Method and device for providing a living hinge in a plastic sheet

Abstract

The invention relates to a method for providing a living hinge in a plastic sheet, which method comprises the steps of: - providing a plastic sheet supported on a support surface; - providing at least one gouge movable relative and parallel to the plastic sheet; - gouging a groove in the plastic sheet with the at least one gouge, by moving the at least one gouge relative to the plastic sheet while maintaining the depth of the groove constant by supporting the gouge onto the surface of the plastic sheet in which the groove is gouged. The invention further relates to a device for providing a living hinge in a plastic sheet.

Description

[0001] The invention relates to a method for providing a living hinge in a plastic sheet. A living hinge is a thin flexible hinge or fold hinge line made from the same material as the two rigid pieces on opposite sides of the living hinge. A living hinge is typically provided in a sheet of material by a thinning operation, such as deforming the material under pressure by a tool.

[0002] For plastic objects it is also possible to provide a living hinge by injection molding. This method is however only suitable for relative small plastic objects and not suitable for extruded plastic sheets.

[0003] To provide plastic sheets, either directly at extrusion, or after the sheet has been cooled off, with a living hinge it is known in the prior art to use a tool with a elongate edge. This elongate edge is pressed into the pre-heated plastic of the sheet and deforms the plastic sheet to provide a living hinge.

[0004] The elongate edge of the tool only can provide linear living hinges, while it is also desired to produce curved living hinges in plastic sheets.

[0005] US 3360420 suggest to use a gouge to cut a groove in the pre-heated plastic sheet in order to provide a living hinge. However, as soon as the cutting edge of gouge enters the material of the plastic sheet, it will cause a pulling force on the plastic sheet, such that the depth of the groove is difficult to control, especially with thinner plastic sheets.

[0006] Accordingly it is an object of the invention to reduce or even remove the above mentioned disadvantages.

[0007] This object is achieved with a method according to the invention, which method comprises the steps of: providing a plastic sheet supported on a support surface; providing at least one gouge movable relative and parallel to the plastic sheet; gouging a groove in the plastic sheet with the at least one gouge, by moving the at least one gouge relative to the plastic sheet while maintaining the depth of the groove constant by supporting the gouge onto the surface of the plastic sheet in which the groove is gouged.

[0008] A gouge is similar to a chisel except that it has a blade edge, which is not flat, but instead curved or angled in cross-section. The curved blade edge defines the cross-section of the groove, which is cut into the plastic sheet and forms the living hinge.

[0009] Because the gouge is supported onto the surface of the plastic sheet it is ensured, that the gouge cannot penetrate deeper into the plastic sheet due to the pulling force which the gouge exerts onto the plastic sheet. As a result galling is prevented and the depth of the gouged groove can be controlled very precise.

[0010] In a preferred embodiment of the method according to the invention the plastic sheet is an extrusion mass, which is transported over the support surface and wherein the position in transport direction of the at least one gouge is stationary relative to the support surface.

[0011] As the extrusion mass already moves over the support surface, the at least one gouge can conveniently be mounted stationary relative to the support surface.

[0012] In another embodiment of the method according to the invention the at least one gouge is movable in the direction perpendicular to the transport direction. This allows for gouging curved living hinges or linear living hinges, which need to be provided at an angle relative to the direction of movement of the plastic sheet.

[0013] The invention also relates to a device for providing a living hinge in a plastic sheet, which device comprises: a frame with a support surface for supporting a plastic sheet; at least one gouge mounted to the frame, supported above the support surface and movable in at least a direction perpendicular to the support surface, which at least one gouge has: + an elongate blade with a curved blade edge at one longitudinal end, in particular a U-shaped curved blade edge and + a first guide element having a guide surface for contact with the top surface of a plastic sheet to be gouged, wherein the longitudinal axis of the blade is arranged under an angle with the support surface, wherein the guide surface is parallel to the support surface and wherein the curved blade edge extends in a direction perpendicular to the support surface beyond the guide surface.

[0014] With the device according to the invention, the at least one gouge is supported with the guide surface onto the plastic sheet in which the groove forming the living hinge is to be gouged. As the curved blade edge extends beyond the guide surface a fixed depth of the gouged groove is set and cannot get any deeper, as the at least one gouge is supported onto the plastic sheet.

[0015] In a preferred embodiment of the device according to the invention the at least one gouge further comprises a second guide element having a guide surface for contact with the top surface of a plastic sheet to be gouged, wherein the second guide element is arranged adjacent the elongate blade and on the opposite side as the first guide element and wherein the guide surface of the second guide element is in the same plane, parallel to the support surface, as the guide surface of the first guide element.

[0016] By having guide elements on both sides of the elongate blade of the gauge the device according to the invention is able to gouge even very thin sheets of plastic. This is because both guide elements will keep the plastic sheet firmly in place when the curved blade edge cuts into the sheet and do not allow for any flexing of the sheet.

[0017] In yet another embodiment of the device according to the invention the at least one gouge further comprises: a cylindrical base with a central channel arranged around the elongate blade, wherein the first guide element and second guide element are arranged to the cylindrical base; and clamping means for clamping the cylindrical base onto the elongate blade.

[0018] The cylindrical base provides for a mounting point to the frame. The elongate blade is easily clamped in the cylindrical base by the clamping means. This also allows for easy exchange of the blade, when the blade edge needs to be sharpened.

[0019] In a preferred embodiment of the device according to the invention the at least one gouge is movable in a first main direction parallel to the support surface. This allows for setting a fixed position relative to the moving direction of the plastic sheet or for dynamic movement to provide a curved living hinge or linear living hinge which is under an angle with the direction of movement of the plastic sheet.

[0020] In a further preferred embodiment of the device according to the invention the at least one gouge is movable in a second main direction parallel to the support surface and perpendicular to the first main direction. This allows for the gouging of a groove in any direction in the plastic sheet, while the plastic sheet is stationary relative to the support surface or when it is moving.

[0021] Preferably, the at least one gouge is rotatable around an axis perpendicular to the support surface. This allows for the at least one gouge to move in opposite directions in one continuous cut.

[0022] In still a further embodiment of the device according to the invention the angle of the longitudinal axis of the blade of the at least one gouge with the support surface is in the range of 30° - 60°.

[0023] These and other features of the invention will be elucidated in conjunction with the accompanying drawings. Figure 1 shows an embodiment of a gouge for a device according to the invention. Figure 2A shows in perspective view an embodiment of a device according to the invention. Figure 2B shows a variant of the embodiment of the device according to figure 2A Figures 3A and 3B show cross-sectional details of the gouge gouging a plastic sheet.

[0024] Figure 1 shows a gouge 1 mounted in a mounting 2 having a sleeve 3, with which the mounting 2 can be arranged on a frame.

[0025] The gouge 1 has two guide elements 4, 5 on opposite sides of an elongate blade 6 with a U-shaped cross-section. The elongate blade 6 has a base 7 and extends through a central channel of a cylindrical base 8 which is mounted in the mounting 2.

[0026] Figure 2A shows a perspective view of an embodiment of a device 10 according to the invention. The device 10 has a frame 11 with a support surface 12 over which an extrusion mass 13 is transported. Two gouges 1, as shown in figure 1, are mounted with their sleeves 3 on a gantry part of the frame 11 extending over the support surface 12. Both gouges 1 cut a groove 14 in the extrusion mass 13 to form living hinges.

[0027] Figure 2B shows a variant of the device 10 of figure 2A. In this embodiment, the two gouges 1 can move along the gantry part of the frame 11, while the extrusion mass 13 is transported over the support surface 12, which allows for the gouging of curved grooves 14.

[0028] If more complex grooves are to be gouged, one could arranged two or more gantries behind each other, each provided with one or more gouges 1, which are movable along the respective gantry. This allows for example for crossing grooves.

[0029] Figure 3A shows a cross-sectional detail of the gouge 1. The guide element 4 rests with the guide surface 15 on the top surface 16 of the extrusion mass 13. The blade edge 6 extends beyond the guide surface 15 and into the extrusion mass 13, such that a groove 14 is gouged and a chip 17 is formed.

[0030] Figure 3B also shows a cross-sectional detail of the gouge 1. This detail shows that on both sides of the elongate blade 6 guide elements 4, 5 are arranged and that the respective guide surfaces 15, 18 rest on the top surface 16 of the extrusion mass 13 to ensure that the depth d is kept constant while gouging the plastic sheet 13.

Claims

1. Method for providing a living hinge in a plastic sheet, which method comprises the steps of: - providing a plastic sheet supported on a support surface; - providing at least one gouge movable relative and parallel to the plastic sheet; - gouging a groove in the plastic sheet with the at least one gouge, by moving the at least one gouge relative to the plastic sheet while maintaining the depth of the groove constant by supporting the gouge onto the surface of the plastic sheet in which the groove is gouged.

2. Method according to claim 1, wherein the plastic sheet is an extrusion mass, which is transported over the support surface and wherein the position in transport direction of the at least one gouge is stationary relative to the support surface.

3. Method according to claim 2, wherein the at least one gouge is movable in the direction perpendicular to the transport direction.

4. Method according to any of the preceding claims, wherein the plastic sheet is pre-heated to a temperature below the Vicat softening point.

5. Device for providing a living hinge in a plastic sheet, which device comprises: - a frame with a support surface for supporting a plastic sheet; - at least one gouge mounted to the frame, supported above the support surface and movable in at least a direction perpendicular to the support surface, which at least one gouge has: + an elongate blade with a curved blade edge at one longitudinal end, in particular a U-shaped curved blade edge and + a first guide element having a guide surface for contact with the top surface of a plastic sheet to be gouged, wherein the longitudinal axis of the blade is arranged under an angle with the support surface, wherein the guide surface is parallel to the support surface and wherein the curved blade edge extends in a direction perpendicular to the support surface beyond the guide surface.

6. Device according to claim 5, wherein the at least one gouge further comprising a second guide element having a guide surface for contact with the top surface of a plastic sheet to be gouged, wherein the second guide element is arranged adjacent the elongate blade and on the opposite side as the first guide element and wherein the guide surface of the second guide element is in the same plane, parallel to the support surface, as the guide surface of the first guide element.

7. Device according to claim 5 or 6, wherein the at least one gouge further comprises: - a cylindrical base with a central channel arranged around the elongate blade, wherein the first guide element and second guide element are arranged to the cylindrical base; and - clamping means for clamping the cylindrical base onto the elongate blade.

8. Device according to any of the claims 5 - 7, wherein the at least one gouge is movable in a first main direction parallel to the support surface.

9. Device according to claim 8, wherein the at least one gouge is movable in a second main direction parallel to the support surface and perpendicular to the first main direction.

10. Device according to any of the claims 5 - 9, wherein the at least one gouge is rotatable around an axis perpendicular to the support surface.

11. Device according to any of the claims 5 - 10, wherein the angle of the longitudinal axis of the blade of the at least one gouge with the support surface is in the range of 30° - 60°.

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