JP2010173146A - Method for manufacturing polypropylene-based resin in-mold foam molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polypropylene-based resin in-mold foam molded body having no failure in fusion bonding near a loading machine attaching portion in a molding mold by using foam particles produced by using carbon hydride such as butane as a foaming agent. <P>SOLUTION: In the method for manufacturing the polypropylene-based resin in-mold foam molded body, after polypropylene-based resin particles are dispersed to a disperse medium in a pressure-resistant container, and a foam agent containing carbon hydride is added, the polypropylene-based resin particles are heated to the temperature not lower than the temperature wherein they are softened, and after the foaming agent containing the carbon hydride is impregnated in the polypropylene-based resin particles, in-mold foam molding is performed by using the polypropylene-based resin foam particles obtained by opening one end of the pressure-resistant container and discharging the polypropylene-based resin particles in the atmosphere lower pressure than the inside of the pressure-resistant container. Multi-stage foam particles further foaming the polypropylene-based resin foam particles are in-mold foam molded. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polypropylene resin in-mold foam molded article.

  Polypropylene-based resin foams are excellent in physical properties such as buffering properties and heat insulating properties, and are therefore used in various applications such as packaging materials, buffer materials, heat insulating materials, and building materials. In particular, the bead method in-mold foam molding method, in which a polypropylene resin foam particle is filled in a mold and heated with water vapor or the like to fuse the foam particles together to obtain a foam with a predetermined shape, is a product with a complicated shape. Since it can be obtained relatively easily, it is used in many applications.

  Polypropylene resin foam particles used in the bead method in-mold foam molding method are obtained by dispersing polypropylene resin particles in a pressure-resistant container using a dispersant in an aqueous dispersion medium and adding a foaming agent such as hydrocarbon or inorganic gas. It can be manufactured by heating to a temperature equal to or higher than the softening temperature of the polypropylene resin particles, impregnating the polypropylene resin particles with a foaming agent, and then releasing it into a pressure range lower than the internal pressure of the pressure vessel. When hydrocarbons such as butane are used as the foaming agent, the heating temperature for impregnating the foaming agent can be lowered compared to the case where an inorganic gas such as carbon dioxide is used, and the expansion ratio of the generated foamed particles can be reduced. There is an advantage that it can be enlarged.

  In the bead method in-mold foam molding method, foam particles are filled into the mold cavity of the mold by using a filling machine attached to the mold. As shown in FIG. 1, the normally used filling machine 16 employs a mechanism for sending foam particles into the mold cavity 7 with the foam particles accompanying the air flow. The mold has a vent 8 that does not allow foam particles to pass but allows air or steam to pass. When the expanded particles are fed into the mold, the air is discharged out of the mold cavity 7 through the vent hole 8, and the expanded particles remain in the mold cavity 7. When the foam particles are sufficiently filled in the mold cavity 7, air does not enter the mold cavity 7 and flows back into the foam particle reservoir 1. At this time, the expanded particles present in the filling machine 16 are pushed back, and the filling machine 16 becomes empty. This process is called natural blow back. After the expanded particles in the filling machine 16 are removed, the expanded particle filling port 18 of the mold is closed by the piston plug 19, and in-mold expansion molding is performed by steam heating.

  However, it is known that in-mold foam moldings are likely to have poor fusion in the vicinity of the foamed particle filling port 18 of the mold. In particular, such a poor fusion is remarkable in an in-mold foam molding method using a filling method of foam particles into a mold cavity called a compression filling method described later. The presence of such defects is not preferable because it significantly impairs the commercial value of the in-mold foam molded article. According to Patent Document 1, the reason why the in-mold foam molding tends to occur near the foamed particle filling port 18 of the mold is explained as follows. The foam particles in the filling machine 16 are not completely removed by the natural blow back (blow back) in the filling process of the foam particles into the mold, and a part of the foam particles remains. The remaining expanded particles are pushed into the mold cavity 7 by the piston plug 19, whereby the expanded particles are excessively filled in the vicinity of the expanded particle filling port 18 of the mold cavity 7. This phenomenon is referred to as overfilling. When overfilling occurs, it becomes difficult for the steam for heating to pass through the part, resulting in an in-mold foam molded article partially having poor fusion at the part. Even when overfilling does not occur, there are cases where there are few air or water vapor vents in the vicinity of the foamed particle filling port 18 of the mold, and it may be difficult for the steam for heating to flow, resulting in poor fusion.

  Patent Document 1 discloses that by adjusting the pressure in the mold so as to be higher than the pressure in the filling machine at the time of blowback, it is possible to prevent poor fusion near the foamed particle filling port. Further, Patent Document 2 uses a shutter provided at the filling port instead of the piston plug to close the foaming particle filling port, and even if the foaming particles remain in the filling machine, the remaining foaming particles are pushed into the mold. A method for preventing overfilling is disclosed. The methods disclosed in Patent Literature 1 and Patent Literature 2 are methods for preventing poor fusion in the vicinity of the foamed particle filling port in the molding apparatus. However, there is no known method for preventing overfilling from the viewpoint of the characteristics of the expanded particles.

JP 2000-15707 A Japanese Patent Laid-Open No. 11-188732

  As a result of intensive studies to prevent poor fusion near the foamed particle filling port, the present inventor, in particular, using a polypropylene resin foamed particle obtained by using a hydrocarbon such as butane as a foaming agent. It has been found that many poor fusion occurs in the vicinity of the foamed particle filling port in the internal foam-molded polypropylene resin mold. That is, an object of the present invention is a polypropylene which does not cause poor fusion in the vicinity of a mold filling machine mounting site in a bead method in-mold foam molding method using foamed particles obtained using a hydrocarbon as a foaming agent. An object of the present invention is to provide a method for producing an in-mold resin mold.

  The present inventor examined a method that does not cause poor fusion in the vicinity of a mold filling machine attachment site in a bead method in-mold foam molding method using foamed particles obtained using a hydrocarbon as a foaming agent. As a result, it was found that by using multistage foamed particles obtained by further foaming foamed particles obtained using a foaming agent containing hydrocarbon as a foaming agent, it is possible to prevent occurrence of poor fusion near the filling machine. It was completed.

  That is, the present invention disperses polypropylene resin particles in a dispersion medium in a pressure-resistant container, adds a foaming agent containing hydrocarbons, and then heats the foaming agent to a temperature equal to or higher than the temperature at which the polypropylene resin particles soften. After impregnation, a polypropylene system in which one end of the pressure vessel is opened and the polypropylene resin particles obtained by releasing the polypropylene resin particles into an atmosphere at a lower pressure than in the pressure vessel is subjected to in-mold foam molding. In the method for producing an in-mold foam molded article, a method for producing an in-mold foam molded article in a polypropylene resin, wherein the polypropylene resin multi-stage foamed particles obtained by further foaming the polypropylene resin foam particles are subjected to in-mold foam molding. About.

As a preferred embodiment,
(1) Filling a mold with polypropylene resin multistage expanded particles in a mold by compression filling, and performing in-mold foam molding;
(2) In-mold foam molding of the polypropylene resin multistage expanded particles to which an internal pressure is applied;
(3) The polypropylene resin is a polypropylene random copolymer comprising monomer units derived from ethylene,
The above-mentioned method for producing an in-mold foam molded product of a polypropylene resin.

  According to the method for producing a foam-molded body in a polypropylene resin mold according to the present invention, a polypropylene-based resin is less prone to fusing defects near a portion where a mold filling machine is attached even with a generally used molding apparatus. An in-mold foam molded article can be obtained.

It is a figure which shows an example of the apparatus used for the manufacturing method of this invention.

The polypropylene resin used in the present invention is not particularly limited as long as it contains propylene as a monomer component. For example, a propylene homopolymer, an α-olefin-propylene random copolymer, and an α-olefin-propylene block copolymer are used. A polymer etc. are mentioned. These may be used alone or in combination of two or more. Particularly preferred is a polypropylene resin containing ethylene as a comonomer component, wherein the α-olefin is ethylene. The ethylene content is preferably 1 to 10% by weight, more preferably 1 to 7% by weight, further 2 to 7% by weight, further 3 to 7% by weight, and 5% by weight or more and 6% by weight or less, particularly 3.5% by weight or more and 5% by weight or less. In addition, content of the ethylene component in a polypropylene resin can be measured using ¹³ C-NMR.

  The polypropylene resin used in the present invention may contain a monomer other than ethylene as a copolymerization component. Moreover, the polypropylene resin containing ethylene as a comonomer component may contain a monomer other than ethylene as a comonomer component. As comonomer components other than ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1- Α-olefins having 4 to 12 carbon atoms such as butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene; cyclopentene, norbornene, tetracyclo [6,2,11,8,13,6 ] Cyclic olefins such as 4-dodecene; 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, etc. Diene: vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, acrylic Butyl, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, vinyl monomers such as divinylbenzene and the like, may be used these one or two or more.

  As the polypropylene resin used in the present invention, either a random copolymer or a block copolymer can be used. In particular, it is preferable to use an ethylene-propylene random copolymer or an ethylene-propylene-butene random terpolymer having high versatility. The ethylene content is 1% to 7% by weight, 3% to 7% by weight, more preferably 3.5% to 6% by weight, particularly 3.5% to 5% by weight. Some ethylene-propylene random copolymers or ethylene-propylene-butene random terpolymers are preferred.

  In addition to polypropylene resins, other thermoplastic resins such as low density polyethylene, linear low 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 ratio (Mw / Mn) of the weight average molecular weight (hereinafter sometimes referred to as Mw) and the number average molecular weight (hereinafter sometimes referred to as Mn) of the polypropylene-based resin is 2.0 or more and 6.0 or less. preferable. Mw / Mn is more preferably 3 or more, and particularly preferably 3.5 or more. When Mw / Mn exceeds 6.0, the surface property and shrinkage of the polypropylene resin-in-mold foam-molded product tend to deteriorate.

Mn and Mw are measured under the following conditions.
Measuring instrument: Alliance GPC 2000 type gel permeation chromatography (GPC) manufactured by Waters
Column: 2 TSKgel GMH6-HT,
Two TSKgel GMH6-HTL (each inner diameter 7.5mm x length 300mm, manufactured by Tosoh Corporation)
Mobile phase: o-dichlorobenzene (containing 0.025% BHT)
Column temperature: 140 ° C
Flow rate: 1.0 mL / min
Sample concentration: 0.15% (W / V) -o-dichlorobenzene injection amount: 500 μL
Molecular weight calibration: Polystyrene conversion (calibration with standard polystyrene)

  The polypropylene resin used in the present invention can be obtained using a catalyst such as a Ziegler catalyst, a metallocene catalyst, or a post metallocene catalyst. When a Ziegler catalyst is used, a polymer having a large Mw / Mn tends to be obtained. Moreover, when the polymer obtained using these catalysts is oxidized and decomposed with an organic peroxide, characteristics such as molecular weight and melt index can be adjusted.

  Examples of the organic peroxide that can be used include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, t-butylperoxylaurate, 2,5-dimethyl2,5-di ( Benzoylperoxy) hexane, t-butylperoxybenzoate, dicumyl peroxide, 1,3-bis (t-butylperoxyisopropyl) benzene, t-butylperoxyisopropyl monocarbonate and the like.

  The amount of the organic peroxide used is preferably 0.001 part by weight or more and 0.1 part by weight or less with respect to 100 parts by weight of the polypropylene resin. In order to oxidatively decompose the polypropylene resin, for example, a polypropylene resin added with an organic peroxide can be heated and melted in an extruder.

  The polypropylene resin used in the present invention is preferably in an uncrosslinked state, but may be crosslinked by treatment with an organic peroxide or radiation. Two or more polypropylene resins may be mixed.

  The melting point of the polypropylene resin used in the present invention is preferably 130 ° C. or higher and 165 ° C. or lower, and more preferably 135 ° C. or higher and 155 ° C. or lower. When the melting point is less than 130 ° C., heat resistance and mechanical strength tend to be insufficient. Moreover, when melting | fusing point exceeds 165 degreeC, there exists a tendency for it to become difficult to ensure the melt | fusion at the time of in-mold foam molding. Here, the melting point is a temperature of 10 to 10 ° C./min from 40 ° C. to 220 ° C., and then cooled to 40 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter. The peak temperature of the endothermic peak in the DSC curve obtained when the temperature is increased again to 220 ° C. at a rate of 10 ° C./min.

  The melt index (hereinafter referred to as MI value) of the polypropylene resin particles that can be used in the present invention is preferably 0.5 g / 10 min to 30 g / 10 min, and more preferably 2 g / 10 min to 20 g / 10. Minutes or less are preferred. If the MI value is less than 0.5 g / 10 minutes, it may be difficult to obtain polypropylene-based resin expanded particles with a high expansion ratio. If it exceeds 30 g / 10 minutes, the bubbles of the polypropylene-based resin expanded particles are likely to break. The open cell ratio of the polypropylene resin expanded particles tends to increase. The MI value is measured according to JIS K7210 at a temperature of 230 ° C. and a load of 2.16 kg.

  Polypropylene resins are usually melted using extruders, kneaders, Banbury mixers, rolls, etc. to produce expanded particles, and processed into resin particle shapes such as cylindrical, elliptical, spherical, cubic, and rectangular parallelepiped shapes. To do. Other resins and additives that are added as necessary can also be added in this step. As for the size of the polypropylene resin particles, the weight of one particle is preferably 0.1 mg or more and 30 mg or less, and more preferably 0.3 mg or more and 10 mg or less. The weight of one polypropylene resin particle is the average resin particle weight obtained from 100 randomly selected polypropylene resin particles, and is hereinafter expressed in mg / grain.

  When producing polypropylene resin particles, if necessary, foam nucleating agent, hydrophilic substance, colorant, antistatic agent, antioxidant, phosphorus processing stabilizer, lactone processing stabilizer, metal deactivator, benzotriazole Additives such as ultraviolet absorbers, benzoate light stabilizers, hindered amine light stabilizers, flame retardants, flame retardant aids, acid neutralizers, crystal nucleating agents, amide additives, and other properties of polypropylene resins are impaired. It can be added within the range. When adding a foam nucleating agent, a hydrophilic substance, or other additives to the resin, it is preferable to mix with the polypropylene resin using a blender or the like before the production of the polypropylene resin particles. Moreover, you may add an additive in the molten polypropylene resin.

  A foam nucleating agent (cell nucleating agent) is a substance that promotes the formation of cell nuclei during foaming. Examples of the foam nucleating agent include inorganic substances such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, and titanium oxide. Among these, talc and calcium carbonate are preferable because they are easy to obtain foamed particles having good dispersibility in a polypropylene resin and having uniform cells. A foam nucleating agent may be used independently and may use 2 or more types together.

  The addition amount of the foam nucleating agent varies depending on the foam nucleating agent to be used and cannot be generally determined, but is preferably 0.005 parts by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. More preferably, the content is 0.01 parts by weight or more and 1 part by weight or less. When the addition amount of the foam nucleating agent is less than 0.005 parts by weight, the expansion ratio of the polypropylene resin foamed particles may not be increased or the uniformity of the bubbles may be deteriorated. When the addition amount of the foam nucleating agent is more than 2 parts by weight, the average cell diameter of the polypropylene resin foamed particles becomes too small, and the in-mold foam moldability tends to be poor.

  For example, when talc is used as the foam nucleating agent, the addition amount is preferably 0.005 parts by weight or more and 1 part by weight or less, more preferably 0.01 parts by weight, with respect to 100 parts by weight of the polypropylene resin. The amount is 0.5 part by weight or less and more preferably 0.02 part by weight or more and 0.2 part by weight or less.

  Polypropylene resin foam particles can be obtained from the polypropylene resin particles using a method called pressure-reducing foaming. Specifically, the polypropylene resin particles are dispersed in a dispersion medium in a pressure-resistant container, and after adding a foaming agent containing a hydrocarbon such as butane, the polypropylene resin particles are heated to a temperature equal to or higher than the temperature at which the polypropylene resin particles are softened. After impregnating the foaming agent, one end of the pressure vessel is opened, and the polypropylene resin particles are released into an atmosphere at a lower pressure than in the pressure vessel, whereby polypropylene resin foam particles can be obtained. The expanded particles obtained by the pressure-reducing foaming method are sometimes referred to as single-stage expanded particles. The softening temperature of the polypropylene resin particles can be measured according to JIS K 2207. Usually, the softening temperature is lower than the melting point.

  The blowing agent of the present invention contains a hydrocarbon. Examples of the hydrocarbon mentioned here include saturated hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, iso-butane, n-pentane, and iso-pentane.

  If the foaming agent contains hydrocarbons, other foaming agents may be used in combination. Examples of other foaming agents include ethers such as dimethyl ether, alcohols such as methanol and ethanol, inorganic gases such as air and nitrogen, water, and the like.

  In the present invention, the polypropylene resin expanded particles (single-stage expanded particles) obtained by the decompression foaming method are further expanded to obtain polypropylene-based resin multistage expanded particles. The foaming method is preferably a method in which the single-stage foamed particles are pressurized with an inorganic gas such as air in a pressure-resistant container, and the foam is further foamed by heating after applying the internal pressure. The two-stage expanded particles may be further expanded. Further expansion of the single-stage expanded particles is referred to as multistage expansion (the process of further expanding the single-stage expanded particles may be referred to as two-stage expansion). Expanded particles obtained by multistage foaming may be referred to as multistage foamed particles. The expanded particles obtained by the two-stage expansion may be referred to as two-stage expanded particles.

  The expansion ratio of the polypropylene resin multistage expanded particles used in the present invention is preferably 20 times or more, more preferably 30 times or more, and further preferably 32 times or more. The expansion ratio of the polypropylene resin multistage expanded particles is preferably 60 times or less. When the expansion ratio is less than 20 times, the advantage of weight reduction is not obtained, and the flexibility and buffering characteristics of the obtained polypropylene resin-in-mold foam-molded product tend to be insufficient, exceeding 60 times. In such a case, the dimensional accuracy, mechanical strength, heat resistance and the like of the obtained polypropylene resin in-mold foam molded product tend to be insufficient. A method for measuring the expansion ratio of the polypropylene resin multistage expanded particles will be described later.

  The average cell diameter of the polypropylene resin multistage expanded particles used in the present invention is preferably from 50 μm to 800 μm, more preferably from 100 μm to 600 μm, still more preferably from 200 μm to 500 μm. When the average cell diameter is less than 50 μm, there are cases where the shape of the foamed molded product in the polypropylene resin mold obtained is distorted and wrinkles are generated on the surface. The cushioning characteristics of the foamed molded product may be deteriorated. The average cell diameter is measured according to ASTM D3576 with respect to the cut surface of the polypropylene-based resin multistage expanded particles, except for the surface layer portion.

  The open-cell ratio of the polypropylene resin multistage expanded particles used in the present invention is preferably 0 to 12%, more preferably 0 to 8%, and still more preferably 0 to 5%. When the open cell ratio exceeds 12%, the foaming property by steam heating is inferior during foam molding in the mold, and the obtained polypropylene resin in-mold foam molding tends to shrink.

  The polypropylene resin multistage expanded particles and polypropylene resin expanded particles used in the present invention preferably have a crystal structure having two or more melting points in a DSC curve obtained by differential scanning calorimetry. In the case of polypropylene-based resin expanded particles having a crystal structure exhibiting two or more melting points, there is a tendency to obtain a polypropylene-based resin in-mold expanded molded article with good in-mold foam moldability and good mechanical strength and heat resistance. . Here, the DSC curve obtained by differential scanning calorimetry of the polypropylene resin expanded particles refers to 1 to 10 mg of polypropylene resin expanded particles from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min by a differential scanning calorimeter. It is a DSC curve obtained when the temperature is raised. In this DSC curve, the temperature indicated by the melting peak that appears is the melting point.

  Also, the melting peak ratio Qh / (Ql + Qh) × 100 (hereinafter referred to as DSC ratio) 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 peak. Is preferably 10% or more and 30% or less. If the DSC ratio is less than 10%, the molding cycle may be extremely extended, and the resulting polypropylene resin in-mold foam-molded product may have poor dimensional shrinkage, surface properties, and mechanical properties. Further, when the DSC ratio exceeds 30%, the secondary foaming force of the polypropylene resin foamed particles at the time of in-mold foam molding is insufficient, and the resulting polypropylene-based resin in-mold foam-molded product has poor fusion and surface properties. There is a case. The melting peak calorie (Qh) based on the melting peak on the high temperature side draws a tangent to the DSC curve on the side where the high temperature side peak ends from the point where the gradient of the DSC curve between the low temperature side peak and the high temperature side peak becomes zero. , The amount of heat indicated by the portion surrounded by the tangent and the high temperature side peak. The melting peak calorie (Ql) based on the melting peak on the low temperature side is the DSC on the side where the low temperature side peak ends from the point where the gradient of the DSC curve between the low temperature side peak and the high temperature side peak becomes 0 in the DSC curve. This is the amount of heat indicated by drawing a tangent line to the curve and enclosing the tangent line and the low temperature side peak.

  As described above, the polypropylene resin multistage expanded particles and the polypropylene resin expanded particles having a crystal structure exhibiting two or more melting points can be easily obtained by setting the pressure-resistant container temperature at the time of foaming to an appropriate value. The temperature is selected from the melting point of the polypropylene resin used as the base material, preferably the melting point + 3 ° C. or more, and less than the melting end temperature, preferably the melting end temperature −2 ° C. or less. Here, the melting end temperature is 1 to 10 mg of a polypropylene resin by a differential scanning calorimeter at a rate of 10 ° C./min from 40 ° C. to 220 ° C., and then at a rate of 10 ° C./min to 40 ° C. This is the temperature at which the melting peak curve obtained when cooling and again raising the temperature to 220 ° C. at a rate of 10 ° C./min returned to the baseline position on the high temperature side.

  Polypropylene resin foamed particles are filled in a mold and heated to foam so that there are no gaps between the foamed particles, and the foamed particles are fused and molded into an arbitrary shape, so-called in-mold foam molding. can do. As the mold, a mold that can circulate a heating medium such as steam but does not flow out the expanded particles to the outside is usually used. Usually, steam of about 0.05 to 0.5 MPa (G) is used as a heating medium, and in-mold foam molding is performed in a heating time of about 3 to 30 seconds.

  The following conventionally known treatments can be performed on the polypropylene resin multistage expanded particles used in the in-mold foam molding method of the bead method. For example, a) a method for use as it is, b) an inorganic gas such as air is press-fitted into the polyolefin resin foam particles in advance to impart foaming ability, and c) a mold in which the polyolefin resin foam particles are compressed. Examples of the method include a compression filling method in which the inside is filled. Among these, when the compression filling method is used, the fusion defect near the filling machine attachment portion of the mold is remarkably improved.

  That is, polypropylene resin foam particles can be compressed to 20 to 80% of the bulk volume of the foam particles before filling using a pressurized gas in a foam particle compression tank, and the compressed foam particles can be closed but sealed. It is a preferred method to produce a polypropylene resin in-mold foam-molded product by filling in a mold that does not, releasing the pressure in the mold, and then heating and fusing the foamed particles with steam. It is also possible to use the compression filling method and the internal pressure applying method in combination.

  An example of the bead method in-mold foam molding method by the compression filling method will be described with reference to the drawings.

  In the apparatus shown in FIG. 1, polypropylene resin multistage expanded particles (hereinafter sometimes simply referred to as “expanded particles”) are supplied from the expanded particle supply port 2 to the expanded particle storage tank 1 and pressurized gas is added. Supplied from the pressurized gas inlet 3. At this time, the pressurized gas is also supplied into the mold that can be closed by the pressure equalizing line 20 but cannot be sealed.

  The pressurized gas used for the compression is mainly composed of carbon dioxide, nitrogen, air, or these (usually preferably 50% by volume or more, and 70 volumes from the viewpoint of economy, productivity, safety, environmental compatibility, etc. %, More preferably, an inert gas such as argon, helium, xenon, or an inorganic gas containing a smaller amount of water vapor, oxygen, hydrogen, ozone, etc. (preferably 50% by volume or less, more preferably 30% by volume or less) However, air is more preferable from the viewpoint of the equipment cost of the compression equipment.

  The pressure in the expanded particle storage tank 1 and the mold 4 is adjusted by a mold gas pressure adjusting valve 13 and is increased to a predetermined pressure. At this time, the exhaust valve 14 is closed. As for the pressure at the time of compression, the lower limit is usually preferably 0.04 MPa (G), more preferably 0.05 MPa (G), and the upper limit is preferably 0.40 MPa (G), more preferably 0. .35 MPa (G). The higher the pressure resistance of the expanded foam compression tank 1, the more the compressed gas pressure can be applied to the expanded particles, so the bulk density range to which the compression filling method can be applied may be expanded. Therefore, the pressure resistance around 0.4 MPa (G) that is normally used is preferable.

  Next, the compressed expanded particles are filled into the mold cavity 7 between the fixed mold 5 and the movable mold 6 by a filling machine 16. The filling is the same as that performed in the ordinary bead method in-mold foam molding, and pressurized gas is supplied from the pressurized gas inlet 17 for filling foam particles. At this time, the mold gas pressure adjusting valve 13 is opened at such an opening that maintains a predetermined mold gas pressure. The foamed particles are fed into the mold cavity 7 by bringing the foamed particles into the pressurized gas supplied from the pressurized gas inlet 17 for filling the foamed particles.

  The mold has a vent 8 that does not allow foam particles to pass through but allows air or steam to pass therethrough. When the foam particles are fed into the mold cavity 7, the air passes through the vent 8 and goes out of the mold cavity 7. The foamed particles are discharged and remain in the mold cavity 7. When the foam particles are sufficiently filled in the mold cavity 7, air does not enter the mold cavity 7 and flows back into the foam particle compression tank 1. At this time, the expanded particles present in the filling machine 16 are pushed back, and the filling machine 16 becomes empty (natural blowback). After the expanded particles in the filling machine 16 are removed, the expanded particle filling port 18 of the mold is closed by the piston plug 19.

  After the filling is completed, excess air in the foamed particle compression tank 1 and the mold is released from the exhaust valve 14, and the pressure of the mold is released to the atmospheric pressure. After that, steam for heating is supplied from the vapor line 10 into the mold 4, and the polypropylene resin expanded particles filled in the mold cavity 7 are heat-sealed. It is preferable that the pressure of the steam is usually 0.18 MPa (G) or more. The heating temperature and heating time of the mold are appropriately adjusted according to the size of the mold and the type of foamed particles, but the normal heating temperature is 116 to 152 ° C., particularly 120 to 145 ° C., and the heating time is 3 It is preferable that it is ˜30 seconds, especially 8 to 20 seconds.

In practice, the following heating process is often employed.
1) Preheating step: With the movable and fixed steam valves 11, the drain valve 12 and the exhaust valve 14 opened, lower pressure steam is allowed to flow into the mold than during double-sided heating described below. 2) One heating step: steam at a lower pressure than during double-sided heating with the mobile steam valve closed, the stationary steam valve opened, the mobile drain valve opened, the stationary drain valve closed and the exhaust valve 14 opened In a mold.
3) Reverse one-side heating process: open steam, close fixed steam valve, close mobile drain valve, open fixed drain valve and open exhaust valve, lower pressure steam than double-sided heating In a mold.
4) Double-sided heating step (main heating step): Steam is allowed to flow into the mold with the movable and fixed steam valves open and the movable and fixed drain valves closed. The mold cavity has the highest temperature in the double-sided heating process. The heating temperature at this time is said 116-152 degreeC.

  After the heating step, the polypropylene resin in-mold foam molded product is cooled by water cooling or the like, and then the mold is opened to take out the polypropylene resin in-mold foam molded product.

  Next, examples and comparative examples will be given to describe the method for producing a polypropylene resin-in-mold foam-molded article of the present invention in more detail, but the present invention is not limited to such examples. Moreover, the evaluation in an Example and a comparative example was performed with the following method.

(DSC ratio)
Using a differential scanning calorimeter, 5-6 mg of polypropylene resin multistage expanded particles were heated from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min. The DSC ratio was measured from the melting peak heat quantity Qh on the high temperature side.

(Bulk density of expanded particles)
The cylindrical container is filled with expanded particles, the expanded particles beyond the opening of the container are removed, the weight of the expanded particles in the container is measured, and the bulk density is obtained by dividing the weight of the expanded particles by the container volume.

(Molded foam expansion ratio)
The weight w (g) and the submerged volume v (cm ³ ) of the polypropylene-based resin-molded foam-molded product are obtained, and obtained from the resin density d (g / cm ³ ) by the following equation.
Foaming ratio = d × v / w

(Number of unfused expanded particles at the expanded particle filling port in the molded product)
The obtained polypropylene resin-in-mold foam-molded product was allowed to stand at 25 ° C. for 2 hours, and then allowed to stand in a thermostatic chamber adjusted to 75 ° C. for 15 hours, then taken out and allowed to cool at 25 ° C. The number of foam particles peeled off when the foam particles in the expanded foam filling body in the polypropylene resin mold were lightly scratched with a nail was defined as the number of unfused foam particles. As described later, a molding machine having two foamed particle filling ports was used. The number of unfused foam particles near the filling port was evaluated by measuring the number of unfused foam particles near the filling port at a total of six locations in three polypropylene resin molds. The total number was divided by the number of filling ports 6 to evaluate by averaging the number of unfused foam particles per filling port. The value of the number of unfused foam particles near the filling port indicates the number of unfused foam particles per one filling port.

(Fusion rate)
The obtained polypropylene resin-in-mold foam-molded product was allowed to stand at 25 ° C. for 2 hours, and then allowed to stand in a thermostatic chamber adjusted to 75 ° C. for 15 hours, then taken out and allowed to cool at 25 ° C. The ratio of the particles that were broken in the expanded particles when the expanded polypropylene resin mold was cut was defined as the fusion rate. The fusion rate is usually good if it is 70% or more.

Example 1
An ethylene-propylene random copolymer (ethylene content 3.6% by weight) having a melting point of 141 ° C. and MI of 6 g / 10 min was used as the base resin. To 100 parts by weight of this resin, 0.03 parts by weight of talc as a foam nucleating agent was added and dry blended, melt-kneaded in an extruder, extruded into a strand form from a circular die, cooled with water, cut with a cutter, Resin particles having a weight of 1.2 mg / grain and a substantially cylindrical shape were obtained. 100 parts by weight of the obtained resin particles, 200 parts by weight of water, 0.5 parts by weight of basic tribasic calcium phosphate and 0.01 parts by weight of sodium alkyl sulfonate are charged into a pressure-resistant autoclave, and further, 14.3 parts by weight of butane are charged. The contents were heated to the foaming temperature of 143.4 ° C. Then, the valve | bulb of the autoclave lower part was opened, the content was discharge | released under atmospheric pressure, and the bulk density 49.2g / L single-stage expanded particle was obtained. The obtained single-stage expanded particles were dried at 60 ° C. for 6 hours, then impregnated with pressurized air in a pressure-resistant container to set the internal pressure to about 0.5 MPa, and then steam of about 0.08 MPa (G) To make two-stage foaming. The resulting two-stage expanded particles had a bulk density of 16.7 g / L and a DSC ratio of 24.5%.

  The two-stage foamed particles were again pressurized with air in a pressure resistant container to give an internal pressure of about 0.17 MPa. The obtained two-stage expanded particles are filled into a expanded particle compression tank, the compression ratio is set to 0.12 MPa, and the compression ratio is 1.3, and a rectangular parallelepiped-shaped mold cavity having dimensions of 400 mm × 300 mm × 20 mm under this pressure is obtained. The two-stage expanded particles that were compressed into the same were transferred. Thereafter, the system pressure was released to atmospheric pressure, and in-mold foam molding was performed by heating with water vapor.

  Heating is performed in 3 seconds of preliminary heating (moving type, fixed drain valve opened), one heating for 3 seconds, reverse one heating for 3 seconds, double-sided heating for 10 seconds (heating pressure during double-sided heating is 0.28 MPa ( G)). After completion of the heating step, precooling (cooling with the drain valve closed) was performed, and then water cooling was performed, followed by mold release to obtain a polypropylene resin in-mold foam molded product. The density of the obtained expanded foam in the polypropylene resin mold was 21.7 g / L, the fusion rate was 70%, and the number of unfused expanded particles near the filler filling port of the expanded foam in the polypropylene resin mold was 0. there were.

(Comparative Example 1)
Single-stage expanded particles with a bulk density of 17.5 g / L were obtained in the same manner as in Example 1 except that the amount of butane charged in the pressure-resistant autoclave was 22.3 parts by weight and the foaming temperature was 138.1 ° C. The obtained foamed particles were pressurized with air in a pressure-resistant container without being subjected to two-stage foaming, and an internal pressure of about 0.17 MPa was applied. The obtained two-stage expanded particles were subjected to in-mold foam molding in the same manner as in Example 1. The density of the obtained expanded foam in the polypropylene resin mold was 22.8 g / L, the fusion rate was 100%, and the number of unfused expanded particles in the vicinity of the filler filling port of the expanded foam in the polypropylene resin mold was 3. there were.

  As is clear from the results of Examples and Comparative Examples, it is obtained by in-mold foam molding using foam particles that are two-stage foamed, although foam particles having the same bulk density manufactured from the same resin are used. It can be seen that the fusion in the vicinity of the filler filling port of the molded polypropylene resin mold is improved.

  The polypropylene resin-in-mold foam-molded product obtained by the production method of the present invention can be used for applications such as a heat insulating material, a cushioning packaging material, an automobile interior member, and a core material for an automobile bumper. It is a particularly desirable usage method to use a polypropylene resin in-mold foam molded product obtained by using the production method of the present invention for a buffer packaging material in which an in-mold foam molded product with a high expansion ratio is often used. is there.

DESCRIPTION OF SYMBOLS 1 Expanded particle storage tank 2 Expanded particle supply port 3 Pressurized gas inlet 4 Mold 5 Fixed type 6 Mobile type 7 Mold cavity 8 Vent 9 Steam chamber 10 Steam line 11 Steam valve 12 Drain valve 13 Mold gas pressure adjustment valve 14 Exhaust gas Valve 15 Exhaust port 16 Filling machine 17 Pressurized gas inlet for filling expanded particles 18 Expanded particle filling port 19 Piston plug 20 Pressure equalization line

Claims (4)

  After dispersing the polypropylene resin particles in a dispersion medium in a pressure vessel, adding a foaming agent containing hydrocarbons, heating to a temperature equal to or higher than the temperature at which the polypropylene resin particles soften, and impregnating the foaming agent, Opening one end of the pressure vessel and releasing the polypropylene resin particles into the atmosphere at a lower pressure than in the pressure vessel, and using the polypropylene resin foam particles obtained by in-mold foam molding in the mold. In the manufacturing method of a body, the polypropylene resin multistage expanded particle which further expanded the said polypropylene resin expanded particle is in-mold foam-molded, The manufacturing method of the polypropylene resin in-mold expanded molded object characterized by the above-mentioned.   The method for producing an expanded molded article in a polypropylene resin mold according to claim 1, wherein the polypropylene resin multistage expanded particles are filled in a mold by a compression filling method and subjected to in-mold foam molding.   3. The method for producing a polypropylene resin in-mold foam-molded product according to claim 1 or 2, wherein in-mold foam molding is performed on the polypropylene resin multistage expanded particles to which an internal pressure is applied.   The polypropylene resin in-mold foam-molded product according to any one of claims 1 to 3, wherein the polypropylene resin is a polypropylene random copolymer comprising a monomer unit derived from ethylene. Production method.