JP6777978B2 - Manufacturing method of foam molded product - Google Patents

Description

The present invention relates to a method for producing a foam molded product. More specifically, the present invention relates to a method for producing a foam molded product which is excellent in rigidity and light weight and has a good appearance by injection molding.

The thermoplastic resin foam molded product exhibits various performances such as heat insulation, heat insulation, sound insulation, sound absorption, vibration isolation, and weight reduction by changing the resin material and the state of the formed bubbles. Because it can be used, it is used for various purposes. As a method for producing such a foam molded product, there is known a method of foam molding a thermoplastic resin with a foaming component such as a chemical foaming agent or a physical foaming agent using an injection molding apparatus (Patent Document 1).

However, since all of the above-mentioned manufacturing methods form bubbles in the resin by the gas generated from the foaming component, the bubbles are caused by a slight difference in the melt viscosity of the thermoplastic resin as a raw material and the pressure of the generated gas. There is a tendency for the state of to change significantly. Therefore, in the above-mentioned manufacturing method, the bubble diameter in the foamed molded product becomes large due to the influence of slight deviation of the molding conditions, the position from the gate in the mold, etc., and open cells are formed. It is inevitable that the rigidity of the obtained foamed molded product will decrease and that the surface of the foamed molded product will have poor appearance such as silver streaks and voids, and it is applicable to applications such as automobile parts where appearance is important. It wasn't enough.

Japanese Unexamined Patent Publication No. 5-318541

An object of the present invention is to provide a method for producing a foam molded product having excellent rigidity and light weight and having a good appearance.

As a result of diligent studies, the present inventors have solved the above problems by indispensably using heat-expandable microspheres as a foaming component in a method for producing a foamed molded product by injection molding and satisfying specific molding conditions. We have found that it can be solved and arrived at the present invention.

That is, the method for producing a foamed molded product according to the present invention is a method for producing a foamed molded product by injection molding, in which a foamed component and a resin component are melt-kneaded in a heating cylinder to produce a molten mixture. The kneading step, the injection filling step of injecting and filling the molten mixture into the cavity space in the mold, and the opening of the mold after the injection filling of the molten mixture is completed expands the cavity space and foams the molten mixture. The foaming component essentially contains a heat-expandable microsphere composed of an outer shell made of a thermoplastic resin and a swelling agent contained therein and vaporized by heating. The time from the completion of injection filling of the melt mixture to the start of opening the mold is 0 to 2 seconds, and in the foaming step, the mold opening speed when expanding the cavity space is 25 mm / sec or more, 100 mm / sec. Ri less der, the specific gravity of the foamed molding is greater than 0.6, less than 0.85, which is the production method.

It is preferable that the method for producing a foamed molded article of the present invention further satisfies at least one selected from the following 1) to 7).
1) In the foaming step, the volume expansion rate of the cavity space when expanding the cavity space is 33% by volume / sec or more and 10,000% by volume / sec, assuming that the volume of the cavity space at the completion of injection filling is 100% by volume. Less than sec.
2) In the injection filling step, the thickness of the molten mixture injected and filled in the cavity space in the mold is 1 to 3 mm, and the thickness of the foamed molded product obtained after foaming in the foaming step is 1. It is 5 to 5 mm.
3) In the injection filling step, the time from the start of injection filling of the molten mixture to the completion of injection filling is 0.1 to 3 seconds.
4) The surface temperature of the mold is 30 to 100 ° C.
5) The specific gravity of the foam molded product is 0.61 or more .
6) In the melt-kneading step, 1 to 10 parts by weight of the foaming component is used with respect to 100 parts by weight of the resin component.
7) The maximum expansion temperature of the heat-expandable microsphere is 170 to 250 ° C.

In the manufacturing method of the present invention, it is possible to manufacture a foam molded product having excellent rigidity and light weight and having a good appearance.

It is a schematic diagram explaining an example of an injection filling process and a foaming process in this invention.

[Manufacturing method of foam molded product]
The method for producing a foamed molded product of the present invention is a method for producing a foamed molded product by injection molding, which is a melt-kneading step of melt-kneading a foam component and a resin component in a heating cylinder to prepare a melt mixture. An injection filling step of injecting and filling the cavity space in the mold with the molten mixture, and a foaming step of expanding the cavity space and foaming the molten mixture by opening the mold after the injection filling of the molten mixture is completed. It is a manufacturing method including and. This will be described in detail below.

The injection molding machine used in the method for producing a foam molded product of the present invention is not particularly limited as long as it includes at least a plasticizing device and a mold device.
Examples of the plasticizing device include a heating cylinder and a screw provided inside the heating cylinder so as to be driveable in the rotational direction and the axial direction. The heating cylinder is provided with a heater for heating the foam component and the resin component, and the number of heaters provided in the heating cylinder is not particularly limited, but from the viewpoint of controlling the temperature of the molten mixture more precisely. , Preferably more than one.
Examples of the mold device include those composed of a fixed mold and a movable mold. A cavity space is formed at the mold mating surface of these molds.
In addition to the plasticizer and mold equipment, the injection molding machine includes a measuring chamber for measuring a predetermined amount of the molten mixture, an injection plunger unit for accumulating the molten mixture, and a shut-off device for preventing foaming inside the cylinder. May be provided.

[Melting and kneading process]
The melt-kneading step is a step of melt-kneading the foaming component and the resin component in a heating cylinder to prepare a melt mixture. The foaming component is a component that essentially contains a heat-expandable microsphere composed of an outer shell made of a thermoplastic resin and a leavening agent contained therein and vaporized by heating. Details of the foaming component, the heat-expandable microspheres and the resin component will be described later.

The method for performing the melt-kneading step is not particularly limited, and examples thereof include a method in which a screw is rotationally driven inside a heating cylinder to melt-knead the foamed component and the resin component to prepare a melt mixture. In the present invention, the molten mixture refers to a mixture in which the foaming component and the resin component are uniformly mixed and in a molten state, and the degree of mixing and the molten state are not particularly limited. Further, the melt mixture obtained in the melt-kneading step is injection-filled in the cavity space in the mold, and the surface is cooled and solidified to form a skin layer, which may also be referred to as a melt mixture.

The temperature at which the foamed component and the resin component are melt-kneaded (hereinafter, may be referred to as the molding temperature) must be at least one temperature inside the heating cylinder that is equal to or higher than the expansion start temperature of the thermally expandable microspheres. However, other conditions are not particularly limited. The molding temperature referred to here refers to the temperature of the molten mixture inside the heating cylinder, and is obtained by measuring the temperature of the molten mixture with a heat transfer thermometer. The molding temperature is controlled by setting the temperature of the heating cylinder or adjusting the rotation speed of the screw.

The molding temperature is preferably higher than the melting point or softening point of the resin component. Further, the molding temperature may be constant in the heating cylinder from the raw material supply port (hopper) toward the injection nozzle, or may have a temperature gradient. When there is a temperature gradient in the molding temperature, for example, (1) the molding temperature gradually increases from the raw material supply port toward the injection nozzle, and (2) molding is performed from the raw material supply port toward the injection nozzle. The temperature gradually decreases, (3) the molding temperature gradually increases from the raw material supply port toward the center of the heating cylinder, and the molding temperature gradually decreases from the center of the heating cylinder toward the injection nozzle, and the like. Can be mentioned. Further, from the viewpoint of increasing the expansion coefficient of the thermally expandable microspheres, the maximum molding temperature is preferably (Tmax-20) to (Tmax + 50) ° C, more preferably (Tmax-10) to (Tmax + 40) ° C. More preferably, it is Tmax to (Tmax + 30) ° C. Here, Tmax means the maximum expansion temperature of the heat-expandable microsphere. At the maximum molding temperature, the vapor pressure of the leavening agent contained in the heat-expandable microspheres is preferably 0.1 to 10.0 MPa, more preferably 0.5 to 7.5 MPa, and particularly preferably 1. It is 0 to 5.0 MPa. The vapor pressure means the vapor pressure of the expander as a whole contained in the heat-expandable microspheres, and when the expander is composed of a plurality of components, the vapor pressure is each at that temperature. It is a value obtained by multiplying the vapor pressure peculiar to a component by the mole fraction of each component in the swelling agent and totaling them.

In the melt-kneading step, it is preferable to pressurize the melt mixture so that the foaming component does not foam. The method of pressurizing the molten mixture is not particularly limited, and examples thereof include mounting a shut-off device and setting the back pressure to be equal to or higher than the foaming pressure of the foaming component at the maximum molding temperature. For the heat-expandable microspheres that are essential for the foaming component, it is necessary to set the back pressure higher than the vapor pressure of the leavening agent contained in the heat-expandable microspheres. In the melt-kneading step, the heat-expandable microspheres are heated to a temperature higher than the expansion start temperature, but by pressurizing the melt mixture as described above, the heat-expandable microspheres can be kept in an unexpanded state. By doing so, it is possible to suppress the unevenness of the surface of the foamed molded product and obtain a foamed molded product having a better appearance.

[Injection filling process]
The injection filling step is a step of injecting and filling the cavity space in the mold with the melt mixture produced in the melt kneading step. In the injection filling step, the molten mixture is injected from a sprue formed in a fixed mold, and the cavity space is filled with the molten mixture. The volume of the molten mixture injected into the cavity space is preferably 90-110%, more preferably 95-105%, particularly preferably 98-102% with respect to the cavity space. When the volume of the molten mixture injected into the cavity space is less than 90% of the volume of the cavity space, the foamed component (thermally expandable microspheres) expands in the cavity, resulting in the appearance of the surface of the foamed molded product. May get worse. Further, when the volume of the molten mixture injected into the cavity space exceeds 110% of the volume of the cavity space, the molten resin may leak from the cavity space and burrs may occur in the molded product.

Examples of the injection molding machine include an injection molding machine such as a plunger type, a screw pre-plastic type, and a screw in-line type.

The injection speed is not particularly limited, but is preferably 30 mm / sec or more, more preferably 60 mm / sec or more, and particularly preferably 100 mm / sec or more. When injection molding is performed at a speed of less than 30 mm / sec, the appearance of the surface of the foamed molded product may be deteriorated due to expansion of the foamed component (thermally expandable microspheres) in the cavity. The upper limit of the injection speed is 500 mm / sec, and when molding is performed at an injection speed higher than the upper limit, burrs may occur on the molded product or the appearance of the molded product may be poor due to resin burning. The injection speed referred to in the present invention indicates the moving speed of the screw during the injection filling process, and can be measured by using a measuring device installed in advance in the injection molding machine or an external measuring device.
The injection pressure is preferably lower than the molding pressure of the fixed mold and the movable mold, preferably 20 to 250 MPa, more preferably 35 to 200 MPa, and particularly preferably 50 to 150 MPa.

In the injection filling step, the portion of the injection-filled molten mixture that is in contact with the mold is quickly cooled to form a skin layer, whereas the inside that is not in contact with the mold is still in a molten state. It is kept and can be foamed. However, since the injection pressure and the filling pressure are applied to the injection-filled molten mixture, foaming hardly or hardly occurs even inside the molten state.

In the injection filling step, the thickness of the molten mixture injected and filled in the cavity space in the mold (hereinafter, may be referred to as the thickness at the time of filling) is not particularly limited, but is preferably 1 to 3 mm, more preferably 1. It is 1.5 to 2.8 mm, particularly preferably 1.8 to 2.5 mm. If the thickness is less than 1 mm, the foaming component may not be sufficiently foamed in the foaming step. If the thickness exceeds 3 mm, overfoaming may occur in the foaming process, resulting in poor appearance. The thickness refers to the thickness at the completion of injection filling of the molten mixture (L _{1 in} FIG. 1B), which is equal to the initial clearance between the fixed mold and the movable mold of the mold.

In the injection filling step, the time from the start of injection filling of the molten mixture to the completion of injection filling (hereinafter, may be referred to as injection filling time) is not particularly limited, but is preferably 0.1 to 3 seconds, more preferably 0. It is 2 to 2 seconds, particularly preferably 0.25 to 1 second. The lower limit of the injection filling time has no particular meaning and may be less than 0.1 seconds, but it is often difficult to make it less than 0.1 seconds due to the design of the equipment. On the other hand, if the injection filling time exceeds 3 seconds, the foaming component may not be sufficiently foamed in the foaming step. The injection filling time can be appropriately adjusted by a method of adjusting the injection speed with respect to the volume of the cavity space or the like.

[Foaming process]
The foaming step is a step of expanding the cavity space and foaming the molten mixture by opening the mold after the injection filling of the molten mixture is completed. In the present invention, opening the mold means moving the movable mold or the movable core built in the movable mold in a direction in which the movable core is separated from the fixed mold. Specifically, the injection molding machine. Movable or movable in the horizontal direction and in the direction of separation from the fixed mold in the case of a horizontal injection molding machine, and in the vertical direction and in the direction of separation from the fixed mold in the case of a vertical injection molding machine. It means the operation of moving the movable core built in the mold. In the foaming step, the foaming component is foamed by the reduced pressure in the cavity accompanying the opening of the mold, and a lightweight foamed molded product is obtained.

The time from the completion of injection filling of the molten mixture to the start of opening the mold (hereinafter, may be referred to as the mold opening delay time) is 0 to 2 seconds, more preferably 0 to 1.5 seconds, and particularly preferably 0 to 0. It is 1 second. In the production method of the present invention, by setting the mold opening delay time to 0 to 2 seconds, a skin layer having an appropriate thickness is formed on the surface of the injection-filled molten mixture, and it is essential for the foaming component inside the molten mixture. The contained thermally expandable microspheres can be sufficiently expanded, and a foam molded product having excellent rigidity and light weight and having a good appearance can be obtained. If the mold opening delay time is more than 2 seconds, the heat-expandable microspheres contained in the foamed component in the molten mixture are cooled by the mold and do not expand sufficiently, so that a low specific gravity molded product cannot be obtained. .. The lower limit of the mold opening delay time is not particularly limited.
Specific methods for setting the mold opening delay time to 0 to 2 seconds include, for example, a detection means for detecting that the filling of the molten mixture is completed, and a control means for controlling the opening of the mold according to information from the detection means. , And a method using a device having a mold opening means for opening the mold by a signal from the control means.
As the detection means, for example, in the injection filling step, a means for detecting the completion of filling of the molten mixture by the position of the screw of the injection molding machine, a pressure sensor is installed at a predetermined position in the mold, and the pressure sensor is installed. Examples thereof include means for detecting as a signal that the position is filled with the molten mixture.

In the foaming step, the mold opening speed when expanding the cavity space is 1 mm / sec or more and less than 100 mm / sec, more preferably 1 mm / sec or more and less than 75 mm / sec, particularly preferably 25 mm / sec or more and 60 mm / sec. Less than sec. In the manufacturing method of the present invention, by setting the mold opening speed to 1 mm / sec or more and less than 100 mm / sec, the bubble state of the cross section of the molded body becomes a uniform closed cell, and further, the unevenness of the surface of the molded body is suppressed. A foam molded product having particularly excellent rigidity and appearance can be obtained. If the mold opening speed is less than 1 mm / sec, the foamed component is cooled and does not expand sufficiently, so that a molded product having a desired thickness cannot be obtained. When the mold opening speed is 100 mm / sec or more, the mold opening speed is faster than the expansion speed, so that the bubble state of the cross section of the molded body is reduced in rigidity due to the generation of non-uniform open cells, and further, the surface of the molded body The appearance is poor, such as unevenness that is not derived from the mold. The mold opening speed in the present invention means the amount of change in the position of the movable mold or the movable core internally installed in the movable mold per unit time when the cavity space is expanded by opening the mold. The time required for the movement (hereinafter referred to as the mold opening time) is the distance traveled by the movable type or the movable core built in the movable type from the start to the stop in the direction of separation from the fixed type. It is the value divided by). The mold opening speed is computer-controlled in a normal injection molding machine, and can be appropriately adjusted by changing the set value.
As a method of opening the mold, as long as the mold opening speed is within the above range, it may be performed in one step or in multiple steps of two or more steps.

In the present invention, as described above, a heat-expandable microsphere is indispensably used as a foaming component, and the time from the completion of injection filling of the molten mixture to the start of opening the mold is set to 0 to 2 seconds, and the mold for expanding the cavity space. By setting the opening speed to 1 mm / sec or more and less than 100 mm / sec, it is possible to produce a foam molded product having excellent rigidity and light weight and having a good appearance.

In the foaming step, the volume expansion rate of the cavity space when expanding the cavity space is not particularly limited, but the volume of the cavity space at the completion of injection filling is 100% by volume, preferably 33% by volume / sec or more and 10,000 volumes. It is less than% / sec, more preferably 50% by volume / sec or more, less than 6000% by volume / sec, and particularly preferably 60% by volume or more and less than 5000% by volume / sec. In the manufacturing method of the present invention, when the mold opening speed is within the above-mentioned predetermined range and the volume expansion speed of the cavity space satisfies the above-mentioned predetermined range, the obtained foamed molded product is lighter and more rigid. And the effect of excellent appearance can be obtained. The volume expansion rate of the cavity space in the present invention is the volume expansion rate of the cavity space per unit time when the cavity space is expanded by opening the mold, assuming that the volume of the cavity space at the completion of injection filling is 100% by volume. It means the amount of change (expansion amount) in volume, and the amount of cavity space that increases from when the movable type or the movable core installed in the movable type starts moving in the direction away from the fixed type until it stops. It is a value obtained by dividing the volume expansion amount by the time required for the expansion (mold opening time).

The sum of the injection filling time, the mold opening delay time and the mold opening time (hereinafter, may be referred to as an injection process time) is preferably 0.5 to 5 seconds, more preferably 0.7 to 4 seconds, and particularly preferably 0.7 to 4 seconds. It takes 1 to 3 seconds. In the manufacturing method of the present invention, by setting the injection process time to 0.5 to 5 seconds, the bubble state of the cross section of the molded body becomes a uniform closed cell, and further, the unevenness of the surface of the molded body is suppressed, and the rigidity and appearance are suppressed. A particularly excellent foam molded product can be obtained.

In the foaming step, the thickness of the foamed molded product obtained after foaming (hereinafter, may be referred to as the thickness of the foamed molded product) is not particularly limited, but is preferably 1.5 to 5 mm, more preferably 2.0 to 2.0 mm. It is 4.5 mm, particularly preferably 2.5 to 4 mm. If the thickness is less than 1.5 mm, the rigidity of the molded product is weakened, which makes it unsuitable as a product. If the thickness exceeds 5 mm, the appearance of the molded product may be poor. The thickness refers to L _{2 in} FIG. 1 (d).

An example of the injection filling step and the foaming step in the present invention is shown in FIG. First, the melt mixture 5 produced in the melt-kneading step is injected from the sprue 1 formed in the fixed mold 2, and the cavity space 4 formed in the mold joint surface of the mold is filled with the melt mixture (FIG. 1 (a). )-(B)).
Next, by moving the movable mold 3 in a direction in which the movable mold 3 is separated from the fixed mold 2, the cavity space in the mold is expanded and the molten mixture is foamed to prepare a foamed molded product 6 (FIG. 1 (c). )-(D)).

After the foaming step, the foamed molded product can be taken out by cooling. The cooling time may be appropriately adjusted depending on the dimensions of the foamed molded product and the like, but generally 30 seconds or more is sufficient.
In the production method of the present invention, the surface temperature of the mold is not particularly limited and may be appropriately set according to the type of resin component used, but is preferably 30 to 100 ° C, more preferably 40 to 80 ° C, particularly. It is preferably 50 to 70 ° C. By setting the surface temperature of the mold in the above range, a skin layer having an appropriate thickness is formed on the surface of the injection-filled molten mixture, and the heat-expandable microspheres essential for the foaming component inside the molten mixture are formed. It can be sufficiently expanded, and it is possible to obtain a foam molded product having excellent rigidity and light weight and having a good appearance.
As the mold device used in the present invention, a mold device using a known heating method such as a steam type, a pressurized hot water type, an oil type, or an electromagnetic induction heating type can be used.

(Foam component)
The foaming component essentially contains a heat-expandable microsphere composed of an outer shell made of a thermoplastic resin and a leavening agent contained therein and vaporized by heating. In the production method of the present invention, in the foaming step, the heat-expandable microspheres essential for the foaming component expand, so that the plastic balloon, which is an inflatable body of the heat-expandable microspheres, is tertiary in the matrix composed of the resin component. A foam molded product having a closed cell structure originally uniformly dispersed and arranged can be obtained. Even if the thermally expandable microspheres expand, the open cell structure that causes a decrease in the rigidity of the foamed molded product or a deterioration in appearance is not formed. Therefore, the production method of the present invention has rigidity and light weight. It is possible to produce a foam molded product having a good appearance as well as being excellent in quality. When the foaming component further contains a foaming component other than the heat-expandable microspheres such as a chemical foaming agent and a physical foaming agent, the resulting foamed molded product has an open cell structure, so that the rigidity such as the flexural modulus is significantly reduced. Or, the appearance of the surface of the foamed molded product may be significantly impaired. Therefore, it is usually not preferable to use a foaming component other than the heat-expandable microspheres in the production method of the present invention, but thermal expansion such as the above-mentioned chemical foaming agent or physical foaming agent is not impaired within the range of the effect of the present invention. It is also possible to use foaming components other than sex microspheres.

Examples of the chemical foaming agent include inorganic foaming agents such as sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium nitrite, azide compound, and sodium borohydride; azodicarboxylicamide, azobisisobutyronitrile, and barium azodi. Carboxylate, dinitrosopentamethylenetetramine, 4,4'-oxybis (benzenesulfonylhydrazide), N, N'-dimethyl-N, N'-dinitrosopentamide, N, N'-dinitrosopentamethylenetetramine, nitrourea , Acetone-p-toluenesulfonyl hydrazone, p-toluenesulfonylamide, nitroguanidine, hydroazodicarboxylicamide, trihydrazinotriazine, 5-phenyltetrazole and other organic foaming agents. Further, a foaming aid may be used in combination with the above chemical foaming agent, if necessary. The foaming aid is an additive that lowers the decomposition temperature of the foaming agent, promotes decomposition, homogenizes bubbles, and the like, and examples thereof include zinc stearate, salicylic acid, and phthalic acid.
Examples of the physical foaming agent include butane, pentane, dichloromethane, water, nitrogen gas, carbon dioxide gas, air and the like.

(Thermal expansion microsphere)
The heat-expandable microspheres are composed of an outer shell made of a thermoplastic resin and a leavening agent contained therein and vaporized by heating. The heat-expandable microspheres can be expanded at various temperatures by the combination of the thermoplastic resin constituting the outer shell and the encapsulating agent, and these combinations are the melting point or softening point of the resin component, the molding temperature, etc. Can be appropriately selected in consideration of.

The thermoplastic resin constituting the outer shell of the heat-expandable microspheres is not particularly limited, but for example, an unsaturated carboxylic acid-based copolymer such as a vinylidene chloride copolymer or a (meth) acrylic acid-based copolymer. , (Meta) acrylic acid ester-based copolymers and other unsaturated carboxylic acid ester-based copolymers, (meth) acrylonitrile-based copolymers and other nitrile-based copolymers, (meth) acrylic acid- (meth) acrylonitrile-based copolymers Examples thereof include unsaturated carboxylic acid-nitrile copolymers such as copolymers.

Examples of the polymerizable monomer used as a raw material for the thermoplastic resin include vinylidene chloride; vinyl chloride; vinyl acetate; nitrile-based monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and fumaronitrile; acrylic acid, methacrylic acid, and itaconic acid. , Fumaric acid, maleic acid and unsaturated carboxylic acid (salt) monomers such as metal salts thereof; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) ) (Meta) acrylic acid ester-based monomers such as acrylates, glycidyl (meth) acrylates, hydroxyethyl (meth) acrylates and hydroxypropyl (meth) acrylates; amide-based monomers such as acrylamide, metaacrylamide, substituted acrylamide and substituted methacrylicamide; Examples thereof include imide-based monomers such as N-phenylmaleimide, N- (2-chlorophenyl) maleimide, and N-cyclohexylmaleimide; vinyl aromatic monomers such as styrene, α-methylstyrene, and chlorostyrene; isoprene; butadiene and the like. These polymerizable monomers may be used alone or in combination of two or more. Further, a monomer (crosslinking agent) having two or more polymerizable double bonds may be used in combination with the above-mentioned polymerizable monomer, if necessary.

In the heat-expandable microsphere, when the thermoplastic resin constituting the outer shell is a nitrile-based copolymer (for example, obtained by polymerizing a polymerizable monomer containing a nitrile-based monomer), the viewpoint of improving the foaming ratio is improved. Is preferable. The weight ratio of the nitrile-based monomer is preferably 20 to 80% by weight, more preferably 30 to 70% by weight of the polymerizable monomer.

Further, in the heat-expandable microsphere, the thermoplastic resin constituting the outer shell is unsaturated (for example, obtained by polymerizing a polymerizable monomer containing an unsaturated carboxylic acid (salt) -based monomer and a nitrile-based monomer). A carboxylic acid-nitrile copolymer is preferable from the viewpoint of improving heat resistance. The total weight ratio of the nitrile-based monomer and the unsaturated carboxylic acid (salt) monomer is preferably 50 to 100% by weight, more preferably 60 to 100% by weight of the polymerizable monomer. At this time, the weight ratio of the unsaturated carboxylic acid (salt) monomer to the total of the nitrile-based monomer and the unsaturated carboxylic acid (salt) -based monomer is preferably 5 to 70% by weight, more preferably 10 to 60% by weight. Is.

The swelling agent is not particularly limited as long as it is contained in an outer shell and vaporized by heating. For example, propane, normal butane, isobutane, normal pentane, cyclopentane, isopentane, neopentane, normal hexane, isohexane, and heptane. , Octane, isopentane, nonane, normal decane, isododecane, hydrocarbons such as petroleum ether, chlorofluorocarbon, fluorine-containing compounds containing no chlorine or bromine atom, compounds that generate gas by thermal decomposition by heating, and the like. .. These swelling agents may be used alone or in combination of two or more.

The heat-expandable microspheres can be produced by a known method. For example, a method of suspend-polymerizing an oily mixture containing the polymerizable monomer, the polymerization initiator and the leavening agent by dispersing it in an aqueous dispersion medium containing a dispersant or the like can be mentioned.
The dispersion stabilizer added to the aqueous dispersion medium is not particularly limited, but for example, colloidal silica, colloidal calcium carbonate, magnesium hydroxide, calcium phosphate, aluminum hydroxide, ferric hydroxide, calcium sulfate, sodium sulfate, etc. Calcium sulphate, calcium carbonate, barium carbonate, magnesium carbonate, alumina sol and the like can be mentioned. In addition, as a dispersion stabilizing aid that may be added to the aqueous dispersion medium as needed, a condensation product of diethanolamine and fatty acid dicarboxylic acid, gelatin, polyvinylpyrrolidone, methylcellulose, polyethylene oxide, polypeptide, polyvinyl alcohol, etc. Polymer-type dispersion stabilizing aids; cationic surfactants such as alkyltrimethylammonium chloride and dialkyldimethylammonium chloride; anionic surfactants such as sodium alkylsulfate; betaine alkyldimethylaminoacetate, betaine alkyldihydroxyethylaminoacetate, etc. Examples thereof include amphoteric surfactants. Further, a water-soluble compound such as a scale inhibitor may be added to the aqueous dispersion medium in combination with a dispersion stabilizer.

The polymerization temperature is appropriately set depending on the type of polymerization initiator. Further, the polymerization may be carried out under pressure, for example, the initial polymerization pressure is preferably in the range of 0 to 5.0 MPa.
In addition, the heat-expandable microspheres are commercially available, and as a representative commercially available product of the heat-expandable microspheres, the heat-expandable microspheres of each part number of Matsumoto Microsphere manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. Can be mentioned.

The average particle size (D50) of the heat-expandable microspheres is not particularly limited, but is usually 1 to 60 μm, more preferably 5 to 50 μm, and further preferably 10 to 45 μm. If it is smaller than 1 μm, uniform dispersion becomes difficult and the foaming ratio becomes low. Further, if it is larger than 60 μm, the strength of the obtained foamed molded product is weakened, which is not desirable. The average particle size of the heat-expandable microspheres in the present invention is measured by the method shown in the examples.
The coefficient of variation CV of the particle size distribution of the heat-expandable microspheres is not particularly limited, but is preferably 35% or less, more preferably 30% or less, and particularly preferably 30% or less, from the viewpoint of obtaining a foamed molded product having a uniform cell diameter. It is 25% or less. The coefficient of variation CV is calculated by the following formulas (1) and (2).

（式中、ｓは粒子径の標準偏差、＜ｘ＞は平均粒子径、ｘ_ｉはｉ番目の粒子径、ｎは粒子の数である。）

(Wherein, s is the standard deviation of the particle size, <x> is an average particle size, x _i is the i-th particle diameter, n is the number of particles.)

The weight ratio of the leavening agent to the total weight of the heat-expandable microspheres (hereinafter, may be referred to as the inclusion ratio of the leavening agent) is not particularly limited, but is preferably 2 to 40% by weight, more preferably 5 to 30% by weight. %. If the weight ratio is less than 2% by weight, the expansion ratio of the thermally expandable microspheres is small, and it may be difficult to obtain a lightweight foam molded product. On the other hand, when the weight ratio is more than 40% by weight, the thickness of the outer shell with respect to the particle size is small, so that the heat-expandable microspheres are easily destroyed in the melt-kneading step, and the heat-expandable microspheres are destroyed and leak out. The expansion agent facilitates the formation of communicating air bubbles in the foamed molded product.

The maximum expansion coefficient of the thermally expandable microsphere is preferably 5 times or more, more preferably 10 times or more, still more preferably 20 times or more, and most preferably 30 times or more. The upper limit of the maximum expansion ratio is not particularly limited, but is usually 400 times or less. The maximum expansion coefficient of the heat-expandable microspheres is the true specific gravity (d ₀ ) of the heat-expandable microspheres before heating and the true _value at the time of maximum expansion after heating the heat-expandable microspheres in an oven for 1 minute. It can be obtained from the ratio (d ₀ / d ₁ ) to the specific gravity (d ₁ ).
There are an expansion start temperature (Ts) and a maximum expansion temperature (Tmax) as indexes indicating the thermal expansion characteristics of the thermally expandable microspheres. In the present invention, the expansion start temperature is the temperature at which the thermally expandable microspheres expand when heated above that temperature, and the maximum expansion temperature is the maximum expansion of the thermally expandable microspheres. It refers to temperature and is defined as being measured by the methods shown in the examples.

The expansion start temperature (Ts) of the heat-expandable microspheres is not particularly limited, but is preferably 130 to 220 ° C, more preferably 140 to 210 ° C, and particularly preferably 150 to 200 ° C. If the expansion start temperature is less than 130 ° C., the expansion agent contained in the thermally expandable microspheres may be removed in the melt-kneading step, and silver streaks may occur on the surface of the foamed molded product. When the expansion start temperature exceeds 230 ° C., the expansion ratio of the thermally expandable microspheres may be low.
The maximum expansion temperature (Tmax) of the heat-expandable microspheres is not particularly limited, but is preferably 170 to 250 ° C., more preferably 180 to 240 ° C., and particularly preferably 190 to 230 ° C. When the maximum expansion temperature (Tmax) of the heat-expandable microspheres is within the above range, foam molding is performed using a general-purpose injection grade polypropylene resin, TPO, TPV, TPS, or ABS resin as a resin component from the viewpoint of molding temperature. It is suitable for manufacturing a body, and the foam molded product thus obtained is particularly preferable because it is excellent in rigidity and light weight.

The weight ratio of the heat-expandable microspheres to the foamed component is preferably 40 to 100% by weight, more preferably 70 to 100% by weight, still more preferably 90 to 100% by weight, and particularly preferably 100% by weight of the entire foamed component. Is. If the weight ratio is less than 40% by weight, the rigidity of the obtained foamed molded product may be lowered or the appearance may be impaired.

The foaming component may be used as it is, but it may be used as a wet product in which the foaming component is previously moistened with a liquid material such as oil, or as a granulated product obtained by hardening the foaming component with wax or the like. Further, a masterbatch containing a foaming component and a resin component may be prepared in advance and mixed with the masterbatch. In these cases, the dispersibility of the foamed component in the molten mixture obtained by melt-kneading in the heating cylinder becomes high, which is preferable.

The method for producing the masterbatch is not particularly limited, and for example, a foaming component, a resin component, and various additives added as needed are added to a single-screw extruder, a twin-screw extruder, a kneader, and the like. A method of kneading using a kneader such as a pressure kneader, a Banbury mixer, or a super mixer, and cutting the obtained kneaded product to a desired size with a pelletizer to form a pellet shape into a master batch pellet is mentioned. Be done.

The liquid material used for the wet product is not particularly limited as long as it has good compatibility with the resin component, and examples thereof include mineral oil, fluid paraffin, silicone oil, process oil, and plasticizer. The weight ratio of the liquid material is preferably 0.1 to 60% by weight, more preferably 0.2 to 50% by weight, still more preferably 0.5 to 40% by weight of the total wet product. If the weight ratio of the liquid material is less than 0.1% by weight, the wetting is not sufficient and the effect of increasing the dispersibility of the foaming component is small. Further, when the weight ratio of the liquid material is more than 60% by weight, the stickiness is large and the workability is poor.
Examples of the wax used for the granulated product include fatty acids and paraffinic waxes. The weight ratio of the wax is preferably 5 to 70% by weight, more preferably 10 to 60% by weight, still more preferably 15 to 50% by weight of the entire granulated product. If the weight ratio of the wax is less than 5% by weight, the granules cannot be formed. Further, if the weight ratio of the wax is more than 70% by weight, there is a concern that the resin component may affect the physical properties.

The resin component used in the masterbatch is not particularly limited as long as it is a resin component specifically exemplified below, but a melting temperature lower than the expansion start temperature of the heat-expandable microspheres and the decomposition temperature of the chemical foaming agent is used. It is preferable that the thermoplastic material has a masterbatch because it can be master-batched without impairing the foaming performance. The weight ratio of the resin component is preferably 25 to 95% by weight, more preferably 30 to 90% by weight, still more preferably 35 to 80% by weight of the entire masterbatch.

(Resin component)
The resin component is a component that is a basis for constructing a foam molded product, and is a component that has a great influence on the physical properties of the foam molded product. The resin component used in the production method of the present invention is not particularly limited, and a generally used thermoplastic resin or thermoplastic elastomer can be used, for example, polyethylene resin, polypropylene resin, polybutene resin, poly. Polyethylene resins such as methylpentene resins, TPOs, TPVs, olefin-based thermoplastic elastomers; ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, polyethylene- (meth) acrylic acid (ester) copolymers, ionomer resins Olefin resin copolymers such as: Polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol and other polyvinyl resins; polyethylene terephthalate, polybutylene terephthalate, polytetramethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, poly Polyester resins such as allylate, polycarbonate, TPEE; acrylic resins such as methyl poly (meth) acrylate, ethyl poly (meth) acrylate, butyl poly (meth) acrylate, poly (meth) acrylonitrile; polystyrene, AS resin , ASA resin, ABS resin, styrene resin such as TPS; polyamide resin such as 6-nylon, 6,6-nylon, TPEA; biodegradable resin such as polylactic acid; fluororesin; polyurethane-based thermoplastic elastomer; Examples include liquid crystal polymers. These resin components may be used alone or in combination of two or more.
Polypropylene resin, TPO, TPV, TPS, and ABS resin are preferable from the viewpoint that unevenness on the surface of the foamed molded product is suppressed and the appearance is excellent.

In the melt-kneading step, in addition to the above-mentioned foaming component and resin component, if necessary, a lubricant, a plasticizer, an antioxidant, a colorant, a filler, an antistatic agent, a flame retardant, wood powder, glass fiber, and carbon fiber. Various additives such as the above may be added to prepare a molten mixture. In that case, the method of adding the various additives is not particularly limited. For example, (1) the foaming component, the resin component and the various additives are separately added directly to the raw material supply port to perform the melt-kneading step, and the melt mixture is obtained. (2) A method in which various additives are kneaded into a resin component in advance, and the foaming component is added to a raw material supply port to perform a melt-kneading step to prepare a melt mixture, etc. Can be mentioned.

In the melt-kneading step, the blending ratio of the foaming component is not particularly limited, but it is preferable to use 1 to 10 parts by weight of the foaming component with respect to 100 parts by weight of the resin component, and 2 to 8 parts by weight of the foaming component is used. It is more preferable to use it. If the blending ratio of the foaming component is less than 1 part by weight, the desired weight reduction effect may not be obtained. On the other hand, if the blending ratio of the foamed component is more than 10 parts by weight, the rigidity of the obtained foamed molded product may decrease.

[Effervescent molded product]
The foam molded product obtained by the production method of the present invention is a foam molded product having closed cells, and has excellent rigidity and light weight, and also has a good appearance.
The specific gravity of the foam molded product is preferably less than 0.85, more preferably less than 0.83, particularly preferably less than 0.81, and most preferably less than 0.75. When the specific gravity is 0.85 or more, the lightness of the foam molded product is not excellent. The lower limit of the specific gravity is not particularly limited, but is preferably more than 0.45, more preferably more than 0.5, and particularly preferably 0., from the viewpoint of emphasizing the balance between the rigidity and the appearance of the foamed molded product. It is more than 55, most preferably more than 0.6.
Further, from the viewpoint of using the foam molded product for automobile interior / exterior parts, the specific gravity is preferably more than 0.6 and less than 0.75. By setting the specific gravity within the above range, it is easy to obtain a foam molded product having excellent rigidity and appearance, which is particularly important for automobile interior / exterior parts. The specific gravity is a value measured by a method based on the JIS K7112 A method (underwater substitution method).

The flexural modulus of the foam molded product is preferably 400 MPa or more and less than 1500 MPa, more preferably 450 MPa or more and less than 1300 MPa, and particularly preferably 500 MPa or more and less than 1200 MPa. If the flexural modulus is less than 400 MPa, the rigidity is too low and it is not practical. When the flexural modulus is 1500 MPa or more, the flexibility is too low and it is not practical. The flexural modulus is a value measured by a method based on JIS K7171.

The average cell diameter of the foamed molded product is not particularly limited, but is preferably 2 to 500 μm, more preferably 3 to 400 μm, and further preferably 5 to 300 μm. If the average cell diameter is smaller than 2 μm, it may be difficult to obtain a lightweight foamed molded product. On the other hand, if the average cell diameter is larger than 500 μm, the rigidity of the obtained foamed molded product may decrease, which is not preferable. The average cell diameter in the present invention means an average value of the bubble diameter existing at an arbitrary position in the foamed molded product, and is a value calculated by the method of Examples described later. The average cell diameter of the foamed molded product can be easily adjusted by the particle diameter of the heat-expandable microspheres.

The closed cell ratio of the foamed molded product is not particularly limited, but is preferably 50% or more, more preferably 60% or more, further preferably 65% or more, particularly preferably 80% or more, and most preferably 95% or more. is there. The upper limit of the closed cell ratio is 100%. If the closed cell ratio is less than 50%, the rigidity of the obtained foamed molded product is lowered, and there is also a problem of water absorption due to the continuous bubbles, which is not preferable.
When the thickness of the foamed molded product is thin or when the rigidity of the foamed molded product is required, select heat-expandable microspheres having a small particle size and increase the weight ratio of the heat-expandable microspheres to the foamed components. Is preferable.

The foam molded product thus obtained is excellent in rigidity and light weight, and has a good appearance, so that it can be suitably used for applications such as automobile interior / exterior, home appliances, and container trays.

Hereinafter, examples of the present invention will be specifically described. The present invention is not limited to these examples. In addition, Example 4 and Example 8 are referred to as a reference example.
The physical properties of the heat-expandable microspheres used below and the foamed molded products produced in Examples and Comparative Examples were evaluated as follows. The thermally expandable microsphere may be simply referred to as a microsphere, and the foam molded product may be simply referred to as a molded product.

[Measurement of average particle size and particle size distribution of thermally expandable microspheres]
A laser diffraction type particle size distribution measuring device (HEROS & RODOS manufactured by SYMPATEC) was used. The dispersion pressure of the dry dispersion unit was 5.0 bar, the degree of vacuum was 5.0 mbar, and the measurement was performed by the dry measurement method, and the D50 value was taken as the average particle diameter.

[Measurement of water content of thermally expandable microspheres]
As a measuring device, a Karl Fischer moisture meter (MKA-510N type, manufactured by Kyoto Denshi Kogyo Co., Ltd.) was used for measurement.

[Measurement of encapsulation rate of leavening agent enclosed in thermally expandable microspheres]
1.0 g of heat-expandable microspheres were placed in a stainless steel evaporating dish having a diameter of 80 mm and a depth of 15 mm, and the weight (W1) thereof was measured. 30 ml of acetone was added, the mixture was uniformly dispersed, left at room temperature for 30 minutes, then heated at 120 ° C. for 2 hours, and the weight (W2) after drying was measured. The encapsulation rate of the leavening agent is calculated by the following formula.
Inclusion rate (% by weight) = (W1-W2) (g) /1.0 (g) x 100- (moisture content) (% by weight)
(In the formula, the water content is measured by the above method.)

[Ts and Tmax]
The expansion start temperature (Ts) and maximum expansion temperature (Tmax) of the heat-expandable microspheres are measured using DMA (DMA Q800 type, manufactured by TA instruments). A heat-expandable microsphere is placed in an aluminum cup, and the sample is heated from 20 ° C. to 300 ° C. at a heating rate of 10 ° C./min with a force of 0.01 N applied from above by a pressurizer. The displacement amount (D) in the vertical direction was measured, the displacement start temperature in the positive direction was defined as the expansion start temperature (Ts), and the temperature when the maximum displacement amount (Dmax) was indicated was defined as the maximum expansion temperature (Tmax).

[Measurement of true specific gravity]
The true specific gravity of the microspheres and the hollow fine particles obtained by thermally expanding the microspheres was measured by the following measuring method.
The true specific gravity was measured by an immersion method (Archimedes method) using isopropyl alcohol in an atmosphere having an environmental temperature of 25 ° C. and a relative humidity of 50%.
Specifically, a volumetric flask having a capacity of 100 ml was emptied, dried, and then the weight of the volumetric flask (WB ₁ ) was weighed. After the weighed volumetric flask was accurately filled with isopropyl alcohol to the meniscus, the weight (WB ₂ ) of the volumetric flask filled with 100 ml of isopropyl alcohol was weighed.

Further, the volumetric flask having a capacity of 100 ml was emptied, dried, and then the weight of the volumetric flask (WS ₁ ) was weighed. The weighed volumetric flask was filled with about 50 ml of particles, and the weight of the volumetric flask filled with the particles (WS ₂ ) was weighed. Then, the volumetric flask filled with particles was accurately filled with isopropyl alcohol to the meniscus so as not to contain air bubbles, and then the weight (WS ₃ ) was weighed. Then, the obtained WB ₁ , WB ₂ , WS ₁ , WS ₂ and WS ₃ were introduced into the following equations, and the true specific gravity (d) of the particles was calculated.
d = {(WS ₂ -WS ₁ ) x (WB _2- WB ₁ ) / 100} / {(WB _2- WB ₁ )-(WS _3- WS ₂ )}
In the above, using microspheres or hollow fine particles as particles, the true specific gravity of each was calculated.

[Measurement of expansion factor]
Make a flat box with a bottom surface of 12 cm in length, 13 cm in width and 9 cm in height with aluminum foil, put 1.0 g of microspheres evenly in it, put it in a gear oven, and keep it at a predetermined temperature for 1 minute. After heat expansion, the true specific gravity of the microspheres was measured. The expansion ratio (E) was calculated by dividing the true specific gravity (d ₀ ) of the microspheres before heating by the true specific gravity (d) of the microspheres after heating. The maximum expansion ratio (E _max ) corresponds to the expansion ratio at the time of maximum expansion.

[Lightness of molded product]
The specific gravity of the obtained molded product was measured using an electron hydrometer (MDS-3000, manufactured by Alpha Mirage Co., Ltd.) by a method based on the JIS K-7112 A method (underwater substitution method).
The lightness of the molded product was determined based on the following evaluation criteria.
◯: Specific gravity of the molded product is less than 0.85 ×: Specific gravity of the molded product is 0.85 or more

[Rigidity of molded product]
The flexural modulus of the obtained molded product was measured using a tensile compression tester (Technograph TG-2KN, manufactured by Minnevia Co., Ltd.) by a method based on JIS K-7171.
The rigidity of the molded product was determined based on the following evaluation criteria.
◯: Rigidity of the molded body is 400 MPa or more and less than 1500 MPa ×: Rigidity of the molded body is less than 400 MPa and 1500 MPa or more

[Bubble state of cross section of molded body]
Using an electron microscope (SEM) device, the state of air bubbles in the cross section of the obtained molded product was confirmed. The ratio of closed cells to the unit area was calculated from the SEM photograph taken at 30 times, and the judgment was made based on the following evaluation criteria.
⊚: Uniformly independent (closed cell ratio 80% or more)
◯: Almost uniformly independent (closed cell ratio 50% or more and less than 80%)
X: Non-uniform (closed cell ratio less than 50%)

[Surface condition of molded product]
The surface condition of the molded product was determined based on the following evaluation criteria.
◯: Good (no unevenness on the surface and no silver streak)
Δ: Slightly defective (the surface is uneven or silver streak has occurred)
×: Defective (the surface is uneven and silver streak is generated)

[Average cell diameter]
It was calculated by a method according to ASTM D3576-77 from an SEM photograph of the cross section of the obtained molded product taken at 100 times.

[Manufacturing Example 1]
(Manufacture of thermally expandable microspheres)
The thermally expandable microspheres used in the following examples and comparative examples were produced.
To 600 g of ion-exchanged water, 150 g of sodium chloride, 70 g of colloidal silica dispersion having 20% by weight of silica active ingredient, 1.0 g of polyvinylpyrrolidone and 0.5 g of ethylenediaminetetraacetic acid / 4Na salt were added, and then the obtained mixture was obtained. The pH was adjusted to 2.8 to 3.2 to prepare an aqueous dispersion medium.
Separately, 150 g of acrylonitrile, 50 g of methacrylic acid, 100 g of methacrylic acid, 1.0 g of 1,9-nonanediol diacrylate, 90 g of isopentane, and 8 g of a di-2-ethylhexyl peroxydicarbonate-containing solution containing 70% of the active ingredient. Was mixed to prepare an oily mixture.
The aqueous dispersion medium and the oily mixture were mixed, and the obtained mixture was dispersed by a homomixer (TK homomixer manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a suspension. This suspension was transferred to a pressure reactor having a capacity of 1.5 liters for nitrogen substitution, and then the initial reaction pressure was 0.5 MPa, and polymerization was carried out at a polymerization temperature of 60 ° C. for 20 hours while stirring at 80 rpm. The polymerization solution obtained after the polymerization was filtered and dried to obtain a heat-expandable microsphere 1. Table 1 shows the physical properties of the heat-expandable microsphere 1. In Table 1, the abbreviations shown in Table 2 are used.
(Manufacturing of masterbatch)
Using a 0.5L pressurized kneader, low density polyethylene (LDPE resin manufactured by Dow Chemical Japan Co., Ltd., DNDV-0405R, melting point 108 ° C., density 0.914 g / cm ³ ) 120 g as a resin component used for master batch Was melt-kneaded, and when the temperature reached 115 ° C., 180 g of heat-expandable microspheres 1 were blended and uniformly mixed to prepare a premix. The obtained premix was supplied to a twin-screw extruder having a cylinder diameter of 40 mm and extruded at a kneading temperature of 115 ° C. to obtain a masterbatch in which the coefficient of thermal expansion microspheres 1 was 60% by weight.

[Production Examples 2 to 4]
The heat-expandable microspheres 2 to 4 were obtained in the same manner as in the production of the heat-expandable microsphere 1 except that the various components and amounts used in the production of the heat-expandable microsphere 1 were changed to those shown in Table 1. It was. Table 1 shows the physical properties of the obtained raw material microspheres.
Master batches using the heat-expandable microspheres were obtained in the same manner as in Production Example 1 except that the blending amounts of the heat-expandable microspheres and the resin components used in the masterbatch were changed to those shown in Table 1.

[Example 1]
17 parts by weight of the masterbatch obtained in Production Example 1 and 100 parts by weight of polypropylene resin (manufactured by Nippon Polypropylene Co., Ltd., Novatec PP BC3F, density 0.90 g / cm ³ ) are mixed, and the obtained mixed pellets are injected. It was supplied to a hopper of a molding machine (manufactured by Japan Steel Works, Ltd., J85AD-110H, mold clamping force 85 tons), melt-kneaded, and injection-molded to obtain a plate-shaped molded product. The molding conditions are set to molding temperature: 210 ° C., injection speed: 30 mm / sec, mold surface temperature: 100 ° C., mold opening delay time: 0 seconds, mold opening speed: 73 mm / sec, and other conditions. Is shown in Table 3.
As a result of evaluating the obtained molded product, a molded product having a specific gravity of 0.63, a flexural modulus of 820 MPa, a closed cell in the cross section of the molded product having an average cell diameter of 65 μm, and a good surface condition of the molded product was obtained. Was done.

[Examples 2 to 10 and Comparative Examples 1 to 3]
A foam molded product was obtained in the same manner as in Example 1 except that the master batch and molding conditions used in Example 1 were changed to those shown in Tables 3 and 4.

[Comparative Example 4]
An inorganic chemical foaming agent (Polyslen, manufactured by Eiwa Kasei Kogyo Co., Ltd.) was used instead of the master batch using heat-expandable microspheres, and 5 parts by weight of the inorganic chemical foaming agent and 100 parts by weight of polypropylene resin were mixed. A foam molded product was obtained in the same manner as in Example 1 except that the molding conditions were changed to those shown in Table 4.

The method for producing a foamed molded article of the present invention can produce a lightweight foamed molded article having closed cells, suppressing irregularities on the surface of the molded article, and having excellent rigidity and appearance. Therefore, the obtained foam molded product is a lightweight foam molded product having excellent heat insulating properties and compressive properties and having a good appearance, and can be used as a mechanical part for an automobile, an interior / exterior material, an exterior of a household electric appliance, or a building material. Widely used.

1 Sprue 2 Fixed type 3 Movable type 4 Cavity space 5 Molten mixture 6 Foam molded product

Claims (8)

A method of manufacturing a foam molded product by injection molding.
A melt-kneading process in which a foamed component and a resin component are melt-kneaded in a heating cylinder to prepare a melt mixture.
An injection filling step of injecting and filling the cavity space in the mold with the molten mixture,
It has a foaming step of expanding the cavity space and foaming the molten mixture by opening the mold after the injection filling of the molten mixture is completed.
The foaming component essentially contains a thermally expandable microsphere composed of an outer shell made of a thermoplastic resin and a leavening agent contained therein and vaporized by heating.
The time from the completion of injection filling of the molten mixture to the start of opening the mold is 0 to 2 seconds.
Wherein in the foaming process, the mold opening speed when enlarging the cavity space 25 mm / sec or more state, and are less than 100 mm / sec,
The specific gravity of the foam molded product is more than 0.6 and less than 0.85.
A method for manufacturing a foam molded product. In the foaming step, the volume expansion rate of the cavity space when expanding the cavity space is 33% by volume / sec or more and less than 10,000% by volume / sec, assuming that the volume of the cavity space at the completion of injection filling is 100% by volume. The method for producing a foamed molded product according to claim 1. In the injection filling step, the thickness of the molten mixture injected and filled in the cavity space in the mold is 1 to 3 mm, and in the foaming step, the thickness of the foamed molded product obtained after foaming is 1.5 to 1. The method for producing a foamed molded article according to claim 1 or 2, which is 5 mm. The method for producing an injection molded product according to any one of claims 1 to 3, wherein in the injection filling step, the time from the start of injection filling of the molten mixture to the completion of injection filling is 0.1 to 3 seconds. The method for producing a foamed molded product according to any one of claims 1 to 4, wherein the surface temperature of the mold is 30 to 100 ° C. The method for producing a foamed molded product according to any one of claims 1 to 5, wherein the foamed molded product has a specific gravity of 0.61 or more . The method for producing a foamed molded product according to any one of claims 1 to 6, wherein 1 to 10 parts by weight of the foamed component is used with respect to 100 parts by weight of the resin component in the melt-kneading step. The method for producing a foamed molded product according to any one of claims 1 to 7, wherein the maximum expansion temperature of the heat-expandable microspheres is 170 to 250 ° C.

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