JPS6344778B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polypropylene resin foam molding. The present applicant has been conducting research on a method for manufacturing a foam molded article by a so-called bead molding method in which pre-expanded polypropylene resin particles are molded in a mold. Normally, in the above bead molding method, pre-expanded particles are molded after an inorganic gas or a mixed gas of an inorganic gas and a volatile blowing agent is introduced inside and an internal pressure is applied. The appearance of the foamed molded product obtained by sequentially molding the pre-expanded particles that have been aged under pressure at This often results in variations in physical properties, and sometimes results in poor quality, and this tendency is particularly noticeable in highly expanded pre-expanded particles. As a result of intensive research to solve the above-mentioned drawbacks, the present inventors found that the factors that cause variations in physical properties such as shrinkage rate, compression hardness, compression set rate, and particle fusion properties of the molded product are as follows. The present invention was completed by discovering that the difference lies in the crystal structure and internal pressure of the pre-expanded particles used for molding. That is, the present invention provides a DSC curve obtained by differential scanning calorimetry of pre-expanded particles of polypropylene resin (however, 1 to 3 mg of pre-expanded particles are measured by a differential scanning calorimeter at a heating rate of 10°C/min up to 220°C). It has a crystal structure in which a high-temperature peak appears on the higher temperature side than the characteristic peak unique to polypropylene resin in the DSC curve obtained when the temperature is increased, and the temperature is 25℃ and 1atm.
It is characterized by imparting foaming ability to pre-expanded particles whose internal pressure reduction rate coefficient k is k≦0.30, and then filling the particles into a mold and heating and foaming them to obtain a molded product according to the mold. The gist of this invention is a method for producing a polypropylene resin foam molded product. As the base resin of the pre-expanded particles used in the present invention, a polypropylene resin is used, and the definition is defined in JIS-K6758-1981. For example, propylene homopolymer, ethylene-propylene block copolymer,
Examples include 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.
Examples of olefin polymers include polyethylene. Examples of blended products include two-type blends such as propylene homopolymer/polyisobutylene, propylene copolymer/polyethylene, and three-type blends 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 the ethylene component.
0.5 to 10 wt% is preferable. The pre-expanded particles used in the present invention have a crystal structure in which a high-temperature peak appears on the higher temperature side than the characteristic peak inherent to the polypropylene resin in a DSC curve obtained by differential scanning calorimetry of the particles. the above
The DSC curve is the DSC obtained when 1 to 3 mg of expanded polypropylene resin particles are heated to 220°C at a heating rate of 10°C/min using a differential scanning calorimeter.
For example, the sample is heated from room temperature to 220℃ for 10
DSC obtained when heating at a heating rate of °C/min
The curve is the first DSC curve, then the DSC curve obtained when the temperature is lowered 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. Let be the second DSC curve,
From these DSC curves, unique peaks and high temperature peaks can be distinguished. That is, the unique peak in the present invention is an endothermic peak unique to the polypropylene resin, and is thought to be due to endotherm at the time of melting of so-called crystals of the polypropylene resin. Usually, 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, but the difference is 5
℃, usually less than 2℃. 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 the polypropylene resin in-mold foam molded product in which this high-temperature peak does not appear in the DSC curve shrinks. compression hardness, compression set rate,
Various physical properties such as particle fusion properties are inferior, and variations in these physical properties become large. The above high temperature peak is
It is thought that this 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 appears in the first DSC curve, but it does not appear in the second DSC curve when the temperature is raised under the same conditions. Doesn't appear. Therefore, the high-temperature peak appears because the pre-expanded particles used in the present invention also have a crystal structure different from the crystal structure exhibiting the characteristic peak inherent to the polypropylene resin.
By foaming a polypropylene resin under specific foaming conditions, it is possible to obtain pre-expanded particles having a crystal structure in which a high temperature peak appears on the DSC curve. 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 addition, the high temperature peak appears in the first DSC curve obtained under the above measurement conditions but does not appear in the second DSC curve, so when the base resin of the pre-expanded particles is a mixture, etc. Even if multiple characteristic peaks may appear, the first and second
By comparing the DSC curves, a unique peak and a high temperature peak can be distinguished, and the presence or absence of a high temperature peak can be confirmed. The pre-expanded particles used in the present invention are as described above.
The pre-expanded particles must have a crystal structure in which a high-temperature peak appears on the DSC curve, and have an internal pressure decrease rate coefficient k of k≦0.30 at 25° C. and 1 atm. When k>0.30, the shrinkage rate is small and a molded product with excellent dimensional accuracy cannot be obtained. The internal pressure reduction rate coefficient k is a rate coefficient of the rate at which gas escapes from within the pre-expanded particles, and is determined by the following method. First, a large number of needle holes are drilled, e.g. 70mm x 100mm.
Pre-expanded particles of known expansion ratio and weight are filled into a polyethylene bag of approximately 100 mL, and the pre-expanded particles are pressurized with air while being maintained at 25°C to apply internal pressure to the pre-expanded particles, and then the weight of the pre-expanded particles is measured. Next, the pre-expanded particles are maintained at 25° C. and 1 atm, and the weight of the pre-expanded particles is measured after 10 minutes. Internal pressure P ₀ of pre-expanded particles immediately after applying internal pressure (Kg/cm ²・G)
Then, the internal pressure P ₁ (Kg/cm ² ·G) of the pre-expanded particles after being maintained at 25° C. and 1 atm for 10 minutes is determined from the following formula. Internal pressure of pre-expanded particles (Kg/cm ²・G) = Increased amount of air (g) x 0.082 x T(K) x 1.0332 / Air molecular weight x Volume of air inside particles () (However, the increased amount of air is determined by internal pressure measurement. The difference between the particle weight at the time and the particle weight before pressure treatment, T is the ambient temperature, and the air volume inside the particle is the value calculated from the expansion ratio of the pre-expanded particles.) Next, P is calculated from the above formula. ₀ and P ₁ , find the internal pressure reduction rate coefficient k using the following formula. logP ₁ /P ₀ = -kt (However, t is time and is 10 minutes in the above case.) The above internal pressure reduction rate coefficient k is k≦0.30 when the number of cells in the foamed particles is small, when the closed cell ratio is high, etc. However, even if the closed cell ratio is high, if a resin containing a crystal nucleating agent is used, k≦0.30 may not be satisfied, which is not preferable. The above used in the present invention has a crystal structure in which a high temperature peak appears in the DSC curve, and has a temperature of 25°C.
Pre-expanded particles having an internal pressure reduction rate coefficient k of 1 atm of k≦0.30 can be produced as follows. First, as raw material polypropylene resin particles,
Select resin particles that do not contain crystal nucleating agents or silica or phosphorus-based stabilizers that can reduce the size of bubbles. Next, a step of incorporating a volatile blowing agent into the polypropylene resin particles, a step of dispersing the resin particles in a dispersion medium in a container, and a temperature T (° C.) of the volatile blowing agent-containing resin particles and the dispersion medium.
without raising the temperature above the melting end temperature Tm (°C) of the resin particles according to the following formula: Tm-20<T<Tm-5
(In the formula, the melting end temperature Tm is approximately 6 to
This is the end temperature of the endothermic curve obtained when 8 mg of a sample is heated at a heating rate of 10°C/min. ) can be produced by a pre-foaming method comprising the step of opening one end of the container while maintaining the temperature within the range represented by () and simultaneously releasing the resin particles and dispersion medium into an atmosphere at a lower pressure than the inside of the container. . Examples of the volatile blowing agent include propane,
Aliphatic hydrocarbons such as butane, pentane, hexane, heptane, etc., cycloaliphatic hydrocarbons such as cyclobutane, cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl Examples include halogenated hydrocarbons such as chloride, ethyl chloride, methylene chloride, etc., and these blowing agents can be used in combination. The amount of the blowing agent used is about 0.04 to 0.20 mol per 100 parts by weight of the polypropylene resin particles. In this method, the polymer particles and the volatile blowing agent are separated or the volatile blowing agent is added to the polymer particles and then dispersed in a dispersion medium. Aluminum and titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc. can be used. The amount of this dispersant added is usually 0.01 to 10 parts by weight per 100 parts by weight of the polymer particles. Further, the dispersion medium may be any solvent that does not dissolve the polymer particles.
Examples include water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof, but water is usually preferred. As described above, pre-expanded particles are obtained which have a crystal structure in which a high-temperature peak appears on the DSC curve and have an internal pressure decrease rate coefficient k of k≦0.30 at 25°C and 1 atm. It has an apparent foaming ratio of 60 times. Furthermore, the pre-expanded particles obtained by these methods are pressurized with air, inorganic gas such as nitrogen, carbon dioxide, or a mixed gas of these and a volatile blowing agent to impart increased internal pressure to the expanded particles. By heating, it is also possible to obtain particles with an apparent expansion ratio of up to about 150 times. In the present invention, foaming ability is imparted to the pre-expanded particles obtained as described above. The foaming ability is imparted to the pre-expanded particles using an inorganic gas such as air, nitrogen gas, carbon dioxide, etc. or volatile foaming of butane, dichlorodifluoromethane, dichlorotetrafluoroethane, etc. used for foaming the pre-expanded particles. This is carried out by pressurizing with an agent or a mixed gas thereof, but usually air is used to apply an internal pressure of at least atmospheric pressure to 3 kg/cm ² ·G to the pre-expanded particles. The pre-expanded particles with the above-mentioned foaming ability (applied with an internal pressure higher than atmospheric pressure) are filled into a mold, heated to foam the pre-expanded particles, and fuse the particles together to form foam molding according to the mold. You get a body. The heating means for the above molding is usually 2
Water vapor of kg/cm ² ·G to 5 kg/cm ² ·G is used. The above-mentioned polypropylene resin foam molded product has a smooth surface, excellent dimensional accuracy, and particle fusion strength, and also has excellent physical properties such as compression hardness, compression set rate, and shrinkage rate. It can be used, for example, in packaging materials, cushioning materials, heat retaining materials, insulation materials, construction materials, vehicle parts, flotation materials, food containers, etc. The present invention will be explained in more detail below by giving Examples and Comparative Examples. Examples 1 to 5 BHT (antioxidant) per 100 parts by weight of base resin
0.1 part by weight, Irganox 1010 (antioxidant)
100 parts by weight of ethylene-propylene random copolymer particles (ethylene component 3.5% by weight, melt index 8 g/10 min, Tm = 150°C) containing 0.03 parts by weight and 0.05 parts by weight of calcium stearate were added to water.
300 parts by weight, 0.3 parts by weight of ultrafine aluminum oxide, and the amount of dichlorodifluoromethane shown in Table 1 were placed in the autoclave No. 5, heated to raise the temperature while stirring, and held for 30 minutes at the foaming temperature shown in the same table. Thereafter, while maintaining the internal pressure of the container at 30 kg/cm ² ·G with nitrogen gas, one end of the container was opened to release the resin particles and water under atmospheric pressure to foam the resin particles to obtain pre-expanded particles. Table 2 shows the expansion ratio of the obtained pre-expanded particles. In addition, in Example 5, Example 2
The pre-expanded particles obtained by foaming were further pressurized with air and then heated, which was repeated twice to obtain a foaming ratio of 65 times. Table 2 shows the internal pressure reduction rate coefficient and differential scanning calorimetry of the pre-expanded particles obtained. Further, the DSC curve of the pre-expanded particles of Example 3 is shown in FIG.
In the figure, a and a' indicate the characteristic peaks, b indicates the high temperature peak, the solid line is the first DSC curve, and the dotted line is the second DSC curve. ) Next, these pre-expanded particles are pressurized with air,
After applying the internal pressure shown in Table 2 to the particles, 300 mm
Fill a mold with ×300mm ×50mm (mold inner diameter), and
The pre-expanded particles were foamed by heating with steam of 3.5 kg/cm ² ·G to obtain a foamed molded product. After leaving the obtained molded body in an open environment at 55°C for 24 hours, the density, compression hardness, compression set rate, shrinkage rate, surface condition, and fusion properties of the pre-expanded particles in the molded body were measured. I did this. The results are also shown in Table 2. Comparative Example 1 100 parts by weight of the same ethylene-propylene random copolymer particles as in Example, 300 parts by weight of water, 0.3 parts by weight of ultrafine aluminum oxide, and dichlorodifluoromethane in the amount shown in Table 1 were placed in an autoclave in Step 5. After raising the temperature to the maximum temperature in the container shown in the same table, the temperature was lowered to 140°C and held for 15 minutes, and then one end of the container was opened while maintaining the container internal pressure at 30 kg/cm ² G with nitrogen gas. The resin particles and water were released under atmospheric pressure to foam the resin particles to obtain pre-expanded particles. The expansion ratio, internal pressure reduction rate coefficient, and differential scanning calorimetry of the obtained pre-expanded particles were measured. The results are shown in Table 2. Further, the DSC curve of the pre-expanded particles is shown in FIG. 2 (in the figure, the solid line shows the first DSC curve, the dotted line shows the second DSC curve, and a and a' indicate the characteristic peaks). After applying the internal pressure shown in Table 2 to the pre-expanded particles, they were molded in the same manner as in Examples to obtain molded bodies. Table 2 shows the physical properties of the molded product obtained. Comparative Examples 2 to 3 For 100 parts by weight of the base resin, Comparative Example 2 contains 0.2 parts by weight of dibenzylidene sorbitol (crystal nucleating agent),
Comparative Example 3 uses silica (antiblocking agent) 0.2
100 parts by weight of ethylene-propylene random copolymer particles (having the same ethylene component, melt index, and Tm as in the example), 300 parts by weight of water, and ultrafine aluminum oxide particles.
0.3 parts by weight and the amount of dichlorodifluoromethane shown in Table 1 were placed in the autoclave in Step 5, and the temperature was maintained at 137°C for 30 minutes without raising the temperature above the maximum temperature in the container shown in the same table. In the same manner as in the example, the resin particles and water were released under atmospheric pressure to obtain pre-expanded particles. Table 2 shows the results of the expansion ratio, internal pressure reduction rate coefficient measurement, and differential scanning calorimetry measurement of the obtained pre-expanded particles. Next, a foamed molded article was obtained in the same manner as in the example using the pre-expanded particles. The physical properties of the molded product are also shown in Table 2.

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[Table] As explained above, the present invention has a crystal structure in which a high temperature peak appears in the DSC curve obtained by differential scanning calorimetry, and the internal pressure decrease rate coefficient k at 25°C and 1 atm is k≦0.30. After imparting foaming ability to the pre-expanded polypropylene resin particles,
By filling the particles into a mold and foaming them to obtain a molded product, the surface condition is good, the dimensional accuracy is excellent, and the shrinkage rate, compression hardness, compression set rate, and particle size are good. It has various effects such as being able to obtain a molded product with excellent physical properties such as fusion bondability.

[Brief explanation of drawings]

FIG. 1 is a graph showing the DSC curve of the pre-expanded particles of Example 3, and FIG. 2 is a graph showing the DSC curve of the pre-expanded particles of Comparative Example 1. a, a'...specific peak, b...high temperature peak.

Claims (1)

[Claims] 1 DSC curve obtained by differential scanning calorimetry of pre-expanded particles of polypropylene resin (however, 1 to 3 mg of pre-expanded particles were measured by differential scanning calorimetry)
It has a crystal structure in which a high-temperature peak appears on the higher temperature side than the characteristic peak inherent to polypropylene resin in the DSC curve obtained when the temperature is raised to 220 °C at a temperature increase rate of 10 °C/min, and at 25 °C and 1 atm. It is characterized by imparting foaming ability to pre-expanded particles whose internal pressure reduction rate coefficient k is k≦0.30, and then filling the particles into a mold and heating and foaming them to obtain a molded product according to the mold. A method for producing a polypropylene resin foam molded product.