KR20040018709A - Polyethylene resin composition for corsslinking rotational molding - Google Patents

Abstract

PURPOSE: A polyethylene resin composition for crosslinking rotational molding is provided, to improve the appearance by enhancing crosslinking efficiency and uniformity, to reduce the generation of bubbles and to enhance mechanical properties, weather resistance, heat resistance and environmental stress crack resistance. CONSTITUTION: The polyethylene resin composition comprises 100 parts by weight of a high density polyethylene resin having a molecular weight distribution of maximum 3 and a catalyst residue of maximum 10 ppm(0.001 wt%); 0.1-5 parts by weight of an organic peroxide crosslinking agent; 0.005-15 parts by weight of a crosslinking additive; and 0.01-5 parts by weight of a UV stabilizer. Preferably the high density polyethylene resin is prepared by using a metallocene catalyst, is an ethylene homopolymer or an ethylene-α-olefin copolymer containing 10 mol% or less of an α-olefin, and has an average density of 0.940-0.970 g/cm¬3 and a melt flow index of 5-40 g/10 min.

Description

Polyethylene resin composition for crosslinking rotational molding {POLYETHYLENE RESIN COMPOSITION FOR CORSSLINKING ROTATIONAL MOLDING}

The present invention relates to a polyethylene resin composition for crosslinking rotational molding. More specifically, the crosslinking rotational molding has a high crosslinking efficiency and uniformity, so that the appearance is smooth and the catalyst residue is less than 10 ppm (0.001%). In addition, the present invention relates to a polyethylene resin composition for crosslinking rotomolding, in which mechanical properties such as impact strength at room temperature and low temperature, weather resistance, environmental stress crack resistance, long-term heat stability, and long-term weather resistance are remarkably improved.

Rotational molding is a molding method that is applied to the production of large containers or hollow products that are empty, and can be usefully applied to the production of various products such as chemical tanks, containers, large and medium-sized amusement rides, and marine structures. This method has the advantage that it is easy to produce and replace various products according to the mold making, which is advantageous for the production of small quantities of various kinds, and also to produce large products economically.

Almost all common thermoplastic resins can be used for rotomolding, but polyethylene resin is the most used among them. Particularly, linear low density polyethylene resins having a certain degree of flowability capable of forming a container in a molten state and having good mechanical properties such as impact strength are frequently used.

Korean Patent Laid-Open Publication No. 2001-46401, which relates to a conventional resin composition for rotomolding, provides improved impact resistance and environmental stress cracking resistance by mixing an antioxidant with a mixed resin composition of a linear low density polyethylene resin and ethylene vinyl acetate resin. It discloses about the resin composition for molding. However, the polyethylene resin composition has a problem that it does not have sufficient mechanical properties to withstand the poor external conditions.

Therefore, efforts have been made to secure sufficient mechanical properties, and one of them has been developed to improve mechanical properties, environmental stress crack resistance, weather resistance and the like by crosslinking rotational molding. Crosslinking rotational molding causes crosslinking between polyethylene molecules by heat while molding a product using a low molecular weight resin having flowability, and has a merit of maximizing physical properties of a molded product by converting the low molecular weight into ultra high molecular weight. These products show excellent impact resistance, environmental stress cracking resistance, weather resistance, etc., which has the advantage of enhancing the characteristics of outdoor long-term use, which are essential characteristics for rotational molding products.

Although research on such a crosslinking rotomolding resin composition is made continuously, there is still much improvement.

Korean Patent Publication No. 2001-18443 discloses a resin composition for crosslinking rotomolding with improved physical properties and weather resistance by mixing an organic peroxide crosslinking agent, a crosslinking aid, and an ultraviolet stabilizer with a mixed resin composition of a linear low density polyethylene resin and an ethylene vinyl acetate resin. Is disclosed. However, in the case of crosslinking rotational molding using the above resin composition, it is difficult to obtain a high degree of crosslinking due to a large amount of catalyst residue by using polyethylene resin polymerized with a Ziegler-Natta catalyst (multiple active site catalyst). There is a problem of causing a large amount of bubbles in the molded product to cause decomposition and causing roughness of the surface of the molded product. In addition, there is a problem such as lowering the releasability of the mold by early crosslinking.

In addition, the polyethylene resin polymerized with a Ziegler-Natta catalyst (multiple active site catalyst) has a low molecular weight and a high molecular weight distribution, so that it is difficult to form a product having a uniform crosslinking degree, especially in outdoor use, cracking and deterioration of physical properties. There is such a problem.

In order to improve the processing, there have been attempts to improve this by using nitrite, mixing crosslinking accelerator and antioxidant, and mixing two kinds of organic peroxide crosslinking agents, but they were not effective in reducing crosslinking degree and suppressing bubble formation. . In addition, a method of suppressing bubble formation in the shaping using a metal oxide has been devised, but there is a problem in that the addition of a small amount is ineffective and the crosslinking degree and physical properties are lowered in an excessive amount.

Therefore, the cross-linking rotational molding is excellent in cross-linking efficiency, there is no bubble generation, and the situation for the cross-linking rotational molding resin composition excellent in mechanical properties is further required.

In order to solve the problems of the prior art as described above, the present invention is smooth in appearance and high in crosslinking efficiency and uniformity in crosslinking rotational molding, and the catalyst residue is not more than 10 ppm (0.001%) without bubbles, and at the same time It is an object of the present invention to provide a polyethylene resin composition for crosslinking rotomolding with improved mechanical properties such as impact strength at room temperature and low temperature, weather resistance, environmental stress crack resistance, long-term heat stability, and long-term weather resistance.

In order to achieve the above object, the present invention is a polyethylene resin composition for crosslinking rotomolding,

a) the molecular weight distribution is up to 3 and the catalyst residue is up to 10 ppm (0.001% by weight);

100 parts by weight of phosphorus high density polyethylene resin;

b) 0.1 to 5 parts by weight of the organic peroxide crosslinking agent;

c) 0.005 to 15 parts by weight of crosslinking aid; And

d) 0.01 to 5 parts by weight of an ultraviolet stabilizer

It provides a polyethylene resin composition for crosslinking rotational molding comprising a.

Hereinafter, the present invention will be described in detail.

The inventors of the present invention are excellent in the crosslinking efficiency during crosslinking rotational molding, there is no bubble generation, and while studying the resin composition for crosslinking rotational molding having excellent mechanical properties, the molecular weight distribution is up to 3, and the catalyst residue is up to 10. By using a high density polyethylene resin (ppm (0.001% by weight)), a crosslinking agent and a crosslinking aid to improve the crosslinking properties, and at the same time, by using a UV stabilizer having thermal stability properties, mechanical properties such as impact strength at room temperature and low temperature, weather resistance, and weather resistance Confirmed that the environmental stress cracking and the like is excellent, to complete the present invention based on this.

Polyethylene resin composition for crosslinking rotomolding of the present invention has a molecular weight distribution of up to 3, 100 parts by weight of a high density polyethylene resin having a catalyst residue of up to 10 ppm (0.001% by weight), 0.1 to 5 parts by weight of an organic peroxide crosslinking agent, a crosslinking aid 0.005 To 15 parts by weight, and 0.01 to 5 parts by weight of an ultraviolet stabilizer.

The high-density polyethylene resin used in the present invention is a polyethylene resin having a molecular weight distribution of up to 3 and a catalyst residue of up to 10 ppm (0.001 wt%), in particular, prepared by contacting with a metallocene catalyst (single active site catalyst) for polymerization. It is preferable that it is a polyethylene resin.

In addition, the high density polyethylene resin is preferably a copolymer of ethylene homopolymer or alpha-olefin comonomer content of 10 mol% or less of ethylene and alpha-olefin. When the content of the alpha-olefin comonomer exceeds 10 mol%, there is a problem in that the crosslink uniformity during physical crosslinking and crosslinking rotational molding during melt kneading of the crosslinking agent is lowered.

The polyethylene resin polymerized with the metallocene catalyst (single active site catalyst) has a relatively narrow molecular weight distribution with a uniform molecular weight compared to the polyethylene resin polymerized with a Ziegler-Natta catalyst (multiple active site catalyst), and alpha-olefin The distribution of comonomers is also uniform, with almost no catalyst residue at levels of 0.001% or less. Relatively narrow molecular weight distribution makes the crosslinking reaction more uniform and less catalyst residue plays a significant role in reducing bubble generation. Therefore, the high density polyethylene resin prepared by polymerizing with a metallocene catalyst is superior to the crosslinking rotomolding resin compared to the polyethylene resin prepared by polymerizing with a Ziegler-Natta catalyst.

It is preferable that the high density polyethylene resin has an average density of 0.940 to 0.970 g / cm 3, and in particular, an average density of 0.950 to 0.960 g / cm 3 is preferable in order to obtain an optimum crosslinking density of a product. In addition, the melt flow index of the high-density polyethylene resin is preferably 5 to 40 g / 10 minutes, and the melt flow index of 15 to 30 g / 10 minutes is particularly good for preliminary cross-linking and physical property deterioration. It is preferable because there is no problem such as poor product molding due to defects.

The organic peroxide crosslinking agent used in the present invention is preferably a high decomposition temperature because the crosslinking can be started after the polymer is melted and the product is molded. As the organic peroxide crosslinking agent, peroxide-based organic compounds such as dialkyl peroxide, diacyl peroxide, peroxy ester and ketone peroxide may be used. Specifically, dicumyl peroxide, 2,5-dimethyl-2. , 5-di (t-butylperoxide) hexyne and the like can be used.

The organic peroxide crosslinking agent is preferably included in 0.1 to 5 parts by weight based on 100 parts by weight of the high density polyethylene resin. If the content is less than 0.1 parts by weight, there is no effect as a crosslinking agent. If the content is more than 5 parts by weight, the crosslinking efficiency is insignificant due to the added amount, which is uneconomical, and there is a problem that an odor occurs due to the unreacted residual crosslinking agent.

The crosslinking aid used in the present invention plays an important role in obtaining a uniform crosslinking density. Examples include 1,2-polybutadiene, triallyl cyanurate, triallyl isocyanate and the like.

The crosslinking aid is preferably included in 0.005 to 15 parts by weight based on 100 parts by weight of the high density polyethylene resin. If the content is less than 0.005 parts by weight, it is less effective as a crosslinking aid, and if it exceeds 15 parts by weight, it may cause problems such as discoloration of the molding. In particular, the crosslinking aid is preferably used at 0.05 to 3 times of the organic peroxide crosslinking agent that can optimize the crosslinking efficiency when used with the organic peroxide crosslinking agent.

As the UV stabilizer used in the present invention, it is preferable to use a hindered amine light stabilizer (HALS). An example is Chimassorb 944LD (poly {[6-[(1,1,3,3-tetramethylbutyl) -amino] -1,3,5-triazine-2,4-diyl]- [(2,2,6,6-tetramethyl-4-piperidinyl) -amino] -1,6-hexanediyl [(2,2,6,6-tetramethyl-4-piperidinyl) -amino ]}), Tinuvin 770 (bis- (2,2,6,6-tetramethyl-4-piperidinyl) decanedioate), UV3346 (poly [(6-morpholino-S-tri Azine-2,4-dil) [2,2,6,6-tetramethyl-4-piperidyl] amino] -hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) Amino]).

The ultraviolet stabilizer is preferably used in 0.01 to 5 parts by weight based on 100 parts by weight of the high density polyethylene resin. If the content is less than 0.01 parts by weight, there is no effect as an ultraviolet stabilizer, if it exceeds 5 parts by weight, there is a problem that the UV stabilizing effect according to the added amount is insignificant and uneconomical.

The high-density polyethylene resin for crosslinking rotational molding according to the present invention has a high crosslinking efficiency and uniformity during crosslinking rotational molding, so that the appearance is not only smooth, but there is no bubble of catalyst residue at 10 ppm (0.001%) or less. . In addition, mechanical properties such as impact strength at room temperature and low temperature, weather resistance, environmental stress crack resistance, long-term thermal stability, and long-term weather resistance is remarkably improved, so that it can be used for a long time even in poor external conditions.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

EXAMPLE

Example 1

100 parts by weight of a high density polyethylene resin (SE9180, LG Chemical) having an average density of 0.958 g / cm 3 and a melt flow index of 18.0 g / 10 min prepared by polymerization with a metallocene catalyst (single active site catalyst), 2,5 as an organic peroxide crosslinking agent. 1 part by weight of dimethyl-2,5-di (t-butylperoxide) hexyne, 1 part by weight of triallyl cyanurate as a crosslinking aid, and 0.15 part by weight of 944LD as a UV stabilizer and 0.15 part by weight of UV3346 using a Henschel mixer Mixed. Then, the die was extruded and pelletized using a twin extruder at a die temperature of 150 ° C. to prevent crosslinking reaction under a nitrogen atmosphere. At this time, the die temperature is careful not to exceed 160 ℃ and to maintain a constant temperature.

Example 2, and Comparative Examples 1-3

Except that in Example 1 mixed with the components and compositions of Table 1 was carried out in the same manner as in Example 1.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 m-HDPE 100 100 - - - HDPE - - 100 100 - MDPE - - - - 100 Crosslinking agent One 2 - One One Crosslinking aid One 2 - One One UV stabilizer 944LD 0.15 0.15 0.15 0.15 0.15 UV3466 0.15 0.15 0.15 0.15 0.15 M-HDPE: High density polyethylene resin (SE9180, LG Chem) with a molecular weight distribution of 2.9, a catalyst residue of 7 ppm, an average density of 0.958 g / cm3, and a melt flow index of 18.0 g / 10 min. HDPE: Generalized high density polyethylene resin (ME9180, LG Chem) having a molecular weight distribution of 12, a catalyst residue of 210 ppm, an average density of 0.958 g / cm3, and a melt flow index of 18.0 g / 10 min, prepared by polymerization with a Ziegler-Natta catalyst. Phosphorous 2,5-dimethyl-2,5-di (t-butylperoxide) hexyne Crosslinking aid: triallyl cyanurate, UV stabilizer: Hindered amine light stabilizer 944LD, UV3346 complex system (Ciba)

The pelletized resin prepared in Examples 1 or 2 and Comparative Examples 1 to 3 was crushed into 35 mesh in a grinder, and crosslinked by using a box mold having a shape of 20 cm × 20 cm × 30 cm. Molded. The thickness of the molded box product was 3.0 mm, and the test evaluation specimens were taken from the molded box product. Physical properties were evaluated using the collected specimens in the following manner, and the results are shown in Table 2 below.

A) Izod impact strength-evaluated according to the conditions of ASTM D256 (test temperature = room temperature (23 ℃) and low temperature (-40 ℃)).

B) Dart impact strength-evaluated according to the conditions of Low Temperature Impact Test specification of ARM (Association of Rotational Molders), 1/8 "specimen (test temperature =-40 ℃).

C) Environmental Stress Cracking Resistance (ESCR)-This was evaluated by measuring the time to F50 (50% fracture) under the temperature condition of 50 ℃ using ASTM D1693, 10% lgepal CO-630 solution.

D) Long-term thermal stability-After 1,000 hours of heat aging in an oven at 100 ℃, the tensile strength was measured according to ASTM D638, and evaluated by calculating the residual ratio to the initial tensile strength value before heating aging.

ㅁ) Long-term weather resistance-After 2,000 hours in UV Weather-O-Meter, the tensile strength was measured according to ASTM D638 to calculate the residual ratio to the initial tensile strength value was evaluated.

외관) Appearance-The appearance of the rotomolded product was evaluated by observing the surface condition, bubble formation, etc.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Izod impact strength (ft-lb) Room temperature (23 ℃) 17 18 3.3 13 12 Low temperature (-40 ℃) 4.5 5.0 2.5 3.9 3.5 Falling Impact Strength (ft-lb) -40 ℃ 78 80 57 65 63 Environmental Stress Cracking Resistance > 1,000 > 1,000 58 > 1,000 > 1,000 Long-term heat stability (%) > 90 > 90 10 > 70 > 70 Long-term weather resistance (%) > 90 > 90 6 > 70 > 70 Exterior Surface condition Good Good Good coarseness coarseness Bubble generation No bubble No bubble No bubble Bubble generation Bubble generation

Through Table 2, the impact strength and the environment of Examples 1 and 2 comprising a high-density polyethylene resin, an organic peroxide crosslinking agent, a crosslinking aid, and an ultraviolet stabilizer prepared by polymerizing with a metallocene catalyst according to the present invention. It was confirmed that the stress cracking properties are significantly superior to Comparative Examples 1 to 3. In addition, the long-term heat stability and long-term weather resistance according to the outdoor long-term use was also improved.

On the other hand, Comparative Examples 1 to 3 containing polyethylene resin polymerized with a Ziegler-Natta catalyst had relatively good impact strength and environmental stress crack resistance, but the surface of the molded article was rough and a large amount of bubbles were generated, thereby resulting in product properties Example 1 And compared with 2 it was confirmed that the degradation.

The polyethylene resin composition for crosslinking rotomolding of the present invention has a high appearance and high uniformity in crosslinking rotomolding and has a smooth appearance, and has no catalyst residue at 10 ppm (0.001%) or less, and at room temperature and Mechanical properties such as impact strength at low temperature, weather resistance, environmental stress crack resistance, long-term heat stability, and long-term weather resistance is excellent.

Claims (8)

In the polyethylene resin composition for crosslinking rotomolding, a) the molecular weight distribution is up to 3 and the catalyst residue is up to 10 ppm (0.001% by weight); 100 parts by weight of phosphorus high density polyethylene resin; b) 0.1 to 5 parts by weight of the organic peroxide crosslinking agent; c) 0.005 to 15 parts by weight of crosslinking aid; And d) 0.01 to 5 parts by weight of an ultraviolet stabilizer Polyethylene resin composition for crosslinking rotomolding comprising a. The method of claim 1, Polyethylene resin composition for crosslinking rotomolding, wherein the high density polyethylene resin is a polyethylene resin produced by polymerization with a metallocene catalyst. The method of claim 1, The polyethylene resin composition for crosslinking rotomolding, wherein the high-density polyethylene resin is a copolymer of ethylene homopolymer or alpha-olefin comonomer content of 10 mol% or less and ethylene and alpha-olefin. The method of claim 1, The high density polyethylene resin has an average density of 0.940 ~ 0.970 g / cm 3, the melt flow index of 5 ~ 40 g / 10 minutes polyethylene crosslinking resin composition for rotational molding. The method of claim 1, The polyethylene resin composition for crosslinking rotomolding, wherein the organic peroxide crosslinking agent is selected from one or more selected from the group consisting of dialkyl peroxides, diacyl peroxides, peroxyesters, and ketone peroxides. The method of claim 1, Polyethylene resin composition for crosslinking rotomolding wherein the crosslinking aid is selected from the group consisting of 1,2-polybutadiene, triallyl cyanurate, and triallyl isocyanate. The method of claim 1, Polyethylene resin composition for crosslinking rotomolding, wherein the crosslinking aid is included at 0.05 to 3 times the organic peroxide crosslinking agent. The method of claim 1, The ultraviolet stabilizer is a poly {[6-[(1,1,3,3-tetramethylbutyl) -amino] -1,3,5-triazine-2,4-diyl]-[(2,2,6 , 6-tetramethyl-4-piperidinyl) -amino] -1,6-hexanediyl [(2,2,6,6-tetramethyl-4-piperidinyl) -amino]}, bis- (2 , 2,6,6-tetramethyl-4-piperidinyl) decanedioate, and poly [(6-morpholino-S-triazine-2,4-dil) [2,2,6,6- Tetramethyl-4-piperidyl] amino] -hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) amino] is a hindered amine compound selected from the group consisting of Polyethylene resin composition for crosslinking rotomolding.