JP4640814B2 - Thermoplastic resin foam - Google Patents

Description

  The present invention relates to a thermoplastic resin foam having good appearance, surface smoothness and rigidity. More specifically, the present invention relates to a thermoplastic resin foam having good appearance, surface smoothness and rigidity obtained by injecting a physical foaming agent into an injection molding machine, mixing it with a molten thermoplastic resin, and performing injection foam molding.

  In the injection molding method using a thermoplastic resin, it has been conventionally studied to perform foaming for the purpose of reducing the material and reducing the weight. As a method of performing injection foam molding, a method in which a thermal decomposition type chemical foaming agent such as azodicarboxylic acid amide is directly applied to pellets or used as a master batch is known.

  Such chemical foaming agents have been widely used in injection foam molding because they are readily available and can be used in ordinary in-line injection molding machines. However, when the chemical foaming agent is applied to the pellets, in addition to the need for a large amount of 1-5% by weight of the foaming agent relative to the thermoplastic resin, in the hopper of the molding machine, The pellets separated and could cause foaming unevenness. Moreover, in the case of a masterbatch, since a part of chemical foaming agent decomposes | disassembles with the heat | fever in an extruder when manufacturing it, the efficiency of the gas amount generate | occur | produced at the time of injection foam molding was bad.

Furthermore, chemical foaming agents are expensive, which causes a rise in material costs. Some generate harmful gases such as carbon monoxide. Furthermore, the decomposition residue of the chemical foaming agent stays in the cylinder of the injection molding machine for a long time, and it appears irregularly on the surface of the molded product, which may impair the appearance.
Physical foaming using propane, nitrogen gas, carbon dioxide or the like as the foaming agent instead of the chemical foaming agent has also been proposed. In particular, extrusion foaming using these physical foaming agents is widely used in the production of polystyrene paper and the like. In this extrusion foaming method, holes are provided in the middle of the extruder cylinder, and a physical foaming agent is press-fitted into the cylinder (for example, JP-A-7-16450, JP-A-8-81590, etc.). In the case of extrusion foaming, a product having a stable size and expansion ratio can be obtained by keeping the supply amount of the raw resin and the supply amount of the physical foaming agent at a constant ratio.

  However, in the case of in-line injection molding using a physical foaming agent for injection molding, even if a hole is formed in the cylinder and the physical foaming agent is injected, the screw moves back and forth in the cylinder, plasticizing and weighing the resin. In order to inject, the positional relationship between the position of the injection hole and the screw is not always constant as in an extruder, and depending on the position of the screw, the physical foaming agent may not be injected.

Thus, the stable supply of the physical foaming agent to the injection molding machine was much more difficult than the extrusion molding. Therefore, proposals for improving the injection foaming method have been made.
For example, as a method of using an organic solvent as a physical foaming agent so that the physical foaming agent is difficult to volatilize when transporting the resin to an injection molding machine, a method of intermittently supplying a mixture of an organic solvent and a resin to the injection molding machine (Japanese Examined Patent Publication No. SHO 46-21184) and a method of mixing an organic solvent and a thermoplastic resin using an extruder and injecting them directly into a mold (JP-A-6-41344) have been proposed.

  Since these methods use organic solvents, it was necessary to modify the explosion-proof equipment. In addition, when injected directly into the mold from the extruder, the molten resin is continuously supplied from the extruder, so the resin is foamed and discharged out of the system when the product is taken out. There is a risk that waste resin may adhere to the surface, and the incidence of defective products is high.

  On the other hand, a method of foaming after impregnating a resin with a physical foaming agent in a supercritical state has been proposed. This technique is known as a microcellular foaming technique (US Pat. No. 5,158,986 (Japanese Patent No. 2625576), US Pat. No. 4,473,665, etc.). In this microcellular foaming technology, by making the cell diameter of the foam smaller than the size at which cell breakage occurs, a product that can maintain impact strength despite being a foamed product is provided.

In order to apply such a foaming agent in a supercritical state to an injection foam molding method, an improvement in the injection method and molding method of the supercritical physical foaming agent has been proposed.
For example, after saturating a physical foaming agent in the molten resin, it is operated so that it becomes supersaturated and unstable, and injected into a cavity that is pressurized (counter pressure) so that the foaming agent does not vaporize. It has been proposed to obtain microcellular foams by expanding (core back) the volume in the cavity (US Pat. No. 4,473,665, US Pat. No. 5,334,356).

  In the injection molding method to obtain a microcellular foam, it is necessary to dissolve a large amount of the physical foaming agent in the molten resin so that the physical foaming agent is saturated, and the physical foaming agent has a high pressure so that it becomes supercritical in the cylinder of the injection molding machine. In some cases, it is necessary to heat and supply, and in addition, a booster pump or the like is required to inject the physical foaming agent at a pressure that overcomes the high resin pressure. In addition, a system that opens and closes the physical blowing agent injection hole provided in the cylinder and controls the movement of the booster pump in response to the movement of the screw is necessary, and a system for many sensors and information processing is also necessary. Therefore, the equipment is complicated and expensive.

  Furthermore, in the mold, when pressurizing the cavity (counter pressure) or core back, it is necessary to seal the metal surfaces of the mold so that they do not leak high pressure gas. Since the mold clamping force of an ordinary injection molding machine is difficult, the gas tightness is usually maintained by packing such as rubber. However, since it is heated and gradually worn, it is difficult to produce a large amount of products.

  In addition, as a result of improving the airtightness in the cavity, the gas for counter pressure does not escape from the cavity during injection, and a gas pool is generated, which creates a recessed part at the end of the product, thus reducing the appearance of the product. There was a risk of causing it.

  In JP-A-11-34129, JP-A-11-34130, and WO98 / 31521, a high pressure is applied so that the physical foaming agent is brought into a supercritical state in the cylinder of the injection molding machine from the middle of the cylinder of the injection molding machine having an in-line screw. It is proposed to supply in In order to inject the physical foaming agent at a high pressure, a booster pump is required, and complicated and expensive equipment is required.

  There has also been proposed a method in which the injection of the physical foaming agent can be performed independently of the movement of the screw. For example, JP-A-8-258096 proposes injecting a physical foaming agent from the position of the tip of the screw through a hole provided in the axial direction of the screw and mixing with the molten resin. In this method, since a breathable sintered metal or the like is used to prevent the molten resin from flowing back into the injection hole, a pressure loss occurs when the physical foaming agent passes through the sintered metal. Furthermore, it is necessary to inject a physical foaming agent at a higher pressure. In JP-A-8-85128, a chamber is provided between a hopper and a cylinder of an injection molding machine, and a physical foaming agent such as carbon dioxide is sufficiently impregnated under pressure in the chamber, and then sent into the cylinder for injection. A method of foam molding is proposed. It is difficult to impregnate a resin with a physical foaming agent in a short time at a temperature around room temperature, which is not suitable for industrial continuous production.

  By continuously injecting the physical foaming agent into the molten resin, supplying the molten resin into the cylinder of the injection molding machine, and storing the resin in an accumulator or releasing it outside the system, except when metering, Methods that can cope with intermittent injection molding have been proposed (Japanese Patent Laid-Open Nos. 10-230528 and 10-24436). According to this method, it is not necessary to inject the physical foaming agent in conjunction with the movement of the mold and the movement of the screw. However, since a pump for pressurization is used, the production apparatus becomes expensive, and the molten resin Since the yield of the material is reduced when the product is released out of the system, it has been difficult to apply it to the production of an inexpensive foamed product.

  In order to solve the above-mentioned problems, the present inventors have reached the present invention as a result of intensive studies.

Japanese Patent Laid-Open No. 7-16450 JP-A-8-81590 Japanese Patent Publication No.46-2184 JP-A-6-41344 US Pat. No. 5,158,986 U.S. Pat. No. 4,473,665 JP-A-11-34129 JP 11-34130 A WO 98/31521

The present invention can inject a physical foaming agent into a cylinder of an injection molding machine at a low pressure without requiring a booster such as a pump, and can inject a physical foaming agent corresponding to mold operation and screw movement. And it aims at providing the thermoplastic resin foam obtained by the injection foaming method which can carry out injection foaming, without maintaining a metal mold | die at high pressure.
An object of this invention is to provide the thermoplastic resin foam which has a favorable external appearance with the smoothness and rigidity of a skin layer.
Another object of the present invention is to provide a thermoplastic resin foam that can be highly reduced in weight in the case of high foaming and capable of obtaining strong rigidity.

The present invention uses an injection molding machine having a two-stage compression screw, and in injection foam molding for supplying a physical foaming agent in a gaseous state from the middle of a cylinder,
(1) A physical foaming agent in a gaseous state is supplied from a storage tank at a pressure lower than the storage pressure by a pressure difference from the cylinder of the injection molding machine,
(2) supplying the physical foaming agent in a range from the starting point of the second stage of the screw in the injection direction to a length 9 times the outer diameter of the screw when the screw is most advanced in the injection direction; and (3) The cavity of the mold of the injection molding machine is almost atmospheric pressure, the cavity volume is kept lower than the amount of the metered resin , and the cavity volume at the injection pressure is injected while injecting the molten resin mixed with the physical foaming agent. It is obtained by injection foam molding of thermoplastic resin by expanding the volume after injection filling and expanding the volume in the cavity,
A thermoplastic resin foam that satisfies the following requirements (i) to (iv) is provided.
(I) The thickness of the skin layer is 0.1 mm or more,
(Ii) The thickness of the foam is 0.1 to 100 mm, and (iii) the average cell diameter is 0.150 to 1 mm.

  The thermoplastic resin is an inorganic filler having an average particle size of 0.5 to 10 μm as a foam nucleating agent, 0.1 to 5% by weight based on the resin, and / or a chemical foaming agent or a decomposition product thereof, The above-described thermoplastic resin foam, which is contained in an amount of 0.01 to 1% by weight in terms of a product, is a preferred embodiment of the present invention.

  The above-mentioned thermoplastic resin foam in which the thermoplastic resin is polypropylene and the expansion ratio is 1 to 5 is a preferred embodiment of the present invention.

  The above-mentioned thermoplastic resin foam in which the thermoplastic resin is a modified polypropylene and the expansion ratio is 1 to 10 times is a preferred embodiment of the present invention.

  The above-mentioned thermoplastic resin foam in which the thermoplastic resin is an amorphous polystyrene-based resin or polycarbonate and the expansion ratio is 1 to 20 times is a preferred embodiment of the present invention.

  The present invention also provides foam products such as automobile-related parts, OA equipment parts, electrical product-related parts, heat insulating materials, and packaging materials made of the thermoplastic resin foam.

By this invention, the thermoplastic resin foam which has a favorable external appearance with the smoothness and rigidity of a skin layer is provided.
The present invention also provides a thermoplastic resin foam that is highly lightweight in the case of high foaming and capable of obtaining strong rigidity.
According to the present invention, foam products such as automobile-related parts, OA equipment parts, electrical product-related parts, heat insulating materials, and packaging materials having excellent properties, which are made of the thermoplastic resin foam, are provided.

The thermoplastic resin foam of the present invention and the injection foaming method capable of producing it will be described in detail below.
The injection molding method of the present invention uses an injection molding machine having a two-stage compression screw. In injection foam molding of a thermoplastic resin that supplies a physical foaming agent from the middle of a cylinder, (1) a physical foaming agent in a gaseous state Supply from the storage tank at a pressure lower than the storage pressure by a pressure difference from the cylinder of the injection molding machine. (2) Injection of the physical foaming agent when the screw is advanced most in the injection direction. In the direction from the starting point of the second stage of the screw to a length that is 9 times the outer diameter of the screw, and (3) the pressure inside the mold cavity after the injection molding machine is set to a low pressure such as atmospheric pressure. An injection foam molding method characterized in that a foam is obtained by expanding a volume in a cavity after injection filling.

  In the present invention, after injecting the resin into the cavity and filling it, an appropriate time is taken to expand the internal volume of the cavity. As a preferred method of expanding, a method of moving a metal plate constituting the wall of the cavitating (core back method) can be mentioned. The simplest method is to move to the movable platen side of the mold mounting plate.

  By filling the cavity at once with a resin and creating a skin layer on the surface of the molded product, a hard product shape is obtained, resulting in uneven foaming inside the product and the generation of bubbles with large cell diameters. However, it produces the advantage of being inconspicuous in appearance. Therefore, as proposed in the prior art, it is not necessary to pressurize the cavity so that the physical foaming agent to be used does not vaporize. Therefore, it is not necessary to keep the inside of the cavity at a high pressure, such as a counter pressure.

For this reason, it is not necessary to provide a rubber packing for maintaining pressure in the mold, and it is not necessary to seal the gap between the molds. Further, as long as it is assembled mold by a plurality of metal plates, since the air that was present during resin filled into the cavity resin freely escape from the gap between the metal plate when the spread in the cavity, in the mold There is no air accumulation, and there is no worry of poor appearance due to air accumulation.

  As the mold clamping mechanism of the injection molding machine used in the present invention, a direct pressure type and an electric type can be preferably used because the speed at the time of core back can be precisely controlled. In addition, a toggle type or other mold clamping mechanism that is difficult to core back can be used by releasing the mold clamping force and then core back by a mechanism such as a spring. Even if the core back is not in the direction of the movable platen, the core back can be achieved by moving the metal plate on the side surface of the cavity using an appropriate hydraulic pressure, electric device, spring or the like. For example, when a box is provided with a gate at the bottom and the core is backed in the direction of the bottom, the side faces hardly foam.

  In the case of such a product, when the core is backed in a direction perpendicular to the bottom surface, foaming is possible in all five directions by core-backing with the remaining four side surfaces at almost the same time.

  For core back in the direction other than the movable platen, a T-shaped or Y-shaped hydraulic cylinder can be used with respect to the clamping cylinder. In this way, since no counter pressure is applied, a machine that cores the mold metal plate in a complicated manner can be easily designed.

  In addition, if it is a box-like object such as a container, it can be molded separately from the bottom and side surfaces by the core back only on the movable platen side, and then it can be made into an assembly box, and the container thus manufactured Can be recovered in a shape that can only be disassembled after the transportation of the luggage is completed. Moreover, if it is a box-shaped thing, it can inject | pour into a shape like a development view, core back to the movable board side, shape | mold, and after taking out a product, it can assemble and use it as needed.

  Furthermore, when such a folded part occurs, assembly work can be done by crushing the foamed part and attaching creases using a mold extrusion mechanism etc. while the resin does not completely solidify the linear part to be folded The box can withstand repeated use by increasing the strength of the bent portion.

  In the present invention, the expansion ratio and appearance performance are appropriately determined depending on the temperature of the resin to be injected, the injection speed, the waiting time from the end of injection to the start of core back, the amount of core back, the core back speed, the cooling time after the end of core back, etc. Can be controlled. Further, the core back can be performed in several stages, thereby obtaining a highly foamed, fine cell product.

  In the injection foam molding of the present invention, when the molten resin is injected into the mold, the resin in the portion in contact with the mold is solidified faster than the resin inside. Therefore, an unfoamed skin layer is generated, and the product shape is maintained with its rigidity. The thickness of this skin layer is preferably 0.1 mm or more, more preferably 0.3 mm or more, and further preferably 0.5 mm or more.

  The core back timing for forming the skin layer having these thicknesses varies depending on the type of resin, the type of foaming agent, the mold temperature, and the resin temperature. For example, carbon dioxide is used as a physical foaming agent, and ordinary polypropylene is used. When used, it is preferably about 0.5 to 3 seconds after completion of injection. If the time from the completion of injection to the core back is too short, a sufficiently thick skin layer will not be formed, and if it is too long, the resin will solidify and a sufficient foaming ratio will not be obtained even if the core is backed.

  The core moving speed during the core back also varies depending on the product thickness, the type of resin, the type of foaming agent, the mold temperature, and the resin temperature. For example, when carbon dioxide is used as the physical foaming agent and normal polypropylene is used, 0 About 0.01-2 mm / min is preferable. If the core moving speed is too slow, the resin will solidify in the middle of the core back, and sufficient foaming ratio will not be obtained.If it is too fast, the cell generation / growth will not follow the core moving, causing the cell to break down and appearance. A good product cannot be obtained.

  As the mold temperature, a mold temperature usually used for molding a resin to be used is sufficient, and when a product with a thin product thickness or a high expansion ratio is obtained, it is preferable to set the mold temperature higher than the normal mold temperature. The thickness and foaming ratio of the product obtained in the present invention vary depending on the type of resin, the type / addition amount of the physical foaming agent, the mold temperature, the resin temperature, etc., for example, using carbon dioxide as the physical foaming agent, When polypropylene is used, a foaming ratio of about 1 to 5 times is obtained with a thickness of about 0.1 to 100 mm.

  A normal polypropylene with a suitable amount of rubber such as ethylene-propylene rubber, ethylene-butene rubber, ethylene-octene rubber, styrene-butene block rubber, or low-density polyethylene is thick, highly foamed, and has a uniform cell diameter. It is easy to get a product. Similarly, a polypropylene having a high molecular weight component in the homo part and a slightly cross-linked polypropylene are also easily thick, highly foamed, and uniform in cell diameter. With these modified polypropylenes, it is possible to obtain a product having a product thickness of about 200 mm and an expansion ratio of about 10 times.

  According to the present invention, a foamed product having a good appearance can be obtained due to the smoothness and rigidity of the skin layer even if some distribution occurs in the cell shape, cell density, and foaming ratio inside the molded product. In the present invention, when obtaining a closed cell product, the average cell diameter is about 0.01 to 1 mm. However, depending on the product shape and product application, even if the cell diameter is several mm, There is no problem even if some of them communicate.

  In the case of a highly foamed product, the cells associate and communicate with each other and become hollow in the product. However, since there are columns of resin stretched as columns in the hollow, the weight is highly reduced and strong. It is possible to produce a product with rigidity. These highly foamed products are ideal for substitutes such as cardboard and for floating.

In the present invention, a hot runner, a shut-off nozzle, a shut-off gate, etc. that are used in normal injection molding can also be used. Hot runners can suppress the generation of runners and increase the yield of materials. Shut-off nozzle, shirts DOO off gate may be prevented from contaminating the product physical foaming agent in melted resin, such as during the product extraction is then molded to the resin leaking into the cavity at a pressure of vaporization. The shirt-off nozzle can be provided at the screw tip of the injection molding machine, and the shut-off gate can be provided in the mold.

  If the volume of the cavity is too small compared to the volume from the shut-off nozzle to the product gate, or if the resin solidification temperature is low, such as rubber or elastomer, and the resin at the gate and runner parts is slow to solidify, When foaming is performed by increasing the volume in the cavity, the resin filled between the gates from the shut-off nozzle tends to flow into the cavity, and the appearance of the product may be poor and the foaming ratio may be reduced. In such a case, it is preferable to use a film gate as the gate. In the case of a bin gate, it is preferable to provide a step around the gate.

  In addition, by reducing the gate hole and vibrating with ultrasonic waves, the fluidity at the time of injection is improved and the time until the gate seal after injection is completed is shortened, or from the shut-off nozzle immediately after the shut-off nozzle is closed. A method of slightly increasing the volume of the resin flow path in the vicinity of the shutoff nozzle immediately after injection so that the resin pressure between the gates sharply decreases is also preferable.

  FIG. 1 shows an example of a mold having a hot runner and a shut-off gate as an example of an embodiment of the present invention. The injection foaming method of the present invention can also be applied to an injection method conventionally performed by unfoamed injection.

  For example, set leather, cloth, thermoplastic elastomer skin, etc. on the movable platen side of the cavity, open the mold, inject while foaming into the cavity, clamp this, and mold the entire cavity After the resin is developed, the core back (injection press) method can be used for manufacturing lightweight interior materials with a skin such as door trims and pillars of automobiles.

  Also, as an application example of multilayer injection molding, a thermoplastic elastomer not containing a physical foaming agent is injected and / or a thermoplastic elastomer containing a physical foaming agent is injected and foamed according to the present invention. The base resin can be injected and foamed by the method of the present invention, and can be applied to the production of a lightweight interior material with an automobile skin. Further, after setting a metal or the like in a mold, it is possible to perform injection foaming (insert molding) by the method of the present invention.

In addition, the mold clamping force is weakened, the cavity volume is kept lower than the amount of metered resin, the cavity volume is expanded by injection pressure while injecting molten resin mixed with physical foaming agent (injection compression method), and injection When the core is backed after completion of the process, a skin layer is formed on the surface of the product in a short time at the start of injection, and defects such as flash silver caused by the rapid evaporation of the physical foaming agent on the surface of the molded product are extremely low. Therefore, a product having an appearance quality equivalent to that of a normal solid molded product can be obtained.

  Furthermore, after producing and installing a mold in the shape of a container, and injecting while foaming while the mold is open, the mold is closed, and after expanding the foamed resin throughout the cavity, the core back is used to increase the expansion ratio. The foamed resin also turns to the wall portion of the container that does not become necessary, and a dombly container with a foamed side surface is obtained. Since it is lightweight, it is optimal for instant food containers.

  In the present invention, even if there is some variation in cell shape, cell density, expansion ratio and the like inside the molded product, there is little restriction on the molten resin mixed with a physical foaming agent because it is not easily affected. Therefore, it is not necessary to disperse the physical foaming agent as proposed in the prior art very uniformly in the molten resin.

  In the present invention, there is no restriction on the design of the injection molding machine screw. In the present invention, it is recommended to use a multistage compression screw, preferably a two-stage multistage compression screw, as an injection molding machine screw. Although the second stage is inferior in stirring ability, it is possible to use a screw with a compressed groove (with wings) which is excellent in feeding ability of molten resin.

  In the present invention, since the resin feeding ability is excellent, the groove next to the end of the first stage compression screw is deepened, and the resin pressure is drastically reduced. In this depressurized portion, the molten resin becomes starved, and a cavity in which no resin is present is generated. In this hollow portion, a physical pressure reduced to a pressure lower than the storage pressure, preferably 80% or less of the storage pressure. Supply blowing agent.

The injection foam molding machine will be described with reference to FIG. The injection foam molding machine includes an injection molding machine cylinder 7 and an injection molding machine two-stage compression cylinder 8. The injection molding machine cylinder is heated by the heater 12. The physical foaming agent is injected into the cylinder from the physical foaming agent injection hole 18 through the physical foaming agent cylinder 13 and the foaming agent supply pipe 14 via the cylinder valve 15, the pressure reducing valve 16 and the check valve 17.
The first stage compression section is 9 and the second stage compression section is 10.

  FIG. 1 is a view when the screw is most advanced in the injection direction. Since the first stage compression unit 9 feeds the pellets supplied from the hopper 19 forward, the screw groove is deep, and the screw groove is usually shallowly or evenly shallower until the front of the first stage, or the screw groove to a certain area. After a certain portion continues, the screw groove becomes shallow, so that the resin is compressed and the air in the resin escapes backward.

  Subsequently, at 11, the screw grooves suddenly deepen, the volume between the screw grooves expands, and there is a space where gas can be injected in addition to the molten resin. This is referred to as the decompression portion 11. This part is also usually the same as the first stage compression part, the screw groove shallows almost evenly to the front of the second stage compression part, or the screw groove continues to a certain area, and then the screw As the groove becomes shallower, the resin is compressed. The physical blowing agent injection hole is 9 times longer than the screw outer diameter (D) (9D) from the starting portion of the second-stage compression portion with the screw most advanced in the injection direction, that is, the second-stage It is preferable to be provided so as to be located at 0 to 9D part, preferably 0 to 3D part of the compression part.

  In the rear of 0D, that is, in the first stage compression section, the physical foaming agent is scattered from the hopper mouth and the ground portion behind the screw and is not utilized as the foaming agent. In front of the 9D part, the area where the subsequent mixing with the physical foaming agent and the area where the resin is compressed continue, the L / D of the entire screw becomes too long, and the strength as a screw of the injection molding machine is inferior. In addition, the overall size of the injection molding machine becomes large, which is not efficient.

Resin from the injection molding machine nozzle 6, hot runner 5, is injected into the shut-off valve 4 through the mold core (movable side) 1 and the mold shell (fixed side) 2 cavity 3 of the mold having.

  FIG. 2 is an enlarged view of a portion around the physical foaming agent injection hole. Since the molten resin is sent forward by the groove of the compression portion 10 and the blade 21 of the screw, a space where no resin exists in the decompression portion 11 is generated. The decompression portion 11 is provided with a physical foaming agent injection hole 18, and the physical foaming agent is injected from the physical foaming agent supply pipe 20.

  In the state shown in FIGS. 1 and 2, the pressure in the cavity is not so high, and injection is possible at a low pressure. In order to realize this state, the ratio L2 / L1 between the last screw groove depth L1 of the first stage and the first screw groove depth L2 of the second stage is in the range of 1.2 to 6, preferably 2 It is desirable to be in the range of 5 to 4.5.

  Further, the first-stage compression section 9 and the second-stage compression section 10 can be appropriately made into one, two, or three in consideration of the resin feeding ability and mixing ability. If the design such as the groove depth of the compression part of the first stage and the second stage is within the range described above, the pressure-resistant structure of the vent part of a commercially available vented injection molding machine can be reinforced and used. . Further, only the screw may be a vented type, and the cylinder may be a normal type provided with a physical foaming agent injection hole.

  Furthermore, in the screw part of the first-stage compression part, the last 0.5-2D part is designed so that the distance between the screws is short and the space between the screw grooves is completely filled with molten resin. The effect of preventing the physical foaming agent from escaping behind the screw of the first stage compression section is great.

  When the screw begins to retract from the state of FIGS. 1 and 2 in the direction opposite to the injection direction (metering / plasticizing step), the plasticized resin is supplied from the compression portion 9 to the decompression portion 11. The supplied molten resin is appropriately mixed with the physical foaming agent injected from the physical foaming agent injection hole 18. In this case, fine dispersion is not particularly required, and the foaming agent to the molten resin may be in a state of being wound by the pressure of the foaming agent and shearing in which the resin is kneaded.

  Also, until the screw tip where the groove is completely filled with molten resin, most of the space occupied by the unmixed physical foaming agent in the groove is a large foam connected or a large lump. It is at a distance that exerts pressure on it. The pressure of the physical foaming agent in the part is substantially equal, and the physical foaming agent of almost equal pressure is gradually kneaded and dispersed in the molten resin while being transported forward by the wings 21 constituting the groove with the molten resin. Mixing of physical foaming agent is achieved to the extent that no problem occurs during injection foaming. When the screw is further retracted, the resin pressure is increased by the compression of the compression unit 10.

A preferred embodiment of an injection molding machine suitable for the injection foam molding method of the present invention includes (1) a physical foaming agent storage tank, (2) a two-stage compression screw, and (3) when the screw is most advanced in the injection direction. in the range from the start of the second stage of the screw to 9 times the length of the screw outer diameter in the projecting direction, a cylinder having a physical foaming agent supply unit, and (4) mold capable of expanding the volume of the cavity It is an injection molding machine for thermoplastic resins.

  In the two-stage compression screw of the injection molding machine, the ratio L2 / L1 between the depth L1 of the last groove of the first stage and the depth L2 of the first groove of the second stage is in the range of 1.2-6. Being an injection molding machine is a preferred embodiment of an injection molding machine.

  Further, an injection molding machine in which a resin check valve is provided in the physical foam supply unit is also a preferred aspect of the injection molding machine.

  If the low pressure part does not fit within the width of the screw metering position, for example because the injection molding machine is used in the production of non-foamed products, the molten resin does not enter the physical foaming agent piping into the physical foaming agent injection hole. A check valve should be attached. 1 and 2 show a mode in which a check valve 17 is attached. FIG. 3 shows an example where the resin pressure is higher than the injection pressure of the physical foaming agent. When the resin pressure becomes higher than the supply pressure of the physical foaming agent, the check valve 17 acts to stop the supply of the physical foaming agent. The molten resin does not enter the physical foaming agent pipe by the action of the check valve 17. However, since the unmixed physical foaming agent present on the rear side (hopper side) is mixed with the molten resin and sent, there is no shortage of dissolution of the physical foaming agent that causes a problem during injection foaming. In addition, the arrow in FIG. 3 shows the flow direction of resin.

  FIG. 4 is a schematic plan view of the second stage compression unit 10 across several grooves. Since the physical foaming agent reservoir 22 constituted by countless foaming in the molten resin does not have a stirring pin or the like between the grooves, it is mixed with the resin by the pressure of the physical foaming agent and shearing by the blades of the screw. Sent to. Even if the screw is retracted, the resin pressure is increased, the check valve is closed, and the supply of the physical foaming agent is stopped, the mixing of the molten resin and the physical foaming agent continues as long as 22 physical foaming agent pools exist. Subsequently, a resin mixed with a physical foaming agent is supplied to the front. In the present invention, since the pressure of the supplied physical foaming agent is not high, dissolution in the molten resin is slow, and the time until the reservoir 22 disappears is sufficiently long. In addition, the arrow in FIG. 4 shows the flow direction of resin.

  Therefore, even if the supply of the physical foaming agent is stopped by the check valve 17, as long as the physical foaming agent reservoir 22 exists, mixing of the molten resin and the physical foaming agent continues for a while, and the physical A resin mixed with a blowing agent is supplied. When plasticization / metering is completed and the screw is stopped, the mixing of the molten resin and the physical foaming agent is temporarily stopped, but the molten resin in which the physical foaming agent is mixed at a substantially constant concentration is stored in the screw. Therefore, there is no problem in the injection molding of foam products.

  Therefore, according to the present invention, the physical foaming agent is intermittently supplied into the cylinder by the movement of the screw, but the mixture of the molten resin and the physical foaming agent is continuously supplied during the plasticizing / metering time. In addition, there is no non-uniformity in the foaming agent concentration which causes problems such as appearance during injection foaming.

  The foaming agent used in the present invention is not particularly problematic as long as it is a normal physical foaming agent. For example, vapors of low-boiling organic solvents such as methanol, ethanol, propane, butane and pentane; vapors of halogen-based inert solvents such as dichloromethane, chloroform, carbon tetrachloride, freon and nitrogen trifluoride; carbon dioxide, nitrogen, argon, Inert gases such as helium, neon, and astatine are included.

  Among these, carbon dioxide, nitrogen, and argon are the most excellent because they do not need to be vaporized, are inexpensive, and have very little environmental pollution and fire hazard. As a physical foaming agent storage method, if it is a small scale production, carbon dioxide, nitrogen, etc. can be used in a cylinder and supplied to the injection molding machine through a pressure reducing valve.

  For facilities that produce foam products on a large scale, install storage tanks for liquefied carbon dioxide, liquefied nitrogen, etc., pass through heat exchangers, vaporize, pass through piping, and supply to injection molding machines through pressure reducing valves.

  In the case of a liquid physical foaming agent, the storage pressure defined in the present invention refers to the pressure that is vaporized and supplied to the pressure reducing valve. The storage pressure is preferably in the range of 0.13 to 100 MPa, and if the pressure is too low, the pressure cannot be reduced and injected into the injection molding machine, and if the pressure is too high, the pressure resistance of the storage equipment must be increased. The size of the equipment is increased, and the damage in case of a pipe rupture accident is increased, which is not preferable for safety.

The following can be mentioned as one of the preferable specific embodiments of the injection foam molding method of the present invention.
(1) The physical foaming agent is depressurized to 80% or less of the storage pressure from the storage tank, and the physical foaming agent is supplied continuously or intermittently due to the pressure difference from the hole in the cylinder of the injection molding machine. (2) In the cylinder, there is a two-stage compression screw that performs compression by reducing the volume between the grooves gradually with respect to the injection direction and sending the resin in the injection direction in stages. The ratio L2 / L1 of the last groove depth L1 and the first groove depth L2 in the second stage is in the range of 1.2 to 6, and (3) when the screw is advanced most in the injection direction, the physical foaming agent The position of the injection hole is in the range of 9 times the screw outer diameter in the forward direction from the beginning of the second stage of the screw. (4) The inside of the mold cavity is set to atmospheric pressure, and after injection filling, the cavity An injection foam molding method for obtaining a foam by expanding the inner volume.

  As the thermoplastic resin of the present invention, any thermoplastic resin that can be injection-molded in a normal unfoamed state can be used without particular limitation. Examples of thermoplastic resins include: low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, cyclic polyethylene, etc .; ethylene-styrene copolymer, ethylene-methacrylic acid copolymer Polymers, ethylene copolymers such as ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer; homopolypropylene; random copolymers of α-olefin and propylene such as ethylene, butene, pentene, hexene, octene; Polypropylene block copolymers such as ethylene-propylene block copolymers; olefin resins such as polybutene and polymethylpentene; polybutylene, polyisobutylene, polybutadiene, natural rubber, thermoplastic polyurethane, isoprene rubber, styrene-butyl Rubber / elastomers such as diene rubber, ethylene-propylene rubber, ethylene-butene rubber, ethylene-octene rubber, ethylene-propylene-diene rubber, chloroprene rubber; It is also possible to improve the fluidity with polypropylene or mineral oil. Among the thermoplastic resins of the present invention, preferred are polyolefins, and particularly preferred are polypropylenes including homopolypropylene, random copolymers of α-olefin and propylene, and polypropylene block copolymers.

  Furthermore, styrenic resins such as polystyrene, AS resin, and ABS resin are suitable for high foaming. It can also be applied to amorphous resins such as polyvinyl chloride, high nitrile resin, polymethyl acrylate, polymethyl methacrylate polycarbonate, and engineer plastics.

  For example, polymethylpentene, polyphenylene ether, polyphenylene oxide, polyacetal, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polylactic acid, polyether ketone, polyether sulfone, nylon 6, nylon 11, nylon 12, nylon 66, nylon 610, Nylon 612, liquid crystal polymer, polyimide, poly-p-phenylene terephthalate, polysulfone, and the like can be given.

  In addition, a foam of a biodegradable resin obtained by mixing polylactic acid, starch or the like with polyolefin can be decomposed in a short time after disposal.

  Furthermore, even if it is a thermosetting resin, a monomer, a prepolymer, a cross-linking agent, etc. having a viscosity that can be injection molded are used alone or mixed, and after injection foaming by the method of the present invention, in the mold or from the mold. It is also possible to take out and crosslink by a method such as heating. Furthermore, the expansion ratio can be increased by the physical foaming agent remaining at the time of this thermal crosslinking and / or by the thermal expansion effect in the foamed cell. Those crosslinked after foaming are excellent in mechanical properties such as compression recovery.

  After injection foaming by the method of the present invention, it is possible to cross-link by a method such as heating by taking it out from the die or from the die. Furthermore, the expansion ratio can be increased by the physical foaming agent remaining at the time of this thermal crosslinking and / or by the thermal expansion effect in the foamed cell. Those crosslinked after foaming are excellent in mechanical properties such as compression recovery.

In particular, if the hardness after crosslinking is rubbery or elastomeric, after the injection foaming into the mold cavity, the cavity volume ratio is suppressed to 0.1 to 50%, and the mold is It is possible to obtain a foam whose volume is further increased by 10 to 500% due to the physical foaming agent remaining inside the product, if the material is taken out from the mold after being heated and crosslinked, due to the physical foaming agent remaining inside the product. .

  Moreover, the thing blended in order to improve a moldability, a mechanical physical property, etc. may be sufficient. In particular, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-butene rubber, ethylene-octene rubber, ethylene-propylene-diene rubber and other rubber blended with polyethylene resin and polypropylene resin have a uniform cell diameter when foamed. It is desirable.

  Furthermore, recycled resin such as recycled pet, recycled polypropylene, and recycled polystyrene can also be used.

  These resins, rubbers, and elastomers may be added as necessary with heat stabilizers, weathering agents, light-proofing agents, flame retardants, antistatic agents, antibacterial agents, carbon black, pigments, talc, mica, calcium carbonate. Further, it may be modified by adding barium magnesium sulfate whisker, potassium titanate whisker, or glass fiber.

  The viscosity of these resins is not constant because the measurement conditions of MFR (melt flow rate), which is the index, differ for each resin, but it is not constant, as long as it is sold and used as a normal injection grade There is no particular problem. In the case of polypropylene, an MFR of 2 to 100 g / 10 min (230 ° C.) can be suitably used. In addition, polypropylene having a broad molecular weight distribution can be preferably used because it corresponds to the fluidity of ordinary polypropylene having an MFR of about 3, even if the MFR is about 3.

  In the present invention, when the foam nucleating agent is added, the cell diameter of the foamed product is made uniform and the product appearance is enhanced. The physical foaming agent dissolved in the resin is likely to become cell nuclei when microscopically uneven portions are generated. Therefore, the types of foaming agents that can be used include fine particles and those that can be used as foaming nucleating agents by molecules generated by reactive decomposition.

  Fine particles include inorganic substances such as talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, barium sulfate, mica, clay, wollastonite, silica, alumina, iron oxide, titanium oxide, magnesia, carbon black, An inorganic filler such as graphite can be used. The average particle size of the inorganic fine particles is preferably 0.5 to 10 μm. In order to improve the dispersion in the resin, those that have been subjected to hydrophobic surface treatment are further excellent in dispersibility.

  As addition amount, 0.1 to 5 weight% is preferable with respect to raw material resin. In addition, considering the contamination of the molding machine hopper, the adhesion of powder to the product surface, and the wear of the screw, for example, it is processed into a masterbatch based on resin, wax and rubber with a foam nucleating agent amount of 5 to 50% by weight. Can also be used.

Examples of the nucleating agent by reaction include chemical foaming agents. The chemical foaming agent decomposes in the cylinder of the injection molding machine, and the foaming residue can be a foam nucleating agent.
Examples of the chemical foaming agent include azodicarboxylic amide, oxybisbenzenesulfonyl hydrazide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, paratoluenesulfonyl hydrazide and the like. Also, polycarboxylic acids such as citric acid, oxalic acid, fumaric acid, phthalic acid, malic acid, tartaric acid, cyclohexane 1,2 dicarboxylic acid, camphoric acid, ethylenediaminetetraacetic acid, triethylenetetramine hexaacetic acid, nitrilolic acid, and hydrogen carbonate Examples thereof include a mixture of inorganic carbonic acid compounds such as sodium, sodium aluminum hydrogencarbonate and potassium hydrogencarbonate, and salts of polycarboxylic acids such as sodium dihydrogen citrate and potassium oxalate.

  In particular, polycarboxylic acids and inorganic carbonic acid compounds are preferably used in combination with polyolefins. Especially, foamed products with good appearance that have a microcellular effect, that is, a large amount of foaming nuclei, in combination with citric acid and sodium bicarbonate. Is obtained.

  Further, the nucleation effect of the combined product of citric acid and sodium hydrogen carbonate is very excellent. For example, a polypropylene composition containing 10 to 30% by weight of talc already has a sufficient nucleation effect. By further adding a combination of sodium bicarbonate and sodium hydrogen carbonate, a further effect of microcellularization can be seen.

  The addition amount of these chemical blowing agents is preferably 0.01 to 1% by weight with respect to the raw material resin. If the amount is less than 0.01% by weight, a sufficient nucleation effect cannot be obtained, and if the amount exceeds 1% by weight, the decomposition product may become visible and may contaminate the product. These chemical foaming agents are processed into particles having an average particle diameter of 1 to 100 μm and can be used by being applied to a raw material resin, but can be used by being applied to a material at the time of injection molding.

  Further, it may be blended with auxiliary agents such as urea, zinc hydroxide, zinc oxide, lead oxide, zinc stearate and calcium stearate. Furthermore, in consideration of contamination of the hopper of the molding machine and adhesion of the powder to the product surface, it can be processed and used as a master batch based on a resin. Alternatively, the chemical foaming agent may be added once, and the chemical foaming agent may be decomposed by pelletization, or the chemical foaming agent having a high concentration may be decomposed in advance and the residue may be added. The addition amount of the chemical foaming agent residue is preferably 0.01 to 1% by weight in terms of undecomposed matter.

  According to the present invention, a commercially available physical foaming agent stored in a cylinder or the like is supplied to an injection molding machine at a low pressure and a constant pressure by a pressure reducing valve. Compared with the method of supplying the agent, the physical foaming agent supply device is simple and inexpensive, and the physical foaming agent piping does not generate pressure higher than the cylinder pressure, making it unlikely that an accident will occur. But there is little damage.

  Further, the supply of the physical foaming agent is started or stopped due to the difference between the physical foaming agent injection pressure and the pressure in the cavity in the cylinder, and a complicated mechanism is not required. In other words, compared with the method of injecting with a pump, there is no need for a large electrical and mechanical device that moves the pump in conjunction with the movement of the mold and the movement of the screw. Can be used with modification. In addition, the inside of the mold may be under atmospheric pressure before injection, and no device such as a counter pressure is required, and the air in the mold escapes from the gap between the metal plates constituting the mold. Appearance defects due to accumulation etc. hardly occur.

  In the present invention, in the case of a resin that does not exhibit rubber elasticity, the expansion ratio is determined by the core back amount of the mold. Excellent quality stability.

Examples of foamed products that can be produced according to the present invention are as follows, according to use.
Stationery, OA equipment: file, mouse pad, pencil / ballpoint pen shaft, staple, letter case, knife handle, safe, PC, printer, external MO housing, chair backrest / armrest, driver handle, etc. .

  Electrical products: refrigerator, TV, video, air conditioner housing, speaker cone, microphone, sonar, radar, parabolic antenna, air conditioner outdoor unit, fan feather, wind generator feather, rice cooker / jar / pot lid, etc.

  Automotive: Armrest, headrest, floor mat, side molding, sound absorbing material, gasoline float, bumper, door handle, glove box, fresh air outlet, console box, ceiling material, foil cap, pillar, instrument panel, air bag cover , Levers, air cleaner case, resonator, cowl top garnish, diff garnish, door trim, spoiler, etc.

Logistics field: Resin pallets, containers, plastic cardboard, CD / DVD mailing cases, bag handles, cushioning materials.

Civil engineering / architectural fields: Insulation pipes for air conditioners, concrete panels, roof insulation, drainage mass, cushion flooring, tatami mats, firewood, wood substitutes for system kitchens, bath tub lids, cocoons, trash cans, benches and tables Board etc.
Sports field: Applicable to sports shoes soles, sandals, slippers, protectors, swimsuit cups, golf packs, life jackets, and beat boards.

  Agriculture and fisheries fields: flower pots, fishing net floats, fenders, water life preservers, oil fence floats, etc.

Food packaging materials field: returnable boxes, instant ramen containers, convenience store lunch boxes, donburi bowls, food trays, packing, glass milk bottle lids, cork substitutes, teacups, dishes, cutting boards, etc. Blood transport containers, pillows, health mats, etc.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited by these examples.

In the embodiment of the present invention, each surveying was performed by the following method.
(1) Addition amount of physical foaming agent: A cylinder of physical foaming agent is connected to the injection molding machine via a pressure reducing valve, and the resin to be used is applied to the mold at the cylinder set temperature during molding and the screw rotation speed during injection. The amount of the physical foaming agent that was continuously discharged out of the system without being injected and consumed was determined from the weight loss of the cylinder, and was determined from a calibration curve that determined the relationship between the injection pressure and the injection amount of the physical foaming agent.

(2) Foaming ratio: It was determined from the specific gravity including the skin layer of the product.
(3) Average cell diameter: The cross section of the foamed part of the foam was observed with a microscope, and the average value of 10 to 20 cell diameters was obtained. Moreover, when the cell diameter exceeded the product thickness, the dimension in the direction perpendicular to the product thickness direction of the cell at a distance of 50 mm or more from the gate was defined as the cell diameter.

(4) Maximum cell diameter: The maximum cell diameter was determined as the average cell diameter.
(5) Skin layer thickness: The average value on the movable platen side and fixed platen side of the product.
(6) Melt flow rate (MFR): measured in accordance with ASTM 1238-65T with a load of 2.16 kg and a predetermined temperature displayed each time.

(Examples 1-3) (Reference Examples 1-3)
As an injection molding machine, Toshiba Machine IS-450GS-27A (clamping force 450 tons, direct pressure type clamping system), L / D is 27, screw outer diameter is 69.8mm, first stage compression part is L / D is 14D (from the bottom of the hopper, the flat part with a groove depth of 7.3 mm is 9D, and the subsequent 5D is a part where the groove depth is uniformly reduced from 7.3 mm to 3.1 mm), the second stage A screw having a compression part of 13D (a flat part having a groove depth of 11 mm is 7D and a part where the groove depth is uniformly reduced from 11 mm to 5 mm is 6D) was attached. The distance between the grooves in the screw was constant. When the cylinder moved forward most in the injection direction, a physical foaming agent injection hole with an inner diameter of 2 mm was provided in the cylinder portion corresponding to the second-stage compression portion 2D, and a check valve was provided on the outside thereof. In addition, a shut-off nozzle mechanism is provided at the tip of the cylinder. Carbon dioxide provided by a commercially available cylinder was used as a physical foaming agent, and a mechanism was provided that could be injected into the cylinder through a pressure reducing valve and a check valve attached to the cylinder. The pressure of the cylinder of carbon dioxide was 7.2 MPa, and the supply pressure to the injection molding machine was kept at 3 MPa by a pressure reducing valve. The amount of carbon dioxide injected was 1% by weight with respect to the resin.

As an injection mold, a product dimensions 95 mm × 340 mm, it can fine-tune the cavity clearance (product thickness) hydraulic molding machine, a mold structure for injection by the direct gate of molten resin from the product center It was attached to a molding machine and set so that the mold temperature was 50 ° C., the mold cooling time was 60 seconds, and the resin temperature during injection was 230 ° C. As a molding material, block polypropylene J704ZA (manufactured by Grand Polymer Co., Ltd., MFR: 5 g / 10 min (230 ° C.)) was used.

Melt in the mold during the injection resin was set at full filling the cavity tee over the gap in the unfoamed. The time from the end of injection to the start of core back was 1 second, and the core back speed was 1 mm / sec. Table 1 shows the gaps in the mold cavity at the time of injection, at the start of core back, and at the end of core back.

Injection foam molding was performed under the above conditions. Larger average cell size, there was the occurrence of flash-silver, no problem with the product shape, appearance and distribution pallets were those which can be as long as the product is not so much emphasized.
Table 1 shows the physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming magnification, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

(Comparative Example 1)
In Example 1, the resin was injected into the cavity in the same manner except that the cavity gap was 4 mm and the core back was not performed.
While foaming at the same time as injection, the resin spread into the cavity and expanded to about 75% of the volume of the cavity, but the end part changed shape with each shot, the appearance of the end part was poor, and there was no product value. .

(Comparative Example 2)
In Example 1, the cylinder of the injection molding machine was provided with a hole for injecting a physical foaming agent in the part 12D from the start part of the second stage of the screw as in Example 1, and further provided with a check valve. Replaced.
An attempt was made to inject carbon dioxide under the same conditions as in Example 1. However, the resin pressure was high and could not be injected at all. The results are shown in Table 1.

(Examples 4 to 6) (Reference Examples 4 to 6)
Injection foaming was carried out in the same manner as in Examples 1 to 3, except that 0.04% by weight of citric acid and 0.06% by weight of sodium bicarbonate were applied to polypropylene as a foam nucleating agent. Compared with Examples 1 to 3, the cell diameter was uniform and microcells were formed. Compared to Examples 1 to 3, the average cell diameter was small, and the appearance performance was more excellent.
Table 2 shows the physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation. Show. Compared to Examples 1 to 3, the average cell diameter was small, and the appearance performance was more excellent.

(Comparative Example 3)
The cavity gap was set to 4 mm, and injection into the cavity was performed in the same manner as in Example 4 except that the core back was not performed. The resin spread in the cavity while foaming at the same time as the injection, and foamed to about 75% of the volume of the cavity. However, the shape of the end portion changed with each shot, the appearance was poor, and there was no product value.
The appearance performance was not changed as compared with Comparative Example 1, and the effect of adding citric acid and sodium bicarbonate was not recognized.
Table 2 shows the physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation. Show.

(Examples 7 to 9)
In Examples 4-6, the cavity gap at the time of injection is set to 1 mm, the mold clamping pressure is eliminated at the time of injection, resin is injected into the cavity, and then the core is backed by the injection pressure, as in Examples 4-6. Molding was performed.
Compared to Examples 4 to 6, there was no occurrence of flash or silver, and the appearance performance was the same as that of the solid product.
Table 3 shows the physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming magnification, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

(Examples 10 to 12)
In Examples 7-9, polypropylene and citric acid or sodium hydrogen carbonate were mixed in the same ratio and used as pellets while being defoamed by venting at 220 degrees using a 50 mm vented single screw extruder. Produced foamed products in the same manner as in Examples 7-9.
There was no occurrence of silver and flash and the appearance performance was the same as in Examples 7-9.
Table 4 shows the physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

(Examples 13 to 17)
In Example 7, to secure the Cavity I over the gap after the core back to 4 mm, and the addition amount of citric acid and sodium bicarbonate, was except that changed as the addition amount Table 5 CO, Example 7 Similarly, a foamed product was obtained.
Table 5 shows the cylinder foam pressure, injection pressure, addition amount, cavity gap, foam product thickness, foam ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status of physical foaming agents. Show.

(Examples 18 to 20)
In Examples 7 to 9, foamed products were obtained in the same manner as in Examples 7 to 9 except that carbon dioxide was replaced with nitrogen as a physical foaming agent, the injection pressure was 4 MPa, and the addition amount was 0.7 wt%. It was.
A slight amount of flash silver was observed compared to Examples 7-9.
Table 6 shows the physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

(Examples 21 to 23)
In Examples 7 to 9, foamed products were obtained in the same manner as in Examples 7 to 9 except that 1% by weight of talc (average particle size: 10 μm) was added instead of citric acid and sodium bicarbonate as the foam nucleating agent. Got.
Table 7 shows the physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

(Examples 24-27)
In Examples 7 to 9, the resin was made of high impact polystyrene H238 (manufactured by Nippon Polystyrene Co., Ltd. MFR: 16 g / 10 min (200 ° C.)) or ABS resin Classic TMGA-501 (manufactured by Nippon A & L Co., Ltd. MFR: 32 g / 10 min. Instead of citric acid and sodium bicarbonate or talc as the foam nucleating agent so that the mold temperature is 50 ° C., the mold cooling time is 60 seconds, and the resin temperature during injection is 230 ° C. The foamed product was obtained in the same manner as in Examples 7 to 9 except that the core back amount was changed as shown in Table 8.
Shows cylinder pressure, injection pressure, addition amount, cavity gap, product thickness of foamed product, expansion ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, flash silver generation status of resin and physical foaming agent It is shown in FIG.

(Examples 28 and 29)
As the thermoplastic resin, an olefin thermoplastic elastomer, ethylene / propylene / 5-ethylidene-2-norbornene having an ethylene content of 78 mol%, an iodine value of 13 and a Mooney viscosity [MLl + 4 (100 ° C.)] of 140 is used. 60 parts by weight of oil-extended EPDM pellets obtained by blending 100 parts by weight of a polymer with 40 parts by weight of a mineral oil softener (Dyna Process Oil PW-380 manufactured by Idemitsu Kosan Co., Ltd.), an ethylene content of 8% by weight, and a melt flow rate 25 parts by weight of 10 g / 10 min (230 ° C.) propylene / ethylene block copolymer pellets, ethylene 4-methyl-1 having an ethylene content of 97 wt% and a melt flow rate of 10 g / 10 min (190 ° C.) 15 parts by weight of butene copolymer pellets and 1,3-bis (tert-butylperoxyisopropyl) benzene A mixture solution of parts by weight and 0.2 parts by weight of divinylbenzene is mixed by a tumbler blender, and this solution is uniformly adhered to the surface of the mixed pellets. The pellets are mixed with a twin screw extruder (TEM-50 manufactured by Toshiba Machine Co., Ltd.). ) Was used at 230 ° C. and subjected to dynamic heat treatment to obtain a crosslinked thermoplastic elastomer having a gel content of 95% by weight.

In Examples 7 to 9, the resin was changed to the thermoplastic elastomer obtained above, the mold temperature was set to 50 ° C., the mold cooling time was 60 seconds, and the resin temperature at the time of injection was set to 230 ° C., A foamed product was obtained in the same manner as in Examples 7 to 9 except that the time from the end of injection to the start of the core back was 2.0 seconds and the core back amount was changed as shown in Table 9. When removed from the mold, a shape larger than the dimensions of the mold was obtained.
Table 9 shows physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming magnification, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

(Examples 30 and 31)
In Examples 7-9, recycled PET (10% by weight of polyethylene recovered from the market, mixed product of 20% by weight of polypropylene) was used as the resin, 1% by weight of talc was used as the foam nucleating agent, the mold temperature was 50 ° C., and the mold The mold cooling time was set to 60 seconds, the resin temperature at the time of injection was set to 270 ° C., the time from the end of injection to the start of core back was set to 0.5 seconds, and the core back amount was changed as shown in Table 10 Produced foamed products in the same manner as in Examples 7-9.
Table 10 shows physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

(Examples 32-34)
In Examples 7 to 9, high-density polyethylene Hi-Zex TM2100J (MFR manufactured by Mitsui Chemical Co., Ltd .: MFR: 6 g / 10 min g / 10 min (190 ° C.)), ethylene-methacrylic acid copolymer Nucrel TM N1525 (Mitsui DuPont Chemical) MFR: 25 g / 10 min (190 ° C., methacrylic acid amount 15% by weight) and polyethylene-methacrylic acid ionomer resin Himiran ™ 1650 (Mitsui DuPont Chemical MFR: 5 g / 10 min (190 ° C.), zinc ion type) Are blended with the composition shown in Table 11 and set so that the mold temperature, 35 ° C., mold cooling time 60 seconds, and resin temperature at injection 180 ° C. are set, and the time from the end of injection to the start of core back is set to 1.0. Except for the seconds, foamed products were obtained in the same manner as in Examples 7-9.
Shows cylinder pressure, injection pressure, addition amount, cavity gap, product thickness of foamed product, expansion ratio, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, flash silver generation status of resin and physical foaming agent 11 shows.

(Examples 35-37)
As a resin, Grand Polypro TM J739 (Grand Polymer Co., Ltd. Block Polypropylene MFR: 90 g / 10 min (230 ° C.)) and ethylene-α-olefin rubber TAFMER TMH3530 ”(MFR Chemicals MFR: 35 g / 10 min (190 ° C.)) 20 parts by weight and pelletized at 200 ° C. with a 36 mm twin screw extruder (MFR: 70 g / 10 min (230 ° C.)), the mold is 550 × 300 mm in length and width, and on the movable platen side A rectangular ship bottom mold with a convex surface and a depth of 50mm (with hot runner (set to 200 ° C), with a two-point shut-off gate) is attached, and a skin layer (sponge layer made of expanded polypropylene (thickness 2mm) on the movable platen side ) And a thermoplastic elastomer sheet skin (thickness 0.5 mm). Can, mold temperature 50 ° C. at the time of injection, mold cooling time of 80 seconds, the resin temperature at the time of injection is set to be 230 ° C., and using carbon dioxide as a physical foaming agent. Injection at the start of the cavity -The gap was 10 mm, the gap was narrowed to 2 mm immediately after injection, and the core was backed up to 4 mm 1 second after injection.
Physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, foamed product thickness, foaming ratio, average cell diameter, maximum cell diameter, skin layer thickness, skin material wrinkles, skin material blistering Table 12 Shown in

(Example 38)
As the mold, bowl container (mouth diameter 140 mm, bottom diameter 110 mm, with a direct gate in the portion of the height 80mm bottom, when the cavity clearance 1mm bottom, cavity clearance 1mm sides) fitted with a mold , Using Grand Poly Pro TMJ707 as resin (Block Polypropylene MFR: 23 g / 10 min (230 ° C)), mold temperature is 50 ° C, mold cooling time is 60 seconds, resin temperature is 220 ° C The gap was set to 0.4 mm at the start of injection, the gap was widened while injecting to 1 mm, and then the core was backed to 2 mm. The time from the end of injection to the start of core back was set to 0.5 seconds. Carbon dioxide was used as a physical blowing agent.
Physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, side and bottom product foam thickness, foaming magnification, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, flash silver generation The situation is shown in Table 13.

(Example 39)
After after injection at the same metering position as in Example 38 in a state of open 20mm mold during injection, immediately mold cavity gap closed mold until 1.6 mm, and the core back to 2 mm. The time from mold clamping to core back was 0.2 seconds. Compared with Example 38, the expansion ratio of the side surface portion of the bowl was high.
Physical foaming agent cylinder pressure, injection pressure, addition amount, cavity gap, side and bottom product foam thickness, foaming magnification, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, flash silver generation The situation is shown in Table 13.

(Examples 40 and 41)
Grand Poly Pro TMJ 709W (block polymer made by Grand Polymer Co., Ltd. MFR: 55 g / 10 min (230 ° C.)) as the resin, and the mold of the lunch box with the shape shown in FIG. 5 is attached as the mold, and injection is performed using a film gate. The gap at the start was set to 0.2 mm, the time from the end of injection to the start of core back was 0.5 seconds, and the core was backed to 0.4 mm or 0.6 mm. The mold temperature during injection was set to 70 ° C., the mold cooling time was 50 seconds, and the resin temperature during injection was 230 ° C.
The lunch box mold shown in FIG. 5 has a film gate 23, a portion 24 for filling side dishes, uneven portions 25 for improving bending strength, a partition portion 26, uneven portions 27 for improving bending strength, and a portion 28 for filling rice. Is provided.
Table 14 shows the cylinder foam pressure, injection pressure, addition amount, cavity gap, foam product thickness, foaming magnification, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status of physical foaming agents. Show.

(Examples 42 and 43)
Gland Polypro TMJ705 (Grand Polymer Co., Ltd. Block Polypropylene MFR: 10 g / 10 min (230 ° C.)) as the mold is attached with a mold of A4 file with the shape shown in FIG. Ejected. The file mold of FIG. 6 is provided with a file cover portion 29, a spine cover portion 30, a gate 31, a hinge portion 32, and a metal fitting attachment portion 33.
The mold is chamfered so that the flange portion of the file has a circular edge. The time to start core back is 0.5 seconds, core back to 1.5 mm or 2 mm, and then compressed to 1.4 mm or 1.9 mm gap, respectively, after 5 seconds. Prevented.
Table 15 shows physical foaming agent cylinder pressure, injection pressure, amount added, cavity gap, foam product thickness, foaming magnification, average cell diameter, maximum cell diameter, skin layer thickness, smoothness, and flash silver generation status. Show.

The thermoplastic resin foam provided by the present invention is a thermoplastic resin foam having a good appearance due to the smoothness and rigidity of the skin layer.
The present invention also provides a thermoplastic resin foam that is highly lightweight in the case of high foaming and capable of obtaining strong rigidity.
As the thermoplastic resin of the present invention, polypropylene, modified polypropylene, amorphous polystyrene-based resin, polycarbonate, or the like is preferably used, and the above-described excellent thermoplastic resin foam is provided.
The thermoplastic resin foam provided according to the present invention is a foam that can be suitably used for foam products such as automobile-related parts, OA equipment parts, electrical product-related parts, heat insulating materials, and packaging materials.

It is sectional drawing of the injection foam molding machine which shows one embodiment of the shaping | molding method of this invention. It is a fragmentary sectional view of the physical foaming agent injection hole surrounding part of the injection foam molding machine of FIG. It is a fragmentary sectional view which shows the state which the check valve screw provided in the physical foaming agent injection hole of FIG. 2 closed. It is the schematic diagram drawn as a continuous top view in order to show the state of the molten resin which flows through the groove part of the 2nd step | paragraph compression part of a screw. It is a top view of the lunch box which is an example of a molded article obtained by injection foaming of the present invention. It is a top view which shows the file which is an Example of the molded article obtained by the injection foam molding of this invention.

1. Mold core (moving side)
2. Mold shell (fixed side)
3. Product 4. 4. Shut-off valve 5. Hot runner 6. Injection molding machine nozzle Injection molding machine cylinder8. Injection molding machine two-stage compression cylinder9. First stage compression section 10. Second stage compression section 11. 11. Depressurized portion due to molten resin starvation Heater 13. Physical foaming agent cylinder14. Foam supply pipe 15. Cylinder valve 16. Pressure reducing valve 17. Check valve 18. Physical foaming agent injection hole 19. Hopper 20. Physical foaming agent supply piping 21. Screw feather 22. A lump of physical foaming agent that is not mixed in the resin.
23. Film gate 24. The part that stuffs the side dishes.
25. Unevenness to improve bending strength 26. Partition part 27. Unevenness to improve bending strength 28. Part of stuffing rice 29. File cover page 30. File back cover 31. Gate 32. Hinge portion formed by crushing the foamed portion by compression after foaming 33. Filing bracket mounting part

Claims (11)

In injection foam molding using an injection molding machine having a two-stage compression screw to supply a physical foaming agent in the gaseous state from the middle of the cylinder,
(1) A physical foaming agent in a gaseous state is supplied from a storage tank at a pressure lower than the storage pressure by a pressure difference from the cylinder of the injection molding machine,
(2) supplying the physical foaming agent in a range from the starting point of the second stage of the screw in the injection direction to a length 9 times the outer diameter of the screw when the screw is most advanced in the injection direction; and (3) The cavity of the mold of the injection molding machine is almost atmospheric pressure, the cavity volume is kept lower than the amount of the metered resin , and the cavity volume at the injection pressure is injected while injecting the molten resin mixed with the physical foaming agent. It is obtained by injection foam molding of thermoplastic resin by expanding the volume after injection filling and expanding the volume in the cavity,
A thermoplastic resin foam that satisfies the following requirements (i) to (iv).
(I) The thickness of the skin layer is 0.1 mm or more,
(Ii) The thickness of the foam is 0.1 to 100 mm, and (iii) the average cell diameter is 0.150 to 1 mm.   An inorganic filler having an average particle diameter of 0.5 to 10 μm as a foam nucleating agent is added to the thermoplastic resin in an amount of 0.1 to 5% by weight based on the resin, and / or a chemical foaming agent or a decomposition product thereof, The thermoplastic resin foam according to claim 1, wherein the thermoplastic resin foam is contained in an amount of 0.01 to 1% by weight.   The thermoplastic resin foam according to claim 1 or 2, wherein the thermoplastic resin is polypropylene and the expansion ratio is 1 to 5 times.   The thermoplastic resin foam according to claim 1 or 2, wherein the thermoplastic resin is a modified polypropylene and has an expansion ratio of 1 to 10.   The thermoplastic resin foam according to claim 1 or 2, wherein the thermoplastic resin is an amorphous polystyrene-based resin or polycarbonate, and an expansion ratio is 1 to 20 times. The thermoplastic resin foam according to claim 1 or 2, wherein the thermoplastic resin is a thermoplastic elastomer. The automobile related part which consists of a thermoplastic resin foam in any one of Claims 1-6 . OA equipment part which consists of a thermoplastic resin foam in any one of Claims 1-6 . An electrical product-related part comprising the thermoplastic resin foam according to any one of claims 1 to 6 . The heat insulating material which consists of a thermoplastic resin foam in any one of Claims 1-6 . A packaging material comprising the thermoplastic resin foam according to any one of claims 1 to 6 .

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