JPH1134151A - Stretched polypropylene container and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the low temperature impact strength, transparency, coloring properties, glossiness, moistureproofness, formability and the like by a method wherein the melt flow rate of a polypropylene and its ethylene content are set to be specified values. SOLUTION: A polypropylene, the ethylene content of which is set to 2.5-15% and the melt flow rate(MFR) of which is set to 5 g/min or less, is used. As the manufacturing method of a container, a stretch blow molding by a hot parison method, which can execute both an injection and a blow molding continuously, is employed. Through the stretch blow molding, molecules are stretch- orientated, resulting in enhancing the strength of the container and also its low temperature impact strength. As for the preferable adding method of an ethylene component, the ethylene component is random-copolymerized at polymerization from the view points of the aspect of cost, the stability of material and the like. Further, the employment of organic phosphate-based crystal nucleating agent is referable in order to improve the heat resistance and formability of the container.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drawn polypropylene container excellent in low-temperature impact strength, transparency, coloring, gloss, moisture-proofing property, moldability, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Polypropylene blow containers are widely used as containers for foods, toiletries, detergents, medical supplies, etc. due to their excellent physical properties such as light weight, low cost, moisture proof, heat resistance, chemical resistance, and transparency. Most of these polypropylene blow containers are made by direct blow molding. Since the direct blow polypropylene container has a problem of insufficient transparency, a polypropylene blow container by an injection blow molding method has recently been developed.

[0003] However, a blow container having sufficient transparency and sufficient moldability has not been obtained by the injection blow molding method. In addition, the direct-blow polypropylene container has a problem that it breaks when dropped from a container stored at a low temperature because polypropylene has a property of low impact strength at low temperature.
As a solution, rubber components such as ethylene propylene rubber have been added to increase the low-temperature impact strength, but it is economically problematic to use blow containers at low unit prices because of the high cost. And it has not been put to practical use.

As a method of improving the low-temperature impact strength,
This is a method in which polypropylene is stretch blown. But,
Although the low-temperature impact strength is slightly improved, the problem has not been completely solved. This is because the stretch blow molding of polypropylene has a high degree of crystallinity (30 to 60%) and its thermal characteristics are not suitable for stretch molding.

[0005] Some polypropylene blown containers require concealment, and some have been developed by a stretch blow molding method in consideration of improvement in low-temperature impact strength.
However, most of them are based on the so-called cold parison method, in which the preform is injection-molded, then cooled, the preform is reheated by another machine, and stretch blow is performed. When the colored stretch blow container is formed by the cold parison method, the inorganic substance of the colorant is affected by infrared rays when the preform is heated. As a result, the preform temperature becomes non-uniform and molding cannot be performed. Further, even if it can be molded, the surface of the bottle becomes cloudy and a glossy container cannot be obtained.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a stretch blown polypropylene container having characteristics such as excellent low-temperature impact strength and moisture resistance, and excellent transparency. Another object of the present invention is to provide a stretch-blown polypropylene container which is opaque and has a glossy coloring.

[0007]

According to the present invention, in order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that the polypropylene has a melt flow rate (MFR) of 5 g / min or less and an ethylene content of 2 g / min. It is a stretch-blow polypropylene container characterized by having a concentration of 0.5 to 15%.

[0008] The invention described in claim 2 is the first invention.
(4) A stretched polypropylene container characterized by adding a crystal nucleating agent to polypropylene used as a resin in the polypropylene container described in (1). The invention according to claim 3 is a drawn polypropylene container characterized in that an organic phosphoric acid-based or sorbitol-based crystal nucleating agent is used as the crystal nucleating agent according to claim 2.

A fourth aspect of the present invention is a stretched polypropylene container characterized in that the container according to any one of the first to third aspects uses a colored resin. A fifth aspect of the present invention is a stretch blown polypropylene container characterized in that a label is placed on the surface of the stretch blow container according to any one of the first to fourth aspects. The invention according to claim 6 is a method for producing a stretch-blow polypropylene container, wherein the stretch-blow polypropylene container is molded using a stretch blow molding method in which injection, pre-blow, and stretch blow are continuously performed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been achieved by using a combination of the following methods as a method for improving the low-temperature impact strength of a polypropylene container. 1) Use polypropylene having an ethylene content of 2.5 to 15%, preferably 3.5 to 8%. 2) As a method for manufacturing a container, stretch blow molding by a hot parison method in which injection and blow molding are continuously performed is used. Here, if the ethylene content is less than 2.5%, the low-temperature impact strength is decoy, and if it exceeds 15%, the flexibility as a container tends to be too large. Further, it is difficult to mold a container with polypropylene having an ethylene content of more than 15%.

The ethylene component may be added by a method such as random copolymerization or block copolymerization of ethylene during the polymerization of polypropylene, or by adding linear low density polyethylene, low density polyethylene, ethylene propylene rubber to polypropylene or a polypropylene copolymer. And the like as an ethylene component. Although the ethylene component may be added by any method, a method of randomly copolymerizing the ethylene component at the time of polymerization is often used from the viewpoint of cost and material stability.

On the other hand, by performing stretch blow molding,
The molecules are stretched and oriented, the strength of the container is increased, and the low-temperature impact strength is also increased. By combining the above two points, the amount of ethylene content can be reduced below normal, and copolymerization or blending with polypropylene so that the ethylene content becomes 2.5% or more is effective in improving the low-temperature impact strength.

Further, in order to improve the stretch blow moldability by the hot parison method, it was achieved under the following conditions. 1) Use a polypropylene having an MFR of 5 g / min or less. 2) Use polypropylene having an ethylene content of 15% or less. 3) A nucleating agent is added in a range of 5000 ppm or less. When polypropylene having an MFR of 5 g / min or more is used, pre-blowing cannot be performed successfully for the above-mentioned reason, and stretch blow molding cannot be performed. By using polypropylene having an MFR of 5 g / min or less, a good stretch blow container can be obtained. Further, by adding a crystal nucleating agent, heat resistance is increased and moldability is improved.

Furthermore, since uniform spherulites are formed during injection molding, distortion during injection molding is reduced, stretch blow molding is facilitated, spherulites of crystals are reduced, and the transparency of molded products is improved, and gloss is improved. The degree improves. The type of the crystal nucleating agent may be a sorbitol type or an organic phosphate type, as long as it is a type that makes spherulites fine.Organic metal carboxylate, and inorganic talc, phosphorus Acid salt, titanium white, alum and the like. The nucleating agent to be used is not particularly limited, but an organic phosphate-based nucleating agent is often used in terms of odor.

Hereinafter, the stretch blow molding method according to the hot parison method of the present invention will be described. As a first step, injection molding of a preform is performed. Depending on the molding machine, rotation or movement is performed, and the process proceeds to the second step. In the second step, the temperature of the preform injection-molded in the first step is controlled, and compressed air is blown into the preform for stretching. Next, moving to the third step, the pre-blow preform formed in the second step is stretch-blown by using both a stretching rod and compressed air.
Obtain container shape. Here, the stretching ratio and the blow pressure for the pre-blow and stretch blow depend on the final container shape, the molding machine, and the resin used. It is desirable to stretch by 2.2 times. The stretch blow ratio is 1.0 to 4.0 in the longitudinal direction.
It is desirable to perform double stretch molding. The preliminary blow pressure is 1 to 10 kgf / cm ² , and the stretch blow pressure is ² kgf / cm ² .
A pressure setting of ４０40 kgf / cm ² is desirable. The shape of the preform is generally a test tube type, but the shape is not limited, and is not limited to a preform shape such as a disk shape or a conical shape.

In the stretched polypropylene container molded as described above, the label is placed on the bottle surface by inserting a heat-adhesive label into a blow mold during stretch blow. Can be. In this case, since the surface resin temperature when stretch blown is lower than that when blown by direct blow, a heat-adhesive label with low-temperature sealability is required as the heat-adhesive label used at this time. It is said. Examples of the label configuration include those coated with an adhesive mainly composed of an ethylene-vinyl acetate copolymer, and those having a polyethylene-based adhesive layer polymerized using a metallocene catalyst.
The material is not limited to this, and any material having an adhesive layer having low-temperature adhesion can be used. In addition to the configuration in which the label is placed by bonding as described above, a configuration in which the label is placed by integrating it around the body after forming the container using a shrink film may be used.

[0017]

【Example】

<Example 1> Hot parison stretch blow molding machine (Nissei AS
Using a random polypropylene copolymer (MFR: 1.8 g / min, ethylene content: 3.8%, containing a crystal nucleating agent) at Nissei ASB50-T manufactured by B Co., Ltd.
An oval container having a capacity of 600 ml was molded. The conditions at this time are as follows. Injection molding temperature: 205 ° C. Injection mold temperature: 15 ° C. Pre-blow stretch ratio: 1 × longitudinal direction, 1.7 × transverse direction Pre-blow air pressure: 5 kgf / cm ² Pre-blow mold temperature: 100 ° C. Stretch blow ratio : Double lengthwise, horizontal (longitudinal) 2.1
2 times, (transverse direction) 1.6 times Stretching blow air pressure: 15 kgf / cm ² Bottle weight: 17 g Bottles molded under these conditions can be molded without any problems during molding, and are extremely transparent. It was excellent. The obtained container was filled with 600 ml of water.
After filling and storing at 5 ° C. for 24 hours, the bottle fell upright on concrete, but did not crack or otherwise, and was a bottle with extremely low-temperature impact strength. The container is filled with 600 ml of water, and the room temperature is set to 40 ° C. and the humidity is set to 2
As a result of preservation at 0%, the container was reduced by only 2.67% in one year and was a container excellent in moisture-proof property.

<Example 2> As in Example 1, a random polypropylene copolymer (MFR: 1.8 g / min, ethylene content: 3.8%, containing a crystal nucleating agent) was used.
An oval container having a capacity of 600 ml was molded. Here, 2% of titanium oxide was added as a coloring agent. The molding conditions were the same as in Example 1. As in Example 1, the molded bottle could be molded without any problems during molding, and was a container having high low-temperature impact strength and excellent moisture resistance. In addition, the opacity when colored was sufficient and the glossiness of the surface was high.

<Example 3> A random polypropylene copolymer (MFR: 1.3 g / min, ethylene content: 3.0%, containing a crystal nucleating agent) was used in the same manner as in Example 1.
An oval container having a capacity of 600 ml was molded. Here, 5% of titanium oxide was added as a coloring agent. The molding conditions are the same as in Example 1. Example 1 shows the molded bottle.
Similarly to the above, the container could be molded without any problems at the time of molding, and had a strong low-temperature impact strength and an excellent moisture-proof property. In addition, the opacity when colored was sufficient and the glossiness of the surface was high.

Comparative Example 1 In the same manner as in Example 1, a random polypropylene copolymer (MFR: 20 g / min, ethylene content: 4.6%, containing a crystal nucleating agent) was used.
An oval container having a capacity of 600 ml was molded. The conditions at this time are as follows. Injection molding die temperature: 15 ° C Pre-blow stretch ratio: 1 time in the vertical direction, 1.7 times in the horizontal direction Pre-blow air pressure: 5 kgf / cm ² Mold temperature for pre-blow: 100 ° C. Stretch blow ratio: 2 times in the vertical direction, Lateral (longitudinal) 2.1
1.6 times (transverse direction) Stretch blow air pressure: 15 kgf / cm ² Bottle weight 17 g However, during pre-blowing, it bursts or deforms, and the optimum molding conditions cannot be found, and the bottle shape cannot be obtained. Was.

<Comparative Example 2> As in Example 1, using a random polypropylene copolymer (MFR: 8 g / min, ethylene content: 4%, containing a crystal nucleating agent), molding an oval-shaped container having a capacity of 600 ml. Was done. The conditions at this time are as follows. Injection molding temperature: 200 ° C Injection mold temperature: 15 ° C Pre-blow stretch ratio: 1 time in the longitudinal direction, 1.7 times in the transverse direction Pre-blow air pressure: 5 kgf / cm ² Mold temperature for pre-blow: 100 ° C. Stretch blow ratio : Double lengthwise, horizontal (longitudinal) 2.1
1.6 times (transverse direction) Stretch blow air pressure: 15 kgf / cm ² Bottle weight 17 g Although bottle shape could be obtained under these molding conditions,
There was a problem in moldability. 600 water in molded bottle
After the container was filled up with ml and stored at 5 ° C. for 24 hours, it fell on concrete in an upright manner, and a phenomenon such as cracking occurred, and the container had a problem of low-temperature impact strength.

[0022]

According to the present invention, the composition of the resin used in the stretched polypropylene container has an ethylene content of 2.5% or more, preferably 3.5% or more, and a melt flow rate (MFR) of 5 g. Since a polypropylene of not more than / min is used, a stretched polypropylene container excellent in transparency, moisture resistance and low-temperature impact resistance can be obtained, and stretch blow moldability is good.

The hot parison method of continuously performing injection and stretch blow is suitable for the production of the present invention. If the melt flow rate in this stretch blow is 5 g / min or more, pre-blowing cannot be performed well and molding cannot be performed. First, MFR
However, if the rate is 5 g / min, the resin tends to be stretched, so that a high temperature portion extends and a low temperature portion does not spread, and pre-blowing cannot be performed well. As a result, stretch blow cannot be performed well, and a good stretched polypropylene container cannot be obtained. Melt flow rate is 5g / m
The use of polypropylene of in or less provides good pre-blow moldability without being affected by temperature differences during pre-blow and injection molding of the preform. Thereby, stretch blow is good and a good stretched polypropylene container is obtained.

Further, by adding a crystal nucleating agent to polypropylene, the transparency and glossiness are improved. Further, by using an organic phosphoric acid-based nucleating agent, the transparency is further improved and the odor is reduced. It can be reduced.

The present invention is configured as described above.
A stretched polypropylene container having excellent physical properties such as low-temperature impact strength, moldability, moisture resistance and the like, and having excellent transparency or being colored and having concealing properties and glossiness can be obtained.

Claims (6)

[Claims] 1. A melt flow rate (MFR) of 5 g / 1
0min or less and ethylene content is 2.5 ~ 1
A stretched propylene container characterized by being stretch blow-molded using 5% polypropylene. 2. The stretched polypropylene container according to claim 1, wherein a crystal nucleating agent is added to polypropylene. 3. The stretched polypropylene container according to claim 2, wherein an organic phosphate-based or sorbitol-based crystal nucleating agent is used as the nucleating agent. 4. The stretched polypropylene container according to claim 1, wherein a colorant is added to the polypropylene. 5. The stretched polypropylene container according to claim 1, wherein a label is placed on the surface. 6. An injection / stretch blow molding method for continuously performing injection / stretch blow and molding.
A method for producing a stretched polypropylene container according to any one of claims 1 to 5.