JPH02258327A - Manufacture of olefin resin foam molded material - Google Patents

Abstract

PURPOSE:To shorten cooling time to a large extent by suck moving a fixed side contact surface of a molded product to a movable side mold and exposing said surface to atmosphere, and then clamping again and immediately opening the mold and releasing as it is. CONSTITUTION:Both drain valves 28 and 29 are clamped before releasing and a movable side vacuum valve 26 is opened to vaccumize, while a fixed side air valve 23 is opened and pressurized. The movable side air valve 23 is closed after about 3 - 8 seconds and mold opening is carried out, and a molded product is sucked and moved to the side of movable side inner mold 13 and mold opening is discontinued in such a manner that a starting section (a) of the molded product may not slip off the fixed side inner mold 12. The molded product can easily be released without pin cracking out of the fixed side inner mold 12 by carrying out said slow mold opening operation. Thus, the cooling time can be shortened to a large extent for releasing to increase molding productivity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an olefin resin foam molded product, and more specifically, the present invention relates to a method for producing an olefin resin foam molded product. The present invention relates to a method for producing an olefin resin foam molded product that achieves a significant reduction in cooling time by releasing from the mold using surface pressure.

[Conventional technology and problems]

Foamed molded products of olefin resins such as polypropylene and polyethylene (hereinafter referred to as molded products) are widely used as energy absorbers such as automobile bumper core materials, loose I1J packaging materials, rain ventilation, and the like.

For molded bodies of olefin resin, pre-expanded particles are filled into a mold as shown in Figure 1, heated with steam etc. to expand and fuse, cooled with water etc., and fixed in an eject bin. A common method is to release the mold by protruding it from the side mold.

By the way, in the above method, the factor that determines the cooling time is the foaming pressure (commonly called surface pressure) of the molded article, which is a maximum of about 0.4 kg/c4G in terms of -M. If the mold is released in a state higher than this surface pressure, the sliding resistance between the molded body in the molded body chamber (16) and the stationary side middle mold (12) will be large, and the eject bin (
9) Because the mold release extrusion pressure becomes higher than usual,
If the mold release extrusion is forced, as shown in FIGS. 2(A) and (B), the molded body (31) will be damaged due to compressive stress (equal to the mold release extrusion pressure) exceeding the elastic limit of the eject pin (9). The pin head (9) of the eject pin (9) that is in contact with the molded body is
An annular crack (32) (commonly known as a pin crack) occurs in the circumferential portion of a). The compressive stress of the compact in this case is
The reason for this is that the temperature inside the molded body is much higher than normal temperature, which is about 60 to 80°C, which is generally lower than the data published in catalogs and the like. The surface temperature of the molded product is around room temperature, but since the molded product is a foam, it has an insulating effect, and it takes a considerable amount of time for the inside to cool down to room temperature, so the inside temperature is lower than the outside temperature. Since the temperature is high, the compressive strength is low.

Incidentally, the compressive strength of a molded article varies depending on the material and the expansion ratio, but is generally inversely proportional to the temperature above room temperature. Therefore, if the eject pin (9) is used for mold release extrusion with the cooling time shortened, the above-mentioned pin cracking is unavoidable.In order to avoid this pin cracking, the eject pin (17) is It is commonly used to send in compressed air to perform a mold release extrusion action from the fixed middle mold (12), but this method also does not have a significant effect.

The reason for this is that the above compressed air for ejecting is
Before extruding the molded product in step 6 from the stationary side middle mold (12), the molded body is molded opposite to the rising part of the stationary side middle mold (12) on the side of the fixed side steam chamber (17) shown in Fig. 1. In order to make a seat pass from the body gap (a) to the moving side steam chamber (18) via the moving side medium mold (13), the fixed side steam chamber (
17) The air pressure on the side does not rise sufficiently, and as a result, the mold release extrusion effect is not developed effectively.Also, the sheet pass of the compressed air for eject is small, and the mold release extrusion effect is observed. In many cases, there are one or more molded body chambers (16), and in this case, compressed air for ejecting may be blown out from the molded body chamber (16) after mold release extrusion, causing damage to other molded bodies. The molded body remaining in the chamber (16) does not undergo the extrusion effect during extrusion, and as a result, the bottle cracking is unavoidable, resulting in defective products.

As mentioned above, in the conventional in-mold foam molding method for polyolefin, bottle cracking occurs when mold release extrusion is performed with a shortened cooling time, so it is impossible to shorten the cooling time.

[Means for solving problems]

In view of the above circumstances, the inventors of the present invention have conducted extensive research, and have determined that the fixed side contact surface of the molded body is partially exposed to atmospheric pressure by suctioning and moving the molded body to the movable mold before the normal removal from the mold. After opening everything, the mold can be re-clamped or the mold can be opened and released immediately, making it easier to release the mold.As a result, it is possible to release the mold with a higher surface pressure than before, greatly shortening the cooling time. The present invention was completed based on the discovery that it is possible to significantly shorten the molding cycle.

That is, the first aspect of the present invention is that when producing a foamed molded article from olefin resin particles, before removing the molded article from the mold, the movable mold is vacuumed and the molded article is suctioned and brought into close contact with the movable mold. The olefin is characterized in that the cooling time is shortened by opening the mold while moving the mold, closing the mold, bringing the movable mold to atmospheric pressure, transferring the molded product to the stationary mold, and then removing it from the mold. The second aspect of the present invention is a method for producing a foamed resin foam, in which when producing a foamed molded product from olefin resin particles, the movable mold is vacuum depressurized before the molded product is released from the mold. Manufacture of an olefin resin foam molded article characterized by shortening the cooling time by bringing the movable mold to atmospheric pressure after opening the mold to a position where the molded article can remain in the stationary mold while being brought into close contact with suction. The contents of each method are as follows.

Examples of the olefin resin used in the present invention include propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene random terpolymer, propylene-vinyl chloride copolymer, and propylene-vinyl chloride copolymer.
Examples include butene copolymers, propylene-maleic anhydride copolymers, etc., but among these, ethylene-propylene copolymers produced by stereoregular polymerization are preferred; these may be used alone or in combination of two or more. Good too.

These olefin resins are preferably in a non-crosslinked state, but they may be crosslinked with peroxide or radiation, or other thermoplastic resins that can be mixed with the olefin resins, such as low-density polyethylene, linear Low density polyethylene, polystyrene, polybutene, ionomer, etc. may be mixed and used as long as the properties of the polypropylene resin are not impaired.For example, when low density polyethylene, linear low density polyethylene, polybutene, ionomer, etc. are used together, It is preferably 5 to 20 parts per 100 parts (by weight, same hereinafter) of the propylene resin, and preferably 5 to 1'0 parts when polystyrene is used in combination.

These olefin resins are usually melted in advance using an extruder, Nigoo mixer, Banbury mixer, roll, etc. so that they can be easily used for pre-foaming, and are shaped into cylinders, elliptical cylinders, spheres, cubes, rectangular parallelepipeds, etc. The desired particle shape is such that the average particle size of the particles is 0.1-10 mm, preferably 0.7 mm.
It is molded to a length of ~5m.

There are no particular limitations on the pre-foaming method, but for example, olefin resin particles are made to contain a volatile blowing agent in a pressure-resistant container, dispersed in water with stirring, heated to a predetermined foaming temperature under pressure, and then A method is used in which the aqueous dispersion is discharged into a low pressure region through an orifice with a diameter of 2 to 10 mm.

Volatile blowing agents to be contained in the olefin resin particles used in the present invention include, for example, aliphatic hydrocarbons such as propane, butane, pentane, and hexane; alicyclic hydrocarbons such as cyclopentane and cyclobutane; Examples include halogenated hydrocarbons such as monofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, methyl chloride, methylene chloride, and ethyl chloride.

These blowing agents may be used alone or in combination of two or more, and the amount used is not particularly limited, and may be used as appropriate depending on the degree of foaming of the desired pre-expanded olefin resin particles. Usually, the amount used is olefin resin 1
00 parts to 5 to 50 parts.

When preparing the aqueous dispersion, dispersants such as tertiary calcium phosphate, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc., and a small amount of surfactant,
For example, sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, sodium α-olefinsulfonate, etc. may be used.

The amount of the dispersant or surfactant used varies depending on the type of the dispersant or surfactant, the type of olefin resin particles used, the amount used, etc., but usually 0 parts of the dispersant per 100 parts of water.
．． 2-3 parts, 0.001-0.1 part in case of surfactants.

In addition, in order to improve the dispersibility of the olefin resin particles containing the volatile blowing agent in water, usually,
It is preferable to add 20 to 100 parts per 100 parts of water.

The present invention is suitably applied to any of the following in-mold foam molding methods using pre-expanded particles of olefin resin.

(a) pre-expanded particles of olefin resin are pressurized with an inorganic gas to impregnate the particles with the inorganic gas, and then the pressure is removed;
A method of filling the particles into a mold that can be closed but cannot be sealed while the internal pressure is 1.18 atm or more, and heating and fusing them with steam etc. to form a molded product according to the mold (Japanese Patent Publication No. 51-22951) (B) Fill a mold that can be closed but cannot be sealed with pre-expanded particles of olefin resin, and after heating and fusing them with steam, etc.
When taken out from the mold, its volume is 70 to 110 of the volume of the mold.
% (Japanese Unexamined Patent Publication No. 60-166442), (c) uniformly applying a mold and a container for pre-expanded particles (pressure filling container); A method (Japanese Unexamined Patent Publication No. 179927/1983) is known in which the particles are brought into a compressed state and the pre-expanded particles are compressed and filled with an inorganic gas.

It should be noted that even if the present invention is applied to styrene-based foamed resin containing a volatile foaming agent, the desired effect will be small; that is, the usual cooling time will not be shortened in foam molding of styrene-based foamed resin. This is because if the mold is released by removing the mold, bulges will occur in the thick wall portion due to partial tertiary foaming after the mold is removed, making it impossible to obtain a normal molded product.

Next, an explanation will be given based on drawings showing an example of the manufacturing apparatus of the present invention used when manufacturing a foam from the pre-expanded particles.

FIG. 3 is a schematic diagram showing a manufacturing apparatus used in the present invention, and the manufacturing apparatus of the present invention is mainly composed of a mold, mold parts, and a vacuum device. The pre-expanded particles (1) are fed and stored in a hopper (2) by a feeding device (not shown). In the step of filling the pre-expanded particles (1) into the molded body chamber (16), the fixed side frame (10) and the movable side frame (
Open the parting line (p) that the shutter (11) is in contact with slightly (approximately 2 to 10 liters) (and open the fixed side drain valve (28) and the movable side drain valve (29), and in this state, open the parting line (p) that the shutter (3 ), open the feeder (6), and open the filling air valve (8).When the filling process is finished, the feeder (6) is closed by the feeder on/off valve (7), and the next Next, the shutter (3) is closed by the shutter opening/closing valve (4).Next, the mold is closed by the mold opening/closing device.The mold opening/closing device is not shown in the figure, but in normal cases, it is connected to the guide plate to which the mold is attached. It consists of a hydraulic cylinder, and the movement of the hydraulic cylinder moves the Goui plate, opening and closing the mold.

Next, the heating process begins.0 In normal heating operation, with both drain valves (28) and (29) open, the fixed side steam valve (19) and moving side steam valve (20) are opened, and the fixed side steam valve (19) and moving side steam valve (20) are opened. In addition to replacing the air and steam in the side steam room (17) and the moving side lid air chamber (1st), the fixed side medium size (12) and the moving side medium type (13) are replaced.
), the moving side steam valve (20) and fixed side drain valve (28) are closed, and the fixed side steam valve (19) and moving side drain valve (29) are opened. One-sided heating operation, followed by reverse one-sided heating operation performed by closing the fixed side air valve (19) and moving side drain valve (29) and opening the moving side steam valve (20) and fixed side drain valve (28), the molded product Then, both drain valves (2B
) (29) and open both steam valves (19) and (20) to heat and fuse the surfaces by double-sided heating. Next, stop the steam supply and close the drain valves (28) and (29). Hold it for a few seconds to keep it warm. This not only uniformly fuses the entire molded body, but also serves to lower the heated residual vapor pressure inside the frame (lO) (11) by dissipating heat from the outside.

Next, the cooling process begins. First, in the pre-cooling operation, the fixed side cooling water valve (21) is opened with the drain valves (28) and (29) closed.
) and moving-side cooling water valve (22) to cool down for a few seconds. This operation can be done by opening both drain valves (2B) (29) and removing residual steam inside the frames (10) and (11). The purpose is to prevent abnormal high-pitched sounds caused by exposure to the atmosphere.Next, water cooling operation is performed with both drain valves (28) and (29) open, and both cooling water valves (21). (22) is opened and the fixed side middle mold (12) and moving side middle mold (13) are cooled with water to reduce the foaming pressure of the molded body in the molded body chamber (16). Time 0 is the size of the molded body. The foaming ratio is not constant depending on the structure of the medium size (12) (13), but it is generally several tens to several hundred seconds.

Next, the normal mold release pressure is increased first, that is, with the mold closed, the drain valves are connected to the fixed side (28) and moving side (29).
Pressure is applied to both steam chambers with the air valve closed.The specific operation is to open the fixed side air valve (23) and the moving side air valve (24).The operating conditions are as follows: For about 2 to 3 seconds, the pressure is about 0.5 to 1.0
kg/dG, and after this operation makes it easy for the molded object to be removed from the mold, the fixed side (23) and moving side (24) of the air valve are stopped, and the fixed side (28) of the drain valve is stopped.
And the moving side (29) is opened to release the pressure inside the mold. Generally speaking, the shape of the middle mold is that the fixed side middle mold (12) is concave, the moving side middle mold (13) is convex, and the molded body is concave. and the molding chamber (16) in the middle of the convex shape.

Next, the molded body is transferred from the fixed side middle mold (12) to the moving side middle mold (13).
), both drain valves (2B)
(29), open the movable side vacuum valve (26) to reduce the pressure, and open the stationary side air valve (23) to pressurize it. After about 3 to 8 seconds, the stationary side air valve (23) is closed and the mold is opened, and the molded body is suctioned and moved toward the movable middle mold (13) by the above action. The mold opening is stopped to such an extent that the rising portion (a) of the molded body shown in FIG. 3 does not come off from the stationary middle mold (12). By carrying out this mold opening throw operation, the molded article can be easily released from the stationary middle mold (12) without causing pin cracks. Specifically, the maximum value of the surface pressure that does not cause pin cracking is 0.3 to 0.4 kg/edG in the conventional mold release method, whereas it is 0.7 to 1.0 kg/edG in the present invention. It is.

Next, by closing the mold, the molded body is again fixed to the stationary middle mold (12). However, it is also possible to omit this mold closing and immediately proceed to the next mold release/removal operation.

The above molded body is transferred from the fixed side middle mold (12) to the moving side middle mold (1
3) In the operation of moving to the side, the following method can also be adopted. That is, after the molded body is suctioned and moved to a position where it can remain in the stationary middle mold (12), the movable side vacuum valve (26) is moved.
) and open the moving side air valve (24) to pressurize the moving side steam chamber (18), thereby leaving the molded body in the stationary side middle mold (12).

As the vacuum device, a known vacuum pump, steam or water injector, etc. can be used.

The next mold release operation is a conventional mold release method, and the mold opening slow operation is performed by closing the fixed side drain valve (28) and moving side drain valve (29) while opening the mold. Open the air valve (23) to make it easier for the molded product to be released from the stationary middle mold (12), and in the next step, open the movable side drain valve (29) with the mold slightly open to continue opening the mold. death,
Finally, the molded body in the fixed-side middle mold (12) is released and extruded using an eject pin (9).

〔Example〕

The present invention will be described below with reference to Examples, but it goes without saying that the present invention is not limited thereto.

Example 1.2, Comparative Example 1.2 (1) Resin used ethylene-propylene random copolymer (ethylene content 3.5% by weight) (2) Pre-foaming method and blowing agent The blowing agent was trichloro in the method explained above. Trifluoroethane (3) molded body Bumper core material for automobiles Total length 1540mm x Width 158mm x Height 98m + a 1st
Molded bodies were manufactured under the conditions shown in the table, and after cooling to an extent that did not cause pin cracking, the molded bodies were taken out and the cooling time and molding cycle were measured.

The results are shown in Table 1, and the cooling time and molding cycle of all the examples of the present invention were significantly shortened compared to the corresponding comparative examples.

[Action/Effect]

With conventional methods, polyolefin foams are prone to pin cracking during mold release extrusion, so sufficient cooling time is required to reduce the surface pressure (foaming force) that causes mold release resistance. It is. Therefore, it was very difficult to shorten the cooling time, but with the present invention, vacuum suction is used as the main force, and compressed air is also used as needed to move the molded product from the stationary mold to the movable air valve. (1m-10
By extruding the mold after moving it, the cooling time can be greatly shortened and the mold can be taken out without damage such as pin cracking, and molding productivity can be dramatically increased.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an example of a mold, Figure 2 (A), CB
) is an explanatory diagram showing the state of pin cracking, (A) is a side view,
(B) is a top view, and FIG. 3 is a schematic diagram showing an example of the device used in the present invention. ! ... Pre-expanded particles, 2... Hopper 3.
...Shutter 4...Shunter on-off valve 5
... Hose, 7... Feeder on-off valve, 9... Eject pin, 11... Moving side frame, 13... Moving side medium size, 15... Moving side slit, 17... Fixed side steam Chamber, 19... Fixed side steam valve, 21... Fixed side cooling water valve, 23... Fixed side air valve, 25... Fixed side vacuum valve, 27... Vacuum device, 29... Moving side drain valve, 31...Molded object, 6...Feeder 8...Filling air valve 10...Fixed side frame 12...Fixed side medium mold 14...Fixed side slit 16... Molded object chamber 18...Movable side steam chamber 20...Movable side steam valve 22...Movable side cooling water valve 24...Movable side air valve 26...Movable side vacuum valve 28...Fixed side Drain valve 30...Drain pipe 32...Cracked

Claims (1)

[Claims] 1. When producing a foamed molded article from olefin resin particles, before removing the molded article from the mold, the movable mold is vacuumed and the molded article is brought into close contact with the movable mold by suction. The olefin-based product is characterized by shortening the cooling time by opening the mold, closing the mold, bringing the movable mold to atmospheric pressure, transferring the molded product to the stationary mold, and then removing it from the mold. Method for manufacturing resin foam. 2. When manufacturing a foamed molded product from olefin resin particles, before removing the molded product from the mold, the movable mold is vacuumed to bring the molded product into close contact with suction, allowing the molded product to remain in the stationary mold. A method for producing an olefin resin foam molded article, characterized in that after the mold is opened to the position, the cooling time is shortened by bringing the movable mold to atmospheric pressure. 3. Surface pressure (foaming pressure) when releasing the molded product is 0.4 kg/c
3. The manufacturing method according to claim 1, wherein the molded body is removed from the mold at m^2G or higher.