A METHOD FOR PREPARING A POLYURETHANE COMPOSITE BY A VACUUM INFUSION PROCESS

Abstract

A method for preparing a polyurethane composite by a vacuum infusion process, a polyurethane composite prepared by said method and use thereof. The method for preparing a polyurethane composite by a vacuum infusion process of the present invention can reduce raw materials and production costs.

Claims

1. A method for preparing a polyurethane composite by a vacuum infusion process, comprising: a) placing at least a core material having a groove spacing, at least a flow medium and at least a reinforcing material in a mold; b) dehumidifying the core material, the flow medium and the reinforcing material by heating under vacuum; c) introducing a polyurethane composition into the mold via a flow runner having a diameter of <25 mm; and d) demolding after curing to obtain the polyurethane composite, wherein the groove spacing is >20 mm, the flow medium has a gram weight of <200 g/m.sup.2 and the flow runner has a diameter of <25 mm.

2. The method according to claim 1, wherein the step b) further comprises: covering the core material, the flow medium and the reinforcing material with a first film, sealing the rim of the first film with the mold, and vacuumizing between the first film and the mold; laying a second film to cover the first film, fixing the second film, sealing the rims of the first film and the second film and preserving an air inlet channel and an air outlet channel; and heating the mold while filling hot air between the first film and the second film and providing a temperature close to the mold temperature for the upper surface of the first film.

3. The method according to claim 1, wherein the heating is selected from the group consisting of electric blanket heating, electric film heating, microwave heating, infrared heating, hot air heating, and any combination thereof.

4. The method according to claim 1, wherein the reinforcing material is selected from the group consisting of entangled glass fiber layers, glass fiber woven fabrics and glass fiber gauzes, cut or ground glass fibers or mineral fibers, fiber mats, fiber nonwovens and fiber knits based on polymer fibers, mineral fibers, carbon fibers, glass fibers or aramid fibers, and mixtures thereof.

5. The method according to claim 1, wherein the core material is selected from a balsa wood, a PVC foam, a SAN foam, a polyurethane foam, a PS foam, a PMI foam, a PET foam, or any combination thereof.

6. The method according to claim 1, wherein the flow medium comprises a peel ply.

7. The method according to claim 6, wherein the peel ply is a polyester peel ply.

8. The method according to claim 1, wherein the polyurethane composition comprises the following components: a component A, comprising one or more organic polyisocyanates; a component B, comprising: b1) one or more organic polyols, which is present in a content of 21 to 60 wt % based on the total weight of the polyurethane composition as 100 wt %; b2) one or more compounds having the structure of formula (I) ##STR00004## wherein R1 is selected from hydrogen, methyl or ethyl; R2 is selected from an alkylene group having 2 to 6 carbon atoms, 2,2-di(4-phenylene)-propane, 1,4-xylylene, 1,3-xylylene, 1,2-xylylene; n is an integer selected from 1 to 6; and a component C, a free radical initiator.

9. The method according to claim 8, wherein the organic polyol has a functionality of 1.7 to 6 and a hydroxyl value of 150 to 1100 mg KOH/g.

10. The method according to claim 8, wherein b2) is present in a content of 4.6 to 33 wt %, based on the total weight of the polyurethane composition as 100 wt %.

11. The method according to claim 9, wherein the component b2) is selected from the group consisting of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and any combination thereof.

12. The method according to claim 1, wherein the method further comprises: providing a reaction injection device, which comprises at least two storage tanks for accommodating the components of the polyurethane composition, a vacuumizing device and feed units, wherein each of the feed units is connected to the storage tank via a feed line and a mixing unit, the components from the feed units are mixed together; wherein the rim of the mold is sealed and the mold is connected to at least a first injection line, which can be used for vacuumizing the mold and supplying the mixed components to the mold; and the mold comprises a drying channel; during the vacuum infusion, a drying gas is supplied to the mold to dry the core material, the flow medium and the reinforcing material placed in the mold; and the mold is vacuumized by means of a vacuum source, and the mold is connected to the reaction injection device via an injection line at the first injection line; and the mold is vacuumized via the injection line through a laterally closable outlet, which is connected to a vacuum source; drying the mold and the core material, the flow medium and the reinforcing material contained therein, as well as the injection line; beginning the vacuum infusion process with introducing the degassed components in the feed line from the storage tanks into the feed units of the reaction injection device, and obtaining the polyurethane composition from the components in the mixing unit, wherein the outlet of the vacuum source is closed before the polyurethane composition arrives; and injecting the polyurethane composition into the mold via the injection line, while vacuumizing the mold via the drying channel by the vacuum source, wherein the injection pressure at the injection port of the injection line is measured and kept lower than the external atmospheric pressure.

13. A polyurethane composite obtained by the method for preparing a polyurethane composite by a vacuum infusion process according to claim 1.

14. A wind turbine blade comprising the polyurethane composite according to claim 13.

15. A polyurethane product comprising a polyurethane composite obtained by the method for preparing a polyurethane composite by a vacuum infusion process according to claim 1.

16. The polyurethane product according to claim 15, wherein the polyurethane product is a wind turbine blade, a spar cap, a web plate, a blade root or a blade housing of a wind turbine blade.

17. The method according to claim 1, wherein the flow runner has a diameter of <18 mm.

18. The method according to claim 1, wherein the groove spacing is ≥25 mm.

19. The method according to claim 1, wherein the flow medium has a gram weight in the range of 90 to 130 g/m.sup.2.

20. The method according to claim 4, wherein the reinforcing material is selected from glass fiber mats or glass fiber nonwovens.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0041] The present invention will now be illustrated with reference to the accompanying drawings in which:

[0042] FIG. 1 shows a mold and layers arranged thereon in the method for preparing a polyurethane composite according to example 1 of the present invention, wherein 1 represents a core material, a fiber reinforcing material, 2 represents a flow runner, 3 represents a peel ply and a flow mesh; 4 represents a vacuumizing line; 5 represents a mold.

[0043] FIG. 2 shows a reaction injection device and a mold of the present invention, wherein 5 represents a mold; 21 represents a core material, a reinforcing material and/or a flow medium; 31 represents injection line; 32 represents a drying channel; 33 represents a drying air; 40 represents a reaction injection device; 41, 42 represent feed lines; 43 represents a mixing unit; 44a, 44b represent feed units; 45 represents injection line; 46 represents closable outlet; 47 represents vacuum source; 48, 49 represent storage tanks; 34, 50 represent vacuumizing devices.

DETAILED DESCRIPTION

[0044] Various aspects of the present invention are now described in detail.

[0045] The first aspect of the present invention is to provide a method for preparing a polyurethane composite by a vacuum infusion process. Said method comprises: [0046] a) placing at least a core material having a groove spacing of >20 mm, preferably ≥25 mm, at least a flow medium having a gram weight of <200 g/m.sup.2, preferably ≤160 g/m.sup.2, more preferably 90 to 130 g/m.sup.2 and at least a reinforcing material in a mold; [0047] b) dehumidifying the core material, the flow medium and the reinforcing material by heating under vacuum; [0048] c) introducing the polyurethane composition into the mold via a flow runner having a diameter of <25 mm, preferably ≤20 mm, more preferably <18 mm; and [0049] d) demolding after curing to obtain the polyurethane composite.

[0050] Preferably, the step b) further comprises: [0051] after placing the core material, the flow medium and the reinforcing material in the mold, covering the core material, the flow medium and the reinforcing material with a first film, sealing the rim of the first film with the mold, and vacuumizing between the first film and the mold; laying a second film to cover the first film, fixing the second film, sealing the rims of the first film and the second film and preserving an air inlet channel and an air outlet channel; heating the mold while filling hot air between the first film and the second film, providing a temperature close to the mold temperature for the upper surface of the first film.

[0052] Preferably, the heating is one, two or more selected from the group consisting of electric blanket heating, electric film heating, microwave heating, infrared heating and hot air heating.

[0053] Preferably, the reinforcing material is selected from the group consisting of entangled glass fiber layers, glass fiber woven fabrics and glass fiber gauzes, cut or ground glass fibers or mineral fibers, as well as fiber mats, fiber nonwovens and fiber knits based on polymer fibers, mineral fibers, carbon fibers, glass fibers or aramid fibers, and mixtures thereof, more preferably glass fiber mats or glass fiber nonwovens.

[0054] Preferably, the core material is one or more selected from balsa wood, PVC foam, SAN foam, polyurethane foam, PS foam, PMI foam and PET foam.

[0055] Preferably, the flow medium comprises a peel ply.

[0056] Preferably, the peel ply is a polyester peel ply.

[0057] Preferably, the polyurethane composition comprises the following components: [0058] a component A, comprising one or more organic polyisocyanates; [0059] a component B, comprising: [0060] b1) one or more organic polyols, which is present in a content of 21 to 60 wt %, preferably 21 to 40 wt %, based on the total weight of the polyurethane composition as 100 wt %; [0061] b2) one or more compounds having the structure of formula (I)

##STR00002## [0062] wherein R1 is selected from hydrogen, methyl or ethyl; R2 is selected from an alkylene group having 2 to 6 carbon atoms, 2,2-di(4-phenylene)-propane, 1,4-xylylene, 1,3-xylylene, 1,2-xylylene; n is an integer selected from 1 to 6; and [0063] a component C, a free radical initiator.

[0064] Preferably, the organic polyol has a functionality of 1.7 to 6, preferably 1.9 to 4.5 and a hydroxyl value of 150 to 1100 mg KOH/g, preferably 150 to 550 mg KOH/g.

[0065] Preferably, b2) is present in a content of 4.6 to 33 wt %, based on the total weight of the polyurethane composition as 100 wt %.

[0066] Preferably, the component b2) is one, two or more selected from the group consisting of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate and hydroxybutyl acrylate.

[0067] Preferably, the method further comprises:

[0068] providing a reaction injection device (40), which comprises at least two storage tanks (48, 49) for accommodating the components of the polyurethane resin, a vacuumizing device (50) and feed units (44a, 44b), wherein each of the feed units (44a, 44b) is connected to the storage tank (48, 49) via a feed line (41, 42) and a mixing unit (43), the components from the feed units (44a, 44b) are mixed together;

[0069] wherein the rim of the mold is sealed and the mold is connected to at least a first injection line (31), which can be used for vacuumizing the mold (5) and supplying the mixed components to the mold (5); and the mold comprises optionally a drying channel (32) for providing a drying gas (33); during the vacuum infusion, the drying gas is supplied to the mold to dry the core material, the flow medium and the reinforcing material (21) placed in the mold; and the mold (5) is vacuumized by means of a vacuum source (34), and the mold is connected to the reaction injection device (40) via an injection line (45) at the first injection line (31); and mold can be vacuumized via the injection line (45) through a laterally closable outlet (46), which is connected to a vacuum source (47); drying the mold (5) and the core material, the flow medium and the reinforcing material (21) contained therein, as well as the injection line (45) and optionally the feed unit (44a, 44b)/mixing unit (43), wherein optionally, the drying gas (33) can be introduced via the drying channel (32); beginning the vacuum infusion process with introducing the degassed components in the feed line (41, 42) from the storage tanks (48, 49) into the feed units (44a, 44b) of the reaction injection device (40), and obtaining the polyurethane resin from the components in the mixing unit (43), wherein the outlet (46) of the vacuum source (47) is closed before the polyurethane resin arrives; injecting the polyurethane resin into the mold (5) via the injection line (31), while vacuumizing the mold (5) via the drying channel (32) by the vacuum source (34), wherein the injection pressure at the injection port of the injection line (31) is measured and kept lower than the external atmospheric pressure.

[0070] The polyester peel ply which can be used in the present invention refers to a peel ply made from polyester fiber. Polyester fiber (PET fiber) or PET fiber for short, commonly referred to as “dacron”, is a general term for fibers made from polyesters obtained by polycondensation of various diols and aromatic dicarboxylic acids or esters thereof.

[0071] Preferably, the polyester peel ply is selected from the group consisting of plain weaves, twill weaves, satin weaves made of continuous fibers by weaving methods or fabrics made by knitting methods or fabrics directly made by stitching methods.

[0072] The flow medium that can be used in the present invention refers to a substance having a porous structure, which may be a material obtained by braiding, weaving, knitting, extruding or crocheting, a foam or a substance having a sieve or a network structure itself. Specifically, it includes but is not limited to woven flow meshs, pressed flow meshs, continuous fiber felts and hybrid flow meshs, for example, those obtained by mixing two or more of fiber fabrics such as woven flow meshs, pressed flow meshs, continuous fiber felts and chopped fiber felts. Those skilled in the art are familiar with materials that can be used as a flow medium, including but not limited to, polystyrene (PS), polyurethane (PUR), polyphenylene oxide (PPO), polypropylene, ABS, and glass fiber fabrics. Flow media are primarily used to aid in vacuumizing during the drying process and in guiding flow during the introduction of the polyurethane liquid material.

[0073] Molds that can be used in the present invention include, but are not limited to, molds of wind turbine blades and/or components thereof, molds of aircrafts and/or components thereof, molds of hulls and/or component thereof, molds of vehicle bodies and/or components thereof, and the like. In an example of the present invention, the mold is preferably a mold that can be used to produce wind turbine blades and/or components thereof in a polyurethane vacuum infusion process. The molds may have a heating function.

[0074] Optionally, the method for heating the peel ply, the fiber reinforcing material, the porous component and/or the core material of the present invention is one, two or more selected from the group consisting of mold heating, electric blanket heating, electric film heating, microwave heating, infrared heating and hot air heating. In the electric blanket heating and the electric film heating, the electric blanket and the electric film are placed under the mold or cover the film outside, and heat by supplying electric current. Other conventional heating methods in the art can all be used in the present invention.

[0075] The experimental results show that the method of the present invention provides a more efficient and energy-saving dehumidification method, thereby greatly improving the production efficiency for polyurethane composites, saving costs and being more environmentally friendly.

[0076] The polyisocyanate of the present invention may be an organic polyisocyanate which may be any aliphatic, cycloaliphatic or aromatic isocyanate known for preparing polyurethane composites. Examples thereof include, but are not limited to, toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polyphenylpolymethylene polyisocyanate (pMDI), 1,5-naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), methylcyclohexyl diisocyanate (TDI), 4,4′-dicyclohexylmethane diisocyanate, isophorone diisocyanate (IPDI), p-phenylene diisocyanate (PPDI), p-xylene diisocyanate (XDI), tetramethylxylene diisocyanate (TMXDI), and polymers or combinations thereof. The isocyanate useful in the present invention has a functionality of preferably 2.0 to 3.5, particularly preferably 2.1 to 2.9. The isocyanate has a viscosity of preferably 5 to 700 mPa s, particularly preferably 10 to 300 mPa s, measured at 25° C. according to DIN 53019-1-3.

[0077] When used in the present invention, the organic polyisocyanate includes isocyanate dimer, trimer, tetramer, pentamer or combinations thereof.

[0078] In a preferred example of the present invention, the isocyanate component A) is selected from the group consisting of diphenylmethane diisocyanate (MDI), polyphenylpolymethylene polyisocyanate (pMDI), and polymers, prepolymers or combinations thereof.

[0079] Blocked isocyanates can also be used as the isocyanate component A), which can be prepared by reacting an excess of organic polyisocyanate or a mixture thereof with a polyol compound. These compounds and their preparation methods are well known to those skilled in the art.

[0080] The polyurethane reaction system of the present invention comprises one or more organic polyols. The organic polyol is present in a content of 21 to 60 wt %, based on the total weight of the polyurethane reaction system as 100 wt %. The organic polyol may be an organic polyol commonly used in the art for preparing polyurethanes, including but not limited to polyether polyols, polyether carbonate polyols, polyester polyols, polycarbonate diols, polymer polyols, vegetable oil based polyol or a combination thereof.

[0081] The polyether polyol can be prepared by a known process, for example, by reacting an olefin oxide with a starter in the presence of a catalyst. The catalyst is preferably, but not limited to, a basic hydroxide, a basic alkoxide, antimony pentachloride, boron fluoride etherate, or a mixture thereof. The olefin oxide is preferably but not limited to tetrahydrofuran, ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, styrene oxide, or a mixture thereof, particularly preferably ethylene oxide and/or propylene oxide. The starter is preferably but not limited to a polyhydroxy compound or a polyamine compound. Said polyhydroxy compound is preferably but not limited to water, ethylene glycol, 1,2-propanediol, 1,3-propanediol, diethylene glycol, trimethylolpropane, glycerol, bisphenol A, bisphenol S or a mixture thereof. Said polyamine compound is preferably but not limited to ethylene diamine, propylene diamine, butanediamine, hexanediamine, diethylenetriamine, toluenediamine or a mixture thereof.

[0082] Methods for measuring the hydroxyl value are well known to those skilled in the art and are disclosed, for example, in Houben Weyl, Methoden der Organischen Chemie, vol. XIV/2 Makromolekulare Stoffe, p. 17, Georg Thieme Verlag; Stuttgart 1963. The entire contents of this document are incorporated herein by reference.

[0083] As used herein, unless otherwise indicated, the functionality and hydroxyl value of organic polyols refer to average functionality and average hydroxyl value.

[0084] Optionally, the polyurethane reaction system of the present invention further comprises one or more compounds b2) having the structure of formula (I)

##STR00003##

wherein R.sub.1 is selected from hydrogen, methyl or ethyl; R.sub.2 is selected from an alkylene group having 2 to 6 carbon atoms; and n is an integer selected from 1 to 6.

[0085] In a preferred example of the present invention, R2 is selected from the group consisting of ethylene, propylene, butylene, pentylene, 1-methyl-1,2-ethylene, 2-methyl-1,2-ethylene, 1-ethyl-1,2-ethylene, 2-ethyl-1,2-ethylene, 1-methyl-1,3-propylene, 2-methyl-1,3-propylene, 3-methyl-1,3-propylene, 1-ethyl-1,3-propylene, 2-ethyl-1,3-propylene, 3-ethyl-1,3-propylene, 1-methyl-1,4-butylene, 2-methyl-1,4-butylene, 3-methyl-1,4-butylene and 4-methyl-1,4-butylene, 2,2-di(4-phenylene)-propane, 1,4-xylylene, 1,3-xylylene, 1,2-xylylene.

[0086] In a preferred example of the present invention, b2) is selected from the group consisting of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate or a combination thereof.

[0087] The compound of the formula (I) can be prepared by a method generally used in the art, for example, by esterification reaction of (meth)acrylic anhydride or (meth)acrylic acid, (meth)acryloyl halide compound with HO—(R2O)n-H. The preparation method is well known to those skilled in the art, for example, in “Handbook of Polyurethane Raw Materials and Auxiliaries” (Yijun Liu, published on Apr. 1, 2005), Chapter 3; “Polyurethane Elastomer” (Houjun Liu, published in August 2012), Chapter 2. The entire contents of these documents are incorporated herein by reference.

[0088] The polyurethane reaction system of the present invention further comprises C) a free radical initiator. The radical initiator used in the present invention may be added to the polyol component or the isocyanate component or both components. Useful free radical initiators include, but are not limited to, peroxides, persulfides, peroxycarbonates, peroxyboric acid, azo compounds, or other suitable free radical initiators which can initiate the curing of double bond containing compounds, examples of which include tert-butyl peroxy isopropyl carbonate, tert-butyl peroxy-3,5,5-trimethylhexanoate, methyl ethyl ketone peroxide, and cumene hydroperoxide. The radical initiator is usually present in a content of 0.1 to 8 wt %, based on the total weight of the polyurethane reaction system of the present invention as 100 wt %. In addition, an accelerator such as a cobalt compound or an amine compound may also be present.

[0089] Optionally, the polyurethane reaction system may further comprise a catalyst for catalyzing the reaction of isocyanate groups (NCO) with hydroxyl groups (OH). Suitable polyurethane reaction catalysts are preferably, but not limited to, amine catalysts, organometallic catalysts, or mixtures thereof. The amine catalyst is preferably but not limited to triethylamine, tributylamine, triethylenediamine, N-ethylmorpholine, N,N,N′,N′-tetramethyl-ethylenediamine, pentamethyldiethylene-triamine, N-methylaniline, N,N-dimethylaniline, or a mixture thereof. The organometallic catalyst is preferably but not limited to an organotin compound such as tin (II) acetate, tin (II) octoate, tin ethylhexanoate, tin laurate, dibutyl tin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin maleate, dioctyltin diacetate, or a mixture thereof. The catalyst is used in an amount of 0.001 to 10 wt %, based on the total weight of the polyurethane reaction system of the present invention as 100 wt %.

[0090] In an example of the present invention, in the polyaddition reaction of isocyanate groups and hydroxyl groups, the isocyanate groups may be those contained in the organic polyisocyanate (component A) or may also be those contained in the reaction intermediate of the organic polyisocyanate (component A) with the organic polyol (component b1) or component b2)). The hydroxyl groups may be those contained in the organic polyol (component b1) or component b2)) or may also be those contained in the reaction intermediate of the organic polyisocyanate (component A) with the organic polyol (component b1) or component b2)).

[0091] In an example of the present invention, the radical polymerization reaction is a polyaddition reaction of ethylenic bonds, wherein the ethylenic bonds may be those contained in the component b2) or may also be those contained in the reaction intermediate of the component b2) with the organic polyisocyanate.

[0092] In the examples of the present invention, the polyurethane polyaddition reaction (i.e., the polyaddition reaction of isocyanate groups with hydroxyl groups) is present simultaneously with a radical polymerization reaction. It is well known to those skilled in the art that suitable reaction conditions can be selected such that the polyurethane polyaddition reaction and the radical polymerization reaction are carried out in succession. However, the polyurethane matrix thus obtained has a different structure from that of a polyurethane resin matrix obtained by simultaneous polyaddition reaction and radical polymerization reaction. Thus, the mechanical properties and processability of the prepared polyurethane composites are different.

[0093] Optionally, the above polyurethane reaction system may further comprise an auxiliary or additive, including but not limited to a filler, an internal demolding agent, a flame retardant, a smoke suppressant, a dye, a pigment, an antistatic agent, an antioxidant, a UV stabilization, a diluent, a defoaming agent, a coupling agent, a surface wetting agent, a leveling agent, a water scavenger, a catalyst, a molecular sieve, a thixotropic agent, a plasticizer, a foaming agent, a foam stabilizer, a foam homogenizing agent, an inhibitor against free radical reaction or a combination thereof. These components may optionally be included in the isocyanate component A) and/or the polyurethane reaction system B) of the present invention. These components may also be stored separately as a component D), which is mixed with the isocyanate component A) and/or the polyurethane reaction system B) of the present invention and then used for the preparation of polyurethane composites. The selection of the above-mentioned auxiliaries or additives and the above-mentioned content that is not described in detail can be found in CN104974502A, which is entirely incorporated herein by reference.

[0094] A second aspect of the present invention is to provide a polyurethane composite which is obtained by the method for preparing a polyurethane composite by a vacuum infusion process of the present invention.

[0095] A third aspect of the invention is to provide use of the polyurethane composite of the present invention in a wind turbine blade.

[0096] A fourth aspect of the invention is to provide a polyurethane product comprising a polyurethane composite obtained by the method for preparing a polyurethane composite by a vacuum infusion process.

[0097] Preferably, the polyurethane product is selected from the group consisting of a wind turbine blade, a radome, a single or sandwich continuous plate, preferably a spar cap, a web plate, a blade root and/or a blade housing of a wind turbine blade.

[0098] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as they are generally understood by those skilled in the art of the present invention. When definitions of the terms in this specification conflicts with the meaning generally understood by those skilled in the art of the present invention, the definitions described herein shall apply.

[0099] Unless stated otherwise, all values expressing quantities of ingredients, reaction conditions, and the like, as used herein, are understood to be modified by the term “about.”

[0100] As used herein, “and/or” refers to one or all of the elements mentioned.

[0101] “Including” and “comprising”, as used herein, cover the cases where only the mentioned elements are present, as well as the cases where there are other unmentioned elements in addition to the mentioned elements.

[0102] Unless indicated otherwise, all percentages herein are percentages by weight.

[0103] The invention is now described using the examples by way of illustration without limitation.

EXAMPLES

[0104] Description of tested performance parameters in the examples of the present application:

[0105] Functionality refers to a value determined according to the formula in the industry: functionality=hydroxyl value*molecular weight/56100; wherein the molecular weight is determined by GPC high performance liquid chromatography;

[0106] Isocyanate index refers to a value determined by the following formula:

[00001]$\mathrm{Isocyanate}\mathrm{index}\left(\%\right)=\frac{\mathrm{Moles}\mathrm{if}\mathrm{isocyanate}\mathrm{groups}\left(\mathrm{NCO}\mathrm{groups}\right)\mathrm{in}\mathrm{component}A}{\begin{array}{c}\mathrm{Moles}\mathrm{of}\mathrm{groups}\mathrm{reactive}\\ \mathrm{toward}\mathrm{isocyanate}\mathrm{groups}\mathrm{in}\mathrm{component}B\end{array}}\times 100\%$

[0107] NCO content refers to the content of NCO groups in the system, measured according to GB/T 12009.4-2016.

[0108] Description of Raw Materials:

TABLE-US-00001 TABLE 1 Specifications and sources of raw materials Name of raw materials Specification/type Suppliers Polyol Baydur 78BD085 Covestro Polymers (China) Co., Ltd. Isocyanate Desmodur 44CP20 Covestro Polymers (China) Co., Ltd. Epoxy resin Hexion RIM 035C Momentive Performance Materials Inc (China) Epoxy curing agent Hexio RIMH037 Momentive Performance Materials Inc (China) Biaxial glass fiber fabric EKT811 (+45°/−45°) Chongqing Polycomp (fiber reinforced Specification: 808 g/m.sup.2 International Corp. material) Flow runner 1 Material: PE Shanghai Leadgo-tech Co., Ltd Specification: Φ18 mm Flow runner 2 Material: PE Shanghai Leadgo-tech Co., Ltd Specification: Φ8 mm Flow mesh 1 Material: PE Shanghai Leadgo-tech Co., Ltd Specification: 200 g/m.sup.2 Flow mesh 2 Material: PE Shanghai Leadgo-tech Co., Ltd Specification: 100 g/m.sup.2 PVC foam core 1 Specification: 60 kg/m.sup.3 3A Composites (China) Ltd Groove spacing 20 mm * 20 mm PVC foam core 2 Specification: 60 kg/m.sup.3 3A Composites (China) Ltd Groove spacing 30 mm * 30 mm Polyester peel ply Gram weight: 95 g/m.sup.2 Shanghai Leadgo-tech Co., Ltd Film/vacuum bag film Thickness: 50 um Shanghai Leadgo-tech Co., Ltd adhesive strip Type: WD209 Shanghai KangdDa New Materials Co., Ltd Warming blanket Specification: width of 1 m, Related market length of 2 m, thickness of 30 mm

[0109] Description of Test Methods:

[0110] Temperature test: an infrared thermometer is used to monitor the surface temperature;

[0111] Gram weight: the weight per unit area, specifically the weight of a fiber fabric, a flow mesh or a peel ply divided by the area thereof.

EXAMPLES

Example 1 and Comparative Example 1

[0112] Two layers of biaxial glass fiber fabric having length×width of 800*700 mm were laid on the mold. A PVC foam core material 2 having length×width of 600*500 mm (in the Comparative Example: PVC foam core material 1) was placed on the glass fiber fabric, wherein the grooved side pointed upward. The core material was placed on the glass fiber fabric, wherein the grooved side pointed upward.

[0113] Two layers of biaxial glass fiber fabric having length×width of 800*700 mm were laid on the core material. A peel ply with the same size was laid on and covered the entire glass fiber fabric.

[0114] A flow mesh 2 having length×width of 700*450 mm (in the Comparative Example 1: flow mesh 1) was placed on the peel ply. Three edges of the flow mesh are 3 to 5 cm away from the edges of the foam core material. The injection edge of the flow mesh is flush with the edge of the glass fiber fabric.

[0115] A flow runner 2 having a length of 300 mm (in Comparative Example 1: flow runner 1) was cut out and placed on the injection edge of the flow mesh. Two loops of adhesive sealing strips were stuck around the layers laid in the mold. Then, said layers were sealed with two layers of vacuum bag.

[0116] After dehumidification by heating under vacuum, the resin (Example 1: infusion of a polyurethane resin/polyurethane composition, Comparative Example 1: infusion of an epoxy resin) was infused, and the infusion time and the amount of the used resin were recorded.

[0117] The product was demolded after curing by heating. The amount of resin in the tubes, the weight of the flow mesh (including the resin) and the weight of the final composite were recorded, as shown in Table 2.

TABLE-US-00002 TABLE 2 Comparison of absorption amounts of Example 1 and Comparative Example 1 Comparative Example 1 (epoxy resin) Example 1 (polyurethane resin) Material Resin Resin category specification size weight absorption specification size weight absorption Remarks Flow mesh 200 g/m.sup.2 44.5 * 54 cm 270.5 g 910.8 g/m.sup.2 100 g/m.sup.2 56.5 * 46 cm   152 g 484.8 g/m.sup.2 46% reduction Flow runner Φ18 mm 300 mm 150.5 g 501.6 g/m Φ8 mm 300 mm 38 94.2 g/m 81% reduction PVC foam groove 42.5 * 36 cm 415.5 g 211.6 g/cm.sup.3 groove 40.5 * 38 cm 328.7 g 153.6 g/cm.sup.3 27% core spacing spacing reduction 20*20 mm 30*30 mm Infusion time 5 min 20 s Infusion time 4 min 30 s Infusion effect good Infusion effect good

[0118] It can be seen from the detection results of the above Example and Comparative Example that the method for preparing a polyurethane composite using appropriate core materials, flow meshes and flow runners of the present invention has good infusion effect. A polyurethane composite with superior quality was obtained. At the same time, the amount of waste resin was greatly reduced, thereby saving raw materials, saving energy and cost, and reducing the weight of the composite. Moreover, as compared with Comparative Example 1, the infusion time was also shortened and the production efficiency was improved in Example 1.

[0119] It should be noted that in actual production, the preparation of large parts requires thicker flow runners than those for the laboratory. In the prior art, the diameter of the flow runner for epoxy resins is usually 25 mm or more. By the method of the present invention, a flow runner having a diameter of 20 mm, 18 mm or less can be used. That is, the diameter of the flow runner can be reduced by 20%, preferably by about 28%.

[0120] While the invention has been described in detail as above for the purposes of the present invention, it is understood that the detailed description is only exemplary. In addition to the contents defined by the claims, various changes can be made by those skilled in the art without departing from the spirit and scope of the invention.