Technical Field

The present invention belongs to the field of polyurethane composite. Specifically, the present invention relates to a polyurethane prepreg, and a preparation method and applications thereof.

Background Art

In the industry, as laws and regulations are perfected constantly, VOC (Volatile Organic Compounds) issue has received widespread attention. Consumers hope to use safe and environmentally friendly products without VOC. Moreover, as compared with traditional composite resin, polyurethane resin is endowed with superior fatigue resistance and chemical resistance, a better impact toughness, and lower shrinkage, while containing no volatile organic compounds such as styrene. Therefore, nowadays polyurethane resin is increasingly applied to the field of composite materials.

In addition to various properties that are concerned, the process operability of a material is equally important in the field of composite materials. Generally, it is desirable that not only the material be not susceptible to the ambient humidity and temperature, easy to handle, can be stored for long period, and capable of being stored at room temperature for a long time, but also that the processing characteristics of the material endow a certain design freedom and flexibility to the subsequent processors.

The unsaturated resin or vinyl ester resin employed in the current compression molding may allow the molding material to be stored at 25 ^° C for at least 3 months due to the selection of a curing agent and addition of a polymerization inhibitor, after which period the molding material will become stiff and be difficult to mold. However, during preparation of polyurethane resin, due to high activity of isocyanate component, it will react with polyol immediately upon mixing together uniformly and cure in seconds to hours. This will make the polyurethane molding material unable to flow or stiff, difficult to cut, and also not easily placed into a mold with a certain shape to be pressed into articles with relatively complicated shapes, thus no qualified products can be obtained. Therefore, the polyurethane molding material prepared in accordance with the current method may have a typical storage period of no more than 24 hours, limiting the application of the polyurethane composites in compression molding greatly.

Therefore, there is a need for developing a new prepreg used to prepare polyurethane composites, which is not susceptible to the ambient humidity and temperature, easy to handle, can be stored for long period, and also endows certain design freedom and flexibility to the subsequent processors. Summary of the Invention

The technical problem to be solved by the present invention is to provide a prepreg used to prepare polyurethane composites, which is not susceptible to the ambient humidity and temperature, easy to handle, can be stored for long period, and also endows certain design freedom and flexibility to subsequent processors.

The above technical problem is solved by the following technical solutions:

According to the first aspect of the present invention, a polyurethane prepreg is provided, comprising:

A) a prepolymer produced with the following components Al), A2), and A3) through an addition reaction between hydroxyl groups and isocyanate groups in the absence of long fibers:

Al) an isocyanate component, the isocyanate component comprising one or more organic polyisocyanate(s);

A2) one or more organic polyol(s), the organic polyol(s) having a hydroxyl value of 10-400 mg KOH/g, a functionality of 1-4, and the content thereof being 10-50 wt. , based on the weight of the prepolymer;

A3) one or more compound(s) of formula (I), the content of the compound(s) of formula (I) being 10-50 wt.%, based on the weight of the prepolymer:

I

wherein, Ri is selected from hydrogen, methyl, or ethyl; R ₂ is selected from alkylenes having 2-6 carbon atoms, 2,2-di(4-phenylene)-propane, 1,4- di(methylene)benzene, l,3-di(methylene)benzene, l,2-di(methylene)benzene; and n is an integer selected from 1-6;

B) a reactive diluent, in an amount of 0-50 parts by weight, based on 100 parts by weight of the prepolymer;

C) a free radical reaction initiator, in an amount of 0-6 parts by weight, based on 100 parts by weight of the prepolymer;

D) a reinforcing material, in an amount of 0-85 parts by weight, based on 100 parts by weight of the prepolymer; and

E) a solvent, in an amount of 0-65 parts by weight, based on 100 parts by weight of the prepolymer.

According to the second aspect of the present invention, a method for preparing the above prepreg is provided, comprising the following steps: allowing the components Al), A2), and A3) to mix under reaction conditions in the absence of long fibers, optionally in the presence of B) the reactive diluent, C) the free radical reaction initiator, D) the reinforcing material, and/or E) the solvent.

According to the third aspect of the present invention, providing a method for preparing a polyure thane composite, comprising the following steps:

(i) reducing the viscosity of the polyurethane prepreg;

(ii) impregnating long fibers with the polyurethane prepreg; and

(iii) curing the polyurethane prepreg in the presence of the long fibers to produce the polyurethane composite, wherein the polyurethane prepreg is cured through free radical polymerization reaction of the active ethylenic bonds therein.

According to the fourth aspect of the present invention, a polyurethane composite prepared by the method of the present invention is provided.

After the prepreg of the present invention is heated to 50-100°C or combined with a solvent or diluent (in particular a reactive diluent), its viscosity will be reduced, thus it can flow and can be used to impregnate long fibers (such as glass fiber fabrics, knitting mats, etc.) as required. After the impregnation is completed, it is cooled to room temperature to be used or it can be placed into a mold with a certain shape, heated to 150°C, hot-pressed to cure into a final article.

The prepreg of the present invention is not susceptible to the ambient humidity and temperature during post-treatment and easy to handle. It is also convenient for subsequent processors to operate since it is not necessarily limited by weather conditions and requires no extra dehumidification renovation to the plant. As compared with epoxy resin, the prepreg of the present invention can be stored for a long period and may be stored at room temperature for a long time, for example, for 6 months. During the storage period, the polyurethane prepreg can remain in a semi-solid state without substantial changes in physical and chemical properties and will not become stiff. Thus, it can be used to prepare polyurethane composites with superior properties. Moreover, due to its unique processing characteristics, the subsequent processors may alter the types and amounts of the reinforcing materials as required, thus high design flexibility can be achieved. „

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Brief Description of the Figures

Fig. 1 is the image of the glass fiber fabric after impregnation with the polyurethane prepreg according to Comparative Example 6.

Fig. 2 is the image of the glass fiber fabric after impregnation with the polyurethane prepreg according to Example 5.

Detailed Description of the Invention

The specific embodiments for carrying out the present invention are described hereinafter. According to the first aspect of the present invention, a polyurethane prepreg is provided, comprising:

A) a prepolymer produced with the following components Al), A2), and A3) through an addition reaction between hydroxyl groups and isocyanate groups in the absence of long fibers:

Al) an isocyanate component, the isocyanate component comprising one or more organic polyisocyanate(s);

A2) one or more organic polyol(s), the organic polyol(s) having a hydroxyl value of 10-400 mg KOH/g, a functionality of 1-4, and the content thereof being 10-50 wt. , based on the weight of the prepolymer;

A3) one or more compound(s) of formula (I), the content of the compound(s) of formula (I) being 10-50 wt.%, based on the weight of the prepolymer:

I

wherein, Ri is selected from hydrogen, methyl, or ethyl; R ₂ is selected from alkylenes having 2-6 carbon atoms, 2,2-di(4-phenylene)-propane, 1,4- di(methylene)benzene, l,3-di(methylene)benzene, l,2-di(methylene)benzene; and n is an integer selected from 1-6;

B) a reactive diluent, in an amount of 0-50 parts by weight, based on 100 parts by weight of the prepolymer;

C) a free radical reaction initiator, in an amount of 0-6 parts by weight, based on 100 parts by weight of the prepolymer;

D) a reinforcing material, in an amount of 0-85 parts by weight, based on 100 parts by weight of the prepolymer; and

E) a solvent, in an amount of 0-65 parts by weight, based on 100 parts by weight of the prepolymer. The organic polyisocyanate in the Al) isocyanate component comprises an organic diisocyanate, which may be any aliphatic, cycloaliphatic, or aromatic isocyanate known to be used to prepare polyurethane.

As examples of the organic diisocyanate, mentions may be made of: 2,2'-,2,4- and 4,4'- diphenyl methane diisocyanate; diphenyl methane diisocyanate homologs with three or more rings

(polymetric MDI); hydrogenated diphenyl methane diisocyanate (HMDI), isophorone diisocyanate (IPDI), the oligomers of isophorone diisocyanate (IPDI); 2,4-toluene diisocyanate (2,4-TDI), 2,6- toluene diisocyanate; tetramethylene diisocyanate, the oligomers of tetramethylene diisocyanate; hexamethylene diisocyanate (HDI), the oligomers of hexamethylene diisocyanate (HDI); naphthalene diisocyanate (NDI); or a compound resulted from the aforementioned organic polyisocyanates with a compound with at least two isocyanate reactive groups or mixtures thereof.

In a preferred embodiment of the present invention, the organic polyisocyanate comprises an isocyanate based on diphenyl methane diisocyanate, especially that comprising polymetric MDI.

The functionality of the organic polyisocyanate is preferably of 1.9-3.5, particularly preferably of 2.0-2.8. The viscosity of the organic polyisocyanate is preferably of 5-700 mPa- s, particularly preferably of 10-300 mPa- s, as measured at 25°C in accordance with DIN 53019-1-3.

The organic polyisocyanate may also be used in the form of a polyisocyanate prepolymer. The polyisocyanate prepolymer may be obtained by the reaction between one or more of the aforementioned organic polyisocyanates in excessive amounts and a compound with at least two isocyanate reactive groups at a temperature of 30-100°C, for example, and preferably of about 80°C.

The compounds with at least two isocyanate reactive groups are well known to those skilled in the art, which, for example, are described in Kunststoff-Handbuch, Chapter 3.1 ("Kunststoffhandbuch, 7, Polyurethanes", Carl Hanser-Verlag, 3 ^rd ed., 1993), which is incorporated by reference herein in its entirety.

The NCO content of the polyisocyanate prepolymer of the present invention is preferably of 12-33wt. , particularly preferably of 20-32wt. .

The organic polyol in the A2) one or more organic polyol(s) has preferably a molecular weight of 280-10000, and the content thereof is 20-50 wt. , preferably of 30-40wt. , based on the weight of the prepolymer.

The molecular weight of the organic polyol described herein means number-average molecular weight, which is generally calculated in accordance with the type and amount of raw material used to prepare the organic polyol.

The organic polyol has a hydroxyl value of 10-400 mg KOH/g, preferably of 28-350 mg KOH/g; a functionality of 1-4, more preferably of 1.5-3, and most preferably of 1.8-2.5. The organic polyol may be the one commonly used to prepare polyurethane in the art, for example, selected from one or more of: polyether polyols, polyether carbonate polyols, polyester polyols, polycarbonate diols, and vegetable oil polyols.

The polyether polyol may be prepared by a known process. For example, it may be prepared by reacting an olefin oxide with a starting agent in the presence of a catalyst. The catalyst is preferably, but not limited to, an alkaline hydroxide, an alkaline alkoxide, antimony pentachloride, boron trifluoride 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 starting agent is preferably, but not limited to, a polyhydric compound or a compound with multiple amino groups. The polyhydric 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. The compound with multiple amino groups is preferably, but not limited to, ethanediamine, propanediamine, butanediamine, hexanediamine, diethylenetriamine, toluenediamine, or a mixture thereof. The polyether polyol may be an unsaturated polyether polyol.

The polyether carbonate polyol may be prepared by addition of carbon dioxide with alkylene oxide on a starting agent comprising reactive hydrogen in the presence of double metal cyanide as a catalyst.

The polyester polyol is prepared by reacting a dicarboxylic acid or a dicarboxylic acid anhydride with a polyol. The dicarboxylic acid is preferably, but not limited to, an aliphatic carboxylic acid containing 2-12 carbon atoms, which is preferably, but not limited to, succinic acid, malonic acid, glutaric acid, adipic acid, octanedioic acid, azelaic acid, sebacic acid, dodecanoic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, or a mixture thereof. The dicarboxylic acid anhydride is preferably, but not limited to, phthalic anhydride, tetrachlorophthalic anhydride, maleic anhydride, or a mixture thereof. The polyol which reacts with the dicarboxylic acid or dicarboxylic acid anhydride is preferably, but not limited to, ethylene glycol, diethylene glycol, 1 ,2-propanediol, 1,3-propanediol, dipropylene glycol, 1,3- methylpropanediol, 1 ,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,10- decanediol, glycerol, trimethylolpropane, or a mixture thereof. The polyester polyol further includes a polyester polyol prepared from a lactone. The polyester polyol prepared from a lactone is preferably, but not limited to, £-caprolactone.

The polycarbonate diol may be prepared by reacting a diol with a dihydrocarbyl carbonate or a diaryl carbonate or phosgene. The diol is preferably, but not limited to, 1 ,2-propanediol, 1,3- propanediol, 1 ,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, trioxane diol, or a mixture thereof. The dihydrocarbyl carbonate or diaryl carbonate is preferably, but not limited to, diphenyl carbonate. When used in the present invention, the polyol based on vegetable oil comprises vegetable oils, vegetable oil polyols, or modified products thereof.

Vegetable oil is a compound prepared from an unsaturated fatty acid and glycerol or an oil extracted from fruits, seeds, or embryos of a plant, which is preferably, but not limited to, peanut oil, soybean oil, linseed oil, castor oil, rapeseed oil, and palm oil. The vegetable oil polyol is a polyol originated with one or more vegetable oils. A starting agent used to synthesize a vegetable oil polyol includes, but not limited to, soybean oil, palm oil, peanut oil, low erucic acid rapesed oil, and castor oil. Hydroxyl groups may be introduced into a starting agent of the vegetable oil polyol via a process such as hydrolysis, oxidation, or transesterification and then the corresponding vegetable oil polyol may be prepared by a process for preparing an organic polyol well known to those skilled in the art.

The method for measuring hydroxyl value is well known to those skilled in the art, which is, for example, disclosed in Houben Weyl, Methoden der Organischen Chemie, vol. XIV/2 Makromolekulare Stoffe, p.17, Georg Thieme Verlag; Stuttgart 1963, which is incorporated by reference herein in its entirety.

When used in the present invention, unless indicated otherwise, the functionality and hydroxyl value of an organic polyol refer to the average functionality and average hydroxyl value, respectively.

In some preferred embodiments, the organic polyol is polyether polyol.

In a preferred embodiment, in the compound of formula(I), R2 is selected from ethylene, propylene, butylene, pentylene, 1 -methyl- 1 ,2-ethylene, 2-methyl-l,2-ethylene, l-ethyl-l,2-ethylene, 2-ethyl-l,2-ethylene, l-methyl-l,3-propylene, 2-methyl- 1,3 -propylene, 3-methyl-l,3-propylene, 1- ethyl- 1,3 -propylene, 2-ethyl- 1,3 -propylene, 3-ethyl-l,3-propylene, 1 -methyl- 1,4-butylene, 2- methyl-l,4-butylene, 3-methyl- 1,4-butylene and 4-methyl- 1,4-butylene, 2,2-di(4-phenylene)- propane, 1 ,4-dimethylene benzene, 1,3-dimethylene benzene, or 1 ,2-dimethylene benzene.

In a further preferred embodiment, the compound of formula (I) is selected from one or more of: hydroxy ethyl methylacrylate, hydroxypropyl methylacrylate, hydroxybutyl methylacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxybutyl acrylate.

The compound of formula (I) may be prepared by a method commonly used in the art, for example, by esterification reaction between (meth)acrylic anhydride, (meth)acrylic acid, or (meth)acryloyl halide and HO-(R20) _n -H. This method is well known to those skilled in the art and is, for example, described in Handbook of Raw Materials and Addictives for Polyur ethanes, Chapter 3, Liu Yijun, published on April 1, 2005, and Handbook of Polyur ethane Elastomers, Chapter 2, Liu Houjun, published in August, 2012, which are incorporated by reference herein in their entirety.

Preferably, the weight ratio of the component A2) to the component A3) is from 30:70 to

70:30. - o -

The reactive diluent is the one comprising a group that may participate in the curing reaction and is classified into mono-functional active diluent and multi-functional active diluent. A group that participates in the curing reaction is, for example, an alkenyl group. That is to say, the reactive diluent described in the present application is an active dilute comprising ethylenic bonds. The reactive diluent mainly functions to reduce viscosity and/or participate in a subsequent curing reaction.

The mono-functional active diluent has only one group that may participate in the curing reaction in each molecule, such as styrene, β-hydroxyethyl acrylate (HPA), or the compound of formula (I) as defined above.

The multi-functional active diluent refers to the one that has two or more groups that may participate in the curing reaction in each molecule, such as 1,6-hexanediol di(meth)acrylate (HDDA).

With a monomer containing more functional groups, in addition to an increased reactivity, the cured film will be imparted with a cross-linked structure, which is due to the fact that a mono-functional monomer will only result in a linear polymer after polymerization while a multi-functional monomer may result in a highly cross-linked network.

The C) free radical reaction initiator includes, but not limited to, peroxides, persulfides, peroxycarbonates, peroxyboric acids, azo compounds, or other suitable free radical initiators that may initiate curing of a compound comprising ethylenic bonds. Representative examples include, but not limited to, i-butyl peroxy isopropyl carbonate, benzoyl peroxide, i-butyl peroxy-3,5,5-trimethyl hexanoate, methyl ethyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide, and the like.

When the amount of the free radical reaction initiator added is zero, thermal initiation may be performed.

Moreover, there may be optionally one or more promoters in the system, such as cobalt compounds or amine compounds, in an amount of 0-5 parts by weight, based on 100 parts by weight of the prepolymer.

The reinforcing material does not include the long fibers used to prepare the fiber- reinforced polyurethane composite. The reinforcing material is selected from one or more of fillers, carbon nanotubes, short fibers, and fiber powder.

The filler is selected from one or more of: aluminium hydroxide powder, bentonite, flyash, wollastonite, perlite powder, floating bead, calcium carbonate, talc powder, mica powder, porcelain clay, fumed silica, expendable microspheres, diatomaceous earth, pozzuolana, barium sulfate, calcium sulfate, glass microspheres, mountain flour, wood flour, wood chips, bamboo flour, bamboo chips, rice grains, chopped crop straw, chopped broomcorn straw, graphite powder, metal powder, recycled powder of thermosetting composites, and plastic particles or powder. The glass microspheres may be solid or hollow.

The solvent may be commonly used organic solvent, such as acetone, butanone, and the like. Those skilled in the art may choose the amount of a solvent such that the system comprising the polyurethane prepreg of the present invention and the solvent has a viscosity suitable for impregnating long fibers (such as glass fiber fabrics) to prepare a prepreg sheet.

The prepreg according to the present invention may further comprise one or more addictives selected from the group consisting of: internal release agents, flame retardants, smoke suppressants, dyes, pigments, antistatic agents, antioxidants, UV stabilizers, diluents, antifoaming agents, coupling agents, surface wetting agents, levelling agent, moisture scavengers, catalysts, molecular sieves, thixotropic agents, plasticizers, foaming agents, foam stabilizers, foam homogenizers, and free radical reaction suppressants.

Those skilled in the art may choose the amounts of the addictives as required, e.g., 0-25 parts by weight, based on 100 parts by weight of the prepolymer.

The internal release agent that may be used in the present invention includes any conventional release agent used to produce polyurethane, examples of which include long-chain carboxylic acids, especially fatty acids such as stearic acid, amides of long-chain carboxylic acids such as stearamide, esters of fatty acids, metal salts of long-chain carboxylic acids such as zinc stearate, or polysiloxanes.

The flame retardant that may be used in the present invention includes triaryl phosphates, trialkyl phosphates, triaryl phosphates, or trialkyl phosphates containing halogen, melamine, melamine resin, halogenated paraffin, red phosphorus, or mixtures thereof.

The moisture scavenger that may be used in the present invention may be molecular sieves. The antifoaming agent may be, for example, polydimethylsiloxane. The coupling agent may be, for example, mono-ethylene oxide, organoamine functionalized trialkoxysilanes, or mixtures thereof. The coupling agent is particularly preferably used to increase the binding strength between a resin matrix and a fiber reinforcing material. Fine particle fillers, such as clay and fumed silica, are commonly used as the thixotropic agents.

The free radical reaction suppressants that may be used in the present invention include polymerization inhibitors, polymerization retarders, and the like, such as some phenol, quinine compounds or hindered amine compounds, examples of which include methylhydroquinone, p- methoxyphenol, benzoquinone, polymethyl piperidine derivatives, low valence copper ions, etc.

The polyurethane prepreg is in a shape of a sheet, a strip, a ribbon, or a ring.

According to the second aspect of the present invention, a method for preparing the above polyurethane prepreg is provided, comprising the following steps:

allowing the components Al), A2), and A3) to mix under reaction conditions in the absence of long fibers, optionally in the presence of B) the reactive diluent, C) the free radical reaction initiator, D) the reinforcing material, and/or E) the solvent.

The reaction conditions of an isocyanate group and an isocyanate reactive group (such as a hydroxyl group) are well known to those skilled in the art. For example, the reactants may be allowed to react under an elevated temperature or a lower temperature (such as 10°C). In a preferred embodiment of the present invention, the reaction temperature is preferably no higher than 80°C, and more preferably no higher than 70°C, such as 50-60°C, whereby the reaction between the isocyanate group and the isocyanate reactive group (such as a hydroxyl group) may occur rapidly, while the free radical polymerization reaction via ethylenic bonds will not occur rapidly. Therefore, the above reaction conditions include a temperature of 10°C to 80°C.

A catalyst may be used to promote the reaction between the isocyanate group and the isocyanate reactive group, which may be those commonly used in the art to catalyze the reaction between an isocyanate group (NCO) and an isocyanate reactive group (such as a hydroxyl group). A catalyst suitable for a polyurethane reaction is preferably, but not limited to, an amine catalyst, an organometallic catalyst, or a mixture thereof. The amine catalyst is preferably, but not limited to, triethylamine, tributylamine, triethylenediamine, N-ethylmorpholine, Ν,Ν,Ν',Ν'-tetramethyl- ethylenediamine, pentamethyldiethylene-triamine, N,N-methylaniline, Ν,Ν-dimethylaniline, or a mixture thereof. The organometallic catalyst is preferably, but not limited to, an organotin compound, such as tin (II) acetate, tin (II) octanoate, tin ethylhexanoate, tin laurate, dibutyl tin oxide, dibutyl tin dichloride, dibutyl tin diacetate, dibutyl tin maleate, dioctyl tin diacetate, or a mixture thereof. The catalyst is included in an amount of 0.001-10 wt. , based on the total weight of the isocyanate reactive component (which refers to the organic polyol and the compound of formula (I) in the present invention) being 100 wt.%.

The reaction between the isocyanate group and the isocyanate reactive group (such as a hydroxyl group) may be carried out for several hours, e.g., 4 to 8 hours.

It is to be understood that during the preparation of the polyurethane prepreg of the present invention, a free radical polymerization reaction may also occur in minimum amount, as long as it will not render the obtained prepreg too rigid to be used for the subsequent processing.

The above Al) isocyanate component, A2) one or more organic polyol(s), and A3) one or more compound(s) of formula (I) are subjected to an addition reaction via a hydroxyl group and an isocyanate group in the absence of long fibers, forming a gel gradually. If the reaction is carried out at a temperature higher than room temperature, the temperature will be lowered to room temperature after gel formation. The obtained polyurethane prepreg is then stored to be used for the subsequent processing.

In the present invention, the polyurethane prepreg may be manufactured into a desired shape by a known plastic processing method in the art, e.g., casting, pressing, rolling, or squeezing, and then cured in the presence of long fibers to prepare the polyurethane composite.

It has surprisingly been found by the inventors of the present application that there are no visual air bubbles in the composites prepared with the polyurethane prepreg of the present invention.

It is known to those skilled in the art that if there are air bubbles in the composite and the article made therefrom, every air bubble will be considered as a defect which will tend to result in ₁ ^ internal cracking within the composite and the article made therefrom whenever under stress, reducing service life and even causing accidents. If there are air bubbles in the composite and the article made therefrom, the overall mechanical properties will be impaired, too.

In some preferred embodiments of the present invention, the polyurethane prepreg may be in a shape of a sheet, a strip, a ribbon, or a ring. Since the hardness of the polyurethane prepreg is not very high, it will be easy to cut the polyurethane prepreg into a desired shape.

When the components used to prepare the polyurethane prepreg are mixed, the polyurethane addition polymerization reaction between the isocyanate group and the isocyanate reactive group (such as a hydroxyl group) therein begins to occur, which may be partially or fully completed, preferably mostly or fully completed.

Under ambient conditions, the active ethylenic bonds within the polyurethane prepreg remain stable and no substantial free radical polymerization reaction will occur. Only under certain conditions (such as heating) will the substantial amount of active ethylenic bonds within the polyurethane prepreg be subjected to the free radical polymerization reaction, which allows the polyurethane prepreg to be cross-linked and cured in the presence of long fibers, and thus, results in the polyurethane composite being obtained. Such a stability of the ethylenic bonds ensures a long- term stability of the prepreg and is advantageous for the storage and transportation of the polyurethane prepreg.

In some embodiments of the present invention, the prepreg is a mixture having a viscosity of at least 30000 mPa-s (25°C) or a semi-solid state.

In some other preferred embodiments of the present invention, the prepreg may be stored at a temperature of 5-45°C for over 6 months without substantial changes in physical and chemical properties, while it still can be used to prepare polyurethane composites with superior properties.

According to the third aspect of the present invention, a method for preparing a polyurethane composite is provided, comprising the following steps:

(i) reducing the viscosity of the polyurethane prepreg;

(ii) impregnating long fibers with the polyurethane prepreg; and

(iii) curing the polyurethane prepreg in the presence of the long fibers to produce the polyurethane composite, wherein the polyurethane prepreg is cured through a free radical polymerization reaction of the active ethylenic bonds therein.

Generally, the viscosity of the polyurethane prepreg is reduced by heating to melt or adding with solvents or dilutes. The viscosity of the polyurethane prepreg is typically reduced to a degree suitable for impregnating long fibers, e.g., 600mPa- s.

In the present invention, the free radical polymerization reaction is the addition polymerization reaction of ethylenic bonds, which may be those in the compound of formula (I) or may be those in the intermediate product of the reaction between the compound of formula (I) and the organic polyisocyanate, excluding those carried by aromatic rings.

The curing step (iii) may be carried out at a temperature of 80-300°C, preferably of 100- 250°C, for example, 150°C and under a pressure of 0.1-50 Mpa, for example, lOMpa. Generally, the curing step is carried out in a specific mold according to the shape requirement of the product.

The long fibers may be loose fibers, fiber bundles, fiber webs, or fiber fabrics formed through bonding or weaving.

In some embodiments of the present invention, the long fibers may be selected from one or more of: glass fibers, carbon fibers, polyester fibers, natural fibers, aramid fibers, nylon fibers, basalt fibers, boron fibers, silicon carbide fibers, asbestos fibers, whiskers, and metal fibers.

The long fibers are in an amount of 5-95 wt. , preferably of 30-85 wt. , based on the total weight of the polyurethane composite.

According to the fourth aspect of the present invention, a polyurethane composite prepared by the method of the present invention is provided. The polyurethane composite is selected from: a motor vehicle fender, a motor vehicle lampshade, a motor vehicle dashboard, a motor vehicle hard roof, a motor vehicle door, a motor vehicle frame, a motor vehicle body shell, a motor vehicle radiator grid plate, a motor vehicle headlamp reflector, a motor vehicle front support, a motor vehicle floor, a motor vehicle seat frame, a motor vehicle air deflector, a motor vehicle radiator cover or bracket, a motor vehicle body guard, a motor vehicle crossbeam, a motor vehicle spoiler, a motor vehicle sun shade, a motor vehicle front and rear bumper, a motor vehicle hood, a motor vehicle decorative panel, a motor vehicle trunk rear liftgate, a motor vehicle interior decoration, an engine valve cover, an engine air inlet manifold, a bottom shell of a fuel tank, a motor vehicle air filter cover, a motor vehicle air director, a motor vehicle gear housing cover, an air intake manifold guard, a motor vehicle fan blade, a motor vehicle fan, a motor vehicle air-guiding ring, a motor vehicle heater cover plate, motor vehicle water tank parts, a motor vehicle water outlet shell, a motor vehicle water turbine, an engine acoustic insulation plate, a motor vehicle door handle, a water tank, a bathtub, an integrated bathroom, a floor, a waterproof disk, a pedestal pan, a water purifying tank, an electric appliance housing, an insulator, a printing circuit board, an electric appliance and cable distribution channel, a telephone booth frame, a highway anti-glare panel and stand column with no anti-collision purpose, a protective barrier, a cable holder, an optical cable cabinet body, a multimedia cabinet body, a distribution box, a cable branch box, a traffic signal control box, a water meter box, a metering instrument shell and its internal parts, a communication device shell and its internal parts, an antenna housing, a railway vehicle window frame, and train toilet components.

Unless defined otherwise, all the technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention pertains. In the case that the definition of a term in the specification conflicts with the one commonly understood by those skilled in the art to which the present invention pertains, the definition described herein controls.

The use of "and/or" herein refers to one or all of the elements mentioned.

The use of "include(s)" or "including" and "comprise(s)" or "comprising" herein covers both cases with only the elements mentioned and cases with other elements not mentioned in addition to those mentioned.

The present invention will be illustrated through the following examples. However, it is to be understood that the scope of the invention is not limited to these examples.

_Λ

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Examples

The raw materials used in the examples are listed as follows:

HPMA: hydroxypropyl methacrylate (HPMA), purchased from Shanghai Pharmaceuticals Holding Co., Ltd.

Polyether 1: polyether polyol 1, prepared by using propylene glycol as the starting agent and propylene oxide as the main polymerization component, hydroxyl value: 280, functionality: 2, viscosity: 70 mP- s@25°C, molecular weight: 400.

Polyether 2: polyether polyol 2, prepared by using propylene glycol as the starting agent and propylene oxide as the main polymerization component, hydroxyl value: 112, functionality: 2, viscosity: 150 mP- s@25°C, molecular weight: 1000.

Polyether 3: polyether polyol 3, prepared by using glycerol as the starting agent and propylene oxide as the main polymerization component, hydroxyl value: 240, functionality: 3, viscosity: 250 mP- s@25°C, molecular weight: 700.

Polyether 4: polyether polyol 4, prepared by using glycerol as the starting agent and propylene oxide as the main polymerization component, hydroxyl value: 470, functionality: 3, viscosity: 475 mP- s@25°C, molecular weight: 350.

Polyether 5: polyether polyol 5, prepared by using sucrose and propylene glycol as the starting agents and propylene oxide as the main polymerization component, hydroxyl value: 380, functionality: 5.8, viscosity: 11250 mP- s@25°C, molecular weight: 850.

Dicumyl peroxide: purchased from Syrgis.

Benzoyl peroxide: purchased from Syrgis.

Antifoaming agent: 066N, purchased from BYK.

Polyisocyanate: NCO : 30.5-32.5%, viscosity: 160-240mP.s @25°C, purchased from Covestro Polymer (China) Co., Ltd.

Glass fiber fabric: uniaxial glass fiber fabric, E-glass UD, EKU1150(0)PU-500, purchased from Chongqing International Composite Materials Co., Ltd.

Comparative Examples 1-5 and Examples 1-4

Comparative examples 1-5 and examples 1-4 are preformed as follows. All the components in accordance with Table 1 were mixed except the polyisocyanate, then the polyisocyanate was added to the resulting mixture stepwise and allowed to react at a temperature of 60°C for 8 hours, resulting in the polyurethane prepreg.

The obtained polyurethane prepreg was heated to be able to flow, forming a homogenous resin liquid with a low viscosity. A glass fiber fabric was laid on a thin film, and the obtained resin liquid with a low viscosity was poured onto the glass fiber fabric and then another thin film was covered thereon, then the thin films were pressed repeatedly with a rubber roll until the glass fiber fabric was impregnated completely. After the obtained was cooled down naturally it was put into an oven to allow the solvent to evaporate, forming a prepreg sheet. The finished sheet can be stored at 25 ^° C for over 6 months.

Before the preparation of the polyurethane composite, the upper and bottom thin films were removed, a sheet with a suitable weight was cut out, put into a mold with a desired shape, and hot- press molded for 3-5 minutes at a mold temperature of about 150 ^° C and a pressure of lOMPa.

Table 1 : Raw Materials and Obtained Polyurethane Prepreg Properties

Comparative Example Comparative Example Example

Raw Material Unit

Example 1 1 Example 2 2 3

Prepolym Prepolym Prepolym

Prepolymer 1 Prepolymer 3

er 2 er 4 er 5

HPMA ppw 100 50 10 50 50

Polyether 1 ppw 10 10

Polyether 2 ppw 40 30 40 40

Polyether 3 ppw 50 10 10

Dicumyl ppw

0.2 0.2 0.2 0.2

Peroxide

Benzoyl ppw

0.2 0.2 0.2 0.2 0.5

Peroxide

Defoaming ppw

0.5 0.5 0.5 0.5 0.5

Agent

Polyisocyanate ppw 90.8 62.4 51.1 61.2 61.2

Isocyanate Index 98 98 98 98 98

bendable,

friable, substantia friable, bendable, bendable,

Prepreg (sheet)

fractured fly not fractured not tacky not tacky tacky

Adding reactive

diluents or soluble soluble poor solubility soluble soluble solvents

Heating to 60- melted, melted, melted, poor melted, melted,

90 ^° C flowable flowable flowability flowable flowable

high high high

Prepreg mold friable, no strength, friable, no strength, strength, pressed article strength good strength good good

toughness toughness toughness ,„

Table 2: Raw Materials and Obtained Polyurethane Prepreg Properties

Comparative Example 6

According to the formulation of Prepolymer 4, the glass fiber fabric was impregnated immediately after all the components were mixed and then the liquid resin was heated at 60 ^° C for another 4 hours to gelatinize gradually before cooled to room temperature again to reach B-stage.

Figure 1 is the image of the glass fiber fabric after impregnation with the polyurethane in Comparative Example 6.

It can be seen from Figure 1 that, at room temperature, the resin was filled with air bubbles of various sizes and the glass fiber interface impregnated in the gel state resin was also filled with air bubbles, resulting in an obscure texture. Example 5

According to the formulation of Prepolymer 4, all the components were heated at 60 ^° C for 4 hours after being mixed to allow the liquid resin to form a gel gradually, then it was cooled to room temperature to reach a state that was not tacky. This gel was then heated to 90 ^° C to become a liquid with a low viscosity in order to have a good flowability. It was used to impregnate the glass fiber fabric immediately and then cooled to room temperature (-25 ^° C) naturally, reaching B -stage.

Figure 2 is the image of the glass fiber fabric after impregnation with the polyurethane prepreg in Example 5.

There are almost no visual air bubbles in Figure 2, and the glass fibers that were impregnated sufficiently with the clear and transparent gel state resin have a distinct texture.

It can be seen from the comparison between Figure 1 and Figure 2 that composites with better properties can be prepared by using the prepreg of the present invention.

Although the present invention has been described above in detail regarding the purpose of the present invention, it is to be understood that such a detailed description is merely exemplary. In addition to those that can be defined by claims, various modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention.