JP2007302720A - Polypropylene-based resin pre-foamed particle and molded article obtained by in-mold foaming of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide polypropylene-based pre-foamed particles excellent in melt-bonding property, capable of being molded even by a low molding steam pressure, further capable of shortening its molding cycle and producing a molded article obtained by the in-mold foaming of the same and excellent in dimensional stability. <P>SOLUTION: The polypropylene-based pre-foamed particles are provided by consisting of a polypropylene-based resin composition containing 1 to 8 wt.% ≥1 resin selected from a petroleum resin and terpene-based resin, and having 18 to 32% DSC (differential scanning calorimetry) ratio and 0.5 to 1.5 mg particle weight. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polypropylene resin pre-expanded particle capable of producing an in-mold foam molded article excellent in dimensional stability and surface property, and capable of shortening a molding cycle in the in-mold foam molding, and the polypropylene based The present invention relates to an in-mold foam molded body made of resin pre-expanded particles.

  Polypropylene resin pre-expanded particles are superior in chemical resistance, heat resistance, buffer performance, and compression strain recovery performance compared to polystyrene resin pre-expanded particles. Since it is excellent in compressive strength, it is widely used as a buffer packaging material, a returnable box, and an automobile member.

  Polypropylene resins usually have a higher softening temperature, which requires a higher molding vapor pressure than in the case of polystyrene resins during in-mold foam molding, resulting in higher molding costs and longer molding cycles. There is. On the other hand, when the molding vapor pressure is lowered, the fusibility between the foamed particles is insufficient, resulting in a fragile molded body, and the desired mechanical properties are not exhibited.

  In view of the actual situation of such polypropylene resin pre-expanded particles, a foam made of a resin composition containing a petroleum resin or the like in a polypropylene resin has been proposed for the purpose of reducing the molding vapor pressure (Patent Document 1). ~ 4). When the polypropylene resin pre-expanded particles containing such a petroleum resin are subjected to in-mold foam molding, the bead surface can be fused more easily, so molding is possible even at a low molding vapor pressure. Strength and thermal strength are improved.

However, these petroleum resins have a plasticizing effect on polypropylene resins in the temperature range above their own softening point, so that the molding cycle becomes long or the molded body immediately after molding lacks rigidity. There is a problem that molding productivity is lowered, such as deformation of the molded body and a long time required to stabilize the size of the molded body.
JP 59-68340 A JP-A 63-145344 JP 2005-8850 A JP 2005-29773 A

  An object of the present invention is to provide a polypropylene resin pre-expanded particle capable of shortening a molding cycle and capable of producing an in-mold foam molded article excellent in dimensional stability and surface appearance.

  The inventors of the present invention have intensively studied to achieve this problem. As a result, by forming the propylene resin pre-expanded particles made of a polypropylene resin composition containing 1 to 8% by weight of one or more selected from petroleum resins and terpene resins with a predetermined DSC ratio and particle weight, a molding cycle It has been found that an in-mold foam-molded article having excellent dimensional stability and surface properties can be obtained, and the present invention has been completed.

  That is, the first of the present invention is a polypropylene resin pre-expanded particle comprising a polypropylene resin composition containing 1 to 8% by weight of a petroleum resin and / or a terpene resin, and in the differential scanning calorimetry, 4-10 mg of resin pre-expanded particles are heated at a rate of 10 ° C./min from 40 ° C. to 200 ° C., and the heat of fusion at the melting peak based on the crystals inherent in the base resin of the polypropylene resin pre-expanded particles Is the total heat of fusion (α + β) of the heat of fusion (β) of the melting peak appearing on the high temperature side, where α (J / g) is the heat of fusion of the melting peak appearing on the high temperature side of the peak, and β (J / g). ) (Hereinafter referred to as DSC ratio) is 18% to 32%, and the particle weight is related to polypropylene resin pre-expanded particles of 0.5 mg to 1.5 mg.

  A preferred embodiment relates to the polypropylene resin pre-expanded particles described above, wherein the softening point of the petroleum resin and / or terpene resin is 135 to 145 ° C.

  According to a second aspect of the present invention, a polypropylene resin mold is obtained by filling the above-described polypropylene resin pre-expanded particles in a mold that can be closed but cannot be sealed, and is molded by heating with water vapor. A third aspect of the present invention relates to the inner foamed molded article, wherein the polypropylene resin pre-foamed particles described above are filled in a mold that can be closed but cannot be sealed, and heated and molded with water vapor. The present invention relates to a method for producing an expanded foam in a polypropylene resin mold.

  According to the pre-expanded propylene resin particles of the present invention, it is possible to provide an in-mold expanded molded article that can shorten the molding cycle and has good dimensional stability and surface properties.

  The polypropylene resin pre-expanded particles of the present invention are composed of a polypropylene resin composition containing 1 to 8% by weight of petroleum resin and / or terpene resin.

  The polypropylene resin composition of the present invention contains 1 to 8% by weight, preferably 2 to 5% by weight of petroleum resin and / or terpene resin. When the content is less than 1% by weight, a molded product with insufficient fusing property tends to be obtained, and the surface elongation is further deteriorated to deteriorate the appearance of the molded product. On the other hand, when it exceeds 8% by weight, the molding cycle is rapidly extended, and the soft texture immediately after the mold release is increased to cause deformation.

As the polypropylene resin constituting the polypropylene resin composition of the present invention, as a monomer, as long as it contains propylene in an amount of 80% by weight or more, more preferably 85% by weight or more, further preferably 90% by weight or more, There is no particular limitation on the composition and synthesis method. For example, propylene homopolymer, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene ternary copolymer. Polymers and the like, as well as these modified products. In addition, these polypropylene resins used a generally known method, that is, a highly active metallocene catalyst in addition to a gas phase polymerization method such as a BASF method, an AMDCD method, a UCC method, a high pole method using an MgCl ₂ type supported catalyst. It can be manufactured by a method or a method using a conventional TiCl ₃ catalyst.

  Moreover, you may add synthetic resins other than a polypropylene resin in the range which does not impair the effect of this invention. 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.

  Although there is no restriction | limiting in particular in the melting point of the polypropylene resin composition in this invention, 130 to 170 degreeC is preferable, 135 to 160 degreeC is more preferable, 140 to 150 degreeC is further more preferable.

  The melt index of the polypropylene resin composition in the present invention is not particularly limited as long as such pre-expanded particles can be produced, preferably 0.2 g / 10 min to 50 g / 10 min, more preferably 1 g / 10 min. It is 30 g / 10 min or less, more preferably 3 g / 10 min or more and 12 g / 10 min or less. When the melt index is within this range, the pre-expanded particles have good dimensional stability and surface properties. When the melt index is less than 0.2 g / 10 min, the melt viscosity tends to be too high and it is difficult to obtain highly expanded pre-expanded particles. When the melt index is greater than 50 g / 10 min, the melt viscosity with respect to the elongation of the resin at the time of expansion is low. It is too low and tends to break. The melt index can be adjusted, for example, by using an organic peroxide.

  In the present invention, the petroleum resin refers to a thermoplastic resin obtained by cationically polymerizing a cracked oil fraction generated by so-called pyrolysis of petroleum, with a mixture, petroleum unsaturated hydrocarbon such as cyclopentadiene, It is a resin mainly composed of higher olefinic hydrocarbons or aromatic hydrocarbons (50% by weight or more). Among these petroleum resins, it is preferable to use a hydrogenated petroleum resin which is a hydrogenated product having high compatibility with a polypropylene resin. Among hydrogenated petroleum resins, those having a hydrogenation rate of 80% or more, particularly 90% or more are preferred.

The terpene resin in the present invention refers to a hydrocarbon compound represented by a composition of (C ₅ H ₈ ) _n , specifically, a terpene homopolymer, or a monomer and a terpene copolymerizable with a terpene. A copolymer, these hydrogenated substances, etc. are mentioned. Usually, the n is an integer of 2 to 30, but is preferably an integer of 8 to 20. Examples of the terpene represented by the composition formula (C ₅ H ₈ ) _n include, for example, pinene, dipentene, karen, myrcene, osymene, limonene, terpinolene, terpinene, sabinene, tricyclene, bisabolen, gingiberene, santalen, camphorene, mylene, Examples include totarene.

  Of these, homopolymers or copolymers comprising pinene and dipentene, and hydrogenated products thereof are particularly preferred, and hydrogenated products having high compatibility with polypropylene resins are preferred. Among the hydrogenated products, those having a hydrogenation rate of 80% or more, particularly 90% or more are preferable.

  Furthermore, the softening point of the petroleum resin and terpene resin in the present invention is preferably 135 ° C. or higher and 145 ° C. or lower. The softening point here is a measured value based on JIS-K2207 (ring and ball type). If the softening point is less than 135 ° C., the heat-resistant rigidity of the in-mold foam molded product may be lowered. Moreover, when a softening point exceeds 145 degreeC, the dispersibility to a polypropylene resin may be inferior.

  In the present invention, if necessary, cell nucleating agents such as talc, antioxidants, metal deactivators, phosphorus processing stabilizers, UV absorbers, UV stabilizers, fluorescent brighteners, metal soaps, etc. Stabilizers or crosslinkers, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, antistatic agents, etc. are added to the extent that the effects of the present invention are not impaired. It is good also as a thing.

  The method for adding the petroleum resin or terpene resin to the polypropylene resin is not particularly limited, but melt kneading is generally used. For example, a dry blend of petroleum resin and polypropylene resin is melt-kneaded using an extruder. Alternatively, a master batch pellet containing a high concentration of petroleum resin and terpene resin separately melt kneaded may be diluted and mixed with a polypropylene resin so that the fusion improver has a desired concentration, and then melt kneaded.

  The particle weight of the pre-expanded particles referred to in the present invention is the weight of one pre-expanded polypropylene resin particle, and the range thereof is 0.5 mg to 1.5 mg, preferably 0.7 mg to 1.2 mg. is there. When the particle weight is less than 0.5 mg, the surface elongation is deteriorated and the appearance of the molded product is impaired, and further, the molded product becomes brittle with insufficient fusibility. On the other hand, when the grain weight exceeds 1.5 mg, the molding cycle becomes long.

  Such adjustment of the particle weight can be performed by adjusting the particle weight of the polypropylene resin particles. For example, the polypropylene resin composition is melt-kneaded in the extruder and then attached to the tip of the extruder. When the melt-kneaded product is extruded in a string shape from a die having fine holes and then cut with a cutting machine equipped with a take-up machine, the resin particles have a particle weight of 0.5 to 1.5 mg / particle, preferably 0.8. It can be obtained by cutting to a weight of 7-1.2 mg.

  As a method of foaming the polypropylene resin particles to obtain pre-foamed particles, for example, the polypropylene resin particles are dispersed in water together with a volatile foaming agent in a pressure-resistant container, and the dispersion is dispersed into the polypropylene resin particles. Heating to a temperature in the range of -20 ° C to + 20 ° C, impregnating the polypropylene resin particles with a foaming agent, keeping the temperature and pressure inside the container constant under a pressure higher than the vapor pressure indicated by the foaming agent. However, there is a method in which a dispersion of the polypropylene resin particles and water is released under a lower pressure atmosphere than in the container.

  In the preparation of the dispersion, as a dispersant, for example, an inorganic dispersant such as tricalcium phosphate, basic magnesium carbonate, calcium carbonate, and so on, for example, sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, α-olefin sulfone. It is preferable to use a dispersion aid such as acid soda. Among these, the combined use of tricalcium phosphate and sodium n-paraffin sulfonate is more preferable. The amount of dispersant and dispersion aid used varies depending on the type and type and amount of resin used, but it is usually preferable to add 0.2 to 3 parts by weight of dispersant to 100 parts by weight of water. It is preferable to add 0.001 to 0.1 part by weight of a dispersion aid. In order to improve the dispersibility of the polypropylene resin particles in water, it is usually preferable to use 20 to 100 parts by weight of polypropylene resin particles with respect to 100 parts by weight of water.

  Examples of the blowing agent include hydrocarbons or halogenated hydrocarbons having a boiling point of −50 to 120 ° C., and specifically, propane, butane, pentane, hexane, dichlorodifluoromethane, dichlorotetrafluoroethane, trichlorotrimethyl. Fluoroethane, methyl chloride, methylene chloride, ethyl chloride and the like can be mentioned, 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 to 50 parts by weight.

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

  When water is used as a foaming agent, it is preferable to add one or more compounds among the hydrophilic polymer and the compound having a triazine skeleton to the polypropylene resin composition. In the present invention, the hydrophilic polymer refers to an ethylene-acrylic acid-maleic anhydride terpolymer, an ethylene- (meth) acrylic acid copolymer, and an ethylene- (meth) acrylic acid copolymer crosslinked with a metal ion. Examples thereof include carboxyl group-containing polymers such as ionomer resins. These may be used alone or in combination of two or more. In particular, an ethylene ionomer resin obtained by crosslinking an ethylene- (meth) acrylic acid copolymer with an alkali metal ion such as sodium ion or potassium ion is preferable because it provides a good water content and good foamability. Further, an ethylene ionomer resin obtained by crosslinking an ethylene- (meth) acrylic acid copolymer with potassium ions is more preferable because it gives a larger average cell diameter.

  The amount of the hydrophilic polymer used is not particularly limited depending on the kind of the hydrophilic polymer, but is usually 0.01 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. More preferred is 5 parts by weight or more. If it is less than 0.01 part by weight, it is difficult to obtain pre-expanded particles having a high expansion ratio, and if it exceeds 20 parts by weight, the heat resistance and the mechanical strength may be greatly reduced.

  In the present invention, the compound having a triazine skeleton preferably has a molecular weight per unit triazine skeleton of 300 or less. Here, the molecular weight per triazine skeleton is a value obtained by dividing the molecular weight by the number of triazine skeletons contained in one molecule. When the molecular weight per unit triazine skeleton exceeds 300, variation in foaming ratio and variation in cell diameter may be noticeable. Examples of the compound having a molecular weight per unit triazine skeleton of 300 or less include melamine (chemical name 1,3,5-triazine-2,4,6-triamine), ammelin (1,3,5-triazine-2- Hydroxy-4,6-diamine), ammelide (1,3,5-triazine-2,4-hydroxy-6-amine), cyanuric acid (1,3,5-triazine-2,4,6-triol) ), Tris (methyl) cyanurate, tris (ethyl) cyanurate, tris (butyl) cyanurate, tris (2-hydroxyethyl) cyanurate, melamine isocyanuric acid condensate and the like. These may be used alone or in combination of two or more. Among these, it is preferable to use melamine, isocyanuric acid, and melamine / isocyanuric acid condensate in order to obtain pre-expanded particles having a high expansion ratio with small variations in expansion ratio and cell diameter.

  The amount of the compound having a triazine skeleton is not generally limited depending on the type, but is usually preferably 0.001 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the polypropylene resin, and 0.01% by weight. More preferred is 1 part by weight or more and 1 part by weight or less. If it is less than 0.001 part by weight, it is difficult to obtain pre-expanded particles having a high expansion ratio, and if it exceeds 1 part by weight, the heat resistance and mechanical strength may be greatly reduced.

  There is no restriction | limiting in particular in the expansion ratio of the polypropylene resin pre-expanded particle obtained as mentioned above, Preferably they are 5 times or more and 40 times or less, More preferably, they are 8 times or more and 20 times or less. The cell diameter of the polypropylene resin pre-expanded particles is preferably 50 μm or more and 800 μm, more preferably 100 μm or more and 500 μm or less, and further preferably 150 μm or more and 300 μm. When the cell diameter is within such a range, it is easy to obtain a molded body having excellent surface appearance and excellent expansion of the pre-expanded particles.

In the differential scanning calorimetry, the polypropylene resin pre-expanded particles of the present invention are heated at a rate of 10 ° C./minute from 40 ° C. to 200 ° C. to 4 to 10 mg of polypropylene resin pre-expanded particles. When the heat of fusion of the melting peak based on the crystals inherent in the base resin of the particles is α (J / g), and the heat of fusion of the melting peak appearing on the higher temperature side than the peak is β (J / g) The ratio (hereinafter referred to as DSC ratio) of the heat of fusion (β) of the melting peak appearing on the high temperature side to the total heat of fusion (α + β) is 18% to 32%. The DSC ratio in the present invention is expressed as Equation 1.
DSC ratio (%) = 100 × (β / (α + β)) (Formula 1)

  In the present invention, the DSC ratio is in the range of 18 to 32%, preferably 20 to 30%, and more preferably 22 to 28%. When the DSC ratio is less than 18%, the molding cycle is extremely extended, and the molded body immediately after mold release is insufficient in rigidity and deforms. On the other hand, when the DSC ratio exceeds 32%, the surface elongation is deteriorated, the appearance of the molded product is impaired, and the molded product becomes brittle with insufficient fusibility. FIG. 1 shows a schematic diagram of a DSC chart obtained under the above conditions.

  Since the DSC ratio varies depending on the temperature and pressure at the time of foaming when producing the polypropylene resin pre-foamed particles, the DSC ratio is 18% to 32% by appropriately adjusting the foaming temperature and the foaming pressure. Expanded particles can be obtained. In general, when the foaming temperature and pressure are increased, the DSC ratio tends to decrease, and it depends on the type of polypropylene resin, the content of petroleum resin, and the type of foaming agent. When the temperature is raised by 1 ° C., the DSC ratio is reduced by about 8 to 15%, and when the foaming pressure is raised by 0.1 MPa, the DSC ratio is reduced by about 5 to 10%.

  The polypropylene resin-in-mold foam-molded article of the present invention is obtained by filling the mold that can be closed but cannot be sealed with the polypropylene resin pre-foamed particles, and heating and molding with steam.

In order to make the polypropylene resin pre-expanded particles of the present invention into an in-mold foam molded product, the polypropylene resin pre-expanded particles are filled in a mold that can be closed but cannot be sealed, and heated and molded with steam. Specifically, for example, a) The foamed particles are pressurized with an inorganic gas to impregnate the particles with an inorganic gas to give a predetermined internal pressure, then filled into a mold, and foamed and heated and melted with steam or the like. (B) A method in which foamed particles are compressed by gas pressure and filled in a mold, and the foaming particles are foamed and heat-sealed by utilizing the recovery force of the foamed particles (special Japanese Patent Publication No. 51-22951). No. 53-33996), and c) filling the foamed particles with a slight gap in the mold, and then closing and compressing the mold to give the foamed particles a resilience and foaming with steam or the like And a method of heat-sealing can be used. Such molding vapor pressure is preferably 1.5~4.5kgf / cm ^2, more preferably 2~4kgf / cm ^2, more preferably 2~3kgf / cm ^2. When the molding vapor pressure exceeds 4.5 kgf / cm ² , not only the steam cost increases, but the compact may shrink due to excessive heating. If it is less than 1.5 kgf / cm < ² >, the limit of the effect of this invention is exceeded and there exists a tendency for a melt | fusion property to be impaired. In this way, an in-mold foam molded article can be obtained by heating and foaming with water vapor.

There is no restriction | limiting in particular in the density of the in-mold foaming molding in this invention, Generally it is the range of 0.015-0.150 g / cm < ³ >.

  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 DSC ratio>
When 4-10 mg of pre-expanded particles were heated from 40 ° C. to 200 ° C. at a rate of 10 ° C./min, the melting heat amount of the melting peak based on the crystals originally possessed by the base resin of the polypropylene resin pre-expanded particles was α (J / g), where β (J / g) is the heat of fusion of the melting peak appearing on the higher temperature side than this peak, the ratio of the heat of fusion of the high temperature side peak represented by Formula 1 to the total heat of fusion. DSC ratio (%) was used.
DSC ratio (%) = 100 × (β / (α + β)) (Formula 1)

<Melt flow index measurement>
The melt flow index was measured under the conditions of orifice 2.0959 ± 0.005 mmφ, orifice length 8.000 ± 0.025 mm, load 2160 g, 230 ± 0.2 ° C. in accordance with JIS-K7210.

<Measurement of expansion ratio of pre-expanded particles>
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.

<In-mold foam molding and molding cycle>
Molding was performed using an in-mold foam molding machine equipped with a rectangular parallelepiped mold having a length × width × thickness of 400 × 300 × 50 mm and a pressure sensor capable of detecting the foaming pressure of the molded body in the mold. First, after (1) the mold is opened, (2) after the mold is closed until the mold gap in the thickness direction becomes 15 mm, (3) without causing the pre-expanded particles to flow out of the mold system. Filled. Next, (4) the pre-expanded particles are compressed by closing the mold so that the gap between the molds becomes 0 mm, and (5) after applying a molding vapor pressure of a gauge pressure of 2.5 kgf / cm ² , (6 ) Cooled with water, (7) When the foaming pressure of the molded body inside the mold reached 0.5 kgf / cm ² , the molded body was released. The series of molding steps from (1) to (7) are automatically operated, and the time required for the other steps except step (6) is constant. The required time from step (1) to (7) was counted to form a molding cycle.

<Dimensional stability evaluation>
Immediately after releasing the molded body, measurement of the mold shrinkage ratio in the longitudinal direction of the molded body was started, and the time required until the shrinkage ratio reached 90% of the equilibrium shrinkage ratio was determined. The equilibrium shrinkage rate is the shrinkage rate in the longitudinal direction of the molded article after standing at room temperature for 24 hours. The shorter the time, the faster the dimensional stabilization and the better the dimensional stability.

<Surface appearance of in-mold foam molding>
The surface appearance of the obtained molded body was evaluated according to the following criteria, and a pass / fail judgment was performed.
○: A molded article with a small surface gap and excellent surface appearance with few irregularities.
X: A molded article having a poor surface appearance with many surface gaps or many surface irregularities.

<Fusibility>
Cleaving the molded body in the mold, visually measuring the number of particle breaks (material breaks) and the number of inter-particle breaks (interface breaks) in the cross section, and the ratio (%) of particle breakage to the total number of both The fusion property was defined as 80% or more as acceptable product and less than 80% as unacceptable product.

Example 1
Alcon manufactured by Arakawa Chemical Co., Ltd., which is a petroleum resin, with respect to 100 parts by weight of an ethylene-propylene random copolymer (resin density 0.90 g / cm ³ , melt flow index 4.8 g / 10 min, crystal melting point 146 ° C.) A resin mixture containing 3 parts by weight of P-140 (softening point 140 ° C.) and 0.05 parts by weight and 0.1 parts by weight of powdered talc and calcium stearate, respectively, was dry-blended. Extrusion was carried out at a resin temperature of 240 ° C. using a 50 mm single-screw extruder equipped with an 8 mm die, taken out, and cut to obtain pellets having a particle weight of 0.75 mg. 150 kg of water, 50 kg of the pellets, 800 g of tricalcium phosphate (manufactured by Ohira Chemical Industry Co., Ltd.), and 38 g of sodium n-paraffin sulfonate were charged into a 250 L pressure vessel and dispersed. While stirring the dispersion, 4.5 kg of isobutane was added and heated to 146.3 ° C. Further, gaseous isobutane was added to adjust the internal pressure of the pressure vessel to 1.44 MPa. Next, while maintaining the pressure in the pressure vessel with gaseous isobutane, the dispersion is discharged into the atmosphere through a circular orifice with a diameter of 3.6 mm attached to the rear end of the discharge valve at the bottom of the pressure vessel, and foamed. Pre-expanded particles having a magnification of 13 times and a DSC ratio of 26% were obtained. When the pre-expanded particles were subjected to in-mold foam molding, a molding cycle was as short as 100 seconds, and a molded article excellent in dimensional stability, surface appearance and fusion property was obtained. The evaluation results are shown in Table 1.

（実施例２）
実施例１において石油樹脂の代わりにテルペン系樹脂であるヤスハラケミカル社製のクリアロンP−１２５（軟化点１２５℃）を用いた以外は実施例１と同様の方法により、発泡倍率１３倍、ＤＳＣ比２８％の予備発泡粒子を得た。該予備発泡粒子を型内成形に供したところ、成形サイクルは９５秒と短く、寸法安定性、表面外観及び融着性に優れた成形体を得た。評価結果を表１に示す。

(Example 2)
In Example 1, instead of petroleum resin, a terpene-based resin, Clearon P-125 (softening point 125 ° C.) manufactured by Yashara Chemical Co., was used. % Of pre-expanded particles. When the pre-expanded particles were subjected to in-mold molding, a molding cycle was as short as 95 seconds, and a molded article excellent in dimensional stability, surface appearance and fusion property was obtained. The evaluation results are shown in Table 1.

(Example 3)
Pre-expanded particles having an expansion ratio of 13 times and a DSC ratio of 22% were obtained in the same manner as in Example 1 except that the petroleum resin was replaced with OPPERA PR100A manufactured by ExxonMobil Chemical in Example 1. When the pre-expanded particles were subjected to in-mold molding, the molding cycle was as short as 106 seconds, and a molded article excellent in dimensional stability, surface appearance and fusion property was obtained. The evaluation results are shown in Table 1.

Example 4
Pre-expanded particles having an expansion ratio of 13 times and a DSC ratio of 23% were obtained in the same manner as in Example 1 except that the particle weight was 1.2 mg. When the pre-expanded particles were subjected to in-mold molding, a molding cycle was as short as 105 seconds, and a molded article excellent in dimensional stability, surface appearance and fusion property was obtained. The evaluation results are shown in Table 1.

(Example 5)
Pre-expanded particles having an expansion ratio of 13 times and a DSC ratio of 25% were obtained in the same manner as in Example 1 except that Alcon P-140 was increased to 5 parts by weight. When the pre-expanded particles were subjected to in-mold molding, the molding cycle was as short as 102 seconds, and a molded article excellent in dimensional stability, surface appearance and fusion property was obtained. The evaluation results are shown in Table 1.

(Comparative Example 1)
Pre-expanded particles having an expansion ratio of 13 times and a DSC ratio of 26% were obtained in the same manner as in Example 1 except that no petroleum resin or terpene resin was added. When the pre-expanded particles were subjected to in-mold molding, the results were poor in fusibility and surface appearance. The evaluation results are shown in Table 1.

(Comparative Example 2)
Pre-expanded particles having an expansion ratio of 13 times and a DSC ratio of 26% were obtained in the same manner as in Example 1 except that Alcon P-140 was increased to 10 parts by weight. When the pre-expanded particles were subjected to in-mold molding, the molding cycle was as long as 170 seconds, resulting in poor dimensional stability. The evaluation results are shown in Table 1.

(Comparative Example 3)
Pre-expanded particles having an expansion ratio of 13 times were obtained in the same manner as in Example 1 except that the DSC ratio was adjusted to 15% by adjusting the foaming temperature and the foaming pressure during the production of the pre-expanded particles. When the pre-expanded particles were subjected to in-mold molding, the molding cycle was as long as 180 seconds, resulting in poor dimensional stability. The evaluation results are shown in Table 1.

(Comparative Example 4)
Pre-expanded particles having an expansion ratio of 13 times were obtained in the same manner as in Example 1 except that the DSC ratio was adjusted to 35% by adjusting the foaming temperature and the foaming pressure during the production of the pre-expanded particles. When the pre-expanded particles were subjected to in-mold molding, the results were poor in fusibility and surface appearance. The evaluation results are shown in Table 1.

(Comparative Example 5)
Pre-expanded particles having an expansion ratio of 13 times and a DSC ratio of 26% were obtained in the same manner as in Example 1 except that the particle weight was 0.4 mg. When the pre-expanded particles were subjected to in-mold molding, the results were poor in fusibility and surface appearance. The evaluation results are shown in Table 1.

(Comparative Example 6)
Pre-expanded particles having an expansion ratio of 13 times and a DSC ratio of 26% were obtained in the same manner as in Example 1 except that the particle weight was 1.8 mg. When the pre-expanded particles were subjected to in-mold molding, the molding cycle was as long as 180 seconds, resulting in poor dimensional stability. The evaluation results are shown in Table 1.

  As shown in Examples 1 to 5 and Comparative Examples 1 to 6, the polypropylene resin pre-expanded particles of the present invention have a fusion cycle and a molding property with a low molding vapor pressure, but have a short molding cycle and dimensions. It turns out that the molded object excellent in stability and surface property can be provided.

The schematic diagram of the DSC chart of the polypropylene resin pre-expanded particles of the present invention is shown.

Explanation of symbols

α Low temperature melting peak heat β High temperature melting peak heat

Claims (4)

  A polypropylene resin pre-expanded particle comprising a polypropylene resin composition containing 1 to 8% by weight of a petroleum resin and / or a terpene resin, wherein 4 to 10 mg of the polypropylene resin pre-expanded particles are measured in differential scanning calorimetry. The temperature is increased from 40 ° C. to 200 ° C. at a rate of 10 ° C./min, and the heat of fusion of the melting peak based on the crystals inherent to the base resin of the polypropylene resin pre-expanded particles is α (J / g), When the heat of fusion of the melting peak appearing on the higher temperature side than the peak is β (J / g), the ratio of the heat of fusion (β) of the melting peak appearing on the higher temperature side to the total heat of fusion (α + β) (hereinafter referred to as DSC ratio) ) 18% to 32%, and polypropylene resin pre-expanded particles having a particle weight of 0.5 mg to 1.5 mg.   The polypropylene resin pre-expanded particles according to claim 1, wherein the petroleum resin and / or the terpene resin has a softening point of 135 to 145 ° C.   The polypropylene resin pre-expanded foam according to claim 1 or 2, which is obtained by filling a mold which can be closed but cannot be sealed, and molded by heating with water vapor. Molded body.   The polypropylene resin pre-expanded particles according to claim 1 or 2 are filled in a mold that can be closed but cannot be sealed, and molded by heating with water vapor and molded in a polypropylene resin mold. Manufacturing method.

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