JP2603858B2 - Method for producing spherical polyethylene expanded particles - Google Patents

Description

The present invention relates to a method for producing expanded spherical polyethylene particles,
More specifically, the present invention relates to a method for producing expanded spherical polyethylene particles using a non-crosslinked linear low-density polyethylene as a base resin.

[Problems to be solved by conventional technology and invention]

In-mold molded articles (bead foams) obtained by filling foamed particles in a mold and heating and foaming with steam or the like are widely used as cushioning materials, packaging materials, heat insulating materials, building materials, and the like. Has increased in recent years.

Conventionally, a molded article of polystyrene expanded particles was used as the seed molded article.However, a molded article of polystyrene expanded particles has a fatal drawback of being brittle, so polyethylene expanded particles are used instead of polystyrene expanded particles. That was suggested. However, polyethylene foam particles are usually used after being crosslinked because of a significant decrease in viscosity near the melting point. However, it is difficult to obtain crosslinked polyethylene foam particles having a low density (high foaming) by in-mold molding, and a strong and low-density molded body is required. When trying to obtain it, only a molded article inferior to a substance having remarkable shrinkage and having a high water absorption was obtained, and a low-density molded article which could be practically used was not obtained. Further, high-pressure method low-density polyethylene is mainly used as a raw material of cross-linked polyethylene because of its good cross-linking property, but high-pressure method low-density polyethylene is inferior in heat resistance and lacks rigidity, so that it is inevitably relatively low. The expansion ratio had to be determined.

As a method for solving these problems, there has been proposed a method of molding using expanded particles made of non-crosslinked linear low-density polyethylene (Japanese Patent Publication No. 60-10047). When non-crosslinked linear low-density polyethylene foamed particles are used, an in-mold molded article having low density and excellent physical properties can be easily provided.However, as resin particles used as a raw material for producing foamed particles, a strand shape is formed from an extruder. When the cylindrical or elliptical resin particles obtained by cutting the extruded material are used as they are, the obtained expanded particles become cylindrical, rugby spherical or flat, and the expanded particles having such a shape are put into a mold. There is a problem that molding is apt to occur due to poor filling, and molding using such expanded particles causes poor molding due to defective fusion between expanded particles and the like, and tends to result in a molded body having a large void. For this reason, conventionally, spherical or oval column-shaped resin particles were formed into spherical particles in a separate step and then expanded to obtain spherical expanded particles.Because there is a step of spheroidizing the resin particles before the expanding step, There is a disadvantage that the manufacturing process becomes complicated.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above-mentioned disadvantages of the prior art, and as a result, after dispersing non-crosslinked linear low-density polyethylene particles together with a foaming agent in a dispersion medium in a closed container and heating, the resin particles and the dispersion medium were dispersed. Simultaneously releasing the resin particles under low pressure to cause foaming, wherein the polyethylene particles use resin particles having a specific relationship between the ratio of length to diameter and the shrinkage ratio of the resin particles, and furthermore, the resin particles and the foaming agent Is dispersed in a dispersion medium in the presence of a specific amount of basic magnesium carbonate and foamed, whereby spheroidization is performed together with foaming, and spherical non-crosslinked linear low-density polyethylene foamed particles are formed. The present inventors have found that they can be obtained in a process and completed the present invention.

That is, the present invention has a melting point of at least 115 ° C. and a density of 0.9 in a closed container.
It is composed of a non-crosslinked linear low-density polyethylene resin of 15 to 0.930 g / cm ³ , where X is the heat shrinkage at the melting point of the resin particles + 4 ° C., L is the length of the particles, and D is the diameter of the particles. Resin particles having a relationship of 0.8 <L / D × (100−X) / 100 <1.5 are added to a volatile blowing agent in the presence of at least 0.05 parts by weight of basic magnesium carbonate per 100 parts by weight of the resin particles. The resin particles are dispersed in a dispersing medium, and the resin particles are heated and maintained in a temperature range of −15 ° C. to the melting point to impregnate the resin particles with a foaming agent. And producing a substantially spherical linear low-density polyethylene expanded particle by simultaneously discharging the resin particles and the dispersion medium from the inside of the container under a low-pressure atmosphere. Things.

The linear low-density polyethylene (hereinafter abbreviated as LLDPE) used in the present invention is ethylene and has 3 to 8 carbon atoms.
And α-olefins, such as propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, 4-methylpentene-1 and the like, The composition of these α-olefins is
It is less than 10 mol%. The above LLDPE has a melting point of 115 ° C. or higher, a density of 0.915 to 0.930 g / cm ³ , and particularly preferably a melting point of 120 to
It has a temperature of 130 ° C. and a density of 0.920 to 0.930 g / cm ³ . Melting point 11
Foamed particles using LLDPE below 5 ° C have poor moldability in the mold,
The in-mold molded body obtained by foam-molding the expanded particles in a mold has poor physical properties. The LLDPE density is less than 0.915 g / cm ³ is insufficient stiffness of the resin is molded of high expansion ratio is difficult to obtain, LLDPE exceeding density 0.930 g / cm ³ becomes close to the high-density polyethylene properties, like this Foamed particles using LLDPE have poor moldability. LLDPE has an MFR of 0.1 to 5.0
g / 10 minutes, particularly 0.5 to 2 grams / 10 minutes, is preferred in terms of spheroidization and closed cell formation.

The above LLDPE particles are, as additives, calcium stearate for neutralizing catalyst residue during polymerization, an antioxidant for preventing oxidative deterioration of the resin, an ultraviolet absorber for preventing deterioration by ultraviolet rays, and a resin. Slip agent to improve the slip property, may contain various additives such as an anti-blocking agent to prevent blocking between resin particles, these are appropriately selected and used depending on the purpose, especially when adding a slip agent This is preferable because spheroidization is performed more effectively. The addition amount of calcium stearate is usually about 500 ppm, but the cell diameter of the expanded particles is 0.02 to 2.0 m
m, preferably 0.05 to 1.5 mm
It is preferable to add about 20 to 300 ppm. Examples of the antioxidant and the ultraviolet absorber include those usually used for LLDPE, and those having little influence on the bubble diameter are preferable. As the slip agent, amide-based slip agents are usually used, and examples thereof include ethylene bis fatty acid (C 16-18) amide, higher fatty acid (C 8-22) amide, oleyl palmito amide and the like. The addition amount of this slip agent is usually 5,000 ppm or less, but it is preferable to add more than in the case where it is added for the purpose of a normal slip agent, and it is particularly preferable to add 300 to 1000 ppm. Silica is usually used as an anti-blocking agent, and its addition amount is about 300 to 1000 ppm.

In the present invention, LLDPE particles are extruded into a strand from an extruder die, cooled in water, and then cut cylindrical or elliptical particles can be used as they are, but the length of the particles is L, When the diameter is D and the heat shrinkage at the melting point of the resin particles + 4 ° C. is X, it is necessary to use resin particles having a relationship of 0.8 <L / D × (100−X) / 100 <1.5. Such resin particles are obtained by first measuring the shrinkage and the diameter of the resin extruded into a strand, and cutting the strand so that the shrinkage and the diameter have a length satisfying the above range.

When particles having a value of L / D × (100−X) / 100 less than 0.8 are used, the foamed particles become flat, and when particles exceeding 1.5 are used, the foamed particles become rugby spherical. As the above-mentioned resin particles, those having an L / D value of about 0.8 to 3, particularly preferably about 0.8 to 2, can be used.

The melting point of the resin particles is the temperature of the peak of the melting peak in differential scanning calorimetry, and is different from the melting end temperature. The heat shrinkage ratio of the resin particles is defined as L, the length of the columnar or elliptic resin particles (pellets) obtained by cutting the extruded material into a strand shape from the extruder. It means the shrinkage in the longitudinal direction when heated for one minute. In the case of cylindrical resin particles, the diameter of the resin particles is a direct line, and in the case of elliptic resin particles, it is the average value of the major axis and the minor axis.

In the method of the present invention, first, the above LLDPE particles are dispersed in a dispersion medium together with a volatile foaming agent in a closed vessel in the presence of basic magnesium carbonate and heated. Examples of the volatile foaming agent include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; monochlorofluoromethane, trichlorofluoromethane, and dichlorofluoromethane. Methane, dichlorotetrafluoroethane, methyl chloride,
Halogenated hydrocarbons such as ethyl chloride and methylene chloride are exemplified. The amount of the foaming agent varies depending on the type of the foaming agent, the desired expansion ratio, and the like, but is usually 5 to 40 parts by weight based on 100 parts by weight of the resin particles. Basic magnesium carbonate is 0.05 per 100 parts by weight of resin particles.
It is necessary to use more than 2 parts by weight, but even if the amount exceeds 2 parts by weight, no further improvement of the spheroidizing effect is obtained, and the addition amount necessary for performing the spheroidization particularly efficiently is 0.4 to 1.5 parts by weight. Department. As the dispersion medium, most solvents can be used as long as they do not dissolve the resin particles, but usually water is used. After the resin particles and the volatile foaming agent are dispersed in the dispersion medium, the heating temperature is the melting point of the resin particles −15.
Temperature in the range of ° C. to melting point. If the heating temperature is lower than this range, the expansion ratio is significantly reduced, and if the heating temperature is higher than this range, the closed cell ratio of the obtained expanded particles is reduced, and excellent expanded particles cannot be obtained. The pressure in the container at the time of heating may be higher than or lower than the vapor pressure of the volatile foaming agent used. When dispersing the resin particles in a dispersion ratio, a surfactant such as sodium dodecylbenzenesulfonate can be used in combination, if necessary, and the amount of the surfactant is preferably about 4 to 3000 ppm based on the dispersion medium.

Next, while maintaining the temperature in the container at a temperature in the range of the melting point of the resin particles −15 ° C. to the melting point, one end of the container is opened and the resin particles and the dispersion medium are simultaneously placed in a lower pressure atmosphere than the inside of the container, usually under atmospheric pressure. To expand the resin particles to obtain spherical LLDPE expanded particles. The foamed particles thus obtained usually have a bulk density of 0.01 to 0.023 g / cm ³ , a closed cell ratio of 60% or more, and an average number of cells of 1000 / mm ² or less.

The foamed particles thus obtained can be used for the production of an in-mold molded product, and the in-mold molded product is usually aged for a predetermined time under normal pressure, and then, if necessary, an inorganic gas or an inorganic gas. After applying pressure and aging with a mixed gas of a gas and a volatile foaming agent to give an internal pressure, filling in a predetermined mold and heating and foaming with steam of about 0.6 to ² kg / cm2G However, since the expanded particles obtained by the method of the present invention are spherical and have a good filling property in the mold, the obtained molded article in the mold has excellent fusion property between the expanded particles, and can be used as a packaging material, a cushioning material, or a building material. ,
It has excellent utility value as heat insulator, food container, flotation material, etc.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

Examples 1 to 12, Comparative Examples 1 to 7 LLDPE having the melting point, density and MFR shown in Table 1 was melted in an extruder and extruded into water in a strand form from a die at the tip of the extruder. The resin particles were cut to have a / D value to obtain columnar resin particles. This LLDPE contained 170 ppm of calcium stearate, 1000 ppm of erucic acid amide, 250 ppm of Irganox 1010, and 750 ppm of phosphite 168 as additives. The properties of the resin particles such as the heat shrinkage are shown in Table 1. FIG. 1 shows the result of plotting the heat shrinkage ratio of these resin particles: X with the value of L / D. In FIG. 1, ○ indicates the resin particles of the example, and x indicates the resin particles of the comparative example.

100 kg of the above particles and the blowing agent (dichlorodifluoromethane) in the amount shown in Table 1 together with the basic magnesium carbonate in the amount shown in Table 1 were dispersed in 220 water in a 400 autoclave, and stirred under stirring. And held for 10 minutes.

Then, at the same temperature, one end of the container was opened while the internal pressure of the container was maintained at 30 kg / cm ² · G with air, and the resin particles and water were released under atmospheric pressure and foamed to obtain foamed particles. The expansion ratio and shape of the obtained expanded particles are shown in Table 1.

After leaving the obtained foamed particles under atmospheric pressure for one day to cure, they are filled into a 300 mm x 300 mm x 60 mm (inner dimension) mold,
It was heated for 5 seconds with steam of 1 kg / cm ² · G to foam and mold. The properties of the obtained molded body were evaluated based on the presence or absence of voids. The results are shown in Table 1.

In addition, the evaluation of the presence or absence of voids in the molded body, observing a 50 mm × 50 mm cut surface of an arbitrary part of the obtained molded body, measuring the length of the longest part of the void, this length is 2 mm or more The following criteria were used to determine the number of voids.

Less than 10 ・ ・ ・ ・ ・ ・ ○ 10 to less than 30 ・ ・ ・ ・ ・ ・ △ 30 or more ・ ・ ・ ・ ・ ・ ・ ・ ・ × [Effects of the Invention] As described above, the method of the present invention provides a method of using the melting point of the resin particles +
Non-crosslinked LLDPE particles having a relationship of 0.8 <L / D × (100−X) / 100 <1.5 between the heat shrinkage at 4 ° C.:X and the length: L and diameter: D of the resin particles are used. Used, the LLDPE particles in a closed container, per 100 parts by weight of resin particles
By dispersing in a dispersion medium together with a volatile foaming agent in the presence of 0.5 parts by weight or more of basic magnesium carbonate and heating to a specific temperature range, and then releasing the foam under low pressure from the container to foam the foam, It is not necessary to perform spheroidization of resin particles in a separate process as in the conventional case, and even when foaming is performed using columnar or elliptical resin particles, spheroidization can be performed simultaneously in the foaming process, and in-mold molding is performed. This has the effect that spherical non-crosslinked LLDPE foamed particles that can be used to produce an excellent molded article having an excellent filling factor and few voids when supplied can be easily produced without going through complicated steps.

[Brief description of the drawings]

FIG. 1 plots the X and L / D values with the X-axis as the abscissa and the L / D value as the ordinate, with respect to the heat shrinkage of each resin particle of Example and Comparative Example. It is the graph which calculated | required the boundary between.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-187035 (JP, A) JP-A-63-113040 (JP, A)

Claims (1)

(57) [Claims] 1. A sealed container having a melting point of at least 115 ° C. and a density of 0.915 to 1.
It is made of 0.930 g / cm ³ of a non-crosslinked linear low-density polyethylene resin.
Resin particles having a relationship of 0.8 <L / D × (100−X) / 100 <1.5, where L is the length of the particles and D is the diameter of the particles, are based on 100 parts by weight of the resin particles. Disperse in a dispersion medium together with a volatile foaming agent in the presence of 0.05 parts by weight or more of basic magnesium carbonate and impregnate the resin particles with a foaming agent by heating and holding the resin particles in the temperature range of -15 ° C. to the melting point, Then, while maintaining the temperature in the container within the above temperature range, one end of the container is opened, and the resin particles and the dispersion medium are simultaneously released from the inside of the container under a low pressure atmosphere to form substantially spherical linear low-density polyethylene foamed particles. A method for producing expanded spherical polyethylene particles.