Rigid polyurethane foam material, preparation method thereof, refrigerator door and refrigerator

Abstract

The invention discloses a rigid polyurethane foam material, a preparation method thereof, a refrigerator door and a refrigerator, and belongs to the technical field of high polymer material foam materials. According to the technical scheme, a material A and a material B are used as raw materials to react to generate the rigid polyurethane foam material; the material A comprises combined polyether polyol, a catalyst and a cross-linking agent; the material B comprises polymerized isocyanate; the catalyst comprises a gel catalyst and a trimerization catalyst; the cross-linking agent is selected from glycerol; the material ratio of the material A to the material B is calculated on the basis of an isocyanate index, and the isocyanate index is selected from any one value of 120-200. The method is applied to the anti-deformation aspect of the refrigerator door, solves the problem that the compression strength of rigid polyurethane foam is improved by improving the isocyanate index in the prior art, but if the value exceeds 1.30, the rigid polyurethane foam cannot be used due to brittleness of the foam, and has the characteristics of improving the compression strength, preventing deformation and improving the foam strength.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer foam materials, and in particular relates to a rigid polyurethane foam material, a preparation method thereof, a refrigerator door and a refrigerator. Background Art

[0002] For a long time, rigid polyurethane foam has been widely used as an insulation material for refrigerators, which can provide basic refrigerator performance including thermal insulation and structural strength. The physical properties required for rigid polyurethane foam (including properties such as density, thermal conductivity, compressive strength and dimensional stability) are measured according to established standards and managed as numerical data. In refrigerator production, quality problems caused by such rigid polyurethane foam occur from time to time, among which appearance defects caused by door deformation are a major quality problem. The refrigerator door is the most conspicuous part of the refrigerator, and any flaws in appearance are unacceptable. The undesirable deformation of the refrigerator door is not limited to the appearance. Depending on the degree of deformation, a gap may occur between the door and the refrigerator cabinet. If this happens, the airtightness of the refrigerator will deteriorate, affecting the maintenance of the temperature in the refrigerator and the power consumption, leading to serious quality problems. In order to suppress the deformation of the refrigerator door, it is necessary to increase the foaming strength of the rigid polyurethane foam, which is generally quantified by a compressive strength test. The thickness direction of the refrigerator door is smaller than the length and width directions, and is thinner than the size of the door. Therefore, if the strength is insufficient, a concave bow deformation will occur inside the chamber with a lower temperature. At this time, as a method for measuring the strength of the rigid polyurethane foam for the door deformation, a more appropriate strength measurement method than the compression strength needs to be devised.

[0003] However, when the strength of the foam increases, the thermal conductivity will be adversely affected, and it is difficult to meet both requirements at the same time. For general rigid polyurethane foams, the isocyanate index used is 120-200 (preferably 131-150). Among them, the isocyanate index used in Chinese patent CN102443134B is 1.20-1.30. As the isocyanate index increases, the compression strength increases, but when the isocyanate index exceeds 1.30, the foam surface will have the defect of becoming brittle, and the isocyanate index in the example is 1.20.

[0004] As can be seen from the above, although the prior art achieves the purpose of improving the compressive strength by increasing the isocyanate index, if the value exceeds 1.30, there is a problem that the foam is brittle and cannot be used. Summary of the invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is that the prior art achieves the purpose of improving the compressive strength of rigid polyurethane foam by increasing the isocyanate index, but if the value exceeds 1.30, there is a problem that the foam cannot be used due to its brittleness. A rigid polyurethane foam material capable of improving the compressive strength, preventing deformation and improving the foam strength, a preparation method thereof, a refrigerator door and a refrigerator are proposed.

[0006] In order to solve the technical problem, the technical solution adopted by the present invention is:

[0007] The invention provides a method for preparing a rigid polyurethane foam, comprising: using material A and material B as raw materials for reaction to generate the rigid polyurethane foam; the material A comprises a combined polyether polyol, a catalyst and a crosslinking agent; the material B comprises a polymerized isocyanate; the catalyst comprises a gel catalyst and a trimerization catalyst; the crosslinking agent is selected from propylene glycol; the material ratio of the material A to the material B is calculated based on an isocyanate index, and the isocyanate index is selected from any value between 120 and 200.

[0008] Preferably, the isocyanate index is selected from any value in the range of 131-150.

[0009] Preferably, the polymeric isocyanate is polymethylene polyphenyl polyisocyanate, the average number of functional groups is 2.3 or more, the isocyanate content is any value in the range of 25-35 mass %, and the viscosity at 25° C. is any value in the range of 50-500 mPa·s.

[0010] Preferably, in parts by weight, the combined polyether polyol comprises 20-60 parts of polyol A1, 15-45 parts of polyol A2, and 15-45 parts of polyol A3; the average number of functional groups of the polyol A1 is any value between 3 and 6, and the hydroxyl value is any value between 300 and 600 mgKOH / g; the average number of functional groups of the polyol A2 is any value between 3 and 6, and the hydroxyl value is any value between 300 and 700 mgKOH / g; the average number of functional groups of the polyol A3 is any value between 2 and 5, and the hydroxyl value is any value between 200 and 600 mgKOH / g.

[0011] Preferably, based on the weight ratio of the gel catalyst to the trimerization catalyst, the gel catalyst accounts for 1.0, and the trimerization catalyst accounts for more than 0.2.

[0012] Preferably, the gel catalyst is selected from triethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine, N,N-dimethyl-1,3-diaminopropane, tris(dimethylaminopropyl)amine, N-methyldicyclohexylamine, N,N-dimethylethanolamine, N-methyl-N-(N,N-dimethylaminoethyl)ethanolamine, N,N,4-trimethylpiperazine-1-ethylamine, N,N,N',N'-tetramethyl -1,6-hexanediamine, triethylamine, tripropylamine, triethanolamine, bis(dimethylamino)ethyl ether, pentamethyldiethylenetriamine, N-methylmorpholine, dimorpholinodiethyl ether 1-3; the trimerization catalyst is selected from 1,3,5-tris(dimethylaminopropyl)-1,3,5-hexahydrotriazine, anhydrous sodium acetate, potassium isooctanoate, potassium acetate, 2-hydroxy-N,N,N-trimethyl-1-propylamine, 2,4,6-tris(dimethylaminomethyl)phenol 1-3.

[0013] Preferably, the material A further comprises a foam stabilizer, water and a foaming agent; the foaming agent is selected from cyclopentane and / or isopentane.

[0014] The present invention also provides a rigid polyurethane foam prepared by the method for preparing a rigid polyurethane foam according to any of the above technical solutions, wherein the bending strength of the rigid polyurethane foam is not less than 250 kPa.

[0015] Another aspect of the present invention provides a refrigerator door, which is prepared from the rigid polyurethane foam material according to claim 8, and has a length of 0.2-2.3 meters, a width of 0.1-1.5 meters, and a thickness of 0.02-0.2 meters.

[0016] The present invention also provides a refrigerator, wherein the refrigerator is equipped with the refrigerator door described in any one of the above technical solutions.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The invention provides a method for preparing a rigid polyurethane foam. By limiting the composition of material A and material B, and specifically limiting the composition of a catalyst and a crosslinking agent, and calculating and determining the material ratio of material A and material B with an isocyanate index of 120-200, isocyanurate groups can be effectively introduced into urethane bonds, so that the two bonds are closely stacked and firm, thereby ensuring the thermal insulation of the rigid polyurethane foam and improving the strength of the rigid polyurethane foam. The invention also provides a refrigerator door, which has the characteristics of good thermal insulation performance and not being easy to deform. DETAILED DESCRIPTION

[0019] The technical scheme in the specific embodiment of the present invention is described in detail and completely below. Obviously, the described embodiment is only a part of the specific implementation of the overall technical scheme of the present invention, rather than all implementations. Based on the overall concept of the present invention, all other embodiments obtained by ordinary technicians in this field fall within the scope of protection of the present invention.

[0020] The present invention provides a method for preparing a rigid polyurethane foam, comprising: reacting material A and material B as raw materials to generate the rigid polyurethane foam; material A comprises a combined polyether polyol, a catalyst and a crosslinking agent; material B comprises a polymerized isocyanate; the catalyst comprises a gel catalyst and a trimerization catalyst; the crosslinking agent is selected from propylene glycol; the material ratio of material A to material B is calculated based on an isocyanate index, and the isocyanate index is selected from any value between 120 and 200. The propylene glycol added as a crosslinking agent has a molecular weight of 92.1 and a functional group number of 3, has excellent affinity with the component A polyol, and is uniformly dispersed in the component A. In a preferred embodiment, the isocyanate index is selected from any value between 131 and 150. The preparation method of the rigid polyurethane foam material is by limiting the composition of A material and B material, and specifically limiting the composition of catalyst and cross-linking agent, and calculating and determining the material ratio of A material and B material with an isocyanate index of 120-200, so that the isocyanurate group can be effectively introduced into the carbamate bond, so that the two bonds are closely stacked and firm, which not only ensures the thermal insulation of the rigid polyurethane foam material, but also improves the strength of the rigid polyurethane foam material. In the present invention, the isocyanate index (NCO index) is set to 120-200, and the trimerization catalyst added in a certain proportion accelerates the trimerization reaction to generate the isocyanurate group, and then the isocyanurate group is effectively introduced into the carbamate bond formed by the reaction between the polyol and the isocyanate. In addition, due to the effect of glycerol as a cross-linking agent, the carbamate bond introduced by the isocyanurate group becomes tight and firm, thereby significantly improving the foam strength and suppressing the deformation of the refrigerator door. Bending strength is used as a parameter for the strength of the foam and is the best way to quantify the strength of rigid polyurethane foam when a flat, thin structure (such as a refrigerator door) is deformed into a bow shape due to temperature stress.

[0021] The isocyanate index of the rigid polyurethane foam commonly used in refrigerators is mostly 100-120 (preferably 103-113), and the isocyanurate foam used for building materials mostly uses an isocyanate index of about 300 to 500. The isocyanate index in the present invention is calculated and used based on 120-200 (preferably 131-150), which is generally not within the scope of the rigid polyurethane foam used in refrigerators. In addition, this is not within the scope of isocyanurate foam use, but the present application can improve the foam strength of the rigid polyurethane foam by adjusting the formula and matching the isocyanate index, thereby suppressing the deformation of the refrigerator door.

[0022] Here, the reaction of the A material combination polyether polyol and the B material polymerized isocyanate is briefly described. The water in the A material combination polyether polyol reacts with the NCO group in the B material isocyanate to generate urea groups and carbon dioxide. The amine in the A material combination polyether polyol reacts with the NCO group in the B material isocyanate to generate urea groups. The OH group in the A material combination polyether polyol reacts with the NCO group in the B material isocyanate to form a urethane bond. In addition, the NCO group in the B material isocyanate undergoes self-polymerization under certain conditions. If two NCO groups react, isocyanate dimers are formed. When three NCO groups react, isocyanate trimers (isocyanurate groups) are formed. In addition, when two NCO groups react, uretonimine groups can be generated by carbodiimide groups. The reaction to generate isocyanurate groups is called isocyanurate reaction. Isocyanurate groups and carbodiimide groups are generated only in the presence of special catalysts or at high temperatures. It is this isocyanurate group that is of concern in the present invention. The reaction between the A-material combination polyether polyol and the B-material isocyanate used in general refrigerators is mostly due to carbamate bonds, and there are few isocyanurate groups. Generally speaking, the heat resistance and strength of the isocyanurate group are excellent, but the thermal insulation is poor in many cases. Focusing on the heat resistance and strength of the isocyanurate group, isocyanurate foam is used as a thermal insulation material for building materials with the purpose of fire resistance and strength required by building materials. However, in refrigerators, thermal insulation is the most important, and fire resistance is often not necessary. Therefore, isocyanurate groups are not actively introduced into thermal insulation materials for refrigerators. The present invention focuses on the strength of the isocyanurate group. In particular, by uniformly arranging the isocyanurate group in the carbamate bond generated in the reaction of the A-material combination polyether polyol and the B-material isocyanate, the two bonds are closely stacked and firm. The substance necessary for the uniform arrangement of the isocyanurate group is a crosslinking agent, and the feature of this patent is that glycerol is used. As mentioned above, the isocyanurate group is generated only in the presence of a special catalyst or at a high temperature. This patent uses a trimerization catalyst as the catalyst. In addition, the isocyanurate reaction becomes active from about 50°C. Therefore, in order to effectively carry out the isocyanurate reaction, the present invention further limits the ratio of the trimerization catalyst and the gel catalyst. The isocyanurate reaction is a reaction in which the NCO groups in the raw material B material isocyanate self-polymerize. Therefore, in addition to the amount of B material isocyanate required for the reaction of the polyether polyol combined with the A material, the amount of the NCO groups in the B material isocyanate self-polymerization is also required.

[0023] In the above technical solution, the isocyanate index refers to the ratio of the molar equivalent of the active isocyanate group of the polyisocyanate to the molar equivalent of the active hydroxyl group of the active hydrogen compound such as polyol and water, also known as the NCO index or NCO Index, expressed as an index multiplied by 100. In other words, the isocyanate index is an index obtained by dividing the molar number of the active NCO group in the polyisocyanate used as material B by the molar number of the active hydroxyl group in the polyol used as material A, and then multiplying the index by the 100 symbol (in some cases, it will be directly written without multiplying by 100). The method of calculating the material ratio of the polyol of material A and the polyisocyanate of material B by incorporating the isocyanate index into the calculation formula will be described below. The isocyanate index (NCO index) is the ratio of the molar equivalent of the active isocyanate (NCO) group of the polyisocyanate to the molar equivalent of the hydroxyl group of the active hydrogen compound such as polyol and water. The isocyanate index is also called Isocyanate Index, NCO Index, NCO INDEX, etc. (in the industry of processing polyurethane, it is sometimes referred to as Index. Index). It is generally expressed as an index obtained by dividing the molar equivalent of active isocyanate groups in the polyisocyanate by the molar equivalent of active hydroxyl groups in the polyol and then multiplying by 100 (in some cases, the value not multiplied by 100 is used as is). The calculation formula is as follows:

[0024] Isocyanate index (NCO index) = (number of moles of active NCO groups in the B material polyisocyanate / number of moles of active hydroxyl groups in the A material polyol) × 100

[0025] Typically, for rigid polyurethane foams, an isocyanate index greater than 100 is set. Rigid polyurethane foams used to make refrigerators use a range of 100-120 (preferably 103-113).

[0026] The number of moles of the active hydrogen compound in the component A polyol to be used is obtained as follows.

[0027] The hydroxyl value of polyol A1 multiplied by the weight percentage, the hydroxyl value of polyol A2 multiplied by the weight percentage, and the hydroxyl value of polyol A3 multiplied by the weight percentage are summed. The hydroxyl value is an index obtained by replacing the proportion of active hydrogen compounds in a substance with KOH, and the unit is (mg KOH / g). The three sums obtained are divided by the molecular weight of KOH of 56.11, and the value obtained by dividing the value by 1000 (unit converted from mg to g) represents the molar equivalent of the active hydrogen compound in the polyol (A1, A2, A3). The weight percentage of water in the foaming agent is divided by the molecular weight of water, 18, and then multiplied by the number of functional groups of water, 2, and the value represents the molar equivalent of the active hydrogen compound in water. The sum of the molar equivalent of the polyols (A1, A2, A3) obtained above and the molar equivalent of water represents the molar equivalent of the active hydrogen compound present in the raw material A polyol.

[0028] Next, the number of moles of reactive isocyanate groups (also referred to as reactive NCO groups) in the material B polyisocyanate to be used is determined.

[0029] The weight fraction of the polyisocyanate used is multiplied by the isocyanate content to obtain the value of the active isocyanate group (active NCO group) in the polyisocyanate used. The value obtained by dividing the value of the active isocyanate group (active NCO group) in the polyisocyanate used by the NCO molecular weight of 42.02 represents the molar equivalent of the active isocyanate group (active NCO group) in the polyisocyanate of raw material B. When the molar equivalent required for the reaction of all active hydrogen compounds in the polyol of component A is the same as the molar equivalent of the active isocyanate group (active NCO group) in the polyisocyanate of component B, the isocyanate index is defined as 100.

[0030] In a preferred embodiment, the polymeric isocyanate is polymethylene polyphenyl polyisocyanate, the average number of functional groups is 2.3 or more, the isocyanate content is any value in the range of 25-35 mass%, and the viscosity at 25°C is any value in the range of 50-500 mPa·s. Further, the average number of functional groups is 2.3-3.1, the isocyanate content is any value in the range of 28-33 mass%, and the viscosity at 25°C is any value in the range of 100-300 mPa·s. Polymethylene polyphenyl polyisocyanate is prepared by first condensing aniline and formalin to form a condensation mixture (polyamine), and then phosgenating and converting the amino group into an isocyanate group (isomerizing if necessary). Polymethylene polyphenyl polyisocyanate refers to a mixture of organic isocyanate compounds with different condensation degrees. By changing the raw material composition ratio and reaction conditions during condensation, the composition of the polymethylene polyphenyl polyisocyanate finally obtained can be changed. The polymethylene polyphenyl polyisocyanate used in the present invention is a reaction solution after isocyanate group conversion, a solution obtained by desolventizing the reaction solution, or a solution obtained by distilling and separating part of MDI, or a mixture that may contain several different reaction conditions, separation conditions, etc. In addition, a part of the isocyanate group can be denatured with biuret, allophanate, carbodiimide, oxazolidone, amide, imide, etc. The polymethylene polyphenyl polyisocyanate contains diphenylmethane diisocyanate (MDI) having two benzene rings and two isocyanate groups in one molecule. There are three isomers constituting MDI: 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate. The isomer composition ratio of MDI is not particularly limited, but when the content of 4,4'-MDI is 70% by mass or more, preferably 90 to 99.9% by mass, the strength of the obtained foam is improved, so it is preferred. Typical product names include WANNATE PM-200 of Wanhua Chemical, Papi-27 of Dow Chemical, Lupranat M20S of BASF Chemical, Desmodur 44V20L of Covestro, and Suprasec 5005 of Huntsman. In the present invention, if necessary, polymeric isocyanates other than the above-mentioned polymethylene polyphenyl polyisocyanates can be used as component B polymeric isocyanates, including isocyanurate-modified, uretonimine-modified, and allophanate-modified MDI. In addition, aromatic diisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,4-xylene diisocyanate, 1,3-xylene diisocyanate, tetramethyl xylene diisocyanate, m-phenylene diisocyanate, and p-phenylene diisocyanate are included. Also included are aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, 3-methyl-1,5-pentane diisocyanate and lysine diisocyanate. Also included are alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated toluene diisocyanate, hydrogenated xylene diisocyanate and hydrogenated diphenylmethane diisocyanate.In addition, these polymers, urethane compounds, urea compounds, allophanate compounds, biuret compounds, carbodiimide compounds, uretonimine compounds, uretdione compounds, isocyanurate compounds, etc. are also included. In addition, mixtures of two or more of these are also included.

[0031] In a preferred embodiment, the combined polyether polyol comprises, by weight, 20-60 parts of polyol A1, 15-45 parts of polyol A2, and 15-45 parts of polyol A3; the average number of functional groups of the polyol A1 is any value between 3 and 6, and the hydroxyl value is any value between 300 and 600 mgKOH / g; the average number of functional groups of the polyol A2 is any value between 3 and 6, and the hydroxyl value is any value between 300 and 700 mgKOH / g; the average number of functional groups of the polyol A3 is any value between 2 and 5, and the hydroxyl value is any value between 200 and 600 mgKOH / g. Among them, polyol A1 is obtained by addition polymerization of propylene oxide or a combination of ethylene oxide and propylene oxide in an initiator with sucrose as the main component, polyol A2 is obtained by addition polymerization of propylene oxide or a combination of ethylene oxide and propylene oxide in an initiator with sorbitol as the main component, and polyol A3 is obtained by addition polymerization of propylene oxide or a combination of ethylene oxide and propylene oxide in an initiator with toluenediamine alcohol as the main component. It should be noted that as the initiator of polyol A1, in addition to sucrose as the main component, propylene glycol, diethylene glycol, glycerol, water, ethylenediamine and other well-known initiators can also be used in combination; as the initiator of polyol A2, in addition to sorbitol as the main component, glycerol, organic amines, water and other well-known initiators can also be used in combination; as the initiator of polyol A3, a known initiator such as triethanolamine can be used together with toluenediamine as the main component. In addition, 10 parts by weight or less of known polyols (such as polyether polyols, polyester polyols, etc.) may be added to the total of 100 parts by weight of the polyols A1, A2, and A3.

[0032] In a preferred embodiment, based on the weight ratio of the gel catalyst to the trimerization catalyst, the gel catalyst accounts for 1.0 and the trimerization catalyst accounts for more than 0.2. The weight ratio of the gel catalyst is 0.5-20 parts, preferably 1-10 parts; the weight ratio of the trimerization catalyst is 0.1-10 parts, preferably 0.5-5 parts.

[0033] In a preferred embodiment, the gel catalyst is selected from triethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine, N,N-dimethyl-1,3-diaminopropane, tris(dimethylaminopropyl)amine, N-methyldicyclohexylamine, N,N-dimethylethanolamine, N-methyl-N-(N,N-dimethylaminoethyl)ethanolamine, N,N,4-trimethylpiperazine-1-ethylamine, N,N,N',N'- 1-3 kinds of tetramethyl-1,6-hexanediamine, triethylamine, tripropylamine, triethanolamine, bis(dimethylamino)ethyl ether, pentamethyldiethylenetriamine, N-methylmorpholine, dimorpholinyldiethyl ether; the trimerization catalyst is selected from 1,3,5-tris(dimethylaminopropyl)-1,3,5-hexahydrotriazine, anhydrous sodium acetate, potassium isooctanoate, potassium acetate, 2-hydroxy-N,N,N-trimethyl-1-propylamine, 2,4,6-tris(dimethylaminomethyl)phenol. Further, the gel catalyst can be supplemented with 1 part by weight or less of a known gel catalyst, and the trimerization catalyst can be supplemented with 0.5 parts by weight or less of a known trimerization catalyst.

[0034] The Chinese and English names and abbreviations corresponding to the above catalysts are explained as follows:

[0035] Triethylene diamine (TEDA), N,N,N',N'-tetramethylethylene diamine (TMEDA), N,N-dimethylcyclohexylamine (DMCHA), N,N-dimethylbenzylamine (DMBA / BDMA), N,N-dimethyl-1,3-diaminopropane 3-(Dimethylamino)propylamine (DMAPA), BIS (3-dimethylaminopropyl)-NN-dimethylpropane diamine (PC-9), N-methyl dicyclohexylamine (PC-12 / MDCHA), N,N-dimethylethanolamine (DMEA), N-methyl-N-(N,N-dimethylaminoethyl)ethanolamine aminoethylethanolamine(Dabco-T), N,N,4-trimethylpiperazine-1-ethylamine N,N',N'-trimethyl aminoethylpiperazine(KAOLIZER NO8), N,N,N',N'-tetramethylhexane-1,6-diamine N,N,N',N'-tetramethylhexane-1,6-diamine(KAOLIZER NO1), triethylamine(TEA), tripropylamine(TPA), triethanolamine(TELA), Bis-(2-dimethyl aminoethyl)ether(Niax-A1), N,N,N',N",N"-pentamethyldiethylene triamine(PMDETA), N-methyl morpholine(NMM), 2,2'-dimorpholino diethylether(DMDEE);1,3,5-Tris(dimethylaminopropyl)-1,3,5-hexahydrotriazine N,N',N"-tris(3-dimethl aminopropyl)hexahydro-s-triazine(PC-41), Sodium Acetate, Potassium octoate(K-15), Potassium Acetate(P-15), 2-Hydroxy-N,N,N-trimethyl-1-propanaminium(TMR / TMR2), 2,4,6-tris(dimethyl aminomethyl)phenol(TMR30).

[0036] In a preferred embodiment, the material A further comprises a foam stabilizer, water and a foaming agent; the foaming agent is selected from cyclopentane and / or isopentane. The foam stabilizer is a foam stabilizer containing 1 to 3 kinds of organosilicon foam stabilizers, and known organosilicon foam stabilizers (for example, Momentive L-6863, L-6869, L-6970, L-6900, L-6988, L-5340, L-5420, L-5740, L-580 and Dow Toray SZ-1642, SZ-1605, DC193, SF-2945 and Evonik B-8423, B-8404, B-8407, B-8465, B-8444, B-8467, B-8433, B-8466, B-8870, B-8450, etc.), and the weight portion is 0.5-8 parts (preferably 1-5 parts by weight); the weight portion of the foaming agent is 5-40 parts (preferably 10-30 parts by weight); the weight portion of water is 0-5 parts (preferably 1-3 parts by weight); the cross-linking agent is glycerol, and the weight portion is 0.1-10 parts (preferably 0.5-5 parts by weight). It should be noted that other additives can be used in the present invention, such additives include plasticizers, fillers, colorants, flame retardants, organic or inorganic fillers, antioxidants, ultraviolet absorbers, plasticizers, pigments / dyes, antibacterial / antifungal agents, etc. The flame retardant may be used in the present invention, and the flame retardant includes phosphoric acid esters such as triethyl phosphate and tris(β-chloropropyl) phosphate, and phosphoric acid ester compounds such as ethyl phosphite and diethyl phosphite.

[0037] Furthermore, the preparation method of the above rigid polyurethane foam material comprises the following steps: (1) as material A, polyol, catalyst, foam stabilizer, blowing agent and crosslinking agent are mixed in a prescribed proportion, and a polyol mixer can also be used for the mixing step; (2) polyisocyanate is prepared as material B; (3) the temperature of material A and material B is controlled at 10-40°C, and they are stirred for 1-20 seconds according to the proportion, and a low-pressure and high-pressure foaming machine can also be used for the stirring and mixing step; (4) they are immediately poured into a mold for reaction, and the mold is opened after 1-60 minutes to take out the molded rigid polyurethane foam. During the molding process, a refrigerator door molding machine can also be used to mold the refrigerator door in one piece. The reaction between the polyol of material A and the polyisocyanate of material B is carried out in the following process:

[0038] In the initial stage of the reaction, the water molecules in the polyol of component A react with the NCO groups in the polyisocyanate of component B to form urea bonds (referred to as reaction 1), and carbon dioxide gas is generated simultaneously with the heat generated by the reaction;

[0039] In parallel with this reaction, the active hydroxyl groups in the polyol of component A react with the active NCO groups in the polyisocyanate of component B to form urethane bonds (referred to as reaction 2). At this time, due to the effect of the crosslinking agent added to component A, the bonds inside the hard segments form denser and stronger bonds.

[0040] The above exothermic reaction (including reaction 1 and reaction 2) proceeds, and when the temperature reaches a certain level or higher, the trimerization catalyst incorporated into the raw material A polyol promotes the following reaction, the active NCO groups in the polyisocyanate of the B material react with each other and bond to form isocyanurate groups (referred to as reaction 3);

[0041] Since Reaction 2 and Reaction 3 proceed simultaneously, the isocyanurate groups generated in Reaction 3 are effectively dispersed and arranged in the urethane bonds generated in Reaction 2 to form a strong hard segment, and as a result, excellent foam strength can be exhibited.

[0042] In the production of rigid polyurethane foam, any equipment can be used as long as the raw material liquid can be mixed uniformly. For example, a small mixer for foaming or a low-pressure or high-pressure foaming machine for foaming, which is used to produce general polyurethane foam, can be used.

[0043] The rigid polyurethane foam obtained by the present invention is most suitable as a heat insulating material for refrigerators, and can also be used for various heat insulating materials such as boards, panels, freezers, eaves, doors, rain curtains, window sashes, concrete houses, bathtubs, low-temperature tank equipment, cold storages, pipe covers, hot water insulation tanks, building floors, etc.

[0044] The present invention also provides a rigid polyurethane foam prepared by the method for preparing a rigid polyurethane foam according to any of the above technical solutions, wherein the flexural strength of the rigid polyurethane foam is not less than 250 kPa. The rigid polyurethane foam has chemical bonds such as polyurethane bonds and urea bonds, and in particular, due to the effect of the added trimerization catalyst, isocyanurate groups are generated during the foaming process.

[0045] Another aspect of the present invention provides a refrigerator door, which is prepared from the rigid polyurethane foam material according to claim 8, and the length of the refrigerator door is 0.2-2.3 meters, the width is 0.1-1.5 meters, and the thickness is 0.02-0.2 meters. As a method for judging the deformation of the refrigerator door body, the measurement of bending strength is used as the physical strength of the manufactured rigid polyurethane foam. The measured bending strength of the rigid polyurethane foam produced according to the present invention is 250 kPa or higher on average.

[0046] The present invention also provides a refrigerator, wherein the refrigerator is equipped with the refrigerator door described in any one of the above technical solutions.

[0047] In order to more clearly and in detail introduce the rigid polyurethane foam material, the preparation method thereof, the refrigerator door and the refrigerator provided in the embodiments of the present invention, they will be described below in conjunction with specific embodiments.

[0048] Example

[0049] Component A is a mixture of polyols: Polyol A1 is a polyether polyol obtained by addition polymerization of propylene oxide with sucrose as the main ingredient as the initiator, with an average functional group number of 4.5 and a hydroxyl value of 460 mgKOH / g; Polyol A2 is a polyether polyol obtained by addition polymerization of propylene oxide with sorbitol as the main ingredient, with an average functional group number of 4.3 and a hydroxyl value of 500 mgKOH / g; Polyol A3 is a polyether polyol obtained by addition polymerization of propylene oxide with toluene diamine as the initiator, with an average functional group number of 4 and a hydroxyl value of 370 mgKOH / g.

[0050] The gelling catalyst (C1) is N,N-dimethylcyclohexylamine (DMCHA) and N,N,N',N",N"-pentamethyl diethylene triamine (PMDETA).

[0051] The trimerization catalyst (C2) is 1,3,5-tris(dimethylaminopropyl)-1,3,5-hexahydrotriazine N,N',N"-tris(3-dimethl aminopropyl)hexahydro-s-triazine (PC-41) and Potassium octoate (K-15).

[0052] The foam stabilizer (D1) was L-6863 from Momentive.

[0053] The blowing agents are cyclopentane (E1) and water (E4).

[0054] The crosslinking agent (F1) is glycerol.

[0055] The polymeric isocyanate (B) is WANNATE PM-200 from Wanhua Chemical.

[0056] The formulation composition and related properties of each example are shown in Table 1.

[0057] Table 1 Formulation composition and properties

[0058]

[0059] Table 1 shows the data of the formulation, isocyanate index, foam core density, thermal conductivity, compressive strength, flexural strength and foam surface condition of Examples 1 to 6. Examples 1 to 3 are comparisons when the isocyanate index increases. As the isocyanate index increases, the density becomes higher, and the values ​​of compressive strength and flexural strength become higher. In addition, the thermal conductivity becomes higher, indicating deterioration. Examples 4 to 6 are comparative examples in which glycerol, a trimerization catalyst and cyclopentane are added to Example 3. Adding glycerol·trimerization catalyst increases density. Therefore, the density is adjusted by changing the amount of cyclopentane added. As the amount of glycerol added increases, the compressive strength and flexural strength increase. In addition, the thermal conductivity is also lower than that of Example 3. Compare Example 3 and Example 4. When glycerol, a trimerization catalyst and cyclopentane are added to Example 3, the compressive strength decreases, the flexural strength increases, and the thermal conductivity decreases, which indicates improvement. In addition, in Example 3, the foam surface becomes brittle, but in Example 4, there is no problem on the foam surface.

[0060] Summarizing Table 1, when the isocyanate index increases, the compressive strength and the bending strength increase. However, the thermal conductivity deteriorates. In addition, the isocyanate index of 130 has the disadvantage that the foam surface becomes brittle. Therefore, the addition of glycerol and a trimerization catalyst further improves the bending strength. In addition, the deterioration of thermal conductivity and the brittleness of the foam surface, which are disadvantages, can also be suppressed.

[0061] Table 2 shows the results of foaming the refrigerator door of Examples 1 to 6 using a high pressure foaming machine.

[0062] Table 2 Results of refrigerator door foaming

[0063]

[0064] The above foaming conditions: flow rate = 350g / sec, mixing pressure = 130bar, material temperature = 20℃

[0065] The refrigerator door adopts SBS type refrigerator door.

[0066] Refrigerator door size: length 1730, width 510, thickness 80 (mm)

[0067] Mold temperature: 40℃

[0068] Demoulding time: 7 minutes

[0069] Examples 1 to 6 were adjusted to have an overfill of 15%, foamed and left to stand for at least 24 hours after demolding. Afterwards, the door was assembled into the cabinet body, and the gap value between the door and the cabinet body during assembly was determined. This value is the "front door spacing at low temperature (mm)". Next, after the door was assembled, the refrigerator was cooled in a constant temperature chamber at -10°C for 48 hours, and the gap value between the door and the cabinet body was measured after cooling. This value is the "rear door spacing at low temperature (mm)". A large difference in values ​​before and after cooling indicates that the door has been deformed due to the influence of cooling, and a small difference in values ​​indicates that the door has excellent structural strength. In Examples 2 to 6, only the difference values ​​are recorded.

[0070] There is no difference between Example 1 and Example 2. The difference of Example 3 is smaller than that of Example 2. The difference of Example 4 is smaller than that of Example 3. The difference of Example 5 is smaller than that of Example 4. The difference between Example 5 and Example 6 is smaller. This indicates that the difference between isocyanate indexes of 110 and 120 is smaller, and that the door deformation is smaller when the isocyanate index is set to 131. In addition, it is shown that the deformation of the door becomes smaller by adding glycerol, a trimerization catalyst, and cyclopentane.

[0071] The results in Tables 1 and 2 are summarized. There is a certain correlation between the bending strength value and the door deformation. That is, by increasing the isocyanate index, the bending strength increases and the door deformation decreases. This relationship is stronger than that of the compressive strength.

[0072] Table 3 Values ​​of reactivity, free foam density and thermal conductivity when changing the isocyanate index in Example 6

[0073]

[0074] Increasing the isocyanate index results in slower reactivity and higher density. In addition, the thermal conductivity becomes higher, indicating degradation. From the results in Table 3, when glycerol, trimerization catalyst and cyclopentane are added, the thermal conductivity is below 21 mW / mK when the isocyanate index is below 201, which is a suitable range for refrigerator door insulation materials. In addition, when the isocyanate index is below 151, the free foam density is 30 kg / m 3 Below, which is better.

Claims

1. A method for preparing a rigid polyurethane foam, characterized in that: include: The rigid polyurethane foam is generated by reacting material A and material B as raw materials; the material A comprises a combined polyether polyol, a catalyst and a cross-linking agent; the material B comprises a polymerized isocyanate; the catalyst comprises a gel catalyst and a trimerization catalyst; the cross-linking agent is selected from propylene glycol; the material ratio of the material A to the material B is calculated based on the isocyanate index, and the isocyanate index is selected from any value between 120 and 200.

2. The method for preparing a rigid polyurethane foam according to claim 1, characterized in that: The isocyanate index is selected from any value in the range of 131-150.

3. The method for preparing a rigid polyurethane foam according to claim 1, characterized in that: The polymeric isocyanate is polymethylene polyphenyl polyisocyanate, has an average functional group number of 2.3 or more, an isocyanate content of any value in the range of 25-35 mass %, and a viscosity of any value in the range of 50-500 mPa·s at 25° C.

4. The method for preparing a rigid polyurethane foam according to claim 1, characterized in that: In parts by weight, the combined polyether polyol comprises 20-60 parts of polyol A1, 15-45 parts of polyol A2, and 15-45 parts of polyol A3; the average number of functional groups of the polyol A1 is any value between 3 and 6, and the hydroxyl value is any value between 300 and 600 mgKOH / g; the average number of functional groups of the polyol A2 is any value between 3 and 6, and the hydroxyl value is any value between 300 and 700 mgKOH / g; the average number of functional groups of the polyol A3 is any value between 2 and 5, and the hydroxyl value is any value between 200 and 600 mgKOH / g.

5. The method for preparing a rigid polyurethane foam according to claim 1, characterized in that: Based on the weight ratio of the gel catalyst to the trimerization catalyst, the gel catalyst accounts for 1.0, and the trimerization catalyst accounts for more than 0.

2.

6. The method for preparing a rigid polyurethane foam according to claim 1, characterized in that: The gel catalyst is selected from triethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine, N,N-dimethyl-1,3-diaminopropane, tris(dimethylaminopropyl)amine, N-methyldicyclohexylamine, N,N-dimethylethanolamine, N-methyl-N-(N,N-dimethylaminoethyl)ethanolamine, N,N,4-trimethylpiperazine-1-ethylamine, N,N,N',N'-tetramethyl-1 , 1-3 of the group consisting of 6-hexanediamine, triethylamine, tripropylamine, triethanolamine, bis(dimethylaminoethyl)ether, pentamethyldiethylenetriamine, N-methylmorpholine, and dimorpholinodiethyl ether; the trimerization catalyst is selected from 1-3 of the group consisting of 1,3,5-tris(dimethylaminopropyl)-1,3,5-hexahydrotriazine, anhydrous sodium acetate, potassium isooctanoate, potassium acetate, 2-hydroxy-N,N,N-trimethyl-1-propylamine, and 2,4,6-tris(dimethylaminomethyl)phenol.

7. The method for preparing a rigid polyurethane foam according to claim 1, characterized in that: The material A also includes a foam stabilizer, water and a foaming agent; the foaming agent is selected from cyclopentane and / or isopentane.

8. The rigid polyurethane foam prepared by the method for preparing a rigid polyurethane foam according to any one of claims 1 to 7, characterized in that: The bending strength of the rigid polyurethane foam is not less than 250 kPa.

9. A refrigerator door, characterized in that: The refrigerator door is made of the rigid polyurethane foam material according to claim 8, and has a length of 0.2-2.3 meters, a width of 0.1-1.5 meters, and a thickness of 0.02-0.2 meters.

10. A refrigerator, characterized in that: The refrigerator is equipped with the refrigerator door according to claim 9.

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