Abstract:
The thermosetting resin composition of the present invention is prepared by mixing an aromatic cyanamide compound with a cyclic ester compound and/or a cyclic amide compound. Although a solventless type composition is preferable, the present invention is not limited thereto. The cured product of the present invention can be prepared by heating and curing said thermosetting resin composition. The obtained cured product of the present invention usually contains melamine rings, isomelamine rings and linear polyester and/or a linear polyamide units.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thermosetting resin composition, its cured product, and a process for producing this cured product, and particularly relates to a thermosetting resin composition applicable to various resin products for which an electrical insulating property, mold-ability and heat resistance are required, such as printed circuit boards, resin-sealed semiconductors, and resin-impregnated coils, its cured product, and a process for producing this cured product. 
     2. Description of the Prior Art 
     Polyaddition type polyimides such as bismaleimide are well-known examples of the resins of heat resistance class H. On the other hand, a homopolymer of aromatic dicyanamide is also known as a heat-resistant resin (See British Pat. No. 1322332). Although this polymer is more excellent in respect of heat resistance than the above polyimides, it is lacking in flexibility, so that it is extremely unsuitable for films, coating materials, prepreg materials and molding materials. Besides, a solvent is necessary to prepare a casting material from the aromatic dicyanamide because it is in the form of powder, and the use of a solvent gives rise to problems such as void formation and dimensional discrepancy, so that it is extremely unsuitable as a molding material. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a thermosetting resin composition excellent in moldability and capable of dispensing with any solvent though it is derived from an aromatic dicyanamide, a cured product obtained by heating and curing this resin composition, and a process for producing the cured product. 
     The thermosetting resin composition of the present invention is prepared by mixing an aromatic cyanamide compound with a cyclic ester compound and/or a cyclic amide compound. Although a solventless type composition is preferable, the present invention is not limited thereto. The cured product of the present invention can be obtained by heating and curing this thermosetting resin composition. The obtained cured product of the present invention usually contains melamine rings, isomelamine rings, and linear polyester and/or linear polyamide units. 
     (Aromatic cyanamide compounds) 
     Typical aromatic cyanamide compounds used in the present invention are represented by the following formula [I]: 
     
         A--NR.sub.1 CN).sub.n                                      [I] 
    
     wherein A is an organic group having at least one aromatic ring, R 1  is selected from the group consisting of hydrogen, a benzenesulfonyl group, and a benzyl group, and n is an integer equal to or greater than 1. 
     This aromatic cyanamide compound forms melamine and isomelamine rings in the cured product of the present invention. These ring groups constitute the heat-resistant skeleton of the cured product. 
     Examples of the melamine rings are represented by the following formula [II], while those of the isomelamine rings are represented by the following formula [III]. 
     In these formulas, the symbols are the same as defined in formula [I]. ##STR1## 
     The aromatic cyanamide compound used in the present invention comprises at least one member selected from the group consisting of, for example, m-phenylenedicyanamide, p-phenylenedicyanamide, 4,4&#39;-dicyanamidodiphenylmethane, 2,2&#39;-bis(4-cyanamidophenyl)propane, 4,4&#39;-dicyanamidophenyl oxide, 4,4&#39;-dicyanamidodiphenyl sulfone, bis(4-cyanamidophenyl)phosphine oxide, bis(4-dicyanamidophenyl)phenylphosphine oxide, bis(4-cyanamidophenyl)methylamine, 1,5-dicyanamidonaphthalene, m-xylylenedicyanamide, 1,1,-bis(p-cyanamidophenyl)furan, p-xylylenedicyanamide, hexamethylenedicyanamide, 6,6&#39;-dicyanamido-2,2&#39;-dipyridyl, 4,4&#39;-dicyanamidobenzophenone, 4,4&#39;-dicyanamidoazobenzene, bis(4-cyanamidophenyl)phenylmethane, 1,1-bis(4-cyanamidophenyl)cyclohexane, 1,1-bis(4-cyanamido-3-methylphenyl)-1,3,4-oxadiazole, 4,4&#39;-dicyanamidodiphenyl ether, 4,4&#39;-bis(p-cyanamidophenyl)- 2,2&#39;-dithiazole, m-bis(4-p-cyanamidophenyl-2-thiazole)benzene, 4,4&#39;-dicyanamidobenzanilide, 4,4&#39;-dicyanamidophenyl benzoate, 2,2&#39;-bis[4-(4-cyanamidophenoxy)phenyl]propane, 2,2&#39;-bis[3-methyl-4-(4-cyanamidophenoxy)phenyl]propane, 2,2-bis[3-ethyl-4-(4-cyanamidophenoxy)phenyl]propane, 2,2-bis[3-propyl-4-(4-cyanamidophenoxy)phenyl]propane, 2,2-bis[3-isopropyl-4-(4-cyanamidophenoxy)phenyl]propane, bis[4-(4-cyanamidophenoxy)phenyl]methane, and cyanamido-terminated sulfone ether oligomer represented by the following formula [IV]: ##STR2## 
     The reason why an aromatic cyanamide compound is used in the present invention is that the aromatic compound is advantageous in respect of heat resistance. 
     (Cyclic ester compounds) 
     Typical cyclic ester compounds used in the present invention are represented by the following formula [V]: ##STR3## wherein R 2  is a bivalent organic group. 
     It can be presumed that the cyclic ester compound forms a linear polyester as represented by the following formula [VI]: ##STR4## wherein m is an integer equal to or greater than 2, and R 2  is as defined in formula [V]. 
     This linear polyester imparts flexibility, especially impact resistance, to the cured product. 
     Although the cyclic ester compound is effective in bringing the powdery aromatic cyanamide compound into a liquid state (in this sense, the cyclic ester acts as a solvent), it not only acts as a solvent but constitutes a component of the cured product after curing. Meanwhile, although this compound is not thermally cured by itself and requires a catalyst for curing, it can undergo an uncatalyzed curing reaction when it is combined with the aromatic cyanamide compound. 
     Examples of the cyclic ester compounds used in the present invention include β-propiolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α,γ-trimethylene-γ-butyrolactone, α,γ-dimethyl-α,γ-trimethylene-γ-butyrolactone, α-anilino-γ-phenyl-γ-butyrolactone, β,δ-dimethyl-δ-valerolactone, α,δ-ethylene-δ-valerolactone, α,δ-ethylene-α,δ-dimethyl-δ-valerolactone, 4-methyl-2-butenolactone, phthalide, coumarin, 3,4-dihydrocoumarin, α,β-dibenzoyloxy-γ-butyrolactone, 2-isobutyl-1-methylcyclopropanecarboxylic acid hemiketal lactone and α-ethyl-γ,γ-dihydroxypimelic acid dilactone. 
     (Cyclic amide compounds) 
     Typical cyclic amide compounds used in the present invention are represented by the following formula [VII]: ##STR5## wherein R 3  is a bivalent organic group and R 4  is hydrogen or a monovalent group. 
     It can be presumed that this cyclic amide compound forms a linear polyamide such as the one represented by the following formula [VIII]: ##STR6## wherein 1 is an integer equal to or greater than 2, and R 3  and R 4  are as defined in formula [VII], in the cured product of the present invention. 
     This linear polyamide is similar to the linear polyester in that it imparts flexibility, especially impact resistance, to the cured product. 
     Like the cyclic ester compound, the cyclic amide compound is liquid, but it not only acts as a simple solvent, but also constitutes a component of the cured product after curing. Although, like the cyclic ester compound, this cyclic amide compound is not thermally cured by itself and requires a catalyst for curing, it can undergo an uncatalyzed curing reaction when it is combined with the aromatic cyanamide compound. 
     Examples of the cyclic amide compounds used in the present invention include glycine anhydride, azetidinone, γ-butyrolactam, N-methyl-2-pyrrolidone, N-vinylpyrrolidone, δ-valerolactam, 3,4-dihydro-2-quinolone, ε-caprolactam, α-methylcaprolactam, ε-methylcaprolactam, γ-methylcaprolactam, α-vinylpyrrolidone, δ-methylcaprolactam, ε-methylcaprolactam, N-methylcaprolactam, ω-enantholactam, ω-caprylolactam, β,γ-dimethylcaprolactam, γ-ethylcaprolactam, γ-isopropylcaprolactam, ε-isopropylcaprolactam, γ-butylcaprolactam, γ-hexacyclobenzylcaprolactam, α-azabicyclo[3.2.1]-octane-3-one, 2-azabicyclo[3.2.2]nonan-3-one, 6-azabicyclo[2.2.3]octane-3-one, and 6-azabicyclo[3.2.1]octan-7-one. 
     (Curing catalysts) 
     Although, as mentioned above, the dicyanamide compound and the cyclic amide compound can cure in the absence of any catalyst if their kinds and curing conditions are suitably selected, it is also possible to add, for example, a catalyst which accelerates the ring opening reaction of the cyclic amide compound or the cyclic ester compound. 
     Examples of the polymerization catalysts for the cyclic amide compound include H 2  SO 4 , α-alanine, β-alanine, hexamethylenediamine hydrochloride, phsophoric acid, boric acid, NaH 2  PO 2 , Na 2  HPO 3 , Na, NaOH, Na 2  CO 3 , NaH, CH 3  -MgBr Grignard reagent, C 2  H 5  -MgBr Grignard reagent, and SnCl 4 . 
     Examples of the polymerization catalysts for the cyclic ester compound include (i) organic amines such as phenylnaphthylamine, pyridine, dimethylaniline, trimethylamine, and trimethylamine oxide, (ii) Lewis acids such as boron trifluoride, anhydrous ferric chloride, anhydrous stannic chloride cupric chloride, and titanium tetrachloride, (iii) boron trifluoride/amine complexes such as boron trifluoride/monoethylamine complex and boron trifluoride/piperidine complex, and (iv) organophosphorus compounds such as triphenylphosphine sulfide, dihexylphosphine oxide, trioctylphosphine oxide, and triphenylphosphine. 
     Although the amounts of the above catalysts are not particularly limited, it is preferable that they are 0.01 to 5% by weight, particularly 0.1 to 2% by weight, based on the total weight of the composition. It is also possible to use these catalysts in the form of a suitable combination. 
     (Mixing ratio) 
     The composition of the present invention can afford good cured products, varnishes, etc., even when the mixing ratio among its components is varies relatively widely. Although the mixing ratio may thus be determined according to its intended use and in no way limited, it is preferable that the total amount of the cyclic ester compound and/or the cyclic amide compound is 5 to 250 parts by weight per 100 parts by weight of the aromatic cyanamide compound. 
     Other components added) 
     The resin composition of the present invention may contain, if necessary, well-known additives such as organic fillers, inorganic fillers, glass fiber, organic fibers, flame retardants, flexibilizers, pigments, coupling agents, and mold releases. It is also possible to mix the resin composition of the present invention with other materials such as another thermosetting resin and cure the mixture in a variety of ways. 
     The composition of the present invention can be brought into a liquid state by suitably selecting the kinds and ratio of the cyclic ester compound and/or the cyclic amide compound to be mixed with the aromatic cyanamide compound, and used, as such, as a varnish for impregnation or casting, that is, it is particularly effective as a cyanamide resin composition which requires no other solvents, i.e., of a solventless type. However, it is also possible to use other solvents in the present invention without any objections. 
     (Cured products and varnishes) 
     With regard to the properties of the cured product of the present invention, its heat resistance is enhanced and its hardness is increased as the mixing ratio of the aromatic cyanamide compound is increased, while there is a tendency of forming a cured product rich in flexibility as the above ratio is decreased. Further, with regard to the properties of a compound varnish, the viscosity is reduced and the fluidity is increased as the mixing ratio of the cyclic ester compound or the cyclic amide compound is increased. 
     It may be presumed that a cured product of the aromatic cyanamide compound/cyclic ester compound system has melamine rings (a trimer of the cyanamide compound), isomelamine rings (likewise, a trimer of the cyanamide compound) and a linear polyester (a ring opening polymer of the cyclic ester compound) unit. The IR spectrum absorption of the melamine ring is 1590 cm -1 , that of the isomelamine ring is 1620 cm -1 , and that of the linear polyester is 1720 cm -1 . 
     It may be presumed that a cured product of the aromatic cyanamide compound/cyclic amide compound system has melamine rings, isomelamine rings and a linear polyamide (a ring opening polymer of the cyclic amide compound) unit. The IR absorption of the linear polyamide is 1640 cm -1 . 
     It may be presumed that a cured product of the aromatic cyanamide compound/cyclic ester compound/cyclic amide compound system contains melamine rings, isomelamine rings, a linear polyester unit and a linear polyamide unit. 
     In any case, it is possible without any objection that a variety of reactions (for example, reactions among the melamine rings, the isomelamine rings, the amide unit and the ester unit) in each of the cured products. 
     When a solventless type composition is used, problems due to solvent evaporation such as void formation or dimensional discrepancy can be solved. 
     (Curing methods) 
     The curing of the thermosetting resin composition of the present invention can be accomplished merely by heating it in a suitable manner. For example, the composition can be cured into a tough product when it is heated at 150° to 300° C. for 10 minutes to 30 hours, especially when this heating is carried out in several stages. 
     (Use) 
     The resin after curing is excellent in electrical properties, chemical resistance, impact resistance, and self-extinguishability, so that it finds wide applications such as casting resins, impregnating resins, mold resins for electronic parts, resins for coating materials, resins for laminated sheets, resins for print wiring, interior resins, resins for FRP, and other resins for structural materials. 
     [EFFECTS OF THE INVENTION] 
     As described above, the present invention is effective in obtaining a thermosetting resin composition excellent in moldability and capable of dispensing with any solvent though it is derived from an aromatic dicyanamide and in affording a cured product which is excellent in mechanical properties at high temperatures, impact resistance, and heat resistance and especially when the composition used is of a solventless type, a cured product which has excellent dimensional accuracy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 through 3 are the IR spectrum of the cured products in the examples of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples 1 through 10 
     An aromatic cyanamide compound and a cyclic ester compound as shown in Table 1 were mixed together under stirring at 80° C. for 30 minutes to form a liquid composition. This liquid composition was poured into a mold, vacuum-defoamed and heated under a curing condition of 120° C./5 hr+150° C./5 hr+180° C./5 hr+200° C./5 hr+250° C./10 hr to obtain a cured product. The obtained cured product was yellow-brown transparent resin. Table 2 shows the weight loss initiating temperature, glass transition point and tensile properties of each of the cured products. The weight loss initiating temperature is a value obtained when the sample was heated in air at a rate of temperature rise of 5° C./min. 
     
                                           TABLE 1__________________________________________________________________________  4,4&#39;-dicyanamido-           4,4&#39;-dicyanamido-  diphenylmethane           diphenyl ether                    ε-caprolactone                             γ-butyrolactone                                      triphenylphosphineExample No.  (parts by weight)           (parts by weight)                    (parts by weight)                             (parts by weight)                                      (parts by weight)__________________________________________________________________________1      100      --       100      --       12      100      --       100      --       --3      100      --        80      --       --4      100      --       --       100      --5      100      --       --       80       --6       50       50      100      --       --7       50       50       50      50       --8      --       100      100      --       19      --       100      100      --       --10     --       100       80      --       --__________________________________________________________________________ 
    
     
                       TABLE 2______________________________________        glassweight loss  tran-  mechanical propertiesExam- initiating sition tensile properties                               Izod impactple   temperature            point  strength                          elonga-                                 strength*No.   (°C.)            (°C.)                   (kg/cm.sup.2)                          (%)    (kg · cm/cm)______________________________________1     330        260    480    10     102     310        240    440    14     163     330        260    500     8      84     320        240    450     8      85     330        260    480     6      76     330        240    460    11     137     330        240    450     8      88     330        260    470    10     109     320        240    460    11     1310    330        260    490     7      8______________________________________ measurement temperature . . . room temperature *a rod (3.17 × 3.17 mm) 
    
     Examples 11 through 15 
     An aromatic cyanamide compound and a cyclic ester compound as shown in Table 3 were dissolved in methyl ethyl ketone (solid content of 30%), and heated at 70° C. for 90 minutes to form a prepolymer. This varnish was infiltrated into a 0.18 mm thick, aminosilane-treated glass cloth and dried at 100° C. for about 10 minutes to form a coated cloth. Ten sheets of this cloth were laid upon one another and pressure-molded at a pressure of 20 kg/cm 2  under a curing condition of 150° C./1 hr+200° C./2 hr+250° C./2 hr to form a laminated sheet. Table 4 shows the weight loss initiating temperature and bending strength ratio of each of the laminated sheets. The bending strength ratio is a retention ratio of a bending strength at a given temperature to that at room temperature (20° C.). 
     
                       TABLE 3______________________________________               ε-capro-                        γ-butyro-                                triphenyl-  4,4&#39;-dicyanamido-               lactone  lactone phosphineExample  diphenylmethane               (parts by                        (parts by                                (parts byNo.    (parts by weight)               weight)  weight) weight)______________________________________11     100          10       --      --12     100          20       --      --13     100          50       --      --14     100          50       --      115     100          --       20      --______________________________________ 
    
     
                       TABLE 4______________________________________  weight loss  initiating  temperature            bending strength ratio (%)Example No.    (°C.)                100° C.                         180° C.                                 220° C.______________________________________11       400         98       88      7712       370         88       84      7313       340         85       80      7014       360         95       87      7815       380         97       88      76______________________________________ 
    
     Example 16 
     According to the procedure of Examples 1 through 15, 1 mol of 4,4&#39;-dicyanamidodiphenylmethane and 2 mol of ε-caprolactone were mixed together and cured under a curing condition of 120° C./1 hr+180° C./15 hr+200° C./2 hr. FIG. 1 is an IR spectrum of the cured product, indicating that it has absorptions near 1590 cm -1 , near 1620 cm -1 , and near 1720 cm -1 . 
     Example 17 
     45 parts by weight of 4,4&#39;-dicyanamidodiphenylmethane was reacted with 30 parts by weight of γ-butyrolactam at 60° to 80° C. for about 60 minutes to form a varnish, and this varnish was poured into a mold and cured therein under a curing condition of 160° C./2 hr+200° C./2 hr+250° C./10 hr to form a resin plate. 
     Example 18 
     45 parts by weight of 4,4&#39;-dicyanamidodiphenylmethane was reacted with 30 parts by weight of ε-caprolactam at 60° to 80° C. for about 60 minutes to form a varnish, and this varnish was poured into a mold and cured therein under a curing condition of 160° C./2 hr+200° C./5 hr+250° C./5 hr to form a resin plate. 
     Example 19 
     45 parts by weight of 4,4&#39;-dicyanamidodiphenylmethane was reacted with 30 parts by weight of γ-butyrolactam and 2 parts by weight of α-alanine at 60° to 80° C. for about 60 minutes to form a varnish, and this varnish was poured into a mold and cured therein under a curing condition of 160° C./2 hr+200° C./2 hr+250° C./5 hr to form a resin plate. 
     Table 5 shows the weight loss initiating temperatures and mechanical properties of the cured products. The values of the weight loss initiating temperatures were those determined when the samples were heated in air at a rate of temperature rise of 5° C./min. 
     
                       TABLE 5______________________________________weight loss   Mechanical propertiesinitiating    tensile properties                        Izod im-Example  temperature             strength elongation                              pact strength*No.    (°C.)             (kg/cm.sup.2)                      (%)     (kg · cm/cm)______________________________________17     350        450      10      918     340        430      12      1219     360        480       8      7______________________________________ measurement temperature . . . room temperature *a rod (3.17 × 3.17 mm) 
    
     Example 20 
     According to the procedure of Examples 17 through 19, 1 mol of 4,4&#39;-dicyanamidodiphenylmethane and 2 mol of ε-caprolactam were mixed together and cured under a curing condition of 120° C./1 hr+180° C./15 hr+200° C./2 hr. FIG. 2 is an IR spectrum of the cured product, indicating that it has absorptions near 1590 cm -1 , near 1620 cm -1  and near 1640 cm -1 . 
     Examples 21 through 25 
     An aromatic cyanamide compound, a cyclic ester compound and a cyclic amide compound as shown in Table 6 were mixed together at 80° C. for 30 minutes to form a liquid composition. This liquid composition was poured into a mold, vacuum-defoamed, and heated under a curing condition of 120° C./5 hr+150° C./5 hr+180° C./5 hr+ 200° C./5 hr+250° C./10 hr to obtain a cured product. The obtained cured product was yellow-brown transparent resin. Table 7 shows the weight loss initiating temperature and mechanical properties of the cured product. 
     
                       TABLE 6______________________________________Ex-   4,4&#39;-dicyanamido-ample diphenylmethane              ε-caprolactone                           ε-caprolactamNo.   (parts by weight)              (parts by weight)                           (parts by weight)______________________________________21    100          20           8022    100          40           6023    100          60           4024    100          80           2025    100          40           40______________________________________ 
    
     
                       TABLE 7______________________________________weight loss   Mechanical propertiesinitiating    tensile properties                        Izod im-Example  temperature             strength elongation                              pact strength*No.    (°C.)             (kg/cm.sup.2)                      (%)     (kg · cm/cm)______________________________________21     330        440      10      1122     340        450      10      1023     340        450      0       924     350        470      8       925     360        490      6       8______________________________________ measurement temperature . . . room temperature *a rod (3.17 × 3.17 mm) 
    
     The weight loss initiating temperatures were those obtained when the samples were heated in air at a rate of temperature rise of 5° C./min. 
     Example 26 
     According to the procedure of Examples 21 through 25, a mixture of 1 mol of 4,4&#39;-dicyanamidodiphenylmethane, 1 mol of ε-caprolactam was cured under a curing condition of 120° C./1 hr+180° C./15 hr+200° C./2 hr. FIG. 3 is an IR spectrum of the cured product, indicating that it has absorptions near 1590 cm -1 , near 1620 cm -1 , near 1640 -1  and near 1720 cm -1 .