JP2010248341A - Polypropylene-based resin prefoamed particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene-based resin prefoamed particle which can easily produce an in-mold foamed product of various shapes including complicated shapes under wide molding conditions, the in-mold foamed product having good surface properties and less inside falling down. <P>SOLUTION: The polypropylene-based prefoamed particles include a polypropylene-based resin having a melt index of 3-20 g/10 min. as a base resin. In the polypropylene-based resin prefoamed particles, the resin melting point is lower than 145°C, measured by using a differential scanning calorimeter by heating from 40°C to 200°C at the rate of 10°C/min., subsequently cooling from 200°C to 40°C at the rate of 10°C/min., then heating again from 40°C to 200°C at the rate of 10°C/min., the ratio of the amount of melting heat at high temperature, which is a ratio of the amount of melting heat from the resin melting point to the end of melting to the total amount of the melting heat of the resin, is 20% or more, and a flexural modulus of the resin is 800 MPa or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polypropylene resin pre-expanded particle, and more particularly to a polypropylene resin pre-expanded particle that enables obtaining an in-mold foam molded article having good surface properties and dimensional properties under a wide range of molding processing conditions.

  Polypropylene resin in-mold foam molded products have superior chemical resistance, heat resistance, buffer performance, and compression strain recovery performance compared to polystyrene resin in-mold foam molded products. Compared to polyethylene resin in-mold foam molded products. Even so, since it is excellent in heat resistance and compressive strength, it is widely used as a buffer packaging material, a returnable box, and an automobile member.

  In particular, as buffer packaging materials of various shapes, they can be molded flexibly and without cutting work in accordance with the shape of products and members to be included, so that they are widely used from electronic machines to industrial materials.

  However, although it can be molded into various shapes, the width of the molding process conditions, such as the range of heating steam pressure, to achieve the desired shape of the molded product while satisfying the fusion between the expanded particles, compared to polystyrene, etc. Since it is narrow, it requires user skill in molding techniques such as adjustment of heating steam pressure, adjustment of heating time, and adjustment of cooling time during in-mold foam molding. In addition, when trying to obtain an in-mold foam-molded product having a complicated shape, a so-called “thin” shape, which is a thin and narrow shape with only a few pre-expanded particles in the thickness direction, When trying to obtain an in-mold foam molded product having a complicated shape that tends to be insufficiently filled with expanded particles, it may be difficult to obtain a satisfactory shape. In addition, the buffering performance and strength are not sufficiently obtained at the location, or the space between the pre-expanded particles is widened to impair the beauty.

  In-mold foam molding using pre-expanded polypropylene resin particles generally uses a raw material with a low resin melting point temperature, which tends to increase the secondary foamability (secondary foaming ratio) when steam heated. Therefore, when molding a thin-walled shape, using a polypropylene resin having a low melting point can be a means for solving the above-mentioned problem, but from the shrinkage of the in-mold foam molding after the in-mold foam molding. In many cases, recovery is not sufficient, and in the in-mold foam molding aiming at a box-shaped in-mold foam-molded product, a phenomenon called “inside-down” tends to occur. Inward tilt means that the difference between the end dimension (c) and the central dimension (b) in FIG. 1 occurs, and this difference varies depending on the size of each product, but the inward tilt is large. In this case, it becomes a defective product that cannot be used as a product. For this reason, the internal fall is reduced by increasing the recovery time from the contraction or the like, but if the recovery time is increased, the productivity is lowered.

  In view of the above problems, as a resin having a low resin melting point and a high resin rigidity instead of the melting point, a propylene / 1-butene random copolymer or a propylene / ethylene / 1-butene random terpolymer (Patent Documents) 1, Patent Document 2) has been proposed. However, the propylene-based random copolymer containing 1-butene comonomer has a problem that the polymerization rate is low because the polymerization rate of 1-butene is low, and the resin price is high.

  In the case of conventional in-mold foam molding of polypropylene resin pre-expanded particles by steam heating, if the heating steam pressure is increased, the above-mentioned inversion and shrinkage tend to increase and the economics such as an increase in the amount of steam used are impaired. In order to obtain the surface beauty of a part or a complicated shape part, the one where a heating steam pressure is high tends to become favorable. In other words, until now, it has been required to strictly control the heating steam pressure conditions to obtain a good in-mold foam molded product, which requires technology and labor, and has a wide heating steam pressure range, that is, molding processing. A polypropylene resin pre-expanded particle having a condition width has been desired. In addition, when pre-expanded particles are produced by a conventional production method using a low-melting-point resin as a raw material in order to obtain an in-mold foam-molded product having a thin-walled part or a complex-shaped surface, there is no internal collapse or shrinkage. When pre-expanded particles are produced by a conventional production method using a high melting point resin as a raw material in order to obtain an in-mold expanded molded body that tends to be large and has little inward collapse and shrinkage, the surface of thin-walled parts and complex shaped parts is beautiful. In many cases, the adhesiveness and the fusibility between the pre-expanded particles are impaired. In other words, the polypropylene resin pre-expanded particles having a sufficient molding processing condition width cannot be obtained only by selecting the base resin.

  In order to improve the secondary processability, a method of mixing and using a polypropylene resin and a propylene-α-olefin resin having a specific Vicat softening point is disclosed (Patent Document 2), but the inversion is improved, and the molding process There is no effect in improving the condition range.

  In Patent Document 3, generally, of the two melting points measured by differential scanning calorimetry, the low temperature side melting point appears in the vicinity of the base resin melting point ± 5 ° C., and the high temperature side melting point is the base resin melting point + 6 ° C. It appears to appear at ~ + 14 ° C. These characteristics are the characteristics under limited conditions in all of the foaming agent type, the amount of the foaming agent, the temperature and time for holding the dispersion medium containing the resin particles, and the cooling condition when the pressure is released. It can be adjusted and controlled by changing the amount of the agent and the temperature and time for holding the dispersion medium containing the resin particles, and further vary depending on the distribution of comonomer components of the polypropylene resin.

  As described above, in the category of the prior art, no method has been found for producing polypropylene resin pre-expanded particles capable of obtaining an in-mold expanded molded article having a beautiful surface and not falling down under a wide range of molding conditions.

JP-A-1-242638 JP 7-258455 A JP 2004-300990 A

  An object of the present invention is to easily produce a foam-in-mold molded product having a good surface property and small inward tilt in a wide range of molding process conditions for various shapes of polypropylene-based resin in-mold foam-molded products including complex shapes. It is to provide a pre-expanded particle based resin.

  In light of the above circumstances, the present inventors have conducted extensive research and as a result, have obtained the following knowledge. That is, in the in-mold foam molding of the polypropylene resin pre-expanded particles, the in-mold foam molding is usually performed by heating steam at a temperature in the temperature range near the low temperature side melting point. At that time, the crystalline resin having a peak at the low-temperature side melting point melts and contributes to the fusion of the pre-expanded particles at the time of in-mold foam molding. It can be considered to play a role in developing stability. If the melting point on the high temperature side is higher, the influence of the heating steam at the time of in-mold foam molding prevents melting of the crystalline resin that contributes to shape retention, and a good product can be obtained under a wide range of molding heating conditions. In addition, if the low-temperature side crystal melting point is lower, it indicates that the resin is easily meltable, and even in low-pressure thermoforming, even in complicated shapes where the thin-walled part and structurally pre-expanded particles are difficult to fill, there is little intergranularity. It becomes easy to obtain an in-mold foam molded article having good transferability. In order to obtain polypropylene-based resin pre-expanded particles having a low resin melting point and low-pressure molding and high resin rigidity and exhibiting sufficient shape retention or dimensional stability, a polypropylene resin It is easy to obtain an in-mold foam molded product having a complicated shape under a very wide range of molding conditions because the melting point temperature of the resin is low, the high-temperature melting crystal is in a certain range, and the flexural modulus of the resin is in a certain range. As a result, the present invention has been completed.

  That is, the first of the present invention is a polypropylene resin pre-expanded particle using a polypropylene resin having a melt index of 3 g / 10 min or more and 20 g / 10 min or less as a base resin, using a differential scanning calorimeter. The temperature is raised from 10 ° C. to 200 ° C. at a rate of 10 ° C./min, subsequently cooled from 200 ° C. to 40 ° C. at a rate of 10 ° C./min, and again from 40 ° C. to 200 ° C. at a rate of 10 ° C./min. The resin melting point is less than 145 ° C., the high-temperature melting heat amount ratio, which is the ratio of the heat of fusion from the resin melting point to the melting end temperature to the total resin heat of fusion, is 20% or more, and the flexural modulus of the resin The present invention relates to pre-expanded polypropylene resin particles characterized by having a Mn of 800 MPa or more.

  The second of the present invention relates to an in-mold foam-molded product obtained by in-mold foam-molding the polypropylene resin pre-expanded particles described above.

  According to the present invention, it is possible to obtain a good in-mold foam-molded product with a wide range of molding process conditions and a good secondary foaming property. Polypropylene resin pre-expanded particles capable of obtaining an in-mold expanded molded article (excellent in dimensional properties) can be provided.

  Therefore, it is possible to easily obtain in-mold foam molded products of various shapes including complicated shapes without obstructing the heat resistance, solvent resistance, heat insulation, and buffering properties inherent to polypropylene resins. Further, it is possible to provide an in-mold foam-molded product that can be used widely and suitably in applications such as a buffer material, a heat insulating material, and an automobile member.

It is a perspective view which shows the shape of the box-shaped in-mold foaming molding used for shaping | molding evaluation. About the polypropylene resin pre-expanded particles of the present invention, using a differential scanning calorimeter, the temperature is raised from 40 ° C. to 200 ° C. at a rate of 10 ° C./min, and subsequently from 200 ° C. to 40 ° C. at a rate of 10 ° C./min. It is an example of a DSC curve obtained when cooling and raising the temperature from 40 ° C. to 200 ° C. at a rate of 10 ° C./min. The horizontal axis is the temperature, and the vertical axis is the endothermic amount. The peak temperature is the resin melting point (° C.) (A), the heat of fusion is the resin heat of fusion (J / g) (C), and the heat of fusion at a temperature higher than the peak temperature (J / g) of the resin heat of fusion. The value obtained by dividing (B) by the total resin heat of fusion was calculated as the high temperature heat of fusion ratio (%). It is an example of the DSC curve obtained when the polypropylene resin pre-expanded particles of the present invention are heated from 40 ° C. to 200 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter. The horizontal axis is the temperature, and the vertical axis is the endothermic amount. The shaded portion on the low temperature side is Ql, and the shaded portion on the high temperature side is Qh.

  As the polypropylene resin constituting the polypropylene resin pre-expanded particles of the present invention, as long as it contains propylene as a monomer in an amount of 80% by weight or more, more preferably 85% by weight or more, and further preferably 90% by weight or more. The composition and the synthesis method are not particularly limited, for example, propylene homopolymer, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene ternary. A copolymer etc. are mentioned.

  In the present invention, the melt index (sometimes referred to as MI) of the polypropylene resin is 3 g / 10 min or more and 20 g / 10 min or less, and preferably 3 g / 10 min or more and 15 g / 10 min or less. When the melt index is within this range, it is easy to achieve both high secondary foamability and good dimensionality. When the melt index is less than 3 g / 10 min, the secondary foaming property is deteriorated and a beautiful surface property cannot be obtained. When the melt index is more than 20 g / 10 min, the dimensional property is deteriorated. The melt index was measured using an MFR measuring device described in JIS-K7210 under the conditions of orifice 2.0959 ± 0.005 mmφ, orifice length 8.000 ± 0.025 mm, load 2160 g, 230 ± 0.2 ° C. Do it.

  The melt index of the polypropylene resin may be adjusted, for example, by using an organic peroxide. Examples of the organic peroxide that can be used include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1- Peroxyketals such as bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) butane; Hydroperoxides such as peroxide, 1,1,3,3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,5-di (T-Butylperoxy) hexane α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxide) Dialkyl peroxides such as oxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; peroxys such as di (3-methyl-3-methoxybutyl) peroxydicarbonate and di-2-methoxybutylperoxydicarbonate Dicarbonate: t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxy Isopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylpa Oxy) hexane, t- butyl peroxy acetate, t- butyl peroxybenzoate, etc. peroxy esters such as di -t- butyl peroxy isophthalate and the like.

  The polypropylene resin of the present invention has a resin melting point of less than 145 ° C, more preferably less than 142 ° C. When the resin melting point of the polypropylene resin is within the above range, both good secondary foamability and dimensionality can be achieved. The practical lower limit is 110 ° C., and if it is lower than that, it is easy to obtain an in-mold foam molding with a beautiful surface with low-pressure steam. However, if in-mold foam molding with high-pressure steam is performed, there will be more wrinkles on the surface. Or dimensionality is often impaired. On the other hand, if the resin melting point is higher than 145 ° C., the fusing property, the surface transfer property, and the mold determination are deteriorated unless the steam heating pressure at the time of in-mold foam molding is increased.

  The term “dimensionality” as used herein means that deformation and shrinkage of the obtained in-mold foam-molded product are small and have a desired shape. For example, in the case of a box shape as shown in FIG. ) And the central dimension (b) are small, so-called “inside-down” is small.

  In general, when the resin melting point is low, it is possible to produce a polypropylene resin in-mold foam molded article with a low vapor pressure that is excellent in equipment cost and energy cost, but the in-mold foam molded article tends to be soft. For this reason, in order to develop satisfactory buffer performance and compression characteristics, the density of the in-mold foam molded body must be increased, and the light weight characteristic of the foam may be impaired. In general, the properties of the in-mold foam-molded product are typically compared at 50% compressive strength, but the polypropylene-based resin properties can be typically correlated by bending elastic modulus. The flexural modulus of the system resin is 800 MPa or more, more preferably 850 MPa or more. When the flexural modulus is less than 800 MPa, the 50% compressive strength of the polypropylene resin in-mold foam molding tends to be low, and the density of the in-mold foam molding may have to be increased. The practical upper limit is about 1200 MPa. Even if the temperature is higher than this range, there is no problem in buffer performance, but generally the resin melting point tends to be high.

  The flexural modulus of the polypropylene resin is such that after drying the polypropylene resin particles at 80 ° C. for 6 hours, using a 35t injection molding machine, the cylinder temperature is 200 ° C., the mold temperature is 30 ° C., and the thickness is 6.4 mm bar ( Width 12 mm, length 127 mm), and a bending test is performed according to ASTM D790 to determine the flexural modulus. In addition, since the flexural modulus is a physical property that hardly changes due to molding processing or the like, as a measurement sample, polypropylene resin particles that have not undergone the foaming step, polypropylene resin pre-foamed particles, and polypropylene resin in-mold foam-molded resin Any of these may be used.

  When the polypropylene resin pre-expanded particles are heated at a rate of 10 ° C./min from 40 ° C. to 200 ° C. in the differential scanning calorimetry (DSC), 4-6 mg of the polypropylene resin pre-expanded particles have two melting peaks. Shown with two melting points.

  In the measurement by the differential scanning calorimetry of the polypropylene resin pre-expanded particles of the present invention, of the two melting peaks, the melting peak calorie Ql (J / g) based on the low-temperature melting point and the melting peak calorie Qh (based on the high-temperature melting point) J / g), the ratio (Qh / (Ql + Qh)) of the melting peak calorie based on the high temperature side melting point to the total melting peak calorie (hereinafter sometimes referred to as DSC peak ratio) is 10% or more and 50% Or less, more preferably 15% or more and 45% or less. When the DSC peak ratio is within this range, it is easy to obtain a wide range of molding process conditions, which is an effect of the present invention.

  Here, the melting peak calorie Ql based on the low temperature side melting point is changed to the melting start baseline from the melting peak based on the low temperature side melting point and the maximum point between the melting peak based on the low temperature side melting point and the melting peak based on the high temperature side melting point. The melting peak calorie Qh based on the high temperature side melting point is between the melting peak based on the high temperature side melting point of the DSC curve, the melting peak based on the low temperature side melting point, and the melting peak based on the high temperature side melting point. The amount of heat enclosed by the tangent line from the local maximum point to the end of melting baseline.

  The low-temperature melting point is close to the resin melting point inherent to the base resin, and the peak temperature and heat of crystallization are affected by the crystallization history during cooling. Further, the high temperature side melting point can be controlled in relation to the temperature and time of annealing as well as the amount of the foaming agent having plasticizing performance as well as the resin composition. If the amount of the foaming agent having high annealing temperature, long-time annealing, and plasticizing performance is large, the high temperature side melting point tends to be high.

  The polypropylene resin of the present invention is heated at a rate of 10 ° C./min from 40 ° C. to 200 ° C. using a differential scanning calorimeter, and subsequently cooled at a rate of 10 ° C./min from 200 ° C. to 40 ° C. The high-temperature fusion heat quantity ratio, which is the ratio of the heat of fusion from the resin melting point to the end of melting temperature to the whole resin fusion heat quantity, obtained by raising the temperature from 40 ° C. to 200 ° C. at a rate of 10 ° C./min, is 20% or more, Preferably it is 25% or more.

  The resin melting point and the resin melting heat amount here refer to 40 to 200 ° C. of 4 to 6 mg of polypropylene resin particles (or pre-foamed particles or those cut out from a molded product) in differential scanning calorimetry (DSC). DSC obtained when the temperature is raised at a rate of 10 ° C./min until it is subsequently cooled from 200 ° C. to 40 ° C. at a rate of 10 ° C./min, and again raised from 40 ° C. to 200 ° C. at a rate of 10 ° C./min. The peak temperature obtained from the curve (FIG. 2) was the resin melting point (° C.) (A), and the heat of fusion was the resin heat of fusion (J / g) (C). Further, among the heats of fusion of the resin, the heat of fusion (J / g) (B) at a temperature higher than the peak temperature divided by the total heat of fusion of the resin is calculated as the high temperature fusion heat quantity ratio (%).

  When the high temperature fusion heat quantity ratio, which is the ratio of the heat of fusion from the resin melting point of the present invention to the end of melting temperature, with respect to the total resin heat of fusion is within this range, the high temperature side melting point can be made higher by short-time annealing. , It becomes difficult to fall down.

  As the polypropylene resin of the present invention, a single polypropylene resin or a polypropylene resin obtained by blending two or more kinds of polypropylene resins with a molten resin can be used. For example, by blending resins having different resin melting points in an appropriate balance, the heat fusion rate can be made 20% or more.

  In addition, a synthetic resin other than the polypropylene resin may be added to the polypropylene resin as long as the effects of the present invention are not impaired. Synthetic resins other than polypropylene resins include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-vinyl acetate copolymer ethylene-acrylic acid. Examples thereof include ethylene resins such as copolymers and ethylene-methacrylic acid copolymers, and styrene resins such as polystyrene and styrene-maleic anhydride copolymers.

  In addition, if necessary, for example, nucleating agents such as talc, antioxidants, metal deactivators, phosphorus processing stabilizers, UV absorbers, UV stabilizers, fluorescent brighteners, metal soaps, etc. Addition of a crosslinking agent, a chain transfer agent, a lubricant, a plasticizer, a filler, a reinforcing agent, a pigment, a dye, a flame retardant, an antistatic agent, etc. to the base resin within a range not impairing the effects of the present invention. It is good also as resin.

  As an additive to the polypropylene resin used in the present invention, when using a hydrocarbon-based blowing agent such as propane, butane, pentane, or hexane as a blowing agent, cell nucleation such as talc, silica, calcium carbonate, etc. It is preferable to add 0.005 parts by weight or more and 0.5 parts by weight or less of the inorganic substance serving as the agent with respect to 100 parts by weight of the polypropylene resin.

  Moreover, when using inorganic foaming agents, such as air, nitrogen, a carbon dioxide gas, and water, as a foaming agent, it is preferable to use the said inorganic substance and / or a water absorbing substance. The water-absorbing substance is a substance that can contain water in the resin particles when the substance is added to the resin particles and the resin particles are brought into contact with water or impregnated with a foaming agent in an aqueous dispersion medium. Specifically, water-soluble inorganic substances such as sodium chloride, calcium chloride, magnesium chloride, borax, zinc borate; special block type polymer (trade name: Pelestat; Sanyo Chemical Co., Ltd.) with polyethylene glycol and polyether as hydrophilic segments ), Alkali metal salt of ethylene (meth) acrylic acid copolymer, alkali metal salt of butadiene (meth) acrylic acid copolymer, alkali metal salt of carboxylated nitrile rubber, alkali metal of isobutylene-maleic anhydride copolymer Hydrophilic polymers such as salts and alkali metal salts of poly (meth) acrylic acid; ethylene glycol, glycerin, Data erythritol, polyhydric alcohols such as isocyanuric acid; melamine, and the like.

  The amount of water-absorbing substance added varies depending on the target foaming ratio, the foaming agent used, and the type of water-absorbing substance used, and cannot be described in general, but when using water-soluble inorganic substances, polyhydric alcohols, melamine, It is preferably 0.01 parts by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the polypropylene resin, and when using a hydrophilic polymer, 0.05 parts by weight or more with respect to 100 parts by weight of the polypropylene resin. The amount is preferably 5 parts by weight or less. Two or more of these water-soluble inorganic substances, hydrophilic polymers, polyhydric alcohols and the like may be used in combination.

  The polypropylene resin of the present invention is melted in advance using an extruder, a kneader, a Banbury mixer, a roll, etc. together with the additive added as necessary, and is cylindrical, elliptical columnar, spherical, cubic, rectangular parallelepiped In the desired particle shape such as the above, the resin is molded into polypropylene resin particles having a particle weight of preferably 0.2 mg to 10 mg, more preferably 0.5 mg to 6 mg.

  In the present invention, for example, the polypropylene resin particles are dispersed in water in a pressure-resistant container together with a foaming agent to form a polypropylene resin dispersion, and the dispersion is heated to a predetermined temperature to be annealed and impregnated with the foaming agent. The dispersion of the polypropylene-based resin particles and water from the pressure vessel is maintained at a pressure equal to or higher than the vapor pressure indicated by the blowing agent, and the pressure vessel is maintained at a suitable pressure to obtain a desired expansion ratio. In addition, polypropylene resin pre-expanded particles can be obtained by releasing them under a low-pressure atmosphere, but the method is not limited to this method.

  In preparing the dispersion, for example, as a dispersant, for example, tricalcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, basic zinc carbonate, aluminum oxide, iron oxide, titanium oxide, aluminosilicate It is preferable to use inorganic dispersants such as salts, barium sulfate, and kaolin, and surfactants such as sodium dodecylbenzene sulfonate, sodium n-paraffin sulfonate, and sodium α-olefin sulfonate as a dispersion aid. . Among these, combined use of tricalcium phosphate and sodium dodecylbenzenesulfonate is more preferable. The amount of the dispersant and the dispersion aid varies depending on the type and the type and amount of the polypropylene resin used, but usually 0.2 parts by weight or more and 3 parts by weight or less of the dispersant with respect to 100 parts by weight of water. It is preferable to mix, and it is preferable to mix 0.001 part by weight or more and 0.1 part by weight or less of the dispersion aid. Moreover, in order to make the polypropylene resin particles have good dispersibility in water, it is usually preferable to use 20 to 100 parts by weight with respect to 100 parts by weight of water.

  Examples of the blowing agent include aliphatic hydrocarbons such as propane, butane, isobutane, pentane and isopentane, halogenated hydrocarbons such as monochloromethane, dichloromethane and dichlorodifluoroethane, inorganic gases such as carbon dioxide, nitrogen and air, and water. It is done. These can be used alone or in combination of two or more. The amount of foaming agent added varies depending on the expansion ratio of the pre-expanded particles, the type of foaming agent, the type of polypropylene resin, the ratio of resin particles to water as a dispersion medium, the impregnation or foaming temperature, and the like. The amount is preferably 5 parts by weight or more and 50 parts by weight or less with respect to parts by weight.

  The expansion ratio of the polypropylene resin pre-expanded particles obtained as described above is preferably 3 to 40 times, and more preferably 5 to 35 times. If necessary, after once producing polypropylene resin pre-expanded particles of 15 times or less, the pre-expanded particles are impregnated with an inert gas such as air to give foaming force, and then heated to be further expanded. A so-called two-stage foaming method may be employed. When the expansion ratio is within the above range, there is a tendency that light weight and satisfactory compressive strength, which are the advantages of the in-mold foam-molded product, are obtained. The expansion ratio here is calculated by calculating the density of the pre-expanded particles from the weight of the pre-expanded particles and the volume obtained by immersing the pre-expanded particles in ethanol in the volumetric flask, and dividing the density of the base resin.

  The cell diameter of the polypropylene resin pre-expanded particles is preferably 50 μm or more and 1000 μm or less, more preferably 50 μm or more and 750 μm or less, and still more preferably 100 μm or more and 500 μm. A cell diameter within this range is preferable because of high moldability and dimensional stability. The cell diameter is an average cell diameter calculated by taking 30 pre-expanded particles arbitrarily from the pre-expanded particles, measuring the cell diameter in accordance with JIS K6402.

  The in-mold foam molded product of the present invention can be obtained by in-mold foam molding using the polypropylene resin pre-expanded particles of the present invention.

  To make the polypropylene resin pre-expanded particles of the present invention into an in-mold expanded molded body, for example, a) Pressurized treatment of the expanded particles with an inorganic gas and impregnation of the particles with an inorganic gas gave a predetermined internal pressure. After that, the mold is filled and heated and fused with steam or the like (Japanese Examined Patent Publication No. 51-22951), b) The expanded particles are compressed by gas pressure and filled into the mold, and the recovery force of the particles is utilized. A method such as heating and fusing with steam or the like (Japanese Patent Publication No. 53-33996) can be used.

The density of the in-mold foam molded product in the present invention is preferably 0.012 g / cm ³ or more and 0.075 g / cm ³ or less. In-mold foam molded products with a density in this range are produced because they have the light weight that is characteristic of in-mold foam molded products, are less likely to shrink and deform during in-mold foam molding, and the proportion of defective products is low. Tend to be good.

  An in-mold foam molded article having a desired density can be obtained by appropriately adjusting the expansion ratio of the polypropylene resin pre-expanded particles and the secondary expansion ratio at the time of in-mold foam molding.

  EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to these Examples.

<Measurement of foaming ratio>
The pre-foamed particle density was calculated from the weight of the pre-foamed particles used as a sample and the volume obtained by immersing the sample in ethanol in a volumetric flask, and the base resin density was divided to obtain the expansion ratio.

<Measurement of low temperature side melting point, high temperature side melting point, DSC peak ratio and resin melting point>
In differential scanning calorimetry (DSC), 4 to 10 mg of polypropylene resin pre-expanded particles are heated from 40 ° C. to 200 ° C. at a rate of 10 ° C./min. A low temperature side melting point, which is a melting point based on the crystalline state that had been obtained, and a high temperature side melting point that appeared on the higher temperature side than the low temperature side melting point were obtained. Of the two melting peaks, the melting peak calorific value Ql (J / g) based on the low temperature side melting point and the melting peak calorific value Qh (J / g) based on the high temperature side melting point are obtained. The ratio (Qh / (Ql + Qh)) to the total heat amount of the melting peak was taken as the DSC peak ratio.

  Subsequently, in the DSC curve obtained when cooling from 200 ° C. to 40 ° C. at a rate of 10 ° C./min and again raising the temperature from 40 ° C. to 200 ° C. at a rate of 10 ° C./min, The inherent resin melting point (A) and heat of fusion were defined as resin heat of fusion (J / g) (C). Further, among the resin heat of fusion, the heat of fusion (J / g) (B) at a temperature higher than the peak temperature divided by the total resin heat of heat was calculated as the high temperature heat of fusion ratio (%).

<Bending elastic modulus of polypropylene resin>
After drying the polypropylene resin particles at 80 ° C. for 6 hours, a 35-ton injection molding machine is used to produce a 6.4 mm bar (width 12 mm, length 127 mm) at a cylinder temperature of 200 ° C. and a mold temperature of 30 ° C. Then, a bending test was performed in accordance with ASTM D790 within one week to obtain a bending elastic modulus.

<Molding evaluation>
The obtained polypropylene resin pre-expanded particles are washed with a hydrochloric acid aqueous solution of pH = 1, and then dried at 75 ° C. The pre-expanded particles are pressure-treated with an inorganic gas, and the pre-expanded particles are impregnated with the inorganic gas. Then, after applying a predetermined internal pressure of the particles (about 0.2 MPa), heating is performed using a mold having a shape shown in FIG. 1 (molded body design outer dimensions: 327 mm × 353 mm × 256 mm, thin wall size: 103 mm × 153 mm × 5 mm). In-mold foam molding was performed at water vapor pressures of 0.20 and 0.35 MPa (gauge pressure), and the thin-walled portion surface a and dimension c (longitudinal central portion) were evaluated.

(1) Surface property About the surface of the in-mold foam molded body obtained by in-mold foam molding at a heating steam pressure of 0.20 and 0.35 MPa (gauge pressure),
In the case where the contour of the pre-expanded particles appearing on the surface of the in-mold foam molded body a is fused with the adjacent pre-expanded particles, and an in-mold foam molded product having a good mold determination at the edge portion is obtained. ... ◎
When most of the contours of the pre-expanded particles appearing on the surface of the in-mold foam-molded body are fused with the adjacent pre-foamed particles, and an in-mold foam-molded product having a generally good mold determination at the edge portion is obtained.・ ・ ・ ○
When an in-mold foam molded product with poor edge determination is obtained, such as many gaps between pre-expanded particles. ... ×

(2) Dimensionality After in-mold foam molding by steam heating at 0.20 or 0.35 MPa (both gauge pressures), the mold was allowed to stand at 25 ° C. for 2 hours and then kept in a temperature-controlled room at 75 ° C. for 5 hours. After placing, the dimensions (b) and (c) of the in-mold foam molded body 3 test body which was taken out and allowed to cool at 25 ° C. for 4 hours were measured, and the amount of inclining calculated by (b)-(c) was measured. The average of three specimens was taken as the amount of deformation.
When the deformation amount (cb) was 3.0 mm or less, it was marked with ◎, and when it exceeded 3.0 mm and was 5.0 mm or less, it was marked with ○, and an in-mold foam molded article with good dimensional properties was obtained. When it was larger than 5.0 mm, it was regarded as defective.

<50% compressive strength of in-mold foam molding>
The obtained polypropylene resin pre-expanded particles were washed with a hydrochloric acid aqueous solution at pH = 1, dried at 75 ° C., and impregnated with pressurized air in a pressure-resistant container to adjust the internal pressure of the pre-expanded particles to 0.2 MPa. Then, in-mold foam molding was performed at a heated steam pressure of 0.20 to 0.35 MPa (gauge pressure) using a 400 mm × 300 mm × 60 mm plate mold for measuring physical properties. The obtained in-mold foamed molded product was allowed to stand at room temperature for 1 hour, and then cured and dried in a constant temperature room at 75 ° C. for 15 hours, and an in-mold foam molded product having a fusion property of 60% or more was selected. The compression strength measurement was performed after leaving it to stand.

A test piece having a length of 50 mm, a width of 50 mm and a thickness of 25 mm was cut out from the obtained in-mold foam-molded product, and compressed at 50% compression (MPa) when compressed at a speed of 10 mm / min according to NDZ-Z0504. The data of 5 points measured were plotted against the green density, and the compression stress at the green density of 20 kg / m ³ was calculated by the least square method.

Example 1
A resin comprising an ethylene-butene-propylene random copolymer (resin density 0.90 g / cm ³ , resin melting point 141.1 ° C., melt index 7.6 g / 10 min, high temperature fusion heat ratio 25%, flexural modulus 880 MPa) On the other hand, 100 parts by weight of the resin was blended with 0.1 parts by weight of powdered talc and 0.5 parts by weight of polyethylene glycol, and the blend was extruded with a 50 mm single screw extruder to obtain 1.2 mg / grain of resin particles. did. 100 parts by weight (2.8 kg) of the obtained resin particles are placed in a 10 L pressure vessel having a stirrer, and 1.0 part by weight of tertiary calcium phosphate (manufactured by Ohira Chemical Industry Co., Ltd.) and sodium normal paraffin sulfonate 0 Dispersed in 170 parts by weight of water in the presence of .05 parts by weight. While stirring the dispersion, 5 parts by weight of carbon dioxide was added and heated, and the dispersion was kept at a temperature shown in Table 1 for 20 minutes. Further, carbon dioxide was added to adjust the internal pressure of the pressure vessel to the pressure shown in Table 1. Next, while maintaining the pressure in the pressure vessel with gaseous carbon dioxide, the dispersion of pellets and water is discharged into the atmosphere through a circular orifice with a diameter of 4 mm attached to the rear end of a discharge valve with an inner diameter of 25 mm. Thus, pre-expanded particles shown in Table 1 were obtained. When the pre-expanded particles were impregnated with air and then subjected to molding evaluation as pre-expanded particles having an expansion ratio of 30 times by two-stage expansion, an in-mold expanded molded article having good surface properties and dimensional properties could be obtained. The 50% compressive strength was 0.17 MPa.

(Example 2)
Instead of using the resin of Example 1, an ethylene-propylene random copolymer (resin density 0.90 g / cm ³ , resin melting point 142.5 ° C., melt index 6.2 g / 10 min, high temperature melting heat ratio 21%, flexural elasticity Pre-expanded particles shown in Table 1 were obtained in the same manner as in Example 1 except that a resin having a rate of 860 MPa was used and the retention temperature of the dispersion was as shown in Table 1. In the same manner as in Example 1, when the molding was evaluated by two-stage foaming with a foaming ratio of 30 times, an in-mold foam molded article having good surface properties and dimensional properties could be obtained, and the 50% compression strength was 0.17. .

(Example 3)
Instead of using the resin used in Example 1, an ethylene-propylene random copolymer (resin density 0.90 g / cm ³ , resin melting point 144.5 ° C., melt index 6.5 g / 10 min, high temperature melting heat ratio 27% , A bending elastic modulus of 960 MPa), 100 parts by weight of the resin was blended with 0.02 part by weight of powdered talc and 0.2 part by weight of glycerin. / Grain resin particles. Subsequently, the dispersion prepared in the same manner as in Example 1 was adjusted to the temperature and pressure shown in Table 1, and released into the atmosphere in the same manner as in Example 1 to obtain pre-expanded particles shown in Table 1. When two-stage foaming was carried out in the same manner as in Example 1 and molding evaluation was carried out, an in-mold foam molded article having good surface properties and dimensional properties could be obtained, and the 50% compression strength was 0.18 MPa.

(Comparative Example 1)
Instead of using the resin used in Example 3, an ethylene-propylene random copolymer (resin density 0.90 g / cm ³ , resin melting point 145.4 ° C., melt index 6.8 g / 10 min, high temperature melting heat ratio 14% In addition, polypropylene resin particles were obtained in the same manner as in Example 3 except that the bending elastic modulus was 1100 MPa. Subsequently, the dispersion prepared in the same manner as in Example 1 was adjusted to the temperature and pressure shown in Table 1, and released into the atmosphere in the same manner as in Example 1 to obtain pre-expanded particles shown in Table 1. When two-stage foaming was carried out in the same manner as in Example 1 and molding evaluation was carried out, an in-mold foam molded product with poor surface properties at 0.2 MPa was obtained, and the 50% compression strength was 0.19 MPa.

(Comparative Example 2)
Instead of using the resin used in Example 1, an ethylene-propylene random copolymer (resin density 0.90 g / cm ³ , resin melting point 141.3 ° C., melt index 0.5 g / 10 min, high temperature melting heat ratio 28% , 0.02 parts by weight of powdered talc and 0.4 parts by weight of glycerin were blended with 100 parts by weight of the resin, and the blend was extruded with a 50 mm single screw extruder to obtain 1.2 mg. / Grain resin particles. Subsequently, the dispersion prepared in the same manner as in Example 1 was adjusted to the temperature and pressure shown in Table 1, and released into the atmosphere in the same manner as in Example 1 to obtain pre-expanded particles shown in Table 1. When two-stage foaming was carried out in the same manner as in Example 1 and molding evaluation was carried out, an in-mold foam molded article with poor surface properties and dimensional properties at 0.2 MPa was obtained, and the 50% compression strength was 0.17 MPa. .

(Comparative Example 3)
Instead of using the resin used in Example 1, an ethylene-propylene random copolymer (resin density 0.90 g / cm ³ , resin melting point 137.5 ° C., melt index 7.2 g / 10 min, high temperature melting heat ratio 30% The resin particles were polypropylene resin particles in the same manner as in Example 1 except that the flexural modulus was 750 MPa. Subsequently, the dispersion prepared in the same manner as in Example 1 was adjusted to the temperature and pressure shown in Table 1, and released into the atmosphere in the same manner as in Example 1 to obtain pre-expanded particles shown in Table 1. When two-stage foaming was performed in the same manner as in Example 1 and molding evaluation was carried out, an in-mold foam molded article having good surface properties and dimensional properties could be obtained, but the 50% compression strength was as low as 0.15 MPa. became.

a Thin-walled part b Location where the center dimension was measured c Location where the end dimension was measured

Claims (2)

  Polypropylene resin pre-expanded particles using a polypropylene resin having a melt index of 3 g / 10 min to 20 g / 10 min as a base resin, and using a differential scanning calorimeter, 10 ° C./min from 40 ° C. to 200 ° C. The resin melting point is 145 ° C. obtained by heating at a rate of 10 ° C./min from 200 ° C. to 40 ° C. and then cooling again at a rate of 10 ° C./min from 40 ° C. to 200 ° C. The ratio of the heat of fusion from the melting point of the resin to the end-of-melting temperature is 20% or more, and the bending elastic modulus of the resin is 800 MPa or more. Pre-expanded polypropylene resin particles.   An in-mold foam-molded product obtained by in-mold foam-molding the polypropylene resin pre-foamed particles according to claim 1.