JP2709395B2 - Non-crosslinked linear low-density polyethylene resin particles for foaming and method for producing non-crosslinked linear low-density polyethylene expanded particles - Google Patents

Description

The present invention relates to non-crosslinked linear low-density polyethylene resin particles for foaming and a method for producing foamed particles using the particles.

[Problems to be solved by conventional technology and invention]

A so-called bead expanded molded article (in-mold molded article) obtained by filling the pre-expanded particles in a mold and heating and foaming is excellent in cushioning property, heat insulating property, etc., cushioning material, packaging material, heat insulating material, building material, etc. It is widely used and its demand has been increasing in recent years.

Conventionally, as a molded article of this type, a molded article made of expanded polystyrene particles has been known, but an expanded molded article of polystyrene beads has a fatal drawback of being brittle and has a drawback of poor chemical resistance. The improvement was desired from an early stage. As a solution to such a drawback, a molded article made of expanded polyethylene particles has been proposed.However, since the viscosity of a polyethylene resin is remarkably reduced near the melting point, a crosslinked polyethylene resin is usually used. When trying to obtain a low-density (high-foamed) molded body by in-mold molding, only a molded body with remarkable shrinkage, high water absorption, and poor physical properties can be obtained, and a low-density polyethylene molded body that can be practically used. Could not get at all. Furthermore, 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. The expansion ratio had to be determined.

As a method for solving these problems, Japanese Patent Publication No. 60-10047
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes a method of molding using foamed particles made of non-crosslinked linear low-density polyethylene.However, foamed particles made of non-crosslinked polyethylene have a narrow heating temperature range during molding and cannot be sufficiently heated. Due to the above and the crystal structure of the non-crosslinked linear low-density polyethylene, unless the foaming ability is provided, sufficient secondary foaming is not performed, and a good molded product cannot be obtained. For this reason, when molding non-crosslinked linear low-density polyethylene foamed particles, a method of applying an internal pressure by adding a blowing agent gas or an inorganic gas such as air to the foamed particles before molding is usually adopted. However, the addition of a foaming gas or an inorganic gas to the foamed particles has a problem that a large expense is required in terms of equipment and cost, and the production cost of the molded body is high. Moreover, in general, polyolefin resin foamed particles are difficult to maintain the foaming ability for a long time because the gas in the particles is easily released even if the foaming ability is imparted by increasing the internal pressure by adding an inorganic gas or the like, In order to obtain an excellent molded body in these conventional methods, the foamed particles must be consumed in a short time after the application of the internal pressure, and the molded body can be easily obtained only by receiving the supply of the foamed particles from the foamed particle manufacturer. Could not be manufactured.

The present applicant has previously filed Japanese Patent Application No. 62-156310 (Japanese Unexamined Patent Application Publication No.
No. 41) proposed non-crosslinked linear low-density polyethylene pre-expanded particles that can be molded without special internal pressure treatment.

The pre-expanded particles are non-crosslinked linear low-density polyethylene pre-expanded particles, and the DSC curve obtained by differential scanning calorimetry (provided that 1 to 5 mg of pre-expanded particles is heated at a rate of 10 ° C./min by a differential scanning calorimeter). DSC curve at the first temperature rise obtained when the temperature is raised to 220 ° C at a temperature rate), two endothermic peaks appear and the energy of the endothermic peak on the high temperature side is 5 J / g or more. Non-crosslinked linear low-density polyethylene pre-expanded particles characterized by having:

However, some of the raw resin particles do not show two endothermic peaks (hereinafter, sometimes simply referred to as “double peaks”) in a DSC curve obtained by differential scanning calorimetry. When trying to obtain pre-expanded particles having a double peak using such resin particles, it is difficult to stably supply particles having excellent in-mold moldability without performing special internal pressure treatment. There was a problem. this is,
This is because, when pre-expanded particles having excellent in-mold moldability are to be obtained from the resin particles, the expansion temperature is limited to a very narrow range, and it is difficult to maintain the narrow temperature range through pre-expansion.

[Means for solving the problem]

The present inventors have conducted intensive studies in view of the above points. As a result, in the differential scanning calorimetry, the temperature was raised and lowered under specific conditions, and two endothermic peaks appeared in the DSC curve obtained at the time of the second temperature rise. By using a non-crosslinked linear low-density polyethylene resin having a crystal structure as a base resin, the low-density polyethylene pre-expanded particles capable of providing a molded article having excellent physical properties can be provided without performing a special internal pressure application treatment. It has been found that the present invention can be obtained.

That is, the present invention provides: (1) a non-crosslinked linear low-molecular-weight polymer in which two endothermic peaks appear in a DSC curve obtained by differential scanning calorimetry and the melting energy of the endothermic peak on the high temperature side is 8 to 25.1 J / g; Non-crosslinked linear low density to obtain high density polyethylene expanded particles (the above DSC curve is a DSC curve obtained when 1-5 mg of expanded particles are heated to 220 ° C. at 10 ° C./min by a differential scanning calorimeter) Polyethylene resin particles, 1 to 5 mg of the resin particles are heated at a rate of 10 ° C./min to 220 ° C. by a differential scanning calorimeter, then cooled at a rate of 10 ° C./min, and then again at a rate of 10 ° C./min.
Linear low-density polyethylene resin particles for foaming, having a crystal structure in which two endothermic peaks appear in a DSC curve obtained when the temperature is raised to 220 ° C.

(2) 1-5 mg of resin particles were measured with a differential scanning calorimeter.
DSC obtained when the temperature is raised to 220 ° C at a rate of 10 ° C / min, then lowered at a rate of 10 ° C / min, and then again raised to 220 ° C at a rate of 10 ° C / min.
After the non-crosslinked linear low-density polyethylene resin particles having a crystal structure in which two endothermic peaks appear in the curve are heated to and above the softening temperature of the particles while being dispersed in a dispersion medium together with a foaming agent in a closed container, Discharging the particles impregnated with the foaming agent and the dispersion medium into the vessel under a low pressure, two DSC curves obtained by differential scanning calorimetry show two endothermic peaks, and the melting energy of the endothermic peak on the high temperature side. Is 8 to 25.1 J / g (provided that the DSC curve indicates that 1 to 5 mg of the expanded particles is 220 ° C. at 10 ° C./min by a differential scanning calorimeter).
A non-crosslinked linear low-density polyethylene foamed particle obtained by obtaining a DSC curve obtained when the temperature is raised to a maximum.

It is the gist.

In the present invention, the non-crosslinked linear low-density polyethylene resin (hereinafter abbreviated as LLDPE) includes a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms,
As the α-olefin having 4 to 10 carbon atoms, 1-butene, 1-pentene, 1-hexene, 3,3-dimethyl-1
-Butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-octene and the like. The content of these α-olefins in LLDPE is usually 3
-25% by weight, preferably 6-20% by weight.

The LLDPE particles of the present invention have a crystal structure in which two endothermic peaks appear in a DSC curve obtained by differential scanning calorimetry. The DSC curve shows that 1 to 5 mg of a resin is measured at a rate of 10 ° C./min to 220 ° C. by a differential scanning calorimeter. After the temperature was raised (first temperature rise), the temperature was lowered at 10 ° C / min, and then again at 10 ° C / min at 220 ° C.
The DSC curve obtained when the temperature was raised up to (the second temperature increase). The LLDPE of the present invention has a D
In the SC curve, two peaks appear depending on the heat history, but when the material is rapidly cooled like the raw material used for foaming of the present invention, only one peak usually appears.

FIG. 1 shows a DSC curve at the time of the second temperature rise of the raw material of the present invention.

The LLDPE particles of the present invention further have an MFR of 0.1 to 5 g / 10 minutes, particularly 0.5
33 g / 10 min is preferred. Further, those having an n-hexane extractable content of 0.3 to 1.5% are preferable because foamed particles having excellent foaming properties and higher cell strength can be produced.

Obtained by a second heating with a differential scanning calorimeter
The present invention L of the crystal structure where two endothermic peaks appear in the DSC curve
In order to obtain LDPE particles, when copolymerizing ethylene and an α-olefin, it is preferable to polymerize so that the bond between them is random.

The LLDPE of the present invention is mainly used as a raw material for producing pre-expanded particles used for in-mold molding. The present invention LLDP
In order to produce the pre-expanded particles using E, the particles made of the LLDPE of the present invention are dispersed in water together with a blowing agent in a closed container in water and heated and held to impregnate the resin particles with the blowing agent. A method is employed in which water and water are released from the inside of the container under a low-pressure atmosphere to foam the resin particles.

The expanded particles obtained in this manner have two endothermic peaks in the DSC curve at the first temperature rise measured by the same method as the resin particles, and the melting energy of the endothermic peak on the high temperature side is 8 to 10%. Foamed particles having a melting energy of 25.1 J / g and an endothermic peak on the high temperature side in the DSC curve within the above range have preferable characteristics in moldability.

The melting energy (J / g) of the high-temperature peak is calculated by the following equation.

Hot peak melting energy (J / g) = (heat quantity chart 1 cm ² per) (area on the chart of the high-temperature peak) × ÷ (measured sample weight) EXAMPLES Hereinafter, the present invention further to Examples This will be described in detail.

Example 1, Comparative Example 1 About 4 mg of two kinds of LLDPE particles (comonomer: 1-butene, comonomer content 5.5 Wt%) having a density of 0.926 g / cm ³ , an MI of 1.0 g / 10 min, and a melting point of 120 ° C. 220 at 10 ° C / min with scanning calorimeter
After cooling to room temperature at 10 ° C./min, the temperature was raised again to 220 ° C. at 10 ° C./min. The DSC curve obtained by the first heating was shown in FIG. The DSC curve obtained by temperature measurement is shown in FIG. 1 (however, in the case of the resin of the comparative example, the DSC curve at the time of the second temperature rise does not have two endothermic peaks. The DSC curve at the time of the temperature rise is substantially the same as the DSC curve shown in FIG. 2).

Next, the resin was melted in an extruder, extruded into a strand from a die, quenched in water, cut, and granulated into pellets of about 4 mg / piece. This resin particle 10
Disperse 1.0 part by weight of basic magnesium carbonate and 300 parts by weight of water in a closed container per 0 parts by weight in a closed container and heat to various temperatures (foaming temperature) as shown in Table 1. After holding for 1 minute, the resin particles and water were simultaneously released under the atmospheric pressure at that temperature to foam the resin particles.

The average expansion ratio (bulk ratio) of the obtained expanded particles and the DSC curve at the first temperature increase obtained by measuring about 4 mg of these expanded particles at a temperature of 10 ° C./min to 220 ° C. with a differential scanning calorimeter. Table 1 shows the melting energy of the high-temperature peak in Table 1. Next, the foamed particles were left to stand at atmospheric pressure for 24 hours, aged,
After filling in a mold of 0 mm × 300 mm × 60 mm, and then evacuating the air in the mold, it was molded by heating with steam of 1.2 kg / cm ² G.
After cooling, the molded body removed from the mold was cured at 80 ° C. for 20 hours, and then the moldability of the molded body was measured. The results are shown in Table 1. From these results, it can be seen that the foamed particles of the examples have a foaming temperature range of 3.5 ° C., whereas the foamed particles of the comparative example have a very narrow temperature of 1 ° C.

Examples 2 and 3 and Comparative Examples 2 and 3 The experiment was carried out in the same manner as in Example 1 except that the resin used, the foaming temperature and the amount of the foaming agent were changed as shown in Tables 2 and 3. The results are shown in Tables 2 and 3.

[Effects of the Invention] As described above, the LLDPE particles of the present invention are resins 1 to 5
mg was heated at a rate of 10 ° C./min to 220 ° C. by a differential scanning calorimeter, then cooled at a rate of 10 ° C./min, and then again at a rate of 10 ° C./min.
By having a crystal structure in which two endothermic peaks appear in the DSC curve obtained when the temperature is raised to 0 ° C., compared to LLDPE particles having a crystal structure in which two endothermic peaks do not appear in the DSC curve at the time of the second temperature rise, It is possible to stably produce foamed particles that can be molded at a wide molding temperature without special treatment and can provide a molded body having excellent physical properties.

Therefore, it is possible to reduce the cost required for the equipment for applying the internal pressure and the internal pressure applying step. Further, the use of the expanded particles made of the LLDPE of the present invention has various effects such as excellent properties such as low shrinkage and low water absorption, and a low-density molded body can be easily produced.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a DSC curve obtained by a second heating of the LLDPE of the present invention by a differential scanning calorimeter,
The figure is a graph showing an example of a DSC curve obtained by the first heating of the particles.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kazuo Tsurukai 5964-2 Tamura, Hiratsuka-shi, Kanagawa Pref. 104, Mitsubishi Gas Chemical Company Housing (56) References JP-A-63-205331 (JP, A) JP-A-1-135806 (JP, A)

Claims (2)

(57) [Claims] 1. Non-crosslinked linear low density polyethylene foamed particles having two endothermic peaks in a DSC curve obtained by differential scanning calorimetry and having a melting energy of 8 to 25.1 J / g at an endothermic peak on a high temperature side. (However, the DSC curve shows that 1 to 5 mg of expanded particles are 220 ° C. at 10 ° C./min by a differential scanning calorimeter.
Non-crosslinked linear low-density polyethylene resin particles for obtaining a DSC curve obtained when the temperature is raised up to 220 ° C. at 10 ° C./min by a differential scanning calorimeter.
After the temperature was raised to 10 ° C / min,
Linear low density polyethylene resin particles for foaming, having a crystal structure in which two endothermic peaks appear in a DSC curve obtained when the temperature is raised to 220 ° C. in minutes. 2. The resin particles are 1 to 5 mg by a differential scanning calorimeter.
Is heated at 10 ° C./min to 220 ° C., then cooled at 10 ° C./min, and then heated again at 10 ° C./min to 220 ° C., resulting in a DSC curve showing two endothermic peaks. The non-crosslinked linear low-density polyethylene resin particles having the foaming agent are dispersed in a dispersion medium together with a foaming agent in a closed container while being heated to a temperature equal to or higher than the softening temperature of the particles, and then dispersed with the particles impregnated with the foaming agent. Foamed particles which release the medium from the container under a low pressure, two endothermic peaks appear on the DSC curve obtained by differential scanning calorimetry, and the melting energy of the endothermic peak on the high temperature side is 8 to 25.1 J / g. (However, the above DSC
The curve shows 1-5 mg of expanded particles at 10 ° C by a differential scanning calorimeter.
/ DSC curve obtained when the temperature is raised to 220 ° C./min).