JPS612741A - Manufacture of polypropylene resin expanded beads - Google Patents

Abstract

PURPOSE:To obtain the titled beads in high stability at high expansion ratio even with inorganic gaseous foaming agent, by low-pressure expansion of resin beads containing both crystal nucleating agent and foaming agent to reduce the amount of volatile organic foaming agent to be used. CONSTITUTION:The objective beads can be obtained by mixing (A) polypropylene resin beads (with a size 0.3-5mm.) containing 0.05-0.5wt% of crystal nucleating agent, (B) a foaming agent (volatile organic compound such as propane or butane, inorganic gas or mixture thereof) and (C) an aquesous medium followed by releasing the resultant mixture at a temperature higher than the softening point of said resin into a reduced pressure zone. Said nucleating agent should be dibenzylidene sorbitol. When an inorganic gas is used as foaming agent, the inner pressure of the expansion vessel should be retained between 15-100kg/cm<2>G.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing expanded polypropylene resin particles.

[Prior art]

Conventionally, polypropylene resin particles containing a volatile organic blowing agent are dispersed in an aqueous medium and heated to a temperature equal to or higher than the softening temperature of the resin while maintaining the pressure inside the container at the vapor pressure of the blowing agent or higher. A method of foaming by discharging into a low-pressure atmosphere from inside a pressurized container is known. 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 those that do not pose much of a problem in terms of danger are expensive and pose practical problems. In addition, it also caused environmental pollution problems, such as destroying the ozone layer when released into the atmosphere. Furthermore, since these volatile organic blowing agents swell the polymer particles, the suitable temperature range for foaming during foaming is narrow, and the influence of foaming temperature on the expansion ratio is large, making it difficult to control the expansion ratio. There was a problem.

〔the purpose〕

As a result of intensive research to solve these problems seen in the prior art, the present inventors have discovered that by containing 0.05% to 0.5% by weight of a crystal nucleating agent in a polypropylene resin, volatile organic It was discovered that the amount of blowing agent can be reduced, and the present invention was completed. Furthermore, in this case, it has been found that the foaming ratio can be improved even when an inorganic gas, which has not been considered as a foaming agent in the past, is used as a foaming agent.

〔composition〕

That is, according to the present invention, when obtaining expanded particles by discharging a mixture of polypropylene 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 polypropylene resin particles, characterized in that polypropylene resin particles containing 0.05% to 0.5% by weight of a crystal nucleating agent are used as the resin particles.

In the present invention, a resin particle fusion inhibitor can be used to prevent fusion of the polypropylene resin during heating. This resin particle anti-fusing agent can be used regardless of whether it is organic or inorganic, as long as it is substantially water-insoluble and does not melt when heated, but in general, it is preferable to use inorganic type. preferable. Typical anti-fusing agents include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and the like. Such anti-fusing agents usually have a grain size of 0.001-100 μm.
, preferably in the form of fine particles of 0.001-30)tm. The amount of this anti-fusing agent added is 10 resin particles.
It is usually in the range of 0.01 to 10 parts by weight relative to 0 parts by weight.

As the polypropylene resin in the present invention, any conventionally known crosslinked or non-crosslinked ones can be used,
Examples of the non-crosslinked polypropylene resin include propylene homopolymer, propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer, etc. However, in the case of the present invention, a propylene-ethylene random copolymer, particularly one having an ethylene content of I weight % or more and less than IO weight %, is preferably used from the viewpoint of foamability. Further, as the crosslinked polypropylene resin, one having substantially crosslinking, that is, one having a gel fraction of 0
1% or more, and includes propylene TL, homopolymers, and various copolymers thereof; specific examples include propylene/ethylene random copolymers, propylene M homopolymers, , propylene/ethylene block polymer, propylene/1-butene random copolymer, and the like. In the case of the invention, particular preference is given to using propylene/ethylene random copolymers.

The method for crosslinking polypropylene resin is to mix the polypropylene resin, aqueous medium, crosslinking agent, and divinylbenzene in a sealed container, impregnate the crosslinking agent and divinylbenzene into the resin particles, and then raise the temperature to the decomposition temperature of the crosslinking agent. This can be done by heating it. In this case, the crosslinking agent is 1,1-bis(butylperoxy)-3,3,5
-trimethylcyclohexane, dicumyl peroxide, di-butylcumyl peroxide, n-butyl-4,
4-bis(butylperoxy)valate, α, α′
-bis(butylperoxy)-m-diisopropylbenzene, 2,5-dimethyl-2,5-di(butylperoxy)hexane, and the like. Such a crosslinking agent is used in an amount of 0.05 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the resin particles. The amount of divinylbenzene used is usually about 0.05 to 5 parts by weight per 100 parts by weight of the resin particles.

The polypropylene resin particles used as a foaming raw material in the present invention can be obtained by molding a polypropylene resin into particles according to a conventionally known method, and in the case of the present invention, a crystal nucleating agent is added at that time. As the method for adding the crystal nucleating agent in this case, any method can be adopted as long as it is a method that allows the crystal nucleating agent to be contained in the resin particles, but generally, the resin and the crystal nucleating agent are melt-kneaded, Examples include a method of molding into particles, and a method of melt-kneading resin pellets containing a large amount of crystal nucleating agent in advance and resin pellets containing no crystal nucleating agent to form pellets into particles.

Generally, any solid substance having the function of accelerating the crystallization rate of the resin can be used as the crystal nucleating agent used in the present invention, but in particular, dibenzylidene sorbitol, p-j-butyl Preference is given to using aluminum benzoate. Dibenzylidene sorbitol exhibits an excellent effect as the crystal nucleating agent, and the foamed particles obtained have relatively large bubbles and have excellent foam moldability, and the foamed particles can be put into a mold to form a foam molded product of the desired shape. When molded, a foamed molded product with good dimensional accuracy can be obtained. The amount of the crystal nucleating agent used in the present invention is generally 0.05 to 0.5% by weight, preferably 0.1 to 0.0% by weight, based on the resin particles.
．． 3% by weight, and if the amount added is too small, the effect of the present invention will not be obtained.On the other hand, if it is added in a larger amount than the above range, the added effect will not be particularly improved, but rather the air bubbles of the resulting expanded particles will be reduced. This is not preferable because it becomes too fine.

The particle size of the crystal nucleating agent-containing resin particles used as a foaming raw material in the present invention is generally about 0.3 to 5 II1 m, preferably about 0.5 to 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 this case, volatile organic blowing agents include conventionally known ones such as propane, butane, pentane, dichlorodifluoromethane, trichlorofluoromethane, etc., and examples of inorganic gas blowing agents include nitrogen, air, Examples include various inorganic substances that are gaseous at room temperature, such as carbon dioxide, argon, and helium. In the blowing agent used in the present invention, the amount of the volatile organic blowing agent used is 2 to 25 parts by weight, preferably 3 to 20 parts by weight, based on 100 parts by weight of the resin. When using an inorganic gas as a blowing agent, the pressure inside the container is preferably higher, but generally 100 kg/
It is preferable to pressurize at a pressure of cJG or less from the viewpoint of particle deformation during foaming, and usually a pressure of 70 kg/alG or less is preferable. Moreover, the pressurization by this inorganic gas is at least 15 kg/a&G, preferably 20 kg/cJG or more. The time to pressurize with inorganic gas varies depending on the pressure, but at temperatures above the melting point of the resin, it takes several seconds to
It takes about 1 hour, and usually about 5 to 30 minutes is sufficient. This pressurization of the contents of the container with the inorganic gas can be performed at any time, and can be performed immediately after filling the contents of the container, while the temperature is rising, or when the foaming temperature is reached.

Note that the rate of temperature increase of the contents of the container due to heating is usually 1-
1°C/min, preferably 2-5°C) minutes.

To carry out the method of the present invention, the above-described crystal nucleating agent-containing polypropylene resin particles, an anti-fusing agent,
and an aqueous medium (usually water) and, after heating to the foaming temperature in the presence of a blowing agent, the contents of the container are discharged from its pressurized zone into a lower pressure zone (usually atmospheric pressure) containing the blowing agent. foam the resin particles. In this case, the foaming temperature is generally higher than the softening point of the resin. Note that the softening point of the resin referred to in this specification is determined under the condition of a load of 4.6 kg/cd in ASTM-D648.

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 expandable resin particles contained in the contents contain secondary crystals. The expandable resin particles in which the secondary crystals are present provide expanded particles with good moldability. When a non-crosslinked polypropylene resin is used as the raw material resin, it is particularly advantageous to have secondary crystals present in the expandable resin particles.

In addition, the presence of secondary crystals in the resin particles.

DS obtained by differential scanning calorimetry of resin foam particles
This can be determined using the C curve. In this case, the DSC curve obtained by differential scanning calorimetry of foamed resin particles is defined as 1 to 3 mg of foamed polypropylene resin particles measured at a heating rate of 10°C/min to 220°C using a differential scanning calorimeter.
For example, the first DSC curve is the DSC curve obtained when the sample is heated from room temperature to 220°C at a heating rate of 10°C/min. ℃ to 10℃ at a cooling rate of 7 minutes
The temperature was lowered to around ℃, and the temperature was increased again to 22℃ at a heating rate of 10"C/min.
The DSC curve obtained when the temperature was raised to 0°C was
The characteristic peak and the high temperature peak can be obtained from these DSC curves. Further, in this case, the characteristic peak is considered to be due to the so-called heat absorption during melting of the polypropylene resin constituting the expanded particles. This unique peak appears in both the first and second DSC curves, and the temperature at the top of the peak may differ slightly between the first and second times, but the difference is 5°C.
below, usually below 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 DSC curve. The presence of secondary crystals in the resin particles is determined by whether or not this high temperature peak appears in the DSC 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 DSC curve and the temperature of the high temperature peak appearing in the first DSC 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 DSC curve obtained by differential scanning calorimetry for expanded particles is shown in the drawing. FIG. 1 relates to expanded particles containing secondary crystals, and FIG. 2 relates to expanded particles containing no secondary crystals. In FIGS. 1 and 2, curves 1 and 2 show DSC curves obtained by measuring expanded particles as a sample (first measurement), and curves 1' and 2' show DSC curves obtained by measuring expanded particles as a sample (first measurement). A DSC 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 curve 1 showing the first measurement results, in addition to the characteristic peak B, there is a high temperature peak A. The presence of this high temperature peak A 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, indicating that the expanded particles contain secondary crystals. It is confirmed that there is no The reason why there are no secondary crystals in the foamed particles shown in Figure 2 is that the raw material unfoamed resin particles were not heat-treated for a sufficient period of time at a temperature that promotes secondary crystallization (melting point to below the melting end temperature), which is higher than the melting end temperature. This is due to the fact that it was foamed at a temperature of .

In addition, in the second measurement, no high-temperature peak appeared in the foamed particles shown in FIGS. 1 and 2, and the characteristic peaks B',
Only b' appears.

In the present invention, in order to obtain expandable resin particles containing secondary crystals, the resin particles are generally heated to about 20°C above their melting point in a pressure-resistant container without being heated above their melting point.
℃ lower temperature (melting point -20℃) or higher and lower than the melting end temperature for a sufficient time, usually 5 to 90 minutes, preferably 1
It may be held for about 5 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 of the characteristic peak, if the temperature is lower than the high temperature peak, foaming with good moldability can be achieved. particles can be obtained.

As mentioned above, the foaming temperature in the present invention is generally a temperature equal to or higher than the softening point of the resin, but the preferred foaming temperature also varies depending on the type of foaming agent. When used alone, the foaming temperature is about 10°C lower than the melting point of the resin, about 5°C higher than the resin melting point, preferably about 5°C lower than the resin melting point, about 5°C lower than the resin melting point. The temperature is not more than 3°C higher, and when an inorganic gas is used alone as a blowing agent, the temperature is not less than the melting point of the resin and not more than about 20°C higher than the melting point of the resin.
Preferably, the temperature is above the melting point of the resin and about 18°C higher than the melting point of the resin, and when a volatile organic blowing agent and an inorganic gas are used together, the temperature is about 5°C lower than the melting point of the resin and about 18°C higher than the melting point of the resin. °C higher, preferably at least about 3 °C below the melting point of the resin, and about 16 °C below the melting point of the resin.
C The temperature is below high.

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-mentioned structure, and by containing a small amount of crystal nucleating agent in the raw material polypropylene resin particles, it is possible not only to reduce the amount of the volatile organic blowing agent that has been conventionally used, but also to increase the expansion ratio. Fluctuations in the value are also reduced, and furthermore, good foamed particles can be obtained even when an inorganic gas, which was conventionally considered to be unsuitable as a foaming agent, is used as a foaming agent. The foamed particles obtained by the present invention can be used as a cushioning material by themselves, but it is usually preferable to use them as pre-expanded particles for foam molding. Give your body.

〔Example〕

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

Example 1 Ethylene/propylene random copolymer (ethylene component 2.8% by weight, non-crosslinked, melting point 145°C, melting end temperature 1
Dibenzylidene sorbitol as a crystal nucleating agent was kneaded into the mixture at a temperature of 55° C. in the amount shown in Table 1, extruded into a strand from a die of an extruder, and quenched in water to prepare resin pellets. 100 parts by weight of the resin pellets, 0.3 parts by weight of finely divided aluminum oxide, 300 parts by weight of water, and dichlorodifluoromethane as a blowing agent in the amounts shown in Table 1 were mixed into a closed container, and the contents were stirred. Raise the temperature while
The temperature was maintained at 40° C. for 30 minutes, and then the foaming temperature shown in Table 1 was maintained for 30 minutes. Next, the inside of the container was filled with nitrogen gas for 40k.
While maintaining g/c+JG, the contents were discharged into the atmosphere from one end of the container to foam the resin particles. Table 1 shows the bulk ratio of the obtained expanded particles to the raw material resin particles.

Table 1 11 Dibenzylidene sorbitol #2 Dichlorodifluoromethane 13 Example 2 showing a comparative example In Example 1, the amount of crystal nucleating agent added was specified at 0.2% by weight, and the amount of blowing agent added was varied. The experiment was conducted in the same manner except for the following. The results are shown as a graph in Figure 1. In FIG. 1, line 1 shows the results when the amount of crystal nucleating agent added is 0.2% by weight, and line 2 shows the results when no crystal nucleating agent was added. As is clear from the results shown in Figure 1, in the case of the present invention, the amount of blowing agent added necessary to obtain foam particles exhibiting the same bulk ratio is greater than that in the case of no addition of a crystal nucleating agent. It can be seen that a significantly reduced amount is sufficient.

Example 3 In Example 1, resin pellets containing 0.2% by weight of aluminum P-butylbenzoate as a crystal nucleating agent and dichlorofluorometa 2 as a blowing agent were used.
The experiment was conducted in the same manner except that 16 parts by weight was used. As a result, foamed particles with a bulk ratio of 48 times were obtained.

Example 4 100 parts by weight of propylene resin containing 0.2% by weight of the crystal nucleating agent shown in Experiment No. 2 of Example 1, 0.3 parts by weight of finely divided aluminum oxide, and 300 parts by weight of water were mixed in a closed container. Then, raise the temperature while stirring the contents.

After being held at 145°C for 30 minutes, the temperature was raised to 155°C, and in the next step (L), the mixture was pressurized with nitrogen gas at the pressure shown in Table 2 and held at this temperature for 30 minutes. Thereafter, the inside of the container was pressurized with nitrogen 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. The high magnification of the obtained expanded particles is shown in Table 2.

Table 2 A comparative example is shown (no crystal nucleating agent added).

Example 5 Ethylene/propylene random copolymer (ethylene component 3.5% by weight, gel fraction 40% by weight, melting point 142°C1
At a melting end temperature of 155° C., 0.2% by weight of dibenzylidene sorbitol was kneaded as a crystal nucleating agent and extruded into a strand from a die of an extruder to produce resin pellets. 100 parts by weight of the resin pellets, 0.3 parts by weight of finely divided aluminum oxide, 300 parts by weight of water, and 216 parts by weight of dichlorosif 0059 as a blowing agent were mixed into a closed container, and the contents were heated to 145°C while stirring. It was held for 30 minutes and then held at 150°C for 30 minutes. Next, while maintaining the inside of the container at 40 kg/cdG with nitrogen gas,
The contents were released into the atmosphere from one end of the container to foam the resin particles. In this case, the high magnification of the obtained expanded particles is 4
0 times, and the presence of secondary crystals was confirmed in the resin of the expanded particles.

[Brief explanation of drawings]

1 and 2 show DSC curves 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. FIG. 3 is a graph showing the relationship between the high magnification of expanded particles and the amount of foaming agent added. Figure 1 Figure 2 Temperature (C) Figure 3 Amount of blowing agent added to raw resin (parts by weight) Procedure
Amendment No. 7B of 1981 Commissioner of the Patent Office Manabu Shiga 1, Indication of the case Patent Application No. 122559 of 1988 2, Name of the invention Method for manufacturing expanded polypropylene resin particles 3, Person making the amendment Case Relationship with Patent Applicant Address: 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name: Masayo Uchiyama, Representative of Japan Styrene Paper Co., Ltd. 4, Agent: 151 Address: 1-58 Lo, Yoyogi, Shibuya-ku, Tokyo No.-
Nishiwaki Building 113 Name (7450) Patent Attorney Toshiaki Ikeura Telephone (370) 2533 5 Date of amendment order Proprietor 6 Number of inventions increased by amendment 07 Column for detailed explanation of the invention in the specification to be amended 8. Contents of amendment The following amendments will be made to the specification of this application. (1) Existence of [Example 5] from line 5 from the bottom of page 19 to line 12 of page 20 of the specification was confirmed. ” is corrected as follows. [Example 5 Ethylene/propylene random copolymer (ethylene component 3.5% by weight, melting point 142°C, melting end temperature 155°C)
Then, as a crystal nucleating agent, 0.0% dibenzylidene sorbitol was added.
2% by weight was kneaded and extruded into a strand from a die of an extruder to produce resin pellets. This resin pellet 1
00 parts by weight, 0.3 parts by weight of fine particulate aluminum oxide,
300 parts by weight of water, 0.5 parts by weight of dicumyl peroxide and 1.0 parts by weight of divinylbenzene were mixed into a closed container, the contents were heated while stirring, kept at 150°C for 1 hour, and then brought to room temperature. 216 parts by weight of dichlorone fluorometa as a blowing agent was added to a sealed container, and the contents were heated while stirring, held at 45°C for 30 minutes, and then held at 150°C for 30 minutes. Next, while maintaining the inside of the container at 40 kg/alG with nitrogen gas, the contents were released into the atmosphere from one end of the container to foam the resin particles. In this case, the high magnification of the obtained expanded particles is 40 times,
In addition, the presence of secondary crystals was confirmed in the resin of the expanded particles. The gel fraction of these particles was 40%. ” Procedural amendment Written on July 10, 1985 Michibe Uga, Commissioner of the Patent Office1, Indication of the case Patent Application No. 122559 of 19812, Name of the invention Process for manufacturing expanded polypropylene resin particles 3, Amendment Patent applicant Address: 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name: Japan Styrene Paper Co., Ltd. Representative: Masayo Uchiyama 4, Agent: 151 Address: 1 Yoyogi, Shibuya-ku, Tokyo 58-10-5,
Date of amendment order: 6. Number of inventions increased by amendment: 07. Subject of amendment: 88. Contents of amendment: The following amendments will be made to the specification of the present application. (1) Page 16 , line 12 "foaming temperature shown in Table 1"
Correct it to "Temperature of 145℃".

Claims (5)

[Claims] (1) When obtaining foamed particles by releasing a mixture of polypropylene 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, as the polypropylene resin particles, 0.05% by weight of crystal nucleating agent
A method for producing expanded polypropylene resin particles, characterized in that polypropylene resin particles containing ~0.5% by weight are used. (2) The method according to claim 1, wherein the crystal nucleating agent is dibenzylidene sorbitol. (3) The method according to claim 1 or 2, wherein the blowing agent is a volatile organic blowing agent. (4) The method according to claim 1 or 2, wherein the blowing agent is an inorganic gas. (5) The method according to claim 1 or 2, wherein the blowing agent is a mixture of a volatile organic blowing agent and an inorganic gas.