JPS60245650A - Preparation of foamed particle of noncrosslinked polypropylene resin - Google Patents

Abstract

PURPOSE:To obtain the titled foamed particles having good moldability, by applying pressure with an inorganic gas to particles of a noncrosslinked polypropylene resin in a liquid dispersion medium, and releasing them from the pressurized zone, in a specified temperature range, into a lower-pressure zone. CONSTITUTION:Particles of a noncrosslinked polypropylene resin are dispersed in a liquid dispersion medium, and pressure is applied to this dispersion with an inorganic gas. Then, the particles of the secondarily crystallized, noncrosslinked polypropylene resin containing the inorganic gas, together with the liquid dispersion medium, are released, in the temperature range in which the secondary crystals will exist, from the pressurized zone into a lower-pressure zone, causing to foam. The examples of the noncrosslinked polypropylene resins to be used are a propylene-ethylene random copolymer and propylene-butene random copolymer, preferably a propylene-ethylene random copolymer containing 1-10wt% ethylene. As the inorganic gas, preferably a nitrogen-containing gas such as nitrogen or air is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing expanded non-crosslinked polypropylene resin particles.

Conventionally, polymer particles containing a volatile organic blowing agent are dispersed in water in a closed container, and the pressure inside the container is maintained at the vapor pressure of the blowing agent or higher, while the temperature is increased to a temperature higher than the softening temperature of the polymer. There is a known method in which foaming is carried out 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, generally known volatile organic blowing agents include propane, butane, pentane, trichlorofluoromethane, dichlorodifluoromethane, and the like. However, the use of such volatile organic blowing agents may result in
It is dangerous because it is toxic and flammable, and even if it is not a big problem in terms of danger, it is expensive and has practical problems, and furthermore, it causes environmental pollution such as depleting the ozone layer. It also had the following problems. Furthermore, since these volatile organic blowing agents swell the polymer particles, the suitable temperature range for foaming during foaming is narrow, and the foaming temperature has a large effect on the foaming ratio, making it difficult to control the foaming ratio. There was a problem.

Furthermore, when a non-crosslinked polypropylene resin is foamed using a volatile organic foaming agent, there is a problem in the moldability of the resulting expanded particles. In other words, in some cases, molded products made of expanded particles have low density, low water absorption, and excellent dimensional stability with a low shrinkage rate, but on the other hand, only molded products with a high shrinkage rate can be obtained. However, there is a problem in that it is difficult to obtain a stable and good molded product.

As a result of intensive research to solve these problems, the present inventors have discovered that by using an inorganic gas as a blowing agent, which has not been considered as a blowing agent for non-foamed polymer particles, it is possible to The suitable temperature range for foaming has been expanded, making it possible to perform pre-foaming operations easily and stably.
It has various advantages that could not be achieved with conventional methods, such as obtaining foamed particles with a high double closed cell ratio and excellent moldability, increasing process safety and preventing environmental pollution problems. It was found that the effect was achieved. Furthermore, it has been found that the influence on moldability when using pre-expanded particles obtained from non-crosslinked polypropylene resin is related to secondary crystallization of the resin.

The present invention was completed based on these findings.

That is, according to the present invention, when foaming non-crosslinked polypropylene resin, the following steps are performed: (i) dispersing non-crosslinked polypropylene resin particles in a liquid dispersion medium; 1i) adding non-crosslinked polypropylene resin particles with an inorganic gas; Pressuring step, 1ii) Foaming the non-crosslinked polypropylene resin particles containing an inorganic gas and having undergone secondary crystallization together with a liquid dispersion medium in a temperature range where secondary crystals exist and from the pressurizing zone to the low pressure zone. Provided is a method for producing expanded non-crosslinked polypropylene resin particles, comprising the steps of:

As the non-crosslinked polypropylene resin in the present invention,
Examples include propylene homopolymer, propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer, etc., but in the case of the present invention, especially The particle size of the polypropylene resin particles is generally 0.3 m+ to 5+ nm, preferably 0.3 m+ to 5+ nm. It is about 0.5 mm to 3 mm.

Note that the melting point of the resin as used in the present invention refers to the melting point of a resin at a rate of 10°C/min of approximately 6 mg at 220°C using the DSC method.
The temperature was raised to 50°C at a rate of 10°C/min.
This is the peak temperature of the endothermic curve obtained when the temperature is raised again to 220°C. Further, the melting end temperature of the resin refers to the temperature at which the endothermic curve obtained for the second time returns to the baseline.

In the present invention, an anti-fusing agent is used to prevent the polypropylene resin from fusing during heating.

This anti-fusing agent may be organic or inorganic as long as it is substantially water-insoluble and does not melt when heated, but it is generally preferable to use an inorganic anti-fusing agent. Typical anti-fusing agents include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and the like. Such an anti-fusing agent usually has a particle size of 0.001 to 100 μm, preferably 0.001 to 30 μm.
Used for micron particles. The amount of the anti-fusing agent is usually 0.01 to 10 parts by weight per 100 parts by weight of the resin particles.
Parts by weight range.

To carry out the method of the present invention, the above-described polypropylene resin, anti-fusing agent, and aqueous medium are mixed in a pressurized container, and the contents (compound) of the container are pressurized with an inorganic gas. Perform heating.

In this case, the inorganic gas may include various gases such as nitrogen gas, air, carbon dioxide, argon, and nitrogen oxide. preferable. Pressurizing the contents of the container with this inorganic gas can be performed at any time, such as immediately after blending the polypropylene resin, anti-fusing agent, and aqueous medium, or during heating.
Alternatively, it can be carried out when the foaming temperature is reached. Further, the rate of temperature increase of the contents of the container by heating in the present invention is usually 1 to b.

In the present invention, when the contents of the container are discharged from the pressurized zone to the low pressure zone and foamed, the pressurized contents must be maintained in a temperature range where secondary crystals exist in the resin contained therein. be. Generally, secondary crystals exist in a temperature range above the melting point of the resin and below the melting end temperature, and when foaming is carried out in this temperature range, foamed particles with good moldability can be obtained. When foaming is carried out in a temperature range equal to or higher than the melting end temperature of the resin, if the secondary crystals disappear and become amorphous, expanded particles with good moldability cannot be obtained. Therefore, when foaming is carried out in a temperature range above the melting end temperature of the resin, in order to avoid such disappearance of secondary crystals, the contents of the container should be sufficiently maintained at a temperature below the melting end temperature of the resin, and the secondary crystals After sufficiently causing crystallization, the temperature is raised to the foaming temperature and foaming is performed. By such a foaming method, even if the foaming temperature of the resin contained in the contents of the container is higher than the melting end temperature, secondary crystals are present and foamed particles with good moldability can be obtained.

The presence of secondary crystals in the resin can be determined based on the 050 curve obtained by differential scanning calorimetry of expanded resin particles. In this case, the 050 curve obtained by differential scanning calorimetry of foamed resin particles refers to the 050 curve obtained when 1 to 3+ ng of expanded polypropylene resin particles are heated to 220°C at a heating rate of 10°C/min using a differential scanning calorimeter. For example, the first 050 curve is the 050 curve obtained when the sample is heated from room temperature to 220°C at a rate of 10°C/min, and then the temperature is increased from 220°C to 10°C/min. The second 050 curve is the 050 curve obtained when the temperature is lowered to around 40°C at a cooling rate of You can hit the peak. Further, in this case, the characteristic peak is an endothermic peak unique to the polypropylene resin constituting the expanded particles, and is thought to be due to the so-called endotherm of the polypropylene resin during melting. This characteristic peak appears in both the first 050 curve and the second 050 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 2℃
less than

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 050 curve. The presence of secondary crystals in the resin is determined by whether or not this high temperature peak appears on the 050 curve. If no substantial high temperature peak appears, it is determined that there are no secondary crystals in the resin. be done.

In the case of the present invention, it is desirable that the difference between the temperature of the characteristic peak appearing in the second Dsc curve and the temperature of the high temperature peak appearing in the first 050 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.

In the present invention, a blend of a non-crosslinked polypropylene resin, an aqueous medium, and an anti-fusing agent is converted into a foamable composition by the above-mentioned pressurization and heating.

The foamable formulation is then discharged into a low pressure zone (usually at or below atmospheric pressure) lower than in the pressurized container to provide expanded particles of non-crosslinked polypropylene resin. In the case of the present invention, the inorganic gas used as the pressurizing medium acts as the blowing agent. That is, this inorganic gas is impregnated into the resin particles during the pressurization and heating steps. The amount of impregnation increases as the pressure increases, but it is generally preferable to pressurize at a pressure of 100kg/c+#G or less in order to prevent deformation of particles during foaming, and usually 70kg/c+#G or less.
g/cn? It is carried out under pressure of G or less. Moreover, the pressurization by this inorganic gas is at least 15 kg/cnYG.
, preferably 20 kg/cnfG or more. The pressurizing time varies depending on the pressure applied, but at temperatures above the melting point of the resin, it is about several seconds to an hour, and usually 5 to 30 hours.
This is achieved by holding for a minute.

As explained above, in the present invention, by using an inorganic gas as a blowing agent, the suitable temperature range for foaming is expanded, foaming can be easily controlled, and since inorganic gas is cheap and safe, it is easy to handle. , and economically advantageous. The foamed particles obtained by the present invention can be used by themselves as a cushioning material, etc. 1 Usually, it is preferable to use them as pre-expanded particles for foam molding. Give a molded body.

Next, the present invention will be explained in detail with reference to Examples and Comparative Examples. In the autoclave of Example 5Q, 100 g of propylene resin particles shown in Table 1, 3000 g of water, and 3 g of fine powder aluminum oxide as an anti-fusing agent were added. The mixture was mixed and heated to the first holding temperature shown in Table 1 while stirring, and held for 30 minutes. Thereafter, the temperature was raised, and the pressure was applied with an inorganic gas at the foaming temperature and maintained for 30 minutes. After that, one end of the container was opened to perform foaming. Table 1 shows the expansion ratio of the expanded particles obtained at that time.

Then 1,5 kg/c+# for each foamed particle
G particle internal pressure is maintained with air, 300mm x 30
Filled into a 0mm x 50mm mold, 3.5kg/c
Molding was performed at a steam pressure of t#G.

Evaluations of the obtained molded bodies are shown in Table 1. In addition, E/P shown in Table 1 indicates ethylene-propylene random copolymer, the number in parentheses after that indicates ethylene content (wt%), and B/P indicates 1-butene-propylene random copolymer. The copolymer is indicated, and the number in parentheses thereafter indicates the butene content (% by weight).

Comparative Example The same formulation as in Example was heated without stirring to the maximum temperature in the container shown in Table 1, and then pressurized with an inorganic gas at the foaming temperature and held for 30 minutes. After that, one end of the container was opened to perform foaming. Table 1 shows the expansion ratio of the expanded particles obtained at that time. Next, the expanded particles were molded in the same manner as in the example. The evaluation of the molded object in this case is
Shown in the table.

The DSC curve obtained by differential scanning calorimetry for soft, expanded particles is shown in the drawing. FIG. 1 shows expanded particles obtained according to the present invention (Example 1), and FIG. 2 shows expanded particles of a comparative example (Comparative Example I). In FIG. 1 and FIG. 2, curve ] and curve 2 are
The DSC curves obtained by measuring expanded particles as a sample (first measurement) are shown, and curves 1' and 2
' indicates a DSC curve obtained by measuring the sample again after the first measurement (second measurement). 1st
As can be seen by comparing the figure and FIG. 2, in the case of the foamed particles of the present invention, in the water production curve 1 as a result of the first measurement,
In addition to the characteristic peak B, a high temperature peak A appears, and the presence of this high temperature peak A confirms that secondary crystals are present in the expanded particles. On the other hand, in the case of the foamed particles of the comparative example,
In curve 2 showing the first measurement results, only the characteristic peak b appears and no high temperature peak appears, confirming that the expanded particles do not contain secondary crystals. The reason why there are no secondary crystals in the foamed particles of the comparative example is that the raw material unfoamed particles were not sufficiently heat-treated at the secondary crystallization promoting temperature (melting point to less than the melting end temperature) and were heated to a temperature above the melting end temperature. This is due to foaming. In the second measurement, no high-temperature peak appears in the foamed particles of the present invention and the comparative example, and only characteristic peaks B' and b' appear.

From the above, it can be seen that foamed particles with good moldability can be obtained by releasing the secondary crystallized thermally crosslinked volepropylene resin from the high pressure zone to the low pressure zone and foaming the expanded particles.

[Brief explanation of drawings]

The figure shows O obtained by differential scanning calorimetry of expanded particles.
The SC curve is shown. FIG. 1 shows DSC curves for the product of the present invention and FIG. 2 shows the DSC curves for the comparative product. Patent applicant Nippon Styrene Paper Co., Ltd. Agent Patent attorney Toshiaki Ikeura

Claims (7)

[Claims] (1) When foaming the non-crosslinked polypropylene resin particles, 1) a step of dispersing the non-crosslinked polypropylene resin particles in a liquid dispersion medium, (ii) a step of pressurizing the non-crosslinked polypropylene resin particles with an inorganic gas, (iii) Consists of a step of foaming non-crosslinked polypropylene resin particles containing an inorganic gas and having undergone secondary crystallization together with a liquid dispersion medium in a temperature range where secondary crystals exist and from a pressurized zone to a low pressure zone. A method for producing expanded non-crosslinked polypropylene resin particles, characterized in that: (2) The method according to claim 1, wherein the non-crosslinked polypropylene resin particles are a random copolymer containing 50% by weight or more of a propylene component. (3) Non-crosslinked polypropylene resin particles are propylene-
The method according to claim 1 or 2, which is an ethylene random copolymer. (4) Non-crosslinked polypropylene resin particles are propylene-
The method according to claim 1 or 2, wherein the method is a butene random copolymer. (5) The method according to any one of claims 1 to 4, wherein the inorganic gas is air. (6) The method according to any one of claims 1 to 4, wherein the inorganic gas is nitrogen. (7) The method according to any one of claims 1 to 6, wherein the temperature of the pressurizing zone during foaming is equal to or higher than the melting point of the resin particles.