JP2010043182A - Polypropylene-based resin foamed particle and in-mold expansion-molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an in-mold expansion-molded body that is obtained by filling polypropylene-based resin foamed particles in a mold and by heat-molding with steam, especially which is excellent in the fusion of the foamed particles from low temperatures and which has little deformation in the molded body and little clearance among the constituent particles one another (owing to the high elongation of the expanded particles) and also which is uniformly fused and excellent in the surface properties. <P>SOLUTION: The solution found out is such that it is necessary to control the heat shrinkage starting temperature of the expanded particles in order not to cause the degradation of the surface properties and the fusion maldistribution in a molded body and also to use a low melting point polypropylene-based resin in order to mold under a low molding pressure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to expanded polypropylene resin particles. More specifically, polypropylene-based resin foam particles that can be suitably used for the production of polypropylene-based resin-molded in-mold foams used for buffer packaging materials, boxing, heat insulating materials, automobile bumper core materials, and the like, and in-mold foam comprising the same It relates to a molded body.

  In-mold foam moldings obtained by filling polypropylene resin foam particles in molds and heat-molding with water vapor are the advantages of in-mold foam moldings, such as shape flexibility, lightness, and heat insulation. have. Compared to in-mold foam moldings using similar synthetic resin foam particles, compared with in-mold foam moldings obtained using polystyrene resin foam particles, chemical resistance, heat resistance, strain recovery rate after compression It is excellent in (mechanical characteristics) and has excellent dimensional accuracy, heat resistance, and compressive strength as compared with an in-mold foam molded article using polyethylene resin expanded particles. Due to these characteristics, in-mold foam molded articles obtained using polypropylene resin foam particles are used in various applications such as heat insulating materials, shock-absorbing packaging materials, automobile interior members, and automobile bumper core materials.

  In-mold foam moldings used for applications such as general cushioning packaging materials, automobile interior members, and returnable boxes that are used in places where the user can see, often have surface properties as important. In these applications, good surface properties are required in addition to physical properties such as rigidity, lightness, and heat insulating properties normally required for in-mold foam molded products. In-mold foam moldings may be deformed immediately after steam molding due to the effect of heating, but there is a curing process that eliminates the deformation by heat curing, and shortening the curing time is desired from the viewpoint of productivity. Yes. The in-mold foam molded product is formed by fusing the foam particles together to form an in-mold foam molded product, so that a gap may occur between the foam particles of the in-mold foam molded product. Many people dislike this gap. In order to make the gap between the foam particles (particle gap) inconspicuous, generally the air pressure in the foam particles is increased to atmospheric pressure or higher in advance during foam molding in the mold, and / or the heating steam pressure of the molding machine is increased, A method is adopted in which the expansion force of the expanded particles is increased so as to eliminate the gap between the expanded particles to promote fusion.

  However, in the in-mold foam molding, it may be difficult to uniformly fuse the entire in-mold foam-molded body due to the presence of heated steam spots or portions with different thicknesses of the in-mold foam-molded body. As an example of the heating steam spots, there is an example in which the foaming particles start to expand due to the heating by the inflowing steam at the initial stage of molding, the steam flow is unevenly distributed, and the fusion is unevenly distributed. In particular, although the surface of the in-mold foam molded product is fused, the inside may not be fused. In addition, when there are portions with different thicknesses in the in-mold foam molded product, the thin portions are excessively exposed to the vapor and fused excessively, and the thick portions are not sufficiently heated and are difficult to fuse. This is also a kind of heated steam spots. In addition, due to heated steam spots, there may be a case where a “particle gap” having a poor fusion property is generated at a specific portion of the in-mold foam molded article. If the heating steam pressure is increased in order to eliminate the heating steam spots, the shape of the entire in-mold foam-molded product may be heated too much, resulting in a large deformation and a longer curing time. Conventional foamed particles have been molded with the heating conditions determined by the balance of “improving fusion”, “suppressing particle gap” and “suppressing deformation” of the in-mold foam molded product. Each time the molding machine or the mold is changed, there is a problem that the conditions are investigated and the optimum conditions are determined. Also, depending on the mold, there are parts that are easy to pass steam and parts that are difficult to pass, so in practice it is difficult to homogenize the temperature in the mold. For example, the steam path of the mold such as remodeling the mold It is very difficult to change the adjustment of each time. Even in the presence of heated steam spots, in other words, there is an in-mold foam molded product that has excellent "uniform fusion" properties that are well-balanced over a wide range of molding temperatures and that does not have "particle gaps" or "deformation". It was desired.

  In addition, even when there is no particle gap in the in-mold foam molding immediately after molding, particle gaps may be generated by curing, and this is due to the strain that the cell membrane was stretched during in-mold foam molding and reheating due to curing. This is thought to be due to contraction.

  In addition, expanded particles that can be molded with steam as low as possible are desired because of recent demands for reducing carbon dioxide emissions due to energy consumption, reducing steam utility costs in terms of reducing molding processing costs, and reducing molding cycles. . In addition, when molding with high-temperature steam is required, it is necessary to use a molding machine or mold with a high pressure resistance specification, and there is a problem that equipment costs increase. From this viewpoint, molding with low-temperature steam is also necessary. It is desired.

As a technique focusing on the melt tension of the resin, the true density obtained by foaming polyethylene resin particles having a density of 0.920 g / cm ³ or more in Patent Document 1 is 0.024 to 0.042 g / cm. ^In the expanded particles of ³ , the melt flow index of the expanded particles measured at 190 ° C. and 2.16 kgf is 0.1 to 10 g / 10 min, the melt tension value measured at 190 ° C. is 2.5 g or less, and It is disclosed that the non-crosslinked polyethylene resin expanded particles having a wide average temperature of bubbles constituting the expanded particles have a wide temperature range capable of being molded.
JP 2000-17079 A

  An object of the present invention is to provide an in-mold foam molded product obtained by filling polypropylene resin foam particles in a mold and heat-molding with water vapor. Widely, since the expansion of foamed particles is good, there are few gaps between the particles constituting the in-mold foam molded body, and there is little deformation of the in-mold foam molded body, and there is to obtain an in-mold foam molded body with excellent surface properties. .

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, when foamed polypropylene resin particles are formed, the foams are uniformly foamed even if there are heated steam spots, “particle gaps”, “fusion spots”, “ It was possible to produce foamed particles that are less likely to undergo “in-mold foam molding deformation”, have less distortion during in-mold foam molding, and are less susceptible to “particle gap” even after curing. Specifically, the surface layer of the foamed particles shrinks in the early stage of molding heating, making it easier for the steam to flow uniformly between the foamed particles, making it difficult for the heated steam spots to occur and foaming uniformly. In-mold foam moldings can be obtained with a low amount of low-temperature steam and less “in-mold foam molding deformation” due to overheating. Further, by using a resin that does not easily remain strained after molding, it is a foamed particle that hardly causes “particle gap” in the curing process after molding. It can be seen that such expanded particles are expanded particles in which shrinkage of 2% occurs when the polypropylene resin is 60 ° C. or higher and the melting point is −25 ° C. or lower. Further, the polypropylene resin has a specific melt viscosity and tension. The present inventors have found that the distortion after molding is improved, and the inventors have completed the following invention.

  That is, the first aspect of the present invention is a foamed polypropylene resin particle having a true magnification of 20 times to 40 times obtained by foaming a polypropylene resin having a melting point of 125 ° C. or higher and 150 ° C. or lower. When the taken-out thin film is heated at a heating rate of 10 ° C./min, it relates to expanded polypropylene resin particles having a 2% shrinkage starting temperature of 60 ° C. or higher and a melting point of −25 ° C. or lower.

As a preferred embodiment,
(1) The polypropylene resin foamed particles have a melt viscosity at 170 ° C. of 7500 poise or more and 12000 poise or less, a melt tension of 0.5 g or more and 1.8 g or less, and the average cell diameter of the polypropylene resin foamed particles is 200 μm or more and 500 μm. Is
(2) Polypropylene resin foamed particles were obtained by a multistage foaming method.
The present invention relates to the expanded polypropylene resin particles described above.

  A second aspect of the present invention is a polypropylene having an expansion ratio of 30 to 50 times, obtained by filling the above-mentioned polypropylene resin expanded particles in a mold and heating them, and fusing the expanded polypropylene resin particles with each other. The present invention relates to an in-mold resin mold.

  By using the expanded polypropylene resin particles of the present invention, the fusion property is good even at a relatively low heat molding pressure, and it can be obtained at a wide molding temperature. There are few particle gaps on the surface of the obtained in-mold foam molded article, the surface is beautiful, and the in-mold foam molded article is excellent in deformation resistance and curing recovery.

  The polypropylene resin used as the base resin in the present invention is a resin containing 50 mol% or more of propylene as a monomer. Examples of monomer components that can be used other than propylene include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, and 3,4-dimethyl-1. Α-olefins having 2 or 4 to 12 carbon atoms such as butene, 1-heptene, 3-methyl-1-hexene, 1-octene and 1-decene, cyclopentene, norbornene, tetracyclo [6,2,11,8, Cyclic olefins such as 13,6] -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6 -Dienes such as octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid Ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene and the like, a combination thereof is also possible. Of these, it is preferable to use ethylene or 1-butene and a binary copolymer in terms of improving cold brittleness resistance and low cost. In addition, since it has a relatively high strength, a terpolymer of ethylene and 1-butene is preferable in terms of deformation resistance.

  The polypropylene resin of the present invention has a melting point of 125 ° C. or higher and 150 ° C. or lower. Preferably, it is 125 degreeC or more and 145 degrees C or less. The melting point here refers to melting the resin particles by heating 5 to 6 mg of polypropylene resin particles from 40 ° C. to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter (DSC). Then, after crystallizing by lowering the temperature from 220 ° C. to 40 ° C. at 10 ° C./min, and further raising the temperature from 40 ° C. to 220 ° C. at 10 ° C./min, the DSC obtained at the second temperature rise It is the melting peak temperature in the curve. When the melting point is higher than 150 ° C., the fusion between the polypropylene resin expanded particles becomes insufficient at a low thermoforming pressure. When it is lower than 125 ° C., the heat resistance is not good.

  The polypropylene resin expanded particles of the present invention have a 2% shrinkage starting temperature of 60 ° C. or higher and a melting point of −25 ° C. or lower when the thin film taken out from the surface of the expanded particles is heated at a rate of temperature increase of 10 ° C./min. . Specifically, as shown in FIG. 1, the 2% shrinkage start temperature is obtained by cutting a thin film having a length of 12 mm, a width of 1 mm, and a thickness of 0.1 mm from the surface of the expanded polypropylene resin particles, and controlling the measurement site length to 10 mm. Then, applying a tensile load of 0.1 g with a thermomechanical analyzer (TMA) and raising the temperature from 25 ° C. to 10 ° C./min, 2% contraction (the measured value on TMA is the starting point of measurement) This means the temperature when the shrinkage is 200 μm. When the 2% shrinkage starting temperature is less than 60 ° C., the air pressure inside the expanded particles may be heated to a pressure higher than the atmospheric pressure as preparation before molding, but the shrinkage is caused by the heating and the true magnification changes. Quality control becomes difficult. In addition, the foaming particles may shrink too much due to initial heating in the mold during the foam molding in the mold, the filling rate in the mold may be reduced, and density unevenness may occur in the mold in the mold. In addition, when the 2% shrinkage start temperature is higher than the melting point −25 ° C., the foam particles are likely to expand due to initial heating in the mold during in-mold foam molding, and the locally expanded foam particles are unevenly distributed in steam flow. And fusion is unevenly distributed.

  In the case of using a volatile foaming agent, the additive as a foaming cell forming agent for polypropylene resin is 0.005 part by weight or more and 0.1 part by weight of an inorganic nucleating agent such as talc, silica or calcium carbonate. It is preferable to add below. When using an inorganic foaming agent such as air, nitrogen, carbon dioxide, water, it is preferable to use the inorganic nucleating agent and / or water-absorbing substance.

  Water-absorbing substances include water-soluble inorganic substances such as sodium chloride, calcium chloride, magnesium chloride, borax and zinc borate, melamine (chemical name 1,3,5-triazine-2,4,6-triamine), ammelin (same as 1, 3,5-triazine-2-hydroxy-4,6-diamine), ammelide (1,3,5-triazine-2,4-hydroxy-6-amine), cyanuric acid (1,3,5-triazine) -2,4,6-triol), isocyanuric acid (1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione), acetoguanamine (1,3,5-triazine-) 2,4-diamine-6-methyl), benzoguanamine (1,3,5-triazine-2,4-diamine-6-phenyl), tris (methyl) isocyanurate, tris (ethyl) Compounds having a triazine skeleton such as sosocyanurate, tris (butyl) isocyanurate, tris (2-hydroxyethyl) isocyanurate, melamine / isocyanuric acid condensate, polyethylene glycol, alkali metal salt of ethylene (meth) acrylic acid copolymer, Hydrophilic properties such as alkali metal salt of butadiene (meth) acrylic acid copolymer, alkali metal salt of carboxylated nitrile rubber, alkali metal salt of isobutylene-maleic anhydride copolymer, alkali metal salt of poly (meth) acrylic acid Examples thereof include hydrophilic organic substances such as polymers. When using a water-soluble inorganic substance, it is preferable that the addition amount is 0.01-1 weight part with respect to 100 weight part of polypropylene resins. When using hydrophilic organic substance, it is preferable that the addition amount is 0.1-5 weight part with respect to 100 weight part of polypropylene resins. Two or more of these water-soluble inorganic substances and hydrophilic organic substances may be used in combination.

  When the addition amount of these inorganic nucleating agents and / or water-absorbing substances is inappropriate, the foamed particle cell diameter may be too large or too fine.

  Additives necessary for polypropylene resins include melt tension modifiers, nucleating agents, water-absorbing agents, surfactant-type or polymer-type antistatic agents, pigments, flame retardants, and conductivity An improving material or the like can be used, and as an addition method, it is usually preferable to add to a molten resin in the production process of polypropylene resin particles.

  Polypropylene resin is usually melt-processed in advance using an extruder, kneader, Banbury mixer, roll, etc. so as to be easily used for foaming, and is desired to have a cylindrical shape, elliptical shape, spherical shape, cubic shape, rectangular parallelepiped shape, etc. It can be set as the polypropylene resin particle of the shape. The production of polypropylene resin particles is usually performed by adding desired additives to polypropylene resin by dry blending or masterbatch blending, melt-kneading in the extruder, and extruding into a strand from the die at the tip of the extruder, water tank For example, a method of cutting the strand sufficiently cooled by a method such as cutting into particles, or an underwater cutting method in which the resin is directly discharged from a die into water while being cut into particles. As the extruder, a single screw extruder, a twin screw extruder or the like is used. The resin temperature during processing is preferably the melting point of the resin + 30 ° C. or more and 250 ° C. or less. If it exceeds 250 ° C., the polypropylene resin may be degraded and deteriorated. When the resin temperature is lower than the melting point + 30 ° C., the kneading may not be sufficient, or an excessive load may be applied to the extruder.

  Produced polypropylene resin particles may be deformed during reheating, especially foaming, and depending on the shape after deformation, filling into the mold during molding becomes worse. It is preferable.

  The average particle weight of the polypropylene resin particles is preferably 0.5 to 3.0 mg, more preferably 0.5 to 2.0 mg, and still more preferably 0.5 to 1.5 mg.

  The polypropylene resin expanded particles of the present invention can be obtained by expanding the above-described polypropylene resin particles under the conditions described later.

  The expanded polypropylene resin particles of the present invention preferably have a melt viscosity at 170 ° C. of 7500 poise or more and 12000 poise or less. More preferably, it is 8000 poise or more and 12000 poise or less. In the present invention, the melting point is the temperature of the melting peak obtained by the DSC curve, but actually shows a distribution in which crystal components at lower and higher temperatures than the melting point exist. For polypropylene resins, a temperature of 170 ° C. is a temperature state in which melt drawing processing is possible but there is some unmelted crystal, and the melt viscosity at that time is during the production of polypropylene resin foam particles and molding It indirectly reflects the viscosity during semi-melting and the tenacity of the resin. When the melt viscosity is less than 7500 poise, the resin does not have sufficient tenacity at the time of foaming, and the closed cell ratio of the polypropylene resin foamed particles becomes low, making it difficult to mold, or in-mold foam molding shape during in-mold steam molding It may be deformed without keeping it, and may remain even if the cocoon at the time of deformation is cured. When the melt viscosity exceeds 12000 poise, the resin at the time of semi-melting is too viscous, and it is difficult to obtain the desired high-magnification polypropylene-based resin expanded particles, or even if obtained, the 2% shrinkage start temperature is 60%. May be less than ℃.

  Moreover, the melt tension at 170 ° C. of the expanded polypropylene resin particles of the present invention is preferably 0.5 g or more and 1.8 g or less. More preferably, it is 0.5 g or more and 1.6 g or less. When the melt tension is less than 0.5 g, the force for holding the bubbles is insufficient at the time of producing the polypropylene resin foamed particles, the bubbles are easily broken, and it may be difficult to keep the closed cells. When the melt tension exceeds 1.8 g, the cell membrane of the polypropylene resin foamed particles tends to be excessively stretched when the polypropylene resin foamed particles are produced or foamed, and as a result, latent distortion occurs in the cell membrane. Sometimes. As a result, shrinkage immediately after foaming or shrinkage due to heating during curing occurs, and the foamed particle gap of the in-mold foamed molding opens, surface properties deteriorate, dimensional accuracy deteriorates, and curing may take a long time to recover. is there.

The melt viscosity and melt tension of the present invention were measured by using a die having a diameter of 1 mmφ × land length of 10 mm and performing extrusion at 170 ° C. and a shear rate of 122 sec ⁻¹ , take-up speed of 6 m / min, die tip and melt tension. The contact distance of the measurement pulley is a value when measured under the condition of 35 cm. At this time, the ambient atmosphere has a humidity of 50% at 25 ° C. The melt tension has an amplitude on the chart, but in the present invention, the median value of the amplitude is the melt tension.

  The melt viscosity and melt tension at 170 ° C. of the polypropylene resin expanded particles hardly change even in the step of foaming as compared with the polypropylene resin, so the melt viscosity of the polypropylene resin expanded particles of the present invention at 170 ° C. The melt tension may be considered to be the same as that of the polypropylene resin before foaming, and can be set to a desired value by adjusting the melt viscosity and melt tension of the polypropylene resin.

  It is important that the polypropylene resin of the present invention has an appropriate strength at the time of semi-melting, has no resistance to stretching, and does not easily generate latent distortion. In designing such a resin, it is preferable that there is less entanglement between the polymers. However, if the melt tension is within an appropriate range, a high molecular weight component, long chain branching, or partial crosslinking may be present in the polypropylene resin. Absent. Although the properties at the time of melting of the polypropylene resin are considered to be determined by the molecular weight distribution and the composition distribution depending on the polymerization conditions of the polypropylene resin, it can be intentionally controlled by a melt tension adjusting agent.

  As a method for intentionally controlling the melt viscosity and melt tension of the polypropylene resin, there is a method using a melt tension adjusting agent. Examples of melt tension adjusting agents include organic peroxides and polypropylene oligomers. Specifically, a method of reducing the melt tension by decomposing a polypropylene resin with an organic peroxide and a method of reducing the melt tension by adding a polypropylene oligomer to the polypropylene resin can be mentioned. For example, in order to decompose a polypropylene resin with an organic peroxide, it is generally performed by adding an organic peroxide to a polypropylene resin heated and melted in an extruder. The amount of the organic peroxide used is preferably in the range of 0.001 to 0.1 parts by weight with respect to 100 parts by weight of the polypropylene resin. Some commercially available polypropylene resins having a narrow molecular weight distribution are those in which the molecular weight distribution is adjusted by this method, which is called rheology control or visbreaking. A polypropylene resin having a narrow molecular weight distribution has few high molecular weight components, so that there is little entanglement between molecules at the time of foaming, that is, half melt stretching, and the melt tension becomes an appropriate value. During the peroxide treatment, the molecular weight of the polypropylene resin used is appropriately selected so that the melt viscosity at 170 ° C. is in the range of 7500 poise or more and 12000 poise or less. Examples of the organic peroxide to be used include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, t-butylperoxylaurate, 2,5-dimethyl2,5di (benzoylperoxide). Oxy) hexane, t-butylperoxybenzoate, dicumyl peroxide, 1,3-bis (t-butylperoxyisopropyl) benzene, t-butylperoxyisopropyl monocarbonate and the like.

  There are no particular restrictions on the foaming agent used to produce the expanded polypropylene resin particles, aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane; inorganic gases such as air, nitrogen, and carbon dioxide; water Etc., and these can be used alone or in combination of two or more. Although the amount of the foaming agent used is different in order to obtain polypropylene resin expanded particles having a desired expansion ratio, it is usually preferably 3 to 100 parts by weight with respect to 100 parts by weight of the polypropylene resin. If the amount is less than 3 parts by weight, the foamed polypropylene resin particles having a desired expansion ratio may not be obtained. If the amount exceeds 100 parts by weight, the amount of the foaming agent dissolved in the polypropylene resin exceeds the saturation amount and does not dissolve. May be wasted. If the amount of the foaming agent is not appropriate, the average cell diameter of the polypropylene resin foamed particles may be too fine.

  The expanded polypropylene resin particles of the present invention are prepared by placing a dispersion containing polypropylene resin particles, a foaming agent, water, a dispersing agent and a dispersion aid in a pressure vessel, heating to a predetermined temperature, Originally, it is obtained by discharging the dispersion into a low-pressure atmosphere rather than in the pressure vessel. Specifically, polypropylene resin particles are dispersed in a pressure vessel together with a foaming agent, water, a dispersant, and a dispersion aid, and the dispersion is preferably a melting point of polypropylene resin particles of −25 ° C. or higher, melting point + 25 ° C. Dispersion under pressure while heating to a temperature in the following range, more preferably in the range of melting point −10 ° C. or higher and melting point + 10 ° C. or lower and impregnating with a foaming agent, keeping the temperature and pressure in the pressure vessel constant. There are no particular restrictions on the pressure-resistant container used for producing polypropylene-based resin expanded particles by producing a polypropylene-based resin expanded particle by releasing the liquid in a low-pressure atmosphere than in the pressure-resistant container. Any material that can withstand the internal pressure and the internal temperature of the container may be used, and examples thereof include an autoclave type pressure resistant container.

  Examples of the dispersant that can be used in the present invention include tribasic calcium phosphate, basic magnesium carbonate, calcium carbonate, basic zinc carbonate, aluminum oxide, iron oxide, titanium oxide, aluminosilicate, barium sulfate, and kaolin. However, the present invention is not limited to these.

  Examples of the dispersion aid that can be used in the present invention include sodium alkyl sulfonate, sodium dodecylbenzene sulfonate, n-paraffin sulfonic acid soda, and α-olefin sulfonic acid soda. The combination of the dispersant and the dispersion aid can be appropriately adjusted depending on the foaming agent.

  The amount of dispersant and dispersion aid used varies depending on the type and the type and amount of polypropylene resin used, but usually 0.2 to 3 parts by weight of dispersant, 100 parts by weight of water, and dispersion aid. It is preferable that it is 0.001-0.1 weight part. Moreover, in order to make a polypropylene resin particle favorable in the dispersibility in water, it is preferable to use normally 20-100 weight part with respect to 100 weight part of water.

  In the present invention, a dispersion liquid containing polypropylene-based resin particles, foaming agent, water, dispersant, and dispersion aid is placed in a pressure vessel, heated to a predetermined temperature, and dispersed under pressure. In some cases, the liquid is discharged in a low-pressure atmosphere from the pressure-resistant container and foamed, and this is referred to as “one-stage foaming”, and the polypropylene-based resin foam particles obtained by one-stage foaming are sometimes referred to as “single-stage foam particles”.

  The polypropylene resin single-stage expanded particles having a true magnification of 5 to 40 times are produced by the above production method. When the expansion ratio of the expanded particles is less than 5 times, even if the multistage expansion described later is performed, the expansion ratio varies greatly, and the quality may be deteriorated.

  In the present invention, polypropylene-based resin expanded particles having a true magnification of 20 times or more and 40 times or less are used for molding. Therefore, when single-stage expanded particles having a true magnification of 5 times or more and less than 20 times are obtained, they are further expanded and desired. The foaming ratio is controlled to be. Specifically, when single-stage expanded particles that do not satisfy the desired magnification are obtained, the pressure in the single-stage expanded particles is increased to normal pressure by a pressure treatment in which the single-stage expanded particles are placed in a sealed container and impregnated with nitrogen, air, or the like. After the above, the first-stage expanded particles are heated and pressurized with steam or the like to remove the pressure and further expand, thereby obtaining polypropylene-based resin expanded particles having an expansion ratio of 20 to 40 times.

  Here, re-foaming the single-stage expanded particles is sometimes referred to as “two-stage foam”, and the foam particles obtained by the two-stage foam are sometimes referred to as “two-stage foam particles”.

  If even the two-stage expanded particles do not reach the desired expansion ratio, the same operation is performed again, and the desired expansion ratio is obtained by repeating the third and fourth stages. Thus, re-foaming is referred to as a multistage foaming method, and foamed particles obtained by the multistage foaming method are collectively referred to as “multistage foamed particles”.

As an example of multi-stage foaming, when performing two-stage foaming, the pressure in the first-stage foamed particles during the two-stage foaming is preferably 1.5 to 7.0 kg / cm ² , particularly 2.0 to 5.5 kg / cm 2. ² is preferred. The heating and pressing conditions are appropriately selected at a temperature at which the particles do not melt or adhere in the sealed container. If the pressure in the first-stage expanded particles is less than 1.5 kg / cm ² , the effect of the second-stage expansion may be small and the magnification may hardly increase. If the pressure is greater than 7.0 kg / cm ² , the variation in the expansion ratio will increase. There is.

  As described above, polypropylene-based resin expanded particles having a true magnification of 20 times or more and 40 times or less that can be used for molding are produced by a multistage foaming method of one-stage foaming or two-stage foaming or more.

  In the present invention, the polypropylene-based resin expanded particles are those immediately before being subjected to in-mold foam molding unless otherwise specified. For example, when two-stage foaming is performed, the two-stage foamed particles. The foamed particles of the present invention have a specific shrinkage behavior when the surface layer of the foamed particles is heated under specific conditions. One method for easily obtaining such properties is a multistage foaming method.

  If polypropylene resin foamed particles having a true magnification of less than 20 times are used for molding, an in-mold foam-molded product having a desired expansion ratio cannot be obtained. When the true magnification is larger than 40 times, the in-mold foam molded product easily contracts and deforms during mold molding, and a desired shape may not be obtained.

Here, the true magnification of the polypropylene resin foam particles is obtained by determining the weight w (g) and the ethanol submerged volume v (cm ³ ) of the polypropylene resin foam particles, and the density d (g / cm ³ ) of the polypropylene resin particles before foaming. ) From the following equation.
True magnification = d × v / w

  The average cell diameter of the expanded polypropylene resin particles of the present invention is preferably 200 μm or more and 500 μm or less. When the average cell diameter is less than 200 μm, the cell membrane is thinly stretched and stretched greatly, which may cause shrinkage / deformation and deterioration of surface properties during molding. On the other hand, if it is larger than 500 μm, wrinkles are generated on the surface of the in-mold foam molded product, and the appearance of the in-mold foam molded product may be poor.

  In order to obtain polypropylene resin foamed particles having an average cell diameter in the above range, it can be obtained by appropriately adjusting the type, amount of use, and foaming pressure of the additive and foaming agent in the polypropylene resin.

The average cell diameter of the expanded polypropylene resin particles is obtained by observing and photographing a cut surface that includes almost the diameter of the expanded polypropylene resin particles with a microscope, and drawing a straight line passing through the approximate center of the expanded polypropylene resin particles. From the distance (L) of the two intersections with the surface of the expanded particle and the number of bubbles (n) through which the straight line penetrates, the following is obtained.
Average cell diameter = L / n

When the polypropylene resin expanded particles of the present invention were measured with a differential scanning calorimeter (DSC), the DSC curve had two melting peaks on the low temperature side and the high temperature side, and the DSC high temperature side melting peak calorie ratio (hereinafter simply referred to as “DSC high temperature side melting peak calorie ratio”). (It may be referred to as DSC peak ratio) is preferably in the range of 10 to 50%. In the DSC curve obtained when the sample is heated at a rate of 10 ° C./min from 40 ° C. to 220 ° C., the DSC peak ratio is measured between the low temperature side peak, the low temperature side peak, and the high temperature side peak. The amount of heat surrounded by the tangent to the melting start baseline from the local maximum point, the melting peak calorie QL on the low temperature side, and the melting end from the local maximum point between the high temperature side peak, the low temperature side peak, and the high temperature side peak of the DSC curve From the high temperature side melting peak calorific value QH, which is the amount of heat surrounded by the tangent to the baseline,
DSC peak ratio (%) = QH / (QH + QL) × 100
As required. When the DSC peak ratio is within this range, an in-mold foam molded article with good surface properties can be easily obtained.

  When the polypropylene resin foamed particles of the present invention are used for in-mold foam molding, a) a method of using as it is, b) a method of previously injecting an inorganic gas such as air into the polypropylene resin foamed particles to impart foaming ability. C) Conventionally known methods such as a method of filling polypropylene resin foamed particles in a mold in a compressed state and molding may be used.

  As a method for forming an in-mold foam molded article from the polypropylene resin foam particles of the present invention, for example, when the method b) is used, the polypropylene resin foam particles are previously air-pressurized in a pressure-resistant container, and air is contained in the particles. Is injected into the mold, which can be closed but cannot be sealed, and is heated to a water vapor pressure of about 0.15 MPa to 0.33 MPa (gauge pressure) using water vapor as a heating medium. In the heating time of about 3 to 30 seconds, the polypropylene resin foamed particles are fused to each other, and then the molding die is cooled with water to the extent that deformation of the in-mold foam molded body after taking out the in-mold foam molded body can be suppressed. Examples of the method include a method of opening a mold after cooling and obtaining an in-mold foam molded article. In the method of (b), when air is press-fitted into the polypropylene resin foam particles in advance, the pressure vessel may be at room temperature, but when the vessel is heated and pressurized with air (heat pressurization), the air is injected into the particles. Can be carried out in a short time, which is preferable because production efficiency is increased.

  Since the polypropylene resin expanded particles of the present invention use polypropylene resin expanded particles having a low melting point, in some cases, the polypropylene resin expanded particles can be molded even when the heat molding pressure of about 0.15 MPa is low. Yes.

  In the present invention, a polypropylene resin in-mold foam molded product can be obtained by in-mold foam molding. The expansion ratio of the obtained in-mold foam molded article is preferably 30 to 50 times.

The expansion ratio of the in-mold foam molded product is obtained by dividing the ethanol submerged volume (cm ³ ) of the in-mold foam molded product by the weight (g) and multiplying by the resin particle density (g / cm ³ ) before foaming. It is.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited to these.

  Table 1 shows the polypropylene resins used in Examples and Comparative Examples, and Table 2 shows conditions for producing expanded particles and various physical properties. The molding evaluation results are shown in Table 3.

Measurement and evaluation of various items were performed as follows.

<Measurement of melting point>
Using a DSC6200 differential scanning calorimeter manufactured by Seiko Instruments Inc., 5-6 mg of polypropylene resin particles are heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min. From the DSC curve obtained by melting and then crystallizing by lowering the temperature from 220 ° C. to 40 ° C. at 10 ° C./min, and then increasing the temperature from 40 ° C. to 220 ° C. at 10 ° C./min. The melting peak temperature when the temperature was raised was defined as the melting point.

<Measurement of melt viscosity and melt tension>
The melt viscosity and melt tension of the polypropylene resin were measured using the resin before foaming. Using a capillograph (manufactured by Toyo Seiki Co., Ltd.), extrusion was performed at 170 ° C. and a shear rate of 122 sec ⁻¹ using a die having a diameter of 1 mmφ × land length of 10 mm, a take-up speed of 6 m / min, a die tip and melt tension measurement. The contact distance of the pulley is a value when measured under the condition of 35 cm. At this time, the ambient atmosphere has a humidity of 50% at 25 ° C. The melt tension has an amplitude on the chart, but in the present invention, the median value of the amplitude is the melt tension.

<True magnification of expanded polypropylene resin particles>
The bulk volume of about 50 cm ³ of weight w of using the molded polypropylene resin expanded particles (g) and ethanol submerged volume v the (cm ³⁾ calculated by the following formula from the density d of before foaming of the resin particles (g / cm ³⁾ Determined by
True magnification = d × v / w
When the foamed particles used were two-stage foamed products, the true magnification of one stage was also described.

<Internal average cell diameter>
10 polypropylene resin expanded particles, each cut surface including substantially the diameter is observed and photographed with a microscope, and a straight line passing through substantially the center of each polypropylene resin expanded particle is drawn, and 2 with the polypropylene resin expanded particle surface. It calculated | required as follows from the distance (Li) of the intersection of a place, and the number of bubbles (ni) which this straight line penetrated, and also set it as the arithmetic mean of ten pieces.
Cell diameter Ri = Li / ni
10 arithmetic averages of average cell diameter = Ri

<Measurement of 2% shrinkage start temperature of foam particle surface part>
Ten polypropylene resin expanded particles were measured by a tensile load method using TMA4000SA manufactured by Bruker AXS. As shown in FIG. 1, a film sample having a length of 12 mm, a width of 1 mm, and a thickness of 0.1 mm is cut out from the surface portion of the expanded particle, and the distance between the chucks (sample measurement length) for sandwiching the sample is set to 10 mm. When the tensile load of 0.1 g was applied and the temperature was stabilized at 25 ° C., the position was zero, the temperature was raised to the vicinity of the melting point at a temperature increase rate of 10 ° C./min, and the temperature contracted by 200 μm was defined as the 2% contraction start temperature. The 2% shrinkage temperature of 10 expanded polypropylene resin particles was determined and used as the arithmetic average.

<Heat and pressure treatment characteristics>
In order to impart foaming force to the polypropylene resin foamed particles, when the air is pressurized with air heated to 50 ° C. in advance in a pressure resistant container and the air is promoted to press into the particles, the magnification change of the foamed particles by the heated air is changed. I investigated whether it happened.
Change in magnification within 5%: ○
When the change in magnification is 5% or more: ×

<Foamed particle DSC peak ratio>
The polypropylene resin expanded particles were measured with a differential scanning calorimeter (DSC). In the DSC curve obtained when 3-6 mg of expanded particles are heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min, the melting start base from the maximum point between the low temperature side peak, the low temperature side peak, and the high temperature side peak Surrounded by the tangent to the melting end baseline from the maximum point between the high temperature side peak and the low temperature side peak and the high temperature side peak of the DSC curve, which is the amount of heat surrounded by the tangent to the line From the high temperature side melting peak calorific value QH, which is the amount of heat generated,
DSC peak ratio (%) = QH / (QH + QL) × 100
As sought.

<Shrinkage against mold (shrinkage)>
A 400 × 300 × 22 mm plate-like in-mold foam molded product was molded and cooled with polypropylene resin foam particles, taken out from the mold, allowed to stand at 25 ° C. and 50% rh for 1 hour, and then cured at 75 ° C. for 8 hours. Thereafter, the sample was left again at 25 ° C. and 50% Rh for 12 hours, and the vertical, horizontal, and thickness dimensions were measured to determine the shrinkage ratio relative to the mold dimensions. Thereafter, the average of the shrinkage ratios of the length, width, and thickness was obtained and used as the average shrinkage ratio. Those having an average shrinkage of 3.0% or less were rated as “○”, and those having an average shrinkage greater than 3.0% were evaluated as “x”. When the average shrinkage rate is larger than 3.0%, the dimensional accuracy of the in-mold foam molded article is deteriorated, and it is considered that there is a problem in practical use.

<In-mold foam molding deformation evaluation (deformation)>
The appearance of the plate-like in-mold foam-molded product whose mold shrinkage was measured was visually observed, and those that had almost no sink marks (dents) or large wrinkles (streaks of 1 cm or more) that would be derived from sink marks were ○. In the case where there is a wrinkle but there is no sink, Δ is marked, and a case where there are many wrinkles and the entire shape is waved is marked with ×.

<Evaluation of molded body side elongation (elongation)>
Observe the 12 sides of the plate-shaped (rectangular) in-mold foam molded body subjected to the deformation evaluation of the in-mold foam molded body, and obtain the number of gaps formed because the foam particles did not extend sufficiently on the side, or the foam particle shape The following judgment was made by observing that no edge was left and no edge was left.
No gap ... ◎
Less than 5 ... ○
5 or more and 10 or less ... △
The edge of the side does not come out ... ×

<Surface property evaluation (particle gap before and after curing)>
The surface of the plate-like in-mold foam molded body subjected to the in-mold foam molded body deformation evaluation was observed, and the average number of depressions or gaps of 1 mm ² or more between the foam particles per 10 cm ² was determined as the following judgment. .
Less than 30 ... ○
30 or more and less than 100 ... △
More than 100 ... ×

<Fusability evaluation (fusion spot)>
The plate-shaped in-mold foam molded body for which surface properties were evaluated was cut with a cutter knife in the thickness direction of the in-mold foam molded body, and then the in-mold foam molded body was broken by hand from the cut portion. By observing the fracture surface, the distribution state of the broken polypropylene resin foam particles and the unbreakable polypropylene resin foam particles was observed.
When fused as a whole: ○
If there are fusing spots: ×

<Foaming ratio of in-mold foam molding>
A block having a bulk volume of about 50 cm ³ is cut out from the plate-like in-mold foam molded body subjected to the evaluation of fusion property, and its weight W (g) and ethanol submerged volume V (cm ³ ) are obtained. It calculates | requires by following Formula from the density d (g / cm < ³ >) of this.
Foaming ratio = d × V / W

Example 1
As a polypropylene resin, an ethylene-propylene random copolymer (A3) having a melting point of 137.2 ° C. obtained by using an organic peroxide as a melt tension adjusting agent in 100 parts by weight of an ethylene-propylene random copolymer (A2). ) And 0.5 parts by weight of polyethylene glycol and 0.1 parts by weight of talc as a cell nucleating agent were dry blended, and then a 50 mm single-screw extruder (20VSE-50-28, manufactured by Osaka Seiki Co., Ltd.) The mixture was melt-kneaded inside. The melt-kneaded resin was extruded in a strand shape from a circular die having a diameter of 2 mm, cooled with water, and cut with a pelletizer to obtain polypropylene resin particles having a weight of 1.2 mg / grain.

  100 parts by weight of the obtained polypropylene resin particles, 300 parts by weight of water, 0.8 part by weight of kaolin (ASP-170 manufactured by Engelhard) as a dispersant, 0.02 part by weight of sodium dodecylbenzenesulfonate as a dispersion aid Into a pressure-resistant autoclave having a capacity of 10 L, 6 parts by weight of carbon dioxide gas was added as a foaming agent under stirring. After the temperature of the autoclave was raised and heated to a foaming temperature of 143 ° C., carbon dioxide was further added to adjust the autoclave internal pressure to 3.0 MPa (gauge pressure). Then, after holding for 30 minutes, the valve | bulb of the autoclave lower part was opened, the autoclave content was discharge | released under atmospheric pressure through the 4.0 mm diameter opening orifice, and the polypropylene resin polypropylene resin expanded particle was obtained. The obtained polypropylene resin expanded particles (single-stage expanded particles) had a true magnification of 11 times and a DSC peak ratio of 21%. Furthermore, the obtained polypropylene resin foamed particles were placed in a pressure resistant container and subjected to a heated air pressurizing treatment, and the air pressure inside the polypropylene resin foamed particles (hereinafter referred to as internal pressure) was set to 0.36 MPa. At this time, the true magnification of the first-stage expanded particles did not change. This one-stage expanded particle with an internal pressure of 0.36 MPa is heated and expanded by steam of 0.12 MPa (gauge pressure), expanded in two stages, and a polypropylene resin (two-stage) with a true magnification of about 30 times, a cell diameter of 320 μm, and a DSC ratio of 21%. Expanded particles (A3C1) were obtained.

  The obtained expanded polypropylene resin particles (A3C1) were heated and pressurized again to adjust the internal pressure to 0.19 MPa. At this time, the expansion ratio did not change. The polypropylene resin expanded particles (A3C1) are filled into a mold having a length of 300 mm, a width of 400 mm and a thickness of 22 mm using a polyolefin foam molding machine KD-345 manufactured by Daisen Co., Ltd., and the thickness thereof is 0.21 MPa (gauge pressure) with water vapor. By compressing 5% in the direction and heat-molding, a polypropylene resin in-mold foam molded product was obtained. The obtained in-mold foam molded product was left to stand at 25 ° C. × 50% rh for 1 hour, then cured and dried in a constant temperature room at 75 ° C. for 8 hours, and again left at 25 ° C. × 50% rh for 1 hour to make various evaluations. Observed. Table 3 shows the evaluation results of the in-mold foam molding.

(Example 2)
As the polypropylene-based resin, A1 shown in Table 1, additive composition shown in Table 2, and foamed particle production conditions, except that the two-stage foaming conditions were appropriately adjusted, the true magnification was about 30-fold polypropylene resin (two-stage) expanded particles (A1C1) were obtained. The obtained polypropylene resin expanded particles (A1C1) were molded at a water vapor pressure of 0.27 MPa (gauge pressure), and a polypropylene resin in-mold foam molded product was obtained in the same manner as in Example 1. The obtained in-mold foam molded article was evaluated in the same manner as in Example 1. Table 3 shows the evaluation results of the in-mold foam molding.

(Comparative Example 1)
A1 of Table 1 same as Example 2 was used as a polypropylene-based resin, 0.1 parts by weight of talc was dry blended as a cell nucleating agent, and then a 50 mm single screw extruder (20 VSE manufactured by Osaka Seiki Co., Ltd.). -50-28 type). The melt-kneaded resin was extruded in a strand shape from a circular die having a diameter of 2 mm, cooled with water, and cut with a pelletizer to obtain polypropylene resin particles having a weight of 1.2 mg / grain.

  3. 100 parts by weight of the obtained polypropylene resin particles, 300 parts by weight of water, 2 parts by weight of tricalcium phosphate (manufactured by Taihei Chemical Industrial Co., Ltd.) as a dispersing agent, and 0.04 part by weight of sodium alkylsulfonate as a dispersing aid. Into a 5 L pressure-resistant autoclave, 28 parts by weight of isobutane was added as a blowing agent with stirring. The autoclave contents were heated to a foaming temperature of 136.0 ° C. Then, after holding for 30 minutes, the valve | bulb of the autoclave lower part was opened, the autoclave content was discharge | released under atmospheric pressure through the opening orifice of diameter 4.0mm, and the polypropylene resin expanded particle was obtained. The obtained expanded polypropylene resin particles (A1B1) had an expansion ratio of about 30 times, a cell diameter of 270 μm, and a DSC peak ratio of 22%.

  The obtained polypropylene resin expanded particles (A1B1) were heat-molded with water vapor of 0.27 MPa (gauge pressure) to obtain a polypropylene resin in-mold expanded foam. The obtained in-mold foam molded article was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Comparative Example 2)
Polypropylene resin having a true magnification of about 30 times (two times) in the same manner as in Example 1 except that the resin type, additive formulation, and foamed particle production conditions shown in Table 2 were used, and the two-stage foaming conditions were appropriately adjusted. Step) Expanded particles (A2C1) were obtained. Prior to molding, the pressure vessel was set to 60 ° C. and heated air pressure treatment was performed to adjust the internal pressure to 0.19 MPa. However, the foam particles contracted and the true magnification decreased, making it impossible to control the magnification of the foam particles. It was.

  In the above Examples, the mold shrinkage ratio of the in-mold foam molded article, the deformation of the in-mold foam molded article, the side elongation, the particle gap, and the fusion spots were all good.

  In Comparative Example 1, the 2% shrinkage start temperature was a melting point of −25 ° C. or higher, which was outside the range of the present invention, was slightly inferior in surface properties, and became an in-mold foam molded product with fusion spots. In Comparative Example 2, the 2% shrinkage start temperature was 60 ° C. or less, which was outside the scope of the present invention, and the foamed particles shrunk in the heat and pressure treatment process, making production management difficult.

  The in-mold foam-molded product obtained by molding the polypropylene resin foam particles of the present invention in-mold is highly deformed and has little dimensional stability even in a shape that easily deforms or shrinks for buffer packaging materials, etc., and has excellent dimensional stability. The elongation between them is excellent, the surface of the in-mold foam molding is beautiful, and there is no fusion spot inside the in-mold foam molding. In addition, it can be molded with a relatively low water vapor pressure and can be produced industrially and economically.

It is the figure showing the image from the thin film collection of a 2% shrinkage | contraction start temperature measurement in this invention to a measurement.

Claims (4)

  In a polypropylene resin foamed particle having a true magnification of 20 times or more and 40 times or less obtained by foaming a polypropylene resin having a melting point of 125 ° C. or higher and 150 ° C. or lower, a thin film taken out from the surface of the foamed particles is 10 ° C./min. Polypropylene resin expanded particles having a 2% shrinkage start temperature of 60 ° C. or higher and a melting point of −25 ° C. or lower when heated at a temperature rising rate.   The polypropylene resin expanded particles have a melt viscosity at 170 ° C. of 7500 poise or more and 12000 poise or less, a melt tension of 0.5 g or more and 1.8 g or less, and the average cell diameter of the polypropylene resin expanded particles is 200 μm or more and 500 μm or less. The expanded polypropylene resin particles according to claim 1.   The expanded polypropylene resin particles according to claim 1 or 2, wherein the expanded polypropylene resin particles are obtained by a multistage foaming method.   A foaming ratio of 30 to 50 obtained by filling the polypropylene resin foamed particles according to any one of claims 1 to 3 in a mold and heating to fuse the polypropylene resin foamed particles with each other. Double expanded polypropylene resin mold.