JPH1058474A - Manufacture of foam molding in polyolefin resin mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold a molding of a thick large size of high quality or a complicated shape in which a thick part and a thin part coexist from non-crosslinked polyolefin prefoamed particles. SOLUTION: The method for manufacturing a foam molding in polyolefin resin mold comprises the steps of preheating prefoamed particles in the mold for a time of 12 sec or less from a start of supplying steam by press rising it to a steam pressure (kg/cm<2> G) in the mold of a range of 20 to 60% of the steam pressure (kg/cm<2> G) in the mold within 3sec at the time of primarily heating (heating both the surfaces), then raising the pressures (kg/cm<2> G) in both the molds to a saturated steam pressure (kg/cm<2> G) corresponding to a temperature of a range of -5 to +5 deg.C of a melting point of a base material resin of the particles within 3sec, and primarily heating it for a time of 6 sec or less, thereby foaming the particles and fusion bonding among the particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-crosslinked polyolefin resin pre-expanded particle, which is filled in a mold and heated and foamed with steam to fuse the particles together to form a foamed molded article. The present invention relates to an improved technique for in-mold foam molding of polyolefin resin pre-expanded particles. In particular, the present invention relates to an improved technique of an in-mold foam molding method suitable for molding a large-sized molded article having a large thickness or a complex-shaped molded article in which a thick portion and a thin portion coexist.

[0002]

2. Description of the Related Art Conventionally, foamed particles of a thermoplastic resin are filled in a mold and foamed to fill gaps formed between adjacent particles, and the foamed particles are closely fused to each other to obtain a shape according to the mold. A method for obtaining a foamed molded product is widely known. This production method has been developed as a method for producing a foamed molded article using a polystyrene resin as a base resin, and has been almost completed as a method for producing a foamed molded article in a polystyrene mold.

However, when a polyolefin (polyethylene, polypropylene) is used in place of polystyrene as the base resin in the method for producing a foamed molded article in a polystyrene mold, a satisfactory foamed molded article cannot be obtained. This is an essential property of polyolefin resin,
In other words, the resin has poor ability to retain gas in a resin for a long time in a state of having a foaming ability, and has poor gas retention (barrier property) such that gas escapes in a short time than resin. The main reason for this is that it is not possible to find appropriate foaming conditions due to the remarkably large temperature dependence of the change in the fluid viscoelastic properties.

[0004] Therefore, as a method for producing a polyolefin resin in-mold foam, a pre-expanded particle is provided with expandability for in-mold foaming. As a method of imparting this expansion ability, for example, the pre-expanded particles are placed in a pressurized atmosphere of an inert gas such as air or nitrogen, and the volume of the expanded particles is reduced to 80% or less of the original volume. Gas pressure compression method (disclosed in JP-B-53-33996), in which the elastic recovery force generated by this compression is the main force of the in-mold expansion ability, or impregnated with inorganic gas in the pre-expanded particles. The gas pressure in the particles is increased to 1.18 atmospheres or more, and the gas pressure addition method is used in which the expansion force of the gas is the main force of the in-mold expansion capability (disclosed in Japanese Patent Publication No. 51-22951). A combination method of combining these methods is known and adopted.

Further, some improved molding methods are disclosed in Japanese Patent Application Laid-Open Nos. 57-174223 and 62-267129. In the method described in these publications, pre-expanded particles are filled in a mold, and air is removed by depressurization through a small hole for ventilation of the mold through a conduit connected to a device under reduced pressure, and steam supplied from a steam supply pipe. After removing air in the mold by degassing, a method is used in which steam is supplied from a steam supply pipe into the mold to foam and fuse the pre-expanded particles in the mold, thereby improving the degree of fusion between the particles. It has the effect of improving the quality of the compact and shortening the molding cycle.

[0006] By these manufacturing methods, it has been considered that the in-mold foam molding method of non-crosslinked polyolefin resin pre-expanded particles has reached a technically complete area. However, the technology of the in-mold foam molding method using the non-crosslinked polyolefin resin pre-expanded particles is a thin-walled small-sized molded product,
It is not an exaggeration to say that the technology has been completed for simple molded products such as corner pads. However, in recent years, as a trend in the market, for example, as shown in a foamed cushioning molded article used for collective packaging of liquid crystal modules, there is a demand for a foamed molded article having a complicated shape having many irregularities, thick and thin portions, and the like. Is growing. At the present time, with respect to plate objects, there is an increasing number of thick and large-sized foam molded plates for the purpose of improving the productivity at the time of forming processing or in accordance with new heat insulation standards.

It is difficult to obtain a foamed molded article having the above-mentioned complicated shape from non-crosslinked polyolefin resin pre-expanded particles by using the conventional in-mold foam molding method. That is, even if the heating efficiency is improved due to the degassing of the air inside the mold due to the depressurization inside the mold, regardless of this, the thin portion tends to be overheated because the steam passes well, and the thick portion has the steam. Since the resistance to passage is large, the temperature is unlikely to rise, and unevenness in heating temperature is likely to occur. Here, if the steam supply heating time is set to a time during which the expansion force of the portion (thin portion) where heating tends to be over (the thin portion) does not decrease, the molded product will have insufficient fusion between particles in the thick portion, and the steam supply heating If the time is adjusted to a portion where the temperature is unlikely to rise, voids between particles remain, or a defective molded product in which a portion having low compressive strength is partially (thin portion) is formed. In addition, the inside of the mold is evacuated by the decompression inside the mold, and at the same time, the particles expand, and the gap between the particles serving as the steam flow path is reduced. This phenomenon is particularly large on the surface. As a result, as the heating proceeds from the surface to the inside, the heating rate of the surface is increased, the flow of water vapor to the inside is reduced, and the fusion rate between the inside and the surface is reduced. Cannot be at the same level, which causes an imbalance in the fusion rate between the surface of the molded body and the inside. In addition, when a large-sized foam molded plate having a thickness of 100 mm is obtained, a sufficient effect cannot be obtained even if the pressure is reduced.
Further, there has been a problem that the non-uniformity of the fusion ratio between the surface portion and the inside of the molded article is increased, which leads to deterioration of quality.

[0008] As described above, these are the characteristics of the non-crosslinked polyolefin resin pre-expanded particles, which are inferior in the gas retentivity that the expanded expanded gas escapes from the resin in a short time. This is because the difference between the temperature at which fusion starts and the temperature at which bubble breakage begins to occur is small.

[0009]

DISCLOSURE OF THE INVENTION The present invention relates to a molded article whose good quality cannot be obtained by the conventional foam molding method as described above, that is, a large-sized molded article having a non-crosslinked polyolefin resin thickness. More economical (high cycle molding) of compacts or complex-shaped compacts in which both thick and thin sections coexist
It is an object of the present invention to provide a suitable method for producing an in-mold foam molded article that can be molded in a proper state.

[0010]

Means for Solving the Problems The inventors of the present invention conducted an improvement study of the in-mold foam molding method to achieve the above-mentioned object. As a result, a large amount of steam was supplied in a short time, It has been found that molding is effective, and the present invention has been completed. That is, the present invention fills the pre-expanded particles in a mold that can be closed but cannot be closed, heats the pre-expanded particles by supplying steam, foams and fuses them to form an in-mold foam molded article. (1) After filling the pre-expanded particles, 20 to 60% of the steam internal pressure (kg / cm ² G) at the time of main heating. A pressure within a range of steam mold pressure (kg / cm ² G) within 3 seconds, and preheating of the pre-expanded particles in the mold within 12 seconds or less from the start of steam supply. (2) Next, the pressure (kg / cm ² G) in both molds is set to a saturated steam pressure (kg / cm ² G) corresponding to the melting point of the base resin of the pre-expanded particles −5 ° C. to + 5 ° C. The pressure is increased within 3 seconds, and the main heating is performed for a time of 6 seconds or less, so that the expansion of the expanded particles and the fusion of the particles are performed. And a method for producing an in-mold expanded molded article of non-crosslinked polyolefin-based resin pre-expanded particles.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a conceptual diagram showing an example of the configuration of a general foam molding apparatus used in the production method of the present invention. In FIG. 1, a foam molding space 51 partitioned into a volume shape of a molded body is formed from a pair of a convex mold 50a and a concave mold 50b molded into a predetermined shape. The molds 50a and 50b are provided with a steam inflow slit so that the foam particles supplied to the foam molding space 51 are directly heated by steam.
a, 52b, inside each of which a steam chamber 5
3a and 53b are formed. In this manner, the particles are closed, but the fluid cannot be sealed, that is, a so-called “closeable but not sealable type”. Each steam chamber 53a, 53b
The drain pipes 54a and 54b are attached to the bottom of the, and can be opened and closed by drain valves 55a and 55b. Further, steam supply pipes 56a and 56b are attached to the steam chambers 53a and 53b, respectively, and the respective flow rates are adjusted by pressure regulating valves 57a and 57b. By adjusting the pressure regulating valve 57, the steam supply pressure to the steam chamber 53 is set. The opening degree adjustment of the pressure regulating valve 57
The operation is performed by a three-way solenoid valve 59 and an electropneumatic regulator 60 via an air supply source 58.

With such an apparatus configuration, the production process of the foam molded article can be roughly divided into a filling process, a heating process, and a cooling process. The heating step is usually performed in a fragmented manner such as a mold heating step, a one-side preheating step, a reverse one-side preheating step (may be omitted), and a main heating step (double-sided heating step).
An example will be described with reference to FIGS. First, mold heating is performed for the purpose of raising the temperature of the convex mold 50a and the concave mold 50b. In this mold heating step, while the drain valve 55 is open, the pressure regulating valve 57 is operated to supply the steam from the steam supply source 64 to the steam chamber 53 through the steam supply pipe 56, and the mold 50
Heat. Next, filling of the pre-expanded particles into the mold is performed. In this filling step, the pre-expanded particles provided with the expansion ability are filled in the foam molding space 51 by using an automatic feeder (automatic filling device) 63. After filling, preheating is performed for the purpose of preheating the pre-expanded particles and eliminating air in the master frame and the mold. The one-side preheating step is performed by closing only the drain valve 55b of the one concave mold 50b and supplying steam only to the concave mold 50b, so that the gap between the pre-expanded particles in the foam molding space 51 is removed. This is a step of discharging the intervening air out of the system through the other-side steam chamber 50a. Normally, the end point of this step is controlled by the entrance side, that is, the point in time when the molding steam pressure in the steam chamber 53b of the concave mold 50b reaches a predetermined value P1, and the subsequent set time T1 of the timer.

Next, reverse one-side preheating is performed in order to balance the temperature gradient of the pre-expanded particles in the mold caused by the preceding one-side preheating step. In the reverse preheating step, the steam is supplied in the reverse route, that is, while only the drain valve 55a of the convex mold 50a is closed and the steam is supplied only to the convex mold 50a, the steam molding space 51, the steam Room 50b
This is the step of discharging through the system. Usually, the end point of this step is the entrance side, that is, the steam chamber 53 of the convex mold 50a.
It is controlled by the point in time when the forming steam pressure of a reaches a predetermined value P2 and the set time T2 of the timer following this point.

In the present invention, the preheated steam pressure is X1, X2, the pressurization time is t1, t2, and the preheat time is t1 + T1 + t2 +.
It means T2. Before or during this preheating, the inside of the mold is depressurized by the suction action of a decompression device (not shown) including a vacuum pump, a vacuum tank, etc. connected to the discharge pipe 54 to shorten the heating time. May be performed. After this preheating, main heating for expanding the pre-expanded particles and finally fusing the particles together (also called double-sided heating)
Is performed.

In this heating step, the two drain valves 55a, 55b
And heating by supplying steam to both steam chambers 53a and 53b for a predetermined time. This main heating is performed in the steam room 5.
The end point T3 is set and controlled by the point in time when the molding steam pressure of No. 3 reaches a predetermined value P3 and a timer subsequent thereto. In the present invention, the main heating steam pressure is X3,
The boosting time is t3, and the main heating time is t3 + T3.

After foam molding, water is sprayed (shown) into the steam chamber 53 to be cooled (water cooling step). After discharging the water (draining step), the steam chamber is left to cool for a certain period of time under normal pressure or reduced pressure (cooling step). Finally, the two molds 50a and 50b are separated from each other,
By the operation of 5, the molded foam is released and removed (release step).

The requirements of the present invention in the above-described series of molding steps will be described. First, after filling which is one of the requirements "pre-expanded particles, the main heating during steam type pressure inside ^{(kg / cm 2 G) 20~60} % range of steam type pressure inside (kg / cm ² G) 3 Pressurization within seconds and preheating the pre-expanded particles in the mold within 12 seconds or less from the start of steam supply ".

The necessity of setting the preheating temperature to a steam type internal pressure (kg / cm ² G) within a range of 20 to 60% of the steam type internal pressure (kg / cm ² G) at the time of the main heating depends on the steam type. When the internal pressure is low (less than 20% of the main heating pressure), water vapor does not easily pass through the entire pre-expanded particles in the mold, and as a result,
The preheating of the pre-expanded particles and the discharge of gas (mainly air) which inhibits the expansion and fusion of the particles become partial and cannot be performed sufficiently, so that local (particularly, the A-thick portion of the molded product in the example) is not sufficiently performed. (See Example 3 and Comparative Example 4). On the other hand, the internal pressure of the steam mold is (60% of the main heating pressure).
% Or more), the particles on the surface of the compact that first come into contact with the water vapor expand significantly to block the flow of the vapor to the inside, and as a result, a phenomenon occurs in which the insufficiently heated internal particles do not fuse. Example 2 and comparison with Comparative Example 3).

In the present invention, the pressure range of the preheating steam is defined within the range of 20 to 60% of the main heating pressure while the preheating steam pressure range is increased within 3 seconds while defining the preheating steam pressure range as described above. However, it is not possible to suppress the expansion of the surface particles that occurs in advance, and to completely exhaust the air between the particles to the inside. In particular, when molding a large-sized molded product having a large thickness or a complex-shaped molded product in which a thick portion and a thin portion coexist, if the pressurizing speed exceeds 3 seconds, only a molded product in which poor fusion of internal particles remains is obtained. No (compared with Example 2 and Comparative Example 1).

The necessity of setting the preheating time to 12 seconds or less from the start of the supply of steam is that when steam is introduced into the mold for more than 12 seconds and heated, the expanded foaming gas in the prefoamed particles in the mold often escapes. In other words, the gap between the particles cannot be sufficiently filled, and as a result, the molded article has poor water absorption (compared with Example 4 and Comparative Example 2). Subsequently, another requirement, “the pressure (kg / cm ² G) in both molds is set to the saturated steam pressure (kg / cm ² ) corresponding to the melting point of the base resin of the pre-expanded particles −5 ° C. to + 5 ° C. cm ² G) within 3 seconds, and perform main heating for 6 seconds or less to foam the expanded particles and fuse the particles together. "

The pressure (kg / cm ² G) in both molds is set to a saturated steam pressure (kg / cm ² G) corresponding to the melting point of the base resin of the pre-expanded particles in the range of −5 ° C. to + 5 ° C. The necessity is a condition range for effectively utilizing the expansion force of a portion that controls expansion of the pre-expanded particles and fusion of the particles. That is, when the temperature is lower than the melting point of the base resin −5 ° C., the viscosity of the resin forming the particles is too high, or the phenomenon of poor fusion of the particles or the increase in the water absorption of the molded body occurs (Examples). 7,
Comparison with Comparative Example 7). On the other hand, when the temperature is higher than the melting point of the base resin + 5 ° C., the properties of the molded article are such that the resin viscosity is too low and the cell structure is collapsed, or the water absorption of the molded article is high and the compressive strength is low. Is observed (compared with Example 8 and Comparative Example 8).

In the present invention, while the main heating steam pressure range is defined as described above, the meaning of raising the internal pressure of the steam within 3 seconds is only required to set the main heating steam pressure condition range. It is not possible to suppress the resulting overheating of the surface particles and reduce the difference in heat history between the surface particles and the internal particles. In particular, when molding a large-sized molded product having a large thickness or a complex-shaped molded product in which a thick portion and a thin portion coexist, if the pressure-increasing speed exceeds 3 seconds, poor fusion due to insufficient heating of the internal particles or the surface portion may not be obtained. A phenomenon of a decrease in compressive strength due to overheating occurs (compared with Example 5 and Comparative Example 5).

The necessity of setting the main heating time to 6 seconds or less is as follows.
When steam is introduced into the mold for more than 6 seconds and heated,
Dissipation of the expanded foaming gas in the pre-expanded particles in the mold increases, and the gaps between the particles cannot be filled sufficiently. As a result, the water absorption is poor, and the pre-expanded particles are overheated to the center due to excessive heat history. Relaxation of the molecular orientation of the bubble film occurs, and therefore, the molded product has only a low compressive strength (compared with Example 6 and Comparative Example 6).

The meaning of "expanding the foamed particles and fusing the particles together" means that the pressure in the mold (both steam chambers) heated (pressurized) to the predetermined temperature is rapidly increased. This means that the particles are expanded and fused all at once in a state where the pressure is released. As described above, the in-mold foam molding method of the present invention is characterized in that the pre-expanded particles in the mold are rapidly heated to a predetermined steam pressure (temperature) and heated for a short time. In order to realize this, it is necessary to be able to supply a large amount of steam in a short time, and the steam source pressure (kg / cm ² ) having a pressure twice or more as high as the pressure in the steam mold (kg / cm ² G) during the main heating. cm ² G), the cross-sectional area of the steam supply pipe 56 into the mold is increased, and the cross-sectional area α (cm ² ) and the internal volume β of the master frame used
(Cm ³ ) and the in-mold pressure rise rate coefficient of α / β defined as 1
It is desirable to use a molding device having a value of × 10 ^-4 or more. It is also effective to reduce the heat capacity as much as possible by reducing the thickness of the mold to the permissible lower limit, or to coat Teflon or the like having low heat conductivity on the mold surface.

The base resin of the non-crosslinked polyolefin resin pre-expanded particles in the present invention includes low-density polyethylene, linear low-density polyethylene, high-density polyethylene,
For example, polypropylene, ethylene propylene random copolymer, ethylene propylene block copolymer, ethylene propylene butene copolymer, polyethylene vinegar copolymer, and polybutene are used. These may be a mixture of two or more.

The melting point (° C.) of the resin referred to in the present invention can be measured by a Perkin-Elme as a measuring device.
r) A sample of about 10 mg was used for 1
After raising the temperature from 30 ° C. to 200 ° C. at a rate of 0 ° C./min, hold the temperature for 1 minute, cool and crystallize to 30 ° C. at a rate of 10 ° C./min, hold the temperature for 1 minute, It was determined from the peak value of the melting curve when the temperature was raised again at a rate of 10 ° C./min.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to examples and comparative examples. The evaluation method of the characteristic values and the evaluation scale used in each example were performed as follows.
In this evaluation, the vertical, horizontal, and height values shown in FIG. 3 obtained in Examples and the like are about 500, 500, and 100 mm, respectively, and the thick and thin parts of the A part (about 100 mm thick) and the C part (about 25 mm thick) In-mold molded articles with (1) Meltability 500 × 100 from the part indicated by the part A (about 100 mm in thickness) and the part C (about 25 mm in thickness) in the molded article of FIG.
mm rectangular parallelepiped test piece, 2m deep at the center
m is cut and bent along the cut to cleave the molded article, and the percentage of the number of particles that have been torn due to material breakage in the bubble section with respect to the total number of particles present in the cut cross section (material breakage rate)
I asked. When the material fracture rate is 90% or more: ○ (good); material fracture rate 90%
Less than 60% or more △ (slightly poor);
In the case of less than 0% ... × (poor) (2) Water Absorption In the molded article of FIG. 3, the length, width, and thickness are 100, more than those indicated by the portions A (about 100 mm thick) and C (about 25 mm thick). A test piece of 100 or 20 mm is cut out, and the molded body whose weight is measured is submerged at a position 25 mm below the surface of the water in fresh water at about 20 ° C., and the volume of the molded body is determined from the buoyancy at that time. After maintaining the submerged state for 24 hours, the molded body is transferred to an ethyl alcohol bath, immersed for 1 minute, taken out, air-dried for 40 minutes and weighed. The following calculation is made based on the weight increase before and after submersion in water and evaluated. Water absorption (%) = [weight increase (g) × 100] ÷ [molded product volume (cm ³ ) × water density (g / cm ³ )] When less than 0.06%: ○ (good); 0.06% or more and less than 0.1%: ... (somewhat bad); 0.1%
(3) Compressive stress index Since the compressive stress is greatly affected by the foam density, it is expressed as an index for uniform evaluation.

Part A (thickness of about 100) in the compact of FIG.
mm), a test piece of 100 mm in length and width was cut out from the portion indicated by the portion C (thickness: about 25 mm), and the density was measured according to JIS.
Determined by the test method of K6767. Then 2 of the test piece
The compressive stress at the time of 5% compression is determined by a test method according to JIS Z0234 (compression speed 10 mm / min), and is evaluated by converting it into a coefficient (no unit) by the following equation. Compressive stress index = Compressive stress at 25% compression (kg / c
m ² ) ÷ Density of test piece (g / cm ³ ): 19 or more: ○ (good); less than 19, 16 or more: △ (slightly poor);

[0029]

Examples 1-8, Comparative Examples 1-8 Non-crosslinked linear low-density polyethylene resin (density: 0.922 g / cm ³ , melting point (DSC crystal melting peak): 123 ° C.) g of the pre-expanded particles were charged into a pressure vessel, and pressure-aged with 2.5 kg / cm ² G of air for 48 hours. The gas pressure of the pre-expanded particles subjected to the pressure treatment was 1.85 atm.

Next, the pre-expanded particles are formed as shown in FIG.
Forming machine (steam supply pipe diameter is 100mmφ, cross section α is 7
8.5cm^Two, The master frame internal volume β is 18900
0cm ^Three, Α / β = 4.15 × 10^-Four) Mounted on
Inside the mold-when the two molds fit together the internal space
However, the dimensions, length, width, and height of each part shown in FIG.
0, 500, 100 mm, part A (thickness 100 mm),
Mold that forms the inner dimensions of the thick and thin part of part C (thickness 25 mm)
The fossa, and the entire internal surface of the male and female, are commonly used
Steam inflow members are arranged at a pitch of 20 mm.
And molded by heating under the conditions shown in Tables 1 and 2.
Then, the mixture was cooled and taken out from a molding die to obtain a molded foam.

The steam source pressure in each molding was 7 kg / cm in Examples 1, 6, and 7 and Comparative Examples 3 and 8.
To ² G, to 5 kg / cm ² G in Examples 2, 3, 4, 8 and Comparative Example 6 In Example 5 and Comparative Examples 2 and 4 to 3 kg / cm ² G, Comparative Examples 1 and 5, In No. 7, the test was performed at 2 kg / cm ² G. The molded article obtained under each condition was cured and dried at 70 ° C. for 20 hours, left at room temperature for 3 days, and then measured for molded article magnification.
cc / g (= density 0.025 g / cc). The fusibility, water absorption, and compressive stress index were measured by the above-described evaluation method for each condition, and the results are shown in Table 2.

As can be seen from Tables 1 and 2, the method of the present invention can provide a high-quality foam molded article having excellent fusibility, water absorption and compressive strength.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

According to the production method of the present invention, a large-sized molded body having a large thickness or a complicated structure having a thick part and a thin part coexisted in a conventional foam molding method where a high-quality molded body could not be obtained. A shaped article can be provided. In other words, the present invention provides suitable in-mold foaming that is excellent in fusion between particles and water absorption, has a sufficient compressive stress (index), and can be molded in a more economical (high cycle molding) state. It is a molding method.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a configuration of a foam molding apparatus used in the present invention.

FIG. 2 is a graph showing an example of a relationship between a forming step and a steam supply pressure.

FIG. 3 is an example of a foamed molded article having a complicated shape and high market demand obtained by the present invention.

[Explanation of symbols]

 Reference Signs List 50 mold 51 foaming space 52 master frame 53 steam chamber 56 steam supply pipe 57 pressure regulating valve 58 air supply source 62 pre-expanded particles 63 feeder 64 steam supply source 65 eject pin 66 foam molded body 67 foaming pressure detector

Claims (1)

[Claims] 1. A mold that can be closed but cannot be closed is filled with pre-expanded particles, steam is supplied to heat the pre-expanded particles, and the pre-expanded particles are foamed and fused to form an in-mold foam molded article. In the method for producing an in-mold foam molded article of non-crosslinked polyolefin resin pre-expanded particles, (1) after filling the pre-expanded particles, a range of 20 to 60% of a steam mold pressure (kg / cm ² G) at the time of main heating. The pressure inside the mold (kg / cm ² G) is raised within 3 seconds, and the pre-expanded particles in the mold are pre-heated within 12 seconds or less from the start of steam supply. (2) Next, the pressure (kg / cm ² G) in both molds is set to a saturated steam pressure (kg / cm ² G) corresponding to the melting point of the base resin of the pre-expanded particles −5 ° C. to + 5 ° C. The pressure is increased within 3 seconds, and the main heating is performed for a time of 6 seconds or less, so that the expansion of the expanded particles and the fusion of the particles are performed. A method for producing an in-mold foam molded article of non-crosslinked polyolefin resin pre-expanded particles, characterized by passing through the following steps.