JP2014218066A - Manufacturing method of polypropylene resin foam molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable and energy-saving manufacturing method of a polypropylene resin foam molding, using a mold apparatus having a concave mold unit including a concave mold and a concave mold housing for holding the concave mold, with the concave mold being supported by the concave mold housing in a cantilever state.SOLUTION: Steam is supplied to the molding space filled with polypropylene resin pre-expanded particles to be foamed and fusion bonded in the manufacturing method of a polypropylene resin foam molding. On the occasion of fusion bonding, the manufacturing method of a polypropylene resin form molding includes: (A) performing first stage heating until reaching the steam pressure P1 to have a fusion bonding rate of the pre-expanded particles of 40% or more and 80% or less; (B) once reducing the steam pressure down to P2, which is lower than the steam pressure P1 reached in the first stage; and (C) once again heating until reaching the steam pressure P3, which is equal to or higher than the steam pressure P1 reached in the first stage heating and maintaining for a constant time period.

Description

  The present invention relates to a method for producing a polypropylene resin foam molding (in-mold foam molding method).

  As a molding technology for foamed molded products, pre-foamed resin particles made of polypropylene resin are filled into the molding space, and this is heated, foamed and fused with steam and then cooled to obtain a foamed molded product of a desired shape. An in-mold foam molding apparatus configured as described above and a molding method therefor are widely known.

  A mold apparatus for the in-mold foam molding apparatus includes a concave unit having a concave mold and a concave housing that holds the concave mold, and a convex unit having a convex mold and a convex housing that holds the convex mold. Widely adopted. The concave housing includes a rectangular cylindrical concave frame provided so as to surround the concave mold, a concave fixing plate that closes the opening on the back side of the concave frame, an end on the front side of the concave mold, and a concave mold and a concave mold. A concave center plate that closes an opening formed between the frames and a concave chamber for supplying steam and cooling water is formed in the concave housing on the back side of the concave. In addition, the convex housing includes a rectangular cylindrical convex frame provided so as to surround the convex mold, a convex fixing plate that closes the opening on the back side of the convex frame, and an end on the convex rear side. A convex center plate for closing the opening formed between the convex mold and the convex frame, and for supplying steam and cooling water into the convex housing on the rear side of the convex mold Those having a convex chamber are widely used.

  The convex fixing plate or the concave fixing plate is provided with a filling device for filling the pre-foamed resin particles, and the convex housing and the concave housing are for supplying steam to the convex chamber and the concave chamber. Steam piping and cooling water piping for supplying cooling water are connected to each other, and drain pipes are connected to the lower portions of both housings. At the time of molding, the pre-foamed resin particles filled in the molding space are heated by the steam supplied to the convex chamber or the concave chamber, and the molded product is cooled by the cooling water sprayed on the back side of the convex chamber or the concave chamber. However, the heating and cooling during molding is not limited to pre-foamed resin particles, but also to molds and housings, fillers and ejector pins, steam piping and cooling water piping that do not require heating or cooling. As a result, there is a problem that a lot of energy is wasted.

  Therefore, Patent Document 1 has a concave mold and a concave housing that holds the concave mold for the purpose of reducing the heat capacity of a portion unnecessary for direct molding other than the concave mold and convex mold of the mold apparatus. A concave unit having a concave chamber formed in a concave housing, and a convex unit having a convex mold and a convex housing for holding the convex mold, and having a convex chamber formed in the convex housing on the back side of the convex mold. In order to obtain a molded product by combining the units and filling the pre-expanded resin particles in the molding space formed by the concave mold and the convex mold, and heating and foaming the pre-expanded resin particles in the molding space. A mold apparatus for in-mold foam molding, wherein the concave mold is supported in a cantilever manner on a concave housing, and a front opening that opens toward the convex unit side is formed between the concave mold and the concave housing. And before In a state in which a combination of a concave and convex, the front opening is closed by the convex unit, wherein the concave chamber die apparatus without the airtight and has been proposed.

  However, when such a mold apparatus structure is used, the molding conditions in the exhaust process, the one heating process, the reverse one heating process, and the double-sided heating process, which are general molding methods for polypropylene-based pre-expanded resin particles, There was a tendency for heating to become non-uniform due to the difference between the concave and convex chamber capacities, resulting in poor fusing and intergranularity on the surface of the product, leading to the problem of deteriorating beauty.

JP 2010-120336 A

The present invention relates to a method for producing a foam molded body using pre-expanded polypropylene resin particles, and a concave mold and a holding mold for the purpose of reducing a heat capacity of a portion unnecessary for direct molding other than a concave mold and a convex mold of a mold apparatus. A concave unit having a concave chamber formed in the concave housing on the back side of the concave shape, a convex type and a convex housing holding the convex unit, and a convex housing on the convex back side. A convex unit having a convex chamber formed therein, and by combining both units, pre-expanded resin particles are filled in a molding space formed by the concave and convex molds, and the pre-expanded resin particles are formed in the molding space. Is a mold apparatus for in-mold foam molding that heats, foams and fuses to obtain a molded product,
The concave mold is supported in a cantilever manner on a concave housing to form a front opening that opens toward the convex unit between the concave mold and the concave housing, and the concave mold and the convex mold are combined. In the case of using a mold apparatus in which the front opening is closed with a convex unit and the concave chamber is hermetically sealed, a manufacturing method for further improving fusion and improving surface beauty is provided. Objective.

As a result of intensive research to solve the above problems, the present inventor has observed the gas dissipation behavior from the pre-foamed particles during the heating process, the relationship between the heating conditions and the product quality, and from the pre-foamed particles. It has been found that the released air affects the product quality.
That is, the amount of air released from the pre-expanded particles is highly correlated with the heating temperature and heating time during molding. Furthermore, it has been found that the air released from the pre-expanded particles during molding hinders uniform temperature rise in order to prevent the vapor from entering between the grains, resulting in poor fusion and deterioration of the surface beauty. It was.

  Based on the above knowledge, the present inventor has a concave mold and a concave housing that holds the concave mold and supports the concave mold in a cantilevered manner on the concave housing, and the convex mold and the convex mold. A mold apparatus comprising a convex unit that has a convex housing to hold, the convex mold is directly fixed to the convex housing, and the space between the convex rear opening and the housing is a convex steam chamber. A manufacturing method (molding method) was devised that suppresses the release of air from the pre-expanded particles during the heating process as much as possible.

That is, by performing an operation to achieve a predetermined fusion rate by heating for a short time, the air space from the pre-expanded particles in the molding space is filled to fill the space between the particles, thereby suppressing air release from the pre-expanded particles. . By this operation, a predetermined amount or more of air remains in the molded product, and the product shape and dimensions can be stabilized.
However, this operation alone is not sufficient to improve the surface aesthetics of the product. Therefore, in order to improve the surface quality of the product again in a state in which the release of foaming gas that inhibits temperature rise is suppressed. A molding method was devised to heat the stage.
Finally, by using the manufacturing method based on the two-stage thermoforming method shown here, the resulting polypropylene resin foam satisfies all of good fusion properties, surface aesthetics, and product size retention. As a result, the present invention has been completed.

That is, the method for producing a polypropylene resin foam molded article of the present invention has the following configuration.
[1] A concave unit having a concave mold and a concave housing that holds the concave mold, and supporting the concave mold in a cantilever manner on the concave housing, and a convex housing that holds the convex mold and the convex mold. The convex mold is directly fixed to the convex housing, and is formed of a concave mold and a convex mold of a mold unit comprising a convex unit in which a space between the convex rear opening and the housing is a convex steam chamber. A polypropylene resin pre-foamed particle is filled in a molding space, and steam is supplied to the molding space to foam and fuse the pre-foamed particle. When doing
(A) First, steam is supplied only from the convex mold, and heating is performed so that the fusion rate of the pre-expanded particles is 0% or more and less than 30%. Stop to fuse the expanded particles, and by supplying steam from the concave mold, perform the first stage heating until reaching the vapor pressure P1 at which the fusion rate of the pre-expanded particles is 40% to 80%,
(B) Once it is lowered to a steam pressure P2 lower than the first stage reached steam pressure P1,
(C) Again, by supplying steam only from the concave mold, it is heated until it reaches a steam pressure P3 that is equal to or higher than the ultimate steam pressure P1 in the first stage heating, and is held for a certain period of time. Body manufacturing method.
[2] (C) The production of the polypropylene resin foam molded article according to [1], wherein in the step of maintaining a pressure equal to or higher than P3, the convex steam pressure is made higher than the concave steam pressure. Method.

  According to the method for producing a polypropylene resin foam molded article of the present invention, a concave mold and a concave housing that holds the concave mold are provided for the purpose of reducing the heat capacity of a portion unnecessary for direct molding other than the concave mold and convex mold of the mold apparatus. And has a concave unit configured to support the concave mold in a cantilevered manner on the concave housing, and a convex housing that holds the convex mold and the convex mold, and the convex mold is directly fixed to the convex housing. In addition to using a mold unit consisting of a convex unit in which the space between the convex back opening and the housing is a convex steam chamber, a manufacturing method based on a two-stage thermoforming method can be used. In addition to being able to reduce the amount of molding steam, it is possible to achieve both the stabilization of the high fusion rate in terms of quality and the improvement of the surface beauty.

It is the figure which showed an example of the metal mold | die apparatus which concerns on this invention. It is a figure of an example which shows the relationship between shaping | molding vapor pressure and a shaping | molding cycle in the conventional manufacturing method at the time of using a general die apparatus. It is a figure of an example which shows the relationship between shaping | molding vapor pressure and a shaping | molding cycle in the manufacturing method of this invention.

  The mold apparatus used in the present invention will be described.

  As shown in FIG. 1, the in-mold foam molding mold apparatus 1 includes a concave unit 10 having a concave mold 11 and a concave housing 12 that holds the concave mold 11, a convex mold 21, and a convex housing 22 that holds the concave mold 21. And having both the units 10 and 20 are combined, the molding space 2 formed by the concave mold 11 and the convex mold 21 is filled with pre-foamed resin particles, and the pre-foaming resin is formed in the molding space 2. The particles are heated and foam-fused to obtain a molded product.

  The concave mold 11 and the convex mold 21 are made of a material having a low specific heat and a high thermal conductivity, such as an aluminum alloy, so that the molded product can be heated and cooled smoothly. In order to reduce the manufacturing cost of the mold apparatus 1 and to ensure sufficient strength and rigidity, the mold apparatus 1 is made of an iron-based metal.

The concave housing 12 includes a rectangular tube-shaped concave frame 13 provided so as to surround the concave mold 11, a concave fixing plate 14 that closes an opening on the back side of the concave frame 13, and the concave mold 11 on the concave fixing plate 14 in a cantilever shape. A concave chamber 16 is formed in the concave housing 12 on the back side of the concave mold 11.
The concave mold 11 is fixed and supported in a cantilever manner on the concave mold fixing plate 14 via the fixing member 15 with the opening side facing the front side (the mating surface side of the concave mold 11 and the convex mold 21). The part 11a is configured with a free end.
A front opening 17 that opens toward the convex unit 20 is formed between the front end 11a of the concave mold 11 and the front end 13a of the concave frame 13, but the concave mold 11 and the convex mold 21 are formed. In this state, the front opening 17 is closed by the convex unit 20, and a concave chamber 16 as a steam chamber is formed in the concave housing 12 in a substantially airtight manner.
The concave unit 10 is connected to a steam supply pipe 18a, a cooling water supply pipe 18b, and a drain pipe 18c that open into the concave chamber 16, and control valves 19a to 19c interposed in the middle of these pipes 18a to 18c. In this operation, steam is supplied into the concave chamber 16 to heat and foam the pre-foamed resin particles, or cooling water is sprayed from the nozzle 18d to the back side of the concave mold 11 to cool the molded product or unnecessary drainage. Or the like can be discharged from the concave chamber 16. The concave mold 11 is formed with a large number of vent holes 11b, and steam is supplied from the concave mold chamber 16 into the molding space 2 through the vent holes 11b.
The filling device 3 is fixed to the concave mold fixing plate 14, and the tip of the filling device 3 is inserted into the molding space 2 through the concave mold 11, and the pre-foamed resin particles are supplied from the filling device 3 into the molding space 2. Thus, the molding space 2 is filled. Although not shown, an ejector pin that can be inserted through the concave mold 11 and protrude into the molding space 2 through the concave mold 11 is supported.

  The convex housing 22 includes a rectangular cylindrical convex frame 23 provided so as to surround the convex mold 21, and a convex fixing plate 24 that closes the opening on the back side of the convex frame 23. Is closed by a convex fixing plate 24, and the convex mold 21 and the convex fixing plate 24 form a convex chamber 26B for each convex mold 21, and a steam supply pipe 28a and a cooling water supply pipe 28b. And a drain pipe 28c are individually connected to each convex chamber 26B.

  The pipe connection of the convex unit 20 will be described in detail. A steam supply pipe 28a, a cooling water supply pipe 28b, and a drain pipe 28c that are opened in the convex chamber 26 are connected, and intermediate portions of these pipes 28a to 28c are connected. By operating the interposed control valves 29a to 29c, steam is supplied into the convex chamber 26 to heat and foam the pre-foamed resin particles, or cooling water is sprayed from the nozzle 28d to the back side of the convex mold 21, The molded product is cooled, and unnecessary drainage can be discharged from the convex chamber 26. A large number of vent holes 21b are formed in the convex mold 21, and steam is supplied from the convex chamber 26 into the molding space 2 through the vent holes 21b.

  In the mold apparatus 1 having such a convex unit, a concave plate and a center plate (an intermediate plate) for fixing the convex mold used in a general mold structure can be omitted. Since the convex fixing member used for fixing the concave mold can be omitted, the heat capacity of the mold apparatus 1 can be set to be small overall, and energy saving can be realized. Moreover, by directly fixing the convex mold 2 to the convex fixing plate 24, the mold apparatus 1 can be made smaller in the mold opening / closing direction, and the capacity of the concave chamber 16 is somewhat larger than that of the conventional one. However, since the convex chamber 26B can be remarkably miniaturized, the amount of steam used can be reduced as a whole, and the surface areas of the inner and outer surfaces of both units 10 and 20B can be reduced. Can be realized.

  1 shows a mold structure in which the drain pipe 28c is connected to the convex chamber 26, but a mold structure capable of exhausting or draining from the convex chamber 26 to the concave space 16 may be used. In this case, it is necessary to adopt a structure in which the direction of exhaust or drainage is limited to only one direction, and it is preferable to use a check valve. Thus, by omitting the drain pipe, the mold structure on the convex side can be simplified.

  In order to further improve the energy saving effect, the thermal conductivity of 2.5 kcal / 2.5 is provided on substantially the entire inner surfaces of the convex housing 22 and the concave housing 12 and on the substantially front surfaces of the inner surfaces of the convex housing 22 and the convex fixing plate 24. A heat insulating material of m · h · ° C. or less is provided, and it is configured to realize further energy saving by reducing heat transfer to both housings 12 and 22 and heat radiation from both housings 12 and 22. Yes. Insulating materials include silicon rubber, fluoro rubber, fluoro resin, polyethylene rubber, chloroprene rubber, butyl rubber, polyethylene, polypropylene, silicon resin, epoxy resin, carbon, polyvinylidene fluoride, polyether imide, polyphenyl sulfide, polyether ether ketone. , Polyamideimide or a composite material thereof can be employed.

  Thus, in this in-mold foam molding mold apparatus 1, since the center plate, which has been necessary in the conventional mold structure, can be omitted, the heating and cooling response speed of the mold apparatus 1 is increased and the molding efficiency is improved. In addition, the number of parts of the mold apparatus 1 can be reduced and the manufacturing cost of the mold apparatus 1 can be reduced.

  Next, the polypropylene resin pre-expanded particles used in the present invention will be described.

  The polypropylene resin that is the base resin of the polypropylene-based pre-expanded particles used in the present invention is not particularly limited, but the propylene monomer unit is 50% by weight or more, preferably 80% by weight or more, more preferably A polymer composed of 90% by weight or more and preferably polymerized with a Ziegler type titanium chloride catalyst or a metallocene catalyst and having high stereoregularity.

  Examples of copolymer components for the propylene monomer include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, and 3,4-dimethyl-1. Α-olefins having 2 or 4 to 12 carbon atoms such as butene, 1-heptene, 3-methyl-1-hexene, 1-octene and 1-decene, cyclic olefins such as cyclopentene and norbornene, 5-methylene-2- Diene such as norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid , Methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methacrylic acid Le, maleic anhydride, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene.

  The polypropylene resin used in the present invention preferably has a melting point of 130 ° C. or higher and 160 ° C. or lower, more preferably 135 ° C. or higher and 160 ° C. or lower, in order to obtain a foamed molded article having excellent mechanical strength and heat resistance. Preferably they are 140 degreeC or more and 155 degrees C or less. When the melting point of the base resin is within this range, it becomes easy to balance the increase in molding pressure (moldability), mechanical strength, and heat resistance during molding in the mold.

  The polypropylene resin used in the present invention is preferably non-crosslinked, but a crosslinked resin can also be used.

A method for producing the polypropylene resin pre-expanded particles used in the present invention will be described.
First, before pre-foaming, it is necessary to process the polypropylene resin particles into an appropriate size. Using an extruder, it is processed into polypropylene resin particles having a weight of 0.2 to 10 mg, preferably 0.5 to 6 mg.
Polypropylene resin particles for foaming are generally produced by a strand cutting method, for example, cooling a polypropylene resin extruded in a strand form from a circular die provided at the tip of an extruder with water, air, etc. The solidified product can be cut to obtain polypropylene resin particles having a desired shape.

  In the production of the resin particles, by adding a cell nucleating agent to the polypropylene resin, the cell diameter can be adjusted to a desired value when making the polypropylene resin pre-expanded particles. As the cell nucleating agent, for example, inorganic nucleating agents such as talc, calcium carbonate, silica, kaolin, titanium oxide, bentonite and barium sulfate are generally used.

A pre-foaming process for producing polypropylene pre-foamed particles will be described.
The polypropylene-based pre-expanded particles are prepared by charging the polypropylene-based resin particles and an aqueous dispersion composed of water, a dispersant and a foaming agent into a pressure-resistant container, heating to a predetermined temperature, and then from the pressurized state, the resin particles and It is obtained by discharging the mixture with water into a lower pressure atmosphere than in the pressure vessel. Specifically, an aqueous dispersion medium containing the polypropylene resin particles, a foaming agent, a dispersing agent and a dispersion aid is charged into a sealed container, and the temperature is increased while stirring to impregnate the resin particles with the foaming agent. In general, after adding a foaming agent as necessary and maintaining the inside of the sealed container at a constant pressure, the contents are discharged from the lower part of the sealed container into an atmosphere lower than the pressure inside the sealed container.

  Examples of the blowing agent include aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane, and mixtures thereof; inorganic gases such as air, nitrogen, and carbon dioxide.

  An in-mold molding method using the polypropylene-based pre-expanded particles in the present invention will be described.

  The polypropylene resin pre-expanded particles obtained as described above can be molded as they are after aging in the atmosphere, but in order to obtain a good product, an operation for imparting foaming force is performed before molding. It is common to do it.

As a method of imparting foaming power to the polypropylene resin pre-foamed particles, a conventionally known method can be adopted, for example,
(A) A method in which the pre-expanded particles are pressurized with an inorganic gas, the pre-expanded particles are impregnated with an inorganic gas, and a predetermined pre-expanded particle internal pressure is applied,
(B) A method of filling the mold with the pre-expanded particles compressed with the gas pressure, and then applying the foaming force using the recovery force of the pre-expanded particles by releasing the gas pressure,
(C) A method of opening the mold in advance before filling the pre-expanded particles into the mold and then closing the mold after filling to mechanically compress the pre-expanded particles to give foaming force, etc. It is done.

  As the inorganic gas used in (a) and (b), air, nitrogen, oxygen, helium, neon, argon, carbon dioxide gas and the like can be used. These may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

The method (A) suitable for the present invention will be described in more detail.
For example, pre-expanded particles are placed in a pressure vessel, and the pre-expanded particles are impregnated with air by allowing the pre-expanded particles to stand for an appropriate pressure and time in a state where compressed air is supplied into the vessel. The suitable internal pressure range is 0.07 to 0.15 MPa (G), more preferably 0.09 to 0.13 MPa (G). If the internal pressure of the pre-expanded particles is out of the above range and is less than 0.07 MPa (G), the product shrinks after molding and the amount of deformation tends to increase. If the internal pressure of the pre-expanded particles exceeds 0.15 MPa (G), rapid expansion of the pre-expanded particles occurs during heating, so that the intrusion of vapor into the product is blocked and uneven fusion inside the product may occur. Or, excessive risk of air release from the pre-expanded particles tends to increase the risk of poor fusion.

Here, the measuring method of the internal pressure of the pre-expanded particles is as follows.
The weight and volume of the pre-expanded particles of about 100 cm ³ after the internal pressure application treatment are measured. The volume was measured by the volume increase when submerged in ethyl alcohol. Subsequently, the pre-expanded particles are heated at 150 ° C. for 30 minutes to dissipate the inorganic gas from the pre-expanded particles. It is obtained from the equation of state of the ideal gas using the weight difference between the pre-expanded particles after the inorganic gas escape, the weight difference between the pre-expanded particles after the internal pressure treatment and the density converted from the volume and the weight.

  Next, the manufacturing method of the polypropylene resin foam molded article of the present invention will be described.

  In the method for producing a polypropylene resin foam molded article of the present invention, the polypropylene resin pre-expanded particles have the aforementioned concave mold and a concave housing for holding the same, and the concave mold is supported in a cantilever manner on the concave housing. And a convex housing that holds the convex shape and the convex shape, the convex shape is directly fixed to the convex housing, and the space between the convex back opening and the housing is convex. A polypropylene-based resin molded body that fills a molding space of a mold apparatus 1 that is a mold apparatus including a convex unit serving as a steam chamber and supplies steam to the molding space to foam and fuse the foamed particles. It is a manufacturing method.

In the conventional heating process, as shown in FIG. 2, it is usually performed in a subdivided manner such as a preliminary heating process, one heating process, reverse one heating process, double-side heating process, auxiliary heating process, and heat retention process.
After filling the pre-expanded particles with the internal pressure into the molding space in the mold and before fusing the pre-expanded particles, the air in the steam chamber, and further, between the inter-particles of the pre-expanded particles filled in the molding space Operation to replace the air inside with steam. This operation is called a preheating step, a one-side heating step, and a reverse one-side heating step.

  In the preheating step, the concave mold side steam regulating valve 8, the convex mold side steam regulating valve 9, the concave mold side drain valve 12, and the convex mold side drain valve 13 are opened in FIG. And a process of passing steam through the convex mold side transfer steam chamber 19 and replacing the air in the steam chamber with steam.

  On the other hand, the heating step is a step in which the convex side drain valve 13 and the concave side steam control valve 8 are closed, the convex side steam control valve 9 and the concave side drain valve 12 are opened, and the steam is passed through the molding space 7, and preliminary foaming is performed. This is a step of replacing air between particles with steam. The one heating shown here is a process of flowing steam from the convex mold side to the concave mold side, but adopting a process of flowing steam from the concave mold side to the convex mold side (reverse one heating process) Or both of them may be adopted.

  In the double-sided heating process, the concave mold side steam pressure regulating valve 8 and the convex mold side steam pressure regulating valve are opened with the concave mold side drain valve 12 and the convex mold side drain valve 13 closed, and foaming and fusion of the pre-expanded particles are performed. This is a step of increasing the pressure to the required predetermined vapor pressure. As the pattern of steam pressure increase, there is a case where the supply of steam is stopped when a predetermined steam pressure is reached, or a control is performed to keep the steam pressure constant after reaching the predetermined steam pressure. Any one of them is selected in accordance with the characteristics.

  On the other hand, in the heating step of the production method of the present invention, as shown in FIG. 3, (A) the first step until the vapor pressure P1 at which the fusion rate of the expanded particles reaches 40% or more and 80% or less is reached. (B) Once the steam pressure is lowered to the steam pressure P2 lower than the first stage ultimate heating pressure P1, (C) again reaches the steam pressure P3 equal to or higher than the steam pressure in the first stage heating. It is characterized by heating until.

  In the evacuation process, the concave side steam control valve 19a and the convex side steam control valve 29a are simultaneously opened while the concave and convex drain valves 19c and 29c are opened, and the air in the chamber is replaced with steam. Here, since the capacity of the concave chamber 16 is much larger than that of the convex chamber 26b, there is a case where steam replacement of the convex chamber is not necessary. In this case, with the drain valves 19c and 29c opened, the exhaust process operation is performed by the concave steam control valve 19a.

  There is also an exhaust method in which the concave and convex steam control valves 19a and 28a are opened with the concave drain valve 19c opened and the convex drain valve 29c closed. In this case, it becomes the process which served as the exhaust process and one heating process of the general shaping | molding method. However, if the convex steam supply capacity is excessive, the pressure in the convex chamber rises and the pre-expanded particles near the convex mold are foamed and fused. This is not preferable.

  The heating time in the preheating step varies depending on the pipe size of the molding machine, the valve size, the heat capacity of the mold, and the mold volume, but is about 2 to 8 seconds, more preferably 2 to 5 seconds.

  In the production method of the present invention, when steam is supplied to the molding space and the pre-expanded particles are heated and fused, (A) the vapor pressure P1 at which the pre-expanded particles have a fusion rate of 40% to 80%. It is characterized in that the first stage heating is performed until it reaches.

The operation of the molding machine is to open the steam pressure regulating valve 29a only with the convex type with both the concave and convex drain valves 19c and 29c closed, and to let the steam flow from the convex chamber to the concave chamber for several seconds. In this operation, it is important that the fusion rate of the pre-expanded particles is 0% or more and 30% or less.
When the fusion rate of the pre-expanded particles is more than 30%, the steam does not reach every corner of the molding space in the subsequent heating process, resulting in poor fusion. In the case of a simple product shape, this step can be omitted, but this step is necessary to stably secure the fusion rate.

Subsequently, the convex steam pressure regulating valve is closed, and the concave steam pressure regulating valve 19a is opened. As shown in FIG. 3, the steam pressure P1 is such that the fusion rate of the pre-foamed particles is 40% or more and 80% or less. The first stage is heated until it reaches. When the convex steam pressure regulating valve is not closed, the heating is uneven due to the difference in volume between the convex and concave steam chambers, and uneven fusion tends to occur. Therefore, it is preferable to heat only the concave type.
(A) In the first heating step, if the fusion rate is less than 40%, the gap between the pre-expanded particles is not filled until the end of heating, and the air as the foaming agent is continuously released from the pre-expanded particles. For this reason, the shrinkage and deformation of the molded body immediately after molding increase, and the mold shrinkage ratio of the final product tends to increase. In addition, if the molded body is greatly deformed immediately after molding, the time required for the drying and curing processes in the next process becomes longer, and productivity may be greatly reduced. It may also lead to the generation of non-defective products. When the fusion rate exceeds 80%, the molded body may be deformed by being pushed by steam during the subsequent second stage heating.

  Therefore, in order to suppress the release of air from the pre-expanded particles, which is an effect of the present invention, (A) the appropriate range of the fusion rate by the first stage heating is 40% or more and 80% or less, more preferably 50%. It is 70% or less.

  (A) The heating steam pressure P1 at which the fusion rate is 40% or more and 80% or less in the first heating step varies depending on the base resin type, the expansion ratio, and the internal pressure to be applied, but is a general propylene-ethylene random system In the case of pre-expanded particles using a resin as a base resin, a value of about 0.20 to 0.25 MPa (G) can be set as a guide.

  In the production method of the present invention, the pressure increase rate in the first heating step is preferably 0.04 MPa / second or more and 0.10 MPa / second or less. If the pressure increase rate in the first heating step is less than 0.04 MPa / second, the expansion rate of the pre-expanded particles becomes slow, and it takes a long time to fill the gap between the particles, so the release of air from the pre-expanded particles is suppressed. There is a tendency not to. When the pressurization speed is 0.10 Mpa or more, the pre-expanded particles only in the vicinity of the surface portion of the mold rapidly expand, so that the steam flow path to the inside of the molding space is blocked, and the molding space can be uniformly heated by steam. There is a tendency that poor fusion is likely to occur.

  In the production method of the present invention, it is preferable to detect the pressure in the steam chamber and control the process using this as the progress condition from the first heating step to the next step.

In the present invention, for example, a device capable of monitoring a signal from a pressure gauge (not shown) installed in a drain valve line and performing an operation of moving to the next step when a predetermined pressure is reached. did.
Here, the vapor pressure, which is the progress condition of the first heating step, is 0.20 to 0.25 MPa (G). In setting the predetermined vapor pressure, pre-expanded particles having a bulk density range of 17 g / L to 50 g / L are prepared, and the internal pressure is adjusted to 0.05 to 0.15 MPa (G), followed by preheating. The process and the heating process of the 1st step | paragraph were performed, and the method of investigating the vapor | steam pressure so that the fusion rate of a subsequent molded object may be 50 to 70% was used.

  By setting it as such an apparatus structure and condition setting, the vapor pressure at the time of completion | finish of the (A) 1st stage heating process can always be made the same. That is, it is possible to always complete the first heating step at the same temperature, and the fusion rate of the pre-expanded particles can always be a predetermined fusion rate.

In the manufacturing method of the present invention, (A) after the completion of the first stage heating, (B) a step of once reducing the vapor pressure to a vapor pressure P2 lower than the first stage ultimate vapor pressure P1 is provided. It is a feature. The step (B) is an important technique for efficiently performing foaming and fusion of the pre-foamed particles.
In order to foam and fuse the pre-expanded particles, a predetermined temperature is required. However, since the polypropylene-based pre-expanded particles have a very high foaming and fusing temperature, the vapor pressure is also high. This results in the contradiction that steam pressure for heating inhibits foaming.

  Therefore, in the production method of the present invention, (A) the pre-expanded particles are heated to a temperature capable of fusing, and (B) the foam pressure is lowered by reducing the vapor pressure once at a high temperature, so that the foaming and fusing are advanced. is there. (B) By performing operation of a process, it is possible to set the heating steam pressure for obtaining the same fusion rate lower than the conventional manufacturing method.

In the step (B), the standard for the decrease in the vapor pressure from the pressure P1 at the end of the first heating step is preferably 0.05 to 0.15 MPa, more preferably 0.05 to 0.10 MPa. is there.
Here, when the pressure drop is less than 0.05 MPa, the effect of foaming and fusing of the pre-foamed particles cannot be sufficiently obtained, and the release of air from the pre-foamed particles is not suppressed. There is a tendency for shrinkage and deformation to increase and the mold shrinkage ratio of the final product to increase. Further, when the pressure drop exceeds 0.15 MPa, the fusion proceeds excessively, so that the product may be deformed when the second stage heating is performed.

In the production method of the present invention, it is preferable that the time of the step (B) for reducing the vapor pressure is set in the range of 2 seconds to 5 seconds.
Once the time of the step (B) for lowering the vapor pressure is less than 2 seconds, the time for foaming and fusing the pre-expanded particles is not ensured, so that the release of air from the pre-expanded particles can be suppressed. There is no tendency. Further, if the time of the step (B) exceeds 5 seconds, the fusion proceeds excessively, so that the product may be deformed when the second stage heating is performed.

  In the step (B), the steam pressure can be reduced to P2 by reducing the steam valve opening to reduce the steam supply amount, closing the steam valve to stop the steam supply, and draining the steam. For example, the opening degree of the valve can be adjusted and the drain valve is slightly opened, and the pressure is decreased while controlling the opening degree of the steam valve and the drain valve.

  In the production method of the present invention, (A) the first heating step, (B) once the pressure reduction step, (C) the vapor pressure P3 equal to or higher than the ultimate vapor pressure P1 in the first heating step. There is a step of performing the second stage heating, in which heating is performed until it reaches, and is maintained for a certain period of time.

(A) The first stage heating is heating in which the fusion rate of the pre-expanded particles is set to 40% or more and 80% or less, and is sufficient as heating for ensuring the fusion rate, but the surface is smoothed. There is not enough heat to beautify. Therefore, (A) by smoothing the surface in a state where air release from the pre-foamed particles is suppressed by performing the first stage heating in which the fusion rate of the pre-foamed particles is 40% or more and 80% or less. (C) The second stage heating is performed.
The heating operation in the pressure increasing process from P2 to P3 uses the concave steam pressure regulating valve 19a with the drain valves of both molds closed. It is preferable to hold for several seconds after the chamber pressure reaches P3. A rough guide is 5 to 10 seconds.

  (C) In the pressure holding step after reaching the pressure of P3, it is preferable to increase the convex steam pressure rather than the concave steam pressure. The heating operation of the present invention is mainly heating centering on the concave mold, and the fusion rate and surface property on the convex mold side may be inferior to those of the concave mold. Further, the product shape is often uneven on the convex side, and it is preferable to perform such heating because a high fusion rate is desired. The standard of the vapor pressure difference between the concave and convex is 0.02 to 0.05 MPa.

  Here, the ultimate vapor pressure P3 in the second heating step (C) varies depending on the type of the base resin, the expansion ratio of the pre-expanded particles, and the internal pressure to be applied, but the general reserve of the propylene-ethylene random resin In the case of expanded particles, the range is about 0.25 to 0.35 MPa. However, the smaller the expansion ratio of the pre-expanded particles, the higher the pressure required.

  (C) The setting of the pressure holding time in the second heating step was 5 to 10 seconds here. Immediately after the specified pressure is reached in the second heating process, the temperature of the mold is uneven due to the difference in the thickness of each part of the mold and the difference in the flow of steam, and it takes time to achieve a uniform temperature. It becomes. Since uneven temperature of the mold greatly affects the surface properties of the product, it is necessary to set an appropriate pressure holding time in consideration of the shape of the mold, the heat capacity of the mold, and the like.

  (C) By performing the second heating step, the temperature of the surface of the molded body can be increased uniformly, and the number of generated grains can be reduced. Here, the intergranular means a gap generated between the pre-expanded particles and the pre-expanded particles found on the surface of the molded body, and the number of intergranular is an evaluation scale of the surface beauty.

  Originally, although the steam heating pressure required for fusion of pre-expanded particles and the vapor pressure required for surface aesthetics are different, the conventional heating pattern uses the same process for fusing and beautifying the surface. Therefore, it was necessary to achieve a high vapor pressure necessary for surface beautification. For this reason, the pre-expanded particles have an excessive foaming force, and there is a problem that the molding cycle becomes long.

  On the other hand, according to the manufacturing method of the present invention, the fusion process [(A)] and the process [(C)] for performing surface beautification are separated, so that the fusion cycle having a great influence on the molding cycle is obtained. It is possible to set the vapor pressure in the attaching step [(A) step] to a low vapor pressure setting necessary only for fusing, and the molding cycle can be shortened.

In the production method of the present invention, after the completion of the second heating step (C), an auxiliary heating step may be provided in which the steam valve on the inferior surface is opened and heated for several seconds. You may provide the heat retention process which is a process hold | maintained for 19 seconds in the state which closed 19c and 29c. You may use an auxiliary heating process and a heat retention process together.
Any process can be expected to improve surface properties, and the process time is preferably set to 3 seconds or more and 10 seconds or less, more preferably 4 seconds or more and 7 seconds or less. If the auxiliary heating step and / or the heat retention time is less than 3 seconds, the surface property improvement effect is not seen, and if it is set to more than 10 seconds, the surface property improvement effect does not change and only the molding cycle is performed. Will be extended.

  In the manufacturing method of the present invention, after the heating steps (A) to (C) are finished, the cooling water valves 19b and 29b are opened to condense the steam in the steam chamber, and then the drain valves 19c and 29c are opened and cooled. By continuing the above, the concave mold 11 and the convex mold 21 are cooled by the cooling water ejected from the spray nozzle, the molded body is solidified, and the mold is released from the mold. As a cooling method in this case, various known methods can be used.

For example, there are a method of water-cooling the mold with the spray nozzles 18b and 26b of the cooling water attached to the molding apparatus described above, and a method of using a vacuum together (not shown).
As described above, according to the production method (molding method) of the present invention, the vapor pressure at the end of the first heating step can always be the same. That is, it is possible to always complete the first heating step at the same temperature, and the fusion rate of the pre-expanded particles can always be a predetermined fusion rate.

  The fusion rate of the polypropylene resin foam molded article obtained by the production method of the present invention is preferably 60% or more, and more preferably 80% or more.

  Furthermore, the preheating step is necessary because the fusion property of the prefoamed particles is improved as compared with the conventional molding method, but the one heating step and the reverse one heating step in the state where the drain valve is released are not necessarily required. Absent. By performing such heating, it is possible to suppress the exhaust of steam to the outside of the mold system as much as possible, so that the amount of steam used can be reduced, and further energy saving can be realized.

  Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

  In addition, evaluation in an Example and a comparative example was performed as follows.

(Steam consumption)
The amount of steam used was measured with a vortex flow meter [manufactured by YOKOGAWA].

(Fusability)
In the obtained foamed molded product, a place where steam is difficult to pass is selected, and a notch of about 5 mm is made in the part using a cutter knife (blade length 100 mm, blade width 18 mm, blade thickness 0.5 mm). Was bent and broken.
Visually observe the state of the fractured surface, measure the number of interfacial fractures at the fracture surface and the number other than that, and fuse the foamed particles that are fractured, and those that are fractured at the interface It calculated by calculating | requiring this ratio as unfused. However, the numerical value of the fusion rate is expressed in the order of 10%.

(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.
◎ ・ ・ ・ Turtle pattern is inconspicuous.
○: A slight turtle shell pattern is observed.
Δ: Tortoise shell pattern is observed, but quality is acceptable.
X: Tortoise shell pattern is remarkable and is a level causing quality problems.

(End deformation)
The deformation of the end portion of the obtained molded body was visually evaluated and expressed as follows.
○ ・ ・ ・ No deformation and good condition.
Δ: Slightly deformed / contracted and wrinkles on the surface, but quality is acceptable.
X: The level is a problem in terms of quality because the edge is deformed / shrinked and crushed.

Example 1
[Preparation of polypropylene pre-expanded particles]
As polypropylene-based pre-expanded particles, air was injected into commercially available polypropylene-based pre-expanded particles [manufactured by Kaneka Co., Ltd., RBK36, bulk density 21 kg / m ³ ] by air pressure treatment, and an internal pressure of 0.10 MPa (G). What was adjusted to was used.
[Production of in-mold foam moldings]
P-300 molding machine [Toyo Machine Metal, pressure resistance 0.4 MPa (G)] has the mold structure shown in FIG. 1, the outer dimensions of the frame are 1450 mm x 1300 mm, and the shape of the product is a box (length 550 mm x A mold having a width of 350 mm and a height of 150 mm and having a three-cavity product on the convex mold side was mounted, and the vapor supply pressure was set to 0.6 MPa (G) for molding evaluation.
In the molding evaluation, the pre-expanded particles are filled into the molding space with the concave mold and the convex mold opened by 10 mm, and then the mold is clamped, and molding is performed under the heating conditions shown in Table 1 in the heating pattern shown in FIG. The cooling process was terminated when 25 seconds had elapsed with water cooling for 60 seconds and the water cooling stopped and the mold clamped, and the molded body was released from the mold.
That is, in the preheating process, both the concave mold side and convex mold side drain valves were opened, both the concave side and convex side steam valves were opened, and the air in the steam chamber was discharged for 5 seconds.
(A) In the first stage heating process, heating from the convex mold side is performed for 8 seconds with both the concave mold side and the convex mold drain valve closed, and the pressure in the convex chamber at the end is The pressure was 0.05 MPa. Subsequently, heating was performed from the concave mold until the pressure in the concave chamber reached 0.25 MPa. The steam pressurization speed at this time was 0.04 MPa / second.
(B) In the pressure reduction step, the steam valve was closed with the concave and convex drain valves closed, and the steam pressure was 0.15 MPa by leaving it for 5 seconds.
(C) In the second stage heating, the concave steam pressure regulating valve is opened, the steam pressure is increased to 0.33 MPa, and after holding for 6 seconds, the steam supply from the convex mold is started, and the convex chamber is set to 0.35 MPa. The state of the concave 0.33 MPa was maintained for 5 seconds. Thereafter, both the concave and convex steam supply were stopped, the drain valve was closed and held for 5 seconds (heat retention step), cooled, and the product was released.
[Evaluation of molded body]
The obtained molded body was allowed to stand at room temperature and atmospheric pressure for 1 hour, and then carried into a drying room at 75 ° C. and dried for 24 hours.
The molded body was evaluated by taking out the molded body from the drying chamber and curing it at room temperature and atmospheric pressure for 24 hours. The evaluation results are shown in Table 1.

(Example 2)
Except for changing the fusion rate at the end of convex heating by changing the time of steam supply from the convex mold side by (A) first stage heating in [Preparation of in-mold foam molded body] The same operation as in Example 1 was performed to obtain a molded body.
The obtained molded body was evaluated after the same drying and curing as in Example 1. The evaluation results are shown in Table 1.

(Examples 3 to 4)
In [Preparation of In-mold Foamed Molding], the same operation as in Example 1 was performed except that the ultimate pressure P1 in the first stage heating was changed as described in Table 1 to obtain a molded body.
The obtained molded body was evaluated after the same drying and curing as in Example 1. The evaluation results are shown in Table 1.

(Example 5)
In [Production of In-mold Foamed Molding], (C) In the pressure holding condition after the pressure is raised to the P3 pressure of the second stage heating, the convex mold side is 0.33 MPa and the concave mold side is 0.35 MPa. A molded body was obtained by performing the same operation as in Example 1 except that the concave mold was set higher than the above.
The obtained molded body was evaluated after the same drying and curing as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 1)
In [Production of in-mold foamed molded product], the same operation as in Example 1 was performed except that (A) the operation of the drain valve during the first stage heating and (B) the pressure reduction step were not performed. A molded body was obtained. Specifically, (A) during the first stage of heating, when the steam is supplied from the concave mold side, the convex drain valve is opened, when the steam is supplied from the convex mold side, the concave drain valve is opened, and further, the first stage heating is performed. The subsequent (B) pressure reduction process was not performed, and corresponds to the conventional heating process shown in FIG.
The obtained molded body was evaluated after the same drying and curing as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 2)
In [Production of In-mold Foamed Molding], (A) The same operation as in Example 1 was performed except that the heating from the convex mold side was not performed in the first stage heating, thereby obtaining a molding.
The obtained molded body was evaluated after the same drying and curing as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 3)
In [Production of In-mold Foamed Molding], (A) The same operation as in Example 1 except that the heating time from the convex mold side was set to 20 seconds and the ultimate pressure at that time was increased by the first stage heating. To obtain a molded body.
The obtained molded body was evaluated after the same drying and curing as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 4)
In [Production of In-mold Foamed Molding], (C) Example 1 except that the conditions for supplying steam from both the concave mold and the convex mold were changed during the pressurization step to P3 pressure in the second stage heating. The same operation was performed to obtain a molded body.
The obtained molded body was evaluated after the same drying and curing as in Example 1. The evaluation results are shown in Table 1.

1 Mold device for in-mold foam molding
2 Molding space 3 Filler
10 Recessed unit 11 Recessed mold
11a Front end 11b Vent
12 Recessed housing 13 Recessed frame
13a Front side end 14 Recessed fixed plate
15 Fixing member 16 Recessed chamber
17 Front opening 18a Steam supply pipe
18b Cooling water supply pipe 18c Drain pipe
18d Nozzle 19a-19c Control valve
20 Convex unit 21 Convex mold
21b Vent 22 Convex housing
23 Convex frame 24 Convex fixing plate
25 Fixing member 26 Convex chamber
27 Center plate 27a Restriction part
27b Opening 28a Steam supply pipe
28b Cooling water supply pipe 28c Drain pipe
28d Nozzle 29a-29c Control valve
30 Center plate
1A Mold unit 20A Convex unit
22A Convex housing 26A Convex chamber
27A Cover plate
1B Mold unit 20B Convex unit
22B Convex housing 24a Regulator
26B Convex chamber

Claims (2)

A concave unit having a concave mold and a concave housing for holding the concave mold, and supporting the concave mold in a cantilever manner on the concave housing, and a convex housing for holding the convex mold and the convex mold It is formed with a concave mold and a convex mold of a mold unit comprising a convex unit in which the convex mold is directly fixed to the convex housing and the space between the convex back opening and the housing is a convex steam chamber. In the molding space
Filling with polypropylene resin pre-expanded particles, supplying steam to the molding space, foaming and fusing the pre-expanded particles, a method for producing a polypropylene resin foam molded article,
When fusing
(A) First, steam is supplied only from the convex mold, and heating is performed so that the fusion rate of the pre-expanded particles is 0% or more and less than 30%. Stop to fuse the expanded particles, and by supplying steam from the concave mold, perform the first stage heating until reaching the vapor pressure P1 at which the fusion rate of the pre-expanded particles is 40% to 80%,
(B) Once it is lowered to a steam pressure P2 lower than the first stage reached steam pressure P1,
(C) Again, by supplying steam only from the concave mold, heating is performed until the steam pressure P3 equal to or higher than the ultimate steam pressure P1 in the first stage heating is reached, and the pressure equal to or higher than P3 is maintained for a certain time. A method for producing a polypropylene resin foam molded article. (C) The method for producing a polypropylene resin foam molded article according to claim 1, wherein the convex steam pressure is made higher than the concave steam pressure in the step of maintaining the pressure equal to or higher than P3.