JP5080842B2 - Polypropylene resin pre-expanded particles and in-mold expanded molded body - Google Patents

Description

  The present invention relates to a polypropylene resin pre-foamed particle and an in-mold foam molded article. More specifically, the present invention relates to a polypropylene resin pre-foamed particle having good surface elongation and good mold followability when used as an in-mold foam molded product, and an in-mold foam molded product obtained from the pre-foamed particle.

  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 molding temperature range for obtaining good products is narrow compared to polystyrene, etc., so adjustment of heating steam pressure, adjustment of heating time, adjustment of cooling time, etc. , User skill in molding technology is required. Also, for example, when trying to obtain a molded body having a concavo-convex shape on the surface, pre-expanded particles expanded by heating enter into the mold everywhere, the pre-expanded particles need to be fused together, and the shape needs to be maintained However, there are cases where it is difficult to obtain a molded body having a sharp corner, in which the uneven shape of the mold is well transferred. For this reason, when used for component trays, etc., the designed overhang is not sufficiently formed, so the retention of the component may be impaired, and when a large number of small pyramidal projections are formed on the surface to prevent slipping, small Since the tip of the protrusion is round, the anti-slip effect may not be sufficiently obtained.

  Generally, the use of raw materials with a low resin melting point tends to increase the secondary foamability (secondary foaming ratio) when steam-heated, so the filling property in the mold tends to be improved. However, the shape is not sufficiently maintained by the shrinkage after the mold release, and as a result, a molded article having a sharp corner cannot always be obtained.

  In view of the above problems, for example, as a polypropylene resin pre-expanded particle capable of easily obtaining a molded article having a complicated shape, a polypropylene resin having a melting point temperature difference of 15 ° C. or more and 30 ° C. or less is mixed. It has been proposed to use a polypropylene resin having a melt index of 3 g / 10 min or more and 20 g / 10 min or less as a base material (Patent Document 1). However, in this method, it is necessary to mix two different types of resins. If uniform mixing is not performed, a portion having poor elongation at the time of molding occurs due to the high melting point component in the pre-foamed particles. In an in-mold foam-molded product having a concavo-convex shape on the surface, the concavo-convex shape of the mold may not be transferred satisfactorily.

  As a technique for modifying a polypropylene resin, there is a method using an organic peroxide. As a technique for degrading a polypropylene resin using an organic peroxide to obtain pre-expanded particles, for example, Patent Document 2 discloses. Is intended to provide polypropylene resin pre-expanded particles having a sufficient coefficient of thermal expansion to fill the particle gap without reducing the pressure inside the mold cavity, and the weight average molecular weight (Mw) and the number average molecular weight The ratio (Mw / Mn) of (Mn) is 6 or less, an MFR measuring instrument described in JIS K-7210 is used, the orifice diameter (lo) is 2.0959 ± 0.005 mmφ, and the orifice length is 8.000 ± 0.00. When measuring MFR of polypropylene resin under the conditions of 025 mm, load 2160 g, 230 ± 0.2 ° C., the diameter l of the resin extruded from the orifice and the orifice Pre-expanded particles based on a polypropylene resin having a ratio (l / lo) to the diameter (lo) of 1.15 or less are disclosed.

Further, in Patent Document 3, the foaming ratio hardly changes even if the foaming temperature varies somewhat. Therefore, the temperature control in the foaming process is easy and the foaming ratio is constant, so that the moldability is excellent and the foaming ratio is also high. For the purpose of providing high-quality expanded particles and a method for producing the same, polypropylene resin expanded particles contain 3 to 10% by weight of ethylene and / or butene-1 as a comonomer component in the resin, The ratio Mz / Mw of the Z-average molecular weight Mz to the weight-average molecular weight Mw of the resin is in the range of 1.5 to 2.5, and the resin foam particles have secondary crystals with a melting energy of 11 to 30 J / g. Polypropylene resin expanded particles characterized by the above are disclosed.
JP 2006-96805 A JP-A-3-152136 JP-A-8-259724

  The object of the present invention is, for example, in the case of an in-mold foam-molded product having a concavo-convex shape on the surface, in which the concavo-convex shape of the mold used for molding can be satisfactorily transferred. An object of the present invention is to provide polypropylene resin pre-expanded particles having good elongation and good mold followability.

  In view of the above circumstances, the present inventors have conducted extensive research to obtain polypropylene resin pre-expanded particles that can transfer the uneven shape of the mold well, and as a result, in the measurement of dynamic viscoelasticity during melting, the angular frequency Using a polypropylene-based resin with a storage elastic modulus in a low region of a specific region as a base material, and determining the weight of the pre-expanded particles and the melting behavior by differential scanning calorimetry, it was made into an in-mold foam molded product It was found that polypropylene resin pre-expanded particles having good surface elongation and good followability to the mold can be obtained.

  In the dynamic viscoelasticity measurement at the time of melting, as a method for setting the storage elastic modulus in a region having a low angular frequency to a specific region, a method using an organic peroxide can be mentioned as described later. Japanese Patent Laid-Open No. 3-152136 and Japanese Patent Laid-Open No. 8-259724 disclose pre-expanded polypropylene resin particles using such a resin. The inventors have Mw / Mn, ballast effect (l / lo) and Mz / Mw described in the above publication, and storage elastic modulus in a low angular frequency region in the dynamic viscoelasticity measurement at the time of melting. It does not necessarily have a correlation, and pre-expanded particles expand well during molding by setting the storage elastic modulus in the low angular frequency range in the dynamic viscoelasticity measurement at the time of melting. In addition, for example, the pre-expanded particles can be sufficiently deformed and filled in the mold at the end of the mold, and the mold shape can be transferred well. Finally, it was found that polypropylene resin pre-expanded particles having good and good followability to the mold were obtained, and the present invention was completed.

That is, the first of the present invention is
Storage modulus at angular frequency 1 rad / s in a dynamic viscoelasticity measurement at 180 ° C. is Ri 100~1000Pa der, polypropylene resin pre to a polypropylene resin having a melting point of 133-150 ° C. as a base resin Foam particles,
The weight per piece is 0.5 to 3.0 mg, and shows two melting peaks as measured by the differential scanning calorimetry method. Of the two melting peaks, the entire melting peak of the melting peak calorie appearing on the high temperature side. Ri ratio 10-50% der against heat, and the difference between the peak temperature of the two melting peaks, wherein der Rukoto 10 ° C. or higher 17.5 ° C. or less, about the pre-expanded polypropylene resin particles.
The second of the present invention is
A storage elastic modulus at an angular frequency of 1 rad / s in a dynamic viscoelasticity measurement at 180 ° C. obtained by melting and kneading a raw material polypropylene resin and an organic peroxide using an extruder is 100 to 1000 Pa. Polypropylene resin particles having a melting point of 133 to 150 ° C. and a weight of 0.5 to 3.0 mg per piece,
Along with at least one volatile foaming agent selected from the group consisting of propane, butane, pentane, hexane, nitrogen, air, carbon dioxide, it is dispersed in water in a pressure-resistant container to form a polypropylene resin dispersion,
The dispersion is heated to a temperature in the range of −25 ° C. to + 10 ° C. of the polypropylene resin particles, the polypropylene resin particles are impregnated with a foaming agent, and the container is pressed under a pressure higher than the vapor pressure indicated by the foaming agent. It is obtained by releasing a dispersion of polypropylene resin particles and water in an atmosphere at a lower pressure than in the container while maintaining the temperature and pressure inside.
Measurement by differential scanning calorimetry shows two melting peaks, of which the ratio of the melting peak calorie appearing on the high temperature side to the total melting peak calorie is 10 to 50%, and the two melting peaks The present invention relates to a method for producing polypropylene resin pre-expanded particles, wherein the difference in peak temperature between the peaks is 10 ° C. or higher and 17.5 ° C. or lower.

In the third aspect of the present invention, the polypropylene resin pre-foamed particles described above are given an internal pressure of 0.1 kg / cm ² -G or more, filled in a mold that can be closed but cannot be sealed, and heated with steam. The present invention relates to a polypropylene resin in-mold foam-molded product characterized by

  The polypropylene resin pre-expanded particles of the present invention have good surface elongation when formed into an in-mold expanded molded article and have good followability to the mold. Therefore, for example, it is possible to easily obtain a molded article having a complex shape having irregularities without hindering the heat resistance, solvent resistance, heat insulation, and buffering properties inherent to polypropylene resins.

  Since the polypropylene resin-in-mold foam-molded article of the present invention has good surface properties and well reflects the complex shape of the mold having irregularities, it can be used for parts trays, cushioning materials, and automobiles. It can be used in a wide range of applications such as members.

  The composition of the polypropylene resin that is the base resin of the polypropylene resin pre-expanded particles (hereinafter sometimes referred to simply as pre-expanded particles) in the present invention is more preferably 80% by weight or more as a monomer. Is 85% by weight or more, more preferably 90% by weight or more. For example, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene Examples thereof include an original copolymer.

  The storage elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement at 180 ° C. of the polypropylene resin, which is the base resin of the pre-expanded particles in the present invention, is 100 to 1000 Pa, preferably 200 to 900 Pa. is there. The storage elastic modulus was measured using a rotary rheometer. The plate-shaped polypropylene resin sample was sufficiently preheated at 180 ° C, and then the stress when strain was applied by changing the rotation angle at a constant period was used. Detect and do. A parallel plate type is used as a measurement jig, and measurement is performed in a nitrogen atmosphere. The measurement is performed in the range of angular frequency from 0.1 rad / s to 100 rad / s, and the storage elastic modulus and loss elastic modulus at each angular frequency are obtained. Among these results, the value of the storage elastic modulus at an angular vibration of 1 rad / s is adopted.

  In the present invention, when the storage elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement at 180 ° C. is in the range of 100 to 1000 Pa, the surface elongation is good when an in-mold foam molded article is obtained, and gold The reason why the following property to the mold is good is not clear, but is considered as follows. An angular frequency of 1 rad / s is generally a low shear region, and a storage elastic modulus of 1000 Pa or less is a relatively low region for a polypropylene resin. During the molding process, the polypropylene resin pre-expanded particles are heated and the pressure in the bubbles rises and expands. However, if the storage elastic modulus is low in the low shear region, the resistance to expansion is reduced, so that the uneven shape of the mold is reduced. It is thought that it will be possible to extend with sufficient follow-up. On the other hand, when the storage elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement at 180 ° C. is less than 100, the closed cell ratio of the pre-expanded particles decreases, and the pressure inside the bubbles is released during the molding process to expand. This is considered undesirable because it is difficult to do.

  The polypropylene resin having a storage elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement at 180 ° C. in the range of 100 to 1000 Pa is, for example, a polypropylene resin obtained by polymerization (hereinafter referred to as a raw material polypropylene system). (Which may be referred to as a resin) can be obtained by treating with a small amount of organic peroxide.

  As the organic peroxide that can be suitably used here, it is preferable that hydrogen abstraction is high, and as a measure of such organic peroxide, it is preferable that the half-life temperature for 1 minute is 100 ° C. or more, Furthermore, it is preferable that it is more than melting | fusing point of raw material polypropylene resin. By using an organic peroxide having a half-life temperature of 1 minute, when a mixture of a polypropylene resin and an organic peroxide is melt-kneaded and processed, the organic peroxide to the polypropylene resin is excellent. It tends to disperse and decompose quickly. Examples of the organic peroxide that can be used in the present invention include 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy). Peroxyketals such as cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) butane; permethane hydroperoxide, 1,1,3 , 3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, etc .; dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane , Α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butyl Dialkyl peroxides such as rucumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; t-butyl peroxyisobutyrate, t -Butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, Examples thereof include peroxyesters such as t-butyl peroxyacetate, t-butyl peroxybenzoate, and di-t-butyl peroxyisophthalate.

  In addition, as a method of treating a polypropylene resin with an organic peroxide, there is a method of melt kneading a mixture of a polypropylene resin and an organic peroxide. From the viewpoint of productivity, a single screw extruder or a twin screw extruder is used. It is preferred to use an extruder such as a machine. The set temperature of the extruder at this time is such that the polypropylene resin is sufficiently melted and substantially all of the organic peroxide is decomposed while passing through the extruder, and excessive decomposition of the polypropylene resin is suppressed. From a viewpoint, it is preferable that it is 180-280 degreeC.

  In addition, in the method of treating a polypropylene resin with an organic peroxide, the amount of the organic peroxide to be used varies depending on the melt flow rate of the raw polypropylene resin, for example, the melt flow rate of the raw polypropylene resin is If it is in the range of 0.5 to 5 g / 10 min, 0.05 to 0.5 parts by weight, and if the melt flow rate of the raw material polypropylene resin is in the range of 5 to 15 g / 10 min, 0.005 to 0.1 It is preferable that it is a weight part. If it is in the said range, since the storage elastic modulus in the angular frequency of 1 rad / s in the dynamic-viscoelasticity measurement in said 180 degreeC is easy to set it as the range of 100-1000 Pa, it is preferable. In the present invention, the melt flow rate of the polypropylene resin is a value measured in accordance with JIS K7210 under conditions of 230 ° C. and a load of 2.16 kgf.

  Furthermore, the melting point of the polypropylene resin which is the base resin of the polypropylene resin pre-expanded particles in the present invention is preferably 130 to 155 ° C, more preferably 133 to 150 ° C.

  Here, the melting point of the polypropylene resin, which is the base resin of the pre-expanded particles, is a temperature between 40 ° C. and 210 ° C. at a rate of 10 ° C./min. After that, the temperature indicated by the crystal melting peak at which the endothermic amount becomes maximum when the temperature is increased again from 40 ° C. to 210 ° C. at 10 ° C./min.

  When the melting point of the polypropylene resin is less than 130 ° C., the shape of the molded body tends to be difficult to maintain due to large shrinkage after release, and when it exceeds 155 ° C., a differential scanning calorimeter of pre-expanded particles described later The temperature difference between the two melting peaks in the measurement by the method tends to be narrow.

  Further, another polypropylene resin or another 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, styrene resins such as polystyrene, styrene-maleic anhydride copolymers, and styrene-ethylene copolymers.

  If necessary, for example, nucleating agents such as talc and boron oxide, water absorbing compounds such as melamine, antioxidants, metal deactivators, phosphorus processing stabilizers, UV absorbers, UV stabilizers Stabilizers or crosslinking agents such as optical brighteners and metal soaps, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, antistatic agents, etc. do not impair the effects of the present invention You may add to base resin in the range.

  In order to obtain polypropylene resin pre-expanded particles, first, the base resin is processed into polypropylene resin particles. For example, in the present invention, a polypropylene resin that is a base resin and the synthetic resin and the additive that are added as necessary are melted and mixed together with an extruder, etc., and extruded into a strand to be pelletized. By cutting from a die immediately after discharge, polypropylene resin particles having a desired particle shape such as a cylindrical shape, an elliptical cylindrical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, and the like are obtained.

  Since the polypropylene resin particles are expanded into polypropylene resin pre-expanded particles, the weight of the polypropylene resin particles is the weight of the polypropylene resin pre-expanded particles. Therefore, the weight per polypropylene resin particle is 0.5 to 3.0 mg, preferably 0.7 to 2.0 mg. When the weight per polypropylene resin particle, that is, the weight per polypropylene resin pre-expanded particle is less than 0.5 mg, the dispersion of the particle weight increases, so the heat to each particle in the foaming process. Unevenness occurs in the surroundings, and the variation in the magnification of the expanded particles increases, which causes sink marks and wrinkles in the molded body. When it exceeds 3.0 mg, the expanded and contracted shape of the mold cannot be transferred because the expanded particles do not expand to every corner of the mold.

  As a method of foaming the polypropylene resin particles to make polypropylene resin pre-expanded particles, for example, dispersed in water in a pressure resistant container together with a volatile foaming agent to form a polypropylene resin dispersion, the dispersion, Preferably, the polypropylene resin particles are heated to a temperature in the range of −25 ° C. to + 10 ° C., more preferably −20 ° C. to + 5 ° C., and the polypropylene resin particles are impregnated with a foaming agent. By releasing the dispersion of the polypropylene resin particles and water in a lower pressure atmosphere than in the container while maintaining the temperature and pressure in the container constant under a pressure higher than the vapor pressure shown, Examples thereof include a method for obtaining pre-foamed particles.

  In the preparation of the dispersion, as a dispersant, for example, inorganic dispersants such as tribasic calcium phosphate, basic magnesium carbonate, calcium carbonate, kaolin, and so on, for example, dodecylbenzene sulfonic acid soda, n-paraffin sulfonic acid soda, α -It is preferable to use a dispersion aid such as sodium olefin sulfonate or magnesium sulfate. Among these, combined use of tricalcium phosphate and sodium dodecylbenzenesulfonate is more preferable.

  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 the dispersant is added to 100 parts by weight of water. It is preferable to add 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 hydrocarbons such as propane, butane, pentane, and hexane, and inorganic gases such as nitrogen, air, and carbon dioxide, and these are used alone or in combination of two or more. The amount of these foaming agents is not limited, and may be set in consideration of the type of foaming agent and the ratio between the amount of resin in the container and the space volume in the container, and the amount used is 100 parts by weight of polypropylene resin particles. The amount is preferably 5 parts by weight or more and 50 parts by weight or less.

  In addition to using the foaming agent, as a method for economically producing polypropylene resin pre-expanded particles, for example, by adding a hydrophilic compound in the polypropylene resin particles, water used for the dispersion medium is added. Methods used as foaming agents (for example, JP-A-10-306179 and JP-A-11-106576) can also be used.

  The expansion ratio of the polypropylene resin pre-expanded particles obtained as described above is preferably 10 to 50 times, and more preferably 15 to 40 times. When the expansion ratio is within this range, light weight and satisfactory compressive strength, which are advantages of the foam obtained by in-mold foam molding, tend to be obtained.

  Further, when the expansion ratio of the polypropylene resin pre-expanded particles does not reach the above range, the inside of the pre-expanded particles is pressurized with an inert gas and heated to increase the expansion ratio (for example, Japanese Patent Laid-Open No. 10-237212). Gazette) is also available.

  The polypropylene resin pre-expanded particles of the present invention are obtained when a sample of polypropylene resin pre-expanded particles 4 to 10 mg is heated from 40 ° C. to 210 ° C. at a rate of 10 ° C./min in measurement by a differential scanning calorimetry method. In the endothermic curve, the melting peak based on the crystalline state originally possessed by the base resin and the melting peak appearing on the higher temperature side than the melting peak by maintaining the temperature near the melting point in the step of obtaining the pre-foamed particles. Two melting peaks are shown. Of these two melting peaks, the ratio of the heat of fusion peak appearing on the high temperature side to the total heat of fusion is 10 to 50%, preferably 15 to 45%.

  If the ratio of the melting peak heat amount appearing on the high temperature side is less than 10%, the shape of the in-mold foam molded product is difficult to maintain due to the large shrinkage after mold release. The polypropylene resin pre-expanded particles do not expand sufficiently and do not fully fill the mold.

  The polypropylene resin pre-expanded particles of the present invention have a temperature indicated by the highest value of the melting peak on the high temperature side (hereinafter referred to as the high temperature melting point) and a maximum value of the other melting peak in the differential scanning calorimetry method. The temperature difference in temperature (hereinafter referred to as the low temperature side melting point) is preferably 10 ° C. or more, and more preferably 13 ° C. or more. Although there is no particular upper limit, in reality, 35 ° C. is the upper limit for manufacturing. When the temperature difference is less than 10 ° C., the range of molding process conditions such as heating steam pressure and temperature range is narrow, and it tends to be difficult to obtain a molded body stably.

  The foam molded article of the present invention is obtained by an in-mold foam molding method using the polypropylene resin pre-expanded particles of the present invention.

In order to form an expanded foam in a polypropylene resin mold from the polypropylene resin pre-expanded particles of the present invention, for example, a) Pressurized foam particles with an inorganic gas and impregnated with the inorganic gas into the particles Method of filling the mold after applying the internal pressure, and heat-sealing with steam or the like (for example, Japanese Examined Patent Publication No. 51-22951), b) Recovery of the particles by compressing the foamed particles by gas pressure and filling the mold A method such as a method of heat-sealing with steam or the like using force (for example, Japanese Patent Publication No. 53-33996) can be used. Among them, the method of forming the polypropylene resin pre-expanded particles by applying an internal pressure of 0.1 kg / cm ² -G or more, filling a mold that can be closed but cannot be sealed, and heating and forming with steam is a thin-walled shape. It is preferable because an in-mold foam molded body having a complicated shape such as a box-shaped molded body having a surface and an in-mold foam molded body having a concavo-convex shape on the surface can be easily beautifully molded. The density of the polypropylene resin in-mold foam molded product thus obtained is preferably in the range of 12 to 75 kg / m ³ . The polypropylene resin in-mold foam molded product having a density in the above range has the lightness that is characteristic of the in-mold foam molded product and has good mold followability, and thus shrinkage and deformation occur during molding. It is difficult and the ratio of defective products is low, so productivity tends 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 application of the particle internal pressure during the 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 storage modulus of base resin>
A polypropylene base resin is hot-pressed at 190 ° C for 5 minutes using a 1.5 mm-thick spacer to produce a 1.5 mm-thick press plate, and punched out using a φ25 mm punch to obtain a test piece. It is dripping. As a measuring device, a viscoelasticity measuring device manufactured by TA Instruments, ARES was used, and a parallel plate jig having a diameter of 25 mm was attached. Set up a thermostat to surround the jig and keep it at 180 ° C. After the jig is preheated, open the thermostat, insert a test piece with a diameter of 25 mm between the parallel plates, close the thermostat and preheat for 5 minutes before paralleling The plate interval was compressed to 1 mm. After compression, the thermostat was opened again, the resin protruding from the parallel plate was scraped off with a brass spatula, the thermostat was closed and the temperature was kept again for 5 minutes, and then dynamic viscoelasticity measurement was started. The measurement is performed in the range of angular frequency from 0.1 rad / s to 100 rad / s, and storage elastic modulus and loss elastic modulus at each angular frequency are obtained. Among these results, the value of the storage elastic modulus at an angular frequency of 1 rad / s was adopted. The amount of strain was 5%, and the measurement was performed in a nitrogen atmosphere.

<Measurement of molecular weight distribution of base resin>
The base resin was dissolved in o-dichlorobenzene to prepare a sample solution of about 2.0 mg / mL. Waters high temperature GPC measuring device, Alliance GPCV200 is used as the measuring device, Showa Denko Shodex UT-807 is used as the column, column temperature is 140 ° C., eluent flow rate is 1.0 mL / min, injection amount is 317 μL. And Mw / Mn (weight average molecular weight / number average molecular weight) and Mz / Mw (z average molecular weight / weight average molecular weight) were determined.

<Weight measurement of pre-expanded particles>
Twenty polypropylene resin pre-expanded particles were taken out at random, and calculated from each weight by arithmetic average.

<Measurement of heat of fusion ratio of pre-expanded polypropylene resin particles>
It is obtained from the melting peak on the low temperature side in the endothermic curve obtained when 4-10 mg of the expanded particle sample is heated from 40 ° C. to 210 ° C. at a rate of 10 ° C./min and melted in the differential scanning calorimetry measurement. The melting point was defined as the low temperature side melting point, and the melting point obtained from the melting peak appearing on the higher temperature side than the low temperature side melting point was defined as the high temperature side melting point. Then, a tangent line is drawn to the rising portion of each melting point from the point where the endotherm becomes the smallest between both melting points, and the heat of fusion at each melting peak is determined from the area surrounded by the tangent line and the endothermic curve. The sum of the heat of fusion of each melting peak was defined as the total heat of fusion, and the ratio of the heat of fusion peak based on the high temperature side melting point to the total heat of fusion was calculated.

<Measurement of resin melting point of base resin>
In the measurement by differential scanning calorimetry, resin particle samples 4 to 10 mg before foaming were heated from 40 ° C. to 210 ° C. at a rate of 10 ° C./min to be melted once, and then 210 ° C. to 40 ° C. at 10 ° C. After the thermal history of cooling at a rate of / min, the crystal melting peak at which the endothermic amount obtained in the endothermic curve obtained when the temperature is increased again from 40 ° C to 210 ° C at a rate of 10 ° C / min and melted is maximized. Was the resin melting point.

<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.

<Molding evaluation>
A 300 mm x 400 mm x 50 mm inner dimension with a 2.5 mm x 2.5 mm, 1.2 mm deep quadrangular pyramid-shaped recess (forms a quadrangular pyramid-shaped projection on the surface of the molded body) on one side of the 300 mm x 400 mm A molding die arranged in the above is used. Then, the pre-expanded particles are allowed to stand under a pressurized air of 2.0 kg / cm ² -G for about 24 hours to apply an internal pressure of 1.5 kg / cm ² -G to the pre-expanded particles, which can be closed but sealed. The molding die was filled and molded by steam heating at 3.0 kgf / cm ² -G. After molding, the mixture was allowed to stand at 25 ° C. for 2 hours, then left in a thermostatic chamber adjusted to 65 ° C. for 5 hours, then taken out, allowed to stand at 25 ° C. for 4 hours and allowed to cool to obtain a molded body.

(1) Surface property The surface of the molded body (a surface on which a quadrangular pyramid-shaped protrusion was formed and other surfaces) was observed and evaluated based on the following criteria.
○: All the contours of the expanded particles appearing on the surface are fused with the adjacent particles, and the surface of the expanded particles exposed on the surface of the molded body is free from wrinkles.
X: A gap is observed between the expanded particles appearing on the surface, or wrinkles are observed on the surface of the expanded particles exposed on the surface of the molded body.

(2) Shrinkage of molded body Measure the vertical and horizontal dimensions (300mm, 400mm sides in the mold inside) of the surface of the molded body on which the quadrangular pyramidal projections are formed, and calculate the shrinkage ratio from the mold. And the shrinkage rate in the transverse direction was arithmetically averaged.

(3) Mold transferability About 30 square pyramidal protrusions formed on the surface of the molded body, arbitrarily select 30 pieces (excluding the portion provided with a small hole to allow water vapor to pass during molding). Cut out on the plane passing through the apex, measure the height of the quadrangular pyramid, and perform the arithmetic average. If the pre-expanded particles are inferior in mold transferability or have a large shrinkage after molding, the tip of the quadrangular pyramidal protrusion is round and the height of the quadrangular pyramid is lowered. evaluated.
○: The average height of the quadrangular pyramidal protrusions is 1.0 mm or more. ×: The average height of the quadrangular pyramidal protrusions is less than 1.0 mm.

Example 1
To 100 parts by weight of ethylene-propylene random copolymer (resin density 0.90 g / cm ³ , resin melting point 142.3 ° C., melt flow index 6.0 g / 10 min at 230 ° C.) t- 50 mm single screw extruder set at 200 ° C. by dry blending 0.01 parts by weight of butyl peroxyisopropyl carbonate (Nippon Yushi, Perbutyl I, 1 minute half-life temperature 159 ° C.) and 0.1 parts by weight of powdered talc Extruded with ethylene-propylene random copolymer resin particles (resin density: 0.90 g / cm ³ , resin melting point: 142.3 ° C., storage elastic modulus at 180 ° C. angular frequency: 1 rad / s, 870 Pa, Mw / Mn 4.8 , Mz / Mw 2.7, weight per piece 1.3 mg). 100 parts by weight (2 kg) of the obtained resin particles are put into a 10 L pressure vessel having a stirrer, and 2.0 parts by weight of tribasic calcium phosphate (manufactured by Ohira Chemical Industry) and 0.03 weight of sodium normal paraffin sulfonate. In the presence of parts, it was dispersed in 300 parts by weight of water. While stirring the dispersion, 12.4 parts by weight of isobutane was added (initial charge amount), and the dispersion was heated to 132.9 ° C. At this time, gaseous isobutane was added to adjust the internal pressure of the pressure vessel to 20.2 kgf / cm ² . Next, while maintaining the pressure in the pressure vessel with gaseous isobutane, the pellet and water dispersion were 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. The foaming ratio is 28.4 times, the weight per piece is 1.3 mg, the calorific ratio of the high-temperature side melting point based on the differential scanning calorimeter is 23.1%, and the difference between the high melting point peak temperature and the low melting point peak temperature is 15. Pre-expanded particles at 7 ° C. were obtained. As a result of molding evaluation of the pre-expanded particles, the surface property was ◯, the compact shrinkage ratio was 2.4%, the height of the quadrangular pyramidal protrusions was 1.1 mm, and the mold transferability was ◯. The evaluation results are shown in Table 1.

(Comparative Example 1)
The kneading was carried out by an extruder without adding the organic peroxide added during blending in Example 1, and ethylene-propylene random copolymer resin particles (resin density 0.90 g / cm ³ , resin melting point 142.4 ° C. And a storage elastic modulus of 1269 Pa at an angular frequency of 1 rad / s of 180 ° C., Mw / Mn 5.2, Mz / Mw 3.0, and a weight of 1.3 mg per piece) were obtained in the same manner as in Example 1. The expansion ratio is 24.5 times, the weight per piece is 1.3 mg, the calorific ratio of the high temperature side melting point based on the differential scanning calorimeter is 22.4%, and the difference between the high melting point peak temperature and the low melting point peak temperature is 15.8. Pre-expanded particles at 0 ° C. were obtained. As a result of molding evaluation of the pre-expanded particles, the surface property was ○, the compact shrinkage was 2.3%, the height of the quadrangular pyramidal protrusions was 0.8 mm, and the mold transferability was x. .

(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 137.7 ° C., melt flow index 2.0 g / 10 min at 230 ° C.) 100 Part by weight and 0.1 part by weight of powdered talc, α, α′-bis (t-butylperoxy-m-isopropyl) benzene (manufactured by NOF Corporation, perbutyl P, 1 minute half-life temperature 175 ° C. as organic peroxide ) 0.08 parts by weight were kneaded by dry blending / extruding machine, and ethylene-propylene random copolymer resin particles (resin density 0.90 g / cm ³ , resin melting point 137.9 ° C., 180 ° C. angular frequency 1 rad) Storage elastic modulus at / s, 525 Pa, Mw / Mn 3.7, Mz / Mw 2.5, weight 0.9 mg per piece). In the same manner as in Example 1, except that the initial charge of isobutane was 15.0 parts by weight, the dispersion was heated to 126.9 ° C., and the internal pressure of the pressure vessel was adjusted to 19.4 kgf / cm ² . The expansion ratio is 25.8 times, the weight per piece is 0.9 mg, the calorific ratio of the high temperature side melting point based on the differential scanning calorimeter is 30.1%, and the difference between the high melting point peak temperature and the low melting point peak temperature is 17.5. Pre-expanded particles at 0 ° C. were obtained. When the pre-expanded particles were evaluated for molding, the surface property was ○, the compact shrinkage was 2.5%, the height of the quadrangular pyramidal protrusions was 1.1 mm, and the mold transferability was ○. .

(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 142.4 ° C., melt flow index 0.5 g / 10 min at 230 ° C.) 100 Dry blending and extrusion of 0.1 parts by weight of powder and 0.1 parts by weight of powdered talc and 0.3 parts by weight of t-butyl peroxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl I, 1 minute half-life temperature 159 ° C) as organic peroxide Kneading with a machine, ethylene-propylene random copolymer resin particles (resin density 0.90 g / cm ³ , resin melting point 142.5 ° C., storage elastic modulus 245 Pa at 180 ° C. angular frequency 1 rad / s, Mw / Mn2.8, Mz / Mw2.1, weight per piece 1.7 mg). In the same manner as in Example 1, except that the initial charge of isobutane was 12.0 parts by weight, the dispersion was heated to 136.2 ° C., and the internal pressure of the pressure vessel was adjusted to 19.0 kgf / cm ² . The expansion ratio is 23.8 times, the weight per piece is 1.7 mg, the calorific ratio of the high temperature side melting point based on the differential scanning calorimeter is 17.7%, and the difference between the high melting point peak temperature and the low melting point peak temperature is 17.1. Pre-expanded particles at 0 ° C. were obtained. As a result of molding evaluation of the pre-expanded particles, the surface property was ◯, the compact shrinkage was 2.7%, the height of the quadrangular pyramidal protrusions was 1.0 mm, and the mold transferability was ◯. .

(Comparative Example 2)
In Example 3, 0.7 parts by weight of the organic peroxide added during blending was dry blended and kneaded by an extruder, and ethylene-propylene random copolymer resin particles (resin density 0.90 g / cm ³ , resin) Except for having obtained a storage elastic modulus of 84 Pa at a melting point of 142.4 ° C. and an angular frequency of 1 rad / s of 180 ° C., Mw / Mn 2.8, Mz / Mw 2.1, and a weight per piece of 1.7 mg). 3, the expansion ratio is 22.8 times, the weight per piece is 1.7 mg, the calorific ratio of the high temperature side melting point based on the differential scanning calorimeter is 25.0%, the high melting point temperature and the low melting point temperature The difference was that 16.9 ° C. pre-expanded particles were obtained. As a result of molding evaluation of the pre-expanded particles, the surface property was a lot of wrinkles, the molded product contraction rate was 3.5%, the height of the quadrangular pyramidal projections was 0.8 mm, and the mold transferability was × Met.

(Comparative Example 3)
The ethylene-propylene random copolymer resin particles (resin density 0.90 g / cm ³ , resin melting point 142.3 ° C, 180 ° C angular frequency 1 rad / Example 1 except that the storage elastic modulus at s, 870 Pa, Mw / Mn 4.8, Mz / Mw 2.7, and the weight per piece of 3.5 mg were obtained, and the initial charge of isobutane was 16.0 parts by weight. In the same manner as above, the expansion ratio is 23.1 times, the weight per piece is 3.5 mg, the calorie ratio of the high-temperature side melting point based on the differential scanning calorimeter is 22.7%, the high melting point peak temperature and the low melting point peak temperature The difference was 15.1 ° C pre-expanded particles. As a result of molding evaluation of the pre-expanded particles, the surface property was x where there was a gap between the expanded particles, the compact shrinkage was 2.5%, and the height of the quadrangular pyramidal projections was 0. The mold transferability was x at 9 mm.

(Comparative Example 4)
Except that the ethylene-propylene random copolymer resin particles of Example 1 were used and the dispersion was heated to 129.5 ° C., the foaming ratio was 27.1 times and the weight per piece was 1 in the same manner as in Example 1. .3 mg, pre-expanded particles having a high-temperature melting point ratio of 52.1% based on a differential scanning calorimeter and a difference between the high-melting point peak temperature and the low-melting point peak temperature of 14.9 ° C. were obtained. As a result of molding evaluation of the pre-expanded particles, the surface property is x where there are gaps between the expanded particles, the compact shrinkage rate is 2.2%, and the height of the quadrangular pyramidal projections is 0. The mold transferability was x at 7 mm.

(Comparative Example 5)
Except that the ethylene-propylene random copolymer resin particles of Example 1 were used and the dispersion was heated to 135.0 ° C., the foaming ratio was 28.7 times and the weight per piece was 1 in the same manner as in Example 1. .3 mg, pre-expanded particles having a high-temperature melting point ratio of 9.4% based on a differential scanning calorimeter and a difference between the high-melting point peak temperature and the low-melting point peak temperature of 15.3 ° C. were obtained. As a result of molding evaluation of the pre-foamed particles, the surface property is that there are no gaps between the foamed particles, but there are many wrinkles, the molded product shrinkage rate is 3.3%, and the height of the quadrangular pyramidal protrusions is The mold transferability was x at 0.8 mm.

It is an example of a DSC curve obtained when a differential scanning calorimeter is used to measure polypropylene resin pre-expanded particles according to the present invention. The horizontal axis is the temperature, and the vertical axis is the endothermic amount. The low temperature side shaded part (Ql) represents the melting peak heat quantity based on the low temperature side melting point, and the high temperature side shaded part (Qh) represents the melting peak heat quantity based on the high temperature side melting point.

Claims (3)

Storage modulus at angular frequency 1 rad / s in a dynamic viscoelasticity measurement at 180 ° C. is Ri 100~1000Pa der, polypropylene resin pre to a polypropylene resin having a melting point of 133-150 ° C. as a base resin Foam particles,
The weight per piece is 0.5 to 3.0 mg, and shows two melting peaks as measured by the differential scanning calorimetry method. Of the two melting peaks, the entire melting peak of the melting peak calorie appearing on the high temperature side. Ri ratio 10-50% der against heat and the difference between the peak temperature of the two melting peaks, wherein der Rukoto 10 ° C. or higher 17.5 ° C. or less, pre-expanded polypropylene resin particles. A storage elastic modulus at an angular frequency of 1 rad / s in a dynamic viscoelasticity measurement at 180 ° C. obtained by melt-kneading a raw material polypropylene resin and an organic peroxide using an extruder is 100 to 1000 Pa. Polypropylene resin particles having a melting point of 133 to 150 ° C. and a weight of 0.5 to 3.0 mg per piece,
Along with at least one volatile foaming agent selected from the group consisting of propane, butane, pentane, hexane, nitrogen, air, carbon dioxide, it is dispersed in water in a pressure-resistant container to form a polypropylene resin dispersion,
The dispersion is heated to a temperature in the range of −25 ° C. to + 10 ° C. of the polypropylene resin particles, the polypropylene resin particles are impregnated with a foaming agent, and the container is pressed under a pressure higher than the vapor pressure indicated by the foaming agent. It is obtained by releasing a dispersion of polypropylene resin particles and water in an atmosphere at a lower pressure than in the container while maintaining the temperature and pressure inside.
Measurement by differential scanning calorimetry shows two melting peaks, of which the ratio of the melting peak calorie appearing on the high temperature side to the total melting peak calorie is 10 to 50%, and the two melting peaks The method for producing polypropylene resin pre-expanded particles, wherein a difference in peak temperature between the peaks is 10 ° C or higher and 17.5 ° C or lower. The polypropylene resin pre-expanded particles according to claim 1 are given an internal pressure of 0.1 kg / cm ² -G or more, filled in a mold that can be closed but cannot be sealed, and heated and molded with water vapor. A foamed molded product in a polypropylene resin mold characterized by the above.

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