JPH11349724A - Foamable polyolefin-based resin particle, foamed particle therefrom and foamed molded material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foamed molded material having an excellent recycling property, heat resistance, a low density and a soft property, and a uniform pore diameter with a high foaming property. SOLUTION: This foamed molded material is obtained by foaming and molding a foamable polyolefin-based resin particle having two endothermic peaks measured by a differential scanning calorimetry measurement and having its high-temperature side peak of >=130 deg.C and its low-temperature side peak of <=65 deg.C and comprising a polyolefin-based resin particle obtained by melt-blending a soft polyolefin-based resin containing 20-60 mol.% of ethylene component and 40-80 mol.% of propylene component, having two endothermic peaks in the above measurement wherein its high-temperature side peak is >=130 deg.C and its low-temperature side peak is <=65 deg.C with a polypropylene-based resin added with a foaming agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed molded article having a desired shape by heating and prefoaming resin particles containing a foaming agent to form foamed particles, and further foaming and molding in a mold. The present invention relates to expandable polyolefin-based resin particles which can be applied to a method for obtaining a polystyrene resin, a foamed particle obtained therefrom, and a foamed molded article. More specifically, it is substantially non-crosslinked, has excellent recyclability and heat resistance, and has low density and excellent softness, and further has a higher foaming ratio than that obtained from a soft polyolefin resin or polypropylene resin. TECHNICAL FIELD The present invention relates to expandable polyolefin-based resin particles capable of obtaining a foamed molded article having a high particle size, foamed particles obtained therefrom, and a foamed molded article.

[0002]

2. Description of the Related Art A polystyrene resin is used as a base resin of a foamed molded article by in-mold molding.
Polyethylene resin, polypropylene resin and the like are widely used. However, when a polystyrene resin is used as the base resin, there is a disadvantage that the obtained foamed molded article is very brittle and has poor chemical resistance.

[0003] When a polyethylene resin is used as a base resin, a flexible and tough foamed article can be obtained, but a crosslinking step is essential for high foaming, and as a result, recyclability is extremely poor. There is a disadvantage that. When a polypropylene resin is used as a base resin, high foaming is possible while being substantially non-crosslinked (Japanese Patent Publication No. 56-1344). -There is a drawback that the processing temperature at the time of molding is high, the equipment such as a foaming machine and a molding machine is expensive, and the durability of the mold is significantly deteriorated.

In order to impart flexibility to the polypropylene resin, an ethylene-propylene copolymer resin or a mixture of the ethylene-propylene copolymer resin and low-density polyethylene has been proposed (JP-B-59-23).
No. 731), especially in the case of a high ethylene component, a cross-linking step is indispensable in the same manner as the polyethylene resin for high foaming, and there is a disadvantage that recyclability is extremely poor.

[0005]

Means for Solving the Problems In view of the above situation, the present inventors have conducted intensive studies and as a result, have found that the ethylene component is 2%.
0 to 60 mol%, the propylene component is 40 to 80 mol%, and the scanning differential calorific value (hereinafter, referred to as “DSC”)
In the measurement, there are two endothermic peaks, and the high-temperature side peak is 1
It is obtained by melting and kneading a soft polyolefin-based resin having a low-temperature side peak of 65 ° C. or less and a polypropylene-based resin at 30 ° C. or higher, and has two endothermic peaks in DSC measurement. The foamed particles obtained by pre-expanding the expandable polyolefin-based resin particles, which are obtained by adding a foaming agent to a polyolefin-based resin particle having a low-temperature peak of 65 ° C. or lower at 130 ° C. or higher, have a cell diameter of Was uniform and very suitable for high foaming. The foamed molded article formed using the foamed particles is substantially non-crosslinked, has excellent recyclability, chemical resistance and heat resistance, has low density and excellent flexibility, and is further heated during molding. The inventors have found that the conditions are stable and completed the present invention.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The soft polyolefin resin used in the present invention is a copolymer having an ethylene component of 20 to 60 mol% and a propylene component of 40 to 80 mol%, and has two endothermic peaks measured by DSC. The peak on the high temperature side is 130 ° C. or higher, and the peak on the low temperature side is 65 ° C. or lower.

[0007] More preferably, the ethylene component is 20 to
40 mol% and a propylene component of 60 to 80 mol%. If the ethylene component is less than 20 mol%, the processing temperature at the time of foaming / molding becomes high, approximating a polypropylene resin foam, and the durability of the mold of the foaming machine and the molding machine is remarkably deteriorated. On the other hand, if the ethylene component exceeds 60 mol%, a crosslinking step is an essential condition for high foaming, and as a result, recyclability is poor.

When the peak on the high temperature side of the soft polyolefin resin is lower than 130 ° C., a difference in viscosity between the polypropylene resin and the soft polyolefin resin occurs during melt-kneading, and depending on the screw shape of the extruder, the soft polyolefin resin may not be melted. It becomes difficult to uniformly disperse in the polypropylene resin. In addition, even when foaming and molding are performed using polyolefin-based resin particles obtained from such a soft polyolefin-based resin, foamability is reduced. On the other hand, if the low-temperature side peak exceeds 65 ° C., not only does the temperature of the extruder during melt-kneading need to be increased, but also there is no difference in viscosity between the polypropylene-based resin and the soft polyolefin-based resin during melt-kneading. It is necessary to use a polypropylene resin having a high melting point. Then, the processing temperature at the time of foaming / molding becomes high, and the durability of the mold of the foaming machine and the molding machine is significantly deteriorated.

The soft polyolefin-based resin used in the present invention is mainly composed of a copolymer of ethylene and propylene, but may be copolymerized with another monomer copolymerizable with ethylene or propylene. The polymer may be contained in the molecule. Such monomers include α
-Olefins, cyclic olefins, diene monomers, vinyl monomers and the like.

The α-olefin as the monomer includes α-olefins having 4 to 12 carbon atoms such as butene-1, isobutene, pentene-1, 3-methyl-butene-1, octene-1, and decene-1. -Olefins. Examples of the cyclic olefin include cyclopentene. Examples of the diene monomer include norbornene and 5-methylene-2-
Norbornene, 1,4-hexadiene, methyl-1,4
-Hexadiene and the like.

The vinyl monomers include vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate,
Examples include acrylic acid, methacrylic acid, and maleic acid. These monomers may be used alone or in combination. Examples of the polypropylene resin used in the present invention include a propylene homopolymer and a copolymer of propylene with one or more other monomers copolymerizable with propylene.

These copolymers may be random, block two-dimensional or three-dimensional copolymers, such as ethylene-propylene random copolymer, butene-1-propylene random copolymer, ethylene-butene-1 copolymer. -Propylene random copolymers are preferred. The above polypropylene resins can be used alone or in combination.

Among the above polypropylene resins, an ethylene-propylene random copolymer having an ethylene component content of 0.5 to 10% by weight and a propylene component content of 90 to 99.5% by weight is particularly preferable. When the ethylene content is less than 0.5% by weight, the processing temperature during foaming / molding becomes high, and not only the durability of the foaming machine and the mold of the molding machine is significantly deteriorated, but also the softness of the foamed particles obtained is low. And the effect as a buffer decreases. 10% by weight
It is not preferable to exceed the value, because the high foaming property, which is a feature of the present invention, is reduced.

The polyolefin resin particles of the present invention can be obtained by melt-kneading the above-mentioned soft polyolefin resin and polypropylene resin at about 180 to 250 ° C. Examples of an apparatus used for melt kneading include a kneader such as a co-kneader, a Banbury mixer, a Brabender, a single-screw extruder, and a twin-screw extruder. Among them, a single-screw or twin-screw extruder is preferable in terms of productivity. . Also,
Melt kneading may be repeated a plurality of times in order to mix each raw material sufficiently uniformly.

The proportion of the polypropylene resin to be melt-kneaded is preferably 30 to 95% by weight, more preferably 60 to 85% by weight. If the proportion of the polypropylene-based resin is less than 30% by weight, the cell diameter when formed into a foam is not stable,
It is difficult to obtain a foam having excellent softness, and the high foamability, which is a feature of the present invention, is reduced. On the other hand, when the proportion of the polypropylene resin exceeds 95% by weight, the processing temperature at the time of foaming / molding becomes high, and the durability of the foaming machine and the mold of the molding machine is remarkably deteriorated. However, the softness is lowered, and the effect as a cushioning material is reduced.

Incidentally, other thermoplastic resins may be melt-kneaded with the polyolefin resin particles as long as the effects of the present invention are not adversely affected. Examples of the thermoplastic resin that can be melt-kneaded include the following. Low density polyethylene, high density polyethylene,
Linear low density polyethylene; α-polyolefin having 4 to 12 carbon atoms such as polybutene-1, polyisobutene, polypentene-1, polymethylpentene-1; cyclic polyolefin containing cyclopentene; 1,2-polybutadiene, 1,3- Homodiene polymers such as polybutadiene; norbornene, 5-methylene-2-norbornene,
Homocopolymers such as 1,4-hexadiene and methyl-1,4-hexadiene; block copolymers of butadiene and styrene and hydrogenated products thereof; vinyl chloride, vinylidene chloride, styrene, acrylonitrile, vinyl acetate, acrylic acid , Vinyl homo- or copolymers such as methacrylic acid and maleic acid; polyolefin resin particles obtained as described above have two endothermic peaks measured by DSC, and the high-temperature side peak thereof is 130 ° C. or higher. And
The low temperature side peak is 65 ° C. or less.

If the peak on the high temperature side is lower than 130 ° C., shrinkage tends to occur immediately after foaming, and as a result, a high expansion ratio cannot be obtained. In addition, when such resin foam particles are molded in a mold, shrinkage after molding tends to occur, and it is difficult to obtain a molded body having good dimensional stability. On the other hand, when the low-temperature side peak exceeds 65 ° C.,
The processing temperature at the time of foaming / molding becomes high, and the durability of the mold of the foaming machine and the molding machine becomes extremely poor.

If necessary, various additives such as an antioxidant, a flame retardant, a flame retardant auxiliary, an antistatic agent, a foam control agent, etc. are extruded, melt-kneaded, or kneaded with the polyolefin resin particles thus obtained. It can also be added during the impregnation of the blowing agent. The polyolefin-based resin particles may be crosslinked or non-crosslinked, but are preferably substantially non-crosslinked from the viewpoint of not impairing the recyclability, which is the object of the present invention.

The blowing agents used in the present invention include volatile organic blowing agents having a normal pressure boiling point in the range of -50 to 100 ° C., for example, propane, n-butane, i-butane, n-butane.
Pentane, i-pentane, cyclopentane, pentene,
Hydrocarbons such as hexane, methylene chloride, dichlorodifluoromethane, trichloromonofluoromethane,
Monochlorodifluoromethane, 1,2-dichlorotetrafluoroethane, halogenated hydrocarbons such as trichlorotrifluoroethane, or carbon dioxide, inorganic gas-based blowing agents such as air and the like, and these blowing agents alone or Two or more kinds can be used as a mixture, and among them, isobutane is particularly preferred in that it shows high foaming properties.

The expandable polyolefin-based resin particles obtained by impregnating the polyolefin-based resin particles with a blowing agent can then be heated to form polyolefin-based resin expanded particles. The foamed particles are obtained, for example, by injecting the foamable resin particles with steam into the preliminary foaming device at a vapor pressure of about 0.5 to 3.0 kg / cm ² G.
The time for injecting water vapor is usually sufficient for 20 to 90 seconds.

The foamed polyolefin resin particles thus obtained are then left to stand at room temperature for about one day, or a volatile organic blowing agent having a normal pressure boiling point in the range of -50 to 100 ° C., a halogenated hydrocarbon. 2.0 to 10.0 kg of expanded particles together with a blowing agent or an inorganic gas-based blowing agent
After holding for about 4 hours in the state of f / cm ² G, it is subjected to foam molding.

In the foam molding, a steam having a vapor pressure of about 0.5 to 4.5 kgf / cm ² G, for example, is introduced into a mold having a desired shape and capable of closing the foam particles but not sealing the foam particles. This can be achieved by introducing the material into a mold. The obtained molded body is taken out of the mold after water cooling or air cooling. The molded article thus obtained has a uniform cell diameter, excellent flexibility, and high foaming.

[0023]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Example 1] (Method for producing expandable polyolefin-based resin particles) Expandable polyolefin-based resin particles were produced by the following method.

In an autoclave having an internal volume of 5 L, 3 L of water,
40 g of magnesium chloride as a suspending agent, 20 g of pyrophosphoric anhydride, and 0.75 g of sodium dodecylbenzenesulfonate as an activator were added to obtain an aqueous medium. Next, in the DSC curve obtained by the scanning differential calorimetry, the high-temperature side peak is 140 ° C. and the low-temperature side peak is 53 ° C., 30% by weight of a soft polyolefin resin (the ethylene component is 30 mol%, the propylene component is 70%). Mol%) and 70% by weight of polypropylene-based resin particles (an ethylene-propylene random copolymer having an ethylene content of 3% by weight) using a twin-screw extruder at an extrusion resin temperature of 220 ° C. 1000 g of pelletized polyolefin-based resin particles having a length of 3.0 mm and a diameter of 1.2 mm (high-temperature peak measured by DSC is 145 ° C., low-temperature peak is 54 ° C.)
Was suspended in the above aqueous medium and stirred at a stirring speed of 350 rpm. Thereafter, 300 g of isobutane was injected using nitrogen pressure. The mixture was heated to 115 ° C., kept at that temperature for 6 hours or more, cooled to 25 ° C., dehydrated and dried, and the product was taken out to obtain expandable polyolefin-based resin particles.

The obtained expandable polyolefin resin particles were prefoamed by a prefoaming machine. Preliminary foaming was performed by heating with steam having a vapor pressure of 2.0 kg / cm ² G to obtain foamed particles having an apparent foaming ratio of 33 times. After leaving the obtained foamed particles for 24 hours, the foamed particles were kept at room temperature under a nitrogen pressurized atmosphere at a pressure of 5.0 kg / cm ² G for 4 hours to impregnate the foamed particles with nitrogen. Next, length 400mm, width 300mm, height 50m
m is filled with foamed particles, and the vapor pressure is 2.5 kg / cm.
^When heated with ² G steam for 50 seconds, a molded product having an apparent molding magnification of 31 times and a closed cell ratio of 80% was obtained. In this molded product, each particle fuses very well,
It was a molded article having a smooth surface, and had very excellent softness. Table 1 shows the results.

In this example, the DSC curve was obtained by the following method. That is, the polyolefin resin particles 3
Up to 7 mg of scanning differential calorimeter (SEIKO DSC 200)
The high temperature side and low temperature side peaks of the resin were determined from a DSC curve obtained when the mixture was heated from 30 to 220 ° C. at a heating rate of 10 ° C./min. The apparent expansion ratio of the expanded particles was determined by the following formula using a method based on JIS K6767.

Apparent expansion ratio = V / W V: Bulk volume of expanded particles (cm ³ ) W: Mass of expanded particles (g) The closed cell ratio of the molded article was obtained by the following method. That is,
The true volume of the test piece with a known density (28 cm ³ ) was measured using a high-precision automatic volume meter VM100 (manufactured by S-Tech Co., Ltd.), and the closed cell rate was calculated based on the following equation.

Closed cell rate (%) = (ED / ρ) / (F
−D / ρ) × 100 where D: weight of test piece (g) E: true volume of test piece <measured value (cm ³ )> F: apparent volume of test piece <measured value (cm ³ )> ρ : Density of the resin used for the test piece (g / cm ³ )
A test sample having a length of 50 mm, a width of 50 mm and a height of 25 mm was cut out, and the following compressive strength and compressive modulus were determined.

(Compression strength) According to JIS K-6767
Obtained by the following method. That is, the test sample is 10 mm
/ Min speed and a response when 5% compression strain occurs.
Force (kgf / cm ^Two).

(Compression modulus) Obtained by a method based on JIS K-7220. That is, the test sample is 10 m
The compression was performed at a speed of m / min, and the maximum slope (dσ / dε) of the curve obtained in the range of the compression strain of 0 to 10% was measured and determined.

Dσ: difference in stress between two points on a straight line (kgf / cm ² ) dε: difference in strain between the same two points

Example 2 Ethylene Content and DSC
Was foamed and molded in the same manner as in Example 1 except that the heating steam pressure during molding was as shown in Table 1 using soft polyolefin-based resin particles having an endothermic peak as shown in Table 1. Table 1 shows the results.

Example 3 Using soft polyolefin resin particles whose DSC endothermic peaks are as shown in Table 1,
Foaming and molding were carried out in the same manner as in Example 1, except that the ratio of the polypropylene resin particles in the polyolefin resin particles and the heating steam pressure during molding were as shown in Table 1. Table 1 shows the results.

Example 4 The foaming and molding were carried out in the same manner as in Example 1 except that the ratio of the polypropylene resin particles in the polyolefin resin particles and the heating steam pressure during molding were as shown in Table 1. . Table 1 shows the results.

Example 5 Using soft polyolefin resin particles having an endothermic peak of DSC as shown in Table 1,
Foaming and molding were carried out in the same manner as in Example 1, except that the ratio of the polypropylene resin particles in the polyolefin resin particles and the heating steam pressure during molding were as shown in Table 1. Table 1 shows the results.

Example 6 Foaming and molding were carried out in the same manner as in Example 1 except that the ratio of the polypropylene resin particles in the polyolefin resin particles and the heating steam pressure during molding were as shown in Table 1. . Table 1 shows the results.

Comparative Example 1 Ethylene Content and DSC
Was foamed and molded in the same manner as in Example 1 except that the heating steam pressure during molding was as shown in Table 1 using soft polyolefin-based resin particles having an endothermic peak as shown in Table 1. Table 1 shows the results.

Comparative Example 2 Ethylene Content and DSC
Using the soft polyolefin-based resin particles whose endothermic peak is as shown in Table 1, foaming and molding were attempted in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the linear low-density polyethylene resin particles having an endothermic DSC peak as shown in Table 1 were used alone instead of the polyolefin resin particles of the present invention. I tried foaming and molding by the method. Table 1 shows the results.

[Comparative Example 4] Instead of the polyolefin-based resin particles of the present invention, a soft polyolefin-based resin particle having an endothermic peak of DSC as shown in Table 1 was used alone, and the heating steam pressure at the time of molding was determined as shown in Table 1. Except as described above, foaming and molding were performed in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 5 In place of the polyolefin resin particles of the present invention, a commercially available ethylene-propylene random copolymer having no ethylene content and two endothermic peaks of DSC as shown in Table 1 Foaming and molding were carried out in the same manner as in Example 1 except that the heating steam pressure during molding was as shown in Table 1 using the polyethylene resin particles of high density. Table 1 shows the results.

Comparative Example 6 In place of the polyolefin resin particles of the present invention, a commercially available ethylene-propylene random copolymer having no ethylene content and two endothermic DSC peaks as shown in Table 1 Using the high density polyethylene resin particles, foaming and molding were attempted in the same manner as in Example 1. Table 1 shows the results.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[Notes in Tables 1, 2 and 3] ○ Foaming factor is significantly higher than before reforming △ Foaming factor is higher than before reforming × Foaming factor as compared before reforming (1) Bubble diameter is not stable and softness is not stable (2) High pressure special molding machine is required

[0048]

The ethylene component is 20 to 60 mol%, the propylene component is 40 to 80 mol%, and there are two endothermic peaks in scanning differential calorimetry, and the high temperature side peak is 130 ° C. or more. And two endothermic peaks in a scanning differential calorimetry obtained by melt-kneading a soft polyolefin-based resin and a polypropylene-based resin, wherein the low-temperature side peak is 65 ° C. or lower, and the high-temperature side The peak is 130 ° C or higher and the low-temperature peak is 65
The foamable resin particles obtained by impregnating the polyolefin resin particles having a temperature of not more than 0 ° C. with a foaming agent are very suitable for high foaming, and for the foamability of the soft polyolefin resin or the polypropylene resin before melt-kneading. Significantly improved. In addition, a foamed molded article that is substantially non-crosslinked, has excellent recyclability and heat resistance, is low in density, has excellent flexibility, and has a uniform cell diameter can be obtained.

Claims (5)

[Claims] 1. An ethylene component is 20 to 60 mol%, a propylene component is 40 to 80 mol%, and two endothermic peaks are present in scanning differential calorimetry, and the high-temperature side peak is 130 ° C. or more, It is obtained by melt-kneading a soft polyolefin-based resin having a low-temperature peak of 65 ° C. or less and a polypropylene-based resin, and has two endothermic peaks in scanning differential calorimetry.
Foamable polyolefin-based resin particles comprising a polyolefin-based resin particle having a peak at a temperature of 30 ° C. or higher and a low-temperature-side peak of 65 ° C. or lower, containing a foaming agent. 2. The expandable polyolefin resin particles according to claim 1, wherein the mixing ratio of the polypropylene resin in the polyolefin resin particles is 30 to 95% by weight. 3. The foaming property according to claim 1, wherein the polypropylene resin is an ethylene-propylene random copolymer of 0.5 to 10% by weight of an ethylene component and 90 to 99.5% by weight of a propylene component. Polyolefin resin particles. 4. Expanded polyolefin resin particles obtained by prefoaming the expandable polyolefin resin particles according to claim 1. 5. A polyolefin resin foam molded article obtained by molding the polyolefin resin foam particles according to claim 4 in a mold.