JP5314411B2 - Method for producing polypropylene resin expanded particle molded body, and molded body - Google Patents

Abstract

The invention relates to a molded product of a polypropylene-based resin expanded particle and a method for producing the same. The object of the invention is to provide a molded product of a polypropylene-based resin expanded particle with a low expansion ratio having excellent fusibility between expanded particles mutually, small density difference between a surface part and an inner part of the molded product, better mechanical properties, such as compressive strength, compared with a conventional one, and also excellent appearance. In an in-mold molding method with the polypropylene-based resin expanded particle, the expanded particle has apparent density of 60-450 g/L, the welding rate of the polypropylene-based resin expanded particle is above 50%, the ratio between the apparent density of the expanded particle molded body to the inner density of the molded body is 1-2 and the molded product of the polypropylene-based resin expanded particle is preferably molded when satisfying the special conditions.

Description

  The present invention relates to a method for producing a polypropylene resin foamed particle molded body and the molded body, and in particular, the density distribution of the foamed particle molded body is reduced by a molding temperature lower than the molding temperature at which conventional polypropylene resin foamed particles are molded in a mold. The present invention relates to a method for producing a polypropylene resin foamed particle molded body capable of obtaining a uniform high-density foamed particle molded body and the molded body.

  Polypropylene resins are expanding their fields of use because of their excellent mechanical strength, heat resistance, processability, incineration, recyclability, and the like. Similarly, a polypropylene resin expanded particle molded body obtained by molding polypropylene resin expanded particles in a mold has additional properties such as cushioning, heat insulation, and light weight without losing the excellent properties of the polypropylene resin. Therefore, it has been widely used for packaging materials, building materials, vehicle shock absorbing materials, etc., and accurate dimensional accuracy and high strength have been demanded for packaging trays for electronic components, automobile weight reduction members, etc. Therefore, it is expected that the demand for low-magnification polypropylene resin expanded particle molded bodies will increase. In order to obtain a high-density foamed particle molded body, foamed particles having a large apparent density are molded in-mold, but the foamed particles having a large apparent density are subjected to secondary foaming and only the surface of the foamed particles is melted. In the conventional technology, there is a difficulty in molding in-mold, etc., and in the conventional technology, the expanded density of foamed particles is controlled by controlling the average density of the foamed particles by suppressing the variation in the apparent density of the foamed particles. However, the method (Patent Document 1) for producing a foamed particle molded body that improves the fusing property and has an excellent appearance and rigidity has only been put into practical use.

  However, a high density (60 g / L or more, particularly 100 g / L or more) polypropylene resin foamed particle molded body has a low-magnification foamed particle used to obtain the molded body compared to a high-magnification foamed particle. Therefore, the fusibility between the foam particles during in-mold molding tends to deteriorate, and the foaming particles are secondary-foamed so that the heating condition at the time of in-mold molding is increased and the molded product surface appearance is sufficient. Regardless, the meltability of the foam particles inside the molded product tends to be insufficient, and in order to satisfy the meltability, the compression rate when filling the foam particles into the mold is increased, It was necessary to further increase the water vapor pressure. And, since the water vapor pressure becomes high, there is a problem that the cooling time at the time of molding in the mold becomes long and the productivity is deteriorated, and the obtained foamed particle molded body has a molding condition such as high water vapor pressure. Therefore, the bubbles in the surface layer part of the foamed particle molded body are crushed and densified, resulting in a density difference between the inside of the foamed particle molded body and the surface layer part, and the mechanical strength such as compression properties is stable. There was a problem of not doing.

JP 2000-63556 A

The present invention has stable and excellent physical properties by molding in a mold at a low heating temperature without impairing excellent properties such as toughness, heat resistance, and easy recyclability, which are characteristics of a polypropylene resin foamed molded article. An object of the present invention is to provide a method for producing a low-magnification (high-density) polypropylene-based resin expanded resin molded body.
In addition, the present invention is excellent in the fusion property between the expanded particles, the density difference between the surface layer portion and the inside of the molded body is small, the mechanical properties such as the compressive strength are excellent, and the appearance is excellent as compared with the conventional one. Another object of the present invention is to provide a low-magnification polypropylene-based resin expanded particle molded body.

  The present invention is superior in fusion property between foamed particles and compressive strength at a temperature lower than the molding temperature of the conventional polypropylene resin foamed particles, without impairing the properties of the conventional molded polypropylene resin foamed particles. For the purpose of developing polypropylene-based resin foam particles that can obtain a low-magnification foam particle molded body having excellent mechanical properties such as, the relationship between the crystal structure of the foam particles and the mechanical properties of the foam particle molded body, We investigated the relationship between the crystal structure of the foam particles and the behavior of the foam particles during in-mold molding, the in-mold molding method, etc., and realized that the molding temperature range for foam particles could be expanded to the low temperature side. In addition, by adopting a molding method that adjusts the compression ratio at the time of filling of the foam particles into the mold in the in-mold molding, a low-magnification foam particle molded body having excellent physical properties can be obtained stably. Heading the door, which resulted in the completion of the present invention.

That is, the present invention
(1) In a foamed particle in-mold molding method in which polypropylene-based resin foam particles are filled into a mold and heat-molded, the polypropylene-based resin foam particles have an apparent density of 100 to 720 g / L, and Apparent density ratio (ρ _R ) of the foamed particles before and after heating when the foamed particles are heated for 10 seconds in a pressure vessel with saturated steam at the melting temperature [(apparent density of the foamed particles before heating [g / L] ) / (Apparent density of expanded particles after heating [g / L])] is 1 to 1.7,
In the first DSC curve obtained by heating the expanded particles from room temperature to 200 ° C. at a rate of temperature increase of 2 ° C./min by differential scanning calorimetry, 70 to 95% of the total endothermic peak heat amount is obtained. A main endothermic peak showing an endothermic peak heat quantity and a peak temperature of the endothermic peak of 100 to 140 ° C., and a crystal structure in which an endothermic peak appears on the high temperature side of the main endothermic peak,
A method for producing a molded product of expanded polypropylene resin particles, wherein the compression rate of the expanded polypropylene resin particles in a mold is 0 to 15%.
(2) The method of producing the polypropylene resin foamed beads molded article according to (1), characterized in that it has two or more endothermic peak Kugagen are crystal structure to a high temperature side of the main endothermic peak.
(3) The polypropylene resin of the base resin constituting the polypropylene resin expanded particles has a low melting point polypropylene resin (A) having a melting point of 100 to 140 ° C. and a melting point higher by 20 ° C. than the melting point of the resin. The method for producing a polypropylene resin expanded resin molded article according to (1) or (2), which is a mixture with the high melting point polypropylene resin (B).
(4) Of the base resin constituting the polypropylene resin expanded particles, the low melting point polypropylene resin (A) is a copolymer of propylene and ethylene or / and an α-olefin having 4 to 20 carbon atoms. The manufacturing method of the polypropylene-type resin expanded particle molding as described in said (3).
(5) Of the base resin constituting the polypropylene resin expanded particles, the low melting point polypropylene resin (A) is a polypropylene resin polymerized using a metallocene polymerization catalyst (3) or ( The manufacturing method of the polypropylene-type resin expanded particle molded object as described in 4).
(6) In a foamed particle molded body obtained by filling polypropylene resin foamed particles in a mold and heat-molding, the density of the molded body is 60 to 450 g / L, the fusion rate of the expanded particles is 50% or more, The ratio (Ds / Dc) of the density (Ds) [g / L] of the surface layer portion of the molded body to the density (Dc) [g / L] inside the molded body is 1-2. Polypropylene-based resin expanded particle molded body.

According to the method for producing a polypropylene resin foamed particle molded body of the present invention, a low-magnification foamed particle molded body excellent in the fusion property between the foamed particles can be obtained under low temperature in-mold molding and heating conditions as compared with the prior art. Since it can be molded, it is possible to shorten the cooling time after heating at the time of molding in the mold, which leads to shortening of the molding time in the mold. In addition, since excessive steam heating is not required in in-mold molding, the mold clamping pressure of the molding machine can be reduced, and the mold thickness can be reduced without increasing the durability of the mold more than necessary. In addition, there are significant advantages in terms of manufacturing costs and durability of molds, and energy costs can be significantly reduced compared to conventional in-mold molding.
In addition, the polypropylene resin expanded resin molded body of the present invention has a low magnification, but the difference in density between the surface layer portion and the inside of the expanded expanded resin molded body is smaller than that of the conventional one, and its breakthrough Due to these features, the effect of improving the compressive strength of the foamed particle molded body is exhibited. Furthermore, the foamed particle molded body of the present invention is excellent in mechanical properties of the molded body due to the excellent fusion property between the foamed particles. In addition, the foamed particle molded body of the present invention has excellent smoothness because the surface thereof has a small gap called a vent hole trace or a void between the foamed particles.

The method for producing a foamed particle molded body of the present invention is a low-magnification polypropylene resin foamed particle molded body that is excellent in fusion property between the foamed particles, and has a small density difference between the surface layer portion and the inside of the molded body. In the low-magnification polypropylene-based resin foam particles used for in-mold molding to obtain a low-magnification foamed-particle molded body, saturated steam at the melting temperature of the foamed particles can be obtained. When the foamed particles are heated in a pressure vessel for 10 seconds, the apparent density ratio (ρ _R ) of the foamed particles before and after heating [(apparent density of the foamed particles before heating [g / L]) / (after heating The first characteristic is that the foamed particles have an apparent density [g / L])] of 1 to 1.7.
The foamed particles used for in-mold molding have the property that by heating the foamed particles, the foamed particles can first be fused to each other, and then the foamed particles can be secondarily foamed. (Hereinafter, the foamed particles having this property are referred to as fusion-advanced-type foamed particles) and by heating the foamed particles, the foamed particles can be in a secondary foamable state, and then the foamed particles are fused to each other. There are some which have the property to be obtained (hereinafter, the expanded particles having this property are referred to as secondary expanded preceding-type expanded particles). Especially in the in-mold molding of the expanded particles at a low heating temperature, the secondary expanded The present inventors have found that the fusion-type advanced foam particles are more preferable than the prior-type foam particles.

As described above, the reason why the fusion precedent foam particles are more preferable than the secondary foam precedent foam particles is that, in the case of the secondary foam precedent foam particles, foaming is performed in the heating process at the time of in-mold molding. The gap between the foamed particles filled in the mold is easily filled by the secondary foaming of the particles, which inhibits the inflow and passage of water vapor into the gap between the foamed particles, and as a result, inhibits the fusion between the foamed particles. On the other hand, the fusion-preceding foamed particles are less likely to cause the above-described inhibition factors seen in the secondary foaming-preceding foamed particles. However, if the secondary foaming temperature is markedly higher than the mutual fusing temperature of the foamed particles, even in the case of the fusion-advanced foamed particles, in order to obtain a foamed particle compact with good appearance, Since the heating temperature must be increased, it is preferable that the temperature at which the foamed particles can be fused and the temperature at which the secondary foaming can be performed are not significantly different.
The apparent density ratio (ρ _R ) of the foamed particles before and after heating when the foamed particles are heated in a pressure resistant container for 10 seconds with the saturated vapor at the melting temperature of the foamed particles in the production method of the present invention is 1-1. .7 means that the expanded particles used in the production method are fusion-advanced-type expanded particles. Among the fusion-advanced-type foamed particles, those having an appropriate secondary foaming power are preferable, and thus the apparent density ratio (ρ _R ) is 1.1 to 1.6, and more preferably 1.2 to 1.5. Is preferred.

In the present invention, the melting temperature of the expanded particles is measured by the method described in “When measuring the melting temperature after performing a certain heat treatment” in JIS K7121 (1987) using a heat flux differential scanning calorimeter. Is the value to be Specifically, the sample was heated from room temperature to 200 ° C. at a rate of 10 ° C./min by a heat flux differential scanning calorimetry using 1 to 3 mg of polypropylene resin foam particles as a sample, and then at a rate of 10 ° C./min. Is the peak temperature of the endothermic peak determined from the DSC curve obtained when the temperature is lowered to 30 ° C. and again raised from 30 ° C. to 200 ° C. at a rate of 10 ° C./min. When there are a plurality of endothermic peaks in the DSC curve, the apex temperature of the endothermic peak with the maximum area is adopted.
The procedure for measuring the apparent density ratio (ρ _R ) is as follows.
A foam particle having a known apparent density of about 100 cm ³ in bulk volume (foamed particle before heating) is placed in a 5 L autoclave and heated for 10 seconds in an autoclave in which the foamed particle is sealed with saturated steam at the melting temperature of the foamed particle. By doing so, the foamed particles after heating are obtained.

Also, the apparent density of the expanded particles before heating was determined by adjusting the state of the expanded particles by allowing them to stand for 48 hours or more under conditions of a temperature of 23 ° C. and a humidity of 50% under normal pressure, and then the weight: W (g) The foamed particle group is submerged in a graduated cylinder containing water by using a wire mesh or the like to obtain the volume of the foamed particle group V (L) obtained from the rise in the water level, and the weight of the foamed particle group is determined as the foamed particle group. This is a value obtained by dividing by the volume of the particle group (W / V).
The apparent density of the foamed particles after heating is adjusted by leaving the foamed particles obtained by heating for 10 seconds in the above-mentioned pressure vessel at a temperature of 23 ° C. and a humidity of 50% under normal pressure for 48 hours or more. Then, the foamed particle group having a weight: W (g) is submerged in a graduated cylinder containing water using a wire mesh or the like, so that the volume of the foamed particle group obtained from the rise in the water level: V (L ) And the weight of the expanded particle group is divided by the volume of the expanded particle group (W / V).

  In the present invention, the base resin constituting the polypropylene resin expanded particles may be a propylene homopolymer, a propylene block copolymer or a propylene random copolymer as long as it satisfies the constituent requirements of the present invention. Can be used. In addition, as said propylene-type copolymer, it consists of a copolymer of propylene and ethylene or / and a C4-C20 alpha olefin, Propylene, ethylene, 1-butene, 1-pentene, 1- Examples thereof include copolymers with hexene, 1-octene, 4-methyl-1-butene and the like. The propylene-based copolymer may be a binary copolymer such as a propylene-ethylene random copolymer or a propylene-butene random copolymer, or a ternary copolymer such as a propylene-ethylene-butene random copolymer. It may be a coalescence. The polypropylene copolymer contains propylene-derived structural units in the copolymer in an amount of 70% by weight or more, further 80 to 99.5% by weight, and / or ethylene and / or α-carbon having 4 to 20 carbon atoms. It is preferable that the structural unit obtained from the olefin is a polypropylene resin containing 30% by weight or less, preferably 0.5 to 20% by weight.

The foamed particles used in the present invention can be molded in-mold at a molding temperature lower than the molding temperature of conventional polypropylene resin foamed particles by satisfying the above apparent density ratio (ρ _R ) condition. In addition, it is possible to stably obtain a foamed particle molded body excellent in the appearance of the foamed particle molded body, the fusion property between the foamed particles, and the like.
The polypropylene resin foamed particles satisfying the condition of the apparent density ratio (ρ _R ) in the present invention are, for example, a method of adjusting the crystal structure of the foamed particles, a closed cell ratio of the foamed particles, a cell diameter, and a skin layer thickness. It can obtain by the method of doing.
In particular, a method for adjusting the crystal structure of the expanded particles, which is a preferable method for obtaining the expanded polypropylene resin particles satisfying the condition of the apparent density ratio (ρ _R ), will be described in detail below.

As polypropylene-based resin expanded particles satisfying the condition of the density ratio (ρ _R ), the polypropylene-based resin expanded particles were heated from normal temperature to 200 ° C. at a temperature increase rate of 2 ° C./min by heat flux differential scanning calorimetry. In the first DSC curve obtained from time to time, a main endothermic peak having an endothermic peak calorific value of 70 to 95% of the total endothermic peak calorific value and a peak temperature of the endothermic peak of 100 to 140 ° C., and the main endothermic peak It is preferable to have a crystal structure in which two or more endothermic peaks appear on the high temperature side.
In the first DSC curve at the rate of temperature increase of 2 ° C./min, when the main endothermic peak with an endothermic peak temperature of 100 to 140 ° C. appears, the apex temperature of the main endothermic peak is the base of the expanded particles. Since it shows a temperature close to the resin melting point of the polypropylene resin that is the material resin, it can be said that it is a non-crosslinked polypropylene resin expanded particle made of a low melting point polypropylene resin. However, the expanded particles are not simply expanded particles made of a polypropylene resin having a low melting point, the effect of lowering the heating temperature at the time of in-mold molding, the appearance of the expanded molded product obtained by the in-mold molding, and the fusion between the expanded particles As a structure for combining molding stability such as property, a crystal structure in which two or more endothermic peaks appear on the high temperature side of the main endothermic peak in the first DSC curve of the expanded particles is shown. In this case, the foamed particles made of the conventional low melting point polypropylene resin, which were the secondary foamed advance type foamed particles, become the fused advance type foamed particles, and the effect of lowering the heating temperature during molding and molding stability It is thought that it will be excellent. Therefore, it is preferable that the expanded particles used in the present invention have a crystal structure in which two or more endothermic peaks appear on the high temperature side of the main endothermic peak, in addition to the configuration of the main endothermic peak.

  The polypropylene resin expanded particles preferably used in the present invention are polypropylene resin expanded particles having a specific crystal structure that can be confirmed by heat flux differential scanning calorimetry as described above. Specifically, by heat flux differential scanning calorimetry of polypropylene resin expanded particles, 1 to 3 mg of polypropylene resin expanded particles are heated to a normal temperature (approximately 25 ° C. at a temperature rising rate of 2 ° C./min with a heat flux differential scanning calorimeter. In the first DSC curve obtained when heated to 200 ° C., three or more endothermic peaks appear, showing an endothermic peak calorific value of 70 to 95% with respect to the total calorific value of all the endothermic peaks, The endothermic peak has a crystal structure in which a main endothermic peak having an apex temperature of 100 to 140 ° C. appears and two or more endothermic peaks appear on the high temperature side of the main endothermic peak. In the differential scanning calorimetry of the foamed particles, the reason for adopting a temperature rising rate of 2 ° C./min is that there is a crystal structure peculiar to the foamed particles, that is, the foamed particles are three in the first DSC curve. In order to determine whether the endothermic peak has a specific crystal structure or not, it is possible to improve the resolution of endothermic peaks based on heterogeneous crystals by lowering the heating rate conditions for heat flux differential scanning calorimetry. It is necessary to carry out the measurement, and for this purpose, the preferable temperature rising rate is 2 ° C./min.

A typical first time obtained when 1 to 3 mg of polypropylene resin expanded particles preferably used in the present invention are heated from normal temperature to 200 ° C. at a rate of temperature increase of 2 ° C./min with a heat flux differential scanning calorimeter. An explanatory diagram of the DSC curve is shown in FIG. In the DSC curve in FIG. 1, a ₁ , a ₂ , and a ₃ each represent an endothermic peak. The total endothermic peak calorific value (ΔH) of the first DSC curve is obtained as follows.
As shown in FIG. 1, a straight line (α−β) connecting a point α corresponding to 80 ° C. on the DSC curve and a point β on the DSC curve corresponding to the melting end temperature Te of the resin is drawn. The amount of heat corresponding to the area surrounded by the base line and the DSC curve is defined as the total endothermic peak heat amount (ΔH) J / g. The amount of heat of the peak is automatically calculated by being calculated by a heat flux differential scanning calorimeter based on the area of the peak. The total endothermic peak heat quantity (ΔH) in the present invention is preferably in the range of 40 to 120 J / g, more preferably in the range of 45 to 100 J / g, and particularly in the range of 45 to 85 J / g. It is preferable that it exists in.

As shown in FIG. 1, the expanded particles preferably used in the present invention have three or more endothermic peaks appearing on the first DSC curve. The amount of heat (ΔHa, ΔHb, Δ Hc...) Can be obtained by a partial area analysis method described below.
The partial area analysis method will be described with reference to FIG. On the obtained DSC curve, a line segment (α−β) connecting the point α on the DSC curve corresponding to 80 ° C. and the point β on the DSC curve corresponding to the melting end temperature Te of the resin is drawn. Next, a straight line parallel to the vertical axis of the graph from the point γ ₁ on the DSC curve corresponding to the valley between the peak a ₁ observed in the low temperature part where the temperature is the lowest and the peak a ₂ adjacent to the peak a ₁ is obtained. The point intersecting the line segment (α−β) is defined as δ ₁ . Further, because the peak a ₃ observed adjacent to the peak a _2, parallel to the longitudinal axis from the point gamma ₂ on the DSC curve corresponding to valleys of the graph between the peak a ₃ adjacent to the peak a ₂ and the peak a ₂ pull the a straight line, the point of intersection with the line segment (α-β) and [delta] _2. Thereafter, when peak a ₄ , peak a ₅ , peak a ₆ ... Are observed, the same operation is repeated. The line segment (δn−γn) (n is an integer of 1 or more) obtained by the above operation becomes each peak boundary line when determining the endothermic peak area.

Therefore, the area of each peak corresponding to the amount of heat of the endothermic peak, in Figure 1, in the peak _{a 1,} the DSC curve shows a peak _{a 1,} the line segment ([delta] _{1-gamma 1),} line (alpha −δ ₁ ), and in peak a ₂ , the DSC curve indicating peak a ₂ , the line segment (δ ₁ −γ ₁ ), the line segment (δ ₂ −γ ₂ ), and the line The area surrounded by the minute (δ ₁ −δ ₂ ). In the peak a ₃ , the DSC curve showing the peak a ₃ , the line segment (δ ₂ −γ ₂ ), and the line segment (δ ₂ −β) Is defined as the area surrounded by. Thereafter, when the peak a ₄ , the peak a ₅ , the peak a ₆ ... Are observed, the peak area can be determined in the same manner. Therefore, the calorific value (ΔHa, ΔHb, ΔHc...) J / g of each peak is automatically calculated by the heat flux differential scanning calorimeter based on the area of each peak determined as described above. Is calculated automatically. In FIG. 1, the total endothermic peak heat quantity (ΔH) corresponds to the total heat quantity of each endothermic peak (ΔH = ΔHa + ΔHb + ΔHc).

In the above measurement method, the reason why the point α on the DSC curve corresponds to the temperature of 80 ° C. in order to draw the line segment (α−β) as the base line is that the point corresponding to 80 ° C. is the starting point. And the baseline with the point corresponding to the end temperature of melting as the end point is suitable for stably obtaining the heat quantity of the endothermic peak with good reproducibility.
The polypropylene resin expanded particles preferably used in the present invention have a peak temperature (PTmA) of 100 to 140 ° C. in the first DSC curve, and the endothermic peak heat quantity is 70 of the total endothermic peak heat quantity (ΔH). It has a crystal structure in which a main endothermic peak of ˜95% appears. Thus, in the DSC curve of PP beads in Figure 1, the endothermic peak a ₁ indicates a main endothermic peak. Furthermore, the polypropylene resin expanded particles have a crystal structure in which two or more endothermic peaks appear on the high temperature side of the main endothermic peak in the first DSC curve. Thus, in the DSC curve of PP beads in FIG. 1, an endothermic peak _a 2, _{a 3} shows two endothermic peaks _a 2, _{a 3} present in the high-temperature side of the main endothermic peak _{a 1.}

In the expanded particles preferably used in the present invention, the peak temperature (PTmA) indicates 100 to 140 ° C. and the endothermic peak heat amount is 70 to 95% of the total endothermic peak heat amount (ΔH). Among any three or more endothermic peaks appearing in the first DSC curve of the resin-based resin expanded particles, the endothermic peak having a peak temperature (PTmA) of 100 to 140 ° C. is relative to the total endothermic peak calorific value (ΔH). It means that the percentage of the endothermic peak heat quantity (for example, (ΔHa / ΔH) × 100 in FIG. 1) is 70 to 95%.
Due to the presence of the main endothermic peak that satisfies the above conditions of the peak temperature and endothermic peak heat amount, the molding temperature during molding of the foamed particles can be sufficiently lowered, and two or more appearing on the high temperature side of the main endothermic peak In combination with the presence of the endothermic peak, it is possible to prevent deterioration of physical properties such as the original mechanical strength and heat resistance of the obtained molded polypropylene resin particle expanded body. Note that the endothermic peak apex temperature (PTmA) of the main endothermic peak is 105 to 135 ° C., more preferably 110 ° C. or more and less than 125 ° C., to further reduce the molding temperature at the time of in-mold molding. It is preferable from the viewpoint.

Further, in the expanded particles preferably used in the present invention, the endothermic peak heat quantity of the main endothermic peak is 80 to 95%, more preferably 85 to 92% of the total endothermic peak heat quantity (ΔH). It is preferable from the viewpoint of balance between improvement in physical properties such as mechanical strength and heat resistance of the molded article and moldability of the foamed particles at low temperature.
Two or more endothermic peaks appearing on the high temperature side of the main endothermic peak can be obtained by using a mixture of a plurality of polypropylene resins or by using a polymerization catalyst and polymerization conditions. In addition to mixing, the isothermal crystallization operation described below (operation for maintaining the polypropylene resin for a predetermined time at a temperature near the resin melting point of the polypropylene resin constituting the foamed particles for a predetermined time) It can be formed easily. In addition, when two or more endothermic peaks appearing on the high temperature side of the main endothermic peak are a crystal structure formed in the expanded particles by mixing a plurality of polypropylene resins and isothermal crystallization operation, the two or more endothermic peaks Is divided into an endothermic peak derived from the propylene-based resin component forming the main endothermic peak of the polypropylene-based resin expanded particles and an endothermic peak due to the other propylene-based resin component.

Of the two or more endothermic peaks, the endothermic peak derived from the propylene-based resin component forming the main endothermic peak is an isothermal crystal of the propylene-based resin forming the main endothermic peak in the step of producing expanded particles. It can be formed by the conversion operation. Note that two or more endothermic peaks appearing on the high temperature side of the main endothermic peak are an endothermic peak derived from the propylene resin component forming the main endothermic peak in the polypropylene resin (hereinafter also referred to as a high temperature peak), and The fact that it consists of an endothermic peak due to other propylene resin components can be confirmed by the following heat flux differential scanning calorimetry method of polypropylene resin foamed particles.
1 to 3 mg of expanded polypropylene resin particles are heated from room temperature (approximately 25 ° C.) to 200 ° C. at a rate of temperature increase of 2 ° C./min with a heat flux differential scanning calorimeter to obtain a first DSC curve. Subsequently, immediately after reaching the temperature of 200 ° C., it is cooled from 200 ° C. to 25 ° C. at a cooling rate of 10 ° C./min, and again from 25 ° C. at a rate of temperature increase of 2 ° C./min immediately after reaching the temperature of 25 ° C. Heat to 200 ° C. to obtain a second DSC curve.

Of the expanded polypropylene resin particles of the present invention, when two or more endothermic peaks appearing on the high temperature side of the main endothermic peak are formed by mixing a plurality of polypropylene resins and isothermal crystallization operation, In the obtained first DSC curve, two or more endothermic peaks appear on the high temperature side of the main endothermic peak, but in the second DSC curve obtained by the above method, it exists on the high temperature side of the main endothermic peak. The number of endothermic peaks is reduced (however, there is one or more endothermic peaks on the high temperature side of the main endothermic peak). Then, by comparing the first DSC curve with the second DSC curve, at least one endothermic peak out of two or more endothermic peaks present on the higher temperature side than the main endothermic peak appearing in the first DSC curve. It can be confirmed that the peak disappears in the second DSC curve. By this comparison, the extinction endothermic peak is the endothermic peak derived from the propylene resin component forming the main endothermic peak, and the endothermic peak remaining on the higher temperature side than the main endothermic peak is due to the other propylene resin component. This is an endothermic peak. For example, in the first DSC curve of the expanded particles used in the present invention in FIG. 1, two endothermic peaks a ₂ and a ₃ appear on the high temperature side of the main endothermic peak a ₁ . In the second DSC curve of the expanded particles in FIG. 2, only one endothermic peak a ₃ appears on the high temperature side of the main endothermic peak, and the endothermic peak a ₂ disappears. In this case, the extincted endothermic peak a ₂ is an endothermic peak derived from the propylene resin component forming the main endothermic peak, and the endothermic peak a ₃ is an endothermic peak due to the other propylene resin component. .

The reason for setting the cooling rate from 200 ° C. to 25 ° C. at 10 ° C./min when obtaining the second DSC curve in the differential scanning calorimetry in the present invention and 25 when obtaining the second DSC curve. The reason for setting the rate of temperature increase from 200 ° C. to 2 ° C./min is the same as the reason for setting the rate of temperature increase at the time of obtaining the first DSC curve to 2 ° C./min. This is because it is not preferable that the measurement conditions are aligned in order to perform the measurement with improved measurement, and to compare the first DSC curve and the second DSC curve, and that the cooling rate is too slow.
The polypropylene resin expanded particles having a crystal structure exhibiting the thermal characteristics represented by the first DSC curve can be molded with a low heating vapor pressure, and a molded product obtained from the polypropylene resin expanded particles Is particularly preferable in obtaining a foamed particle molded body having mechanical properties comparable to those of conventional polypropylene resin foamed particle molded bodies.

Of the two or more endothermic peaks present on the higher temperature side than the main endothermic peak in the first DSC curve of the polypropylene resin expanded particles preferably used in the present invention, the endothermic peak calorific value of the high temperature peak is 2 It is preferably in the range of ˜15 J / g, more preferably 3 to 12 J / g. By adjusting the endothermic peak heat amount within the above range, it is possible to lower the heating temperature condition at the time of in-mold molding of the foamed particles, and to obtain a foamed particle molded body having excellent dimensional stability and mechanical properties. Excellent foam particles.
In addition to the method using the isothermal crystallization operation, a crystal structure having two or more endothermic peaks on the high temperature side of the main endothermic peak by a method of mixing a plurality of polypropylene resins having different melting points without performing the isothermal crystallization operation. The endothermic peak heat quantity of the endothermic peak at the lowest temperature among the two or more endothermic peaks appearing on the high temperature side of the main endothermic peak is 2-15 J / g, even 3-12 J It is preferable to adjust the mixing ratio of a plurality of polypropylene resins having different melting points so as to be in the range of / g for the same reason as the adjustment of the amount of heat at the high temperature peak. Of the two or more endothermic peaks appearing on the high temperature side of the main endothermic peak, the method of adjusting the endothermic peak heat quantity of the high temperature peak within the above range is the stable adjustment method by the isothermal crystallization operation at the time of foamed particle production described below. It is preferable to obtain a foamed particle molded article having mechanical properties.

In the present invention, the main endothermic peak in the first DSC curve (the first DSC curve obtained by the heat flux differential scanning calorimetry method at a heating rate of 2 ° C./min) of FIG. The peak temperature of the endothermic peak at the peak temperature (PTmA) and the second DSC curve of FIG. 2 (second DSC curve obtained by the heat flux differential scanning calorimetry method at a heating rate of 2 ° C./min) of the expanded particles. (TmA) approximates.
The polypropylene resin used in the present invention is not particularly limited as long as it satisfies the constituent requirements of the present invention, but a polypropylene resin polymerized using a metallocene polymerization catalyst should be used. However, it is preferable because it becomes easy to obtain expanded particles having the specific crystal structure.

  In the present invention, the base resin constituting the polypropylene resin expanded particles is preferably prepared by mixing a plurality of polypropylene resins in order to obtain the polypropylene resin expanded particles having the crystal structure. Further, the plurality of polypropylene resins to be mixed have a melting point temperature difference of 20 ° C. or higher, preferably 25 ° C. or higher, more preferably 30 ° C. or higher, and a low melting point polypropylene resin and a high melting point polypropylene resin. It is preferable to contain at least two kinds of resins. By setting the melting point temperature difference within the above range, two or more endothermic peaks on the higher temperature side than the main endothermic peak on the first DSC curve of the expanded particles among the specific crystal structure in the polypropylene resin expanded particles. It becomes easy to adjust the foamed particles so as to have a crystal structure. In addition, by selecting a polymer that has been polymerized using a metallocene polymerization catalyst as a low melting point polypropylene resin and mixing it with a high melting point polypropylene resin, the low melting point polypropylene resin component of the mixed resin Since the melting point shifts to a low temperature side, for example, around 5 ° C., compared to the melting point of the low melting point polypropylene resin used for mixing, the foamed particles obtained from the mixed resin have a heating temperature at the time of in-mold molding. It can be further lowered.

In the present invention, the base resin constituting the polypropylene resin expanded particles is a low melting point polypropylene resin having a melting point of 100 to 140 ° C. (hereinafter referred to as a low melting point polypropylene resin (A)) and the low melting point polypropylene resin. A mixture of the resin (A) and a polypropylene resin having a high melting point of 20 ° C. or higher, preferably 25 ° C. or higher, and more than 30 ° C. (hereinafter referred to as a high melting point polypropylene resin (B)). Preferably it consists of.
In this case, the resin melting point of the polypropylene resin is a value obtained in the same manner as in the method for measuring the melting temperature of the polypropylene resin expanded particles described above.
The low melting point polypropylene resin (A) is preferably a random copolymer of propylene and ethylene or / and an α-olefin having 4 to 20 carbon atoms, in order to obtain a resin having a melting point of 100 to 140 ° C. Therefore, it is preferable for obtaining a main endothermic peak having a vertex temperature of 100 to 140 ° C. on the first DSC curve of the foamed particles obtained. The low melting point polypropylene resin (A) has a melting point of 100 to 140 ° C, preferably 105 to 135 ° C, more preferably 105 to 130 ° C, and particularly preferably 110 to 125 ° C. It is preferable in that the heating temperature at which a good foamed particle molded body of a foamed particle obtained from a mixed resin containing a resin is obtained during molding can be lowered, and the heat resistance of the resulting foamed particle molded body can be secured. .

When the low melting point polypropylene resin (A) is made of a polypropylene resin random copolymer as described above, the comonomer copolymerized with propylene is ethylene, 1-butene, 1-pentene, 1-hexene, 1- Examples include octene and 4-methyl-1-butene. Therefore, specific examples of the low melting point polypropylene resin (A) include propylene-ethylene random copolymer, propylene-butene 1 random copolymer, propylene-ethylene-butene-1 random copolymer, and the like. Further, the ethylene unit component and / or the α-olefin unit component having 4 to 20 carbon atoms in the low melting point polypropylene resin (A) is 0.01 to 8% by weight, more preferably 0.05 to 0.05% from the viewpoint of melting point and strength. It is preferably 5% by weight.
Examples of the low melting point polypropylene resin (A) include a propylene-ethylene random copolymer, propylene-butene 1 random copolymer, propylene obtained by copolymerizing propylene and a comonomer using a so-called metallocene polymerization catalyst. -An ethylene-butene-1 random copolymer is more preferable. Further, the low melting point polypropylene resin (A) obtained using the metallocene polymerization catalyst is excellent in compatibility with the high melting point polypropylene resin (B), and has a crystal structure peculiar to the expanded polypropylene resin particles. It is particularly preferable because it is easy to form.

Examples of the high melting point polypropylene resin (B) mixed with the above low melting point polypropylene resin (A) include propylene homopolymer, propylene, and ethylene and / or an α-olefin having 4 to 20 carbon atoms. Examples of the block copolymer include a random copolymer of propylene having a low comonomer content and ethylene or / and an α-olefin having 4 to 20 carbon atoms.
In the present invention, in the mixture of the low melting point polypropylene resin (A) and the high melting point polypropylene resin (B), which is preferably exemplified as the structure of the base resin of the expanded particles, for example, the mixing ratio of the two in weight ratio The low melting point polypropylene resin (A): the high melting point polypropylene resin (B) = 98: 2 to 90:10, preferably 95: 5 to 92: 8. Thereby, the ratio of the main endothermic peak to the total endothermic peak heat quantity can be easily adjusted to 70 to 95%.

The melt flow rate (MFR) of the base resin of the expanded particles used in the present invention is preferably 5 to 60 g / 10 minutes, more preferably 10 to 40 g / 10 minutes. When the base resin is composed of the low melting point polypropylene resin (A) and the high melting point polypropylene resin (B), the low melting point polypropylene resin (A) has an MFR of 1 to 100 g / 10 min. Further, it is preferable that the high melting point polypropylene resin (B) has a MFR of 0.1 to 50 g / 10 minutes, more preferably 0.2 to 20 g / 10 minutes. MFR is a value measured under test condition M (temperature 230 ° C., load 2.16 kg) of JIS K7210 (1999).
What consists of the mixture of the said polypropylene resin preferably illustrated as base resin which comprises the expanded particle in this invention is obtained by mixing at least 2 sort (s) of resin which has the above-mentioned melting | fusing point temperature difference with a kneader. It is important to mix the two so that they are sufficiently uniform. If the mixing is insufficient, it becomes difficult to obtain polypropylene resin expanded particles having two or more endothermic peaks on the high temperature side of the main endothermic peak on the above-described crystal structure, particularly the first DSC curve. The above mixing is usually performed by heating to a temperature at which both resins are melted and kneading with a highly kneading extruder such as a twin-screw kneader, or by starvation as described in, for example, JP-A-2006-69143. It is preferable to employ a general molding method and knead in an extruder. After the kneading, the kneaded product is extruded into a string from an extruder, cut into an appropriate length, and granulated into resin particles having a size suitable for producing foamed particles.

The average weight per foamed particle used in the present invention is usually from 0.01 to 10.0 mg, particularly preferably from 0.1 to 5.0 mg. It can be adjusted by a pelletizing process for obtaining resin particles for obtaining expanded particles.
The polypropylene resin constituting the base resin of the expanded particles used in the present invention may contain other polymer components and additives in the pelletizing step and the like within a range not impairing the effects of the present invention. it can.
Examples of the other polymer component include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid. Polyethylene resins such as copolymers, ethylene-methacrylic acid copolymers, or polystyrene resins such as polystyrene and styrene-maleic anhydride copolymers, ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1- Examples include rubbers such as butene rubber, ethylene-propylene-diene rubber, isoprene rubber, neoprene rubber, and nitrile rubber, and thermoplastic elastomers such as styrene-diene block copolymers and hydrogenated styrene-diene block copolymers. . These resins, rubbers, or elastomers can be used in combination of two or more. When the other polymer component is blended with the polypropylene resin, the content of these other polymer components is preferably adjusted to be 10 parts by weight or less with respect to 100 parts by weight of the polypropylene resin.

Examples of the additive include a bubble adjusting agent, an antistatic agent, a conductivity imparting agent, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a metal deactivator, a pigment, a dye, a crystal nucleating agent, or an inorganic filler. And various additives such as these can be included in the polypropylene resin constituting the expanded particles as desired. The content of these various additives varies depending on the purpose of addition, but is preferably 25 parts by weight or less, more preferably 15 parts by weight or less, and still more preferably 8 parts by weight or less, based on 100 parts by weight of the base resin. 5 parts by weight or less is most preferable.
The base resin constituting the expanded particles is preferably a non-crosslinked polypropylene resin from the viewpoints of recyclability, expanded particle productivity, and the like.
In the production of the foamed particles used in the present invention, for example, propylene resin particles obtained by granulation by the above-described method and the like and a foaming agent are dispersed in a dispersion medium such as water in a closed container and stirred. To soften the resin particles and impregnate the resin particles with a foaming agent, then release the resin particles into a low pressure region (usually atmospheric pressure region) at a temperature equal to or higher than the softening temperature of the resin particles to foam The known foaming methods described in JP-B-49-2183, JP-B-56-1344, JP-B-62-61227 and the like can be applied. In addition, when the contents in the sealed container are released from the sealed container to a low pressure region in order to obtain expanded particles, back pressure is applied to the sealed container with the used foaming agent or an inorganic gas such as nitrogen or air. From the viewpoint of uniforming the apparent density of the obtained expanded particles, it is preferable to release the contents in such a manner that the pressure in the container does not drop rapidly. The dispersion medium for dispersing the resin particles in the production of the expanded particles is not limited to the above-described water, and any medium that does not dissolve the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like, but usually water is used.

  In the above method, in the dispersion medium, if necessary, poorly water-soluble such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, and kaolin so that the resin particles are uniformly dispersed in the dispersion medium. It is preferable to disperse a dispersing aid such as a dispersing agent such as an inorganic substance and an anionic surfactant such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate. The amount of the dispersant added to the dispersion medium when producing the foamed particles is such that the ratio of the weight of the resin particles to the weight of the dispersant (the weight of the resin particles / the weight of the dispersant) is 20 to 2000, and further 30. It is preferable to set it to -1000. Further, the ratio of the weight of the dispersing agent to the weight of the dispersing aid (the weight of the dispersing agent / the weight of the dispersing aid) is preferably 1 to 500, more preferably 5 to 100.

The average cell diameter of the expanded particles used in the present invention is usually 30 to 500 μm, and preferably 50 to 350 μm. The foamed particles having an average cell diameter in the above range show good foamability because there is no risk that the bubbles constituting the foamed particles break up during molding of the foamed particles described later from the relationship of the strength of the foam film.
The average cell diameter of the foamed particles can be obtained by the following operation based on an enlarged photograph obtained by photographing a cell cross section obtained by cutting the foamed particles into approximately two equal parts. In the enlarged photograph of the bubble cross section, four straight lines passing from the surface of the foamed particle to the other surface and passing through the center of the bubble cross section are drawn radially in 8 directions from the center toward the surface of the foamed particle. Subsequently, the total number of bubbles: N (pieces) intersecting the four straight lines is obtained. Then, the sum of the lengths of the line segments from the surface of the expanded particle to the other surface in each of the four straight lines: L (μm) is divided by the total number of bubbles: N (number) (L / N ) Is the average cell diameter of the expanded particles.

In addition, since the average cell diameter is increased by increasing the MFR of the base resin, increasing the foaming temperature, decreasing the foaming agent, decreasing the cell regulator, and the like, appropriately adjust these average cell diameter fluctuation factors. Thus, expanded particles having a target average cell diameter can be obtained.
In addition, as a method for adjusting the average cell diameter of the above-mentioned expanded particles, an inorganic substance such as talc, aluminum hydroxide, silica, zeolite, borax or the like is mainly used as a cell regulator and is 0.01 to 100 parts by weight with respect to 100 parts by weight of the base resin. In the proportion of 5 parts by weight, it is carried out by blending into the base resin during the production of the resin particles for obtaining the foamed particles. Since the bubble diameter changes, it is necessary to set conditions by conducting a preliminary experiment in order to obtain an object having the target average bubble diameter.

The polypropylene resin expanded particles used in the present invention usually have an apparent density of 100 g / L or more and 720 g / L or less. The upper limit of the apparent density of the foamed particles of the present invention is determined from the viewpoint of improving basic properties such as light weight and buffering property of the foamed molded article to be obtained, preferably 500 g / L, more preferably 300 g / L. On the other hand, if the apparent density of the expanded particles is too low, it is difficult to obtain the foamed molded product targeted by the present invention. Therefore, the lower limit of the apparent density is preferably 120 g / L, and 150 g / L. More preferably.
The apparent density of the foamed particles is determined by subtracting the foamed particle group having a weight of W (g) into a graduated cylinder containing water using a wire mesh or the like from the rise in water level. Volume: V (L) is obtained, and the weight is determined by dividing the weight of the expanded particle group by the volume of the expanded particle group (W / V).

  In the present invention, the foamed particles having the high temperature peak are also referred to as melting end temperatures (hereinafter referred to as Te) of the resin particles when the resin particles are dispersed in a dispersion medium in a closed container and heated in the known foaming method. ) Heating is stopped at an arbitrary temperature Ta within a range of 15 ° C. or higher and lower than Te without melting the resin particles (hereinafter also referred to as Tm) without increasing the temperature, and the temperature Ta is sufficient. Hold for about 10 to 60 minutes, and then adjust to an arbitrary temperature Tb in the range of (Tm-5 ° C.) to (Te + 5 ° C.), and release the resin particles from the container to the low pressure range at that temperature. Thus, it can be appropriately obtained by the foaming method. In addition, as the holding within the above (Tm−15 ° C.) and less than Te for forming the high temperature peak, it may be set in multiple stages within the temperature range, or the temperature range. The temperature may be increased slowly over a sufficient time.

  The formation of the high-temperature peak of the expanded particles and the magnitude of the heat quantity of the high-temperature peak are mainly due to the temperature Ta with respect to the resin particles when the expanded particles are produced, the retention time at the temperature Ta, the temperature Tb, and (Tm− 15 ° C.) to (Te + 5 ° C.). The amount of heat at the high temperature peak of the expanded particles is such that the lower the temperature Ta or Tb within the above temperature ranges, the longer the holding time in the range of (Tm−15 ° C.) or more and less than Te, and (Tm− 15 ° C.) or higher and lower than Te. In addition, the said temperature increase rate is normally selected within the range of 0.5-5 degreeC / min. On the other hand, the amount of heat at the high temperature peak of the expanded particles is such that, as the temperature Ta or Tb is higher in each of the above temperature ranges, the retention time in the range of (Tm−15 ° C.) or more and less than Te is shorter. Tm−15 ° C.) or more, the higher the temperature rising rate within the range of Te, the lower the temperature rising rate within the range of Te to (Te + 5 ° C.). If the preliminary experiment is repeated in consideration of these points, it is possible to know the production conditions of the expanded particles exhibiting a desired high-temperature peak heat quantity. In addition, the temperature range which concerns on formation of the high temperature peak mentioned above is a suitable temperature range at the time of using an inorganic type physical foaming agent as a foaming agent. Therefore, when the foaming agent is changed to an organic physical foaming agent, the appropriate temperature range shifts by about 0 to 30 ° C. to the lower temperature side than the above temperature range depending on the type and amount of use.

  As the foaming agent used in the above method, an organic physical foaming agent, an inorganic physical foaming agent, or a mixture thereof can be used. Organic physical foaming agents include aliphatic hydrocarbons such as propane, butane, hexane, pentane and heptane, alicyclic hydrocarbons such as cyclobutane and cyclohexane, halogenated hydrocarbons such as methyl chloride, ethyl chloride and methylene chloride, dimethyl ether , And dialkyl ethers such as diethyl ether and methyl ethyl ether. These may be used in combination of two or more. Moreover, as an inorganic type physical foaming agent, nitrogen, carbon dioxide, argon, air, water, etc. are mentioned, These can be used in mixture of 2 or more types. When an organic physical foaming agent and an inorganic physical foaming agent are mixed and used, those arbitrarily selected from the above-described organic physical foaming agent and inorganic physical foaming agent can be used in combination. In addition, when using together an inorganic type physical foaming agent and an organic type physical foaming agent, it is preferable that an inorganic type physical foaming agent contains at least 30 weight% or more.

Among the above foaming agents, an inorganic physical foaming agent is particularly preferable from the viewpoint of environmental considerations, and nitrogen, air, carbon dioxide, and water are particularly preferable. In addition, when water is used as a dispersion medium together with the resin particles in the sealed container when obtaining the foamed particles, the water that is the dispersion medium is efficiently obtained by using the resin particles kneaded with a water absorbent resin or the like. It can be used as a blowing agent.
The amount of foaming agent used is determined in consideration of the apparent density of the intended foamed particles, the type of base resin, the type of foaming agent, and the like. Usually, it is preferable to supply the physical foaming agent into the container so that the pressure in the space inside the sealed container is 0.05 to 10 MPa (G), and further 1 to 8 MPa (G).
The polypropylene resin foamed particles obtained by releasing the softened resin particles containing the foaming agent from the sealed container to the low pressure region by the above-described method are subjected to a curing step in an atmospheric pressure range that is usually performed after the release. After that, it becomes a polypropylene resin expanded particle for molding.

  The foamed particle molded body of the present invention, if necessary, puts the polypropylene resin foam particles for molding obtained by the above-described method in a sealed container for pressurization, and pressurizes the sealed container with a pressurized gas such as air. The pressure in the expanded particles was adjusted to 0.01 to 0.2 MPa (G) by adjusting the pressure to 0.01 to 1 MPa (G) and increasing the pressure in the expanded particles by pressure treatment. Thereafter, it is filled in a cavity of a conventionally known thermoplastic resin foam particle molding mold that can be heated and cooled, and can be opened and closed, and then the saturated vapor pressure is 0. The foamed particles are heated by supplying water vapor at a pressure of 05 to 0.30 MPa (G), preferably 0.08 to 0.25 MPa (G) to expand and fuse the foamed particles together, and then obtained foam Cool the particle compact Batch type in molding is taken out from the inner (e.g., Kokoku 4-46217 and JP-molding method described in KOKOKU 6-49795 Patent Publication) can be produced by employing a. In addition, as the method of steam heating in the above in-mold molding method, a conventionally known method that appropriately combines heating methods such as one-side heating, reverse one-side heating, and simultaneous heating in both directions can be adopted. On the other hand, a method of heating the foamed particles in the order of heating and simultaneous heating in both directions is preferable. The saturated vapor pressure of 0.05 to 0.30 MPa (G) at the time of foamed particle molding is the maximum value of the saturated vapor pressure of water vapor supplied into the mold in the in-mold molding step.

Moreover, the foamed particle molded body of the present invention has a foamed particle in a passage having a heating region and a cooling region after adjusting the pressure in the foamed particle to 0.01 to 0.2 MPa (G) as necessary. Is continuously fed into a mold formed by a belt continuously moving along the upper and lower sides of the sheet, and when passing through the heating region, the saturated vapor pressure is 0.05 to 0.30 MPa (G), preferably 0.8. Steam of 08 to 0.25 MPa (G) is supplied into the mold to heat the foamed particles to expand and fuse the foamed particles, and then cooled by passing through a cooling region, and then obtained foamed particles A continuous in-mold molding method (for example, disclosed in JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.) in which a molded body is taken out from the mold and sequentially cut to an appropriate length. Manufacturing method) You can also.
In-mold molding with the polypropylene resin foam particles of the present invention is such that the surfaces of the foam particles can be fused together by heating with the water vapor, and then the foam particles themselves are softened and can be secondary foamed. As a result, it becomes a good foamed particle molded body having both excellent appearance and fusion property between the foamed particles, and at the same time, even if some heating unevenness occurs during molding in the mold, the foamed particle is good due to the wide molding temperature range. It becomes a molded body.

In the case of obtaining a foamed molded article having a high density, in the conventional molding of polypropylene resin foamed particles, foamed particles having an apparent density of 70 g / L or more are produced, and the foamed particles are filled into the mold cavity. It is difficult to obtain a good foamed particle molded body unless the compression ratio at the time is set to a high state of 20% or more and the molding is performed by saturated steam heating at a high steam pressure exceeding 0.30 MPa (G). However, according to the method for producing a polypropylene resin foamed particle molded body of the present invention, the low-magnification foamed particles can be obtained without using such a method or without increasing the pressure in the foamed particles as in the prior art. It has the characteristics which can obtain a molded object.
Therefore, the method for producing a foamed particle molded body of the present invention has a second feature that the compression rate at the time of filling in the mold in the polypropylene resin foamed particle in-mold molding is 0 to 15%.

The compression rate at the time of filling the above-mentioned foamed particles into the mold cavity is determined from the mold cavity internal volume: MV (L) and the bulk volume of the foamed particles filled in the mold: BV (L). , (BV-MV) / MV × 100. In addition, the volume volume of the foamed particles filled in the mold: BV is the volume density of the foamed particles, the foamed particles are put into an empty graduated cylinder, and the volume (L) indicated by the scale of the graduated cylinder is the graduated cylinder. Obtained by dividing the weight (g) of the foamed particles contained in the mold, filled with foamed particles having a known bulk density in the mold, and the weight (g) of the foamed particles filled in the mold was determined as the foamed particles. It is calculated by dividing by the bulk density.
As described above, the foamed particle molded body of the present invention has a density of 100 to 720 g / L and is heated when the foamed particles are heated in a pressure resistant container for 10 seconds with saturated vapor at the melting temperature of the foamed particles. The apparent density ratio (ρ _R ) of the foamed particles before and after [(apparent density of the foamed particles before heating [g / L]) / (apparent density of the foamed particles after heating [g / L])] is 1-1. .7 can be easily obtained by adjusting the compression rate when filling the foamed particles into the mold to 0 to 15% and molding in the mold. In addition, it is preferable that the said compression rate is 3 to 15%, and also 5 to 13% from a viewpoint of the fusion | melting property between foam particles of a foamed particle molded object, and an external appearance.

In the foamed particle molded body of the present invention thus obtained, the foamed particles are closely fused, and the fusion rate of the foamed particles described in detail in the examples is 50% or more, preferably 70% or more. It exhibits mechanical properties such as good compressive strength. Further, the surface of the foamed particle molded body is extremely small and smooth, and is excellent in dimensional stability. In addition, the density of the foamed particle molded body of the present invention is preferably 60 to 450 g / L, more preferably 90 to 300 g / L, from the intended purposes such as mechanical strength, buffering property, and lightness. The density (g / L) of the foamed particle molded body can be determined by dividing the weight (g) of the foamed particle molded body by the volume (L) determined from the external dimensions of the foamed particle molded body. .
Furthermore, the foamed particle molded body of the present invention has a ratio (Ds / Dc) between the density (Ds) [g / L] of the surface layer portion of the molded body and the density (Dc) [g / L] inside the molded body. ) Is 1 to 2, which means that the density distribution of the foamed particle molded body is uniform as compared with the conventional one. The conventional low-magnification expanded particle molded body has a surface layer part density much higher than the internal density of the molded body due to restrictions on the production method of the expanded particle molded body, as if it had a high density expanded layer It has a multilayer structure in which a low-density foam layer is sandwiched between them. Therefore, in the conventional foamed particle molded body, the density of the surface layer is much higher than the average density of the entire molded body, and the internal density is much lower than the average density of the entire molded body. It was a thing.

The compressive strength of such a conventional foamed particle molded body is such that when the molded body is compressed, the internal foam having a much lower density is deformed first, so that a high compression property equivalent to the overall density can be obtained. It was difficult. On the other hand, since the expanded particle molded body of the present invention has a uniform density distribution of the expanded particle molded body as compared with the conventional one as described above, it is possible to express a high compression property equivalent to the density. In addition, the stability of mechanical properties is excellent, and the problem of variation in physical properties during secondary processing can be improved. From the above viewpoint, the ratio (Ds / Dc) in the foamed particle molded body of the present invention is preferably 1.1 to 1.7, more preferably 1.1 to 1.5, and particularly preferably 1.2 to 1.4. . The ratio (Ds / Dc) of the foamed particle molded body of the present invention satisfies the relationship of the above ratio (Ds / Dc) for both the front surface portion and the back surface portion.
In addition, the measuring method of the density (Ds) [g / L] of the surface layer part and the internal density (Dc) [g / L] of the foamed particle molded body of the present invention is as follows.

The surface layer portion of the foamed particle molded body of the present invention includes a surface called a skin surface of the foamed particle molded body and is a portion from the surface of the foamed particle molded body to a depth of 5 mm in the thickness direction. And the density (Ds) of the surface layer part of the foamed particle molded body is obtained by cutting out the surface layer part from the foamed particle molded body (including the surface of the foamed particle molded body and 5 mm in the thickness direction from the surface of the foamed particle molded body). A portion up to the depth is cut out as a rectangular parallelepiped sample having a length of 50 mm, a width of 50 mm, and a thickness of 5 mm), and the weight (g) of the cut sample is divided by the volume (L) of the sample.
On the other hand, the inside of the foamed particle molded body of the present invention is the central portion in the thickness direction of the foamed particle molded body, does not include the surface of the foamed particle molded body, and is mainly from the center in the thickness direction of the foamed particle molded body. It is a portion up to 5 mm each toward the front and back surfaces. Then, the density (Dc) inside the foamed particle molded body is cut out from the foamed particle molded body (not including the surface of the foamed particle molded body and from the center in the thickness direction of the foamed particle molded body). A portion of up to 5 mm toward the surface and the back surface is cut out as a rectangular parallelepiped sample having a length of 50 mm, a width of 50 mm, and a thickness of 10 mm), and the weight (g) of the cut sample is divided by the volume (L) of the sample. be able to.
Further, in the foamed particle molded body of the present invention, the open cell rate based on the procedure C of ASTM-D2856-70 is preferably 40% or less, more preferably 30% or less, and 25% or less. Is most preferred. A foamed particle molded body having a smaller open cell ratio is superior in mechanical strength.
The foamed particle molded body of the present invention has characteristics such as shock-absorbing property, dimensional stability, rigidity, and lightness, and can be widely used for packaging materials, building materials, vehicle impact absorbing materials, and the like. It is suitable for packaging materials for electric and electronic parts and thin parts for automobiles.

Hereinafter, the present invention will be described with reference to examples and comparative examples.
Table 1 below shows resins used in Examples and Comparative Examples and their properties.

[Examples 1 to 6 and Comparative Examples 1 and 2]
(1) Production of expanded polypropylene resin particles Using a 65 mmφ single-screw extruder, the polypropylene resin listed in Table 1 was melt kneaded in an extruder together with 500 ppm by weight of zinc borate (Table 2). However, about Examples 1-4, it melt-kneaded with the extruder under the following starvation operation conditions.), The kneaded product was extruded into a strand shape from a small hole of a die attached to the tip of the extruder, and a water tank The strand was cut to a weight of approximately 1 mg and dried to obtain resin particles. The above starvation operation conditions are a method for kneading so that resins having greatly different melting points and melt viscosities are well dispersed by the above-mentioned starvation molding method. Fill the resin pellets and fill the extruder with resin. Is supplied and extruded while adjusting the supply with a capacity-type feeder. In Examples 1-4, the discharge amount at the time of starvation operation with respect to the time of full operation was 70%.
1 kg of the resin particles obtained as described above was charged into a 5 L sealed container equipped with a stirrer together with 3 L (liter) of water as a dispersion medium, and further 0.3 parts by weight of kaolin as a dispersant, a surfactant in the dispersion medium. Sodium alkylbenzene sulfonate (trade name: Neogen S-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 0.004 parts by weight (provided that 0.004 parts by weight is the amount of sodium alkylbenzene sulfonate in Neogen S-20), and Add 0.01 parts by weight of aluminum sulfate, press the compressed air as a foaming agent into the airtight container up to the pressure shown in Table 2, raise the temperature to the foaming temperature shown in Table 2 with stirring, and continue at that temperature for 15 minutes. After holding and adjusting the high temperature side endothermic peak heat amount, the contents were released under atmospheric pressure to obtain expanded particles having an apparent density shown in Table 2. In addition, the said weight part is a weight part with respect to 100 weight part of resin particles. The properties of the obtained expanded particles are also shown in Table 2.

(2) Production of Foam Molded Body The foam particles obtained above are filled into a flat plate mold having a length of 250 mm, a width of 200 mm, and a thickness of 50 mm, and in-mold molding by steam heating is performed under the in-mold molding conditions shown in Table 3. It went and obtained the plate-shaped foaming molding. The obtained foamed molded body was cured in an oven at 80 ° C. for 12 hours to obtain a polypropylene resin foamed particle molded body. The properties of the obtained foamed particle molded body are also shown in Table 3.

(3) Evaluation of Expanded Particles and Expanded Particle Molded Body Evaluation of the expanded particles and the expanded particle molded body in Table 3 was performed according to the following (A) to (F).
(A) Measurement of fusion pressure of foamed particles Based on the first DSC curve of the foamed particles, a lower limit of the temperature at which the surface of the foamed particles melts is predicted, and the foamed particles by steam having a saturated vapor pressure corresponding to the lower limit temperature The foamed particle molded body obtained by in-mold molding is evaluated for the fusing property between the following foamed particles to confirm that the fusion rate of the foamed particle molded body is less than 50%. Next, the above-described fusion property was evaluated in the same manner except that the steam saturated vapor pressure was set higher by 0.01 MPa. The operation for evaluating the fusing property by setting the saturated vapor pressure of steam high by 0.01 MPa is sequentially performed until the fusing rate of the foamed particle molded body becomes 50% or more, and the fusing rate is 50% or more for the first time. The saturation vapor pressure (the lowest saturated vapor pressure at which the fusion rate is 50% or more) at that time was taken as the fusion pressure. The mold used in the in-mold molding has a rectangular parallelepiped shape with a molding space of 250 mm in length, 250 mm in width, and 20 mm in thickness, and the compression rate when the foam particles are filled in the mold is 10 %. Further, as the expanded particles used for the above measurement, those which were conditioned by leaving them to stand for 48 hours under conditions of an air temperature of 23 ° C., a relative humidity of 50% and atmospheric pressure were used. In addition, the fusion rate of said foamed particle molded object is a value calculated | required by the below-mentioned method.

(B) Measurement of secondary foaming pressure of foamed particles Based on the first DSC curve of the foamed particles, a lower limit of the temperature at which the foamed particles undergo secondary foaming is predicted, and the container is sealed with steam having a saturated vapor pressure corresponding to the lower limit temperature. The foamed particles put in an appropriate amount are heated for 10 seconds, and the apparent density of the obtained foamed particles after heating is measured. A density ratio between the apparent density (g / L) of the expanded foam after heating measured as described above and the apparent density (g / L) of the expanded foam before heating was determined, and [the apparent density before heating (g / L) L)] / [apparent density after heating (g / L)] is confirmed to be less than 1.5. Subsequently, the secondary foaming property was evaluated in the same manner except that the saturated vapor pressure of steam was set higher by 0.01 MPa. The operation for evaluating the fusing property by setting the saturated vapor pressure of steam as high as 0.01 MPa is carried out by the density ratio of foamed particles [[apparent density before heating (g / L)] / [apparent density after heating (g / L)]] until the value becomes 1.5 or more, and the saturated vapor pressure when the density ratio value becomes 1.5 or more for the first time (the density ratio value becomes 1.5 or more). The lowest saturated vapor pressure) was taken as the secondary foaming pressure. In addition, as the expanded particles used for the above measurement, those whose state was adjusted by leaving them to stand for 48 hours under conditions of an air temperature of 23 ° C., a relative humidity of 50% and atmospheric pressure were used.

(C) Measurement of 50% compressive stress (i) 50% compressive stress of the test piece with skin 50 mm vertical, 50 mm wide, 50 mm thick (total thickness of the molded product) test piece with skin was cut out from the foamed molded product, and JIS Based on K6767 (1999), a compression test was performed in which the test piece was compressed in the thickness direction at a compression rate of 10 mm / min, and the 50% compression stress of the foamed particle molded body was determined.
(Ii) 50% compressive stress of skin-free test piece A cube having a length of 50 mm, a width of 50 mm, and a thickness (total thickness of the molded body) of 50 mm is cut out from the foamed particle molded body, and further the skin present on the upper and lower surfaces in the thickness direction of the molded body In order to cut off the skin, the skin is cut at a thickness of 12.5 mm from the upper and lower surfaces in the thickness direction to obtain a test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm, and a compression speed of 10 mm / min based on JIS K6767 (1999). A compression test for compressing the test piece in the thickness direction was performed to obtain a 50% compression stress of the foamed particle molded body.

(D) Density of test piece (i) Density of test piece with skin Cut out a test piece with a skin of 50 mm in length, 50 mm in width and 50 mm in thickness (total thickness of the molded product) from the foamed particle molded body, It was obtained by dividing by the volume (L) of the test piece.
(Ii) Density of skin test piece To cut out a 50 mm long, 50 mm wide, 50 mm thick (total thickness of the molded body) 50 mm cube from the foamed particle molded body, and to cut out the skin existing on the upper and lower surfaces in the thickness direction of the molded body The skin is cut from the upper and lower surfaces in the thickness direction at a thickness of 12.5 mm each to obtain a test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm, and the test piece weight (g) is the volume (L) of the test piece. It was calculated by dividing.

(E) Fusing property In the foamed particle molded body, Charpy of JIS K7111-1 (2006) was used except that the measurement of the fusion rate of the foamed particles was changed to a test piece size of 10 mm in length, 10 mm in width, and 80 mm in length. A test was conducted in accordance with the notch test method for impact strength, and the test piece was broken and obtained from the ratio of foamed particles whose material was broken on the fracture surface. When the test piece does not break, the fusion rate is 100%.
Fusing rate = Number of expanded particles with material destruction (number) / total number of expanded particles (number) in cross section (vertical 10 mm, horizontal 10 mm) × 100
Evaluation was made according to the following criteria based on the fusion rate obtained as described above.
A: Fusing rate is 70% or more B: Fusing rate is 50% or more and less than 70% B: Fusing rate is 30% or more and less than 50% X: Fusing rate is less than 30%

(F) Appearance The surface of the expanded particle molded body was observed with the naked eye and evaluated according to the following criteria.
A: A good surface state in which there are almost no particle gaps or irregularities on the surface of the foamed particle molded body.
Δ: Particle gaps and / or irregularities are clearly observed on the surface of the foamed particle molded body.
X: The particle | grain space | interval and / or unevenness | corrugation are remarkable on the surface of a foaming particle molding.

As shown in Table 3, the polypropylene resin expanded particle molded body according to the example of the present invention is excellent in the fusion property between the expanded particles while being a low-magnified expanded particle molded body, and also in the appearance of the molded body. It was good. Further, the density ratio between the surface layer portion and the inside of the foamed particle molded body is 2 or less, which is much closer to 1 than the conventional one as shown in the comparative example, and the density of the foamed particle molded body The uniformity is high.
The comparative example polypropylene-based resin expanded particle molded body of Table 3 according to the prior art is insufficient in the fusion property and appearance between the expanded particles, or the fusion property and appearance are within the allowable range. However, the density uniformity between the surface layer portion and the inside of the foamed particle molded body was insufficient.

Further, regarding the compressive strength of the foamed particle molded body, the difference in the base resin was found by comparing the 50% compressive stress in Table 3 of the same density of Examples 3 and 4 according to the present invention and Comparative Example 1 according to the prior art. However, it can be seen that the foamed particle molded body of the present invention is superior in compressive strength to the conventional one. Moreover, from the comparison with Examples 1-6 and Comparative Examples 1 and 2 about the value of the compression property ratio of Table 3, the foamed particle molded body of the present invention has a surface layer portion and an inside of the molded body rather than the conventional one. It can be seen that the difference in compressive strength is small and the compressive strength uniformity is excellent.
The foamed polypropylene resin particles shown in the examples of the present invention in Table 2 have low steam pressure during in-mold molding as shown in Table 3 (particularly in Example 1, although the steam pressure is extremely low). It can be seen that it is possible to obtain a foamed particle molded body having a good fusion property between the foamed particles and a good appearance.

Explanatory drawing of the 1st DSC curve of the polypropylene resin expanded particle which concerns on the manufacturing method of the molded object of this invention is shown. Explanatory drawing of the 2nd DSC curve of the polypropylene resin expanded particle which concerns on the manufacturing method of the molded object of this invention is shown.

Explanation of symbols

The point corresponding to 80 ° C on the α DSC curve The point corresponding to the melting end temperature on the β DSC curve γ The valley of the low temperature side peak and the high temperature side peak δ Intersection of the straight line α-β and the perpendicular from γ Te End of melting temperature a ₁ main endothermic peak a ₂ main endothermic peak on the high temperature side of the endothermic peak a ₃ main endothermic peak on the high temperature side of the endothermic peak TmA, PTMA endothermic peak apex temperature △ Ha main endothermic peak heat quantity △ Hb endothermic peak of the endothermic peak _{a 2} heat △ Hc endothermic peak heat quantity of the endothermic peak _{a 3}

Claims (6)

In a foamed particle in-mold molding method in which polypropylene resin foam particles are filled into a mold and heat molded, the polypropylene resin foam particles have an apparent density of 100 to 720 g / L and a melting temperature of the foam particles. Apparent density ratio (ρ _R ) of the foamed particles before and after heating when the foamed particles are heated in a pressure vessel for 10 seconds with saturated steam [(apparent density of the foamed particles before heating [g / L]) / ( The apparent density [g / L])] of the foamed particles after heating is 1 to 1.7,
In the first DSC curve obtained by heating the expanded particles from room temperature to 200 ° C. at a rate of temperature increase of 2 ° C./min by differential scanning calorimetry, 70 to 95% of the total endothermic peak heat amount is obtained. A main endothermic peak showing an endothermic peak heat quantity and a peak temperature of the endothermic peak of 100 to 140 ° C., and a crystal structure in which an endothermic peak appears on the high temperature side of the main endothermic peak,
A method for producing a molded product of expanded polypropylene resin particles, wherein the compression rate of the expanded polypropylene resin particles in a mold is 0 to 15%. Method for producing PP beads molded article according to claim 1, characterized in that it comprises two or more endothermic peak Kugagen are crystal structure to a high temperature side of the main endothermic peak. The polypropylene resin as the base resin constituting the polypropylene resin expanded particles is a low melting point polypropylene resin (A) having a melting point of 100 to 140 ° C. and a high melting point polypropylene having a melting point higher by 20 ° C. than the melting point of the resin. The method for producing a foamed molded product of polypropylene resin particles according to claim 1 or 2, wherein the product is a mixture with the resin based resin (B). The low melting point polypropylene resin (A) is a copolymer of propylene and ethylene or / and an α-olefin having 4 to 20 carbon atoms among the base resin constituting the polypropylene resin expanded particles. 4. A method for producing a polypropylene resin expanded resin molded article according to 3. The polypropylene according to claim 3 or 4, wherein, among the base resins constituting the polypropylene resin expanded particles, the low melting point polypropylene resin (A) is a polypropylene resin polymerized using a metallocene polymerization catalyst. For producing a molded resin-based foamed particle molded body. In a foamed particle molded body formed by filling polypropylene resin expanded particles into a mold and heat-molding, the density of the molded body is 60 to 450 g / L, the fusion rate of the expanded particles is 50% or more, A polypropylene resin characterized in that the ratio (Ds / Dc) of the density (Ds) [g / L] of the surface layer part and the density (Dc) [g / L] inside the molded body is 1-2. Expanded particle molded body.

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