JP4656569B2 - Manufacturing method of hollow molded product - Google Patents

Description

  The present invention forms a bottomed cylindrical preform by blow molding using a cylindrical parison formed by extrusion molding, and a blow molded product of the final product by stretch blow molding using the preform. The present invention relates to a method for manufacturing a hollow molded product for forming (manufacturing) a stretch blow bottle using a so-called direct blow molding method.

  A method itself for forming a stretch blow bottle using this type of direct blow molding method has been known (see, for example, Patent Document 1 or Patent Document 2). Among them, in Patent Document 1, in order to prevent the parison from being stretched downward by its own weight to cause a drawdown when the parison is stretch blow-molded and the wall thickness is changed at the top and bottom, Disclosing that the outer surface of the parison is cooled by air blowing, and in Patent Document 2, in order to prevent the accumulation of meat and the occurrence of uneven thickness especially at the bottom of the preform, It is disclosed that the shape is formed in a substantially spherical arc shape.

JP-A-8-323851 JP 2001-170994 A

  By the way, as a method for forming a stretch blow bottle, an injection blow molding method is generally known in addition to the direct blow molding method described above. The injection blow molding method includes a cold parison method in which a preform is molded by injection molding, naturally cooled to remove residual distortion, and then reheated and stretch blow molding is performed. There is a hot parison system that eliminates the need for extra energy consumption for reheating by performing stretch blow molding subsequently. In such injection blow molding, an injection grade (MFR; Melt Flow Rate: JIS K 7210 is, for example, 10 to 50 g / 10 min) that has poor stretchability and lacks rigidity must be used as a thermoplastic molding material. Thus, a stretch blow bottle having high barrier properties and transparency and relatively good mouth dimensional accuracy can be obtained.

  On the other hand, in the above direct blow molding method, stretch blow using an extrusion grade molding material (MFR of 0.2 to 7 g / 10 min, for example) having high rigidity capable of stable and excellent blow molding. Although a bottle can be obtained, it tends to be difficult to obtain sufficient mouth dimensional accuracy, transparency, barrier properties, and impact resistance as compared with the injection blow molding method.

  That is, because a preform is formed by sandwiching a parison that is continuously extruded with the same thickness from an extruder with a mold, the bottle mouth portion and the barrel portion have the same thickness, Or, since the body is normally inflated in the circumferential direction, the body is thinner. For this reason, the mouth part that is originally cooled to the melting point or lower of the molding material is thick, so that it has a large amount of heat and is difficult to cool, but it is originally higher than the melting point for stretch blow molding in the next process. Since the trunk part to be maintained is thin, the amount of heat held is small, and it becomes easy to be cooled. As a result, the thin barrel does not have a temperature suitable for stretch molding and the stretching effect is weakened, and it becomes difficult to obtain sufficient transparency, impact resistance and barrier properties. Is not sufficiently cooled and solidified, and is sandwiched between molds that define the final product shape. Therefore, it is necessary to provide a gap in order to avoid scratching the mouth. It will be difficult.

  In order to avoid this, it is conceivable to adjust the heating temperature of the body to a predetermined temperature, but energy consumption for heating is required.

  The present invention has been made in view of such circumstances, and its object is to produce a stretch blow bottle by the direct blow molding method while reducing the energy consumption and to the same degree as that of the injection blow molding. The object is to obtain dimensional accuracy, barrier properties, and impact resistance.

In order to achieve the above object, the present invention forms a bottomed cylindrical preform by first forming a cylindrical parison extruded using a heat-melted resin molding material into a preform mold. Then, the following specific matters are provided for a method for manufacturing a hollow molded product in which a stretch molded product is manufactured by performing stretch blow molding on the preform. That is, as the preform mold, there is used a lip mold that molds the mouth portion and a trunk mold that molds the trunk portion, and these lip mold and barrel mold can be opened independently of each other. In the primary molding, the lip mold is kept in a closed state until a cooling time required for the mouth to become lower than the melting point elapses by heat exchange cooling due to contact between the mouth and the inner surface of the mold. A thin solidified layer is formed on the surface of the body by heat exchange cooling by contact between the body and the inner surface of the mold for a time shorter than the cooling time so that the shape of the body can be held only for a while. After the mold is opened, the heat exchange cooling by contact with the body mold against the outer surface of the body part is stopped and held in the air until the cooling time elapses. When the parison is extruded, the temperature inside the body is kept by heating the resin molding material based on the heating of the resin molding. If the above The stretch-blowing mold die opening formed preform was be performed (claim 1).

If the present invention, in a primary molding, while it becomes possible to ensure high dimensional accuracy of the neck portion by sufficient cooling of the mouth portion, a body portion potential heat required stretch blow molding to be subsequently performed well Can be maintained in the state of being held. However also be conducted to the extent capable of maintaining the shape of the preform by the formation of the thin skin solidified layer cooling to the outer surface of the body portion in the heat exchanger cooled by contact between the body portion and the inner mold surfaces, then mouth until the cooling is completed, because the are held in by a heat exchanger cooling is stopped due to contact exposed to air between the barrel die to the outer surface of the body portion, the resin molding during extrusion molding of the parison The retained heat inside the body based on the heating of the material is transmitted to the outer surface, so that the outer surface and the inside are temperature-equalized. Thus, a continuing said stretch blow molding to be performed after the primary molding of that will be capable of performing uniform over the entire torso, barrier property by uniform stretching effect, etc., so it is possible to obtain impact resistance Become. As described above, it is possible to obtain energy saving that can stably mold until the final stretch blow only by the retained heat by heating at the time of extrusion molding of the parison while sufficiently cooling the mouth portion to ensure high dimensional accuracy. It becomes like this.

In particular, cooling is the cooling from the outer surface of the mouth portion and the body portion by heat exchange cooling by contact with the respective inner mold surfaces of the lip type and barrel type, thereby the dimensional stability of the outer shape of the mouth and while the dimensional accuracy is ensured, the barrel will be thin pellicle solid layer is formed on the outer surface side to keep the preform shape. And since the heat exchanger cooling by the contact with the body mold with respect to the outer surface of the body portion is stopped until the cooling time elapses due to the mold opening of the body mold, the molding material for the parison extrusion molding is stopped. internal potential heat of the body based on heating Ru is Yutakaka equalizing allowed to warm a solidified layer of the thin skin transmitted to the outer surface. Thereby, only the heating with respect to the molding material at the time of the extrusion molding of a parison can perform the whole process until the primary shaping | molding of a preform and the last shaping | molding by extending | stretching blow. For this reason, high energy savings can be achieved in the manufacture of hollow molded products, and the original functions of the molding material can be effectively ensured with little heat history with respect to the molding material. And barrier properties can be secured. In here, the lip-type and barrel type described above, in addition to the heat exchange cooling power which the forming material has, it may be attached to active cooling capability of the cooling water circuit and the like therein.

To above the present invention, furthermore, when the extrusion of the parison, it is also possible that be cooled by targeting only the outer surface of the parison (claim 2). By doing so, even while ensuring the weldability without lowering the internal temperature of the parison, and only the outer surface to a low temperature, Ru lowers the surface transfer property of the outer surface during molding of the preform, i.e. adhesion sex becomes possible and Sageruko a. This eliminates the need for fine irregularities for air bleeding in the preform mold during preform molding, and the mirror surface and transparency of the preform surface can be improved accordingly. sex, ing to be transparency can be secured. In the present invention, an extrusion-grade thermoplastic molding material having a melt flow rate measured by JIS K 7210 of 0.2 to 7 g / 10 min can be used as a resin molding material used for extrusion molding ( Claim 3). As a result, the direct blow according to the present invention is carried out, in which the primary molding of the preform and the secondary molding of the hollow molded article by the stretch blow are performed using the parison extruded using a high-rigidity extrusion-grade molding material as a starting material. Also in the molding method, the same performance (impact resistance, barrier property, transparency) as the injection blow molding method can be obtained.

  As described above, according to the method for producing a hollow molded product of the present invention, the final portion is only obtained by the retained heat by heating at the time of parison extrusion molding while sufficiently cooling the mouth portion to ensure high dimensional accuracy. Thus, it is possible to stably form the film until stretching blow, and energy saving can be achieved.

In other words, to open the mold a body mold after cooling just be being thin pellicle solid layer is formed on the outer surface side of the body part by heat exchange cooling by contact with the barrel die to maintain the preform shape, Thereafter, until the cooling time for the mouth portion elapses, the heat exchange cooling due to the contact with the outer surface of the barrel portion by the contact with the barrel die is stopped and held in the air. Therefore, the potential heat inside the barrel that is based on heating the resin molding material during extrusion molding of the parison is Yutakaka equalizing allowed to warm thin skin solidified layer transferred on an outer surface, performing the stretch blow molding thereon be able to. Thereby, only the heating with respect to the molding material at the time of the extrusion molding of a parison can carry out the whole process until the primary molding of the preform and the subsequent final molding by the stretch blow. For this reason, high energy savings can be achieved in the manufacture of hollow molded products, and the original functions of the molding material can be effectively ensured with little heat history with respect to the molding material. And barrier properties can be secured.

Further, according to claim 2 , the surface transferability of the outer surface at the time of molding the preform can be lowered, thereby improving the mirror surface property and transparency of the preform surface to improve the mirror surface property and transparency in the final product. Can be secured . Further, according to the third aspect, the primary molding of the preform and the secondary molding of the hollow molded article by stretch blow are performed using the parison extruded using the extrusion-grade molding material having high rigidity as the starting material. In the direct blow molding method according to the present invention, the same performance (impact resistance, barrier property, transparency) as the injection blow molding method can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1-5 shows the detailed process in the manufacturing method of the hollow molded article which concerns on embodiment of this invention. This method is broadly divided into a parison extrusion process A of the parison 2 by an extruder, a preform molding process B (B1 to B4) for molding the preform 3 by pre-blowing using the parison 2, Adjustment process C, stretch blow molding process D (D1 to D6) for forming a stretch blow bottle 4 having a final product shape by performing biaxial stretch blow molding on the preform 3 after temperature adjustment, and take-out process E (E1) To E3). Among these, the temperature control step C is characteristic, and in addition, cooling of the outer surface of the parison 2 in the extrusion molding step A and formation of the bottom of the preform 3 in the preform molding step B are also performed. It is characteristic. Hereinafter, it demonstrates in order of a process.

  In the parison extrusion step A (see FIG. 1), an extrusion-grade thermoplastic molding material is heated and melted and extruded from the extrusion molding machine 5 into a tube shape to form the parison 2. At this time, the outer surface of the parison 2 is extruded while being cooled by the extrusion head 51 of the extrusion molding machine 5. That is, as shown in FIG. 6, a cooling die 54 is provided on the front end side of the extrusion die 52 of the extrusion head 51 with a heat insulating plate 53 interposed therebetween, and the outer surface (outer periphery) of the parison 2 passes through the cooling die 54. Surface) is cooled by contact heat exchange. The cooling die 54 is formed with a cooling water circulation circuit 541 through which the cooling water is circulated and supplied through the cooling die 54, and the cooling and circulation supply of the cooling water causes the cooling die 54 to heat with the constituent material itself of the cooling die 54. In addition to the exchange, it is strengthened. In the figure, reference numeral 55 denotes a passage having a donut annular cross section through which the molding material passes, and 56 denotes a passage for weakly blowing air into the parison 2.

  By cooling the outer surface of the parison 2 described above, while maintaining the weldability without lowering the temperature inside the parison 2, only the outer surface is lowered to reduce the surface transferability at the time of preform molding described later. The adhesion is lowered. Thereby, as will be described later, the outer surface of the preform 3 is formed into a mirror surface to increase transparency. In FIG. 1, reference numeral 6 is a preform mold, 7 is a preform blowing pin equipped with a stretching rod, 8 is a blow mold, and 9 is a blow pin equipped with a stretching rod. The preform mold 6 includes a lip mold (screw mold) 61 for molding the mouth portion 32 of the preform 3 (see FIG. 2) and a trunk mold 62 for molding the body portion 35 of the preform 3. Thus, both the preform mold 6 and the blow mold 8 are constituted by split molds. In addition, one of the upper extrusion molding machine 5, the preform blowing pin 7 and the blow pin 9, and the lower preform mold 6 and the blow mold 8 can be moved relative to each other as the process proceeds. Yes. In the illustrated example, the lower preform mold 6 and blow mold 8 are moved left and right.

  In the next preform molding step B, first, the above-described parison 2 is sandwiched by the preform mold 6 moved after the parison extrusion step A (step B1), and after the parison 2 is cut in this state, the extrusion head 51 is moved backward. (Step B2). Then, after the preform mold 6 sandwiching the parison 2 is moved to the position of the preform blowing pin 7 (step B3; see FIG. 2), the stretch rod of the preform blowing pin 7 is inserted into the parison 2 to perform the preform. 3 is performed (step B4). Reference numeral 31 in FIG. 2 denotes an upper loss portion that is expanded by blowing air into the upper end portion of the parison 2 and becomes a molding loss. The mouth 32 of the preform 3 is formed around the outer periphery of the parison 2 by clamping with the lip mold 61, and the lower position of the parison 2 is sandwiched and closed by clamping with the barrel mold 62. 3, and a lower portion thereof becomes a lower loss portion 34 that is cut by the above-described sandwiching and becomes a molding loss. Further, the middle portion of the parison 2 is swelled by air blowing from the preform blowing pin 7 and pressed against the cavity surface of the barrel die 62, and the barrel portion 35 is formed. When the bottom 33 is formed, the molding material of the sandwiched portion is turned to the surface side by rotating around the axis while the tip of the stretching rod of the preform blowing pin 7 is pressed against the inner bottom surface. The weldability is increased by stirring. That is, the bottom portion 33 is formed by closing the welded joint line formed by the above-mentioned sandwiching with a solid and firm weld without leaving a weld. Thereby, the intensity | strength of the bottle bottom part from which it is difficult to acquire the extending | stretching effect only by simple clamping and the press by an extending | stretching rod can be increased.

  Then, the mouth portion 32 is cooled by being in contact with the inner surface of the lip mold 61, and the body portion 35 is cooled by being in contact with the inner surface (cavity surface) of the body mold 62. Both the lip mold 61 and the body mold 62 are provided with a cooling water circuit inside, and are circulated and supplied with cooling water, so that heat exchange cooling is promoted by the contact of the mouth portion 32 and the body portion 35 described above. Yes.

  Before a very long time has passed as the cooling time for the body portion 35, the process proceeds to the next temperature adjustment step C. In this temperature control step C, the lip mold 61 is kept clamped, and only the barrel mold 62 is opened and maintained in this state for a predetermined time. By opening only the body mold 62 described above, the body section 35 of the preform 3 is held in a state where the heat exchange cooling by the contact with the body mold 62 so far is stopped and exposed to the air, while the mouth section 32 is held. The heat exchange cooling by the contact with the lip mold 61 is continued. That is, the mouth portion 32 is sufficiently cooled so as to have a temperature lower than the melting point to ensure the dimensional accuracy, while the body portion 35 has a cooling time of only a short time and exceeds the melting point required for the subsequent stretch blow molding. By securing the retained heat and holding in the air for the predetermined time described above, the temperature difference between the surface layer portion and the inner portion of the body portion 35 can be eliminated and the temperature can be equalized. In short, the mouth portion 32 is sufficiently cooled in order to ensure its shape stability and dimensional accuracy, while the body portion 35 is difficult to secure the required amount of heat during the next stretch blow molding if it is cooled too much. By forming the thin skin solidified layer, cooling is performed for a short time so that the shape of the preform 3 can be held only for a while, and thereafter, the surface temperature on the thin skin solidified layer side rises due to heat from the inside by holding in the air. The inner and outer regions are soaked and uniform stretching is performed. The lower loss portion 34 is separated from the bottom portion 33 by opening the body die 62 in the temperature adjustment step C.

  Then, when a predetermined time for cooling the mouth portion 32 and soaking the body portion 35 has elapsed, the lip die 61 is also opened and the preform 3 is pushed in order to enter the stretch blow molding step D. It is made the state hold | maintained at the reform blowing pin 7 (step D1; refer FIG. 3). At this time, the mold opening of the blow mold 8 and the extrusion molding of the parison 2 by the extrusion head 51 are simultaneously performed. Next, the preform mold 6 and the blow mold 8 are moved, and the preform 3 held by the preform blowing pin 7 is put into the blow mold 8 and clamped with the mouth 32 sandwiched therebetween (step D2). ). At the same time, the parison 2 is sandwiched between the preform dies 6 for preform molding (step B1) in the next cycle. Then, the preform blowing pin 7 is moved backward to separate the upper loss portion 31 (step D3), and the blow mold 8 holding the preform 3 is moved to the position of the blow pin 9 (step D4; see FIG. 4). In this step, the upper loss portion 31 attached to the preform blowing pin 7 is discarded. In step D3, the adjacent preform mold 6 performs the same process as in step B2, and in step D4, the adjacent preform mold 6 performs the same process as in step B3.

  Next, the stretching rod of the blow pin 9 moves downward, pushes the inner bottom surface of the preform 3 and stretches downward until it hits the inner bottom surface of the blow mold 8 and presses it as it is (step D5). Air is blown to extend the body part to the outer peripheral side and press it against the inner peripheral surface (cavity surface) of the blow mold 8 (step D6). As a result, biaxial stretch blow is performed and the final molded product is stretched. A blow bottle 4 is formed. Here, in the preform 3, the mouth 32 is already formed with high dimensional accuracy, and the mouth 32 becomes the mouth of the stretch blow bottle 4 as it is.

  Thereafter, as a taking-out process E, the blow mold 8 is opened to the left and right to open the mold to release the stretch blow bottle 4 (step E1: see FIG. 5), and the blow mold 8 and the preform mold 6 are moved (step E2). ) And separation of the stretch blow bottle 4 from the blow pin 9 (step E3), the manufacture by blow molding is completed. Of course, in the adjacent blow mold 8 and preform mold 6, the steps of the respective molding steps in the next cycle are executed simultaneously.

  In particular, in FIG. 2 or FIG. 4, if the opening and closing direction of the preform 6 is the left and right of the drawing, the lower loss portion 34 is seen from the side and becomes flat, but the lower loss portion 34 is viewed from the front. The state as seen is illustrated.

  Considering the above forming method, first, the mouth portion 32 can be sufficiently cooled at the stage of forming the preform 3 using the parison 2 and formed with high dimensional accuracy. The subsequent stretch blow molding can be performed uniformly by keeping the cooling period of the mouth portion 32 in the air while keeping the cooling period of the mouth portion 32 in the air while maintaining the shape of 3 in a short time so that the shape can be temporarily held. it can. That is, while the cooling of the mouth portion 32 is sufficiently realized, the body portion 35 can be maintained at the retained heat above the melting point, so that the preform can be formed only by heating the molding material at the time of parison 2 extrusion molding. All processes can be executed until the molding of 3 and the final molded product (stretched blow bottle 4) are stretched. For this reason, high energy saving can be achieved in the production of the stretch blow bottle 4, and the original function of the molding material can be effectively ensured with little heat history with respect to the molding material. Impact and barrier properties can be secured.

  Next, regarding the securing of the transparency of the stretched blow bottle 4 which is the final product, first, only the outer surface of the parison 2 is cooled by the cooling die 54 when the parison 2 is extruded, thereby transferring the surface at the time of molding the preform 3. Because of this, fine irregularities are added to the inner surface (for example, by sand blasting) to release air from the internal air reservoir (gas reservoir) as in the preform mold in normal direct blow molding. The need to escape air can be eliminated. Thereby, it is usually difficult to obtain transparency in direct blow molding, but in the case of this embodiment, it is not necessary to attach the unevenness as described above to the inner surface (cavity surface) of the preform mold 6, The surface of the preform 3 can be formed into a mirror surface, and transparency can be ensured. Next, although the surface temperature rises due to internal heat retention due to the temperature equalization treatment by holding the body portion 35 of the preform 3 in the air, the overall temperature is lowered by stretching (thinning) by stretch blow molding, The specularity and transparency of the stretched blow bottle 4 of the final product can be ensured.

  Therefore, the direct forming of the present application is performed in which the primary molding of the preform 3 and the secondary molding of the stretch blow bottle 4 by stretch blow are performed using the parison 2 extruded using a molding material having high rigidity as the starting material. Also in the blow molding method, the same performance (impact resistance, barrier property, transparency) as the injection blow molding method can be obtained.

  In addition, since the parison 2 is cooled by the cooling die 54, the preform 3 can be formed by extruding a thick and short thick parison as the parison 2, so that conventionally, the draw down is used. Even molding materials having a large MFR such as PS (polystyrene) and PC (polycarbonate), which have been difficult to perform stable parison extrusion, can be stably stretched using such a molding material. The blow bottle 4 can be manufactured.

In the above embodiment, the preform 3 is formed by preliminary blow molding with respect to the parison 2. However, the air blow is not performed on the parison 2, and the mouth portion is formed and the bottom portion is formed. The preform may be formed in a bottomed cylindrical shape having a mouth portion and a body portion, and the present invention may be applied to the preform. The lip die 61 and the body die 62 of the preform die 6 may both be used. What does not have a cooling water circuit can also be used. This is because even if there is no cooling water circuit, it is possible to cool the mouth and body of the preform by heat exchange cooling by contact with the respective forming materials of the lip type and the body type.

  Furthermore, in the said embodiment, although the process name was divided and demonstrated to the preform shaping | molding process B and the temperature control process C, it is good also as a preform shaping | molding process including the preform shaping | molding process B and the temperature control process C. Needless to say.

It is explanatory drawing which shows the process of embodiment of this invention. It is explanatory drawing which shows the next process of FIG. FIG. 3 is an explanatory diagram showing a next process of FIG. 2. It is explanatory drawing which shows the next process of FIG. It is explanatory drawing which shows the next process of FIG. It is expansion sectional explanatory drawing of an extrusion head.

Explanation of symbols

2 Parison 3 Preform 4 Stretch blow bottle (hollow molded product)
32 Portion 35 Body 51 Extrusion Head 54 Cooling Die 61 Lip Type 62 Body

Claims (3)

A cylindrical parison extruded using a heat-melted resin molding material is placed in a preform mold to form a bottomed cylindrical preform, and stretch blow molding is performed on this preform. In the method of manufacturing a hollow molded product to carry out and produce a hollow molded product,
As a preform mold, a lip mold that molds a mouth part and a trunk mold that molds a body part, and a lip mold and a body mold that can be opened independently of each other,
In the primary molding, the lip mold is maintained in a closed state until the cooling time required for the mouth part to be lower than the melting point by heat exchange cooling due to contact between the mouth part and the inner surface of the mold. A thin solidified layer was formed on the surface of the body part by heat exchange cooling by contact between the body part and the inner surface of the mold for a time shorter than the above cooling time so that the shape of the body part can be held only for a while. The mold is opened later , and thereafter the heat exchange cooling by the contact with the body mold with respect to the outer surface of the body part is stopped until the cooling time elapses , and the parison is kept in an exposed state in the air. Advance temperature equalization to eliminate the temperature difference between the surface layer part and the inner part of the body part due to the retained heat inside the body part based on the heating to the resin molding material at the time of extrusion molding,
If the cooling time elapses, the lip mold is opened and stretch blow molding is performed on the preform formed .
A method for producing a hollow molded article, characterized in that It is a manufacturing method of the hollow molded article according to claim 1 ,
During extrusion of the parison, by you cool intended for only the outer surface of the parison Unisuru method of hollow molded article. A method for producing a hollow molded article according to claim 1 or 2,
A method for producing a hollow molded article, wherein an extrusion-grade thermoplastic molding material having a melt flow rate measured by JIS K 7210 of 0.2 to 7 g / 10 min is used as a resin molding material used for extrusion molding.

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