JP3537001B2 - Expanded polypropylene resin particles and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 a pressure in a container is heated to a temperature equal to or higher than a softening temperature of a resin while maintaining a pressure equal to or higher than a vapor pressure of a foaming agent, and then released from a pressurized container to a low-pressure atmosphere to foam. Volatile organic blowing agents in this case are propane, butane, pentane, trichlorofluoromethane, dichlorodifluoromethane, etc., but many of these organic blowing agents are toxic or flammable, which is dangerous. Even organic foaming agents that are almost nonexistent are often expensive and involve practical problems. In addition, the foaming agent causes environmental pollution problems such as destruction of the ozone layer when released to the atmosphere. In addition, since the resin particles swell, the suitable foaming temperature range during foaming is narrowed. Is greatly changed. If foamed particles having significantly different expansion ratios are used, the moldability of the foamed particles is reduced. Therefore, a new foamed particle and a method for producing a novel foamed particle are desired from this point of view.

In order to solve the above-mentioned problems, research has been carried out from various fields, and the present inventors have also proposed a method of using an inorganic gas as a blowing agent and a method of reducing the amount of a volatile organic blowing agent. Proposed. For example, a method for producing expanded resin particles using carbon dioxide as a foaming agent (Japanese Patent Publication No. 62-612)
No. 27); a crystal nucleating agent such as dibenzylidene sorbitol is added to the polypropylene resin particles, whereby the amount of the volatile organic foaming agent used when foaming the resin particles is reduced, or the volatile organic foaming agent is used. And a method of using an inorganic gas such as nitrogen as a blowing agent (Japanese Patent Publication No. 5-10374); adding an inorganic substance such as aluminum hydroxide or calcium carbonate to polypropylene-based resin particles, thereby expanding the resin particles. A method of reducing the amount of the volatile organic foaming agent used, or using an inorganic gas such as nitrogen together with the volatile organic foaming agent (JP-A-61-473).
No. 8); and the like.

[0004] The above-mentioned method of using an inorganic gas-based blowing agent or a method of reducing the amount of volatile organic blowing agent used or enabling the combined use of the blowing agent and an inorganic gas-based blowing agent is advantageous from the viewpoint of environmental conservation. Is large and the swelling of the resin particles is suppressed,
It was expected that the appropriate temperature range for foaming during foaming would also be expanded.
However, since the volatile organic foaming agent and the inorganic gas greatly differ in the plasticizing effect of the resin particles and the gas permeation rate into the inside of the resin particles, even if the above-described method using an inorganic gas-based foaming agent or the like is employed, it is slightly It was not possible to eliminate fluctuations in the expansion ratio due to a large expansion temperature difference, and it was found that there were many problems in producing a high-quality foam having a high expansion ratio and a constant expansion ratio.

[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 is slightly changed. It is an object of the present invention to provide high-quality foamed particles which are easy to control the temperature in the process and have a constant foaming ratio so that the moldability is excellent and the foaming ratio is high, and a method for producing the same.

[0006]

Means for Solving the Problems The present inventors have made 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 expanded polypropylene resin particles, the resin contains ethylene and / or butene-1 as a comonomer component in an amount of 3 to 10% by weight, and has a Z-average molecular weight Mz and a weight-average molecular weight of the resin. The ratio Mz / Mw of Mw is in the range of 1.5 to 2.5,
The present invention provides foamed polypropylene-based resin particles, characterized in that the foamed resin particles have secondary crystals having a melting energy of 11 to 30 J / g, and a method for producing the same.

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

[0008] Mz and Mw are defined as above,
The actual Mz and Mw measurements are made by gel permeation chromatography (GPC). In the present specification, Mz and Mw measured under the following conditions using GPC150C manufactured by Waters and using o-dichlorobenzene as a solvent for the polypropylene resin particles are employed. 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 described above. It can be similarly obtained by GPC.

As described above, the foamed particles of the present invention are foamed particles having secondary crystals, and the secondary crystals are formed only in foamed particles produced under specific foaming conditions, and are formed in all foamed particles. It is not done. The expanded particles of the present invention are expanded particles in which secondary crystals are formed by a method described later. The presence or absence of secondary crystals is determined by a DSC curve obtained by differential scanning calorimetry of the expanded particles. D
The SC curve is, for example, expanded polypropylene resin particles 2
4 mg was used as a sample.
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 a C curve was obtained, the temperature was lowered to around 40 ° C. at the above-mentioned rate, and then the temperature was raised again to 220 ° C. at the above-mentioned rate to obtain a 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. In addition, the peak on the low temperature side observed in both the DSC curves of FIGS. 2 and 3 is called a unique peak, which is a melting endothermic peak unique to the resin.

[0010] When the presence or absence of a secondary crystal is determined by the above method, the high temperature peak does not exist in the second DSC curve because the sample was 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 temperature decreasing rate of the molten sample exceeds the range of the temperature decreasing rate necessary for forming the secondary crystal. The melting energy of the secondary crystal (hereinafter, abbreviated as SCME) is an energy obtained from a DSC curve forming a high-temperature peak, and is an energy corresponding to an area indicated by oblique lines in FIG. is there. That is, in FIG. 2, a point at a temperature of 80 ° C. on the DSC curve is A, a melting end point on the DSC curve is B, and a perpendicular line drawn from the valley C between the high temperature peak and the specific peak to the line segment AB. When the intersection of the line segment AB with 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 an SCME of 11 to 30 J / g, preferably 13 to 2 J / g.
The SCME indicates the amount of energy required for melting all of 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 obtained by oxidizing and decomposing a normal polypropylene copolymer resin with an organic peroxide such as peroxide, thereby narrowing the high molecular weight region. And
By appropriately adjusting the amount of decomposition, the high molecular weight region can be controlled. The reduction of the value of Mz by decomposing a polypropylene resin with peroxide seems to be sometimes carried out when used as a raw material for polypropylene fibers in the field of textile industry. Index (MI) is 80 [g / 10min]
When such a material is used as raw resin particles of expanded particles, it becomes particles exhibiting open cells, and a good product cannot be obtained. The polypropylene 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 ×
10 ^5, the ratio Mw / Mn of Mw to number average molecular weight Mn of 4.
It is a resin of 5 or less, preferably 3.5 or less. The polypropylene-based copolymer resin suitable for the foamed particle raw material of the present invention, even when foamed, and further molded into a foamed particle molded product, since its molecular weight distribution and the like only change within an error range, the expanded particles. 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 a raw material of the expanded particles 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 within this range, the expansion ratio and the closed cell ratio are high, and the cell diameter is 70 to 35.
Good foamed particles of 0 μm can be easily obtained, and the moldability of the foamed particles is improved. And the MI of the raw material resin is 3
In less than g / 10 minutes, the expansion ratio does not improve, and the MI is 20 g.
When the rate exceeds / min, the cells become fine and the closed cell ratio is reduced, and therefore, the moldability of the expanded particles is reduced. In this specification, the MI value obtained under the test conditions of a test temperature of 230 ° C. and a test load of 2.16 kgf specified in JIS K-7210 is adopted. Foaming ratio is the ratio of the apparent volume of the base resin increased by foaming,
In the present specification, the expanded density is obtained by dividing the foamed particle weight by the apparent volume indicated by the scale of the graduated cylinder by putting the expanded particles in the measuring cylinder to determine the bulk density of the expanded particles, and dividing the base resin density by the bulk density. calculate.

When the polypropylene resin has an Mz / Mw value of 1.5 to 2.5, preferably 1.7 to 2.4,
The fluctuation width of the expansion ratio due to the fluctuation of the foaming temperature can be reduced. The reason for this is unknown, but according to detailed studies by the present inventors, this effect is surprisingly large, and an example of the effect is shown in FIG. This figure is
It is a figure which shows the relationship between the foaming temperature and foaming ratio when the foaming conditions, such as a foaming agent, are the same, and 1 is a case where Mz / Mw used in this invention is 2.3 as a raw material resin, 2 is Mz
The case where a resin with / Mw of 3.3 is used, the case with 3 using a resin with Mz / Mw of 3.2 and the case with 4 with Mz / Mw of 2.7 are used. As can be seen from the figure, the foaming temperature and the foaming ratio are proportional, and the proportionality constant varies greatly depending on the type of resin. When foaming the polypropylene copolymer resin having Mz / Mw of 3.2, the foaming temperature is 1
The expansion ratios at 42 ° C. and 145 ° C. are 7.5 and 1, respectively.
Although the ratio is 7.5, the expansion ratio of the resin used in the present invention having an Mz / Mw of 2.3 is 26 and 27 at the expansion temperature, and there is almost no difference in the expansion ratio.

As can be seen from FIG. 4, the polypropylene copolymer resin used in the present invention is easier to foam than a normal resin of the same kind, and the foaming ratio at around 144 ° C. of a normal resin is only about 15 times. Sometimes, the resin used in the present invention has a foaming ratio of 25 times or more. Therefore, according to the present invention, a foamed resin can be obtained with a stable foaming ratio even if the foaming temperature varies to some extent, and a high foaming ratio can be obtained even if foaming is performed at a lower temperature than when using a conventional polypropylene resin for producing foamed particles. It can be seen that particles are obtained. We have found that Mz / Mw
Is examined in more detail about 1.5-2.5 polypropylene copolymer resin, depending on the type and amount of the comonomer component contained in the copolymer, the physical properties of the expanded particles obtained from the copolymer resin are slightly I found things to change. That is,
When the content of the comonomer component composed of ethylene and / or butene-1 is in the range of 3 to 10% by weight, preferably 3.5 to 6% by weight, the foaming temperature is slightly increased. Even if it varies, expanded particles containing secondary crystals having the same SCME can be obtained. And when the foamed particles are ripened and molded in a mold to produce a molded product,
Good shrinkage due to good secondary foaming property during maturation molding provides high quality molded products with a smooth surface.

The expanded beads of the present invention have an expansion ratio of 5 to 10
It is a foamed particle having 0 times and having secondary crystals. And SCM
E is a foamed particle of 11 to 30 J / g, preferably 13 to 25 J / g. When SCME is too large, the secondary foaming property is reduced during molding of the foamed particle, and when SCME is too small, the foamed particle shrinks. There are problems such as. Further, the expanded particles of the present invention preferably have a change in expansion ratio per 1 J / g of SCME.
0.6 to -0.08 g / J, more preferably -0.3 to
-0.08 g / J expanded particles, and this value is -0.6
If the ratio is less than g / J, the expansion ratio greatly varies due to a slight difference in SCME, and the expansion of the expansion ratio of the obtained expanded particles becomes large. In addition, it is more preferable that this value exceeds -0.08 g / J and approaches 0, but such expanded particles cannot be obtained. The secondary crystals are presumed to be formed by the growth of secondary crystals generated on the crystal surface after the formation of the primary crystals. Heat treatment in an accelerated temperature range) forms secondary crystals. Accordingly, secondary crystals are formed 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. .

[0016] SCME can be obtained by a method such as slowing down the heating or cooling rate for the purpose of forming secondary crystals, increasing the time during which the resin is maintained at the secondary crystallization accelerating temperature, and lowering the foaming temperature. can do. On the other hand, if the above method is reversed, the SCME will decrease, and for example, if the foaming temperature is increased, the SCME will decrease. As described above, when the foaming temperature is low, SCME increases, and both are proportional with a negative proportionality 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 conventional products. Further, as can be seen from FIG. 4, since the foaming temperature and the foaming ratio are proportional with a positive proportionality constant, it is clear that SCME and the foaming ratio are in a proportional relationship with a negative comparative example constant. According to the study of the present inventors, both are in a proportional relationship having a negative slope. That is, SC particles are used for expanded particles having a high expansion ratio.
Secondary crystals having a small ME are formed, and secondary crystals having a large SCME are formed in the expanded particles having a low expansion ratio. Note that the proportional constant between SCME and the expansion ratio is also different from the expansion temperature and SC.
As with the proportionality constant between MEs, the resin used in the present invention has significantly smaller absolute values than conventional products.

As described in detail above, the foaming temperature and the SCM
There is a proportional relationship between E and between SCME and the expansion ratio with a negative proportional constant, 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 FIG. 4 are the same as those in FIG. 4, and a straight line 1 is a 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 also in this case, the gradient (proportional constant) of the straight lines is almost the same. is there. Accordingly, the gradient of the straight line shown in FIGS. 4 to 6 may be an important factor indicating the relationship between the foamability and moldability of the resin foam particles and the type of the resin, and this gradient is preferably close to zero. As can be seen from FIG. 6, the expansion ratio of the present invention does not decrease significantly even when SCME is large,
The expanded particles have a small correlation between SCME and expansion ratio.
Therefore, in the expanded particles of the present invention, even if the expansion ratio is increased, SC
Since the ME is kept high and the shrinkage of the expanded particles that occurs when the SCME is small is small, a high-quality molded product having a smooth surface can be manufactured. Although the reason why the expanded particles are likely to shrink when the SCME is small is not exactly known, the polymer structure related to the secondary expandability and the shrinkage of the expanded particles is limited to SC.
The ME will have an effect.

Change in foaming ratio per 1 J / g of SCME V
Can be obtained from FIG. That is, if the expansion ratio and SCME at point A in line 1 in FIG. 6 are B ₁ and G ₁ and those at point B are B ₂ and G ₂ , V = (B ₂
−B ₁ ) / (G ₂ −G ₂ ). Since the measurement of V is preferably performed on high-quality expanded particles having a high expansion ratio, it may be determined, for example, from expanded particles produced under the following conditions. In the case of measuring the expanded particles formed by two-stage expansion in which the expanded particles are further expanded, the following conditions may be used as well as the expansion conditions during the two-stage expansion. [I] Conditions for producing expanded particles having an expansion ratio of B ₁ and SCMEG ₁ J / g Base resin (containing inorganic substance) 100 parts by weight Water (dispersion medium) 220 parts by weight Kaolin (anti-fusing agent) 0.5 part by weight Dodecyl Sodium benzenesulfonate (fusion prevention aid) 0.006 parts by weight Carbon dioxide (blowing agent) 8 parts by weight Heating rate 2 ° C / min Holding temperature 141 ° C Holding time 15 minutes Foaming temperature 147 ° C Foaming temperature holding time 15 [II] Production conditions of expanded particles having an 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 in which SCME does not greatly decrease even when the foaming temperature is high unlike conventional products. Expanded particles. Since such foamed particles have good moldability, even if an attempt is made to produce foamed particles having similar performance to the foamed particles of the present invention using a conventional resin, in this case, the cost is increased due to the use of a large amount of a foaming agent. In addition, it is difficult to sufficiently reduce the problem of shrinkage of the expanded particles. Therefore, the expanded particles of the present invention can be said to be high-performance expanded particles that cannot be expected from conventional products. Also,
Expanded particles in which the peak temperature of the intrinsic peak appearing in the second DSC curve (FIG. 3A) is lower than the peak temperature of the high temperature peak appearing in the first DSC curve (FIG. 2B) by 5 ° C. or more, particularly 10 ° C. or more. Shows that the secondary crystals are hard to melt. Therefore, in this case, even if the foaming temperature is high, the secondary crystals are unlikely to melt, and thus foamed particles having a high foaming ratio and good moldability can be obtained.

In the present invention, the polypropylene-based copolymer resin having the above specified Mz / Mw, comonomer content, etc. may be used as the base resin, and the base resin may be cross-linked or non-cross-linked. However, it is preferable to use a non-crosslinked product in consideration of recycling and the like. Specific examples of resins 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, propylene -Ethylene-butene terpolymer. And among these, propylene-ethylene random copolymer, propylene-butene random copolymer and propylene-ethylene-
Butene terpolymers are preferred because of their excellent physical properties required for molded articles such as low-temperature brittleness and flexibility, and especially 3.5.
Copolymers containing up to 6.0% by weight of ethylene are preferred. When the rigidity of the molded article is strongly required, a copolymer having a high butene content and a high ethylene content of 3.0% by weight or less is preferably used as the base resin. Next, auxiliary materials, a foaming method, and the like necessary for producing the foamed particles of the present invention will be specifically described. These are the same as those in the conventional production of foamed particles.

In the present invention, a fusion inhibitor 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 non-melting at the time of heating, but usually an inorganic one is preferred. Representative 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-fusing 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 amount of addition is generally in the range of 0.01 to 10 parts by weight per 100 parts by weight of the resin particles.
The effect of the anti-fusing agent detailed above can be further enhanced when used in combination with an emulsifier such as sodium dodecylbenzenesulfonate or sodium oleate. As the emulsifier, an anionic surfactant is preferable, and its addition amount 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 blowing agent or an inorganic gas blowing agent is used as the blowing agent, and both may be used in combination. And organic foaming agents include propane, butane, pentane,
Hexane, cyclobutane, cyclohexane, dichlorodifluoromethane, known products such as 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 parts. When the inorganic gas is used as the foaming agent, the amount of the foaming agent except for nitrogen and air is 2 to 50 parts by weight per 100 parts of the resin, and the pressure in the container is 15 to 70 kg /
It is desirable that the solution is supplied into the container so as to have a density of cm ² G, preferably 20 to 50 kg / cm ² G. Of the above, the use of an inorganic gas or a mixture of an inorganic gas and a volatile organic foaming agent as the foaming agent is preferable from the viewpoint of safety because the amount of the volatile organic foaming agent used is reduced. Further, when a mixture of an inorganic gas and a volatile organic blowing agent is used as the blowing agent, there is an advantage that the expansion ratio is higher than when only the inorganic gas is used as the blowing agent. When only the inorganic gas is used as the foaming agent, the fluctuation range of the foaming ratio becomes small, and therefore, the decrease in the foaming ratio of the foamed particles obtained at the latter stage of the foaming step, which is observed when the volatile organic foaming agent is used, is suppressed.

When the 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 pressure, but it is higher than the melting point of the resin. In this case, it may be several tens of seconds to one hour, and usually, it is preferably five to 30 minutes. And
Since the resin particles may be impregnated with the blowing agent at any time, immediately after filling the resin particles or the like in 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 a blowing agent, the step of impregnating the resin particles with the organic blowing agent may be performed before or after the step of dispersing the resin particles in a dispersion medium,
Usually, it is performed simultaneously with dispersing the resin particles in the dispersion medium. 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, a desired amount of resin particles, a dispersion medium, and an organic foaming agent are placed in a pressure-resistant container, and the container is sealed, and then heated and stirred 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,
Preferably, it is 5 to 30 minutes.

The dispersion medium used in the present invention may be any liquid that does not dissolve the polypropylene resin particles, and an aqueous medium such as water, ethylene glycol, glycerin, methanol, or ethanol can be used. used. The amount of the dispersion medium is not particularly limited, but is usually 1.5 to 3 times the weight of the resin particles. The polypropylene copolymer resin particles used in the present invention have a 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 the shape is 0.3-5mm in particle size,
Preferably, it is in the form of particles of 0.5 to 3 mm. Further, fine particles of an inorganic substance or a crystal nucleating agent such as dibenzylidene sorbitol may be added to the resin particles, and the addition thereof may improve the foaming property and the moldability of the foamed particles.

In the present invention, examples of inorganic fine powder suitable for adding to the resin particles include hydroxides such as aluminum hydroxide, calcium hydroxide and magnesium hydroxide; and calcium hydroxide, magnesium carbonate and barium carbonate. Carbonate; sulfites such as calcium sulfite and magnesium sulfite; sulfates 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 and calcium chloride;
Clay or natural minerals such as borax, talc, clay, kaolin and zeolite; These have a particle size of 0.
It is desirably in the form of fine powder having a particle size of 1 to 100 µm, preferably 1 to 15 µm. The inorganic fine powder may be added alone or as a mixture of two or more kinds. In addition, these inorganic fine powders may be added at the time of granulation of the polypropylene-based copolymer resin particles,
The addition is preferably performed in a masterbatch.

The amount of the inorganic fine powder varies depending on the type of the inorganic fine powder, but is generally 0.001 to 5%, preferably 0.002 to 3% of the weight of the resin. When the inorganic fine powder is talc fine powder, the content is particularly preferably 0.003 to 0.5% by weight; and when the inorganic fine powder is borax, aluminum hydroxide and zeolite fine powder, the content is particularly preferably 0.1 to 2% by weight. The addition of the inorganic fine powder improves foaming performance when producing foamed particles as described above, and is expected to improve the foamability of foamed particles by making the foamed particles uniform and having the desired foamed diameter. it can. However, when the inorganic fine powder is added in an amount exceeding 5% by weight, the moldability of the expanded particles is reduced. When the amount is less than 0.001% by weight, the above-mentioned effects are not sufficiently exhibited.

The expanded polypropylene resin particles of the present invention are prepared by charging the above-mentioned polypropylene-based copolymer resin particles, an anti-fusing agent and an aqueous medium (usually water) in a pressure-resistant container, and reaching the expansion temperature in the presence of the blowing agent. After heating, the contents of the container are released from the pressurized zone to a low-pressure zone (usually atmospheric pressure), whereby the resin particles impregnated with the foaming agent are foamed to produce. The foaming temperature is generally a temperature equal to or higher than the softening point of the resin. If the temperature is equal to or lower than the peak temperature of the high temperature peak (FIG. 2B), foamed particles having 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.
/ Cm ² . A suitable foaming temperature range varies depending on the type of the resin and the type of the foaming agent, but is preferably around the melting point of the resin. In the case of a non-crosslinked polypropylene copolymer resin, the range is 5 ° C. lower to 15 ° C. higher than the melting point, preferably 3 ° C. The temperature ranges from a low temperature of 10 ° C to a high temperature of 10 ° C. The rate of temperature rise when the content of the container is raised from room temperature to the foaming temperature is not particularly limited, but is about 1 to 10 ° C / min, particularly 2 to 5 ° C / minute.
Minutes are preferred. When the temperature rise rate exceeds 5 ° C./min, it is necessary to hold the contents of the container at the secondary crystallization acceleration temperature for 5 minutes or more. In order to stably form crystals, it is preferable to hold the contents of the container at a secondary crystallization promoting temperature for 5 minutes or more.

[0028]

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 percentages are based on weight.

Example 1, Comparative Examples 1 to 5 In an extruder, 100 parts of an ethylene-propylene random copolymer resin shown in Table 1 below and 0.05 part of aluminum hydroxide having an average particle diameter of 3 μm were charged and melted. After kneading, the mixture was extruded into a strand from a die at the end of the extruder, quenched in water, and then cut to produce 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 master batch.

[Table 1]

100 kg of the above-mentioned pellets, 200 liters of water, 300 g of kaolin and 7 kg of carbon dioxide were charged into a closed vessel having an internal volume of 400 liters, and stirred.
The temperature was raised to the holding temperature shown in Table 2 at a rate of ° C./min, and held at this temperature for 15 minutes. Next, at a rate of 2 ° C./min.
And maintained at this temperature for 15 minutes. While keeping the contents of the sealed container obtained as described above at the foaming temperature, 40 kg / cm ² (G) with carbon dioxide
After applying a back pressure to prevent the pressure in the closed container from dropping rapidly, foamed particles were produced by a method in which one end of the container was opened to release the contents under atmospheric pressure. 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 was used.
Change in expansion ratio per J / g V [(B ₂ −B ₁ ) / (G ₂
-G ₁ )] is also shown in Table 2. In addition, the evaluation of the moldability of the expanded particles was performed according to the following criteria.

1. Dimensional precision expanded particles are charged into a mold and this is 3.2 kg / cm
² (G) was heat-formed with steam to produce a plate-shaped formed body having a length of 30 cm, a width of 30 cm and a thickness of 5 cm. The plate-shaped molded body is cured in an oven at 60 ° C. for 24 hours, and the shrinkage in the surface direction is measured by averaging the changes in the center line length in the vertical and horizontal directions before and after the curing. ; Shrinkage 3
% And less than 4% are represented by Δ, and shrinkage ratios of 4% or more are represented by x. 2. The plate-shaped molded body produced by the above-described method was cut so that the vertical cross section in the width direction was 1 cm thick and 5 cm wide to prepare a sample, and this sample was manufactured by Toyo Baldwin UTMIII.
Pull in the longitudinal direction by a tensile tester until breaking at a chuck distance of 50 mm and a pulling speed of 500 mm / min,
When the fracture surface is visually observed and the material fracture 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 was represented by X. 3. Secondary foaming property The surface condition of the plate-like molded article produced by the above method is visually observed, and the case where there is almost no unevenness on the surface is ○; the case where the surface is partially uneven is △; When there is, it was represented by X. 4. Comprehensive evaluation The above-described evaluation was performed on a sample obtained by using foamed particles foamed at various foaming temperatures as a raw material and formed into a molded body as described above. Both preferred cases were represented by O; and cases with any problem were represented by X.

[0032]

[Table 2]

From Table 2, it can be seen that the foamed particles of the present invention show good moldability even when the holding temperature and the foaming temperature are slightly different from each other, even though the expansion ratio is small. It can be seen that the foaming ratio greatly fluctuates only by changing the temperature by 3 ° C., and the moldability is greatly reduced. It is considered that this variation is because the value of SCME greatly varies depending on the temperature. Further, when Mz / Mw exceeds 2.5 even when the ethylene content is substantially the same, the maximum value of the ultimate expansion ratio of the expanded particles having good dimensional accuracy, fusion property and secondary expandability is inferior to that of the present invention. It is recognized that. In these phenomena, the moldability changes drastically only by a slight change in the polymer structure closely related to the moldability, but the polymer physical properties are different even if a part of the structure less related to the moldability changes. This indicates that it is difficult to uniquely evaluate the moldability of the expanded particles from the properties of the polymer. 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 is first obtained. Can be reached.

[0034]

According to the first aspect of the present invention, the foamed particles are polypropylene resin foamed particles having a substantially higher foaming ratio even if the foaming temperature and the like are slightly changed, and having a higher foaming ratio than conventional ones. These foamed particles are foamed particles having good secondary foaming properties, and are foamed particles capable of easily producing a high-quality molded article having a smooth surface. Further, it is a foamed particle obtained at a high foaming ratio even at a low foaming temperature. Therefore, even if the foaming temperature fluctuates somewhat, it is possible to obtain a high expansion ratio at a relatively low temperature at a relatively low temperature. Therefore, the foaming cost is lower than that of the conventional product due to easy temperature control in the foaming process. It is a high quality expanded particle that can easily produce a higher quality molded article. The method for producing expanded particles according to claim 2 is a method for producing high-quality expanded particles as described above, and is a method for producing expanded particles having a lower production cost than conventional expanded particles.

[Brief description of the drawings]

FIG. 1 is a comparison diagram of the molecular weight distribution of a base resin used for the expanded particles 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 the foamed resin particles.

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

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

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

[Explanation of symbols]

a Peak temperature of intrinsic peak b Peak temperature of high temperature peak

(56) References JP-A-3-254930 (JP, A) JP-A-63-258939 (JP, A) JP-A-60-245650 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C08J 9/16

Claims (3)

(57) [Claims] 1. A foamed polypropylene resin particle comprising 3 to 10% by weight of ethylene and / or butene-1 as a comonomer component in the resin 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 foamed resin particles have secondary crystals having 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 an aqueous medium is charged into a pressure vessel, and the mixture is discharged into the 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 resin expanded particles having the same, a comonomer content of 3 to 10% by weight and a ratio Mz / Mw of Z average molecular weight Mz to weight average molecular weight Mw of 1.5 to 2.5 as a raw material resin of the resin particles A method for producing expanded polypropylene resin particles, comprising using the resin described in (1). 3. The method for producing expanded polypropylene resin particles according to claim 2, wherein the blowing agent is an inorganic gas-based blowing agent.