JP2007253443A - Method of manufacturing thermoplastic resin foam molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a thermoplastic resin foam molding whose poor appearances called 'silver streaks' are improved and the foamed state of which is uniform. <P>SOLUTION: The manufacturing method has a process (1) of adjusting the pressure in a mold cavity formed by clamping a pair of molds to 0.04 MPa or lower, a process (2) of supplying a molten thermoplastic resin containing a foaming agent into the mold cavity with a pressure of ≤0.04 MPa so that the filling rate R becomes 80% or higher, wherein R is defined according to formula (1) R=(W1/W2)×100 (wherein, W1 is the weight of the thermoplastic resin foam molding; W2 is the weight of the unfoamed molding obtained by melting a thermoplastic resin of a melt flow rate (MFR) of 30-150 g/10 min and charging the molten resin into the mold cavity formed in the process (1)), in order to fill the mold cavity with the molten thermoplastic resin containing the foaming agent, a process (3) of increasing the volume of the mold cavity to such an extent as to give a desired shape for the thermoplastic resin foam molding and a process (4) of opening the mold and removing the thermoplastic resin foam molding. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

Thermoplastic resin foam moldings are used in automobile parts and household appliance parts that are required to be lightweight and rigid. As a manufacturing method of a thermoplastic resin foam molding, the method currently disclosed by patent document 1, for example is mentioned. That is, a mold comprising a pair of males and females having a suction port on the molding surface of at least one mold is used, and a heat-foamable thermoplastic resin is filled in the cavity in a molten state, and the surface of the molded body is along the mold surface. After the layer is almost formed, the cavity volume is expanded while vacuuming the surface layer to foam the foamable thermoplastic resin.
Moreover, the method currently disclosed by patent document 2 is also mentioned as another method of manufacturing a thermoplastic resin foaming molding. That is, in a foam molding method in which a molten resin in which an inert gas is dissolved is injected, filled into a mold cavity and foamed, a counter pressure is sealed in the mold cavity with a gas, and then a short shot is performed. An injection process for injecting the molten resin in a state, a filling completion process for driving and expanding the molten resin injected in the injection process in a direction in which the volume of the cavity decreases, and the filling completion A holding step for holding the position of the mold during the process until the temperature of the injected and filled molten resin drops to a predetermined foaming temperature, and after completion of the holding step, the counter pressure of the cavity is released. , A molding method of a thin-walled foamed molded article comprising a foaming step of foaming by driving the mold to a predetermined position in a direction in which the volume of the cavity increases.

JP-A-7-9461 JP 2004-17285 A

In the former production method, a foam is obtained by forming a surface layer before the heat-foamable thermoplastic resin filled in the cavity foams, and then foaming the resin at the center while vacuuming the surface layer. It is done. However, the foam obtained by such a method sometimes has a poor appearance called silver streak on the surface.
On the other hand, in the latter production method, the occurrence of silver streaks can be suppressed, but the foamed cells near the flow end of the molten resin are likely to be coarsened in order to perform injection filling so as to be in a short shot state. The foamed state sometimes became non-uniform.

  The present invention provides a method for producing a thermoplastic resin foam molded article having improved appearance defects called silver streaks and a uniform foamed state.

That is, according to the present invention, a molten thermoplastic resin in which a foaming agent is contained in a thermoplastic resin having an MFR of 30 to 150 g / 10 min is filled in a mold cavity formed by a pair of molds and foamed. It is a manufacturing method of a thermoplastic resin foam molded article, and is a manufacturing method of a thermoplastic resin foam molded article including the following steps.
(1) The step of setting the pressure in the mold cavity formed by closing a pair of molds to 0.04 MPa or less (2) The foaming agent in the mold cavity having a pressure of 0.04 MPa or less Is supplied so that the filling rate R represented by the formula (1) is 80% or more, and the mold cavity contains the foaming agent. Step of filling with resin R = (W1 / W2) × 100 Formula (1)
W1: Weight of thermoplastic resin foam molding W2: Non-foaming obtained by melting the thermoplastic resin having an MFR of 30 to 150 g / 10 min and filling the mold cavity formed in step (1) Weight of molded body (3) Step of increasing mold cavity volume until desired thermoplastic resin foam molded body shape (4) Step of opening mold and taking out thermoplastic resin foam molded body

  According to the method for producing a thermoplastic resin foam molded article of the present invention, it is possible to obtain a thermoplastic resin foam molded article having an improved appearance defect called silver streak and having a uniform foamed state.

  The present invention is a heat which fills a mold cavity formed by a pair of molds and foams a molten thermoplastic resin in which a foaming agent is contained in a thermoplastic resin having an MFR of 30 to 150 g / 10 min. It is a manufacturing method of a plastic resin foaming molding. Step (1) of the production method of the present invention is a step of setting the pressure in a mold cavity formed by closing a pair of molds to 0.04 MPa or less. As a method of setting the pressure in the mold cavity to 0.04 MPa or less, a mold having a pressure adjusting function in the mold cavity such as a vacuum pump was used as at least one mold, and a foaming agent was contained. There is a method in which the inside of the cavity is vacuumed before supplying the molten thermoplastic resin.

As a mold having a pressure adjusting function in the mold cavity, for example, a mold having a groove or a gap in the outer peripheral portion of the mold cavity, and the groove or the gap and the vacuum suction device are connected, or a cavity A die having a predetermined gap in a part of the surface and a pin, which are connected to a vacuum suction device, and at least a part of the die cavity surface is made of a porous material, and the porous material and the vacuum Examples include a mold connected to a suction device. A chamber may be installed between the mold and the vacuum suction device.
In particular, when vacuum suction is performed from the outer peripheral portion of the mold cavity, the gas for reducing the gas pressure loss is relatively large through the gas vent groove provided in the outer peripheral portion of the mold cavity. A method of vacuum suction in the mold cavity using a mold in which a runner is connected and a gas runner is connected to a vacuum suction device is preferable. The groove in the outer peripheral portion of the mold cavity and the clearance of the predetermined gap are appropriately selected in consideration of the type and temperature of the thermoplastic resin to be used, the mold temperature, etc., but preferably about 5 μm to 500 μm.
The position where the pressure adjusting mechanism is provided is appropriately determined depending on the product shape, but in the case of a mold consisting of a cavity part, a parting line, and a pair of males and females having little influence on the appearance of the thermoplastic resin foam molded body, It is preferable to provide the sliding portion.
Further, it is preferable to use a mold having a structure in which the outside of the mold pressure adjusting mechanism is sealed by an O-ring or the like.

The step (2) of the present invention is a molten state in which a foaming agent is contained in a thermoplastic resin having an MFR of 30 to 150 g / 10 min in the mold cavity whose pressure is 0.04 MPa or less in the step (1). In the step of supplying the thermoplastic resin so that the filling rate R represented by the formula (1) is 80% or more and filling the mold cavity with the molten thermoplastic resin containing the foaming agent. is there.
R = (W1 / W2) × 100 Formula (1)
W1: Weight of thermoplastic resin foam molding W2: Non-foaming obtained by melting the thermoplastic resin having an MFR of 30 to 150 g / 10 min and filling the mold cavity formed in step (1) The weight of the molded body is generated in the vicinity of the flow front of the supplied molten thermoplastic resin by supplying the molten thermoplastic resin containing the foaming agent into a mold cavity having a pressure of 0.04 MPa or less. Bubbles are broken, thereby suppressing the occurrence of silver streaks on the final product surface. The pressure in the mold cavity when the molten thermoplastic resin is supplied is more preferably 0.02 MPa or less.

  In the present invention, the inside of the cavity may be 0.04 MPa or less when the supply of the molten thermoplastic resin into the mold cavity is started. The vacuum suction may be stopped before the start of resin supply, or the vacuum suction may be continued after the start of resin filling. The vacuum suction is preferably stopped when the cavity is completely filled with the molten thermoplastic resin containing the foaming agent. Further, in the step (3), from the viewpoint of mold transferability to the foam molded body, the mold cavity volume is increased and the vacuum suction is stopped immediately after the desired thermoplastic resin foam molded body is formed. preferable.

In the step (2), the molten thermoplastic resin containing the foaming agent to be supplied is supplied into the mold cavity so that the filling rate R represented by the following formula (1) is 80% or more. The mold cavity is completely filled with a molten thermoplastic resin containing the foaming agent.
R = (W1 / W2) × 100 Formula (1)
W1: Weight of thermoplastic resin foam molding W2: Non-foaming obtained by melting the thermoplastic resin having an MFR of 30 to 150 g / 10 min and filling the mold cavity formed in step (1) Molded body weight

The non-foamed molded body is formed by step (1) in the production method of the present invention by melting a thermoplastic resin having an MFR of 30 to 150 g / 10 min used for the production of the thermoplastic resin foam molded body of the present invention. It is a non-foamed molded article obtained by filling the mold cavity. When the non-foamed molded body is manufactured, the mold cavity is filled with a molten thermoplastic resin under normal injection molding conditions, and molded while maintaining pressure so that no sink marks appear on the surface of the molded body. The mold cavity volume is not changed from the start of injection filling until the molding of the non-foamed molded body is completed. In the present invention, a non-foamed molded body is produced in advance by such a method, and its weight W2 is measured. The foaming of the thermoplastic resin is performed so that the filling rate R calculated by the formula (1) is 80% or more. The weight W1 of the molded body is determined, and the amount of resin to be supplied is determined. In the present invention, the filling rate R is 80% or more, preferably 85% or more, and more preferably 90% or more. In addition, when the resin volume and the pressure are increased, the filling rate R may be 100% or more when the cavity volume is larger than the mold cavity volume at the start of resin supply due to the resin pressure. . The upper limit of the filling rate R is not particularly limited, but is preferably set to 130% or less, and more preferably set to 120% or less in order not to significantly reduce the lightness.
In the step (2), when the filling rate R is less than 80%, the foamed cells near the flow end of the molten thermoplastic resin supplied into the mold cavity are likely to be coarsened, and the foamed state of the obtained foamed molded product is It becomes uneven.

  In the step (2) of the present invention, it is necessary to supply a molten thermoplastic resin containing the above-mentioned amount of foaming agent and fill the mold cavity. For example, a method of supplying the molten thermoplastic resin so as to have the same volume as the cavity volume, or a method of compressing the resin after supplying the molten thermoplastic resin into a mold cavity is exemplified. As the latter method, even if the mold cavity is completely filled with the resin, the supply of the resin is continued, and the resin is supplied and filled so that the peak pressure is generated when the filling is completed in the overpack state. After the mold cavity is completely filled with resin, the resin is further filled by holding pressure and the resin is compressed, or after the resin filling is completed, the mold cavity volume is reduced. The method of compressing resin is mentioned. In step (2), after the molten thermoplastic resin containing the foaming agent is supplied into the cavity or when the pressure is maintained, the cavity volume increases from the mold cavity volume at the start of injection filling due to the pressure of the resin. May be.

Step (3) is a step of increasing the mold cavity volume until a desired thermoplastic resin foam molded body shape is obtained. As a method of increasing the mold cavity volume, the mold cavity surface is retracted to enlarge the entire cavity, the slide core is used to partially and / or enlarge the entire cavity, and the above methods are combined. Method.
Step (4) is a step of opening the mold and taking out the thermoplastic resin foam molded article.

  The production method of the present invention may be carried out in combination with any method such as gas assist molding, melt core molding, insert molding, and two-color molding.

  The shape of the thermoplastic resin foam molded article obtained by the present invention is not particularly limited. The expansion ratio of the thermoplastic resin foam molded article obtained in the present invention is not particularly limited, but is usually 1.4 times or more, preferably 1.5 times or more. The upper limit of the expansion ratio is not particularly limited, but is usually 10 times or less. The expansion ratio can be controlled by the addition amount of a foaming agent described later and the expansion amount of the cavity volume in the step (3).

  The thermoplastic resin used in the present invention is a resin having a melt flow rate (MFR) measured in accordance with JIS-K6758 of 30 to 150 g / 10 minutes. When a resin having a melt flow rate of less than 30 g / 10 minutes is used, silver streaks occur on the surface of the obtained thermoplastic resin foam molded article. When a resin exceeding 150 g / 10 minutes is used, the resulting thermoplastic resin foam molded article is obtained. Is weak. The MFR of the thermoplastic resin to be used is more preferably 40 to 130 g / 10 minutes, and further preferably 50 to 120 g / 10 minutes. In addition, when mixing and using a some thermoplastic resin, it is necessary for MFR of a mixture to be the said range.

  The type of the thermoplastic resin to be used is not particularly limited. For example, an olefin resin, a styrene resin, an acrylic resin, an amide resin, a thermoplastic ester resin, a polycarbonate, a thermoplastic elastomer, or the like may be used. Two or more of these may be used. Among these thermoplastic resins, an olefin resin or a mixture of an olefin resin and a thermoplastic elastomer is preferably used.

The olefin resin is a resin containing 50% by weight or more of olefin-derived repeating units. For example, ethylene, propylene, butene-1, pentene-1, hexene-1, 3-methylbutene-1, 4-methylpentene- A homopolymer of an α-olefin having 20 or less carbon atoms such as 1; a copolymer obtained by copolymerizing at least two monomers selected from these α-olefins; and a copolymer with the α-olefin. Examples thereof include a copolymer of another possible unsaturated monomer and the α-olefin.
Examples of unsaturated monomers copolymerizable with α-olefin include unsaturated carboxylic acids such as acrylic acid and methacrylic acid; methyl (meth) acrylate, 2-ethylhexyl acrylate, ethyl (meth) acrylate, butyl (meth) ) Alkyl ester derivatives of unsaturated carboxylic acids such as acrylates; unsaturated dicarboxylic acids or acid anhydrides such as fumaric acid, maleic acid, maleic anhydride, itaconic acid; acrylamide, N- (hydroxymethyl) acrylamide, glycidyl (meth) Examples thereof include unsaturated carboxylic acid or unsaturated dicarboxylic acid derivatives such as acrylate, acrylonitrile, methacrylonitrile, mono- or diethyl ester of maleic acid, N-phenylmaleimide, N, N′-metaphenylene bismaleimide, and the like.

In the present invention, it is preferable to use a propylene resin as the olefin resin. Examples of the propylene-based resin include a propylene homopolymer, and a copolymer of propylene and at least one selected from the group consisting of ethylene and an α-olefin having 4 to 12 carbon atoms. These homopolymers or copolymers may be used alone or in combination of two or more. Here, examples of the α-olefin having 4 to 12 carbon atoms include 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.
When a copolymer of propylene and at least one selected from the group consisting of ethylene and an α-olefin having 4 to 12 carbon atoms is used, the propylene-derived repeating unit is used with respect to 100% by weight of the copolymer. A copolymer containing at least 50% by weight is used. Further, when the copolymer has a repeating unit derived from two or more kinds of monomers other than the propylene unit, the total amount of the repeating units derived from the monomer other than the propylene unit is 35% by weight or less. It is preferable. The flexibility and impact resistance of the copolymer can be controlled by the amount of the repeating unit derived from ethylene or the α-olefin having 4 to 12 carbon atoms in the copolymer. When the propylene-based resin is a copolymer, the copolymer may be a random copolymer or a block copolymer.

In the present invention, it is also preferable to use, for example, a mixture of the propylene resin and a copolymer of ethylene / α-olefin copolymer as the olefin resin.
The ethylene / α-olefin copolymer is a copolymer of ethylene and an α-olefin having 4 to 12 carbon atoms, and examples thereof include ethylene and butene-1, hexene-1, octene-1, and decene-1. And the like. Preferred ethylene / α-olefin copolymers include, for example, ethylene / butene-1 copolymer rubber (EBR), ethylene / hexene copolymer rubber (EHR), and ethylene / octene copolymer rubber (EOR). It is done.
The content of ethylene-derived repeating units in the ethylene / α-olefin copolymer is usually 50 to 90% by weight, and preferably 60 to 90% by weight. The repeating unit content derived from ethylene in the ethylene / α-olefin copolymer can be measured based on the ¹³ C-NMR method.
The density of the copolymer of ethylene and α-olefin is usually 0.85 to 0.89 g / cm ³ , and preferably 0.86 to 0.88 g / cm ³ . The density is a value measured based on JIS-K7112.
In the present invention, when a mixture of a propylene-based resin and an ethylene / α-olefin copolymer is used as the thermoplastic resin, the mixing ratio of the mixture is not particularly limited as long as the object of the present invention is not impaired. However, a preferred example is a mixture of 98 to 60% by weight of a propylene resin and 2 to 40% by weight of an ethylene / α-olefin copolymer.

Furthermore, as the thermoplastic resin used in the present invention, a resin obtained by adding a vinyl aromatic compound-containing elastomer to the olefin resin may be used.
Examples of the vinyl aromatic compound-containing elastomer include styrene-ethylene-butene-styrene rubber (SEBS), styrene-ethylene-propylene-styrene rubber (SEPS), styrene-butadiene rubber (SBR), and styrene-butadiene-. Examples thereof include block copolymers such as styrene rubber (SBS) and styrene-isoprene-styrene rubber (SIS) or block copolymers obtained by hydrogenating these rubber components.
A rubber obtained by reacting an olefin copolymer rubber such as ethylene-propylene-nonconjugated diene rubber (EPDM) with a vinyl aromatic compound such as styrene can also be suitably used. Moreover, at least 2 or more types of vinyl aromatic compound containing elastomer may be used together.
The vinyl aromatic compound-containing elastomer is an elastomer obtained by polymerization using a vinyl aromatic compound as a kind of monomer, for example, a block comprising a vinyl aromatic compound polymer block and a conjugated diene polymer block. Copolymer, a block polymer in which the double bond of the conjugated diene portion of the block copolymer is hydrogenated, and the like. The double bond of the conjugated diene portion of the block copolymer is hydrogenated by 80% or more. It is preferable. Further, when the vinyl aromatic compound-containing elastomer is 100% by weight, the content of the repeating unit derived from the vinyl aromatic compound monomer is preferably 10 to 20% by weight.
The vinyl aromatic compound-containing elastomer to be used preferably has an MFR of 1 to 50 g / 10 min measured at 230 ° C. based on JIS-K6758.
In the present invention, when a thermoplastic resin having a vinyl aromatic compound-containing elastomer added to the olefin resin is used, the vinyl aromatic compound-containing elastomer is in the range of 1 to 40 parts by weight with respect to 100 parts by weight of the olefin resin. It is preferable to add at.

The thermoplastic resin used in the present invention includes talc, mica, clay, calcium carbonate, aluminum hydroxide, magnesium hydroxide, wollastonite, barium sulfate, glass fiber, carbon fiber, silica, calcium silicate, potassium titanate, etc. Inorganic fillers and bright materials such as aluminum flakes may be blended in the range of 0.05 to 30% by weight. (However, the goodness of the thermoplastic resin is 100% by weight.)
In addition, antioxidants such as phenolic, organic phosphite, organic phosphorus, and thioethers; heat stabilizers such as hindered amines; ultraviolet absorbers such as benzophenones, benzotriazoles, and benzoates; nonionics and cationics , Anionic antistatic agents; bisamide, wax, organometallic salt dispersants; chlorine scavengers; amide, wax, organometallic salt, ester lubricants; oxides, hydrotals Site-based decomposing agents; hydrazine-based and amine-based metal deactivators; brominated organic, phosphoric acid-based, antimony trioxide, magnesium hydroxide, red phosphorus and other flame retardants; organic pigments; inorganic pigments; organic Filler: Inorganic, organic antibacterial agents such as metal ions, crystal nucleating agents such as organic phosphates, sorbitol compounds, etc. are blended in thermoplastic resins. It may be.

  The foaming agent used by this invention is not specifically limited, A well-known chemical foaming agent and a physical foaming agent can be used.

The chemical foaming agent is not particularly limited as long as it does not decompose below the melting temperature of the thermoplastic resin used, and decomposes or reacts above the melting temperature of the thermoplastic resin. There may be two or more kinds in combination.
Examples of the inorganic compound that can be used as the chemical foaming agent include hydrogen carbonates such as sodium hydrogen carbonate and ammonium carbonate. Examples of the organic compound include polycarboxylic acid, azo compound, sulfone hydrazide compound, nitroso compound, p- Examples include toluenesulfonyl semicarbazide and isocyanate compounds. Examples of the polycarboxylic acid include citric acid, citric acid, oxalic acid, fumaric acid, and phthalic acid. Examples of the azo compound include azodicarbonamide, and examples of the sulfone hydrazide compound include p-methylurethanebenzenesulfonyl hydrazide, 2,4-toluene disulfonyl hydrazide, and 4,4′-oxybisbenzenesulfonyl hydrazide. Examples of the nitroso compound include dinitrosopentamethylenetetramine.

  Examples of the physical foaming agent include inert gases such as nitrogen and carbon dioxide, and volatile organic compounds other than chlorofluorocarbons such as butane and pentane. Two or more physical foaming agents may be used in combination, or a chemical foaming agent and a physical foaming agent may be used in combination.

  The foaming agent used in the present invention is preferably an inert gas. The inert gas is preferably a gaseous inorganic substance at normal temperature and normal pressure that does not show reactivity with the resin used and does not cause deterioration of the resin. Examples of the inert gas include carbon dioxide, nitrogen, argon, neon, helium, oxygen, and the like. These may be used alone or in combination of two or more. Among these, carbon dioxide, nitrogen, and a mixture thereof are preferably used because they are inexpensive and highly safe, and supercritical carbon dioxide, supercritical nitrogen, and a mixture thereof are more preferably used.

As a method for obtaining a molten thermoplastic resin containing a foaming agent, a method in which a thermoplastic resin and a chemical foaming agent are mixed and melt-kneaded, or a physical foaming agent is added to the molten thermoplastic resin in a nozzle of an injection molding apparatus. Or the method of inject | pouring in a cylinder is mentioned. The method of injecting into the cylinder is preferable from the viewpoint of uniformly mixing, dispersing, and dissolving the molten thermoplastic resin and the physical foaming agent so that the foamed molded product has a uniform foamed state as a whole and shortens the molding cycle. .
The addition amount of the foaming agent of the present invention is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 8 parts by weight, relative to the thermoplastic resin.

  The thermoplastic resin foam molded article obtained by the present invention may be a decorative foam molded article by pasting a known skin material by a method such as insert molding or adhesion. Examples of the skin material include woven fabrics, nonwoven fabrics, knitted fabrics, films and sheets made of thermoplastic resins and thermoplastic elastomers. Furthermore, you may use the composite skin material which laminated | stacked non-foamed sheets, such as a polyurethane, rubber | gum, and a thermoplastic elastomer, to these skin materials. A cushion layer can be further provided on the skin material. Examples of the material constituting the cushion layer include polyurethane foam, EVA foam, polypropylene foam, and polyethylene foam.

  According to the method for producing a thermoplastic resin foam molded article of the present invention, it is possible to obtain a foam molded article having improved appearance defect called silver streak and having a uniform foamed state. The thermoplastic resin foam molded article obtained by the method of the present invention can be suitably used for applications such as automobiles, household appliances, and other industrial products.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, it is needless to say that the present invention is not limited to the examples.

[Evaluation methods]
(1) Pressure in the mold cavity (simply referred to as “gas pressure” in the examples)
A vacuum gauge is installed at the mold connecting part of the piping connecting the vacuum pump and the chamber and the mold, the gas pressure in the mold in the manufacturing process is measured, and the molten thermoplastic resin containing the foaming agent The pressure in the mold cavity at the start of injection was measured.

(2) Filling rate Except for not adding a foaming agent, using the same thermoplastic resin used in the examples, the mold cavity having the same shape as in step (1) is filled, and the mold cavity volume is increased. A non-foamed molded body was molded without enlarging to determine the weight W2. In each Example, the filling rate R was calculated | required by Formula (1) from the weight W1 of the obtained thermoplastic resin foaming molding, and said W2.
R = (W1 / W2) × 100 Formula (1)
W1: Weight of thermoplastic resin foam molding W2: Non-foaming obtained by melting the thermoplastic resin having an MFR of 30 to 150 g / 10 min and filling the mold cavity formed in step (1) Molded body weight

(3) Foaming ratio The foaming ratio of the foam is a value obtained by measuring the specific gravity with a hydrometer (Mirage Trading Co., Ltd., electronic hydrometer EW-200SG) and dividing the specific gravity of the non-foamed molded product by the specific gravity of the foam molded product. It showed in.

(4) Appearance Evaluation (4-1) Silver Streak The vicinity of the center of the top surface shown in FIG. 1 of the obtained thermoplastic resin foamed molded article was visually evaluated and determined as shown below.
◎: Silver streaks on the surface of the foamed molded product cannot be visually confirmed ○: Silver streaks are hardly noticeable ×: Silver streaks are very conspicuous

(4-2) Foamed State The cross section of the obtained thermoplastic resin foamed molded product in the vicinity of the top surface gate and the top surface end shown in FIG. 1 was visually evaluated and determined as shown below.
◎: The foam cell structure near the top gate and the top end is almost the same, and the foamed state of the foam molded product is uniform. ○: The foam cell near the top end of the foam molded product is slightly larger. The foamed state of the foamed molded product is almost uniform. X: The foamed cell near the top end of the foamed molded product is torn, cracked, etc., and the foamed state of the foamed molded product is not uniform.

[Reference Example 1]
As a thermoplastic resin, 100 parts by weight of a propylene / ethylene block copolymer (“WPX5343” manufactured by Sumitomo Chemical Co., Ltd., MFR: 50 g / 10 min), and 100 parts by weight of the thermoplastic resin, a carbon black masterbatch (Sumika) A blend of 1 part by weight of “SPPM865” manufactured by Color Co., Ltd. was used. As an injection molding machine, ES2550 / 400HL-MuCell (clamping force 400 tons) manufactured by Engel was used. The molding was performed using a mold having a cavity that is a box shape having a molded body schematic dimension of 290 mm × 370 mm and a height of 45 mm as shown in FIG. 1, and the cavity clearance was 2 mmt. Side gates were used for the gate structure. As shown in FIG. 2, the mold structure is provided with a gas runner having a depth of 1 mm on the outer periphery of the mold cavity, and a gas release groove having a depth of 20 μm and a width of 5 mm is connected to the mold cavity at intervals of 50 mm. ing. Further, the outer side of the gas runner is sealed by an O-ring to prevent inflow of air (vacuum leakage). Further, the mold is connected to a chamber and a vacuum pump through the gas runner.
Using the material and the apparatus, the cylinder temperature was set to 230 ° C. and the mold temperature was set to 60 ° C. After mold clamping, injection of molten thermoplastic resin was started. After the resin was completely filled in the mold cavity, holding pressure was carried out at 40 MPa for 6 seconds. The resin was further cooled and solidified to obtain a non-foamed molded body, which was evaluated. The results are shown in Table 1.

[Reference Example 2]
As a thermoplastic resin, propylene / ethylene block copolymer (“AU161C” manufactured by Sumitomo Chemical Co., Ltd., MFR: 80 g / 10 minutes) 80% by weight and ethylene-butene 1 copolymer (“CX5505” manufactured by Sumitomo Chemical Co., Ltd.), ethylene content : 75% by weight, density: 0.87) Except that a 20% by weight mixture (MFR: 65 g / 10 min) was used, injection molding was carried out in the same manner as in Reference Example 1 to obtain a non-foamed molded article. And evaluated. The results are shown in Table 1.

[Reference Example 3]
Non-foam molding was performed by the same method as in Reference Example 1 except that a propylene / ethylene block copolymer (“AY564” manufactured by Sumitomo Chemical Co., Ltd., MFR: 20 g / 10 min) was used as the thermoplastic resin. A body was obtained and evaluated. The results are shown in Table 1.

[Example 1]
As a thermoplastic resin, 100 parts by weight of a propylene / ethylene block copolymer (“WPX5343” manufactured by Sumitomo Chemical Co., Ltd., MFR: 50 g / 10 min), and 100 parts by weight of the thermoplastic resin, a carbon black masterbatch (Sumika) A blend of 1 part by weight of “SPPM865” manufactured by Color Co., Ltd., and a chemical foaming agent (“MB3064” manufactured by Sankyo Kasei Co., Ltd.) as a foaming agent, 100 weight of propylene / ethylene block copolymer 2 parts by weight was added to the part and dry blended with the thermoplastic resin.
Using the same equipment as in the reference example, set the cylinder temperature to 230 ° C and the mold temperature to 60 ° C. After clamping, start vacuum suction in the mold cavity, and after 2 seconds of vacuum suction, add foaming agent. Supply of molten thermoplastic resin was started. The gas pressure at the start of injection was 0.01 MPa. The resin is completely injected and filled in the mold cavity, and after filling for 1.0 second, the cavity wall surface of the mold is retreated by 1.5 mm to increase the cavity volume, and then vacuum is applied. Aspiration was terminated. The foamed resin was cooled and solidified to obtain a thermoplastic resin foam molded article, which was evaluated. The results are shown in Table 2.

[Example 2]
As a thermoplastic resin, propylene / ethylene block copolymer (“AU161C” manufactured by Sumitomo Chemical Co., Ltd., MFR: 80 g / 10 minutes) 80% by weight and ethylene-butene 1 copolymer (“CX5505” manufactured by Sumitomo Chemical Co., Ltd.), ethylene content : 75% by weight, density: 0.87) Except for using a mixture with 20% by weight (MFR: 65 g / 10 min), foam molding was carried out in the same manner as in Example 1 to obtain a foam molded body, Evaluation was performed. The results are shown in Table 2.

[Example 3]
Except that the vacuum suction in the mold cavity was 1 second and the gas pressure at the start of injection was 0.03 MPa, foam molding was carried out in the same manner as in Example 2 to obtain a foam molded body. went. The results are shown in Table 2.

[Example 4]
The foam molding was carried out in the same manner as in Example 2 except that the measurement of the molten thermoplastic resin containing the foaming agent into the injection cylinder was reduced and the weight of the foam molding was reduced. Obtained and evaluated. The results are shown in Table 2.

[Comparative Example 1]
Except not carrying out vacuum suction, foam molding was implemented by the same method as Example 1, and the foam molded body was obtained and evaluated. The results are shown in Table 3.

[Comparative Example 2]
Foam molding was carried out in the same manner as in Example 1 except that a propylene / ethylene block copolymer (“AY564” manufactured by Sumitomo Chemical Co., Ltd., MFR: 20 g / 10 min) was used as the thermoplastic resin. And evaluated. The results are shown in Table 3.

[Comparative Example 3]
Foam molding was carried out in the same manner as in Example 2 except that the amount of molten thermoplastic resin containing a foaming agent was reduced in the injection cylinder and the weight of the foamed molding was further reduced from that in Example 4. The foamed molded product was obtained and evaluated. The results are shown in Table 3.

The perspective view of the molded object manufactured in the Example Drawing of a pair of mold structures used in the examples

Explanation of symbols

1: Gate 2: Near top gate 3: Near top center 4: Near top end 5: Mold 6: Gas vent groove 7: Gas runner 8: Gas inlet / outlet path 9: O-ring 10: Vacuum pump 11: Chamber

Claims (3)

Thermoplastic resin foam molding in which a molten thermoplastic resin containing a foaming agent in a thermoplastic resin having an MFR of 30 to 150 g / 10 min is filled in a mold cavity formed by a pair of molds and foamed. A method for producing a thermoplastic resin foam molded article comprising the following steps.
(1) The step of setting the pressure in the mold cavity formed by closing a pair of molds to 0.04 MPa or less (2) The foaming agent in the mold cavity having a pressure of 0.04 MPa or less Is supplied so that the filling rate R represented by the formula (1) is 80% or more, and the mold cavity contains the foaming agent. Step of filling with resin R = (W1 / W2) × 100 Formula (1)
W1: Weight of thermoplastic resin foam molding W2: Non-foaming obtained by melting the thermoplastic resin having an MFR of 30 to 150 g / 10 min and filling the mold cavity formed in step (1) Weight of molded body (3) Step of increasing mold cavity volume until desired thermoplastic resin foam molded body shape (4) Step of opening mold and taking out thermoplastic resin foam molded body The method for producing a thermoplastic resin foam molded article according to claim 1, wherein the thermoplastic resin is an olefin resin. The method for producing a thermoplastic resin foam molded article according to claim 2, wherein the olefin resin is a propylene resin.

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