JPH02310026A - Manufacture of molded object of ethylenic resin foamed particle - Google Patents

Abstract

PURPOSE:To obtain economically the molded object which is excellent in the mutual adhesion and the water-absorbing property of particles and in the quality of appearance and has small permanent compression strain by specifying the molding condition in which the molded object in a mold of ethylene resin foamed particles is obtained by using the expansion property of compressed foamable particles. CONSTITUTION:The compression of prefoamed particle is kept in the range of 55-75% (45-25% in compression density) of original apparent bulk volume. The filling of a mold with compressed particle is carried out under the pressure (gauge pressure) keeping its compressed state. After the filling of the mold, the pressure in the mold is kept in the range of 0.2-0.7kg/mm<2> (gauge pressure) and is reduced to the pressure (gauge pressure) of 70-30% of the filling pressure. While steam is passed to the particles in the mold, the particle in the mold are preheated at the mold temperature in the range of at least 100 deg.C to the temperature lower than the melting point of base resin. Next, the temperature in the mold is raised to the range of the melting point of the base resin plus at least 5 deg.C to at most 14 deg.C by feeding high pressure steam into the mold, whereby the expansion of the foamed particles and the mutual adhesion of the particles are carried out.

Description

Detailed Description of the Invention "Industrial Field of Application" The present invention involves filling pre-expanded particles of ethylene resin into a mold in a compressed state, heating them with steam, and increasing the expansion ability of the compressed foam particles. This invention relates to an improved technique for an in-mold foam molding method in which particles are expanded and fused together to form a molded object.

[Prior art] Pre-expanded particles of ethylene resin are filled into a mold in a compressed state, heated with steam, and the expansion ability of the compressed expanded particles is used to expand and fuse the particles to each other to form the mold. For example, the in-mold foam molding method for forming the body is described in
Publication No. 996, ■Specification of British Patent No. 1560630, ■Japanese Unexamined Patent Publication No. 1984-1984, ■Japanese Unexamined Patent Publication No. 1984-1984
-212131 is described in publications and the like and is well known.

The molding methods described in the above ■~■ may be an in-mold foam molding method in which pre-expanded particles filled in the same mold are heated with steam to expand and fuse the particles to each other to form a molded product. 5
In the foam molding method described in Japanese Patent Publication No. 1-22951, the expansion ability of the foamed particles used for expansion in the instant mold is the expansion ability of the gas pressure added to the pre-expanded particles in advance. It is completely different from other foam molding methods and constitutes a different technical field.

1) Compared to the method disclosed in, for example, Japanese Patent Publication No. 51-2295, method (1) above can shorten the time required for imparting expansion ability to the pre-expanded particles for use in the mold.
This is an excellent method with advantages such as ease of management, but
The obtained molded product may be one in which the particles tend to be insufficiently fused together, local density unevenness tends to occur, or a low-density molded product is obtained.
There are problems such as ft. The methods of ■ to ■ are attempts to improve these problems.Specifically, method (■) expands the particles by increasing the filling pressure of the compressed particles filled in the mold by -gI-Jj and increasing the pressure I7. It is proposed to heat the particles with water vapor at a pressure equal to or higher than the pressure at the time of filling the mold into I-expansion fusion. In method 2, the filling pressure of the compressed particles filled in the mold is maintained to suppress the expansion of the particles, and steam is vented at a pressure slightly higher than the internal pressure of the filling mold to remove the air between the particles. After venting the mold, the pressure inside the mold is temporarily released to allow the particles to expand, and then the mold is heated with the water vapor pressure necessary for molding to expand and fuse the particles inside the mold. .

On the other hand, in the method for producing pre-expanded particles to be subjected to in-mold molding, expandable resin particles impregnated with a blowing agent are soaked in water, as described in Example 1 of the above-mentioned Japanese Patent Publication No. 51-22951. A method of heating and foaming with air to obtain pre-expanded particles, in which expandable resin particles impregnated with a blowing agent as described in Example 1 of Japanese Patent Publication No. 1344/1980 is placed in a pressure-resistant container. The particles are made into a suspension state in a high-temperature, high-pressure aqueous liquid, and the particles are then discharged into a low-temperature, low-pressure foaming region together with the aqueous liquid to form pre-expanded particles. There are methods such as extrusion using a die having a large number of small holes to foam the particles, and cutting the particles into pre-expanded particles into pre-expanded particles.

Therefore, the in-mold foam molding method using pre-expanded particles has been considered to have reached the level of technological perfection.

However, the pre-foaming method for ethylene-based resins mentioned above and the in-mold foaming molding method for ethylene-based resins are limited to saturated chloromethane such as dichloromethane, trichloromonofluoromethane, 1゜2-dichlorotetrafluoroethane, etc. It is no exaggeration to say that this technology was perfected in 7S when fluorocarbons were used as blowing agents. However, in recent years, the problem of reducing the amount of saturated chlorofluorocarbons used or during use has attracted attention. The prevailing opinion is that saturated chlorofluorocarbons have the effect of destroying the ozone layer in the stratosphere, making them a global environmental conservation issue. Therefore, the restriction on the use of saturated chlorofluorocarbons poses new and serious problems in the in-mold foam molding industry for ethylene resins.

That is, it is a blowing agent that is said to have relatively little or no destructive effect on the ozone layer, such as 1-chloro-1,1-difluoroethane, 1,1-difluoroethane,
Since blowing agents such as butane are flammable gases, when they are used as blowing agents for pre-foaming, the blowing agent gas escaping from the foam mixes with air and creates a flammable mixture. Because gas is formed, there is a problem in that manufacturing processes and environmental equipment require costly countermeasure equipment and monitoring systems.

Chlorodifluoromethane, chlorotrifluoromethane, 1
．． 1.1.2-When using flame-retardant gases such as tetrafluoroethane, ethyl chloride, methylene chloride, etc. as a blowing agent, it is difficult to obtain foamed particles that have poor closed cell properties and can withstand re-foaming. Even if the particles are devised to improve their low closed-cell properties and irregular cell structure, there is a problem that for some reason it is difficult to form a molded product of good quality when the particles are placed in a mold. Furthermore, attempts have been made to use inorganic gases such as air, nitrogen, carbon dioxide, and argon as blowing agents for pre-foaming, but these are not economical and result in irregular cell structures, making them difficult to use industrially. It has not yet reached the practical stage.

In other words, since the basic problem of ethyl 1/one resin being subjected to foaming has not been solved, it is difficult to find a suitable blowing agent to replace saturated chlorofluorocarbons.

[Problems to be Solved by the Invention] As stated above, the present invention is directed to the following: Due to the blowing agent employed, etc., it is difficult to obtain foamed particles that have poor closed cell properties and can withstand re-foaming. Even if the low closed-cell nature and irregularity of the cell structure are improved by devising methods, pre-expanded particles are difficult to form into good quality moldings when they are placed in a mold. This is what we are trying to deal with.

In other words, the purpose of the present invention is to produce a high-quality foam even when using pre-expanded particles, which are difficult to form into a high-quality molded product using conventional molding methods, that is, with excellent particle fusion properties and water absorption, and with sufficient compressive stress ( To provide an in-mold molding method capable of molding a molded article having a low compression set, no cracks, and superior appearance quality, in a more economical manner and using a smaller amount of steam. That's true.

[Means for Solving the Problems] In a conventional method for manufacturing a molded body for obtaining an in-mold molded body of expanded ethylene resin particles by utilizing the expansion ability of compressed expanded beads, (1), , I = molecule + iti Compression of expanded particles,
55-75% of the original apparent bulk volume (45-2
5%), (211) The filling of the compressed particles in the mold is carried out under pressure (gauge pressure) that maintains the compressed state; (3) The filling in the mold is as follows. After that, reduce the pressure inside the mold to 0.2 to 0.7 kg/cm.
” (gauge pressure) and the above filling pressure is 70~
The pressure is reduced to 30% (gauge pressure), and the temperature in the mold is reduced to 100% by passing water vapor through the particles in the mold.
The particles in the mold are preheated to a temperature in the range from 7°C to below the melting point of the base resin.

(4) Next, high-pressure steam is supplied into the mold and the temperature inside the mold is heated to a temperature within the range of the melting point of the base resin plus [5°C or more and 14°C or less] to cause expansion of the foamed particles and mutual fusion of the particles. The present invention relates to a method for producing an in-mold molded article of expanded ethylene resin particles, which is characterized by carrying out the following steps.

The contents of the present invention will be explained in detail below using drawings and the like.

FIG. 1 is a conceptual diagram showing the process principle of a method for manufacturing an ethylene resin foam particle in-mold molded article using the expansion ability of compressed foam particles, which is utilized in the present invention.

In FIG. 1, the mold used here is a core mold 1) having a steam chamber, 2. Cavity type I having a steam chamber, 2. When 2 are combined, a mold cavity D between the two molds:
(This is a combination type in which
When heating the foamed particles supplied to , with water vapor, etc., each foamed particle is directly heated by the water vapor.There are countless small holes in the mold wall constituting the mold cavity D, so that the particles are heated directly by the water vapor. It is the so-called type J, which closes but cannot seal the fluid. When the burr-shaped cavity is formed, its exterior is sealed with a steam chamber with a heating steam valve 12, 12", a cooling water valve 10°, a drain valve 0,0", and a steam chamber 12. By opening and closing these valves as appropriate, operations such as exhaust, pressurization, depressurization, pressure release, heating and cooling can be performed.

On the other hand, the pre-expanded particles in raw material tank A (actually large capacity) are
The gas is supplied (1,0) to a compression container B separated by a valve 10, pressurized with gas pressure from a high-pressure gas supply line 15 whose source is a compressor E, and adjusted to a desired bulk density by a pressurization control valve 1. Adjust compression. The compressed particles in the compression container B pass through the feeder 4 via the filling pressure supply valve 5, and are transferred from the gate valve 3 of the compression container B through the raw material port C into the mold cavity D3 by the suction force generated by the high-pressure gas jetted out. supplied to,
The high-pressure gas that has finished its role is discharged to the atmosphere through the PIC and the filling pressure release valve 7. The filling pressure in the mold during this filling process is adjusted by using a steam chamber with a compression container I3 and a drain valve 6,6.
□, 12. The pressure equalizing pipeline 13, 1.4 connects the compressor vessel I3 and the steam chamber 2, 1 through the pressure equalizing valve 8.
After that, the predetermined pressure is maintained by the pressure regulator PIC which detects the pressure in the steam chamber and 2+I□ and instructs to release excess gas from the filling pressure release valve 7. That's what I do. From then on, follow the desired procedure, e.g. steam room, □, 12.
By operating the drain valves 6, 6' and the collective drain valve 9, the pressure inside the mold can be reduced, depressurized, or drained. A heating steam line 11 connecting the steam room, □, and the steam room 12.
The temperature inside the mold is controlled by the temperature detection device T I of 12, and the cooling water line j7 connects the steam chamber 2 and the steam chamber 2 via the water source E (and the cooling water valve), 6.16". A series of in-mold molding is performed by combining operations such as cooling and the like, but since it is easy to understand, the explanation of the procedure will be omitted here.

What should be noted in the above-mentioned molding process?

a) There is a step in the series of systems that compresses the pre-expanded particles (providing them with the ability to expand in the mold), and b) When heated in the mold, the voids between the particles are compressed. It is believed that the expansion capacity required to tightly fuse the particles together is due to the restoring force of the compressed and folded cell walls. In particular, in processes such as "double series", it is customary to store foamed particles in excess of one shot (usually several shots) in the compression table "aB", and the particles in the raw material hose are Since the compression container side is depressurized and returned to the compression container each time the particles are released, some of these particles will undergo repeated pressurization and depressurization operations in the compression container.

Figure 2 1. It and III are enlarged cross-sectional views of expanded particles; I is expanded particles obtained using conventional saturated chlorofluorocarbons as a blowing agent; These foamed particles were created by devising the foaming conditions.

In FIG. 2, 1, 1.1, and III, 11 is inferior to 1.11 in both closed cell properties and cell shape alignment, but 1.1. I do not think that I is significantly inferior to l. However, III is essentially different from I in terms of molding.

Table 1 shows the results of qualitative evaluation of the differences in this area (Experimental Example 1
). This experimental phenomenon is also a reproduction of a defect phenomenon that was finally discovered through the efforts of the inventors to analyze the cause of the defect. In other words, the way the foamed particles corresponding to Figure 2 1, 11, and 1.11 are compressed under the same pressure and the difference in their recovery properties were evaluated by changing the number of pressurization-release cycles. It's a shitty thing.

According to the results in Table 1, even for particles 1, 1.1, and 11.1 with the same expansion density (expansion ratio), the degree of compression and the degree of recovery differ depending on the cell structure and the history of pressure applied. It shows that it will come. In other words, the degree of compression and recovery of conventional particles do not change significantly depending on the history of pressurization. On the other hand, II.

It can be seen that the size of the compressed particle and the recovery performance of the particles No. 1.11 deteriorate significantly due to the pressure history.

In particular, it can be seen that particles II cannot be used in the molding method targeted by the present invention because of their poor compression recovery properties.

And the results in Table 1 (change in blowing agent type) are as follows.

★We set the degree of compression of particles using a master graph of the relationship between foam density and gas pressure, and reviewed the conventional control system and equipment that used this as an indicator for quality control of molded products. This study teaches the necessity of new setting of molding conditions suitable for easily foamed particles.

The requirements of the invention will be explained below.

14) First, the density of the pre-expanded particles is 0.020 to 0.0488/
The limit on cm' is the foaming density of particles that can be applied to a molding method that utilizes the heat recovery properties of compressed particles as expansion ability during molding. Therefore, in the present invention, the pre-expanded particles to be used are selected from the above particle density range in accordance with the target density of the molded article.

Next, the above requirement (1), that is, the compression of the pre-expanded particles,
55-75% of the original apparent bulk volume (45-2
5%) We will discuss the necessity of keeping it within the range of 1.

Table 2 shows the expanded particles 1. I
Regarding II, it shows the degree of compression and its recoverability. According to the results in Table 2, even if 10 particles are compressed beyond 55% (45% in compression) of their original apparent bulk volume, their recovery remains unchanged and exceeds 90%. On the other hand, when Ill particles are compressed to a state of 55% (45% compression) of their original apparent bulk volume, their recovery decreases to 90% recovery. Phenomena below are observed. This phenomenon is presumed to be due to the fact that the cell walls of No. 111 particles (expanded particles obtained using unsaturated chlorofluorocarbons as a blowing agent) were significantly damaged by pressurization.

By the way, in the target in-mold molding, the expansion capacity required to fill the voids of the filled particles requires compression to at least 75% of the original apparent bulk volume (25% in compression degree), and In the case of Zu A1, the recovery of the particles in the compressed state is 9
It is known that 0% or more is necessary to obtain a molded article of good quality. Therefore, from the two series of phenomena and knowledge, it can be seen that the requirement in (1) above is the necessary condition in (2) for molding expanded particles as in 11.1 above.

The next requirement (2) above, ie, the necessity of filling the compressed particles in the mold under pressure (gauge pressure) that maintains the compressed state, will be described based on 4=1.

In this type of in-mold molding, the target density of the molded body is determined by the density of the expanded particles used and the degree of compression of the particles in the two conditions (1, l).-The degree of compression of the particles in the force compression state. changes depending on the pressure environment in which the particles are placed.Therefore, requirement (2) is necessary to ensure that the target molded product set in requirement (1) above is obtained in a stable state without unevenness. It can be said that it is a thing.

Next, we meet requirement (3), that is, after filling the r mold, the pressure inside the mold is reduced to 0.
．． The pressure is reduced to a pressure (gauge pressure) in the range of 2 to 0.7 kg/cm2 (gauge pressure) and 70 to 30% of the above filling pressure, and water vapor is passed through the particles in the mold in that state. The necessity of preheating the particles in the mold to a temperature in the mold range of 100° 0 or more to less than the melting point of the base resin will be described.

First, let us consider the significance of 1 reduced pressure 1 in this case. The essence of this necessity is considered to be to facilitate the discharge of air interposed between particles during the next preheating step 1, thereby increasing the heating efficiency during forming heating. If we look at the importance of this point in the conventional in-mold foam molding method, for example, in the method of ■ Japanese Patent Publication No. 53-33996,
This is not specifically mentioned. and ■ British Patent No. 156
In the method of Publication No. 0630, "releasing the pressure"
, ■Japanese Unexamined Patent Publication No. 82-498444.

■The method disclosed in Japanese Patent Application Laid-Open No. 62-212131 [maintains the internal pressure of the mold during filling to suppress recovery of compressed particles]
are requirements for each invention.

However, when foamed particles such as III referred to in the present invention are targeted, following the above-mentioned conventional requirements will not result in a molding method that can economically obtain the targeted molded product.

Table 3 (corresponding to Comparative Example 1) demonstrates the situation here. In other words, in the above method (1,216+), a phenomenon in which the particles are partially fused together occurs in the resulting molded product, and when trying to improve this (TN (1,216+), the foam properties partially deteriorate. The phenomenon of forming a molded product with uneven spots occurred, and suitable conditions could not be found.Also, the above method (■■) (T No. 3.
In 7), a phenomenon occurs in which the surface layer of the molded body is well fused, but the internal particles are hardly fused. Although the heating conditions intended to improve this (T No. 4.8) improved the poor fusion of the internal particles, the result was a molded product with partial particle fusion defects remaining, and suitable conditions could not be found. It is.

Examining this phenomenon from the phenomenon shown in Table 4 (corresponding to Example/Comparative Example 2), which proves the necessity of requirement (3) of the present invention, shows that the pressure inside the mold (hereinafter referred to as gauge pressure ; kg
/ cm2) is lowered by more than 0.2 (for example, T
No. 18) is the result of the above method (■), and when the pressure inside the mold is set to a high state exceeding 0.7 (e.g. T No. 14), the method of the above (■) and (■) is the result. A defective phenomenon with the same tendency as that of the previous one is observed.

This phenomenon is probably due to the fact that when the mold internal pressure is lower (than 0.2), the compressed particles expand and the particle spacing becomes narrower, which obstructs the flow of steam, resulting in partially insufficient air evacuation. Adhesive spots occur. Heating to eliminate these fusion spots results in excessive heating of the areas where steam easily flows, causing local particle bubble destruction and resulting in a molded product with spots where the foam properties have partially deteriorated. It is estimated that this will occur. On the other hand, if the mold internal pressure is higher (than 0.7), the pressure of the water vapor that can overcome this internal pressure and be supplied to the mold increases, so the particles on the surface of the molded product that first come into contact with this water vapor expand and expand first. As a result of the fusion and blocking of the flow of steam into the interior, a phenomenon occurs in which the underheated konatsu l and internal particles are not fused together. The preheating conditions to suppress the expansion and fusion of the surface particles and increase the fusion of the internal particles are as follows:
It is presumed that a phenomenon occurs in which the air between particles cannot be sufficiently discharged, leaving spots of fusion of particles in various places.

In the present invention, while the pressure inside the mold r is defined as a range j of 0.2 to 0.7 (gauge pressure), the pressure inside the mold is defined as
Setting the pressure at 70 to 30% of the filling pressure (gauge pressure) means that the filling pressure of compressed particles must be reduced in the mold.For example, if the pressure inside the mold is 0,7
(gauge pressure)'' does not include cases in which the filling pressure (gauge pressure) of particles into the mold is maintained as it is.

The importance of this "pressure reduction" is as explained above.In other words, in short, the "preheating" that follows in requirement (3)
This is to perfect the effectiveness of the liquid at a lower temperature. In other words, in this case, preheating by passing water vapor through the r-type internal particles is an economical and complete way to completely eliminate the gas (mainly air) that exists between the particles and inhibits the expansion and fusion of the particles during heating. It is thought that it was intended for the purpose of

Therefore, in the present invention, it is possible to easily preheat the particles in the mold to a temperature within the range of 100° 0 or more to less than the melting point of the base resin using steam at a relatively low pressure. And the need for temperature regulation is as follows: Even under the pressure inside the mold, if the temperature inside the mold is less than IOO'C (for example, T No. 15), poor fusion of particles will occur, and conversely, if the temperature inside the mold is less than IOO'C (for example, T No. 15), If the temperature (for example, TNo. 14.17) is reached, local fusion of particles may occur or bubbles may burst, resulting in deterioration of the properties of the molded product.

In the present invention, the evacuation of air between particles and the rise in particle temperature during preheating are sufficient, so after the step of requirement (3) above, the process moves to requirement (4) immediately (without releasing pressure inside the mold). (e.g. TNo. 11'). However, since the fusion of the particles becomes more complete and the amount of steam used does not increase so much, it is desirable to include a step of ``releasing the pressure inside the mold during preheating'' as an intermediate step. This pressure release step can be easily carried out after the preheating process step, for example, by closing the heating steam supply side valve and increasing the opening of the discharge side valve instantaneously to the extent that atmospheric backflow does not occur. Wear.

Next, meet the above requirement (4), that is, first, high-pressure steam is supplied into the mold to raise the temperature inside the mold to the melting point of the base resin plus [5°C or more].
The necessity of heating the expanded particles to a temperature in the range of 14° C. or below to cause expansion of the expanded particles and fusion of the particles to each other will be described below.

Table 5 (corresponding to Example/Comparative Example 3) shows the experimental results regarding the above requirement (4).

According to Table 5, the necessity of this condition range is due to the thermal recovery of the residual compressed state of the foamed particles as referred to in 11.1 in the present invention, the expansion of the foamed particles in the mold, and the interaction between the particles. This is considered to be a condition for effective use of the expansion force that governs the fusion and adhesion of the particles. That is, the melting point of the base resin plus 5°C
If the temperature is less than 14°C (for example, T No. 24, 26), the expansion force is insufficient, resulting in poor particle fusion and increased water absorption of the molded product.
(For example, TNo. 21.23.
In No. 28), phenomena such as increased sink marks and deterioration of the properties of the molded product were observed, probably due to the collapse of the cell structure.

Here, the meaning of 1. Expanding the expanded particles and fusion of the particles with each other means 2. Heating (pressurizing) to a predetermined temperature.
The pressure inside the mold (both front air chambers) is suddenly released, and the particles are expanded and fused all at once.This part is a conventional known method. There is no difference.

As has been demonstrated and clarified above, according to the molding method of the present invention, pressure, heating, etc. as shown in FIG. 2 111 (expanded particles obtained using unsaturated chlorofluorocarbons as a blowing agent) Even when using expanded particles that easily deteriorate due to external forces, a molded article of good quality can be obtained. This is extremely effective as a measure to regulate the use of saturated chlorofluorocarbons. By the way, according to the molding method of the present invention,
Naturally, it was confirmed that even when using the conventional high-quality particles (expanded particles obtained using saturated chlorofluorocarbons as a blowing agent) shown in Figure 2 I, a high-quality molded article could be obtained (TNo. 29). I'm ill.

From the viewpoint of making the molding method of the present invention more complete and reliable, the pre-expanded particles used have a density of 0.025 to 0.
．． It is desirable to select S1 from the range of 0.048 g/Ωm3.

In the present invention, the ethyl-1/one-based resin has an ethylene component of 5
It is a general term for polymer resins, copolymer resins, mixed resins of these resins, and mixed resins of other resins that can be mixed with these resins, where the amount is 0% by weight or more. Specifically, for example, ethylene polymer resins represented by high, 4J, and low density polyethylene, copolymer resins of ethylene and α-olefin represented by the names LLDPE and VLDPE, ethylene and vinyl acetate, and chloride. Vinyl, ethyl acrylate.

1 of monomers such as methacrylate and acrylic acid
These include copolymer resins with more than one species, mixed resins of two or more of these, and mixed resins with other resins mainly consisting of these resin components. Among them, the density is 0°935~0.900
(g/cm3), commonly known as polyethylene, LLD
Resins called PE, VLDPE, and mixed resins thereof are preferable. These are used either uncrosslinked or crosslinked, but in order to stabilize the foamed state, it is preferable to use them crosslinked. A common and well-known crosslinking method in this case is to impregnate a resin with a predetermined amount of a chemical crosslinking agent such as dicumyl peroxide, and then heat and crosslink the resin.

In the present invention, saturated chlorofluorocarbons refer to hydrocarbons in which the hydrogen portion is filled with halogens such as fluorine and chlorine, with no portion remaining as hydrogen; What are unsaturated chlorofluorocarbons?
It means that the hydrogen part of the hydrocarbon remains.

(blank below) The evaluation method used in the present invention is as follows.

Note that this evaluation was performed on plate-shaped in-mold molded bodies having a length and width of 300 mm each and a thickness of 80 mm obtained in Examples and the like.

i) A slit is made in the fusion-adhesive molded body (of particles) at a depth of 2 mm across the lateral dimension in the thickness direction, and the molded body is pushed apart in the thickness direction through the slit. The ratio of material-broken particles to the total number of particles existing on the fracture surface is determined and evaluated using the following scale.

ii) The molded product whose water absorption weight has been measured is submerged in fresh water at a temperature of about 20'C at a position 25 mm+ below the water surface, and the volume of the molded product is determined from the buoyancy at that time. After maintaining the submerged state for 24 hours, the molded body is transferred to an alcohol bath, immersed for 1 minute, taken out, air-dried for 40 minutes, and weighed.

Evaluate by calculating the weight increase before and after submersion as follows.

Water absorption (%) = [weight increase (g) x 100] ÷ [molded object volume (cm3) x water density (g/am3)] mountain)
A horizontal ruler is placed on the top surface of the molded product in the diagonal direction, and the maximum dimension of the gap created between the surface of the molded product and the ruler is determined and evaluated as follows.

(Blank below) iv) Compressive Stress Index Compressive stress is greatly influenced by the density of the foam, so it is expressed as an index in order to make a -law evaluation.

A sample piece of 100 mm in length and width is cut out from the molded body, and its density is determined by the test method of JIS K [3767]. Next, the compressive stress at 25% compression of the sample piece was determined according to JIS ZO2.
34 (compression speed 10 mm/min), and evaluated by converting it into a coefficient (without unit) using the following formula.

Compressive stress index = 25% 25% compressive stress (kg/cm2
) ÷ Density of sample piece (g/cm3) (blank below) ■) Cut a sample piece of 50 mm in length and width and 25 mm in thickness from the compression set molded body, and determine the compression set using the test method of JIS K6707, as follows. evaluate.

vi) Economic efficiency (amount of steam used) The amount of steam used for molding was measured using a steam flow meter [Turbo Steam Meter G5-11081B-Zr2 (manufactured by Oval Equipment Industry), and the amount of steam consumed per shot was determined. The average of 10 consecutive shots was calculated and evaluated as follows.

vii) Comprehensive evaluation The above evaluation results of i) to vi) were combined and evaluated as follows.

vii) Closed cell ratio (%) Evaluated using an air compression vicinometer (930 old model manufactured by Beracman) and calculated using the following formula.

Closed cell ratio (%) = 100X (VX-W÷D)÷(RX
W-W+D) However, R: Foaming ratio = reciprocal of foam density (cm3/g)■8
; Volume of expanded particles (cm3) W; Weight of expanded particles (g) D; Resin density of expanded particles (g/cm3) [Example] Resin row used in the following experimental examples, working examples, and comparative examples summarized in.

Symbol Contents A: High-pressure low-density polyethylene (Santic LD Q951.1 manufactured by Asahi Kasei Shisha)
Density, 0.930, M I ; 2.4, Melting point; II
6°C B: High pressure low density polyethylene (Santic LDM2115 manufactured by Asahi Kasei Corporation) Density;
o, 921, M I ; 1.5, melting point; I08°C
; Linear low-density polyethylene (Dowlex 2032 manufactured by Dow Chemi ■) Density: 0
．． 925, M I; 2.0, melting point; 121°C D
;Ultra low density polyethylene (Nacflex DFDA-1137 Nippon Unicar■
company) Density: 0.906, M! , 1. Melting point: 118℃
Example 1 In this example, pre-expanded particles were prepared to be used in the following experimental examples, examples, comparative examples, etc.

The resin used, blowing agent type, pre-foaming conditions, etc. shown in Table 6 are as follows:
This is an explanation of the actual situation at that time.

- Secondary foaming and secondary foaming refer to a two-step foaming process to produce pre-foamed particles, and - secondary foaming, secondary foaming and tertiary foaming refer to a three-stage foaming process to produce pre-foamed particles. This means that each foaming process was carried out separately. In addition, in the "bubble internal pressure imparting process" in the second and third foaming sections, foamable particles consume all of their foaming ability in one foaming process, so air is used as the foaming ability for foaming at each stage. In the meaning of impregnating the particles into the bubbles, the column describes the conditions for this purpose and the density of the foamed particles reached.

The obtained pre-expanded particles were numbered from ■ to X and summarized in Table 6.

In order to make it easier to understand the relationship with the drawings, experimental examples, examples, comparative examples, etc. shown below, the following table has been prepared.

T No. 9 to 18 are in Table 4 (corresponding to Example/Comparative Example 2) T No. I 9 to 28 are in Table 5 (corresponding to Example/Comparative Example 3)
) 'rNo. 29 is Example 4 "Experimental Example" This experiment is for comparing and demonstrating the performance of foamed particles.

Experiment-1 Expanded particles with a density of 0.03 g/cm' obtained in Example 1 (.

1.1, 1.1. For each of I, when compression (compression) and release (expansion) were repeated, it was evaluated what changes occurred in the way the expanded particles were compressed and the degree of recovery.

In other words, foamed particles placed in a pressure-resistant glass container with graduations,
Compress the particles with pressurized air at 1.0 kg/cm"G for 30 seconds and measure the bulk volume of the particles at the time of compression, and measure the bulk volume of the particles when the pressure inside the container is released. The above operation was repeated five times, and the degree of compression and (3F3) recovery of the particles with respect to the number of compressions were determined from the relationship with the bulk volume of the original particles, and the results are summarized in Table 1.

Experiment-2 For each of the foamed particles with a density of 0.03 g/cm30 and 1°11.1 obtained in Example 1, the degree of pressurization (compression) was changed and the pressure was released (expanded). We evaluated how the compression and the degree of recovery changed. That is, under the conditions of Experiment 1 above, the pressurized air was 0.9°1, 0.1.2.1
．． 3.1.4 The same experiment as above Experiment 1 was repeated using 5 levels of 1 kg/cm"G and the number of compressions was changed to 1. The degree of compression and recovery of the particles were determined and the results are shown in Table 2. summarized in.

In addition, the expanded particles 1, II, and III used in the above re-experiment
The closed cell ratio was 98% for 1, 88% for IJ, and 93% for Kawa. The enlarged (partial) cross-sectional view is shown in Figure 1.1. Shown as II and III.

Comparative Example 1 This comparative example demonstrates that conventionally known molding methods similar to the present invention are unsuitable for molding expanded particles targeted by the present invention.

The molding device shown in Fig. 1 was used, and the mold had dimensions of 311 x 311 x 82 mm when the core mold and cavity mold D2 were combined, so-called "closeable but not airtight". I used a type that could not be done.

In the reproduction of these conventional methods, efforts are made to reproduce the description of the target specification as faithfully as possible, but due to space constraints, detailed process steps are omitted, and the features of the technology are omitted. Please keep it in the description. In addition, since the control items for molding differ depending on each method and are complicated, the control items adopted in the present invention are unified so that they can be easily compared with the present invention.

The relationship between the conditions and results is summarized and expressed in Table 3. The pre-expanded particles used in this molding experiment were
Expanded particles No., IIl and No. corresponding to the particles in Figure III
, V.

(i) Study using the method described in British Patent No. 1,500,030 The feature of this manufacturing method (indicated by ff j) is that compressed particles are filled into a mold, the pressure inside the mold is released, and water vapor is added to the mold. A molding method in which the particles are introduced and heated to a state where the pressure is equal to or greater than the effective pressure when the particles are filled into the mold, and the pressure inside the mold is released to expand and fuse the particles. It is.

This manufacturing method was reproduced with T No. 1.2.5°6 in Table 3, of which T No. 1 and 5 were reproduced as they were, while T No. 2 and 6 were reproduced with different heating conditions. This is a reproduction. In other words, in the reproduction shown in T No. 1.5, a phenomenon occurs in which the obtained molded body becomes partially defective in fusion, so in T No. 2 and 6, the heating is increased to eliminate the defect in fusion. This refers to the situation where the level of heating conditions is changed to the extent possible. However, the results showed that although the partially existing poor fusion could be improved somewhat, on the contrary, the collapse of particle bubbles, which appeared to be caused by overheating, became noticeable and the properties of the molded product deteriorated, so it was difficult to find the optimal conditions. I was unable to do so. This phenomenon is probably due to a feature of this manufacturing method, namely, the fact that the pressure inside the mold is released after filling the compressed particles (particles in a compressed state naturally expand)1. It is presumed that this reduces the effect of heating by exhausting air and creates conditions that are inconvenient for heating the target expanded particles.

(ii) Japanese Patent Application Publication No. 12-212131, Japanese Patent Application Publication No. 02-
Study using the method described in Publication No. 198444 The feature of this manufacturing method (indicated by r This is a molding method in which particles are preheated by introducing water vapor at a pressure of 11, the pressure inside the mold is released, 1 steam for heating is introduced into the mold, the particles are heated, and then the internal pressure of the mold is released to expand and fuse the particles. . And JP-A-02-198444 is JP-A-82-2121.
It is presumed that this is an improved technology for the preheating conditions of No. 31, and the difference is that in JP-A No. 82-198444, the filling pressure +0.2 kg/cm is separately added to the R-type steam chamber during the preheating process.
A step 1 is added in which water vapor is introduced at a pressure of 2G or more.

T No. in Table 3. 7 corresponds to the exact reproduction of the manufacturing method of JP-A No. 82-212131. However, in the resulting molded article, a defective phenomenon occurs in that although the particles on the surface of the molded body are reasonably well fused without causing a slight overheating, the internal particles are hardly fused. Therefore, T No. In No. 8, we shortened the heating time for preheating to improve the above-mentioned phenomenon of the surface side being fused first, and tried to heat the internal particles more, but the entire molded body seemed to have poor fusion. The result is a molded product with poor water absorption and foam properties, making it impossible to find suitable conditions.

Therefore, as i' Ni1.3, the
Adopting the method of No. 44, 1.14 was also applied to the r-type steam chamber.
An attempt was made to improve the preheating conditions by introducing water vapor at a rate of kg/cm2G, but this did not resolve the phenomenon in which only the particles on the surface were fused first and the internal particles were hardly fused. Therefore, for T No. 4, we tried to lower the preheating temperature and shorten the heating time so that the internal particles could be heated more, but the entire molded product seemed to have poor fusion and the molded product had poor water absorption and foam properties. You can only get it.

This phenomenon is probably due to the characteristics of the manufacturing methods of JP-A No. 62-212131 and JP-A No. 62-198444, that is, the internal pressure of mold 1 is maintained and the compressed state of the packed particles is maintained while j and r (filling pressure + 0. One characteristic condition of preheating, which introduces water vapor at a pressure of 2 kg/cm" or higher), is that the effect of discharging the air existing between particles is poor, and preheating at high pressure (high temperature) to try to push it out is It is estimated that the conditions would be inconvenient for heating the target expanded particles.

The results shown in ``2'' demonstrate that conventionally known molding methods similar to the present invention are unsuitable for molding the expanded particles targeted by the present invention.

Example/Comparative Example 2 This molding experiment was carried out based on the “requirement (3) of the structure” in the molding method of the present invention, that is, the “in-mold pressure during preheating (in-mold pressure after particle filling)” part of the molding method of the present invention. This is to demonstrate the necessity of preheating method and its temperature condition J.Therefore, other conditions, such as particle compression bulk volume ratio (compressibility degree), compaction ``temperature inside the mold at the time'' is fixed at the level of the present invention, ``resin used'', ``expanded particle density'' and
It was also decided that the content of this demonstration would be limited to the minimum change that would allow for the scope of application of the "density of the compact". Therefore, the foam particles used are No., III, and I.
V.

There were five types: Vl, Vll, and ■.

In addition, the same molding equipment and mold as in Comparative Example 1 were used,
All of the control items (molding conditions and results) are summarized in Table 4. In this item, "mold pressure after depressurization" indicates whether the pressure is in the range of RO, 2 to 0.7 kg/cm"GJ, and [(ratio to filling pressure)" indicates that the pressure must be reduced. Check whether the degree of pressure reduction is in the range of 70 to 30% of the filling pressure, and whether the temperature inside the mold during preheating has reached a temperature in the range of 100℃ or higher to 1 below the melting point of the base resin. The "mold internal pressure during preheating" is used to confirm whether or not a reduced pressure state is maintained during preheating. 3)” is proven. If necessary, the mold filling pressure of the particles can also be determined by dividing the "mold pressure after decompression" by "(ratio to the filling pressure)".

By the way, in the molding apparatus shown in Figure 1, the operation of "depressurizing the inside of the mold after one filling" in the experiment involved setting the pressure regulator PIC in two stages: "setting the filling pressure" and "setting the mold internal pressure after depressurization." This was achieved by moving to a reduced pressure after the filling was completed, and releasing excess compressed gas during the reduced pressure from the filling pressure release valve 7. Furthermore, in the present invention, the "preheating operation of passing water vapor through the particles in the mold" is carried out in the cavity mold D with the drain valve 6' closed.
So-called one-sided heating is performed by supplying steam at a predetermined pressure of 12゜ into the steam chamber of the core type D1, □, and flowing it out from the drain valve 6 whose opening degree is narrowed through the steam chamber of the core type D1, □. I achieved it by doing it.

In Table 4, Examples are shown in T No. 9 to 13, and Comparative Examples are shown in T No. 14 to 18. And T No. 1
1. ' indicates that the same conditions as T No. 11 are adopted, but the process of releasing the mold internal pressure during preheating, which is an intermediate process of heating after preheating and heating during molding, is omitted.

In view of the comprehensive evaluation of the results of the molding experiment, the ones that can give satisfactory results marked with a ■ are those with a T number that satisfies each condition of "Construction Requirements (3)" of the molding method of the present invention, and a T that includes 11°.
Only those with No. 9 to 13 (Examples) and those with T No. 14 to 18 (Comparative Examples) that do not meet this condition are marked with △: Unsatisfactory, and X: The molded product is not practical. I understand.

(Blank below) Example/Comparative Example 3 This molding experiment was conducted to evaluate the “requirement (4) of the structure” in the molding method of the present invention, that is, the “temperature j inside the mold during molding” in the present invention. This is to demonstrate the necessity.Therefore, other conditions 1, for example, "Construction Requirements (3)" verified in Example/Comparative Example 2 are fixed within the scope of the present invention, and "Inside the mold during molding" is It was designed to focus on changes in temperature 1.On the other hand,
The "resin used", "foamed particle density", and "molded object density" obtained have been slightly changed to make it clear that the content of this demonstration has a scope of application, and Table 5 is shown as a management item along with the obtained results. summarized in. Therefore, the expanded particles used were changed to No., III, ■, [X, and X, and the same experiment as in Example/Comparative Example 2 was repeated. At this time, after heating to reach the "temperature inside the mold during molding", the pressure inside the mold is released to complete the expansion and fusion of the particles, and the molded product must be cooled and taken out. As this is a well-known fact, its description is omitted, as in the case of Example and Comparative Example 2.

In Table 5, the example is TNo. 1.9.20.22
．． 25.27 and the comparative example is T'No, 2 I, 23
, 24°26.28.

In view of the overall evaluation of the results of the molding experiment, those marked with a mark (■) that leave out the satisfactory results are T' No. 19, which satisfy the condition of "Construction Requirement (4)" of the molding method of the present invention.

20.22, 25.27 (Example) are the only TNos that do not satisfy this condition, 21.23, 24, 26.
28 (comparative example) is marked △; unsatisfactory?
It can be seen that this results in a molded product that is not practical.

Example 4 This example demonstrates that the molding method of the present invention can also be applied to conventional high-quality pre-expanded particles made of saturated chlorofluorocarbons with a blowing agent. That is, the TN of Example/Comparative Example 3 was used except that the expanded particles used were changed to 1.
The molding of T No. 19 was repeated under the same conditions as f-mouth 90, and 'I' No. 29 was obtained.The molding condition was good and no different from that of T No. 1.9, and it was economical. The evaluation was O.

The obtained molded body was evaluated for fusion adhesion, water absorption, compressive stress index, compression set, and sink mark, all of which were marked O.
The symbol for the overall evaluation is now @.

[Effects of the Invention] As has been explained in detail and clarified, the present invention has the advantage that when the blowing agent of saturated chlorofluorocarbons, which has been commonly used in the stage of obtaining pre-expanded particles, is changed to, for example, unsaturated chlorofluorocarbons, This problem in the in-mold foam molding technology for ethylene resin foamed resin particles, which ``makes it impossible to obtain high-quality molded objects,'' which occurs, has been solved by improving the molding method.

According to the present invention, pre-expanded particles can be used in areas where it is difficult to obtain a high-quality molded product using conventional molding methods due to problems such as irregularity in the cell shape structure and the tendency for the cell structure to deteriorate due to external forces. We also offer high-quality foams, that is, molded products with excellent particle fusion properties and water absorption, sufficient compressive stress (index), low compression set, no sink marks, and excellent appearance quality, in a more economical manner. It has the advantage of being able to be molded in a state where the amount of steam used is small. Naturally, therefore, it can also be applied to obtaining a high-quality foamed body using high-quality pre-expanded particles where a high-quality molded body can be obtained by conventional molding methods.

51) From the above viewpoint, the present invention, having the above-described configuration, can at least take one step forward in countering the problem of restricting the use of saturated chlorofluorocarbons, which is currently considered a global environmental issue. This is a highly significant invention.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram showing the principle of the molding process, Figure 2 I and II
, III are experimental diagrams showing the structure of expanded particles. [Diagram symbol] Type: combination of core type D1 and cavity type D2

Claims (1)

[Claims] 1) Made of ethylene resin with a density of 0.020 to 0.048
g/cm^3 of the pre-expanded particles to 8 of the original apparent bulk volume.
After compressing with pressurized gas to a volume of 0% or less and filling it into a mold, steam is supplied into the mold and heated to expand the foamed particles and fuse the particles together. In the method for producing an in-mold molded body of expanded ethylene resin particles to form a molded body, (1) the pre-expanded particles are compressed to 55 to 75% of the original apparent bulk volume (45 to 25% in compression degree). (2) Filling the compressed particles into the mold under a pressure (gauge pressure) that maintains the compressed state; (3) After filling the mold, 0.2 to 0.7 kg/cm
^2 (gauge pressure) and 70% of the above filling pressure
The pressure is reduced to ~30% pressure (gauge pressure), and water vapor is passed through the particles in the mold to bring the temperature inside the mold to 100%.
Preheating the particles in the mold to a temperature in the range of ℃ or higher to lower than the melting point of the base resin (4) Next, high-pressure steam is supplied into the mold to increase the temperature inside the mold to the melting point of the base resin plus [5℃]. An in-mold molded article of expanded ethylene resin particles, characterized by passing through the following steps: heating the expanded particles to a temperature in the range of 14°C to 14°C to cause expansion of the expanded particles and fusion of the particles to each other. manufacturing method. 2) The ethylene resin foam particles according to claim 1, wherein the pre-expanded particles contain monochlorodifluoromethane and have a density of 0.020 to 0.048 g/cm^3. A method for producing an in-mold molded body.