JPS6042434A - Production of polypropylene resin foam molding - Google Patents

Abstract

PURPOSE:To obtain a molding having a good surface appearance and excellent dimensional accuracy, shrinkage, compressive hardness, etc., by imparting expandability to pre-expanded PP resin particles having a specified crystal structure and a specified decreasing rate of an internal pressure, filling a molding die with the particles, and expansion-molding them. CONSTITUTION:Expandability is imparted to pre-expanded particles which have such a crystal structure that a DSC curve obtained when 1-3mg of the pre- expanded PP particles are heated to 220 deg.C at a temperature rise rate of 10 deg.C/ min on a differential scanning calorimeter has a high-temperature peak on the high temperature side in relation to the temperature of the intrinsic peak inherent in the PP resin, and show an internal pressure drop rate at 25 deg.C and 1atm, k, in the range: k<=0.30. These particles are placed in a molding frame and heat-expanded to produce a molding of the shape of the mold. According to this process, it is possible to obtain a molding having a good surface appearance, excellent dimensional accuracy, and excellent properties such as shrinkage, compressive hardness, compression set, and fusion of particles.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polypropylene resin foam molded article.

The present applicant has conventionally conducted research on a method for manufacturing a foam molded article by a so-called bead molding method in which pre-expanded particles of a polypropylene resin are molded in a mold. usually,
In the above bead molding method, the 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 molding the pre-expanded particles that have been pressure-ripened at Variations in physical properties often occur, and sometimes they result 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 is based on the 080 curve obtained by differential scanning calorimetry of polypyrene resin pre-expanded particles (however, the pre-expanded particles 1 to 3 were heated to 220 C at a heating rate of 10 C/min using a differential scanning calorimetry needle). DS sometimes obtained
C curve a) has a crystal structure in which a high temperature peak appears on the higher temperature side than the characteristic peak unique to polypropylene resin, and 2
The internal pressure decreasing rate coefficient k at 5C, latm is ≦0.
A polypropylene resin foam molded product characterized by imparting foaming ability to the pre-expanded particles of No. 30, then filling the particles into a forming mold, and heating and foaming them to obtain a molded product that passes through the mold. The gist is the manufacturing method.

Preliminaries used in the present invention! ! ii! ! Foam particles 2! I!
: Polypropylene resin is used as the resin,
As the definition, the one specified in JIS-675B-1981 is used. Examples include tetrapyrene homopolymer, ethylene-propylene block copolymer, ethylene-propylene random copolymer, and so-called polymer blends and products in which these polymers are blended with elastomers and 1-olefin polymers.

Examples of elastomers used for blending include:
Examples of 1-olefin polymers include polyisobutylene, ethylene propylene rubber, and polyethylene. Examples of blended products include two-type blends such as glopylene homopolymer/polyisobutylene and propylene copolymer/polyethylene, and three-type blends such as propylene homopolymer/ethylene propylene 2 bar/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 component 0.5
~10vt is preferred.

The pre-expanded particles used in the present invention have a crystal structure in which a high-temperature peak appears on the high-temperature side of the characteristic peak inherent to the polypyrene resin in the 080 curve obtained by differential scanning calorimetry of the particles. The above DSCIllil is the 080 curve obtained when Volip V pyrene resin foam particles 1 to 3 cm are heated to 220C at a heating rate of 10C/min using a differential scanning calorimetry needle. The 080 curve obtained at the time of death by heating up to 220C at a heating rate of 10'C-/B is the first DSCIII line, and then from 220C at a cooling rate of IO'C,A to 4
The temperature was lowered to around 0C, and the temperature was raised again to 220 C1 at a heating rate of /Qt-/min. The DSCa line obtained at the time of death was taken as the second 080 curve, and from these 080 curves, the characteristic 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 during melting of so-called crystals of the polypropylene resin. Usually, the characteristic peak appears in both the first 080 curve and the second 080 curve, and the temperature at the top of the peak may be slightly different between the first and second times, but the difference is less than 5C. Usually less than 2C.

On the other hand, the high temperature peak and forest in the present invention, the first DS
This is an endothermic peak that appears on the high temperature side of the above-mentioned characteristic peak in the Ca curve, and polypropylene resin in-mold foam molded products in which this high temperature peak does not appear on the 080 curve have a high shrinkage rate, compression hardness, compression set rate, and particle size. It is inferior in various eyelid properties such as fusion adhesion, and the dispersion of these physical properties becomes large. The above-mentioned high-temperature peak is thought to be due to the existence of a specific crystal structure that differs from the structure that appears as the above-mentioned characteristic peak, and the high-temperature peak appears clearly in the 080 curve of the first time, but the second time when the temperature was raised under the same conditions. It does not appear on the second 080 curve. Therefore, the high temperature peak is due to the pre-expanded particles used in the present invention.
It appears because it has a crystal structure different from the crystal structure that shows the characteristic peak inherent to polypropylene resin (6J), and when polypropylene resin is foamed under specific foaming conditions, a high temperature peak appears on the 080 curve. Pre-expanded particles with a crystalline structure can be obtained.

It is desirable that the difference between the temperature of the characteristic peak appearing in the second 080 curve and the temperature of the high temperature peak appearing in the first 080 curve is large;
The difference between the temperature at the top of the characteristic peak of the I line and the temperature at the top of the high temperature peak is 5C or more, preferably 10C or more.

Moreover, the high temperature peak is the first peak obtained under the above measurement conditions.
It appears on the second DEC curve, and the second DSC song i1j
! Since IC does not appear, D at the 1st and t42nd times also applies when multiple characteristic peaks may appear in the DSC curve, such as when the base resin of the pre-expanded particles is a mixture.
By comparing the SC 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 have a crystal structure in which a high temperature peak appears in the above DSC curve, and
C, latm Internal pressure decreasing rate coefficient k at K≦0.
The pre-expanded particles should be 30. k) O1
In the case of 30, the shrinkage rate is small and a molded article with excellent dimensional accuracy cannot be obtained. The internal pressure reduction rate coefficient 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, pre-expanded particles of known expansion ratio and weight are filled into a polyethylene bag measuring, for example, 70 mm x 100 mm, with a large number of needle holes, and pressurized with air while holding 25 CK to form pre-expanded particles. After applying internal pressure, the weight of the pre-expanded particles is measured. The pre-expanded particles were then heated to 25C, la
The weight of the pre-expanded particles is measured after 10 minutes of holding at tm. Internal pressure P of pre-expanded particles immediately after applying internal pressure. (
νzono・G) and the internal pressure P+ (KP/c!l・
G) can be requested using the following formula.

(However, the increased air volume is the difference between the particle weight at the time of internal pressure measurement 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, calculate the internal pressure reduction rate coefficient k in the equation below from PO+Pl obtained from the above equation.

Log-! □=-kt O (However, t is time and is 10 minutes in the above case.) The above internal pressure reduction rate coefficient will be ≦0.30 when the number of cells in the expanded particles is small or when the closed cell ratio is high. However, when the closed cell ratio is high and a resin containing a nucleating agent is used, ≦0.30 may not be achieved, which is not preferable.

The pre-expanded particles used in the present invention, which have a crystal structure in which a high-temperature peak appears in the DSC curve and have an internal pressure decrease rate coefficient k≦0.30 at 251r and 1 atm K, have a K as follows. It can be manufactured using

First, as the raw material polypropylene resin particles, resin particles that do not contain crystal nucleating agents, silica, phosphorus stabilizers, etc. that cause the size of bubbles to become fine are selected. 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 (tl') of the volatile blowing agent-containing resin particles and the dispersion medium. is the melting end temperature Tm (U
) without raising the temperature above the following formula: Tm-Tm-20(
T (T (where, the melting end temperature Tm is the end temperature of the endothermic curve obtained when a sample of about 6 to 8 mg is heated at a heating rate of to'c- by the DEC method.) Open one end of the container while maintaining the temperature within the indicated range,
It can be produced by a pre-foaming method that includes a step of simultaneously releasing the resin particles and dispersion medium into a low-pressure atmosphere inside a container.

Examples of the above-mentioned volatile blowing agents include butane, butane,
Aliphatic hydrocarbons exemplified by pentane, hexane, heptane, etc., cyclic aliphatic hydrocarbons exemplified by cyclobutane, cyclopentane, etc., and trichlorofurotetramethane, dichlorodifluoromethane, dichlorotidrafluoroethane, Examples include /%Q-genated hydrocarbons such as methyl chloride, ethyl chloride, methylene chloride, etc., and these blowing agents can be used in combination. The amount of the above blowing agent used is 10 polypropylene resin particles.
It is used in an amount of about 0.04 to 0.20 mol per 0 part by weight.

In this method, the polymer particles and a volatile blowing agent are added to the open side or the volatile blowing agent is contained in the polymer particles and then dispersed in a dispersion medium. Aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc. can be used.

The amount of the dispersant added is usually 0.01 to 10 parts by weight per 100 parts by weight of the polymer particles. The dispersion medium may be any solvent that does not dissolve the polymer particles, such as one of water, ethylene glycol, glycerin, methanol, and ethanol, or a mixture of two or more thereof, but water is usually used. is preferred.

As described above, pre-expanded particles are obtained which have a crystal structure in which a high-temperature peak appears on the DSC 1tll line and have an internal pressure decrease rate coefficient k≦0.30 at 25r, latm. It has an apparent foaming ratio of 5 to 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 varying sizes with an apparent expansion ratio of about 150 times.

In the present invention, foaming ability is imparted to the pre-expanded particles obtained as described above. The foaming ability can be imparted to the pre-expanded particles by using an inorganic gas such as air, nitrogen gas, carbon dioxide, or the like, butane, dichlorodifluoromethane, dichlorotetra-70-ethane, etc. used for foaming the pre-expanded particles. This is done by pressurizing with a volatile blowing agent or a mixed gas of these, but usually air is pressurized and the pre-expanded particles are brought to a pressure above atmospheric pressure, up to 3? /cflIIG or less internal pressure is applied.

Added the above foaming ability (provided with internal pressure higher than atmospheric pressure)
The pre-expanded particles are filled into a mold, heated to foam the pre-expanded particles, and fuse the particles to each other, thereby obtaining a foam molded article with a through-hole shape. The heating means for the above-mentioned molding pot is usually 2°Ky/ctl・G to 5Ky/c.
Water vapor of rl·G is used.

The above polypropylene resin foam molded product has a smooth surface, excellent dimensional accuracy, and particle fusion strength, and also has high compression hardness and
It has excellent physical properties such as compression set rate and shrinkage rate, and the molded product can be used for example in packaging materials, cushioning materials, heat insulating materials, insulation materials, construction materials, vehicle parts, flotation materials, food containers, etc. I can do it.

The present invention will be explained in more detail below by giving Examples and Comparative Examples.

Examples 1 to 5 Base resin 100 layers B) IT (antioxidant) 0.1 part by weight, Irganox toto <oxidant) 0.03 parts by weight, calcium stearate 0.0
5 parts by weight of an ethylene-propylene random copolymer, 0.3 parts by weight of ultrafine aluminum oxide, and dichlorodifluoromethane in the amount shown in Table 1 were placed in a 5-ton autoclave, and the mixture was heated and heated while stirring. After maintaining the foaming temperature shown in the same table for 30 minutes, one end of the container was opened while maintaining the internal pressure of the container at 3oKp/c/l・G using nitrogen gas, and the resin particles and water were brought under atmospheric pressure. The resin particles were discharged and foamed to obtain pre-expanded particles. Table 1 shows the expansion ratio of the obtained pre-expanded particles. In Example 5, the pre-expanded particles obtained by foaming in Example 2 were further pressurized with air, and then heated twice (returning was performed to expand the particles 65 times).
It is a magnification. Table 1 shows the results of internal pressure reduction rate coefficient and differential scanning calorimetry of the obtained pre-expanded particles, and the DSC curve of the pre-expanded particles of Example 3 is shown in Fig. 1 (in Fig. 1, a1 Color 1 indicates the characteristic peak, b indicates the high temperature peak, the solid line is the first DSC curve, and the dotted line is the second concave DSC1!lI heave.)

Next, these pre-expanded particles were pressurized with air to give the particles the internal pressure shown in Table 2, and then heated for 300 hours x 300 hours x
Fill a mold with a diameter of 50 mm (mold inner diameter) and produce 28 to 3.5 KP/
cn! - The pre-expanded particles were foamed by heating with G steam to obtain a foamed molded product. After leaving the obtained molded body in a 55U open environment 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-tetrapyrene random copolymer particles as in Example, 300 parts by weight of water, 0.3 parts by weight of ultrafine aluminum oxide, and the amount of dichlorosiflomethane shown in Table 1 were placed in a 5-ton autoclave. After heating up the container to the maximum temperature shown in the same table, the temperature was lowered to 140C and held for 15 minutes, and then nitrogen gas was introduced to reduce the container internal pressure to 3.
The container was opened while maintaining the pressure at 0.2/crl-G, and 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 1. Further, the DSC line 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,
a and a' indicate unique peaks. ).

Next, after applying the internal pressure shown in Table 2 to the pre-expanded particles, they were molded in the same manner as in the examples to obtain molded bodies. Table 2 shows the physical properties of the molded product obtained.

Comparative Examples 2 to 3 0.2 parts by weight of dibenzylidene sorbitol (crystal nucleating agent) was added in Comparative Example 2, and 0.2 parts by weight of silica (antiblocking agent) was added in Comparative Example 3 to 100 parts by weight of the base resin. Ethylene-tetrapyrene random copolymer particles (same ethylene component, melt index, Tm as in Example)
has. ) 300 parts by weight of 100 Chokei Chokeisui, 0.3 parts by weight of ultrafine aluminum oxide, and the amount of dichlorosifuromethane shown in Table 1 were placed in a 5 ton autoclave, and while stirring, the temperature in the container was higher than the maximum temperature shown in the same table. After holding at 137C for 30 minutes without raising the temperature of the button, the resin particles and water were discharged to atmospheric pressure in the same manner as in Examples to obtain pre-expanded particles. The results of the expansion ratio, internal pressure reduction rate coefficient measurement, and differential scanning calorimetry [1114 measurement] of the obtained pre-expanded particles are shown in Table 1.

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.

*1 ΔT is the temperature difference between the high temperature peak temperature and the characteristic peak temperature.

*2 Measured according to JIS-6767 method, and determined that the value of compressive hardness/density is 25 or more...O Less than 25...×

*a Measured according to JIs-ic6r6vtai, compression set rate is less than 15q6...0 15 inches or more, less than 30 inches...Δ30 inches or more...
It was determined as ・・・・・・×.

4 Shrinkage rate of the molded body in the plane direction with respect to the mold (2))
Measured, less than 3%...0 3t or more, less than 5%...Δ5t or more...
It was determined as ・・・・・・×.

*5 Observe the condition of the surface of the molded product and find that there is no shrinkage on the surface......OI
Shrinkage/footing...Δ 〃 Severe shrinkage...Judged as ×.

*6 Only material failure of the molded body occurs when the tensile strength test is conducted using the JIS-6?67A method.
...○l material failure and interparticle failure occur...
Only interparticle destruction of Δl occurs...
...It was determined as ×.

As explained above, the present invention provides a polypropylene resin reserve which has a crystal structure in which a high temperature peak appears in a DSC curve obtained by differential scanning calorimetry, and has an internal pressure reduction rate coefficient k≦0.30 at 25C, latm. After imparting foaming ability to foamed particles, the particles are filled into a mold and foam-molded to obtain a molded product. rate,
'It has tremendous effects such as being able to obtain molded bodies with excellent physical properties such as compression hardness, compression set rate, and particle fusion properties.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the 080 curve of pre-expanded particles of gIl Example 3, and FIG. 2 is a graph showing the 080 curve of pre-expanded particles of Comparative Example 1.
It is a graph showing a curve. @, a+...Four unique peaks b...Yuyu...High temperature peak

Claims (1)

[Claims] DEC curve obtained by differential scanning calorimetry of polypropylene resin pre-expanded particles (pre-expanded particles 1 to
DSC song M obtained when 1g of 3ff is heated at 2200t at a heating rate of 10C/min using a differential scanning calorimeter.
25U,
At latm, the internal pressure decrease rate coefficient k≦0.30
Production of a polypropylene resin foam molded product, which is characterized by imparting foaming ability to pre-expanded particles, then filling the particles into a mold, and heating and foaming them to obtain a molded product that can pass through the mold. Method.