JP5058557B2 - Polypropylene resin pre-expanded particles, and in-mold foam moldings - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene resin pre-expanded particle that can easily afford an in-mold molded item having a complicated shape at a low cost utterly without detriment to heat resistance, solvent resistance, heat insulating properties, and shock-absorbing properties inherent in the polypropylene resin as it can solve a problem of inward inclination by a short-time drying and realizes good surface beautifulness, particularly excellently beautiful appearances at a portion having a thin-walled shape in in-mold molding of an item having a complicated shape. <P>SOLUTION: The polypropylene resin pre-expanded particle comprises as a substrate resin a polypropylene resin, which comprises at least 70 wt.% and at most 95 wt.% of a polypropylene resin comprising 1-butene and ethylene as comonomers and having an MFR of at least 10 g/10 min and at most 30 g/10 min and at least 5 wt.% and at most 30 wt.% of a polypropylene resin comprising ethylene as a comonomer and having an MFR of at least 0.1 g/10 min and at most 3 g/10 min and has an MFR of at least 5 g/10 min and at most 20 g/10 min and a melting point of not lower than 140&deg;C and not higher than 155&deg;C, and a petroleum resin and/or a terpene resin. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  TECHNICAL FIELD The present invention relates to a polypropylene resin pre-expanded particle used for a buffer wrapping material, a pass box, an automobile interior member, a core material for an automobile bumper, a heat insulating material, and the like, and an in-mold foam-molded article obtained by using the pre-expanded particle. It is.

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

  On the other hand, in recent years, the number of in-mold foam moldings whose appearance is important is increasing. This is often used for applications such as general cushioning packaging, automobile interior parts, and returnable boxes used in places where users can see. Physical properties such as rigidity, lightness, and heat insulation that are usually required for in-mold foam moldings. In addition, a good appearance is required. In-mold foamed moldings show gaps between particles and turtle shell patterns due to the manufacturing method, but many products that emphasize the appearance dislike them. In order to make the gaps between the particles inconspicuous, generally, a method is adopted in which the heating steam pressure at the time of in-mold foam molding is increased to promote fusion between the particles. As can be seen from these technologies, in order to obtain an in-mold foam molded article with a good appearance with no conspicuous gaps between particles, that is, an in-mold foam molded article with a high surface beauty, The vapor pressure needs to be higher than the pressure required for fusion between particles.

  In addition, in the case of a shock-absorbing packaging material, which is one of the most important uses of the propylene-based resin-molded foam-molded body, particularly in a box shape, a phenomenon called “inside-down” is observed immediately after molding by heating steam. . “Inclined” means that the center dimension is smaller than the end dimension of the box-shaped molded product, and there is a difference. The absolute value varies depending on the size of each designed product, but it falls inward. If is large, it becomes a defective product that cannot be used as a product. Most of the internal collapse may be recovered by drying at a high temperature of 60 ° C. or more and 80 ° C. or less, but the introduction of such a drying step significantly deteriorates productivity.

  With respect to the inversion phenomenon due to shrinkage of the molded body after heat molding, a polypropylene resin having a high resin rigidity is used to impart a molded body rigidity that acts as a reaction force, and deformation can be suppressed.

  However, polypropylene resin with high rigidity that can suppress the internal falling phenomenon is generally a resin with a low comonomer content and a high melting point, but it is necessary to obtain a good molded product as the melting point of the resin increases. The pressure of the formed heating steam tends to increase. For this reason, when a higher rigidity is required, a large amount of heating steam is consumed, resulting in an increase in utility cost, resulting in an increase in molding processing cost. Further, when a highly rigid resin is used, the heat molding pressure becomes high, so that it is necessary to use a molding machine or a mold having a high pressure resistance specification, which increases the equipment cost in addition to the utility cost. At present, most of the molding machines for in-mold foam molding of polypropylene resin pre-expanded particles occupy a specification with a pressure resistance of 0.4 MPa, and the molding heating steam pressure normally produced by using the molding machine is approximately. Up to about 0.36 MPa. Polypropylene-based resin pre-expanded particles used for in-mold foam molding use a resin having such a characteristic that can cope with this, and generally, ethylene-random polypropylene having a melting point of about 140 to 150 ° C. is used.

Up to now, various techniques have been studied for improving the rigidity of the in-mold foam molded article. In order to obtain high rigidity with a polypropylene resin, it is conceivable to simply use homopolypropylene. For example, Patent Document 1 discloses a DSC obtained by a differential scanning calorimeter with a tensile elastic modulus of 15,000 to 25000 kg / cm ^2. The technique regarding the homopolypropylene-type resin pre-expanded particle | grains whose calorie | heat amount of the high temperature side peak of a curve is 30-60 J / g is disclosed. Patent Document 1 also discloses that pre-foamed particles capable of obtaining an in-mold foam-molded product at a relatively low molding temperature can be produced using a homopropylene resin having an MFR in the range of 20 to 100 g / 10 min. Technology is disclosed. However, in the technique described in Patent Document 1, it is described that the pressure of the heating steam at the time of molding necessary for obtaining a good foamed molded product is 0.4 to 0.6 MPa. It cannot be molded with a molding machine of 4 MPa pressure resistance specification. Moreover, there is no special description about the surface beauty of a molded object.

  Further, in the technique described in Patent Document 2, homopolypropylene or a random polypropylene resin having a low comonomer content is used, but there is no particular description regarding the surface beauty. As a similar evaluation standard, the evaluation is based on the standard that the fusion between the foamed particles is 60% or more, but the standard is an evaluation standard in which the particles inside the in-mold foam molded product are partially fused, Compared to the standard for obtaining surface aesthetics, this is a standard that can be satisfied even with a low molding heating steam pressure. With the technique described in this publication, it is difficult to obtain a molded article having a beautiful surface with a molding machine that uses 0.4 MPa pressure.

  Although high rigidity cannot be obtained as compared with homopolypropylene, a technique using a polypropylene random copolymer has been studied with emphasis on moldability. For example, Patent Document 3 discloses a technique in which a propylene-based random copolymer having a melting point of 149 to 157 ° C., an MFR of 1 to 20 g / 10 minutes, and a half crystallization time of a certain value or less is used as the base resin. Is disclosed.

  Patent Document 4 describes the high-temperature-side crystal amount of a melting crystal curve obtained by using differential scanning calorimetry (hereinafter abbreviated as DSC) for the crystalline state of polypropylene resin pre-expanded particles used for in-mold foam molding. A technique for improving the compressive strength of the obtained in-mold foam molded article by setting the relationship between the low-temperature side crystal amount within a certain range is disclosed.

  However, regarding these techniques, the pressure of the heating steam required for in-mold foam molding is as high as 0.4 to 0.5 MPa, and, as in the techniques described in Patent Documents 2 to 4, molding with particularly high pressure resistance performance. This technology is made possible by using a machine.

  Further, in Patent Document 5, when a polypropylene resin containing 1-butene as a comonomer is used, a resin having a high tensile elastic modulus, that is, a rigidity is obtained with respect to the resin melting point. By using this, a mold having a high rigidity is obtained. A technique is disclosed in which an inner foamed molded product can be obtained.

  However, even with this technology, the pressure of the heating steam required for in-mold foam molding is around 0.4 MPa. The lowest is 0.36 MPa, which is the lower limit level of the molding machine performance of the 0.4 MPa pressure resistance specification that is often used at present. Further, there is no particular description regarding the surface aesthetics and also the aesthetics of the thin-walled portion, and it is considered that higher molding heating steam pressure is required to obtain the surface aesthetics.

  Further, Patent Document 6 discloses a polypropylene having high rigidity by using polypropylene resin pre-expanded particles whose base resin is a propylene / 1-butene random copolymer containing 3 to 12% by weight of 1-butene component. A technique for obtaining a resin-based foamed molded article is disclosed. When this technology is used, it is described that molding can be performed even with a molding machine having a pressure resistance of 0.4 MPa, which is often used at present, with the pressure of the molding heating steam being around 0.3 MPa. However, a 1-butene homopolypropylene resin random copolymer that does not contain a component having a low MFR that is a high molecular weight component and does not contain an ethylene component described in the patent document is a polypropylene resin random copolymer containing an ethylene component. There is a hard and brittle property compared to coalescence, and this property has a negative effect on repeated cushioning performance when used as a base resin for foams, especially in the case of cushioning packaging materials. Properties, dimensional recoverability after compression, and impact properties in a low temperature region are inferior. Polypropylene resin foam molded products are superior to polystyrene resin foam molded products, which are the same in-mold foam molded products, in terms of rigidity, but have superior resistance to repeated impacts and flexibility. Some aspects are used for such purposes. For this reason, the technique described in the technology also has a drawback that it is not suitable for general cushioning packaging applications other than those intended only for rigidity.

  As described above, in order to form pre-expanded particles based on a polypropylene-based resin having high rigidity, there is currently a special molding machine that can withstand high molding heating steam pressure. However, in order to increase the pressure resistance of the molding machine, it is necessary to increase the size of the machine in order to increase the strength of the molding machine, and it is also necessary to increase the thickness of the mold. is there. Increasing the pressure of the molding heating steam also increases the amount of steam necessary for heating during molding, which increases utility costs such as increasing the amount of cooling water for cooling the molding steam. Furthermore, the heating time at the time of molding becomes longer in order to heat to a higher temperature, and more time is required for the process of cooling the heated mold with cooling water, so the production cycle per product becomes longer. Productivity deteriorates. Furthermore, since the mold shape is complicated in in-mold foam molding, depending on the shape, stress may concentrate on a part of the mold during molding heating, and the mold may be damaged, which further increases costs. .

  As described above, the high molding heating steam pressure in the in-mold foam molding has various drawbacks, and it is desirable that molding can be performed with the lowest possible molding heating steam pressure. In the category of existing technology, it is difficult to obtain in-mold foam-molded polypropylene resin pre-foamed particles having high rigidity that can be stably produced by a molding machine of 0.4 MPa pressure resistance specification that is widely used at present.

  On the other hand, in the case of a packaging material for precision parts, particularly for cushioning packaging materials, the box-shaped interior often has a complicated shape. When trying to obtain a molded body with a complicated shape, if there is a thin and narrow shape, so-called “thin-walled” shape, that only a few of the pre-expanded particles enter in the thickness direction, It may be difficult to obtain surface aesthetics. For this reason, in this part, buffer performance and strength are not sufficiently obtained, and problems such as poor fusion between the pre-expanded particles are likely to occur, which greatly restricts the shape design.

  For example, in Patent Document 7, in order to obtain pre-foamed particles having good secondary foamability and fusing property with polyolefin-based prefoamed particles for in-mold foam molding, a polypropylene resin is contained in a dispersion medium in which an organic peroxide is present. A method of modifying the surface of the resin by dispersing the resin is shown. However, this method requires equipment that takes into account metal erosion due to organic peroxides, tends to cause non-uniform effects in the dispersion medium, and tends to cause quality variations.

  In Patent Document 8, in order to obtain an in-mold molded article having excellent surface appearance and mechanical properties, a polypropylene resin in which a terpene resin or a petroleum resin is contained in a polypropylene resin having a specific structure is pre-expanded particles. However, there is no mention of the moldability and aesthetics of the thin portion when applied to a molded body having a thin shape. Further, since a specific expensive polypropylene resin is used, there is a problem in terms of economy.

  It has been found in Patent Document 9 that the pre-expanded polypropylene-based resin particles with a specific melt index resin obtained by mixing a resin with a specific melt index have good surface properties and fusion. When applied to a molded body having a thin wall shape that requires high secondary foaming and fusing properties, the effect may not be sufficient.

As described above, it is difficult to obtain pre-expanded particles based on a high-rigidity resin that is not easily “inside-down” with a general-purpose molding machine at a low cost, and it is thin. It was further difficult to obtain satisfactory moldability and surface aesthetics with an in-mold foam molded body having a complex shape such as a part.
JP-A-8-277340 Japanese Patent Laid-Open No. 10-45938 Japanese Patent Laid-Open No. 10-316791 JP-A-11-156879 JP 7-258455 A JP-A-1-242638 JP 2002-167460 A JP 2005-29773 A JP 2000-327825 A

The object of the present invention is to form in-mold foam having a complicated shape having a so-called thin-walled portion having a shape that tends to fall inward, such as a box shape, and a thickness of about 1 to 3 particle diameters of the foamed particles. An object of the present invention is to provide a returnable box made of an in-mold foam molded body that can eliminate the internal collapse of the molded body and that has good surface aesthetics, and that is excellent in aesthetics of a thin-walled portion.

As a result of diligent research in view of the above problems, the present invention, as a comonomer, contains 1-butene and ethylene, and a polypropylene resin (A) having an MFR of 10 g / 10 min to 30 g / 10 min of 70 wt% to 95 wt%. % Of polypropylene resin (B) containing ethylene as a comonomer and having an MFR of 0.1 g / 10 min or more and 3 g / 10 min or less. In the molding process, by using polypropylene resin pre-expanded particles characterized in that the base resin is a polypropylene resin containing a polypropylene resin within a predetermined range and a petroleum resin and / or a terpene resin. Although the molding process temperature is low, it suppresses inward tilting and has a beautiful surface, especially a thin-walled part with a low density. In it found that returnable containers made of mold expansion molding of the box-shape is obtained, in which the present invention has been completed.

That is, according to the first aspect of the present invention, the density is 10 kg / m ³ or more and 300 kg / m ³ or less obtained by using the polypropylene resin pre-expanded particles, and the particle size of the polypropylene resin pre-expanded particles is 1 to 3 particles. It is a returnable box made of a polypropylene resin-in-mold foam-molded body having a box-like shape having a thin-walled portion ,
The polypropylene resin pre-expanded particles contain 70 wt% or more and 95 wt% or less of the following polypropylene resin (A) and 5 wt% or more and 30 wt% or less of the following polypropylene resin (B) in the propylene resin (C). A polypropylene resin composition comprising a polypropylene resin (C) having an MFR of 5 g / 10 min to 20 g / 10 min and a melting point of 140 ° C. to 155 ° C. and a petroleum resin and / or a terpene resin. A pass-through box made of a polypropylene resin-in-mold foam-molded product, characterized by being a polypropylene resin pre-expanded particle as a base resin . Polypropylene resin (A): 1-butene and ethylene as comonomers MFR of 10 g / 10 min or more and 30 g / 10 min or less polypropylene resin (B): ethylene as a comonomer Wherein, MFR is about about 0.1 g / 10 min or more 3 g / 10 minutes or less.
As a preferred embodiment,
(1) The addition amount of petroleum resin and / or terpene resin is 1 wt% or more and 20 wt% or less with respect to polypropylene resin (C),
(2) The MFR of the polypropylene resin composition is 5 g / 10 min to 20 g / 10 min, the melting point is 140 ° C. to 155 ° C., and the following conditional expression is satisfied:
[MFR (g / 10 min)] ≧ 1.6 × [melting point (° C.)]-235 (1)
(3) The polypropylene resin pre-expanded particles have two melting peaks in the measurement by the differential scanning calorimetry method, and calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side among the melting peaks. The ratio Qh / (Ql + Qh) × 100 of the melting peak on the high temperature side is 13% or more and 50% or less,
The present invention relates to a returnable box made of the above-mentioned polypropylene-based in-mold foam molded article.

According to the present invention, it is possible to prevent the falling of the inside, and the return box made of the expanded foamed polypropylene resin mold having high rigidity and high surface beauty is stably lower without using a special molding machine. It can be manufactured at the molding temperature.

In the present invention, the polypropylene resin is a resin mainly composed of propylene as a monomer, and the copolymerization component includes ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene. , 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene, etc. Olefin, cyclopentene, norbornene, cyclic olefin such as tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4 -Dienes such as hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, vinyl chloride, vinylidene chloride, acryloni Examples include vinyl monomers such as ril, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methylstyrene, vinyltoluene, and divinylbenzene. . Among these, it is preferable to use ethylene and 1-butene from the viewpoint of improving cold brittleness resistance and low cost.

  The base resin constituting the polypropylene resin pre-expanded particles in the present invention comprises a polypropylene resin composition containing a polypropylene resin (C) and a petroleum resin and / or a terpene resin.

The polypropylene resin (C) used in the present invention has an MFR of 5 g / 10 min to 20 g / 10 min, a melting point of 140 ° C. to 155 ° C., and preferably satisfies the following conditional expression.
[MFR (g / 10 min)] ≧ 1.6 × [melting point (° C.)]-235 (1)
Furthermore, the polypropylene resin (C) comprises 70% by weight or more and 95% by weight or less of a polypropylene resin (A) described later, and 5% by weight or 30% by weight or less of the polypropylene resin (B). When the polypropylene resin (A) is contained in the polypropylene resin (C) in an amount of 70% by weight or more and 95% by weight or less, the mold is obtained from polypropylene resin pre-expanded particles whose base resin is a resin composition comprising the polypropylene resin. The rigidity of the inner foamed molded product tends to increase.

  The polypropylene resin (A) in the present invention is a copolymer mainly composed of propylene and containing 1-butene and ethylene. Specifically, the ethylene-butene-propylene random terpolymer, ethylene-butene- Examples include propylene block terpolymers, and ethylene-butene-propylene random terpolymers are preferred. The polypropylene resin (A) has a melt flow rate (MFR) of 10 g / 10 min to 30 g / 10 min, more preferably 10 g / 10 min to 20 g / 10 min.

  The polypropylene resin (B) in the present invention refers to a copolymer mainly composed of propylene and containing ethylene, and specifically includes an ethylene-propylene random copolymer, an ethylene-butene-propylene random terpolymer, and an ethylene-propylene. Examples thereof include block copolymers and ethylene-butene-propylene block terpolymers, and ethylene-propylene random copolymers and ethylene-butene-propylene random terpolymers are preferred. The polypropylene resin (B) has an MFR of 0.1 g / 10 min or more and 3 g / 10 min or less, and more preferably an MFR of 0.3 g / 10 min or more and 2 g / 10 min or less.

  The polypropylene resin composition of the present invention contains a polypropylene resin (C) and a petroleum resin and / or a terpene resin.

  The petroleum resin is at least one selected from conventionally known petroleum resins and hydrogenated petroleum resins.

  This petroleum resin is a resin mainly composed of petroleum unsaturated hydrocarbons such as cyclopentadiene, higher olefinic hydrocarbons, or aromatic hydrocarbons (50% by weight or more). Among these petroleum resins, hydrogenated hydrogenated petroleum resins having high compatibility with polypropylene resins are preferable.

Examples of the terpene-based resin include a hydrocarbon compound represented by a composition of (C ₅ H ₈ ) _n , that is, a terpene homopolymer, or a copolymer of a monomer and a terpene copolymerizable with the terpene. 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, carene, myrcene, osymene, limonene, terpinolene, terpinene, sabinene, tricyclene, bisabolen, gingiberene, santalen, camphorene, mylene, Examples include totarene.

  The terpene resin refers to these homopolymers or copolymers. Among these homopolymers or copolymers, polymers such as pinene and dipentene are particularly preferable, and hydrogenated products having high compatibility with polypropylene resins are preferable. Among the hydrogenated products, those having a hydrogenation rate of 80% or more, particularly 90% or more are preferable.

  Among these petroleum resins and terpene resins, those having a softening point of 80 ° C. to 150 ° C. measured by the ring and ball method are preferably used. The amount of the petroleum resin and / or terpene resin added is preferably 1 part by weight or more and 20 parts by weight or less, and more preferably 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the polypropylene resin (C). When the amount is less than 1 part by weight, it tends to be difficult to obtain a beautiful surface property or fusion during heat molding of pre-expanded particles, and when it exceeds 20 parts by weight, the polypropylene resin constituting the base resin There is a risk of harming the inherent rigidity and heat resistance of the resin.

  The MFR of the polypropylene resin composition is preferably 5 g / 10 min or more and 20 g / 10 min or less, more preferably 7 g / 10 min or more and 15 g / 10 min or less. If the MFR is within the range, the balance between the molding temperature and molding time at the time of in-mold foam molding is good, and good surface aesthetics, especially when there is a thin part in the mold shape, the part has good surface aesthetics. It tends to be easy.

  The melting point of the polypropylene resin composition is preferably 140 ° C. or higher and 155 ° C. or lower, more preferably 145 ° C. or higher and 152 ° C. or lower. If the melting point is within this range, a good in-mold foam molded product tends to be obtained even with a molding machine of 0.4 MPa pressure resistance specification that is often used at present.

Moreover, it is preferable that a polypropylene resin composition satisfy | fills the following conditional expression (1) between MFR and melting | fusing point.
[MFR (g / 10 min)] ≧ 1.6 × [melting point (° C.)]-235 (1)
Each of the MFR and the melting point is within the above range, and when the conditional expression (1) is satisfied, it is likely that an in-mold foam molded article having a high surface beauty can be obtained without increasing the molding heating steam pressure. .

  These polypropylene resins are preferably in a non-crosslinked state, but may be crosslinked by peroxide or radiation. Also, other thermoplastic resins that can be mixed with polypropylene resin, such as low density polyethylene, linear density polyethylene, polystyrene, polybutene, ionomer, etc., may be mixed and used as long as the properties of the polypropylene resin are not lost. good.

  The above polypropylene resin is usually melted in advance using an extruder, kneader, Banbury mixer, roll, etc. so as to be easily used for pre-foaming, and has a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, etc. In such a desired particle shape, the average particle weight of the particles is molded to 0.5 to 3.0 mg, preferably 0.5 to 2.0 mg, more preferably 0.5 to 1.5 mg. . Surfactant-type or polymer-type antistatic agents, pigments, flame retardancy improving materials, conductivity improving materials, and other necessary components such as surfactants can be usually added to the molten resin in the resin particle production process. preferable.

  In producing the pre-expanded particles, the blowing agent is not particularly limited, and aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane and mixtures thereof; inorganic gases such as air, nitrogen, and carbon dioxide; water However, it is preferable to use water that is excellent in equipment cost and production cost as a foaming agent.

  When water is used as a foaming agent, it is preferable to add one or more compounds among the compounds having a hydrophilic polymer and a triazine skeleton to the polypropylene resin in order to obtain pre-expanded particles having a high expansion ratio. Here, the hydrophilic polymer is an ionomer obtained by crosslinking ethylene-acrylic acid-maleic anhydride terpolymer, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid copolymer with metal ions. Examples thereof include carboxyl group-containing polymers such as 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 less than 20 parts by weight with respect to 100 parts by weight of the polypropylene resin (C). More preferred is 5 parts by weight or more and less than 5 parts by weight. If it is less than 0.01 parts by weight, it is difficult to obtain pre-expanded particles having a high expansion ratio, and if it is 20 parts by weight or more, the heat resistance and mechanical strength may be greatly reduced.

  The triazine skeleton preferably has a molecular weight of 300 or less per unit triazine skeleton. 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 polypropylene resin particles are dispersed in water in a pressure vessel using a conventionally known method, for example, to form a propylene resin dispersion, and the dispersion is preferably a melting point of the polypropylene resin particles. Heat to a temperature in the range of −25 ° C. to + 25 ° C., more preferably −10 ° C. to + 10 ° C. and pressurize with an inorganic gas such as nitrogen or air to impregnate the polypropylene resin particles with water. While keeping the temperature and pressure inside the container constant, the polypropylene-based pre-expanded particles are produced by releasing the dispersion of the polypropylene resin particles and water in a lower pressure atmosphere than in the container. When discharging into a low-pressure atmosphere, the low-pressure atmosphere is preferably maintained at a high temperature in order to increase the expansion ratio, and is preferably 80 ° C. or higher and 100 ° C. or lower, more preferably 90 ° C. or higher and 100 ° C. with high-temperature air or water vapor. Hold below. When the temperature is less than 80 ° C., it is difficult to obtain pre-expanded particles having a high expansion ratio, and the pre-expanded particles tend to shrink due to the effect of cooling the pre-expanded particles immediately after expansion. When the temperature is 100 ° C. or higher, the pre-expanded particles may be fused.

  There are no particular limitations on the sealed container at the time of producing the pre-foamed particles, and any container that can withstand the pressure and temperature in the container at the time of producing the pre-foamed particles may be used. For example, an autoclave type pressure-resistant container may be mentioned.

  In the preparation of the dispersion, as the dispersant, for example, inorganic dispersants such as tribasic calcium phosphate, basic magnesium carbonate, calcium carbonate, and so on, for example, sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, α-olefinsulfone. It is preferable to use a dispersion aid such as acid soda. Among these, the 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 to 0.1 parts by weight of a dispersion aid. Moreover, in order to make a polypropylene resin particle favorable in the dispersibility in water, it is preferable to use normally 20-100 weight part with respect to 100 weight part of water.

The expansion ratio of the polypropylene resin pre-expanded particles obtained by the above production method is preferably 5 to 50 times, and more preferably 7 to 45 times.
Moreover, once the pre-expanded particles of 5 times to 35 times are manufactured, the pressure in the pre-expanded particles is made higher than the normal pressure by pressurizing the pre-expanded particles in a sealed container and impregnating with nitrogen, air, etc. Then, the foamed particles may be heated by steam or the like to obtain two-stage foamed pre-foamed particles 50 times or more by a method such as a two-stage foaming method for further foaming.

  The polypropylene-based pre-expanded particles of the present invention have two melting peaks in the measurement by the differential scanning calorimetry method, and were calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side among the melting peaks. The ratio Qh / (Ql + Qh) × 100 (hereinafter abbreviated as DSC ratio) of the melting peak on the high temperature side is preferably 13% or more and 50% or less, more preferably 18% or more and 40% or less. When the DSC ratio is within the above range, an in-mold foam molded product having a high surface beauty is easily obtained.

  When the polypropylene resin pre-foamed particles of the present invention are used for in-mold foam molding, a) a method of using as it is, b) a method of previously injecting an inorganic gas such as air into the pre-foamed particles and imparting foaming capability, C) A conventionally known method such as a method in which pre-expanded particles are filled in a mold in a compressed state and molded may be used.

  As a method for molding an in-mold foam molded body from the polypropylene resin pre-foamed particles of the present invention, for example, the pre-foamed particles are preliminarily air-pressurized in a pressure-resistant container, and air is injected into the particles to give foaming ability. The polypropylene mold is filled in a mold that can be closed but cannot be sealed, and is molded with a water vapor pressure of about 0.20 to 0.4 MPa and a heating time of about 3 to 30 seconds using water vapor as a heating medium. The resin pre-expanded particles are fused together, and then the mold is cooled by water cooling to such an extent that the deformation of the in-mold foam molded product can be suppressed, and then the mold is opened and foamed in the mold. The method of obtaining a molded object etc. are mentioned.

The density of the in-mold foam molded product obtained using the polypropylene resin pre-expanded particles of the present invention is preferably 10 kg / m ³ or more and 300 kg / m ³ or less, more preferably 15 kg / m ³ or more and 250 kg / m. ³ or less.

  The in-mold foam molded body of the present invention can be suitably used for general cushioning packaging materials, automobile interior members, returnable boxes, etc., because it can prevent inward collapse in a molded body having a thin wall portion and can improve the elongation of the thin wall portion. I can do it.

  Next, the measuring method of MFR, melting | fusing point, and DSC ratio in this invention is demonstrated.

  MFR is measured using the MFR measuring instrument 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. This is the value when

  The melting point is measured by using a DSC6200 differential scanning calorimeter manufactured by Seiko Instruments Inc. to heat 5 to 6 mg of polypropylene resin particles from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. From the DSC curve obtained when the particles were melted and then crystallized by lowering the temperature from 220 ° C. to 40 ° C. at 10 ° C./min and then further heated from 40 ° C. to 220 ° C. at 10 ° C./min, This is a value obtained as the melting peak temperature at the second temperature increase.

  The DSC ratio is measured using a DSC6200 type differential scanning calorimeter manufactured by Seiko Instruments Inc., and 5-6 mg of polypropylene resin pre-expanded particles are heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. The melting curve (illustrated in FIG. 1) obtained at this time has two peaks, and the melting on the high temperature side calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side of the melting peaks. This is a parameter represented by the peak ratio Qh / (Ql + Qh) × 100.

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

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

Calculated on the weight of the [expansion ratio of pre-expanded particles] bulk pre-expanded polypropylene resin particles having a volume of about 50cm ³ w (g) and ethanol submerged volume v (cm ^3), Density d (g / cm of before foaming resin particles ³ ) Obtain from the following equation.
Foaming ratio = d × v / w
[Minimum forming heating steam pressure] Using a polyolefin foam molding machine Pearlstar P-150N manufactured by Toyo Kikai Metals Co., Ltd., in a block mold measuring 270 mm long, 290 mm wide and 40 mm thick, the air pressure inside the particles is set to 2.0 atm in advance. Filled with polypropylene resin pre-expanded particles adjusted so as to be first, expelling the air in the mold with water vapor of 0.1 MPa, then heat-molded for 10 seconds using heating steam of any pressure, polypropylene-based A resin foam molding is obtained. By observing the surface state of this foamed molded product, the lowest pressure among the heating steam pressures that can obtain a molded product having no irregularities on the surface and almost no conspicuous gaps between the particles is referred to as the lowest molded heating steam pressure. did. The lowest molding heating steam pressure that gives good surface aesthetics, which is a measure of surface aesthetics and moldability, and is a pressure capable of continuous production when using a generally used 0.4 MPa pressure molding machine 0.34 MPa Based on the following:

  [Molding evaluation] After molding by 0.28 MPa steam heating using a polyolefin foam molding machine Pearlstar P-150N manufactured by Toyo Machine Metal Co., Ltd., left at 25 ° C. for 2 hours, and then controlled at 65 ° C. After leaving still indoors for 5 hours, it took out and cooled at 25 degreeC, and the molded object shown in FIG. 3 was obtained. The dimension (b) of the molded body 2 test body was measured and averaged, and the difference from the required product quality of 345 mm was determined. The difference from the required quality was −2.0 to +2.0 mm. Moreover, in evaluation of the surface property of a thin-walled part, it was set as a pass ((circle)) that there were almost no wrinkles and shrinkage marks.

  Using polypropylene resin having MFR and melting point shown in Table 1, talc is 0.3 parts by weight and melamine is 0.5 parts by weight with respect to 100 parts by weight of the resin having the ratio shown in Table 2. Addition, mixing, kneading with a 50 mmφ single screw extruder and granulation were carried out to produce polypropylene resin particles (1.3 mg / grain).

該樹脂粒子１００重量部、分散剤としてパウダー状塩基性第３リン酸カルシウム２重量部および分散助剤としてｎ−パラフィンスルホン酸ソーダ０．０５重量部を含む水系分散媒３００重量部を、内容量１０Ｌの耐圧容器に仕込み、攪拌しながら表２記載の温度まで昇温し、窒素を圧入して表２記載の圧力に調整し、３０分間保持した。その後、窒素を圧入しながら容器内温、圧力を３．０ＭＰａに保持しつつ、耐圧容器下部のバルブを開いて、水系分散媒を開孔径４．０ｍｍφのオリフィス板を通して蒸気により９５℃に調節された大気圧下に放出することによってポリプロピレン系樹脂予備発泡粒子をえた。得られた予備発泡粒子内に空気含浸により３．０ＭＰａの内圧を付与し、６０〜９０ｋＰａの蒸気により加熱し、表２に示すように発泡倍率約２９倍の発泡粒子を得た。

300 parts by weight of an aqueous dispersion medium containing 100 parts by weight of the resin particles, 2 parts by weight of powdered basic tricalcium phosphate as a dispersant, and 0.05 parts by weight of sodium n-paraffin sulfonate as a dispersion aid, The mixture was charged into a pressure vessel, heated to the temperature shown in Table 2, while stirring, and nitrogen was injected to adjust the pressure to the value shown in Table 2 and held for 30 minutes. Thereafter, the pressure inside the vessel is kept at 3.0 MPa while nitrogen is being injected, the valve at the bottom of the pressure vessel is opened, and the aqueous dispersion medium is adjusted to 95 ° C. by steam through an orifice plate having a 4.0 mm diameter hole. Polypropylene resin pre-expanded particles were obtained by releasing under high atmospheric pressure. The obtained pre-expanded particles were impregnated with an internal pressure of 3.0 MPa by air impregnation and heated with steam of 60 to 90 kPa to obtain expanded particles having an expansion ratio of about 29 times as shown in Table 2.

Next, using the obtained foamed particles, the minimum molding heating steam pressure and the molding evaluation results (inside-down amount, surface property of the thin portion) of the box-shaped form were performed.

  It shows with the polypropylene-type resin pre-expanded particle using the resin shown in an Example, and Comparative Examples 1-4. When comparing the evaluation results of each of the commonly used polypropylene resin pre-expanded particles, the examples using the technique described in the present invention are excellent in all of the minimum molding steam overheating pressure, the amount of inclining, and the surface property of the thin wall portion. On the other hand, in Comparative Example 4, the minimum heating pressure exceeded the apparatus limit. In Comparative Examples 2 and 3, the amount of inclining was large. In Comparative Examples 1, 2 and 4, the surface property of the thin portion was Did not reach the product level.

  As described above, in the polypropylene resin pre-expanded particles, when the technique described in the present invention is used, a molded body having a beautiful surface and a short drying time is obtained by using a molding machine of 0.4 MPa pressure resistance specification which is often used at present. Therefore, it is possible to efficiently produce a molded body.

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 shaded portion on the low temperature side is Ql, and the shaded portion on the high temperature side is Qh. It is a perspective view which shows the shape of the box-shaped molded object used for shaping | molding evaluation.

Explanation of symbols

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

Claims (4)

A box shape having a density of 10 kg / m ³ or more and 300 kg / m ³ or less, and having a thin-walled portion having a thickness of 1 to 3 particle diameters of the polypropylene resin pre-expanded particles, obtained using the polypropylene resin pre-expanded particles It is a returnable box made of a foamed molded product in a polypropylene resin mold having a shape,
The polypropylene resin pre-expanded particles contain 70 wt% or more and 95 wt% or less of the following polypropylene resin (A) and 5 wt% or more and 30 wt% or less of the following polypropylene resin (B) in the propylene resin (C). A polypropylene resin composition comprising a polypropylene resin (C) having an MFR of 5 g / 10 min to 20 g / 10 min and a melting point of 140 ° C. to 155 ° C. and a petroleum resin and / or a terpene resin. A returnable box made of a polypropylene resin-in-mold foam-molded product, which is a polypropylene resin pre-expanded particle as a base resin.
Polypropylene resin (A): 1-butene and ethylene as comonomer, MFR 10 g / 10 min or more and 30 g / 10 min or less Polypropylene resin (B): ethylene as comonomer, MFR 0.1 g / 10 min More than 3g / 10min The polypropylene resin in-mold foam-molded article according to claim 1 , wherein the amount of petroleum resin and / or terpene resin added is 1 wt% or more and 20 wt% or less based on the polypropylene resin (C). A returnable box consisting of 3. The polypropylene according to claim 1 , wherein the polypropylene resin composition has an MFR of 5 g / 10 min to 20 g / 10 min, a melting point of 140 ° C. to 155 ° C., and the following conditional expression: A returnable box made of a foamed product in a resin mold.
[MFR (g / 10 min)] ≧ 1.6 × [melting point (° C.)]-235 (1) The polypropylene resin pre-expanded particles have two melting peaks in the measurement by the differential scanning calorimetry method, and the high temperature calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side among the melting peaks, melting peak ratio Qh / (Ql + Qh) × 100 of the side, characterized in that 50% or less 13% or more, a polypropylene resin mold foamed articles according to any one of claims 1 to 3 A going-to box .

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