JP3802970B2 - Propylene polymer container excellent in impact resistance and method for producing the same - Google Patents

Description

【００３８】
【表２】

【００３９】
【表３】

【００４０】
【表４】

【００４１】
【発明の効果】
本発明によれば、従来のコールドパリソン法では困難であったプロピレン系重合体の延伸ブロー成形容器における内面側と、外面側との分子配向の偏りを解消し、耐衝撃性が顕著に改善されたプロピレン系重合体の延伸ブロー成形容器及びその製法を提供するができた。
本発明によればまた、プロピレン系重合体の目付、即ち内容積当たりの樹脂重量を低減させた場合にも、尚優れた耐衝撃性が維持され、軽量性、透明性等にも優れたプロピレン系重合体の延伸ブロー成形容器を提供することができる。
【図面の簡単な説明】
【図１】プリフォームと延伸ブロー成形容器との対応関係を示す説明図である。
【符号の説明】
１ 有底プリフォーム
２ 口部
３ 胴部
４ 閉塞底部
５ 密閉用端部
６ 外周のスクリュー部
７ サポートリング
８ 内面
９ テーパー部
１０ 肉厚のほぼ一定な長い部分
１１ 次第に肉厚の減少する部分
２１ 延伸ブロー成形容器
２２ 口部（首部）
２３ 肩部
２４ 胴部
２５ 底部
２６ 底部中央部
２７ 底部接地部
２８ 曲率部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a propylene-based polymer container excellent in impact resistance and a method for producing the same, and more specifically, formed by stretch blow molding of a bottomed preform made of a propylene-based polymer, The present invention relates to a propylene polymer container having improved impact resistance by having uniform orientation on both the inner surface and the outer surface, and a method for producing the same.
[0002]
[Prior art]
Blow molded plastic hollow containers are excellent in light weight and impact resistance, and are widely used as packaging containers for various foods, seasonings, toiletries and the like. In blow molding, the stretch temperature is the stretch temperature, and the stretch blow molded container obtained by stretching in the axial direction and expanding in the circumferential direction is compared with the direct blow container blow molded at the melting temperature. It is also known that it is excellent in terms of transparency, impact resistance, rigidity, gas barrier properties and the like.
[0003]
As resins for stretch blow molded containers, crystalline and molecularly oriented thermoplastic resins are used, and those made of polyethylene terephthalate are common, but those made of propylene polymers have also been known for a long time. ing.
[0004]
In the method for producing a stretch blow molded container from a propylene polymer, a propylene polymer parison (pipe-shaped molded product) at a stretching temperature is held by two clamps and stretched in the axial direction. A method in which this is sandwiched in a split mold and expanded and stretched by blowing, or a propylene-based polymer is injection-molded to produce a bottomed preform in a supercooled state. There is known a cold parison method in which the film is heated and then attached to a split mold to perform stretch blow molding.
[0005]
[Problems to be solved by the invention]
However, in the former molding method, there is an advantage that a preform injection step is unnecessary, but it is difficult to mold the container mouth portion according to the size and shape of the split mold, and there is an accuracy between the lid and the lid. There is a problem that it is difficult to form a high seal.
[0006]
On the other hand, in the case of the latter cold parison method, it is possible to improve the sealing accuracy of the container mouth because the container mouth is formed in advance by injection molding, but the cold parison method is used. The propylene polymer container thus obtained is inferior in impact resistance, and it is recognized that the trunk portion near the bottom portion is easily cracked by an impact such as dropping. This tendency is particularly noticeable when the weight of the container is reduced for weight reduction of the container or resource saving.
[0007]
Accordingly, an object of the present invention is to eliminate the above-mentioned drawbacks in a propylene polymer stretch blow molded container produced by the cold parison method, and to significantly improve the impact resistance of the propylene polymer stretch blow molded container. In providing its manufacturing method. Another object of the present invention is that even when the weight of the propylene-based polymer, that is, the resin weight per internal volume is reduced, excellent impact resistance is maintained, and light weight, transparency and the like are also excellent. It is in providing the stretch blow molding container of a propylene-type polymer, and its manufacturing method.
[0008]
[Means for Solving the Problems]
According to the present invention, in a container formed by stretch blow molding of a bottomed preform made of a propylene-based polymer and having a substantially unstretched neck, a stretched barrel, and a bottom, an inner surface and an outer surface of the barrel The following formula (1)
d = | Δ _O −Δ _I | (1)
_{Δ O = N ZO -N XO ...} (1a)
_{Δ I = N ZI -N XI ...} (1b)
_Where N _ZO is the refractive index in the height direction on the outer surface of the trunk,
N _XO is the refractive index in the thickness direction on the outer surface of the trunk,
N _ZI is the refractive index in the height direction on the inner surface of the body,
N _XI is the refractive index in the thickness direction on the inner surface of the body part,
The difference (d) in birefringence defined by the formula (1) is 0.0025 or less in absolute value, and the basis weight is 1.50 to 6.00 g / 100 ml. A polymeric container is provided.
In the stretch blow molded container of the present invention,
1. The propylene-based polymer is an ethylene / propylene random copolymer, particularly an ethylene / propylene random copolymer having an ethylene content of 3 to 5 mol% and a melt flow rate (MFR) of 15 to 35 g / 10 min;
2. Having a density of 0.885 to 0.915 g / cm ^{3 at} the unstretched neck and 0.0015 g / cm ³ higher than the unstretched neck at the body;
3. The center of the bottom is raised 5 to 15 mm higher than the surrounding installation part and formed on the bottom,
4). The connecting portion between the body portion and the bottom portion is formed as a curvature portion having a curvature radius of 10 mm or more;
Is preferred.
According to the present invention, the propellant-based polymer is injection-molded so that the weight of the container of the bottomed preform provided with the lid and the mouth to be sealed is 1.5 to 6.00 g / 100 ml. A step of manufacturing, a step of heating the preform from the periphery and the inside to heat to a stretch forming temperature so that a temperature difference between the inside and the outside of the preform is within 5 ° C., and a step of heating the preform Provided is a method for producing a propylene polymer container excellent in impact resistance, characterized by being stretch-drawn in the height direction and blow-drawn in the circumferential direction.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
[Action]
As a result of repeated studies to improve the impact resistance of a propylene-based polymer stretch blow molded container formed by the cold parison method, the present inventors have found the following interesting fact.
1. Even in a stretch blow molded container of propylene polymer, the vessel wall of the body portion is generally biaxially oriented in the container height direction and the container circumferential direction, but the propylene polymer container by the conventional cold parison method is used. However, the molecular orientation is relaxed on the inner surface side of the vessel wall, while the molecular orientation is relaxed on the outer surface side of the vessel wall, and this tendency is particularly noticeable in the molecular orientation in the height direction. The propylene-based polymer container having a crack is easily cracked by an impact such as dropping (see the comparative example described later).
2. The molecular orientation of the plastic can be evaluated by birefringence (Δ). Assuming that the container wall of the container has a refractive index N _X in the thickness direction, a refractive index N _{Y in} the circumferential direction, and a refractive index N _Z in the height direction, the refractive index N _{X in the} thickness direction is related to the molecular orientation. Birefringence Δ _Y = N _Y -N _X
Denotes the degree of molecular orientation in the circumferential direction, and birefringence Δ _Z = N _Z −N _X
Represents the degree of molecular orientation in the height direction.
3. In the conventional cold parison propylene-based polymer container, the birefringence Δ _Z on the inner surface side of the body portion is as large as 0.0171, while the birefringence Δ _Z on the outer surface side of the body portion is as large as 0.0022. A large value is shown, and the difference (d) is as large as 0.0149.
4). Thus, the orientation structure of the vessel wall whose inner surface is strongly stretched and whose outer surface is oriented is very weak against tearing in the direction perpendicular to the height direction (circumferential direction). Easily cracks.
5). In the present invention, the difference in molecular orientation between the inner surface side and the outer surface side of the body part wall is eliminated, and the difference (d) in absolute value of birefringence defined by the above formula (1) is 0.0025 or less, particularly By setting it to 0.0020 or less, resistance to impacts such as dropping can be remarkably improved, and this fact will become clear by referring to the description of Examples described later. In particular, in the present invention, it should be noted that excellent impact resistance can be obtained even when the basis weight is reduced to 5 g / 100 ml or less.
6). In the production method of the present invention, a step of producing a bottomed preform having a mouth and a mouth to be sealed by injection molding a propylene-based polymer, a step of heating the preform to a stretch molding temperature, It consists of a step of drawing and stretching the heated preform in the height direction and blow-drawing in the circumferential direction. When the preform is preheated, the preform is heated from the inside and outside of the preform, and the inside and outside of the preform. And the temperature difference is within 8 ° C., particularly within 5 ° C., thereby eliminating the difference in molecular orientation between the inner surface side and the outer surface side of the body wall, The difference (d) in the absolute value of the birefringence defined in (1) can be made 0.0025 or less, particularly 0.0020 or less.
7). In other words, the propylene-based polymer has low thermal conductivity, and when the preform is heated from the surroundings, there is a considerable temperature difference between the temperature of the outer surface of the preform and the temperature of the inner surface. Since the allowable temperature range of molding is narrow, the orientation distribution structure described above is obtained, but by applying the heating method and temperature control of the present invention, it is possible to impart uniform molecular orientation on the inner and outer surfaces. is there.
8). In the present invention, the central portion of the bottom portion is further raised 5 to 15 mm higher than the surrounding grounding portion, or the bottom portion is further formed as a curvature portion having a curvature radius of 10 mm or more. This also makes it possible to further improve the impact resistance of the container.
[0010]
[Propylene polymer]
In the present invention, a propylene copolymer mainly composed of homopolypropylene or propylene is used as the propylene polymer. Examples of the propylene copolymer include an ethylene / propylene random copolymer and an ethylene / propylene block copolymer. In general, the melt flow rate is suitably in the range of 0.3 to 80 g / 10 min, but in the present invention, it is in the range of 15 to 35 g / 10 min, particularly 20 to 30 g / 10 min. Desirable in terms.
[0011]
The type of propylene polymer to be used varies depending on the use of the container and the required characteristics. For example, homopolypropylene may be used for applications that require strength, while ethylene / propylene random copolymers may be used for applications that require transparency.
[0012]
As the propylene polymer, it is desirable to use a propylene polymer having a wide molding allowable temperature range. Examples of such a propylene polymer include an ethylene / propylene random copolymer having an ethylene content of 3 to 5 mol% and a melt flow rate (MFR) of 20 to 30 g / 10 min.
[0013]
The reason why the range of the ethylene / propylene random copolymer is as described above is that when the ethylene content is less than the above range, the elongation at the time of stretch blow molding tends to decrease, whereas the ethylene content is within the above range. It is because there exists a tendency for the intensity | strength of a container to fall when more than it is. Further, when the melt flow rate is outside the above range, the stretch moldability tends to decrease.
[0014]
It goes without saying that the propylene-based polymer used in the present invention may contain a stabilizer known per se, for example, an antioxidant, a heat stabilizer, a nucleating agent, a lubricant, a colorant and the like according to a formulation known per se. is there.
[0015]
[preform]
In the present invention, a propylene-based polymer is injection-molded to first produce a bottomed preform having a lid and a mouth portion to be sealed.
[0016]
In FIG. 1, which shows an example of the correspondence between a bottomed preform and a stretch blow molded container, the bottomed preform 1 has the shape of a test tube as a whole, and has a mouth portion 2, a trunk portion 3, and a closed bottom portion. It consists of four. The mouth portion 2 has the same shape and dimensions as the mouth portion of the final container, and includes a sealing end portion 5, an outer peripheral screw 6, and a support ring 7.
[0017]
The preform 1 to be used should not change in extreme shape and dimensions. This is because if there is a thin part in the preform, that part will be extended first. In the preferred preform shown in FIG. 1, the inner surface 8 of the body portion 3 has a tapered shape whose diameter gradually decreases toward the bottom portion, and the bottom portion 4 has a hemispherical surface on both the inner surface and the outer surface. On the other hand, the outer surface of the body portion is connected to a long portion 10 having a substantially constant thickness through a tapered portion 9 that gradually increases in thickness following the connection portion with the mouth portion, and gradually decreases in thickness. It is connected to the bottom part 4 via the part 11 which performs. A thickness distribution of the preform 1 is shown in FIG.
[0018]
The injection conditions of the preform are not particularly limited, but generally, the injection is performed at an injection temperature of 180 to 240 ° C. and an injection pressure of 200 to 1000 kg / cm ² , cooled in the mold, and a bottomed preform. Can be molded.
[0019]
[Preheating]
According to the present invention, prior to stretch blow molding, a propylene-based polymer preform is heated from the surroundings and the inside so that the temperature difference between the inside and the outside of the preform is within 8 ° C. Heat to.
[0020]
In general, the stretch molding temperature of the propylene polymer is in the range from a temperature 50 ° C. lower than the melting point (Tm) of the propylene polymer to a temperature 10 ° C. lower than the melting point (Tm). The stretch molding temperature (Tb) in which the difference (d) between the birefringence and the inner surface side birefringence falls within the range defined in the present invention is not so wide, and this temperature (Tb) varies depending on the type of resin. For example, in the case of the ethylene-propylene random copolymer described above, 130 ° C. ± 10 ° C., particularly 130 ° C. ± 5 ° C. is suitable.
[0021]
That is, if this stretch molding temperature is too low, stretch molding becomes difficult, and even if stretch blow molding is possible, there is an adverse effect due to overstretching. On the other hand, when the stretch molding temperature is too high, impact resistance tends to decrease, white turbidity due to crystallization of the propylene-based polymer on the vessel wall tends to occur, and the container mouth tends to be thermally deformed. In this sense, it is extremely important to heat the preform so that the temperature difference between the inside and outside of the preform falls within the above range.
[0022]
For this purpose, and because the thermal conductivity of the propylene-based polymer is low, in the present invention, it is necessary to perform heating from both the periphery and the center side of the preform. Although there is no particular limitation, heating is performed from the periphery of the preform with a quartz heater, and an iron core is inserted in the approximate center of the preform so as to be heated from the inside. By performing heating from both sides, uniform heating can be performed in a short time of 30 to 60 seconds.
[0023]
[Stretch blow molding]
Holding the preheated preform in the split mold, inserting a stretching rod through the preform mouth, pulling and stretching the preform in the axial direction, and expanding and stretching the preform in the circumferential direction by blowing gas. . Blowing by gas blowing may be performed in a single stage, or pre-blowing may be performed with a fluid having a relatively low pressure, and then final blowing may be performed with a fluid having a relatively high pressure.
In such a case, the stretching speed is determined with reference to the material after stretching by pre-blow. The initial high speed blow stretching speed in the present invention is generally 100 to 280 area times / second, particularly 140 to 240 area times / second.
[0024]
In order to produce a container having a birefringence difference (d) as defined in the present invention, it is advantageous to slowly inflate the preform at a low pressure. For this purpose, the capacity of the final container and the thickness of the preform are advantageous. However, the initial pressure of the gas generally used is preferably in a relatively low range of 0.50 to 5.00 kg / cm ² . In the present invention, as the pressurizing fluid, unheated air or inert gas, heated air or inert gas can be used, but generally unheated ordinary air can be used.
[0025]
The draw ratio in the final container is suitably 4 to 20 times, especially 5 to 16 times in terms of area magnification, while the axial draw line ratio is 2 to 4 times, particularly 2.5 to 3.5 times, and the circumferential direction. The draw line magnification is preferably 2 to 5 times, particularly 2.5 to 4 times.
[0026]
[Stretch blow molded container]
Returning to FIG. 1 described above, the stretch blow molded container 21 of the present invention includes an unstretched mouth portion (neck portion) 22, a bulging frustoconical shoulder portion 23, a cylindrical trunk portion 24, and a closed bottom portion 25. Consists of. The shape and dimensions of the mouth 22 are the same as those of the preform.
[0027]
On the other hand, in the bottom portion 25, the center portion 26 of the bottom portion is formed 5 to 15 mm higher than the surrounding grounding portion 27 and formed on the bottom, and has a structure that is more resistant to dropping impact. Further, the connecting portion between the body portion 24 and the bottom portion grounding portion 27 is formed as a curvature portion 28 having a radius of curvature of 10 mm or more, which also helps to make the structure resistant to impacts such as dropping.
[0028]
Below the body portion 24, a bulging ring portion 29 having a relatively large diameter and a grooved ring portion 30 having a relatively small diameter adjacent to the bulging ring portion 29 are provided, and a slight amount in the container axial direction is provided. Deformation is also allowed. Further, an inward wavy bead portion 31 having a relatively small diameter is formed in a main portion of the trunk portion, and the trunk portion is reinforced.
[0029]
In the body portion 24, the birefringence difference (d) defined by the formula (1) is 0.0025 or less, particularly 0.0020 or less in absolute value, but the outer surface side complex defined by the formula (1a) is not larger. The refraction Δ _O is generally in the range of 0.0035 to 0.0080, and it can be seen that the molecular orientation is effectively imparted not only to the inner surface side but also to the outer surface side.
[0030]
On the other hand, the birefringence in the circumferential direction Δ _Y = N _Y −N _X is generally 0.0025 or less, and there is no molecular orientation in the circumferential direction, or if any, it is smaller than the molecular orientation in the height direction. In the stretch blow molded container of the present invention, uniaxial orientation is prioritized, and it is surprising that it is excellent in impact resistance.
[0031]
In FIG. 1, the correspondence between each position of the body portion of the preform 1 and each position of the vessel wall of the stretch blow molded container 20 is shown by connecting both in a straight line. Further, the thickness distribution of the stretch blow molded container 20 is shown in a graph in FIG. 1B. From this graph, it is understood that the stretch blow molded container 20 of the present invention has no uneven thickness and is uniformly stretched, and is excellent in thickness uniformity.
[0032]
The degree of orientation of the propylene polymer in the stretch blow molded container can also be evaluated by the density of the vessel wall. In the case of the ethylene / propylene random copolymer described above, the density of the unstretched neck is 0.885 to 0.915 g / cm ³ , and the body has a density higher than the unstretched neck by 0.0015 g / cm ³ or more. This value also confirms that molecular orientation is effectively performed.
[0033]
The stretch blow molded container of the present invention has sufficient impact resistance even when the basis weight is 1.50 to 6.00 g / 100 ml, and is a container excellent in lightness, transparency and appearance characteristics. It is useful as a container for filling and sealing foodstuffs.
[0034]
【Example】
The invention is further illustrated by the following examples.
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.
In the following examples, tests and evaluations were performed as follows.
The measurement methods used in this example and comparative example are described below.
(1) Measurement of birefringence The refractive index in the thickness direction, the circumferential direction, and the height direction was measured with an Abbe refractometer, and birefringence was determined therefrom.
(2) Measurement of density The density was measured with a density gradient tube.
(3) Measurement of low temperature drop impact strength After filling a molded bottle with a specified amount of water and storing it in a refrigerator at 5 ° C for a whole day and night, the bottle can be dropped upright and horizontally from any height to check for damage. Check. The higher the breaking height, the stronger the impact strength, and the lower the breaking height, the weaker the impact strength.
[0035]
Example 1
A propylene polymer is injection molded to produce a bottomed preform. The bottomed preform is heated to a stretching temperature, and then attached to a split mold and stretch blow molded to produce the propylene polymer container of the present invention.
The propylene-based polymer used is an ethylene / propylene random copolymer having an ethylene content of 3 to 5 mol% and a melt flow rate (MFR) of 20 to 30 g / 10 min.
In the stretch blow molded container of propylene-based polymer, the vessel wall of the body is generally biaxially oriented in the container height direction and the container circumferential direction. In the present invention, by reducing the difference in molecular orientation between the inner surface side and the outer surface side of the vessel wall, the resistance to impacts such as dropping can be remarkably improved.
The degree of molecular orientation by stretching was confirmed by birefringence and density.
The degree of drop impact was confirmed by a low temperature drop test.
The obtained results are shown in Tables 1, 3 and 4.
[0036]
Comparative Example 1
A bottomed preform is produced in the same manner as in the examples, and stretch blow molding is performed by a conventional cold parison method. In the conventional method, the temperature difference between the inner side and the outer side of the preform is 6 ° C. or more. When molded by this molding method, the molecular orientation is strongly oriented on the inner surface side of the vessel wall, whereas the molecular difference is present on the outer surface side of the vessel wall. The orientation is relaxed, and this tendency is particularly remarkable in the molecular orientation in the height direction, and the propylene polymer container having such orientation characteristics is easily cracked by an impact such as dropping. This is because such an oriented structure is extremely weak against tearing in the direction perpendicular to the height direction (circumferential direction).
The degree of molecular orientation by stretching was confirmed by birefringence and density.
The degree of drop impact was confirmed by a low temperature drop test.
The obtained results are shown in Table 2, Table 3 and Table 4.
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
[Table 3]

[0040]
[Table 4]

[0041]
【The invention's effect】
According to the present invention, the deviation in molecular orientation between the inner surface side and the outer surface side in the stretch blow molded container of a propylene polymer, which was difficult with the conventional cold parison method, is eliminated, and the impact resistance is remarkably improved. A propylene-based polymer stretch blow molded container and a method for producing the same were provided.
According to the present invention, even when the weight of the propylene-based polymer, that is, when the resin weight per inner volume is reduced, the excellent impact resistance is maintained, and the propylene has excellent lightness, transparency, etc. A stretch blow molded container of a polymer can be provided.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a correspondence relationship between a preform and a stretch blow molded container.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Bottomed preform 2 Mouth part 3 Body part 4 Closed bottom part 5 Sealing end part 6 Outer screw part 7 Support ring 8 Inner surface 9 Tapered part 10 Thick part with almost constant thickness 11 Part 21 with gradually decreasing thickness Stretch blow molded container 22 mouth (neck)
23 shoulder part 24 trunk part 25 bottom part 26 bottom center part 27 bottom part ground contact part 28 curvature part

Claims (6)

In a container formed by stretch blow molding of a bottomed preform made of a propylene polymer and having a substantially unstretched neck, stretched barrel and bottom, the following formula (1) on the inner and outer surfaces of the barrel
d = | Δ _O −Δ _I | (1)
_{Δ O = N ZO -N XO ...} (1a)
_{Δ I = N ZI -N XI ...} (1b)
_Where N _ZO is the refractive index in the height direction on the outer surface of the trunk,
N _XO is the refractive index in the thickness direction on the outer surface of the trunk,
N _ZI is the refractive index in the height direction on the inner surface of the body,
N _XI is the refractive index in the thickness direction on the inner surface of the body part,
The difference (d) in birefringence defined by the formula (1) is 0.0025 or less in absolute value, and the basis weight is 1.50 to 6.00 g / 100 ml. Polymer container. The propylene-based polymer is an ethylene / propylene random copolymer having a density of 0.885 to 0.915 g / cm ³ at the unstretched neck and 0.0015 g / cm at the body than the unstretched neck. The container according to claim 1, wherein the container has a density of ³ or more. The container according to claim 1 or 2, wherein the propylene polymer is an ethylene / propylene random copolymer having an ethylene content of 3 to 5 mol% and a melt flow rate (MFR) of 15 to 35 g / 10 min. The container according to any one of claims 1 to 3, wherein a central part of the bottom part is formed at a bottom which is raised 5 to 15 mm higher than a surrounding installation part. The container according to any one of claims 1 to 4, wherein a connecting portion between the body portion and the bottom portion installation portion is formed as a curvature portion having a curvature radius of 10 mm or more. A step of producing a bottomed preform having a lid and a mouth to be sealed by injection-molding a propylene-based polymer so that the basis weight of the container is 1.5 to 6.00 g / 100 ml; A process of heating the reform from the periphery and the inside to heat the stretch so that the temperature difference between the inside and the outside of the preform is within 5 ° C., and stretching the heated preform in the height direction. And a method of producing a propylene polymer container excellent in impact resistance, characterized by being blow-drawn in the circumferential direction.

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