JP2009221258A - Pre-expanded polypropylene resin particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide pre-expanded polypropylene resin particles which can give a high-fusion rate (≥75%) in-mold expanded molding at a low molding heating steam pressure in performing the in-mold molding of pre-expanded polypropylene resin particles comprising polypropylene resin particles produced by an underwater cutting system. <P>SOLUTION: Provided are pre-expanded polypropylene resin particles characterized by having a surface melting temperature of 130°C or lower and being particles obtained by feeding polypropylene resin particles obtained by melt-kneading a polypropylene resin composition with an extruder, extruding the resulting mixture into water through a die nozzle fitted on the front end of the extruder, and cutting the extrudate with a cutter edge rotating in the water, water, a dispersant, and blowing agent into a pressure vessel, heating the contents to a temperature not less than the softening point of the polypropylene resin particles to infiltrate the blowing agent into the polypropylene resin particles under elevated pressure, and releasing the resultant mixture into an atmosphere of a pressure lower than that inside the pressure-resistant vessel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing polypropylene resin pre-expanded particles used for buffer packaging materials, pass boxes, automobile interior members, automobile bumper core materials, heat insulating materials, and the like.

  The in-mold foam molded article obtained by using the polypropylene resin pre-expanded particles has characteristics such as shape flexibility, light weight, and heat insulation, which are advantages of the in-mold foam molded article. Compared to similar in-mold foam moldings, it is superior in chemical resistance, heat resistance and strain recovery after compression compared to in-mold foam moldings obtained using polystyrene resin pre-expanded particles. In addition, the dimensional accuracy, heat resistance, and compressive strength are excellent as compared with the in-mold foam molded body obtained using the polyethylene resin pre-expanded particles. Due to these characteristics, in-mold foam molded articles obtained using polypropylene resin pre-expanded particles are used in various applications such as automotive interior members, automotive bumper core materials, heat insulating materials, and cushioning packaging materials. .

  As a method for producing polypropylene resin pre-expanded particles, polypropylene resin as a raw material is melt kneaded with various additives in an extruder, and any particle can be formed by a strand cut method, an underwater cut method, a hot cut method, or the like. A polypropylene resin particle having a size is obtained, and the polypropylene resin particle is charged into a pressure vessel together with water, a dispersant, a foaming agent, etc., heated to a temperature equal to or higher than the softening point of the polypropylene resin particle, and the pressure is increased under pressure. It is known that it is obtained by impregnating a polypropylene resin particle with a foaming agent and then releasing it in an atmosphere at a lower pressure than in the pressure vessel.

  As a method for producing the polypropylene resin particles for obtaining polypropylene resin pre-expanded particles, a strand cut method is widely used. In the strand cut method, uniform cylindrical resin particles can be obtained with relatively inexpensive equipment. However, in order to improve the filling property in the in-mold molding, particles having a small particle weight are often required. When trying to obtain polypropylene resin particles having a relatively small weight, the occurrence of miscuts and the occurrence of strand breakage tends to increase, and the productivity tends to deteriorate. In addition, there are problems such as relatively low productivity because there is a limit to increasing the number of strands due to handling problems at the start of production when introducing strands into the pelletizer. Further, the residual strain is large from the cooling step of the polypropylene resin strands, and when the pre-foamed particles are produced, the resin particles are greatly contracted in the extrusion direction, and the shape of the pre-foamed particles may be greatly changed. It is required to accurately grasp and precisely manage this shape deformation.

  On the other hand, in the underwater cut method, since it is not necessary to operate the strand, it is easy to start granulation, and it is known that homogeneous polypropylene resin particles with less miscuts can be obtained with high productivity. ing. When pre-expanded particles are produced for in-mold molded products that require filling properties, etc., resin particles having a particle weight of 2.0 mg or less, which are smaller particles, will be produced. Therefore, productivity is remarkably lowered due to miscutting and operability deterioration, and easy granulation by the underwater cut method is advantageous in terms of productivity. However, the polypropylene resin pre-expanded particles using the polypropylene resin particles produced by this method are the same as the polypropylene resin pre-expanded particles produced by the widely used strand cut method. If it is used, the fusing property at the time of molding is significantly reduced. The cause is not clear, but due to this quality problem, the underwater cut method is not currently used for producing polypropylene resin pre-expanded particles for in-mold molding.

  Patent Document 1 describes a problem in which the meltability of the polypropylene resin pre-expanded particles during molding in the mold tends to be poor in the method for producing polypropylene resin particles for the polypropylene resin pre-expanded particles of the underwater cut method. As a countermeasure, a technique for adding a poorly water-soluble inorganic substance and a surfactant to circulating water in a water box that is extruded from a die nozzle and cut by a rotating cutter is disclosed. However, there is a problem that water pollution occurs.

  Patent Document 2 discloses a method for producing fine particles having a good shape to be used for producing pre-foamed particles for in-mold foam molding in which a thermoplastic resin is granulated by an underwater cut method using a large amount of circulating water. Yes. When performing in-mold molding with pre-expanded particles manufactured with the manufactured polypropylene-based resin particles, resin particles and pre-expanded compared to using polypropylene-based resin particles manufactured with a strand cut method that cannot be manufactured with high productivity Although the shape of the particles themselves is improved, it does not mention that the fusion property at the time of in-mold molding tends to be poor, and therefore it is necessary to increase the molding heating vapor pressure. It cannot be produced.

In Patent Document 3, α--having a specific bending rigidity is provided for the purpose of providing a polyolefin resin-in-mold foam-molded article having excellent buffering performance, high impact resistance, and excellent heat resistance. Pre-expanded particles using a mixture of 55 to 95% by weight of an olefin / propylene copolymer and 5 to 45% by weight of a linear polyethylene resin as a base resin are disclosed. When the polypropylene resin contains a polyethylene resin, the shrinkage of the molded product may increase, and when the linear polyethylene resin is simply contained, a problem may occur in the production of the molded product.
Japanese Patent Laid-Open No. 10-119037 JP-A-1-234212 Japanese Patent Laid-Open No. 4-253741

  The present inventor made polypropylene resin particles by using an underwater cut method for the polypropylene resin, charged the polypropylene resin particles with water, a dispersant, and a foaming agent in a pressure resistant container, and the softening point of the polypropylene resin particles or higher. In the mold using the polypropylene resin pre-expanded particles obtained by impregnating the polypropylene resin particles with a foaming agent under pressure and then releasing them under a lower pressure atmosphere than in the pressure vessel When trying to obtain a foamed molded product, it is equivalent to pre-foaming at the time of in-mold foam molding compared to in-mold foam molded product using polypropylene resin pre-foamed particles obtained from polypropylene-based resin particles produced by the strand cut method In order to obtain an in-mold foam-molded product that can be fused with each other, a problem is that high molding heating steam pressure is required. And which, furthermore, a problem that actually tensile strength and tensile elongation of the resulting mold expansion molded article give only mold expansion molded article having a reduced was confirmed.

  In view of such problems, the object of the present invention is to achieve low molding pressure when in-mold foam molding of polypropylene resin pre-expanded particles made of polypropylene resin particles manufactured with good productivity by an underwater cut method. It is an object of the present invention to provide polypropylene resin pre-expanded particles that can obtain sufficient fusing property and can obtain the tensile strength and tensile elongation of the obtained in-mold foam molded article.

In view of the above circumstances, the present inventors have made extensive studies and as a result, obtained the following knowledge.
That is, a so-called underwater cut obtained by melting and kneading a polypropylene resin composition with an extruder, extruding into a water from a die nozzle attached to the tip of the extruder, and cutting with a cutter blade rotating in the water. Polypropylene resin particles produced by the method are charged into a pressure vessel with water, a dispersant, a foaming agent, etc., heated to a temperature above the softening point of the polypropylene resin particles, and expanded into the polypropylene resin particles under pressure. Polypropylene resin pre-expanded particles obtained by impregnating with an agent and then released into an atmosphere at a pressure lower than that in the pressure vessel, wherein the surface melting temperature is 130 ° C. or less. The pre-expanded particles are excellent in fusion property even in low-pressure molding, and the tensile strength and tensile elongation of the obtained in-mold foam molded product are good. It was found.

  That is, in the first aspect of the present invention, a polypropylene resin composition is melt-kneaded with an extruder, extruded into water from a die nozzle attached to the tip of the extruder, and cut with a cutter blade that rotates in the water. The obtained polypropylene resin particles, water, a dispersant, and a foaming agent are charged in a pressure vessel, heated to a temperature equal to or higher than the softening point of the polypropylene resin particles, and the foaming agent is applied to the polypropylene resin particles under pressure. Polypropylene resin pre-foamed particles obtained by impregnating and releasing the polypropylene-based resin pre-foamed particles in an atmosphere at a pressure lower than that in the pressure vessel, and having a surface melting temperature of 130 ° C. or lower. Concerning particles.

  As a preferred embodiment, the present invention relates to the polypropylene resin pre-expanded particles described above, wherein the polypropylene resin pre-expanded particles have a particle weight of 0.5 to 2.0 mg / particle.

  The second of the present invention relates to an in-mold foam-molded product formed by using the polypropylene resin pre-foamed particles described above.

  According to the present invention, a polypropylene resin pre-expanded particle using polypropylene resin particles obtained by an underwater cut method, wherein the surface melting temperature is 130 ° C. or less. Can reduce the molding heating steam pressure required at the time of molding in order to obtain good fusing property. Moreover, the tensile strength and tensile elongation of the obtained in-mold foam molded article are good.

  The polypropylene resin used in the present invention is a polymer comprising propylene monomer units of 50% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and is a Ziegler type titanium chloride catalyst, metallocene catalyst, post Those having high stereoregularity polymerized with a metallocene catalyst or the like are preferred. Specific examples include, for example, propylene homopolymer, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene-butene random copolymer, ethylene-propylene block copolymer, maleic anhydride- A propylene random copolymer, a maleic anhydride-propylene block copolymer, a propylene-maleic anhydride graft copolymer and the like can be mentioned, and each can be used alone or in admixture of two or more. In particular, an ethylene-propylene random copolymer, a propylene-butene random copolymer, and an ethylene-propylene-butene random copolymer can be suitably used. Further, these polypropylene resins are preferably non-crosslinked, but crosslinked resins can also be used.

  The polypropylene resin used in the present invention preferably has a melt index (hereinafter referred to as MI) of 0.1 to 15 g / 10 minutes measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210. Preferably it is 2-12 g / 10min. When the MI is less than 0.1 g / 10 min, the foaming power when producing the polypropylene resin pre-expanded particles is low, and it may be difficult to efficiently obtain the polypropylene resin pre-expanded particles having a high expansion ratio. . On the other hand, if the MI exceeds 15 g / 10 minutes, the cell may break when producing the pre-expanded polypropylene resin particles.

  The polypropylene resin used in the present invention has a melting point of preferably 130 to 168 ° C., more preferably 135 to 160 ° C., particularly preferably in order to obtain an in-mold foam molded article excellent in mechanical strength and heat resistance. 135-155 ° C. If the melting point is within this range, the moldability, mechanical strength, and heat resistance tend to be easily balanced.

  In the present invention, the melting point of the polypropylene resin (hereinafter sometimes referred to as “Tm”) is 10 ° C. from 40 ° C. to 220 ° C. from 1 to 10 mg of polypropylene resin by a differential scanning calorimeter. The peak temperature of the endothermic curve in the DSC curve obtained when the temperature is raised at a rate of 10 ° C / minute, then cooled to 40 ° C at a rate of 10 ° C / minute, and again raised to 220 ° C at a rate of 10 ° C / minute. .

  In the present invention, a polyethylene composition can be mixed with a polypropylene resin and used as the polypropylene resin composition of the present invention. By mixing the polyethylene composition, the surface melting temperature of the resulting polypropylene resin pre-expanded particles tends to be 130 ° C. or less, in other words, the polypropylene resin of the present invention is mixed with the polyethylene composition. In some cases, the elastic modulus and mechanical strength may be lower than in the case of not performing the process, but the effect of improving the fusion at the time of molding is easily exhibited.

  Specific types of polyethylene compositions that can be mixed include, for example, high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (L-LDPE), and the like. Ethylene homopolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, and the like. These can be used alone or in combination of two or more. Among these resins, low density polyethylene (LDPE) is preferable, and linear low density polyethylene (LLDPE) is more preferable. Further, the content of the polyethylene composition in the polypropylene resin is preferably 1 part by weight or more and 20 parts by weight or less, more preferably 3 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. It is. If the content of the polyethylene composition is less than 1 part by weight, it may be difficult to obtain sufficient fusing property by in-mold molding at a low steam pressure. On the other hand, if the amount exceeds 20 parts by weight, the resulting molded foam molded product tends to cause sink marks, and the mold shrinkage rate tends to increase.

  The melt viscosity at 140 ° C. of the polyethylene composition that can be mixed is preferably 50 mPa · s to 1000 mPa · s, more preferably 50 mPa · s to 500 mPa · s. When granulating fine particles of 2.0 mg / grain by the underwater cut method, when the polyethylene composition is in the above range, a large amount of the polyethylene composition tends to exist on the surface of the polypropylene resin pre-foamed particles, and It is difficult to reduce the rigidity of the polypropylene resin used as a material. When the melt viscosity of the polyethylene composition is less than 50 mPa · s, it becomes easier to elute from the surface of the polypropylene resin pre-foamed particles or from the surface of the polypropylene resin pre-foamed particles in the mold, and in the case of a buffer packaging molding , It may adhere to or contaminate the inclusions. When the melt viscosity of the polyethylene-based composition exceeds 1000 mPa · s, poorly expanded polypropylene resin pre-expanded particles and in-mold expanded molded articles such as reduced secondary foamability due to heating during molding and easy breakage It is easy to become. On the other hand, when it exceeds 1000 mPa · s, the polyethylene composition and the polypropylene composition are easily phase-separated, the polypropylene resin pre-expanded particles are easily broken, and the shrinkage rate of the obtained in-mold foam molded product is likely to be large. In the present invention, the melt viscosity of the polyethylene composition refers to a value obtained by heating and melting the polyethylene composition and measuring the melt viscosity at 140 ° C. with a Brookfield viscometer.

  In the present invention, when the polypropylene resin particles are produced, various additives can be added as necessary within a range not impairing the properties of the polypropylene resin composition. Examples of the additive include an antioxidant, an ultraviolet absorber, a lubricant, an antistatic agent, a flame retardant, a filler, a nucleating agent, and a colorant.

  In the present invention, the polypropylene resin composition is melt kneaded with an extruder. Examples of the extruder include a single-screw extruder, a twin-screw extruder, a tandem extruder in which two single-screw or two-screw extruders are connected, and it is preferable to use a twin-screw extruder. Furthermore, it is preferable to stabilize the discharge pressure of the polypropylene resin composition discharged from the extruder using equipment such as a gear pump. The resin temperature after passing through the gear pump is preferably 200 to 280 ° C. When the temperature is lower than 200 ° C., nozzle clogging is likely to occur, and stable production may not be possible. When the temperature exceeds 280 ° C., thermal degradation of the polypropylene resin may occur and physical properties may decrease.

  In the present invention, the diameter of the die nozzle attached to the tip of the extruder is preferably 0.2 to 1.0 mm, more preferably 0.4 to 0.7 mm. If the die nozzle diameter is less than 0.2 mm, nozzle clogging is likely to occur, and productivity may be reduced. When the thickness exceeds 1.0 mm, polypropylene resin particles having a particle weight of 2.0 mg / grain or less with such a die nozzle diameter are produced. Fillability at the time of molding may deteriorate. In the present invention, the polypropylene resin composition is extruded from a die nozzle and cut by a cutter in a water box, and the circulating water temperature introduced into the water box is preferably 30 to 100 ° C. If the circulating water temperature is less than 30 ° C., nozzle clogging is likely to occur, and productivity may be reduced. If the temperature exceeds 100 ° C., agglomeration between polypropylene resin particles tends to occur. The circulating water temperature is more preferably 80 ° C to 100 ° C, still more preferably 90 to 100 ° C. When the temperature is within this range, sufficient fusibility tends to be easily obtained without including the polyethylene composition. Moreover, it is preferable that the circulating water pressure in the water box is 0.1 to 2.0 MPa. When the circulating water pressure is less than 0.1 MPa, when the polypropylene resin composition discharged from the die nozzle is cut, a vacuum is generated in the vicinity of the rotating cutter blade, and water vapor bubbles are likely to be generated. It becomes easy to generate. If the water pressure exceeds 2.0 MPa, the facility becomes large, and the convenience may be impaired. You may add dispersing agents and surfactant, such as a slightly water-soluble inorganic compound for preventing the fusion | melting of polypropylene-type resin particles mutually to circulating water. Moreover, it is preferable that the peripheral speed of a cutter blade is 10 m / sec or more, More preferably, it is 15 m / sec or more. If it is less than 10 m / sec, the resin particle shape tends to be indefinite, and the resin particles may be fused to each other.

  Generally, the polypropylene resin particles produced by the underwater cut method have a nearly spherical shape as compared to the polypropylene resin particles produced by the strand cut method. The polypropylene resin particles produced by the strand cut method have a cylindrical shape, and the polypropylene resin pre-expanded particles made of the polypropylene resin particles are also close to a cylindrical shape. On the other hand, the polypropylene resin particles produced by the underwater cut method are close to spherical, and the polypropylene resin pre-expanded particles made of the polypropylene resin particles are also close to spherical. It is possible to discriminate the production method from polypropylene resin particles and polypropylene resin pre-expanded particles obtained from the polypropylene resin particles.

  The polypropylene resin pre-expanded particles according to the present invention are charged with a dispersion containing the above-mentioned polypropylene resin particles and water, a dispersing agent and a foaming agent in a pressure-resistant container, and the softening point of the polypropylene resin particles is higher than the softening point. After heating up to a temperature and impregnating the polypropylene resin particles with a foaming agent under pressure, the polypropylene resin is released by releasing the mixture of the polypropylene resin particles and water into an atmosphere at a lower pressure than in the pressure vessel. Obtained by foaming the particles. Specifically, in a pressure-resistant container, a dispersion containing polypropylene resin particles, water, a foaming agent, a dispersing agent and a dispersion aid is charged, and the temperature is increased while stirring to a temperature equal to or higher than the softening point of the polypropylene resin particles. After heating to a temperature (hereinafter sometimes referred to as the foaming temperature) and impregnating the polypropylene resin particles with a foaming agent under pressure, an additional foaming agent is added as necessary to keep the inside of the pressure-resistant container constant. An example is a method in which the content is released from the lower part of the pressure-resistant container to a lower pressure atmosphere than the pressure inside the pressure-resistant container after being held at a pressure (hereinafter sometimes referred to as foaming pressure). The pressure vessel to be used is not particularly limited, and any pressure vessel that can withstand the pressure in the vessel and the temperature in the vessel at the time of producing the pre-foamed particles may be used. For example, an autoclave type pressure vessel may be mentioned.

  The blowing agent may be a known one, and examples thereof include aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane, and mixtures thereof; air, inorganic gases such as nitrogen and carbon dioxide, and water. It is done. The amount of the foaming agent used varies depending on the type of polypropylene resin used, the composition of the base resin, the type of foaming agent, the expansion ratio of the target polypropylene resin pre-foamed particles, etc. It is preferably about 2 to 60 parts by weight with respect to 100 parts by weight of the polypropylene resin particles. Moreover, when using water as a foaming agent, the water currently used as a dispersion medium can be utilized.

  As the dispersant, for example, it is preferable to use a poorly water-soluble inorganic compound such as basic tricalcium phosphate, basic magnesium carbonate, calcium carbonate, aluminum oxide, and kaolin. In addition, as the dispersion aid, it is preferable to use an anionic surfactant such as sodium dodecylbenzene sulfonate or sodium linear alkyl fin sulfonate. The amount of the dispersant and the dispersion aid used is preferably 0.1 to 3 parts by weight of the dispersant and 0.0001 to 0.1 parts by weight of the dispersion aid with respect to 100 parts by weight of water.

  Further, for the purpose of reducing the amount of the dispersant adhering to the polypropylene resin pre-expanded particles, an acid may be mixed with water in which the polypropylene resin is dispersed to make the dispersion acidic.

  The dispersion containing the polypropylene resin particles prepared in the pressure vessel as described above is heated to a predetermined foaming temperature under stirring, and is for a fixed time, usually 5 to 180 minutes, preferably 10 to 60. While being held at that temperature for a minute, the pressure in the pressure vessel rises, and the foaming agent is impregnated into the polypropylene resin particles. Thereafter, the foaming agent is additionally supplied until a predetermined foaming pressure is reached, and is maintained for a certain period of time, usually 5 to 180 minutes, preferably 10 to 60 minutes. Thus, the dispersion containing the polypropylene resin particles held at the foaming temperature and the foaming pressure is released by opening the valve provided at the lower part of the pressure vessel and releasing it under a low pressure atmosphere, usually at atmospheric pressure. -Based resin pre-expanded particles are obtained.

  When the dispersion is discharged into a low-pressure atmosphere, it can be discharged through an opening orifice having a diameter of 2 to 10 mm for the purpose of adjusting the flow rate and reducing variation in magnification. In some cases, the low-pressure atmosphere is filled with saturated steam for the purpose of increasing the expansion ratio.

  The foaming temperature varies depending on the melting point [Tm (° C.)] of the polypropylene-based resin to be used, the type of foaming agent, etc., and cannot be defined unconditionally, but is generally determined from the range of (Tm−30) to (Tm + 10) ° C. The foaming pressure varies depending on the type of polypropylene resin used, the type of foaming agent, the expansion ratio of the desired polypropylene resin pre-foamed particles, etc., and cannot be specified unconditionally, but is generally in the range of 1 to 8 MPa (gauge pressure). Determined from.

  The polypropylene resin pre-expanded particles of the present invention have a surface melting temperature of 130 ° C. or lower. Preferably it is 128 degrees C or less, More preferably, it is 126 degrees C or less. Here, a method for measuring the surface melting temperature will be described. A thermal probe is brought into contact with the polypropylene resin pre-expanded particles, and the tip is disposed at a position less than 10 nm deep from the surface layer. Heating is performed, and displacement in the height direction of the probe is detected along with resin melting. The surface melting temperature is measured from the detected displacement curve. For example, nano-TA2 (thermal probe tip diameter φ 30 nm) manufactured by Nippon Thermal Consulting Co., Ltd. is used, and the surface of any polypropylene resin pre-expanded particles is heated from 40 ° C. to 200 ° C. at 5 ° C./sec. The inflection point at the height position due to melting of the temperature-displacement spectrum at that time is calculated from the intersection of two tangents, and the inflection point temperature is measured at five points at a distance of 30 μm or more, and the inflection calculated The point temperatures are averaged to obtain the surface melting temperature of the present invention. In a general thermal analyzer such as differential scanning calorimetry (DSC), the entire sample is heated to analyze the calorific value of the average melting behavior, whereas the thermal probe for measuring the surface melting temperature of the present invention is a surface probe. The extremely local melting behavior can be measured. Therefore, the surface melting temperature of the present invention is often different from the melting temperature peak measured by DSC. Further, the surface melting temperature of the present invention strongly correlates with the melting temperature for obtaining fusion of polypropylene resin pre-expanded particles by steam heating during in-mold molding, and generally 0.20 to 0.30 MPa. The surface melting temperature is 130 ° C. in order to obtain sufficient fusion property between the polypropylene resin pre-expanded particles by heating at a relatively low pressure of 0.20 to 0.24 MPa. It is necessary that:

  A method for setting the surface melting temperature to 130 ° C. or lower is generally difficult to determine, but, for example, a polyethylene-based composition having a melting temperature lower than that of the polypropylene-based composition and having the above-described melt viscosity characteristics is included. The surface melting temperature of the base resin can be lowered. In addition, by controlling the crystallization history received on the particle surface as described above by setting the circulating water temperature at 80 ° C. to 100 ° C. when granulating by the underwater cut method, The state or crystallinity can be reduced and the surface melting temperature can be reduced. By appropriately adjusting these methods and various conditions such as the resin temperature and the extrusion speed, the surface melting temperature can be made 130 ° C. or lower.

  In the differential scanning calorimetry (DSC), the polypropylene resin pre-expanded particles of the present invention have two DSC curves obtained when the temperature of a sample of 4 to 10 mg is increased from 40 ° C. to 200 ° C. at a rate of 10 ° C./min. Alternatively, it is preferred that there are three melting peaks and that there are two or three melting points indicated by the melting peaks. In two or three melting peaks appearing in the DSC curve, the high temperature that is the amount of heat surrounded by the hottest peak of the DSC curve and the tangent line from the maximum point between the hot peak and the adjacent peak to the melting end baseline Side melting peak calorie Qh, one or two melting peaks appearing on the lower temperature side than the high temperature side melting peak, and the amount of heat surrounded by the tangent to the melting start baseline from the maximum point between the high temperature side peak and the adjacent peak The ratio Qh / (Ql + Qh) × 100 of the melting peak on the highest temperature side calculated from the melting peak heat quantity Ql on a certain low temperature side is called the DSC peak ratio (%). The DSC peak ratio is preferably adjusted so as to be 10% or more and 50% or less, and more preferably adjusted so as to be 15% or more and 45% or less. When the DSC peak ratio is less than 10%, the compact tends to shrink. When the DSC peak ratio is 50% or more, it is difficult to obtain a fusion property at a low molding pressure, which is an effect of the present invention.

  The bulk density of the pre-expanded polypropylene resin particles of the present invention is preferably 10 to 200 g / L, more preferably 15 to 150 g / L. In addition, the bulk density here means that the polypropylene resin pre-expanded particles are allowed to freely fall into the container of a certain volume from a certain height, and the container is completely filled with the polypropylene resin pre-expanded particles. It is a value (XY / V) obtained by subtracting the weight (Y) of the container from the total weight (X) at that time and dividing the value (XY) by the volume (V) of the container.

  The polypropylene resin pre-expanded particles obtained as described above can be formed into an in-mold expanded molded article by a known molding method. For example, A) A method in which pre-expanded particles are filled in a mold and then compressed so that the volume of the pre-expanded particles is reduced by 15 to 50% and heated and fused with water vapor. B) The pre-expanded particles are compressed with gas pressure. A method of heating and fusing with water vapor using the recovery power of the pre-expanded particles, and C) impregnating the pre-expanded particles with inorganic gas by pressurizing the pre-expanded particles with an inorganic gas. , A method in which pre-expanded particle internal pressure is applied, and then filled in a mold and heat-sealed with water vapor, and D) a method in which pre-foamed particles are filled in a metal mold and heat-sealed with water vapor without any pretreatment. Etc. can be used.

  As the inorganic gas, air, nitrogen, oxygen, helium, neon, argon, carbon dioxide gas or the like can be used. These may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

  Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited only to these examples.

  Moreover, the evaluation in an Example and a comparative example was performed with the following method.

[Measurement of melt viscosity of polyethylene-based composition]
The polyethylene composition was heated and melted, and the melt viscosity at 140 ° C. was measured with a Brookfield viscometer.

[Resin particle weight]
100 particles were selected at random and the total weight was measured, and the value divided by 100 was taken as the resin particle weight.

[Surface melting temperature of pre-expanded particles]
Using a nano-TA2 (thermal probe tip diameter φ30 nm) manufactured by Nippon Thermal Consulting Co., Ltd., the surface of randomly selected pre-expanded particles is heated from 40 ° C. to 200 ° C. at 5 ° C./sec. The inflection point at the height position due to melting of the temperature-displacement spectrum at that time is calculated from the intersection of two tangents, and the inflection point temperature is measured at five points at a distance of 30 μm or more, and the calculated inflection point. The point temperatures were averaged to obtain the surface melting temperature of the present invention.

[Bulk density of pre-expanded particles]
A pre-expanded particle is allowed to fall freely into a container having a constant volume (10.74 L) from a certain height (30 cm), and the container is obtained from the total weight when the container is completely filled with the pre-expanded particles. The value obtained by subtracting the weight of the product and dividing the value by the volume of the container was used as the bulk density of the polypropylene resin pre-expanded particles.

[Measurement of DSC peak ratio]
In differential scanning calorimetry, 2-5 mg of pre-expanded particles were heated from 40 ° C. to 220 ° C. at 10 ° C./min to obtain a DSC curve. In the DSC curve, the highest temperature side peak of the DSC curve and the high temperature side A high-temperature side melting peak calorie Qh that is the amount of heat surrounded by a tangent to the melting end baseline from the maximum point between the peak and the adjacent peak, one or two melting peaks that appear on the low-temperature side from the high-temperature side melting peak, The low-temperature side melting peak heat quantity Ql, which is the heat quantity surrounded by the tangent to the melting start baseline from the maximum point between the high-temperature side peak and the adjacent peak, was obtained and calculated from Qh / (Ql + Qh) × 100.

[Fusion rate of in-mold foam moldings]
The in-mold foam molded body is divided along a crack with a depth of about 5 mm put on the surface of the in-mold foam molded body with a cutter, and the fracture surface is observed to melt the ratio of the fractured particles to the total number of pre-foamed particles. It calculated | required as a dressing rate. In this example, an in-mold foam molded body having a length of 400 mm, a width of 300 mm, and a thickness of 40 mm was produced, and the fusion rate was evaluated.

[Minimum molding heating steam pressure]
After filling the block mold with polypropylene resin pre-expanded particles using DAISEN KD-345, the volume in the mold was compressed so as to reduce by 27%. The air was expelled, and then heat-molded for 10 seconds using heating steam at an arbitrary pressure of 0.20 to 0.40 MPa (gauge pressure). The lowest pressure at which the fusion rate of the obtained in-mold foam molded product was 75% or more was defined as the lowest molding heating steam pressure. In this example, an in-mold foam-molded body having a length of 400 mm, a width of 300 mm, and a thickness of 40 mm was produced, and the minimum molding heating steam pressure was evaluated.

[Mold shrinkage ratio of in-mold foamed molded product]
After drying the in-mold foam-molded body in the shape of a rectangular parallelepiped immediately after foam molding in a block mold of length 400 mm × width 300 mm × thickness 40 mm at 75 ° C. for 15 hours, then left at 23 ± 2 ° C. for 24 hours, Measure the vertical, horizontal, and thickness dimensions, determine the shrinkage ratio for the dimensions of the block mold (length 400 mm x width 300 mm x thickness 40 mm), and average the shrinkage ratios for length, width, and thickness. Calculated as a rate.

Example 1
90 parts by weight of an ethylene-propylene random copolymer (Tm: 146 ° C., MI: 6 g / 10 min, comonomer amount: 3% by weight) and a polyethylene composition (ethylene-butene copolymer, melt viscosity 265 mPa · s) 10 A composition comprising 150 parts by weight of talc as a part by weight and 150 parts by weight of talc as a nucleating agent was charged into a twin screw extruder of 150 kg per hour, φ40 mm, and after melt kneading, a die nozzle diameter of 0. Circulating water at a rate of 25 m ³ per hour from a 6 mm die (number of holes: 56), 60 ° C., 0.2 MPa circulating water (tap water not added with a dispersant or a surfactant composed of a poorly water-soluble inorganic compound) Used) and extruded with a rotating cutter blade (10 blades) to produce polypropylene resin particles having a particle weight of 1.2 mg / particle. In addition, the instruction | indication of the resin thermometer attached to the extruder was 232 degreeC. Subsequently, 100 parts by weight of the obtained polypropylene resin particles, 150 parts by weight of water, 1.21 parts by weight of basic tribasic calcium phosphate and 0.03 parts by weight of sodium dodecylbenzenesulfonate were charged into a pressure-resistant autoclave, After adding 11 parts of isobutane as a foaming agent, the autoclave contents were heated and heated to a foaming temperature of 142.9 ° C. Thereafter, isobutane was additionally injected and the pressure was increased to a foaming pressure of 1.65 MPa (gauge pressure). After maintaining at the foaming temperature and the foaming pressure for 30 minutes, the valve at the bottom of the autoclave was opened and passed through an opening orifice having a diameter of 4.0 mm. The autoclave contents were released under atmospheric pressure. The polypropylene resin pre-expanded particles thus obtained had a surface melting temperature of 123 ° C., a bulk density of 35 g / L, and a DSC peak ratio of 26%.

  After filling the obtained polypropylene resin pre-expanded particles in a block mold having a length of 400 mm × width of 300 mm × thickness of 60 mm, the volume of the polypropylene resin pre-expanded particles is compressed to reduce by 27%, and then 0.20-0. It was heated and fused at a molding heating steam pressure of 40 MPa (gauge pressure) to obtain an in-mold foam molded article. Table 1 shows the evaluation results of the polypropylene resin pre-foamed particles and the in-mold foam molded product thus obtained.

(Example 2)
Without adding polyethylene resin, 100 parts by weight of ethylene-propylene random copolymer (Tm: 146 ° C., MI: 6 g / 10 min, comonomer amount: 3% by weight) and 0.01 part by weight of talc as a nucleating agent A polypropylene resin particle was produced in the same manner as in Example 1 except that the composition consisting of the following was introduced into an extruder and the molten resin having a resin temperature of 250 ° C. was extruded into circulating water at 96 ° C. and 0.4 MPa, The polypropylene resin particles were heated in the same manner as in Example 1 except that the autoclave contents were heated to a foaming temperature of 142.2 ° C. and the pressure was increased to 1.80 MPa (gauge pressure) by additional press-fitting of isobutane. Resin pre-expanded particles and in-mold expanded molded articles were obtained. The polypropylene resin pre-expanded particles thus obtained had a surface melting temperature of 126 ° C., a bulk density of 35 g / L, and a DSC peak ratio of 24%. Table 1 shows the evaluation results of the polypropylene-based foamed resin particles and the in-mold foam-molded product thus obtained.

(Example 3)
Table 1 using 95 parts by weight of an ethylene-propylene random copolymer (Tm: 146 ° C., MI: 6 g / 10 min, comonomer amount: 3% by weight) and 5 parts by weight of an ethylene homopolymer having a melt viscosity of 60 mPa · s Except for the above conditions, polypropylene resin particles were produced in the same manner as in Example 1, and polypropylene resin pre-foamed particles were obtained from the polypropylene resin particles to obtain an in-mold foam molded article. The polypropylene resin pre-expanded particles thus obtained had a surface melting temperature of 128 ° C., a bulk density of 35 g / L, and a DSC ratio of 23%. Table 1 shows the evaluation results of the polypropylene resin pre-foamed resin particles and the in-mold foam molded product thus obtained.

(Comparative Example 1)
Polypropylene resin particles were produced in the same manner as in Example 2 except that the molten resin was extruded into circulating water at 60 ° C. and 0.2 MPa, and polypropylene resin pre-expanded particles were obtained from the polypropylene resin particles. A foamed molded product was obtained. The polypropylene resin pre-expanded particles thus obtained had a surface melting temperature of 145 ° C., a bulk density of 35 g / L, and a DSC ratio of 22%. Table 1 shows the evaluation results of the polypropylene-based foamed resin particles and the in-mold foam-molded product thus obtained.

(Comparative Example 2)
Polyethylene resin was changed to 10 parts by weight of an ethylene homopolymer having a melt viscosity of 10000 mPa · s, and polypropylene resin particles were produced in the same manner as in Example 1 except for the conditions described in Table 1. Polypropylene resin particles were obtained from the polypropylene resin particles. -Based resin pre-expanded particles were obtained, and an in-mold foam molded article was obtained. The polypropylene resin pre-expanded particles thus obtained had a bulk density of 31 g / L and a DSC ratio of 24%. Table 1 shows the evaluation results of the polypropylene resin pre-foamed resin particles and the in-mold foam molded product thus obtained.

(Comparative Example 3)
Polypropylene resin particles were produced in the same manner as in Example 1 except that the amount of polyethylene resin added was 0.5 parts by weight, except for the conditions described in Table 1. Polypropylene resin pre-expanded particles were produced from the polypropylene resin particles. An in-mold foam molded article was obtained. The polypropylene resin pre-expanded particles thus obtained had a surface melting temperature of 134 ° C., a bulk density of 35 g / L, and a DSC ratio of 24%. Table 1 shows the evaluation results of the polypropylene resin pre-foamed resin particles and the in-mold foam molded product thus obtained.

  As shown in Table 1, when the surface melting temperature of the polypropylene resin pre-expanded particles is 130 ° C. or less, the heating steam pressure required for molding an in-mold foam molded product having a fusion rate of 75% or more is 0.24 MPa. It was possible to obtain with the following low molding pressure.

It is an example of the temperature-displacement spectrum for calculating the surface melting temperature of the polypropylene resin pre-expanded particles according to the present invention. The horizontal axis represents temperature, and the vertical axis represents the probe position (height). The inflection point temperature (Tmst) calculated from the intersection of two tangents sandwiching the inflection point is calculated.

Claims (3)

  Polypropylene resin composition obtained by melting and kneading a polypropylene resin composition in an extruder, extruding into water from a die nozzle attached to the tip of the extruder, and cutting with a cutter blade rotating in the water, and Water, a dispersant, and a foaming agent are charged into a pressure vessel, heated to a temperature above the softening point of the polypropylene resin particles, and after impregnating the polypropylene resin particles with a foaming agent under pressure, from within the pressure vessel Polypropylene resin pre-expanded particles obtained by releasing in a low-pressure atmosphere, and having a surface melting temperature of 130 ° C. or lower.   The polypropylene resin pre-expanded particles according to claim 2, wherein the polypropylene resin pre-expanded particles have a particle weight of 0.5 to 2.0 mg / particle.   An in-mold foam-molded article formed by molding the polypropylene resin pre-foamed particles according to claim 1 or 2.