Method for blow molding hollow articles and device for the same

Abstract: In a blow molding process, a fused thermoplastic polymer parison (2) is interposed between a pair of split molds (1a,1b). The split molds (1a,1b) are closed around the parison (2) to seal the ends (2a,2b). A small diameter hollow needle (6) is inserted through one of the split molds (16) and fluid is blown into the parison (2) forming a balloon (2'). After the balloon (2') begins to form, a large diameter hollow needle (7) is inserted while internal pressure is applied to the parison (2) via the small diameter hollow needle (6), and a large amount of fluid is blown in. If the balloon (2') contacts the sides of the molds (1a,1b) before fluid is blown through the large diameter hollow needle (7), a glossy (2'') is formed. This process is highly productive and reduces the conventional blow molding cycle by 60 percent due to the rapid cooling of the hollow article.

Description: BACKGROUND OF THE INVENTION The present invention relates to an improved method and device for blow molding and shaping hollow articles. In particular, the present invention relates to a highly productive method and device for direct blow molding which allows rapid cooling of articles shaped by parison expansion or blowing. Blow molding is a technique adopted from the glass industry for molding plastic bottles and other articles from thermoplastic material. The direct blow molding process has been widely used for the shaping of hollow articles made of thermoplastic synthetic resins. It consists of blowing a thin balloon of molten thermoplastic material against the inside walls of a mold and chilling it to a rigid solid. In its most common form, this process includes extruding or injecting a parison downward between the opened halves of a mold, closing the mold to pinch off and seal the parison at top and bottom, injecting air or other fluid through a needle inserted through the parison wall, cooling the mass in contact with the mold, opening the mold, and removing the formed article. It is difficult to insert a thick needle into the parison to inject air or other fluid because the parison is relatively soft at high temperatures. It is therefore necessary to use a hollow needle having a thin and sharp tip. Air is a fluid and as such is limited in its ability to flow through an orifice. If the air entrance channel is too small, the required blow time is excessively long or the pressure exerted on the parison is inadequate to reproduce the surface details of the mold. Furthermore, while a small amount of air may be adequate for expanding the parison, it might not be enough for cooling the expanded hollow article. Although small articles can be shaped this way, it is not possible to shape large articles. --One technique to improve the amount of air introduced in a parison is shown in Peters et al. (U.S. Patent 3,492,106) which also describes an apparatus according to the preamble of claim 1. In this technique, a second, larger hollow needle is introduced to an interior of a parison after a first thinner hollow needle partially inflates the parison. A greater volume of air can then be injected into the parison through the second hollow needle. In this way, the required blow time can be reduced. Peters et al. and Di Settembrini (French Patent 2 306 820) disclose a method for molding hollow articles in which a hollow needle is introduced in an area corresponding to the flash section of the mold. If also discloses a method in which two needles for a double blowing or a blowing combined with a degassing are used. In the direct blow molding method, a technique used to prevent cosmetic damage to the shaped article includes forming an exhaust opening through an unnecessary section of the article that is cut off after formation to serve as an opening (referred to as the flash section). Another technique includes inserting the hollow needle from an angle perpendicular to the main axis of the parison. In blowing air into the hollow article from this position, it is desirable to blow in the direction of the body of the article, i.e., downward along the axis of the parison, so that the air can flow easily. However, thin needles can only be designed with an opening at the tip of the needle due to the size constraints. A needle bent to a 90 degree angle cannot penetrate the parison. Thus, it is only possible to blow air in a direction perpendicular to the direction of the parison axis, and effective circulation of the air within the parison is prevented. Since a large amount of air for cooling can not be blown into the parison, more time is required for cooling the article. Cooling is particularly important because it consumes much of the cycle time and therefore bears on product economics. Cooling can take as much as two thirds of the entire "mold-closed" time in a cycle. Results are best when uniform temperatures are maintained throughout the mold. Standard cooling techniques are directed towards either external systems or internal systems or a combination thereof. External systems cool the mold by circulating coolants around the outside or through the walls of the mold. Mold cooling can be improved by increasing the rate of coolant flow through the mold or by making the mold of material with better heat transfer. Internal systems rely on injecting fluids such as air, a mixture of air and water, or carbon dioxide into the blown part to cool the inside of the parts while they are in the mold. Typical commercial methods include (1) injecting liquid carbon dioxide into the blown part, followed by vaporization, superheating, and exhaustion of the coolant as a gas through the blow pin, (2) injecting highly pressurized moist air into the blown part where it expands to normal blow pressures and produces a cooling effect, (3) passing air through a refrigeration system and into the hot parison, and (4) cycling normal plant air into and out of the blown parts by a series of timers and valves. The size of the hollow needle used for injecting the fluid limits both the speed of the process and the size of articles made using the process. OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and device for the direct blow molding of hollow articles using a large diameter hollow needle in addition to a conventional small diameter hollow needle. A further object of the present invention is to provide a highly productive method and device for shaping hollow articles made of thermoplastic polymers. According to the present invention these objects have been achieved with the features of independent claims 1 and 19. Dependent device claims 2 to 18 and dependent method claims 20 to 34 disclose some particular aspects of the present invention. When shaping a hollow article by the direct-blow method according to the present invention, blowing fluid through a large diameter hollow needle allows a large amount of fluid to be blown into the parison and provide effective cooling. This makes it possible to form large articles. In addition, using a large diameter hollow needle allows the position of its orifice to be changed freely, thus allowing efficient expansion of the parison. The orifice need not be located at a tip of the large diameter hollow needle. Large diameter hollow needles can not directly puncture a parison wall because the parison wall is relatively soft at high temperatures. When the large diameter needle is forced against the outside of the parison wall, the softness of the thermoplastic material permits substantial deformation. However, by initially using a small diameter hollow needle to puncture the parison and blow fluid into the parison, the parison is given internal pressure. This internal pressure counteracts the elasticity of the balloon wall and thereby makes it possible to insert the large diameter hollow needle shortly after the small diameter hollow needle is inserted without producing undesired distortion. By using a combination of a large diameter hollow needle and a small diameter hollow needle, the present invention enables the use of larger diameter needles than could be used in the prior art. Using a large diameter needle allows a large amount of fluid to be rapidly blown into the parison. This permits the rapid expansion of the parison as well as adequate cooling, thus making it possible to improve the formation process. Since a large amount of fluid can be blown in, large bottles can be formed quickly and efficiently. A parison having a bottom or a tube-shaped parison can be used as the parison in the present invention. The flash section is arranged in the area above the section that forms the opening of the article. Arranging a protrusion or cavity in the flash section where the large diameter hollow needle is inserted keeps this section thin during blowing, which is especially desirable because it makes inserting the large diameter hollow needle easier. Briefly stated, in a blow molding process, a fused thermoplastic polymer parison is interposed between a pair of split molds. The split molds are closed around the parison to seal the ends. A small diameter hollow needle is inserted through one of the split molds and fluid is blown into the parison forming a balloon. After the balloon begins to form, a large diameter hollow needle is inserted while internal pressure is applied to the parison via the small diameter hollow needle, and a large amount of fluid is blown in. If the balloon contacts the sides of the molds before fluid is blown through the large diameter hollow needle, a glossy bottle is formed. This process is highly productive and reduces the conventional blow molding cycle by 60 percent due to the rapid cooling of the hollow article. The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a section view of an embodiment of the present invention showing a split mold in an open state and hollow needles in an inactive (retracted) position. Fig. 2a is a section view of an embodiment of the present invention showing the split mold in a closed state and the small diameter hollow needle in an active (inserted) position in a normal bottle parison. Fig 2b is a section view of an embodiment of the present invention showing the split mold in a closed state and the small diameter hollow needle in an active (inserted) position in a glossy bottle parison. Fig. 2c is a section view of an embodiment of the present invention showing the split mold in a closed state with both hollow needles in an active (inserted) position. Fig. 3 is a detailed section view showing both of the hollow needles in an inactive position. Fig. 4 is a detailed section view showing the small diameter hollow needle in the active position with a fluid being blown therethrough and the large diameter hollow needle in the inactive position. Fig. 5 is a detailed section view showing both hollow needles in the active position with fluid being blown through both needles. Fig. 6 is a detailed section view showing the small diameter hollow needle beginning to retract while fluid is still being blown through the large diameter hollow needle. Fig. 7a is a side section view showing a cam control mechanism for controlling the timing of the movement of the hollow needles. Fig. 7b is a section view of the cam movement of part A of Fig. 7a. Fig. 7c is a section view of the cam movement of part B of Fig. 7a. Fig. 8 is a timing diagram showing the relation between the cam movements shown in Figs. 7a-7c and the injecting of fluid through the hollow needles. Fig. 9 is a valve diagram showing a control mechanism according to an embodiment of the present invention. Fig. 10 is a detailed section view of the hollow needles inserted into the parison adjacent each other according to an alternative preferred embodiment. Fig. 11 is a section view depicting a thinning cavity inside the flash cavity according to an alternative embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, a pair of split molds 1a and 1b, which can be opened and closed, include pinch-off sections 3a and 3b, cavity sections 4a and 4b, and flash cavity sections 5a and 5b. Pinch-off sections 3a and 3b seal parison top 2a when the split molds close. Parison bottom 2b is already closed from the extrusion process that produces parison 2. Small diameter hollow needle 6 and large diameter hollow needle 7 are arranged at the top of split mold 1b such that, when inserted into parison 2, they penetrate flash cavity section 5b. Fluid supply mechanism 10 and control device 11 allow for air or other fluid to be injected into parison 2 through small diameter hollow needle 6 and large diameter hollow needle 7 at the proper times. Exhaust opening formation mechanism 8 allows any air trapped between parison 2 and a side of closed split molds to vent, and also allows the injected air or other fluid to vent to the outside of parison 2 and mold after expansion of parison 2 is completed. After the hollow article cools sufficiently, knockout pin 9 removes the cooled hollow article from split mold 1b as split molds 1a and 1b separate. Referring to Fig. 2a, when split molds 1a and 1b are closed, cavity sections 4a and 4b form cavity 4 and flash cavity sections 5a and 5b form flash cavity 5. Pinch-off sections 3a and 3b seal parison top 2a and the portion of the extruded tube (not shown) that becomes parison bottom 2b of the next parison to enter the mold. The air or other fluid blown through small diameter hollow needle 6 and large diameter hollow needle 7 inflates parison 2 against the sides of the mold to form the hollow article. Exhaust opening formation mechanism 8 allows the injected air or other fluid to vent to the outside of parison 2 and the mold. After the hollow article cools sufficiently, knockout pin 9 removes the cooled hollow article from split mold 1b as split molds 1a and 1b separate. Flash section 5c is then trimmed. Flash section 5c is a section formed on an upper opening of the hollow article where small diameter hollow needle 6, large diameter hollow needle 7, exhaust opening formation mechanism 8, and knockout pin 9 are formed. Since flash section 5c is cut off after the blowing process, the final article bears no cosmetic damage caused by the production process. Small diameter hollow needle 6 and large diameter hollow needle 7 move forward and backward between the inactive or retracted position shown in Fig. 1 and the active position shown in Fig. 2c. Pressurized fluid supply mechanism 10a supplies pressurized fluid to parison 2 through small diameter hollow needle 6 and pressurized fluid supply mechanism 10b supplies pressurized fluid through large diameter hollow needle 7. Two control devices 11a and 11b control the timing of the movement of the hollow needles and the action of the fluid from a pressurized fluid source (not shown in the drawings) via pressurized fluid supply mechanism 10. The pressurized fluid is preferably compressed air. In this embodiment, the fluid is used to move the hollow needles between the active and inactive positions in addition to being used to inflate parison 2. Referring to Fig. 3, small diameter hollow needle 6 and large diameter hollow needle 7 are forced to the rear of their respective fluid cylinders by fluid flowing from fluid supply openings 14a and 14b at the front of the cylinders. Small diameter hollow needle 6 and large diameter hollow needle 7 are in the inactive position. Small diameter hollow needle 6 and large diameter hollow needle 7 are held within fluid cylinders 13a and 13b respectively, which are included in drive devices 12a and 12b respectively. The hollow needles move forward and backward within these cylinders. Drive devices 12a and 12b also include fluid supply openings 14a, 14b, 15a, and 15b, which are formed on the sides of fluid cylinders 13a and 13b for supplying pressurized fluid. Fluid supply openings 14a and 14b pass through the front side of fluid cylinders 13a and 13b. Fluid supply openings 15a and 15b pass through the rear side of fluid cylinders 13a and 13b. The fluid supplied through these fluid supply openings either flows within the cylinders or flows from the back of each hollow needle to the front and into parison 2. Drive device 12a for small diameter hollow needle 6 and drive device 12b for large diameter hollow needle 7 are arranged so that they can move in parallel. This permits the control mechanism and the pressurized fluid supply mechanism to be used in common, and also contributes to simplifying the devices required for supplying fluid and moving the hollow needles. Referring now to Fig. 4, fluid from fluid supply opening 14a is stopped and fluid from fluid supply opening 15a is started. Small diameter hollow needle 6 moves forward toward the parison and penetrates it in flash cavity 5. Once the rear end of small diameter hollow needle 6 clears fluid supply opening 15a, fluid flows through small diameter hollow needle 6 into parison 2, thereby creating internal pressure in balloon 22 inside the mold. Large diameter hollow needle 7 remains retracted since fluid is still supplied from fluid supply opening 14b which forces large diameter hollow needle 7 to the rear. Referring now to Fig. 5, fluid from fluid supply opening 14b to large diameter hollow needle 7 is stopped and fluid from fluid supply opening 15b is started. This causes large diameter hollow needle 7 to move forward to penetrate parison 2. Since the parison is given internal pressure which counteracts the elasticity of the wall of balloon 22, it is possible to insert large diameter hollow needle 7 shortly after small diameter hollow needle 6 is inserted. Once the rear end of large diameter hollow needle 7 clears fluid supply opening 15b, fluid flows through large diameter hollow needle into parison 2 and balloon 22, thereby greatly increasing the total rate of flow of fluid inside parison 2. Referring now to Fig. 6, while fluid is being supplied to large diameter hollow needle 7 from fluid supply opening 15b, the fluid from fluid supply opening 15a to small diameter hollow needle 6 is stopped and fluid from fluid supply opening 14a is started. This causes small diameter hollow needle 6 to move to the rear. At the completion of the blowing cycle, large diameter hollow needle 7 retracts in a similar manner (not shown). When expansion of the parison is almost complete, a small diameter exhaust opening is formed in order to circulate fluid blown into the parison. As shown in Figs. 1-2, exhaust opening formation mechanism 8 includes a nozzle which is inserted into flash section 5c, where small diameter hollow needle 6 and large diameter hollow needle 7 are inserted. Exhausting the fluid through exhaust opening formation mechanism 8 while fluid is still being fed through large diameter hollow needle 7 increases the circulation of fluid inside the hollow article and enhances the cooling process. However, as noted in Japanese laid-open patent 59-3260, it is also possible to form an exhaust opening using the pressurized fluid within the upper pinch-off section of the split mold. After the fluids are exhausted, the shaped hollow article is removed from the mold using a knock-out pin such as knock-out pin 9. This completes the shaping of the hollow article. Positioning large diameter hollow needle 7 more toward the parison body side than small diameter hollow needle 6, which is roughly centered within the diameter of flash cavity 5, makes it possible for the large amount of fluid blown in through large diameter hollow needle 7 to circulate more efficiently. The well known small diameter needles used in conventional direct blow methods can also be used as the small diameter needle in the present invention. The orifice diameter of small diameter hollow needle 6 varies according to the size of the article to be formed, but generally the diameter is between 0.5 mm and 5 mm, and in particular, 1.5 mm to 3 mm is desirable. The orifice diameter of large diameter hollow needle 7 is 3 to 15 times larger than that of small diameter hollow needle 6, and in particular, a factor of 4 to 10 is desirable. In other words, based on a conventional small diameter hollow needle 6 size between 0.5 mm and 5 mm, the orifice diameter of large diameter hollow needle 7 is 1.5 mm to 75 mm, and in particular, a diameter of 2.0 mm to 50 mm is desirable. A smaller diameter needle does not supply enough fluid for cooling and a larger diameter needle is very difficult to insert into the parison. Unlike small diameter hollow needle 6, large diameter hollow needle 7 can be constructed so that the orifice through which fluid is blown is located other than at the tip of the needle. Thus, the orifice can be arranged at the side of large diameter hollow needle 7 instead of at the end. Figs. 5-6 depict orifice 21 located on the side of large diameter hollow needle 7 which permits fluid to be blown into parison 2 in the direction of balloon 22, i.e., in the vertical axis direction. This arrangement allows the fluid to circulate efficiently within the parison body. Referring to Figs. 7a through 7c, an alternative embodiment is shown using cams instead of fluid pressure to control small diameter hollow needle 6 and large diameter hollow needle 7. Cam 16a controls the movement of small diameter hollow needle 6 via pilot valve 17a and cam 16b controls the movement of large diameter hollow needle 7 via pilot valve 17b. Pilot valves 17a and 17b are connected to a pressurized fluid supply (not shown). Cam 16a and cam 16b rotate in the direction indicated by the arrows in Figs. 7b and 7c respectively. The split mold closing position is 0 degrees (not shown). Small diameter hollow needle 6 and large diameter hollow needle 7 do not move while cams 16a and 16b are between 0 degrees and point A. When cam 16a reaches point A, cam roller 28 opens pilot valve 17a and small diameter hollow needle 6 is inserted into the parison by the action of the pressurized fluid. Fluid is blown into the parison from small diameter hollow needle 6 while cam 16a is between point A and point B thus applying an internal pressure to the parison. When cam 16b reaches point C, cam roller 29 opens pilot valve 17b and large diameter hollow needle 7 is inserted into the parison by the action of the pressurized fluid. Fluid is blown into the parison from large diameter hollow needle 7 while cam 16b is between point C and point D. Referring also to Fig. 8, the relation between the cam movements and the closing and opening of split molds 1a and 1b is depicted. The split mold closing position is 0° and the split mold opening position is 360°. When cam 16a reaches point A, small diameter hollow needle 6 is inserted into parison 2 and fluid is blown in. Fluid flows through small diameter hollow needle 6 during a time L After a short time S, during which fluid is blown in through small diameter hollow needle 6 only, cam 16b has rotated to position C, and large diameter hollow needle 7 is inserted into parison 2. Large diameter hollow needle 7 penetrates the parison wall because the internal pressure created by small diameter hollow needle 6 counteracts the elasticity of the balloon wall. Fluid flows through large diameter hollow needle 7 during a time Q. During a time W, fluid flows into parison 2 through both hollow needles. Time W ends when cam 16a reaches point B and small hollow needle 6 retracts. Fluid continues to flow into parison 2 through large diameter hollow needle 7 until cam 16b reaches point D, at which point large diameter hollow needle 7 retracts. The parison 2 expands during time L, forming the desired shape and size. For small articles, the inside of the shaped hollow article is cooled during time Q by the fluid blown through large diameter hollow needle 7. For large articles, some expansion of parison 2 continues during part of time Q, after which cooling occurs. In normal bottle molding according to the present invention, small diameter hollow needle 6 blows pressurized fluid into parison 2 for a short time. The bottle shape is not formed yet and is shown in Fig. 2a. The pressurized fluid from small diameter hollow needle 6 supports parison 2 to permit large diameter hollow needle 7 to penetrate flash section 5c without substantial distortion. Large diameter hollow needle 7 is then used to blow pressurized fluid into parison 2, performing the blow molding, causing parison 2 to expand and shape itself against the contours of cavity 4, as shown in Fig. 2c. Small diameter hollow needle 6 is inserted into parison 2 about 0.1 to 0.2 seconds after split molds 1a, 1b close. The time L is 0.1 to 10 seconds, and in particular, 0.5 to 4 seconds is desirable. The time S is 0.2 to 2 seconds, and in particular, 0.3 to 1 second is desirable. If time S is shorter than this interval, the internal pressure within parison 2 is inadequate to allow the insertion of large diameter hollow needle 7. If time S is longer than this interval, the production cycle is unnecessarily slowed down. Time Q is 3 to 30 seconds, and in particular, 3 to 20 seconds is desirable. Time W is 0.1 to 10 seconds, and in particular, 0.1 to 5 seconds is desirable. If time W is shorter than this interval, the fluid supplied by large diameter hollow needle 7 may back up into small diameter hollow needle 6. If time W is longer than this interval, the production cycle is unnecessarily slowed down. However, if a glossy bottle is molded, it is necessary to blow in pressurized fluid while waiting for parison 2' to expand substantially against the walls of cavity 4 under pressure of the fluid from small diameter hollow needle 6, as shown in Fig. 2b, before inserting large diameter hollow needle 7. If this step is not performed, there is no glossiness to the hollow bottle. Therefore, the blowing by small diameter hollow needle 6 lasts somewhat longer for a glossy bottle than for a normal bottle. The second blowing through large diameter hollow needle 7 takes place once the bottle shape is formed to speed up the cooling of parison 2" as show in Fig. 2c. In the present invention, time S is 0.5 seconds, plus or minus 0.2 seconds, for normal bottles. For glossy bottles, time S is 0.8 seconds, plus or minus 0.2 seconds. Referring now to Fig. 9, conventional valves and techniques are used for controlling the operation of the hollow needles according to an embodiment of the present invention. A pressurized fluid, such as compressed air or dry nitrogen, flows from fluid supply 24 to pilot valves 17a and 17b. Cam roller 28 controls pilot valve 17a, and in a like fashion, cam roller 29 controls pilot valve 17b. When pilot valve 17a is activated, fluid flows through master valve 19, through control valve 20, and into fluid supply opening 15a. Small diameter hollow needle 6 is thus moved forward. As pilot valve 17b is activated, fluid flows through master valve 26 and into fluid supply opening 15b. Large diameter hollow needle is thus moved forward. When master valve 23 is activated by fluid from master valve 26, the fluid flow to small diameter hollow needle 6 is cut off. The role of master valve 23 is to ensure fluid is blown through small diameter hollow needle 6 for a short period even after fluid begins blowing through large diameter hollow needle 7. This timing prevents the fluid inside the parison from backing up into small diameter hollow needle 6. After cam 16a rotates to point B as shown in Fig. 7b, the fluid flow to small diameter hollow needle is stopped. Fluid continues to flow through large diameter hollow needle 7 until cam 16b rotates to point D in Fig. 7c. The exhaust opening formation mechanism 8 shown in Fig. 2 retracts shortly after fluid begins blowing through large diameter hollow needle 7, and the pressure of the fluid creates an opening in flash cavity 5c. Fluid continues to be blown through large diameter hollow needle 7 and circulates inside the hollow article before being exhausted. This fluid circulation cools the thermoplastic material quickly. After fluid is cut off by pilot valve 17b, large diameter hollow needle 7 and small diameter hollow needle 6 retract. Any conventional control techniques, such as pneumatic, hydraulic, electronic, or digital, may be used to ensure the proper timing of the movement of the hollow needles and the blowing of fluid through the needles. For example, the timing of blowing the fluid through the hollow needles can be controlled using electronic timers. Referring to Fig. 10, an alternative embodiment is shown in which the drive devices for the hollow needles are not parallel. When the drive devices are parallel, the minimum distance between the hollow needles equals the radius of drive device 12a plus the radius of drive device 12b. Instead, the hollow needles are disposed at angles to each other perpendicular to the article axis. Large diameter hollow needle 7 and small diameter hollow needle 6 are positioned so that they are angled with respect to each other instead of parallel to each other. This positioning allows large diameter hollow needle 7 and small diameter hollow needle 6 to be inserted into flash section 5c of parison 2 at close to the same longitudinal position on the article axis. The size of flash section 5c can thus be minimized. In an embodiment with large or bulky drive devices 12a and 12b, this arrangement allows the hollow needles to be positioned much closer to each other along the article axis than would otherwise be possible. A cycle begins when parison 2 is moved into mold 1. Parison guide pins 30 and 31, shown extended for illustrative purposes only, are fully retracted into their respective cylinders at the beginning of the cycle. In a similar fashion, small diameter hollow needle 6 is fully retracted into drive device 12a and large diameter hollow needle 7 is fully retracted into drive device 12b at the beginning of the cycle. Cooling passage 32 allows cooling water to circulate inside the body of mold 1 to reduce the temperature. Drive devices 12a and 12b include fluid supply openings 14a, 14b, 15a, and 15b, which supply pressurized fluid. Fluid supply openings 14a and 14b pass through the front side of drive devices 12a and 12b. Fluid supply openings 15a and 15b pass through the rear side of drive devices 12a and 12b. Fluid flows through fluid supply openings 14a and 14b and does not flow through fluid supply openings 15a and 15b, thus keeping both needles in the inactive (retracted) position. After parison 2 enters mold 1, parison guide pins 30 and 31 extend to hold parison 2 in place. After mold 1 is fully closed, parison guide pins 30 and 31 keep parison 2 centered while small diameter hollow needle 6 penetrates it. Other conventional means can be used as parison guides. In the next step of the cycle, the fluid flowing through fluid supply opening 14a is stopped and fluid flow through fluid supply opening 15a is started. Small diameter hollow needle 6 moves forward toward the parison and penetrates it. Once the rear end of small diameter hollow needle 6 clears fluid supply opening 15a, the fluid flows through the inside of small diameter hollow needle 6 and into parison 2, thereby creating internal pressure inside parison 2. Large diameter hollow needle 7 remains in its inactive position while fluid is supplied from fluid supply opening 14b, thus forcing large diameter hollow needle 7 to the inactive position. In the next step of the cycle, the fluid through fluid supply opening 14b to large diameter hollow needle 7 is stopped and fluid through fluid supply opening 15b is started. This causes large diameter hollow needle 7 to move forward to penetrate parison 2. The internal pressure provided by small diameter hollow needle 6 resists deformation of parison 2 when large diameter hollow needle 7 is inserted. Once the rear end of large diameter hollow needle 7 clears fluid supply opening 15b, fluid passes through large diameter hollow needle 7 inside parison 2, thereby greatly increasing the total rate of flow of fluid into parison 2. Parison 2 is blown to conform to the inner surface of mold 1 and then cools. At the completion of the blowing cycle, the fluid through fluid supply openings 15a and 15b to small diameter hollow needle 6 and large diameter hollow needle 7 is stopped and fluid from fluid supply openings 14a and 14b is started. This causes small diameter hollow needle 6 and large diameter hollow needle 7 to retract for the beginning of the next cycle. Referring to Fig. 11, an alternative embodiment includes a thinning cavity 5d in flash cavity 5 which reduces the thickness of parison 2 at the site of large diameter hollow needle 7. Thinning cavity 5d is entirely within flash section 5c. Since the surface area of thinning cavity 5d is greater than the corresponding surface area of the hollow mold, the portion of parison 2 that is blown into thinning cavity 5d is thinner than the remainder of parison 2. Reducing the thickness of parison 2 at the site of large diameter hollow needle 7 further reduces the elasticity of the balloon wall and makes it easier for large diameter hollow needle to penetrate. A protrusion in the flash section (not shown) surrounding large diameter hollow needle 7 would have the same effect as thinning cavity 5d of increasing the surface area. In an application using an embodiment of the present invention, a molten parison 2 extruded from an extruder is given a first blow through a small diameter hollow needle 6 for about 3 seconds within a blow mold (split mold) using room temperature air at a blow pressure of 6 kg/cm 2 . About one second after the first blow is begun, a second blow is performed wherein a large diameter hollow needle 7 blows room temperature air at a blow pressure of 8 kg/cm 2 for about 9 seconds. After this, the pressurized air within the article is exhausted in approximately 0.1 seconds. Compared to the prior art blow molding method using only one hollow needle, the blow molding method with the large and small hollow needles of the present invention reduces blow time by about 11 seconds and exhaust time by about 1.9 seconds. The molding cycle is improved about 60 percent. Various conventional fluids can be used, and different fluids can be used for each hollow needle. Examples of conventional fluids include air, either room temperature or refrigerated, and liquid or gaseous carbon dioxide. Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the invention as defined in the appended claims.

Claims: A blow molding device for blow molding a hollow article comprising: a mold having an open position for receiving a parison (2) and a closed position for forming said hollow article; a first and at least a second hollow needle (6, 7); first means for inserting (12a) said first hollow needle (6) into said parison (2) and retracting (12a) said first hollow needle (6) out of said parison (2); second means for inserting (12b) said at least second hollow needle (7) into said parison (2) and retracting (12b) said at least second hollow needle (7) out of said parison (2); first blowing means for blowing a fluid through said first hollow needle (6) into said parison (2) thereby ballooning and supporting said parison (2); and second blowing means for blowing said fluid through said at least second hollow needle (7) into said parison (2), characterized by : said mold having a flash section (5) and a body cavity (4); said first and at least second hollow needles (6, 7) being located in an area corresponding to said flash section (5) of said mold; first control means for controlling said first means for inserting and retracting (12a) and second control means for controlling said second means for inserting and retracting (12b), whereby the times at which said second means for inserting and retracting (12b) operate are different than the times at which said first means for inserting and retracting (12a) operate; and exhaust opening forming means (8) located in an area corresponding to said flash section (5) of said mold effective to exhaust said fluid from an inside of said parison. A blow molding device according to claim 1, wherein said blow molding device is a rotary blow molding machine. A blow molding device according to claim 1, wherein said mold is a split mold (1a, 1b). A blow molding device according to claim 1, wherein said mold is a unit mold (1). A blow molding device according to claims 1-4, wherein said first and second control means permit said second inserting means to operate only after said first inserting means is permitted to operate. A blow molding device according to claim 5, wherein: said first inserting means is linked to said first blowing means whereby said first blowing means is permitted to operate only after said first inserting means operates; and said second inserting means is linked to said second blowing means whereby said second blowing means is permitted to operate only after said second inserting means operates. A blow molding device according to claim 6, wherein operation of said first blowing means and operation of said second blowing means are separated by a time sufficient to permit said parison (2) to balloon against said mold before said second blowing means operates. A blow molding device according to claims 1-7, wherein said first hollow needle (6) is a small diameter hollow needle (6), and said at least second hollow needle (7) is a large diameter hollow needle (7). A blow molding device according to claims 1-5, wherein said first hollow needle (6) and said at least second hollow needle (7) are at an angle to each other, whereby a tip of said first hollow needle (6) and a tip of said at least second hollow needle (7) are close to a same longitudinal position on an axis of said parison (2) when said first hollow needle (6) and said at least second hollow needle (7) are both inserted. A blow molding device according to claims 1-9, wherein: said first control means includes a first cam (16a) linked to said first hollow needle (6) whereby said first hollow needle (6) is inserted into said parison (2) and retracted from said parison (2); said second control means includes a second cam (16b) linked to said at least second hollow needle (7) whereby said at least second hollow needle (7) is inserted into said parison (2) and retracted from said parison (2); and said first cam (16a) and said second cam (16b) are linked whereby said fluid is supplied through said first hollow needle (6) into said parison (2) before said fluid is supplied through said at least second hollow needle (7) into said parison (2). A blow molding device according to claim 10, further characterized by : said flash section (5) having a portion with increased surface area (5d) surrounding said large diameter hollow needle (7) whereby a portion of said parison (2) is thinned when said parison (2) is expanded; said thinned portion effective to allow insertion of said large diameter hollow needle (7) through said parison (2) with reduced distortion of said parison (2). A blow molding device according to claim 11, wherein said increased surface area (5d) results from a protrusion surrounding said large diameter hollow needle (7). A blow molding device according to claim 11, wherein said increased surface area (5d) results from a cavity surrounding said large diameter hollow needle (7). A blow molding device according to claims 8-13, wherein said at least second hollow needle (7) has an orifice diameter three to fifteen times larger than an orifice diameter of said first hollow needle (6). A blow molding device according to claims 8-14, wherein said first hollow needle (6) has an orifice diameter of 0.5 mm to 5 mm. A blow molding device according to claims 8-14, wherein said at least second hollow needle (7) has an orifice diameter of 1.5 mm to 75 mm. A blow molding device according to claims 1-8, wherein said at least second hollow needle (7) includes an orifice axially aligned with a major axis of said hollow article. A blow molding device according to claims 1-17, wherein said fluid includes compressed air. A method for blow molding hollow articles comprising the steps of: positioning a parison (2) in a mold having a flash section; retaining said parison (2) in said mold; inserting a first hollow needle (6) into a portion of said parison in an area corresponding to said flash section; blowing a fluid through said first hollow needle (6) into said parison (2) thereby forming and pressurizing a balloon (22) by expanding said parison (2); inserting a second hollow needle (7) into a portion of said expanded parison (2) in an area corresponding to said flash section; blowing said fluid through said second hollow needle (7) into said expanded parison (2); forming a discharge port in a portion of said expanded parison (2) in an area corresponding to said flash section; cooling said hollow article by continuing to blow said fluid through said second hollow needle, whereby said fluid is circulated inside said hollow article and exhausted through said discharge port; retracting said first hollow needle; retracting said second hollow needle; and removing said hollow article from said mold. A method for blow molding hollow articles according to claim 19, wherein said first hollow needle (6) blows fluid into said parison (2) and expands said parison (2) against said mold before said second hollow needle (7) is inserted into said expanded parison (2). A method for blow molding hollow articles according to claims 19-20, further including the steps of: thinning a portion of said flash section surrounding a location of said second hollow needle (7); and inserting said second hollow needle (7) into said expanded parison (2) in a location corresponding to said thinned portion. A method for blow molding hollow articles according to claim 21, wherein said portion of said flash section (5c) is thinned by providing a protrusion with increased surface area formed around said location of said second hollow needle (7). A method for blow molding hollow articles according to claim 21, wherein said portion of said flash section (5c) is thinned by providing a cavity with increased surface area formed around said location of said second hollow needle (7). A method for blow molding hollow articles according to claims 19-23, wherein: said mold is a split mold; and said parison (2) is sealed and retained in place at first and second ends. A method for blow molding hollow articles according to claims 19-23, wherein: said mold is a unit mold; and said parison is retained in place with parison guides. A method for blow molding hollow articles according to claims 19-25, wherein an orifice diameter of said second hollow needle (7) is between 3 and 15 times an orifice diameter of said first hollow needle (6). A method for blow molding hollow articles according to claims 19 - 26, wherein: said fluid is blown through said first hollow needle (6) into said parison (2) for a time L; said fluid is blown through said second hollow needle (7) into said parison (2) for a time Q; said time Q beginning a time S after said time L begins; and said time L and said time Q overlapping for a time W whereby L=S+W. A method for blow molding hollow articles according to claim 27, wherein said time L is between 0.1 second and 10 seconds. A method for blow molding hollow articles according to claims 27 - 28, wherein said time Q is between 5 seconds and 30 seconds. A method for blow molding hollow articles according to claims 27 - 29, wherein said time W is between 0.1 second and 10 seconds. A method for blow molding hollow articles according to claims 27 - 29, wherein said time S is between 0.2 seconds and 2 seconds. A method for blow molding hollow articles according to claims 19 - 31, wherein said second needle (7) blows said fluid in a direction axially aligned with a major axis of said hollow article. A method for blow molding hollow articles according to claims 19 - 32, wherein said fluid is compressed air. A method for blow molding hollow articles according to claims 19-33, further including the step of actuating a knock-out pin (9) to remove said hollow article from said mold.

Inventors: MATSUHASHI SETSU, MATSUHASHI, SETSU
Applicants: TOYO SEIKAN KAISHA LTD, TOYO SEIKAN KAISHA, LTD.
Application year: 1995
Main classification: B29C49
IPC codes: B29C49