JP2738643B2 - Polyethylene composition for hollow molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-density polyethylene 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, the basic items are (1) excellent high-speed moldability, (2) easy molding with less uneven thickness, (3) clean surface skin, and (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, it has been attempted to increase 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 composition having an enlarged molecular weight distribution is used for hollow molding, vertical lines and weld marks may be formed, and the surface skin may not be sufficiently clean. Further, the polyethylene composition containing additives such as stabilizers sometimes becomes colored due to catalyst residues and the like, and the color tone is not preferable. Here, the vertical streak generally refers to a streak generated in the extrusion direction by transferring the shape of a scratch on the die surface near the die lip or a degraded product of the retained resin to the surface of the molded product.
In addition, a weld mark refers to a line-like unevenness generated at a joint when two or more flows of the resin are not completely fused when a resin in a flow state is filled in a mold and molded. Note that the mechanical strength in the direction orthogonal to the weld mark decreases.

[0007]

According to the present invention, the surface of the molded article, that is, the vertical stripes and weld marks are improved by adding a specific additive while maintaining the color tone of the resin at a high level. . According to the present invention, the melt flow rate is 0.1 to 1 g / 10 min. With a density of 0.945
100 parts by weight of polyethylene which is 0.960;
A polyethylene composition for hollow molding comprising 001 to 1 part by weight of a metal carboxylate, wherein the polyethylene has (A) a melt flow rate of 0.001 to 0.2 g.
/ 10 min. Having a density of 0.920 to 0.95
5 g / cm ³ of 5-80 parts by weight of polyethylene, and (B)
Melt flow rate is 0.2 to 100 g / 10 min.
And 95 to 20 parts by weight of polyethylene having a density of 0.940 to 0.973 g / cm ³ , and the metal carboxylate is (a) 10 to 90% by weight of calcium stearate or calcium 12-hydroxystearate.
And (b) 90 to 10% by weight of basic magnesium 12-hydroxystearate.

[0008]

According to 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 19
76 Under the conditions of Table 4, 190 ° C., load 2.16 k
It is a value measured under the condition of gf. (A) component and (B)
The polyethylene component has a melt flow rate of 0.
When less than 1g / 10min., The melt viscosity is too high,
Extrusion molding becomes difficult. On the other hand, if the melt flow rate is 1
If it is larger than g / 10 min., the melt tension of the parison is insufficient, and the drawdown property is not preferable. Also, (A)
The density of the polyethylene comprising the component and the component (B) is 0.1.
It is 945 to 0.960 g / cm ³ . 0.94 density
If it is less than 5 g / cm ³ , the rigidity of the composition is insufficient, and the mechanical strength is also 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 0.2 g / 10
min. And preferably 0.01 to 0.1 g. The density is from 0.920 to 0.955 g / cm ³ , preferably from 0.925 to 0.950. 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. The density is from 0.940 to 0.973 g / cm ³ , preferably from 0.950 to 0.970 g / cm ³ .

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

In order to obtain the polyethylene 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, preferably 20/80 to 65. / 35 (weight ratio). (A) When the amount of the polyethylene component exceeds 80 parts by weight, the resin pressure during molding rises,
Also, good surface texture cannot be obtained, and when the amount of the polyethylene component (A) is less than 5 parts by weight, fish eyes tend to occur frequently in the molded 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)
It means that a polymer mixture is produced by sequentially producing the polyethylene component and the (B) polyethylene component.

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 a metal carboxylate are incorporated. By blending the metal carboxylate, the vertical streaks and weld marks of the hollow molded article are reduced.

The metal carboxylate used in the composition of the present invention comprises two components. That is, 10 to 90% by weight, preferably 20 to 80% by weight of the metal carboxylate is
Calcium stearate or calcium 12-hydroxystearate;
%, Preferably 80 to 20% by weight of basic 12-
It is magnesium hydroxystearate.

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 polyethylene composition for blow molding of the present invention may contain additives such as a stabilizer, an ultraviolet absorber, an antistatic agent, a flame retardant, or a coloring agent. These additives or coloring agents are those usually used in polyethylene compositions. As the stabilizer, for example, butylhydroxytoluene (BHT), octadecyl β- (3,5-ditert-butyl-4-hydroxy-phenyl) propionate (for example, a trade name of Ciba-Geigy Co., Ltd.,
A phenolic stabilizer such as IRGANOX 1076) or a tris (2,4-di-tert-butyl-phenyl) phosphite (for example, trade name ADK STAB 2112 or trade name, Ciba Geigy Co., Ltd., IRGAFOS 168). Phosphorus stabilizers 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 in a polymerization vessel, using a titanium-based solid catalyst as a catalyst and triethylaluminum as a co-catalyst, supplying a predetermined amount of hydrogen as a melt flow rate regulator, and keeping the temperature at 75 ° C. Butene-1 was introduced as a comonomer, and then ethylene, which is a main component of the polymerization, was continuously supplied so as to maintain the total pressure at 4 kg / cm ² , thereby performing slurry polymerization. The following melt flow rate (g / 10min.) And density (g / cm ³ )
(A) which is an ethylene-butene-1 copolymer having the following formula:

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 / c
Component (B), which is an ethylene-butene-1 copolymer having m ³ ), was obtained.

[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 Co., Ltd.), 0.01
Parts by weight of basic magnesium 12-hydroxystearate (trade name EM-644 of Kosei Co., Ltd.) and 0.04
Parts by weight of calcium stearate were mixed in a tumbler. In Table 2, calcium stearate was replaced with Ca-S
Notated as t. EM-644 is a white powder;
It contains 3 ± 0.2% Mg, has free 12-hydroxystearic acid of 2.0% or less, moisture of 2.0% or less, and has a melting point of 220 to 230 ° C.

Next, the above mixture was granulated at 180 ° C. using a twin-screw granulator (trade name: TEM-35B, manufactured by Toshiba Corporation) to obtain pellets. Melt flow rate (g / 10 min.) And density (g / cm ³ ) of the pellet
Is described in the column of composition in Table 1 above. Using this pellet as a sample, the color tone (bL) was measured with an SM color computer SM-4-CH (manufactured by Suga Test Instruments Co., Ltd.). 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 more the whiteness is increased.

The pellets are blow-molded (Tahara,
A detergent bottle with a handle having a capacity of 1 liter was manufactured under the trade name of TPF-505). The molding temperature is 170 ° C., the output per hour is 20 kg, and the diameters of the die and the core are 65.5 mm and 64.5 mm, respectively. The vertical stripes of this molded product were visually classified into five levels. This criterion is as follows. 5: Not noticeable 4: Almost unnoticeable 3: Slightly noticeable 2: Very noticeable 1: Very noticeable

Further, a pellet and a powdery milky white pigment (white dry color manufactured by Tokyo Ink Co., Ltd.)
Was mixed with a tumbler, and then a detergent bottle with a handle having a capacity of 1 liter was formed with the above blow molding machine (trade name: TPF-505, manufactured by Tahara). The presence or absence of a weld mark on this molded product was visually determined. These results are summarized in Table 2. That is, Table 2 shows the color tone (b
L), vertical lines of the detergent bottle without pigment, and weld marks of the detergent bottle with pigment are described.

(Examples 2 and 3, Comparative Example) In the same manner as in Example 1, pellets, a detergent bottle containing no pigment, and a detergent bottle containing pigment were produced. However, Examples 2 and 3 differ from Example 1 only in the amounts of calcium stearate and basic magnesium 12-hydroxystearate. In Comparative Examples, basic magnesium 12-hydroxystearate was not blended. In each of Examples 1 to 3 and Comparative Example, the total amount of calcium stearate and basic magnesium 12-hydroxystearate was constant at 0.05 with respect to 100 parts by weight of the high-density polyethylene.
Parts by weight were used.

Example 4 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 and a density of 0.955 g.
/ Cm ³ . In addition, the polyethylene obtained in the first stage had a melt flow rate of 35 g / 10 min and a density of 0.960 g / cm ³ . Except for using 100 parts by weight of this polyethylene, additives were blended in the same manner as in Example 1 to produce pellets, a detergent bottle containing no pigment, and a detergent bottle containing pigment.

[0027]

[Table 2]

As can be seen in each of the examples, a basic magnesium stearate was blended with calcium stearate from the comparative example using calcium stearate alone as the metal carboxylate, thereby obtaining the longitudinal streaks and hollow streaks of the hollow molded article. It can be seen that the weld mark is reduced and the color tone is improved.

[0029]

According to the present invention, the use of calcium stearate or calcium 12-hydroxystearate in combination with basic magnesium 12-hydroxystearate as a metal carboxylate as an additive makes it possible to obtain a weld mark of a hollow molded article, An excellent effect of reducing vertical streaks and improving color tone is exhibited.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Soichi Komaki 11-2, Goi south coast, Ichihara-shi, Chiba Maruzen Polymer Co., Ltd. (56) References JP-A-4-293944 (JP, A) JP-A-4 -258650 (JP, A) JP-A-55-155038 (JP, A)

Claims (1)

(57) [Claims] 1. The melt flow rate is 0.1 to 1 g / 1.
0 min. And the density is 0.945 to 0.960 1
A polyethylene composition for hollow molding, comprising 00 parts by weight of polyethylene and 0.001 to 1 part by weight of a metal carboxylate, wherein the polyethylene has (A) a melt flow rate of 0.1 part by weight.
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 of 0.2~100g / 1
0 min. With a density of 0.940 to 0.973 g / cm
³ to 95 to 20 parts by weight of polyethylene, wherein the metal carboxylate is (a) calcium stearate or calcium 12-hydroxystearate.
A polyethylene composition for hollow molding, comprising 90% by weight and (b) 90 to 10% by weight of basic magnesium 12-hydroxystearate.