JPS6344779B2 - - 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 by the present inventors to investigate the cause of this problem, we found that the DSC curve obtained by differential scanning calorimetry of expanded polypropylene resin particles used for in-mold molding shows a temperature side higher than the characteristic peak unique to polypropylene resin. It was discovered that a good in-mold molded product can be obtained when foamed polypropylene resin particles having a crystal structure in which a high-temperature peak appears and the melting energy of the high-temperature peak is 1.0 cal/g or more, and the present invention has been achieved. It was completed. That is, the present invention provides a DSC curve obtained by differential scanning calorimetry of foamed polypropylene resin particles (with the exception of 1 to 3 mg of foamed polypropylene resin particles).
using a differential scanning calorimeter at a heating rate of 10°C/min.
A high-temperature peak on the higher temperature side than the characteristic peak unique to polypropylene resin appears in the DSC curve obtained when the temperature is raised to 220 ° C., and the melting energy of the high-temperature peak is 1.0 cal / g 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 the definition thereof is as defined in JIS-K6758-1981. Examples include propylene homopolymers, ethylene-propylene block copolymers, ethylene-propylene random copolymers, and so-called polymer blend products in which these polymers are blended with elastomers and 1-olefin polymers. Examples of elastomers used for blending include polyisobutylene and ethylene propylene rubber, and examples of 1-olefin polymers include polyethylene.
Examples of blend products include propylene homopolymer/polyisobutylene, propylene copolymer/
Examples include two-type blend products such as polyethylene and three-type blend products such as propylene homopolymer/ethylene propylene rubber/polyethylene. These may be crosslinked or non-crosslinked, but non-crosslinked ones are preferred. Among the above-mentioned polymers, ethylene-propylene random copolymers are preferred, especially ethylene content of 0.5 to 10 wt%
Preferably. 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 a DSC curve obtained when the temperature is raised to 220°C. 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 inherent to the propylene resin appears in the DSC curve, and is distinguished by the following method. First, the DSC curve obtained when the sample was heated from room temperature to 220℃ at a heating rate of 10℃/min was used for the first DSC.
The second DSC curve is the DSC curve obtained when the temperature is raised from 220°C to around 40°C at a cooling rate of 10°C/min, and then raised again to 220°C at a heating rate of 10°C/min. Make it a curve. The characteristic peaks specific to polypropylene resins are generally found in the first DSC.
It appears in both the curve and the second DSC curve, and the temperature at the top of the peak may be slightly different between the first and second runs, but the difference is less than 5 °C, usually 2 °C.
less than 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. Expanded polypropylene resin particles in which this high-temperature peak does not appear in the DSC curve have poor in-mold moldability, making it impossible to obtain a good molded product. Even if a high-temperature peak appears, if the melting energy of the high-temperature peak is less than 1.0 cal/g, the shrinkage during molding will be large. It is thought that the above-mentioned high-temperature peak is due to the existence of a crystal structure different from the structure that appears as the above-mentioned characteristic peak, and the high-temperature peak is caused by the first
Although it appears in the DSC curve, it does not appear in the second DSC curve obtained by raising the temperature under the same conditions. 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. Expanded polypropylene resin particles having a high temperature peak are prepared by storing 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 melting temperature is Tm - 25°C without increasing the temperature above the melting end temperature Tm.
~Tm-5℃ (Tm is the melting end temperature of polypropylene resin, and in the present invention, 6 to 8 mg of sample
220 at a heating rate of 10℃/min using a differential scanning calorimeter.
℃ and then 40℃ at a cooling rate of 10℃/min.
After the temperature has cooled down to around
The temperature was raised to 220°C, and the temperature at which the tail of the endothermic peak of the DSC curve obtained by the second temperature rise 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, by setting the foaming temperature within the above-mentioned constant temperature range during foaming without increasing the temperature above the melting end temperature Tm, foamed polypropylene resin particles that exhibit a high temperature peak on the DSC curve can be obtained. If the temperature is outside the above range, or even if it is within the above range, once the temperature is raised above the melting end temperature Tm, only the characteristic peak will appear in the DSC curve of the obtained expanded particles, and the high temperature peak will not appear. . 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, and the conditions for the melting energy to be 1.0 cal/g or more include, for example, when polypropylene resin is ethylene-propylene random compound. If the polymer is a foaming agent and dichlorodifluoromethane is used as a blowing agent, the foaming temperature should be kept below Tm-7℃ without raising the temperature above Tm-7℃, and the amount of blowing agent used should be 100 parts by weight of the resin. For example, the content may be 20 parts by weight or less. 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), 0.3 parts of ultrafine aluminum oxide (dispersant), and 1st
The volatile blowing agent shown in the table was blended, and the mixture was heated under stirring with the maximum temperature set to the maximum temperature in the container shown in the table. After holding the foaming temperature shown in Table 1 for 30 minutes, the pressure inside the container was reduced to 30Kg/cm ² (G) using nitrogen gas.
One end of the container was opened while the container was held in place, and the resin particles and water were released into the atmosphere at the same time, and the resin particles were foamed to obtain foamed particles. Table 1 shows the apparent (bulk) expansion ratio of the obtained expanded particles. Next, each foamed particle obtained was measured using a differential scanning calorimeter (DT made by Shimadzu Corporation).
30 type) at a heating rate of 10°C/min to 220°C, then lowered the temperature to 40°C at a cooling rate of 10°C/min, and then again at 10°C/min. A second measurement was performed by raising the temperature to 220°C at a heating rate of 1 minute. The melting energy of the high-temperature peak of the pre-expanded particles in which the high-temperature peak appeared in the obtained DSC curve was determined from the following formula and is shown in Table 1. Melting energy (cal/g) (area of high temperature peak on the chart (cm ² ) x amount of heat per 1 cm ² of chart (j/cm ² )) x 0.239 (cal/j) ÷ (measured sample weight (g)) Here So, the area of high temperature peak b on the chart is
For example, in Figure 1, each point A, B, C and the first
It is determined from the area of the part surrounded by the second DSC curve (indicated by a solid line), and is the area of the part shown by diagonal lines in FIG. However, A is the melting end temperature, B is the straight line (passing through A) directly extrapolated from the complete melting part c (the part of about 170 to 200°C) on the DSC curve to the low temperature side, and the second line.
The intersection of the first DSC curve (indicated by a dotted line) with the straight line passing perpendicularly through the melting end temperature D indicates the intersection of the first DSC curve with the straight line passing through B and D. The DSC curve of the expanded particles of Example 1 is shown in Figure 1.
The DSC curve of the expanded particles of Comparative Example 2 is shown in FIG.
Figures 1 and 2 are DSC recorded on the chart.
This is a graph showing the relationship between heat absorption rate (mj/sec) and temperature based on the curve, and the horizontal axis on the actual chart is time, but it is converted to the temperature corresponding to that time and displayed. It is something. Furthermore, Figure 1,
In FIG. 2, the peak a indicates a unique peak. Next, each expanded particle of Examples 1 to 3 and Comparative Examples 1 to 2 was pressurized with 2 kg/cm ² (G) of air for 24 hours, and then
The mixture was filled into a mold having internal dimensions of 50 mm x 300 mm x 300 mm, and heated with steam at 3.2 Kg/cm ² (G) to perform foam molding. Each molded product obtained was dried in an oven 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 quality of the fusion was evaluated based on the water absorption rate. I judged it. The results are shown in Table 1.

[Table] 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 DSC curve, and the melting energy of the high temperature peak is
By having a crystal structure of 1.0 cal/g or more, the high-temperature peak does not appear on the DSC curve. Unlike in-mold molding using polypropylene resin foam particles, the molded product does not shrink significantly, making it possible to It has excellent in-mold moldability and can easily produce a low-density (highly foamed) molded product.
The obtained molded product has excellent physical properties with low shrinkage and water absorption. In addition, the in-mold molded product made of polypropylene thread resin foam particles does not have the disadvantage of being brittle like the in-mold molded product made of polystyrene resin foam particles, and can provide a molded product 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 drawings]

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 2.
It is a DSC curve.

Claims (1)

[Claims] 1 DSC curve obtained by differential scanning calorimetry of foamed polypropylene resin particles (1 to 3 mg of foamed polypropylene resin particles were heated to 220°C at a heating rate of 10°C/min using a differential scanning calorimeter) A polypropylene characterized by having a crystal structure in which a high-temperature peak on the higher temperature side than the characteristic peak specific to the polypropylene resin appears in the DSC curve obtained when the polypropylene resin is foamed resin particles.