Abstract:
A method for preparing a polyisocyanurate composite obtained by injecting a formulated liquid comprises an organic polyisocyanate, a polyol and a trimerization catalyst into a mold in which a fibrous reinforcing material is previously set by use of a reaction injection molding machine, wherein: 
     (1) a single or mixed polyether polyol having a hydroxyl value of 40 to 400 is used as the polyol; and 
     (2) the formulation ratio of the organic polyisocyanate and the polyol in terms of the isocyanurated isocyanate concentration [NCO] T  defined by the following formula (1) is in the range of 3.0 to 5.5 mmol/g: ##EQU1## [NCO] T  : theoretical concentration of isocyanate group consumed in isocyanuration; 
     [NCO] O  : isocyanate group concentration in organic polyisocyanate (mmol/g); 
     OH-V: hydroxyl value of single or mixed polyol; 
     W A  : weight fraction of organic polyisocyanate.

Description:
This is a continuation of copending application Ser. No. 07/206,019 filed on June 10, 1988 and now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a rapid curable method for preparing a polyisocyanurate composite which is highly rigid and excellent in heat resistance. 
     2. Related Background Art 
     In the art of fiber reinforced plastics (FRP) molding technique, the method of obtaining a FRP by injecting a thermosetting resin reaction liquid such as unsaturated polyester resin, vinyl ester resin, epoxy resin, etc. into a mold in which a fibrous reinforcing material is previously set has been generally called the resin injection method or the resin transfer molding method and known as the method with good economical efficiency utilizing in-mold polymerization. 
     In industrial fields, particularly the field of automotive industry, it has been demanded to manufacture structural materials having heat resistance in short molding cycle time. However, in the above method, no material satisfactory in both aspects of rapid curability and heat resistance has been obtained. 
     On the other hand, in the field of polyurethane elastomer, the reaction injection molding (hereinafter called RIM) technique has been well developed and applied particularly to molding of bumper, facia, etc. of automobile. Since this technique is suitable for manufacturing large size molding, specific features reside in that integration of a large number of parts is possible, and also that the molding cycle time is by far shorter as compared with the above resin injection method. 
     In recent years, it has been attempted to obtain a composite of thermosetting resin by means of rapid curing by combining the RIM technique with the resin injection method. 
     More specifically, it is a method in which a fibrous reinforcing material is previously set in a mold, and a thermosetting resin reaction liquid is injected by a RIM machine into the mold. 
     However, with the reaction liquid for RIM of the prior art, particularly in the case of polyurethane, the reaction begins simultaneously with mixing to cause increase in viscosity, whereby there is the problem that penetrability into the fibrous reinforcing material is inferior. Also, other RIM systems have been investigated, but no material satisfactory in such points as penetrability, rapid curability, high rigidity, heat resistance, etc. has been obtained. 
     The present inventors have intensively studied in order to obtain a composite having high rigidity and heat resistance in short molding cycle time by rapid curing, and consequently accomplished the present invention. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a method for preparing a polyisocyanurate composite obtained by injecting a formulated liquid comprising an organic polyisocyanate, a polyol and a trimerization catalyst into a mold in which a fibrous reinforcing material is previously set by use of a reaction injection molding machine, wherein: 
     (1) a single or mixed polyether polyol having a hydroxyl value of 40 to 400 is used as the polyol; and 
     (2) the formulation ratio of the organic polyisocyanate and the polyol in terms of the isocyanurated isocyanate group [NCO] T  defined by the following formula (1) is in the range of 3.0 to 5.5 mmol/g: ##EQU2## in which [NCO] T  : theoretical concentration of isocyanate group consumed in isocyanuration; 
     [NCO] O  : isocyanate group concentration of organic polyisocyanate (mmol/g); 
     OH-V: hydroxyl value of single or mixed polyol; 
     W A  : weight fraction of organic polyisocyanate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the present invention, by combining the polyol having a hydroxyl value of 40 to 400, the concentration of isocyanurated isocyanate group [NCO] T  which is 3.0 to 5.5 mmol/g and a fibrous reinforcing material, excellent characteristics well balanced in both aspects of moldability of a formulated liquid and physical properties of a prepared polymer can be obtained. 
     As to moldability of the formulated liquid according to the present invention, viscosity increase by urethane reaction at the initial stage can be gently suppressed, whereby penetrability, fillability into the fibrous reinforcing material are excellent, and also the isocyanuration reaction becomes the main reaction after completion of filling to be rapidly cured and therefore demolding within a short time (usually 1 to 3 minutes) can be accomplished. In other words, the isocyanuration reaction exhibits generally &#34;S-form&#34; reaction behaviors, with the reaction at the initial stage of mixing being very slow substantially without viscosity increase at the initial stage of the reaction. 
     In aspect of physical properties, the prepared polymer can retain both of excellent impact resistance possessed by polyurethane and excellent heat resistance possessed by polyisocyanurate. 
     Examples of organic polyisocyanates available in the present invention may include aliphatic polyisocyanates such as hexamethylene-1,6-diisocyanae, 2,2,4- or 2,4,4-trimethylhexamethylene-1,6-diisocyanate, etc.; alicyclic polyisocyanates such as cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4&#39;-diisocyanate, etc.; aromatic polyisocyanates such as p-phenylene diisocyanate, tolylene-2,4- or -2,6-diisocyanate, diphenylmethane-2,4- or -4,4&#39;-diisocyanate, naphthylene-1,5-diisocyanate, xylylene-1,3- or -1,4-diisocyanate, diphenyl ether-4,4&#39;-diisocyanate, etc. 
     It is also possible to use a polyphenylene polymethylene polyisocyanate of the type obtained by condensation of aniline and formalin before phosgenation, or diphenylmethane diisocyanates liquid at normal temperature having carbodiimide group or uretonimine group, or modified polyisocyanates containing urethane bond, allophanate bond, biuret bond and urethidione ring, etc. Isocyanate based prepolymers obtained by the reaction by use of an excess of the above polyisocyanate and polyols can be also employed. 
     Of these are preferred those which are liquid and have low viscosity at normal temperature, diphenylmethane-4,4&#39;-diisocyanate or polyphenylene polymethylene polyisocyanate, etc having carbodiimide group or uretonimine group. 
     The polyol which can be used in the present invention is a single or mixed polyether polyol having a hydroxyl value of 40 to 400, preferably 50 to 300. Representative examples of polyether polyol may include polyether polyols obtained by addition of ethylene oxide, propylene oxide, etc. to polyols such as propylene glycol, glycerine, trimethylolpropane, pentaerythritol, α-methylglycoside, cane sugar etc.; aminoalcohols such as diethanolamine, triethanolamine, tripropanolamine, etc.; amines such as ethylene diamine, 1,6-hexanediamine, diethylenetriamine, triethylenetetramine, toluylenediamine, methylenebisaniline and the like; phosphorus compounds such as phosphoric acid, pyrophosphoric acid or partial esters of these; and mixtures of these. 
     Also, there may be included halo-containing polyether polyols having a hydroxyl value within the above range obtained by addition of epihalohydrins to polyols such as glycerine, trimethylolpropane, pentaerythritol, sorbitol, etc. in the presence of a cationic catalyst such as BF 3 , etc. 
     In the present invention, the organic polyisocyanate and the polyol are formulated at a ratio so that the isocyanurated isocyanate concentration may be within the range of 3.0 to 5.5 mmol/g preferably 3.5 to 5.0 mmol/g. 
     In this case, if the concentration of isocyanurated isocyanate group [NCO] T  is less than 3.0 mmol/g, viscosity increase at the initial stage of mixing is so excessive, whereby it is difficult to control the reaction with the trimerization catalyst, that penetrability into the fibrous reinforcing material is poor to give, and only a material with low mechanical strength under elevated temperature is obtained. If the concentration of isocyanurated isocyanate group [NCO] T  exceeds 5.5 mmol/g, drawbacks such as remarkable lowering in impact resistance may be caused to occur. 
     Examples of the trimerization catalyst which can be used in the present invention may include tertiary amines such as triethylamine, N-methylmorpholine, 2,4,6-tris(dimethylaminomethyl)phenol, 2,4,6-tris(dialkylaminoalkyl)hexahydro-S-triazine, aziridine compounds, etc.; phosphines as represented by triethylphosphine; alkali metal salts such as potassium acetate, potassium 2-ethylhexanoate, etc.; further co-catalyst systems of tertiary amine and epoxy compound, carbamate compound, etc. These trimerization catalysts can be also used as a mixture. 
     Among the trimerization catalysts, preferable catalyst is a co-catalyst system of a tertiary amine and an epoxy compound, particularly preferably a co-catalyst system of triethylenediamine or 2-methyltriethylenediamine and an epoxy compound. 
     In the present invention, if necessary, flame retardants, plasticizers, colorants, various fillers, inner mold releasing agents and other processing additives can be used by addition. 
     Also in the present invention, for the purpose of making the molded product light weight or improving flowability by lowering the viscosity of the stock liquid, blowing agent and/or water (which reacts with isocyanate to generate carbon dioxide gas) can be added in the stock liquid or alternatively a gas can be mixed and dissolved into the stock liquid by means of an air loading equipment in carrying out molding, thereby mixing intentionally gas bubbles into the molded product. 
     For the fibrous reinforcing material which can be used in the present invention, there can be included chopped strand mat, continuous strand mat, surfacing mat, glass cloth, roving cloth, etc. Also, carbon fibers, aramide fibers can be similarly used. The above fibrous reinforcing materials can be also used in combination of two or more kinds. 
     For these fibrous reinforcing materials, it is particularly preferable to use a glass continuous strand mat partially or singly. 
     By use of a continuous strand mat singly or in combination with another fibrous reinforcing material, penetrability of the formulating liquid can be improved to enhance filling characteristic, and therefore uniform molded product can be obtained. 
     In the present invention, if necessary, various metal meshes, network moldings of synthetic resins can be also used in combination with the fibrous reinforcing material. 
     The polyisocyanurate composition which is obtained in short molding cycle time by the present invention is excellent in moldability, and yet has excellent heat resistance, rigidity, and therefore it is extremely useful as structural material for bumper beam, floor panel, door inner panel, various trays in the field of automobile; housing cases in the field of electricity; and other general industrial members. 
     [Examples] 
     The present invention is described in more detail by referring to Examples, but the present invention is not limited thereto. 
     The physical properties of polymer products were measured at 25° C. according to the following methods. 
     Specific gravity: according to JIS K-7112 
     Flexural modulus, flexural strength: according to JIS K-7203 
     Tensile strength, elongation: according to JIS K-7113 
     Izod impact, notched: according to JIS K-7110 
     EXAMPLES 1-3, AND COMPARATIVE EXAMPLES 1, 2 
     Previously, a glass continuous strand mat was set in a mold cavity, and the two components of the component A (organic polyisocyanate and epoxy compound) shown in Table 2 and the component B (polyol and tertiary amines) shown in Table 2 were injected thereinto by use of a high pressure reaction injection molding machine (MC-102 Model, produced by Polyurethane Engineering), followed by curing to give a test plate. 
     During this operation, the molding was carried out by varying the concentration of isocyanurated isocyanate group [NCO] T . 
     The molding conditions are shown in Table 1, and the recipes and the results in Table 2 and Table 3. 
     
                       TABLE 1______________________________________Molding condition______________________________________Mold shape            Flat plateLiquid temperature    35 ± 2° C.Mold temperature      70 ± 2° C.Demolding time        one minute______________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________                  No.                                    Comparative                                           ComparativeItem                   Example 1                        Example 2                              Example 3                                    example 1                                           example__________________________________________________________________________                                           2Formulation  Components         Millionate MTL.sup.1                  69.1  69.1  82.9  62.6   90.3(parts by  A      Phenylglycidyl                  3.0   3.0   3.0   3.0    3.0weight)       ether  Components         Adeka polyether.sup.2                  30.9  30.9  17.1  37.4   9.7  B      CM54         DABCO.sup.3                  0.2   0.2   0.2   0.2    0.2Hydroxy value of polyol                  225   225   225   225    225[NCO].sub.T (mmol/g)   3.5   3.5   5.0   2.8    5.8M8609.sup.4 (Wt %)     23-24 34-35 23-24 23-24  23-24__________________________________________________________________________ Note to Table 2 .sup.1 Organic polyisocyanate (liquid diphenylmethane diisocyanate containing carbodiimide; NCOcontent 28.8%) produced by Nippon Polyurethan Industry Co., Ltd, trade name .sup.2 Polyether polyol (hydroxyl value 225), produced by Asahi Denka Kogyo, trade name .sup.3 Triethylenediamine, produced by Sankyo Air products, trade name .sup.4 Glasslon continuous strand mat, produced by Asahi Fiberglass, trad name 
    
     
                                           TABLE 3__________________________________________________________________________             No.                                  Comparative                                         ComparativeItem              Example 1                    Example 2                           Example 3                                  example 1                                         example 2__________________________________________________________________________Physical Specific gravity             1.33   1.38   1.34   1.32   1.34properties Flexural modulus             62,000 75,000 65,000 51,000 66,000 (kgf/cm.sup.2) Flexural strength             1,820  2,010  1,900  1,530  1,500 (kgf/cm.sup.2) Tensile strength             840    1,100  850    820    700 (kgf/cm.sup.2) Elongation (%)             2      2      2      2      1 Izod impact 37     46     32     38     22 (kgf cm/cm) Flexural modulus             39,000 54,000 42,000 22,000 42,000 (kg/cm.sup.2 at 140° C.) 140° C./25° C. Flexural             63     72     65     43     64 modulus retention (%)__________________________________________________________________________ 
    
     EXAMPLES 4-7 AND COMPARATIVE EXAMPLES 3, 4 
     The molding was carried out by varying the hydroxyl value of polyol. The molding methods, molding conditions, etc. were the same as in Examples 1-3 and Comparative examples 1, 2 to obtain molded products, and the recipes and the results of measurement of the physical properties of the molded products are shown in Table 4 and Table 5. 
     
                                           TABLE 4__________________________________________________________________________                  No.                                            Comparative                                                   ComparativeItem                   Example 4                        Example 5                               Example 6                                     Example 7                                            example                                                   example__________________________________________________________________________                                                   4Formulation  Components         Millionate.sup.1                  76.7  65.6   68.4  71.3   83.4   64.6(parts by  A      MR200weight)       Epikote.sup.7                  4.0   5.0    --    4.0    4.0    --         828  Components         SANNIX.sup.2                  --    --     3.7   --     16.6   --  B      PP-200         Adeka polyether.sup.3                  23.3  --     --    12.0   --     --         CM-43         Adeka polyether.sup.4                  --    34.4   --    16.7   --     --         AM-302         Adeka polyether.sup.5                  --    --     27.9  --     --     35.9         AM-502         Methyl.sup.6                  0.2   0.5    --    0.2    0.2    --         DABCO         Potassium 2-                  --    0.1    0.2   0.1    --     0.2         ethylhexanoateHydroxyl value of polyol                  280   56     98    150    560    36[NCO].sub.T (mmol/g)   4.5   4.5    4.5   4.5    4.5    4.5M8609 (Wt %)           25-26 25-26  25-26 25-26  25-26  25-26__________________________________________________________________________ Note to Table 4: .sup.1 trade name of polyphenylene polymethylene polyisocyanate, (NCO content of 31.0%), produced by Nippon Polyurethane Industry Co., Ltd.; .sup.2 trade name of polypropylene glycol, (hydroxyl value of 560), produced by Sanyo Kasei Kogyo; .sup.3 trade name of polyether polyol, (hydroxyl value of 280), produced by Asahi Denka Kogyo; .sup.4 trade name of polyether polyol, (hydroxyl value of 56), produced b Asahi Denka Kogyo; .sup.5 trade name of polyether polyol, (hydroxyl value of 36), produced b Asahi Denka Kogyo; .sup.6 2methyltriethylenediamine, produced by Sankyo Air products; .sup.7 trade name of bisphenol A, epichlorohydrin condensation type epoxy resin, produced by YukaShell Epoxy. 
    
     
                                           TABLE 5__________________________________________________________________________             No.                                           Comparative                                                  ComparativeItem              Example 4                    Example 5                            Example 6                                   Example 7                                           example                                                  example__________________________________________________________________________                                                  4Physical Specific gravity             1.34   1.34    1.32   1.33    1.34   1.32properties Flexural modulus             65,000 60,000  58,000 63,000  67,000 51,000 (kgf/cm.sup.2) Flexural strength             1,780  1,640   1,620  1,720   1,380  1,540 (kgf/cm.sup.2) Tensile strength             890    920     890    900     820    810 (kgf/cm.sup.2) Elongation (%)             2      2       2      2       2      2 Izod impact 34     30      31     34      35     26 (kgf cm/cm) Flexural modulus             45,000 48,000  42,000 43,000  25,000 33,000 (kgf/cm.sup.2 at 140° C.) 140° C./25° C. Flexural             78     80      65     68      37     65 modulus retention %__________________________________________________________________________