JP4279651B2 - Screw, injection molding apparatus and foam manufacturing method - Google Patents

Description

  The present invention relates to a screw, an injection molding apparatus, and a foam manufacturing method.

Conventionally, the manufacture of the foam using an injection molding apparatus is performed. As a method for producing a foam, there is a chemical foaming method in which a foam is obtained by adding a chemical foaming agent to a thermoplastic resin as a raw material, and melt-kneading and foaming (for example, see Patent Document 1).
Such a chemical foaming method is widely used because it is simple to add a chemical foaming agent to a thermoplastic resin as a raw material and knead it.

JP 2003-2111485 A (second page)

  In general, in the chemical foam molding method, a screw for ordinary thermoplastic resin injection molding that does not contain a foaming agent is used. Such an ordinary thermoplastic resin injection molding screw has a supply part for transferring the raw material from the raw material supply side toward the downstream side, a compression part for compressing and plasticizing the raw material, and weighing the plasticized raw material. Since it is configured as a metering unit that pushes out in a fixed amount and does not have a shape that takes into account the dispersion of the foaming agent and foaming gas, for example, when compressed in the compression unit, the foaming gas is pushed out to the raw material supply side Thus, there is a problem that the escape of the foaming gas from the plasticized thermoplastic resin is promoted. Therefore, it becomes difficult to obtain a foam in which foam cells are uniformly dispersed.

  An object of the present invention is to provide a screw, an injection molding apparatus, and a method for producing a foam capable of obtaining a foam in which foam cells are uniformly dispersed.

The screw of the present invention is a screw used for chemical foaming and is provided in a cylinder to which raw materials are supplied, and is used for chemical foaming, and supplies raw materials containing a foaming agent and a thermoplastic resin. A first stage having a supply section for transferring from the side toward the downstream side, a compression section for compressing and plasticizing the raw material from the supply section, and a measuring section for kneading and weighing the raw material plasticized by the compression section And a compression unit that is provided downstream of the first stage and compresses and plasticizes the raw material extruded from the first stage, and includes a weighing unit that kneads and measures the plasticized plastic material in the compression unit. A second stage, the groove depth of the supply section of the first stage is H1, the groove depth of the weighing section is H2, the groove depth of the compression section of the second stage is H3, and the groove depth of the weighing section When H4 is H4, it is indicated by H1 / H2. The compression ratio of the first stage is larger than the compression ratio of the second stage indicated by H3 / H4, and the groove depth H4 of the measuring part of the second stage is the groove depth of the measuring part of the first stage. It is characterized by being shallower than H2.
In addition, the groove depth of the compression part of the second stage gradually decreases toward the measuring part of the second stage, but the groove depth H3 refers to the deepest part of the compression part of the second stage.
Here, chemical foam molding means that the foaming agent itself volatilizes and releases gas under a predetermined temperature and pressure, thereby forming a foam cell, or the foaming agent decomposes to foam the gas, This means what forms a foam cell.
As foaming agents used for chemical foaming, chemical foaming agents such as azodicarbonamide, N, N-dinitrosopentatetramine, azobisisobutyronitrile, citric acid, sodium bicarbonate, butane, pentane, dichlorodifluoromethane, etc. Not only an inorganic compound containing crystal water, but also an organic compound containing water or the like in a microcapsule can be exemplified.

  The thermoplastic resin may be any material that can be subjected to normal foam molding, such as styrene resin (polystyrene, butadiene / styrene copolymer, acrylonitrile / styrene copolymer, acrylonitrile / butadiene, styrene copolymer, etc. ), Polyethylene, polypropylene, ethylene-propylene resin, ethylene-ethyl acrylate resin, polyvinyl chloride, polyvinylidene chloride, polybutene, polycarbonate, polyacetal, polyphenylene oxide, polyvinyl alcohol, polymethacrylate, saturated polyester resin (polyethylene terephthalate, polybutylene terephthalate) Etc.), biodegradable polyester resins (condensates of hydroxycarboxylic acids such as polylactic acid, and condensation of diols and dicarboxylic acids such as polybutylene succinate) Things like), polyamide resins, polyimide resins, fluorocarbon resins and the like.

According to the present invention, since the screw includes two stages, the raw material is kneaded at a temperature lower by at least 20 ° C. than the gas foaming temperature of the foaming agent in the first stage, and in the second stage, The raw material can be kneaded at a temperature equal to or higher than the gas foaming temperature of the foaming agent. Thereby, in the compression part and the measurement part of the first stage, the foaming agent can be dispersed in the thermoplastic resin without foaming in a state where the viscosity of the thermoplastic resin is high, and the escape of foaming gas is prevented. Can do. And in the compression part and metering part of a 2nd stage, since a raw material can be knead | mixed above the gas foaming temperature of a foaming agent, while the viscosity of a thermoplastic resin becomes small, a foaming agent foams. Since the viscosity of the thermoplastic resin on the first stage side is high, the foaming gas is difficult to escape to the first stage side, the escape of the foaming gas can be prevented, and the foaming gas is uniformly dispersed.
As described above, the temperature of the first stage and the second stage can be changed and the foamed cells formed by the foamed gas are uniformly dispersed by configuring the screw with two stages as described above. A foam can be obtained.
Moreover, in such this invention, the compression ratio of the 1st stage is made larger than the compression ratio of the 2nd stage. In general, the larger the compression ratio, the easier it is for the foaming gas to escape, but by making the compression ratio of the second stage smaller than the compression ratio of the first stage, it is possible to prevent the escape of foaming gas in the second stage. it can.
Further, according to the present invention, since the groove depth H4 of the weighing unit of the second stage is shallower than the groove depth H2 of the weighing unit of the first stage, in the weighing unit of the second stage The foaming gas is difficult to escape to the first stage side. This makes it possible to obtain a foam in which foam cells are more uniformly dispersed.

An injection molding apparatus according to the present invention includes a cylinder to which a raw material containing a foaming agent and a thermoplastic resin is supplied, and a screw provided in the cylinder so as to be rotatable and movable back and forth, and is used for chemical foam molding. An injection molding apparatus, wherein the screw is any one of the screws described above.
According to such this invention, since the injection molding apparatus of this invention is equipped with one of the screws mentioned above, there can exist an effect similar to one of the screws mentioned above. That is, a foam in which foam cells are uniformly dispersed can be obtained.
Conventionally, a physical foaming method in which a foam is formed by degassing the supercritical gas after infiltrating the supercritical gas into the thermoplastic resin has been performed. The injection molding device used requires equipment for injecting supercritical gas into the thermoplastic resin. On the other hand, since the injection molding apparatus according to the present invention is used for chemical foam molding, a facility for injecting the supercritical gas into the thermoplastic resin becomes unnecessary. Therefore, in the injection molding apparatus of the present invention, the apparatus can be downsized as compared with the injection molding apparatus used in the physical foaming method.

The foam production method of the present invention is a foam production method for producing a foam by foaming a foaming agent in a thermoplastic resin, and is performed using the above-described injection molding apparatus. And a feeding step of feeding the raw material containing the thermoplastic resin into the injection molding device, and a feeding step of feeding the fed raw material toward the downstream side by the supply part of the first stage of the screw of the injection molding device. The first compression step of plasticizing the raw material by the compression unit of the first stage, and the first measurement of kneading the raw material by the measurement unit of the first stage, weighing it, and extruding it quantitatively toward the second stage The raw material is compressed and plasticized by the process and the compression part of the second stage, and the raw material is kneaded and measured by the weighing part of the second stage, and the raw material is fed from the screw tip into the cylinder tip. Push out Characterized in that it comprises a two metering process.
According to such this invention, since the injection molding apparatus mentioned above is used, there can exist an effect similar to the injection molding apparatus mentioned above. That is, a foam in which foam cells are uniformly dispersed can be obtained.

At this time, from the transfer step to the first metering step, the raw material is transferred, plasticized, and metered at a temperature that is at least 20 ° C. lower than the gas foaming temperature of the foaming agent, the second compression step, and the second metering step. Then, it is preferable to plasticize and measure the raw material at a temperature equal to or higher than the gas foaming temperature of the foaming agent.
According to the present invention, the steps from the transfer step to the first metering step are performed at a temperature that is at least 20 ° C. lower than the gas foaming temperature of the foaming agent, and in these steps, the thermoplastic resin has a high viscosity. Thus, the foaming agent can be dispersed in the thermoplastic resin without foaming, and the escape of foaming gas can be prevented.
And in a 2nd compression process and a 2nd measurement process, since a raw material can be knead | mixed above the gas foaming temperature of a foaming agent, while the viscosity of a thermoplastic resin becomes low, a foaming agent foams. Since the viscosity of the thermoplastic resin on the first stage side of the screw is high, it is difficult for the foaming gas to escape to the first stage side, the escape of the foaming gas can be prevented, and the foaming gas is uniformly dispersed.
Thereby, the foam in which the foam cells are uniformly dispersed can be obtained.

Further, in the present invention, in the second measuring step, the raw material moves to the tip of the cylinder and the pressure from the screw is not applied to the raw material until the measurement is completed, and the back pressure from the screw is applied after the measurement is completed. It is preferable to control to increase the raw material pressure.
Here, the raw material is not pressurized until the second weighing step is completed, but the pressurization referred to here means intentionally applying pressure to the raw material, for example, when transferring the raw material, By extruding the raw material, the pressure applied to the raw material is not included.

Generally, in the measuring process, the back pressure from the screw is adjusted, the raw material pressure is increased, the raw material is plasticized, and the measurement is performed. By doing in this way, escape of foaming gas can be prevented. When measuring, the screw moves backward due to the pressure of the raw material moved into the cylinder tip, and the metering ends when a predetermined amount of material accumulates in the cylinder tip. It takes time to weigh because it hinders the retreat.
In the present invention, since the pressure is not applied to the raw material until the measurement is completed, the raw material can be measured smoothly. And since predetermined back pressure is applied after measurement is completed, escape of foaming gas can be prevented.
As described above, the time required for measurement can be shortened, and a foamed body in which foamed cells are uniformly dispersed can be obtained.
Here, it is preferable that the pressure of the raw material after the measurement is completed (that is, the back pressure from the screw) is 3 MPa or more and 20 MPa or less.
When the pressure is less than 3 MPa, the foaming gas may be easily released from the thermoplastic resin. Further, when the pressure exceeds 20 MPa, the foaming gas may not easily diffuse into the thermoplastic resin.

Furthermore, in this invention, it is preferable that the average particle diameter of a foaming agent is 10 micrometers or less.
According to such this invention, it becomes easy to disperse | distribute a foaming agent uniformly in the thermoplastic resin contained in a raw material by the average particle diameter of a foaming agent being 10 micrometers or less. In addition, by setting the average particle size of the foaming agent to 10 μm or less, the number of foamed cells per unit volume can be increased compared to the case where the particle size exceeds 10 μm, and thereby the foamed cells are more uniformly dispersed. A foam can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an injection molding apparatus 1 according to this embodiment.
The injection molding apparatus 1 is for producing a foam by chemical foam molding, and includes an injection molding apparatus main body 11 and a mold 12.
Here, chemical foam molding means that the foaming agent itself volatilizes and releases gas under a predetermined temperature and pressure, thereby forming a foam cell, or the foaming agent decomposes to foam the gas, This means what forms a foam cell.
The injection molding apparatus main body 11 plasticizes the raw material to be charged and injects it into the mold 12. The cylinder 111 having the heater 111 </ b> A, the screw 2 disposed in the cylinder 111, and the raw material in the cylinder 111. , A hydraulic device 114 that rotates the screw 2, and a nozzle 115 that connects the cylinder 111 and the mold 12.
The raw material charged from the hopper 113 and heated by the heater 111 </ b> A of the cylinder 111 is plasticized by the screw 2, moves to the nozzle 115 side, and is injected into the mold 12 through the nozzle 115 at a high pressure.

Here, the raw material contains a thermoplastic resin, a foaming agent and the like.
The thermoplastic resin is not particularly limited as long as it can be foam-molded. For example, styrene resin (polystyrene, butadiene / styrene copolymer, acrylonitrile / styrene copolymer, acrylonitrile / butadiene, styrene copolymer, etc.), polyethylene, Polypropylene, ethylene-propylene resin, ethylene-ethyl acrylate resin, polyvinyl chloride, polyvinylidene chloride, polybutene, polycarbonate, polyacetal, polyphenylene oxide, polyvinyl alcohol, polymethacrylate, saturated polyester resin (polyethylene terephthalate, polybutylene terephthalate, etc.), raw Degradable polyester resin (hydroxycarboxylic acid condensate such as polylactic acid, diol and dicarboxylic acid condensate such as polybutylene succinate), Polyamide resins, polyimide resins, fluorocarbon resins and the like.

In addition, as a foaming agent, not only chemical foaming agents such as azodicarbonamide, N, N-dinitrosopentatetramine, azobisisobutyronitrile, citric acid, sodium bicarbonate, butane, pentane, dichlorodifluoromethane, crystal Examples thereof include inorganic compounds containing water, and those containing an organic solvent, water and the like in the microcapsule. Here, the average particle diameter of the foaming agent is preferably 10 μm or less.
Furthermore, the raw material may contain fillers such as talc and reinforcing fibers as necessary in addition to the foaming agent and thermoplastic resin, and various commonly used additives such as pigments, lubricants, antistatic agents, A stabilizer or the like may be blended.

The screw 2 is provided so as to be rotatable and advanceable / retreatable in the cylinder 111, and a thread groove is formed on the outer surface thereof. As shown in FIG. 2, the screw 2 includes a first stage 21 including a supply unit 211, a first compression unit 212, and a first weighing unit 213 from the hopper 113 side (raw material supply side), a second compression unit 221, A second stage 22 including a second weighing unit 222, a head unit 23 provided at the tip of the second stage 22, a connecting unit 24 that couples the head unit 23, and the second weighing unit 222 of the second stage 22; Is provided.
The diameter D of such a screw 2 is, for example, 50 mm, the total length L is, for example, 1000 mm, and the ratio (L / D) of the diameter D of the screw 2 to the total length L is, for example, 20.

The supply unit 211 of the first stage 21 is for transferring the raw material charged from the hopper 113 toward the downstream side (mold 12 side), and the groove depth H1 of the screw groove is constant. . For example, H1 is about 9 mm. The number of pitches of the supply unit 211, that is, the number of screw grooves is, for example, 8.
The first compression unit 212 is for compressing and plasticizing the raw material transferred from the supply unit 211, and the groove depth of the screw groove is from the supply unit 211 side to the second stage 22 side. It is getting shallower. Thereby, the thermoplastic resin in the conveyed raw material can be gradually compressed and melted by shear heat generation or friction heat generation. The number of pitches of the first compression unit 212 is less than the number of pitches of the supply unit 211, for example, five.
The 1st measurement part 213 knead | mixes the raw material transferred from the 1st compression part 212, and also plasticizes and makes it uniform. In the first metering unit 213, the raw material is transferred to the second stage 22 at a constant speed and a constant amount.
The groove depth H2 of the first measuring unit 213 is constant and is shallower than the groove depth H1 of the supply unit 211, and is, for example, about 3 mm. As described above, by reducing the groove depth H2 of the first measuring unit 213, heat from the cylinder 111 is easily transferred to the raw material, and the raw material is made uniform.
Further, the number of pitches of the first measuring unit 213 is, for example, 1.

The second compression part 221 of the second stage 22 is for compressing and plasticizing the raw material from the first metering part 213 of the first stage 21, and the groove depth of the thread groove is the first compression part. Similar to 212, it gradually becomes shallower from the first weighing unit 213 side toward the second weighing unit 222 side.
Here, the deepest groove depth of the second compression portion 221 is H3. The groove depth H3 is deeper than the groove depth H2 of the first measuring unit 213 and shallower than the groove depth H1 of the supply unit 211. For example, H3 is about 6.25 mm.
The number of pitches of the second compression unit 221 is, for example, 4.

The second measuring unit 222 of the second stage 22 kneads the raw material from the compression unit 221 and further plasticizes and homogenizes it. The second metering unit 222 measures the raw material and accumulates it at the tip of the cylinder 111 in a fixed amount.
The groove depth H4 of the second measuring unit 222 is constant and is shallower than the groove depth H2 of the first measuring unit 213 of the first stage 21, for example, about 2.5 mm. Further, the number of pitches of the second measuring unit 222 is two.

  The compression ratio (H1 / H2) of the screw 2 in the first stage 21 is larger than the compression ratio (H3 / H4) of the second stage 22. For example, when H1 = 9 mm, H2 = 3 mm, H3 = 6.25 mm, and H4 = 2.5 mm, the compression ratio of the first stage 21 is 3, and the compression ratio of the second stage 22 is 2.5. Become.

  In the cylinder 111 in which the screw 2 as described above is disposed, the set temperature of the portion from the hopper 113 to the first stage 21 is set to a temperature that is at least 20 ° C. lower than the gas foaming temperature of the raw material foaming agent. The temperature of the second stage 22 is set to be equal to or higher than the gas foaming temperature of the foaming agent.

As shown in FIG. 1, the mold 12 again includes a fixed mold 12A attached to the nozzle 115, and a movable mold 12B that can be moved forward and backward with respect to the fixed mold 12A. A mold clamping device (not shown) is used for the advance and retreat.
A gap 121 having a predetermined shape is formed between the fixed mold 12A and the movable mold 12B. The raw material injected from the injection molding apparatus main body 11 is filled in the gap 121, and the filled raw material is molded into the shape of the gap 121.

Next, the manufacturing method of the foam using the above injection molding apparatuses 1 is demonstrated.
First, the raw material is charged into the hopper 113 of the injection molding apparatus 1 (charging process).
Next, the raw material is transferred to the downstream side (first compression unit 212 side) by the supply unit 211 of the first stage 21 of the screw 2 (transfer process).
Furthermore, in the 1st compression part 212, a raw material is compressed and plasticized (1st compression process).
Then, the raw material plasticized by the first compression unit 212 is transferred to the first metering unit 213, kneaded by the first metering unit 213, and further plasticized and homogenized (first metering step).
As described above, in the first stage 21 portion, the temperature of the cylinder 111 is set to a temperature that is at least 20 ° C. lower than the gas foaming temperature of the raw material foaming agent. Without being dispersed in the thermoplastic resin. Further, since the set temperature of the cylinder 111 is set to a low temperature that is at least 20 ° C. lower than the gas foaming temperature of the foaming agent, the viscosity of the thermoplastic resin is high.

Next, the raw material is quantitatively fed from the first metering unit 213 to the second compression unit 221 of the second stage 22. In the 2nd compression part 221, a raw material is compressed and plasticized (2nd compression process).
Further, the raw material plasticized by the second compression unit 221 is kneaded and measured by the second measuring unit 222 (second measuring step).
In the second stage 22 portion, the temperature of the cylinder 111 is set to be equal to or higher than the gas foaming temperature of the foaming agent, so that the foaming agent is foamed and the foamed gas is dispersed in the thermoplastic resin. Further, since the second stage portion is set to a high temperature equal to or higher than the gas foaming temperature of the foaming agent, the viscosity of the thermoplastic resin is lower than that of the first stage 21.
The raw material weighed by the second weighing unit 222 is accumulated at the tip of the cylinder 111 in a fixed amount.

Here, in this embodiment, the screw 2 is rotated at the same position until the weighing in the second weighing step is completed, and the pressure (excluding the pressure due to being pushed out during transfer) is applied to the raw material. Almost no added.
When the metering is completed, the back pressure of the screw 2 is controlled, a predetermined pressure is applied to the raw material, and the raw material pressure is increased.
Here, the pressure applied to the raw material (the pressure actually applied to the raw material) is preferably 3 MPa or more and 20 MPa or less. When the pressure is less than 3 MPa, the foaming gas may be easily released from the thermoplastic resin. In addition, when the pressure exceeds 20 MPa, the foaming gas may not easily diffuse into the thermoplastic resin.

Next, the measured raw material is injected into the gap 121 of the mold 12 by moving the screw 2 forward.
Then, after the filling of the raw material into the mold 12 is completed, the movable mold 12B of the mold 12 is retracted. After cooling and solidifying in this state and a predetermined cooling time has elapsed, the mold 12 is opened and the foamed product is taken out.

According to this embodiment, the following effects can be achieved.
(1) Since the screw 2 includes two stages 21 and 22, the raw material is kneaded at a temperature lower by at least 20 ° C. than the gas foaming temperature of the foaming agent in the first stage 21, and in the second stage 22, The raw material can be kneaded at a temperature equal to or higher than the gas foaming temperature of the foaming agent. Thereby, in the 1st compression part 212 and the 1st measurement part 213 of the 1st stage 21, in a thermoplastic resin used as a state with a high viscosity, it can be made to disperse without foaming, and foaming gas Omission can be prevented.
And in the compression part 221 and the 2nd measurement part 222 of the 2nd stage 22, since a raw material can be knead | mixed above the gas foaming temperature of a foaming agent, while the viscosity of a thermoplastic resin becomes low, a foaming agent foams. . Since the raw material pressure on the first stage 21 side is applied to the raw material on the second stage 22 side, and the viscosity of the thermoplastic resin on the first stage 21 side is high, the foaming gas is on the first stage 21 side. It is difficult to escape, the escape of the foam gas can be prevented, and the foam gas is uniformly dispersed.
In this way, by configuring the screw 2 to include the two stages 21 and 22, the temperature at which the raw materials in the first stage 21 and the second stage 22 are kneaded can be changed, and foaming formed by foaming gas. A foam in which the cells are uniformly dispersed can be obtained.

(2) The compression ratio of the first stage 21 is made larger than the compression ratio of the second stage 22. In general, the larger the compression ratio, the easier the foaming gas escapes. However, by making the compression ratio of the second stage 22 smaller than the compression ratio of the first stage 21, the foaming gas escapes in the second stage 22. Can be prevented.
As described above, since the viscosity of the raw material is high on the first stage 21 side and the temperature of the cylinder 111 is set lower than the foaming temperature, the foaming agent is difficult to foam. Therefore, even if the compression ratio of the first stage 21 is increased, there is no possibility that the foaming gas will escape.
(3) Since the groove depth H4 of the second measuring unit 222 of the second stage 22 is shallower than the groove depth H2 of the measuring unit 213 of the first stage 21, the second measuring unit of the second stage 22 At 222, the foaming gas is less likely to escape to the first stage 21 side. This makes it possible to obtain a foam in which foam cells are more uniformly dispersed.

(4) Generally, in the weighing process, the raw material is plasticized and measured while applying back pressure to the raw material. By doing in this way, escape of foaming gas can be prevented. However, when measuring, the screw will move backward due to the pressure of the raw material moved into the tip of the cylinder, and when a predetermined amount of raw material has accumulated in the tip of the cylinder, the measurement will end. Since it prevents the screw from moving backward, it takes time to weigh.
In this embodiment, since the pressure is not applied to the raw material until the measurement in the second measuring step is completed, the raw material can be measured smoothly. And since predetermined back pressure is applied after measurement is completed, escape of foaming gas can be prevented.
As described above, the time required for measurement can be shortened, and a foamed body in which foamed cells are uniformly dispersed can be obtained.
(5) Furthermore, in this embodiment, since the average particle diameter of the foaming agent is 10 μm or less, the foaming agent is easily dispersed uniformly in the thermoplastic resin. Moreover, compared with the case where a particle size exceeds 10 micrometers, the number of the foam cells per unit volume can be increased, and, thereby, the foam in which the foam cells were disperse | distributed more uniformly can be obtained.

(6) Conventionally, a physical foaming method for forming a foam by degassing the supercritical gas after infiltrating the supercritical gas into the thermoplastic resin has been performed. The injection molding apparatus used in the above requires equipment for injecting the supercritical gas into the thermoplastic resin. On the other hand, the injection molding apparatus 1 of the present embodiment is used for chemical foam molding, and does not require equipment for injecting the supercritical gas into the thermoplastic resin. Therefore, in the injection molding apparatus 1 of this embodiment, the apparatus can be downsized as compared with the injection molding apparatus used in the physical foaming method.
(7) Furthermore, in this embodiment, chemical foam molding is performed, and the foaming ratio can be freely controlled by the amount of foaming agent added, etc., so the shape, dimensions, etc. of the foam are molded with high accuracy. It becomes possible.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the second embodiment, in the second measuring step, the raw material moves to the tip of the cylinder 111 and the pressure from the screw 2 is not applied to the raw material until the measurement is completed. Although the pressure is applied to the raw material, the present invention is not limited to this, and the pressure from the screw 2 may be applied to the raw material while measuring. By doing so, although time is required for measurement, since measurement is performed while pressure is applied, it is possible to more reliably prevent the escape of the foaming gas.

Furthermore, in the said embodiment, although the groove depth H4 of the 2nd measurement part 222 of the 2nd stage 22 was shallower than the groove depth H2 of the 1st measurement part 213 of the said 1st stage 21, it is not restricted to this. Alternatively, the depth may be the same, and the groove depth of the weighing part of the second stage may be deeper than the groove depth of the weighing part of the first stage.
Moreover, in the said embodiment, although the compression ratio of the 2nd stage 22 shall be smaller than the compression ratio of the 1st stage 21, it is not restricted to this, For example, the compression ratio of a 2nd stage is set to the compression ratio of a 1st stage. May be larger.
Even in this case, since the viscosity of the thermoplastic resin on the first stage side is high and the foam gas on the second stage side is difficult to escape to the first stage side, the escape of the foam gas does not occur. It can be prevented and the foaming gas is uniformly dispersed.
Moreover, in the said embodiment, although the average particle diameter of the foaming agent was 10 micrometers or less, it is good not only as this but exceeding 10 micrometers. In this case, the raw material may be kneaded more strongly in order to uniformly disperse the foaming agent in the thermoplastic resin.

In order to confirm the effect of the present invention, the following experiment was conducted.
A foam was manufactured using the same injection molding apparatus as in the above embodiment.
[Example 1]
(material)
5 parts by weight of a foaming agent was added to 100 parts by weight of the thermoplastic resin.
(1) Masterbatch pellets containing 20 wt% of a blowing agent containing carbon dioxide as a blowing agent (ewakasei trade name: EE205)
(2) Thermoplastic resin polypropylene (trade name: IDEMITSU PP: J966HP)
MFR (melt flow rate) 30g / min

(Screw)
The specification of the used screw is the same as that of the above embodiment.
(1) First stage supply section: 8 pitches, groove depth 9 mm
1st compression part: 5 pitch 1st measurement part: 1 pitch, groove depth 3mm
Compression ratio: 3
(2)
Second compression part: 4 pitches Second weighing part: 2 pitches, groove depth 2.5 mm
Compression ratio: 2.5
(Production method)
The manufacturing method is the same as that of the above embodiment, but detailed conditions are shown below.
The set temperature of the cylinder was 160 ° C. from the hopper to the first stage of the screw. Moreover, the part of the 2nd compression part of the 2nd stage was 190 degreeC, and the part of the 2nd measurement part was 200 degreeC.
First, the raw material was charged into the hopper, and the same first compression step, first weighing step, second compression step, and second weighing step as in the above embodiment were performed.
Here, the back pressure applied to the raw material from the screw before the end of the second measuring step is set to 0, and after the second measuring step is completed, the back pressure applied to the raw material is controlled to 10 MPa by controlling the back pressure of the screw. did.
Then, the raw material maintained at 10 MPa was injected into the 2 mm gap of the mold, and after filling the raw material, the movable mold was retracted 2 mm.

[Example 2]
In Example 2, the back pressure applied from the screw to the raw material was set to 2 MPa until the second measuring step was completed, and no pressure was applied to the raw material after the second measuring step was completed. Other points are the same as those of the first embodiment.

[Comparative Example 1]
The same raw material as in Embodiment 1 was used.
(Screw specifications)
In the comparative example 1, the general full flight screw provided with a supply part, a compression part, and a measurement part was used.
Supply section: 10 pitches, groove depth 8.4mm
Compression part: 7 pitch Weighing part: 3 pitch, groove depth 2.8mm
Compression ratio: 3 (Damage is used for 1 pitch at the tip of 3 pitches in the measuring section)
(Production method)
The raw material was introduced from the hopper, and the raw material was supplied downstream by the screw supply unit. Next, the raw material was compressed and plasticized in the compression section. Furthermore, it knead | mixed in the measurement part, further plasticized and homogenized, and transferred in the screw front-end | tip part. Here, a pressure (back pressure) of 10 MPa was applied to the raw material while measuring.
Then, the raw material maintained at 10 MPa was injected into the 2 mm gap of the mold, and after filling the raw material, the movable mold was retracted 2 mm.

[Comparative Example 2]
A back pressure of 5 MPa was applied to the raw material while weighing. The other points are the same as in Comparative Example 1.

[Results and Evaluation of Example 1 and Comparative Example 1]
The results of Example 1 are shown in FIG. Moreover, the result of the comparative example 1 is shown in FIG. These FIG.3 and FIG.4 is a photograph which shows the cross section of a foam.
In Example 1, it was confirmed that the foamed cells were uniformly distributed. On the other hand, in Comparative Example 1, it was confirmed that the foamed cells were not uniformly dispersed, and the variation in the diameter of the foamed cells was large.
From the above, it was possible to confirm the effect of the present invention that a foam in which foam cells were uniformly dispersed could be obtained.

[Results and Evaluation of Example 2 and Comparative Example 2]
The result of Example 2 is shown in FIG. Moreover, the result of the comparative example 2 is shown in FIG. These FIG.5 and FIG.6 is a photograph which shows the cross section of a foam.
In Example 2, the back pressure applied to the raw material from the screw by 2 MPa until the end of the second measuring step was set to 2 MPa, and after the second measuring step was completed, no pressure was applied to the raw material, but the foaming gas did not escape, It was confirmed that the foamed cells were uniformly dispersed.
In Comparative Example 2, since the pressure applied to the raw material was small, it was confirmed that the foaming gas escaped and the distribution of the foamed cells was uneven.
From the above, it was possible to confirm the effect of the present invention that a foam in which foam cells were uniformly dispersed could be obtained.

  The present invention can be used for production of a foam by a chemical foaming method.

The schematic diagram which shows the injection molding apparatus concerning embodiment of this invention. The schematic diagram which shows the principal part of the said injection molding apparatus. The figure which shows the cross section of the foam of Example 1. FIG. The figure which shows the cross section of the foam of the comparative example 1. FIG. The figure which shows the cross section of the foam of Example 2. FIG. The figure which shows the cross section of the foam of the comparative example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection molding apparatus 2 Screw 21 1st stage 22 2nd stage 111 Cylinder 211 Supply part 212 1st compression part 213 1st measurement part 221 2nd compression part 222 2nd measurement part

Claims (6)

It is a screw used for chemical foaming as it is provided in a cylinder to which raw materials are supplied and can be rotated and moved back and forth.
A supply unit for transferring a raw material containing a foaming agent and a thermoplastic resin from the raw material supply side toward the downstream side, a compression unit for compressing and plasticizing the raw material from the supply unit, and a raw material plasticized by the compression unit A first stage equipped with a weighing unit for kneading and weighing;
A second unit provided downstream of the first stage, and includes a compression unit for compressing and plasticizing the raw material extruded from the first stage, and a measuring unit for kneading and weighing the raw material plasticized by the compression unit. With a stage ,
When the groove depth of the supply part of the first stage is H1, the groove depth of the weighing part is H2, the groove depth of the compression part of the second stage is H3, and the groove depth of the weighing part is H4,
The compression ratio of the first stage indicated by H1 / H2 is greater than the compression ratio of the second stage indicated by H3 / H4,
The screw characterized in that the groove depth H4 of the weighing part of the second stage is shallower than the groove depth H2 of the weighing part of the first stage. An injection molding apparatus used for chemical foam molding, comprising a cylinder to which a raw material containing a foaming agent and a thermoplastic resin is supplied, and a screw provided in the cylinder so as to be rotatable and movable back and forth.
2. The injection molding apparatus according to claim 1, wherein the screw is the screw according to claim 1. A foam production method for producing a foam by foaming a foaming agent in a thermoplastic resin,
Performed using the injection molding apparatus according to claim 2,
A charging step of charging a raw material containing a foaming agent and a thermoplastic resin into the injection molding device;
A transfer step of transferring the charged raw material toward the downstream side by the supply unit of the first stage of the screw of the injection molding apparatus; and a first compression step of plasticizing the raw material by the compression unit of the first stage; The first metering step of kneading the raw material by the metering unit of the first stage, weighing it and pushing it to the second stage in a fixed amount,
A second compression step in which the raw material is compressed and plasticized by the compression unit of the second stage, and the raw material is kneaded and measured by the weighing unit of the second stage, and the second is extruded from the screw tip into the cylinder tip. A foam manufacturing method comprising: a weighing step. In the manufacturing method of the foam of Claim 3,
From the transfer step to the first metering step, the raw material is transferred, plasticized, and metered at a temperature that is at least 20 ° C. lower than the gas foaming temperature of the foaming agent. In the second compression step and the second metering step, foaming is performed. A method for producing a foam, characterized in that the raw material is plasticized and measured at a gas foaming temperature or higher. In the manufacturing method of the foam of Claim 3 or 4,
In the second metering step, the raw material moves to the tip of the cylinder, and the pressure from the screw is not applied to the raw material until the metering is completed,
A method for producing a foam, comprising: controlling a back pressure from a screw to increase a raw material pressure after completion of measurement. In the manufacturing method of the foam of Claim 3 to 5,
The foaming agent has a mean particle size of 10 μm or less, and the method for producing a foamed product.

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