Unsaturated Polyester Resin Composition and Sheet-Form Molding Material Using the Same

1. Field of the Invention

This invention relates to an unsaturated polyester resin composition, more particularly an unsaturated polyester resin composition capable of affording a cured product having a superior surface quality, a sheet-form molding material using the same for producing a fiber-reinforced plastic molded product.

2. Description of the Related Art

Unsaturated polyester resins are accompanied with 5 to 10% of volume shrinkage, when they are cured. Thus, usually the so-called low shrinking agent-blended unsaturated polyester resins, obtained by blending a thermoplastic resin as a low shrinking agent, such as polystyrene, polyvinyl acetate, polymethyl methacrylate, block copolymers of conjugated dienes with aromatic vinyl compounds, saturated polyesters, etc. have been used. Such low shrinking agent-blended unsaturated polyester resins have a very small shrinkage factor of cured volume, so that occurrence of cracks, deformation, etc. accompanying the curing shrinkage are few.

When the low shrinking agent-blended unsaturated polyester resins are used as an molding material represented by sheet-molding compound (SMC) and bulk molding compound (BMC), it is possible to improve the dimensional accuracy, the surface quality, of molded products; hence the resins have been used not only for parts of housing facilities such as bath, water tank panel, toiletory bowl, etc., but also for parts of automobiles such as spoiler, air intake, roof, engine hood, deck lid, etc.

The effect of the low shrinking agent varies depending upon the kind and the blended quantity of the low shrinking agent. As the low shrinking agent for unsaturated polyester resin molding material, polyvinyl acetate, saturated polyester resins, conjugated diene compounds, etc. have been used in the aspect of the surface quality of molded products.

However, when polyvinyl acetate or conjugated diene compounds are used as a low shrinking agent, the viscosity of the resulting unsaturated polyester resin composition is increased, the rate for impregnating fiber reinforcing materials with the resin composition are reduced so that the surface quality of molded products is inferior. Further, when saturated polyester resins are used as a low shrinking agent, the viscosity of the resulting resin composition is low and the rate for impregnating fiber reinforcing materials with the resin composition are superior, but in the thickened material obtained by reacting the resin composition with an alkaline earth metal oxide or hydroxide, the saturated polyester resins are separated off from the resin composition, so that the low shrinking effect is insufficient and the surface quality of the resulting molded products is notably inferior. As countermeasures for solving such problems, a process of using a saturated polyester resin having a low molecular weight (Japanese patent application laid-open No. Sho 59-122514), a process of reacting an unsaturated polyester resin with a saturated polyester resin at a high temperature (120.degree. to 180.degree. C.) (Japanese patent application laid-open No. Sho 63-43948), etc. have been proposed, but the resulting low shrinking effect is insufficient.

The object of the present invention is to provide an unsaturated polyester resin composition having solved the problems of the prior art and capable of affording a molded product having a small shrinkage factor of cured volume, a superior dimensional accuracy and surface quality and a high hardness, a sheet-form molding material using the composition, and further, a process for producing a fiber-reinforced plastic molded product using the composition.

The present inventors have made extensive research in view of the above problems, and as a result, have found that when a specified saturated polyester having a number average molecular weight and an acid value each being in a specified range is used, it is possible to obtain an unsaturated polyester resin molded product having a superior surface quality.

The present invention resides in;

(1) an unsaturated polyester resin composition comprising a saturated polyester obtained by reacting a saturated dibasic acid component containing 20% by mol or more adipic acid with a saturated glycol component, and having a number average molecular weight of 4,000 or more and an acid value of 2 to 8 KOH mg/g, an unsaturated polyester and an ethylenic unsaturated monomer;

(2) a sheet-form molding material having the unsaturated polyester resin composition together with a fiber reinforcing material placed between two films; and

(3) use of the sheet-form molding material in a fiber-reinforced plastic molded product, which is obtained by compression-molding of the sheet-form molding material by means of a mold.

FIG. 1 shows a view illustrating an embodiment of the apparatus for producing the sheet-form molding material of the present invention.

A saturated polyester used in the present invention has a number average molecular weight of 4,000 or more, preferably 4,000 to 30,000 and an acid value of 2 to 8 KOH mg/g, preferably 3 to 7 KOH mg/g. If the number average molecular weight is less than 4,000, a sufficient low shrinking effect cannot be obtained. The number average molecular weight can be adjusted by a reaction time. Further, if the acid value is less than 2 KOH mg/g, the saturated polyester separates during thickening of the unsaturated polyester resin molding material and the low shrinking effect is inferior, while if the acid value exceeds 8 KOH mg/g, a thickening rate becomes high and the rate of impregnating fiber reinforcing materials with the resin composition are reduced; hence the surface quality of the molded product is inferior.

The saturated polyester is obtained by reacting a saturated dibasic acid component with a saturated glycol component according to a known process.

As the saturated dibasic acid component, adipic acid, suberic acid, azelaic acid, sebacic acid, auccinic anhydride, dimethyl succinate, maloic acid, phthalic anhydride, phthalic acid, isophthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, halogenated phthalic anhydride, etc. are exemplified, but, in the present invention, it is necessary that the saturated dibasic acid component contain 20% by mol or more, preferably 50% by mol or more of adipic acid. The content of adipic acid may be 100% by mol.

As the saturated glycol component, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, tripropylene glycol, polyoxyethylene glycol, 1,2-butanediol, 1,4-butanediol, 2,3-butanediol, 2,4-pentanediol, 2,2-dimethyltrimethylene glycol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,10-decanediol, 1,12-dodecanediol, tetraethylene glycol, tripropylene glycol, etc. are exemplified.

In order to impart a superior hardness to a resulting fiber-reinforced plastic molded product, it is preferred to use as the saturated glycol component, a saturated glycol component including a saturated glycol expressed by the formula (I) ##STR1##

Wherein n represents an integer of 0 to 9, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each represent a hydrogen atom or an alkyl group of 1 to 4 carbon atoms and at least one of R.sub.1 to R.sub.4 is an alkyl group.

As the saturated glycol expressed by the formula (I), for example, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 1,3-butanediol, etc. are used. The content of the saturated glycol is preferably in the range of 0.5 to 50% by mol based upon the total saturated glycol component.

As to the preparation of the saturated polyester, 1.0 to 2.0 mols of the saturated glycol component is reacted with one mol of the saturated dibasic acid component, and in the preparation, a catalyst such as titanium tetrabutoxide, di-n-butyl-tin oxide, zinc oxide, antimony trioxide, etc. may be also used. Further, a stabilizer such as hydroquinone, hydroquinone monomethyl ether, triphenyl phosphite, etc, may be also used. The reaction may be carried out while removing the condensed water generated during the esterification reaction, and finally the reaction temperature may be elevated up to 180.degree. to 280.degree. C. The reaction time is properly selected depending upon the scale of a batch, the catalyst and the reaction conditions.

The acid value of the saturated polyester may be adjusted by adding the above saturated dibasic acid component to the terminal of the saturated polyester resin after completion of the preparation.

The unsaturated polyester used in the present invention is obtained by subjecting the unsaturated dibasic acid component and if necessary a polybasic acid other than the unsaturated dibasic acid, and a glycol component to condensation reaction.

As the unsaturated dibasic acid component, maleic anhydride, fumaric acid, chloromaleic acid, itaconic acid, citraconic acid, mesaconic acid, etc. may be used, and as the polybasic acid other than the unsaturated dibasic acid used if necessary, adipic acid, suberic acid, azelaic acid, sebacic acid, succinic anhydride, dimethylsuccinic acid, maloic acid, phthalic anhydride, phthalic acid, isophthalic acid, tetrahydrophthalic acid, tetraphthalic anhydride, halogeneted phthalic anhydride, trimellitic acid, pyromellitic acid, etc. are exemplified.

As the glycol component, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, tripropylene glycol, polyoxyethylene goycol, polyoxypropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2,4-pentanediol, 2,2-dimethyltrimethylene glycol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,10-decanediol, 1,12-dodecanediol, 2,2-dimethyl-1,3-propanediol, etc. are exemplified.

The quantity of the unsaturated polyester used is preferably 1.5 to 5 times the weight of the saturated polyester.

The ethylenic unsaturated monomer used in the present invention has no particular limitation, and for example, styrene, vinyltoluene, .alpha.-methylstyrene, diallylphthalate, cholrostyrene, vinylacetate, acrylic acid esters, methacrylic acid esters, etc. are exemplified. The quantity of the ethylenic unsaturated monomer used is preferably 30 to 200% by weight based upon the total quantity of the saturated polyester and the unsaturated polyester.

In the unsaturated polyester resin composition of the present invention, a filler, a polymerization initiator and if necessary, a release agent are usually used.

As the filler, calcium carbonate, clay, aluminum hydroxide, talc, calcium sulfate, etc. are exemplified. Among them, calcium carbonate is preferred in the aspect of cost and capability of filling.

As the polymerization initiator, organic peroxides such as 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, t-butylperoxy-3,3,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxy benzoate, dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylperoxy(2-ethylhexanoate), di-t-butylhydroperoxide, t-butylperoctoate, benzoylperoxide, etc. are used. In order to obtain a superior surface quality in a usual molding time, it is preferred to use t-buthylperoxybenzoate alone or in an admixture with another compound.

As the release agent, fatty acids such as stearic acid, milistic acid, palmitic acid, etc., metal salts of fatty acids such as calcium stearate, zinc stearate, etc., and surface-active agent as phosphoric acid esters, etc. may be used.

The quantity of the filler used is usually 1.0 to 3.5 times the total quantity of the unsaturated polyester resin composition. The quantities of the polymerization initiator and the release agent each have no particular limitation, and they are used in a usual quantity.

Further, in the unsaturated polyester resin composition of the present invention, if necessary, a thickener, a pigment, a curing accelerator, a curing retarder, a viscosity-lowering agent, etc. may be blended.

FIG. 1 shows a view illustrating an embodiment of an apparatus for provucing a sheet-form molding material of the present invention.

This apparatus comprises a belt conveyer system 5 for carrying and processing films 1a and 1b, a pressure roll 16 provided on the belt conveyer system 5, for laminating and contact-bonding films 1a and 1b rolls 11 and 20 each for feeding the films 1a and 1b to the belt conveyer system 5, tanks 12 and 22 each for storing unsaturated polyester resins 2 and 21, doctor knives 13, 23 each for adjusting the thickness of the respective composition layers on the films, a cutter 15 for cutting a roving 14 of fibers to a definite length, provided above the belt conveyer system 5 so that the resulting chopped strands are scattered on the composition layer and a wind-up roll 17 for winding up the resulting contact-bonded sheet 7.

In this apparatus, films 1a and 1b are respectively released from rolls 11 and 20; the respective unsaturated polyester resin compositions 2 and 21 fed from the respective tanks 12 and 22 are applied onto the respective films 1a and 1b to form the respective unsaturated polyester resin composition layers 2a and 2b so that the respective applied quantities are adjusted by means of the respective doctorknives 13 and 23; chopped strands (fiber reinforcing material) 3 obtained by cutting roving 14 to a definite length by means of cutter 15 are laid in a definite quantity onto the composition layer 2a; thereafter, the resulting material is laminated with another composition layer 2b so as to put the fiber reinforcing material 3 between the two composition layers; the resulting laminate is contact-bonded by means of the pressure rolls 16, wound up on the wind-up roll 17, and seasoned for a definite period to obtain a sheet-form molding material.

The resulting sheet-form molding material is cured e.g. by heat-compressing it under a pressure of 50 to 120 kgf/cm.sup.2 at a temperature of 110.degree. C. in a mold, whereby it is possible to obtain a fiber-reinforced plastic molded product having a superior surface quality.

As the fiber reinforcing material 3, e.g. inorganic fibers such as glass fibers, carbon fibers, boron fibers, etc., organic fibers such as polyvinyl alcohol fibers, nylon fibers, aramid fibers, etc. may be used. The fiber reinforcing material may be blended usually in a proportion of about 10 to 50% by weight based upon the total weight of the composition.

As the films 1a and 1b used for producing the sheet-form molding material, general films such as polyethylene film, polypropylene film, polyethylene terephthalate film, etc. may be used.

The present invention will be described in more detail by way of Examples and Comparative examples, but it should not be construed to be limited thereto.

(1) Preparation of saturated polyester (A):

Into a 500 ml preparation flask provided with a stirrer, a thermometer, a nitrogen gas-introducing tube and a Viglew fractionating tube, were fed adipic acid (200.02 g, 1.37 mol), ethylene glycol (55.21 g, 0.89 mol), 1,4-butylene glycol (49.32 g, 0.548 mol), hydroquinone (0.03 g) and triphenyl phosphite (0.3 g), followed by elevating the temperature inside the flask up to 215.degree. C. over about 8 hours, while distilling off the condensed water at a temperature of 105.degree. C. or lower at the top of the frartionating tube, thereafter carrying out reaction for about 4 hours, while keeping the reaction temperature of 215.degree. C., then removing the fractionating tube, and carrying out reaction under a reduced pressure of 5.1.times.10.sup.4 Pa for about 10 hours to obtain a saturated polyester (A) (234.1 g) having an acid value of 4 KOH mg/g. The molecular weight of the saturated polyester was sought using a gel permeation chromatography and converted as a standard polystyren (hereinafter this applies to the subsequent), to give a number average molecular weight of 14,100 and a weight average molecular weight of 29,200.

(2) Preparation of saturated polyester (B):

Into a 500 ml preparation flask provided with a stirrer, a thermometer, a nitrogen gas-introducing tube and a McMahon packing type fractionating tube, were fed adipic acid (189.8 g, 1.3 mol), ethylene glycol (64.48 g, 1.04 mol), 1,4-butylene glycol (46.8 g, 0.52 mol), zinc oxide (0.3 g) and triphenyl phosphite (0.3 g), followed by elevating the temperature inside the flask up to 250.degree. C. over about 5 hours, while distilling off the condensed water at a temperature of 105.degree. C. or lower at the top of the fractionating tube, thereafter carrying out reaction for about 5 hours, while keeping the reaction temperature of 250.degree. C., then removing the fractionating tube, carrying out reaction for about 7 hours under a reduced pressure of 2.5.times.10.sup.2 Pa to obtain a pale yellow resin, adding phthalic anhydride (1.95 g) to the pale yellow resin and agitating the mixture at 160.degree. C. till phtalic anhydride was dissolved, to obtain a saturated polyester (B) (225.2 g) having an acid value of 4.9 KOH mg/g, a number average molecular weight of 13,500 and a weight average molecular weight of 26,700.

(3) Preparation of saturated polyester (C):

The above item (2) was repeated except that adipic acid (189.8 g, 1.3 mol), ethylene glycol (72.54 g, 1.17 mol), propylene glycol (19.76 g, 0.26 mol), 2-ethyl-1,3-hexanediol (18.98 g, 0.13 mol), zinc oxide (0.3 g) and triphenyl phosphite (0.3 g) were fed and phthalic anhydride was not added, to obtain a saturated polyester (C) (226.2 g) having an acid value of 3.8 KOH mg/g, a number average molecular weight of 12,400 and a weight average molecular weight of 24,800.

(4) Preparation saturated polyester (D):

Into the same preparation apparatus as in item (2) were fed adipic acid (189.8 g, 1.3 mol), ethylene glycol (72.54 g, 1.17 mol), propylene glycol (19.76 g, 0.26 mol), 2,2,2-trimethyl-1,3-pentanediol (18.98 g, 0.13 mol), di-n-butyltin oxide (0.3 g) and triphenyl phosphite (0.3 g), followed by elevating the temperature inside the flask up to 250.degree. C. over about 5 hours, while distilling off the condensed water at a temperature of 105.degree. C. or lower at the top of the fractionating tube, thereafter carrying out reaction for 6 hours, while keeping the reaction temperature of 250.degree. C., then removing the fractionating tube, carrying out reaction for 4 hours under a reduced pressure of 2.5.times.10.sup.2 Pa to obtain a pale yellow resin, adding phthalic anhydride (1.92 g) to the pale yellow resin and agitating the mixture at 160.degree. C. till phthalic anhydride was dissolved, to obtain a saturated polyester (D) (221.7 g) having an acid value of 5.0 KOH mg/g, a number average molecular weight of 12,300 and a weight average molecular weight of 26,500.

(5) Preparation of saturated polyester(E):

Into the same preparation flask as in item (2) were fed adipic acid (189.8 g, 1.3 mol), ethylene glycol (72.54 g, 1.17 mol), propylene glycol (19.76 g, 0.26 mol), 2-ethyl-1,3-hexanediol (9.49 g, 0.065 mol), 2,2,4-trimethyl-1,3-pentanediol (9.49 g, 0.065 mol), zinc oxide (0.3 g) and triphenyl phosphite (0.3 g), followed by elevating the temperature inside the flask up to 250.degree. C. over about 4 hours, while distilling off the condensed water at a temperature of 105.degree. C. or lower at the top of the fractionating tube, thereafter carrying out reaction for about 7 hours, while keeping the reaction temperature of 250.degree. C., removing the fractionating tube, carrying out reaction for about 6 hours under a reduced pressure of 8.0.times.10 Pa to obtain a pale yellow resin, adding phthalic anhydride (1.89 g) to the pale yellow resin, and agitating the mixture at 160.degree. C. till phthalic anhydride was dissolved, to obtain a saturated polyester (E) (225.4 g) having an acid value of 4.1 KOH mg/g, a number average molecular weight of 10,200 and a weight average molecular weight of 21,400.

(6) Preparation of saturated polyester (F):

The above item (2) was repeated except that adipic acid (122.64 g, 0.84 mol), sebacic acid (84,84 g, 0.42 mol), ethylene glycol (49.48 g, 0.798 mol), propylene glycol (41.50 g, 0.546 mol), 2-ethyl-1,3-hexanediol (12.26 g, 0.084 mol), zinc oxide (0.3 g) and triphenyl phosphite (0.3 g), to obtain a saturated polyester (F) (221.7 g) having an acid value of 4.5 KOH mg/g, a number average molecular weight of 8,500 and a weight average molecular weight of 18,700.

The compositions of the saturated polyesters (A) to (F) prepared and the resin properties thereof are shown in Table 1.

(7) Preparations of saturated polyester (G) to (L) to be used in Comparative examples:

Saturated polyesters (G) to (L) having resin properties shown in Table 2 were prepared in the same manner as the above, in proportions of components fed, shown in Table 2.

With the respective saturated polyesters (A) to (L) (each 15 parts by weight) were blended an unsaturated polyester (Polyset, tradename of product made by Hitachi Chemical Company) (35 parts by weight), styrene (50 parts by weight), a filler (CaCO.sub.3, slite 1200, tradename of product made by Nitto Funka Kogyo K,K.) (200 parts by weight), a polymerization initiator (t-butylperoxy-benzoate (1.5 parts by weight) and a release agent (zinc steatate) (2.5 parts by weight), to prepare unsaturated resin compositions A to L.

With the respective compositions A to L was blended MgO as a thickener in a quantity of 1.2% by weight based upon the weight of the respective unsaturated polyesters, followed by agitating and feeding the resulting respective materials to an apparatus for producing a sheet-form molding material shown in FIG. 1, to obtain sheet-form molding materials containing glass fibers of 25% by weight.

The resulting sheet-form molding materials were cut to a definite size and compression-molded by means of a mold heated to 150.degree. C. under a molding pressure of 100 kgf/cm.sup.2, to obtain fiber-reinforced plastic molded products.

The respective surface qualities of the resulting flat sheet molded products were evaluated with the area of 10.times.10 inch of samples of the flat sheet molded products, by means of a surface smoothness-measuring machine (Rolia, tradename of product made by Ashland Company, U.S.A.). The surface quality was evaluated with the surface smoothness (Index Number value: IN value) and distinctness of image (DOI value). The IN value shows that the smaller its numeral value, the better the surface smoothness, and the DOI value shows that the lager its value, the better the distinctness of image.

The results are shown in Table 3.

As seen from Table 3, the fiber-reinforced plastic molded products molded from the sheet-form molding materials obtained using the unsaturated polyester resin compositions A to F according to the present invention each have a small IN value and a large DOI value, that is, a superior surface smoothness and a superior distinctness of image.

(8) Preparation of saturated polyester (M-1):

Into a 500 ml preparation flask provided with a stirrer, a thermometer, a nitrogen gas-introducing tube and a McMahon packing type fractionating tube, were fed adipic acid (189.8 g, 1.3 mol), ethylene glycol (72.54 g, 1.17 mol), porpylene glycol (19.76 g, 0.26 mol), 2-ethyl-1,3-hexanediol (18.98 g, 0.13 mol), zinc oxide (0.3 g) and triphenyl phosphite (0.3 g), followed by elevating the temperature inside the flask up to 250.degree. C. over about 5 hours, while distilling off the condensed water at a temperature of 105.degree. C. or lower at the top of the fractionating tube, thereafter carrying out reaction for about 5 hours, while keeping the reaction temperature of 250.degree. C., then removing the fractionating tube, and carrying out reaction for about 7 hours under a reduced pressure of 2.5.times.10.sup.2 Pa, to obtain a saturated polyester (M-1) (226.2 g) having an acid value of 3.8 KOH mg/g. The molecular weight of this saturated polyester (M1) was sought using a gel permeation chromatography and converted as a standard polystylene, to give a number average molecular weight of 14,100 and a weight average molecular weight of 29,200.

(9) Preparation of saturated polyesters (M-2) to (M-4):

The above item (1) was repeated except that proportions of components fed, shown in Table 3 were used. The acid values, the number average molecular weights and the height average molecular weights of the resulting saturated polyesters are shown in Table 4.

Using the above obtained saturated polyesters (M-1) to (M-4), each as a low shrinking agent, and in the blending proportions shown in Table 5, the respective unsaturated polyester resin compositions were prepared. MgO as a thickener was blended with the resulting compositions so as to give 1.2 part by weight based upon 100 parts by weight of the unsaturated polyesters, followed by agitating and feeding the mixture to the apparatus for producing a sheet-form molding material, shown in FIG. 1, to obtain sheet-form molding material containing glass fibers of 25% by weight.

The resulting sheet-form molding materials were cut to a definite size and compression-molded under a molding pressure of 100 kgf/cm.sup.2, by means of a mold heated to 150.degree. C., to obtain fiber-reinforced plastic molded products.

Example 7 was repeated except that polyvinyl acetate (Gosenyl NZ-5, trademark of product made by Nippon Gosei Kagaku Kogyo K.K. Ltd, molecular weight: 34,000) was used, to obtain a fiber-reinforced plastic molded product.

The surface quality of the resulting flat sheet molded products was evaluated in the same manner as above, using a surface smoothness-measuring machine (Rolia, tradename of product made by Ashland Company, U.S.A.) and with the area of 10.times.10 inch of flat sheet molded products as sample.

Father, the hardness was measured using a hardness meter (Barcol hardness meter, tradename of product made by Rockford Company), according to JIS K 6911. The results are shown in Table 6.

As seen from Table 6, in Example 7 to 9 containing saturated polyesters (M-1) to (M-3), IN value is small, and DOI value is large, that is, the surface smoothness and the distinctness of image are superior.

According to the unsaturated resin composition of the present invention, the curing shrinkage factor at the time of curing is so small that it is possible to obtain a fiber-reinforced plastic molded product having a superior surface quality and hardness by using the sheet-form molding material obtained by using the composition.