JP2006281722A - Method of manufacturing heat resistant blow molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a method capable of manufacturing a heat resistant blow molding with sufficient accuracy by bringing a primary blow molding close to the shape of the final blow molding using the thermal shrinkage of the primary blow molding. <P>SOLUTION: A preform P is blow molded, and an intermediate blow molding 1 in which discontinuous ribs 6a-6d are formed in the peripheral surface of a cylinder-shape body 2 is molded. The intermediate blow molding 1 is heat treated and given by a heat resistance. When thermal shrinking is carried out, the amounts of contraction of the rib forming part are few, and the curvature of an outward direction is also little. Therefore, the body 12 of the intermediate blow molding 11 after the thermal shrinking becomes a quadrangle with roundness smaller than the tube-shape body 22 of the final blow molding 21, and resembles to the body shape of the final blow molding as compared with that before the thermal shrinking. The amounts of extension of respective parts at the time of quadratic blow molding become substantially equal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a blow molded product in which a preform made of a synthetic resin is blow molded to form a beverage container or the like. More specifically, after blow-molding a preform using a primary blow-molding mold in a heated state, heat-treating the blow-molded product with the mold to impart heat resistance, and then using a secondary blow-molding mold The present invention relates to a method for producing a heat-resistant blow-molded product in which a blow-molded product after heat treatment is blown again to produce a final blow-molded product.

  As a blow molding method for producing a heat-resistant beverage container by blow molding a synthetic resin preform, heat treatment is applied to the intermediate blow molded product obtained by primary blow molding, and after heat treatment There is known a method for producing a final blow molded product having a final shape by blow molding (secondary blow molding) of the primary blow molded product again. In this method, the primary blow molding die is kept in a heated state, the intermediate blow molded product is held in the primary blow molding die for a predetermined time, and the intermediate blow molded product is heat-treated by the heat of the die. To give heat resistance.

Blow molded articles produced by such a method are generally containers such as beverages having a cylindrical body. In this case, the shape after heat shrinkage of the intermediate blow-molded product obtained by the primary blow molding is set to be equal to or slightly smaller than the shape of the final blow-molded product. Thereby, the distortion which generate | occur | produces in a blow molded product at the time of secondary blow molding can be substantially disregarded. Such a method is disclosed in Patent Document 1, for example.
JP 58-81131 A

  However, if the body shape of the final blow-molded product is not circular, for example, when it is a polygon such as a quadrangle, the difference in the stretch amount of each part of the blow-molded product during secondary blow molding is greatly different. Also, the strain to be generated cannot be ignored, and there is a possibility that the moldability and productivity are lowered.

  That is, as shown in FIG. 3A, when the body portion 32 of the intermediate blow-molded product has a cylindrical shape and the body portion 22 of the final blow-molded product has a polygonal shape (in the illustrated case, an irregular octagon). The intermediate blow molded product cylinder corresponding to each corner 22e to 22h of the final blow molded product barrel compared to the outer peripheral surface portion of the intermediate blow molded product barrel 32 corresponding to each surface 22a to 22d of the final blow molded product. The stretch amount of the outer peripheral surface portion of the portion 32 is large. Thus, if the stretching amount is significantly different, the molding accuracy by the secondary blow molding is deteriorated and the productivity is lowered.

  Also, as shown in the figure, in the case of a deformed octahedron whose body is a rectangular shape, such as a large blow-molded container, the intermediate blow-molded product body 32 set in the secondary blow mold is In order not to be pinched by the mold forming surface, the diameter of the intermediate blow-molded product barrel 32 must be equal to or less than the length of the short side of the final blow-molded product barrel 22. As a result, the stretch amount in the long side direction becomes large, and a difference occurs not only between the corner portion but also the stretch amount of the outer peripheral surface portion corresponding to the short side and the stretch amount of the outer peripheral surface portion corresponding to the long side. As a result, blow molding accuracy may be further deteriorated.

  In order to avoid such an adverse effect, the shape of the intermediate blow-molded product may be approximated to the shape of the final blow-molded product. However, in this case, the shape of the molding surface of the primary blow molding die for blow molding of the intermediate blow molded product becomes complicated, and the die cost is significantly increased compared to a die having a circular molding surface. This is not preferable.

  In view of these points, the object of the present invention is to obtain a heat-resistant blow-molded product with high accuracy by bringing the primary blow-molded product closer to the shape of the final blow-molded product by utilizing the heat shrinkage of the primary blow-molded product. It is to propose an inexpensive method that can be manufactured.

In order to solve the above problems, the method for producing a heat-resistant blow-molded product of the present invention comprises
In a primary blow molding die heated to a predetermined temperature, a primary blow molding step for blow molding a preform to obtain an intermediate blow molded product,
A heat treatment step of imparting heat resistance by applying heat treatment to the intermediate blow-molded product by the heated primary blow-molding die by holding the intermediate blow-molded product in the primary blow mold for a predetermined time;
The intermediate blow-molded product after the heat treatment is blow-molded again in a secondary blow-molding mold to obtain a final blow-molded product,
In the primary blow molding step, the intermediate blow molded product with ribs is blow molded in order to regulate the shape of the intermediate blow molded product after heat shrinkage in the heat treatment step.

  By forming an appropriately sized rib in an appropriate part of the intermediate blow-molded product, the shape of the intermediate blow-molded product after heat shrinkage can be regulated. Therefore, the rib attached to the intermediate blow-molded product allows the shape of the intermediate blow-molded product after heat shrinkage to be closer to the final blow-molded product than the shape of the intermediate blow-molded product before heat shrinkage. Can be controlled. In this way, the intermediate blow-molded product after heat shrinkage is approximated to the final blow-molded product without using an expensive secondary blow mold with a complicated molding surface that approximates the shape of the final blow-molded product. It can be made into the shape. As a result, the stretch amount of each part of the blow molded product at the time of secondary blow molding can be made substantially equal, so that the molding accuracy can be increased and the productivity can be increased.

  Generally, the final blow-molded product is a container having a cylindrical body with a bottom. In addition, since an inexpensive one for blow molding a container having a cylindrical body is used as the primary blow molding die, the intermediate blow-molded product before and after the heat shrinkage is a container having a cylindrical body. Become. In this case, in the primary blow step, a plurality of ribs that are discontinuous in the circumferential direction or the body axis direction are formed in the cylindrical body of the intermediate blow-molded product. The outer peripheral surface portion with the ribs has less thermal distortion and less bending in the out-of-plane direction. On the other hand, the outer peripheral surface portion without the rib has a relatively large thermal strain, and the bending in the out-of-plane direction is also large. As a result, the body portion of the intermediate blow-molded product after heat shrinkage has a cross-sectional shape that approximates a polygonal cross-section having corners on the outer peripheral surface portion without ribs. Therefore, if the ribs are arranged so as to approximate the shape of the cylindrical body of the final blow molded product, the shape of the body of the intermediate blow molded product after heat shrinkage is approximated to the shape of the body of the final blow molded product. be able to.

  Therefore, when the cylindrical body portion of the final blow-molded product has a polygonal cross section, in the primary blow step, the final blow-molded product in the cylindrical body portion of the intermediate blow-molded product is A plurality of ribs are formed on the outer peripheral surface corresponding to each surface of the cylindrical body, and a rib is formed on the outer peripheral surface corresponding to each corner of the cylindrical body of the final blow molded product. Don't do that.

  In this case, the intermediate blow-molded product in the softened state after heat treatment taken out from the primary blow-molding die is set with its cylindrical body portion in the secondary blow-molding die in a predetermined direction. Need to be transported.

  For this purpose, the intermediate blow-molded product is removed from the primary blow-molded mold while maintaining a state in which each surface of the cylindrical body portion of the intermediate blow-molded portion is in a predetermined orientation. What is necessary is just to convey.

  As described above, in the method for producing a heat-resistant blow-molded product of the present invention, a rib is attached to the intermediate blow-molded product obtained by the primary blow-molding process, and the shape after heat shrinkage of the intermediate blow-molded product by the rib. To regulate. Therefore, by forming an appropriate shape and the number of ribs in an appropriate part of the intermediate blow molded product, the shape of the intermediate blow molded product after heat shrinkage can be approximated to the shape of the final blow molded product. it can. As a result, at the time of secondary blow molding, the stretch amount of each part of the blow molded product can be made substantially equal. Therefore, a heat-resistant blow molded product can be manufactured with high accuracy.

  Below, with reference to drawings, the manufacturing method of the heat resistant blow molded product to which this invention is applied is demonstrated.

  FIG. 1 is a schematic flowchart showing a method for producing a heat-resistant blow-molded product of this example. In the manufacturing method of this example, first, a preform made of a synthetic resin manufactured in advance by injection molding is prepared (step ST1), and while the preform is being conveyed, a temperature suitable for blow molding, that is, a glass transition temperature or higher. To below the melting point temperature (step ST2: preform heating step). Next, the heated preform is set in a primary blow molding die heated to 160 ° C. or more and 200 ° C. or less, and blow molding is performed with compressed air. Thereby, an intermediate blow molded product is obtained (step ST3: primary blow molding step).

  Thereafter, the intermediate blow-molded product is held for a predetermined time in the primary blow-molding mold with the mold closed. Here, the primary blow molding die is heated to a predetermined temperature from the time before closing the mold, and the heat from the primary blow molding die in a heated state is heat-treated to impart heat resistance. (Step ST4: heat treatment step).

  After the heat treatment, the intermediate blow molded product in the softened state is taken out from the primary blow molding die and transferred to the secondary blow molding die, and the intermediate blow molded product in the softened state is transferred to the secondary blow molding die. (Step ST5: transfer step). Thereafter, the intermediate blow-molded product is blow-molded in the secondary blow mold. As a result, a final blow molded product having the final shape is obtained (step ST6: secondary blow molding step).

  2 (a) and 2 (b) are a front view and a cross-sectional view showing an intermediate blow-molded product obtained in the primary blow molding step. The intermediate blow-molded product 1 of this example is continuous with a bottomed cylindrical body 2, a neck 3 that is tapered from the upper end of the cylindrical body 2, and an upper end of the neck 3. A mouth portion 4 is provided, and a screw portion 5 is formed on the outer peripheral surface of the mouth portion 4. In the figure, the cross-sectional shape of the body portion 22 of the preform P and the final blow-molded product 21 is shown by an imaginary line.

  When viewed along the circumferential direction, the cylindrical body portion 2 of the intermediate blow-molded product 1 is formed with discontinuous convex or concave ribs 6a to 6d at four positions at intervals of 90 degrees. The body portion of the final blow-molded product 21 is a horizontally long odd-shaped octagon, and long ribs 6a and 6b are formed on the outer peripheral surface portion corresponding to the long side, and the outer peripheral surface portion corresponding to the short side is formed on the outer peripheral surface portion. Short ribs 6c and 6d are formed. Further, each of the ribs 6a to 6d is formed in parallel by six when viewed along the direction of the axis 1a (body axis direction). In this example, three are formed in the middle part of the body part 2 in the vertical direction, two are formed in the part on the bottom side, and one is formed in the boundary part with the neck part 3.

  FIGS. 2C and 2D are a front view and a cross-sectional view showing the shape of the intermediate blow-molded product after heat shrinkage in the heat treatment step. As described above, ribs 6a to 6d are formed at four locations in the discontinuous state along the circumferential direction in the cylindrical body portion 2 of the intermediate blow-molded product 1. In the outer peripheral surface portion to which the ribs 6a to 6d are attached, the amount of heat shrinkage in the radial direction is reduced, and bending in the out-of-plane direction is also reduced. For this reason, it becomes a slightly flat shape compared with the outer peripheral surface part without the ribs 6a to 6d. The outer peripheral surface portion without the ribs 6a to 6d is greatly curved in the out-of-plane direction.

  The intermediate blow-molded product 11 after heat shrinkage is generally smaller than the intermediate blow-molded product 1 before heat shrinkage. Moreover, the trunk | drum 12 in which the ribs 6a-6d are formed is a little smaller than the trunk | drum cross-sectional shape of the final blow molded product 21 shown by an imaginary line, and also rounded to the said trunk | drum cross-sectional shape. It has a square cross-sectional shape.

  2 (e) and 2 (f) are a front view and a cross-sectional view of the final blow-molded product. The intermediate blow-molded product 11 after being thermally contracted as described above is set in a secondary blow-molding mold, subjected to secondary blow molding, and molded into a final blow-molded product 21. The shape of the barrel 12 of the intermediate blow-molded product 11 after heat shrinkage is an approximate rounded quadrangle that is slightly smaller than the odd-shaped octagon of the barrel 22 of the final blow-molded product 21.

  Accordingly, when the stretch amount A on the long side, the stretch amount B on the short side, and the stretch amount C on the corner portion are compared, the stretch amounts A and B are substantially the same, and the stretch amount C is also the stretch amount. It is only slightly larger than A and B. Therefore, since the stress generated in the body portion of the blow molded product during the secondary blow molding can be substantially uniformed, the molding accuracy can be maintained well, and the productivity is improved.

  Note that the ribs 6a to 6d attached to regulate the shape after heat shrinkage cannot be completely erased by the secondary blow molding, and remain as a slightly rib-like pattern. Therefore, in the mold of the final molded product that is the secondary blow molding, a shape having a similar rib in advance is given to the portion where the ribs 6a to 6d remaining in the intermediate blow molded product 31 are blow molded into the final shape in advance. Can be solved. Furthermore, since vertical and horizontal ribs are required to enhance the strength of the final molded product, the ribs 6a to 6d of the intermediate blow molded product 31 may be attached to locations corresponding to the ribs of the final molded product.

  FIG. 3 is an explanatory view showing a comparison with a case where an intermediate blow-molded product without ribs is subjected to secondary blow molding. As shown in FIG. 3 (a), when an intermediate blow molded product 31 having a cylindrical body 32 that is slightly smaller than the final blow molded product 21 is used, the outer peripheral surface portion corresponding to the long side is stretched. The amount A and the stretch amount B of the outer peripheral surface portion corresponding to the short side are significantly different. Furthermore, the stretch amount of the outer peripheral surface portion corresponding to the corner portion is also greatly increased. For this reason, at the time of secondary blow molding, non-uniform distortion stress is generated in the body portion of the blow molded product, the molding accuracy is deteriorated, and the productivity is also lowered. On the other hand, as shown in FIG. 3B, according to the method of this example in which the shape after the heat shrinkage is regulated by the rib, such an adverse effect can be eliminated as described above.

  Further, the rib to be formed may be concave or convex, and does not remain in the final blow molded product. Therefore, it is not necessary to form the molding surface of the primary blow molding die for forming the rib with high accuracy as the molding surface of the secondary blow molding die. Therefore, the increase in the manufacturing cost of the primary blow molding die is also slight.

  Next, the shape after thermal contraction of the intermediate blow-molded product can be changed by changing the rib forming position and the forming region. As shown in FIG. 4A, when the arc-shaped ribs 16a to 16d are formed on the cylindrical body portion 42 of the intermediate blow-molded product 41 so as to have an equal angle at an interval of 90 degrees, The shape can be a rounded square.

  As shown in FIG. 4 (b), when the ribs 26a to 26c are formed in the cylindrical body 52 of the intermediate blow-molded product 51 in an arc shape so as to form an equal angle at intervals of 120 degrees, The shape after contraction can be a rounded equilateral triangle.

  As described above, by adjusting the rib forming place, the forming region, and the like, the intermediate blow-molded product can be thermally contracted so as to have a shape approximate to the shape of the final blow-molded product.

  On the other hand, in the transfer step of transferring the intermediate blow-molded product 11 after heat shrinkage to the secondary blow mold and setting it in the mold, the cylindrical shape of the intermediate blow-molded product 11 taken out from the primary blow mold The intermediate blow-molded product 11 is conveyed while maintaining the state where each surface of the body portion 12 after thermal deformation is in a predetermined direction. That is, with reference to FIG. 2 (f), the intermediate blow-molded product barrel is formed on the molding surface portion of the secondary blow mold corresponding to the long side portion of the cylindrical barrel 22 of the final blow-molded product 21. The outer peripheral surface portions on which the long ribs 6a and 6b are formed face each other, and the intermediate blow molded product body portion 12 is formed on the molding surface portion of the secondary blow molding die corresponding to the short side portion of the cylindrical body portion 22. The short ribs 6c and 6d are transferred so that the outer peripheral surface portions thereof face each other.

  In general, as shown in FIGS. 5 (a) and 5 (b), the intermediate blow molded article 11 is transported by a cylindrical carrier 7 having a projection 71 into which the mouth portion 14 of the intermediate blow molded article 11 can be inserted from above. Is done by. The carrier 7 is configured such that the large-diameter flange 72 slides on the left and right guide rails 73 and 74 along the guide rails. The same carrier 7 is used until the preform P becomes the final blow-molded product 21. When the preform P is transported, the protrusion 71 is rotated around its central axis in order to uniformly heat the entire preform P.

  However, in the transfer step of taking out the intermediate blow-molded product from the primary blow mold and feeding it to the secondary blow mold, for example, as shown in FIGS. 2 (d) and (f), the primary blow mold (22) and It is necessary to place the secondary blow molding die (12) and send the intermediate blow molded product 11 taken out from the primary blow molding die to the secondary blow molding die by the carrier 7 as it is without rotating. There is.

  Therefore, as shown in FIGS. 5C and 5D, at the time of the transfer, the rotation restraining member 8 for restraining the rotation of the carrier 7 from the side may be pressed against the side surface of the carrier 7. For example, it is desirable to press an elastic member 81 such as urethane against the side surface of the carrier 7. As a result, the intermediate blow-molded product 11 is set at a predetermined position of the secondary blow mold.

It is a schematic flowchart which shows the manufacturing process of the heat resistant blow molded product to which this invention is applied. It is explanatory drawing which shows the state of the shape change of the blow molded product in each process of FIG. It is explanatory drawing which shows the difference by the case by the case of the manufacturing process of FIG. 1, and the case by the conventional manufacturing process. It is explanatory drawing which shows the shape after the heat contraction by a rib. It is explanatory drawing which shows the carrier for transferring an intermediate | middle blow molded product to a secondary blow molding die.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intermediate blow molded product, 2 Cylindrical body part, 3 neck part, 4 mouth part, 5 thread part, 6a-6d rib, 7 carrier, 8 Rotation restraint member, 11 Intermediate blow molded product after heat shrink, 12 After heat shrink Cylindrical body, 21 final blow molded product, 22 cylindrical body, 81 elastic member, A, B, C

Claims (6)

In a primary blow molding die heated to a predetermined temperature, a primary blow molding step for blow molding a preform to obtain an intermediate blow molded product,
A heat treatment step of imparting heat resistance by applying heat treatment to the intermediate blow-molded product by the heated primary blow-molding die by holding the intermediate blow-molded product in the primary blow mold for a predetermined time;
The intermediate blow-molded product after the heat treatment is blow-molded again in a secondary blow-molding mold to obtain a final blow-molded product,
In the primary blow molding step, the intermediate blow molded product with ribs is blow molded in order to regulate the shape of the intermediate blow molded product after heat shrinkage in the heat treatment step. Manufacturing method. In claim 1,
The rib attached to the intermediate blow-molded product is such that the shape of the intermediate blow-molded product after heat shrinkage is closer to the final blow-molded product than the shape of the intermediate blow-molded product before heat shrinkage. And a method for producing a heat-resistant blow-molded product, which is for regulating thermal deformation of the intermediate blow-molded product. In claim 2,
The final blow molded product is a container having a cylindrical body with a bottom,
The intermediate blow-molded product before heat shrinkage is a container having a cylindrical body,
In the primary blow step, a plurality of discontinuous ribs in the circumferential direction or the body axis direction are formed in the cylindrical body portion of the intermediate blow-molded product. Method. In claim 3,
The cylindrical body of the final blow molded product has a polygonal cross section,
In the primary blow step, a plurality of ribs are respectively formed on outer peripheral surface portions corresponding to the surfaces of the cylindrical body portion of the final blow-molded product in the cylindrical body portion of the intermediate blow-molded product, A method for producing a heat-resistant blow-molded product, characterized in that ribs are not formed on outer peripheral surface portions corresponding to the respective corner portions of the cylindrical body portion of the final blow-molded product. In claim 3 or 4,
The intermediate blow-molded product in a softened state after heat treatment taken out from the primary blow-molding die is transferred so that its cylindrical body is set in a predetermined orientation in the secondary blow-molding die. A method for producing a heat-resistant blow-molded product comprising a transfer step. In claim 5,
In the transfer step, the intermediate blow-molded product is removed from the primary blow-molded mold while maintaining the state in which the surfaces after thermal deformation of the cylindrical body of the intermediate blow-molded product are in a predetermined direction. A method for producing a heat-resistant blow-molded product, characterized by being conveyed.

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