JPH08259724A - Expanded polypropylene-based resin particle and its production - Google Patents

Abstract

PURPOSE: To obtain high-quality expanded particles which have almost an invariable expansion ratio even when the expanding temperature somewhat varies, is excellent in moldability, etc., because the temperature control in the expansion step is easy and the expansion ratio is constant, and have a high expansion ratio. CONSTITUTION: In the expanded polypropylene resin particles, the resin contains 3-10wt.% ethylene and/or butene-1 as comonomer component, the ratio Mz/Mw is 1.5-2.5 (wherein Mz is the Z-average molecular weight of the resin, and Mw is its weight-average molecular weight, and the expanded resin particles have secondary crystals having a melting energy of 11-30J/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expanded polypropylene resin particles and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, polypropylene resin particles containing a volatile organic foaming agent are dispersed in an aqueous medium,
A method is known in which the pressure in the container is heated to the softening temperature or higher of the resin while maintaining the pressure equal to or higher than the vapor pressure of the foaming agent, and then the resin is discharged from the pressurized container into a low-pressure atmosphere to foam. Volatile organic foaming agents in this case are propane, butane, pentane, trichlorofluoromethane, dichlorodifluoromethane, etc., but such organic foaming agents are often toxic or flammable, and therefore dangerous. Even organic foaming agents that are scarcely used are often expensive and have practical problems. In addition, the foaming agent causes environmental pollution problems such as destruction of the ozone layer when it is released into the atmosphere, and swells the resin particles, so that the foaming temperature range during foaming is narrowed. There is a problem such as a large change. Further, the use of expanded particles having a significantly different expansion ratio lowers the moldability of expanded particles. From this point as well, new expanded particles and a method for producing new expanded particles are desired.

Research has been conducted in various fields to solve the above-mentioned problems, and the inventors of the present invention have also used a method of using an inorganic gas as a foaming agent and a method of reducing the amount of a volatile organic foaming agent used. About. For example, a method for producing expanded resin particles using carbon dioxide as a blowing agent (Japanese Patent Publication No. 62-612).
No. 27); a crystal nucleating agent such as dibenzylidene sorbitol is added to polypropylene-based resin particles to reduce the amount of volatile organic foaming agent used when foaming the resin particles, or volatile organic foaming agent. Together with a method of using an inorganic gas such as nitrogen as a foaming agent (Japanese Patent Publication No. 5-10374); when an inorganic substance such as aluminum hydroxide or calcium carbonate is added to polypropylene resin particles, thereby foaming the resin particles The amount of the volatile organic foaming agent used is reduced, or an inorganic gas such as nitrogen is used as the foaming agent together with the volatile organic foaming agent (JP-A-61-473).
No. 8); and so on.

The above-mentioned method of using an inorganic gas-based foaming agent, or a method of reducing the amount of a volatile organic foaming agent or allowing the combined use of the foaming agent and an inorganic gas-based foaming agent is advantageous from the viewpoint of environmental protection. Is large and the swelling of the resin particles is suppressed,
It was expected that the proper foaming temperature range during foaming would be expanded.
However, since the plasticizing effect of the resin particles and the gas permeation rate into the resin particles are greatly different between the volatile organic foaming agent and the inorganic gas, even if the above-mentioned method using an inorganic gas-based foaming agent is adopted, it is slightly It has been found that there are many problems in producing a high-quality foam having a high expansion ratio and a constant expansion ratio because it is not possible to eliminate the fluctuation of the expansion ratio due to such a difference in foaming temperature.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems encountered in the production of expanded polypropylene resin particles, and the expansion ratio hardly changes even if the expansion temperature slightly fluctuates. It is an object of the present invention to provide high-quality foamed particles which are easy to control in the process temperature and have a constant expansion ratio so that they have excellent moldability and a high expansion ratio, and a method for producing the same.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, in the polypropylene resin expanded particles, ethylene and / or butene-1 as a comonomer component is contained in the resin in an amount of 3 to 10% by weight, and the Z average molecular weight Mz and the weight average molecular weight of the resin are also included. The ratio Mz / Mw of Mw is in the range of 1.5 to 2.5,
There is provided a polypropylene-based resin expanded particle having a melting energy of 11 to 30 J / g and a secondary crystal thereof, and a method for producing the same.

The inventors of the present invention investigated a large number of commercially available polypropylene resins, and found that the ratio Mz / Mw of the Z-average molecular weight Mz and the weight-average molecular weight Mw was 1.5 to 2.5, particularly 1.7 to 2. It was found that the resin of No. 4 had almost no change in the expansion ratio even if the expansion temperature was slightly different, and the present invention could be completed based on this result. Note that Mz and Mw are values defined by the following equations (1) and (2), and Mi in the equation
Represents the molecular weight of the i-th molecule contained in the resin, and Ni represents the number of molecules. Mz = ΣMi ³ Ni / ΣMi ² Ni (1) Mw = ΣMi ² Ni / ΣMiNi (2) As can be seen from the equations (1) and (2), Mz / Mw can be said to be an index showing the molecular weight distribution. Generally, this value is 3 or more in polypropylene-based resin for producing expanded beads. Therefore, the polypropylene resin used in the present invention having this value of 1.5 to 2.5 has a narrower molecular weight distribution in the high molecular weight region than general products as shown in FIG. That is, FIG.
The molecular weight distribution in the high molecular weight region is narrower than the general product only in the shaded area shown in. The horizontal axis of FIG. 1 is the logarithmic value of the molecular weight, and the vertical axis is the weight%.

Mz and Mw are defined as above,
Actual Mz and Mw measurements are made by gel permeation chromatography (GPC). In this specification, GPC150C manufactured by Waters is used, o-dichlorobenzene is used as a solvent for polypropylene resin particles, and Mz and Mw measured under the following conditions are adopted. Column GPC AT-807 / S (Shodex manufactured by Showa Denko KK) Column temperature 135 ° C. Injection temperature 135 ° C. Pump temperature 55 ° C. Sensitivity 64 Solvent amount 1.0 ml / min Injection volume 100 μl Running time 30 minutes In addition, the number average molecular weight Mn is also above. It can be similarly determined by GPC.

As described above, the expanded particles of the present invention are expanded particles having secondary crystals, but the secondary crystals are formed only in expanded particles produced under specific expansion conditions, and are formed in all expanded particles. It is not something that will be done. The expanded particles of the present invention are expanded particles in which secondary crystals are formed by the method described below. The presence or absence of secondary crystals is determined by the DSC curve obtained by differential scanning calorimetry of expanded particles. D
The SC curve shows, for example, polypropylene foamed resin particles 2 to
4 mg was used as a sample, which was measured by a differential scanning calorimeter to 10
It is determined by a method of raising the temperature from room temperature to 220 ° C. at a rate of ° C./min. Specifically, the sample was heated from room temperature to 220 ° C. at a rate of 10 ° C./min, and the first DS shown in FIG.
When the C curve was obtained, the temperature was lowered to about 40 ° C. at the above rate, and then the temperature was raised to 220 ° C. at the above rate again to obtain the second DSC curve shown in FIG.
If there is an endothermic peak on the high temperature side (high temperature peak) observed only in the C curve, it is determined that there is a secondary crystal. The peaks on the low temperature side observed in both DSC curves of FIG. 2 and FIG. 3 are called intrinsic peaks, which are melting endothermic peaks specific to the resin.

When the presence or absence of secondary crystals is determined by the above method, the high temperature peak does not exist in the second DSC curve because the sample is heated to 220 ° C., which is higher than the melting end temperature of the sample. This is because all the crystals in the sample are melted, and the cooling rate of the melted sample exceeds the range of the cooling rate required for secondary crystal formation. Further, the melting energy of the secondary crystal (hereinafter, this energy is abbreviated as SCME) is the energy obtained from the DSC curve forming the high temperature peak, and is the energy corresponding to the area shown by the diagonal line in FIG. is there. That is, in FIG. 2, the point at the temperature of 80 ° C. on the DSC curve is A, the melting end point on the DSC curve is B, and the perpendicular line drawn from the valley portion C between the high temperature peak and the characteristic peak to the line segment AB. When the intersection between the line segment AB and the line segment AB is D, the energy corresponding to the area of the portion surrounded by the line segment DB, the line segment DC, and the DSC curve is SCME. The expanded polypropylene resin particles of the present invention have SCME of 11 to 30 J / g, preferably 13 to 2
The SCME represents the amount of energy required for melting all the secondary crystals contained in 1 g of the resin.

The resin having a narrow molecular weight distribution in the high molecular weight region used in the present invention is a resin in which a general polypropylene copolymer resin is oxidatively decomposed with an organic peroxide such as peroxide to thereby narrow the high molecular weight region. And, and
By appropriately adjusting the amount of decomposition, it is possible to control the high molecular weight region. It seems that decomposition of polypropylene resin with peroxide to reduce the value of Mz may be carried out when it is used as a raw material for polypropylene fiber in the field of textile industry. Index (MI) is 80 [g / 10min]
However, when such a material is used as the raw material resin particle of the expanded particle, it becomes a particle exhibiting open cells and a good particle cannot be obtained. Further, the polypropylene-based copolymer resin used in the present invention has Mz of 3 × 1.
0 ^{5 to} 5 × 10 ⁵ , preferably 3.5 × 10 ^{5 to} 4.5 ×
The ratio Mw / Mn of Mw to the number average molecular weight Mn at 10 ⁵ is 4.
The resin is 5 or less, preferably 3.5 or less. The polypropylene-based copolymer resin suitable for the expanded particle raw material of the present invention is a foamed particle because the molecular weight distribution and the like change only within an error range even when foamed, or even when it is molded into an expanded particle molded article. Alternatively, it can be said that Mz, Mw and Mn of the resin forming the expanded particle molded body are the same as those of the raw material resin.

The polypropylene copolymer resin used as the raw material for the expanded beads in the present invention is a resin having a melt index (hereinafter abbreviated as MI) of 3 to 20 g / 10 min, preferably 5 to 14 g / 10 min. is there. When the MI is in this range, the expansion ratio and the closed cell ratio are high, and the cell diameter is 70 to 35.
A good expanded particle of 0 μm can be easily obtained, and therefore the moldability of the expanded particle is improved. And the MI of the raw material resin is 3
If it is less than g / 10 minutes, the expansion ratio does not improve and MI is 20 g.
If it exceeds / min, the cells become finer and the closed cell rate decreases, which reduces the moldability of the expanded beads. In this specification, the MI value obtained under the test conditions of the test temperature of 230 ° C. and the test load of 2.16 Kgf specified in JISK-7210 is adopted. The expansion ratio is the ratio by which the apparent volume of the base resin increases due to expansion,
In this specification, the expanded density is obtained by dividing the expanded resin weight by dividing the expanded particle weight by the apparent volume indicated by the scale of the graduated cylinder by inserting the expanded particles into the graduated cylinder, and dividing the base resin density by the bulk density to obtain the expansion ratio. calculate.

The polypropylene resin has an Mz / Mw value of 1.5 to 2.5, preferably 1.7 to 2.4.
It is possible to reduce the fluctuation range of the foaming ratio due to the fluctuation of the foaming temperature. The reason for this is unclear, but according to the detailed study by the present inventors, this effect is surprisingly large, and an example of the effect is shown in FIG. This figure is
FIG. 3 is a diagram showing a relationship between a foaming temperature and a foaming ratio when the foaming conditions such as a foaming agent are the same, where 1 is a resin used in the present invention having Mz / Mw of 2.3, and 2 is Mz
When a resin having a Mz / Mw of 3.3 is used, 3 is a resin having a Mz / Mw of 3.2, and 4 is a resin having a Mz / Mw of 2.7. As can be seen from the figure, the foaming temperature and the foaming ratio are in proportion to each other, and the constant of proportionality greatly differs depending on the type of resin. When the polypropylene-based copolymer resin having Mz / Mw of 3.2 is foamed, the foaming temperature is 1
Expansion ratios of 7.5 and 1 at 42 ° C and 145 ° C, respectively.
However, in the resin used in the present invention having Mz / Mw of 2.3, the expansion ratios are 26 and 27 at the foaming temperature, respectively, and there is almost no difference in the expansion ratio.

As can be seen from FIG. 4, the polypropylene-based copolymer resin used in the present invention is easier to foam than ordinary homogenous resins, and the foaming ratio of ordinary resin is about 15 times and around 144 ° C. At times, the resin used in the present invention has a foaming ratio of 25 times or more. Therefore, according to the present invention, it is possible to obtain a foamed resin with a stable expansion ratio even if the foaming temperature varies to some extent, and to obtain a high expansion ratio even when foamed at a lower temperature than when using a conventional polypropylene resin for producing expanded particles. It can be seen that particles are obtained. We have Mz / Mw
Of the polypropylene-based copolymer resin of 1.5 to 2.5, the physical properties of the expanded beads obtained from the copolymer resin are delicately varied depending on the kind and amount of the comonomer component contained in the copolymer. I found that it changed. That is,
When the polypropylene-based copolymer resin having a comonomer component content of ethylene and / or butene-1 in the range of 3 to 10% by weight, preferably 3.5 to 6% by weight is used, the foaming temperature may be slightly different. Expanded particles containing secondary crystals having the same SCME even if dispersed are obtained. Then, when the foamed particles are aged and molded in a mold to produce a molded article,
Since the secondary foaming property during aging molding is good, there is little shrinkage, and therefore the surface is smooth and high quality molded products can be obtained.

The expanded particles of the present invention have an expansion ratio of 5 to 10.
The expanded particles have secondary crystals at 0 times. And SCM
E is 11 to 30 J / g, preferably 13 to 25 J / g of expanded particles, and when SCME is too large, the secondary foaming property is lowered during molding processing of the expanded particles, and when it is too small, the expanded particles shrink. There is a problem such as. Further, the expanded particles of the present invention preferably have an expansion ratio change amount per SCME of 1 J / g of −.
0.6 to -0.08 g / J, more preferably -0.3 to
-0.08 g / J of expanded particles, and this value was -0.6
If it is less than g / J, the expansion ratio greatly changes due to a slight difference in SCME, and thus the expansion ratio of the obtained expanded particles becomes large. It is more preferable that this value exceeds −0.08 g / J and approaches 0, but such expanded particles cannot be obtained. It is presumed that the secondary crystal is formed by the secondary growth generated on the crystal surface after the formation of the primary crystal, and the resin in the molten state is melted to the melting end temperature (the secondary crystallization in this temperature range). A secondary crystal is formed by heat treatment in the accelerated temperature range). Therefore, when the molten resin is cooled or heated at a low rate of 5 ° C./min or less, or when the resin without secondary crystals is kept in the temperature range for 5 minutes or more, preferably 5 to 30 minutes, secondary crystals are formed. .

In SCME, the heating and cooling rates for the purpose of forming secondary crystals are slowed down; the time during which the resin is held at the secondary crystal accelerating temperature is prolonged; the foaming temperature is lowered; can do. On the other hand, if the above method is performed in reverse, SCME is lowered, and, for example, if the foaming temperature is raised, SCME is lowered. As described above, when the foaming temperature is low, SCME increases, and both are proportional with a negative proportional constant. The proportional constant between the two greatly varies depending on the type of resin, and the resin used in the present invention has a significantly smaller absolute value (gradient) of the proportional constant than the conventional product. Further, as can be seen from FIG. 4, since the foaming temperature and the foaming ratio are proportional with a positive proportional constant, it is clear that SCME and the foaming ratio also have a proportional relationship with a negative comparative example constant. According to the research conducted by the present inventors, the two have a proportional relationship with a negative slope. That is, SC is used for expanded particles with a high expansion ratio.
Secondary crystals with a small ME are formed, and secondary crystals with a large SCME are formed on the expanded beads having a low expansion ratio. Note that the proportional constant between SCME and the expansion ratio is also the expansion temperature and SC
Like the proportionality constant between MEs, the resin used in the present invention has a significantly smaller absolute value than conventional products.

As described in detail above, the foaming temperature and the SCM
There is a proportional relationship with a negative proportional constant between E and between SCME and the expansion ratio, which is shown in FIGS. These figures are obtained by using the same resin as in FIG. 4 and using the same foaming conditions such as a foaming agent as in the case of FIG. The reference numerals on the straight lines are the same as those in FIG. 4, and the straight line 1 is the case where the resin used in the present invention has Mz / Mw of 2.3. Further, even if the base resin is the same, if the foaming conditions such as the type and amount of the foaming agent are different, the positions of the straight lines shown in FIGS. 4 to 6 are different, but in this case as well, the slopes (proportional constants) of the straight lines are almost the same. is there. Therefore, it can be said that the linear gradients shown in FIGS. 4 to 6 are important factors showing the relationship between the foamability and moldability of the resin expanded particles and the type of resin, and it is preferable that this gradient be close to zero. As can be seen from FIG. 6, the expansion ratio of the present invention does not decrease significantly even if SCME is large,
The expanded particles have little correlation between SCME and expansion ratio.
Therefore, in the expanded beads of the present invention, SC
ME is kept high, and when SCME is small, shrinkage of the foamed particles generated is small, so that a high-quality molded product having a smooth surface can be manufactured. The reason why the expanded particles tend to shrink when SCME is small is not exactly known, but the secondary structure of the expanded particles, and the polymer structure related to the shrinkability are SC.
The ME will influence.

Change in foaming ratio V per SCME 1 J / g V
Can be obtained from FIG. That is, if the expansion ratio and SCME at point A on the straight line 1 in FIG. 6 are B ₁ and G _1, and that at point B is B ₂ and G ₂ , then V = (B ₂
Represented by _{-B 1) / (G 2 -G} 2). Since it is preferable to measure V on high-quality expanded particles having a high expansion ratio, it may be determined from expanded particles produced under the following conditions, for example. In addition, in the case of measuring the expanded particles formed by the two-step expansion in which the expanded particles are further expanded, the following conditions may be applied in addition to the following conditions. [I] Foaming ratio B ₁ and SCMEG ₁ J / g foamed particle production conditions Base resin (can contain inorganic substances) 100 parts by weight Water (dispersion medium) 220 parts by weight Kaolin (anti-fusion agent) 0.5 parts by weight Dodecyl Sodium benzenesulfonate (adhesion-prevention aid) 0.006 parts by weight Carbon dioxide (foaming agent) 8 parts by weight Temperature rising rate 2 ° C / min Holding temperature 141 ° C Holding time 15 minutes Foaming temperature 147 ° C Foaming temperature holding time 15 Minute [II] Conditions for producing expanded particles with expansion ratio B ₂ and SCMEG ₂ J / g Same as [I] except that the expansion temperature is 143 ° C.

As described above, the foamed particles of the present invention are foamed particles which do not significantly reduce the SCME as in the conventional products even when the foaming temperature is high, and therefore, they do not shrink much even in the case of high foaming. It is an expanded particle. Since such expanded particles have good moldability, even if an attempt is made to produce expanded particles having similar performance to the expanded particles of the present invention using a conventional resin, in this case, a large amount of a foaming agent is used, resulting in high cost. In addition, it is difficult to sufficiently solve the problem of shrinkage of expanded particles. Therefore, it can be said that the expanded particles of the present invention are high-performance expanded particles that cannot be predicted from conventional products. Also,
Expanded particles in which the peak temperature of the unique peak appearing in the second DSC curve (a in FIG. 3) is lower than the peak temperature of the high temperature peak appearing in the first DSC curve by 5 ° C. or more, particularly 10 ° C. or more. Then, it is recognized that the secondary crystal is difficult to melt. Therefore, in this case, the secondary crystals are difficult to melt even if the foaming temperature is high, and thus foamed particles having a high expansion ratio and good moldability can be obtained.

In the present invention, the polypropylene-based copolymer resin having the above-mentioned Mz / Mw and the amount of comonomer components in a specific range may be used as the base resin, and the base resin may be crosslinked or non-crosslinked. However, it is preferable to use a non-crosslinked product in consideration of the recycling and the like. Specific examples of the resin suitable as the base resin in the present invention include propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer, propylene-butene block copolymer, and propylene. -Ethylene-butene terpolymer and the like. And among these, propylene-ethylene random copolymer, propylene-butene random copolymer and propylene-ethylene-
The butene terpolymer is preferable because it has excellent physical properties required for a molded article such as low-temperature brittleness and flexibility, and is particularly preferably 3.5.
Copolymers containing up to 6.0% by weight of ethylene are preferred. When the rigidity of the molded product is strongly required, a copolymer having a high butene content and an ethylene content of 3.0% by weight or less is preferably used as the base resin. Next, the auxiliary materials and the foaming method necessary for producing the expanded beads of the present invention will be specifically described, but these are the same as in the conventional production of expanded beads.

In the present invention, an anti-fusing agent can be used to prevent fusion when heating the polypropylene copolymer resin. The anti-fusing agent may be organic or inorganic as long as it is substantially infusible when heated, but an inorganic material is usually preferable. Typical anti-fusing agents include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, tricalcium phosphate, magnesium pyrophosphate, talc, mica, kaolin and the like. . These anti-fusion agents generally have a particle size of 0.001 to 100 μm,
It is preferably used in the form of fine particles of 0.001 to 30 μm. Further, the addition amount thereof is generally in the range of 0.01 to 10 parts by weight per 100 parts by weight of the resin particles.
The anti-fusion agent detailed above can further enhance the effect when used in combination with an emulsifier such as sodium dodecylbenzene sulfonate or sodium oleate. As the emulsifier, an anionic surfactant is preferable, and the addition amount thereof is generally 0.001 to 5 parts by weight per 100 parts by weight of the resin particles.

In the present invention, a volatile organic foaming agent or an inorganic gas foaming agent is used as the foaming agent, and both may be used together. And, as the organic foaming agent, propane, butane, pentane,
Known products such as hexane, cyclobutane, cyclohexane, dichlorodifluoromethane, trichlorofluoromethane,
As the inorganic gas foaming agent, various room temperature gaseous inorganic substances such as nitrogen, air, carbon dioxide, argon and helium can be used. The amount of the organic foaming agent used is 10% by weight of the resin.
It is 2 to 25 parts, preferably 3 to 20 parts per 0 part. When the inorganic gas is used as the foaming agent, the amount of the above-mentioned foaming agent except nitrogen and air is 2 to 50 parts per 100 parts by weight of the resin, and nitrogen and air have a container internal pressure of 15 to 70 kg /
It is desirable to supply into the container so as to be cm ² G, preferably 20 to 50 kg / cm ² G. Of the above, the use of a blowing agent made of an inorganic gas or a mixture of an inorganic gas and a volatile organic blowing agent reduces the amount of the volatile organic blowing agent used, which is preferable in terms of safety. Further, when a mixture of an inorganic gas and a volatile organic foaming agent is used as the foaming agent, there is an advantage that the expansion ratio becomes higher than when only the inorganic gas is used as the foaming agent. Further, when only the inorganic gas is used as the foaming agent, the fluctuation range of the foaming ratio becomes small, so that the reduction of the foaming ratio of the foamed particles obtained in the latter stage of the foaming process, which is observed when using the volatile organic foaming agent, is suppressed.

When resin particles are impregnated with an inorganic gas or a mixture of an inorganic gas and a volatile organic foaming agent, the time for impregnating the resin particles with the foaming agent varies depending on the temperature and the pressure, but is higher than the melting point of the resin. In this case, it may be several tens of seconds to one hour, and usually 5 to 30 minutes is desirable. And
Since it is sufficient to impregnate the resin particles with the foaming agent at any time, immediately after filling the resin particles and the like into the container, during the temperature rise of the container contents or when the container contents reach the foaming temperature, etc. Can be done. When the volatile organic compound is used as the foaming agent, the step of impregnating the resin particles with the organic foaming agent may be performed before or after the step of dispersing the resin particles in the dispersion medium.
Usually, it is performed at the same time when the resin particles are dispersed in the dispersion medium. Then, according to this method, it is considered that the organic foaming agent is once dissolved or dispersed in the dispersion medium and then impregnated into the resin particles.
Specifically, it is sufficient to put a desired amount of resin particles, a dispersion medium, and an organic foaming agent in a pressure-resistant container, heat and stir the container after sealing the container to impregnate the resin particles with the organic foaming agent. The time varies depending on the impregnation temperature and the like, but usually 1 to 60 minutes,
It is preferably 5 to 30 minutes.

The dispersion medium used in the present invention may be any liquid which does not dissolve the polypropylene resin particles, and an aqueous medium such as water, ethylene glycol, glycerin, methanol or ethanol can be used, but usually water is used. used. The amount of the dispersion medium used is not particularly limited, but is usually 1.5 to 3 times the weight of the resin particles. The polypropylene-based copolymer resin particles used in the present invention have Mz /
Resin particles having Mw of 1.5 to 2.5 and containing 3 to 10% by weight of ethylene and / or butene-1 as a comonomer component. And its shape is a particle size of 0.3-5 mm,
It is preferably 0.5 to 3 mm in particle form. Further, fine particles of an inorganic substance, a crystal nucleating agent such as dibenzylidene sorbitol, or the like may be added to the resin particles, and the addition of these may improve the foamability and the moldability of the foamed particles.

In the present invention, fine powders of inorganic substances suitable for addition to resin particles are exemplified by hydroxides such as aluminum hydroxide, calcium hydroxide and magnesium hydroxide; calcium carbonate, magnesium carbonate, barium carbonate and the like. Carbonate; Sulfite such as calcium sulfite and magnesium sulfite; Sulfate such as calcium sulfate, aluminum sulfate, manganese sulfate and nickel sulfate; calcium oxide,
Oxides such as aluminum oxide and silicon oxide; chlorides such as sodium chloride, magnesium chloride, calcium chloride;
Fine powder of borax, talc, clay, kaolin, clay such as zeolite or natural minerals; These have a particle size of 0.
It is desirable that it is in the form of fine powder having a size of 1 to 100 μm, preferably 1 to 15 μm, and the inorganic fine powder may be added alone or as a mixture of two or more kinds. Further, these inorganic fine powders may be added at the time of granulating the polypropylene-based copolymer resin particles,
The addition is preferably done in a masterbatch.

The amount of the inorganic fine powder added varies depending on the type of the inorganic fine powder, but is generally 0.001 to 5%, preferably 0.002 to 3% by weight of the resin. And, when the inorganic fine powder is talc fine powder, 0.003 to 0.5 wt% is particularly preferable; when it is borax, aluminum hydroxide and zeolite fine powder, 0.1 to 2 wt% is particularly preferable. By the addition of the above-mentioned inorganic fine powder, in addition to improving the foaming performance in the production of foamed particles as described above, it is expected that the foamability of the foamed particles will be improved by making the foamed particles uniform and having the desired foamed diameter. it can. However, if the inorganic fine powder is added in an amount of more than 5% by weight, the moldability of the expanded beads is deteriorated, and if the addition amount is less than 0.001% by weight, the above effect is not sufficiently exhibited.

The expanded polypropylene resin particles of the present invention are prepared by charging the polypropylene copolymer resin particles, the anti-fusing agent and an aqueous medium (usually water) in a pressure resistant container, and in the presence of the expansion agent, up to the expansion temperature. After heating, the contents of the container are discharged from the pressure zone to the low pressure zone (usually atmospheric pressure), thereby foaming the resin particles impregnated with the blowing agent. The foaming temperature is generally a temperature above the softening point of the resin, and if the temperature is below the apex temperature of the high temperature peak (b in FIG. 2), foamed particles with good moldability can be easily obtained. The peak temperature of the high temperature peak is generally 5 to 20 ° C. higher than the melting point shown in FIG. The softening temperature is based on ASTM-D648 and the load is 4.6 kg.
Temperature measured in / cm ² . Although a suitable foaming temperature range varies depending on the type of resin and the type of foaming agent, it is preferably close to the melting point of the resin, and in the case of the non-crosslinked polypropylene copolymer resin, it is in the range of 5 ° C to 15 ° C higher than the melting point, preferably 3 ° C. It is in the range of ℃ low temperature to 10 ℃ high temperature. The rate of temperature increase when raising the contents of the container from room temperature to the foaming temperature is not particularly limited, but is about 1 to 10 ° C./minute, particularly 2 to 5 ° C./minute.
Minutes are preferred. When the temperature rising rate exceeds 5 ° C / minute, it is necessary to hold the contents of the container at the secondary crystallization promoting temperature for 5 minutes or more. In order to stably form crystals, it is preferable to hold the contents of the container at the secondary crystallization promoting temperature for 5 minutes or more.

[0028]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The following parts and% are based on weight.

Example 1 and Comparative Examples 1 to 5 100 parts of ethylene-propylene random copolymer resin shown in Table 1 below and 0.05 part of aluminum hydroxide having an average particle size of 3 μm were charged in an extruder and melted. After kneading, the mixture was extruded in a strand form from a die at the tip of the extruder, rapidly cooled in water and then cut to prepare pellets having a length of 2.5 mm and a cross-sectional diameter of 1 mm. The addition of aluminum hydroxide was performed by a masterbatch.

[Table 1]

100 kg of the pellets, 200 liters of water, 300 g of kaolin, and 7 kg of carbon dioxide were placed in a closed container having an internal volume of 400 liters, and the mixture was stirred.
The temperature was raised to the holding temperature shown in Table 2 at a rate of ° C / min, and this temperature was held for 15 minutes. Then, in Table 2 at a rate of 2 ° C / min.
The temperature was raised to the bubbling temperature shown in (1) and held at this temperature for 15 minutes. 40 kg / cm ² (G) of carbon dioxide was added to the contents of the closed container obtained as described above while maintaining the foaming temperature.
A back pressure was applied to prevent the pressure inside the closed container from dropping sharply, and then one end of the container was opened to release the contents under atmospheric pressure to produce expanded particles. Table 2 shows the average expansion ratio (bulk ratio) of the obtained expanded particles, the melting energy (SCME) of the secondary crystal, the average cell diameter, and the moldability of the expanded particles. In addition, SCME 1 obtained by the above method
Amount of change in foaming ratio per J / g V [(B ₂ −B ₁ ) / (G ₂
-Amount represented by G ₁ )] is also shown in Table 2. The moldability of the expanded beads was evaluated according to the following criteria.

1. Dimensional accuracy Charge the foamed particles into a mold and use 3.2 kg / cm
² (G) was heat-molded by steam to prepare a plate-shaped molded body having a length of 30 cm, a width of 30 cm and a thickness of 5 cm. This plate-shaped molded body is aged in an oven at 60 ° C. for 24 hours, and the shrinkage rate in the surface direction is measured by averaging the changes in the centerline lengths in the longitudinal and transverse directions before and after the curing. Contraction rate 3
% And less than 4% are represented by Δ, and shrinkage ratio of 4% or more are represented by X. 2. Fusing Property The plate-shaped formed body produced by the above method is cut so that the vertical cross section in the width direction has a thickness of 1 cm and a width of 5 cm to produce a sample, and this sample is manufactured by Toyo Baldwin UTMIII.
With a tensile tester, pull in the longitudinal direction at a chuck distance of 50 mm and a pulling speed of 500 mm / min until it breaks,
When the fracture surface is visually observed and the material destruction of the fracture surface is 60% or more, ○; when the material fracture of the fracture surface is 40% or more and less than 60%, Δ: the material fracture of the fracture surface is less than 40% The case is represented by X. 3. Secondary foaming property The surface condition of the plate-shaped molded product produced by the above method is visually observed, and ○ when the surface has little unevenness; Δ when the surface has partial unevenness; unevenness on the entire surface The case where there is is represented by X. 4. Comprehensive evaluation The above evaluation was performed on a sample of foamed particles that were foamed at various foaming temperatures as a raw material, and this was used as a molded product. The case where both are preferable is represented by O; the case where there is some problem is represented by X.

[0032]

[Table 2]

It can be seen from Table 2 that the expanded particles of the present invention have a small change in expansion ratio and exhibit good moldability even if the holding temperature or the expanding temperature is slightly different, but the expanded particles of the comparative example have a holding temperature or an expanding temperature of 2 or more. It can be seen that the foaming ratio fluctuates greatly and the moldability is significantly reduced only by a change of 3 ° C. It is considered that this variation is because the value of SCME varies greatly depending on the temperature. Further, even if the ethylene contents are almost the same, if Mz / Mw exceeds 2.5, the maximum value of the ultimate expansion ratio in the expanded particles having good dimensional accuracy, fusion property, and secondary expandability is inferior to that of the present invention. Is recognized. These phenomena show that the moldability changes drastically with a slight change in the polymer structure, which is closely related to the moldability, but the polymer physical properties are different even if a part of the structure that is less related to the moldability changes. , It is difficult to uniquely evaluate the moldability of expanded beads from the physical properties of polymers. Therefore, as shown in the claims of the present invention, by narrowing down the base resin as the raw material of the expanded particles from various aspects such as chemical composition and physical properties, the raw material resin of the expanded particles having good moldability and expandability can be obtained for the first time. Can be reached.

[0034]

EFFECT OF THE INVENTION The expanded beads of claim 1 are expanded polypropylene resin particles having a higher expansion ratio than conventional ones even if the expansion temperature or the like changes to some extent. The foamed particles are foamed particles having a good secondary foaming property and capable of easily producing a high-quality molded product having a smooth surface. Further, the expanded particles can be obtained with a high expansion ratio even if the expansion temperature is low. Therefore, even if the foaming temperature fluctuates to some extent, it can be obtained at a relatively low temperature with a high expansion ratio, and the foaming cost is lower than conventional products because the temperature control in the foaming process is easy. It is a high-quality expanded particle that can easily produce a higher-quality molded body. The method for producing expanded beads of claim 2 is the method for producing high-quality expanded beads as described above, which is a method for producing expanded beads having a lower production cost than conventional expanded beads.

[Brief description of drawings]

FIG. 1 is a comparison diagram of a molecular weight distribution between a base resin used for the expanded beads of the present invention and that of a conventional product.

FIG. 2 is a first DSC curve of expanded resin particles.

FIG. 3 is a second DSC curve of expanded resin particles.

FIG. 4 is a diagram showing a relationship between a foaming temperature of resin particles and a foaming ratio.

FIG. 5 is a diagram showing the relationship between the foaming temperature of resin particles and the melting energy of secondary crystals formed in the foamed particles.

FIG. 6 is a diagram showing the relationship between the melting energy of secondary crystals formed in expanded beads and the expansion ratio of the expanded particles.

[Explanation of symbols]

 a Peak temperature of unique peak b Peak temperature of high temperature peak

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Oshima 2-5 Miyukicho, Utsunomiya City, Tochigi Prefecture

Claims (3)

[Claims] 1. A polypropylene-based resin expanded particle comprising ethylene and / or butene-1 as a comonomer component in the resin in an amount of 3 to 10% by weight, and a ratio of the Z-average molecular weight Mz to the weight-average molecular weight Mw of the resin. Mz / Mw is in the range of 1.5 to 2.5, and the expanded resin particles have secondary crystals with a melting energy of 11 to 30 J / g. 2. A blowing agent and ethylene and / or butene-1.
A mixture of copolymer resin particles of propylene and propylene and an aqueous medium is charged into a pressure vessel, and the mixture is discharged to a low pressure region from the pressure vessel at a temperature equal to or higher than the softening point of the resin particles to form secondary crystals. In obtaining the expanded resin particles, a comonomer content as a raw material resin for the resin particles is 3 to 10% by weight, and a ratio Mz / Mw of Z average molecular weight Mz and weight average molecular weight Mw is in the range of 1.5 to 2.5. A method for producing expanded polypropylene resin particles, which comprises using the resin according to 1. 3. The method for producing expanded polypropylene resin particles according to claim 2, wherein the foaming agent is an inorganic gas type foaming agent.