JP2003334846A - Method for manufacturing foamed thermoplastic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamed thermoplastic resin having a non-foamed layer having a uniform thickness on the surface of a thermoplastic resin and to provide a method for manufacturing the foamed thermoplastic resin having a fine pattern formed on the non-foamed layer. <P>SOLUTION: The method for manufacturing the foamed thermoplastic resin comprises a step of: previously impregnating, for example, a molten resin with pressurized CO<SB>2</SB>of a supercritical state. Meanwhile, before the molten resin is filled, the CO<SB>2</SB>is previously filled in a cavity. The molten resin is filled in the cavity in the state that the volume of the cavity filled with the CO<SB>2</SB>is maintained in a predetermined volume, or while the volume of the cavity is increased from the predetermined volume. The method further comprises the steps of: reducing the volume of the cavity by using the mold clamping mechanism of an injection molding machine immediately after the molten resin of the predetermined volume is filled completely in the cavity, and thereby compressing the molten resin. Further, the method comprises the steps of: reducing the mold clamping pressure of the cavity, and again increasing the volume of the cavity. Thus, the internal pressure of the cavity is lowered, and the pressurized CO<SB>2</SB>in the molten resin is foamed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic resin foam using a supercritical fluid.

[0002]

2. Description of the Related Art Recently, a method for forming a thermoplastic resin foam material using a supercritical fluid has been developed. Since the supercritical fluid has a solubility close to that of a liquid and a diffusivity and permeability similar to those of a gas, the supercritical fluid is impregnated in a resin in a short time. Further, by using a supercritical fluid, it is possible to form a fine foam cell inside the resin, which was difficult by the conventional chemical foaming method or gas foaming method. You can The underlying method of forming this foam is described in US Pat. No. 5,158,986.
According to this publication, 1) a thermoplastic resin is extruded into a sheet, and the sheet is introduced into a pressure chamber filled with CO ₂ in a supercritical state, whereby CO ₂ as a supercritical fluid is introduced into the resin sheet. A method of forming a foam by impregnating and heat-foaming in a foaming chamber at atmospheric pressure, or 2) melting the resin with an extruder while adding C in a supercritical state into the resin.
A molded product that is impregnated with O ₂ and is extruded into a sheet shape is introduced into a pressure chamber, a cell nucleus that becomes a foam is formed by a pressure change in the pressure chamber, and the cell nucleus is heated and cooled to obtain a desired cell nucleus. A method for obtaining the cell diameter and the cell density is disclosed.

As an example of molding the above foam by injection molding, a thermoplastic resin melted in a cylinder of an injection molding machine is impregnated with an inert gas such as CO ₂ in a supercritical state, and the thermoplastic resin is molded into a mold. An apparatus and a molding method for foaming by injecting and filling the inside of the mold and then depressurizing the inside of the mold are disclosed in JP-A-08-258096 and JP-A-10-230528.
It is proposed in Japanese Patent Laid-Open No. 2001-9882. JP-A-1
In 0-230528, after injection and filling of the molten resin, a part or the whole surface of the mold is retracted to increase the cavity volume, and the inside of the cavity is depressurized to control the foaming of the thermoplastic resin.

[0004]

However, in the above injection molding method, since the molten resin impregnated with the supercritical fluid is injected and filled with the cavity closed by mold clamping, a molded product having a thin wall and a large surface area is particularly preferable. in the case of,
The pressure difference in the resin becomes large between the molten resin filling port and the cavity end. Therefore, in order to fill the molten resin up to the end of the cavity, it is necessary to increase the injection filling pressure of the molten resin. Along with this, a mold clamping pressure of the cavity that can withstand the filling pressure is required, but increasing the mold clamping pressure increases the flow resistance of the molten resin to be filled,
It becomes a factor to further increase the pressure difference in the cavity.

The supercritical fluid impregnated in the molten resin pressurized by the plasticizing cylinder of the injection molding machine is gasified by being depressurized when injected into the cavity and foamed from the surface of the molten resin. To do. Therefore, when forming a smooth non-foamed layer on the resin surface layer, it is necessary to prevent the surface of the molten resin from being cooled and solidified by the mold in the foamed state. Therefore, in the conventional molding method using a supercritical fluid, by suppressing the heat quantity of the molten resin to the mold by using a material having a low thermal conductivity on the mold surface and its vicinity, A method of suppressing rapid cooling has been proposed. In this method, polyimide or the like needs to be formed as a heat insulating layer on the surface of the mold, but there are problems that a complicated molded body is difficult and the life of the heat insulating layer is short. There is also a method of previously filling the mold with a supercritical fluid or pressurized CO ₂ as counter pressure to suppress the pressure reduction of the supercritical fluid impregnated in the resin.

On the other hand, when the cavity volume is fixed by clamping the mold, high pressure CO ₂ gas is introduced into the mold as counter pressure, whereby CO ₂ acts as a plasticizer for the molten resin, and the CO ₂ acts on the mold surface. JP-A 2001-62862 discloses that the solidification of the resin is delayed and the transferability of the die surface to the resin is improved. However, according to this method, high-pressure CO ₂ must be permeated from the resin flow front into the resin during the short-time injection filling. Therefore, when transferring a fine structure of a submicron order or less or a high aspect ratio structure, CO ₂ may remain inside the fine structure without permeating into the molten resin. That is, in conventional foam molding using a supercritical fluid, when high pressure gas such as CO ₂ is used as counter pressure in the mold,
Gas remains between the molten resin and the mold surface. As a result, in the case of a fine structure, sufficient transferability may not be obtained.

By the way, in a general injection molding method, in order to fill the molten resin up to the end of the cavity closed by the narrow width, it is necessary to inject and fill the molten resin at a high pressure as described above. This causes a pressure difference in the molten resin in the cavity, which causes a problem such as molecular orientation and distortion of the molded product. As a way to solve this problem,
The injection compression molding method is known. In this injection compression molding method, when the cavity is filled with the molten resin, the cavity volume is temporarily increased to keep the pressure inside the molten resin low, and after the filling of the predetermined amount of the molten resin is completed, The molten resin is compressed under pressure using a tightening mechanism or the like.
As a result, it is possible to obtain a molded product in which the occurrence of molecular orientation of the resin is suppressed and the residual stress is small.

A method incorporating the injection compression molding method into foam molding is disclosed in, for example, Japanese Patent No. 1975597. This publication discloses a method in which a foaming resin maintained at a resin pressure that does not foam is filled while expanding the volume of a cavity defined by molds fitted to each other and then compressed. Further, in this publication, when injecting the expandable molten resin into the cavity defined by the molds fitted to each other, a gas pressure of such a magnitude that the expandable molten resin does not foam is supplied into the cavity. Next, an injection compression molding method is also disclosed, in which the cavity is compressed and gas is discharged, after the resin surface is cooled and solidified, the cavity is expanded to a foaming start pressure to foam the inside of the resin, and the resin is taken out after cooling. There is. Example 6 of this publication
As described in, when filling the resin, a gas corresponding to the resin injection amount is discharged from the gas supply flow path, and further,
Since the gas pressure applied to the gas supply passage is released when the resin is compressed, all the gas is discharged from the cavity to the outside of the mold.

A first object of the present invention is to provide a method for producing a thermoplastic resin foam having a uniform thickness of a non-foamed layer on the surface of a thermoplastic resin and having a uniform foaming state.
A second object of the present invention is to provide a method for producing a thermoplastic resin foam having a fine pattern formed on the non-foamed layer.

[0010]

According to the present invention, there is provided a method for producing a thermoplastic resin foam by filling a cavity with a molten resin, wherein the molten resin is impregnated with CO ₂ in a supercritical state. C; in a cavity of a predetermined volume
Filling with O ₂ ; filling the cavity with a predetermined volume filled with the CO ₂ , or filling the cavity with the cavity volume while increasing the volume of the cavity from the predetermined volume; filling with a molten resin Compressing the molten resin by reducing the volume of the cavity;
There is provided a method for producing a thermoplastic resin foam, which comprises compressing the molten resin and then increasing the volume of the cavity again to foam the molten resin.

In the present invention, the molten resin is impregnated with CO ₂ in a supercritical state in advance, and the molten resin is injected and filled in the cavity. On the other hand, before the molten resin is filled, CO ₂ is filled in the cavity having a predetermined volume in advance. The molten resin is filled into the cavity while maintaining the volume of the cavity filled with CO ₂ at a predetermined volume, or
It is performed while increasing the volume from a predetermined level. Then, immediately after completing the filling of the predetermined amount of the molten resin in the cavity, the volume of the cavity is reduced by using the mold clamping mechanism of the injection molding machine or the like to compress the molten resin in the cavity.
Furthermore, after a lapse of a predetermined time, the mold clamping pressure of the cavity is reduced, and the volume of the cavity is increased again. As the volume of the cavity increases, the internal pressure of the cavity decreases, and the pressurized CO ₂ inside the molten resin foams.

In the present invention, the flow resistance of the molten resin is reduced by increasing the volume of the cavity when the molten resin is injected and filled in the cavity. In particular, it is desirable to fill the cavity with molten resin after increasing the volume of the cavity to a predetermined volume. Since the CO ₂ inside the cavity is kept at a constant pressure, it is not necessary to perform complicated pressure control when filling the molten resin. In the present invention, since the open space into which the molten resin flows is wide, the flow of the molten resin becomes smooth and it becomes easier to make contact with CO ₂ . Further, since there is a compression step later, it is not necessary to fill the cavity with the molten resin at the time of injection filling. For this reason, the flow length of the molten resin becomes shorter, so that there is a space where CO ₂ stays at the cavity end and the resin flow end.
Further, by pre-filling the cavity with CO ₂ , in addition to suppressing surface foaming due to a decrease in resin internal pressure, CO ₂ functions as a plasticizer for the molten resin, so that the molten resin is When it enters the inside, CO ₂ permeates from the surface of the resin, so that the solidification of the resin on the surface of the mold is suppressed. In order to further enhance the effects of suppressing foaming and solidification, it is desirable to seal the cavity so that CO ₂ does not leak from the cavity. To seal the inside of the cavity,
For example, it is possible to use a sealing member such as an O-ring on the mating surfaces of the pair of molds or a mechanism that is driven independently of the movable mold to limit the cavity or the mating surfaces of the molds.

In the present invention, the volume of the cavity is reduced immediately after filling the molten resin to compress the molten resin in the cavity. By this compression, the molten resin is pressed by the mold with a uniform pressure and is completely filled up to the end of the cavity. At this time, it is desirable to seal the cavity so that CO ₂ does not leak even when the molten resin is compressed. In this case, the high-pressure CO ₂ staying in the space at the end of the cavity and the flow end of the resin after the completion of filling is volume-compressed, so that the pressure in that space rises again, so that the viscosity of the molten resin that reflows due to compression increases Can be further suppressed. Then, during injection filling for a short period of time, CO is formed between the fine pattern on the mold and the resin layer.
Even if ₂ remains, the pressure of CO ₂ rises again during compression, so that it almost completely penetrates into the molten resin.
Therefore, the residual CO ₂ which is a problem in the conventional counter pressure method is eliminated.

Further, in the present invention, by compressing the molten resin in a state in which the cavity is closed so that CO ₂ does not leak from the cavity, the pressure of the CO ₂ retained in the cavity rises again, and as a result, The surface viscosity of the resin in contact with the mold is lower than immediately after injection filling. Therefore, even if the resin foams on the surface of the resin due to the pressure drop at the time of injection filling, the resin can penetrate into the pattern on the surface of the mold while maintaining the low viscosity of the resin on the surface of the mold. Sufficient transfer is possible even for various dies. Further, CO ₂ gasified and foamed once by compression permeates into the resin again, so that there is no trace of foaming on the resin surface. Further, due to the above-mentioned effects, the higher the pressure of CO ₂ permeates into the flow end portion (flow front), the viscosity of the molten resin in the cavity further decreases, and a uniform foaming state is obtained. In the method of the present invention, after the contact surface of the molten resin with the mold is solidified, the cavity volume is increased again to reduce the internal pressure of the cavity. By this operation, CO ₂ impregnated inside the molten resin foams. When the molten resin is solidified with CO ₂ foamed, a foamed layer is formed inside the resin. This makes it possible to produce a thermoplastic resin foam having a non-foamed layer having a uniform thickness on the surface and having a fine pattern transferred to the non-foamed layer.

In the present invention, it is desirable that the flow end of the molten resin filled in the cavity is regulated by an independently drivable member. As a result, the filling of the molten resin is limited by the frame member. For example, when a rectangular molded product is manufactured, the molten resin can be sufficiently filled up to the corners of the rectangular frame member.

In the present invention, the drivable member may be driven by using pressurized gas. Further, the pressurized gas is pre-filled in the cavity C
It may be O ₂ . Accordingly, it is not necessary to use a means for moving the drivable member separately from the moving means of the movable mold, and the drive system of the injection molding machine can be simplified.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[0018]

Example 1 A mold for injection molding used for forming a thermoplastic resin foam of the present invention will be described with reference to FIGS. As shown in FIGS. 1A and 1B, the mold used in the present invention is composed of a fixed mold 52 and a movable mold 53. The fixed mold 52 and the movable mold 53 are both rectangular flat plates and are arranged so as to face each other such that their centers AX are coaxial. Opposing surfaces 52a and 53a of the molds define a cavity. As can be seen from FIG. 3, a frame-shaped convex portion 50 is provided around the surface 52a of the fixed mold 52 in a circular manner. In addition, the fixed mold 52
A spool bush 10 for filling the cavity with molten resin is installed in the center of the so as to penetrate the fixed mold 52 with the axis AX as the central axis. further,
A fixed block 13 having a mirror-finished surface is fitted in a concave portion between the convex portion 50 and the spool bush 10. On this fixed block 13, a stamper 7 having a fine groove pattern with a line and space of 0.2 μm and a height of 0.6 μm formed on the surface is placed. One end of the stamper 7 is fixed on the fixed block 13 by a stamper retainer 9 installed so as to surround the outside of the spool bush 10. Further, one end and the other end of the stamper 7 are vacuum-sucked to the fixed block 13 via the suction port 8 formed in the fixed block 13. As a result, the stamper 7 is fixed on the fixed block 13 in a more stable state. In the center of the convex portion 50, a width of 6 mm and a depth of 3
mm groove 55 is formed along the convex portion 50, and the groove 5
An O-ring 11 having a diameter of 5 mm is installed at 5.
The fixed mold 52 and the movable mold 53, which will be described later, are combined via the O-ring 11 so that their respective central axes AX are aligned with each other, whereby the fixed mold 52 and the movable mold 53 are combined.
The closed state of the cavity defined by is maintained.

At the center of the movable mold 53, as shown in FIG. 1, the movable member 2 is installed so as to be movable in the axis AX direction toward the cavity side of the movable mold 53. . Further, as can be seen from FIG. 2, two frame members 1 are installed symmetrically so as to sandwich the movable member 2. An outer peripheral portion 51 is provided on the outer side of the frame member, and the outer peripheral portion 51 comes into contact with the O-ring of the fixed mold 52 as described later. The frame member 1 is connected to the piston plate 5 via the rod 6, respectively, and is movable independently of the movable mold 53 by driving the piston plate 5. That is, when the piston plate 5 is pushed out to the cavity side by a piston (not shown), the frame member 1 projects from the surface 53a of the movable mold 53 and comes into contact with the outer peripheral portion of the stamper 7 installed in the fixed mold 52. This limits the molten resin filling area in the cavity. Further, in the outer peripheral portion 51 of the movable mold 53, CO for supplying CO ₂ into the cavity is provided in the vicinity of both ends in the mold longitudinal direction.
_Two supply paths 3 are provided.

In the fixed mold 52, as shown in FIG. 3, recesses 15 and 16 are formed on the surfaces of the spool bush 10 and the stamper retainer 9 facing the cavity, respectively. The recess 15 and the recess 16 are formed so as to extend continuously from the mold center AX toward the stamper 7. Moreover, in the movable mold 53, as shown in FIG.
As shown in, concave portions 14 and 17 are formed on the surfaces of the movable member 2 and the frame member 1 that face the cavities, respectively. The recess 14 and the recess 17 are formed so as to extend continuously from the mold center AX toward the surface 12 forming the cavity of the movable mold 53. Therefore, when the fixed mold 52 and the movable mold 53 are combined, the recesses 14 and 15 and the recesses 17 and 16 are combined.
Respectively form a runner (resin filling path) between the nozzle 10a and the cavity. As a result, the molten resin injected through the nozzle 10a of the spool bush 10 is filled into the cavity through the runner formed by the recesses 14 to 17. Since the cross-sectional area of the runner is very small compared to the size of the molten resin nozzle 10a and the volume of the cavity, when the molten resin is filled in the cavity, the molten resin in the runner is larger than the molten resin in the cavity. It cools and solidifies quickly. This prevents the molten resin that has not solidified in the cavity from flowing back to the spool bush 10 side. In the present invention, when the molten resin is compressed, in order to prevent the molten resin in the cavity from backflowing from the runner or gate and causing pressure loss, the molten resin in the runner or gate is cooled and solidified before being compressed. Is desirable. Also, as a method of solidifying the molten resin of the runner and the gate, by driving the movable member of the movable mold to cut the gate,
It is possible to adopt any method such as separating the molten resin near the molten resin filling port from the molten resin of the runner or the gate to improve the cooling efficiency of the molten resin of the runner or the gate.

The molten resin filled in the cavity of the mold in the present invention is optional as long as CO _{2 of the} supercritical fluid is dissolved, and a known plasticizing filling mechanism for impregnating the supercritical fluid is used. You can In this embodiment, it is obtained by a plasticizing device equipped with an in-line type screw having a vent mechanism (not shown). In the plasticizer, the thermoplastic resin was plasticized into a molten state, and the molten resin was impregnated with CO ₂ in a supercritical state at a pressure of 7 MPa in the depressurized vent portion. In this example, polycarbonate having a glass transition temperature of 140 ° C. was used as the thermoplastic resin, but the thermoplastic resin is not limited to this, and examples thereof include polyethylene, polystyrene, polyolefin, polyacetal, polycarbonate, polyphenylene oxide, polymethylpentene, and polyether. An imide, an ABS resin or the like, or a copolymer thereof can be used.

Next, the thermoplastic resin foam according to the present invention
A method of forming the above will be described with reference to FIGS.
It First, as shown in FIG. 4, the tip of the convex portion 50 on the movable mold side.
Distance between end face and inner peripheral part 51 (parting line
The movable die 53 is fixed so that the distance (T) is 1 mm.
Move the cavity away from the fixed mold 52 to reduce the cavity volume.
Increased. The thickness of the cavity 20 at this time is 2 mm
Became. Then CO _TwoCO from supply channel 3_TwoThe cab
The inside of the cavity is filled with CO_TwoPressure of 5
The pressure was adjusted to MPa (counter pressure). This
At the time of, CO filled in the cavity_TwoIs O-phosphorus
Since the cavity is blocked by the plug 11,
_TwoDoes not leak out of the mold. In addition, in this embodiment
In the mold, CO_TwoO-li that maintains the sealing performance of
Between the parting lines within the crushing margin of ring 11.
The distance can be changed. Also, the die hit
Member that forms the surface (for example, the inner periphery of the movable mold 53)
The part 51) can be operated independently from the mold body.
It may be configured as follows. A member that constitutes the abutting surface of the mold
Is pressed against the fixed mold to seal the inside of the cavity.
The state is maintained and it is movable independently of this member
The movable mold body can be moved. By this
Increase the cavity volume, or
It is possible to further increase the amount of compression to fat. Next
Built in the movable platen of the injection molding machine (not shown).
Piston plate by driving the piston
5 was pressed against the cavity side at a pressure P1 = 9 MPa. Pi
The stone plate 5 is connected to the frame member 1 via the rod 6.
By moving the piston plate 5.
The frame member 1 to the cavity side surface 53a of the movable mold 53.
From, it can be projected toward the fixed mold 52.
it can. For the protrusion of the frame member 1, the front end surface of the frame member 1 is fixed.
Stamper 7 placed on the fixed block 13 of the mold 52
It is performed until the outer peripheral portion of is pressed. This allows the frame member
1 is injection-filled onto the stamper 7 and is filled with molten resin RS
Limit the area. CO by the frame member 1_TwoFilled
The cavities can be further restricted so that
The airtightness inside the tee is further maintained and CO _TwoIs Cavite
Further suppress leaking out.

Next, the molten resin RS was filled in a desired amount into the cavity 20 through a spool bush 10 from a nozzle (not shown) of the injection molding machine. Spool bush 1
The molten resin RS filled through 0 is recessed 14 to 17
The inside of the cavity 20 is filled through the runner formed in (1). At this time, the movable member 2 is pressed by the piston provided in the injection molding machine (not shown) toward the fixed mold 52 at a pressure P2 = 10 MPa. This prevents the molten resin RS from leaking from the runner during the filling of the molten resin RS. Then, as shown in FIG.
While the frame member 1 is pressed against the stamper 7, the protrusion 50
The distance T between the movable mold side tip surface and the inner peripheral portion 51 is 0.
The main body of the movable mold 53 was pressed toward the fixed mold 52 at a pressure P3 = 30 MPa (mold clamping) so that As a result, the thickness inside the cavity 20 became 0.8 mm.
The molten resin RS filled in the cavity 20 is compressed with a uniform pressure and is filled up to the end portion of the region restricted by the frame member 1. At the time of filling the molten resin, the surface of the stamper 7 having a fine structure with a high aspect ratio and the filling resin R
The CO ₂ supplied as counter pressure may remain at the interface with S, but the internal pressure of the molten resin rises again due to the compression of the molten resin in the closed cavity, and the CO ₂ in the cavity melts. By completely penetrating the resin, a fine mold pattern can be transferred. Further, after the completion of filling, the CO ₂ retained in the space between the flow end portion and the frame member 1 re-flows by being compressed because the pressure increases again due to the decrease in the cavity volume due to the compression of the molten resin. At the end of the molten resin, CO ₂ having a higher pressure than when it was filled is impregnated. Due to this effect,
The increase in viscosity of the molten resin can be suppressed more than in the conventional injection molding method using counter pressure. Further, compared with the conventional foam molding method using injection compression, the pressure in the cavity can be made uniform.

Then, after the stamper contact surface of the molten resin RS is solidified, as shown in FIG. 6, with the frame member 1 pressed against the stamper 7, the movable mold 53 is moved away from the fixed mold 52 in the direction of 0. It was moved by 1 mm. At this time, as the volume of the cavity 20 increases, the cavity 20
Internal pressure drops. At the same time, CO ₂ which is the supercritical fluid previously impregnated in the molten resin RS is vaporized due to the pressure decrease, and the molten resin RS is in a foaming state. Then
After the foaming inside the resin, the movable mold 53 is fixed again to the fixed mold 52.
Was moved in the direction of 0.1 mm to clamp the molten resin RS. By cooling and solidifying the molten resin in this state, a resin molded product having a non-foamed layer on the surface and a foamed layer on the inside is formed. Next, the pressurized air supplied from the air supply path 21 was jetted from the gap between the stamper retainer 9 and the stamper 7 to open the mold while separating the molded product from the stamper 7. Next, after the mold is opened, the frame member 1 is further protruded to the fixed mold side to form the molded product in the movable mold 53.
Released from. As a result, it was possible to obtain a thermoplastic resin foam having a non-foamed layer having a uniform thickness on the mold surface and a foamed layer having a uniform foaming inside. The diameter of the foam cells in the foam layer formed in the molded product (foam cell diameter) was measured by observing the cross section of the molded body at a measurement point in an arbitrary cavity with an SEM. It was confirmed that the average value of the foamed cell diameter was 5 μm, and the difference between the minimum foamed cell diameter and the maximum foamed cell diameter was within 10% based on the minimum cell diameter. Furthermore, as a result of observing the surface of the resin molded product using AFM and SEM, it was found that the transfer rate was 98%. From this, it can be seen that the fine pattern of the stamper is accurately and faithfully transferred onto the foam. In the present invention,
After the molten resin is compressed and the mold pattern is transferred to the surface of the resin, some CO ₂ in the cavity may be released to the outside of the cavity.

[0025]

Comparative Example As a comparative example with the above example, injection molding was performed under the following conditions. The fixed mold and the movable mold were arranged so that T = 0 mm, and CO ₂ was previously filled as counter pressure in the cavity of the mold. Next, the molten resin was injected and filled while the mold was clamped at 30 MPa. At this time, the opening amount T between the fixed mold and the movable mold was 0.05 mm at maximum due to the influence of the injection filling pressure of the molten resin. In particular, a resin molded product was obtained by cooling and solidifying the molten resin in this state without compressing the molten resin. The mold transfer surface of this molded product is AFM
As a result of observation by the above, the transfer rate was 70%. It can be seen that the transfer rate is deteriorated by 28% as compared with the above example.

[0026]

Second Embodiment Another embodiment of the present invention will be described with reference to FIG. In this embodiment, except that the frame member 1 ′ and the movable member 2 ′ of the movable mold 53 in the above embodiment are moved by using a pressurized gas instead of the piston plate,
The configuration is similar to that of the first embodiment. In the first embodiment, the space in which the piston plate 5 and the rod 6 are housed functions as a passage for the pressurized gas in this embodiment.
As shown in FIG. 7, coil springs 23 are installed in the pressurized gas passages so as to bias the frame member 1 ′ toward the cavity side. In this state, the pressurized gas was supplied from the air supply path 4 ′ at a pressure P4 = 6 MPa, and the frame member 1 ′ and the movable member 2 ′ were urged toward the fixed mold 52. As a result, similarly to the first embodiment, the area filled with the molten resin in the cavity is limited by the frame member 1 ′, and the leakage of the molten resin from the runner can be prevented. Further, in this embodiment, it can be used 'as the pressurized gas supplied from, CO ₂ supply passage 3' air supply passage 4 for supplying CO ₂ from the cavity. Equilibrium with CO ₂ 'pressure P3 of supplied CO ₂ from' supply channel 3, 'by adjusting the pressure P4 of the supplied CO ₂ from the movable die 53' air supply channel 4 the pressure inside the cavity 20 ' Put in a state. As a result, the O-rings 55, 57 and 59 for preventing the leakage of CO ₂ from the inside of the cavity to the movable mold side can be omitted. Further, the driving device for independently moving the frame member 1'and the movable member 2'as used in the first embodiment can be omitted. Although the coil spring is used as an auxiliary means for the pressurized gas in this embodiment, the coil spring is omitted and the frame member 1'and the movable member 2'are controlled only by the balance between the pressurized gas P4 and the pressure in the cavity. You can go.

[0027]

[Modification] In this modification, the filling region of the molten resin in the cavity is limited without using the frame member in the above embodiment. Hereinafter, the mold used in this modification will be described with reference to FIG. A convex portion 86 is formed on the outer peripheral portion of the surface forming the cavity of the movable mold 83. On the other hand, on the outer peripheral portion of the fixed mold 82, a concave portion 87 that fits with the convex portion 86 of the movable mold 83 is provided. CO for supplying CO ₂ to the convex portion 86 from the outside of the movable mold 83 into the cavity 80 defined by the movable mold 83 and the fixed mold 82.
_Two supply paths 85 are provided. The CO ₂ supply path 85 is
When the movable mold 83 is separated from the fixed mold 82 by a predetermined distance, it is electrically connected to the cavity 80. Recess 8
7, a groove 88 is formed, and an O-ring 81 is installed in this groove 88. The O-ring 81 seals the gap when the convex part 86 of the movable mold 83 and the concave part 87 of the fixed mold 82 are fitted. In this example, the stamper 89 is installed on the side surface of the cavity of the movable mold 83.

Next, a method of molding the thermoplastic resin foam of this modification will be described with reference to the same drawing. First, the movable mold 83 is kept at a predetermined distance from the fixed mold 82 by using a driving means (not shown), and the cavity 8
Pressurized CO ₂ is supplied to 0 from the CO ₂ supply path 85. Next, the cavity 80 is injection-filled with the molten resin RS which is preliminarily impregnated with pressurized CO ₂ in a supercritical state (FIG. 8A).
As the molten resin RS, the same one as that used in the above-mentioned examples can be used. Immediately after filling the molten resin RS, the movable mold 83 is moved toward the fixed mold 82 by using a driving unit (not shown). At this time, the moving die 83 is moved until the O-ring 81 is compressed and the convex portion 86 and the concave portion 87 are completely fitted (FIG. 8B). As a result, the volume in the cavity 80 is reduced, and the filled molten resin RS is
Fill up to the end of 0. Further, in this state, the CO ₂ supply passage 85 of the movable mold 83 is connected to the recess 87 of the fixed mold 82.
Is blocked by the wall surface of. This stops the supply of CO ₂ in the cavity 80 during compression of the molten resin,
The pressure inside the cavity 80 becomes constant. The molten resin RS is
By contact with the mold, the surface is cooled and solidified. Next, the movable mold 83 is moved again in the direction away from the fixed mold 82 so that the inside of the cavity has a desired thickness. As a result, the volume of the cavity increases and the internal pressure decreases. At the same time, CO ₂ which is a supercritical fluid previously impregnated in the molten resin RS is vaporized due to the pressure drop,
The molten resin RS is in a foamed state. By cooling the molten resin in this state, the molten resin is solidified and a resin molded product having a foam layer inside can be more easily formed.

In this modification, the convex portion 86 and the concave portion 8 of the mold are used.
Since the cavity is restricted by fitting 7 in, the number of mold elements may be smaller than that in the above-described embodiment using the frame member.

[0030]

INDUSTRIAL APPLICABILITY According to the present invention, a thermoplastic resin foam having a non-foamed layer having a uniform thickness on the surface and having a fine pattern formed on the non-foamed layer can be produced. Molded products made of this foam can be made 20% lighter than conventional molded products, and can be applied to various molded parts such as millimeter-wave antennas for weight reduction and low dielectric constant. Further, since a fine pattern can be transferred onto the surface, it can be applied to a molded product having a fine pattern electric circuit, a film surface incident type optical disk, and the like.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of the vicinity of a mold of an injection molding machine used in Example 1 of the present invention.

FIG. 2 is a schematic plan view of a movable mold used in Example 1 of the present invention.

FIG. 3 is a schematic plan view of a fixed mold used in Example 1 of the present invention.

FIG. 4 is a diagram schematically showing a state of injection molding in Example 1.

FIG. 5 is a diagram schematically showing a state of injection molding in Example 1.

FIG. 6 is a diagram schematically showing a state of injection molding in Example 1.

FIG. 7 is a diagram schematically showing how the mold used in Example 2 of the present invention operates.

FIG. 8 is a diagram schematically showing an operation state of a mold used in a modified example of the present invention.

[Explanation of symbols]

1,1 'Outer peripheral frame 2,2' Movable member 3,3 'CO ₂ supply path 7,87 Stamper 8 Stamper suction port 9 Stamper retainer 10 Spool bush 11,81 O-ring 14, 15, 16, 17 Recess 20 Cavity 52,82 Fixed mold 53,53 ', 83 Movable mold RS Molten resin

Claims (6)

[Claims] 1. A method for producing a thermoplastic resin foam by filling a cavity with a molten resin, wherein the molten resin is impregnated with CO ₂ in a supercritical state;
And filling the CO ₂ in the cavity of predetermined volume; a cavity of a predetermined volume filled with the CO _2, or, in the cavity while increasing the cavity volume from the predetermined volume, and filling the molten resin; Compressing the molten resin by reducing the volume of the cavity filled with the molten resin; a thermoplastic resin comprising compressing the molten resin and then increasing the volume of the cavity again to foam the molten resin Method for producing foam. 2. The thermoplastic resin foam according to claim 1, further comprising regulating a flow end portion of the molten resin filled in the cavity by an independently drivable member. Production method. 3. The method for producing a thermoplastic resin foam according to claim 2, wherein the drivable member is driven by using a pressurized gas. 4. The method for producing a thermoplastic resin foam according to claim 3, wherein the pressurized gas is CO ₂ with which the cavity is filled. 5. The method for producing a thermoplastic resin foam according to claim 1, wherein the cavity is filled with a molten resin while maintaining CO ₂ . 6. The cavity is compressed while maintaining CO ₂ in the cavity.
The method for producing a thermoplastic resin foam according to any one of 1.