductivity of insulation is one of the key challenges that insulation materials applied to LNG vessels must address.

[0015] The present invention is a technology that aims to improve the thermal insulation performance of polyurethane foam insulation by reducing the cell size of the polyurethane foam.

[0016] According to one embodiment of the present invention, a method for manufacturing a polyurethane foam is provided, comprising the steps of: (S1) synthesizing a multi-arm linear polymer by reacting a branched monomeric polyol, a first isocyanate, and a linear polyol; and (S2) mixing the multi-arm linear polymer, a second isocyanate, and a linear polyol to foam.

[0017] Hereinafter, (S1) a step of synthesizing a multi-arm linear polymer by reacting a branched monomeric polyol, a first isocyanate, and a linear polyol is described.

[0018] In one embodiment of the present invention, a branched monomeric polyol may refer to a compound having three or four branches bonded to a central carbon atom. Examples of branched monomeric polyols include, but are not limited to, 3-branched polyethylene glycol (3-arm PEG), 4-branched polyethylene glycol (4-arm PEG), glycerol ethoxylate (Gly-EO).

[0019] In one embodiment of the present invention, a branched monomeric polyol can react with a first isocyanate to form a urethane bond (-NHCOO-). The first isocyanate compound may include hexamethylene diisocyanate (HDI), polymethylene diphenyl diisocyanate (poly-MDI), toluene diisocyanate (TDI), etc., and any compound having two or more isocyanate groups (NCO) may be used without special limitations. Preferably, hexamethylene diisocyanate (HDI) may be used.

[0020] In one embodiment of the present invention, a linear polyol refers to a polyol in which repeating units are bonded into a single chain, and examples of such linear polyols include polytetramethylene ether glycol (PTMEG), polypropylene glycol (PPG), polyethylene glycol (PEG), etc., but are not limited thereto.

[0021] As examples of multi-arm prepolymers synthesized by the reaction of a branched monomer polyol, a first isocyanate, and a linear polyol, the structures of a 3-branched prepolymer and a 4-branched prepolymer are illustrated in FIG. 1. As illustrated in FIG. 1, the multi-arm prepolymer comprises a core containing a unit structure derived from a branched monomer polyol, and at least one branch comprising a unit structure derived from a first isocyanate and a unit structure derived from a linear polyol, wherein the unit structure derived from the branched monomer polyol and the unit structure derived from the first isocyanate are connected by urethane bonds, and the unit structure derived from the first isocyanate and the unit structure derived from the linear polyol are connected by urethane bonds. In each branch of the multi-arm prepolymer, the unit structure derived from the first isocyanate and the unit structure derived from the linear polyol may exist in a sequentially bonded form. In addition, as described above, the branched monomeric polyol comprises at least one branch, and preferably may comprise three or four branches.

[0022] In one embodiment of the present invention, the chain length of the multi-branched prepolymer may increase as the input amounts of the first isocyanate and the linear polyol relative to the branched monomer polyol increase. It is desirable to determine the input amounts of the branched monomer polyol, the first isocyanate, and the linear polyol in consideration of this. According to one embodiment of the present invention, in step (S1), the branched monomer polyol, the first isocyanate, and the linear polyol may react in a molar ratio of 1:4:4 to 1:19:19. If the molar ratio is less than 1:4:4, the chain length of the prepolymer becomes excessively short, which may reduce the pore size reduction effect. On the other hand, if the molar ratio exceeds 1:19:19, the prepolymer may entangle due to the increase in chain length, which may reduce compatibility with other raw materials excluding the prepolymer. To manufacture a polyurethane foam with a smaller pore diameter, it is preferable to use a branched monomeric polyol, a first isocyanate, and a linear polyol in a molar ratio of 1:9:9.

[0023] A multi-branched prepolymer according to one embodiment of the present invention may have a weight-average molecular weight of 1,000 to 200,000, but is not limited thereto. Generally, as the chain length of the multi-branched prepolymer increases, the weight-average molecular weight also increases; therefore, it is desirable to appropriately adjust the weight-average molecular weight by considering the pore size of the polyurethane foam to be finally manufactured and compatibility with other raw materials.

[0024] Next, (S2) a step of mixing and foaming a multi-branched linear polymer, a second isocyanate, and a linear polyol is described.

[0025] (S2) The second isocyanate compound used in step (S2) may be hexamethylene diisocyanate (HDI), polymethylene diphenyl diisocyanate (poly-MDI), toluene diisocyanate (TDI), etc., and is not particularly limited as long as it is a compound having two or more isocyanate groups (NCO). Preferably, polymethylene diphenyl diisocyanate (poly-MDI) may be used.

[0026] In one embodiment of the present invention, the linear polyol used in step (S2) may be polytetramethylene ether glycol (PTMEG), polypropylene glycol (PPG), polyethylene glycol (PEG), etc., but is not limited thereto. At this time, the weight-average molecular weight of the linear polyol may be 4500 to 7000.

[0027] In one embodiment of the present invention, in step (S2), the multi-branched prepolymer and the linear polyol may be mixed in a weight ratio of 1:9 or higher, and if the weight ratio is less than 1:9, it is undesirable because the compatibility between the multi-branched prepolymer and the linear polyol decreases. For example, a polyurethane foam may be manufactured by mixing 10 parts by weight of a multi-branched prepolymer and 90 parts by weight of a linear polyol, mixing 40 parts by weight of a second isocyanate, and then foaming. In addition, for example, a polyurethane foam may be manufactured by mixing 5 parts by weight of a multi-branched prepolymer and 95 parts by weight of a linear polyol, mixing in a second isocyanate, and then foaming.

[0028] In the above step (S2), the second isocyanate may be mixed to be 1 to 3.5 times the equivalent amount of hydroxyl groups (OH) present in the multi-branched linear polymer and linear polyol, but is not limited thereto.

[0029] According to one embodiment of the present invention, a composition for manufacturing a polyurethane foam is provided, comprising a branched monomeric polyol, a first isocyanate, and a linear polyol to form a multi-arm linear polymer; a second isocyanate; and a linear polyol, wherein the multi-arm linear polymer may have a branch comprising a central carbon atom and a urethane bond.

[0030] The technical features described in relation to the above-described polyurethane foam manufacturing method apply equally to the composition for manufacturing polyurethane foam, so they are not described redundantly.

[0031] A polyurethane foam manufactured according to one embodiment of the present invention may have an average cell diameter of 200 μm or less, preferably 150 μm or less, and a thermal conductivity of 40 mW / mK or less.

[0032] According to the polyurethane foam manufacturing method and the polyurethane foam manufacturing composition described above, by introducing a multi-branched prepolymer, the elongation viscosity at the cell walls is increased, thereby enabling the production of a polyurethane foam with reduced cell size. Reducing the cell size of the polyurethane foam prevents collisions between gas molecules within the cells, which can drastically reduce the thermal conductivity of the gas; consequently, the thermal insulation performance of the polyurethane foam can be significantly improved regardless of the type of foam.

[0033] Examples

[0034] Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are for the purpose of understanding the present invention only and are not intended to limit the invention.

[0035] 1. Synthesis of Multibranched Linear Polymers

[0036] 3-branched PEG (Mn=1000) and 4-branched PEG (Mn=797) as branched monomeric polyols, and PTMEG (Mn=2000) as a linear polyol were added to a glass bottle in the molar ratios listed in Table 1 below. Subsequently, a dibutyltin dilaurate (DBTDL) catalyst was added to the glass bottle, and moisture was removed by stirring at a stirring speed of 500 rpm for 1 hour under a vacuum at 70°C. After creating a nitrogen environment inside the glass bottle, anhydrous toluene was added. Then, hexamethylene diisocyanate (HDI, molecular weight 168 g / mol) was added, and a urethane reaction was carried out for 1 hour at a reaction temperature of 70°C while stirring at 700 rpm. After the reaction was finished, the product was repeatedly washed with a 1:1 (v / v) mixed solution of hexane and diethyl ether and filtered to obtain a multi-branched linear polymer.

[0037] Supply cost (mall) Branched monomer polyol Linear polyol (PTMEG) Isocyanate (HDI) Example 1 3-branched PEG 1 4 4 Example 2 3-branched PEG 1 9 9 Example 3 3-branched PEG 1 19 19 Example 4 4-branched PEG 1 4 4 Example 5 4-branched PEG 1 9 9 Example 6 4-branched PEG 1 19 19

[0038] 2. Analysis of Multibranched Prepolymer Synthesis Results

[0039] (1) FT-IR (infrared spectroscopy), NMR (nuclear magnetic resonance spectroscopy) analysis

[0040] FT-IR and NMR equipment were used to analyze whether multi-branched linear polymers were synthesized in Examples 1 to 6, and the results are shown in Figures 2 and 3.

[0041] Referring to Fig. 2, the FT-IR analysis results show 2250 cm⁻¹ -1 At this location, all isocyanate groups are removed, and 3300 cm -1 Functional groups formed by urethane bonds were observed at the location. From this, it was confirmed that all reactants formed a multi-branched linear polymer through a urethane reaction without any unreacted raw materials.

[0042] Referring to Figures 3(a) and 3(b), it was confirmed that the chain length of the multi-branched linear polymer increased as the molar ratio of the branched monomer polyol, isocyanate, and linear polyol increased from 1:4:4 to 1:19:19 through the area ratio of the peak (a) corresponding to hydrogen in the branched monomer polyol and the peaks (e, f) corresponding to hydrogen in the linear polyol.

[0043] (2) GPC (Gel Penetration Chromatography) Analysis

[0044] The multi-branched prepolymers synthesized in Examples 1 to 6 were analyzed using GPC equipment, and the results are shown in Figure 4. As a result of the GPC analysis, it was confirmed that multi-branched prepolymers with Mn of 35,000 to 105,000 were synthesized, and it was found that the weight-average molecular weight increases as the chain length of the multi-branched prepolymer increases.

[0045] 3. Polyurethane Foam Manufacturing

[0046] Solution A was prepared by mixing PTMEG (Mn=2000) as a linear polyol, the multi-branched linear polymer synthesized in Examples 2 and 5, a DBTDL catalyst, a silicone surfactant (TEGOSTAB® B 8404), and distilled water as a blowing agent in the weight ratios listed in Table 2 below. Subsequently, Solution B, containing 43.2 parts by weight of polymethylene diphenyl diisocyanate (poly-MDI, Mn~340, number of functional groups~2.7), was added to Solution A (NCO index: 110), and then mixed and foamed using an electric drill at a speed of 1400 rpm for 10 to 15 seconds to produce the polyurethane foams of Examples 7 to 10. Meanwhile, Comparative Example 1 refers to a polyurethane foam prepared under the same conditions as Examples 7 to 10 using a linear polyol corresponding to the total mass of the linear polyol and the multi-branched linear polymer used in Examples 7 to 10, without using a multi-branched linear polymer.

[0047] A solution (parts by weight) B Solution (parts by weight) linear polyol Multibranched linear polymer catalyst silicone surfactants blowing agent Poly-MDI Comparative Example 1 100 0 1 2 2 43.2 Example 7 90 3-branched linear polymer of Example 2 10 1 2 2 43.2 Example 8 90 4-branched linear polymer of Example 5 10 1 2 2 43.2 Example 9 95 3-branched linear polymer 5 of Example 2 1 2 2 43.2 Example 10 95 4-branched linear polymer 5 of Example 5 1 2 2 43.2

[0048] (In Table 2 above, 'parts by weight' refers to the mass relative to the total mass of the linear polyol and the multi-branched linear polymer.)

[0049] 4. Measurement of polyurethane foam cell diameter

[0050] For the polyurethane foams prepared in Examples 7 to 10 and Comparative Example 1, platinum plating was performed on the samples to impart conductivity, and then the cells were observed using a Hitachi S4800 scanning electron microscope (SEM) in a 10 kV environment, and the results are shown in FIG. 5. In addition, the cell diameters of more than 200 of the polyurethane foams were measured, and their average values ​​are shown in Table 3 below.

[0051] Comparative Example 1 Example 7 Example 8 Example 9 Example 10 Cell diameter (μm) 243 170 110 216 188

[0052] Referring to Table 3, it can be seen that in Examples 7 to 10 using multi-branched prepolymers, the cell size of the polyurethane foam was reduced compared to Comparative Example 1. In particular, the polyurethane foam prepared in Example 8 showed a cell size of 110 μm, confirming that the cell size was reduced by up to 55% compared to Comparative Example 1.

[0053] 5. Measurement of Thermal Conductivity of Polyurethane Foam

[0054] The thermal conductivity of polyurethane foam was measured using a double spiral sensor based on the Transient Plane Source (TPS) theory, and the results are shown in Table 4 below.

[0055] Comparative Example 1 Example 7 Example 8 Example 9 Example 10 Thermal conductivity (mW / mK) 40 ± 1.7 38 ± 0.7 36 ± 0.7 39 ± 1.5 39 ± 0.9

[0056] Referring to Table 4, it can be seen that the thermal conductivity of the polyurethane foam in Examples 7 to 10, which used a multi-branched linear polymer, decreased compared to Comparative Example 1. In particular, in the case of Example 8, the thermal conductivity was improved by about 10% compared to Comparative Example 1.

[0057] 6. Measurement of Polyurethane Foam Density

[0058] After filling a beaker with water, a polyurethane foam of known mass was placed into the beaker so that it was completely submerged in the water, and the volume of the polyurethane foam was measured by measuring the amount of water that overflowed. The density of the polyurethane foam was calculated from the measured mass and volume, and the results are shown in Table 5 below.

[0059] Comparative Example 1 Example 7 Example 8 Example 9 Example 10 Density (kg / m³) 3 ) 105 ± 4 127 ± 7 132 ± 10 112 ± 6 119 ± 4

[0060] Referring to Table 5, it can be seen that the density of Examples 7 to 10, which used a multi-branched linear polymer, increased compared to Comparative Example 1.

[0061] 7. Measurement of compressive strength of polyurethane foam

[0062] The compressive strength of polyurethane foam was measured using a universal testing machine (UTM) with a stress-strain curve obtained by applying a strain rate of 10% / min to a specimen with dimensions of 1cm x 1cm x 1cm x width, and the results are shown in Fig. 6 and Table 6 below.

[0063] Comparative Example 1 Example 7 Example 8 Example 9 Example 10 Compressive strength (MPa) 0.007 0.018 0.021 0.011 0.014

[0064] Referring to Table 6, the compressive strength of the polyurethane foams prepared in Examples 7 to 10 increased by at least 58% and up to 200% compared to the polyurethane foam prepared in Comparative Example 1, which is due to the reduction in cell size of the polyurethane foam.

[0065] Meanwhile, in this embodiment, the polyurethane foam is manufactured using a linear polyol with a weight-average molecular weight of 4500 to 7000 and a multi-branched prepolymer as raw materials, and although it does not meet the compressive strength standards for LNG ship insulation materials, considering that the compressive strength is significantly improved in Examples 7 to 10 with the addition of a multi-branched prepolymer, it is expected that the target compressive strength (≥0.05 MPa) can be achieved when using a general raw material for rigid materials (a linear polyol with a weight-average molecular weight of 300 to 1000).

Claims

Claim 1 (S1) a step of synthesizing a multi-arm prepolymer by reacting a branched monomer polyol, a first isocyanate, and a linear polyol, and (S2) a step of mixing the multi-arm prepolymer, a second isocyanate, and a linear polyol to foam, wherein the multi-arm prepolymer comprises a core having a unit structure derived from the branched monomer polyol, and three or four branched portions having a unit structure derived from the first isocyanate and a unit structure derived from the linear polyol. Claim 2 A method for manufacturing polyurethane foam according to claim 1, wherein the branched monomeric polyol is a compound having three or four branches bonded to a central carbon atom. Claim 3 A method for manufacturing a polyurethane foam according to claim 1, wherein the branched monomeric polyol is one or more compounds selected from 3-branched polyethylene glycol (3-arm PEG), 4-branched polyethylene glycol (4-arm PEG), and glycerol ethoxylate (Gly-EO). Claim 4 A method for manufacturing a polyurethane foam according to claim 1, wherein the linear polyol is one or more compounds selected from polytetramethylene ether glycol (PTMEG), polypropylene glycol (PPG), and polyethylene glycol (PEG). Claim 5 A method for manufacturing a polyurethane foam according to claim 1, wherein the first isocyanate and the second isocyanate are each independently one or more compounds selected from hexamethylene diisocyanate (HDI), polymethylene diphenyl diisocyanate (poly-MDI), and toluene diisocyanate (TDI). Claim 6 A method for manufacturing a polyurethane foam according to claim 1, wherein in step (S1), the molar ratio of the branched monomer polyol, the first isocyanate, and the linear polyol is 1:4:4 to 1:19:

19. Claim 7 A method for manufacturing a polyurethane foam according to claim 1, wherein in step (S2), the weight ratio of the multi-branched linear polymer and the linear polyol is 1:9 or higher, and the second isocyanate is mixed such that the equivalent number of isocyanate groups (NCO) present in the second isocyanate is 1 to 3.5 times the equivalent number of hydroxyl groups (OH) present in the multi-branched linear polymer and the linear polyol. Claim 8 Polyurethane foam manufactured by a manufacturing method according to any one of claims 1 to 7.

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