Method for producing polyurethane foam, and polyurethane foam

Abstract

To provide a method for producing a polyurethane foam that is repeatedly regenerable, and to provide a polyurethane foam that is repeatedly reusable.SOLUTION: The method of manufacturing a polyurethane foam disclosed herein comprises a heating regeneration step of heating a polyurethane foam molded by a heat compression molding to restore it to its shape before the heat compression molding. The polyurethane reaction composition of the polyurethane foam contains 10 wt.% or more of a polymer polyol.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing recycled polyurethane foam and to reusable polyurethane foam. [Background technology]

[0002] There are technologies for returning polyurethane foam molded into a predetermined shape to its original shape. For example, Patent Document 1 discloses a shape-memory polymer foam that has good moldability and exhibits a large change in elastic modulus around the glass transition point (Claim (1)). This shape-memory polymer molded product is deformed at a temperature above the glass transition point of the polymer but below the molding temperature, and the deformed shape is fixed by cooling to below the glass transition point while maintaining the deformation. The original molded shape is restored by heating to above the glass transition point (page 131, right column, lines 12-17).

[0003] Patent Document 2 also discloses a shape-memory porous sheet that can be heated to 130 to 230°C in a desired shape and maintained in that shape for usually 1 minute to 20 hours, preferably 5 minutes to 10 hours, thereby memorizing the shape as an original shape; that can be deformed at a temperature of 130°C or less, preferably room temperature to 100°C, and that can be fixed and maintained even after the external force is removed by cooling the sheet to near room temperature (40°C or less) while maintaining the deformation; and that the porous sheet with the fixed deformation can be restored to the original shape by heating the sheet to 40°C or more, preferably 45 to 100°C (page 552, lines 3-14 in the lower left column).

[0004] Thus, Patent Documents 1 and 2 disclose a technology that uses polyurethane that softens when heated to make it easier to process and solidifies and molds when cooled, in order to return a polyurethane foam that has been molded into a predetermined shape to its original shape before molding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2-113016 [Patent Document 2] Japanese Patent Application Publication No. 2-167349 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional polyurethanes have not been sufficiently durable for repeated recycling. However, if polyurethane foams that have been molded into a predetermined shape could be repeatedly recycled by returning them to their original shape, it would be possible to make effective use of polyurethane foam raw materials, reduce waste, and even reduce costs.

[0007] The present disclosure has been made in view of the above, and an object of the present disclosure is to provide a method for producing a repeatedly recyclable polyurethane foam, and a repeatedly reusable polyurethane foam. [Means for solving the problem]

[0008] The means for solving the above problems include the following aspects.

[0009] A first aspect of the present disclosure is a method for producing polyurethane foam, comprising a thermal regeneration step of heating polyurethane foam molded by thermal compression molding to return it to the shape it had before the thermal compression molding, wherein the polyurethane reaction composition of the polyurethane foam contains 10 wt % or more of a polymer polyol.

[0010] A second aspect of the present disclosure is a polyurethane foam that can be cycled at least five times to be molded by thermal compression molding and then restored to its original shape before thermal compression molding by thermal regeneration.

[0011] A third aspect of the present disclosure is the polyurethane foam of the second aspect, in which the repeatability (%) calculated by the following formula (1) after each cycle is 85% or more. Repeatability (%) = (thickness after recycling) / (thickness before thermal compression molding) × 100 ···(1)

[0012] A fourth aspect of the present disclosure is a polyurethane foam according to the second or third aspect, wherein the repeated compression set (%) calculated according to JIS K6401 using the following formula (2) after each cycle is 15% or less: Repeated compression set (%) = (thickness before compression - thickness after release) / thickness before compression x 100 ···(2) [Effects of the Invention]

[0013] The method for producing repeatedly renewable polyurethane foam and the repeatedly reusable polyurethane foam according to the present disclosure enable effective use of polyurethane foam raw materials, reduction of waste, and reduction of costs. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating a flat polyurethane foam having a three-dimensional pattern with projections and depressions "molded" (shaped) on the surface of the flat polyurethane foam. [Figure 2] This is a diagram illustrating the state in which polyurethane foam that has been "molded" with a three-dimensional pattern with unevenness on its surface has been "regenerated" into the original flat polyurethane foam without unevenness. [Figure 3] This is a diagram illustrating the process by which polyurethane foam that has been "molded" into an inverted U-shape with a three-dimensional, uneven surface pattern is "regenerated" back into its original, flat, smooth shape. [Figure 4] FIG. 1 is a diagram for explaining the "molding->regeneration" cycle. [Figure 5] 1 is a table showing the raw materials used in Examples 1-6 and Comparative Examples 1-5. [Figure 6] 1 is a table showing the blending amounts and evaluation results of Examples 1 to 6. [Figure 7]1 is a table showing the blending amounts and evaluation results of Comparative Examples 1-5. [Figure 8] 1 is a table showing the repeated molding retention (%) of Examples 1-6 and Comparative Examples 1-5. [Figure 9] 1 is a table showing the repeatability (%) of Examples 1-6 and Comparative Examples 1-5. [Figure 10] 1 is a table showing repeated compression residual strains (%) of Examples 1-6 and Comparative Examples 1-5. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of a method for producing a polyurethane foam and a polyurethane foam according to the present disclosure will be described with reference to the drawings. In the following description, the term "method for producing a polyurethane foam" may be read as "method for regenerating a polyurethane foam."

[0016] The polyurethane foam according to the present disclosure has shape retention properties and can be molded by thermal compression molding so as to maintain a predetermined shape. As used herein, "thermal compression molding" (also referred to as "molding") refers to processing a polyurethane foam into a predetermined shape by placing it in a predetermined temperature environment for a predetermined time and then pressing it in a mold at a low temperature (50°C or less). "Molding" also includes processing into a three-dimensional shape different from the three-dimensional shape before molding, and also includes reducing only the thickness of the polyurethane foam (the length perpendicular to the surface area). Figure 1 shows an example of a flat polyurethane foam being "molded" into a predetermined shape.

[0017] After being molded by thermal compression molding, the polyurethane foam according to the present disclosure can be restored to its original shape before thermal compression molding by placing it in a predetermined temperature environment for a predetermined time (i.e., by heating). In this manner, polyurethane foam can be produced by recycling. As used herein, "thermal recycling" (also referred to as "recycling") refers to the process of heating a polyurethane foam molded by thermal compression molding to return it to its original shape before thermal compression molding. Figure 2 shows an example of "recycling" a polyurethane foam molded into a predetermined shape into its original flat shape. A polyurethane foam molded into a predetermined shape can be restored to its original flat shape by heating, for example, as shown in Figure 3.

[0018] In this specification, performing both "molding" and "recycling" may be described as one cycle (molding → recycling) as shown in Figure 4. The polyurethane foam according to the present disclosure can be regenerated by heating even after being molded by thermal compression molding, and the regenerated polyurethane foam can be molded again. In this way, the "molding → recycling" cycle can be repeated multiple times. It is also possible to mold the foam into a different shape each time it is molded. As described above, the polyurethane foam according to the present disclosure can be reused multiple times even if it has been molded once.

[0019] [Polyurethane foam] The polyurethane foam according to the present disclosure may be a polyurethane foam produced by a mechanical froth method from a polyurethane reaction composition and a foam-forming gas such as an inert gas. The mechanical froth method is a method for producing polyurethane foam by feeding a mixed raw material, in which a foam-forming gas is compressed and mixed into a polyurethane reaction composition, into an O-X mixer or a nozzle with a tapered tip, discharging the mixed raw material from the O-X mixer or nozzle, and then heating and curing the mixture. The mixed raw material can be discharged either continuously onto a release paper or by a molding method into a mold. In the mechanical froth method, the foam-forming gas, which had been compressed during the discharge of the mixed raw material, expands to form bubbles, and the polyol component and isocyanate component react and harden in this state, producing a polyurethane foam. This polyurethane foam uses a foam-forming gas, such as an inert gas, as a foaming agent (foaming agent) for the polyurethane reaction composition, and the foam-forming gas is contained within the cells of the polyurethane foam.

[0020] [Polyurethane reaction composition] The polyurethane reaction composition contains a polyol component and an isocyanate component. The polyurethane reaction composition may further contain an acid-modified polyolefin powder or a normal polyolefin powder, a foam stabilizer, a catalyst, etc.

[0021] (1) Polyol component The polyol component includes polymer polyols as well as polyols other than polymer polyols.

[0022] Polymer polyol (POP) In this specification, polymer polyol refers to a compound or mixture obtained by polymerizing a monomer having a polymerizable unsaturated group in a polyether polyol, and the monomer includes acrylonitrile (AN) and / or styrene (ST). For example, polymer polyol is a modified polyether polyol in which polymer fine particles obtained by radically polymerizing vinyl monomers such as acrylonitrile and / or styrene in a polyether polyol such as polyoxypropylene glycol (PPG) are stably dispersed in the polyether polyol. One type of monomer may be used alone, or multiple types may be used. When multiple types of monomers are used, the composition, for example, the composition of acrylonitrile and styrene, may be 1:1 by weight. The polymer polyol preferably has a molecular weight of 2000 to 5000 and a functional group number of 2 to 4. The solid content of acrylonitrile, styrene, etc. in the polymer polyol is preferably 18 to 50 wt %, more preferably 20 to 44 wt %, and particularly preferably 20 to 43 wt %. Two or more types of polymer polyols may be used in combination. By including a polymer polyol in the polyurethane reaction composition, the polyurethane foam can be preheated to a temperature higher than the glass transition temperature of the solid content of the polymer polyol, and the polyurethane foam can be thermoplastically deformed (thermocompression molded) at a temperature below the decomposition temperature of the urethane bond.

[0023] The amount of polymer polyol in the polyurethane reaction composition is preferably 10 wt% to 60 wt%, more preferably 13 wt% to 50 wt%, and particularly preferably 15 wt% to 40 wt%. When the amount of polymer polyol is 10 wt% or more, a suitable hardness is obtained, while when it is 60 wt% or less, the viscosity of the polyurethane reaction composition does not increase too much, and it is possible to avoid difficulty in foaming by mechanical froth. The solids content of the polymer polyol in the polyurethane reaction composition is preferably 5 wt% to 20 wt%, more preferably 5.5 wt% to 17 wt%, and particularly preferably 6 wt% to 15 wt%. When the solids content of the polymer polyol is 5 wt% or more, thermal shaping is facilitated and shape retention is improved. Conversely, when the solids content is 20 wt% or less, thermal shaping is facilitated and it is possible to avoid an excessive increase in the viscosity of the polymer polyol, which makes it difficult to handle.

[0024] Polyol As the polyol other than the polymer polyol, known polyols such as polyether polyols and polyester polyols can be used. The polyether polyols preferably have a molecular weight of 400 to 5000 and a functional number of 2 to 4. The polyester polyols preferably have a molecular weight of 300 to 3000 and a functional number of 2 to 4. Examples of polyether polyols include polyether polyols obtained by adding alkylene oxides such as ethylene oxide and propylene oxide 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, with an aliphatic glycol such as ethylene glycol, diethylene glycol, or propylene glycol, etc. Alternatively, examples include polycaprolactone polyols such as polycaprolactone diol obtained by ring-opening polymerization of ε-caprolactone. Two or more of the above polyols may be used in combination.

[0025] (2) Acid-modified polyolefin powder / normal polyolefin powder The polyurethane reaction composition may contain an acid-modified polyolefin powder or a normal polyolefin powder, but it is preferred to use an acid-modified polyolefin since it has better effects in terms of shape retention and shape retention rate. Acid-modified polyolefin powders include powders of polyethylene (PE), polypropylene (PP), polybutene (PB), polypentene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, styrene-ethylene-butene-styrene copolymer (SEBS), etc., modified with an acid of an unsaturated carboxylic acid or its anhydride.

[0026] Among acid-modified polyolefins, acid-modified polyolefins modified with maleic anhydride are preferred. Examples of acid-modified polyolefins modified with maleic anhydride include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, and maleic anhydride-modified ethylene-propylene copolymers. Maleic anhydride-modified polypropylene includes polypropylene, which is a random copolymer with ethylene, modified with maleic anhydride, while maleic anhydride-modified ethylene-propylene copolymer includes polypropylene, which is a so-called block copolymer in which ethylene and propylene are copolymerized, modified with maleic anhydride. Maleic anhydride-modified polyethylene and maleic anhydride-modified polypropylene are particularly preferred because they have better mold retention than other acid-modified polyolefins. The acid-modified polyolefin powder is not limited to one type, and may contain multiple types. The powder refers to a particle size of 5 μm to 250 μm. The melting point of the acid-modified polyolefin is 80°C to 165°C, preferably 85°C to 150°C, and particularly preferably 90°C to 140°C. By including an acid-modified polyolefin powder in a polyurethane reaction composition together with a polymer polyol, the polyurethane foam can be preheated at a temperature higher than the glass transition point of the acid-modified polyolefin powder, and the polyurethane foam can be thermoplastically deformed (thermal compression molded) at or below the decomposition temperature of the urethane bond, resulting in good distortion characteristics.

[0027] Typical polyolefin powders include polyethylene (PE), polypropylene (PP), polybutene (PB), polypentene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and styrene-ethylene-butene-styrene copolymer (SEBS).

[0028] The amount of the acid-modified polyolefin powder or the ordinary polyolefin powder in the polyurethane reaction composition is preferably 0 wt% to 35 wt%, more preferably 5 wt% to 30 wt%, and particularly preferably 10 wt% to 25 wt%. The inclusion of the acid-modified polyolefin powder or the ordinary polyolefin powder facilitates thermal shaping, and if the content is 35 wt% or less, it is possible to avoid a problem in which the viscosity increases and foaming by mechanical froth becomes impossible.

[0029] The total weight (total resin proportion) of the polymer polyol solids and the acid-modified polyolefin powder (and / or normal polyolefin powder) is preferably 5 wt% to 90 wt% of the polyurethane reaction composition weight, more preferably 5.5 wt% to 70 wt%, and particularly preferably 6 wt% to 50 wt%. When the total weight (total resin proportion) of the polymer polyol solids and the acid-modified polyolefin powder (and / or normal polyolefin powder) is 5 wt% or more, thermal shaping is possible and the shape retention is also high. Conversely, when the total resin proportion is 90 wt% or less, the viscosity of the polyurethane reaction composition increases too much, preventing foaming by mechanical froth.

[0030] (3) Foam stabilizer As the foam stabilizer, those known for polyurethane foams can be used. Examples include silicone-based foam stabilizers, fluorine-based foam stabilizers, and known surfactants. The amount of foam stabilizer is determined appropriately, but is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 7 parts by weight, and particularly preferably 0.5 to 5 parts by weight per 100 parts by weight of the polyol component.

[0031] (4) Catalyst The catalyst may be an amine catalyst or an organometallic catalyst for polyurethane foam, used alone or in combination. Examples of the amine catalyst include monoamine compounds, diamine compounds, triamine compounds, polyamine compounds, cyclic amine compounds, alcohol amine compounds, and ether amine compounds. These may be used alone or in combination. Examples of the organometallic catalyst include organotin compounds, organoiron compounds, organobismuth compounds, organolead compounds, and organozinc compounds. These may be used alone or in combination. The amount of catalyst is determined appropriately, but is preferably 0.01 to 10 parts by weight, more preferably 0.03 to 8 parts by weight, and particularly preferably 0.05 to 5 parts by weight per 100 parts by weight of the polyol component.

[0032] (5) Isocyanate component The isocyanate component may be any of aromatic, alicyclic, and aliphatic isocyanates, and may also be a bifunctional isocyanate having two isocyanate groups in one molecule, or a trifunctional or higher isocyanate having three or more isocyanate groups in one molecule, and these may be used alone or in combination.

[0033] For example, bifunctional isocyanates include aromatic isocyanates such as 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate (TDI), m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 2,4'-diphenylmethane diisocyanate (MDI), 2,2'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, and 3,3'-dimethoxy-4,4'-biphenylene diisocyanate. Alternatively, alicyclic isocyanates such as cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and methylcyclohexane diisocyanate can be used. Alternatively, aliphatic isocyanates such as butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, and lysine isocyanate can be used.

[0034] Furthermore, an example of a difunctional or higher functional isocyanate is polymethylene polyphenylisocyanate (polymeric MDI). Examples of trifunctional or higher functional isocyanates include 1-methylbenzene-2,4,6-triisocyanate, 1,3,5-trimethylbenzene-2,4,6-triisocyanate, biphenyl-2,4,4'-triisocyanate, diphenylmethane-2,4,4'-triisocyanate, methyldiphenylmethane-4,6,4'-triisocyanate, 4,4'-dimethyldiphenylmethane-2,2',5,5'tetraisocyanate, and triphenylmethane-4,4',4"-triisocyanate. The number of isocyanates is not limited to one, and may be one or more. For example, one aliphatic isocyanate and two aromatic isocyanates may be used in combination.

[0035] The isocyanate index is preferably 80 to 120, more preferably 90 to 110, and particularly preferably 95 to 105. When the isocyanate index is 80 or more, it is possible to avoid insufficient mechanical strength (tensile strength and elongation) and insufficient hardness, and when it is 120 or less, it is possible to avoid excessive mechanical strength and hardness (stiffness) that result in loss of flexibility. The isocyanate index is the value obtained by multiplying the number of moles of isocyanate groups per mole of active hydrogen groups contained in the urethane raw material by 100, and is calculated as [(isocyanate equivalents in the foaming raw material / active hydrogen equivalents in the foaming raw material) x 100]. The isocyanate index in the examples of this disclosure is 103.

[0036] (6) Other Any other additives may be added to the polyurethane reaction composition, such as crosslinkers, fillers, dyes, pigments, antioxidants, and flame retardants. Examples of the crosslinking agent include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1-4 butanediol, 1,6-hexanediol, etc. The amount of the crosslinking agent is determined appropriately, but is, for example, preferably 5 to 35 parts by weight, more preferably 10 to 30 parts by weight, and particularly preferably 15 to 25 parts by weight per 100 parts by weight of the polyol component. Examples of fillers include alumina trihydrate, silica, talc, calcium carbonate, clay, etc. The amount of filler is determined appropriately, but is, for example, preferably 5 to 60 parts by weight, more preferably 10 to 55 parts by weight, and particularly preferably 15 to 50 parts by weight per 100 parts by weight of the polyol component.

[0037] [Foaming agent] As the foam-forming gas such as an inert gas used as a foaming function agent (foaming agent), a gas that does not adversely affect the reaction between the polyol and the isocyanate, such as dry air or nitrogen, is suitable. The inert gas is preferably mixed in a proportion of 31 to 91% by volume in the polyurethane reaction composition. The mixing proportion of the inert gas refers to the volume percentage of the foam-forming gas relative to 100 parts by volume of the polyurethane reaction composition excluding the inert gas (the amount corresponding to 31 to 91% by volume of 100 parts by volume).

[0038] [Physical Properties] The polyurethane foam of the present disclosure has a compression set (JIS K 6401:2011) of 10% or less after production of the polyurethane foam but before molding, and is less susceptible to plastic deformation over long-term use. Furthermore, the polyurethane foam of the present disclosure has a compression set (JIS K 6401:2011) of 15% or less after each cycle of "molding → recycling" after production of the polyurethane foam, and exhibits little plastic deformation even after recycling.

[0039] [Molding] The polyurethane foam of the present disclosure can be produced into a molded article by thermal compression molding, which involves preheating the polyurethane foam and compressing it using a mold at room temperature, thereby forming a shape such as concaves and convexes. Thermal compression molding is carried out by preheating the polyurethane foam to 160 to 210°C, more preferably 190 to 210°C, and then compressing it using a mold at a low temperature (50°C or less). The preheating time is preferably 3 to 10 minutes, more preferably 4 to 8 minutes, and particularly preferably 5 to 6 minutes. The mold surface is provided with concaves and convexes depending on the intended use of the molded article, and the concaves and convexes are formed on the surface of the molded article. The compression ratio during compression pressing is preferably 25% to 75%. The compression ratio is calculated using the following formula: Compression rate (%) = (original thickness - compressed thickness) / original thickness x 100

[0040] [reproduction] The polyurethane foam of the present disclosure can be used to return molded articles that have been given irregularities or other shapes by heating the polyurethane foam to their pre-shaping shape. The restoration of the pre-shaping shape is achieved by heating the polyurethane foam at 160 to 210°C, more preferably 190 to 210°C. The heating time is preferably 3 to 10 minutes, more preferably 4 to 8 minutes, and particularly preferably 5 to 6 minutes. Thus, simply by leaving the polyurethane foam to stand for a predetermined time in a predetermined temperature environment, the shape of the polyurethane foam can be restored to its pre-shaping (pre-heat-compression) shape, producing a re-shapeable polyurethane foam. The polyurethane foam thus regenerated can maintain sufficient physical properties to be reused after regeneration, and can be regenerated at least five times. [Example]

[0041] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples and can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0042] Using the raw materials shown in Figure 5, a polyurethane reaction composition having the formulations of Examples 1-6 in Figure 6 and Comparative Examples 1-5 in Figure 7 was mixed with an inert gas (nitrogen) at a mixing ratio of 85 volume %, and the mixture was mixed and stirred in a mechanical froth foaming machine, continuously discharged onto release paper, and heated to 120 to 200°C to produce a sheet-like (flat) polyurethane foam with a thickness of 10 mm. Since both ordinary polyethylene powder and acid-modified polyethylene powder are thermoplastic resin powders, they are classified as "thermoplastic resin powder" in Figures 6 and 7. 6 and 7, "wt%" refers to the wt% of the polyurethane reaction composition. The total resin proportion (wt%) refers to the wt% of the total amount of the thermoplastic resin powder and polymer polyol solids in the polyurethane reaction composition relative to the polyurethane reaction composition.

[0043] The foaming state of each example and comparative example was visually judged, and the evaluation was given as "Excellent" when there were no broken bubbles or the like, and "Poor" when there were any defective parts such as broken bubbles.

[0044] Furthermore, each of the examples and comparative examples was subjected to thermal compression molding to measure initial moldability. For the thermal compression molding, a polyurethane foam sheet with a thickness of 10 mm (original thickness) was preheated in an environment of 200°C for 5 minutes, then compressed to a thickness of 5 mm (compression rate of 50%) in a press at room temperature and maintained in that state for 5 minutes. During pressing, 5 mm thick spacers were placed on both sides of the polyurethane foam sheet to adjust the pressing amount to 5 mm. The initial formability (%) is a value calculated from the following formula for the shape retention rate immediately after forming, in which the compressed state is maintained for 5 minutes. Initial formability (%) = (original thickness - thickness immediately after forming) / (original thickness - spacer thickness) x 100 For initial formability, a mold retention rate of less than 40% was rated "×", a retention rate of 40% or more but less than 70% was rated "△", a retention rate of 70% or more but less than 90% was rated "◯", and a retention rate of 90% or more was rated "◎".

[0045] Furthermore, the compression set was measured for each of the examples and comparative examples. The compression set (%) is a value calculated according to JIS K6401 by compressing a 50 x 50 mm sample by 50% in the thickness direction, leaving it to stand at a predetermined temperature (70°C) for 22 hours, and then releasing the compressive stress at room temperature. After 30 minutes, the thickness of the sample (thickness after release) is measured and calculated using the following formula. Compression set (%) = (thickness before compression - thickness after release) / thickness before compression x 100 The compressive residual strain was rated as "◎" if the value was 5% or less, "〇" if it was more than 5% and 10% or less, "△" if it was more than 10% and 15% or less, and "×" if it was more than 15%.

[0046] Furthermore, for each example and comparative example, the repeatability of molded shape was measured. The repeatability of molded shape is the rate of shape retention after molding when a polyurethane foam sheet is repeatedly molded and recycled in the following order: thermal compression molding (molding) → recycling → molding → recycling → molding → recycling → ... For the thermal compression molding, the polyurethane foam sheet was preheated in an environment of 200°C for 5 minutes, then compressed in a room temperature press to a compression ratio of 50%, and maintained in this state for 5 minutes. During pressing, spacers were placed on both sides of the polyurethane foam sheet to adjust the pressing amount to approximately 50% of the thickness before thermal compression molding (original thickness). The repeated molding retention (%) is the value calculated from the thickness before thermal compression molding (original thickness) and the thickness after thermal compression molding (molded thickness) by the following formula, which shows the molding retention rate after maintaining the compressed state for 5 minutes and leaving it for 30 minutes after molding. Repeated molding retention (%) = (original thickness - molded thickness) / (original thickness - spacer thickness) x 100 For repeated molding retention, a molding retention of 90% or more was rated as "◎", 70% or more but less than 90% was rated as "〇", 40% or more but less than 70% was rated as "△", and less than 40% was rated as "×". However, if regeneration was not possible for five or more cycles (repeated molding and regeneration five times), it was rated as "×".

[0047] FIG. 8 shows the repeated molding retention (%) of the polyurethane foam after each cycle for each Example and Comparative Example, where multiple cycles of "molding → regeneration" are repeated as shown in FIG. 4.

[0048] Furthermore, for each example and comparative example, the recyclability was measured. The recyclability is the rate at which the shape is retained after recycling when a polyurethane foam sheet is repeatedly molded and recycled in the following order: thermal compression molding (molding) → recycling → molding → recycling → molding → recycling → ... For regeneration, the molded polyurethane foam was kept in a 200°C environment for 5 minutes. The repeatability (%) is the mold retention rate after leaving it for 30 minutes after regeneration, calculated using the following formula from the thickness before thermal compression molding (original thickness) and the thickness after regeneration (regenerated thickness). Repeatability (%) = (recycled thickness) / (original thickness) x 100 For repeated recyclability, a molding retention rate of 95% or more was rated as "◎", a retention rate of 90% or more but less than 95% was rated as "〇", a retention rate of 80% or more but less than 90% was rated as "△", and a retention rate of less than 80% was rated as "×". However, if regeneration was not possible for five or more cycles (repeated molding and regeneration five times), a "×" was given.

[0049] FIG. 9 shows the repeatability (%) of polyurethane foams after each cycle, where one cycle is "molding → recycling" as shown in FIG. 4, for each Example and Comparative Example.

[0050] Furthermore, for each example and comparative example, repeated compression set was measured. Repeated compression set is the compression set after recycling when a polyurethane foam sheet is repeatedly molded and recycled in the following order: thermal compression molding (molding) → recycling → molding → recycling → molding → recycling →... The repeated compression set (%) was calculated according to JIS K6401 by compressing a 50 x 50 mm sample of recycled polyurethane foam sheet by 50% in the thickness direction, leaving it to stand at a specified temperature (70°C) for 22 hours, and then releasing the compressive stress at room temperature. The thickness of the sample (thickness after release) was measured 30 minutes later, and the value was calculated using the following formula: Repeated compression set (%) = (thickness before compression - thickness after release) / thickness before compression x 100 For repeated compression set, if the value of the compression set was 5% or less, it was marked as "◎", if it was more than 5% and less than 10%, it was marked as "〇", if it was more than 10% and less than 15%, it was marked as "△", and if it was more than 15%, it was marked as "×". However, if regeneration was not possible after 5 cycles (repeated molding and regeneration 5 times), it was marked as "×".

[0051] FIG. 10 shows the repeated compression set of the polyurethane foam after each cycle, where "molding → recycling" is one cycle as shown in FIG. 4, for each Example and Comparative Example.

[0052] An overall evaluation was performed for each example and comparative example according to the results of each test item. The overall evaluation was determined to be the lowest evaluation among the evaluations of each test item. For example, if there was even one "x" in the evaluation of a test item, the overall evaluation was "x." If all the evaluations of the test items were "△" or higher ("△," "〇," "◎") and even one "△," the overall evaluation was "△." If all the evaluations of the test items were "〇" or higher ("〇," "◎") and even one "〇," the overall evaluation was "〇." If all the evaluations of the test items were "◎," the overall evaluation was "◎." Note that "◎" means excellent, "〇" means good, "△" means average, and "×" means poor.

[0053] Example 1 is an example in which 50.7 parts by weight of polymer polyol (POP) was added to 76.6 parts by weight of the crosslinking agent and polyol component, and 30 parts by weight of acid-modified polyethylene powder was added as a thermoplastic resin powder, resulting in a polymer polyol content of 33.2 wt% in the polyurethane reaction composition, a polymer polyol solids content of 12.2 wt%, an amount of acid-modified polyethylene powder added to the polyurethane reaction composition of 19.6 wt%, and a total resin proportion of 31.9 wt%. For Example 1, the foaming state was "◎", the initial moldability was 97.8%, rated "◎", the compression set was 4.2%, rated "◎", the repeated molding retention was "◎", the repeated recyclability was "◎", the repeated compression set was "◯", and the overall rating was "◯".

[0054] In Example 2, 55.7 parts by weight of polymer polyol (POP) was added to 76.6 parts by weight of the crosslinker and polyol component, and 30 parts by weight of acid-modified polyethylene powder was added as a thermoplastic resin powder, resulting in a polymer polyol content of 39.0 wt% in the polyurethane reaction composition, a polymer polyol solids content of 14.6 wt%, an amount of acid-modified polyethylene powder added to the polyurethane reaction composition of 21.0 wt%, and a total resin proportion of 35.6 wt%. For Example 2, the foaming state was "◎", the initial moldability was 96.5%, rated "◎", the compression set was 3.4%, rated "◎", the repeated molding retention was "◎", the repeated recyclability was "◎", and the repeated compression set was "◎", giving an overall rating of "◎".

[0055] In Example 3, 38.0 parts by weight of polymer polyol (POP) was added to 76.6 parts by weight of the crosslinking agent and polyol component, and 30 parts by weight of acid-modified polyethylene powder was added as a thermoplastic resin powder, resulting in a polymer polyol content of 24.9 wt% in the polyurethane reaction composition, a polymer polyol solids content of 9.2 wt%, an amount of acid-modified polyethylene powder added to the polyurethane reaction composition of 19.6 wt%, and a total resin proportion of 28.8 wt%. For Example 3, the foaming state was "◎", the initial moldability was 95.7%, rated "◎", the compression set was 3.8%, rated "◎", the repeated molding retention was "◎", the repeated recyclability was "〇", the repeated compression set was "〇", and the overall rating was "〇".

[0056] Example 4 is an example in which 50.7 parts by weight of polymer polyol was added to 76.6 parts by weight of crosslinking agent and polyol component, and 30 parts by weight of ordinary polyethylene powder was added as thermoplastic resin powder, resulting in a polymer polyol content of 33.2 wt% in the polyurethane reaction composition, a polymer polyol solids content of 12.2 wt%, an ordinary polyethylene powder content in the polyurethane reaction composition of 19.6 wt%, and a total resin proportion of 31.9 wt%. In Example 4, the foaming state was "◎", the initial moldability was 77.3%, and the evaluation was "◯", the compression set was 3.4%, and the evaluation was "◎", the repeated moldability was "△", and the repeated recyclability was "◯". The repeated compression set was "good" and the overall evaluation was "fair".

[0057] Example 5 is an example in which 50.7 parts by weight of polymer polyol (POP) was used in 76.6 parts by weight of crosslinker and polyol component, no thermoplastic resin powder was contained, the polymer polyol content in the polyurethane reaction composition was 33.2 wt%, the polymer polyol solids content was 12.2 wt%, and the total resin proportion was 12.2 wt%. For Example 5, the foaming state was "◎", the initial moldability was 57.3%, rated "△", the compression set was 3.3%, rated "◎", the repeated molding retention was "△", the repeated recyclability was "△", and the repeated compression set was "◯", giving an overall rating of "△".

[0058] Example 6 is an example in which 25.4 parts by weight of polymer polyol (POP) was added to 76.6 parts by weight of the crosslinker and polyol component, and 30 parts by weight of acid-modified polyethylene powder was added as a thermoplastic resin powder, resulting in a polymer polyol content of 16.6 wt% in the polyurethane reaction composition, a polymer polyol solids content of 6.1 wt%, an amount of acid-modified polyethylene powder added to the polyurethane reaction composition of 19.6 wt%, and a total resin proportion of 25.8 wt%. For Example 6, the foaming state was "◎", the initial moldability was 93.1%, rated "◎", the compression set was 3.2%, rated "◎", the repeated molding retention was "○", the repeated recyclability was "△", the repeated compression set was "△", and the overall rating was "△".

[0059] Comparative Example 1 is an example in which the polyol component does not contain polymer polyol, and ordinary polyethylene powder is added as the thermoplastic resin powder. In Comparative Example 1, the foaming state was "◎", the initial moldability was 39.2%, rated "×", the compression set was 2.0%, rated "◎", the repeated molding retention was "×", the repeated recyclability was "×", and the repeated compression set was "×", resulting in an overall rating of "×".

[0060] Comparative Example 2 is an example in which the polyol component did not contain a polymer polyol, and both an acid-modified polyethylene powder and a normal polyethylene powder were added as thermoplastic resin powders. In Comparative Example 2, the foaming state was "◎", the initial moldability was 59.4%, rated "△", the compression set was 1.6%, rated "◎", the repeated molding retention was "×", the repeated recyclability was "×", the repeated compression set was "×", and the overall rating was "×".

[0061] Comparative Example 3 is an example in which the polyol component did not contain a polymer polyol, and an acid-modified polyethylene powder was added as the thermoplastic resin powder. In Comparative Example 3, the foaming state was "◎", the initial moldability was 70.9%, rated "◯", the compression set was 2.7%, rated "◎", the repeated molding retention was "×", the repeated recyclability was "×", the repeated compression set was "×", and the overall rating was "×".

[0062] Comparative Example 4 is an example in which 12.7 parts by weight of polymer polyol (POP) was added to 76.6 parts by weight of crosslinking agent and polyol component, and 30 parts by weight of acid-modified polyethylene powder was added as thermoplastic resin powder, resulting in a polymer polyol content of 8.3 wt% in the polyurethane reaction composition, a polymer polyol solids content of 3.1 wt%, an amount of acid-modified polyethylene powder added to the polyurethane reaction composition of 19.6 wt%, and a total resin proportion of 22.7 wt%. In Comparative Example 4, the foaming state was "◎", the initial moldability was 75.9%, rated "◯", the compression set was 3.5%, rated "◎", the repeated molding retention was "×", the repeated recyclability was "×", and the repeated compression set was "×", resulting in an overall rating of "×".

[0063] Comparative Example 5 is an example in which the polyol component did not contain polymer polyol, and acid-modified polyethylene powder was added as the thermoplastic resin powder. Comparative Example 5: foaming state: "◎", initial moldability: 68.1%, rating: "△", compression set: 4.7%, rating: "◎", repeated molding retention: "×", repeated recyclability: "×", repeated compression set: "×", and overall rating: "×".

[0064] As shown in Figures 7-10, Comparative Examples 1-3 and 5, which did not contain polymer polyol, and Comparative Example 4, in which the polymer polyol content was less than 10 wt% relative to the polyurethane reaction composition, were only able to undergo the "molding → recycling" cycle about twice, and by the third cycle, discoloration, smoking, etc. occurred, resulting in severe deterioration. Comparative Example 3, which did not contain polymer polyol and contained the highest amount of acid-modified polyethylene powder among the Examples and Comparative Examples, only underwent about two "molding → recycling" cycles. On the other hand, as shown in Figures 6, 8-10, Examples 1-6, which contained 10 wt% or more of polymer polyol relative to the polyurethane reaction composition, were able to undergo the "molding → recycling" cycle at least five times. In particular, Example 1-3 was able to withstand more than 10 cycles of "molding → recycling," and no deterioration of the polyurethane foam was observed even after 10 cycles. Furthermore, as shown in Figure 10, the repeated compression set of Examples 1-6 indicated that the strain characteristics (physical properties) could be maintained before and after the "molding → recycling" cycle. 8-9, comparing Examples 1, 4, and 5, Example 4, which contained normal polyethylene powder, showed improved repeated molding retention and repeated recyclability compared to Example 5, which did not contain thermoplastic resin powder. Also, Example 1, which contained acid-modified polyethylene powder, showed even further improved repeated molding retention and repeated recyclability compared to Example 4, which contained normal polyethylene powder.

Claims

1. A heating regeneration step is provided in which the polyurethane foam molded by the thermal compression molding is heated to return it to the shape before the thermal compression molding. The polyurethane reaction composition of the polyurethane foam contains 10 wt % or more of a polymer polyol. A method for producing polyurethane foam.

2. The cycle of molding by thermal compression molding and returning to the shape before thermal compression molding by thermal regeneration can be repeated at least five times. Polyurethane foam.

3. After each cycle, the repeatability (%) calculated by the following formula (1) is 85% or more. The polyurethane foam according to claim 2. Repeated recyclability (%) = (thickness after recycling) / (thickness before thermal compression molding) x 100 ・・・（１）

4. After each cycle, the compression set (%) based on JIS K6401 calculated by the following formula (2) is 15% or less. The polyurethane foam according to claim 2 or 3. Repeated compression set (%) = (thickness before compression - thickness after release) / thickness before compression x 100 ・・・（２）

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