JP3330708B2 - Improved polyethylene resin composition for hollow molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-density polyethylene resin composition having excellent suitability for hollow molding.

[0002]

2. Description of the Related Art High-density polyethylene is obtained by polymerizing ethylene or the like using a highly active Ziegler catalyst. The highly active Ziegler catalyst is, for example, a catalyst comprising a solid component obtained by contacting or reacting a transition metal compound such as a titanium compound with a magnesium compound, and an organoaluminum compound.

[0003] High-density polyethylene is used as a material for hollow molded articles. The hollow molded article refers to a molded article having a hollow inside, and specific examples include shampoos, liquid detergents, containers for cosmetics, kerosene cans, industrial chemical cans, and the like.

[0004] The hollow molded article is formed by hollow molding. Here, the hollow molding is also called blow molding or blow molding. The hollow molding refers to a method in which a parison of a thermoplastic plastic softened by heating is expanded using air pressure or the like, and is brought into close contact with a mold and cooled to obtain a hollow body.

[0005] The properties required of a resin for hollow molding are as follows:
Although there are differences depending on the intended use, as a basic item,
(1) It is excellent in high-speed moldability, (2) It is easy to mold with less uneven thickness, (3) The surface skin is clean, (4)
High pinch-off strength and (5) excellent environmental stress crack resistance are listed. However, high-density polyethylene produced using a Ziegler-based catalyst, particularly a high-activity Ziegler-based catalyst, had a narrow molecular weight distribution, and thus had the above-mentioned properties except for (5). As a means for solving this problem, an attempt has been made to expand the molecular weight distribution by mixing two types of high-density polyethylene having a molecular weight by two-stage polymerization or blending. Thereby, (1) moldability, (2) drawdown property (uneven thickness) for hollow molding, (3)
The surface skin, etc. has been considerably improved.

[0006]

However, when a polyethylene resin composition having a widened molecular weight distribution is used for hollow molding, there are the following problems. (1) Since the moldability, particularly the fusing property of the pinch-off part, is insufficient, the thickness of the fusing part becomes thin and the strength is often insufficient. (2) Vertical streaks are formed on the surface of the molded product, and the skin is not sufficiently clean. (3) It is difficult to widely control the surface gloss so as to be suitable for various types of hollow molded articles. Further, (4) the polyethylene resin composition containing an additive such as a stabilizer is colored due to a catalyst residue or the like, and the color tone is unfavorable. Here, the pinch-off portion refers to a blade-shaped portion for fusing the parison at the same time as closing the mold with the hollow molding mold and for fusing or removing unnecessary portions thereof. For example, a detergent bottle 10 as shown in FIG.
Has a through hole 15 for forming the handle 11. In this detergent bottle 10, a pinch-off portion is provided around the bottom 13 and the through-hole 15, and the thickness is reduced at the pinch-off portion around the through-hole 15 from the bottom 13. When the thickness of the pinch-off portion is reduced, the mechanical strength at the pinch-off portion decreases, which is a problem. The thickness of the pinch-off portion around the through hole 15 was particularly reduced at the portion 17 corresponding to the upper portion thereof. In addition, the vertical streak generally refers to a streak in the extrusion direction generated on the surface of a molded product due to a scratch on a die surface near a die lip or a degraded resin product that has accumulated.

[0007]

Therefore, in the present invention, by blending a specific additive, the fusing property and the surface skin of the pinch-off portion of the molded article are improved, and the formation of vertical streaks is suppressed. The color tone of the resin was maintained at a high level. Further, in the present invention, a wide range of surface gloss that can be applied to hollow molded articles for various uses has been achieved. According to the present invention, the melt flow rate is 0.1 to 1 g / 10 min. With a density of 0.945
A polyethylene resin composition for hollow molding, comprising 100 parts by weight of polyethylene of 0.960 g / cm ³ and 0.001 to 1 part by weight of an additive, wherein the polyethylene comprises (A) melt flow Rate 0.001
0.2 g / 10 min. With a density of 0.920 to 0.9
5 to 80 parts by weight of polyethylene which is 55 g / cm ³ ,
(B) Melt flow rate is 0.2 to 100 g / 10 m
in. And 95 to 20 parts by weight of polyethylene having a density of 0.940 to 0.973 g / cm ³ , wherein the additive comprises (a) 0 to 100% by weight of basic magnesium 12-hydroxystearate; b) A polyethylene resin composition for hollow molding, comprising 100 to 0% by weight of hydrotalcite.

[0008]

In the present invention, the melt flow rate of polyethylene comprising the components (A) and (B) having different molecular weights is 0.1 to 1 g / 10 min. It is. The melt flow rate of polyethylene is JIS K7210 1
976 Under the conditions of Table 4, 190 ° C., load 2.16
It is a value measured under the condition of kgf. If the melt flow rate of the polyethylene comprising the components (A) and (B) is less than 0.1 g / 10 min., The melt viscosity is too high, and extrusion molding becomes difficult. On the other hand, when the melt flow rate is larger than 1 g / 10 min., The melt tension of the parison becomes insufficient, which has an unfavorable effect on the drawdown property.

The density of the polyethylene comprising the components (A) and (B) is 0.945 to 0.960 g / c.
m is ^3. When the density is less than 0.945 g / cm ³ , the rigidity of the composition is insufficient and the mechanical strength is poor. On the other hand, when the density exceeds 0.960 g / cm ³ , the resistance to environmental stress cracking is reduced, and the material is easily cracked. The polyethylene component (A) used in the present invention has a melt flow rate of 0.001 to 0.001.
0.2 g / 10 min. And preferably 0.01
0.1 g / 10 min. It is. Also, if the density is 0.9
20 to 0.955 g / cm ³ , preferably 0.1 to 0.95 g / cm ³ .
It is 925 to 0.950 g / cm ³ . The (B) polyethylene component used in the present invention is a polyethylene having a lower molecular weight than the (A) polyethylene component, and has a melt flow rate of 0.2 to 100 g / 10 min. And preferably 1 to 50 g / 10 min. It is. Further, the density is 0.940 to 0.973 g / cm ³ , and preferably 0.950 to 0.970 g / cm ³ .

[0010] The polyethylene component (A) or the polyethylene component (B) is not limited to a polymer of ethylene alone, and ethylene and another α-olefin such as 1-propene,
Includes copolymers with 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, or any mixture thereof.

In order to obtain the polyethylene resin composition for blow molding of the present invention, the polyethylene component (A) and the polyethylene component (B) are mixed in a weight ratio of 5/95 to 80/20,
It is preferably obtained by mixing in the range of 20/80 to 65/35 (weight ratio). If the amount of the polyethylene component (A) exceeds 80 parts by weight, the resin pressure at the time of molding will increase, and a good surface texture will not be obtained. If the amount of the (A) polyethylene component is less than 5 parts by weight, the molding will fail. Fish eyes tend to occur frequently on the product.

The method of mixing the (A) polyethylene component and the (B) polyethylene component is not particularly limited. For example, a method of mechanically mixing separately polymerized components, a method of uniformly mixing after polymerizing each component in one polymerization reaction system, or a high melt flow rate component in the first stage And then a second step to polymerize the low melt flow rate component to obtain a desired composition. In order to mechanically mix the components to obtain the composition of the present invention, it is necessary to pay careful attention so that the components do not cause poor dispersion. Examples of the melt kneader used for mixing include a Banbury mixer, a kneader, a twin-screw extruder, and a single-screw extruder. Polymerizing in one polymerization reaction system means that in one or more reactors, (A)
This means that the polyethylene component and the (B) polyethylene component are sequentially produced, or that the reverse process is performed to produce a polymer mixture.

The polyethylene component (A) and the polyethylene component (B) used in the present invention are produced by a so-called medium / low pressure method using a transition metal catalyst, wherein ethylene or ethylene and an α-olefin having 3 to 20 carbon atoms have a required density. It is obtained by polymerizing at a ratio such that At that time, in order to obtain a desired melt flow rate, a molecular weight regulator such as hydrogen may be used. The polymerization can be performed by various methods such as slurry polymerization, gas phase polymerization, and high temperature solution polymerization. A method for synthesizing high-density polyethylene using such a highly active Ziegler catalyst is disclosed, for example, in JP-A-49-1334.
No. 88, Japanese Patent Publication No. 52-13232, Japanese Patent Publication No. 6
It is disclosed in 2-54326.

In the composition of the present invention, 0.001 to 1 part by weight, preferably 0.01 to 0. 1 part by weight, per 100 parts by weight of the polyethylene comprising the components (A) and (B).
3 parts by weight of the particular additive are incorporated. By blending the specific additives, various required properties of the hollow molded article are improved.

The additive used in the composition of the present invention comprises two components. That is, 0 to 100% by weight of the additive,
Preferably 20-80% by weight is basic magnesium 12-hydroxystearate and 100-80% of the additive.
0% by weight, preferably 80 to 20% by weight, is hydrotalcite.

Magnesium 12-hydroxystearate means (C ₁₇ H ₃₅ (OH) COO) ₂ Mg.
The term "basic" means that in a salt of 12-hydroxystearic acid, which is a carboxylic acid, and magnesium, which is a metal, an equivalent amount of the metal is a little excessive than an equivalent amount of the carboxylic acid. At this time, the excess metal is preferably in the form of an oxide or a hydroxide. The hydrotalcite used in the present invention is a hydrated basic carbonate containing magnesium and aluminum, and may be naturally occurring or synthesized. For those that naturally occur,
Given the composition of Mg ₆ Al ₂ (OH) ₁₆ (CO ₃ ) .4H ₂ O, also known as manasseite, the X-ray diffraction pattern is described on the ASTM card. The synthesized hydrotalcite can be prepared by various known methods, for example, “Pharmaceutics” Vol. 29 (1).
969) p. 215, "Nippon Kagaku Magazine" Vol. 92 (1
971) on page 514. The synthetic hydrotalcite, were obtained a variety of compositions, for _{example, Mg 4. 5 Al 2 (OH} ) 13 (CO 3) · 3.5H 2 O, M
g ₅ Al ₄ (OH) ₂₀ (CO ₃ ) 4H ₂ O, Mg ₇ Al ₃ (OH) ₁₉ (CO ₃ ) ₂ 2H ₂ O,
Etc.

The polyethylene resin composition for hollow molding of the present invention may contain additives such as a stabilizer, an ultraviolet absorber, an antistatic agent and a flame retardant, or a coloring agent. These additives or coloring agents are those usually used in polyethylene resin compositions. As the stabilizer, for example, butylhydroxytoluene (BHT), octadecyl β- (3,
A phenolic stabilizer such as 5-di-tert-butyl-4-hydroxy-phenyl) propionate (for example, trade name, IRGANOX 1076 manufactured by Ciba Geigy KK), or tris (2,4-di-tert-butyl-phenyl) phos Fight (for example, trade name ADK STAB 211
2, or Ciba Geigy Co., Ltd. product name, IRGAFOS 16
Phosphorus stabilizers such as 8) can be used.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. However, the present invention is not limited by the following examples. Using n-hexane as a polymerization solvent, a solid catalyst containing titanium and magnesium as a catalyst, and triethylaluminum as a cocatalyst, a predetermined amount of hydrogen was supplied as a melt flow rate regulator, and the temperature was raised to 75 ° C.
Butene-1 as a comonomer while maintaining at
Then, ethylene, the main component of the polymerization, was converted to a total pressure of 4 kg / c.
m ² , slurry polymerization was performed. The component (A) which was an ethylene-butene-1 copolymer having the following melt flow rate (g / 10 min.) And density (g / cm ³ ) was obtained.

When the polymerization temperature is 85 ° C. and the total pressure is 8 kg / cm
Except for using ² (A) component and similarly polymerized by following the melt flow rate (g / 10min.) And density (g /
(B), which is an ethylene-butene-1 copolymer having a cubic centimeter (cm ³ ).

[0020]

[Table 1]

Example 1 40 parts by weight of component (A), 6
0 parts by weight of the component (B), 0.05 parts by weight of a stabilizer (ADK STAB HP-10, trade name of Asahi Denka Kogyo KK);
05 parts by weight of hydrotalcite (trade name: DHT-4)
A) was mixed with a tumbler. In Table 2, calcium stearate is referred to as Ca-St. DHT-4A
It is white with _{Mg 4.5 Al 2 (OH) 13} (CO 3) · 3.5H 2 O of Formula is a fine powder odorless. DHT-4A has an M of 34%
It contains gO and 19% Al ₂ O _3, and the molar ratio of MgO to Al ₂ O ₃ is 4.5. 3 hours at 105 ° C.
The moisture when dried is 0.34%. 1 heavy metal
0 ppm or less, and the specific surface area is 10 ± 5 m ² / g. The particle size distribution measured by the LUZEX method was 95.7% for those having a particle size of 1 μm or less, and 3 for those having a particle size of 1 to 2 μm.
It is 4%, and that of 2-3 μm is 0.7%.

Next, a twin-screw granulator (manufactured by Toshiba Machine Co., Ltd.,
Using the product name TEM-35B), heat the mixture at 180 ° C.
And pelletized. The melt flow rate (g / 10 min.) And density (g / c
m ³ ) is described in the column of composition in Table 1 above. Using this pellet as a sample, the color tone (bL value) is set to SM
It was measured by a color computer SM-4-CH (manufactured by Suga Test Instruments Co., Ltd.). Note that the larger the bL value is on the plus side, the more the yellowness of the pellet is increased, and the larger the bL value is on the minus side, the lower the yellowness is, which makes the pellet more white.

The pellets were molded into a 1 liter-capacity detergent bottle with a handle using a blow molding machine (trade name: TPF-505, manufactured by Tahara Co., Ltd.). The molding temperature is 170 ° C., the output per hour is 20 kg, and the diameters of the die and the core are 56.0 mm and 54.5 mm, respectively.
The shape of this detergent bottle is shown in FIGS. A- of FIG.
A section along line A ′ is substantially elliptical as shown in FIG.
The wall thickness differs between the major axis direction and the minor axis direction. Detergent bottle 1
The thickness of the pinch-off portion 17a at the zero point 17 was measured with a micrometer. This part is the part having the smallest thickness. The vertical stripes on the surface of the molded product were visually classified into five levels. This criterion is as follows. 5: Not noticeable 4: Not noticeable 3: Slightly noticeable 2: Very noticeable 1: Very noticeable Further, the body of the detergent bottle was cut, and the gloss of the surface was measured by a reflection method using a gloss meter. This gloss meter is a digital variable angle gloss meter, UGV-5D type, manufactured by Suga Test Instruments Co., Ltd.
It was measured at an incident angle of 60 °. These results are summarized in Table 2. That is, Table 2 describes the thickness (mm, PO thickness) of the pinch-off portion, the vertical stripe of the detergent bottle, the color tone (bL value) of the pellet, and the gloss (%).

[0024]

[Table 2]

(Examples 2 to 5 and Comparative Example) Pellets and detergent bottles were produced in the same manner as in Example 1. However, in Examples 2 to 5, not only hydrotalcite but also 1
Example 2 differs from Example 1 in that magnesium 2-hydroxystearate is also added. As magnesium 12-hydroxystearate, EM-644 (trade name) of Kosei Co., Ltd. was used as it was. EM-644 is a white powder,
Containing 5.3 ± 0.2% Mg, free 12-hydroxystearic acid 2.0% or less, moisture 2.0% or less,
A powder having a melting point of 220 to 230 ° C. and a particle size of 149 μm or more is 0.1% or less. In Examples 1 to 5,
The combined amount of hydrotalcite and magnesium 12-hydroxystearate was a fixed 0.05 part by weight based on 100 parts by weight of the high-density polyethylene powder. On the other hand, in the comparative example, hydrotalcite or magnesium 12-hydroxystearate was not blended, and instead, calcium stearate, a general-purpose additive, was blended.

Compared with the comparative example using calcium stearate alone, in the example in which magnesium 12-hydroxystearate and / or hydrotalcite are blended, the thickness of the pinch-off portion is increased and the vertical streaks on the surface of the hollow molded article are reduced. You can see that Also, the color tone is equivalent or improved. The thickness of the portion 17 of the detergent bottle 10 is apt to be the thinnest, but even such a portion 17 can maintain a certain thickness. Therefore, the composition of the present invention can be suitably used for a hollow molded article having any complicated shape. For example, it is a hollow molded product having a shape having a through hole. Also, by changing the ratio of magnesium 12-hydroxystearate and hydrotalcite,
The gloss, which is an index corresponding to the smoothness of the surface of the molded product, can be controlled. That is, when the content of hydrotalcite was 100% by weight as an additive, the surface of the molded product was in a so-called sharkskin shape having fine irregularities, and the gloss (%) was small. Reduce the amount of hydrotalcite, 1
As the amount of magnesium 2-hydroxystearate was increased, the gloss (%) became larger, the unevenness of the molded product surface decreased, and the molded product became smoother. When the amount of magnesium 12-hydroxystearate was 100% by weight, the surface of the molded article became the smoothest.

Example 6 The first stage polymerization was carried out in the same manner as in the component (B), except that the polymerization temperature was 80 ° C. When the supply amounts of ethylene and butene-1 reached 110 kg, the temperature was lowered to 60 ° C, and ethylene, butene-1 and hydrogen were purged. Next, the temperature was increased to 75 ° C., and the second-stage polymerization was performed while newly supplying ethylene, butene-1, and hydrogen, to obtain 200 kg of polyethylene powder. This polyethylene powder has a melt flow rate of 0.57 g / 10 min. With a density of 0.955
g / cm ³ . The polyethylene obtained in the first stage had a melt flow rate of 35 g / 10 min.
And the density was 0.960 g / cm ³ . Except for using 100 parts by weight of this polyethylene, the additives were blended in the same manner as in Example 2 to produce pellets and detergent bottles. Table 2 shows the results.

[0028]

According to the present invention, by blending basic magnesium 12-hydroxystearate and / or hydrotalcite as an additive, the fusing property of the pinch-off portion of the hollow molded article is improved. In addition, it has an excellent effect of reducing vertical streaks and maintaining the color tone of the resin at a high level. Further, in the present invention, the surface gloss can be adjusted to have a wide range of surface gloss so as to be adaptable to a hollow molded product for various uses.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing the shape of a detergent bottle.

FIG. 2 is an explanatory diagram of a cross section taken along line A-A ′ of FIG. 1;

FIG. 3 is an explanatory view of an enlarged cross section of FIG. 1B.

FIG. 4 is an explanatory diagram of a partition wall that forms a through hole.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Detergent bottle, 11 ... Handle, 13 ... Bottom, 15 ... Through-hole, 17 ... Part, 17a ... Measurement place, 19 ... Pinch-off part

──────────────────────────────────────────────────続 き Continued on the front page Examiner Satoshi Morikawa (56) References JP-A-5-185490 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08L 23/04-23 / 08 C08L 23/16

Claims (1)

(57) [Claims] 1. The melt flow rate is 0.1 to 1 g / 1.
0 min. With a density of 0.945 to 0.960 g / cm
³ , 100 parts by weight of polyethylene and 0.001 to
A polyethylene resin composition for hollow molding containing 1 part by weight of an additive, wherein the polyethylene has (A) a melt flow rate of 0.1%.
001 to 0.2 g / 10 min. With a density of 0.920
Polyethylene 5 to 80 parts by weight of ~0.955g / cm ^3, (B) a melt flow rate 0.2~100g
/ 10 min. And the density is 0.940 to 0.973 g /
95 to 20 parts by weight of polyethylene having a molecular weight of ³ cm.sup.3, and the additive comprises (a) 0 to 100% by weight of basic magnesium 12-hydroxystearate and (b) 100 to 0% by weight of hydrotalcite. A polyethylene resin composition for hollow molding, comprising: