Method for producing a foamed flat molded article and mold for carrying out the method

Abstract

The invention relates to a process for producing foamed flat polyurethane (PUR) / polyisocyanurate (PIR) moldings, in which a polyurethane / polyisocyanurate reactive mixture is injected into a mold under elevated pressure, then depressurized, thereby initiating the foaming process, and after the reaction the molding is demolded, and to a mold for carrying out the process.

Description

[0001] The present invention relates to a method for producing foamed flat polyurethane (PUR) / polyisocyanurate (PIR) molded articles, wherein a polyurethane / polyisocyanurate reactive mixture is injected into a mold under elevated pressure, followed by depressurization, thereby initiating a foaming process, and the molded article is demolded after the reaction, and relates to a mold for carrying out said method.

[0002] Foamed, open-cell, and flat molded articles are ideally suited as core materials for applications such as vacuum insulation panels (VIPs). They are excellent thermal insulators, their insulating effect particularly generated by the vacuum within the panel. The core material, such as a polyurethane / polyisocyanurate matrix with very basic open pores, prevents the panel from collapsing under vacuum. Typical applications of foamed flat molded articles include metal panels and insulation boards for building insulation and walls of refrigeration equipment. Vacuum insulation panels are particularly widely used in refrigeration equipment insulation, such as in household refrigerators. A manufacturing variation in the prior art involves injecting a starting mixture of polyols, isocyanates, additives, and supercritical CO2 or a blowing agent under pressure into a mold filled with a gas (e.g., air or nitrogen) and applying overpressure. The overpressure is then reduced by controlled depressurization, thereby evaporating the blowing agent dissolved in the liquid PUR / PIR reactive mixture and initiating the foaming process. By selecting appropriate depressurization parameters, one can influence foam formation and important foam properties, such as cell structure, which in turn affects the thermal and mechanical properties of VIP.

[0003] Decompression techniques used in foam production are extensively described in the literature: WO18 / 162372 describes a method for producing PUR / PIR rigid foams with open and ultra-fine pores. The method comprises introducing a reactive mixture containing supercritical CO2 as a blowing agent into a mold, foaming in the mold, and demolding. In a preferred embodiment, the mold is under internal pressure, which is depressurized in a controlled manner after injection. Depressurization is achieved within 1 to 40 s at a depressurization rate of up to 90 bar / s.

[0004] WO11 / 085847 A1 describes the production of a foam material molded article with desired anisotropic shape memory properties, and the foam material molded article itself. The molded article comprises at least one shape memory polymer having a foam structure. The cells are asymmetrically oriented (aspect ratio > 2) and substantially oriented in one spatial direction. The asymmetric cell orientation with shape memory effect is achieved by releasing the foaming agent in a polymer melt (e.g., TPU) with a foaming agent added to the molded article cavity during the depressurization process in the pressure chamber. Depressurization is initiated by a valve and carried out at a maximum of 25 bar / second. It is also described that the molded article cavity opens towards the main expected growth side of the foam within the pressure chamber. Corresponding to the cell orientation of the foam, anisotropic mechanical properties are generated in the molded article. The depressurization process and its effect on the foam orientation are not described in more detail, and in particular, the effect of the cavity geometry on the flow behavior of the foam during the depressurization process is not considered.

[0005] WO13 / 075991 A1 describes a method for producing nanoporous polymer foam materials from thermoplastic polymers with supercritical blowing agents and extremely high depressurization rates (15,000 to 2,000,000 MPa / s). The method involves loading a supercritical blowing agent into a thermoplastic polymer, temperature conditioning the loaded polymer melt, depressurizing, and possibly pulverizing the foam to produce foam particles. Depressurization can preferably be carried out continuously in an extruder or discontinuously in an autoclave. In the continuous method, depressurization occurs at a die plate with a narrow die (through which the melt is extruded). The pressure load is thus simultaneously applied to the molding of the melt. In the discontinuous variant in the autoclave, depressurization occurs via valves, rupture discs, or an increase in the die cavity volume. No description is provided regarding the adjustment of cell size and orientation (particularly due to the geometry of the die) and the connection to depressurization devices (e.g., valves). The requirement for a supercritical blowing agent and extremely high depressurization rates in this method limits its operation.

[0006] WO 2007 / 099445 A2 describes the production of foam molded articles using a mold. During venting of the mold, a gate element driven by rising foam closes the venting position relative to the surrounding environment. Because this gate is not closed relative to the surrounding environment during the injection of the polymer mixture, the mold cavity cannot be under overpressure, which would be beneficial for controlling foaming and cell orientation.

[0007] WO18 / 222714 A1 describes the injection of a single-phase solution consisting of a polymer composition and a gas into a mold under overpressure and the subsequent depressurization to produce foam. Depressurization is achieved either through volume expansion or via a pressure regulator.

[0008] WO2015 / 183639 A1 describes a mold and method operation in which foam expansion (= volume expansion) in a mold is achieved by increasing the cavity volume and inherently depressurizing through the movement of the mold wall. The method involves injecting a polymer mixture into a pressurized mold cavity and depressurizing it through controlled movement of the wall in a piston-like manner. Moving components are disadvantageous because they are particularly prone to leakage and unpredictable pressure drops in pressurized methods and require additional actuators. No consideration is described regarding how cell orientation can be influenced by adjusting depressurization parameters.

[0009] The aim is to provide a method or mold for achieving complete filling of the mold cavity in a simple manner and reducing foam inhomogeneity, such as the preferred orientation or severe anisotropy of cells in certain areas of the molded article, because greater uniformity of the cell structure has a favorable effect on important properties of the part, such as thermal insulation and mechanical stability. Here, production time should not be extended compared to methods according to the prior art.

[0010] Surprisingly, this can be achieved using the following method and the following mold.

[0011] The present invention provides a method for producing a foamed flat polyurethane / polyisocyanurate (PUR / PIR) molded article having a thickness (LF2) in a mold cavity having an inlet area, a mold cavity, and a pressure relief unit, wherein the method comprises the following steps: i) Injecting a polyurethane / polyisocyanurate reactive mixture into the mold cavity through at least one inlet opening in the inlet region, the mold cavity being subjected to an initial pressure of 5 bar to 40 bar, preferably 6 bar to 30 bar, and particularly preferably 7 bar to 25 bar. ii) After the polyurethane / polyisocyanurate reactive mixture is injected, the pressure in the mold cavity is depressurized to atmospheric pressure or to a pressure below the initial pressure and of 1 bar to 5 bar, preferably 1 bar to 2 bar, for a duration of 0.1 to 10 seconds, preferably 0.2 to 2 seconds, by means of at least one valve in the depressurization unit, wherein the reactive mixture is foamed along the main flow direction from the inlet area through the mold cavity to the depressurization unit. iii) Curing, cooling, and demolding the foamed flat polyurethane / polyisocyanurate molded product. Its features The mold cavity has two long dimensions (LF1) and (LF3) and one shorter dimension (LF2), and one of the long dimensions (LF3) represents the main flow direction of the foam. The mold cavity has at least one wall (A3) in a plane opened by dimensions (LF1) and (LF2) or at least one portion (K2) of a wall (A2) in a plane opened by dimensions (LF1) and (LF3), wherein the portion (K2) of the wall (A2) corresponds to a region extending in dimension (LF3) on a 1 / 10 portion of the wall (A2) opposite to the inlet region, and wherein the at least one wall (A3) or the at least one portion (K2) of the wall (A2) has at least one opening (340) connecting the mold cavity (100) and the pressure relief unit (300). The ratio of the total area of ​​the at least one opening to the area of ​​the wall (A3) containing the opening or the area of ​​the portion (K2) of the wall (A2) containing the opening is 1:20 to 1:100. The at least one opening has a length (LS1) in the long dimension (LF1) direction of the mold cavity, and The ratio of the length or total length of the at least one opening (LS1) to the length of the mold cavity (LF1) is greater than 1:4, preferably greater than 1:2, and particularly preferably greater than 3:4.

[0012] Dimensions (LF1) and (LF3) are each greater than (LF2). For the purposes of this application, a dimension (LF2) shorter than dimensions LF1 and LF3 means that it is at most half the length of LF1 and LF3, respectively. The ratio of (LF1) to (LF2) and the ratio of (LF3) to (LF2) are preferably each independently greater than 3, and particularly preferably greater than 6.

[0013] The opening connecting the mold cavity to the pressure relief unit preferably has an aspect ratio of at least 2, and particularly preferably at least 5.

[0014] The main flow direction of the reactive mixture preferably corresponds to the main dimension of the mold cavity.

[0015] The at least one opening is preferably located in the wall (A3), which is opposite to the region containing the inlet opening in the main flow direction.

[0016] However, the at least one opening may also be located in other walls. In this case, it is preferably located in a portion (K2) of the other wall, wherein the portion (K2) corresponds to a region extending in dimension (LF3) at 1 / 10 of the length opposite to the inlet opening. In this case, the pressure relief unit is also adjacent to the at least one opening.

[0017] For the purposes of this application, the area A of wall W corresponds to the area within the perimeter of the wall. Therefore, for example, a rectangular wall with sides a and b of lengths 1 m and 2 m respectively has an area A = a * b = 2 m. 2 It does not depend on any openings that may exist in the wall W.

[0018] For the purposes of this invention, the duration of pressure relief corresponds to the period during which the pressure in the mold cavity drops from high pressure to low pressure.

[0019] Depressurization is preferably performed 0 to 20 seconds after the injection of the polyurethane / polyisocyanurate reactive mixture.

[0020] The mold is temperature adjustable. The normal temperature range for the mold is 20 to 80°C.

[0021] The design of the gate area can vary. For example, a center gate with a baffle, a disc gate, or a coplanar gate can be provided. These gates are known in themselves. An advantageous arrangement represents a direct gate with a deflection system, a flow-limiting zone, and an increased cross-sectional area of ​​convergence.

[0022] Another subject of the present invention is a mold for producing foamed flat polyurethane / polyisocyanurate molded articles having a thickness (LF2), said mold having (i) An entrance area having at least one entrance opening (110, 210), (ii) Adjacent mold cavities (100), (iii) A pressure relief unit having at least one valve (130, 310), Its features The mold cavity (100) has two long dimensions (LF1) and (LF3) and one shorter dimension (LF2). The mold cavity has a wall (A3) in a plane opened by dimensions (LF1) and (LF2) or a portion (K2) of a wall (A2) in a plane opened by dimensions (LF1) and (LF3), wherein the portion (K2) of the wall (A2) corresponds to a region extending in dimension (LF3) on a 1 / 10 portion of the wall (A2) opposite to the inlet region, and wherein the wall (A3) or the portion (K2) of the wall (A2) has at least one opening (340) connecting the mold cavity (100) and the pressure relief unit (300). The ratio of the total area of ​​the at least one opening (340) to the area of ​​the wall (A3) containing the opening or the area of ​​the portion (K2) of the wall (A2) containing the opening is 1:20 to 1:100. The at least one opening (340) has a length (LS1) in the long dimension (LF1) direction of the mold cavity (100). The ratio of the length or total length of the at least one opening (LS1) to the length (LF1) of the mold cavity (100) is greater than 1:4, preferably greater than 1:2, and particularly preferably greater than 3:4.

[0023] The term "flat molded article" is understood to refer to an article formed in a mold cavity where one dimension is smaller than the other two dimensions. These can be plates, tubes, or hollow cylinders, where the plate thickness or tube thickness is smaller than the other two dimensions. The plate thickness (LF2) can vary along dimensions (LF1) and (LF3) and, for example, have a profile. This profile can, for example, correspond to a geometry that may be applied, such as the geometry of a refrigerator wall.

[0024] The dimensions of the mold cavity (LF1) and (LF3) are each greater than (LF2). The ratio of (LF1) to (LF2) and the ratio of (LF3) to (LF2) are preferably greater than 3 independently in each case, and particularly preferably greater than 6.

[0025] The at least one opening connecting the mold cavity to the pressure relief unit preferably has an aspect ratio of at least 2, and particularly preferably at least 5.

[0026] The opening is particularly preferably an elongated hole, gap, or slot. These openings preferably have a constant gap width. However, they can also be elliptical, banana-shaped, concave, or convex, and thus have a width that varies along the gap length. Particularly preferred is that the at least one opening in the wall (A3) between the mold cavity and the pressure relief unit consists of a single opening extending along the entire dimension (LF1) of the mold cavity. However, it can also be a combination of openings that are connected to each other in the (LF1) direction and optionally arranged side by side, for example, openings separated from each other by a partition. Less preferred are openings with an aspect ratio of approximately 1 that are distributed along the length (LF1), such as a combination of circular or slightly elliptical openings. By varying the gap width or the local height of the flow-limiting rod (320) optionally present in the pressure relief unit (300), the flow resistance of the foam along the entire length (LF1) of the mold cavity can be homogenized, resulting in a uniform velocity distribution of the airflow in the mold cavity during pressure relief. This, in turn, results in uniform rise of the foam throughout the entire length (LF1) of the mold cavity, which promotes uniform molded product properties and complete foaming within the mold cavity.

[0027] Preferably, the at least one opening and flow-limiting area in the wall (A3) is centered in the cavity thickness (LF2).

[0028] The flow-limiting bar (320) also increases the flow resistance to the rising foam, which helps the foam to be compacted as required in the gap of the flow-limiting bar and reduces the risk of uncontrolled foam escape.

[0029] Preferably, an overflow zone (330) is present, which is connected to an optional flow-limiting rod (320). Particularly preferred is that the pressure relief unit has an overflow zone (330) in which the foamed reactive mixture optionally discharged from at least one opening in the mold cavity can be collected. This can then be removed incidentally when the molded article is removed. The overflow zone (330) prevents contamination of the valve (310) located thereafter without the need to install an additional screen and potentially replace or clean it periodically.

[0030] It has been found that, in order to achieve favorable component properties, it is important to design depressurization during the reaction process in the mold. The compressed gas in the mold is controlled and uniformly discharged from the mold cavity by means of the method according to the invention or by the mold according to the invention.

[0031] The method according to the invention achieves higher uniformity of the cell structure without extending production time, and in particular, significantly reduces undesirable orientations of cells in areas near the pressure relief unit or pressure relief valve. It also allows for the production of parts that completely fill the mold cavity. Air inclusions are observed if the location of at least one opening connecting the mold cavity to the pressure relief zone does not conform to the invention.

[0032] The PUR / PIR reactive mixture preferably contains isocyanate reactive component A), which preferably contains at least one polyol component A1 selected from polyether polyols, polyester polyols, polyether ester polyols, polycarbonate polyols and polyether polycarbonate polyols, as well as a polyisocyanate component B).

[0033] Based on the total number of terminal OH functionalities of all polyols used in component A), the proportion of primary OH functionalities is preferably at least 30%.

[0034] The functionality f of the polyol component A1) is preferably > 2.5. Optimal viscosity improvement is achieved during injection until the back pressure decreases through a polyol formulation in which the polyol component A1) has a functionality within the stated range. The foam also allows for rapid demolding.

[0035] The hydroxyl value of the polyol component A1 is preferably between 280 and 600 mg KOH / g. This has a particularly favorable effect on the mechanical properties of the foam.

[0036] The polyether polyols mentioned above are polyether polyols or mixtures of different polyether polyols known to those skilled in the art and that can be used in the synthesis of polyurethane / polyisocyanurate.

[0037] Suitable polyether polyols include, for example, polytetramethylene glycol polyether, which can be obtained by cationic ring-opening polymerization of tetrahydrofuran. Also suitable polyether polyols are addition products of styrene oxide, ethylene oxide, propylene oxide, butane oxide, and / or epichlorohydrin to difunctional or polyfunctional initiator molecules.

[0038] The isocyanate reactive component A) preferably comprises at least 50% by weight of a polyether polyol based on its total weight. This component is characterized by particularly good hydrolysis resistance.

[0039] Available polyether ester polyols are those compounds containing ether groups, ester groups, and OH groups. Organic dicarboxylic acids or their derivatives having up to 12 carbon atoms are suitable for producing said polyether ester polyols. An additional component used in the production of polyether ester polyols is the polyether polyol obtained by alkoxylation of an initiator molecule such as a polyol. The initiator molecule is at least bifunctional, but optionally may contain a certain proportion of higher functional, particularly trifunctional, initiator molecules. Polyether ester polyols can also be produced by alkoxylation of the reaction product obtained from the reaction of an organic dicarboxylic acid or its derivative with a component containing zelevitinov's active hydrogen.

[0040] Suitable polyester polyols, especially diols, triols, and tetraols, are condensations of dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids, hydroxycarboxylic acids, or lactones. Instead of free polycarboxylic acids, corresponding polycarboxylic anhydrides or corresponding low-carbon alcohol esters of polycarboxylic acids can also be used to produce polyesters.

[0041] In particular, bio-based raw materials and / or their derivatives may also be considered for the production of polyester polyols. Esters of ricinoleic acid and polyfunctional alcohols, such as glycerol, are particularly preferred.

[0042] Available polycarbonate polyols are polycarbonates with hydroxyl groups, such as polycarbonate diols. They can be obtained by reacting carbonate derivatives, such as diphenyl carbonate, dimethyl carbonate, or phosgene with polyols, preferably diols, or by copolymerizing epoxides, such as propylene oxide, with CO2.

[0043] In addition to pure polycarbonate diol, polyether polycarbonate diol can also be used, which can be obtained, for example, by copolymerization of epoxides, such as propylene oxide, with CO2.

[0044] The isocyanate reactive component A) may also contain a low molecular weight isocyanate reactive compound A2), particularly one with a molar mass M of less than 400 g / mol. n Di- or trifunctional amines and alcohols.

[0045] In component A), in addition to the polyols and isocyanate reactive compounds mentioned above, other isocyanate reactive compounds may also be included, such as grafted polyols, polyamines, polyamino alcohols and polythiols.

[0046] The preferred isocyanate reactive component A) consists of at least 65% by weight, particularly at least 80% by weight, and very particularly preferably at least 90% by weight of a polyol component A1) having a hydroxyl value of 280 to 600 mg KOH / g and a functionality f of ≥ 2.8 to ≤ 6.0, and the proportion of terminal primary OH functionality in component A) is at least 35% (based on all terminal OH functionality in component A).

[0047] Component A) may contain auxiliaries and additives, such as pore-opening compounds, preferably in an amount of up to 1% by weight based on isocyanate reactive component A).

[0048] Other auxiliaries and additives are common auxiliaries and additives in the prior art and known to those skilled in the art; for example, surfactants, stabilizers, especially foam stabilizers, cell regulators, fillers, dyes, pigments, flame retardants, antistatic agents, hydrolytic stabilizers and / or substances with antifungal and antibacterial effects.

[0049] Catalysts are also preferred for the production of PUR / PIR rigid foams. Typically, catalysts are compounds that accelerate the reaction between compounds containing hydroxyl or isocyanate reactive groups in component B and the isocyanate groups in component B.

[0050] In the production of PUR / PIR rigid foam, a blowing agent component is used to form the foam. The amount used is the amount required to achieve a dimensionally stable foam matrix and the desired apparent density. Preferred blowing agents are physical blowing agents (e.g., pentane) and / or supercritical CO2. Chemical blowing agents (e.g., water) may also be used in addition to or instead of physical blowing agents.

[0051] Component B) is a polyisocyanate, i.e., an isocyanate having an NCO functionality of ≥ 2. Examples of such polyisocyanates are 1,4-butanediisocyanate, 1,5-pentanediisocyanate, 1,6-hexanediisocyanate (HDI), isophorone diisocyanate (IPDI), 2,2,4- and / or 2,4,4-trimethylhexanediisocyanate, isomeric bis(isocyanate cyclohexyl)methane or mixtures thereof having any isomer content, 1,4-cyclohexanediisocyanate, 1,4-phenylene diisocyanate, 2,4- and / or 2,6-toluenediisocyanate. Isocyanates (TDI), 1,5-naphthalene diisocyanate, 2,2'- and / or 2,4'- and / or 4,4'-diphenylmethane diisocyanate (MDI) and / or higher homologues, 1,3- and / or 1,4-bis(2-isocyanate prop-2-yl)benzene (TMXDI), 1,3-bis(isocyanate methyl)benzene (XDI), and alkyl esters of 2,6-diisocyanate hexanoate having C1 to C6-alkyl groups (lysine diisocyanates).

[0052] Preferred isocyanate component B is a mixture of isomers of diphenylmethane diisocyanate (“monomer MDI”, abbreviated as “mMDI”) and their oligomers (“oligomeric MDI”). “Polymerized MDI” (pMDI) generally refers to a mixture of monomeric MDI and oligomeric MDI. The oligomers of MDI are polyphenyl polymethylene polyisocyanates with more rings, i.e., having an NCO functionality f > 2 and having the following structural formula: C 15 H 10 N2O2[C8H5NO] n A mixture of diphenylmethane diisocyanate homologues with more rings, where n = integer > 0.

[0053] In addition to the polyisocyanates mentioned above, a certain proportion of modified diisocyanates having structures of urea diketone, isocyanurate, carbamate, carbodiimide, urea ketone imide, urea carbamate, biuret, amide, iminooxadiazine diketone and / or oxadiazine triketone can also be used together.

[0054] In addition to or besides the polyisocyanates mentioned above, suitable NCO prepolymers can also be used as organic isocyanate component B). This prepolymer can be prepared by reacting one or more polyisocyanates with one or more polyols, the polyols corresponding to those described under component A1).

[0055] The ratio of the number of NCO groups in polyisocyanate component B) to the number of isocyanate reactive groups in component A) can be, for example, a ratio of ≥50:100 to ≤500:100 relative to each other. For the production of rigid polyurethane foam, components A) and B) are typically reacted in amounts such that the isocyanate index of the formulation is 80-150. For the production of foam with a high proportion of isocyanurate groups, components A) and B) are typically reacted in amounts such that the isocyanate index of the formulation is 150-400.

[0056] By means of the method according to the invention, flat PUR / PIR rigid foam molding articles with an apparent density of 25 to 300 kg / m³ can be obtained, which simultaneously possess numerous open and particularly small cells. Therefore, rigid foams with an open-cell content of >70% can be produced, wherein the average cell diameter is <180 µm. This foam exhibits good mechanical properties, such as good compressive strength and low thermal conductivity.

[0057] Regarding the composition of the preferred PUR / PIR reactive mixture, reference is made in particular to WO 2018162372 A1. The preferred PUR / PIR reactive mixture is described in detail herein.

[0058] Figure 1The structure of a mold (10) having a cavity (100) is shown in principle. Such molds are known in themselves. They have an inlet opening (110) and a valve (130).

[0059] Figure 2 A mold (10) according to the invention is disclosed. The mold cavity (100) has a width (LF1), a height (LF3), and a thickness (LF2). The mold cavity (100) has a wall (A3) having an opening (340) connecting the mold cavity (100) and the pressure relief unit (300). Figure 2 The pressure relief unit (300) shown has a valve (310), a flow restrictor (320), and an overflow area (330).

[0060] Figure 2 It also reveals, for example, region K2, in which at least one opening is preferably located if it is not located in the wall, and this region is opposite to the region containing the inlet opening in the main flow direction.

[0061] Figure 3 The wall (A3) of the mold cavity (100) is shown. This wall (A3) contains a plurality of openings (340) with different shapes. These openings each have a length (LS1) in the direction of the length (LF1) of the mold cavity (100).

[0062] Figure 4 Showing the results of the comparison.

[0063] Figure 5 The results are shown according to an embodiment of the present invention.

[0064] The invention will be explained in more detail with reference to the following embodiments.

[0065] Comparative Example Foam was produced using a mold with a plate-shaped cavity from existing technology, wherein depressurization was performed via a valve eccentrically positioned on the wall (A3) of the cavity through a circular opening for venting. The mold was heated to approximately 55°C. In the experiment, polyol formulation A (including a loaded CO2 blowing agent) and isocyanate component B (composition shown in Table 1) were mixed together using a high-pressure mixing head (process parameters shown in Table 1).

[0066] The anti-baffle is used to inject the mixture into the mold cavity through a circular injection opening at the bottom of the mold cavity within 2.5 seconds at approximately 160 bar and approximately 40°C (method step i). During this stage, the pressure in the mold cavity is approximately 8 bar.

[0067] After a milky whitening time of 3.5 s, the mold cavity pressure is reduced to ambient pressure within 2 s (method step ii)). Depressurization causes CO2 to expand, generating foam that fills the mold cavity. The part can then be demolded after cooling (method step iii)).

[0068] The foamed molded articles produced using this mold and the process conditions described in Table 1 exhibit elongated cell shapes with openings. The average density of the foam is 81 kg / m³.

[0069] The ratio of the opening area to the wall area is 1:13. The ratio of the opening length LS1 to the mold cavity length LF1 is 1:5.25.

[0070] Despite injecting sufficient material, the mold cavity was not completely filled with foam. The corners of wall A3, opposite the outlet, were not filled (see...). Figure 4 ).

[0071] Example (according to the present invention): The comparative experiments were repeated, the difference being the use of the mold according to the invention. Increasing the mold size, particularly the increase in dimension LF1, made the depressurization process more demanding than in a smaller mold. Therefore, various process parameters (pressure, injection time, milking time) had to be adjusted to achieve comparable foam properties, especially comparable density.

[0072] In the entrance area, injection is made through a direct gate positioned along the cavity width (LF1). From the direct gate, the mixture transitions to a predetermined depth in the cavity (LF2) via a converging, opening slot. The mixture is injected at approximately 51°C (polyol) and approximately 35°C (isocyanate) and at a pressure of approximately 155 bar. The mold is then heated to 53°C, and the cavity is subjected to an internal pressure of 8 bar.

[0073] The pressure relief unit of the mold has a slotted opening that narrows towards the center and leads to the mold cavity. The ratio of the opening area to the wall area is 915:50400 (1:55). The ratio of the opening length LS1 to the mold cavity length LF1 is 1:1.

[0074] The bubbles in the molded part are non-oriented and have a uniform shape and narrow size distribution. The mold cavity is completely and uniformly filled (see...). Figure 5 ).

[0075] Table 1: Example Comparative Example According to embodiments of the present invention Isocyanates [parts by weight] 97.19 97.19 Polyol 1 [parts by weight] 13 13 Polyol 2 [parts by weight] 32.50 32.50 Polyols 3 [parts by weight] 50 50 Stabilizer [parts by weight] 1.5 1.5 <![CDATA[CO2 blowing agent [parts by mass]]]>[[-END]] 5.16 5.16 1 part by weight of pore-opening agent 0.4 0.4 2 parts by weight of pore-opening agent 0.1 0.1 Catalyst 1 [parts by weight] 2.5 2.5 Catalyst 2 [parts by weight] 1.65 1.65 Mold pressure [bar] 8 8 Pressure on the polyol side [bar] 164 155 Pressure on the isocyanate side [bar] 159 159 Mold temperature [°C] 55 53 Temperature on the polyol side [°C] 47 51 Temperature on the isocyanate side [°C] 35 35 Injection time [s] 2.5 3.4 Milky white time [s] 3.5 1.6 Depressurization time [s] 2 2 Opening: Ratio of A3 area 1:13 1:55 The ratio of opening length LS1:LF1 1:(5.25) 1:1 LF1:LF2 ratio 210:80 630:80 LF3:LF2 ratio 300:80 740:80 Molding density [kg / m³] 81 80 .

[0076] For the purposes of this application, injection time is the injection duration.

[0077] For the purposes of this application, the milky time is the time from the end of injection to the start of depressurization.

[0078] The chemicals used in the experiment were: Isocyanate: Desmodur® 44V20L from Covestro Deutschland AG, a mixture of monomer and polymeric MDI, with a viscosity of 160-240 mPa·s (25°C) and an NCO content of 30.5-32.5% by weight. Polyol 1: A polyether polyol based on trimethylolpropane and propylene oxide, with a hydroxyl value of 800 mg KOH / g, a functionality of 3, and a viscosity of 6100 mPa·s at 25°C. Polyol 2: A polyether polyol based on trimethylolpropane and ethylene oxide, with a hydroxyl value of 550 mg KOH / g, a functionality of 3, and a viscosity of 505 mPa·s at 25°C. Polyol 3: A mixture of the following components: - 27% by weight of a polyether polyol based on 1,2-propanediol and propylene oxide, having a hydroxyl value of 56 mg KOH / g, a functionality of 2, and a viscosity of 310 mPa·s at 25°C. - 19% by weight of a polyether polyol based on 1,2-propanediol and propylene oxide, having a hydroxyl value of 112 mg KOH / g, a functionality of 2, and a viscosity of 140 mPa·s at 25°C. - 54% by weight of a glycerol and propylene oxide-based polyether polyol with a hydroxyl value of 231 mg KOH / g, a functionality of 3, and a viscosity of 350 mPa·s at 20°C. Stabilizer: Tegostab® B 8443, a foam stabilizer from Evonik Industries AG, based on polyether polydimethylsiloxane. Opener 1: Ortegol 500 from Evonik Industries AG, an organic polymer based on polybutadiene. Cavity opener 2: Ortegol 501 from Evonik Industries AG, a mixture of amine-stabilized macromolecular unsaturated hydrocarbons and phthalates. Catalyst 1: Desmorapid 1792 from Covestro Deutschland AG, based on potassium acetate in diethylene glycol. Catalyst 2: Dabco NE1070 from Evonik Industries AG, based on dimethylaminopropylurea.

Claims

1. A method for producing a foamed flat polyurethane / polyisocyanurate molded article of thickness in the mold cavity (100) of a mold (10) having an inlet area, a mold cavity (100) and a pressure relief unit (300), wherein the method comprises the following steps: i) A polyurethane / polyisocyanurate reactive mixture is injected into the mold cavity (100) of the mold (10) through at least one inlet opening (110, 210) in the inlet region, the mold cavity being subjected to an initial pressure of 5 bar to 40 bar. ii) After the polyurethane / polyisocyanurate reactive mixture is injected, the pressure in the mold cavity (100) is depressurized to atmospheric pressure or to a pressure of 1 bar to 5 bar below the initial pressure for a duration of 0.1 to 10 seconds by means of at least one valve (310) in the depressurization unit (300), wherein the reactive mixture is foamed along the main flow direction from the inlet area through the mold cavity (100) to the depressurization unit (300). iii) Curing, cooling, and demolding the foamed flat polyurethane / polyisocyanurate molded product. Its features The mold cavity has two long dimensions, namely the first dimension (LF1) and the third dimension (LF3), and one shorter dimension, namely the second dimension (LF2). One of the long dimensions, namely the third dimension (LF3), represents the main flow direction of the foam. The mold cavity (100) has at least one first wall (A3) in a plane opened by a first dimension (LF1) and a second dimension (LF2) or at least one portion (K2) of a second wall (A2) in a plane opened by a first dimension (LF1) and a third dimension (LF3), wherein the portion (K2) of the second wall (A2) corresponds to a region extending in the third dimension (LF3) on a 1 / 10 portion of the second wall (A2) opposite to the inlet region, and wherein the at least one first wall (A3) or at least one portion (K2) of the second wall (A2) has at least one opening (340) connecting the mold cavity (100) and the pressure relief unit (300). The ratio of the total area of ​​the at least one opening (340) to the area of ​​the first wall (A3) containing the opening or the area of ​​the portion (K2) of the second wall (A2) containing the opening is 1:20 to 1:

100. The at least one opening (340) has a length (LS1) in the direction of the first dimension (LF1) of the length of the mold cavity (100), and The ratio of the length (LS1) of the at least one opening (340) or the sum of the lengths (LS1) to the first dimension (LF1) of the length of the mold cavity (100) is greater than 1:

4.

2. The method as described in claim 1, wherein the ratio of the first long dimension (LF1) to the second short dimension (LF2) of the mold cavity (100) and the ratio of the third long dimension (LF3) to the second short dimension (LF2) of the mold cavity (100) are each independently greater than 3:

1.

3. The method as claimed in claim 1 or 2, wherein the at least one opening (340) connecting the mold cavity (100) to the pressure relief unit (300) has an aspect ratio of at least 2.

4. The method as described in claim 1 or 2, wherein In step i), the mold cavity is subjected to an initial pressure of 7 to 25 bar. In step ii), the pressure in the mold cavity (100) is depressurized to atmospheric pressure or to a pressure 1 to 2 bar below the initial pressure for a duration of 0.2 to 2 seconds. The ratio of the length (LS1) of the at least one opening (340) or the sum of the lengths (LS1) to the first dimension (LF1) of the length of the mold cavity (100) is greater than 3:

4.

5. A mold for producing foamed flat polyurethane / polyisocyanurate molded articles of thickness, said mold having (i) An entrance area having at least one entrance opening (110, 210), (ii) Adjacent mold cavities (100), (iii) A pressure relief unit (300) having at least one valve (130, 310), Its features The mold cavity (100) has two long dimensions, namely the first dimension (LF1) and the third dimension (LF3), and one shorter dimension, namely the second dimension (LF2). The mold cavity (100) has at least one first wall (A3) in a plane opened by a first dimension (LF1) and a second dimension (LF2) or at least one portion (K2) of a second wall (A2) in a plane opened by a first dimension (LF1) and a third dimension (LF3), wherein the portion (K2) of the second wall (A2) corresponds to a region extending in the third dimension (LF3) on a 1 / 10 portion of the second wall (A2) opposite to the inlet region, and wherein the at least one first wall (A3) or at least one portion (K2) of the second wall (A2) has at least one opening (340) connecting the mold cavity (100) and the pressure relief unit (300). The ratio of the total area of ​​the at least one opening (340) to the area of ​​the first wall (A3) containing the opening or the area of ​​the portion (K2) of the second wall (A2) containing the opening is 1:20 to 1:

100. The at least one opening (340) has a length (LS1) in the direction of the first dimension (LF1) of the length of the mold cavity (100). The ratio of the length (LS1) of the at least one opening (340) or the sum of the lengths (LS1) to the first dimension (LF1) of the length of the mold cavity (100) is greater than 1:

4.

6. The mold as claimed in claim 5, wherein the ratio of the first long dimension (LF1) to the second short dimension (LF2) of the mold cavity and the ratio of the third long dimension (LF3) to the second short dimension (LF2) of the mold cavity are each independently greater than 3:

1.

7. The mold as claimed in claim 5 or 6, wherein the at least one opening (340) connecting the mold cavity (100) to the pressure relief unit (300) has an aspect ratio of at least 2.

8. The mold as claimed in claim 5 or 6, wherein the ratio of the length (LS1) of the at least one opening (340) or the sum of the lengths (LS1) to the first dimension (LF1) of the length of the mold cavity (100) is greater than 3:

4.

9. The mold as described in claim 5 or 6, wherein the ratio of the first long dimension (LF1) to the second short dimension (LF2) of the mold cavity and the ratio of the third long dimension (LF3) to the second short dimension (LF2) of the mold cavity are each independently greater than 6:

1.

10. The mold as claimed in claim 5 or 6, wherein the at least one opening (340) connecting the mold cavity (100) to the pressure relief unit (300) has an aspect ratio of at least 5.

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