Polypropylene container

Abstract

To provide a polypropylene container exhibiting superior blow moldability, transparency, and resistance to impact.SOLUTION: A polypropylene container comprises a mixture of an ethylene-propylene random copolymer and an ethylene-propylene block copolymer. The melt mass flow rate (MFR) of the mixed composition at 230°C under a load of 2.16 kgf (21.2 N) ranges from 18 g or more to 35 g or less per 10 minutes. In thermal analysis using a differential scanning calorimeter on a container section, the melting peak temperature (MT) ranges 140°C or more to 150°C or less. The difference between the temperature at 40% melting of the crystalline portion and the melting peak temperature ranges from 15°C or more to 17.5°C or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polypropylene container having excellent transparency and impact resistance against dropping.

Background Art

[0002] A general ethylene-propylene random copolymer (also referred to as random PP) has a wider melting temperature range of the crystalline part and a more gradual appearance of the melting point peak compared to a propylene homopolymer (also referred to as homopoly PP). Therefore, it is particularly suitable for biaxially stretched blow molded containers, and has excellent impact resistance and flexibility due to a large amount of amorphous part. In addition, an ethylene-propylene random copolymer has great advantages in terms of physical properties such as good transparency because the amount of crystals causing light scattering is small.

[0003] Examples of the techniques disclosed in Patent Documents 1 and 2 are cited for containers using polypropylene. In the techniques disclosed in Patent Documents 1 and 2, a plurality of materials are mixed (blended) and used to ensure desired physical properties.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, from the viewpoint of environmental consideration, that is, the recyclability of the container, it is preferable to use a single material. On the other hand, as the container itself is thinned (lightened) and enlarged for the purpose of reducing the environmental load, the impact resistance (especially the low-temperature dropping impact resistance) becomes insufficient, and container breakage and defects during use and distribution become prominent problems.

[0006] Therefore, in view of the above-mentioned conventional problems, an object of the present invention is to provide a polypropylene container that has good blow molding suitability and transparency of random PP, and excellent impact resistance without sacrificing them.

Means for Solving the Problems

[0007] The polypropylene container of the present invention developed to achieve the above object has a composition in which an ethylene-propylene random copolymer and an ethylene-propylene block copolymer are mixed, the melt mass flow rate (MFR) of the composition after mixing at 230 °C and a load of 2.16 kgf (21.2 N) is in the range of 18 g or more and 35 g or less per 10 minutes, in the thermal analysis obtained by a differential scanning calorimeter of the container section, the temperature of the melting peak is in the range of 140 °C or more and 150 °C or less, and is characterized in that the difference between the temperature at which 40% of the crystalline part melts and the temperature of the melting peak is in the range of 15 °C or more and 17.5 °C or less.

[0008] In addition, the polypropylene container of the present invention preferably has a wall thickness at the center of the body in the range of 0.1 to 2.0 mm and is composed of a single layer, which is processed by biaxial stretch blow molding from a preform having a bottomed cylindrical shape.

Advantages of the Invention

[0009] According to the stretch polypropylene container of the present invention, a hollow polypropylene container excellent in transparency and impact resistance can be provided. In addition, it is industrially useful because it is easy to process and has excellent recyclability.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an example of a polypropylene container according to the present invention. FIG. 1(a) is a top view, and FIG. 1(b) is a front view. This polypropylene container 1 has a cylindrical shape and is processed, for example, by biaxial stretch blow molding. In the example of FIG. 1, a cylindrical container is shown, but it may have an elliptical cross-section or be substantially square, and the body 2 may be provided with designs such as constrictions or recesses.

[0012] In this embodiment, a composition obtained by mixing an ethylene-propylene random copolymer (random PP) and an ethylene-propylene block copolymer (block PP) is processed by blow molding to obtain a polypropylene container.

[0013] <Composition> Random PP is a copolymer in which ethylene is randomly connected between propylenes. Random PP has higher transparency and improved impact strength compared to a propylene homopolymer (hereinafter also referred to as homopolymer PP).

[0014] Block PP is also called a heterophasic copolymer. Here, polyethylene (hereinafter also referred to as PE) is dispersed in homopolymer PP. There is an EPR phase (rubber phase) around the PE, and due to this structure, the impact resistance of block PP is higher than that of homopolymer PP. If homopolymer PP is likened to the sea, PE / EPR looks like islands, so it is also called an island-sea structure. It is said that the high impact performance of block PP compared to homopolymer PP is due to the contribution of the island structure of PE / EPR.

[0015] The composition obtained by mixing random PP and block PP should have a melt mass flow rate (MFR) at 230 °C under a load of 2.16 kgf (21.2 N) in the range of 18 g or more and 35 g or less per 10 minutes. If the MFR of the composition is less than the lower limit, the fluidity of the resin is poor, making it difficult to produce a preform with a bottomed cylindrical shape (test tube shape) by injection molding. If the MFR of the composition is more than the upper limit, the productivity decreases due to the reduction in tensile strength during blow molding. The MFR can be measured in accordance with JIS K7210-1:2014.

[0016] For the composition of this embodiment, when thermally analyzed by a differential scanning calorimeter (DSC) in accordance with JIS K7121-01:2012, the melting peak temperature (MT) should be in the range of 140 °C or more and 150 °C or less. In addition, the difference ΔT between the temperature at 40% melting of the crystalline part and the melting peak temperature (MT) should be in the range of 15 °C or more and 17.5 °C or less. If ΔT is less than the lower limit, the proportion of random PP is too low and the transparency decreases. On the other hand, if ΔT exceeds the upper limit, the proportion of block PP is too low and the impact resistance characteristics decrease. Here, the temperature at 40% melting of the crystalline part is generally the preheating temperature at which blow molding is possible. If heated up to the melting peak temperature (MT), the composition will melt too much and blow molding will not be possible. Note that the "preheating temperature" refers to the temperature at which the preform (preformed body) is heated before blow molding.

[0017] Transparency can be evaluated by the HAZE value, for example, using a section 3 taken from the center of the body 2 of the polypropylene container 1 shown in Fig. 1(b) in accordance with JIS K7136:2000.

[0018] The impact resistance characteristics can be evaluated as follows: for example, fill a container as shown in Fig. 1 almost full with water, close the lid, and leave it standing in a constant temperature bath at 5 °C for 24 hours. Then, drop it upright from a height of 1 m onto a concrete surface 5 times. Subsequently, drop the same container 5 times from a height of 1 m onto the concrete surface in a state where it is lying on its side at 90°. Then, observe the container after the drop test and check for cracks or fissures.

[0019] The polypropylene container according to this embodiment preferably has a wall thickness at the central part of the body in the range of 0.1 to 2.0 mm. Here, the "wall thickness at the central part of the body" means the central position in the vertical direction in the body 2 of the container. Also, the average wall thickness of the body 2 is preferably approximately equal to the wall thickness at the central part of the body. Further, it is more preferable that the wall thickness of the body 2 is in the range of 0.2 to 0.5 mm at any position measured. Within that range, the polypropylene container can be made thin-walled, and irregular deformation and damage during the filling operation of the contents can be suppressed, resulting in a container with excellent transparency and impact resistance. The container is preferably manufactured by biaxial stretch blow molding from a preform in the shape of a bottomed cylinder. By this manufacturing method, a thin-walled polypropylene container with excellent productivity and precision can be obtained.

Example

[0020] The physical properties of the composition for the polypropylene container were investigated. Random PP used was J246M manufactured by Prime Polymer Co., Ltd. Block PP used was J557E manufactured by Prime Polymer Co., Ltd. These materials were mixed at the composition ratios shown in Table 1 and the container illustrated in FIG. 1 was molded by biaxial stretch blow molding. The wall thickness at the central part of the container body was set to 0.25 mm. The internal volume was set to 650 ml when fully filled.

[0021] The melt mass flow rate (MFR) of the resin composition was measured in accordance with JIS K7210-1:2014 using a semi-automatic melt indexer C-5059D manufactured by Toyo Seiki Seisakusho Co., Ltd. The measurement results are shown in Table 1.

[0022] Thermal analysis was measured in accordance with JIS K7121-01:2012 using a DSC8500 differential scanning calorimeter manufactured by PerkinElmer, with the composition sampled from the mouth of the blow-molded polypropylene container as the test piece. The DSC curve had temperature on the horizontal axis and differential heat quantity, for example, endothermic quantity, on the vertical axis, and was a graph in the heating direction. The temperature of the melting peak (MT) of the graph was listed in Table 1. Also, the difference ΔT between the temperature at 40% melting of the crystalline part and the melting peak temperature (MT) was listed in Table 1. The temperature at 40% melting of the crystalline part was calculated from the DSC curve as the temperature corresponding to the heat of fusion of 40% of the total heat of fusion.

[0023] Transparency was measured in accordance with JIS K7136:2000 using a Haze Mater NDH200 manufactured by Nippon Denshoku Industries Co., Ltd. on the section 3 sampled from the center of the body part 2 shown in Fig. 1(b), and the HAZE value was listed in Table 1. A HAZE value of 15 or less was evaluated as having high transparency.

[0024] Impact resistance was measured as the drop strength. A container with an internal volume of 650 ml filled to the brim as shown in Fig. 1 was filled with 630 g of water, sealed, and left standing in a constant temperature bath at 5°C for 24 hours. Then, it was dropped 5 times in an upright state from a height of 1 m onto a concrete surface. Subsequently, the same container was dropped 5 times in a state of being lying on its side at 90° from a height of 1 m onto the concrete surface. Then, the container after the drop test was observed to check for cracks or fissures, and the results were listed in Table 1.

[0025]

Table 1

[0026] Test Nos. 3 and 4 are excellent in transparency and drop strength, and ΔT is also in the range with good blow moldability. Test Nos. 1 and 2 have a small proportion of block PP and are inferior in low-temperature impact resistance. Test Nos. 5 to 7 have a small proportion of random PP and the transparency deteriorates.

Industrial Applicability

[0027] The polypropylene container of the present invention is excellent in transparency and cold impact resistance, can be easily blow-molded, and thus can be used as a container with excellent recyclability.

Explanation of Signs

[0028] 1 Polypropylene container 2 Barrel part 3 Slice acquisition part

Claims

1. The composition is a mixture of an ethylene propylene random copolymer and an ethylene propylene block copolymer, The melt mass flow rate (MFR) of the composition after mixing at 230° C. and a load of 2.16 kgf is in the range of 18 g or more and 35 g or less per 10 min, In a thermal analysis of a slice of the container obtained by a differential scanning calorimeter, the melting peak temperature is in the range of 140° C. or more and 150° C. or less. A polypropylene container, wherein the difference between the temperature when 40% of the crystalline portion is melted and the melting peak temperature is in the range of 15°C or more and 17.5°C or less.

2. The thickness of the central part of the body is in the range of 0.1 to 2.0 mm, The polypropylene container according to claim 1, which is made of a single layer and is processed by biaxial stretch blow molding from a preformed cylindrical body with a bottom.

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