KR102298955B1 - Injection molding method of plastic article using polypropylene resin composition - Google Patents

Abstract

The present invention relates to a method of injection molding of a molded article using a polypropylene resin composition, and more particularly, by foaming the polypropylene resin composition with a foaming agent and then core-back injection molding in a supercritical state, the existing mechanical properties can be improved to equal or higher It relates to an injection molding method of a molded article using a polypropylene resin composition that can be maintained at the same level while improving the appearance moldability by foaming and reducing the weight to reduce the weight.

Description

Injection molding method of a molded article using a polypropylene resin composition {INJECTION MOLDING METHOD OF PLASTIC ARTICLE USING POLYPROPYLENE RESIN COMPOSITION}

The present invention relates to a method of injection molding of a molded article using a polypropylene resin composition, and more particularly, by foaming the polypropylene resin composition with a foaming agent and then core-back injection molding in a supercritical state, the existing mechanical properties can be improved to equal or higher It relates to an injection molding method of a molded article using a polypropylene resin composition that can be maintained at the same level while improving the appearance moldability by foaming and reducing the weight to reduce the weight.

Plastic materials used in automobiles are contributing to weight reduction through performance improvement, such as replacing metals or lowering the specific gravity within the same plastic material from the viewpoint of eco-friendliness and weight reduction. In this trend, development of materials with a lower specific gravity is being made, and efforts to reduce weight such as foam molding or supercritical injection are bearing fruit in terms of part molding.

Polypropylene (PP), one of the most used general-purpose plastics among plastics used for automobiles, has a relatively low weight compared to other plastics, so it is already used in many large interior and exterior parts. As a result, usage is on the rise. In particular, continuous development is being made in an effort to lower the specific gravity while maintaining the same required physical properties.

Conventional U.S. Patent No. 8,114,332 discloses a technique capable of inducing light weight of parts by controlling the volume of the melt index using a core-back injection molding method, but this method also expresses appearance characteristics such as surface roughness of parts. However, there is a disadvantage that there is a limitation in the public law.

In addition, Korean Patent Application Laid-Open No. 2010-0027322 discloses a polypropylene resin composition comprising a highly crystalline polypropylene resin having an isotactic peptide fraction of 96% or more, an impact modifier and an inorganic filler by C-NMR method, The weight reduction by weight reduction is not recognized at all.

In addition, Korean Patent Application Laid-Open No. 1483914 discloses a low specific gravity composite polypropylene resin composition with a specific gravity of about 5 to 6% reduced compared to the reference product, but has a weak rigidity due to low appearance characteristics and low coefficient of linear expansion. have.

Therefore, it is necessary to develop a technology for a molding method that achieves the maximum light weight effect while maintaining high rigidity characteristics in line with the trend of reducing automobile weight.

US Patent No. 8114332 Korean Patent Publication No. 2010-0027322 Korean Patent Publication No. 1483914

In order to solve the above problems, the present invention provides for core-back injection molding in a supercritical state after foaming a polypropylene resin composition with a foaming agent, thereby maintaining the existing mechanical properties at the same or higher level and at the same time, appearance moldability by foaming. By improving and reducing the weight, it was found that it could be made light, and the invention was completed.

Accordingly, an object of the present invention is to provide a method for injection molding of a molded article using a polypropylene resin composition that is lightweight by reducing the weight while maintaining mechanical properties.

Another object of the present invention is to provide a molded article manufactured by the injection molding method with improved appearance moldability by foaming.

The present invention is 50 to 97 wt% of a high crystalline polypropylene resin having an isotactic peptide fraction of 96% or more by ^{C 13 -NMR method;} 1 to 30% by weight of a rubber component; 1-10 wt% of inorganic filler; and 1 to 10% by weight of microtalc; preparing a mixture by mixing; And it provides an injection molding method of a molded article using a polypropylene resin composition comprising a; and the step of foaming by introducing a foaming agent to the mixture, and then core-back injection molding.

In addition, the present invention provides a molded article manufactured by the injection molding method.

In the injection molding method of a molded article using the polypropylene resin composition according to the present invention, the polypropylene resin composition is foamed with a foaming agent, and then core-back injection molding is performed in a supercritical state, thereby maintaining the existing mechanical properties at the same or higher level while foaming. There is an effect of improving the appearance moldability by the and reducing the weight to reduce the weight.

1 shows a cross-sectional photograph of a molded article prepared in Example 3 according to the present invention.

Hereinafter, the present invention will be described in more detail by way of one embodiment.

The present invention is 50 to 97 wt% of a high crystalline polypropylene resin having an isotactic peptide fraction of 96% or more by ^{C 13 -NMR method;} 1 to 30% by weight of a rubber component; 1-10 wt% of inorganic filler; and 1 to 10% by weight of microtalc; preparing a mixture by mixing; And it provides an injection molding method of a molded article using a polypropylene resin composition comprising a; and the step of foaming by introducing a foaming agent to the mixture, and then core-back injection molding.

According to a preferred embodiment of the present invention, the high crystallinity polypropylene resin may be a high crystallinity homo polypropylene resin, a block copolymer polypropylene resin, or a mixture thereof.

According to a preferred embodiment of the present invention, the highly crystalline polypropylene resin may have a polydispersity index (PI) of 3 to 6, and a melt index of 1 to 110 g/10min (load 2.16 kg and 230 °C). Specifically, the high crystalline polypropylene resin preferably includes a block copolymer with a wide molecular weight distribution, which has excellent flow properties under a given injection pressure due to its easy flow characteristics during the injection molding process, which can increase work productivity. can work Here, if the PI is less than 3, moldability may be a problem and appearance defects such as flow marks may occur, and if the PI is more than 6, long-term reliability such as durability due to increased low molecular weight may be adversely affected. It is preferable to use a PI of 3.8 to 5.8. In addition, if the melt index is less than 1 g/10 min, it is difficult to completely mold the product due to reduced flowability during processing and molding, and if it exceeds 110 g/10 min, it is difficult to control the molding process variable due to excessive flow characteristics, There may be a problem of deterioration of physical properties.

According to a preferred embodiment of the present invention, the high crystalline polypropylene resin is from the group consisting of isotactic polypropylene, propylene-ethylene comonomer, propylene 1 butene copolymer, propylene 1 hexene copolymer and propylene 4 methyl 1 pentene copolymer. Any one selected copolymer, random copolymer, or a mixture thereof may be used.

According to a preferred embodiment of the present invention, the high crystalline polypropylene resin is a resin having a high isotactic index of 96% or more, and 50 to 97% by weight is preferably used. Specifically, if the content is less than 50% by weight, the characteristics of polypropylene are deteriorated, so that it is difficult to express the function.

According to a preferred embodiment of the present invention, the rubber component is used to improve impact strength properties such as flexibility and low-temperature impact properties, and includes ethylene-octadiene, ethylene-butadiene, amorphous ethylene-α-olefin copolymer and styrene-based copolymer. At least one selected from the group consisting of thermoplastic elastomers may be used. Specifically, in the amorphous ethylene-α-olefin copolymer, the α-olefin may be at least one selected from the group consisting of propylene, butene 1, pentene 1, octene 1, 4-methyl pentene 1, and heptene 1. In addition, the styrene-based thermoplastic elastomer may be a styrene-ethylene-butene-styrene copolymer (SEBS).

According to a preferred embodiment of the present invention, the rubber component may be used in an amount of 1 to 30% by weight. Specifically, if the content is less than 1% by weight, flexibility is lowered, the impact mitigation effect by the rubber component is insufficient, and if it exceeds 30% by weight, there is a problem in that the ductility is strengthened to cause a decrease in rigidity.

According to a preferred embodiment of the present invention, the inorganic filler is used to express physical properties such as balanced flexural rigidity and impact strength, and nanoclay, glass fiber, talc, mica, calcium carbonate, wollastonite, barium sulfate, magnesium sulfate, etc. and at least one selected from the group consisting of whiskers may be used.

According to a preferred embodiment of the present invention, the inorganic filler is preferably used in an amount of 1 to 10% by weight. Specifically, if the content is less than 1% by weight, the effect of supplementing the stiffness is insignificant, and if it is more than 10% by weight, a problem may occur in improving the physical properties and properties of the part.

According to a preferred embodiment of the present invention, the microtalc may have a particle size of 0.1 to 1 μm. Specifically, if the particle size is less than 0.1 μm, a feeding defect may occur during the mixing process, and if it exceeds 1 μm, granulation is easy, but mechanical strength such as flexural modulus may be relatively low. In addition, the fine talc may be used in an amount of 1 to 10% by weight. If the content is less than 1% by weight, the improvement in mechanical strength may be insignificant, and if it is more than 10% by weight, the weight is increased, which may limit the granulation of the desired lightweight material. have.

According to a preferred embodiment of the present invention, in the step of preparing the mixture, a colorant and a reinforcing material may be further included in the mixture. Specifically, the colorant includes inorganic pigments and organic pigments. In addition, the reinforcing material may further include one or more additives selected from the group consisting of, for example, a long-term heat-resistant stabilizer, a weather-resistant stabilizer, an antistatic agent, a lubricant, a slip agent, a nucleating agent, and a flame retardant.

According to a preferred embodiment of the present invention, in the injection molding step, the foaming agent may be a supercritical fluid. Specifically, the supercritical fluid may be a hydrocarbon-based or non-hydrocarbon-based fluid. The hydrocarbon-based is at least one selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, and halogenated hydrocarbons, and the non-hydrocarbon-based is at least one selected from the group consisting of organic gas, carbon dioxide, nitrogen and air.

According to a preferred embodiment of the present invention, in the injection molding step, the injection temperature is 150 ~ 250 ℃, the injection pressure may be performed in a supercritical state under the conditions of 60 ~ 100 bar. Specifically, if the injection temperature is less than 150 ℃ may inhibit the melt flow of the material, if it exceeds 250 ℃, some low molecular weight carbonization may occur.

According to a preferred embodiment of the present invention, the foaming rate of the mixture in the injection molding step may be 20 to 35%. Specifically, the foaming rate of the mixture is large, and the more uniform the foaming state is, the better. In this case, if the foaming rate is less than 20%, the light weight effect may be insignificant, and if it exceeds 35%, the surface and appearance characteristics may be deteriorated. Preferably, it is good that it is 27.4-29.3%.

On the other hand, the present invention provides a molded article manufactured by the injection molding method.

Therefore, in the injection molding method of a molded article using the polypropylene resin composition according to the present invention, the polypropylene resin composition is foamed with a foaming agent and then core-back injection molding in a supercritical state to maintain the existing mechanical properties at the same or higher level. At the same time, there is an effect of improving the appearance moldability by foaming and reducing the weight to reduce the weight. The weight of automobile interior and exterior parts can be reduced to about 20-30%, and the specific gravity can be reduced by 5-7%. In addition, by controlling the molecular weight distribution of the polypropylene resin composition, the flow characteristics are good even at the same MI, so the appearance moldability is advantageous, and the injection moldability is excellent because the inorganic content is small.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the following examples.

Examples 1-3 and Comparative Examples 1-4

The components and properties of the materials used in the present invention are shown in Tables 1, 2, and 3 below. Table 1 shows that homo and block copolymer polypropylene resins with high crystallinity are used as the base resin for the resin composition. Some products show the properties of polypropylene with widely controlled molecular weight distribution. , and Table 3 shows the specifications of the inorganic filler.

Using the raw materials shown in Tables 1 to 3 below, polypropylene resin compositions were prepared according to the composition ratios in Table 4 below. Then, the composition was dried in an oven at 90° C. for 3 hours in consideration of deterioration of physical properties due to moisture absorption. The dried composition was injected using a Si180-III (clamping force = 180 tons) injection machine manufactured by Toyo of Japan in a supercritical state. The injection temperature was 180/200/200/210/210 ℃ in the order from the raw material supply hopper to the nozzle, and the injection pressure was 60 to 100 bar. In this case, the injection molding was performed by adding 9 wt% of a supercritical fluid (nitrogen) as a foaming agent. In addition, the kneading extruder was manufactured after pre-kneading by measuring the input amount of each component at a diameter of 32 mm (L/D, 40:1) manufactured by SM Platek. was used.

division flow index
[g/10min]
(230℃, 2.16Kg) PI* (230℃) weight average molecular weight
[g/mol] isotactic peptide
fraction** PP　Homo-1 11 3.8 230,000 97.2 PP Block-1 22 3.7 210,000 96.4 PP Block-2 40 4.1 190,000 96.8 PP Block-3 46 5.8 185,000 96.9 *PI (Poly dispersity Index) is a measure of molecular weight distribution as a cross over point of G' (loss modulus) and G" (Storage modulus) for rheological properties
**Isotactic peptide fraction measured by ^{C 13 -NMR.}

division Flow index [g/10min]
(190℃, 2.16Kg) Density [Kgf/cm] etc rubber component-1 1.0 0.857 Ethylene-octene copolymer elastomer rubber component-2 0.5 0.862 Ethylene-Butene Copolymer Elastomer

division Sample classification Size [㎛] Filler-1 talc Average diameter: 3 to 6 filler-2 fine talc Average diameter: 0.65 filler-3 Whisker Average length: 15
Average diameter: 0.5

division comparative example Example One 2 3 4 One 2 3 PP　Homo-1 - - - 20 10 10 10 PP Block-1 70 65 10 40 - - - PP Block-2 - - 55 - 20 20 25 PP Block-3 - - - - 45 35 35 rubber component-1 15 10 18 22 15 25 20 rubber component-2 - 10 - - - - - Filler-1 15 15 17 18 - - - filler-2 - - - - 4 8 6 filler-3 - - - - 6 2 4

Experimental example: measurement of physical properties of specimens

Physical properties of the molded articles and test pieces for evaluation of appearance tests prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were measured in the following manner, and the results are shown in Tables 5 and 6 below.

The test method for the physical property results shown in Table 5 below is as follows.

1) Flow index: Measured at 230 ℃ by the method of ASTM D1238.

2) Tensile strength: It was measured at room temperature by the method of ASTM D638.

3) Flexural modulus: It was measured at room temperature by the method of ASTM D790.

4) Izod impact strength: It was measured at room temperature by the method of ASTM D256.

5) Heat deflection temperature (HDT): It was measured at room temperature by the method of ASTM D648.

6) Specific gravity (Density): was measured at room temperature (23 ℃) by the method of ASTM D1505.

division comparative example Example One 2 3 4 One 2 3 flow index
[g/10min]
(230℃, 2.16Kg) 15.9 14.5 23.6 11.1 25.4 19.7 22.5 tensile strength
[Kgf/cm ² ] 198 194 190 188 233 210 220 flexural modulus
[Kgf/cm ² ] 17,030 15,020 16,880 14,040 21,230 19,100 18,500 Izod impact strength
(-30℃)
[Kgfcm/cm] 4.2 5.4 4.8 5.8 5.5 6.2 5.0 Heat deflection temperature [℃] 124 120 109 112 120 114 117 importance 0.997 0.996 1.006 1.010 0.955 0.947 0.947

According to the results of Table 5, in the case of Comparative Examples 1 to 4, the specific gravity was about 0.996 to 1.010, and mechanical properties were relatively low, whereas in Examples 1 to 3, the specific gravity was 0.947 to 0.955. It was confirmed that the stiffness and impact properties of flow index, tensile strength, flexural modulus, and impact strength were maintained at the same or higher level or improved. In addition, it was possible to reduce the weight of the molded article because the specific gravity was lower than those of Comparative Examples 1 to 4.

In addition, according to the results of Table 6, it was confirmed that Examples 1 to 3 significantly reduced the weight of the specimen compared to the weight of Comparative Example 3. In addition, it was confirmed with the naked eye that the pores increased as the foaming rate increased, as shown in the cross-sectional photograph, and the weight decreased. Through this, it was found that the rigidity characteristics and the like could be improved to equal or greater than that of the prior art, and at the same time, the specific gravity of the polypropylene resin composition could be lowered, and the weight could be reduced by reducing the weight.

Therefore, in Examples 1 to 3, the injection molding method of a molded article using the polypropylene resin composition is performed by foaming the polypropylene resin composition with a foaming agent and then core-back injection molding in a supercritical state to improve the existing mechanical properties to an equal or higher level. It was confirmed that there is an effect of improving the appearance moldability by foaming while maintaining it, and reducing the weight to reduce the weight.

Claims (15)

50 to 97 wt% of a highly crystalline polypropylene resin having an isotactic peptide fraction of 96% or more by C ^{13 -NMR method;} 1 to 30% by weight of a rubber component; 1-10 wt% of inorganic filler; and 1 to 10% by weight of microtalc; preparing a mixture by mixing; and
After foaming by adding a foaming agent to the mixture, core-back injection molding;
including,
The inorganic filler is a whisker,
The injection molding method of the molded article using the polypropylene resin composition, characterized in that the content ratio of the fine talc: whisker is 4: 6 to 4: 1.
According to claim 1,
The high crystallinity polypropylene resin is a high crystallinity homopolypropylene resin, a block copolymer polypropylene resin, or a method of injection molding a molded article using a polypropylene resin composition, characterized in that a mixture thereof.
According to claim 1,
The high crystalline polypropylene resin has a polydispersity index (PI) of 3 to 6, and a melt index of 1 to 110 g/10 min (load 2.16 kg and 230 ° C.) Injection molding of a molded article using a polypropylene resin composition, characterized in that Way.
According to claim 1,
The high crystalline polypropylene resin is any one copolymer selected from the group consisting of isotactic polypropylene, propylene-ethylene comonomer, propylene 1 butene copolymer, propylene 1 hexene copolymer and propylene 4 methyl 1 pentene copolymer, random air Injection molding method of a molded article using a polypropylene resin composition, characterized in that it is a coalescence or a mixture thereof.
According to claim 1,
The rubber component is an injection molding method of a molded article using a polypropylene resin composition, characterized in that at least one selected from the group consisting of ethylene-octadiene, ethylene-butadiene, amorphous ethylene-α-olefin copolymer and styrenic thermoplastic elastomer.
6. The method of claim 5,
In the amorphous ethylene-α-olefin copolymer, the α-olefin is at least one selected from the group consisting of propylene, butene 1, pentene 1, octene 1, 4-methyl pentene 1 and heptene 1. Injection molding method of the used molded product.
6. The method of claim 5,
The styrene-based thermoplastic elastomer is an injection molding method of a molded article using a polypropylene resin composition, characterized in that the styrene-ethylene-butene-styrene copolymer (SEBS).
delete According to claim 1,
The fine talc is an injection molding method of a molded article using a polypropylene resin composition, characterized in that the particle size is 0.1 ~ 1㎛.
According to claim 1,
Injection molding method of a molded article using a polypropylene resin composition, characterized in that the foaming agent in the injection molding step is a supercritical fluid.
11. The method of claim 10,
The supercritical fluid is an injection molding method of a molded article using a polypropylene resin composition, characterized in that hydrocarbon-based or non-hydrocarbon-based.
12. The method of claim 11,
The hydrocarbon-based is at least one selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, and halogenated hydrocarbons, and the non-hydrocarbon-based is poly, characterized in that at least one selected from the group consisting of organic gas, carbon dioxide, nitrogen and air. An injection molding method of a molded article using a propylene resin composition.
According to claim 1,
Injection molding method of a molded article using a polypropylene resin composition, characterized in that in the injection molding step, the injection temperature is 150 ~ 250 ℃, the injection pressure is performed in a supercritical state under the conditions of 60 ~ 100 bar.
According to claim 1,
Injection molding method of a molded article using a polypropylene resin composition, characterized in that the foaming rate of the mixture in the injection molding step is 20 to 35%.
A molded article manufactured by the injection molding method of any one of claims 1 to 7, and claims 9 to 14.

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