JPH0364543B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing pre-expanded non-crosslinked polypropylene random copolymer resin particles, and more particularly to a method for producing pre-expanded non-crosslinked polypropylene random copolymer resin particles having good moldability. Conventionally, foamed polystyrene and foamed polyethylene have been mainly used for various purposes such as cushioning materials and packaging materials. Along with these foams, polypropylene resin foam moldings have been used, and the applicant has already filed an application for a method for obtaining pre-expanded particles for use in a polypropylene resin bead molding method (Japanese Patent Publication No. 56-1344). issue). This method is revolutionary in that it is possible to easily obtain relatively highly foamed pre-expanded particles from polypropylene resin particles, which have been considered extremely difficult to foam. This method has some problems and still leaves room for improvement. In other words, (1) Although relatively high foaming can be obtained, 25
The limit is about twice as much, and even if you try to obtain a product with a magnification higher than this, the closed cell ratio will decrease and it will not be possible to use it for molding. (2) The air bubbles in the resulting pre-expanded particles tend to be fine, and even when trying to obtain a molded product using such pre-expanded particles, it is difficult to obtain a foam with good dimensional accuracy and firmness (high flexibility). The body is hard to come by. As a method to solve these drawbacks of the prior art, the present applicant has developed a method for heating and foaming pre-expanded particles in which the true expansion ratio E and the number of bubbles n per 1 mm ² of the pre-expanded particles are both within a specific range. proposed a method of obtaining pre-expanded particles with a larger expansion ratio than the original expansion ratio E, and filed an application earlier.
No. 57-172590, patent application No. 58-7743). Although the pre-expanded particles obtained by these manufacturing methods can solve the above-mentioned conventional drawbacks, even if the expansion ratio and the number of cells are the same as the initial pre-expanded particles and they are heated and foamed under the same conditions, the final There is a problem that the expansion ratio of the obtained pre-expanded particles is not the same (the expansion ratio varies greatly between lots),
There is still room for improvement. As a result of intensive research in view of the above points, the present inventors have found that the factor that determines the variation in expansion ratio between lots of obtained pre-expanded particles is the difference in the crystal structure of the initial pre-expanded particles. This discovery led to the completion of the present invention. That is, the present invention has a relationship of 2 < E ^1/3 × n ^1/2 < 60, where E is the true expansion ratio and n is the number of bubbles per 1 mm ² of cross section, and the differential of the pre-expanded particles is DSC curve obtained by scanning calorimetry (however, 1 to 3 mg of pre-expanded particles were measured by differential scanning calorimeter at 10
A non-crosslinked polypropylene random copolymer resin with a crystal structure in which a high-temperature peak appears on the higher temperature side than the characteristic peak unique to the base resin in the DSC curve obtained when the temperature is raised to 220 °C at a heating rate of °C/min. A foaming ability is imparted to the pre-expanded particles, and then the pre-expanded particles are heated and foamed to achieve the original expansion ratio E.
The gist of the present invention is a method for producing pre-expanded non-crosslinked polypropylene random copolymer resin particles, which is characterized by obtaining pre-expanded particles having a larger expansion ratio. As the material for the pre-expanded particles used in the present invention, for example, non-crosslinked propylene random copolymers such as non-crosslinked ethylene-propylene random copolymers and butene-propylene random copolymers are used. Among them, ethylene-propylene random copolymer is preferred, especially ethylene component 0.5~
10wt% is preferred. The non-crosslinked polypropylene random copolymer resin pre-expanded particles to be subjected to foaming in the present invention have the following formula 2<E ^1/ where the true expansion ratio is E and the number of cells per 1 mm ² of cross section is n. These are pre-expanded particles that satisfy ³ ×n ^1/2 <60. If E ^1/3 ×n ^1/2 is less than 2, the bubbles in the pre-expanded particles obtained by heating and foaming will become too coarse, making it difficult to obtain a foamed molded product with good physical properties. If E ^1/3 × n ^1/2 is 60 or more (in such a case, the expansion ratio E is extremely high, the number of bubbles n is extremely large, or both), Even if you try to foam these pre-expanded particles by heating, they tend to shrink, resulting in extremely poor foaming efficiency, and if you try to foam them forcibly, it will lead to a decrease in the closed cell ratio. Even if foam molding is performed using pre-expanded particles, the resulting foam molded product has poor dimensional accuracy and does not have satisfactory physical properties. The true expansion ratio E is determined as the reciprocal of the value obtained by dividing the density of the pre-expanded particles by the resin density of the base resin. Here, the density of the pre-expanded particles can be measured, for example, as follows. First, a predetermined amount of pre-expanded particles with a known weight is placed in a predetermined amount of water previously placed in a graduated cylinder, and the total volume is then measured. The volume of the pre-expanded particles is then determined by subtracting the original water volume from the total volume, and can be determined by dividing the weight by the volume. Also, the cross section is 1mm ²
The number of bubbles n can be determined by observing the cut surface of the pre-expanded particles using a microscope. The pre-expanded non-crosslinked polypropylene random copolymer resin particles subjected to foaming in the present invention are:
It has the above relationship 2 < E ^1/3 × n ^1/2 < 60 and has a crystal structure in which a high temperature peak appears on the higher temperature side than the characteristic peak specific to the base resin in the DSC curve obtained by differential scanning calorimetry. . Pre-expanded particles in which the above-mentioned high-temperature peak does not appear on the DSC curve tend to shrink even when heated and foamed, resulting in poor foaming efficiency and large variations in expansion ratio between lots. Further, even if pre-expanded particles produced from such pre-expanded particles are used for molding, it is not possible to obtain a molded article with low shrinkage rate and excellent dimensional stability. In the present invention, a DSC curve obtained by differential scanning calorimetry of non-crosslinked polypropylene random copolymer resin pre-expanded particles refers to a DSC curve obtained by differential scanning calorimetry of non-crosslinked polypropylene random copolymer resin pre-expanded particles. DSC obtained when the temperature is raised to 220°C at a heating rate of 10°C/min using a meter
It is a curve. The above characteristic peak and high temperature peak can be distinguished as follows. That is, 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, and then the sample is heated from room temperature to 220°C at a cooling rate of 10°C/min. ℃
The temperature is lowered to around 220℃, and then the temperature is increased again at a heating rate of 10℃/min.
The DSC curve obtained when the temperature is raised to ℃ is the second DSC curve. Next, the first DSC curve and the second DSC curve are compared. The characteristic peak is usually found both in the first DSC curve and in the second one.
The temperature at the top of the peak, which also appears in the DSC curve, may differ slightly between the first and second runs, but the difference is less than 5°C and 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 characteristic peak in the first DSC curve. It is thought that the above-mentioned high-temperature peak is due to the presence of a crystal structure different from the structure that appears as the above-mentioned characteristic peak, and although the high-temperature peak appears in the first DSC curve, the temperature was raised under the same conditions. It does not appear in the second DSC curve. Therefore, the structure that appears as a high-temperature peak indicates that the initial pre-expanded particles used in the present invention also have a crystal structure that is different from the crystal structure that exhibits the characteristic peaks inherent to polypropylene resins. By foaming a non-crosslinked polypropylene random copolymer resin under certain conditions, pre-expanded particles having a crystal structure in which a high temperature peak appears on the DSC curve can be obtained. 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, and the temperature at the peak of the characteristic peak of the second DSC curve and the high temperature are preferably large. The difference from the peak temperature is 5°C or more, preferably 10°C or more. In the present invention, the magnitude of the melting energy at the high temperature peak is not particularly limited, but it is particularly preferable that the melting energy is 1.0 cal/g or more. The melting energy is as follows: Melting energy (cal/g) = Area of high temperature peak on the chart (cm ² ) × (heat amount per 1 cm ² of chart (j/cm ² ) × 0.239 (cal/j) ÷ (measured sample weight ( g)) The above used in the present invention, 2<E ^1/3 ×n ^1/2 <60
Pre-expanded non-crosslinked polypropylene random copolymer resin particles having a crystal structure having the following relationship and a high temperature peak appearing in the DSC curve are produced as follows. That is, in a closed container, non-crosslinked polypropylene random copolymer resin particles, 100 to 400 parts by weight of water per 100 parts by weight of the resin particles, and 3 to 30 parts by weight of a volatile blowing agent (for example, dichlorodifluoromethane) are placed.
parts by weight, and 0.1 to 3 parts by weight of a dispersant (for example, finely divided aluminum oxide), and without raising the temperature above the melting end temperature Tm, Tm-25℃ to Tm-5℃.
(Tm is the melting end temperature of the non-crosslinked polypropylene random copolymer resin, and in the present invention, 6 to 8 mg of the sample is heated to 220°C at a heating rate of 10°C/min using a differential scanning calorimeter. Next, the temperature was lowered to around 40°C at a cooling rate of 10°C/min, and then the temperature was raised again to 220°C at a heating rate of 10°C/min. The temperature at which the tail of the peak returned to the baseline position on the high-temperature side was defined as the melting end temperature.) After raising the temperature to a temperature of It can be obtained by foaming the resin particles. As mentioned above, by setting the foaming temperature within the above-mentioned constant temperature range without increasing the temperature above the melting end temperature Tm during foaming, 2<E ^1/3 ×n ^1/2
It is possible to obtain expanded particles having a relationship of <60 and having a structure in which a high temperature peak appears in the DSC curve. If the foaming temperature is outside the above range, or even if it is within the above range, the melting end temperature Tm
If the temperature is increased above, the relationship of 2 < E ^1/3 × n ^1/2 < 60 is not satisfied, or the resulting foamed particles are
Only the characteristic peak appears in the DSC curve, and the high temperature peak does not appear. In the present invention, foaming ability is imparted to the pre-expanded particles. Foaming ability is imparted to pre-expanded particles by inorganic gas,
This is done by containing a volatile blowing agent or a mixed gas of an inorganic gas and a volatile blowing agent, and it usually depends on the degree of the desired expansion ratio.
An internal pressure of 1.5 to 10 Kg/cm ² (abs.) is applied. Examples of inorganic gases include air, nitrogen, argon,
Examples include helium, but air is usually used. Examples of volatile blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, and hexane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; and trichlorofluoromethane and dichlorodichloromethane. Halogenated hydrocarbons such as fluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc. are used. Next, the above-mentioned pre-expanded particles imparted with foaming ability are heated and foamed. As a heating method, heating with steam is generally performed, but heating with hot air may also be performed. The heating temperature varies depending on the desired expansion ratio, but usually, when heating with steam, 0.8 to 1.5 kg/cm ² (G) of steam is supplied, and when heating with hot air, is heated by supplying hot air of 100℃ or higher. Further, the heating time is preferably within 1 minute in the case of steam, and within 8 minutes in the case of hot air. In the present invention, the heat-foaming is not limited to a single operation, but may be repeated by further heating and foaming the pre-expanded particles that have been heat-foamed. Such an operation ensures that the non-crosslinked polypropylene random copolymer resin pre-expanded particles to be subjected to heat foaming satisfy the relationship 2<E ^1/3 × n ^1/2 <60 and that a high temperature peak appears on the DSC curve. It may be repeated any number of times as long as it has a crystal structure. The pre-expanded particles obtained by the present invention usually have an expansion ratio of 1.15 times or more, for example 3 to 100 times, preferably 10 to 60 times, the true expansion ratio E of the original pre-expanded particles, and 0.1 It has a bubble count of ~300/ ^mm2 . The pre-expanded particles obtained by the present invention are used for producing foam molded articles. First, the pre-expanded particles are aged at room temperature and pressure for a predetermined time, and then pressure aged at a predetermined pressure for a predetermined time using an inorganic gas such as nitrogen or air, or a mixed gas of an inorganic gas and a volatile blowing agent. . Next, the pre-expanded particles to which internal pressure has been applied by ^the above-mentioned pressure aging are filled into a mold having, for example, small holes on the mold surface through which a heating medium such as steam can pass. By heating and foaming, it is possible to obtain a foam molded product according to the pattern. The above-mentioned foam molded product can be used, for example, as a packaging material, a cushioning material,
Heat insulation materials, insulation materials, construction materials, vehicle parts, flotation materials,
It can be used for food containers, etc. The present invention will be explained in more detail below with reference to Examples and Comparative Examples. Examples 1 to 17 and Comparative Examples 1 to 16 3000 g of water and non-crosslinked ethylene-propylene random copolymer resin particles (Tm = 153°C) in a closed container
1000g, ultrafine aluminum oxide (dispersant) 3
g and the volatile blowing agent shown in Table 1 were mixed and heated while stirring and keeping the temperature inside the container below the maximum temperature shown in the same table. Next, after maintaining the foaming temperature shown in 1 and 2 of Table 1 for 30 minutes, one end of the container was opened while the pressure inside the container was maintained at 30 kg/cm ² (G) with nitrogen gas, and the resin particles and Water and water were simultaneously discharged to atmospheric pressure to foam the resin particles to obtain foamed particles. The true expansion ratio and number of cells of the obtained foamed particles were measured, and the results are shown in Table 2, 1 and 2, under the heading of pre-expanded particles subjected to heat foaming. Of the pre-expanded particles subjected to heat foaming, Example 12 is from Example 9, Example 13 is from Example 7, Example 16 is from Example 5, Example 17 is from Example 6, and Comparative Example. Comparative Example 11 used the two-stage expanded particles of Comparative Example 7, Comparative Example 12 used the two-stage expanded particles of Comparative Example 8, Comparative Example 15 used the two-stage expanded particles of Comparative Example 5, and Comparative Example 16 used the two-stage expanded particles of Comparative Example 6. The number of bubbles was adjusted by adding 0.05 to 0.2 parts of silica to 100 parts of the base resin. After performing the first measurement by heating each of the obtained expanded particles to 220°C at a heating rate of 10°C/min using a differential scanning calorimeter (Model DT-30 manufactured by Shimadzu Corporation), The temperature was lowered to 40°C at a cooling rate of 10°C/min, and the temperature was again raised to 220°C at a heating rate of 10°C/min, and a second measurement was performed. Then, measure the high temperature peak from the obtained DSC curve and calculate the melting energy (cal/g) of the high temperature peak.
was calculated and the results are shown in Table 2. The DSC curve of the expanded particles of Example 1 is shown in FIG. 1 (in the figure, a indicates the characteristic peak, b indicates the high temperature peak, and the shaded area indicates the area of the high temperature peak). or,
The DSC curve of the expanded particles of Comparative Example 3 is shown in FIG.
In FIGS. 1 and 2, the solid line indicates the DSC curve obtained in the first measurement, and the dotted line indicates the DSC curve obtained in the second measurement. Next, each of the above pre-expanded particles was pressurized with 3 kg/cm ² (G) air for a predetermined period of time to give the internal pressure shown in Table 2, and then heated with steam at the pressure shown in the same table for 10 seconds to foam. I forced it. The foaming ratio index was determined as an index for comparing the number of cells, the true foaming ratio, and the variation in the foaming ratio of the obtained pre-expanded particles, and the results are shown in Table 12 of Table 2. Next, each of the expanded particles of Examples 1 to 4 and Comparative Examples 1 to 4 was pressurized with 3 kg/cm ² (G) of air for 24 hours,
Thereafter, the mixture was filled into a mold having internal dimensions of 50 mm x 300 mm x 300 mm, and heated with steam at 3.3 Kg/cm ² (G) to perform foam molding. 80 pieces of each molded body obtained
After drying in an oven at ℃ for 24 hours and slowly cooling to room temperature, the foaming ratio and shrinkage rate of the foam molded product were measured. In addition, the water absorption rate was measured using the JIS-K6767B method.
The quality of the fusion properties was determined based on the water absorption rate. The results are shown in 1 and 2 of Table 2. Further, the results obtained by plotting the obtained data with log E on the horizontal axis and log n on the vertical axis (examples are shown with ○, comparative examples with ●) are shown in FIG. In Figure 3, straight line 1 shows log n=-2/3log E+2log60, and straight line 2 shows log n=-2/3log E+2log2, and straight line 1 has the formula: E ^1/3 ×n ^1/2 = 60, and straight line 2 corresponds to the formula: E ^1/3 ×n ^1/2 =.

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[Table] As explained above, according to the present invention, it is possible to obtain pre-expanded particles with a higher degree of foaming than in the past, and to minimize the variation between lots in the expansion ratio of the obtained expanded particles. Therefore, pre-expanded particles having a desired expansion ratio can be easily produced, and process control for achieving this purpose can also be made easier. In addition, the pre-expanded particles obtained by the present invention are highly foamed and have an excellent closed cell ratio similar to that of conventional pre-expanded particles. It has various effects such as excellent properties such as high fusion properties and high flexibility.

[Brief explanation of drawings]

FIG. 1 is a graph showing the DSC curve of the pre-expanded particles of Example 1, FIG. 2 is a graph showing the DSC curve of the pre-expanded particles of Comparative Example 3, and FIG. 3 is a graph showing the DSC curve of the pre-expanded particles of Example 1.
Based on the data on the expansion ratio E and the number of bubbles n of the pre-expanded particles obtained in the comparative example, the horizontal axis is log E,
It is a diagram in which the vertical axis is plotted as log n.

Claims (1)

[Claims] 1. When the true expansion ratio is E and the number of bubbles per 1 mm ² of cross section is n, the relationship is 2 < E ^1/3 × n ^1/2 < 60, and the differential scanning calorific value is DSC curve obtained by measurement (however, if the pre-expanded particles are 1 to 3 mg)
using a differential scanning calorimeter at a heating rate of 10°C/min.
DSC curve obtained when the temperature is raised to 220℃)
First, foaming ability is imparted to pre-expanded particles of a non-crosslinked propylene random copolymer resin having a crystal structure in which a high-temperature peak appears on the higher temperature side than the characteristic peak inherent to the base resin, and then the pre-expanded particles are heated. A method for producing pre-expanded non-crosslinked polypropylene random copolymer resin particles, which comprises foaming the particles to obtain pre-expanded particles having a larger expansion ratio than the original expansion ratio E.