JP2001096560A - Method for in-mold foam molding polyolefin resin and assembly package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for in-mold foam molding a polyolefin resin having a small weight unevenness of a molding between molding shots and a suitably adjustable packing density of prefoamed beads in respective parts of a molding space. SOLUTION: The method for in-mold foam molding a polyolefin resin comprises the steps of temperature regulating prefoamed beads made of a polyolefin resin at a predetermined temperature of ±5 deg.C of a set temperature in a range of 30 to 50 deg.C as a center, compression packing the beads in molds 11, 12 having a partition wall molding part 13b for molding a partition wall having a thickness of 20 mm or less to the molding in a state in which a compression packing pressure is set to larger than an atmospheric pressure of a pressure adapted to the set temperature and a predetermined pressure of a value or less obtained by formula of (70-set temperature [ deg.C])/10} kg/cm2, thereafter heat fusion bonding the resin by vapor, then cooling the resin, and removing the resin from the molds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for in-mold foam molding of a polyolefin resin and a collective package.

[0002]

2. Description of the Related Art As an in-mold foam molding apparatus for producing molded articles using pre-expanded beads made of a thermoplastic synthetic resin,
As shown in FIG. 13, a pair of molding dies 10
0, 101 and the pre-expanded beads in both molds 100, 10
1 and a filling device 111 for filling the molding space 104 formed by the first and second molding dies 100 and 101. , 103
And a large number of ventilation holes 105, 1
No. 06 is formed, and the working fluid such as steam, air and cooling water necessary for molding is supplied to the molding space 104 via the chambers 102 and 103. In this case, each chamber 1
02 and 103 are provided with upper ports 107 and 108 for supplying heated steam, and lower ports 109 and 110 connected to a decompression pump or a drain pipe are provided at a lower portion. It is configured to supply steam.

In addition, a large number of ventilation holes 105, 106 formed in the molds 100, 101 are actually 0.5 mm.
A core vent formed of a cylindrical body having a lid having an outer diameter of 7 to 12 mm and having a plurality of through holes formed of a round hole having a diameter of about 0.5 mm and a slit having a width of about 0.5 mm. The one formed by fitting into the mounting hole and the one directly formed on the molds 100 and 101
mφ core vent holes, and these ventilation holes 105 and 106
They are provided at a pitch of 50 mm.

[0004] In the case of molding a foam molded article using such a foam molding apparatus, first, a molding die is closed to form a molding space 104, and pre-expanded beads made of pre-expanded polystyrene or the like are used as raw materials. Filler 11 from tank (not shown)
1 to fill and fill the molding space 104, and then heat the pre-expanded beads in the molding space 104 with heated steam;
After foaming and fusion, they are solidified by cooling, and the molds 100, 101
And the foam molded article is taken out.

[0005] On the other hand, molded articles molded using the molding apparatus have a problem that the weight of the molded articles varies greatly. In order to solve this problem, for example, Japanese Patent Publication No. Hei 8-15746 discloses that the temperature of a pre-expanded bead is measured before the start of compression filling and the compression filling pressure is set so as to adapt to the temperature. A foam molding method configured to set the temperature of foam beads constant is described.

[0006]

However, in such a molding method, one of the problems particularly required to be improved is the filling density of the pre-expanded beads in a specific portion in the molding space 104 and the other portions. The problem is that a great difference may occur between the packing density and the packing density. The specific portions include (1) a deep portion of the molding space 104 for molding details of a molded article having a complicated shape, and (2) an outer peripheral end portion 104a of the molding space 104.

Hereinafter, the causes of the fluctuation of the packing density in (1) and (2) will be described in detail. Before that, a method of filling the pre-expanded beads which is most generally employed will be briefly described. As the method of filling the pre-expanded beads, [1] cracking filling method, [2] pressure filling method, [3] compression filling method, and the like are widely adopted.

[1] The cracking filling method is a method adopted when the air used for filling cannot be sufficiently exhausted only from the vent holes arranged in the core mold and the cavity mold. The mold and the mold are not completely closed (cracking), for example, when the bottom thickness of the molded product is 10
%, And the air used for filling is also discharged from the gap between the core mold and the cavity mold.

[2] In the pressure filling method, the inside of a raw material tank containing pre-expanded beads is pressurized to about 0.2 to 1.5 kg / cm ² , and the inside of the molding space is opened to the atmospheric pressure through a vent and a chamber. In this state, the pre-expanded beads are conveyed and filled into the molding space using the pressure difference between the raw material tank and the molding space.

[3] The compression filling method uses a pressure p in the raw material tank.
1.0 to 5.0 kg / cm ² higher than the pressure filling method.
Pressure in one chamber, and the pressure difference (p−p) of the pressure p1 in the molding space communicating through the vent hole.
This is a method in which prefoamed beads are conveyed and filled while maintaining p1).

Next, the cause of the fluctuation of the packing density will be described in detail. (1) Regarding the deep part of the molding space for molding the details of the molded article having a complicated shape The above three filling methods basically provide an appropriate differential pressure between the raw material tank and the molding space, and based on the differential pressure, The pre-expanded beads are fed in along with the generated air flow. In the case of the molding space 104 having a relatively simple shape as illustrated in FIG. 13, the pre-expanded beads are sufficiently distributed to all corners. Since the resin was filled in a state and a state where partial filling unevenness was small was obtained, even in the final foamed molded article, there was little density unevenness and relatively uniform quality could be obtained.

However, as shown in FIG. 14 (a), a shape in which a deep and narrow concave portion 112 (two upper and lower portions in FIG. 14) having a bag-like cross section is provided in the central plane of the core mold 101, or As illustrated in FIG. 14B, in the case of a shape in which a deep and narrow concave portion 113 having a bag-shaped cross section (two upper and lower portions in FIG. The flow of air, which serves as a driving force for filling the expanded beads, stagnates in this portion, and it is difficult for the pre-expanded beads to fill the inner part of the bag-shaped concave portion 112 or 113, resulting in extreme density unevenness or the degree of the unevenness. At worst, problems such as molding failure due to lack of filling occurred.

In order to cope with such a problem, an attempt has been made to arrange a special filling device toward the recess, which is difficult to fill. There has been a problem that the number of possible compacts has to be reduced, and the productivity is significantly reduced. The reason is that the number of fillers to be attached to one molding apparatus is usually fixed in view of the capacity of the raw material tank or the supply capacity of pressurized air. For example, in the most general-purpose model, the number of fillers to be attached is set to 18, and when the shape of a molded product is simple, three fillers are provided for one molding space. Assuming that 6 are required due to the complexity of
This is because, although there is room for six pieces, only three molds can be designed, and productivity is reduced by half.

Further, when the number of fillers increases, the amount of air supplied to the molding space per unit time increases, so that the air pressure in the molding space decreases instantaneously immediately after filling or the like. In some cases, this may result in fluctuations in the packing density, such as the inability to keep up with the discharge of air. For this reason, the number of used filling machines and the arrangement of the filling machines are troublesome for mold designers,
In addition, there were many trial and error elements, and this was an area where standardization was extremely difficult. In particular, the filling density of the pre-expanded beads for a portion away from the filling device or a narrow bottomed portion such as the above-described concave portion tends to be low, and the filling density for these difficult-to-fill portions is set to an appropriate value. , It is necessary to increase the packing density as a whole, and the weight of the molded product becomes heavier than when the density is uniform.

Further, from the viewpoint of moldability, when the filled pre-expanded beads are heated by steam, the pre-expanded beads are so formed that the pre-expanded beads in the portion having a low filling density are sufficiently fused. It is necessary to make the foam larger, and it is necessary to increase the heating steam pressure. However, when the heating vapor pressure is increased in accordance with the portion having a low filling density, the portion having a high filling density is in an excessively heated state, and the foaming pressure is higher than that in normal molding. For this reason, when cooling the molded article, it takes a long time to reduce the high foaming pressure to the foaming pressure at which the mold can be released, and the molding cycle becomes longer, thereby lowering productivity. In addition, during heating and cooling, the foaming pressure of each part of the molded article becomes non-uniform, so that the releasability is poor, and since the filling property is poor, productivity and yield are reduced.

(2) Regarding the outer peripheral end portion of the molding space In the pressure filling method or the compression filling method, as shown in FIG. 13, the pre-expanded beads are formed in the molding space with both molding dies 100 and 101 completely closed. Due to filling in the space 104, the outer peripheral end portion 104a of the molding space 104 has a dead end shape. Therefore, the inside of the raw material tank (not shown) and the molding space 10
The air flow generated by the differential pressure in
stagnation in a, pre-expanded beads are difficult to fill,
Density unevenness is likely to occur.

On the other hand, in the cracking filling method, the core mold and the cavity mold are not completely closed, but are opened, for example, by 10% of the bottom thickness of the molded product. However, due to the closing of the core mold and cavity mold after filling, there is another problem that the density of the bottom of the molded product is higher than the other parts by the cracking gap, resulting in uneven density. .

In the cracking filling method, both molds are completely closed after filling the pre-expanded beads.
Since the outer peripheral end of the molding space has a dead end, the following problems occur when heating the pre-expanded beads with steam, cooling with cooling water, and releasing the molded product.

At the time of heating the pre-expanded beads, for example, by supplying the heated steam from one chamber to the other chamber, the heated steam is passed through the pre-expanded beads in the molding space, as shown in FIG. So, the molding space 10
4 has a dead-end shape, it is difficult for heated steam to reach the outer peripheral tip portion 104a and the outer peripheral portion 10a of the molding die having a relatively large heat capacity.
Since the amount of heat flows to 0a and 101a, the temperature of the pre-expanded beads at the outer peripheral end portion 104a is hard to rise, and the temperature rise is considerably delayed compared to other portions, so that the time of the heating step has to be lengthened. There is a problem that the entire molding time becomes longer.

When the molded article is cooled, the chambers 102, 1
The mold 100, 1
Spraying the cooling water on the
03 is decompressed to evaporate the water adhering to the mold and the water in the molding space 104, and the foamed molded body is cooled together with the mold by the heat of vaporization at this time. Contrary to the heating of the beads, the heat is transferred from the outer peripheral portions 100a and 101a of the molding die to form the molding space 104.
However, there is a problem that it takes time to sufficiently cool the portion of the molding space 104 of the foam molded article located at the outer peripheral tip portion 104a.

When the molded product is released, the molding dies 100, 10
While the mold 1 is opened, the foam molded body is pushed out from the back side of the cavity mold 100 with an ejector pin (not shown), and the foam molded body is taken out of the mold.
When the mold is opened, the outer peripheral portions 100a and 101a of the mold are opened.
In addition, there is a problem that water accumulated in the inter-cavity 116, which is a joint of the mold device, surrounded by the frames 114 and 115 flows down and wets the foamed product as a product.

An object of the present invention is to provide a method for in-mold foam molding of a polyolefin resin capable of appropriately adjusting the filling density of pre-expanded beads between molding shots and at various parts of a molding space, and between molding shots and at various parts of a molded product. An object of the present invention is to provide a collective package having a small weight variation.

[0023]

According to a first aspect of the present invention, there is provided a method for in-mold foam molding of a polyolefin resin, comprising the steps of:
The temperature is adjusted to a constant temperature of ± 5 ° C. around a set temperature in the range of 0 ° C., and the compression filling pressure is a pressure adapted to the set temperature, which is larger than the atmospheric pressure, and Δ (70
−Set temperature [° C.] / 10 kg / cm ² , while maintaining a constant pressure equal to or less than the value obtained by the formula,
The mold is compression-filled into a mold having a partition wall forming portion for molding a partition wall of 0 mm or less, then heated and fused by steam, cooled, and taken out of the mold.

In this molding method, the temperature is adjusted to a set temperature of 30 to 50 ° C., and the compression filling pressure (the internal pressure of the molding space at the time of compression filling) is a pressure adapted to this set temperature and is larger than the atmospheric pressure. , {(70−set temperature [° C.]) / 10} kg / cm ² , so that the weight variation of the molded product between molding shots can be significantly reduced. In other words, the pre-expanded beads are difficult to foam one bead at a time in the same bulk density due to the manufacturing restrictions, and the pre-expanded beads are mixed with particles having a magnification distribution before and after the target bulk density. Become. For this reason, in the transfer process from the silo to the molding space, classification occurs inevitably, so that the bulk density of the pre-expanded beads used for each molding shot varies, and the weight of the molded product varies for each molding shot. However, in the present invention, by controlling the temperature of the pre-expanded beads to a fixed set temperature and setting the compression filling pressure to a pressure adapted to the set temperature, it is possible to prevent weight variation of the molded product. . In particular, when a molded article having a partition wall having a thickness of 20 mm or less is molded, it is difficult to sufficiently secure the density of the pre-expanded beads in the molded part of the partition wall, so that the weight variation of the molded article tends to increase. This is preferable.

The compression filling pressure may be set according to the apparent density of the pre-expanded beads, or according to the apparent density and the temperature. However, the means for measuring the apparent density is rather large. In addition, since the ability to adjust the variation of the bulk density (expansion ratio) is smaller than that of the temperature adjustment, it is preferable to adjust the temperature to be constant. It is also possible to adjust the compression filling pressure according to the fluctuating temperature of the pre-expanded beads, but since the adjustment of the compression filling pressure requires more complicated control than the temperature adjustment, the temperature of the pre-expanded beads is reduced. It is preferable to make the adjustment constant.

The temperature of the pre-expanded beads is most preferably strictly adjusted to the set temperature, but it is difficult to directly measure the temperature, so that the pre-expanded beads may have a certain range with respect to the set temperature. , Its width is set temperature ± 5 ℃
Within this range, the temperature can be adjusted relatively easily, and the variation in the bulk density of the molded product between molding shots can be reduced to such an extent that the quality of the molded product is not adversely affected.

Further, the pre-expanded beads made of polyolefin resin have a much more deformed particle shape than the pre-expanded beads made of polystyrene resin having the same expansion ratio because the material itself is soft and the gas permeability is high. This is preferable since the filling property can be further improved and the filling property can be further improved.

According to a second aspect of the present invention, the compression ratio of the pre-expanded beads obtained by dividing the density of the molded article by the bulk density of the pre-expanded beads under the temperature condition of the pre-expanded beads before the start of the compression filling is 1. The compression filling pressure is set to 2 to 1.5. In other words, when the compression ratio is less than 1.2, the pre-expanded beads do not sufficiently expand, and the molded article largely shrinks after release from the mold, or a gap is formed between the beads, and a good product is obtained. There is no problem. Also, when the compression ratio is 1.
If it exceeds 5, the space between the bead particles in the molding space after filling becomes very narrow, and the heating steam does not pass between the bead particles, resulting in poor fusion or excessive foaming only at the location where the heating steam has passed. Since there is a problem that cracks occur in the molded product and the cooling time becomes longer, the compression ratio is set to 1.
It is preferable to set the compression filling pressure to be 2 to 1.5.

In the conventional molding method, the compression ratio is generally set at 1.4 in order to secure sufficient filling performance.
In the case of molding a thin-walled deep molded article having a partition wall of 20 mm or less as set in the above, as in the present invention,
It is necessary to keep 1.5 to 1.6 or more. However, when the compression ratio is set to a high value, the resin foaming pressure becomes higher than the steam temperature required for fusing the pre-expanded beads to each other, which requires a long cooling cycle and lowers productivity. I do. In the present invention, since the compression ratio is set as low as 1.2 to 1.4, the productivity can be improved, and the bulk density of the molded article and the bulk density of the pre-expanded beads are brought close to each other, so that the pre-expanded It is possible to increase the efficiency of transport and storage of beads. In particular, by molding as described in claim 4, since the filling density of the pre-expanded beads in each part of the molded article can be set uniformly, it is possible to improve the productivity while sufficiently securing the quality of the molded article. Becomes

According to a third aspect of the present invention, the pre-expanded beads are made of a polyolefin resin, have a cell diameter of 100 to 900 μm, an expansion ratio of 5 to 60 times, and a DSC.
The pre-expanded beads made of a polyolefin resin having a 2'nd peak ratio of 8 to 60% and a closed cell ratio of 65% or more are used.

In this molding method, the pre-expanded beads have a cell diameter of 100 to 900 μm and an expansion ratio of 5 to 5.
60 times, the DSC 2'nd peak ratio is 8 to 60%, and the closed cell rate is 65% or more. Therefore, the surface property of the molded product is improved as follows, and the appearance of the molded product is improved. In addition to this, the restrictions on the heating conditions during molding can be relaxed, and the moldability and energy saving can be improved.

When the cell diameter is less than 100 μm, there is a problem that the surface elongation is poor at molding, the sink is easy, and the appearance of the surface is inferior.
Since the cell diameter tends to be non-uniform, and the cell diameter is large, the surface is rough and the surface appearance is poor.
It is preferable to set within the range of 00 to 900 μm.
The expansion ratio is not particularly limited, but is preferably about 5 to 60 times (bulk ratio of expanded beads).

The DSC 2'nd peak ratio is 8% to 60%
It is preferable to set The DSC 2'nd peak ratio is defined as the two DSCs formed on the low-temperature side and the high-temperature side, which are formed due to the crystal melting point of the base resin when the base resin is heated.
(Differential scanning calorimetry) is the ratio of the area of the peak on the high temperature side to the total area of the peaks. When the DSC 2'nd peak ratio is less than 8%, the heating condition width during molding is narrow, and Easy to shrink and sink. On the other hand, if it exceeds 60%, it is necessary to greatly increase the heating conditions, it is necessary to increase the size of the molding machine, and it becomes negative from the viewpoint of energy saving. Therefore, it is preferably set to 8 to 60%.

When the closed cell ratio is less than 65%, even if the heating pressure at the time of molding is increased to somehow fuse the beads, shrinkage and sink of the molded body are likely to increase.
Since it becomes difficult to obtain a molded body of the target quality, it is preferable to set the ratio to 65% or more.

According to a fourth aspect of the present invention, there is provided a method for in-mold foam molding of a polyolefin resin, comprising: a molding space having a partition wall molding portion for molding a partition wall having a thickness of 20 mm or less on a molded product; At least three chambers for controlling the utility fluid, a first chamber on the back side of the core mold communicating with the molding space, a second chamber on the back side of the cavity mold communicating with the molding space, and 3rd communicating with the difficult filling part where the pre-expanded beads are difficult to fill
A pre-expanded bead is adjusted to the set temperature using an in-mold foam molding apparatus having a chamber, and the inorganic gas pressure of each chamber is compressed with the inorganic gas to the compression filling pressure adapted to the set temperature. Are individually or individually controlled, and the foaming beads are compression-filled into the molding space.

In this molding method, the pre-expanded beads made of a polyolefin resin are compressed with an inorganic gas, and the inorganic gas pressures of the three chambers are controlled individually or in any combination to form the compressed pre-expanded beads. A new compression filling method of filling the molding space with the flow of inorganic gas, so that the pre-expanded beads are filled first for difficult-to-fill portions where the pre-expanded beads are difficult to fill. By controlling the inorganic gas pressure in each chamber, the packing density in each part of the molded article can be set uniformly. Therefore, even in a molded product having a thin partition wall having a thickness of 20 mm or less that is difficult to be filled with the pre-expanded beads, the filling density in each part of the molded product can be set to an appropriate value without increasing the number of fillers. . Further, if the pre-expanded beads are filled in a portion where the strength and rigidity are to be increased first, the filling density in the portion can be locally increased to increase the strength. The operation of feeding the pre-expanded beads into the difficult-to-fill portion may be performed a plurality of times so that the pre-expanded beads are intensively filled into the difficult-to-fill portion.

According to a fifth aspect of the present invention, the third chamber includes one or more chambers that communicate with the molding space via a clearance between the core mold and the cavity mold. In this case, the filling inorganic gas that has flowed into the outer peripheral portion of the molding space through the clearance can be efficiently discharged to the outside, and thus, for example, when manufacturing a deep-bottomed container or the like, it corresponds to the opening edge of the container. By configuring so that the clearance is formed at the position, the filling density of the pre-expanded beads can be appropriately set without increasing the number of filling devices, and the quality of the container can be improved.

According to a sixth aspect of the present invention, there is provided the molding method, wherein the third chamber includes one or more chambers communicating with the interior of the partition wall forming section, and the third chamber is formed with respect to the partition wall forming section when the pre-expanded beads are filled. The inorganic gas pressure of the three chambers is controlled so that the pre-expanded beads are filled first.
In this case, since the packing density cannot be sufficiently ensured, a thickness of 20 mm, which was conventionally considered to be difficult to form, was used.
Even in a molded article having a complicated shape such as having the following partition wall, by filling the pre-expanded beads in the partition wall forming section first, the filling density of the pre-expanded beads in the partition wall forming section is increased, and It is possible to produce a molded article with high quality of density.

The method according to claim 7, wherein the third chamber includes one or more chambers communicating with a deep part of a remote part of the molding space remote from the pre-expanded bead filler. During the filling, the inorganic gas pressure is controlled so that the pre-expanded beads are first filled in the remote portion. With this configuration, it is possible to sufficiently secure the packing density of the remote portion where the packing density of the pre-expanded beads tends to decrease, and it is possible to manufacture a high-quality molded product.

According to the molding method of the present invention, when the height of the partition wall to be molded is H (mm) and the thickness is T (mm), the relational expression of H / T ≧ 10 is satisfied. It has a partition wall forming part. A molded article having a partition wall having such a configuration has conventionally been considered to be difficult to form because a sufficient filling density of the pre-expanded beads in the partition wall forming section cannot be ensured. By molding by the molding method of the first aspect, in particular, by the molding method of the sixth aspect, it is possible to increase the filling density of the pre-expanded beads in the partition wall molded portion, and to produce a molded article of appropriate density and good quality. It becomes possible.

As the pre-expanded beads, any material may be used as long as it is made of a polyolefin resin. However, since it is inexpensive and easily available, it is possible to use a polypropylene resin or a polypropylene resin. , Claim 10
As described above, it is preferable to employ a resin made of a polyethylene resin.

According to a eleventh aspect of the present invention, a draft is formed in the partition wall forming portion. Since the partition wall that can be formed by this new forming method is thin and high, it is preferable to form a draft in the partition wall forming portion to prevent breakage of the molded product during mold release.

According to a twelfth aspect of the present invention, the collective package is formed using pre-expanded beads made of a polyolefin resin, and is internally provided with a partition wall having a thickness of 20 mm or less in order to separately store a plurality of articles. Are divided into a plurality of accommodation spaces. The collective package having such a configuration has conventionally been considered to be difficult to mold because the density of the beads on the partition wall is much lower than the other parts, and sufficient strength cannot be secured. By molding by the molding method described in any one of 4 to 11, the packing density of the beads in the partition wall is appropriately set, and a collective package having a uniform density as a whole can be realized.

According to a thirteenth aspect of the present invention, when the height of the partition wall is H (mm) and the thickness is T (mm),
It has a partition wall such that the relational expression of H / T ≧ 10 holds. 12. The molding wall according to any one of claims 4 to 11, wherein the partition wall satisfying such a relational expression is thin and has a high height, so that the packing density of beads cannot be sufficiently secured and molding is difficult. By molding by the method, the packing density of beads in the partition wall can be appropriately set, and a collective package having a uniform density as a whole can be realized.

As the material of the beads constituting the collective package, any material can be adopted as long as it is a polyolefin resin, but it is inexpensive and easily available. It is preferable to adopt the one made of polyethylene resin as described in claim 15.

According to a sixteenth aspect of the present invention, there is provided a collective package in which a draft is formed in the partition wall. Since the partition wall of this collective package is thin and high as described above, it is preferable to form a draft in the partition wall forming portion to prevent breakage of the molded product at the time of mold release.

[0047]

Embodiments of the present invention will be described below with reference to the drawings. First, the configuration of a molded product will be described. As shown in FIG. 1 and FIG.
Is formed integrally with a pre-expanded bead made of polyolefin resin using an in-mold foam molding apparatus 10 described later, and has a box-shaped bottomed main body 2 and a plurality of storage spaces in the main body 2. 3 is a collective package that includes a partition wall 4 that is divided into three, and is configured to accommodate various articles in the accommodation space 3 in an aligned manner. Note that the size and shape of the molded article 1 and the number of the accommodation spaces 3 are not limited to the configurations illustrated in FIGS. 1 and 2, but may be arbitrarily determined according to the size and shape of the articles to be accommodated, the number of accommodations, and the like. Can be set. The in-mold foam molding apparatus 10 and the molding method described below are suitable for molding the molded article 1 having such a complicated shape, but the molded article having a simple shape such as a simple box or plate is molded. It is also possible.

The thickness T of the partition wall 4 is set to 20 mm or less, and the height H (mm) and the thickness T (mm) of the partition wall 4 are
The relational expression of H / T ≧ 10 is established. The molded article 1 having the partition wall 4 having such a configuration has been difficult to mold by the conventional molding method, but can be molded without lowering the quality by the molding method of the present invention described later. Further, a predetermined draft is formed in the partition wall 4 so that the partition wall 4 is not damaged when the molded article 1 is released from the mold.

Next, the pre-expanded beads used in the in-mold foam molding apparatus will be described. As the material of the pre-expanded beads, a material having physical properties corresponding to the use conditions of the molded article 1 to be manufactured is selected, but a polyolefin-based synthetic resin material such as a polyethylene resin or a polypropylene resin, or a synthetic resin thereof is used. Copolymers of resin materials and the like are employed. Specifically, ethylene propylene random polypropylene resin, ethylene propylene block polypropylene resin, homopolypropylene ethylene propylene butene random terpolymer, linear low-density polyethylene (LLDPE), cross-linked low-density polyethylene (cross-linked LDPE), and the like can be suitably used. . As the pre-expanded beads, it is possible to use pre-expanded beads made of polystyrene resin.However, the pre-expanded beads of polyolefin resin have the same expansion ratio because the material itself is softer and the gas permeability is higher. Since the particle shape is much more likely to be deformed than the pre-expanded beads made of a polystyrene resin, it is preferable in that the effect of improving the filling property, which is the object of the present invention, is exhibited. In addition, since polystyrene resins generally have larger variations in the shape of the pre-expanded beads than polyolefin resins and are inferior in filling properties, the pre-expanded beads made of a polyolefin-based synthetic resin material are preferred in the present invention. The effect of the filling method is easy to appear.

If the cell diameter of the pre-expanded beads is less than 100 μm, there is a problem that surface elongation is poor during molding, sinks easily, and the appearance of the surface is inferior. If it exceeds 900 μm, the cell diameter is inadequate. There is a problem that the surface is coarse and the surface appearance is inferior because the cell diameter is large and the cell diameter is large. Therefore, it is in the range of 100 to 900 μm, more preferably 150 to 700 μm, and particularly preferably 170 to 5 μm.
It will be set to 50 μm. The expansion ratio is not particularly limited, but is preferably about 5 to 60 times (bulk ratio of expanded beads).

DSC 2'nd peak ratio is 8% to 60%
It is preferable to set The DSC 2'nd peak ratio is defined as the two DSCs formed on the low-temperature side and the high-temperature side, which are formed due to the crystal melting point of the base resin when the base resin is heated.
(Differential scanning calorimetry) is the ratio of the area of the peak on the high temperature side to the total area of the peaks. When the DSC 2'nd peak ratio is less than 8%, the heating condition width during molding is narrow, and Easy to shrink and sink. On the other hand, if it exceeds 60%, it is necessary to greatly increase the heating conditions, it is necessary to increase the size of the molding machine, and it becomes negative from the viewpoint of energy saving, so it is 8 to 60%, more preferably 10 to 50%. %, Particularly preferably 15 to 40%.

When the closed cell ratio is less than 65%, even if the heating pressure at the time of molding is increased to somehow fuse the beads, shrinkage and sink of the molded body are liable to increase.
Since it becomes difficult to obtain a molded product of the target quality, it is 65% or more, more preferably 75% or more, and particularly preferably 85%.
The above is set.

Next, the configuration of the in-mold foam molding apparatus will be described. As shown in FIGS. 3 and 4, in-mold foam molding apparatus 1
0 denotes a core mold 11 and a cavity mold 12 which are arranged to face each other.
A bead filling means for filling the pre-expanded beads into the molding space 13 formed by the core mold 11 and the cavity mold 12, heating the pre-expanded beads filled in the molding space 13 by steam, foaming, Steam supply means for fusing,
Cooling means for cooling the molded article 1.
The filling of the pre-expanded beads into the molding space 13 includes:
Although an inorganic gas such as nitrogen gas other than air may be used,
Here, the case of filling with clean air will be described.

The core mold 11 and the cavity mold 12 are respectively mounted on a housing 16 having a frame-shaped frame 14 and a back plate 15. A first chamber 17 is provided on the back side of the core mold 11, and the back face of the cavity mold 12 is provided. A second chamber 18 is formed on each side.

As shown in FIGS. 3 to 6, the core mold 11 and the cavity mold 12 are formed with a vent 22 including a core vent 20 and a core vent hole 21.
The chambers 17 and 18 are communicated with each other through a vent hole 22. The core vent 20, as shown in FIGS. 5 and 6,
Mounting hole 23 formed in core mold 11 and cavity mold 12
And a bottomed cylindrical body formed with a plurality of through holes 22a or long holes 22b having a diameter smaller than the diameter of the pre-expanded beads on the bottom surface.
Are the core mold 11 and the cavity mold 1 as shown in FIG.
2 is a through hole having a diameter smaller than the diameter of the pre-expanded beads.

In this embodiment, the molds 11 and 12 each having a plurality of ventilation holes 22 are used. However, a molding die in which these ventilation holes 22 are almost completely or completely omitted is used. Is also good. When such a mold is used, the molding space and the external piping are communicated with the two molds in a state where the molds are closed, at the joint portion of the two molds, in the vicinity thereof, or around the filler or the ejector pin. By forming a slit or a through-hole for the purpose, the working fluid such as air or vapor for filling the pre-expanded beads is controlled. When such a mold is used, traces of the ventilation holes 22 are not formed in the molded product, so that a molded product with a beautiful surface can be obtained, and the work of forming the ventilation holes is almost unnecessary or completely unnecessary. The manufacturing cost of the mold can be reduced, and the mold can be made thin, so that the responsiveness such as heating by steam can be improved, and the working fluid such as steam in the mold space and the chambers 17 and 18 can be individually controlled. Therefore, it is possible to independently control the surface property and the internal fusion rate of the molded product, and to obtain excellent effects such as expansion of the degree of freedom with respect to the characteristics of the molded product.

The chambers 17, 18 are provided with service valves SV1, S
V2 and switching valves SWV1 and SWV2 are connected to the steam supply pipe 25 and the air supply pipe 26, respectively, and the drain valves DV1 and DV2 and the switching valves SWV3 and SW
Via V4, they are connected to a drain pipe 27 and a pressure reducing pipe 28 in which a vacuum pump P is interposed. By operating the utility valves SV1 and SV2, the drain valves DV1 and DV2, and the switching valves SWV1 and SWV2, the chamber 17,
It is configured such that utility fluids such as steam and compressed air can be individually supplied to or discharged from the fuel cell 18.

The bead filling means will be described with reference to FIG.
As shown in FIG. 2, a raw material tank 29 for storing the pre-expanded beads is provided, an intake pipe 30 is connected to the raw material tank 29, and an intake valve V1 is interposed in the middle of the intake pipe 30. By controlling V1, the internal pressure of the raw material tank 29 is adjusted.

A filling device 31 opening to the molding space 13 is attached to the back plate 15 on the side of the cavity mold 12, a shutter 32 is attached to the raw material tank 29, and the filling device 31 is connected to the raw material tank 29 through a filling pipe 33. The pre-expanded beads connected to the shutter 32 and filled in the raw material tank 29 are:
It is configured to be supplied from the filling device 31 into the molding space 13 on the flow of air. A filling air supply pipe 34 is connected to the filling device 31, and the filling air at an appropriate pressure is supplied by a filling air valve V <b> 2 provided in the middle of the filling air supply pipe 34.

The raw material tank 29 is set to a pressurized state higher than the internal pressures of the chambers 17 and 18, and the pre-expanded beads stored in the raw material tank 29 are compressed, and the air from the raw material tank 29 to the molding space 13 is compressed. Is formed so as to be filled in the molding space 13 along the flow.

An adjustment air supply pipe 35 is connected between the shutter 32 and the filling pipe 33, and the adjustment air supply pipe 3
The filling pipe 3 is controlled by the regulating air valve V3
Adjustment air at an appropriate pressure is supplied to 3, and the prefoamed beads are supplied from the raw material tank 29 to the filling pipe 33 while being diluted with the adjustment air. Further, by changing the supply amount of the adjustment air, the supply amount of the pre-expanded beads supplied to the filling tube 33 per unit time, that is, the final dilution degree described later is adjusted. However, it is also possible to supply the pre-expanded beads from the raw material tank 29 to the filling pipe 33 by a supply means such as a screw conveyor. In this case, the adjusting air valve V3 and the adjusting air supply pipe 35 are omitted,
By changing the rotation speed of the screw conveyor,
The supply amount of the pre-expanded beads to the molding space 13 per unit time is adjusted.

The first configuration of the present invention is characterized in that a third chamber communicating with a difficult-to-fill portion of the molding space 13 where the pre-expanded beads are difficult to fill is provided, and a filling chamber for filling is provided via the third chamber. By discharging the air, the inflow of the pre-expanded beads into the difficult-to-fill portion is promoted, and the filling density of the pre-expanded beads in the difficult-to-fill portion is set appropriately.

As the difficult filling portion, for example, the outer peripheral tip portion 13 a of the molding space 13, the back portion of the partition wall forming portion 13 b for forming the partition wall 4, or the remote portion of the molding space 13 distant from the filling device 31. The back and the like are conceivable.

In order to improve the filling property of the outer peripheral tip portion 13a in the difficult-to-fill portion, a slit-shaped clearance 40 is provided between the core mold 11 and the cavity mold 12 with the mold closed.
Is formed between the flanges 11a, 12a of the core mold 11 and the cavity mold 12, and an inter-mold cavity 41 as a third chamber is formed. It is communicated with the cavity 41. The inter-cavity 41 is provided with a utility valve SV3 and a switching valve SW.
V1 and SWV2 are connected to the steam supply pipe 25 and the air supply pipe 26, respectively, and via the drain valve DV3 and the switching valves SWV3 and SWV4, the drain pipe 27 and the pressure reducing pipe 28 in which the vacuum pump P is interposed. The inner pressure of the difficult-to-fill portion of the outer peripheral tip portion 13a can be adjusted by controlling the internal pressure of the inter-mold cavity portion 41. However, the inter-mold cavity portion 41 may be connected only to the drain pipe if only the filling property of the pre-expanded beads is improved, and is not necessarily required to be the steam supply pipe 25 or the air supply pipe 26.
It is not necessary to connect the pre-expanded beads to the pre-expanded beads by controlling the working fluid other than the air for filling in the inter-cavity 41 as described later. This is preferable because various advantages can be obtained when cooling and releasing the molded article 1.

The opening width of the clearance 40 is set smaller than the diameter of the pre-expanded beads. At the time of filling of the pre-expanded beads, only the filling inorganic gas supplied to the molding space 13 together with the pre-expanded beads passes. The pre-expanded beads are configured to remain in the molding space 13. However, the clearance 40 is the core mold 11 and the cavity mold 1
2 may be formed over the entire circumference, or may be locally provided only at necessary portions. As shown in FIG. 7, the clearance 40 is divided into a plurality (two in the example in the figure) by the partition walls 42, and inter-mold cavities 41 are provided corresponding to the plurality of clearances 40. The air for filling and other working fluids may be individually controlled with respect to 41.

In order to improve the filling property at the difficult filling portion at the back of the partition wall forming portion 13b, a through hole 43 is formed at the back of the partition wall forming portion 13b, and the exhaust pipe connected to the through hole 43 is formed. 44 is a drain valve DV4 and a switching valve SWV3,
They are connected to a drain pipe 27 and a decompression pipe 28 via SWV4. In this case, the internal space 45 of the exhaust pipe 44 functions as a third chamber, and the partition wall forming section 1
The filling air that has flowed into the inner part of 3b is configured to be discharged through the through hole 43 and the exhaust pipe 44. still,
As with the clearance 40, the through hole 43 may be connected to only the drain pipe 27 if only the filling property is to be improved.
It may be connected to another pipe such as the pressure reducing pipe 28 or the like to control the working fluid more finely.

The through-hole 43 can be formed in an arbitrary shape such as a round hole or a slit. In any case, the pre-foamed beads pass through the through-hole 43 and pass through the exhaust pipe 4.
The opening width is formed so as not to flow into the fourth side.
Also, in the remote part and other parts separated from the filling device 31, when it is difficult to fill the pre-expanded beads, a through hole is formed as in the inner part of the partition wall forming part 13 b and connected to the exhaust pipe. It can be configured to discharge the filling air.

A second feature of the present invention is that the temperature of the pre-expanded beads to be supplied to the molding space 13 is adjusted to a predetermined set temperature, and the compression filling pressure (the molding space at the time of compression filling) is adjusted accordingly. (Internal pressure). Specifically, the raw material beads are heated to the set temperature in the bead temperature adjusting tank 38 and supplied to the raw material tank 29 via the raw material supply valve V4. Here, a heating means 39 for heating the pre-expanded beads is provided in the bead temperature regulating tank 38, and a temperature sensor 37a is provided. The heating temperature of the heating means 39 is controlled based on a signal from the temperature sensor 37a. Then, the temperature of the pre-expanded beads is adjusted to the set temperature. However, the inner wall of the bead temperature control tank 38 is formed of a heat insulating material, or the outer wall is formed of a heat insulating material, so that the heat retention of the bead temperature control tank 38 is increased and the ambient temperature in the bead temperature control tank 38 becomes uniform. As described above, it is preferable to use a hot air blower as the heating means 39 and control the temperature while stirring the beads. Further, in order to more precisely adjust the temperature of the pre-expanded beads, a plurality of temperature sensors 37a may be provided, and the average temperature thereof may be used as the temperature of the pre-expanded beads. It is preferable that the piping for transporting the pre-expanded beads from the bead temperature adjusting tank 38 to the raw material tank 29 is kept warm, and the temperature of the air for transporting the raw material is also adjusted in advance. The raw material tank 29 is provided with a temperature control means 36 and a temperature sensor 37b for measuring the ambient temperature in the raw material tank 29, and the temperature setting of the bead temperature control tank 38 is changed based on a signal from the temperature sensor 37b. Alternatively, by controlling the temperature of the temperature control means 36, the temperature of the pre-expanded beads before filling can be made constant.

As the heating means 39, a heating means having an arbitrary structure can be adopted. However, since heating steam is used at the time of molding,
It is preferable in terms of equipment economy to provide a heating means using heated steam. In addition, an electric heater or the like may be used as a heating unit, and a heating unit using heating steam and a heating unit such as an electric heater may be used in combination. As the temperature control means 36, the temperature of the cooling water is controlled at 30 to 50 ° C. in the molding factory, so that the temperature control using the cooling water is preferable in terms of equipment economy. The heating temperature of the pre-expanded beads can be set to any temperature not lower than the normal temperature and not higher than the melting point. However, considering the deterioration of the beads in a high temperature range, the temperature control in summer in a low temperature range, and the energy saving in winter, 30 ° C. to 80 ° C. 30 ° C. to 50 ° C. in consideration of the control accuracy of the compression filling pressure in the low compression pressure range or the high compression pressure range of the molding machine and the bead compression characteristics.
It is preferable to set to ° C. Further, in order to stabilize the mechanical strength and weight of the molded article, it is preferable to adjust the temperature of the pre-expanded beads within the range of the set temperature ± 5 ° C.

The compression filling pressure of the pre-expanded beads is as follows:
For example, the following test is performed to set in advance. First, a description will be given of a test performed to determine an optimum compression filling pressure for the set temperature. As a molded product, using polypropylene pre-expanded beads, the outer dimensions are 1158.6 mm in length, 144.3 mm in width, and 11 in thickness.
A 4.3 mm automobile bumper core was manufactured as follows.

First, a plurality of types of pre-expanded beads having different bulk densities were used, and the pre-expanded beads were compression-filled into a molding space at a compression-filling pressure of 4.0 kg / cm ² while being maintained at a set temperature of 24 ° C.
Thereafter, the pre-expanded beads were heat-sealed with steam to produce a plurality of types of molded articles having different bead bulk densities of the pre-expanded beads. Also, only the compression filling pressure is changed, and
Molded products were set in the same manner when they were set to 5 kg / cm ² and 3.0 kg / cm ² , respectively. Then, the relationship between the bead bulk density of the pre-expanded beads and the weight of the molded article after drying at each compression filling pressure was obtained, and the results shown in FIG. 8 were obtained.

Next, a plurality of types of pre-expanded beads having different bulk densities are used, and the pre-expanded beads are compression-filled into the molding space at a compression-fill pressure of 3.5 kg / cm ² while maintaining the set temperature of 40 ° C.
Thereafter, the pre-expanded beads were heat-sealed with steam to produce a plurality of types of molded articles having different bead bulk densities of the pre-expanded beads. Also, only the compression filling pressure is changed, and
Molded articles at 0 kg / cm ² , 2.5 kg / cm ² , and 2.0 kg / cm ² were produced in the same manner. Then, the relationship between the bead bulk density of the pre-expanded beads and the weight of the molded product after drying at each compression filling pressure was obtained, and the results shown in FIG. 9 were obtained.

Next, a plurality of types of pre-expanded beads having different bulk densities were used, and the pre-expanded beads were compression-filled into the molding space at a compression-fill pressure of 3.0 kg / cm ² while maintaining the set temperature of 55 ° C.
Thereafter, the pre-expanded beads were heat-sealed with steam to produce a plurality of types of molded articles having different bead bulk densities of the pre-expanded beads. Also, only the compression filling pressure is changed, and
5 kg / cm ² , 2.0 kg / cm ² , 1.5 kg / cm ² , 1.0 kg / cm ²
The molded products in the cases where the above-mentioned settings were made were manufactured in the same manner. Then, the relationship between the bead bulk density of the pre-expanded beads and the weight of the molded product after drying at each compression filling pressure was obtained, and the results shown in FIG. 10 were obtained.

The most preferable molding conditions in the present invention are as follows:
Even if the bulk density of the pre-expanded beads fluctuates due to classification in the process of transferring the pre-expanded beads from the silo to the molding space, it is necessary to obtain molding conditions such that the weight of the molded article becomes uniform. As can be seen from the test results shown in FIG.
When the temperature of the pre-expanded beads was set to 24 ° C., the compression filling pressure was set to 3.5 kg / cm ² , and when the temperature of the pre-expanded beads was set to 40 ° C., the compression filling pressure was set to ² kg / cm 2. when set to .0kg / cm ^2, further in the case of setting the pre-expanded beads temperature 55 ° C., the compressive filling pressure when set at 1.0 kg / cm ^2, the diagram becomes approximately horizontally respectively Thus, it can be seen that even if the bulk density of the pre-expanded beads changes, the weight of the molded article hardly changes.

That is, by setting the compression filling pressure in accordance with the temperature of the pre-expanded beads to be filled in the molding space, the molded article is kept in such a manner that the weight of the molded article does not change even if the bulk density of the pre-expanded beads changes. You can see that it can be manufactured. In addition, since it is easier to control the temperature of the pre-expanded beads than adjusting the compression filling pressure, the temperature of the pre-expanded beads to be filled in the molding space is adjusted to a preset temperature, The compression filling pressure is preferably fixed at a compression filling pressure corresponding to the set temperature.

The set temperature is set so that the energy consumption for temperature adjustment is reduced and the running cost is reduced.
It is preferable to set the temperature within the range of 30 to 50 ° C. In addition, since it is difficult to directly measure the temperature of the pre-expanded beads, a temperature sensor is attached to a raw material tank or the like which is filled with the pre-expanded beads, and the measurement is performed.
If the temperature difference between the measurement temperature and the actual temperature increases, the weight of the molded article greatly varies depending on the bulk density of the pre-expanded beads. Therefore, it is preferable to set the measurement temperature within the set temperature ± 5 ° C.

The compression filling pressure is set to a pressure adapted to the set temperature. Specifically, the pressure is set to be larger than the atmospheric pressure and equal to or less than the value obtained by the equation of {(70-set temperature [° C.]) / 10} kg / cm ² as can be seen from FIGS. . More preferably, 0.5 kg / cm ² or more,
The value is set to be equal to or less than the value obtained by the formula of {(70−set temperature [° C.]) / 10} kg / cm ² .

Next, a verification test performed to verify the test results will be described. In order to produce a molded article of the same size as the above-mentioned molded article, a plurality of types of polypropylene pre-expanded beads having a bulk density of 59 to 64 g / L were used, and these were kept at a set temperature of 40 ° C. .5 kg
The molding space was compression-filled at a compression-filling pressure of / cm ² , and then the prefoamed beads were heat-sealed with steam to produce 100 molded products having different bead bulk densities. Then, the relationship between the bead bulk density of the pre-expanded beads of these molded articles and the molded article weight was obtained, and the results shown in FIG. 11 were obtained.

Next, in order to produce a molded article having the same size as the above-mentioned molded article, a plurality of types of polypropylene pre-expanded beads having a bulk density in the range of 51 to 58 g / L were used, and this was set at a set temperature of 40 ° C. While keeping the pressure at 2.0 kg / cm ² , the pre-expanded beads are heat-sealed with steam to form beads having different bulk densities.
00 molded articles were produced. Then, the relationship between the bead bulk density of the pre-expanded beads of these molded products and the molded product weight was obtained, and the results shown in FIG. 12 were obtained.

As shown in FIGS. 11 and 12, by appropriately setting the relationship between the temperature of the pre-expanded beads to be filled in the molding space and the compression filling pressure, the weight of the molded article can be reduced by the bulk density of the pre-expanded beads. Is slightly increasing in response to
There is no large increase, and the variation in the weight of the molded article is small, and it can be seen that the test results are suitable even in mass production.

The compression ratio of the pre-expanded beads obtained by dividing the density of the molded product by the bulk density of the pre-expanded beads under the temperature condition of the pre-expanded beads before the start of the compression filling is 1.2 to 1.
5, preferably set to a compression filling pressure of 1.25 to 1.45. In other words, when the compression ratio is less than 1.2, the pre-expanded beads do not sufficiently expand, and the molded article largely shrinks after release from the mold, or a gap is formed between the beads, and a good product is obtained. There is no problem. On the other hand, if the compression ratio exceeds 1.5, the space between the bead particles in the molding space after filling becomes very narrow, and the heating steam does not pass between the bead particles, resulting in poor fusion, Since there is a problem that excessive foaming occurs only in the passed portion, cracks are generated in the molded product, and the cooling time is prolonged, it is necessary to set the compression filling pressure so that the compression ratio is 1.2 to 1.5. preferable.

Next, an example of a method for filling pre-expanded beads using the in-mold foam molding apparatus 10 will be described. First, the pre-expanded beads are filled in a composition tank (not shown), and 0.3 to 2.0 kg / cm ^{2 of} an inorganic gas is pressed into the pre-expanded beads. In other words, the pre-expanded beads used in the present invention are made of a polyolefin-based resin, and generally have a lower foaming power than a polystyrene-based resin. It is conceivable that the quality of the molded product is deteriorated, for example, the adhesion is reduced, the gap between the beads is increased, and the appearance is reduced. For this reason, it is preferable to inject an inorganic gas into the pre-foamed beads in advance to increase the foaming power. However, this composition step may be used depending on the raw materials used, but is generally omitted.

The pre-expanded beads thus obtained are supplied to a bead temperature adjusting tank 38, and the inside of the bead temperature adjusting tank 38 is heated by a heating means 39 while measuring the temperature of the pre-expanded beads in the bead temperature adjusting tank 38. After the temperature of the pre-expanded beads is adjusted to a predetermined set temperature of 30 to 50 ° C., the pre-expanded beads are supplied to the kept raw material tank 29.

Next, after closing the core mold 11 and the cavity mold 12, the chamber 1 is adjusted so that the inside of the molding space 13 is adjusted to the compression filling pressure adapted to the set temperature of the pre-expanded beads.
7, 18 and the cavity 41 between the molds and the space 45 in the tube are pressurized to a preset compression filling pressure.
Is set slightly lower than the pressure in the molding space 13. As described above, the temperature of the pre-expanded beads during compression filling is set to the set temperature, and the compression filling pressure is set to a pressure adapted to this set temperature. Even if there is a variation, it is possible to produce a molded article having a uniform weight.

Next, the filler of the filling device 31 and the shutter 3
2. Open the filling air valve V2 and the adjusting air valve V3 to start filling the pre-foamed beads. The filling air pressure in the filling air valve V2 is at least 2 kg higher than the internal pressure of the raw material tank 29.
/ Cm ² or more, and set to an absolute value of 4 kg / cm ² or more.

During the filling, the pre-expanded beads flow into the molding space 13 while being diluted with the compressed air in the raw material tank 29, the compressed air from the regulating air valve V3, and the compressed air from the filling air valve V2. . At this time, the molding space 13
The volume ratio of the air flowing into the pre-expanded beads to the pre-expanded beads is defined as a value obtained by dividing the volume of the air supplied to the molding space 13 by the volume of the pre-expanded beads as the final dilution degree.
The final dilution degree is set to be 5 or more, preferably 10 to 50.

If the final dilution degree of the pre-expanded beads is larger than 50, the amount of the pre-expanded beads to be filled per unit time decreases, so that it takes time to fill, the molding cycle time increases, and the air consumption increases. There is a problem that the amount increases. If the final dilution degree is smaller than 10, the number of times of contact or collision between the pre-expanded beads in the filling tube 33, the filling device 31, or the molding space 13 increases, so that the resistance that hinders the filling of the pre-expanded beads increases. In addition, since the pre-expanded beads obstruct the flow of air, there is a problem that the filling cannot be performed satisfactorily. However, when the pre-expanded beads are supplied by a feeding means such as a screw conveyor, the rotational speed of the screw conveyor is controlled so that the final dilution degree becomes a desired value, and the unit of the pre-expanded beads with respect to the molding space 13 is controlled. The supply amount per hour will be set.

Thus, the compressed air that has flowed into the molding space 13 passes through the vent hole 22, the clearance 40, and the through hole 43, and increases the pressure in the chambers 17, 18, the mold cavity 41, and the tube space 45. At this time, chambers 17 and 1
8 and the pressure in the inter-cavity 41 and the space 45 in the pipe
By controlling individually or in combination with any one of V1 to DV4, the pre-expanded beads are first filled into the portion where the pre-expanded beads are difficult to be filled, and the density variation in each part of the molded article 1 is controlled. And the packing density can be properly secured.

For example, the drain valves DV1 to DV4 are sequentially opened when the internal pressures of the chambers 17 and 18, the mold cavity 41 and the pipe space 45 become equal to or higher than a set pressure. Chamber 18> First chamber 1
If 7> inter-cavity section 41> pipe space 45, first, the drain valve DV4 is opened to fill the difficult-to-fill portion 40 with the pre-expanded beads. When completed, the chambers 17 and 18 and the mold cavity 4
When the internal pressure of 1 increases, the drain valve DV3 is opened,
The outer edge of the molding space 13 is filled with pre-expanded beads.
In this way, the drain valves are opened in order from the one with the smaller set pressure, and the pre-expanded beads are filled in the molding space 13.

As another control method, the filling step is divided into four steps. In the first step, the air pressure in the pipe space 45 is controlled using only the drain valve DV4, and in the second step, the drain valve is controlled. The air pressure in the cavity 41 between the molds and the space 45 in the pipe is controlled by using DV3 and DV4.
V1, DV3, and DV4 are used to control the air pressure in the first chamber 17, the mold cavity 41, and the in-pipe space 45. In the fourth step, the exhaust valves DV1 to DV4 are used to control the chamber 17,
The prefoamed beads are sequentially filled into the molding space 13 while controlling the air pressure in the cavity 18, the inter-cavity 41, and the in-tube space 45.

Thus, after filling the pre-expanded beads,
The filler of the filling device 31 is closed and the adjusting air valve V3 is closed, and the pre-expanded beads remaining in the filling device 31 and the filling tube 33 are returned to the raw material tank 29 using the filling air.
Thereafter, the charging cycle is completed by closing the charging air valve V2 and the shutter 32, and a series of normal molding steps of heating, cooling, and release are sequentially performed to obtain a predetermined molded product 1.

Since the clearance 40 and the inter-cavity 41 are formed in the in-mold foam molding apparatus 10, the working fluid in the clearance 40 and the inter-cavity 41 is effectively utilized. Heating, cooling, and release can be performed while controlling as follows.

That is, in the heating step, the inter-cavity 41
In addition, steam is introduced into the clearance 40 to heat the peripheral portion of the clearance 40, and at the same time, is sent into the molding space 13 to compensate for the heating of the pre-expanded beads at the outer peripheral end portion 13a of the molding space 13. .

In this case, since the flange portions 11a and 12a constituting the outer peripheral portions of both the molding dies 11 and 12 which are relatively large in the heat capacity and the temperature is hardly increased in the prior art are directly heated, the outer peripheral end portion is heated. Since the temperature of the pre-expanded beads in the portion 13a can be rapidly increased, the advantage that the total molding time can be reduced is obtained.

In addition, since the air purge of the outer peripheral end portion 13a by the steam is ensured or the pressure regulation operation can be performed independently through the clearance 40, the steam pressure is controlled to be plus or minus with respect to the chamber pressure. The temperature balance in the molds 11 and 13 can be set to the most preferable state, and significant cycle time reduction or energy saving effect can be expected.

In the cooling step, in addition to injecting cooling water, the inside of the molding space 13 is depressurized through the clearance 40 to promote cooling by vaporization of water that has entered the molding space 13 due to the injection of water, and discharges drainage. Perform the operation. Also in this case, the flange portions 11a, 12 of the molds 11, 12, which have a large heat capacity and are difficult to lower the temperature.
Since the temperature reduction of a can be promoted, the cycle time can be greatly reduced.

In the releasing step, the clearance 4
0. An operation of discharging the drain accumulated in the mold cavity 41 is performed. As a result, it is possible to remove the drain accumulated in the clearance 40 and the inter-mold cavity 41 caused by the water injection at the time of cooling, so that even if the mold is opened for releasing the mold, it is possible to solve the problem that the work place is in a wet state. .

In the above description, the case where the partition wall forming portion 13b is provided on the core mold 11 has been described. However, when the partition wall forming portion 13b is provided on the cavity mold 12 side, By adopting a method in which the chambers 17 and 18 in the above description are read in reverse, completely the same operation and effect can be obtained.

The molded article 1 molded in this manner has a partition wall 4 having a thickness of, for example, 20 mm or less, preferably 3 to 15 mm.
Conventionally, it is considered that it is difficult to fill, such as one having a small thickness of 5 mm, more preferably 5 to 10 mm, or one having three or less beads arranged in the thickness direction of the partition wall 4 of the molded article 1. Even if it is the molded article 1 as described above, the density at each part is set to within ± 5% of the average density, preferably within ± 4%, more preferably within ± 3%. A good molded product 1 is obtained. Further, since the temperature of the pre-expanded beads is kept at the set temperature and the compression filling pressure is kept at a pressure adapted to the set temperature, molding is performed. What is 10% in the conventional molding method can be adjusted to 3% or less, the weight variation of the molded product between each molding shot is small, and the molded product has good molded product quality and yield.

The present invention is effective when molding a package having a relatively large and complicated shape, for example, more than the small and simple shaped product 1 such as a cup noodle container. Things. In particular, it is useful for a collective package having both a thick portion and a thin portion. In addition, since the variation in weight between molding shots is reduced, it can be suitably used for molded products having severe restrictions on mechanical strength and weight, such as a core material of an automobile bumper.

Next, a description will be given of a quality evaluation test of the molded article 1 formed by filling the pre-expanded beads by this filling method. In manufacturing the molded article 1 having the shape as shown in FIGS. 1 and 2, as a method of filling the pre-expanded beads, a case where the pre-expanded beads are filled by the cracking filling method, the pressure filling method, the compression filling method, and In the four filling methods when pre-expanded beads are filled by the filling method of the present invention,
The pre-expanded beads were filled to produce four types of molded articles.
Then, as shown in FIG. 2, the densities of the partition wall 4 of the molded article 1 at the distal end 4a, the middle part 4b, and the proximal end 4c were measured, and the results shown in Table 1 were obtained. In addition, the molding method of the present invention and the conventional compression filling method each perform molding 100 times, measure the molded product weight of each molded shot, and calculate the average weight, the maximum and minimum weight, and the maximum weight difference. And the weight variation 3σ of the molded product was obtained, and the results shown in Table 2 were obtained.

[0102]

[Table 1]

As shown in Table 1, in the molded article manufactured by filling the pre-expanded beads by the conventional filling method, the partition wall 4
The density decreases from the base end portion 4a to the tip end portion 4c side, whereas the molded article manufactured by filling the pre-expanded beads by the filling method of the present invention has a substantially uniform density. It turns out that there is. In other words, it can be seen that the filling method of the present invention can produce a high-quality molded product with little variation in density. Further, in the conventional molded product, it is necessary to design the molded product based on the low-density portion so that sufficient strength can be obtained even in the low-density portion, and there is a problem that the molded product becomes heavy. In the molded article of the present invention, since the density in each part of the molded article is substantially uniform, the molded article can be configured to be lightweight while securing sufficient strength of the molded article, and the use amount of the pre-expanded beads is reduced. As a result, the production cost of the molded product can be reduced.

[0104]

[Table 2]

As shown in Table 2, when the pre-expanded beads were filled and molded by the filling method of the present invention, the weight variation of the molded product between the molding shots was larger than that by the conventional compression filling method. Is small, and it can be seen that it is accurately molded to a desired weight.

Next, an evaluation test of a molding cycle will be described. As a compression-molded product, it has a shape as shown in FIGS. 1 and 2 and has an outer dimension of 450 mm in length, 300 mm in width and 180 in height.
mm box shape, 5 vertical ribs 8 mm thick, 8 m thick
In manufacturing a molded product with one horizontal rib having a bulk density of 20 g / m as pre-expanded beads as an example of the present invention.
L using polypropylene beads of L, the molded articles of Examples 1 to 3 in which the bulk density of the molded article was set to 28 g / L, 26 g / L, and 24 g / L;
Using the g / L polyethylene beads, molded articles of Examples 4 to 6 were manufactured in which the bulk density of the molded article was set to 33 g / L, 30 g / L, and 29 g / L.

As a comparative example, polypropylene beads having a bulk density of 20 g / L were used as the pre-expanded beads, and the bulk densities of the molded articles were 30 g / L, 28 g / L, and 26 g.
/ L and polyethylene beads having a bulk density of 25 g / L as pre-expanded beads, and the bulk density of the molded product is 40 g / L, 38 g / L, 35 g / L.
The molded products of Conventional Examples 4 to 6 set to g / L were produced. Tables 3 and 4 were obtained by measuring the molding cycles and molded article quality of Examples 1 to 6 and Comparative Examples 1 to 6. However, Tables 3 and 4
In the quality of the molded product, the state of adhesion between the beads was evaluated in three steps, and the quality of the molded product was evaluated as "good" if the product was sufficiently adhered to the product. It is indicated by “△”, and those that do not withstand use at all are indicated by “×”.
Displayed with.

[0108]

[Table 3]

[0109]

[Table 4]

As shown in Tables 3 and 4, in the conventional molding method, when polypropylene beads were used as the pre-expanded beads, the molded article had a bulk density of 30 as in Comparative Example 1.
g / L (compression ratio of 1.5) or more, a high-quality molded product cannot be obtained, and when polyethylene beads are used, the bulk density of the molded product is 40 g as in Comparative Example 4.
Unless the ratio is set to / L (compression ratio 1.6) or more, a high quality molded product cannot be obtained. On the other hand, in the molding method of the present invention, when polypropylene beads are used as the pre-expanded beads, the bulk density of the molded article is 2 as in Example 2.
6 g / L (Even when the compression ratio is set to 1.3, a molded product of sufficient quality can be obtained. When polyethylene beads are used, the molded product has a bulk density of 30 g / L as in Example 5.
Even when L (compression ratio 1.2) or more is set, a high quality molded product can be obtained. In addition, the molding cycle becomes longer as the compression ratio obtained by dividing the bulk density of the molded product by the bulk density of the pre-expanded beads increases, and in Comparative Examples 1 and 4 in which molded products of sufficient quality are obtained, 180 sec, 210
sec in the second and third embodiments.
c, 120 sec, which indicates that the molding method of the present invention can significantly shorten the molding cycle while ensuring sufficient quality as compared with the conventional molding method.

In this embodiment, the internal pressures of the chambers 17 and 18, the mold cavity 41 and the pipe space 45 are adjusted so that the density of each part of the molded article 1 becomes uniform. It is also possible to increase the packing density of the pre-expanded beads in the portion where it is desired to increase the density. In addition, the present invention can of course be applied to a case where a molded article having various shapes other than the molded article 1 is molded.

[0112]

According to the method for in-mold foam molding of a polyolefin resin according to the first aspect, the pre-expanded beads whose temperature has been adjusted to a set temperature of 30 to 50 ° C. are subjected to a pressure applied to the set temperature and a large value. Since the pressure of the pre-expanded beads is larger than the atmospheric pressure and is compressed and filled into the molding space at a compression filling pressure of not more than a value obtained by the formula of {(70−set temperature [° C.]) / 10} kg / cm ² , Even if it fluctuates due to classification during the transfer of the pre-expanded beads between molding shots, a molded article having a uniform weight can be manufactured without being affected by the fluctuation, so that the quality stability of the molded article can be remarkably improved. In addition, since the temperature of the pre-expanded beads is set within the range of the set temperature ± 5 ° C, the temperature can be adjusted relatively easily, and the variation in the bulk density of the molded product between molding shots can be reduced to the quality of the molded product. This is preferable because it can be reduced to such an extent that no adverse effects are caused. Furthermore, since the material itself is soft and the gas permeability is high, the pre-expanded beads made of polyolefin resin are much easier to deform the particle shape than the pre-expanded beads made of polystyrene resin of the same expansion ratio, This is preferable because the properties can be further improved.

As described in claim 2, the compression ratio of the pre-expanded beads obtained by dividing the density of the molded article by the bulk density of the pre-expanded beads under the temperature condition of the pre-expanded beads before starting the compression filling is 1.2. When set to a compression filling pressure of ~ 1.5,
The productivity can be improved by shortening the molding cycle time, and a high-quality molded product in which beads are properly adhered to each other can be molded. Further, since the bulk density of the molded article and the bulk density of the pre-expanded beads are close to each other, it is possible to increase the transport efficiency and the storage efficiency of the pre-expanded beads.

The pre-expanded beads are made of a polyolefin resin and have a cell diameter of 100.
９００900 μm, expansion ratio 5 to 60 times, DSC 2'nd
When pre-expanded beads made of a polyolefin resin having a peak ratio of 8 to 60% and a closed cell ratio of 65% or more are used,
The surface property of the molded article can be improved, the appearance of the appearance can be improved, and the restriction on the heating conditions at the time of molding can be relaxed, and the moldability and energy saving can be improved.

According to the in-mold foam molding method for a polyolefin resin according to the fourth aspect, the inorganic gas pressure in the three chambers is controlled individually or in any combination, and the compressed pre-expanded beads are subjected to the flow of the inorganic gas. To fill the molding space, for example, by controlling the inorganic gas pressure of each chamber so that the pre-foamed beads are filled first in the difficult-to-fill portion that is difficult to be filled with the pre-foamed beads,
The filling density in each part of the molded article can be set uniformly. For this reason, it is difficult to fill the pre-expanded beads, and the thickness is 20 mm.
Even in a molded product having a thin partition wall as described below, the packing density in each part of the molded product can be set to an appropriate value without increasing the number of fillers. Further, if the pre-expanded beads are filled in a portion where the strength and rigidity are to be increased first, the filling density in the portion can be locally increased to increase the strength.

According to a fifth aspect of the present invention, when the third chamber is provided with a chamber communicating with the molding space via a clearance between the core mold and the cavity mold, the charge flowing into the outer peripheral portion of the molding space via the clearance is provided. Can be efficiently discharged to the outside, for example, when manufacturing a container with a deep bottom, etc., by configuring so that a clearance is formed at a position corresponding to the opening edge of the container, the number of filling devices The filling density of the pre-expanded beads can be appropriately set without increasing the number of the beads, and the quality of the container can be improved.

As described in claim 6, if the third chamber is provided with a chamber communicating with the inner part of the partition wall forming portion, it is conventionally considered difficult to form the molding because a sufficient filling density cannot be ensured. Even if the molded article has a complicated shape such as having a partition wall having a thickness of 20 mm or less, the filling density of the pre-expanded beads in the partition wall forming section is increased by first filling the pre-expanded beads in the partition wall forming section. Thus, it is possible to produce a high-quality molded product having an appropriate density.

As described in claim 7, when the third chamber is provided with a chamber that communicates with the deep part of the remote part of the molding space remote from the pre-expanded bead filler, the packing density of the pre-expanded beads is reduced. It is possible to sufficiently secure the packing density of the remote portion which is easy to perform, and it is possible to manufacture a high quality molded product.

When the partition wall forming portion having the structure as described in claim 8 is formed, the height H (mm) and the thickness T (mm) are H
It is possible to mold a molded article having a partition wall that satisfies the relational expression of / T ≧ 10. Conventionally, it has been considered that such a molded portion is difficult to mold because the filling density of the pre-expanded beads in the partition wall molded portion cannot be sufficiently ensured, but the molding according to any one of claims 1 to 7. By molding by a method, particularly a molding method according to claim 6, high quality molding can be achieved.

As the pre-expanded beads, any material may be used as long as it is made of a polyolefin resin. However, since it is inexpensive and easily available, it is possible to use a polypropylene resin or a polypropylene resin. , Claim 10
As described above, it is preferable to employ a resin made of a polyethylene resin.

According to the molding method, a molded product having a thin and high partition wall can be molded. However, when a draft is formed in a partition wall molding portion, such a molded product can be formed. This is preferable because breakage at the time of release can be prevented.

According to the collective package according to the twelfth aspect, since the internal space is defined by the partition walls in the thin wall, the space for storing the articles in the collective package can be set as large as possible. As a result, the efficiency of storing and transporting the articles can be improved. In addition, a collective package having such a thin partition wall has conventionally been considered to be difficult to form, but the partition wall is formed by the molding method according to any one of claims 1 to 11. By appropriately setting the packing density of the beads in the above, a collective package having a uniform density can be realized as a whole.

As described in claim 13, the height is H (m
m), and when the thickness is T (mm), it is preferable to provide a partition wall that satisfies the relational expression of H / T ≧ 10 because articles of various sizes can be stably stored. The partition wall satisfying such a relational expression is thin and has a high height, so that the packing density of the beads cannot be sufficiently ensured, so that it is difficult to form the partition wall. By using the molding method described in (1), the packing density of the beads in the partition wall is appropriately set, and a collective package having a uniform density as a whole can be realized.

As the material of the beads constituting the collective package, any material can be adopted as long as it is a polyolefin resin. However, since it is inexpensive and easily available, it is possible to use a polypropylene resin, It is preferable to adopt the one made of polyethylene resin as described in claim 15.

[0125] When a draft is formed in the partition wall, it is easy to put articles into and out of the storage space. Further, at the time of molding the collective package, the release from the molding die becomes smooth, and damage to the collective package at the time of release can be prevented.

[Brief description of the drawings]

FIG. 1 is a perspective view of a molded product.

FIG. 2 is a longitudinal sectional view of a molded product.

FIG. 3 is a longitudinal sectional view of an in-mold foam molding apparatus.

FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is a longitudinal sectional view showing the vicinity of an air hole.

FIG. 6 is a front view of a core vent.

FIG. 7 is a view corresponding to FIG. 4 of an in-mold foam molding apparatus having another configuration.

FIG. 8 is a diagram showing the relationship between the bulk density of pre-expanded beads and the weight of a molded product.

FIG. 9 is a diagram showing the relationship between the bulk density of pre-expanded beads and the weight of a molded product.

FIG. 10 is a diagram showing the relationship between the bulk density of pre-expanded beads and the weight of a molded product.

FIG. 11 is a diagram showing the relationship between the bulk density of pre-expanded beads and the weight of a molded product.

FIG. 12 is a diagram showing the relationship between the bulk density of pre-expanded beads and the weight of a molded product.

FIG. 13 is a longitudinal sectional view of an in-mold foam molding apparatus according to a conventional technique.

FIG. 14 is a longitudinal sectional view of an in-mold foam molding apparatus having another configuration according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molded product 2 Main part 3 Housing space 4 Partition wall 4a Tip part 4b Midway part 4c Base end part 10 In-mold foam molding apparatus 11 Core mold 12 Cavity mold 11a, 12a Flange part 13 Molding space 13a Peripheral tip part 13b Partition wall molding Part 14 Frame-shaped frame 15 Back plate 16 Housing 17 First chamber 18 Second chamber 20 Core vent 21 Core vent hole 22 Vent hole 23 Mounting hole 22a Through hole 22b Long hole SV1 to SV3 Utility valve SWV1 to SWV4 Switching valve DV1 to DV4 Drain valve V1 Intake valve V2 Filling air valve V3 Regulating air valve 25 Steam supply pipe 26 Air supply pipe 27 Drain pipe P Vacuum pump 28 Decompression pipe 29 Raw material tank 30 Intake pipe 31 Filler 32 Shutter 33 Filling pipe 34 Filling air supply pipe 35 Adjustment air supply pipe 36 Temperature control means 37a Degree sensor 37b temperature sensor 38 between the beads temperature control tank 39 heating means 40 clearance 41 type hollow portion 42 partition wall 43 through holes 44 exhaust pipe 45 pipe space

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 23:04 B29C 67/22 23:10 B65D 81/06 101A F-term (Reference) 3E066 AA01 BA01 CA01 DA01 KA20 LA16 MA01 4F074 AA16 CC03Y CC04Y CC07Y CC24Y CC32Y CC34Y CC46 CC47 CC62 CC63 DA02 DA33 4F212 AA03 AA11 AG20 AH56 AH81 AR02 AR06 UA01 UA02 UB01 UE06 UE26 UF31 UF34

Claims (16)

[Claims] 1. Pre-expanded beads made of a polyolefin resin are temperature-controlled to a constant temperature of ± 5 ° C. around a set temperature in a range of 30 to 50 ° C., and a compression filling pressure is adjusted to the set temperature. Pressure, which is greater than the atmospheric pressure, {(70-set temperature [° C.]) / 10} kg / cm ²
In a state set to a constant pressure equal to or less than the value obtained by the formula, the molded product is compression-filled into a mold having a partition wall forming portion for forming a partition wall having a thickness of 20 mm or less, and then steam-filled. An in-mold foam molding method for a polyolefin-based resin which is heated and fused, then cooled and taken out of the mold. 2. The compression ratio of the pre-expanded beads obtained by dividing the density of the molded article by the bulk density of the pre-expanded beads under the temperature condition of the pre-expanded beads before the start of the compression filling is 1.2 to 1.5. The method of claim 1, wherein the pressure is set at a compression filling pressure. 3. The pre-expanded beads are made of a polyolefin resin, have a cell diameter of 100 to 900 μm, an expansion ratio of 5 to 60 times, and a DSC 2′nd peak ratio of 8 to 6.
The in-mold foam molding method for a polyolefin resin according to claim 1 or 2, wherein pre-expanded beads made of a polyolefin resin having 0% and a closed cell ratio of 65% or more are used. 4. A molding space having a partition wall forming portion for forming a partition wall having a thickness of 20 mm or less for a molded product,
At least three chambers for controlling a working fluid in the molding space, a first chamber on the core mold rear side communicating with the molding space, and a second chamber on the cavity mold rear side communicating with the molding space; A pre-expanded bead is adjusted to the set temperature and adapted to the set temperature by using an in-mold foam molding apparatus having a third chamber communicating with a difficult-to-fill portion of the molding space where the pre-expanded beads are difficult to be filled. The pre-expanded beads are compression-filled into the molding space while controlling the inorganic gas pressure of each chamber individually or in any combination in a state where the gas is compressed by the inorganic gas to the compression filling pressure. An in-mold foam molding method for the polyolefin resin according to any one of the preceding claims. 5. The method for in-mold foam molding of a polyolefin resin according to claim 4, wherein the third chamber includes one or more chambers that communicate with a molding space via a clearance between a core mold and a cavity mold. 6. A third chamber comprising one or more chambers communicating with the interior of the partition wall forming section, wherein the pre-expanded beads are first filled into the partition wall forming section when the pre-expanded beads are filled. 6. The method for in-mold foam molding of a polyolefin resin according to claim 4, wherein the pressure of the inorganic gas in the three chambers is controlled so that the pressure is controlled. 7. The method according to claim 1, wherein the third chamber includes one or more chambers communicating with a deep portion of a remote portion of the molding space remote from the pre-expanded bead filling device. The in-mold foam molding method for a polyolefin resin according to any one of claims 4 to 6, wherein the pressure of the inorganic gas is controlled so that the pre-foamed beads are filled first. 8. The height of the formed partition wall is H (mm),
The in-mold foaming of the polyolefin-based resin according to any one of claims 1 to 7, further comprising a partition wall forming portion that satisfies a relational expression of H / T ≧ 10 when the thickness is T (mm). Molding method. 9. The method for in-mold foam molding of a polyolefin resin according to claim 1, wherein the pre-expanded beads are made of a polypropylene resin. 10. The method according to claim 1, wherein the pre-expanded beads are made of a polyethylene resin. 11. The method for in-mold foam molding of a polyolefin resin according to claim 1, wherein a draft is formed in the partition wall molding portion. 12. Formed using pre-expanded beads made of a polyolefin resin, and divided into a plurality of storage spaces through a partition wall having a thickness of 20 mm or less in order to separately store a plurality of articles. Collective package. 13. A partition wall having a relational expression of H / T ≧ 10 when the height of the partition wall is H (mm) and the thickness is T (mm). Collective package. 14. The collective package according to claim 12, wherein the pre-expanded beads are made of a polypropylene resin. 15. The collective package according to claim 12, wherein the pre-expanded beads are made of a polyethylene resin. 16. The collective package according to claim 12, wherein a draft is formed in said partition wall.