JP2826769B2 - Method for producing expanded polymer particles - Google Patents

Description

The present invention relates to a method for producing expanded polymer particles.

[Problems to be solved by conventional technology and invention]

Conventionally, polymer particles containing a volatile foaming agent are dispersed in a dispersion medium such as water in a closed vessel, and the temperature in the vessel is maintained at a pressure equal to or higher than the softening temperature of the polymer particles while maintaining the pressure in the vessel at or above the vapor pressure of the foaming agent. It is known that the polymer particles are foamed by releasing the polymer particles and a dispersion medium under an atmosphere at a lower pressure than the inside of the container by opening one end of the container and then opening one end of the container.
As the volatile foaming agent used in this method, for example, hydrocarbons such as propane, butane, and pentane, and halogenated hydrocarbons such as trichlorofluoromethane and dichlorodifluoromethane are used. However,
The compounds used as these volatile foaming agents have dangers such as toxicity and flammability, have the problem of depletion of the ozone layer like fluorocarbons, or have the danger or destruction of the environment. At present, many of them have problems such as being expensive and impractical even if they do not have much problems. In addition, volatile foaming agents narrow the appropriate temperature range for foaming during foaming in order to swell the polymer particles.Therefore, the influence of the foaming temperature on the foaming ratio becomes large, and it is difficult to control the foaming ratio. there were.

Many studies have been made to solve such a problem, and as a result of intensive studies to solve such a problem, the present applicant has made use of an inorganic gas-based foaming agent which has never been considered as a conventional foaming agent. Methods for obtaining polymer foamed particles have been previously proposed (for example, Japanese Patent Publication No. 62-12727, Japanese Patent Application Laid-Open No. 61-2741, and Japanese Patent Application Laid-Open No. 61-4738). However, when using an inorganic gas-based blowing agent,
The impregnating property of the foaming agent into the polymer particles is poor, and the secondary crystallization of the polymer particles is difficult to promote, so that it is difficult to foam at a high temperature, and thus it is difficult to obtain a foam having a high expansion ratio. there were.

The present inventors have conducted intensive studies in order to solve the above problems, and as a result, even when polymer foamed particles are produced on an industrial scale using an inorganic gas-based foaming agent, polymer foamed particles having a high expansion ratio are obtained. When a conventional volatile foaming agent is used, the amount of the foaming agent used can be reduced, and the amount of the foaming agent used is smaller and more stable than the method described in JP-A-61-4738. The present inventors have found that expanded particles having a high expansion ratio can be obtained, and have completed the present invention.

[Means for solving the problem]

That is, the present invention relates to (1) dispersing foamable polymer particles made of either a propylene polymer, a high-density polyethylene or a linear low-density polyethylene impregnated with an inorganic gas blowing agent in a closed container. At a temperature equal to or higher than the softening temperature of the expandable polymer particles dispersed in a medium, the expandable polymer particles and the dispersion medium are released under a lower pressure atmosphere than in the container to expand the expandable polymer particles. A method for producing expanded polymer particles, wherein the expandable polymer particles contain a water-soluble inorganic substance, and (2) the water-soluble inorganic substance is borax. (1) The method for producing polymer foamed particles according to the above (1).

As the polymer particles used in the present invention, propylene homopolymer, propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer, propylene-ethylene-
Propylene-based polymers such as butene random copolymers, or high-density polyethylenes, and linear low-density polyethylenes which are copolymers of ethylene and a small amount of α-olefins (eg, having 4, 6, 8 carbon atoms, etc.). Examples include an ethylene-based copolymer. Of these, propylene-based polymers such as propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer, and linear low density polyethylene are particularly preferred. These polymers may be crosslinked,
Non-crosslinked ones are particularly preferred.

In the present invention, a polymer particle containing a water-soluble inorganic substance is used. In the present invention, the water-soluble inorganic substance has a solubility of 1 g or more in 100 g of water at 40 ° C., and particularly preferably 5 g or more. Examples of the water-soluble inorganic substance include borax, nickel sulfate, manganese sulfate, sodium chloride, magnesium chloride, calcium chloride and the like, and among them, borax is preferred. These inorganic substances can be used alone or in combination of two or more, and are usually added when granulating polymer particles. Minerals are usually
It is added as a powder, but the particle size is not particularly limited. However, in general, the particle size is between 0.1 and 150 μm, in particular between 1 and 10 μm.
It is preferable to use one having a thickness of 0 μm. These inorganic substances have a content in the polymer particles of 0.01 to 2% by weight,
It is preferable to add so that it may be １1% by weight. If the inorganic material is contained in a large excess, the obtained expanded particles are likely to shrink, which is not preferable from the viewpoint of foam moldability. On the other hand, if the amount of the inorganic substance is too small, the effect of the present invention cannot be obtained. As the polymer particles containing the inorganic substance, those having a particle size of generally 0.3 to 5 mm, particularly preferably 0.5 to 3 mm are preferable.

In the present invention, the step of impregnating the polymer particles with a foaming agent may be before or after the step of dispersing the polymer particles in a dispersion medium in a closed container, but is usually performed simultaneously in the step of dispersing the polymer particles. Do. In this case, the foaming agent is once dissolved or dispersed in the dispersion medium and then impregnated into the polymer particles, and the foaming agent is heated and pressurized while stirring the polymer particles, the foaming agent and the dispersion medium in a closed container. The polymer particles can be impregnated by such a method.

In the method of the present invention, an inorganic gas-based blowing agent such as nitrogen, carbon dioxide, argon, or air is used as the blowing agent, and nitrogen and air are particularly preferable. When using these inorganic gas-based foaming agents, it is preferable to supply them so that the pressure in the container is 50 kg / cm ² · G or less.

The dispersion medium for dispersing the polymer particles may be any one that does not dissolve the polymer particles.Examples of such a dispersion medium include water, ethylene glycol, glycerin, methanol, ethanol, and the like. Water is used.

When the expandable polymer particles are dispersed in a dispersion medium and heated to a foaming temperature, an anti-fusing agent can be used to prevent fusion of the polymer particles. As the anti-fusing agent, any inorganic or organic one can be used as long as it does not dissolve in a dispersion medium such as water and does not melt by heating. In general, an inorganic one is preferable. Examples of the inorganic anti-fusing agent include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, tricalcium phosphate, magnesium pyrophosphate, and the like. Is preferably added in combination. Anionic surfactants such as sodium dodecylbenzenesulfonate and sodium oleate are suitable as emulsifiers. The anti-fusing agent preferably has a particle size of 0.01 to 100 μm, particularly preferably 0.001 to 30 μm. Usually, the addition amount of the anti-fusing agent is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the polymer particles. The emulsifier is usually preferably added in an amount of 0.001 to 5 parts by weight per 100 parts by weight of the polymer particles.

In the method of the present invention, secondary crystals are preferably present in the expandable polymer particles. The expanded particles obtained from the expandable polymer particles having the secondary crystals have excellent moldability. In particular, when the polymer particles are a non-crosslinked polypropylene resin or a non-crosslinked linear low-density polyethylene resin, it is advantageous that secondary crystals are present in the expandable polymerizable particles. The presence of the secondary crystals is indicated by a DSC curve obtained by differential scanning calorimetry of the obtained expanded particles,
The determination can be made based on whether or not a high-temperature peak appears on a higher temperature side than an intrinsic peak due to the so-called endotherm at the time of melting of the polymer. The characteristic peak and the high-temperature peak can be determined by performing differential scanning calorimetry twice for the same sample. In this method, first, 1-3mg of sample (polymer)
Was measured at a rate of 10 ° C./min to 220 ° C. by a differential scanning calorimeter to obtain a first DSC curve, and then the temperature was lowered from 220 ° C. to about 40 ° C. at a rate of 10 ° C./min. 220 ℃ in minutes
The temperature was measured until the second DSC curve was obtained. By comparing the two DSC curves thus obtained, the characteristic peak and the high-temperature peak can be determined. Since the intrinsic peak is an endothermic peak associated with the so-called melting of the polymer, it is a peak that appears in both the first DSC curve and the second DSC curve. The difference may be slightly different from the second time, but the difference is less than 5 ° C, usually 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 intrinsic peak in the first DSC curve. The presence of a secondary crystal is confirmed by the appearance of this high-temperature peak, and when no substantial high-temperature peak appears, it is determined that no secondary crystal exists. 2 above
It is desirable that the difference between the temperature of the peak of the unique peak appearing in the second DSC curve and the temperature of the peak of the high temperature peak appearing in the first DSC curve in one DSC curve is large, and the temperature difference between the two is 5 ° C. Above, particularly preferably 10 ° C. or higher.

1 and 2 show DSC curves obtained by differential scanning calorimetry of the expanded particles. FIG. 1 shows the expanded particles containing secondary crystals, and FIG. 2 shows the expanded particles not containing secondary crystals. belongs to. In FIGS. 1 and 2, curves 1 and 2 are DSC curves obtained by the first measurement, and curves 1 'and 2' show DSC curves obtained by the second measurement. As shown in FIG. 1, in the expanded particles containing the secondary crystals, in the curve 1 obtained by the first measurement, in addition to the characteristic peak B, the curve 1 ′ obtained by the second measurement A high temperature peak A that does not exist is present (only the characteristic peak B 'appears in the curve 1' obtained in the second measurement), and the presence of the high temperature peak A confirms the presence of a secondary crystal. You. On the other hand, in the expanded particles containing no secondary crystal, only the characteristic peaks b and b 'appear in both of the curves 2 and 2' as shown in FIG. It is confirmed that no crystals exist. As shown in FIG. 2, particles in which the presence of secondary crystals is not recognized, such as the expanded particles shown in FIG. 2, are obtained only for a sufficient time at the secondary crystallization accelerating temperature (melting point to melting end temperature).
This is the case where foaming is performed at a temperature higher than the melting end temperature without heat treatment. When an inorganic gas-based foaming agent is used, foamed particles having secondary crystals as shown by curve 1 can be produced, for example, by the following method. In the case of a non-crosslinked polypropylene-based resin, generally, without raising the temperature of the polymer particles above the melting end temperature in a pressure vessel, the melting point is about -20 ° C or more, and a sufficient time at a temperature lower than the melting end temperature, usually. It can be obtained by holding for 5 to 90 minutes, preferably for 15 to 60 minutes. Further, in the case of particles formed to form secondary crystals while maintaining such a temperature, the foaming temperature (temperature at the time of release) at which the polymer particles are released under a lower pressure atmosphere than the inside of the container and foamed.
Even if the temperature is equal to or higher than the melting end temperature, expanded particles having good moldability can be obtained as long as the temperature is equal to or lower than the high temperature peak. In the case of non-crosslinked linear low-density polyethylene, generally, the resin particles are not heated above the melting end temperature in a pressure vessel, and a melting point of about -15 ° C. or more and a temperature lower than the melting end temperature for a sufficient time. , Usually 5 to 90 minutes, preferably 5 minutes
Hold for ~ 30 minutes. It should be noted that the above-mentioned temperature maintenance is desirably performed a plurality of times in order to facilitate temperature management. In this case, a method of raising the holding temperature after the holding temperature is adopted. It is desirable that the final holding temperature be the foaming temperature.

In the method of the present invention, the foaming temperature at which the foamable polymer particles and the dispersion medium are released under a low-pressure atmosphere from the container to cause foaming is a temperature equal to or higher than the softening temperature of the polymer particles,
Particularly, a temperature near the melting point is preferable. The preferred foaming temperature range varies depending on the type of the resin. For example, in the case of a non-crosslinked polypropylene resin, the melting point is −5 ° C. or higher, and the melting point is + 15 ° C. or lower.
In particular, the melting point is preferably -3 ° C or higher and the melting point + 10 ° C or lower. In the case of polyethylene resin, the melting point is preferably -10 ° C or higher and + 5 ° C or lower. Further, the heating rate at the time of heating to the foaming temperature is preferably 1 to 10 ° C / min, particularly preferably 2 to 5 ° C / min. The atmospheric pressure when the expandable polymer particles and the dispersion medium are released from the inside of the container may be lower than that in the container, but is usually at atmospheric pressure.

Incidentally, in the present invention, the melting point of the above-mentioned polymer was measured by means of a differential scanning calorimeter by measuring about 6 mg of a sample at a rate of 10 ° C./min.
℃, then cooled to about 50 ℃ at a rate of 10 ℃ / min, and then heated to 220 ℃ again at a rate of 10 ℃ / min peak of the endothermic peak (inherent peak) in the DSC curve obtained Temperature. The melting end temperature means the melting end temperature at the endothermic peak (intrinsic peak) of the second DSC curve obtained by the above measurement. Further, the softening temperature of the polymer particles means a softening temperature determined under a load of 4.6 kg / cm ^{2 by} the ASTM-D-648 method.

〔Example〕

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

Examples 1 to 5 Non-crosslinked ethylene-propylene random copolymer (ethylene component 2.3% by weight, melting point 146.5 ° C, melting end temperature 165
° C) per 100 parts by weight of the water-soluble inorganic material shown in Table 1 was added in the amount shown in the table, melt-kneaded in the extruder, extruded into a strand from the die at the tip of the extruder, quenched in water, and cut. And granulated into pellets (length 2.4 mm, cross-sectional diameter 1.1 mm). A mixture of 100 kg of these pellets, 400 g of finely divided aluminum oxide and 220 g of water,
The temperature was raised to and maintained at the single-stage temperature shown in the table without raising the temperature to a temperature higher than the melting temperature while stirring in). Next, the temperature was raised to the two-stage holding temperature shown in the table, and immediately thereafter, the blowing agent shown in Table 1 was supplied so that the internal pressure of the container became the pressure shown in the table, and was maintained at the same temperature. One end of the container was opened while holding the inside of the container at the pressure shown in Table 1 by applying a back pressure with nitrogen gas or air (matched to the foaming agent used) while maintaining the step holding temperature. The particles and water were released under atmospheric pressure and allowed to foam. The average bulk expansion ratio and the maximum value and the minimum value of the bulk expansion ratio of the obtained expanded particles are shown in Table 1.

Comparative Examples 1 and 2 The same ethylene-propylene random copolymer as in Example 1 was used, except that the water-insoluble inorganic substance shown in Table 1 was added and granulated, and the conditions of Examples 1 to 2 were used. Bubbling was carried out according to 5. The average bulk expansion ratio and the maximum value and the minimum value of the bulk expansion ratio of the obtained expanded particles are shown in Table 1.

Examples 6 to 7 The polymer particles in Examples 1 to 5 were replaced with propylene-butene random copolymer particles (butene component 6% by weight, melting point 15
0 ° C., melting end temperature 163 ° C. (Example 6) and linear low density polyethylene particles (butene component 4.1% by weight, melting point 121 ° C.,
Expanded particles were produced according to Examples 1 to 5, except that the melting end temperature was 135 ° C) (Example 7).

However, in Example 7, the foaming agent was supplied after holding at a constant temperature without performing the two-stage holding. This holding temperature is shown in the column of the first-stage holding temperature in Table 1 for convenience. Table 1 shows the average bulk expansion ratio and the maximum and minimum values of the bulk expansion ratio of the obtained expanded particles.

Comparative Examples 3 and 4 Foaming was performed according to Examples 6 and 7, except that CaCO ₃ was used as an inorganic substance in Examples 6 and 7. The average bulk ratio and the maximum value and the minimum value of the bulk ratio of the obtained expanded particles are also shown in Table 1.

Examples 8 to 9 Uncrosslinked ethylene-propylene random copolymer (ethylene component 2.3% by weight, melting point 146.5 ° C, melting end temperature 165)
° C) per 100 parts by weight of the water-soluble inorganic material shown in Table 1 was added in the amount shown in the table, melt-kneaded in the extruder, extruded into a strand from the die at the tip of the extruder, quenched in water, and cut. And granulated into pellets (length 2.4 mm, cross-sectional diameter 1.1 mm). 100 kg of these pellets, 1.5 kg of finely divided tricalcium phosphate, 4 sodium dodecylbenzenesulfonate
7.5 g (Example 8) or 7.0 kg (Example 9) of 0 g, water 220, and solid carbon dioxide (dry ice) as a foaming agent
Was stirred and stirred in a closed vessel (volume 400) without raising the temperature to a temperature higher than the melting temperature, and maintaining the temperature at the one-stage holding temperature shown in the same table. Next, the temperature was raised to the two-stage holding temperature shown in the same table, and immediately thereafter, a blowing agent (carbon dioxide) shown in the first table was supplied so that the internal pressure of the container became the pressure shown in the same table (however, in Example 9). Was supplied with no foaming agent.) After that, the container was kept at the same temperature, and then back-pressured with carbon dioxide while maintaining the two-stage holding temperature, and the inside of the container was kept at the pressure shown in Table 1 while keeping the inside of the container at the pressure shown in Table 1. One end was opened, and the polymer particles and water were released under atmospheric pressure to cause foaming. The average bulk expansion ratio and the maximum value and the minimum value of the bulk expansion ratio of the obtained expanded particles are shown in Table 1.

[Effects of the Invention] As described above, the method of the present invention is based on a propylene-based polymer impregnated with an inorganic gas-based blowing agent, or an expandable polymer particle composed of any of high-density polyethylene or linear low-density polyethylene. Is dispersed in a dispersion medium in a closed container, and at a temperature equal to or higher than the softening temperature of the expandable polymer particles, the expandable polymer particles and the dispersion medium are released under an atmosphere at a lower pressure than in the container, and foaming is performed. A method for producing a polymer foamed particle for foaming a conductive polymer particle, wherein the foamable polymer particle employs a structure containing a water-soluble inorganic substance, so that an inorganic gas-based foaming agent is used without using a volatile foaming agent. Even when is used, foaming can be performed at a high temperature, and foamed particles having a high expansion ratio can be easily obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a DSC curve of expanded particles having secondary crystals in the particles, and FIG. 2 is a graph showing a DSC curve of expanded particles having no secondary crystals in the particles. It is.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-208333 (JP, A) JP-A-61-138645 (JP, A) JP-A-64-65141 (JP, A) JP-A-59-208 111823 (JP, A) JP-B-45-41101 (JP, B1) (58) Field surveyed (Int. Cl. ⁶ , DB name) C08J 9/16-9/22

Claims (2)

(57) [Claims] 1. An expandable polymer particle comprising a propylene polymer, a high-density polyethylene or a linear low-density polyethylene impregnated with an inorganic gas-based blowing agent is dispersed in a dispersion medium in a closed container. At least at a temperature equal to or higher than the softening temperature of the expandable polymer particles, the expandable polymer particles release the expandable polymer particles and the dispersing medium under a lower pressure atmosphere than in the container to expand the expandable polymer particles. A method for producing particles, wherein the expandable polymer particles contain a water-soluble inorganic substance. 2. The method according to claim 1, wherein the water-soluble inorganic substance is borax.