JPS6324617B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to foamed 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 excellent cushioning properties, heat insulation properties, etc., and can be used as cushioning materials, packaging materials, heat insulation materials, construction materials, etc. It is widely used and the demand for it has increased tremendously 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, it is difficult to obtain a molded product with low density (high foaming) by in-mold molding. Only molded bodies with high physical properties and poor physical properties were obtained, and it was impossible to obtain any molded bodies that could be put to practical use. Therefore, the present inventors have focused on the excellent physical properties of polypropylene resin, and have conducted research on in-mold molded bodies made of expanded polypropylene resin particles in order to solve the drawbacks of conventional in-mold molded bodies. .
However, polypropylene resin foam particles molded in a mold have a low density (high foaming) and a low water absorption rate.
Moreover, while there are cases in which a molded product with a small shrinkage rate and excellent dimensional stability can be obtained, there are also cases in which only a molded product with a large shrinkage rate can be obtained, which poses the problem that it is not always possible to obtain a stable and good molded product. Was. As a result of further intensive research to find out the cause of this, the present inventors found that the DSC curve obtained by differential scanning calorimetry of polypropylene resin foam particles (pre-expanded particles) used for in-mold molding has a unique characteristic of polypropylene resin. The present inventors have discovered that a good in-mold molded product can be obtained when foamed polypropylene resin particles having a crystal structure in which a characteristic peak and a high temperature peak higher than the characteristic peak appear, have led to the completion of the present invention. That is, in the present invention, polypropylene resin particles and a volatile foaming agent are blended in a closed container, and the melting end temperature is
Tm (melting end temperature Tm
The temperature was increased to 220℃ at a heating rate of ℃/min, then 10
After lowering the temperature to around 40℃ at a cooling rate of ℃/min, the temperature was raised again to 220℃ at a heating rate of 10℃/min, and then
This is the temperature at which the tail of the endothermic peak of the DSC curve obtained by the second temperature increase returns to the baseline position on the high temperature side. ) After the temperature has been raised to the foaming temperature without increasing the temperature above 100%, one end of the container is opened to release the resin particles and water into a lower pressure atmosphere from inside the container, and the resin particles are foamed. A DSC curve obtained by differential scanning calorimetry of foamed polypropylene resin particles (1 to 3 mg of foamed polypropylene resin particles was measured at a heating rate of 10°C/min using a differential scanning calorimeter). Obtained when the temperature is raised to 220℃
The object of the present invention is to provide foamed polypropylene resin particles characterized by having a crystal structure in which a characteristic peak specific to the polypropylene resin and a high temperature peak higher than the temperature of the characteristic peak appear in the DSC curve. In the present invention, as the polypropylene resin, propylene homopolymer, ethylene-propylene block copolymer, ethylene-propylene random copolymer, etc. are used, but in particular ethylene-propylene
Propylene random copolymers are preferred. In the present invention, the DSC curve obtained by differential scanning calorimetry of foamed polypropylene resin particles is defined as 1 to 3 mg of foamed polypropylene resin particles.
using a differential scanning calorimeter at a heating rate of 10°C/min.
This is the DSC curve obtained when the temperature is raised to 220°C. For example, the DSC curve obtained when the sample is heated from room temperature to 220°C at a heating rate of 10°C/min is the first DSC curve, Then 10 from 220℃
The temperature was lowered to around 40°C at a cooling rate of 10°C/min, and then
The second DSC curve is the DSC curve obtained when the temperature is raised to 220°C at a heating rate of °C/min, and the characteristic peak and high temperature peak can be determined from these DSC curves. That is, the characteristic peak in the present invention 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. The characteristic peak appears in both the first DSC curve and the second DSC curve, and the temperature at the top of the peak may be slightly different between the first and second times.
The difference is less than 5°C, usually less than 2°C. On the other hand, the high temperature peak in the present invention is an endothermic peak that appears on the higher temperature side than the above-mentioned characteristic peak in the first DSC curve, and foamed polypropylene resin particles that do not have this high temperature peak in the DSC curve have poor in-mold formability. This is bad, and a good molded product cannot be obtained. 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 appearing as a high temperature peak was possessed by the expanded 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 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. The expanded polypropylene resin particles of the present invention contain polypropylene resin particles in a closed container, 100 to 400 parts by weight of water per 100 parts by weight of the resin particles, and 5 to 5 parts by weight of a volatile blowing agent (for example, dichlorodifluoromethane).
30 parts by weight, and 0.1 to 3 parts by weight of a dispersant (for example, finely divided aluminum oxide), and the temperature is Tm-25℃ to Tm-5℃ without increasing the temperature above the melting end temperature Tm.
(Tm is the melting end temperature of polypropylene resin,
In the present invention, 6 to 8 mg of a 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 in the high temperature measurement was defined as the melting end temperature. ), one end of the container is opened to release the resin particles and water into a lower pressure atmosphere than inside the container,
It can be obtained by foaming 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, the product has a structure in which a specific peak and a high temperature peak appear in the DSC curve.
Expanded particles of the present invention can be obtained. Once the temperature is raised above the melting end temperature Tm, the DSC curve of the obtained foamed particles shows only a characteristic peak and no high temperature peak, and the foamed particles give a molded product with good moldability and less shrinkage. can't get it. Hereinafter, the present invention will be explained in more detail by giving Examples and Comparative Examples. Examples 1 to 3 and Comparative Examples 1 to 3 In a sealed container, 300 parts by weight of water, 100 parts by weight of ethylene-propylene random copolymer particles (Tm = 153°C), 0.3 parts by weight of ultrafine aluminum oxide (dispersant) and The volatile foaming agents shown in Table 1 were blended and heated while stirring. After maintaining the foaming temperature shown in Table 1 for 30 minutes, the pressure inside the container was reduced to 30 minutes using nitrogen gas.
While maintaining the pressure at Kg/cm ² (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 foamed particles obtained was measured using a differential scanning calorimeter (Model DT-30 manufactured by Shimadzu Corporation) at a heating rate of 10°C/min.
After raising the temperature to 220℃ and performing the first measurement
The temperature was lowered to 40℃ at a cooling rate of 10℃/min, and then
A second measurement was carried out by raising the temperature to 220°C at a heating rate of °C/min. Expanded particles of Examples 1 to 3
Among the DSC curves, the DSC curve of the expanded particles of Example 1 is shown in FIG. Regarding Comparative Example, the DSC curve of expanded particles of Comparative Example 3 is shown in FIG. 1st
In the figures and FIG. 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. Difference ( ΔT) was determined and shown in Table 1. Next, Examples 1 to 3 and Comparative Examples 1 to
Each of the foamed particles in step 3 was pressurized with 2Kg/cm ² (G) of air for 24 hours, and then filled into a mold with internal dimensions of 50 mm x ³⁰⁰ mm x 300 mm. It was heated with steam and foam molded. Each molded body obtained
After drying in an oven at 80°C for 24 hours and slowly cooling to room temperature, the expansion ratio, shrinkage rate, and water absorption rate of the foamed molded product were measured, and the quality of the fusion property was judged based on the magnitude of the water absorption rate. The results are shown in Table 1.

【table】

[Table] As explained above, the expanded polypropylene resin particles of the present invention have a crystal structure in which a characteristic peak specific to the polypropylene resin and a high temperature peak on the high temperature side of the characteristic peak appear in the DSC curve, so that the foamed particles can be used at high temperatures. The molded product does not shrink significantly unlike in-mold molded products using expanded polypropylene resin particles that do not have peaks in the DSC curve.
Excellent in-mold moldability when molding expanded particles in a mold,
A low-density (highly foamed) molded product can be easily obtained, and the resulting molded product has excellent physical properties such as low shrinkage and water absorption. In addition, 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 foamed particles, and can provide a molded body with excellent impact 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 the drawing]

The drawing is obtained by differential scanning calorimetry
Figure 1 shows the DSC curve of the expanded particles of Example 1, and Figure 2 shows the DSC curve of the expanded particles of Comparative Example 3.
It is a DSC curve.

Claims (1)

[Claims] 1. Polypropylene resin particles and a volatile blowing agent are blended in a closed container, and the melting end temperature Tm (melting end temperature Tm is 220°C at a heating rate of 10°C/min for a sample of 6 to 8 mg). ℃, then lowered the temperature to around 40℃ at a cooling rate of 10℃/min, and then raised the temperature again to 220℃ at a heating rate of 10℃/min. This is the temperature at which the tail of the endothermic peak of the DSC curve returns to the baseline position on the high-temperature side. The polypropylene resin foam particles are obtained by discharging and water from inside a container into a low-pressure atmosphere and foaming the resin particles, and the DSC curve obtained by differential scanning calorimetry of the polypropylene resin foam particles ( However, polypropylene resin foam particles 1 to 3 mg
using a differential scanning calorimeter at a heating rate of 10°C/min.
Polypropylene resin foam characterized by having a crystal structure in which a characteristic peak specific to the polypropylene resin and a high temperature peak on the higher temperature side than the temperature of the characteristic peak appear in the DSC curve obtained when the temperature is raised to 220 ° C. particle. 2. The polypropylene resin foam particles according to claim 1, wherein the difference between the temperature at the apex of the characteristic peak and the temperature at the apex of the high temperature peak is 5° C. or more.