Source: http://www.google.com/patents/US5849339?dq=6076065
Timestamp: 2016-10-01 12:41:56
Document Index: 140883004

Matched Legal Cases: ['art 51', 'art 52', 'art 4', 'art 3', 'art 3', 'art 4', 'art 3', 'art 4', 'art 3', 'art 3', 'art 4', 'art 4', 'art 3', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4']

Patent US5849339 - Apparatus for producing biodegradable resin foam - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsFoam forming techniques are capable of permitting foaming of biodegradable resin to be positively and uniformly accomplished to provide a biodegradable resin foam with satisfactory quality. The biodegradable resin including foam is made of biodegradable resin a main biodegradable resin ingredient of...http://www.google.com/patents/US5849339?utm_source=gb-gplus-sharePatent US5849339 - Apparatus for producing biodegradable resin foamAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS5849339 APublication typeGrantApplication numberUS 08/734,957Publication dateDec 15, 1998Filing dateOct 23, 1996Priority dateJul 13, 1993Fee statusLapsedAlso published asDE69406366D1, DE69406366T2, DE69432606D1, DE69432606T2, EP0634261A1, EP0634261B1, EP0785055A2, EP0785055A3, EP0785055B1, US5602188, US6228898, US6626654Publication number08734957, 734957, US 5849339 A, US 5849339A, US-A-5849339, US5849339 A, US5849339AInventorsMotoyasu NakanishiOriginal AssigneeSuzuki Sogyo Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (23), Referenced by (10), Classifications (19), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetApparatus for producing biodegradable resin foam
US 5849339 AAbstract
Foam forming techniques are capable of permitting foaming of biodegradable resin to be positively and uniformly accomplished to provide a biodegradable resin foam with satisfactory quality. The biodegradable resin including foam is made of biodegradable resin a main biodegradable resin ingredient of 100� C. or more in melting point and a low-melting biodegradable resin ingredient of 100� C. or less in melting point. The biodegradable resin foam is produced by placing a starting material of at least biodegradable resin and a substantial amount of moisture in a heated and pressurized environment, releasing the starting material from the environment to foam the biodegradable resin, and subjecting the foamed resin to forming by a forming mold. An apparatus for producing the foamed biodegradable resin foam includes a pressure adjusting chamber, an air-permeable forming mold, a pressure reducing tank and an injection machine.
1. An apparatus for producing a biodegradable resin foam, comprising:a pressure adjusting chamber constructed so as to be able to be opened and hermetically closed; a pressure reducing means connected to said pressure adjusting chamber for rapidly reducing pressure in said pressure adjusting chamber; an air-permeable forming mold in said pressure adjusting chamber; and an injection machine comprising a cylinder having a narrow opening at a front portion thereof, said cylinder being for heating and fluidizing biodegradable resin such that moisture is trapped therein, forcibly transferring the biodegradable resin toward said narrow opening, and extruding the biodegradable resin therefrom into said air-permeable forming mold so as to rapidly release the biodegradable resin from heat and pressure in said cylinder, whereby the biodegradable resin is foamed by an expansion force due to the vaporization of the moisture. 2. The apparatus of claim 1, wherein said pressure reducing means comprises a pressure reducing pump.
3. The apparatus of claim 2, wherein said pressure reducing means further comprises a pressure reducing valve connected between said pump and said pressure adjusting chamber.
4. The apparatus of claim 1, and further comprising an air introducing means for introducing air into said pressure adjusting chamber such that said pressure adjusting chamber is returned to atmospheric pressure.
5. The apparatus of claim 4, wherein said air introducing means comprises an atmospheric pressure releasing valve.
6. An apparatus for producing a biodegradable resin foam, comprising:a pressure adjusting chamber constructed so as to be able to be opened and hermetically closed; a pressure reducing means connected to said pressure adjusting chamber for rapidly reducing pressure in said pressure adjusting chamber; an air-permeable forming mold in said pressure adjusting chamber; and an injection machine comprising a cylinder having a narrow opening at a front portion thereof, said cylinder being for heating and fluidizing biodegradable resin such that moisture is trapped therein, forcibly transferring the biodegradable resin toward said narrow opening, and extruding the biodegradable resin therefrom into said air-permeable forming mold so as to rapidly release the biodegradable resin from heat and pressure in said cylinder, whereby the biodegradable resin is foamed by an expansion force due to the vaporization of the moisture; wherein said pressure adjusting chamber, said pressure reducing means and said air-permeable forming mold together define a means for enabling gas to escape from said air-permeable forming mold into said pressure adjusting chamber. 7. The apparatus of claim 6, wherein said pressure reducing means further comprises a pressure reducing valve connected between said pump and said pressure adjusting chamber.
8. The apparatus of claim 6, and further comprising an air introducing means for introducing air into said pressure adjusting chamber such that said pressure adjusting chamber is returned to atmospheric pressure.
9. The apparatus of claim 8, wherein said air introducing means comprises an atmospheric pressure releasing valve.
10. The apparatus of claim 6, wherein said pressure adjusting chamber comprises a door.
11. The apparatus of claim 6, wherein said air-permeable forming mold comprises first and second mold parts that are moveable away from each other, one of said first and second mold parts being moveable together with said door.
12. An apparatus as defined in claim 1, wherein said injection machine includes:a forcible transfer mechanism for forcibly transferring a biodegradable resin starting material containing biodegradable resin charged in said cylinder and raising a temperature of the biodegradable resin, to thereby fluidize and extrude the fluidized biodegradable resin through said narrow opening into said forming mold; and an access mechanism for reciprocating said narrow opening and forming mold relative to each other and retracting said narrow opening relative to said forming mold during injection of the fluidized biodegradable resin through said narrowed opening into said forming mold. 13. An apparatus as defined in claim 2, wherein said injection machine includes:a forcible transfer mechanism for forcibly transferring a biodegradable resin starting material containing biodegradable resin charged in said cylinder and raising a temperature of the biodegradable resin, to thereby fluidize and extrude the fluidized biodegradable resin through said narrow opening into said forming mold; and an access mechanism for reciprocating said narrow opening and forming mold relative to each other and retracting said narrow opening relative to said forming mold during injection of the fluidized biodegradable resin through said narrowed opening into said forming mold. 14. An apparatus as defined in claim 3, wherein said injection machine includes:a forcible transfer mechanism for forcibly transferring a biodegradable resin starting material containing biodegradable resin charged in said cylinder and raising a temperature of the biodegradable resin, to thereby fluidize and extrude the fluidized biodegradable resin through said narrow opening into said forming mold; and an access mechanism for reciprocating said narrow opening and forming mold relative to each other and retracting said narrow opening relative to said forming mold during injection of the fluidized biodegradable resin through said narrowed opening into said forming mold. 15. An apparatus as defined in claim 4, wherein said injection machine includes:a forcible transfer mechanism for forcibly transferring a biodegradable resin starting material containing biodegradable resin charged in said cylinder and raising a temperature of the biodegradable resin, to thereby fluidize and extrude the fluidized biodegradable resin through said narrow opening into said forming mold; and an access mechanism for reciprocating said narrow opening and forming mold relative to each other and retracting said narrow opening relative to said forming mold during injection of the fluidized biodegradable resin through said narrowed opening into said forming mold. Description
This is a divisional application of Ser. No. 08/274,038 filed Jul. 12, 1994 now U.S. Pat. No. 5,602,188.
A third problem occurs due to releasing of biodegradable resin fluidized by heating and pressurizing from a heated and pressurized environment. Releasing of the resin fluidized causes moisture contained in the resin to be vaporized and expanded, resulting in foaming of the resin, to thereby provide cells, during which the cells are decreased in temperature to a level of about 100� C. due to vaporization of the moisture. This causes the cells to be somewhat shrunk and then solidified while being kept shrunk. Also, the cells are somewhat shrunk by water vapor surrounding the cells. Such cells are integrated together to form a foam. Thus, cavities and/or voids occur in the foam solidified, so that boundaries between the cells are discontinuous, to thereby cause the foam to be unsuitable for use for a cushioning material.
Also, in accordance with this aspect of the present invention, an apparatus for producing a biodegradable resin foam is provided. The apparatus comprises a pressure adjusting chamber constructed in a manner to be capable of being opened and closed hermetically, an airpermeable forming mold arranged in the pressure adjusting chamber, a pressure reducing tank connected through a pressure reducing valve to the pressure adjusting chamber to rapidly reduce a pressure in the pressure adjusting chamber, an evacuation valve connected to the pressure adjusting chamber, a compressor connected to the pressure adjusting chamber, a valve controller for controlling operation of each of the valves, and an injection machine for injecting, into the forming mold, fluidized biodegradable resin placed in a heated and pressurized environment and having moisture trapped therein. The valve controller functions to initiate actuation of the compressor before or at the time when injection of the biodegradable resin into the forming mold by the injection machine is started, carry out termination of actuation of the compressor and opening of the evacuation valve in the course of the injection, and carry out closing of the evacuation valve and opening of the pressure reducing valve after the injection. Thus, the pressure adjusting chamber may be controlled to pressurization, evacuation or pressure reduction in association with a timing of injection of the resin into the forming mold.
The present invention is directed to a biodegradable resin foam, which is generally designated at reference character B in FIGS. 2 and 3. The biodegradable resin foam B is produced by foaming biodegradable resin by means of expansion force due to vaporization of moisture. The biodegradable resin consists of a first biodegradable resin ingredient of 100� C. or more in melting point (hereinafter also referred to as "main biodegradable resin ingredient") and a second biodegradable resin ingredient of 100� C. or less in melting point (hereinafter also referred to as "lowmelting biodegradable resin ingredient").
The first biodegradable resin ingredient of 100� C. or more or main biodegradable resin ingredient which is commercially available includes resin sold under "Mater-Bi" (registered trademark) from Nippon, Gosei Kagaku Kabushiki Kaisha, Japan. The resin was developed by Novamont belonging to a Montedison group, Italy and is said to be a thermoplastic biodegradable polymer comprising derivatives from a plurality of agricultural products such as starch and the like and denatured polyvinyl alcohol wherein the derivatives and alcohol get into each other at a molecular level, to thereby bonded to each other by hydrogen bonding. Also, it is said that the biodegradable resin is swollen due to absorption of moisture, resulting in biodegradation thereof being promoted, to thereby exhibit substantially the same biodegradability as paper in an environment in which microbes exist. In addition to "Mater-Bi" described above, for example, acetate which is an ester compound of cellulose may be of course used as the first biodegradable resin ingredient having a melting point of 100� C. or more. In this instance, the biodegradable resin may comprise only the first biodegradable resin ingredient of 100� C. or less in melting point or main biodegradable resin ingredient, to thereby eliminate addition of the second biodegradable ingredient of 100� C. or less in melting point or low-melting biodegradable resin ingredient described hereinafter thereto.
The low-melting biodegradable resin ingredient, even when any cavity or void occurs in the biodegradable resin during formation of the biodegradable resin into a foam, functions to permit walls of cells of the foam to adhere to each other as much as possible. In the present invention, for example, polycaprolactone or a material containing polycaprolactone may be preferably used for the low-melting biodegradable resin ingredient. Such a low-melting biodegradable resin ingredient which may be commercially available includes resin sold under a tradename "Tone" from Nippon Unicar Kabushiki Kaisha, Japan. The commercially available resin "Tone" comprises polycprolactone which is aliphatic polyester chemically synthesized and is of the full decomposition type.
When the biodegradable resin starting material for the biodegradable resin foam B of the present invention comprises moisture, the biodegradable resin and a water repellent material, the water repellent material and moisture may be previously contained in or added to the biodegradable resin, followed by charging the starting material into an injection molding machine, because the biodegradable resin is placed under a heating and pressurizing condition in the presence of the water repellent material and substantial moisture. The water repellent material, may include silicone compounds, fluorine compounds, waxes, polymers of a higher fatty acid and the like. In the illustrated embodiment, a commercially available material which is manufactured by Kabushiki Kaisha Sigma Gijutu Kenkyujo and sold from Tonen Kabushiki Kaisha under a tradename "Sigma coat" and mainly consists of polymers of a higher aliphatic acid and waxes may be used as the water repellent material. Addition of the water repellent material to the biodegradable resin may be carried out, for example, by diluting the water repellent material ("Sigma Coat") with water and then heating it to form an emulsion, followed by addition of the emulsion thereto. This permits the water repellent material and moisture to be concurrently added to the biodegradable resin. Alternatively, addition of the water repellent material to the biodegradable material and that of moisture thereto may be carried out separately from each other. For this purpose, the water repellent material may be added to the biodegradable resin containing moisture. The biodegradable resin foam B of the present invention thus formed is not limited to an application to a cushioning material. It may be directed to various applications such as a heat insulating material, a sound insulating material and the like as in a conventional foamed styrol material.
First, the forming mold A is clamped through the mold clamp mechanism 40 and the pressure reducing valve V1 is closed to keep the chamber 5 at an atmospheric pressure. Then, as shown in FIG. 1, the hopper 11 is fed with biodegradable resin particles 10 in which moisture is contained, which are then forcedly forwardly transferred in the cylinder 1 by means of the screw 2. The biodegradable resin particles 10 are increased in temperature to a level of a softening point of the resin or melting point thereof by shearing force due to rotation of the screw 2 and heating applied thereto from the heater 13, resulting in being fluidized in an inner space of the cylinder 1 defined on a distal end side of the screw 2.
At this time, the inner space of the cylinder 1 is kept heated and pressurized, so that moisture contained in the biodegradable resin particles 10 is kept trapped in the fluidized biodegradable resin without evaporating therefrom. Then, rotation of the screw 2 is stopped and then the piston 23 in the injection cylinder 22 is actuated to forwardly move the screw as shown in FIG. 2(a), resulting in the fluidized biodegradable resin being injected through the narrowed opening 1a into a forming space R defined in the forming mold A at a stretch.
In the foaming, the moisture is decreased in temperature after the vaporization and expansion, resulting in drifting inside and outside the forming mold A in a steam state or condensing on a surface of each of the forming mold A and foam product due to contact therewith, so that the moisture tends to form water droplets. In order to avoid formation of water droplets, the pressure reducing valve V1 is open immediately after extrusion of the biodegradable resin into the forming mold A as shown in FIG. 2(b), to thereby reduce a pressure in the chamber 5 to a gauge pressure of, for example, about 750 mmHg by evacuation through the pressure reducing pump P1. During the evacuation, water vapor is partially sucked in the pressure reducing pipe L1 prior to formation of water droplets. Also, moisture which tends to form water droplets on the surface of each of the forming mold A and resin form product B due to condensation is likewise removed by evacuation under a reduced pressure.
An injection molding machine of Type PS60E12ASE manufactured by Nissei Jushi Kogyo Kabushiki Kaisha, Japan was used as the injection machine S. The injection molding machine had a screw diameter of 36 mm, an injection rate of 12.3 cm/sec, an injection pressure of 1825 kgf/cm2, a screw rotation speed of 0 to 190 rpm at high torque and 0 to 250 rpm at low torque, and a back pressure of 60 kgf/cm2. The experiment was made under injection conditions that the injection rate, injection pressure, screw rotation speed, back pressure and variable are set to be 98%, 98%, 90%, 30% and 40 mm, respectively.
The forming mold A used was constructed by forming a punched metal wholly formed with holes of about 1.2 mm in diameter and having a thickness of 1.5 mm into a box-like shape (100 mm�100 mm�50 mm) by welding and the like. The chamber 5 was formed into a volume 50 1 in such a manner as shown in FIG. 4 uated to a gauge pressure of 750 mmHg.
TABLE 1______________________________________Release Lapse     Pressure Reduction                  Volume   DensityTime (sec)     Time (sec)   (cc)     (g/cc) State______________________________________0         5            635      0.041  .increment.5         0            454      0.050  X5         10           504      0.046  &#8728;5         20           502      0.046  &#8728;5         30           526      0.043  &#8728;5         120          531      0.043  &#8728;1         30           608      0.042______________________________________
In Table 1, X indicates that the resin foam exhibited remarkable shrinkage, Δ indicates that the resin foam was formed with a lot of voids, ◯ indicates that the foam was decreased in shrinkage, and ⊚ indicates that the foam was substantially free of shrinkage. The pressure reduction time "0" indicates that the chamber 5 was kept from being evacuated for pressure reduction, resulting in being kept at an atmospheric pressure. As will be noted from the results shown in Table 1, evacuation for pressure reduction permits shrinkage of the biodegradable resin to be decreased.
Although narrowed opening 1a is kept open and the hopper 11 of the cylinder 1 is also kept open, the cylinder 1 is kept closed to a certain degree. However, a decrease in degree of closing of the cylinder 1 causes pressurization in the cylinder 1 to be insufficient, so that there is a possibility that a relationship between a softening point or melting point of the biodegradable resin and a boiling point of moisture or water pressurized in the cylinder causes the moisture to be partially vaporized, resulting in foaming of the biodegradable resin occurring in the cylinder 1 prior to injection of the resin into the forming mold. Also, this tends to cause foaming of the biodegradable resin extruded from the narrowed opening 1a while causing it to hang down from the narrowed opening 1a. In order to avoid such a problem, it is preferable that the illustrated embodiment is provided with a means for increasing a degree of closing of the cylinder 1. For this purpose, the narrowed opening 1a may be provided with a nozzle equipped with a shut-off valve. Alternatively, the hopper 11 for feeding the starting material to the cylinder 1 may be constructed so as to be tightly closed. Also, the hopper may be provided with a rotary valve. Further, foaming of the biodegradable resin in the cylinder 1 prior to the injection may be restrained by dissolving a non-volatile solute such as polyethylene glycol in water and then adding the resultant solution to the biodegradable resin to increase a boiling point of water.
In the illustrated embodiment, it is not necessarily required to add the hygroscopic fine-particle material to the biodegradable resin. The biodegradable resin may have water previously contained therein. Alternatively, biodegradable resin containing equilibrium moisture under an atmospheric pressure may, be used for the present invention. Also, the biodegradable resin and moisture or water may be separately added to the hopper 1.
An inner space of the chamber 5 is kept pressurized, so that a cavity 31 and a core 41 of an air-permeable forming mold A communicating through pores of the forming mold A with the inner space of the chamber 5 is likewise pressurized. In this instance, when a pressure in the forming space R defined by the cavity 31 and core 41 is set at a level of, for example, 10 kgf/cm2 higher than a water vapor pressure at a temperature of the biodegradable resin injected through the narrowed opening or port 1a or, for example, at 170� C., the biodegradable resin may be extruded into the forming space R while keeping moisture trapped therein.
After the biodegradable resin is charged in the forming space R of the forming mold A, the pressure reducing and releasing valve V4 is rapidly and fully rendered open to permit a pressure in the chamber 5 to be reduced to an atmospheric pressure, so that the biodegradable resin in a heated and pressurized state is rapidly exposed to an atmospheric pressure, resulting in moisture trapped in the resin being instantaneously vaporized to foam the biodegradable resin. Also, vaporization of the moisture causes expansion force of water vapor to occur in the biodegradable resin. However, an outermost portion of the biodegradable resin is kept contacted with an outer surface of the forming mold A, to thereby be regulated by a configuration of the cavity 31 and core 41 and the water vapor is outwardly discharged through the pores of the forming mold A, so that such a biodegradable resin foam B integrally formed as shown in FIG. 3 may be obtained.
In the method described above, the forming space R defined by the cavity 31 and core 41 is kept pressurized until the fluidized biodegradable resin is injected from the cylinder 1 through the narrowed opening 1a into the forming space R, to thereby prevent foaming of the biodegradable resin. Then, a pressure in the forming space R is rapidly decreased to lead to foaming of the resin, so that the biodegradable resin foam B obtained may conform to a configuration of the forming mold A and exhibit uniformity, resulting in being effectively applied to a satisfactory cushioning material.
Then, as shown in FIG. 13(b), rotation of the screw 2 is stopped and a piston 23 in an injection cylinder 22 is actuated to advance the screw 2, resulting in the fluidized biodegradable resin being injected at a stretch through the narrowed opening 1a into the forming space R defined by the cavity 31 and core 41 while being kept atomized.
Also, in the illustrated embodiment, at least one nozzLe 12 may be arranged with respect to the narrowed opening 1a as shown in FIG. 14. In FIG. 14, a plurality of such nozzles 12 are arranged on the cylinder 1. Alternatively, the cylinder 1 may be provided at a distal end thereof with a shower 15 formed with a plurality of fine injection ports 14. Also, when the embodiment: is so constructed that the biodegradable resin is injected into the forming mold A through a runner and a gate (not shown), the runner and gate each may be formed into a small diameter to ensure that the injection is carried out while keeping it atomized.
The apparatus of the illustrated embodiment may be modified in such a manner as shown in FIG. 20. More particularly, in a modification of FIG. 20, a forming mold A is arranged in an airtight chamber 5 which can be divided into a movable-side part 51 and a fixed-side part 52, so that a pressure reducing valve V1 is rendered open at a predetermined timing such as, for example, in a one second before or after extrusion of the biodegradable resin through a narrowed port 1a into a forming mold A, to thereby reduce a pressure in the chamber 5 through a pressure reducing pipe L1 by means of a pressure reducing pump P1. Alternatively, the illustrated embodiment may be constructed in substantially the same manner as the apparatus described above with reference to FIG. 5, wherein the forming mold A is arranged in the ventilation duct D which is forcibly ventilated by means of the suction fan f. Such constructions each permit moisture to be forcibly removed from the forming mold A, to thereby more positively prevent shrinkage of the biodegradable resin. In FIG. 20, reference character L0 designates an atmospheric pressure releasing pipe and V0 is an atmospheric pressure releasing valve arranged in the middle of the pipe L0.
The chamber 5 has a pressure reducing pipe L1 connected thereto, which is provided in the middle thereof with a pressure reducing valve V1 and then connected through the pressure reducing valve V1 to a pressure reducing tank T1. The pressure reducing tank T1 is also connected thereto a pressure reducing pump P1. The pressure reducing tank T1 is reduced in pressure to a predetermined level near, for example, a vacuum and is adapted to communicate with the chamber 5 when the pressure reducing valve V1 is open. The pressure reducing tank T1 is required to have a volume sufficient to permit a pressure in the chamber 5 to be rapidly reduced when it communicates with the chamber 5. The remaining part of the apparatus of the illustrated embodiment may be constructed in substantially the same manner as the apparatus shown in FIG. 1.
First, the chamber 5 is clamped by the mold clamp mechanism 40 and closed while keeping an inner space thereof at, for example, an atmospheric pressure. Biodegradable resin fluidized as previously described is injected at a stretch from a cylinder 1 through the narrowed opening 1a into the forming mold A. After the injection, the pressure reducing valve V1 is rendered open to communicate the pressure reducing tank T1 with the chamber 5, to thereby rapidly reduce a pressure in the chamber 5 to a gauge pressure of, for example, about 750 mmHg. This causes moisture trapped in the biodegradable resin to be instantaneously vaporized to foam the resin. The resultant water vapor is caused to be discharged at a stretch through pores of the forming mold A to the pressure reducing tank T1. Concurrently, expansion force due to vaporization of the water vapor is exerted in the biodegradable resin, however, an outermost portion of the resin is kept contacted with the forming space R defined by the cavity 31 and core 41, resulting in being regulated by a configuration of the space R. Thus, a biodegradable resin foam of a predetermined configuration is provided.
Then, the pressure reducing valve V1 is closed to interrupt communication between the pressure reducing tank T1 an the chamber 5 and then a screw 2 is retracted while being rotated, during which the following or subsequent biodegradable resin is collected in an internal space of the cylinder 1 defined on a side of a distal end of the screw 2 while being fluidized, resulting in being ready for the next operation. Concurrently, the pressure reducing pump P1 is actuated to reduce a pressure in the pressure reducing tank T1 to the initial level again, during which the biodegradable resin foam in the forming mold A is allowed to be cooled and solidified. Then, the movable mold part 4 is moved away from the fixed mold part 3 to open the forming mold A, so that the biodegradable resin foam may be removed from the mold A, followed by re-clamping of the mold A for the next operation.
When the evacuation valve V2, as shown in FIG. 23, is rendered open in the course of injection of biodegradable resin into a forming mold A by means of an injection machine S to expose an interior of the chamber 5 to an atmospheric pressure. After the injection, the evacuation valve V2 is closed and the pressure reducing valve V1 is open to permit the pressure reducing tank T1 to communicate with the chamber 5, resulting in a pressure in the chamber being rapidly reduced. A timing at which the evacuation valve V2 is rendered open may be set between starting of the injection and termination thereof, therefore, the timing is not limited to any specific setting. It is determined depending on various factors such as a configuration of the forming mold A, a size of the chamber 5, a degree to which the cylinder 1 is pressurized during injection of the biodegradable resin, and the like.
Pressurization of the chamber 5 is carried out to obtain a pressure higher than a saturated water vapor pressure at a temperature at which the biodegradable resin is injected through a narrowed opening 1a into a forming mold A. For example, the pressure may be about 10 kg/cm2 when the injection takes place at 170� C. When the chamber 5 has the compressor C rather than a pressuring tank T3 connected thereto through the pressurizing valve V3 as described hereinafter, the pressurizing valve V3 may be kept open without being controlled or the pressurizing valve V3 may be eliminated.
In the embodiment of FIG. 25, a chamber 5 acting as a pressure adjusting chamber has a pressurizing pipe L3 connected thereto, which is provided in the middle thereof with a pressuring valve V3 and connected through the pressuring valve V3 to a compressor C. The pressurizing valve V3, as shown in FIG. 26, is rendered open at the time when injection of biodegradable resin into a forming mold A by means of an injection machine S is started, to thereby pressurize the chamber 5 through the compressor C. In the course of the injection, the pressurizing valve V3 is closed to interrupt pressurization of the chamber 5 through the compressor C and an evacuation valve V2 is open, resulting in the chamber 5 being exposed to an atmospheric pressure. After the injection, the evacuation valve V2 is closed and a pressure reducing valve V1 is open to permit a pressure reducing tank T1 to communicate with the chamber 5 to rapidly reduce a pressure in the chamber 5. The remaining part of the embodiment of FIG. 25 may be constructed in substantially the same manner as the apparatus shown in FIG. 22.
In the embodiment of FIG. 28, a chamber 5 functioning as a pressure adjusting chamber has a pressurizing pipe L3 connected thereto, which is provided in the middle thereof with a pressurizing valve V3 and connected through the pressuring valve V3 to a pressuring tank T3, which is then connected to a compressor C. The pressurizing tank T3 is permitted to communicate with the chamber 5 at the time when or before injection of biodegradable resin into a forming mold A by means of an injection machine S is started, to thereby rapidly pressurize the chamber 5. In the course of the injection, the pressurizing valve V3 is closed to interrupt communication between the tank T3 and the chamber 5 and an evacuation valve V2 is rendered open to expose the chamber 5 to an atmospheric pressure. After the injection, the evacuation valve V2 is closed and a pressure reducing valve V1 is rendered open, to thereby carry out communication between a pressure reducing tank T1 and the chamber 5, resulting in rapidly reducing a pressure in the chamber 5. The remaining part of the apparatus of FIG. 28 may be constructed in substantially the same manner as the apparatus of FIG. 22
Referring now to FIG. 29, a further embodiment of an apparatus of the. present invention is illustrated. An apparatus of the illustrated embodiment includes a chamber 5 which serves as a pressure adjusting chamber and in which an air-permeable forming mold A is arranged. The chamber 5 has a pressure reducing pipe L1 and a pressurizing pipe L3 connected thereto. The pressure reducing pipe L1 is connected thereto a pressure reducing tank T1 for rapid pressure reduction and the pressurizing pipe L3 is connected thereto a compressor C. The pressure reducing pipe L1 is provided in the middle thereof with a pressure reducing valve V1. An evacuation pipe L2 is connected to a portion of the pressure reducing pipe L1 between the pressure reducing valve V1 and the chamber 5 and provided in the middle thereof with an evacuation valve V2. The evacuation pipe L2 is open on an outlet side thereof to an ambient atmosphere. Actuation of the compressor C for pressurization and operation of each of the evacuation valve V2 and pressure reducing valve V1 are controlled by a valve controller 8. Reference character S designates an injection machine for injecting, into a forming mold A, fluidized biodegradable resin in a heated and pressurized state in which moisture is trapped.
Then, the pressurizing valve V3 is closed before completion of the injection and concurrently the compressor C is turned off, resulting in actuation of the compressor for pressurization being interrupted, and the evacuation valve V2 is kept open for a predetermined period of time. This causes the biodegradable resin being injected under pressure to be open to an ambient atmosphere in the course of the injection, leading to a reduction in injection resistance, so that the biodegradable resin may be spread throughout the forming model A. A timing at which the pressurizing valve V3 is closed and concurrently the compressor C is turned off to open the evacuation valve V2 is not necessarily definitely determined and is suitably adjusted depending on a configuration of the forming mold A, a volume of the chamber 5, a degree of the pressurization and evacuation, and the like.
FIG. 34 shows an additional embodiment of an apparatus of the present invention which is constructed so as to accomplish such an object. More particularly, an apparatus of the illustrated embodiment includes a forming mold A arranged forward of an injection machine S. The forming mold A includes a fixed mold part 3 formed with a cavity 31 communicating with a narrowed opening 1a and a movable mold part 4 formed with a core 41. The fixed mold part 3 and movable mold part 4 are mounted on a fixed-side mold plate 40A of a mold operating mechanism for the forming mold A and a movable-side mold plate 40B thereof, respectively. The cavity 31 is formed- into, for example, a rectangular shape and cooperates with the core 41 to define a forming space R in the forming mold A. The fixed mold part 3 is provided with an inlet port 81, communication holes 82 for releasing airtightness of the forming space R and an O-ring 83 for holding airtightness.
The forming space R of the forming mold A is tightly closed when the fixed mold part 3 and movable mold part 4 are clamped together by means of the mold operating mechanism of the forming mold A. The mold operating mechanism permits the movable mold part 4 to take a released position 01, an airtightly closed position 02, an airtightness released position 03 and the released position 01 in turn. The mold operating mechanism includes tie bars 42 and 43 for guiding the fixed-side mold plate 40A and movable-side mold plate 40B so as to permit the fixed mold part 3 and movable mold part 4 to access to each other while being opposite to each other and an actuation mechanism 44 for accessibly actuating the movable mold part 4.
Then, rotation of the screw 2 is stopped and a piston 23 in an injection cylinder 22 is driven to advance the screw 2, so that the fluidized biodegradable resin may be injected at a stretch from the cylinder 1 through the narrowed opening 1a and inlet port 81 into the forming space R. After the injection, the movable mold part 4 of the forming mold A is moved to the airtightness released position 03 through the mold operating mechanism, so that the forming space R is rapidly reduced in pressure to a level of an atmospheric pressure through the communication holes 82, so that moisture trapped in the fluidized biodegradable resin is instantaneously vaporized to foam the resin and then outwardly discharged in the from of water vapor through the communication holes 82. At this time, expansion force due to formation of the water vapor is exerted in the foamed biodegradable resin, however, an outermost portion of the foamed resin is regulated by the forming space R defined by the cavity 31 and core 41, so that a biodegradable resin foam of a predetermined configuration may be produced.
Then, the screw 2 is retracted while being rotated, during which the next biodegradable resin fluidized is collected in the inner space of the cylinder defined on the side of the distal end of the screw 2 for the next operation. During the period, the biodegradable resin foam formed in the forming space R is allowed to be cooled and solidified, thus, actuation of the mold operating mechanism permits the movable mold part 4 to be moved to the released position 01 for removal of the resin foam B and then returned to the airtightly closed position 02 for the next operation.
First, the movable mold part 4 of the forming mold A is moved to the released position 01 by means of the mold operating mechanism. Then, the biodegradable resin is placed in the forming space R defined by the cavity 31 and core 41 and then actuation of the mold operating mechanism causes the movable mold part 4 to be moved to the airtightly closed position 02 to keep the forming space R airtight. Under such conditions, the forming mold A is heated by the heating means 9 to cause the biodegradable resin to be fluidized. The forming space R is in a heated and pressurized state, to thereby prevent moisture contained in the biodegradable resin from being vaporized, resulting in being forcibly trapped in the resin. Then, the movable mold part is moved to the airtightness released position 03 through the mold operating mechanism to reduce a pressure in the forming space R to a level of an atmospheric pressure through the communication holes 82, so that moisture trapped in the biodegradable resin may be instantaneously vaporized to foam the resin by expansion force due to vaporization of moisture and the resultant water vapor is outwardly discharged from the forming space R through the communication holes 82, resulting in a biodegradable resin foam of a desired configuration being produced in the forming space R. The resin foam is allowed to be cooled and solidified and then the movable mold part 4 is moved to the released position 01 through actuation of the mold operating mechanism, followed by removal of the resin foam therefrom. The above-described procedure is repeated for the next operation.
Referring now to FIG. 36, even another embodiment of an apparatus of the present invention is illustrated. In FIG. 36, reference numeral 5 designates a chamber, which is constituted by a mold M of a so-called injection molding machine and includes a fixed mold part m1 formed with a cavity communicating with a narrowed opening 1a and a movable mold part m2. The fixed mold part m1 and movable mold part m2 are mounted on a fixed-side mold plate 40A of a mold clamp mechanism and a movable-side mold plate 40B thereof, respectively. The cavity is formed into a rectangular shape and more particularly a rectangular parallelepiped shape, resulting in forming an inner chamber in the chamber 5, in which an air-permeable press die N corresponding to the forming mold M is arranged.
The air-permeable press die N is formed with a plurality of pores which permit water vapor to pass through as in the forming mold A described above and may be made of a sintered metal material such as foamed metal sintered and formed, a sintered ceramic material such as ceramic sintered to which a void forming filler is added, or the like. Alternatively, it may be formed of a wire mesh, a punched metal plate formed with a number of holes or the like. The press die N is divided into an upper die part n1 and a lower die part n2, which are adapted to be movable between a foaming position 04 and a pressing position 06 through access mechanisms 60a and 60b, respectively.
The chamber 5 is tightly closed when the fixed mold part M and movable mold part m2 of the mold M are clamped together through the mold clamp mechanism. The chamber and mold clamp mechanism may be arranged while being exposed to an atmospheric pressure. The chamber 5 has a pressure reducing pipe L1 connected thereto, which is provided in the middle thereof with a pressure reducing valve V1 and connected to a pressure reducing pump P1 through the pressure reducing valve V1. A pressure reducing tank may be connected between the pressure reducing valve V1 and the pressure reducing pump P1 as required.
First, the pressure reducing valve V1 is closed to render the chamber 5 airtight and the upper and lower die parts n1 and n2 of the press die N are positioned at the foaming position 04. Then, biodegradable resin fluidized or melted is injected through the narrowed opening 1a into the press die N. Then, the pressure reducing valve V1 is open to reduce a pressure in the chamber 5, so that moisture trapped in the resin is instantaneously evaporated or vaporized to foam the resin and the resultant water vapor is outwardly discharged through the pores of the press die N and pressure reducing valve V1. At this time, expansion force due to vaporization of the water vapor is exerted in the biodegradable resin, however, an outermost portion of the resin is kept contacted with an inner surface of the press die N, so that a foamed portion of the resin is regulated by a configuration of the press die N at the foaming position 04. After the foaming, the upper and lower die parts n1 and n2 of the press die N are rapidly moved to the pressing position 05 by means of the access mechanisms 60a and 60b, respectively, resulting in the forming space R being reduced in volume, so that: the foamed resin may be compressed as compared with the initial foamed state. Thus, any cavity and/or void occurring in the foamed resin in the initial foaming stage are extinguished due to the compression, thus, a biodegradable resin foam exhibiting satisfactory quality is provided. Reduction of the forming space R after the foaming should be carried out under the condition that moisture still remains in the forming space R; because cells of the foamed resin are hard to adhere to each other when cooling and solidification of the foamed resin are substantially advanced, resulting in the space R being substantially free of water vapor.
The above-described construction of the apparatus of FIG. 36 may be incorporated in the apparatus of each of FIGS. 34 and 35. The apparatus of FIG. 34 may be constructed so as to move the movable mold part 4 of the forming mold A in an order of the released position 01, the airtightly closed position 02, the airtightness released position 03, the pressing position and the released position 01 rather than in an order of the released position 01 the airtightly closed position 02, the airtightness released position 02 and the released position 01. In the illustrated embodiments, the airtightly closed position 02 and pressing position 05 are substantially the same.
Thus, after the forming, the movable mold part 4 of the forming mold A is rapidly moved to the pressing position 05 by means of the mold operating mechanism to reduce a volume of the forming space R. so that the biodegradable resin foam is formed while being kept compressed as compared with a volume thereof obtained in the initial foaming stage. This permits any cavity and/or void occurring in the initial foaming stage to be effectively extinguished, to thereby provide the biodegradable resin foam with improved quality. Also, the forming space R is rendered open through the communication holes 82 to a pressure reduced atmosphere such as, for example, an ambient atmosphere after the movable mold part 4 is moved to the airtightness released position 03, so that it may be instantaneously reduced in pressure in bulk, to thereby prevent softening and collapsing of the resin foam due to re-adhesion of moisture thereto, resulting in ensuring satisfactory quality of the resin foam.
Also, the illustrated embodiment may be so constructed that the movable mold part 4 of the forming mold A takes the airtightness released position 03, pressing position 05 and released position 01 and is moved to the released position 01, airtightness released position 03, pressing position 05 and released position 01 in order. Such construction permits the fluidized and water-trapped biodegradable resin in a heated and pressurized state to be injected into the forming mold A through the inlet port 81 by means of the injection machine S at the airtightness released position 03 to which the movable mold part 4 has been moved by means of the mold operating mechanism. At this time, the forming space R is permitted to communicate with an ambient atmosphere through the communication holes 82, resulting in being released from pressure, so that expansion force due to vaporization of moisture contained in the resin leads to formation of the biodegradable resin foam. Immediately after the foaming, actuation of the mold operating mechanism permits the movable mold part 4 to be rapidly moved to the pressing position 05 to reduce a volume of the forming space R, so that formation of the biodegradable resin foam may be carried out while keeping the product compressed. Thus, it will be noted that such injection of the biodegradable resin into the forming space R at the airtightness released position 03 exhibits the same function and advantage as described above.
The above-described construction of the illustrated embodiment may be incorporated in the apparatus shown in FIG. 35. Thus, movement of the movable mold part 4 of the forming mold A to the pressing position 05 by means of the mold operating mechanism upon the foaming causes a decrease in volume of the forming space R, resulting in the biodegradable resin foam B being provided while compressed. After the foam product B is cooled, to thereby be solidified, the movable mold part 4 is moved to the released position 01 by means of the mold operating mechanism, followed by removal of the resin foam B from the forming mold A. Such construction exhibits the same function and advantage as described above.
As can be seen from the foregoing, the biodegradable resin foam of the present invention comprises a combination of the main biodegradable resin ingredient or first biodegradable resin ingredient having a melting point of 100� C. or more and the low-melting biodegradable resin ingredient or second biodegradable resin ingredient having a melting point of 100� C. or less. Thus, in the resin foam, the second biodegradable resin ingredient is kept from being immediately solidified, to thereby function as an adhesive with respect to the first biodegradable resin ingredient. Thus, even when any cavity and/or void are generated in the foamed biodegradable resin, cells of the foamed resin are permitted to adhere to each other, resulting in the biodegradable resin foam being provided with satisfactory quality.
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