Blow molding method and apparatus

Abstract

In a method of forming a container from a thermoplastic material, a thermoplastic preform can be introduced into a blow cavity at a temperature that is greater than or equal to a glass transition temperature of the thermoplastic material and less than a melting temperature of the thermoplastic material. A fluid pressure can be introduced into the preform that can cause the preform to expand radially outward to form a semi-finished container. An outer surface of the semi-finished container can be engaged with a wall of the blow cavity. The wall of the blow cavity can be rapidly heated. Heat can be transferred to the outer surface of the semi-finished container. A surface finish from the wall of the blow cavity can be formed onto the outer surface of the semi-finished container.

Description

Technical Field

[0001] This invention relates to thermoplastic containers; more specifically, it relates to a method and apparatus for achieving a high-quality surface finish on blow-molded thermoplastic containers. Background Technology

[0002] like Figure 1 As shown, blow molding is a process of forming a molten tube (hereinafter referred to as a "preform" or "preform") containing a thermoplastic material of polymer and / or resin and placing the preform or preform within a blow molding cavity. The molten tube is inflated with compressed air to form the shape of the cavity and cooled before being removed from the mold.

[0003] Currently, conventional methods for achieving high-end surface finishes on blow-molded thermoplastic containers may require secondary finishing processes, such as spraying, heat transfer, screen printing, and mechanical embossing. These secondary processes are typically applied to the molded container. In other words, achieving high-end surface finishes on thermoplastic containers usually requires further processing of the container after molding.

[0004] Heating and cooling techniques can be used in injection molding applications to achieve transfer from the mold to the part or surface finishing. In injection molding, the thermoplastic material enters the mold or cavity with the desired surface finish at a temperature above its melting point. The melt temperature is the actual temperature of the thermoplastic material when it leaves the nozzle. Therefore, the thermoplastic material can be in a fully molten state and solidify within the mold during the process, allowing the mold surface finish to be transferred to the part as the thermoplastic material solidifies. This molten state of the thermoplastic material facilitates the transfer of surface finish to the part.

[0005] The purpose of this invention is to solve the problems discussed above and others, and to provide advantages and aspects not offered by prior thermoplastic containers, as well as methods for their manufacture. The features and advantages of the invention will be fully discussed in the following detailed description, which will be taken into account the accompanying drawings. Summary of the Invention

[0006] One aspect of the present invention relates to a method for forming a container from a thermoplastic material. The method includes the following steps:

[0007] i. The thermoplastic preform is introduced into the blow molding cavity at a certain temperature, which is greater than or equal to the glass transition temperature of the thermoplastic preform and less than the melting temperature of the thermoplastic preform;

[0008] ii. Fluid pressure is introduced into the preform to expand the preform radially outward, thereby forming a semi-finished container;

[0009] iii. Join the outer surface of the semi-finished container to the wall of the blow molding cavity;

[0010] iv. Heating the walls of the blow molding cavity;

[0011] v. to transfer heat to the outer surface of a semi-finished container; and

[0012] vi. To form a surface finish from the walls of the blow molding cavity onto the outer surface of the semi-finished container.

[0013] The first aspect of the invention may include, alone or in any reasonable combination, one or more of the following features. The method may further include a step of softening the outer surface of the semi-finished container during a heat transfer step. The heating step may be achieved by induction heating. The method may further include a step of applying an electric current to a conductor within the mold and generating a magnetic field within the mold. The current may be an alternating current between 10 kHz and 50 kHz. The temperature of the walls of the blow molding cavity may be heated to a range between 60°C and 130°C. The method may further include a step of performing the heating step for less than 6 seconds. The method may further include a step of cooling the walls of the blow molding cavity after the heating step. A cooling step may be performed after the heating step. The cooling step may include introducing cooling fluid pressure into the mold via a channel embedded in the mold body. The heating and cooling steps may be performed together for less than 40 seconds, or until the mold reaches a temperature below 60°C.

[0014] A second aspect of the invention relates to a thermoplastic blow molding apparatus. The apparatus includes a mold comprising a mold body and a concave blow molding cavity formed therein. One or more inductors are located within the mold body. An alternating current power supply is connected across the inductors, wherein the frequency of the alternating current is between 10 kHz and 50 kHz.

[0015] The second aspect of the invention may include, individually or in any reasonable combination, one or more of the following features: The mold may be made of a magnetic material. The magnetic material may be tool steel. The thermoplastic blow molding apparatus may also include cooling channels within the mold body. One or more inductors may be located within the cooling channels. An annular space may be formed around the inductor within the cooling channels. One or more inductors may include circumferentially spaced portions surrounding a concave blow molding cavity. The thermoplastic blow molding apparatus may also include a surface finish on the walls of the blow molding cavity, the walls being configured to engage a semi-finished container within the blow molding cavity. The thermoplastic blow molding apparatus may also include a cooling fluid source fluidly connected to the cooling channels.

[0016] Other features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings. Attached Figure Description

[0017] To understand the present invention, it will now be described by way of example with reference to the accompanying drawings, in which:

[0018] Figure 1 This is a diagram of the existing blow molding process;

[0019] Figure 2 This is a diagram of the blow molding operation of the present invention;

[0020] Figure 3 This is a front view of the mold used in the blow molding operation of the present invention;

[0021] Figure 4 This is a cross-sectional view of half of a mold used in the blow molding operation of the present invention, which shows the temperature changes inside the mold;

[0022] Figure 5 yes Figure 4 Alternative views of the mold;

[0023] Figure 6 This is a schematic diagram of the blow molding equipment of the present invention, which further shows the preform extending radially outward until the semi-finished container joins the wall of the blow molding cavity;

[0024] Figure 7 This is a partial cross-sectional view of a mold used in the blow molding operation of the present invention, showing an enlarged view of an inductor including a tubular conductor, an annular cooling channel surrounding the inductor, and a cooling channel through the tubular conductor.

[0025] Figure 8 It is a graph showing the rapid heating and cooling cycles of blow molding;

[0026] Figure 9 This is a comparison table of a first container (hereinafter referred to as "Container E") manufactured according to existing methods and a second container (hereinafter referred to as "Container R") manufactured according to the method and using the apparatus of the present invention; and

[0027] Figure 10 The comparison is a side-by-side of the container on the right (hereinafter referred to as "R") manufactured according to the present invention and the container on the left (hereinafter referred to as "L") manufactured in the same blow molding cavity without the application of rapid induction heating. Detailed Implementation

[0028] While the invention allows for many different embodiments, preferred embodiments of the invention are shown in the accompanying drawings and will be described in detail herein, wherein the content of the invention should be understood as an example of the principles of the invention and not intended to limit the broad aspects of the invention to the illustrated embodiments.

[0029] In blow molding, a preform or preform (hereinafter referred to as "preform") enters the blow molding cavity in a solid state above its glass transition temperature (Tg). This makes it challenging to replicate and transfer the etched surface finish from the wall height of the blow molding cavity to the finished or semi-finished part. However, the inventors have discovered that by rapidly heating the blow molding cavity wall and controlling the blow molding pressure, a thermoplastic material above its glass transition temperature can be forced into the etched surface of the blow molding cavity wall, thereby replicating or transferring the etched surface to the outer surface of the finished or semi-finished part.

[0030] Process control of rapid heating, preform temperature, and blow molding pressure are key variables for achieving the desired surface finish. Controlling these parameters achieves greater consistency, repeatability, and part quality compared to conventional secondary methods of applying surface finish. Furthermore, unlike injection molding, where the fine surface finish on the blow cavity surface is not transferred to the part during the blow molding process without rapid heating of the blow cavity, in injection molding, most surface finish is transferred without heat-cooling, albeit at a lower resolution.

[0031] Therefore, the main factor affecting the surface finish of finished blow-molded parts is the cavity wall temperature. However, the preform temperature is important for ensuring proper blow molding. While the preform temperature varies depending on the material, it should be at least at or above the Vicat softening temperature of the material being blow-molded. It should be understood that the Vicat softening temperature can be used to compare the thermal properties of materials.

[0032] Here, "semi-finished product" refers to the container as it expands from the preform to the part removed from the blow molding process and includes that part. This term envisions that the part may undergo further processing after the blow molding process, such as labeling, adding a container lid, etc. It should be understood that the part can be a container, bottle, package, or other form of component.

[0033] Therefore, one aspect of the blow molding method and apparatus disclosed herein is that a high-quality surface finish (macroscopic, microscopic, and nanoscopic) visually and physically similar to that formed by a secondary method can be achieved within the blow molding cavity of the mold by transferring such fine surface finish etched into the blow molding cavity to the blow-molded part in the blow molding cavity, thereby eliminating the need for secondary processes.

[0034] Compared to conventional processes, this new method and equipment delivers improved consistency and repeatability of up to approximately 97%; improved decorative adhesion for screen printing, thermoforming, and heat transfer. Improved container compatibility is achieved due to the absence of a spray coating layer that could affect potential adhesion. Surface treatments, including but not limited to spraying and secondary finishing, do not introduce incompatibility or stress into the container. Therefore, cycle time is improved by at least 25% when using rapid cooling and induction heating. This allows for a wider range of target surface finishes without the need for tooling or spraying modifications. Furthermore, a wider range of materials can be utilized compared to injection molding because surface replication is not dependent on materials with high melt temperature properties. As understood by one of ordinary skill in the art, a "spray coating layer" is a layer formed on an article of matter via a coating process in which material is sprayed onto the surface of the article.

[0035] refer to Figure 2 The novel method of the present invention includes the following steps: taking a heat-conditioned thermoplastic preform 10 ( Figure 6 ) Introducing blow molding cavity 14 ( Figure 6 (Step 100); the blow molding fluid pressure is increased to 18 ( Figure 6 ) is introduced into the preform 10 (step 200) and abuts against the wall 22 of the blow molding cavity 14 ( Figure 6 ) Radial outward expansion of the preform 10; heating of the wall 22 of the blow molding cavity 14 (step 300); and removal of the finished or semi-finished product container 26 from the mold ( Figure 6 (Step 400). These are standard steps, as understood by those skilled in the art of blow molding. Figure 6 As shown, extending the preform 10 into a semi-finished container 26 provides an intermediate stage, as indicated by the dashed lines for the semi-finished container 26.

[0036] The method also includes the step of rapidly heating the wall 22 of the blow molding cavity 14. This step allows for heat transfer between the semi-finished containers 26, wherein the surface finish of the wall 22 of the blow molding cavity 14 is transferred to the outer surface 30 of the semi-finished containers 26. This step requires a suitably designed apparatus including a mold with means for rapidly heating the wall 22 of the blow molding cavity 14. Such a mold is... Figures 3 to 7 As shown in the diagram, the mold is heated via induction heating.

[0037] Induction heating is a process that uses electromagnetic induction to heat a conductive mold (usually metal). Eddy currents generate heat within the mold.

[0038] An alternating current 34 from power supply 36 is applied to inductor 42 at a frequency between 10 kHz and 300 kHz. This induces currents in opposite directions in channel 50 and electromagnetic field 38, causing heat to diffuse to the walls of blow molding cavity 14 (see [link]). Figure 6This operation continues until the temperature of the wall 22 of the blow molding cavity 14 is heated to a range between 60°C and 130°C. This temperature is suitable for softening the outer surface 30 of the semi-finished container 26 when engaged with the wall 22 of the blow molding cavity 14. Combined with the blow molding fluid pressure 18 delivered to the interior 58 of the semi-finished container 26, softening allows the desired surface finish to be transferred to the outer surface 30 of the semi-finished container 26.

[0039] Therefore, the mold is made of conductive materials, such as metals. Ferrous alloys are typically metallic. 1.2343 (H11) magnetic tool steel has a resistivity of about 40 Ω·m, a relative permeability of about 55, and a thermal conductivity of about 27 W / m·°K.

[0040] One or more inductors 42 are incorporated into the mold body 46 near the wall 22 of the blow molding cavity 14. The inductors 42 are uniformly distributed in the magnetic material surrounding the wall 22 of the blow molding cavity 14. In other words, the inductors 42 are equidistantly spaced around the blow molding cavity 14 within the mold body 46. However, while equidistantly spaced inductors are ideal, design constraints typically preclude such spacing, and the desired result is achieved even when the inductors 42 are not equidistantly spaced.

[0041] The inductor 42 includes electrical conductors 44, such as braided copper wire. These conductors 44 are located within channels 50 or a network of channels 50 in a mold. The channels 50 may be in the form of tubular channels, trenches, conduits, etc. The conductors 44 are lined with one or more insulating layers 54.

[0042] An AC induced current 34 with a frequency between 10 kHz and 300 kHz can be delivered from an AC power source 36, which can be electrically connected to an inductor 42. This induces currents in opposite directions in the channel 50 and the electromagnetic field, causing heat to diffuse and propagate to the wall 22 of the blow molding cavity 14. Figure 6 ).

[0043] The method also includes a step of rapidly cooling the mold after the heating step. Therefore, the apparatus includes means for cooling the mold. This can take the form of an additional channel 50 that passes through the mold, longitudinally and / or laterally to the height of the mold, and is fluidly connected to a cooling fluid pressure source 62. Cooling fluid can be injected into the channel 50 to rapidly cool the mold and / or control heat diffusion. Alternatively or additionally, the cooling means may include a tubular conductor 70 that allows cooling fluid pressure 66 to flow through it.

[0044] Alternatively or otherwise, the cooling device includes a space 74 between the circumferential wall of the conductor channel 50 and the insulating layer 54 of the conductor 44. Cooling fluid can then be introduced into the space 74 to cool the mold. Here, the space 74 is formed by increasing the cross-sectional area of ​​the channel 50 such that the cross-sectional area of ​​the channel 50 is substantially larger than the cross-sectional areas of the conductor 44 and the insulating layer 54. The term "substantially" as used herein is intended to cover a structure in which the space 74, formed by the distance between the radially outermost portion of the conductor / insulator and the channel wall, is large enough to allow fluid to flow through it. The space 74 is preferably annular, such that the space 74 forms a circumferential gap around the circumference of the conductor / insulator. In each case, cooling fluid is prepared to flow through the mold between two heating cycles.

[0045] The equipment and blow molding method are controlled by a suitable controller 78, such as a computer, microcontroller, hardwired control panel, data processor, etc. The controller 78 may have non-transitory memory containing one or more software routines. The software routines can control the heating / cooling cycle or duration, the operation of the blow molding fluid pressure source 82 according to the duration pressure, volume, etc., the AC power supply 36, and the cooling fluid pressure source 62.

[0046] In a specific embodiment of the invention, a thermoplastic preform 10 is introduced into a blow molding cavity 14 at a temperature greater than or equal to the glass transition temperature of the thermoplastic preform 10 and less than the melting temperature of the thermoplastic preform 10. Blow molding fluid pressure 18 is introduced into the preform 10 to radially expand the preform 10, thereby forming a semi-finished container 26. Blow molding fluid pressure 18 is continued to be introduced, wherein the outer surface 30 of the semi-finished container 26 engages with the wall 22 of the blow molding cavity 14. The wall 22 of the blow molding cavity 14 is heated by induction heating. An electric current is applied to a conductor 44 within a mold body 46, generating a magnetic field within the mold body 46. The current is an alternating current 34 between 10 kHz and 300 kHz. Heat is transferred to the outer surface 30 of the semi-finished container 26. The temperature of the wall 22 of the blow molding cavity 14 is heated to a range between 60 degrees Celsius and 130 degrees Celsius for a duration of less than 6 seconds. The heat from the heat transfer softens the outer surface 30 of the semi-finished container 26. The surface finish of the wall 22 from the blow molding cavity 14 is formed onto the outer surface 30 of the semi-finished container 26. After the heating step, the wall 22 of the blow molding cavity 14 is cooled. Cooling of the wall 22 includes the introduction of cooling fluid pressure 66 into the mold via channels 50 embedded in the mold body 46. The heating and cooling steps are performed for a total of less than 40 seconds, or until the mold reaches a temperature below 60 degrees Celsius.

[0047] refer to Figure 8An exemplary heating / cooling cycle according to an embodiment of this disclosure is shown. The heating cycle lasts for 5 seconds and can increase the mold temperature from less than 60 degrees Celsius to approximately 90 to 108 degrees Celsius. Heat continues to diffuse to heat the mold to above 110 degrees Celsius. A cooling step begins and continues for approximately 35 seconds until the mold temperature reaches approximately 50 degrees Celsius.

[0048] refer to Figure 9 This illustration shows an exemplary example comparing a container R manufactured according to the above-described embodiment with a container E manufactured according to the prior art. Container E is manufactured using a conventional blow molding method with a plain (i.e., no surface finish) cavity. The surface finish of container E is achieved by a secondary spraying process (conventional spraying method) in the prior art. Container R is manufactured using a blow molding cavity with a surface finish. The surface finish is transferred to container R at a replication rate of 97% or higher. Figure 9 As shown, R a It is the average surface roughness; R z It is the difference between the highest "peak" and the deepest "valley" on the surface; and R Sm This is the average peak width. Container E can provide an R value of approximately 0.4012 micrometers (μm). a R is approximately 2.7845 μm z And R at approximately 41.6655 μm Sm The container R can provide approximately 1.5294 μm of R. a R is approximately 8.5857 μm z And R of approximately 109.5578 μm Sm .

[0049] refer to Figure 10 The container R on the right, manufactured according to the same embodiment described above, is compared with the container L on the left, manufactured according to the prior art. Containers E and L are manufactured using blow molding cavities with substantially the same cavity wall surface finish. The transfer of the blow molding cavity wall surface finish to container R is greater than the transfer to container L. In other words, container R is manufactured with induction heating applied, while container L is manufactured without induction heating but with the same surface finish on the blow molding cavity surface. Although container L is blow-molded in a cavity containing a fine surface finish, effective transfer is not achieved due to the lack of induction rapid heating and cooling. Although container R is blow-molded in the same cavity, induction is turned on therein, allowing the fine surface finish to be successfully transferred.

[0050] The advantages of this invention include the ability to blow-mold high-quality surface finishes onto packaging within the mold itself by applying heating / cooling techniques to provide a fine finish transferred from the wall 22 of the blow molding cavity 14. This technology can be used in conjunction with, for example, extrusion blow molding, injection blow molding, and injection stretch blow molding. This method achieves high-quality surface finishes at the macroscopic, microscopic, or nanoscopic level. It allows for the blow molding of different types and levels of surface finishes without requiring different tools or spray modifications. Importantly, it eliminates the need for secondary finishing of containers while achieving a fine and high-quality surface finish. The new process achieves uniformity, consistency, and repeatability in surface finishing.

[0051] Although specific embodiments have been described and illustrated, many modifications are contemplated without significantly departing from the spirit of the invention, and the scope of protection is limited only by the scope of the appended claims.

Claims

1. A method for forming a container from a thermoplastic material, the method comprising the following steps: A thermoplastic preform is introduced into a blow molding cavity at a certain temperature, wherein the temperature is greater than or equal to the glass transition temperature of the thermoplastic preform and less than the melting temperature of the thermoplastic preform. Fluid pressure is introduced into the preform to expand the preform radially outward, thereby forming a semi-finished container; The outer surface of the semi-finished container is joined to the wall of the blow molding cavity; Heating the wall of the blow molding cavity; Heat is transferred to the outer surface of the semi-finished product container; as well as The surface finish of the wall from the blow molding cavity is formed on the outer surface of the semi-finished container.

2. The method according to claim 1, further comprising the following step: The outer surface of the semi-finished product container is softened during the heat transfer step.

3. The method according to claim 2, wherein the heating step is achieved by induction heating.

4. The method according to claim 3, further comprising the following steps: An electric current is applied to a conductor inside the mold, generating a magnetic field within the mold.

5. The method of claim 4, wherein the current is alternating current between 10 kHz and 50 kHz.

6. The method of claim 5, wherein the temperature of the wall of the blow molding cavity is heated to a range between 60 degrees Celsius and 130 degrees Celsius.

7. The method according to claim 6, further comprising the following step: The heating step is performed in less than 6 seconds.

8. The method according to claim 7, further comprising the following step: The walls of the blow molding cavity are cooled after the heating step.

9. The method of claim 8, wherein the cooling step is performed after the heating step.

10. The method of claim 9, wherein the cooling step comprises introducing fluid pressure into the mold via a channel embedded in the body of the mold.

11. The method of claim 10, wherein the heating step and the cooling step are performed for a total of less than 40 seconds, or until the mold reaches a temperature below 60 degrees Celsius.

12. A thermoplastic blow molding apparatus, comprising: A mold, the mold comprising a mold body and a concave blow molding cavity formed therein; One or more inductors, the one or more inductors being located within the mold body; and An alternating current power supply connected across the inductor, wherein the frequency of the alternating current is between 10 kHz and 300 kHz.

13. The thermoplastic blow molding apparatus according to claim 12, wherein the mold is made of magnetic material.

14. The thermoplastic blow molding equipment according to claim 13, wherein the magnetic material is tool steel.

15. The thermoplastic blow molding equipment according to claim 14 further includes a cooling channel located within the mold body.

16. The thermoplastic blow molding apparatus of claim 15, wherein the inductor of the one or more inductors is located within the cooling channel.

17. The thermoplastic blow molding apparatus of claim 16, wherein the annular space is formed around the inductor within the cooling channel.

18. The thermoplastic blow molding apparatus of claim 17, wherein the one or more inductors include circumferentially spaced portions surrounding the concave blow molding cavity.

19. The thermoplastic blow molding apparatus of claim 18, further comprising a surface finish on the wall of the blow molding cavity, the wall being configured to engage a semi-finished container within the blow molding cavity.

20. The thermoplastic blow molding apparatus of claim 19, further comprising a cooling fluid source fluidly connected to the cooling channel.

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