JPS6010048B2 - Non-crosslinked high-density polyethylene pre-expanded particles and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to non-crosslinked high-density polyethylene pre-expanded particles and a method for producing the same.

BACKGROUND ART Conventionally, a so-called bead molding method using pre-expanded particles has been used as a method for obtaining polyethylene resin foam moldings.

However, if the pre-expanded particles used therein are not crosslinked, it is difficult to obtain a highly foamed molded product, and the molded product also shrinks significantly, so that it has not been put to practical use. For this reason, currently cross-linked pre-expanded particles are used to obtain foamed molded products, but this requires a cross-linking process, consumes chemicals and energy, and is difficult to reuse, so non-cross-linked pre-expanded particles are used. The development of a molding method using expanded particles is eagerly awaited. The present invention aims to provide non-crosslinked high-density polyethylene pre-expanded particles and a method for producing the same, and as a result of intensive research by the present inventors on the above points, we have found that The present invention has been completed by successfully developing non-crosslinked high-density polyethylene pre-expanded particles having excellent bending fatigue resistance, pressure striping resistance, in-mold moldability, etc., and a method for producing the same.

That is, the present invention provides a Vikat softening point of 11,500 or higher,
It is made of non-crosslinked high-density polyethylene with a density exceeding 0.950 polyethylene, has a high density of 0.01 to 0.3 m/g, an average cell diameter of 20 to 500 fre, and a closed cell ratio of 65% or more. This article focuses on the characteristics of non-crosslinked high-density polyethylene pre-expanded particles. Another gist of the present invention is the step of incorporating a volatile blowing agent into non-crosslinked high-density polyethylene particles having a Vicat softening point of 11,500 or more and a density of more than 0.950 m/m; A step of dispersing the particles, and opening one end of the container while maintaining the temperature in the closed container within the range of 100 degrees lower than the Vicat softening point of the particles to 1000 degrees higher than the melting point, and simultaneously dispersing the particles and the dispersion medium into the container. A method for producing pre-expanded particles of non-crosslinked high-density polyethylene, which comprises a step of discharging into a lower pressure atmosphere. The base resin used in the present invention is non-crosslinked high density polyethylene (hereinafter referred to as non-crosslinked HDPE) having a Vicat softening point of 11,500 or more and a density of more than 0.950 Ta'.

If the Vicat softening point is less than 115 qo, the in-mold moldability will be poor, and the physical properties of the resulting molded product will be poor, which is not preferable. Further, if the density is less than 0.950 ta', preliminary foaming becomes difficult. A particularly preferable range of Vicat softening point is 118qC
or more, and a particularly preferable range of density is 0.950 to 0
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The non-crosslinked HDPE of the present invention can be obtained, for example, by a conventional low-pressure method, and may contain additives such as antioxidants and ultraviolet absorbers during the Z step of pelletizing and forming spherical particles. Volatile blowing agents used in the present invention include, for example, aliphatic hydrocarbons such as propane, butane, bentane, hexane, heptaso, etc.; cycloaliphatic hydrocarbons such as cyclobentane; and trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride,
Halogenated hydrocarbons such as ethyl chloride and methylene chloride are used.

The amount of the foaming agent added varies depending on the type of foaming agent and the desired degree of foaming, but is usually 5 to 4 parts by weight.
In the method for producing non-crosslinked HDPE pre-expanded particles of the present invention,
A volatile blowing agent is added to the non-crosslinked HDPE particles, but the timing is not particularly limited. The HDPE particles and the blowing agent may be dispersed in the dispersed soot in a closed container, or the HDPE particles and the blowing agent may be placed in a closed container and the HDPE particles and the blowing agent may be dispersed in the dispersed soot in the closed container.
A blowing agent may be included in the PE particles.

Further, in the process of heating the particles to a predetermined temperature in the closed container, a blowing agent may be introduced into the closed container to disperse the particles and the blowing agent, and the blowing agent may be contained in the particles. Note that the temperature at which the blowing agent is incorporated into the particles is also arbitrary and is not particularly limited. In the method of the present invention, HDPE particles and a volatile blowing agent may be used separately or the volatile blowing agent may be mixed with HDPE particles.
After being contained in the particles, they are dispersed in a dispersion medium. At this time, if necessary, a dispersant such as finely divided aluminum oxide and titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc. can be used.

The amount of this dispersant added is usually 0.01 to 1 part by weight per 100 parts by weight of HDPE particles. In addition, when dispersing HDPE particles, it is necessary to have a melting point of 20o0 or more and an HLB value of 1 to 1.
It is also possible to add up to 5 parts by weight of an organic compound such as stearamide. The dispersed soot may be any solvent that does not dissolve the HDPE particles, such as water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof; In the pre-foaming method of the present invention, one end of the container is opened and the HDPE particles and dispersed soot are simultaneously released into an atmosphere at a lower pressure than the inside of the container, but the temperature at this time is below the Vicat softening point of the HDPE particles. more than 1000
The temperature ranges from low to 1ooC above the Vicat softening point.

At temperatures below 1000 degrees lower than the Vicat softening point, there is almost no foaming, and at temperatures above 1000 degrees higher than the Vicat softening point, the closed cell ratio decreases significantly and the mechanical strength decreases. The preferred range is from 5°C lower than the Vicat softening point to 8°C higher than the Vicat softening point.The pressure at this time may be either higher than or lower than the vapor pressure of the volatile blowing agent, and the atmosphere to be released is usually The pre-expanded particles of the present invention obtained by the above method have a high density of 0.
01 to 0.3 Ta', a closed cell ratio of 65% or more, and an average cell diameter of 20 to 500 France.

If the density is less than 0.01 ta', the shape of the pre-expanded particles tends to become distorted, and if the density exceeds 0.3 ta', not only the shape of the particles tends to become distorted, but also the foamed state becomes unstable. It becomes uniform. A particularly preferred range of bulk density is 0.015-0.
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When the closed cell ratio is 65%, the foamed particles tend to become distorted and the compressive elasticity decreases. A particularly preferred range of closed cell ratio is 75% or more. If the average cell diameter is less than 20 mm, the shape of the foamed particles will be distorted and the mechanical strength will be reduced, and if it exceeds 500 mm, the moldability in the mold will be poor and it will be difficult to obtain a good molded product. Even if a molded product were obtained, the surface would be hard and significantly uneven. A particularly preferable range of the average cell diameter is 50 to 400 pores. Further, the particle size of the pre-expanded particles is not particularly limited, but is preferably 0.5 to 2 m in diameter from the viewpoint of fluidity. The pre-expanded particles of the present invention as described above are usually aged at room temperature and pressure for a predetermined period of time, and then, if necessary, are aged under pressure using an inorganic gas or a mixed gas of an inorganic gas and a volatile blowing agent at a predetermined pressure for a predetermined period of time. Ru.
The pre-expanded particles to which internal pressure has been applied as described above are filled into a mold, and heated and foamed at (G), usually at a water vapor pressure of 1.2 to 3.5 ta', to obtain a foam molded product according to the mold. The foam molded product obtained as described above can be used as a packaging material, a cushioning material, a heat insulating material, etc.
It can be used for food containers, flotation materials, etc. As explained above, the pre-expanded particles of the present invention have excellent film resistance, heat resistance, tear strength, bending fatigue resistance, pressure stripe elasticity, in-mold formability, etc. The foamed molded product obtained is a good product having the above-mentioned excellent properties.

Further, according to the present invention, pre-expanded particles having excellent properties can be obtained from non-crosslinked HDPE particles, and the process can be simplified by eliminating the need for a crosslinking step, and the energy and energy associated with it can be simplified. It has various advantages, such as being able to reduce costs because it does not require the consumption of chemicals, and being reusable because it is non-crosslinked. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 5 and Comparative Examples 1 to 9 10 parts by weight of non-crosslinked HDPE particles having the density, Vicat softening point and melting point shown in Table 1, 25 parts by weight of dichlorodifluoromethane, 0.0 parts by weight of finely divided aluminum oxide. Put 5 parts by weight and 30 parts by weight of water into an autoclave and raise the temperature under concentrated steam to bring the temperature inside the container to 90 to 150 degrees and reduce the pressure to 2.
One end of the container was opened while the mixture was maintained at a temperature of 0 to 50 m/day), and the mixture was discharged into the atmosphere to cause foaming, thereby obtaining various pre-expanded particles shown in Table 1.

In addition, as comparative examples, low density polyethylene (hereinafter referred to as LDPE), crosslinked LDPE, and non-crosslinked HDPE outside the scope of the present invention
Pre-expanded particles shown in Table 1 were obtained in the same manner as in the examples. The obtained pre-expanded particles were left at room temperature and pressure for 4 hours, then filled into a sealed container and heated for 2.5 ta'.
), and was pressure-ripened in air at 35°C for 4 hours.

Next, the pre-expanded particles were filled into a mold and heated and molded with steam at a flow rate of 1.2 to 3.5 ta' at a temperature higher than the Vicat softening point of each resin to obtain a foamed molded product. Various physical property tests were conducted on the pre-expanded particles and the obtained foamed molded product. The results are shown in Table 2. Note that the average bubble diameter was measured by observing the cut surface with an electron microscope. Table 1 Table 2 *1...The particles were treated with a weatherometer for 200 hours, and the particles were eroded due to changes in coloring, deformation, and elasticity.

◎...Almost no coloring and deformation, but elasticity ○...Slight discoloration and deformation, but elasticity △...
...Discoloration and deformation are observed, and the elasticity is decreased.
... Judgment was made based on changes in coloration, deformation, and elasticity after 1000 hours at 100°C in a jar oven.

◎”…There is almost no change in coloring, deformation, or elasticity ○…Some coloring or deformation is observed, but the elasticity is △…
Discoloration and deformation are observed, and the elasticity is decreased.
The loss remained constant according to the above.

◎……Do not break more than 500 times○・・・300~
Broken after less than 500 cycles △... Broken after 100 to less than 300 cycles ×... 1... Broken after less than 100 cycles *4... Measured according to JIS K6767K.

◎”…729/10 More than skin width○…329/1
729/10 skin width exceeding 0 skin width △・・・19
/10 rib width exceeds 329/10 rib width×,. ．． ．．・．． 1
Less than 9/10 rib width *5...Using Bunshiron, it was compressed to a maximum stress of 4K at a rate of 10 skins/skin, and the elastic recovery rate of the residual strain was measured after the stress was removed.

◎“Recovery of 95% or more ○…Recovery of less than 85-95* △……Recovered less than 75-85 shots ×・・・Less than 75 shots *6... Judgment was made using the following criteria.

◎……Good molding ○……Molding normal △・・・・Some molding defects occur ×・・・・・・Poor molding

Claims (1)

[Claims] 1. Vikatsu softening point: 115°C or higher, 0.950g/cm
Made of non-crosslinked high-density polyethylene with a density exceeding ^3, bulk density 0.01 to 0.3 g/cm^3, average cell diameter 2
Non-crosslinked high-density polyethylene pre-expanded particles characterized by having a particle size of 0μ to 500μ and a closed cell ratio of 65% or more. 2 Vikatsuto softening point 115℃ or higher, 0.950g/cm
A step of incorporating a volatile blowing agent into non-crosslinked high-density polyethylene particles having a density exceeding ^3, a step of dispersing the particles in a dispersion medium in a closed container, and a step of controlling the temperature in the closed container to 10° below the Vikato softening point of the particles. It is characterized by a step of opening one end of the container while maintaining the temperature within a range of 10°C higher than the Vikatto softening point from a temperature lower than 10°C, and simultaneously releasing the particles and the dispersion medium into an atmosphere at a lower pressure from inside the container. A method for producing pre-expanded non-crosslinked high-density polyethylene particles.