METHOD FOR TRANSMFERRING A NEGATIVE STRUCTURE OF A SURFACE OF AN INNER WALL OF A BLOW MOLDING TOOL, AND PLASTIC CONTAINER

Abstract

A method for transferring a negative structure of a surface of an inner wall (51) of a blow molding tool (1) onto a surface of a plastic container. The method comprises the steps of heating at least one region (511) of a mold cavity (6) of a molding body (4) of the blow molding tool (1), on which the negative structure is formed, inserting a preform into the mold cavity (6), closing the blow molding tool (1), molding the plastic container by inflating the preform and bringing the preform to lie against the inner wall (51) of the mold cavity (6), cooling the region (511) by supplying a coolant through temperature control channels (54), and removing the plastic container from the mold.

Claims

1-13. (canceled)

14. A method for transferring a negative structure of a surface of an inner wall (51) of a blow molding tool (1) to a surface of a plastic container, the method comprising the steps of heating at least one region (511) of a mold cavity (6) of a molding body (4) of the blow molding tool (1) on which the negative structure is formed, introducing a preform into the mold cavity (6), closing the blow molding tool (1), shaping the plastic container by inflating the preform and abutting the preform against the inner wall (51) of the mold cavity (6), cooling the at least one region (511) by feeding a coolant through temperature control channels (54), and demolding the plastic container.

15. The method according to claim 14, wherein the at least one region (511) comprises the entire mold cavity (6).

16. The method according to claim 14, wherein during the shaping of plastic containers, consisting substantially of polyolefins, and the at least one region (511) is heated to at least 212° F. (100° C.).

17. The method according to claim 14, wherein during cooling, the at least one region (511) is cooled at an average cooling rate of at least 5 K/s to a demolding temperature of 100° F. (60° C.) in a case of plastic containers consisting of substantially of polyolefins.

18. The method according to claim 14, wherein the preform consists substantially of a polyolefin and the heating medium is supplied at a temperature of between 248° F. to 392° F. (120° C. to 200° C.), and the cooling medium is supplied at a temperature of between 41° F. to 104° F. (5° C. to 40° C.).

19. The method according to claim 14, wherein the at least one region (511) is thermally insulated from the molding body (5) and/or from a baseplate (4).

20. The method according to claim 14, wherein the at least one region (511) has, in an associated section of the molding body (5), separate temperature control channels (54) for controlling the temperature of the at least one region (511).

21. The method according to claim 14, wherein an insulating element (16) made of a thermally insulating material is arranged between the molding body (4) and the baseplate (5) of the blow mold half (2).

22. The method according to claim 14, wherein a wall thickness, between the temperature control channel (54) and the at least one region (511), is at least 0.059 inches (1.5 mm) and at most 0.472 inches (12 mm) thick.

23. The method according to claim 14, wherein the at least one region (511) has a uniformly structured surface as the negative structure.

24. The method according to claim 23, wherein the structured surface is designed as a reflection grating, having a grating constant of less than 0.000394 inches (10 μm), the structured surface is transferred to the surface of the plastic container by the method with a deviation of less than 0.0000394 inches (1 μm).

25. A plastic container made of a polyolefin produced according to a method according to claim 14, wherein the container has a surface that is structured at least in one region, the structure of the surface deviates less than 0.0000394 inches (1 μm) from the negative structure of the blow mold corresponding to the container.

26. The plastic container according to claim 25, wherein the structured surface is designed as a reflection grating, and the grating constant is preferably less than 0.000394 inches (10 μm).

27. The method according to claim 15, wherein an insulating element (16) made of a thermally insulating material is arranged between the molding body (4) and the baseplate (5) of the blow mold half (2).

Description

[0108] Exemplary embodiments of a blow molding tool are explained in more detail below with reference to schematic figures. These show:

[0109] FIG. 1: a prior-art blow molding tool having two blow mold halves;

[0110] FIG. 2: a first blow mold half;

[0111] FIG. 3: a vertical sectional view of FIG. 2;

[0112] FIG. 4: a second blow mold half;

[0113] FIG. 5: a perspective view of the molding body of the blow mold half from FIG. 4; and

[0114] FIG. 6: a perspective view of the rear side of the molding body from FIG. 5.

[0115] FIG. 1 shows a blow molding tool 1 from the prior art for explaining the basic structure of such a tool. The blow molding tool, which as a whole is provided with reference sign 1, comprises a first blow mold half 2 and a second blow mold half 3. In the present case, said blow mold halves are laterally displaceable relative to one another in order to open and close the blow molding tool 1 periodically. Each blow mold half 2, 3 comprises a baseplate 4, which forms part of a closing unit of a blow molding machine. Mounted on the baseplate 4 is a molding body 5 in which one or more mold cavities 6 are formed. According to the exemplary embodiment shown, the molding body 5 has two mold cavities 6, each defining one half of the shape of a body of a plastic container. Since the mold cavities correspond to one another, the two mold cavities are, for better clarity, not provided with all reference signs, although the explanations apply in each case to both mold cavities.

[0116] A head plate 7 is provided with a cavity 8 for defining a neck section of the plastic container. In the case of a blow molding tool for an extrusion blow-molding machine, a neck blade 9 for separating an extruded plastic parison inserted into the blow molding tool 1 can also be provided on the headplate 7. A bottom part 10 closes the mold cavities 6 at the other end of the blow molding tool 1. On the mutually facing surfaces 11, 12 of the blow mold halves 2, 3, which define a separating plane of the blow molding tool 1, venting slots 13 can be formed. On one of the blow mold halves 3, guide pins 14 are formed, which slide into guide bushes 15 of the other blow mold half 2 when the blow mold halves 2, 3 are closed. The molding body 5 has a wall surface, i.e., an inner wall 51, which forms a part of the mold cavity 6.

[0117] FIG. 2 shows a first blow mold half 2 of a blow molding tool for carrying out the method according to the invention. The blow mold half 2 has a baseplate 4. Arranged on the baseplate 4 is a distributor block 21 with two connections 211 and 212 for supplying a temperature control medium. A molding body 5 and a bottom part 10, which adjoins the molding body 5, are arranged on the base body 4. A headplate 7 is embedded in the molding body 5. The entirety consisting of molding body 5, bottom part 10 and headplate 7 provides a mold cavity 6. As part of the mold cavity 6, the molding body 5 has an inner wall 51. The inner wall 51 has two regions 511, wherein an associated section with separate temperature control channels 54 (see FIG. 3 in this respect) is assigned to each region 511. The temperature control channels 54 are connected to the connections 211 and 212 via the distributor block 21. The surfaces of the regions 511 each have a reflection grating.

[0118] FIG. 3 shows a vertical sectional view through one of the regions 511 of FIG. 2. From this sectional view, it can be seen that the region 511 is formed as part of the inner wall 51. The reflection grating is not shown in more detail for the sake of clarity. The region 511 has an associated section, on which a molding part 20 formed separately from the molding body 5 is formed. At its end facing the mold cavity 6, the molding part 20 is embedded in the molding body 5 and subsequently, in the direction of the baseplate 4, spaced apart from the molding body 5 with an insulating element 16. For better insulation, the insulating element 16 is additionally spaced apart from the molding body 5 by two O rings.

[0119] The temperature control channels 54 are formed within the molding part 20. To this end, a hole 541 is provided in the molding part 20 and a tube 542 opens into or penetrates through this hole 541 lengthwise so that an annular gap is formed between the tube 542 under the inner wall of the hole 541 through which the temperature control medium can be conducted into the vicinity of the region 511 or can be discharged therefrom. The tube 542 opens into a corresponding channel on the distributor block 521 and accordingly, the annular gap opens into a further channel on the distributor block 21. These channels open correspondingly into the connections 211 and 212 (see FIG. 2).

[0120] The cooling channel 54 has an extension at its end adjacent to the region 511 so that the cooling channel 54 forms a chamber. This chamber connects the ring gap and the tube so that a cooling circuit can be provided. The chamber is spaced from the mold cavity 6 with a wall thickness, which in the present case is 3 mm. This ensures that the heat that this wall thickness has, for example, after blow molding, can be dissipated quickly, or that the wall thickness can be rapidly heated with a suitable heating medium so that its temperature substantially corresponds to that of the preform that is introduced into the mold cavity 6 for blow molding.

[0121] FIG. 4 shows a blow mold half 2 of a blow molding tool 1 that is an alternative to FIG. 2 for carrying out the method according to the invention.

[0122] The blow mold half 2 in turn comprises a baseplate 4 and a molding body 5, in which a mold cavity 6 is formed. The mold cavity 6 defining half the shape of a container body is bounded by a shaping inner wall 51. The inner wall 51 is entirely designed as region 511 and is provided with a reflection grating not shown here. In contrast to the blow mold half shown in FIG. 2, the molding body 5 is embedded in an insulation block 16. The insulation block 16 consists of a thermally insulating plastic or plastic composite material and thermally insulates the molding body 5 from the baseplate 4, a frame 17 fastened thereto, a neck insert 18 which corresponds to the head plate 7 in FIG. 1, and the bottom part 10. The insulation block 16 prevents thermal bridges between the molding body 5 and the surrounding parts of the blow molding tool. According to the exemplary embodiment shown, the neck insert 18 is formed as a separate part which is brought into position when the blow mold halves are closed and lifted off again when they are opened. However, the neck insert 18 may also be fixedly connected to the frame 17.

[0123] FIG. 5 shows the molding body 5 according to FIG. 4. Said molding body is embedded in an insulation block 16. The mold cavity in turn bears reference sign 6. The inner wall delimiting the mold cavity 6 is provided with reference sign 51. The mold cavity 6 defines, for example, half of the shape of a container body. The inner wall 51 can be polished, for example, but in the present case has a reflection grating, which is not shown for the sake of better clarity. The molding body 5 is completely embedded in the insulation block 16 in order to ensure that no undesired thermal bridges to the baseplate 4 can occur. The molding body 5 is dimensioned, for example, in such a way that space remains in the insulation block 16 for a headplate or for a foot part for the production of the container neck or of the container bottom. In this way, the headplate and the foot part (not shown in each case) are also thermally insulated from the baseplate and the frame of the blow mold half, and possible thermal bridges can be prevented.

[0124] The shaping inner wall 51 has a shortest possible distance from a rear side 53 of the molding body 5. In other words, the molding body 5 has a wall thickness of about 1.5 mm to 12 mm in the region of the mold cavity 6. This ensures that the heat that this wall thickness has, for example, after blow molding, can be dissipated quickly, or that the wall thickness can be rapidly heated with a suitable heating medium so that its temperature substantially corresponds to that of the preform that is introduced into the mold cavity 6 for blow molding.

[0125] FIG. 6 shows a perspective view of the rear side 53 of the molding body 5 from FIG. 3. In the side of the molding body 5 facing away from the viewer, the mold cavity 6 is formed. The rear side 53 of the molding body 5 is provided with temperature control channels 54 for the throughflow of a heating medium/coolant, for example water. The temperature control channels 54 can be produced by machining, for example milling and drilling, the molding body 5. They are delimited from one another by ribs. In an alternative embodiment variant, the temperature control channels 54 can be produced during casting of the molding body or by alternative manufacturing methods, for example laser melting or metal printing. The rear side 53 of the molding body 5 with the temperature control channels 54 is embedded in the insulation block in the assembled state of the blow molding tool (FIG. 3). The insulation block serves not only to thermally insulate the molding body 5 from the remaining components of the blow mold half. In fact the insulation block is also equipped with channels and/or holes for the supply and discharge of the heating medium/coolant to the channels formed on the rear side of the molding body. It may be provided that all connections for the supply and discharge of hot and cold media are provided on the insulation block. The connections then have no thermal contact with the baseplate, for example, or other components of the blow molding tool.

[0126] Depending on the size of the mold cavity 6 in the molding body 5, two or more separate heating/cooling circuits can also be provided on the rear side 52 of the molding body 5. In the exemplary embodiment illustrated, a partition 55 divides the temperature control channels 54 into two heating/cooling circuits 56, 57. The individual heating/cooling circuits are formed as a meandering arrangement of channels. The provision of a plurality of heating/cooling circuits 56, 57 permits a faster introduction or displacement of the heating medium/coolant in order to heat or re-cool the molding body. The pressure of the heating/cooling medium is advantageously up to 15 bar. In connection with a plurality of heating/cooling circuits 56, 57, a very rapid heating or cooling of the molding body 5 is thereby made possible, which has an advantageous effect on the cycle times. Water is usually used as heating/cooling medium for the molding body 5. The heating medium/coolant flows in the closest possible proximity to the shaping inner wall 51, which delimits the mold cavity 6 and provides the region 511 here. The rear side 53 of the molding body 5 together with the temperature control channels 54 thus constitutes the section associated with the region. Due to the arrangement of the temperature control channels 54, the heat of the container wall abutting against the shaping inner wall 51 can be dissipated very well, in particular when cooling the molding body 5. The dissipation of the heat is additionally improved by the ribs forming the channels. In contrast to, for example, injection molding, the heat can only be dissipated on one side via the cooled shaping inner wall of the molding body during blow molding.

[0127] In the method for transferring a negative structure, in the present case a reflection grating, of a surface of an inner wall of a blow molding tool, which is described comprehensively across all figures, the region 511 of the mold cavity 6 of the molding body 5 of a first blow mold half 2 of the blow molding tool 1 is first heated to the range of the temperature of the preform by supplying a temperature control medium through separate temperature control channels 54. The preform is then introduced into the mold cavity 6. Subsequently, the blow molding tool 1 is closed and the plastic container is shaped by inflating the preform and by abutting the preform against the inner wall 51 of the mold cavity 6. After the shaping, the region is cooled at a rate of 5 K/s by feeding a coolant through the temperature control channels 54 and the plastic container is demolded when a specific cooling temperature is reached. Due to the high temperature of the region and the rapid cooling of the region after the plastic container has been inflated, the reflection grating can be transferred to the plastic container almost without modification.