JPH0755991B2 - Method for producing modified polyethylene resin particles with improved weather resistance - Google Patents

Description

The present invention relates to a method for producing modified polyethylene resin particles, and more particularly to a method for producing polyethylene resin particles having excellent weather resistance.

[Conventional technology]

Currently, as a method for producing modified polyethylene-based resin particles, in an attempt to combine the advantages of polyethylene-based resin and the advantages of polystyrene-based resin and to obtain a foam that is easy to foam and mold, for example, polyethylene particles are added with styrene monomer. It has been proposed to use, as a raw material resin, a resin improved by impregnation and then polymerizing it (see Japanese Patent Publication No. 58-51009 and Japanese Patent Publication No. 62-280237). In order to produce a foam from the composite resin thus obtained, a volatile foaming agent is absorbed in the resin to form a foamable resin, and this is foam-molded to obtain a bead method foam-molded body.

The molded body thus obtained, particularly the foamed molded body, is used as a heat insulating material or a heat insulating material. In particular, those using a bead method foam molded article obtained by including a foaming agent are food transport containers, since it is possible to obtain any foam molded article,
Widely used for heat insulation and cold insulation of tanks.

[Problems to be Solved by the Invention]

However, this improved polyethylene resin has a drawback that when it is used outdoors for a long period of time, when it is exposed to weather conditions such as sunlight, wind and rain, cold heat, the molded product deteriorates, that is, turns yellow, and loses its commercial value. .

Conventionally, benzoyl peroxide, t-butyl peroxybenzoate, which is generally used as a polymerization catalyst for styrene monomers as a catalyst for polymerizing styrene monomers absorbed in polyethylene resin particles, and dicumyl peroxide for crosslinking. , An organic peroxide such as t-butyl-cumyl peroxide is used (JP-A-61-123633), and a foaming agent is added to the resin thus obtained to obtain a molded article. These catalysts had a benzene ring in the structural formula, were liable to form an aromatic compound as a decomposition product, and were likely to remain in polyethylene, and the weather resistance of the molded product was poor.

It is an object of the present invention to solve the above-mentioned problems and provide a method for producing expanded polyethylene resin particles having weather resistance.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present inventor (et al.) Has conducted extensive studies, and as a result, by using an organic peroxide having no benzene ring as a polymerization catalyst and a polyethylene crosslinking agent, the decomposition product of the catalyst is water-soluble. However, most of them are dissolved in water and the rate of remaining in the polymer is small,
The inventors have found that the weather resistance of the expanded beads can be improved, and have completed the present invention.

That is, the present invention is to disperse polyethylene particles, a polyethylene crosslinking agent, a styrene-based monomer and a polymerization catalyst in an aqueous medium, and to add a styrene-based monomer to the polyethylene particles to polymerize and crosslink the polymerization catalyst. As a catalyst having a benzene ring-free organic peroxide having a 10-hour half-life temperature of 60 ° C to 105 ° C as a polyethylene crosslinking agent, the organic peroxide having no benzene ring has a 10-hour half-life temperature of 100 ° C. A method for producing modified polyethylene resin particles, which comprises polymerizing and cross-linking using a catalyst at ℃ to 125 ℃.

Is the gist.

[Action]

 The configuration and operation of the present invention will be described.

In the present invention, polyethylene particles, a polyethylene cross-linking agent, a styrenic monomer and a polymerization catalyst are dispersed in an aqueous medium to cause polyethylene particles to substantially absorb a vinyl aromatic monomer and polymerize the monomers in the particles. For the polymerization catalyst and polyethylene cross-linking agent, the selection of an organic peroxide having no benzene ring, the 10-hour half-life temperature of the polymerization catalyst of 60 ℃ ~ 105 ℃,
A polymerization treatment method has been established, which is characterized by using a catalyst having a time half-life temperature of 100 to 120 ° C. and using a decomposition product of the catalyst which is expected to be water-soluble.

In the present invention, due to the combination of catalysts having no benzene ring, most of the products from the catalysts are acetone and lower alcohols, which are dissolved in water and remain in the polymer at a very small rate. Even if they remain, their boiling points are low, so that they deviate from the polymer in the foaming and molding steps, and when evaluated as a molded article, they have excellent weather resistance.

The polymerization catalyst selected is generally a benzene ring-free radical polymerization initiator having a decomposition temperature of 60 ° C to 105 ° C for obtaining a half-life temperature of 10 hours, specifically, lauroyl peroxide (62 ° C). , T-butylperoxy-2-
Ethyl hexanate (73 ° C), t-butylperoxy-
Laurate (96 ° C), t-butylperoxyisopropyl carbonate (98 ° C), t-butylperoxyacetate (102 ° C). These may be used alone or in combination of two or more. The amount used is 0.02-0.2 with respect to the monomer
% Is preferred. Also, as a polyethylene crosslinking agent of choice
A benzene ring-free polyethylene crosslinker having a decomposition temperature of 100 ° C to 125 ° C for obtaining a half-life of 10 hours,
Specifically, 2,2-bis- (t-butylperoxy) -butane (103 ° C), 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexane (118 ° C), Di-t-butyl peroxide (124 ° C.) and the like. The polymerization reaction is preferably 80 ° C to 90 ° C, and the crosslinking reaction is preferably 120 to 1 ° C.
It is carried out at 45 ° C.

It was confirmed that the molded product obtained by adding a foaming agent to the resin thus obtained and foaming the beads was excellent in weather resistance.

〔Example〕

 The present invention will be described more specifically by way of examples.

Example 1 5 pellets of polyethylene particles in a suspension consisting of 2500 cc of water in an autoclave, 30 g of sodium pyrophosphate as a dispersant, 34 g of magnesium chloride, and 0.2 g of sodium dodecylbenzene sulfonate (trade name: Yucaron HE manufactured by Mitsubishi Yuka) −
60) 760 g was suspended.

2,2-bis- (t-butylperoxy) was added to this suspension.
326 g of styrene monomer in which 0.39 g of butane was dissolved was added dropwise. After the dropping, the temperature was raised to 60 ° C, and stirring was continued at this temperature for 30 minutes to allow polyethylene particles to absorb the styrene monomer. After absorption, the temperature was raised to 120 ° C and the temperature was maintained at 1 ° C.
The stirring was continued for 30 minutes.

After that, the temperature was lowered to 85 ° C and styrene monomer was added to the suspension.
To 914 g, 2.7 g of t-butylperoxy-2-ethylhexanate as a polymerization catalyst, 0.2 g of t-butyl-peroxyisopropyl carbonate, and as a polyethylene crosslinking agent.
A monomer solution in which 10.2 g of 2,2-bis- (t-butylperoxy) -butane was dissolved was added dropwise. 3 at this temperature after dropping
After stirring for an hour, the temperature was raised to 143 ° C. and kept for 2 hours and 30 minutes.

Then, it was cooled to room temperature and taken out. The shape after taking out was spherical and there were no coalesced particles. Product 2kg after removal
Is put into a pressure resistant V-blender and refined as a solvent.
20 g and 300 g of butane as a foaming agent were poured into a V-blender. After the injection, the temperature was raised to 70 ° C. and the mixture was rotated for 3 hours.
Then, it cooled to normal temperature and took out the product. This product was pre-expanded 33 times, and after aging, a plate molded product (30 × 40 × 2.5 cm) having an expansion ratio of 30 was obtained by an expansion molding machine. The foamed molded product was heated in an oven at 50 ° C. for 1 day and dried to obtain a weather resistance test sample. The results are shown in FIG.

Example 2 The same composition as in Example 1 was used, and t-butylperoxy-2-ethylhexanate, t-butylperoxyacetate, 2,5-dimethyl-2.5-di- (t-) was used as a polymerization catalyst and a crosslinking catalyst.
Butyl peroxy) -hexane was used and prefoaming and molding were carried out in the same manner as in Example 1. The results are shown in FIG.

Example 3 The same composition as in Example 1 was used, except that lauroyl peroxide, t-butylperoxy-laurate, and di-t-butyl peroxide were used as the polymerization catalyst and the crosslinking catalyst.
Pre-foaming and molding were performed in the same manner as in. The results are shown in FIG.

Comparative Example 1 Polyethylene particles in pellet form (Mitsubishi Yuka Co., Ltd., trade name Yucaron HE in a suspension consisting of 2500 cc of water in an autoclave, 2500 g of sodium pyrophosphate as a dispersant, 34 g of magnesium chloride and 0.2 g of dodecylbenzenesulfonic acid) -60)
760 g was suspended.

To this suspension, 326 g of styrene monomer in which 0.39 g of dicumyl peroxide was dissolved was added dropwise. After the dropping, the temperature was raised to 60 ° C., and stirring was continued at this temperature for 30 minutes to allow polyethylene particles to absorb the styrene monomer. After absorption 130 ℃
The temperature was raised to and the stirring was continued at this temperature for 1 hour and 30 minutes.

After that, the temperature was lowered to 88 ° C and styrene monomer was added to the suspension.
A monomer solution containing 2.0 g of benzoyl peroxide, 0.03 g of t-butylperoxybenzoate and 6.9 g of dicumyl peroxide as a cross-linking agent was added dropwise to 914 g of the catalyst. After dropping, stir at this temperature for 3 hours and 30 minutes, then
The temperature was raised to 140 ° C. and kept for 4 hours.

After that, it was cooled to room temperature and taken out in the same manner as in Example 1.
The shape after taking out was spherical and there were no coalesced particles.

Put 2 kg of the product after removal into a pressure resistant V-blender,
Toluene 30g as a solvent and butane 300g as a foaming agent
-Injected into the blender. After the injection, the temperature was raised to 70 ° C. and the mixture was rotated for 3 hours.

Then, it cooled to normal temperature and took out the product.

Similar to Example 1, a plate molded product having a foaming ratio of 30 times (30 × 40 ×
2.5 cm) was obtained. This foam molded product is put in an oven at 50 ° C
It was heated for one day and dried to obtain a sample for weather resistance test. The results are shown in FIG.

The measurement item of the weather resistance is an accelerated exposure test according to JIS-A-1411, the irradiation device is a sunshine weather meter, and the irradiation condition is black panel temperature 63 ° C for 150,300,500,700 hours. This change is the yellowing degree JIS-K-7103 (Dye: K
-7105), the device was measured using a color difference meter.

The foaming properties of Comparative Example 1 and Example 1 were almost the same, the shrinkage ratio after molding was the same, and the fusion of particles was also the same, and a good foamed molded product was obtained.

Comparative Example 2 The same composition as in Comparative Example 1 was used, the same benzoyl peroxide, t-butyl peroxybenzoate as in Comparative Example 1 was used as the polymerization catalyst, and t-butyl-cumyl peroxide was used as the crosslinking catalyst. Pre-foam molding was performed in the same manner as in. The results are shown in FIG.

From the graph of FIG. 1, it is clear that the yellowing speed of Comparative Examples 1 and 2 is high and the weather resistance is poor.

The test method and measurement conditions in the weather resistance test shown in FIG. 1 were as follows.

(1) Test method: Accelerated exposure test JIS-A-1411 (2) Measurement conditions: 1. Molded product multiple of 30 times 2. Irradiation device Sunshine weather meter 3. Irradiation conditions Black panel temperature: 63 ° 4. Yellowing degree Measuring device Color difference meter manufactured by Nippon Denshoku Industries Co., Ltd. [Advantages of the Invention] The present invention is configured as described above, and thus the polymerization catalyst and the polyethylene crosslinking agent have a benzene ring in the production of a modified polyethylene resin. A foam obtained by foaming a resin obtained by using an organic peroxide that does not have the effect of significantly improving the weather resistance is extremely advantageous for industrial purposes.

[Brief description of drawings]

FIG. 1 is a graph showing the results of a weather resistance test of foamed molded articles according to Examples and Comparative Examples of the present invention.

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Claims (1)

[Claims] 1. A polyethylene particle, a polyethylene crosslinking agent,
Disperse styrene monomer and polymerization catalyst in aqueous medium, add styrene monomer to polyethylene particles, 10 hours of benzene ring-free organic peroxide as polymerization catalyst when polymerized and crosslinked Half-life temperature 60 ℃ ~ 105 ℃
The 10-hour half-life temperature of the organic peroxide that does not have a benzene ring as a polyethylene crosslinking agent is 100
A method for producing modified polyethylene resin particles, which comprises polymerizing and cross-linking using a catalyst at ℃ to 125 ℃.