JPS62151325A - In-mold molding methof for polypropylene series resin foamed particle - Google Patents

Abstract

PURPOSE:To obtained a foamed molded material having uniform density distribution, by a method wherein the inside of a mold, whose pressure has been made into predetermine pressure by gas pressure, is filled with foamed particles by filling in many steps while the foamed particles are being compressed with pressurized gas whose pressure is higher by a specific value than that of the inside of the mold, the inside of the mold is restored to normal pressure after the filling, the particles are fused through heating with steam and a compression ratio of the particles is controlled to a specific value. CONSTITUTION:Pressurized gas of 1.0-6.0kg/cm<2>G is pressed into a steam chamber 16 of a mold device B. Then foamed particles in a hopper 1 is packed in a mold, which is formed of a recessed mold 11 and protruded mold 12, by a filling gun 15 by filling in many steps by controlling a compression ratio at 40-70% while the foamed particles in the hopper 1 is being compressed by a rotary supply device A through pressurized gas whose pressure is higher by 0.5kg/cm<2> than the foregoing pressure. Molding is completed by heating the inside of the steam chamber 16 by supplying the steam having predetermined temperature after the inner pressure of the mold has been restored to atmospheric pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention The present invention relates to a method for molding expanded polypropylene resin particles in a lid.

(Industrial Application Field) The molding method of the present invention is more advantageous in molding molded foam molded products with complex shapes and uniform density distribution than polypropylene resin foam particles. used for.

(Prior art) Conventionally, as a method for manufacturing molded products having a cellular structure, a styrene resin containing a blowing agent is pre-foamed, the obtained pre-foamed product is left in the air for a while, and then the product is foamed under reduced pressure. A method of continuously filling a mold that can be closed but cannot be sealed under normal pressure, heating and foaming it, and fusing it is widely practiced industrially.

This method can easily produce molded products with complex shapes used as fish boxes, cushioning packaging materials, heat insulating materials, and the like.

However, this method is limited to foam molding of polystyrene resin, and it is impossible to obtain a foam molded product with a complicated shape using a similar method using polyolefin resin. The reason for this is that polyolefin resins are inferior to polystyrene resins in their ability to retain gas within the resin for long periods of time in a foaming state, and gases escape within a shorter time than resins. It's because it's put away.

Furthermore, as a method for molding foamed polyolefin resin particles in a lid, a method is known in which foamed particles of the same resin are compressed to impart foaming ability.

For example, US Pat. No. 3,504,068 discloses that particles made of a foamy olefin polymer are pressurized in a heated state of 100° C. or higher, and the particles are compressed to an initial apparent volume of 0.9 to 40 cm. There is a method in which particles in their original state are filled into a mold under pressure, and the pressure in the mold is released to return to atmospheric pressure to expand and fuse the particles, or particles made of heated foamy olefin polymer are A method is described in which particles are filled into a mold, the pressure inside the mold is increased to compress the particles, the volume of the mold is reduced, and the pressure inside the mold is then released to atmospheric pressure to expand and fuse the particles. ing. However, these methods require a lot of equipment and operating costs to heat the expanded particles outside the mold, which hinders industrial implementation.

JP-A-53-33996 discloses that porous crosslinked polyolefin resin particles are compressed to 80% or less of the original apparent bulk volume using pressurized gas in a pressure-resistant cylindrical cylinder. A method is described in which the particles are blown into a mold, filled, heated, and shaped. Also, JP-A-51
Publication No. 147567 describes a method in which foamed ethylene resin particles are compressed using gas pressure in a pressure-resistant honkoku, and while the compressed state is maintained, they are air-transported, filled into a mold, and then heated and molded. There is.

However, these two methods compress particles several times to several tens of times the volume of the particles to be filled into the mold at once, and keep the inside of the mold at normal pressure or slightly pressurized. Particles are filled into the mold using the pressure difference with the pressure container.
It is difficult to fill molds with complex product shapes. If such filling is difficult, the parting parts of the convex and concave molds may be separated and filled (cracking filling), and after the filling is completed, contact molding may be performed, but the molded product obtained at this time is There is a disadvantage that the density near the portion corresponding to the portion becomes significantly high, and the density distribution of the molded product becomes non-uniform.

Furthermore, when compressing the foamed particles using a pressure tank in the various methods described above, the foamed particles may be made of a low-magnification polyethylene foam (high-density foam) or a relatively hard material such as polypropylene (with high compressive stress). ) In the case of foamed particles, a large amount of equipment and operating costs are required to compress the foamed particles with pressurized gas and then fill them into a mold, which is a significant disadvantage in industrial practice.

(Problems to be Solved by the Invention) The present invention uses foamed polypropylene resin particles to easily mold foamed products with a uniform density distribution even for products with complex shapes. This is an attempt to provide a possible method.

(b) Structure of the Invention (Means for Solving the Problems) The present inventors have conducted various studies to solve the above problems, and as a result, the present inventors have discovered that the present inventors have developed a system in which a mold is heated to a predetermined pressure using gas pressure. ,
The foamed particles are compressed using a pressurized gas that has a predetermined pressure higher than the pressure inside the mold, and is filled in multiple times using the same gas pressure, and after filling is completed, the inside of the mold is returned to normal pressure to form foam. This purpose was achieved by restoring the particles and then fusing them by steam heating, and controlling the compressibility of the expanded particles to a specific value at that time.

That is, the in-lid molding method for foamed polypropylene resin particles of the present invention is a method in which foamed polypropylene resin particles are filled into a mold and the foamed particles are fused together by steam heating to form a molded foam. 1.0~ with pressure gas
The foamed particles are compressed in a mold pressurized to 6.0 kg/crlG using a pressurized gas that is 0.5 ky higher than the mold pressure, and is divided into multiple batches. Filling is carried out sequentially, and the pressure inside the mold is maintained at the above-mentioned pressure inside the mold during the filling, and then, after the filling is completed, the pressure inside the mold is returned to atmospheric pressure, and then the above-mentioned heating is performed to fuse the expanded particles together. , the formula of the expanded particles at that time [where W, ■ and σ represent the following, respectively.

W...Weight of the molded product (1) ■...Volume of the molded product (l) σ...Bulk density of expanded particles in the atmosphere CF/l>
) is a method characterized by controlling the compression ratio expressed by 40 to 70%.

The expanded polypropylene resin particles used in the method of the present invention include, for example, polypropylene, ethylene/propylene copolymer, ethylene/propylene/butene-1 copolymer; blends of these polymers;
In addition to these polymers, other polymers such as polyisobutylene, ethylene/propylene rubber, polyethylene,
Examples include foamed particles of a blend of ethylene/vinyl acetate copolymer or the like in a proportion of less than 50% by weight, with a bulk density of 10 to 905'/l and a particle diameter of 2 to 10 m. The expanded particles may be crosslinked or non-crosslinked.

As a method for manufacturing such expanded polypropylene resin particles, for example, polypropylene resin is kneaded with a foaming agent in an extruder and extruded, and after exiting the nozzle of the extruder, the pressure is released to cause foaming, and then the foamed particles are cut. Alternatively, in a pressure-resistant container, polypropylene resin particles are heated with a dispersion medium such as water, a blowing agent 1 dispersant, etc. at a temperature around the temperature at which the resin particles soften, and the resin particles are foamed. There is a method of foaming the resin particles by impregnating the resin particles with the agent and then opening one end of the container to release the resin particles and dispersion medium into a low-pressure atmosphere inside the container. The shape of the expanded particles includes a spherical shape, a cylindrical shape, and the like.

Further, in the method of the present invention, the pressurized gas used for pressurizing the mold and compressing and filling the expanded particles is preferably an inorganic gas such as air or nitrogen gas, but other gases such as propane, butane, isobutane, Aliphatic hydrocarbon gases such as 4-tonthane: halogenated hydrocarbon gases such as dicyclodifluoromethane, dichlorotetrafluoroethane, methyl chloride, etc. can also be used, and furthermore, the above-mentioned inorganic gases are mainly used, and a small amount of Gases mixed with the other gases mentioned above can also be used. However, compressed air is generally preferred.

The degree of compression of the expanded polypropylene resin particles by the pressurized gas in the present invention, that is, the compression ratio, can be expressed by a relational expression between the internal volume of the mold and the volume of the expanded particles filled in the mold in the atmosphere. The volume of the mold is the volume of the space formed by the convex and concave molds, and although it is difficult to measure directly, it is virtually the same as the volume of the product molded in this space. The compressibility (%) of foamed particles can be determined by the following formula (in the formula, W, ■, and σ are as described above).

W/σ And, in the method of the present invention, this compression ratio is 40~
It is controlled to 70%, preferably 50 to 65%. If the compression ratio is too small, foaming ability will not be sufficiently imparted, and gaps will be created at the interface where the foamed particles are fused, resulting in poor appearance. On the other hand, if the compression rate becomes too high, excessive compression will result, resulting in poor steam flow between the foamed particles and poor fusion of the foamed particles.

In the method of the present invention, the pressure inside the mold is increased to 1.0 to 6.0 with pressurized gas before and during filling of expanded particles.
Try to keep it at +g, 'cIIc. This is the normal
l The bulk density of the foamed polypropylene resin particles is 10 to 9.
0 f/l, and the compressibility of such expanded particles is 40-7
This is because pressurization within this range is optimal for achieving 0%. In other words, if the pressurized gas pressure becomes 11g/ejG, it becomes difficult to obtain a compression ratio of 40%, and 61w10
This is because if it exceeds +lG, the compression ratio may exceed 70 inches.

In addition, in the method of the present invention, the foamed particles are compressed using a pressurized gas that is higher than the above-mentioned in-mold pressure by at least 0, s kg/di, and is heated in the mold by the same gas pressure.

Moreover, the foamed particles are divided into a plurality of times and filled sequentially. The purpose of compressing and filling the mold with a gas having a pressure higher than 9/cI/ is to facilitate the press-fitting of the expanded particles into the mold and their movement within the mold. Pressure inside the mold: j) If a high pressure of less than 0.51 w/ad is used, the expanded particles will not be sufficiently pressed into the mold. Furthermore, the reason why the filling of the foamed particles is divided into a plurality of times and carried out sequentially is to uniformly fill every corner of the complex-shaped mold with the foamed particles.

Next, examples of embodiments of the present invention will be described based on the accompanying drawings. The accompanying drawings show, in partial longitudinal sectional front view, one example of the apparatus used to carry out the present invention, in which A is a rotary feeder for compressing and filling foamed particles, and B is a molding apparatus. It is.

First, the concave mold (11) or convex mold (12) of mold device B
The space formed by the frame (13) and the back plate (14), that is, the steam chamber (16) and (1
6) When the pressure PR, that is, the pressure is 1.0 to 6.0 k
g/cliG pressurized gas, such as compressed air, is injected to pressurize the inside of the mold to a predetermined pressure within the above range.

Next, the rotary supply device B operates the casing (
It mainly consists of a rotor (2) and a rotor (3).
3) is provided with a plurality of chambers (4),
One end of the chamber (4) coincides with the foamed particle supply port (5) provided in the casing (2), and the other end of the chamber (4) coincides with the suction port (7) of the vacuum line at the front end position.
, the expanded particles in the hopper (1) are transferred into the chamber (4) by the reduced pressure and fill it. The chamber (4) filled with foamed particles rotates with both ends sealed, so that one end of the chamber (4) coincides with the foamed particle outlet (6), and the other end of the chamber (4) coincides with the foamed particle outlet (6). When the end reaches a rotational position that coincides with the pressurized gas outlet (9) pressurized to a pressure P higher than the pressure P2 by 0.5 #/m or more, foaming in the chamber (4) is completed. The particles are compressed by the pressurized gas pressure P and filled into a mold formed by a concave mold (11) and a convex mold (12) which are pressurized to the pressure P by a filling gun (15). It will be done. And rotation supply device B
Since the rotor (3) is provided with a plurality of chambers (4) as described above, the foamed particles in the hopper (1) are divided into multiple times and sequentially by repeating the above operation K. It will be filled into the mold.

Next, after the mold is filled with a predetermined amount of foamed particles, the pressure inside the mold is once returned to atmospheric pressure, and then steam at a predetermined temperature is supplied into the steam chambers (16) and (16) to heat them. The expanded particles are fused together, completing the molding of the present invention.

(Examples, etc.) Hereinafter, the present invention will be further described in detail with reference to Examples and Comparative Examples.

Example 1 In an autoclave with an inner volume of 3 tons and a pressure resistance of 50, 1 liter of water was added.
400 parts (by weight, the same applies hereinafter), 600 parts of ethylene/propylene random copolymer (Mitsubishi Yuka Co., Ltd. trade name: Mitsubishi Noprene FG3. Ethylene content: 3% by weight), 15 parts of tribasic calcium phosphate as a suspending agent, and a surfactant. 0.05 part of sodium dodecylbenzenesulfonate and 100 parts of butane as a blowing agent were charged, and the temperature was raised from room temperature to 135°C over 1 hour while stirring at 430 rpm, and when the same temperature was maintained for 10 minutes, the temperature of the autoclave was increased. Internal pressure is 2
It became 5'Q/cdG. Open the discharge nozzle valve at the bottom of the autoclave and discharge the contents into the atmosphere for 2 seconds while stirring at 18 Orpm to cause foaming. The foamed particles obtained had a bulk density of 30 Pll.

In-mold molding was performed using these foamed particles, using a molding machine of DAIYA-600LF (product name of Daishichi Kogyo Co., Ltd.) and a mold with a width of 300 mm x length of 300 mm x height of 12.5 ynx. A mold with an internal volume of 1.1 t for obtaining a product was used as a rotary supply device for compressing and filling expanded particles.
An apparatus as shown in the accompanying drawings having two chambers (each chamber having an IL diameter of 35 mm, a length of 52 mm, and a volume of 5 occ) was used, and a filling gun of caliber 30 was used as the filling gun.

The molding method was as follows: First, the mold was closed, and the internal pressure (P,) of the mold was increased to 3.5 kg/cdG using compressed air. Then,
2.8 tons of expanded particles having a bulk density of 309-/l produced as described above were used as pressurized gas at a pressure (Pt) of 4.
kp/, -a (using compressed air with a pressure of G, 0
．． It was divided into 1-second intervals and filled sequentially. During filling, the mold internal pressure (Pl) was maintained at 3.5 kg/iG.
A pressure regulating valve (not shown) was activated.

After filling, the filling gun is closed and the mold internal pressure (Pl) is returned to atmospheric pressure to restore the expanded particles to their original shape, and then the convex mold (1
2) side, that is, in the chamber (16) on the movable side.
'Kg/iG steam (temperature approximately 133°C) was introduced for 20 seconds, and then the convex mold (movable mold) side and the concave mold (11)
At the same time, steam of 3 Y/G was introduced into the steam chambers (16) and (16) on the fixed mold side for 20 seconds to heat and fuse the expanded particles together.

After the mold was cooled, the mold was taken out and dried, and the resulting foamed molded product had a weight of 85 yen, and the compression ratio of the foamed particles at the time of molding was 61%. The obtained foamed molded product was filled with foamed particles to every corner, had no gaps between the particles, and had good fusion bonding.

Comparative Example 1 Expanded particles 2 having a bulk density of 309-/l produced in Example 1
．． Pour 8 tons of compressed air into the pressure hopper tank and fill it with 4.
0 kg/+! It was pressurized with G. Open the pulp at the bottom of this tank and apply the same internal pressure as used in Example 1 to 3.5 #/
The mold was continuously filled at dG.

After filling, the filling gun was closed and the pressure in the mold was returned to atmospheric pressure to restore the foamed particles to their original shape, followed by heat fusion in the same manner as in Example 1 to obtain a foamed molded product. The pressure ratio of the foamed particles in this case was 61 inches.

The obtained foamed molded product had many gaps between particles due to insufficient filling of the foamed particles in every corner, and could not be put to practical use.

Comparative Example 2 In Example I, the pressure (P, ) of compressed air for compressing and filling expanded particles was 3.7 ky/cdG.

or using compressed air of 3.9 kg/cdG, respectively,
Other than that, molding was carried out under the same conditions as in Example 1. The compression ratio of the expanded particles in this case is 49% or 55%, respectively.
Met.

All of the molded products obtained had large interparticle gaps and were inferior in commercial value.

Example 2 Comparative Examples 3 to 4 1.71, 2.31, or 4.5 t of the foamed particles with a bulk density of 30 Vt manufactured in Example 1 were used, and the mold internal pressures were 1.8 kg/cdG and 2, respectively. ．．
The pressure (P,) was set to 5 kg/ff1G or 4.0 kg/iG as a pressurized gas for compressing and filling expanded particles, respectively, at 2.3 kg/iG and 3.0 kg/iG.
Compressed air of kg/cmG or 4°7 Yu/mG was used, and the filling was otherwise carried out in accordance with the method of Example 1, and heat molding was carried out in the same manner.

The results are shown in Table 1.

Table 1 Examples 3 to 4 In the production of expanded particles of Example 1, by changing the amount of butane charged, the bulk density was 151/l or 60/l.
Expanded particles of f/l were produced respectively.

2.8 tons of each of the obtained particles were used, and the mold internal pressure (Pl) and filling pressure (P2) were changed as shown in Table 2, and the other filling methods were as in Example 1. And molding was performed. The results are shown in Table 2.

Table 2 (c) Effect of the invention The molding method of the present invention provides the following excellent effects.

(1) Since the expanded particles are compressed and filled in the mold using pressurized gas, there is no need for large-scale factory equipment and premises such as large-capacity pressure-resistant hopper tanks as in the conventional method, and there is no need for pressurization. Gas usage is also low.

01) The foamed particles are divided into multiple parts and sequentially filled while being compressed, and the compression ratio of the foamed particles is controlled within a certain range, so even if the molded product has a complex shape, the foamed particles can be packed in every corner. An excellent polypropylene resin foam molded product can be obtained which can be uniformly filled up to the IC, has a uniform density distribution, and has no particle gaps.

[Brief explanation of drawings]

The accompanying drawings are partial longitudinal cross-sectional views of an example of an apparatus used to carry out the present invention, and each reference numeral in the drawings indicates the following. A...Rotary supply device for compressing and filling expanded particles, B
... Mold device, 1... Hoknoya for foamed particles - 12.
... Casing, 3... Rotor, 4... Chamber, 5... Foamed particle supply port, 6... Foamed particle discharge port,
7...Reduction line suction port, 8...Reduction line, 9.
... Pressurized gas outlet, 10... Pressurized gas line, 11
...Concave, 12...Convex, 13...Frame, 1
4...back metal, 15...filling gun, 16...steam chamber.

Claims (1)

[Scope of Claims] 1) A method for molding a molded foam by filling a mold with polypropylene resin foam particles and fusing the foam particles with each other by steam heating, in which the foamed material is heated to a temperature of 1.0 to 6. 0k
The foamed particles are compressed in a mold pressurized to g/cm^2 using a pressurized gas that is 0.5 kg/cm^2 or more higher than the pressure inside the mold, and are sequentially divided into multiple times. The pressure inside the mold is maintained at the above-mentioned pressure inside the mold during the filling, and then after the filling is completed, the pressure inside the mold is returned to atmospheric pressure, and then the above-mentioned heating is performed to fuse the expanded particles together, Formula compression ratio (%) of foamed particles at that time = [(W/σ-V)/(W/σ)]×10
0 [In the formula, W, V and σ each represent the following. W...Weight of the molded product (g) V...Capacity of the molded product (l) σ...Bulk density of foamed particles in the atmosphere (g/l)] 40 to 70 An in-lid molding method for polypropylene resin foam particles, which is characterized by controlling the polypropylene resin foam particles to %.