KR100580020B1 - Polypropylene resin composition for bumper of automobile - Google Patents

Abstract

The present invention relates to a polypropylene resin composition for automobile bumpers, and more particularly, to highly crystalline polypropylene resins, reactive polypropylene resins, styrene-ethylene-butene-styrene copolymer rubbers, disproportionated rosin and inorganic fillers. By appropriately blending, the present invention relates to a polypropylene resin composition for automobile bumpers that has excellent stiffness, low temperature impact strength and dimensional stability, can be used even in extreme climates, and can be reduced in weight.

Responsive polypropylene resin, styrene-ethylene-butene-styrene copolymer, disproportionated rosin, low temperature impact strength, dimensional stability

Description

Polypropylene resin composition for automobile bumper {POLYPROPYLENE RESIN COMPOSITION FOR BUMPER OF AUTOMOBILE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin composition for automobile bumpers, and more particularly, to highly crystalline polypropylene resins, reactive polypropylene resins, styrene-ethylene-butene-styrene copolymer rubbers, and disproportionated rosin. ) And inorganic fillers, and having excellent stiffness, low temperature impact strength and dimensional stability, can be used even in extreme climates, and the present invention relates to a polypropylene resin composition for automobile bumpers that can be lightened.

The automobile bumper currently produced by the injection molding process has high flowability for excellent injection moldability, high stiffness to prevent deformation due to long time use and climate change, and excellent impact strength for safety in a collision. Widely used bumper material manufacturing technology, based on polypropylene resin, which is cost-effective, based on ethylene-propylene rubber or ethylene-octene rubber (rubber) to improve impact resistance, and talc, an inorganic filler for rigid reinforcement Melt kneading in an extruder.

Polypropylene is the most inexpensive general-purpose resin, and generally has some degree of impact strength and stiffness. However, its impact strength and stiffness are not enough to be used as a bumper material alone. If the impact strength is lowered, but the rigidity is lowered, and the addition of talc component only increases the rigidity, but the impact is lowered, and the rubber / tark is properly blended for excellent impact strength / stiffness balance in the bumper material technology. This is very important.

As above, it is widely used as a material for bumpers as a balanced physical property of impact strength / stiffness through proper mixing of rubber / talk components, but recently automobile companies and bumper molding companies have a bumper thickness of 2.5 to reduce costs and improve productivity. Designing less than mm requires more improved impact strength and stiffness of the material, making it impossible to use as a proper blend of polypropylene / rubber / talc. If the thickness of the bumper is reduced, it is difficult for the material to be filled in the mold during injection molding, and since the injection molded bumper also has a small thickness, the impact strength and rigidity of the bumper itself that withstand external forces are reduced.

Therefore, in order to solve this problem, the physical properties of the bumper material itself should be improved. However, in the conventional simple blend of polypropylene / rubber / talc, there is a limit to simultaneously improving impact strength / stiffness. In other words, when a large amount of rubber is added to improve the impact strength, the impact strength is improved, but the rigidity is weakened, and when a large amount of talc is added to compensate for this, the rigidity is improved. However, the impact strength / stiffness balance is limited, and consequently, the excessive density of talc component is added, resulting in an increase in weight and a reduction in fuel efficiency.

In order to solve the impact strength and stiffness degradation caused by the thickness reduction of the bumper as described above, the present inventors use high crystalline polypropylene instead of the general polypropylene in the appropriate combination of the general polypropylene / rubber / talc stiffness and impact strength The polypropylene resin composition [Korean Patent Application No. 2002-42507] dmf which partially improved is proposed.

However, the polypropylene resin composition according to the above method is not enough to improve the impact strength at low temperatures, and the dimensional change at low temperatures is severely used only in warmer regions at present, and thus it is impossible to use in extreme climates.

Accordingly, the present invention has been researched to solve the above problems, and as a result, a polypropylene resin, a styrene-ethylene-butene-styrene copolymer rubber, a disproportionated rosin and a reactive polypropylene resin By adding talc in an appropriate amount, it was found that the prepared polypropylene resin composition was excellent in rigidity, low temperature impact strength and dimensional stability.

Accordingly, an object of the present invention is to provide a polypropylene resin composition for an automobile bumper having excellent physical properties that can be used even in extreme climates and can be used for a bumper having a thickness of 2.5 mm or less.

The present invention is a homopolymer of propylene or a binary copolymer of propylene and ethylene, having a melt index of 30 to 80 g / 10 minutes (230 ° C.), a crystallinity of 60% or more, and a flexural rigidity of 17000 to 19000 kgf / cm 2. 40-70% by weight of highly crystalline polypropylene resin having an impact strength of 8 to 14 kgf · cm / cm and a copolymer of propylene and ethylene having an ethylene content of 18 to 30% by weight, having a melt index of 15 g 10-20% by weight of reactive polypropylene resin, 10-60% by weight of styrene, and 40-90% by weight of butadiene and ethylene with a melt index of 5-20 g / 10 to 20% by weight of styrene-ethylene-butene-styrene copolymer rubber for 10 minutes (200 ° C., 5 Kgf), 1 to 5% by weight of disproportionated rosin and 5 to 20% by weight of talc as inorganic filler Polypropylene resin composition for automobile bumper containing% The features.

Hereinafter, each component constituting the polypropylene resin composition of the present invention will be described in detail.

The present invention has been proposed by the present inventors in order to provide a polypropylene resin composition for automobile cuffs that can maintain even higher stiffness, impact strength and dimensional stability so that it can be used even in extreme climates. [Korean Patent Application No. 2002-42507 In addition to the highly crystalline polypropylene resin, a reactive polypropylene resin having excellent impact strength is used, and the low temperature impact strength is excellent in place of the existing impact strength reinforcing material, ethylene-propylene rubber or ethylene-octene rubber. Styrene-ethylene-butene-styrene copolymer rubber is used and disproportionated rosin and talc are appropriately controlled to improve dimensional stability, thereby improving the stiffness, low temperature impact strength and dimensional stability of the material itself. Has its features.

(a) Highly crystalline polypropylene resins:

The polypropylene resin composition of the present invention is a propylene homopolymer or a copolymer of propylene-ethylene, having high crystalline ethylene content of 4 to 12% by weight, melt index of 30 to 80 g / 10 minutes (230 ° C), and crystallinity of 60% or more. Polypropylene resins are used. Preferably, a high flow, high crystalline polypropylene resin having a melt index of 40 to 70 g / 10 min crystallinity of 65% or more is preferable. The high crystalline polypropylene resin has been used to improve the rigidity and impact strength even in the technology [Korean Patent Application No. 2002-42507] proposed by the present inventors, and the impact / rigidity than the conventional polypropylene resin The property balance is excellent.

Conventionally, high crystalline polypropylene (also called high isotactic polypropylene (HCPP)) refers to a polypropylene resin having a degree of crystallinity of 60% or more by differential scanning calorimeter (DSC) analysis of polypropylene. It is a polypropylene resin that has high rigidity and maintains the same impact strength.

Conventional polypropylene resins have an inverse relationship in which impact strength decreases as the flexural stiffness increases, but high crystalline polypropylene resins have high stiffness and high impact since the flexural stiffness increases while maintaining the impact strength of the existing polypropylene resin. Optimum use is possible for bumper materials that require.

General polypropylene resins produced by Ziegler-Natta catalysts are called semi-crystalline resins and are evaluated by differential scanning calorimetry analysis. The higher the crystallinity, the higher the flexural stiffness at the same impact strength.

That is, the common polypropylene resin is 45 ~ 55% has a degree of crystallinity of, and has a flexural rigidity of 12,000 - 14000 kg _f / cm ² and 8 - 14 kg _f impact strength of .cm / cm.

In contrast, highly crystalline polypropylene resins are prepared using expensive, improved Ziegler-Natta catalysts designed to increase crystallinity, have high crystallinity values of more than 60%, and have a flexural stiffness of 17000 to 19000 kg _f / cm ² . , impact strength have the same range of values of 8 ~ 14 kg _f .cm / cm and common polypropylene resin. The most distinctive feature of this highly crystalline polypropylene is that the impact value remains the same as the flexural stiffness increases.

In the present invention, 40 to 70% by weight of the total composition is used, and if the content is less than 40% by weight, relatively poor moldability during injection, on the contrary, if the content exceeds 70% by weight, the rigidity and dimensional stability become weak. .

(B) Reactor Type polypropylene resin;

Reactive polypropylene resin used to improve the impact strength of the polypropylene resin composition of the present invention is a copolymer of propylene and ethylene 18 to 30% by weight ethylene content, melt index 15 g / 10 minutes (230 ℃) The above is a reactive polypropylene resin of an uncrosslinked form.

In general, conventional polypropylene resins prepared through Ziegler-Natta catalysts and commercialized polymerization reactors have an ethylene content of less than 18% by weight due to the limitations of the catalyst and the reactor when copolymerized with ethylene. When it is produced in excess, it is called a reactive polypropylene resin because it has to be polymerized with a special catalyst and a reactor.

Polypropylene having an ethylene content of less than 18% by weight has a weak impact strength, and currently reactive polypropylene resins having an ethylene content of more than 30% by weight are not available for catalysts and reaction technologies.

The reactive polypropylene resin used in the present invention is different from the ethylene-α-olefin copolymer rubber, commonly referred to as rubber, and has a low catalyst cost and a low impact, but excellent injection moldability. Such a reactive polypropylene resin may have a melt index of 15 g / 10 minutes or more but a melt index of 15 or less is not good in injection moldability.

Therefore, in the present invention, the reactive polypropylene resin is limited to the reactive polypropylene resin having an ethylene content of 18 to 30% by weight and a melt index of 15 g / 10 minutes or more. In addition, such a reactive polypropylene resin is used in the total composition of 10 to 20% by weight, if the amount is less than 10% by weight, the low temperature impact strength is weak, on the contrary, when the content exceeds 20% by weight, the rigidity, dimensional stability and injection molding Sex becomes vulnerable.

(C) Styrene-ethylene-butene-styrene copolymer rubber:

Styrene-ethylene-butene-styrene copolymer rubber of the present invention is a core raw material used for improving the low temperature impact strength, and due to its unique structure, the low temperature impact strength is much better than that of the ethylene-α-olefin copolymer rubber. .

The styrene-ethylene-butene-styrene copolymer rubber used in the present invention has mechanical properties such as vulcanized rubber even at a relatively low viscosity, and has a very good low temperature impact property because the glass transition temperature is very low at -80 ° C. It is the best material to solve the stiffness and impact strength degradation caused by the thick bumper.

The styrene-ethylene-butene-styrene copolymer rubber of the present invention is preferably a styrene copolymer rubber composed of styrene, butadiene and ethylene copolymer, more preferably 10 to 60% by weight of styrene, and the sum of butadiene and ethylene. The amount is composed of 40 to 90% by weight, and a styrene copolymer rubber having a melt index of 5 to 20 g / 10 minutes (200 ° C., 5 Kgf) is used. The styrene, butadiene, and ethylene in accordance with the form of the bond, there are a variety of forms such as binary copolymers, terpolymers, star terpolymers, the styrene-ethylene-butene-styrene copolymer rubber is 20 to 40% by weight, It is more preferable in view of the balance between low temperature impact and formability to use a butadiene and ethylene of 60 to 80% by weight and a melt index of 10 g / 10 minutes or more. If the styrene content is less than 10% by weight, the injection moldability is not good, and if the styrene content is more than 60% by weight, the low temperature impact strength is lowered. In addition, if the melt index is less than 5 g / 10 minutes, injection molding is difficult, and if it is 20 g / 10 minutes or more, the low temperature impact strength is lowered.

The content of the styrene-ethylene-butene-styrene copolymer rubber is used in the total composition of 10 to 20% by weight, if the content is less than 10% by weight, the low temperature impact strength is lowered. Stiffness and dimensional stability become weak.

(D) Disproportionated Rosin

The polypropylene resin composition of the present invention uses a disproportionated rosin, wherein the disproportionated rosin is a component used for improving rigidity and dimensional stability by temperature and reducing weight.

This is a powder component made by distilling natural rosin by a commercial method. The main component is resin acid such as abiate, neo-abiate, repopimaric acid and hydroavieric acid, and maximizes the dispersion of fillers such as talc. In addition, it improves the crystallinity of polypropylene and also plays a role as a filler itself, so it is excellent in improving rigidity and dimensional stability. Even when used alone, there is an effect of increasing rigidity and dimensional stability, but when used with inorganic fillers such as talc, the effect is maximized, and since there is little impact reduction effect when talc is added, high stiffness / impact strength properties can be exhibited. Currently, the disproportionated rosin has been used in other industries, such as paints, but is never used in addition to polypropylene to improve rigidity, impact strength and dimensional stability.

In the present invention, the disproportionated rosin is used in the total composition of 1 to 5% by weight, and when the amount is less than 1% by weight, the rigidity and dimensional stability are weak, and when it exceeds 5% by weight, it is expensive and the actual cost burden increases. It is not applicable to industrial sites.

(E) Inorganic fillers

In the present invention, an inorganic filler is used for reinforcing rigidity, and specifically, among them, it is preferable to use talc having a marked increase in rigidity of the resin composition with increasing content. The talc is preferably an average particle diameter of 1 to 30 µm, preferably 5 to 10 µm. Such talc is used in an amount of 5 to 20% by weight in the total composition, but when the amount is less than 5% by weight, the rigidity and dimensional stability are not sufficient. .

As described above, high crystalline polypropylene resin, reactive polypropylene resin, styrene-ethylene-butene-styrene copolymer rubber, disproportionated rosin and inorganic fillers are suitably blended to provide excellent rigidity and low temperature even for bumpers less than 2.5 mm thick. With impact strength and dimensional stability, it can be used even in extreme climates and the polypropylene resin composition for bumpers can be completed.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the following Examples.

Examples 1-6 and Comparative Examples 1-6

After mixing the components shown in Table 1 by the amount used, the mixture was extruded in an extruder at a temperature range of 190 ~ 250 ℃, cooled, and solidified to obtain a pellet-like composition. The obtained composition prepared an injection specimen for measuring physical properties in the temperature range of 180 ~ 250 ℃.

Experimental Example: Measurement of Physical Properties

Physical properties of the specimens prepared according to Examples 1 to 6 and Comparative Examples 1 to 6 were measured by the following methods, and the results are shown in Table 1 below.

Evaluation items that can be used as a bumper are good moldability, stiffness, low temperature impact strength and temperature dimensional stability during injection. Specific evaluation methods are as follows.

(1) Injection moldability: It is evaluated as the melt index. If the melt index is 20 g / 10 minutes or more, the filling in the mold is possible, and molding can be performed well. If the melt index is 20 g / 10 minutes or less, the filling in the mold is not possible. Not forming. Melt index was measured by ASTM D-1238 and the test conditions were: test temperature: 230 ℃, test load: 2.16 kgf.

(2) Stiffness: evaluated as flexural modulus and if flexural modulus is more than 16000 kg _f / cm ² , it remains unchanged during transport, long-term storage and weather resistance test after injection, but flexural stiffness is less than 16000 kg _f / cm ² Back deformation occurs. Flexural modulus is measured by ASTM D-790 method, and the test conditions are as follows.

Specimen size: 12.7 × 127 × 6.4 ㎜,

Crosshead speed under test conditions: 10 mm / min

(3) Low temperature impact strength: -40 DEG C It is evaluated as low temperature IZOD impact strength. -40 DEG C IZOD impact strength is 5 kgf.cm/cm or more. Izod impact strength is measured by ASTM D-256 method and the specimen size is 63.5 × 12.7 × 6 mm.

(4) Dimensional stability by temperature: Evaluated by the coefficient of linear expansion, the length is changed while raising the temperature from -30 ℃ to 80 ℃ by 1 ℃ / min, and the result is passed if the result is 5 x 10 ^-5 x 1mm / ℃ or less, If it is more than that, it is determined to fail. The coefficient of linear expansion is measured by ASTM D-696 and the specimen dimensions are 50 × 12.5 × 3.2 mm.

division Ingredients (% by weight) Properties A A-1 B C C-1 D E Injection moldability Rigidity Low temperature impact strength Dimensional stability Synthesis Example One 55 15 15 2 13 23 17,700 6.3 3.8 Good 2 60 10 10 One 19 24 18,300 5.9 3.7 Good 3 70 10 10 3 7 27 17,800 6.2 4.0 Good 4 50 20 20 5 5 22 16,800 6.9 4.2 Good 5 40 20 20 One 19 22 17,500 6.4 3.3 Good Comparative example One 55 15 15 2 13 24 14,500 6.8 5.7 Bad 2 55 15 15 2 13 23 16,700 4.4 4.6 Bad 3 30 25 25 5 20 12 13,800 7.2 5.8 Bad 4 53 5 25 3 15 14 14,900 6.7 4.6 Bad 5 75 5 5 3 13 28 17,900 3.8 4.8 Bad 6 55 15 15 0.5 14.5 24 15,200 4.6 5.9 Bad ■ Component A: Highly crystalline polypropylene resin (melt index 60 g / 10 minutes, ethylene content 8 wt%, flexural modulus 18,000 kg _f / cm ² ), ■ Component A-1: general polypropylene resin (melt index 60 g / 10 minutes, Ethylene content 12% by weight, Flexural modulus 13000 kg _f / cm ² ) Component B: Reactive polypropylene resin (melt index 18 g / 10 minutes, Ethylene content 18% by weight, Flexural modulus 80 Mpa) : Styrene-ethylene-butene-styrene copolymer rubber ■ C-1 component: Ethylene-octene copolymer rubber ■ D component: Disproportionated Rosin ■ E component: Talc with an average diameter of 7 micrometers

As described above, in the polypropylene resin composition for automobile bumpers of the present invention, a highly crystalline polypropylene resin, a reactive polypropylene resin, a styrene-ethylene-butene copolymer rubber, a disproportionated rosin (fine crystal) and an inorganic filler By appropriately blending it, it has excellent stiffness, low temperature impact strength and dimensional stability, so that it can be used even in extreme climates and can produce resin compositions for automobile bumpers with a thickness of 2.5 mm or less. The automobile bumper according to the present invention has excellent stiffness, low temperature impact strength, dimensional stability, and has excellent performance compared to the existing bumper cover, and can be lightened, thereby improving automobile fuel economy.

Claims (1)

A homopolymer of propylene or a binary copolymer of propylene and ethylene, having a melt index of 30 to 80 g / 10 minutes (230 ° C.), a crystallinity of 60% or more, and a flexural stiffness of 17000 to 19000 kgf / cm 2. 40 to 70% by weight of highly crystalline polypropylene resin having an impact strength of 8 to 14 kgf · cm / cm, Copolymer of propylene and ethylene having an ethylene content of 18 to 30% by weight, 10 to 20% by weight of a reactive polypropylene resin having a melt index of at least 15 g / 10 minutes (230 ° C), Styrene-ethylene-butene-styrene copolymers having a melt index of 5 to 20 g / 10 min (200 ° C., 5 Kgf), consisting of 10 to 60% by weight of styrene and 40 to 90% by weight of butadiene and ethylene. 10 to 20% by weight of rubber, 1-5 wt% of Disproportionated Rosin and Talc 5-20 wt% as inorganic filler Polypropylene-based resin composition for an automobile bumper comprising a.