JPS5849384B2 - Manufacturing method of ethylene resin foam molded product - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a foamed molded article by filling a closed mold with foamed particles of a crosslinked ethylene resin and heating it, and furthermore, This invention relates to a method that allows foamed particles to be shaped into a certain shape without increasing the internal pressure of the cells.

Methods for forming foamed molded products from crosslinked ethylene resin foam particles are disclosed in JP-A-47-34458, JP-A-49-85158, and JP-A-49-128,065 (methods described therein). It has been known.

These techniques have some fatal flaws in their industrial implementation.

In other words, in all of these technologies, the foamed particles are kept in a high-pressure atmosphere of organic or inorganic gas for a long time, so that the internal pressure of the cells in the foamed particles is pressurized, and then the foamed particles are placed inside the mold (which must be filled). No.

Therefore, it is necessary for each shape processing factory to be equipped with a pressure vessel with high pressure resistance and large capacity. Moreover, the gas inside the bubbles escapes quickly, and the foamed particles taken out from the pressure vessel are immediately supplied to the shape. Otherwise, it will become impossible to produce the product, so if it is produced on an industrial scale, large capital investment is required, the risk is high, and the quality of the product is unstable (it may have fatal defects such as snarling). was.

The present invention was made as a result of intensive research in order to solve the drawbacks of the conventional methods and to establish a technique that allows shaping without going through a holding process at high pressure.

That is, the present invention provides a method for obtaining a foamed molded article by filling a closed mold with foamed ethylene resin particles and heating. After this is fused together and integrated, the molded product is cooled to below the softening temperature of the base resin while maintaining a reduced pressure atmosphere that does not cause deformation, and then the pressure is increased to atmospheric pressure, and the base material is cooled to below the softening temperature of the base resin. The object of the present invention is to provide a method for producing a crosslinked ethylene resin or shaped article, which is characterized by ripening at a temperature not more than 50'C lower than the softening temperature of the resin.

In the present invention, the crosslinked ethylene resin foam particles include:
Impregnating or kneading organic peroxide into ethylene resin particles and then or simultaneously heating them (crosslinked ethylene resin particles obtained thereby, or ethylene resin particles (irradiating with ionizing radiation such as electron beams) Q
The thus obtained crosslinked ethylene resin particles are foamed by a known method using a chemical foaming agent or a volatile foaming agent whose boiling point is below the softening temperature of the base resin.

Further, by appropriately combining the above-mentioned crosslinking method and incorporation method, crosslinking and foaming can be carried out simultaneously, or crosslinking can be carried out after foaming.

The shape of the foamed particles is not particularly limited, but it is preferable to have a shape that allows for as high a degree of filling in the mold as possible, that is, a shape that is close to a spherical shape.

Furthermore, the smaller the particle size is, the more voids between the particles will form in the shaped product, so it is desirable, and those with a diameter of less than ICrfL are usually used.

One of the features of the present invention is that a good foamed molded product can be obtained without taking the trouble of increasing the internal pressure of the cells of the foamed crosslinked ethylene resin particles.

Therefore, as the foamed particles used in the present invention, it is possible to use foamed particles that have been pre-foamed and then left in the atmosphere so that the pressure inside the bubbles becomes almost the same as atmospheric pressure. When implemented, this is extremely advantageous compared to the prior art.

However, it goes without saying that even if the method of the present invention is carried out using foamed particles having a cell internal pressure equal to or higher than atmospheric pressure, a good shaped article can be obtained without any problem.

Furthermore, there is an advantage that foamed particles having a bubble internal pressure of less than 1.18 atmospheres, which was considered impossible in the prior art (herein), can be used.

Note that the bubble internal pressure in the present invention is defined by the following equation.

The expanded particles are then filled into a closed mold, and the closed mold as referred to in the present invention is generally used in the field of polystyrene beads.

It is a type of mold that has a small hole or slit for convenient removal of the shaped item (this is a type of mold that can be broken into two pieces and closed by putting them together).

Air flow is most commonly used to fill the mold with foamed particles.

In order to increase the degree of filling of the mold, there is also a method in which the inside of the mold is pressurized to above atmospheric pressure and the inside of the expanded particle transport system is also pressurized while filling.

In this case, the degree of filling is increased because the expanded particles are compressed by pressure.

The foamed particles uniformly filled into the mold are then heated.

The heating temperature is preferably at least the softening temperature of the base resin, preferably at or 30°C higher than the melting point of the base resin.

The higher the heating temperature is, the stronger the fusion between the particles will be, and the better the shape of the product with less gaps between the particles. However, if the heating temperature is too high, the resin will flow excessively, causing the cell structure to collapse ( Not only does this result in poor-quality molded products, but also the molding cycle is long, and higher temperatures than necessary require increased pressure and heat resistance of the mold and other parts of the equipment, among other disadvantages.

As the heating medium, steam is most advantageous for industrial purposes, but heated air, heated water, superheated steam, etc. can also be used.

The most significant feature of the present invention is the subsequent treatment of a shaped article {ζ that has been heated.

In the conventional molding method, the temperature of the molded product is lowered immediately after heating (under atmospheric pressure), and the temperature of the molded product is continued to be lowered to the point where deformation does not occur when removed from the mold.
In the present invention, cooling after heating is performed under reduced pressure below atmospheric pressure.

As long as the reduced pressure can be maintained at a level that does not cause shrinkage in the mold during cooling, the pumping pressure will not be increased unnecessarily.

Therefore, it is preferable to lower the degree of pressure reduction at the beginning of cooling and gradually increase the degree of pressure reduction.

The required minimum value of the maximum degree of pressure reduction during the pressure reduction process is determined by the internal pressure of the foamed particles subjected to molding, the softening temperature of the base resin, and the cooling temperature (
Although it varies depending on the situation, it is usually in the range of -50 mmHj;l to -50QmmH9, preferably -10
0 mmH & -300 mmH. 9
It is.

The decompression step may be started immediately after the heating step is completed, or may be started after being left for a while.

Further, after the completion of heating, the depressurization process may be started after cooling the shaped product in the mold (within a range that does not cause significant shrinkage).

What is necessary is to prevent the hollow part from being cooled from a temperature above the softening temperature to a temperature below the softening temperature in a contracted and deformed state.

Note that the term "shrinkage deformation" as used herein refers to a state in which the ratio of the volume of the molded product to the volume of the mold is 80% or less.

If the decompression process is carried out when the temperature of the molded product is higher than the softening temperature of the base resin, the effect of reducing the gap between particles that could not be completely filled during heating may be reduced. Therefore, it is particularly advantageous when it is desired to obtain a shaped product with an excellent appearance.

During the decompression step, at least the surface portion of the molded product is preferably cooled to a temperature below the softening temperature, preferably at least 1°C lower than the softening temperature, to room temperature.

If the cooling is insufficient, the final product will remain deformed and its commercial value as a molded product will be significantly impaired.

There are no particular restrictions on the means for cooling the shaped product under reduced pressure, and there are methods such as spraying cooling water over the mold Q while maintaining a sealable heating chamber surrounding the mold at reduced pressure, or a simple method.
After heating with water vapor, the steam chamber surrounding the mold is sealed, and the mold and the steam chamber are cooled with water.

In any case, the most practical method is to carry out the process while the molded product is still in the mold, but if no harmful deformation occurs when the product is removed from the mold, it must be cooled by bringing it under a reduced pressure atmosphere (such as a You may go.

After completing the depressurization and cooling process, it is released to atmospheric pressure and taken out from the mold, or it is further cooled and taken out from the mold.

Generally, the shaped product removed from the mold is often shrunk, but depending on the selection of the internal pressure, softening temperature, cooling temperature, etc. of the foamed particles, shrinkage may not occur in some cases.

In either case, the shaped article is ripened in an atmosphere under atmospheric pressure (wherein the temperature is below the softening temperature and not more than 50'C below the softening temperature).

This ripening process recovers the shrinkage caused by the difference between the pressure inside the bubbles of the shaped product taken out of the mold and the outside, or completely cools the shaped products that did not shrink to room temperature. This is done to prevent the contraction that inevitably occurs.

The ripening temperature may be maintained at a constant temperature within the above temperature range, or may be gradually lowered.

In either case, the ripening time is preferably 1 hour or more (rubbing is preferred; if the ripening time is too short, the molded product will still shrink even after ripening is completed, which is not preferred).

However, if ripening is started at the same temperature, a method of gradually lowering the temperature is advantageous because it can significantly shorten the ripening time.

If the ripening temperature is higher than the softening temperature, or if the molded product is aged for a long time at a temperature higher than the softening temperature, the resin itself will shrink during ripening, and the dimensions of the resulting molded product will be larger than the dimensions of the mold. Something extremely small

Furthermore, ripening at a temperature 50°C or more lower than the softening temperature would result in a molded product without shrinkage (this would require an impractically long ripening time, or (It becomes impossible to contract even if it is left to ripen for a long time.)

As the ethylene resin used in the present invention, homobolymers, copolymers, and blend polymers containing 60% or more of ethylene fraction are used, such as high-pressure polyethylene, low-pressure polyethylene, ethylene propylene copolymer, ethylene-vinyl acetate copolymer, and ethylene-ethyl methacrylate. Examples include acid copolymers, ethylene ionomers, mixtures thereof, and blend polymers of these resins and other resins.

In particular, resins that exhibit remarkable effects by using the method of the present invention have a softening temperature of 84°C or higher.

When a resin with a softening temperature of less than 84°C is used, the aging time is relatively long, which is somewhat disadvantageous from an industrial perspective.

It should be noted that when molded foamed articles are formed from expanded styrene resin particles (when the method of the present invention is applied, some shaped articles taken out from the vacuum cooling process (this shrinkage may occur due to aging). Either it cannot be restored, or even if it can be recovered, the cushioning performance of the obtained molded product will be significantly reduced.
becomes unusable.

This seems to be caused by the brittleness of the styrene resin.

Therefore, it can be said that the method of the present invention is effective only when using foamed ethylene resin particles with high toughness.

Next, Examples (thereby, the present invention will be explained in detail).

Example 1 High pressure polyethylene (density -0.9189/cc, MI
-1.0, melting point 113℃, softening temperature 85℃) using dicumyl peroxide to a degree of crosslinking of 60% (after crosslinking, dichlorodifluoromethane solution was contacted at 80℃ for 1 hour in a pressure container, then The mixture was cooled, taken out, fed to a pre-foaming machine with a conveyor set, and foamed with steam at 100°C.

The expansion ratio of the obtained expanded particles was 18 CC/g, and the particle size was spherical with a diameter of 7 mm.

The foamed particles were left indoors for 24 hours to bring the internal pressure of the bubbles back to atmospheric pressure (ECHO-1), which was modified by connecting a Q-vacuum tank to reduce the pressure in the steam chamber used to heat the mold.
The shape was made using a type 20 shape machine (manufactured by Toyo Machinery and Metals).

The mold used had an inner dimension of 1 5X1 5X8 (m) and an outer dimension of 2.
It was a rectangular mold measuring 0x20x12 (m).

The pressure of steam during heating is 1. Using steam adjusted to 5 kg/it, the heating time was adjusted so that the steam pressure in the steam chamber was at a maximum of 1.0 kg/crt.

The total time required for heating was 20 seconds.

Immediately after heating, the pressure in the steam chamber is reduced from the vacuum tank Q (at the same time as water is sprinkled into the steam chamber to cool it down, and the cooling time is varied. Therefore, various surface temperatures of the shaped product were selected).

The surface temperature of the shaped product is 55mm from the surface of the shaped product in the mold.
A thermocouple was installed so that the temperature at the location could be measured.

When the mold was cooled to a predetermined temperature, the reduced pressure was released and the mold was brought to atmospheric pressure, and the mold was opened and the molded product was taken out.

Next, the molded product was placed in an air-heated ripening chamber for a predetermined temperature and time, and then taken out, and the state of shrinkage was measured after the molded product reached room temperature (after approximately 3 hours had elapsed).

Table 1 (various selections of these conditions and the state of shrinkage of the obtained hollow parts) is shown.

Example 2 When the foamed particles used in Example 1 were taken out of a container (in a container) and pressurized with air at 20'C for 30 minutes at lkg/ail (gauge), the internal pressure of the bubbles was 1.15 atm. .

The foamed particles were shaped using the shaping machine, mold, and shaping heating conditions used in Example 1, and then cooled under reduced pressure in Experiment A62 for 60 minutes.
When aged at 1.5 hours, a molded product with good shrinkage was obtained.

Example 3 The foamed particles used in Example 1 were heated in the same manner as in Example 1. After the round-shaped heating was completed, cooling water was poured into the steam chamber while the steam chamber remained sealed to cool the mold and the steam chamber. It took 7 seconds until the surface temperature of a certain molded product reached 90'Cf, during which time the pressure inside the steam chamber was reduced to -300mmH&.

Leave it as it is for 30 seconds, and the surface temperature of the molded product will be 50'.
Atmospheric pressure (returning to normal), the mold was opened and the impressive item was taken out.

At this point, the volume of the shaped product was 60% of the mold volume.

When this shrunken shaped product was subjected to the same drying process as in the experiment/%1 of Example 1, the shrinkage state was good.

Example 4 Polyethylene (density -0.9 2 1 9 /CC,
MI30, melting point 115°C, softening temperature 92°C) diameter 2m
Output 15Mr to rn pellets using IMV's furnace beam accelerator.
When irradiated with ad electron beam, crosslinked pellets with 5.0% crosslinking were obtained.

The crosslinked pellets were immersed in a 2:1 mixture of dichlorodifluoromethane and trichloromonofluoromethane at 60'C for 1 hour in a pressure vessel.

0.0% of this foamable pellet. When heated for 20 seconds with 5ky/CIIL (gauge) steam, the foaming ratio is 16cc/
, p were obtained.

The foamed particles were left in a room at 201 h Oc for 24 hours, and then shaped using the same molding machine, mold, and certain acceleration conditions as used in Example 1.

Immediately after the acceleration is finished, the mold is cooled with water, and when the surface temperature of the molded part in the mold reaches 95℃, the temperature in the steam chamber is reduced to -130mmH.
The pressure was reduced to El and cooling was continued, and when the surface temperature of the molded product reached 40°C, it was taken out, and no shrinkage was observed in the molded product.

When this molded product was left in a room at 20°C for 5 hours, it began to shrink.
When the same ripening process as above was performed, no shrinkage occurred anymore, and the state of shrinkage was evaluated as good.

Comparative Example Using the expanded particles, shaping machine, mold, and shaping heating conditions used in Example 1, shaping was carried out under conditions outside the scope of the method of the present invention, and the results shown in Table 2 were obtained. .

Claims (1)

[Claims] 1 A method of obtaining a foamed shaped product by filling a closed mold with foamed ethylene resin particles and heating (here, crosslinked ethylene resin foam particles are filled into a closed mold and heated to fuse the foamed particles to each other) After the molded product is assembled into one piece, it is cooled to below the softening temperature of the base resin while maintaining a reduced pressure atmosphere that does not cause deformation (after cooling, the pressure is increased to atmospheric pressure to soften the base resin). 5 below the softening temperature and above the softening temperature.
A method for producing an ethylene-based resin foam product, which comprises ripening at a temperature not lower than 0'C.