JP2008254270A - Method for manufacturing in-mold foamed molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an in-mold foamed molding in which the clogging of a steam hole such as a core vent or a core vent hole formed in a mold is suppressed, and good fusion is obtained although molding/heating pressure is not increased. <P>SOLUTION: In the method for manufacturing the in-mold foamed molding by heating/expanding foamable thermoplastic resin particles by a heating process including a mold heating process for feeding steam to the mold comprising a core mold and a cavity mold, a one-way heating process in which steam is fed from the cavity mold side, passed through a molding space, and discharged from the core mold side, a reverse one-way heating process in which steam is fed from the core mold side, passed through the molding space, and discharged from the cavity mold side, and a double sides heating process in which steam is introduced from both steam chambers on the core mold side and on the cavity mold side into the molding space, a time necessary for the mold heating process is made at least twice as long as a time necessary for a process selected from the one-way heating process and the reverse one-way heating process because it takes a longer time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an in-mold foam molded article.

  A so-called bead foam molded body obtained by filling thermoplastic resin foam particles in a molding space composed of a pair of molds consisting of a core mold and a cavity mold, heat-sealing with steam, then cooling and releasing ( Hereinafter, in-mold foam moldings) are widely used for cushioning materials, packaging materials, heat insulating materials, building materials, automobile materials, and the like. The process of heating and fusing with water vapor generally adopts a method of dividing into a mold heating process, one heating process, reverse one heating process, double-sided heating process, etc. (see, for example, Patent Documents 1 and 2). There are many. The mold heating process is performed mainly for the purpose of raising the temperature of the mold, and an operation is performed in which steam is supplied into the steam chamber of each mold for a certain period of time and the drain is discharged to the outside of the mold. . On the other hand, the heating process is performed for the purpose of eliminating air in the molding space (air-to-steam replacement) and preheating for foaming and fusing the foamed particles. For example, it is a process of flowing through the gap between the foamed particles in the molding space through the vapor chamber of the cavity mold) and discharging this to the outside of the mold through the vapor chamber of the other mold (core mold). The reverse one-side heating process is introduced into the steam chamber by the reverse route to the previous process in order to compensate for the area where the air in the molding space is not sufficiently replaced with steam by the process of the previous process (one-side heating). And performing the heat treatment. The double-sided heating step is a step of finally foaming and fusing the foamed particles in the molding space, and is performed by an operation of simultaneously introducing steam into both steam chambers of the molding die.

  As a problem during the heating process, when the molding space has a complicated shape, the end becomes a bag shape, and it is difficult to exhaust the air from the end to the outside of the molding space. This was not sufficient, and the fusion rate and surface property of the end of the molded product tended to decrease. In addition, foreign particles such as resin powder contained in the pre-expanded particles are deposited in the core vent (or core vent hole), causing clogging, and molding the pre-expanded particles filled in the molding space before foaming and fusing. Replacing the air in the space with steam greatly affects the fusion and surface properties of the product. Further, when clogging occurs in the core vent (or core vent hole), the mold release tends to be unstable. Therefore, conventionally, in order to prevent and suppress this, the pressure of compressed air has been set high, or the release time has been extended. As a result, there has been a problem that the productivity of the mold is reduced due to breakage of the mold and extension of the molding cycle.

  As a method for removing clogging of the core vent (or core vent hole), it is common to disassemble the mold, perform heat treatment, and perform fine powder cleaning called water jet cleaning or sand blast cleaning. This task is problematic in that it requires a great deal of labor, time and money.

In order to prevent and suppress this, the heating time has been extended or the heating steam pressure has been set high. As a result, there has been a problem of a decrease in productivity due to an extended molding cycle and an increased defective rate. In the heating process, the heating time is shortened as the amount of steam or the vapor pressure is increased, but there is a problem of waste of energy and durability of the apparatus, and the conditions for supplying different steam for each process are appropriately satisfied. There is also a need. In addition, if the time of the one heating process or the reverse one heating process is extended or the heating steam pressure is set high, the internal temperature of the expanded particles becomes high during the one heating process or the reverse one heating process, and the amount of air in the pre-expanded particles Decreases, and the secondary foaming power during the heating step is reduced. As a result, there was a problem that the deformation or shrinkage (sink) of the molded body increased, and the drying curing time was extended.
JP 58-51123 A JP 59-1231 A JP 63-21133 A

  In view of the above situation, the object of the present invention is to reduce the clogging of steam holes such as core vents and core vent holes provided in the mold, and to achieve low surface pressure and good surface foam molding. It is in providing the manufacturing method of a body.

  As a result of intensive studies to solve the above problems, the present inventors have reduced the time required for the mold heating step in the heating step of the method for producing an in-mold foam molded body using the thermoplastic resin pre-foamed particles. By setting the heating process or reverse one heating process to more than twice the time required for the longer process, the above problems can be solved and clogging of the steam holes such as core vents and core vent holes is reduced. It was found that an in-mold foam molded article having good surface elongation can be obtained with a low molding pressure, and the present invention has been completed.

That is, the first of the present invention is a mold heating step in which thermoplastic resin foam particles are filled in a molding space constituted by a pair of molds consisting of a core mold and a cavity mold, and steam is supplied to each mold. , While supplying steam from the cavity mold side and discharging steam from the core mold side through the molding space, heating process, and then supplying steam from the core mold side and discharging steam from the cavity mold side through the molding space A foamed molded article is produced by heating and foaming thermoplastic resin foam particles by a heating process including a heating process and a double-sided heating process for introducing steam from both the steam chambers on the core mold side and the cavity mold side into the molding space. In the method
A process for producing an in-mold foam-molded product, characterized in that the process time required for the mold heating process is doubled or longer than the process of either the one heating process or the reverse one heating process, which is longer.

As a preferred embodiment,
(1) The process time of each of the one heating process and the reverse one heating process is 5 seconds or less,
(2) omitting one of the one heating step and the reverse one heating step;
The method for producing an in-mold foam-molded article as described above.

  In the method for producing an in-mold foam molded article using the thermoplastic resin foam particles according to the present invention, it is possible to reduce clogging to the core vent (or core vent hole), which has been a drawback of the conventional production method, and to reduce the maintenance frequency. Thus, an in-mold foam molded article with stable quality can be obtained. Further, it is possible to obtain an in-mold foam-molded article having a uniform overall quality by preventing the end portion of the in-mold foam-molded article from being fused and the surface property from being lowered and shrinkage (sink). Furthermore, it is effective in reducing the amount of steam used, shortening the molding cycle time, and shortening the drying curing time.

  A general mold structure used for manufacturing a foam molded body using pre-expanded particles made of a thermoplastic resin will be described with reference to FIG. In the mold apparatus for in-mold foam molding shown in FIG. 1, the cavity-side middle mold 6 and the core-side middle mold 7 are opposed to each other so as to form a molding space 1 filled and molded with pre-foamed particles. It is fixed to the frame-like frame 9 via the plate 8. On its back side, it is provided with a cavity-type back steam chamber 3 and a core-type back steam chamber 2 formed from a cavity-side middle mold 6 or a core-side middle mold 7 and a middle plate 8, a frame-like frame 9 and a back plate 10, respectively. The upper service ports 11 to 14 for supplying steam and cooling water are provided at the upper part of each steam chamber, and the lower service ports 15 and 16 connected to the drain pipe are provided at the lower part. Yes. The cavity-side middle mold 6 and the core-side middle mold 7 have a large number of core vents (or core vent holes) 17 on their surfaces, and the steam supplied to the steam chambers 2 and 3 from the upper service ports 11 and 12 is It passes through the core vent (or core vent hole) 17 and is supplied to the molding space 1. Here, the core vent is a through-hole consisting of a round hole having a diameter of about 0.5 mmφ and a slit having a width of about 0.5 mm, which is usually fitted in holes arranged at a pitch of 20 to 30 mm in the cavity side middle mold and the core side middle mold. It is a cylindrical body having a lid with an outer diameter of 6 to 12 mm and a plurality of through holes. A core vent hole is a through hole of about 0.5 mm to 1.5 mmφ formed directly in the cavity side middle mold and the core side middle mold. Say that.

  As a method of manufacturing the in-mold foam molded body, the upper part of the mold is filled with thermoplastic resin foam particles in the molding space 1 in which the core mold back surface steam chamber 2 and the cavity type back surface steam chamber 3 are combined, and connected to both molds. Steam is introduced from the ports 11 and 12 to heat-fuse the thermoplastic resin foam particles. The heating and fusing step includes (1) mold heating step, (2) one heating step, (3) reverse one step, and (4) double-side heating step.

  (1) In the mold heating step, steam is introduced into the steam chambers of both the core-type backside steam chamber 2 and the cavity-type backside steam chamber 3 from the upper service ports 11 and 12, and the drain valves DV1 and In this process, the DV2 is opened, the steam is discharged from the lower service ports 15 and 16, and the mold is heated by the steam passing through each steam chamber. That is, steam is introduced from the cavity-side upper service port 12, steam is discharged from the cavity-side lower service port 16, steam is introduced from the core-side upper service port 11, and steam is delivered from the core-side lower service port 15. Is a step of warming the cavity-side middle mold 6 and the core-side middle mold 7.

  (2) In the one heating step, steam is introduced only into one steam chamber and the drain valve of the opposite steam chamber is opened, so that the steam passes from the one steam chamber through the molding space 1 and the opposite steam. This is a step for discharging the air from the drain valve of the chamber and expelling the air between the raw material particles simultaneously with the heating of the molding space 1 to facilitate the fusion of the raw material particles.

  That is, steam is introduced from the cavity side upper service port 12 in a state where the drain valve DV2 of the cavity side lower service port 16 is closed and the drain valve DV1 of the core side lower service port 15 is opened. The introduced steam passes through the molding space 1 and is discharged from the core side lower port 15.

  (3) The reverse one-side heating step is a step in which heat treatment is performed by introducing the vapor chamber into the steam chamber through a route opposite to the one-side heating step. That is, steam is introduced from the core side upper service port 11 with the drain valve DV1 of the core side lower service port 15 closed and the drain valve DV2 of the cavity side lower service port 16 opened. The introduced steam passes through the molding space 1 and is discharged from the cavity side lower port 16. However, the order of the one heating process and the reverse one heating process may be reversed.

  (4) The double-sided heating step is a step of finally foaming and fusing the foamed particles in the molding space. The steam is simultaneously introduced into both the core mold side and the cavity type side steam chambers, and the drains of the respective steam chambers are drained. The valves DV1 and DV2 are closed and the thermoplastic resin foam particles in the molding space 1 are completely heat-sealed.

  In the present invention, in the method for producing the foamed molded article, the time required for the mold heating step is more than doubled compared to the longer one of the one heating step and the reverse one heating step. Is. By setting it as such a structure, the time which a one heating process or a reverse one heating process requires can be shortened. That is, clogging of the core vent and the core vent hole can be suppressed by shortening the time for the vapor to pass through the core vent (or the core vent hole). In addition, it is possible to prevent the air impregnated in the foamed particles in the molding space from being lost and to suppress the shrinkage (sink) of the foamed molded product.

  As a preferable aspect, by setting the process time of each of the one heating process and the reverse one heating process to 5 seconds or less, the total time required for the conventional heating process can be shortened, and the quality of the foam molded article is maintained. The effect of suppressing clogging of the core vent and the core vent hole can be obtained.

  Also, by omitting either the one heating process or the reverse one heating process, the process of passing steam in the molding space can be omitted, and the total time required for the heating process can be further shortened. This is preferable because it maintains the body quality and suppresses clogging of the core vent and core vent hole.

  The thermoplastic resin applicable to the present invention is a polystyrene resin typified by polystyrene, an ethylene-propylene random copolymer, an ethylene-propylene-butene random terpolymer, a homopolypropylene, or a linear low density polyethylene. Examples thereof include polyolefin resins such as (LLDPE) and crosslinked low-density polyethylene (crosslinked LDPE), and among them, they can be suitably used for polyolefin resins. The foamed thermoplastic resin particles used in the present invention can be obtained from the thermoplastic resin by a known method.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to a following example. Evaluation was performed as follows.

(Fusability)
The obtained foamed molded product was cut into a notch of about 5 mm with a cutter knife, and bent and broken along the notch. The state of the fracture surface was visually observed and evaluated according to the following criteria.
○: On the fracture surface, the ratio of fracture at the interface of the expanded particles is 20% or less.
(Triangle | delta): The ratio which is fractured | ruptured by the expanded particle interface in a fracture surface is 20 to 40%.
X: On the fracture surface, the ratio of fracture at the expanded particle interface is 40% or more.

(Surface property)
The voids between the pre-expanded particles on the surface of the molded body at the end and the center of the obtained molded body were visually evaluated and expressed as follows.
○… The tortoiseshell pattern is inconspicuous. Δ ・ ・ ・ A little tortoiseshell pattern is observed when you look closely.

(Clogging evaluation)
The clogging of the core vent and the core vent hole is visually observed periodically (every 100 shots), and the molding shot when the cross-sectional area of 50% of the total opening cross-sectional area of the core vent and the core vent hole is clogged. The number was evaluated and expressed as follows:
○ ... 10,000 shots or more Δ ... 5000 shots or more and less than 10,000 shots × ... less than 5000 shots

(Examples 1-4, Comparative Example 1)
The mold used was a bumper core model (long bar shape) mold (approximately L1200 × W130 × T100 mm) having a volume of 11.85 L, one piece, and four fillers. The thermoplastic resin expanded particles use “Eperan PP LBS13 (manufactured by Kaneka Co., Ltd., bulk density 56.5 g / L)”, and air is press-fitted into the pre-expanded particles by air pressure treatment, and finally The expanded particle internal pressure was 0.2 MPa in absolute pressure. The expanded particles were molded under the following conditions.

  After filling the molding space 1 with a gap of 5 mm between the filling machine 19 and the core mold back steam chamber 2 and the cavity mold back steam chamber 3 of the molding machine, foaming in the mold is performed under the following heating / cooling conditions: A molded body was obtained. Subsequently, after standing to cool in the atmosphere for 1 hour, left in a drying room at 75 ° C. for 24 hours, taken out from the drying room and allowed to cool at room temperature for 3 hours to obtain an in-mold foam molded article. .

Heating process Refer to Table 1. Cooling process Precooling: 10 seconds
Water cooling: 70 seconds Table 1 shows the configurations and results of Examples 1 to 4 and Comparative Example 1.

In comparison between Example 1 and Comparative Example 1, a foamed molded article having good fusion property and surface property was obtained. However, Comparative Example 1 had a problem in clogging. In Example 1, the clogging property was improved. In Examples 2 and 3, the conditions for omitting one of the one-side heating and reverse one-side heating steps were omitted, but as in Example 1, good results were obtained. As in Example 4, when both the one-side heating and reverse one-side heating steps were omitted, there was a slight problem with the fusing property, but a foamed molded article with good surface properties was obtained. Also, clogging hardly occurred and the amount of steam used per shot was small.

  Therefore, in the method for producing a foamed molded product, the foamed molded product has a structure in which the time required for the mold heating step is doubled or longer than the longer one of the one heating step and the reverse one heating step. It has been found that clogging of the core vent hole (or core vent hole) is reduced without degrading the quality of the product, and the number of shots until a release failure occurs can be delayed. It was also found that the amount of steam used can be reduced.

Cross-sectional view of a typical in-mold foam molding tool

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molding space 2 Core side type back side steam chamber 3 Cavity side concave back side steam chamber 4 Space between molds 5 Parting part 6 Cavity side middle mold 7 Core side middle mold 8 Middle plate 9 Frame-shaped frame 10 Back plate 11 Core side upper part role Mouth (steam)
12 Cavity side upper port (steam)
13 core side upper port (cooling water)
14 Cavity side upper port (cooling water)
15 Core side lower port 16 Cavity side lower port 17 Core vent (or core vent hole)
18 Drain piping 19 Filling machine 20 Eject pin SV1 Service valve (core side steam valve)
SV2 service valve (Cavity side steam valve)
SV3 service valve (core cooling water)
SV4 service valve (cooling water on cavity side)
DV1 Drain valve (core side)
DV2 drain valve (cavity side)

Claims (3)

Filling the molding space consisting of a pair of molds consisting of a core mold and a cavity mold with thermoplastic resin foam particles, a mold heating process for supplying steam to each mold, and supplying steam from the cavity mold side One heating process that discharges steam from the core mold side through the molding space, then reverse one heating process that supplies steam from the core mold side and discharges steam from the cavity mold side, core mold side, cavity In a method for producing a foamed molded article by heating and foaming thermoplastic resin foam particles by a heating process comprising a double-sided heating process for introducing steam from both steam chambers on the mold side,
A process for producing an in-mold foam-molded product, characterized in that the process time required for the mold heating process is doubled or longer than the process of either the one heating process or the reverse one heating process, which is longer.   The method for producing an in-mold foam molded product according to claim 1, wherein the process time of each of the one heating step and the reverse one heating step is 5 seconds or less.   3. The method for producing an in-mold foam molded product according to claim 1, wherein either one of the heating step and the reverse one heating step is omitted.