JPH0386737A - Production of foamed polyolefin resin particle - Google Patents

Abstract

PURPOSE:To produce foamed polyolefin resin particles with a large cell diameter and a high expansion ratio even when an inorg. gas is used as the blowing agent by ejecting a mixture of specific polyolefin resin particles contg. a blowing agent with an aq. medium into a low-pressure region at a temp. higher than the m.p. of the polyolefin resin. CONSTITUTION:A mixture of polyolefin resin (e.g. ethylene-propylene random copolymer) particles contg. a blowing agent pref. comprising an inorg. gas (e.g. air) and 0.5-5wt.% wax (e.g. PE wax) with an aq. medium are ejected into a low-pressure region at a temp. higher than the m.p. of the resin particles to convert them into foamed particles.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing expanded polyolefin resin particles.

[Prior Art] Conventionally, polypropylene resin particles containing a volatile organic blowing agent are dispersed in an aqueous medium, and the pressure inside the container is maintained at the vapor pressure of the blowing agent or higher, while the temperature rises above the softening temperature of the resin. A method is known in which foaming is caused by heating the material to a temperature of 100% and then releasing it into a low-pressure atmosphere from inside a pressurized container. In this case, known volatile organic blowing agents include, for example, propane, butane, pentane, trichlorofluoromethane, dichlorodifluoromethane, and the like. However, such volatile organic blowing agents can be dangerous due to their toxicity and flammability depending on the blowing agent, and even if they are not a big problem in terms of danger, they are expensive and pose practical problems. Furthermore, when released into the atmosphere, there were problems of environmental pollution such as destruction of the ozone layer. Furthermore, since these volatile organic blowing agents swell the polymer particles, the appropriate temperature range for foaming during one foaming is narrow, and the influence on the foaming ratio at one foaming temperature is large, making it difficult to control the foaming ratio. There was a problem.

[Problem that the invention attempts to solve]

Therefore, one of the present inventors proposed the following as a method to reduce the amount of volatile organic blowing agents and to enable the use of inorganic gases, which had not been considered as blowing agents in the past.
We have previously proposed a method for producing foamed polypropylene resin particles using polypropylene resin particles containing 0.05 to 2 by weight of an inorganic substance (Japanese Unexamined Patent Publication No. 61-4738). ), although this method allows the amount of volatile organic blowing agents to be reduced and allows the use of inorganic gases as blowing agents.

When an inorganic gas is used as a foaming agent, there is a problem that the cell diameter becomes fine, and even if a high expansion ratio is obtained through multistage foaming, the moldability may be poor or the physical properties may be poor. Ta.

Therefore, an object of the present invention is to not only reduce the amount of volatile organic blowing agent, but also to achieve high-magnification foaming with a large cell diameter and excellent moldability, physical properties, etc. even when inorganic gas is used as a blowing agent. An object of the present invention is to provide a method for producing expanded polyolefin resin particles.

[Means to solve the problem]

As a result of intensive research to solve the problems seen in the prior art, the present inventors discovered that the above object can be achieved by incorporating a small amount of wax into the raw material polyolefin resin particles. Reached.

That is, according to the present invention, in a method for obtaining expanded particles by discharging a mixture of polyolefin resin particles containing a blowing agent and an aqueous medium into a low pressure region at a temperature equal to or higher than the softening point of the resin particles, There is provided a method for producing expanded polyolefin resin particles, characterized in that polyolefin resin particles containing 0.5% to 5% by weight of waxes are used as the polyolefin resin particles.

In the present invention, a resin particle anti-fusing agent can be used to prevent the polyolefin resin from fusing during heating. This resin particle anti-fusing agent can be of any organic or inorganic type as long as it is substantially water-insoluble and does not melt when heated, but inorganic types are generally used. Examples of typical anti-fusing agents include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, tricalcium phosphate, etc. . Such an anti-fusing agent usually has a particle size of 0.001 to 100 μm, preferably 0.001 to 3 μm.
It is used in the form of fine particles of 0 μm. The amount of this anti-fusing agent added is based on 100 parts by weight of the resin particles.

Usually, it is in the range of 0.01 to 10 parts by weight.

As the polyolefin resin in the present invention.

Non-crosslinked ones are preferred. Non-crosslinked polyolefin resins include propylene homopolymers, propylene/ethylene random copolymers, propylene/ethylene block copolymers, propylene/butene random copolymers, and propylene/ethylene/butene random copolymers. Examples of ethylene copolymers include high-density polyethylene, ethylene and a small amount of 04,
c,,c.

The combination of the present invention includes linear low-density polyethylene which is a copolymer with α-olefin such as.

In particular, propylene/ethylene random copolymers with an ethylene component of I to 10% by weight, propylene/butene random copolymers with a butene component of 5 to 10% by weight, and ethylene components of 1 to 5% by weight and a butene component A propylene/ethylene/butene random copolymer having a weight of 0.5 to 3 $ is preferably used from the viewpoint of moldability.

The polyolefin resin particles used as a foaming raw material in the present invention can be obtained by molding a polyolefin resin into particles according to a conventionally known method, but in the case of the present invention, waxes are added as an auxiliary agent. . In this case, any method can be used to add the waxes as long as the waxes can be contained in the resin particles, but in general, the resin and the waxes are melt-kneaded,
Examples include a method of molding into particles, and a method of melting and mixing resin pellets containing a large amount of wax and resin pellets containing no wax to form pellets into particles.

The waxes used in the present invention include polyethylene wax, polypropylene wax, paraffin wax,
Examples include microwaxes and mixtures thereof, and among these, polyethylene waxes and polypropylene waxes with molecular weights of to, ooo or less are particularly preferred.The amount of waxes added is generally 0.5% to the resin particles.
-5 weight meters, preferably 1 to 4 weight 2. If the amount added is less than 0.5% by weight, the effects of the present invention cannot be obtained,
On the other hand, if the amount exceeds 5% by weight, the effect of addition will not be particularly improved, and the foamed particles obtained will instead become too soft, which is not preferable.

The particle size of the wax-containing resin particles used as the foaming raw material in the present invention is generally 0.3 to 5 cm, preferably 0.
．． It is about 5-3+mm.

As the blowing agent in the present invention, a volatile organic blowing agent and an inorganic gas blowing agent are used, and both blowing agents can also be used in combination. In the present invention, a great effect is achieved when an inorganic gas blowing agent is used.

As the volatile organic blowing agent, conventionally known ones, for example,
Propane, butane, pentane, dichlorodifluoromethane, trichlorofluoromethane, 1,2-dichloro-1
, 1,2,2-tetrafluoroethane, 1゜l-dichloro-2,2,2-trifluoroethane, 1,2,2.2
-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane, chlorodifluoromethane, etc., and examples of the inorganic gas blowing agent include nitrogen, Examples include various room temperature gaseous inorganic substances such as air, carbon dioxide, argon, and helium. The amount of the volatile organic blowing agent used in the present invention is 0.5 to 10 parts by weight per 100 parts by weight of the resin. ,
Preferably the proportion is 1 to 5 parts by weight.

Furthermore, when using an inorganic gas as a foaming agent, the pressure inside the container is preferably as high as possible; however, in general, it is preferable to pressurize at a pressure of 100 kg/cdG or less in order to prevent deformation of particles during foaming. Pressurization of 70 kg/dG or less is preferable, and pressurization with this inorganic gas is at least 10 kg/c
jG, preferably 20 kg/cdG or more.

The time for pressurizing with an inorganic gas varies depending on the pressure applied, but at temperatures above the melting point of the resin, it is about several seconds to about 1 hour, and usually about 5 to 30 minutes is sufficient. Pressurizing the contents of the container with this inorganic gas can be performed at any time, and can be performed immediately after filling the contents of the container, during heating, or when the foaming temperature is reached6.
The rate of temperature increase of the contents of the container by heating is usually 1 to 10°C.
minutes, preferably 2 to b, in a pressure vessel to carry out the method of the invention.

The wax-containing polyolefin resin particles described above, an anti-fusing agent, and an aqueous medium (usually water) are blended.

After heating to the foaming temperature in the presence of the blowing agent, the container contents are discharged from the pressurized zone to a lower pressure zone (usually at atmospheric pressure) to foam the resin particles containing the blowing agent. In this case, the foaming temperature is generally higher than the softening point of the resin. In addition, the softening point of the resin referred to in this specification is AST
In M-0648.

This was determined under the condition of a load of 4.6 kg/d.

In the present invention, when the contents of the container are discharged from the high pressure zone to the low pressure zone, it is preferable that the foamable resin particles contained in the contents contain secondary crystals. The expandable resin particles provide expanded particles with good moldability. When a non-crosslinked polypropylene resin or a non-crosslinked polyethylene resin is used as the raw material resin, it is particularly advantageous to have secondary crystals present in the expandable resin particles.

The presence of secondary crystals in the resin particles can be determined based on the 030 curve obtained by differential scanning calorimetry of the expanded resin particles. In this case, the 030 curve obtained by differential scanning calorimetry of 411J foamed resin particles refers to the 030 curve obtained by measuring polyolefin resin foamed particles 1 to 311Ig with a differential scanning calorimeter at a heating rate of 10°C/min.
5 For example, the entire DSCSC line is the 030 curve obtained when the sample is heated from room temperature to 220°C at a heating rate of 10°C for 7 minutes, and then from 220°C. The second 030 curve is the 030 curve obtained when the temperature is lowered to around 40 °C at a cooling rate of 10 °C/min, and the temperature is raised again to 220 °C at a temperature increase rate of 10 °C/min, and from these 030 curves. Unique peaks and high temperature peaks can be determined. Further, in this case, the characteristic peak is considered to be due to the so-called endotherm during melting of the polyolefin resin constituting the expanded particles. This characteristic peak appears in both the first 030 curve and the second 030 curve, and the temperature at the top of the peak may be slightly different between the first and second runs, but the difference is usually less than 5°C. is less than 2°C.

On the other hand, the high temperature peak is an endothermic peak that appears on the higher temperature side than the above-mentioned characteristic peak in the first 030 curve. The presence of secondary crystals in the resin particles is determined by whether or not this high temperature peak appears in the 030 curve, and if no substantial high temperature peak appears, it is assumed that there are no secondary crystals in the resin. It will be judged. In the case of the present invention, it is desirable that the difference between the temperature of the characteristic peak appearing in the second 030 curve and the temperature of the high temperature peak appearing in the first 030 curve is large; The difference between the temperature at the peak and the temperature at the peak of the high temperature peak is 5°C or more, preferably 10°C or more.

Next, the 030 curve obtained by differential scanning calorimetry for one expanded particle is shown in the drawings. Figure 1 is for expanded particles containing secondary crystals, and Figure 2 is for expanded particles containing no secondary crystals. It is related to. In FIGS. 1 and 2, curves 1 and 2 indicate 030 curves obtained by measuring expanded particles as a sample (first measurement), and curves 1' and 2' indicate the 030 curves obtained by measuring expanded particles as a sample (first measurement). The 030 curve obtained by measuring the sample again after the first measurement (second measurement) is shown. As can be seen by comparing Figures 1 and 2, in the case of expanded particles containing secondary crystals, in addition to the characteristic peak B, there is a high temperature peak A in the curve 11A1 indicating the first measurement result. The presence of this high temperature peak confirms the presence of secondary crystals in the expanded particles. On the other hand, in the case of expanded particles that do not contain secondary crystals, in curve 2 showing the first measurement results,
Only the characteristic peak b appears, and no high-temperature peak appears, confirming that the 1-expanded particles do not contain secondary crystals. The reason why there are no secondary crystals in the foamed particles shown in Figure 2 is that the raw material unfoamed particles were not heat-treated for a sufficient period of time at a secondary crystallization promoting temperature (melting point to below the melting end temperature), and This is due to foaming due to temperature. In the second measurement, no high-temperature peak appears in the expanded particles shown in FIGS. 1 and 2, and only the characteristic peak B'b' appears.

In the present invention, in order to obtain expandable resin particles containing secondary crystals, in the case of non-crosslinked polypropylene, the melting point of the resin particles is generally kept in a pressure container without being heated above the melting end temperature. Temperature approximately 20℃ lower than
It is sufficient to maintain the temperature at a temperature not lower than the melting point (-20° C.) and lower than the melting end temperature for a sufficient time, usually about 5 to 90 minutes, preferably about 15 to 60 minutes.

In addition, when foaming the expandable resin particles that have been secondary crystallized in this way, even if the foaming temperature is higher than the melting end temperature, as long as the temperature is lower than the high temperature peak, foamed particles with good moldability can be obtained. be able to.

In the case of non-crosslinked linear low-density polyethylene, the resin particles are generally kept at a temperature approximately 15°C lower than the melting point (melting point -15°C) without raising the temperature above the melting point in the pressure container. Sufficient time to maintain the temperature below the melting end temperature 1 Usually 5 to 90 minutes, preferably 5 to 30 minutes
It may be held for about a minute. Moreover, when foaming the expandable resin particles that have been secondary crystallized in this way, expanded particles with good moldability can be obtained.

As mentioned above, the foaming temperature in the present invention is a temperature higher than the softening point of the resin in the shell, but the preferred foaming temperature varies depending on the type of blowing agent, and the type of raw polyolefin resin. It also varies somewhat depending on the

In the case of non-crosslinked polypropylene, when an inorganic gas is used alone as a blowing agent, the melting point of the resin is -5°C or higher,
Melting point of resin +15°C or less, preferably melting point of resin -3°C
Above, the melting point of the resin is +10°C or lower, and when a volatile organic blowing agent and an inorganic gas are used together, the melting point of the resin is -5°C or higher,
Melting point of resin +18℃ or less, preferably melting point of resin -3℃
The melting point of the resin is +16°C or lower.

Also, in the case of polyethylene resin.

When a volatile organic blowing agent and an inorganic gas are used together as a blowing agent, the foaming temperature is higher than the melting point of the resin -15°C, higher than the melting point of the resin +8°C, preferably higher than the melting point of the resin -12°C,
The melting point of the resin is +5°C or lower. In addition, when using an inorganic gas alone as a blowing agent, the melting point of the resin is -10°C or higher,
The melting point of the resin is preferably +5°C or lower.

In addition, the melting point of the resin as used in this specification refers to the temperature of approximately 6 mg of a sample raised to 220 °C at a rate of 10 °C/min using the DSC method, then lowered to approximately 50 °C at a rate of 10 °C/min, and then heated again to 220 °C at a rate of 10 °C/min. 2
This is the peak temperature of the endothermic curve obtained when the temperature is raised to 20° C., and the melting end temperature of the resin means the end temperature of the second endothermic curve.

〔effect〕

The method of the present invention has the above configuration, and by containing a small amount of wax in the raw material polyolefin resin particles,
Even if an inorganic gas, which was conventionally considered to be inappropriate as a blowing agent, is used as a blowing agent, good foamed particles with large cell diameters can be obtained. Therefore, from the expanded particles obtained according to the present invention, a good molded article can be obtained without applying internal pressure such as pressure treatment as in the conventional method.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 5 and Comparative Examples - 2 Ethylene/propylene random copolymer (ethylene fraction 2.5% by weight, thermal crosslinking, melting point 146°C, melting end temperature 1
The waxes shown in Table 1 were kneaded at 60° C. in the proportions shown in Table 1, extruded into a strand from a die of an extruder, and quenched in water to create a resin pellet. 100 parts by weight of this resin pellet and 0 particulate aluminum oxide
．． 3 parts by weight and 300 parts by weight of water were mixed in a sealed container, the contents were heated while stirring, held at 150°C for 15 minutes, then heated to 155°C, and then heated with the inorganic gas shown in Table 1. Pressure was applied and held at this temperature for 15 minutes. Thereafter, the inside of the container was pressurized with an inorganic gas, and while the pressure was kept constant, the contents were released into atmospheric pressure from one end of the container to foam the resin particles. Table 2 shows the bulk ratio, cell diameter, and heat of fusion of the obtained expanded particles with respect to the raw material resin particles.

Next, the foamed particles thus obtained were filled into a mold for molding, and molding was performed at a steam pressure of 3.2 kg/aJG. The molded product thus obtained was inspected to evaluate the moldability of the expanded particles. Table 2 shows the properties of the expanded particles.

Table 1 Table 2 (A) (B) Dimensional accuracy ○... Shrinkage rate in the plane direction less than 3% Δ... Shrinkage rate in the plane direction 3 to less than 41 ×... Shrinkage rate in the plane direction 4% Weldability O...Material failure is 60% or moreΔ...Material failure is 40 to less than 60'1×...Material failure is less than 40$

[Brief explanation of drawings]

1 and 2 show DSCdM lines obtained by differential scanning calorimetry of expanded particles. FIG. 1 shows DSC curves for expanded particles with secondary crystals, and FIG. 2 shows DSC curves for expanded particles without secondary crystals.

Claims (3)

[Claims] (1) In a method for obtaining foamed particles by discharging a mixture of polyolefin resin particles containing a blowing agent and an aqueous medium into a low pressure region at a temperature equal to or higher than the softening point of the resin particles, the polyolefin resin particles are A method for producing foamed polyolefin resin particles, which comprises using polyolefin resin particles containing 0.5% to 5% by weight of waxes. (2) The method according to claim (1), wherein the blowing agent is an inorganic gas. (3) The method according to claim 1, wherein the blowing agent is a mixture of a volatile organic blowing agent and an inorganic gas. (4) The method according to any one of claims (1) to (3), wherein the wax is polyethylene wax, polypropylene wax, or a mixture thereof.