KR20060038491A - Polyolefin resin composition for ejection molding - Google Patents

Abstract

The present invention relates to a polyolefin resin composition for injection molding, and more particularly, the weight average molecular weight / number average molecular weight (M _w / M _n ) ratio and z-average molecular weight / weight average molecular weight (M _z / M _w ) ratio It has a high flow and mechanical strength, especially a flow mark (tiger stripe), which comprises a broad molecular weight distribution of ethylene-propylene copolymer that is above a certain level or has a Polydispersity Index (PI) above a certain level. The present invention relates to a polyolefin resin composition for injection molding that can suppress generation.

When the polyolefin resin composition for injection molding according to the present invention is used, it is possible to manufacture an injection molded article having excellent surface appearance by minimizing generation of flow marks during injection molding while having excellent mechanical properties.

Injection Molding, Polyolefins, Compositions, Flow Marks, Molecular Weight Distribution

Description

Polyolefin resin composition for injection molding {POLYOLEFIN RESIN COMPOSITION FOR EJECTION MOLDING}

1 is a photograph showing a surface state of a spiral flow measurement specimen of the resin composition prepared in Example 2,

Figure 2 is a photograph showing the surface state of the spiral flow measurement specimen of the resin composition prepared in Comparative Example 1.

The present invention relates to a polyolefin resin composition for injection molding, and more particularly, a weight average molecular weight / number average molecular weight ratio (M _w / M _n ) and z- average molecular weight / weight average molecular weight ratio (M _z / M _w ) Has a high flow rate and mechanical strength, in particular a tiger stripe, comprising a wide molecular weight distribution of ethylene-propylene copolymers having a specific level or above or a polydispersity index (PI) above a certain level. The present invention relates to a polyolefin resin composition for injection molding that can suppress the occurrence of the resin.

Thermoplastic polyolefin resins are widely used commercially for their excellent price-to-performance ratio, and are particularly widely used for molding into various interior / exterior materials for automobiles due to their excellent weatherability.

Automotive parts are mainly processed by injection molding. In the case of large injection molded products such as bumper dashboards, tiger stripe similar to tiger pattern is generated. This flow mark occurs because in the injection molding process, cooling is started before the molten resin is filled in the mold before it is completely filled in the mold, which results in poor surface appearance, color or gloss of the injection molded article.

In particular, by adding an inorganic filler and an impact modifier to the resin composition for injection molding, the rigidity and flowability of the resin composition have been improved. Injection molding of such a resin composition deteriorates the surface characteristics of the injection molded product, and is particularly applicable to large injection molded products. In this case, since there is a problem such as a flow mark occurs, it was not suitable for the production of large injection molded articles requiring particularly excellent surface properties such as automotive interior and exterior materials.

Therefore, in the manufacture of large-scale injection molded articles having excellent surface appearance by suppressing generation of flow marks during injection molding, while having various physical properties such as stiffness and flowability which are improved or better than those of conventional injection molding resin compositions. There is a need for development of a suitable resin composition for injection molding.

The present invention is to solve the problems of the prior art as described above, the object of the present invention is to include an ethylene-propylene copolymer having a broad molecular weight distribution of a certain level or more as a base resin, while excellent mechanical properties, injection molding Since it is possible to produce an injection molded article having an excellent surface appearance by minimizing the occurrence of sea flow marks, it is to provide a polyolefin resin composition for injection molding that is particularly suitable for the production of large injection molded articles.

According to the present invention, the weight average molecular weight / number average molecular weight ratio (M _w / M _n ) is 7.0 or more, and the z-average molecular weight / weight average molecular weight ratio (M _z / M _w ) is 5.0 or more; Or a polyolefin resin composition for injection molding comprising 55 to 100% by weight of an ethylene-propylene copolymer having a polydispersity index (PI) of 8 or more is provided.

The ethylene-propylene copolymer included in the polyolefin resin composition for injection molding according to the present invention has M _w / M _n of 7.0 or more and M _z / M _w of 5.0 or more; Or having a broad molecular weight distribution with a polydispersity index of 8 or greater, wherein M _w / M _n is less than 7.0 or M _z / M _w is less than 5.0; If the polydispersity index is less than 8, there is a problem in that a flow mark occurs in manufacturing an injection molded article.

The ethylene content of the ethylene-propylene copolymer is preferably 5 to 15 mol%, and the melt index at 230 ° C and 2.16 kg is preferably 10 to 50 g / 10 minutes, and is 15 to 40 g / 10 minutes. More preferred. If the ethylene content is less than 5 mol%, physical properties such as flexural modulus and impact strength deteriorate, and if it exceeds 15 mol%, mechanical strength and dimensional stability deteriorate. In addition, when the melt index is less than 10 g / 10 minutes, the flowability of the resin composition is lowered, so that unmolded and flow marks are generated, and when the melt index exceeds 50 g / 10 minutes, mechanical strength and dimensional stability deteriorate.

In addition, the ethylene-propylene copolymer contains 55 to 100% by weight in the polyolefin resin composition for injection molding according to the present invention. If the content is less than 55% by weight, the processability and flowability of the resin composition are reduced, resulting in process. It is disadvantageous, and there is a problem in that the quality of the resultant molded article is poor.

The polyolefin resin composition for injection molding according to the present invention may further include an inorganic filler or a rubber component in order to improve the releasability, high temperature dimensional stability and rigidity of the resulting molded article.

As the inorganic filler that may be further included in the injection molding polyolefin resin composition according to the present invention, various inorganic fillers that may be applied to the injection molding resin composition may be used, and among them, talc is preferable, and among them, talc is preferred. Talc having a plate-like particle shape having an aspect ratio of 2 to 50 and having an average particle size of 1 to 20 µm is particularly preferable. If the aspect ratio of the talc is less than 2, there is a problem of lowering the rigidity, and if it exceeds 50, there is a problem of poor appearance and impact resistance of the molded article. In addition, if the average particle size of the talc is less than 1㎛ the particles agglomeration phenomenon occurs during processing, the dispersibility and productivity is lowered, if it exceeds 20㎛ there is a problem of poor appearance and impact resistance of the molded article.

In addition, as the rubber component which may be further included in the injection molding polyolefin resin composition according to the present invention, various natural or synthetic rubbers that may be applied to the injection molding resin composition may be used, and among them, ethylene-propylene copolymer rubber ( Preference is given to using ethylene-alpha olefin rubbers such as EPR).

When the inorganic filler is further included in the injection molding polyolefin resin composition according to the present invention, it is preferable that the inorganic filler of 5 to 25% by weight is contained. When this content is less than 5 weight%, it is difficult to anticipate the effect of an inorganic filler addition, and when it exceeds 25 weight%, the flowability and processability of a resin composition will worsen.

Moreover, when the said rubber component is further contained in the injection molding polyolefin resin composition which concerns on this invention, it is preferable that 5-25 weight% of a rubber component is contained. When this content is less than 5 weight%, it is difficult to expect the effect of a rubber component input, and when it exceeds 25 weight%, the surface appearance characteristic and workability of a resulting molded article will worsen.

Injection molding polyolefin resin composition according to the present invention, in addition to the above components, are commonly included in injection molding resin compositions such as antioxidants, heat stabilizers, weather stabilizers, antistatic agents, lubricants, slip agents, flame retardants, pigments, dyes, etc. Various additives may be further included within the scope of not impairing the object of the present invention.

The polyolefin resin composition for injection molding according to the present invention is not particularly limited in its production method, and thus can be manufactured using a method for producing a polyolefin resin composition which is widely known. That is, for example, the ethylene-propylene copolymer, if necessary, the amount of inorganic filler and / or rubber components and other additives is kneaded by kneading, kneader, roll, kneader mixer, etc. It can be produced by a method of melt-extruding and kneading using a single screw or twin screw extruder.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these examples are for illustrative purposes only, and the present invention is not limited thereto.

Examples 1-2 and Comparative Examples 1-2

In Examples and Comparative Examples, ethylene-propylene copolymer resins having resin properties shown in Table 1 below were used.

For each of Examples 1 and 2 and Comparative Examples 1 and 2, each of the ethylene-propylene copolymer resins shown in Table 2 below was added to a twin screw extruder alone, followed by melt kneading to prepare Examples 1 and 2 and Comparative Examples 1 to 2. Each resin composition was prepared, and various specimens for measuring physical properties were prepared using the same, and the measured physical properties are shown in Table 2 below.

In addition, in order to observe the presence or absence of the flow mark, the surface state of the spiral flow measurement specimen of the resin composition prepared in Example 2 was taken with a photograph, as shown in Figure 1, the resin composition prepared in Comparative Example 1 for the same purpose The surface state of the spiral flow measurement specimen of the photograph was taken, it is shown in FIG.

Examples 3-4 and Comparative Example 3

For each of Examples 3 to 4 and Comparative Example 3, 62% by weight of each ethylene-propylene copolymer resin shown in Table 3 below, talc (KCM6300, manufactured by KOCH, Aspect Ratio: 4, Average particle size: about 10 µm) ) 20% by weight and 18% by weight of ethylene-alpha olefin rubber (Engage 8842, manufactured by DOW) were added to a twin screw extruder and melt kneaded to prepare resin compositions of Examples 3 to 4 and Comparative Example 3, respectively. Various physical properties of the test specimens were prepared, and the measured physical properties are shown in Table 3 below.

Resin Properties and Property Measurement Method

The resin properties of the ethylene-propylene copolymer resins shown in Table 1 and the properties of the resin compositions shown in Tables 2 and 3 were measured as follows:

① Melt index (g / 10min): measured at 230 ° C and 2.16kg load according to the method of ASTM D1238.

② M _w / M _n and M _z / M _w : Calculated from the weight average molecular weight (M _w ), number average molecular weight (M _n ) and z-average molecular weight (M _z ) measured by gel permeation chromatography (GPC) method .

③ Polydispersity Index: For a circular specimen of 25 mm diameter, which was compression molded into a resin composition and then stamped, using a programmed Rheometrics Dynamic Spectrometer (RDS; manufactured by Rheometrics), 2.0 Measured at 200 ° C with 25 mm parallel plate geometry with mm spacing.

④ Flexural modulus (kg / ㎠): measured according to ASTM D790 method.

⑤ Izod impact strength at room temperature and low temperature (kgf / cm): measured at room temperature (23 ℃) and low temperature (-30 ℃), respectively, according to ASTM D256.

⑥ Heat deflection temperature (℃): measured according to ASTM D648 method.

⑦ Spiral Flow (cm): Measure the length of the specimen injected by injection into spiral mold at 235 ℃ using 110ton injection machine.

⑧ Flow strip (tiger stripe): Spiral flow measurement Visually measure the presence or absence of a flow mark on the surface of the specimen.

⑨ Density (g / cm 3): measured according to ASTM D1505 method.

TABLE 1

 Resin properties Ethylene-propylene Copolymer #One #2 # 3 #4 Ethylene Content (mol%) 12.0 11.4 10.9 11.8 Melt Index (g / 10min) 35.4 30.9 33.7 32.5 M _w / M _n 20.29 8.46 6.58 5.34 M _z / M _w 8.17 5.84 4.24 3.30 Polydispersity index 20.13 8.89 6.61 3.55

TABLE 2

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Ethylene-propylene copolymer type #One #2 # 3 #4 Flexural modulus (kg / ㎠) 17,800 16,800 15,900 14,100 Izod impact strength at room temperature (23 ℃, kgf / cm) 10.9 10.4 11.1 11.8 Low Temperature Izod Impact Strength (-30 ℃, kgf / cm) 5.7 5.7 4.7 5.5 Heat Deflection Temperature (℃) 115 112 111 116 Spiral Flow (cm) 175.8 162.3 157.1 149.5 Flowmark none none has exist has exist

TABLE 3

Example 3 Example 4 Comparative Example 3 Ethylene-propylene copolymer type #One #2 # 3 Melt Index (g / 10min) 16.5 17.1 15.9 Density (g / cm 3) 0.9921 0.9916 0.9903 Flexural modulus (kg / ㎠) 17,100 16,540 15,600 Izod impact strength at room temperature (23 ℃, kgf / cm) 59.0 57.1 63.3 Low Temperature Izod Impact Strength (-30 ℃, kgf / cm) 6.1 6.3 5.4 Heat Deflection Temperature (℃) 123.1 122.9 122.4 Spiral Flow (cm) 138 126 117 Flowmark none none has exist

As can be seen from Tables 2 and 3, # 1 and # 2 copolymers are ethylene-propylene copolymers having M _w / M _n of 7.0 or more, M _z / M _w of 5.0 or more, and a polydispersity index of 8 or more. The resin compositions of Examples 1-4, including one of, have an ethylene content and melt index similar to those of # 1 and # 2 copolymers, but M _w / M _n is less than 7.0 and M _z / M _w is 5.0 Compared to the resin compositions of Comparative Examples 1 to 3, which include one of the # 3 and # 4 copolymers, which are ethylene-propylene copolymers having a polydispersity index of less than 8, which is less than 8, and exhibits excellent or equivalent mechanical properties, spiral The flow was higher and no flow mark was generated on the molded article surface.

As described above, the injection molding polyolefin resin composition according to the present invention exhibits superior or equivalent mechanical properties as compared to the conventional injection molding resin composition, and has a higher spiral flow and a flow mark on the surface of the molded article. Since it is not made, it can be suitably used for the manufacture of injection molded articles of a complicated shape or a large size that requires particularly excellent appearance and surface properties, such as automotive interior / exterior materials such as automobile bumpers and grills. In addition, the polyolefin resin composition for injection molding according to the present invention is excellent in melt tension to be applicable to a process such as a foaming process, a vacuum molding process, a blow molding process and the like. In addition, since the polyolefin resin composition for injection molding according to the present invention is not a crosslinked form, the properties of the thermoplastic resin can be maintained as it is, and thus there is an advantage that recycling is possible.

Claims (5)

The weight average molecular weight / number average molecular weight ratio is 7.0 or more, and the z-average molecular weight / weight average molecular weight ratio is 5.0 or more; Or 55 to 100% by weight of an ethylene-propylene copolymer having a polydispersity index of 8 or more. The polyolefin resin composition for injection molding according to claim 1, wherein the ethylene content of the ethylene-propylene copolymer is 5 to 15 mol%, and the melt index at 230 ° C and 2.16 kg is 10 to 50 g / 10 minutes. The injection molding polyolefin resin composition according to claim 1, further comprising an inorganic filler or a rubber component. The polyolefin resin composition for injection molding according to claim 3, wherein the inorganic filler is talc. The polyolefin resin composition for injection molding according to claim 3, wherein the rubber component is ethylene-alpha olefin rubber.

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