JPS6049040A - Polypropylene resin expanded beads - Google Patents

Abstract

PURPOSE:To provide titled beads of good moldability, giving a peak higher in temperature than the specific peak for the polypropylene resin on the DSC-curve measured by the differential scanning calorimetry, said peak corresponding to specific energy of fusion. CONSTITUTION:The following components, namely, water, polypropylene resin particles, dispersant such as extremely fine aluminum oxide powder, and volatile expanding agent are blended in a closed vessel, being heated under agitation, followed by discharging the resultant dispersion into the atmosphere, while maintaining the pressure in the vessel higher than the external level, to effect expansion, thus obtaining the objective beads giving (a) peak b higher in temperature than the specific peak a for the polypropylene resin on the DSC-curve (obtained, using 1-3mg of the expanded beads, by raising temperature to 220 deg.C at a rate of 10 deg.C/min) measured by the differential scanning calorimetry, and also having such crystal structure that the energy of fusion for the peak b falls >=1.0cal/g.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to expanded polypropylene resin particles having good in-mold moldability.

The so-called bead foam molded product (in-mold molded product), which is obtained by filling pre-expanded particles into a mold and heating and foaming them, has cushioning properties,
It has excellent heat insulating properties and is widely used in cushioning materials, packaging materials, heat insulating materials, construction materials, etc., and the demand for it has increased greatly in recent years.

Conventionally, molded bodies made of polystyrene foam particles have been known as this type of molded body, but polystyrene foam molded bodies have the fatal disadvantage of being brittle and have the disadvantage of being inferior in chemical resistance. , improvements have been desired for a long time. A molded body made of crosslinked polyethylene foam particles has been proposed as a solution to these drawbacks. However, in the case of cross-linked polyethylene foam particles from Kotobuki, it is difficult to obtain a low-density (highly foamed) molded product by in-mold molding. Only molded products with high water absorption and poor physical properties were obtained, and no molded products that could be put to practical use could be obtained. .

Therefore, the present inventors have focused on the excellent physical properties of polypropylene resins, and have been conducting research on in-mold moldings similar to foamed polypropylene resin particles in order to solve the drawbacks of conventional in-mold moldings. Ta.

However, with polypropylene resin foam particles molded in a mold, although it may be possible to obtain a molded product with low density (high foaming), low water absorption, and excellent dimensional stability with a low shrinkage rate, on the other hand, a molded product with a high shrinkage rate can be obtained. Even if you only get the body
(b) There was a problem in that it was difficult to obtain a stable and good molded product.

The inventors have conducted further research to find out the cause of this fc
As a result, a high-temperature peak on the high-temperature side of the characteristic peak specific to the polypropylene-based resin appears in the DSCdh peak obtained by differential scanning calorimetry of polypropylene-based resin expanded particles used for in-mold molding, and the melting energy of the high-temperature peak is 1. The present invention was completed by discovering that a good in-mold molded product can be obtained when expanded polypropylene resin particles having a crystal structure of 0 m/, 9 or more are used.

That is, the present invention deals with D8C@, 1il obtained by differential scanning calorimetry of foamed polypropylene resin particles (however, foamed polypropylene resin particles 1 to 37R9 are heated to 220°C with a differential scanning calorimetry needle at a heating rate of 10°C/kil). A high temperature peak on the higher temperature side than the characteristic peak specific to the polypropylene resin appears in the T) SC curve obtained when the temperature is raised, and the melting energy of the high temperature peak is 1.0 m/p or more. This article focuses on the characteristic foamed polypropylene resin particles.

As the material of the pre-expanded particles used in the present invention, polypropylene resin is used, and as defined by J Is-
6758-1981 is used. For example, propylene homopolymer, ethylene-propylene block copolymer, ethylene-propylene random copolymer, and elastomer or monomer are added to these polymers.
- Examples include so-called polymer blend products that are blended with olefin polymers. Examples of elastomers used for blending include polybutylene and ethylene propylene rubber, and examples of 1-olefin polymers include polyethylene. Examples of blend products include two-type blend products such as propylene homopolymer/polyisobutylene and propylene copolymer/polyethylene, and three-type blend products such as propylene homopolymer/ethylene propylene rubber/polyethylene. These may be crosslinked or inherently crosslinked, but non-crosslinked ones are preferred. Among the above polymers, ethylene-propylene random copolymers are preferred, particularly ethylene components 05-1.

Preferably, it is wt.

In the present invention, the DSC80 curve obtained by differential scanning calorimetry of foamed polypropylene resin particles, the temperature of foamed polypropylene resin particles 1 to 31n9 is heated to 220'Ct at a heating rate of 10°C/min using a differential scanning calorimeter. This is the DEC curve obtained when

In the present invention, the high temperature peak is an endothermic peak that appears on the higher temperature side than the temperature at which the characteristic peak indicating the endotherm of solidification of polypropylene resin appears in the 080 curve, and is distinguished by the following method. First, the 080 obtained when the sample was heated from room temperature to 220°C at a heating rate of 10°C/min.
The curve is first [DD8CIIIlli, then -1'
The D80 curve obtained when the temperature was lowered to around 40°C at a cooling rate of 1°C/min from 220"C and then raised again to 220"Ct at a heating rate of 10°C/min is the second DEC curve. do. The characteristic peak specific to polypropylene resin generally appears in the first DaC curve MK4 and the second 080 curve, and the temperature at the top of the peak may be slightly different between the first and second runs, but the difference is is less than 5℃ 1 normal 2
It is less than ℃.

On the other hand, the high temperature peak in the present invention refers to the first Da
This is an endothermic peak that appears on the higher temperature side of the above characteristic peak in the C1tII line. Expanded polypropylene resin particles in which this high-temperature peak does not appear in the D8C[lIl line have poor in-mold moldability, and a good molded product cannot be obtained. Further, even if a high temperature peak appears, if the melting energy of the high temperature peak is less than 1.0 m/7, the shrinkage during molding will be large.

The above-mentioned high-temperature peak is thought to be due to the existence 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 080 curve, It does not appear in the second D8C curve. Therefore, the structure appearing as a high temperature peak was possessed by the foamed polypropylene resin particles of the present invention itself.

It is desirable that the difference between the temperature of the characteristic peak appearing in the second D8C curve and the temperature of the high temperature peak appearing in the first D8C curve is large;
The difference between the temperature at the top of the characteristic peak of III and the temperature at the top of the high temperature peak is 5°C or more, preferably 10°C or more.

Polypropylene resin foam particles with high temperature peaks are
A sealed container contains polypropylene resin particles, 100 to 400 parts by weight of water, 5 to 30 parts by weight of a volatile blowing agent (e.g. dichlorodifluoromethane), and a dispersant (e.g. fine particulate oxidation agent) per 100 parts by weight of the resin particles. aluminum) 0.1~
3 parts by weight, without raising the temperature above the melting end temperature Tm - Tm -25°C to Tm -5°C (Tm is the melting end temperature of the polypropylene resin, in the present invention,
Samples 6 to 8111i7 were heated to 220°C at a temperature increase rate of 10°C/min using a differential scanning calorimeter, then cooled to around 40°C at a cooling rate of 1037 minutes, and then heated again at 10°C/min. The temperature was raised to 220° C. at a rapid rate, and the temperature at which the tail of the endothermic peak of the DEC curve obtained by the second temperature increase returned to the baseline position on the high temperature side was defined as the melting end temperature. ), one end of the container is opened and the resin particles and water are released into a lower pressure atmosphere from inside the container to foam the resin particles.

As mentioned above, during foaming, the foaming temperature is set to the melting end temperature Tm.
By setting the temperature within the above-mentioned constant range without increasing the temperature above, it is possible to obtain foamed polypropylene resin particles in which a high-temperature peak appears on the DEC curve. Even so, once the temperature is raised to the melting end temperature Tm or higher, only solid peaks and no high temperature peaks appear in the DSC curve of the obtained expanded particles.

Furthermore, the melting energy of the above-mentioned high temperature peak is determined by the type and amount of the blowing agent used for foaming, and the foaming temperature.
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When using lolomethane, conditions include keeping the foaming temperature below Tm-7°C without raising the temperature above Tm-7°C, and using the amount of blowing agent below 20 parts by weight per 100 parts by weight of resin. .

Hereinafter, the present invention will be explained in more detail by giving Examples and Comparative Examples. All parts represent parts by weight.

Examples 1 to 3 and Comparative Examples 1 to 2 In a sealed container, 300 parts of water, 100 parts of ethylene-propylene random copolymer particles (Tm = 153°C), 03 parts of ultrafine aluminum oxide (dispersant), and Table 1 The volatile blowing agent shown in the table was mixed and heated under stirring with the maximum temperature in the container shown in the same table.

Next, after maintaining the foaming mIf shown in Table 81 for 30 minutes, the pressure inside the container was reduced to 30 Kf/, d(
G), one end of the container was opened, and the resin particles and water were simultaneously discharged into the atmosphere to foam the resin particles to obtain foamed particles. Table 1 shows the apparent (bulk) expansion ratio of the obtained expanded particles. Next, each of the obtained foam particles was measured at 10'C using a differential scanning calorimeter (Shima SL! Model DT-30 manufactured by Seisakusho).
After the first measurement was performed by raising the temperature to 220'G at a heating rate of 10°C/min, the temperature was lowered to 40°C at a cooling rate of 10°C/min, and then again to 220°C at a heating rate of 10°C/min. A second measurement was performed after raising the temperature to . The melting energy of the high temperature peak of the pre-expanded particles in which the high temperature peak appeared on the obtained D8C curve is shown in Table 1 using the following formula.

Melting energy (14'II) = (surface i (crI) on the chart of high temperature peak) X (chart 1 a4
Our enthusiasm (j/c++ri)X O,239(m/D÷
(Measurement sample weight (g)) Here, the area of the high temperature peak b on the chart can be determined by, for example, the points A, C and C in FIG. 1 and the first DSC curve (indicated by a solid line). It is calculated from the area of the enclosed part, and is the Tm product of the shaded part in Figure 1.

However, A is the melting end temperature, and the opening is the straight line (passing through A) directly extrapolated from the complete melting part C (about 170 to 200°C) on the DSC curve to the low temperature side, and the second DSC curve (the dotted line). The intersection with the straight line passing perpendicularly through the melting end temperature 2 at ) indicates the intersection between the first D8C curve and the straight line passing through the mouth and 2.

FIG. 1 shows the DSC1ll line of the foamed particles of Large Example 1, and FIG. 2 shows the DEC curve of the foamed particles of Comparative Example 2.

Note that Figures 1 and 2 are graphs showing the relationship between endothermic rate (mj/5ec) and temperature based on the DEC curve recorded on the chart, and the horizontal axis on the actual chart is Although it is a time, it is converted into a temperature corresponding to that time and displayed. In addition, in FIGS. 1 and 2, the peak a indicates a unique peak.

Next, 2 pieces of each foamed particles of Examples 1 to 3 and Comparative Examples 1 to 2 were added.
The mixture was pressurized for 24 hours with a sudden blow of Kp/cri (0), and then filled into a mold with internal dimensions of 50mm x 300mm x 300m to give 3.2 KP/cnl (G).
It was heated with steam and foam molded. Each molded product obtained was dried in an open room at 80°C for 24 hours, and after cooling slowly to room temperature, the expansion ratio, shrinkage rate, and water absorption rate of the foamed molded product were measured, and the size of the water absorption rate and the quality of the weldability were determined. was determined. The results are shown in Table 1.

(Ei) As explained above, the expanded polypropylene resin particles of the present invention have a high temperature peak on the higher temperature side than the characteristic peak inherent to the polypropylene resin in the DEC curve, and the melting energy of the high temperature peak is 1° (At By having a crystal structure of /9 or more, the high-temperature peak does not appear on the D8C curve. Unlike in-mold moldings using polypropylene resin foam particles, the molded product does not shrink significantly, and the foamed particles It has excellent in-mold moldability during in-mold molding, and a low-density (highly foamed) molded product can be easily obtained, and the obtained molded product has excellent physical properties such as low shrinkage and water absorption.

ti The in-mold molded body made of polypropylene resin foam particles does not have the disadvantage of being brittle like the in-mold molded body made of polystyrene resin foam particles, and can provide a molded body with excellent #* resistance and chemical resistance. In addition, it has various effects such as being able to provide an excellent molded product with low shrinkage and water absorption even when the density is lower (highly foamed) than in-mold molded products made of crosslinked polyethylene foam particles.

[Brief explanation of drawings]

The drawings show the DSCSC curve obtained by differential scanning thermometry; Fig. 1 shows the DEC curve of expanded particles of Example 10;
The figure shows the D8C curve of Comparative Example 20 expanded particles. Patent applicant: Japan Styrene Paper Co., Ltd. Agent: Isamu Hosoi, patent attorney.

Claims (1)

[Claims] DSC curve obtained by differential scanning calorimetry of foamed polypropylene resin particles (However, the DSC curve obtained when foamed polypropylene resin particles 1 to 3 cm were heated to 220'C at a heating rate of 10°C/Sae using a differential scanning calorimeter) D
8C curve), a high-temperature peak appears on the higher temperature side than the characteristic peak specific to the polypropylene resin, and the melting energy of the high-temperature peak is 1. , polypropylene resin foam particles having a crystal structure of Om/J9 or more.