WO2008140196A1

WO2008140196A1 - Polyamide resin composition and moldings

Info

Publication number: WO2008140196A1
Application number: PCT/KR2008/002443
Authority: WO
Inventors: Eun-Ha Park; Ji-Hyuk Park
Original assignee: Kolon Industries, Inc.
Priority date: 2007-05-14
Filing date: 2008-04-30
Publication date: 2008-11-20
Also published as: KR20080100730A; KR101299068B1

Abstract

The present invention relates to a glass fiber reinforced polyamide resin composition. More concretely, the polyamide resin composition includes a polyamide resin, glass fiber, an acid modified polyolefin, an acid modified rubber elastomer, which has an impact strength of at least 8 kg -cm/ cm according to the assessment of ASTM D256, a flexural modulus of elasticity of at least 40,000 kg/ cm2 according to the assessment of ASTM D790, a shrinkage variation of at least 130%, and a heat deflection temperature of at least 180 °C according to the assessment of ASTM D648. Because the polyamide resin composition is optimized in impact strength, flexural modulus of elasticity, and heat deflection temperature, the moldings prepared from the polyamide resin composition have a superior mechanical strength, which is greatly improved in dimensional stability caused by a shrinkage variation according to flow direction in the process of molding. Also, titie moldings have a superior flow index, so that it is improved in the surface defect of the same and is preferably used for an internal component such as a door frame inner cover.

Description

TITLE OF THE INVENTION

POLYAMIDE RESIN COMPOSITION AND MOLDINGS

CROSS REFERENCES TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0046779 filed in the Korean Industrial Property Office on May 14, 2007, which is hereby incorporated by reference for all purpose as if fully set forth herein.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a polyamide resin composition reinforced with a glass fiber, and polyamide resin moldings including the same.

(b) Description of the Related Art

Recently, with the development of the automobile industries, research for substituting electric/ electronic components with plastics has been actively proceeded, and polyamide resin is considered as an important material for the research. Particularly, it is known that polyamide resin is good as a substitute for aluminum or steel in an automobile. Although it has not yet been applied to a door frame inner cover among the internal components of the automobile, there are proceeding a lot of researches for applying the material to various kinds of cars because polyamide resin has a good mechanical strength, molding property, and long-life property.

To improve the defects of polyamide resin as a material for automobiles and to provide high performance polyamide resin, it has been required to improve rigidity stiffness, impact resistance, and shrinkage aeolotropy that occur by the difference of the molding shrinkage ratios according to flow direction in a molding process. Especially, for components of recent automobiles, it has been developed to substitute steel or aluminum material in a module system rather than in a single component. Therefore, it is necessary to acquire technical components for the wide, long, and big molding applications of an automobile. In order to satisfy the necessary components, it has been required to improve the rigidity stiffness, impact resistance, molding shrinkage, and shrinkage aeolotropy of polyamide resin.

To provide high performance polyamide resin, there is a process to prepare a novel resin by polymerization of the polyamide resin or alloying with another polymer, which is well known. Also, according to the application for the resin, it has been known that high performance polyamide resin is prepared by reinforcing with glass fiber in the manner of fusion extruder mixing.

However, it needs a lot of time and expense to prepare a novel polyamide by polymerization, and then it is well suggested to alloy the polyamide resin with another polymer. The alloy may be processed with a general plastic, an acid modified elastomer, or an engineering plastic. Polypropylene, polystyrene, an olefin based elastomer, etc., may be used as the polymer for the alloy, which is not compatible with the polyamide, and then it can be used through a compatibility process to prepare a functional polyamide. Also, in the case of a polyamide resin reinforced with an inorganic filler, an addition of glass fiber or mineral as the inorganic filler can improve the rigid stiffness, heat resistance, and molding shrinkage, which has been well known and applied in a wide area. For the representative technology in this area, it has been suggested that the addition of an inorganic filler after alloying with another polymer improves heat resistance and dimensional stability. Particularly, there are mentioned that the inorganic filler is reinforced after adding a polyolefin elastomer, which is disclosed in US Patent No. 5,206,284 and EP Patent No. 1 312 647. In the publications, it is disclosed to improve the functional property for a defect of an impact resistance caused by reinforcing the inorganic filler.

However, according to the disclosures of US Patent No. 5,206,284 and EP Patent No. 1 312 647, there is a problem of deteriorating heat resistance and making a surface defect in a molding process, and then it is difficult and limited in its usage. In particular, an addition of glass fiber alone deteriorates dimensional stability and impact resistance, and then it is limited to apply as a component of an automobile.

Alternatively, there is disclosed in EP Patent No. 0 177 998 that a coupling agent can be further added together with an inorganic filler to enhance an adhesive with the polyamide resin. It is described that the reinforcement of the inorganic filler promotes improvement of strength and a surface defect in the molding process. However, there is a problem that the addition of a coupling agent deteriorates weather resistance and long-term heat resistance, and increases the expense for the process. As disclosed above, there has been known that polyamide resin alone or an alloy with another polymer can be used together with reinforcement of an inorganic filler and addition of a coupling agent or an elastomer, etc., in order to improve the properties and solve the defects. In particular, they are mainly related to adding of another polymer or additive rather than reinforcing the inorganic filler.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a polyamide resin composition having superior mechanical strength and dimensional stability. It is another aspect of the present invention to provide a polyamide resin moldings prepared from the same.

Hence, the present invention provides a polyamide resin composition having an impact strength of at least 8 kg" cm/ cm according to the assessment of ASTM D256, a flexural modulus of elasticity of at least 40,000 kg/ cm² according to the assessment of ASTM D790, a shrinkage variation of at least 130% according to the following Equation 1, and a heat deflection temperature of at least 180 ^°C according to the assessment of ASTM D648: [Equation 1]

„, . , . . rectangular direction shrinkage ratio _{1 ΛΛ /n/x} Shrinkage variation = x 100 (%) . flow direction shrinkage ratio

The present invention also provides a polyamide resin composition comprising (a) 50 to 80 wt% of polyamide resin, (b) 10 to 30 wt% of glass fiber, (c) 5 to 20 wt% of acid modified polyolefin which is grafted with 5 to 15 weight parts of functional dicarboxylic acid or its anhydride, and 2 to 8 weight parts of organic peroxide on the basis of 100 weight parts of the polyolefin resin, and (d) 3 to 10 wt% of acid modified rubber elastomer that is grafted with 0.4 to 3 weight parts of α,β-unsaturated carbonic acid on the basis of 100 weight parts of the rubber elastomer.

The present invention also provides a polyamide resin moldingsincluding the polyamide resin composition.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the present invention is explained in more detail.

The present inventors found the fact that the polyamide resin composition that is optimized for impact strength, flexural modulus of elasticity, and heat deflection temperature is good in mechanical strength, dimensional stability, and appearance without surface defects, and accomplished the present invention.

It is well known that a polyamide resin can be reinforced with an inorganic substance effectively. Thus, the method for reinforcing with an inorganic material is well known in various technical areas. In general, the polyamide resin composition prepared by reinforcing with an inorganic material is applied to preparing the components of an automobile. The present invention also relates to the technical area for reinforcing with the inorganic material. Especially, in view of solving the problems of the related art, the present invention is developed in conformity to the demanded characteristics for the technical area. The present invention is novel and improved in the area for reinforcing with the inorganic material, and can be used broadly and commercially.

The present invention provides the polyamide resin composition including an inorganic material, especially, glass fiber, based to the polyamide resin, which is to solve the technical problem and the application problem in the related arts. Also, the present invention provides the polyamide resin composition that can produce the moldings with a good performance in an economically low-priced method.

The polyamide resin composition of the present invention preferably has high flexural modulus of elasticity, impact strength, and heat deflection temperature, and preferably a low shrinkage variation. Particularly, the present invention provides the polyamide resin composition having an impact strength of at least 8 kg¹ cm/ cm according to the assessment of ASTM

(American Society for Testing Materials) D256, a flexural modulus of elasticity of at least 40,000 kg/ cm² according to the assessment of ASTM D790, a shrinkage variation of at least 130% according to the following Equation 1, and a heat deflection temperature of at least 180 ^°C according to the assessment of

ASTM D648.

[Equation 1]

_, . , . . rectangular direction shrinkage ratio , ._ ,_ ..

Shrinkage variation = x 100 (%) . flow direction shrinkage ratio If the flexural modulus of elasticity, the impact strength, the heat deflection temperature, and the shrinkage variation of the polyamide composition is beyond the specific contents range, the final moldings are deteriorated in mechanical strength such as rigidity stiffness, impact resistance, and heat resistance. Also, in that case, deflection and deformation of the moldings may occur because of a flow defect and the problem of the molding process.

More particularly, the present inventors found the fact that based on the polyamide resin, a glass fiber as an inorganic material can be added to improve stiffness, deflection, and deformation, a thermoplastic rubber elastomer can be added to improve the impact strength, and an acid modified polyolefin prepared by fusion-grafting can be further added in order to minimize flow defects, improve the appearance of the moldings, assure the dimensional stability without deflection and deformation caused by shrinkage aeolotropy, and accomplished the present invention.

Especially, the present invention is characterized with maintaining the merits of the polyamide resin, i.e., toughness and heat resistance, superior additive effect, and chemical resistance, additionally acquiring rigidity stiffness, heat resistance, and dimensional stability by reinforcing with glass fiber, assuring impact resistance by adding the acid modified rubber elastomer, and solving the flow defects and further acquiring dimensional stability by using the acid modified polyolefin. Also, the present invention can achieve the technical objects to assure the surface characteristics and dimensional stability as the important characteristics for applying as an internal component.

For an illustration of the present invention, the polyamide resin composition of the present invention can be used for the wide, long, and big molding application of an automobile, and the present invention can also provide a resin suitable for a door frame inner cover. Also, the present invention can be used suitably for an automobile engine component such as intercooler air duct, timing belt cover, and engine cover, or for a roof rack, etc. More preferably, the polyamide resin composition of the present invention can be used preferably for the door frame inner cover in view of the technical application characteristics. In particular, the present inventors found the fact that it is difficult to achieve the technical objects of the present invention as stated above and that there are a lot of limitations to becoming thinner and bigger in molding for preparing a commercial product. Thus, in order to accomplish the purpose as said above, the present inventors provide the present invention where the polyamide resin is combined with a rubber elastomer and a modified polyolefin having a chemical functional group to improve a flexural modulus of elasticity classified into rigidity stiffness, an impact strength classified into impact resistance, and difference between shrinkage of rectangular direction and shrinkage of flow direction

The present invention uses nylon 6, nylon 66, or their mixture as the polyamide resin, which is not specifically limited. The number average molecular weights of nylon 6 and nylon 66 are preferably from 200 to 15,000 in view of the superior heat resistance and impact resistance of the final resin composition.

In the preferred illustration, polyamide resin such as nylon 6 and nylon 66 may be used in the range from 50 to 80 wt%, more preferably from 52 to 77 wt% in the overall composition. If the polyamide resin is below 50 wt%, the molding characteristics may be deteriorated and a shrinkage aeolotropy may become larger. Also, if the polyamide resin is more than 80 wt%, the impact resistance and the heat resistance may become lower, because of the lower contents of the other ingredients.

Also, the polyamide resin of the present invention may be formed in a chip and dried sufficiently in a dehumidifier. The polyamide resin of the present invention may have from 2.5 to 3.5 of relative viscosity, which is measured at 20 °C in the solution having Ig of polymer in 100 mL of sulfonic acid (96%), and it is not specifically limited. If the relative viscosity of the polyamide resin is blow 2.5, the rigidity stiffness and impact strength may be deteriorated. If the relative viscosity of the poly amide resin is more than 3.5, the added inorganic material may be exposed on the surface caused by the flow defects and the molding from the composition may be difficult.

Meanwhile, a glass fiber of the polyamide resin of the present invention may be used which is well-known in this technical area, and it is not specifically limited. Typically, a glass fiber formed as a chop may be used, which is called as "G" or "K" glass. The glass fiber may have CaO-SiO₂-Al₂Os as a main ingredient, which is comprised of 10 to20 wt% of CaO, 50 to 70 wt% of SiO₂, 2 to 15 wt% of AI2O3. Also, the surface of the glass fiber may be treated with a coupling of silane in order to improve the interfacial adhesive property of the final composition. Especially, the glass fiber of the present invention may have from 10 to 13 μm average diameter, and from 3 to 6 mm average length. Also, the glass fiber of the present invention can be used in the range from 10 to 30 wt%, and more preferably from 12 to 25 wt% in the overall composition. If the glass fiber is below 10 wt%, a flexural modulus of elasticity may be deteriorated. Also, if the glass fiber is more than 30 wt%, the improvement for a shrinkage aeolotropy cannot be enough.

In the polyamide composition of the present invention, an acid modified polyolefin can be used to further improve a good flow, a good surface appearance, and a good shrinkage aeolotropy. In particular, the polyolefin may be a copolymer that is fusion-grafted with 5 to 15 weight parts of reactive dicarboxylic acid or its anhydride, and 2 to 8 weight parts of organic peroxide on the basis of 100 weight parts of polyolefin resin.

In general, the polyolefin is a hydrocarbon with a large molecular weight, as compared with an inexpensive price, and so it has good mechanical, optical, and chemical properties and it is sufficiently easy for molding to apply to a wide area. However, the typical polyolefin is a fully nonpolar material so that it is difficult to have affinity with another polymer and compatibility with a pigment, filler, etc. Especially, it is difficult to blend with another polymer. Therefore, for making up the defects of the polyolefin, a polyolefin such as polypropylene, polyethylene, etc., in the present invention is modified chemically to improve the thermal stability, the hygroscopic property, stainability, antistatic property, and adhesive property. For the modification of the polyolefin, dicarboxylic acid or its anhydrides, acrylic acid or its derivatives, etc., rrmy be used, and a graft copolymerization may be used.

In the polyolefin of the present invention, the reactive dicarboxylic acid or its anhydride may be at least one selected from the group consisting of maleinic acid, phthalic acid, itaconic acid, citraconic acid, alkenyl succinic acid, cis-l,2,3,6-tetrahydrophthalic acid, 4-methyl-l,2,3,6-tetrahydrophthalic acid, and their anhydrides. The organic peroxide of the present invention may be at least one selected from the group consisting of benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl -2,5-di(t-butyloxy)hexyne-3, di-t-butylperoxide, l,3-bis(t- butylperoxy-isopropyl) benzene, di-t-butylperoxyagellate, 2,5-dimethyl-2,5-di(t- butylperoxy)hexane, t-butyl cumylperoxide, t-butylperoxy -3,5,5- trimethylhexoate, p-chlorobenzoylperoxide, t-butyloxybenzoate, metylethylketoneper oxide, tris(t-butylperoxy)triazine, t-butylperoxyacetate, and t-butylperoxy isoprocarbonate. Also, the acid modified polyolefin of the present invention may be grafted with maleinic acid or its anhydride as the functional dicarboxylic acid or its anhydride and benzoyl peroxide as the organic peroxide.

The acid modified polyolefin of the present invention may be prepared with a common process for a grafted copolymer, which is well known in this area, and it may be prepared in solution, fusion, or solid phase. In an illustration of the present invention, the polyolefin resin of the present invention may be polypropylene resin (flow index 10 g/10 min, ASTM Dl 238) as a base resin, which is grafted with maleinic acid, phthalic acid, itaconic acid, citraconic acid, alkenyl succinic acid, cis-l,2,3,6-tetrahydrophthalic acid, 4-methyl-l,2,3,6-tetrahydrophthalic acid, their anhydrides, etc., classified into a radical reactive dicar boxy lie acid or its anhydride. In the present invention, maleinic acid may be preferably used. In the poly olefin resin of the present invention, the dicarboxylic acid or its anhydride may be used in the range from 5 to 15 weight parts based on 100 weight parts of polyolefin resin. If the dicarboxylic acid or its anhydride is below 5 weight parts, the efficiency of the grafting may be deteriorated. Also, if the dicarboxylic acid or its anhydride is more than 15 weight parts, unreacted material may remain.

Also, a radical initiator may be used for efficiency of the reaction. The organic peroxide may be used as the radical initiator, and for example, benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl -2,5-di(t-butyloxy)hexyne-3, di-t- butylperoxide, l,3-bis(t-butylperoxy-isopropyl) benzene, di-t- butylperoxyagellate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl cumylperoxide, t-butylperoxy-3,5,5-trimethylhexoate, p-chlorobenzoylperoxide, t-butyloxybenzoate, metylethylketoneperoxide, tris(t-butylperoxy)triazine, t- butylperoxyacetate, t-butylperoxy isoprocarbonate, etc., may be used. In the present invention, the organic peroxide may be used in the range from 2 to 8 weight parts based on 100 weight parts of polyolefin resin. If the organic peroxide is below 2 weight parts, the performance of the radical initiator efficiency may be deteriorated. Also, if the organic peroxide is more than 8 weight parts, a problem that the grafting ratio is rather deteriorated may occur. The acid modified polyolefin of the present invention may be prepared by using a common fusion extruder.

The acid modified polyolefin of the present invention may be used in the range from 5 to 20 wt%, and more preferably from 7 to 17 wt% in the overall composition. If the acid modified polyolefin is below 5 wt%, the flowing of the resin may be deteriorated. Also, if the acid modified polyolefin is more than 20 wt%, it is not preferred since the rigid stiffness and the heat resistance may become lower.

Meanwhile, an acid modified rubber elastomer of the present invention may be added as a modifier for impact resistance and water resistance. The acid modified rubber elastomer includes a rubber elastomer prepared from at least one unsaturated monomer selected from the group consisting of α-olefins, acrylic acid and its derivatives, aromatic vinyl monomer, cyanized vinyl monomer, and a diene based monomer, and the rubber elastomer is grafted with α,β-unsaturated carbonic acid. Particularly, the rubber elastomer may be prepared from a random or block copolymer of the aromatic vinyl monomer and a cyanized vinyl monomer.

The α,β-unsaturated carbonic acid includes ethylene, propylene, butylenes, 1-pentene, isobutylene, isoprene, 1-hexene, 1,2-hexadiene, 1-heptene, etc., and vinyl ester of saturated carbonic acids such as vinyl acetate, propionate, etc.

The acylic acid or its derivates includes metacrylate, methylacrylate, buthylacrylate, glycidylacrylate, ethylmethacrylated, 2-ethylhexylmethacrylate, hy dry lethylmethacry late, aminomethacrylate, and glycidylmethacrylate, and meleimide compound such as N-phenylmeleimide, N-methylmaleimide, N- cyclohexylmeleimide, etc.

The aromatic vinyl monomer may be styrene, α-methylstyrene, o- methylstyrene, p-methylstyrene, tetrabuthylstyrene, dimethylstyrene, chlorostyrene, dichlorostyrene, vinylnaphtalene, etc.

The cyanized vinyl monomer may be acrylonitrile, metacrylonitrile, fumaronitrile, etc.

The diene based monomer may be butadiene, 1,3-cyclohexadiene, 1,4- cyclohexadiene, cyclopentadiene, or 2,4-hexadiene. Also, α,β-unsaturated carbonic acid or α,β-unsaturated anhydride and their derivates, which is grafted, may include a functional group that is superior to be reacted with the amino group. It may be at least one selected from the group consisting of maleic acid, itaconic acid, citraconic acid, acrylic acid, methacrylic acid, allyl succinic acid, 2-dicarbonic acid, maleinic acid, fumalic acid, their anhydrides, and their derivates. More concretely, anhydrous maleic acid, anhydrous itaconic acid, anhydrous citraconic acid, acrylic acid, methacrylic acid, allyl succinic acid, 2-dicarbonic acid, maleinic acid, fumaric acid, maleinic diethyl, maleinic dimethyl, maleinic anhydride, itaconic anhydride, citraconic anhydride, allyl succinic anhydride, or 4-methyl-4- cyclohexene-1.

Especially, the acid modified rubber elastomer of the present invention may include a rubber elastomer grafted with α,β-unsaturated carbonic acid or α,β-unsaturated anhydride, and the rubber elastomer may be ethylene-octene copolymer, styrene ethylene butadiene styrene (SEBS) copolymer, styrene butadiene styrene (SBS) copolymer, metacrylate butadiene styrene (MBS) copolymer, or ethylene ethyl aery late. In the acid modified rubber elastomer, the α,β-unsaturated carbonic acid or α,β-unsaturated anhydride may be used in the range from 0.4 to 3 weight parts based on 100 weight parts of rubber elastomer. If α,β-unsaturated carbonic acid or α,β-unsaturated anhydride is below 0.4 weight parts, the compatibility with a polyamide resin may be deteriorated. Also, if α,β-unsaturated carbonic acid or α,β-unsaturated anhydride is more than 3 weight parts, an increase of the viscosity may occur to make mixing difficult. The acid modified rubber elastomer of the present invention may be prepared in the state of a solution or the fused olefins in the presence of the peroxide, which is well known in this area.

The acid modified rubber elastomer of the present invention may be used in the range from 3 to 10 wt%, and more preferably from 4 to 9 wt% in the overall composition. If the acid modified rubber elastomer is below 3 wt%, impact strength may be deteriorated. Also, if the acid modified polyolefin is more than 10 wt%, it is not preferred since the rigid stiffness and the heat resistance may become lower and the shrinkage aeolotropy may become larger to give an appearance defect. Additionally, the present invention provides polyamide resin moldings including a resin substrate containing a fusion of (a) a polyamide resin, (b) an acid modified polyolefin grafted with functional dicarboxylic acid or its anhydride and organic peroxide, and (c) an acid modified rubber elastomer grafted with α,β-unsaturated carbonic acid; and a glass fiber is dispersed in the resin substrate. The polyamide resin moldings may be used for a door frame inner cover, an intercooler air duct, a timing belt cover, an engine cover, or a roof rack.

Hereinafter, the technical features and effects are presented through preferable examples and comparative examples for understanding the present invention. However, the following examples are only for illustrating the present invention and the present invention is not limited to or by them.

Examples

The inorganic reinforced polyamide resin composition of the present invention was prepared by using a twin screw extruder, of which the cylinder barrel was adjusted to the range from 275 ^°C to 285 °C (from 275 ^°C to 285 °C in the case of nylon 6). The twin screw extruder was equipped with three inlets, in order to maximize the physical property of the resin composition. Polyamide resin and acid modified polyolefin was input through the first inlet, acid modified rubber elastomer was input through the second inlet, and glass fiber was input through the third inlet. Preferably, the third inlet was mounted closely to the outlet of the extruder, so as to minimize the destruction of glass fiber caused by shear of the screw in the extruder. In the melting extrusion process, in order to maximize the physical property of the resin composition, job flow time was adjusted as shortly as possible and a pressure reducing device was mounted near to the third inlet and the oulet, which was called Vent. The process was effectively performed in the range of 150 mmHg, by using the pressure reducing device.

Examples 1 to 14 and Comparative Examples 1 to 14 of the present invention were performed as follows. The physical properties of the polyamide resin composition of Examples 1 to 14 and Comparative Examples 1 to 14 were measured according to the following assessment standards.

* Flexural modulus of elasticity: according to ASTM D790, a sample of 1/8 inch was prepared and a flexural modulus of elasticity thereof was measured. Then, it was determined as defective in a case below 40,000 kg/ cm². * Impact strength: according to ASTM D256, a sample of 1/4 inch was prepared and the Izod notched impact strength thereof was measured at ambient temperature. Then, it was determined as defective in a case below 8 kg -cm/ cm.

* Shrinkage variation: according to ASTM D995, a disc sample having 100 mm of diameter was prepared and was placed under the condition of 50% of specific humidity for 45 hours. Then, the molding shrinkage ratios of rectangular direction and flow direction thereof, which were centered on a gate of the extruder were measured, respectively, and shrinkage variation was assessed according to the following Equation 1. It was determined as defective in a case over 130%. [Equation 1]

_,. . . . . rectangular direction shrinkage ratio _{1 ΛΛ /n/ N}

Shrinkage variation = x 100 (%) . flow direction shrinkage ratio

* Heat deflection temperature: according to the assessment of ASTM D648, a sample of 1/4 inch was prepared and heat deflection temperature thereof was measured. Then, it was determined as defective in a case below 180 ^°C under the condition of 4.6 kg/ cm² of the load.

Examples 1 to 14 As described in the following Table 1, the ingredients were heated to 280 °C (250 ^°C in the case of nylon 6) and fused by using a twin screw extruder to form chips. The chips were dried by using a dehumidifier at 90 ^°C for 5 hr. Then, the dried chips were proceeded to prepare a sample by using a twin screw extruder in conditions the same as for the melting extrusion process, respectively.

Particularly, the acid modified polyolefins were prepared from polyolefin, dicarboxylic acid, and organic peroxide, as described in the following Table 1. The ingredients of polyolefin, dicarboxylic acid, and organic peroxide were processed under the condition below 150 mmHg by using a twin screw extruder having at least 5 zones for changing the temperature thereof. The first zone was adjusted to 180 ^°C, the other zones were adjusted to 200 "C, and the last zone was adjusted to 205 "C . In this process, the revolution per minute of the screw was 150 rpm. Then, the acid modified polyolefins were formed in chips and dried at 80 ^°C for 4 hr.

The samples prepared as the above were proceeded in the assessments of the physical properties thereof, as described above, and the results of the assessments are disclosed in the following Table 2.

[Table 1]

*Glass fiber: Trademark CS311 made by Kumkang Chemicals Ind.

*APO 1: grafted copolymer of maleinic acid 7 weight parts, benzoyl peroxide 3 weight parts, and polypropylene 100 weight parts

*APO 2: grafted copolymer of alkenyl succinic acid 10 weight parts, benzoyl peroxide 3 weight parts, and polypropylene 100 weight parts

*APO 3: grafted copolymer of cis-l,2,3,6-tetrahydrophthalic acid 13 weight parts, di-t-butyl peroxide 7 weight parts, and polypropylene 100 weight parts

*APO 4: grafted copolymer of itaconic acid 10 weight parts, p-chlorobenzoyl peroxide 5 weight parts, and polypropylene 100 weight parts

*APO 5: grafted copolymer of maleinic acid 13 weight parts, di-t-butyl peroxide

7 weight parts, and polypropylene 100 weight parts

*TPE 1: grafted copolymer of maleinic anhydride 1 weight parts and ethylene- octene rubber elastomer 100 weight parts

*TPE 2: grafted copolymer of maleinic anhydride 2 weight parts and ethylene- octene rubber elastomer 100 weight parts

Comparative Examples 1 to 14

The samples were prepared substantially according to the same method as in Examples 1 to 14, except that the compositions of ingredients were used as described in the following Table 3. The assessments of the physical properties thereof, as described above, and the results of the assessments are disclosed in the following Table 4.

[Table 3]

*Glass fiber: Trademark CS311 made by Kumkang Chemicals Ind. *APO 1: grafted copolymer of maleinic acid 7 weight parts, benzoyl peroxide 3 weight parts, and polypropylene 100 weight parts

*APO 2: grafted copolymer of alkenyl succinic acid 10 weight parts, benzoyl peroxide 3 weight parts, and polypropylene 100 weight parts *APO 3: grafted copolymer of cis-l,2,3,6-tetrahydrophthalic acid 13 weight parts, di-t-butyl peroxide 7 weight parts, and polypropylene 100 weight parts

*APO 5: grafted copolymer of maleinic acid 13 weight parts, di-t-butyl peroxide 7 weight parts, and polypropylene 100 weight parts

*APO 6: grafted copolymer of maleinic acid 4 weight parts, benzoyl peroxide 7 weight parts, and polypropylene 100 weight parts

*APO 7: grafted copolymer of itaconic acid 18 weight parts, di-t-butyl peroxide

7 weight parts, and polypropylene 100 weight parts *APO 8: grafted copolymer of maleinic acid 10 weight parts, benzoyl peroxide

1.5 weight parts, and polypropylene 100 weight parts

*APO 9: grafted copolymer of cis-l,2,3,6-tetrahydrophthalic acid 10 weight parts, benzoyl peroxide 10 weight parts, and polypropylene 100 weight parts

*APO 10: grafted copolymer of acrylic acid 7 weight parts, benzoyl peroxide 3 weight parts, and polypropylene 100 weight parts

*APO 11: grafted copolymer of acrylic acid 3 weight parts and polypropylene

100 weight parts

*TPE 1: grafted copolymer of maleinic anhydride 1 weight parts and ethylene- octene rubber elastomer 100 weight parts *TPE 2: grafted copolymer of maleinic anhydride 2 weight parts and ethylene- octene rubber elastomer 100 weight parts

* TPE 3: grafted copolymer of maleinic anhydride 0.3 weight parts and ethylene-octene rubber elastomer 100 weight parts

* TPE 4: grafted copolymer of maleinic anhydride 5 weight parts and ethylene- octene rubber elastomer 100 weight parts

[Table 4]

In view of the results of the measurements, the samples of Examples 1 to 14 have superior properties such as good flexural modulus of elasticity, impact strength, shrinkage variation, and heat deflection temperature, simultaneously, in comparison with the samples of Comparative Examples 1 and 2, as listed in the above Tables 1 to 4.

As apparent from the above description, because the polyamide resin composition of the present invention includes a polyamide resin, glass fiber, an acid modified poly olefin, and an acid modified rubber elastomer in a specific composition ratio, it has a superior mechanical strength and a greatly improved dimensional stability that is caused by a shrinkage variation according to flow direction in the process of molding. Also, the polyamide resin composition has a superior flow index to minimize a flow defect thereof and then to improve the good appearance of the moldings prepared thereof. It has a superior dimensional stability without deflection, deformation, etc., which is caused by a shrinkage aeolotropy.

The moldings that are prepared from the polyamide resin composition of the present invention are light in weight and have a low-priced manufacturing process. Also, the moldings have good stiffness, impact resistance, and heat resistance, simultaneously with a good appearance without deflection, deformation, etc., and can be preferably used for an internal component such as a door frame inner cover. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A poly amide resin composition having an impact strength of at least 8 kg cm/ cm according to the assessment of ASTM D256, a flexural modulus of elasticity of at least 40,000 kg/ cm² according to the assessment of ASTM D790, a shrinkage variation of at least 130% according to the following Equation 1, and a heat deflection temperature of at least 180 °C according to the assessment of ASTM D648:

[Equation 1]

„ . . rectangular direction shrinkage ratio , „„ ,„,.

Shrinkage variation = x 100 (%) flow direction shrinkage ratio

2. The polyamide resin composition according to Claim 1, which comprises:

(a) 50 to 80 wt% of polyamide resin;

(b) 5 to 20 wt% of acid modified polyolefin that is grafted with 5 to 15 weight parts of reactive dicarboxylic acid or its anhydride, and 2 to 8 weight parts of organic peroxide on the basis of 100 weight parts of the polyolefin resin; (c) 3 to 10 wt% of acid modified rubber elastomer that is grafted with 0.4 to 3 weight parts of α,β-unsaturated carbonic acid in the basis of 100 weight parts of the rubber elastomer; and (d) 10 to 30 wt% of glass fiber.

3. The polyamide resin composition according to Claim 2, wherein the polyamide resin has from 2.5 to 3.5 of relative viscosity.

4. The polyamide resin composition according to Claim 2, wherein the polyamide resin is nylon 6, nylon 66, or their mixture.

5. The polyamide resin composition according to Claim 2, wherein the glass fiber has from 3 to 6 mm average length and from 10 to 13 μm average diameter.

6. The polyamide resin composition according to Claim 2, wherein: the reactive dicarboxylic acid or its anhydride is at least one selected from the group consisting of maleinic acid, phthalic acid, itaconic acid, citraconic acid, alkeny] succinic acid, cis-l,2,3,6-tetrahydrophthalic acid, and their anhydrides; and the organic peroxide is at least one selected from the group consisting of benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl -2,5-di(t-butyloxy)hexyne-3, di-t-butylperoxide, l,3-bis(t-butylperoxy-isopropyl) benzene, di-t- butylperoxyagellate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl cumylperoxide, t-butylperoxy -3,5,5-trimethylhexoate, p-chlorobenzoylperoxide, t-butyloxybenzoate, metylethylketoneperoxide, tr is (t-butylperoxy) triazine, t- butylperoxy acetate, and t-butylperoxy isoprocarbonate.

7. The polyamide resin composition according to Claim 2, wherein the acid modified rubber elastomer comprises a rubber elastomer prepared from at least one unsaturated monomer selected from the group consisting of α-olefins, acrylic acid and its derivatives, an aromatic vinyl monomer, a cyanized vinyl monomer, and a diene based monomer, and the rubber elastomer is grafted with α,β-unsaturated carbonic acid.

8. The polyamide resin composition according to Claim 7, wherein the α,β- unsaturated carbonic acid is at least one selected from the group consisting of maleic acid, itaconic acid, citraconic acid, acrylic acid, methacrylic acid, allyl succinic acid, 2-dicarbonic acid, maleinic acid, fumaric acid, their anhydrides, and therir derivatives.

9. The polyamide resin composition according to Claim 7, wherein the acid modified rubber elastomer is an ethylene-octene copolymer that is grafted with

0.4 to 3 weight parts of maleic acid.

10. A polyamide resin moldings comprising a resin substrate containing a fusion of: (a) a polyamide resin;

(b) an acid modified polyolefin grafted with reactive dicarboxylic acid or its anhydride and organic peroxide; and

(c) an acid modified rubber elastomer grafted with α,β-unsaturated carbonic acid; and a glass fiber is dispersed in the resin substrate.

11. The polyamide resin moldings according to Claim 10, which is used for a door frame inner cover, an intercooler air duct, a timing belt cover, an engine cover, or a roof rack.