JP2008143125A - Method for producing foamed molded article made of thermoplastic resin - Google Patents

Abstract

Disclosed is a method for producing a foamed molded article made of a thermoplastic resin having excellent surface smoothness.
A method for producing a thermoplastic resin foamed molding by further foaming a thermoplastic resin foamed sheet 1 in a mold using a pair of molds that can be sealed. (1) The manufacturing method of the foaming molding made from a thermoplastic resin including the process of (4). (1) Heat softening the foamed sheet made of thermoplastic resin, (2) Heat softening in the step (1) on the porous member of the mold in which a part of the inner wall surface of the mold is made of the porous member 4 Placing the thermoplastic resin foam sheet 1 so that one surface thereof is in contact; (3) expanding the thermoplastic resin foam sheet by reducing the pressure after sealing the mold; A step of forming the desired thermoplastic resin foamed molded body 7; (4) a step of taking out the thermoplastic resin foamed molded body 7 from the mold after the inside of the mold is brought to normal pressure; Figure 1

Description

The present invention relates to a method for producing a thermoplastic resin foam molded article.

Thermoplastic resin foam sheets are used in a wide range of applications such as packaging materials, building materials, and automobile materials because of their light weight and heat insulation properties. The thermoplastic resin foam sheet may be used in the form of a flat plate, but depending on the application, it is often used after being subjected to punching, thermal ruled line processing, vacuum forming or the like.
A method for vacuum forming a thermoplastic resin foam sheet is a double-sided vacuum forming method for a foamed polypropylene resin sheet using a male and female mold capable of vacuum forming, wherein the polypropylene resin has an expansion ratio of 5.5 times or less. After using laminated sheets each laminated with a thermoplastic resin film on both sides of the sheet, the laminated sheet was heat-softened with a far-infrared heater, and then the mold gap was 1.0% of the thickness after heat-softening of the laminated sheet. There is known a double-sided vacuum forming method for a laminated sheet of up to 2.5 times (see Patent Document 1).
Japanese Patent Publication No. 5-28974

However, in the above method, when vacuum suction is performed, an air pool is generated at the interface between the thermoplastic resin foam sheet and the molding die, and the surface smoothness of the foam sheet obtained after vacuum molding may deteriorate.

An object of the present invention is to provide a method for producing a thermoplastic resin foamed molded article having excellent surface smoothness.

That is, the present invention is a method for producing a thermoplastic resin foam molded article by further foaming a thermoplastic resin foam sheet in the mold using a pair of sealable molds, and comprising at least the following: (1) It is a manufacturing method of the foaming molding made from a thermoplastic resin including the process of (4).
(1) Step of heat-softening a foam sheet made of thermoplastic resin (2) A part of the inner wall surface of the mold has holes with a hole diameter of 1000 μm or less, and the air permeability is 900 to 2500 cm ³ / cm ² / s. (3) The molding die, wherein the thermoplastic resin foam sheet softened by heating in the step (1) is placed on the porous member of the molding die made of a certain porous member so that one surface thereof is in contact with the molding die. The step of expanding the thermoplastic resin foamed sheet by reducing the pressure after sealing the interior and shaping the foamed molded article of the desired thermoplastic resin (4) After the inside of the mold is at normal pressure, The process of taking out the thermoplastic resin foam molded body from the mold

According to the method for producing a thermoplastic resin foam molded article of the present invention, a thermoplastic resin foam molded article having excellent surface smoothness can be produced.

First, the thermoplastic resin foam sheet used in the present invention will be described.
The thermoplastic resin constituting the thermoplastic resin foam sheet used in the present invention is not particularly limited, and a known resin can be used, for example, low density polyethylene, medium density polyethylene, high density polyethylene or linear Examples thereof include ethylene resins such as low density polyethylene and olefin resins such as propylene resins. The resin constituting the foam sheet may be one type or two or more types.

In particular, from the viewpoint of heat resistance and rigidity, it is preferable that 50% by weight or more of the resin constituting the foamed sheet is made of a propylene-based resin. Examples of the propylene resin include a propylene homopolymer, a copolymer of propylene and a small amount of ethylene and / or α-olefin, or a polymer in which an amorphous ethylene / α-olefin copolymer is dispersed. Examples include coalescence. From the viewpoint of foamability, 5% by weight or more of the entire resin constituting the foamed sheet has a melt tension (MT (190)) at 190 ° C. and a melt flow rate (MFR (230)) at 230 ° C. of the following formula 1. A satisfactory propylene-based resin is preferable.
MT (190) ≧ 7.52 × MFR (230) ^(−0.576) [Formula 1]

The melt flow rate at 230 ° C. (MFR (230)) is a value measured in accordance with JIS K7210 at a temperature of 230 ° C. and a load of 2.16 kgf (unit: g / 10 minutes). Melt tension at 190 ° C. (MT (190)) means a commercially available melt tension tester with a sample amount of 5 g, a heating temperature of 190 ° C., a heating time of 5 minutes, a piston lowering speed of 5.7 mm / min, and a length of 8 mm. The tension when a strand is extruded from an orifice having a diameter of 2 mm and the strand is wound at a winding speed of 100 rpm using a roller having a diameter of 50 mm (unit: g).

Examples of the propylene resin satisfying the formula 1 include a branched propylene resin and a linear propylene resin containing a high molecular weight component.

Examples of the branched propylene-based resin include resins obtained by irradiating a linear propylene-based resin as disclosed in JP-A No. 62-121704. Such branched propylene-based resins are commercially available as PF814 and SD632 from Sun Aroma Co., Ltd.
As the linear propylene-based resin, a propylene-based resin into which an ultrahigh molecular weight component as disclosed in JP-A-11-228629 is introduced, that is, a crystalline propylene polymer having an intrinsic viscosity of 5 dl / g or more. Obtained by a polymerization method comprising a step of producing part (A) and a step of producing a crystalline propylene polymer part (B) having an intrinsic viscosity of less than 3 dl / g, wherein the intrinsic viscosity is less than 3 dl / g, And a propylene resin in which the proportion of the propylene-based polymer portion (A) is 0.05 wt% or more and less than 35 wt%.

The expansion ratio and closed cell ratio of the thermoplastic resin foam sheet to be used are not particularly limited, but the expansion ratio is preferably 1.2 to 5.0 times, and the closed cell ratio is 80 to 100%. It is preferable that Since such a foamed sheet made of a thermoplastic resin is less likely to break when reduced in pressure and further foamed, a foamed molded article made of a thermoplastic resin having a high expansion ratio and a closed cell ratio can be obtained. In particular, a thermoplastic resin composed of a propylene-based resin containing 5 to 20% by weight of a propylene-based polymer satisfying the above formula 1, having an expansion ratio of 1.5 to 2.5 times and a closed cell ratio of 90 to 100%. It is preferable to use a foamed sheet.

  The thickness of the thermoplastic resin foam sheet to be used is not particularly limited, but is usually 1 to 10 mm. In addition, the foam sheet may be a single layer or may have a multilayer structure composed of a plurality of layers including at least one foam layer. As the layer structure, for example, 2 types 2 layers (non-foamed layer / foamed layer), 2 types 3 layers (non-foamed layer / foamed layer / non-foamed layer) and 3 types 5 layers (non-foamed layer / non-foamed layer / foamed layer) / Non-foamed layer / non-foamed layer) and the like.

The production method of the thermoplastic resin foam sheet is not particularly limited, and a known production method such as an extrusion foaming method, a batch foaming method, or a bead type foaming method can be adopted, but from the viewpoint of productivity, the extrusion foaming method. Is preferred.
In the extrusion foaming method, a resin, a foaming agent, and the like are melt-kneaded in an extruder to obtain a molten resin composition, and the molten resin composition is sent into a die connected to the extruder. The molten resin composition sent to the die is extruded from the die outlet into the atmosphere and foamed. The extruded foam sheet can be cooled and cut into a desired size by a cutting machine to produce a foam sheet. As the die shape, a T die or a circular die can be used.
In the case of a foam sheet having a multilayer structure, a non-foamed layer or the like may be bonded to the above-mentioned foam sheet by a known bonding technique to form a multilayer structure, but from the viewpoint of productivity, a multilayer coextrusion using a known multilayer die It is preferable to manufacture by a foaming method.

The foaming agent used for manufacture of a foam sheet is not specifically limited, A well-known physical foaming agent and a chemical foaming agent can be used individually or in combination.
As the physical foaming agent, carbon dioxide gas, nitrogen gas, air, propane, butane, pentane, hexane, dichloroethane, dichlorodifluoromethane, dichloromonofluoromethane, trichloromonofluoromethane, etc. can be used, such as nitrogen gas, carbon dioxide gas, It is preferable to use a highly safe inorganic gas such as air.
When the resin constituting the foamed sheet is a propylene resin, it is preferable to use carbon dioxide as a foaming agent from the viewpoint of safety and solubility in the propylene resin. When carbon dioxide gas is used, it is preferable to inject it into the resin in a supercritical state of 7.4 MPa or more and 31 ° C. or more from the viewpoint of diffusion into the resin and solubility.

Chemical foaming agents include organic acids such as citric acid, sodium citrate and stearic acid, baking soda, azodicarbonamide, tolylene diisocyanate, isocyanate compounds such as 4,4'diphenylmethane diisocyanate, azobisbutyronitrile, barium azo Azos such as dicarboxylate, diazoaminobenzene, trihydrazinotriazine, diazo compounds, benzene, sulfonyl, hydrazide, P, P'-oxybis (benzene, sulfonyl, hydrazide), hydrazine derivatives such as toluene, sulfonyl, hydrazide, N , N'-dinitroso-pentamethylene-tetramine, N, N'-dimethyl-N, N'-dinitroso-terephthalamide and other nitroso compounds, P-toluene-sulfonyl-semicarbazide, 4,4'oxybis Semicarbazide compounds such as emissions Zen semicarbazide, azide compounds, etc. can be used triazole compound. In particular, it is preferable to use any of sodium bicarbonate, citric acid, and azodicarbonamide.

When a chemical foaming agent is used, a foaming aid may be used in combination to adjust the decomposition temperature and decomposition rate. For example, since the decomposition temperature of azodicarbonamide alone is as high as about 200 ° C., zinc oxide, zinc stearate, urea or the like can be added and used as a foaming aid when processing at low temperatures.

When a physical foaming agent is used, a cell nucleating agent may be used in combination. Cell nucleating agents include talc, silica, diatomaceous earth, calcium carbonate, magnesium carbonate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium silicate, zeolite, mica, clay, wollastonite, hydrotalcite In addition, polymer beads such as magnesium oxide, zinc oxide, zinc stearate, calcium stearate, PMMA, synthetic aluminosilicate, the above chemical foaming agents, and the like can be used.

Various layers of a low molecular type or high molecular type additive may be blended in each layer of the foam sheet having a single layer or a multilayer structure, if necessary. For example, conductive agents, antistatic agents, flame retardants, fillers, antioxidants, copper damage inhibitors, weathering agents, ultraviolet absorbers, lubricants, pigments, adhesion improvers and the like are used. In the case of a multilayer, the function according to a use can be provided especially by mix | blending the additive according to a use with the outermost layer.

Next, a pair of sealable molds used in the present invention will be described. As an example of the molding die used in the present invention, one is a storage portion composed of a bottom surface and a wall surface surrounding the periphery of the bottom surface, and the other is a flat plate-shaped molding die serving as a lid for the storage portion, And a combination of a mold, a female mold and a male mold. However, in any combination described above, one of the molds has a porous part of which the inner wall surface has pores with a pore diameter of 1000 μm or less and the air permeability is 900 to 2500 cm ³ / cm ² / s. The mold must be made of a quality member. The inner wall surface made of a porous member is a surface to be a molding surface. As the porous member, a member different from the molding die may be embedded in the wall surface of the molding die, or a part of the inner wall surface of the molding die itself may be used as the porous member by drilling the molding die. In addition, the molding die in which a part of the inner wall surface used in the present invention is made of a porous member may be a porous member on all one surface among the plurality of inner wall surfaces, or a part of one surface. May be a porous member. However, in the latter case, when a foamed sheet made of a thermoplastic resin is disposed on the porous member, it is necessary that all portions that are in contact with the foamed sheet are porous members. The mold is usually made of aluminum or iron. The pair of molds can be sealed when the parting surfaces of the molds are in contact with each other. The parting surface is preferably provided with a rubber-like sealing member such as silicon rubber in order to improve sealing performance.
It is preferable to control the temperature in the range of about 10 to 90 ° C. by circulating cooling water or the like in the mold. It is preferable that the temperature of each mold can be adjusted separately in order to reduce the warpage of the foam molded article. In consideration of releasability from the foamed molded article, it is also preferable to treat the molding surface of each mold with a surface treatment such as Teflon (registered trademark) or anodized (registered trademark).

  Next, as a pair of molding dies, one is a storage portion including a bottom surface with the porous member as a part of a wall surface and a wall surface surrounding the periphery of the bottom surface, and the other is a flat plate and has a lid for the storage portion. The manufacturing steps (1) to (4) of the thermoplastic resin foam molded body, which is the first aspect of the present invention when using the molding die, will be described in more detail.

  Step (1) in the embodiment of the present invention is a step of heat-softening the thermoplastic resin foam sheet. The heating method is generally a method using a hot plate, hot air, infrared heater, microwave, etc., but from the viewpoint of avoiding the drawdown of the thermoplastic resin foam sheet and not impairing the appearance. A method of heating the sheet while supporting the sheet is preferable. Further, from the viewpoint of cycle time, a method of heating from both sides of the foam sheet using two hot plates is more preferable. In order to prevent the hot plate and the foam sheet from being fused by heating, More preferably, the distance between the hot plates is set to be larger than the thickness of the thermoplastic resin foam sheet, and the heating plate is heated without being compressed. The surface of the hot plate is preferably subjected to a known surface treatment such as Teflon (registered trademark) or anodized (registered trademark) in consideration of peelability from the foamed sheet made of thermoplastic resin. Further, the size and shape of the hot plate are not particularly limited, and may be appropriately selected in consideration of the size and shape of a desired thermoplastic resin foam molded body. Examples of the shape include a square, a rectangle, and a circle. In the case of a square, a shape in a range of 200 to 2000 mm square is common.

The temperature of the hot plate at the time of heating is not particularly limited, and may be set as appropriate depending on the thermoplastic resin constituting the foamed sheet. When the thermoplastic resin is a crystalline resin, the temperature of the hot plate is preferably set in the vicinity of the melting point of the resin. If the temperature of the hot plate is too higher than the melting point, bubbles are easily broken, and it is difficult to obtain a foamed molded article having a high expansion ratio and closed cell ratio. In addition, when the temperature of the hot plate is lower than the melting point and near the crystallization temperature, the elasticity is too strong and it is difficult to obtain a foamed molded article with a high expansion ratio. The temperature of the hot plate is preferably in the range of the melting point ± 1.0 ° C. of the thermoplastic resin constituting the thermoplastic resin foam sheet. When the foamed sheet is composed of two or more types of thermoplastic resins, the melting point of the thermoplastic resin, which is the main component, is used as a reference as a weight.

The heating time varies depending on the type of resin constituting the foamed sheet, the foaming ratio, the thickness, etc., but is appropriately adjusted so that the central temperature in the thickness direction of the thermoplastic resin foamed sheet reaches the temperature range of the hot plate. That's fine. For example, even if the expansion ratio is the same, the heating time becomes longer as the thickness increases. It is preferable to set a heating time and temperature by attaching a thermocouple to both sides of the foamed sheet and in the center in the thickness direction, measuring the temperature, examining the relationship between temperature and time in advance.
The foam sheet is usually at room temperature, but may be preheated to shorten the heating time. Further, in the step (1), heat softening may be performed with a thermoplastic resin foam sheet placed on a sheet-like non-porous member. Examples of the sheet-like non-porous member include a sheet-like material formed from a material that can be maintained in shape even when heated, such as a Teflon (registered trademark) -treated sheet, film, or metal plate.

In the step (2) in the aspect of the present invention, a part of the inner wall surface of the mold has a porous member having pores having a pore diameter of 1000 μm or less and an air permeability of 900 to 2500 cm ³ / cm ² / s. In this step, the thermoplastic resin foam sheet softened by heating in the step (1) is placed on the porous member of the mold so that one surface thereof is in contact. When the thermoplastic resin foam sheet is placed on the non-porous member and softened by heating in the step (1), the non-porous member is removed and then placed on the porous member.

By arranging the thermoplastic resin foam sheet on the porous member in this way, the air between the thermoplastic resin foam sheet and the molding surface is reduced when the pressure is reduced in the step (3). Since it is discharged through the member, there is no air accumulation. Therefore, the thermoplastic resin foam molded article obtained is excellent in surface smoothness.

The air permeability of the porous member that forms a part of the inner wall surface of the mold is such that when the member different from the mold is embedded in the wall surface of the mold as the porous member, The fragile method (Method A) described in JIS L1096. In addition, when the porous member has an air permeability that is too high to be measured, the air permeability is measured by stacking a plurality of the same porous members, and the value multiplied by the number of the porous members is measured. Considered air permeability. The air permeability when a part of the inner wall surface of the mold itself is a porous member can also be measured by the Frazier method (A method) by cutting out a part of the inner wall surface and using it as a measurement piece. .
The porous member in the present invention has an air permeability of 900 to 2500 cm ³ / cm ² / s, and preferably 900 to 2000 cm ³ / cm ² / s. The porous member may be in a state in which porous members having the same air permeability are overlapped or porous members having different air permeability are overlapped. When using the same type or different types of porous members in a stacked state, the air permeability of the porous members when stacked is preferably in the range of the above-mentioned numerical values. By using a mold in which a part of the inner wall surface is made of a porous member having such an air permeability, a thermoplastic resin foam molded body having further excellent surface smoothness can be obtained. The pore diameter of the porous member is preferably 600 μm or less. The pore diameter of the porous member can be obtained by analyzing an image obtained by a microscope or SEM. If the number of meshes and the wire diameter are known, it can be obtained by dividing 1 inch by the number of meshes and then subtracting the wire diameter. The pore diameter of the porous member means the diameter of the pore.

When the mold is closed in the step (3), the distance between the molding surface on which the foam sheet is disposed and the molding surface facing the molding surface is 1.1 to 1.1 of the thickness of the thermoplastic resin foam sheet. It is preferable to be 3.0 times. As the distance is increased, the closed cell ratio of the obtained foamed molded product tends to decrease. If the distance is too long, adjustment may be made by providing a spacer between the molding surface on which the foam sheet is disposed and the molding surface facing the molding surface.

The step (3) expands the thermoplastic resin foam sheet by decompressing the space formed by closing the pair of molds, and the porous member of the thermoplastic resin foam sheet This is a step of bringing the non-contact surface into contact with the molding surface of the mold.
As a method for reducing the pressure in the space formed by closing the mold, there is a method of opening the joint valve of a vacuum pump connected to the mold and vacuuming the mold. As the vacuum pump, it is preferable to use a vacuum pump having a capability of exhausting air in the space in a short time from the viewpoint of improving the expansion ratio and the closed cell ratio of the thermoplastic resin foam molding. Further, depending on the size of the mold used, it is preferable to provide a vacuum tank in order to quickly exhaust.
The closer the pressure in the mold is to vacuum, the better from the viewpoint of improving the expansion ratio. The absolute pressure in the mold is preferably 0.01 MPa or less, and the pressure reduction rate is preferably 0.01 MPa / s or more.

By reducing the pressure in the space formed by closing the mold in this way, the porous member non-contact surface, that is, the surface not in contact with the porous member of the thermoplastic resin foam sheet, and the molding die molding Make contact with the surface. Further, by maintaining the reduced pressure, the foamed sheet made of thermoplastic resin expanded in the mold is cooled and solidified, and shaped according to the space shape formed by closing the mold. The foamed sheet made of thermoplastic resin foamed in the mold has the same thickness as the space formed by closing the mold, but the sheet width direction does not necessarily have to be expanded to the same size.

In order to shape the thermoplastic resin foam sheet into a desired shape by reducing the pressure in step (3), the process is performed while the temperature of the thermoplastic resin foam sheet heated in step (1) is not lowered. It is necessary to decompress and shape in (3). In the step (3), it is preferable that the inside of the mold is decompressed and shaped while the surface temperature of the thermoplastic resin foam sheet is within 5 ° C. from the temperature of the hot plate used in the step (1).

In the step (3), the porous member non-contact surface of the thermoplastic resin foam sheet is brought into contact with the molding surface of the molding die to form, but the time for cooling and solidification is not particularly limited, and the shape is stable. If it is time to do. Usually, it is about 20 seconds to several minutes in total time of shaping and cooling time.

Step (4) is a step of taking out the thermoplastic resin foamed molded article by opening the mold after the inside of the space is brought to normal pressure. The junction valve between the mold and the vacuum pump may be closed and the purge valve opened to bring the inside of the mold to normal pressure.

The thermoplastic resin foam molded article obtained by the above-described method of the present invention can be used for packaging, boxing, partition plates, food containers, stationery, building materials, automobile interior materials, and the like.

In addition, the thermoplastic resin foam molded article obtained in the present invention may be subjected to a surface treatment applied to the surface of a conventional foam sheet such as corona treatment, ozone treatment or antistatic agent application. These surface treatments may be performed on the thermoplastic resin foam molded article obtained in the present invention, or may be performed in advance on the thermoplastic resin foam sheet used in the production method of the present invention.

A surface material such as a sheet or a film may be laminated and bonded to the surface of the thermoplastic resin foam molded article obtained in the present invention, depending on the application. As a skin material such as a sheet or film for lamination, known materials can be used depending on the application. For example, a thin plate made of metal such as aluminum or iron, thermoplastic resin, paper, synthetic paper, etc. Can be mentioned. You may laminate the nonwoven fabric and woven fabric which consist of plant materials, such as a thermoplastic resin or hemp, and inorganic materials, such as glass. Moreover, decoration, such as embossing and printing, may be given to the thin plate surface to be used. You may laminate and laminate a foam as a skin material.

For example, when the thermoplastic resin foam-molded article obtained in the present invention is used for food packaging, it is preferable to use a 10-100 μm-thick propylene-based resin film or gas barrier resin film laminated. As the gas barrier resin, an ethylene / vinyl alcohol copolymer, polyvinylidene chloride, polyvinyl alcohol, polyamide or the like can be used. These gas barrier resins may be used alone or in combination, or two or more films made of gas barrier resins may be laminated and used.

When the thermoplastic resin foam molded article is used for automobile interior materials, it is preferable to laminate a nonwoven fabric, a woven fabric, a carpet or the like. In addition, when using as a partition for packaging purposes, for example, a box, a buffer sheet may be laminated to protect the contents.

Lamination and lamination of these skin materials may be performed on the thermoplastic resin foam molded body obtained in the present invention, or may be performed in advance on the thermoplastic resin foam sheet used in the production method of the present invention. Further, the method of laminating the skin material is not particularly limited, for example, a method of applying and laminating an adhesive on the surface of a foamed molded product or a foamed sheet, using a skin material laminated with an adhesive resin film, A method of laminating an adhesive resin film surface by heating and melting and laminating it with a foam molded body or foam sheet, a method of melting and laminating a laminating surface of a skin material and a foam molded body or sheet using a heater or hot air, etc., a molten resin And a method of laminating by extruding between a skin material and a foamed molded product or a foamed sheet.

The thermoplastic resin foam molded article obtained in the present invention can be further subjected to thermoforming such as vacuum molding. Examples of thermoforming include known methods such as vacuum forming and heat ruled line processing.

Reference example

Hereinafter, as a reference example, a method for producing a flat-plate foam molded article using a propylene-based resin foam sheet will be described. In the reference example, a mold having no porous member on the inner wall surface is used as the mold as shown in FIG. 2B, and the porous member is disposed between the propylene-based resin foam sheet and the bottom surface of the mold. I used it like this. What is important in the present invention is that air between the thermoplastic resin foam sheet and the molding surface is discharged through the porous member when the pressure is reduced in the step (3). As a result, a foamed molded body made of a thermoplastic resin having excellent surface smoothness is obtained. It can be said that this reference example also has the same effect.

The evaluation method of the used resin, a thermoplastic resin foamed sheet, and the obtained thermoplastic resin foamed molded article is as follows.
(1) MFR (230)
According to JIS K7210, measurement was performed at a temperature of 230 ° C. and a load of 2.16 kgf. The unit is g / 10 minutes.

(2) MT (190)
Using a melt tension tester MT-501D3 manufactured by Toyo Seiki Co., Ltd., a strand is drawn from an orifice having a length of 8 mm and a diameter of 2 mm at a sample amount of 5 g, a heating temperature of 190 ° C., a heating time of 5 minutes, a piston lowering speed of 5.7 mm / min. Extrusion was performed, and the tension when the strand was wound at a winding speed of 100 rpm using a roller having a diameter of 50 mm was measured as melt tension (MT). The unit is g.

(3) Foaming ratio X
The density ρ (water) of the foamed sheet or foamed molded product is determined using the underwater substitution method described in JIS K7112. Next, the expansion ratio X was calculated by the following formula 2 using the resin density ρ (PP) of the propylene-based resin constituting the foam sheet (the unit is dimensionless). In addition, 0.90 g / cm ³ was used as ρ (PP) below.
X (X1, X2) = ρ (PP) / ρ (water) [Formula 2]
ρ (PP): Resin density (g / cm ³ )
ρ (water): density of foamed sheet or foamed molded product (g / cm ³ )

(4) Closed cell ratio Y
The density ρ (air) of the foamed sheet or foamed molded product was determined using the measurement method by the air pycnometer method described in ASTM-D2856, and the closed cell ratio Y was calculated by the following formula 3 (unit:%).
Y = (ρ (PP) / ρ (air) −1) / (ρ (PP) / ρ (water) −1) × 100 [Formula 3]
(5) Air permeability of porous member Measurement was performed by the Frazier method (Method A) described in JIS L1096. The unit is cm ³ / cm ² / s. In the measurement, based on the value measured by overlapping three stainless steel meshes (made by Taiyo Wire Mesh Co., Ltd.) used as the porous member, a value calculated by multiplying the value by 3 (number of sheets), The air permeability of one porous member was defined.
(6) Porous member pore diameter The pore diameter was obtained by dividing 1 inch by the number of meshes and then subtracting the wire diameter. A stainless steel mesh (made by Taiyo Wire Mesh Co., Ltd.) having a mesh number of 20, 80 mesh was used. The unit is μm.
(7) Maximum height Ry
The maximum height Ry described in JIS B0601 was measured using a surface roughness meter manufactured by Mitutoyo Corporation. In addition, it was thought that smoothness was so favorable that the maximum height Ry was small. The unit is μm.

<Preparation of a propylene-based resin foam sheet used as a raw material>
As the propylene-based resin foam sheet, a non-foamed layer / foamed layer / non-foamed layer two-layer / three-layer propylene-based resin multilayer foam sheet was prepared by a coextrusion method.
As the resin constituting the foam layer, four types of propylene polymer PP1, which satisfies the following formula 1, general propylene resins PP2 and PP3, and linear low density polyethylene PE1 were used.
PF814 manufactured by Sun Aroma Co., Ltd. was used as the propylene-based polymer PP1 that satisfies Formula 1. Since MFR (230) of PF814 is 3.0 g / 10 min, MT (190) is 47 g, and the right side of Formula 1 is 4.0, Formula 1 was satisfied.
MT (190) ≧ 7.52 × MFR (230) ^(−0.576) [Formula 1]
Nobrene AW191 manufactured by Sumitomo Chemical Co., Ltd. was used as a general propylene-based resin PP2, and Noblen Y101 manufactured by Sumitomo Chemical Co., Ltd. was used as PP3. In both AW191 and Y101, MFR (230) was 11 g / 10 min, MT (190) was 0.9 g, and since the right side of Formula 1 was 1.89, Formula 1 was not satisfied.
In addition, Excellen FX and CX3502 manufactured by Sumitomo Chemical Co., Ltd. were used as the linear low density polyethylene PE1. The MFR of CX3502 was 4 g / 10 min as measured at 190 ° C. in the same manner.
The above-mentioned PP1 is blended at 10% by weight, PP2 at 65% by weight, PP3 at 15% by weight and PE1 at 10% by weight. The main propylene resin is PP2, and its melting point is 164.7 ° C. Met.

As the resin constituting the non-foamed layer, 90% by weight of a general-purpose propylene resin PP4 and 10% by weight of a polymer antistatic agent were used. As general-purpose propylene-based resin PP4, Nobrene AS171L manufactured by Sumitomo Chemical Co., Ltd. was used. The MFR (230) of AS171L was 1 g / 10 min. As the polymer type antistatic agent, Pelestat 300 manufactured by Sanyo Chemical Industries, Ltd. was used.

As the cell nucleating agent master batch, an azodicarbonamide having an average particle diameter of 4.48 μm and a density of 1.65 g / cm ³ was used, and a master batch having a concentration of 30% by weight with respect to the base resin of the ethylene-based resin. Using.

  A 104 mmφ co-rotating twin screw extruder (L / D = 32, L is the effective screw length, D is the screw diameter) with a gear pump at the tip as the foam layer extruder, and a 75 mmφ single unit as the non-foam layer extruder. A multi-manifold type multilayer T die having a die exit channel width of 1600 mm was used using a shaft extruder (L / D = 32).

A foam nucleating agent master batch of 0.3 PHR blended with 100% by weight of the foam layer resin is introduced into a foam layer extruder hopper via a quantitative feeder, melted and kneaded in the extruder, and melted. In a position (L / D = 20) in which liquefaction has advanced, liquefied carbon dioxide gas 0.15PHR was injected at a high pressure using a diaphragm metering pump. After sufficiently melting and kneading the molten resin and carbon dioxide, the temperature was adjusted to 180 ° C., and the mixture was stably introduced into the multi-manifold multi-layer T-die using a gear pump at a discharge rate of 160 kg / h.
The non-foamed layer resin is introduced into a non-foamed layer extruder hopper through a quantitative feeder, melt kneaded in the extruder, adjusted to 200 ° C., and a multi-manifold multi-layer T-die with a discharge rate of 80 kg / h. Introduced in.
A flat multilayer molten sheet extruded from the die outlet is cooled and formed by a plurality of 210 mmφ rolls adjusted to a cooling temperature of about 60 ° C. installed immediately after the die, and taken by a take-up machine equipped with a nip roll, and then a cutting machine And cut into predetermined dimensions.
The foaming ratio (X1) of the obtained foamed sheet was 1.9 times, the closed cell ratio (Y1) was 98%, the total thickness (T1) was 2.00 mm, and the thickness of the non-foamed layer was 175 μm.

[Reference Example 1]
Of the pair of upper and lower hot plates installed in parallel as shown in FIG. 2 (a), the porous member and one surface of the propylene-based resin foam sheet were brought into contact with the hot plate installed below. In this state, the porous member was placed in contact with the lower hot plate and softened by heating. At this time, the distance between the hot plates is set to be larger than the sum of the thickness of the propylene-based resin foam sheet and the thickness of the porous member, and the propylene-based resin foam sheet is compressed with the hot plate. Without heating. Further, the heating plate was heated for 80 seconds within the range of the melting point of 165.0 ± 1.0 ° C. of the propylene-based resin PP2 which is the main component of the foam sheet. As the porous member, a stainless steel wire mesh (made by Taiyo Wire Mesh Co., Ltd.) having an air permeability of 1104 cm ³ / cm ² / s and a pore diameter of 198 μm was used.
As shown in FIG. 2 (b), the heat-softened propylene resin foam sheet and porous member are interposed between the propylene resin foam sheet and the bottom of the mold. Arranged. The distance between the bottom surface of the mold and the bottom surface and the opposite surface, that is, the mold lid portion, was a distance obtained by adding the thickness of the desired thermoplastic resin foamed molded body (4.2 mm) to the thickness of the porous member.
After the mold is sealed, a joint valve with a vacuum pump is opened, and the pressure is reduced to a complete vacuum (absolute pressure 0) at a pressure reduction rate of 0.018 MPa / s to expand the propylene-based resin foam sheet. It was shaped into a flat plate and cooled and solidified. The temperature of the mold lid and the bottom surface was 20 ° C., and the time from depressurization to cooling and solidification was 60 seconds.
After closing the joint valve with the vacuum pump and opening the purge valve to normal pressure (0.1 MPa), the flat foam molded body was taken out from the mold.
The obtained foamed molded article had an expansion ratio X2 of 4.0, an closed cell ratio Y2 of 90%, a thickness of 4.2 mm, and good surface smoothness. The results are summarized in Table 1.

[Comparative Example 1]
A thermoplastic resin foamed molded article was obtained in the same manner as in Reference Example 1 except that the porous member was not used. The evaluation results of the obtained foamed molded product are summarized in Table 1.

Diagram of foam sheet made of thermoplastic resin (A): Schematic diagram showing step (1) (b): Schematic diagram showing step (2) (c): Step (3) Schematic

Explanation of symbols

1: Thermoplastic resin foam sheet 2: Thermoplastic resin foam sheet thickness 31: Hot plate (1)
32: Hot plate (2)
4: Porous member 5: Mold 51: Surface facing sheet placement surface (mold lid)
52: Sheet placement surface (bottom of mold)
6: Distance between sheet arrangement surface and opposing surface (molding lid) 7: Foam molded body made of thermoplastic resin 8: Joint valve with vacuum pump 9: Purge valve

Claims (2)

Using a pair of molds that can be sealed, a foamed product made of a thermoplastic resin is produced by further foaming a foamed sheet made of a thermoplastic resin within the mold, and at least the following (1)-( A method for producing a foamed molded article made of a thermoplastic resin comprising the step 4).
(1) Step of heat-softening a foam sheet made of thermoplastic resin (2) A part of the inner wall surface of the mold has holes with a hole diameter of 1000 μm or less, and the air permeability is 900 to 2500 cm ³ / cm ² / s. (3) The molding die, wherein the thermoplastic resin foam sheet softened by heating in the step (1) is placed on the porous member of the molding die made of a certain porous member so that one surface thereof is in contact with the molding die. The step of expanding the thermoplastic resin foamed sheet by reducing the pressure after sealing the interior and shaping the foamed molded article of the desired thermoplastic resin (4) After the inside of the mold is at normal pressure, A step of taking out the thermoplastic resin foam molded body from the mold The method for producing a thermoplastic resin foam molded article according to claim 1, wherein the porous member has an air permeability of 900 to 2000 cm ³ / cm ² / s and a pore diameter of 600 µm or less.

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