Method of producing pressed paper piece and apparatus therefor

Abstract

The objective of the present invention is to provide a method of forming a pressed paper piece by deep drawing a sheet of blank that is primarily made of paper in use of a punch and a die, and a production apparatus for implementing the method, whereby no distinguishable wrinkles are formed in upright portions of the pressed paper piece. The method of producing a pressed paper piece according to the present invention, implemented when deep drawing a sheet-like blank that is primarily made of paper in use of a punch and a die, includes maintaining a predetermined gap between a first blank holder and the die in an outer peripheral region of a process portion of the blank and applying a pressure to a radially inner region thereof via a second blank holder, thereby reducing wrinkling by an effect of integrated functions exerted in both regions of the blank.

Claims

1. An apparatus for producing a pressed paper piece by deep drawing a sheet-like blank that is primarily made of paper in use of a punch and a die, the apparatus comprising: means for maintaining a predetermined gap S between a lower surface of a first blank holder and an upper surface of the die during deep drawing, with the first blank holder being arranged in an outer peripheral region of a process portion of the blank, and a second blank holder having pressing means being arranged in a radially inner region in the process portion of the blank, wherein the second blank holder has a lower surface protruding more than the lower surface of the first blank holder, with a difference Z therebetween being STZ<S, where T is the thickness of the blank.

2. The apparatus for producing a pressed paper piece according to claim 1, wherein the first blank holder has a sharp outer circumferential edge that also serves as a cutter for cutting the blank.

3. The apparatus for producing a pressed paper piece according to claim 2, further comprising a lubricating oil supply member for lubricating the upper surface of the die arranged opposite a lower end face of the first blank holder.

4. The apparatus for producing a pressed paper piece according to claim 1, further comprising a lubricating oil supply member for lubricating the upper surface of the die arranged opposite a lower end face of the first blank holder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram illustrating an embodiment of the apparatus of the present invention;

(2) FIG. 2 is a diagram for explaining the forming process according to the present invention;

(3) FIG. 3 shows results of analysis from a CD direction of a product processed according to the present invention;

(4) FIG. 4 shows results of analysis from a CD direction of a conventional product (1);

(5) FIG. 5 shows results of analysis from a CD direction of a conventional product (2); and

(6) FIG. 6 is a diagram for explaining the structure of a two-piece paper cup.

EXPLANATION OF REFERENCE NUMERALS

(7) 1: first blank holder 1a: lower end face of first blank holder 1b: stepped portion of first blank holder 2: second blank holder 2a: lower end face of second blank holder 2b: stepped portion of second blank holder 3: die 3a: upper surface of die 4: pressure application mechanism 4S: spring 5: backing member 6: cutter 7: punch 8: ejector member 9: sheet-like paper material 9a: blank 10: lubricating oil supply felt 50: pressing member with a constant gap of conventional apparatus

BEST MODE FOR CARRYING OUT THE INVENTION

(8) FIG. 1 shows the structure of processing parts of the apparatus for producing the pressed paper piece according to the present invention in cross section. The left side of the central part shows a state before the processing, while the right side shows a state during the processing. The lower left and right diagrams each show enlarged views of essential parts, while the upper left diagram shows part of the structure of a conventional apparatus with a constant gap design. Reference numeral 1 denotes a first blank holder, and 2 denotes a second blank holder. The second blank holder 2 is arranged on the inner side of the first blank holder 1, and their lower end faces are opposite the upper surface 3a of a die 3. A pressure application mechanism 4 is disposed in this second blank holder 2 to apply a constant pressure. In the example of configuration shown here, the pressure application mechanism 4 is a spring 4s arranged between a backing member 5 integral with the first blank holder 1 and the second blank holder 2. While a spring is used as the pressure application mechanism in this configuration, a pneumatic cylinder, a hydraulic cylinder, or an elastic member such as rubber may also be used depending on the pressure application capability and apparatus size.

(9) Reference numeral 6 denotes an annular cutter placed on the upper surface on the outer side of the die 3, which punches out a blank from a sheet-like paper material in cooperation with the first blank holder 1. The first blank holder 1 has a sharp outer circumferential edge so that the paper material is cut clean. Reference numeral 7 denotes a deep drawing punch, and 8 denotes an ejector member fitted inside the lower end of the punch for removing the pressed product from the die 3. In the state before the processing in which the lower end faces 1a and 2a of the first and second blank holders 1 and 2 are not in contact with the paper material 9, the second blank holder 2 is pressed downward with a predetermined force by the spring 4s arranged between the backing member 5 integrally formed to the first blank holder 1 and the second blank holder 2, as shown on the left side of the central part of the drawing. The first and second blank holders 1 and 2 engage with each other at their stepped portions 1b and 2b so that, as can be seen from the enlarged view shown in the lower left, the lower end face 2a of the second blank holder 2 is located lower by a difference Z than the lower end face 1a of the first blank holder 1. In the state in which the first blank holder 1 has moved downward to punch out a blank 9a, or a piece that is going to be processed, from the sheet-like paper material 9, as can be seen from the enlarged view shown in the lower right, a constant gap S is maintained between the lower end face 1a of the first blank holder 1 and the upper surface of the die 3. With the first and second blank holders 1 and 2 employing the configurations described above, the apparatus could be designed to produce pressed paper pieces of desired shapes without substantial remodeling of the conventional apparatus, as there was no need to change the outer shape of the pressing member 50 with a constant gap of the conventional apparatus with a constant gap design shown in the upper left of the drawing.

(10) Reference numeral 10 in the drawing denotes an annular lubricating oil supply felt arranged on the inner side of the annular cutter 6 such that its upper surface is at the same height as, and continuous with, the upper surface 3a of the die 3. While a felt is used as the lubricating oil supply member in this configuration, a porous member (metal, ceramics, plastics, and so on), or an annular oil groove, for example, may also be used.

(11) The lubricating oil supply member should preferably have a smaller width than the width of the first blank holder 1. This is because, if the lubricating oil supply member has a larger width than that of the first blank holder 1 and is made of a soft material such as felt, the pressure from the second blank holder 2 fails to be properly applied, as a result of which the intended effect of reducing wrinkles may not be achieved, and also the lubricating oil supply member itself may be damaged.

(12) The operation according to the present invention will be described with reference to FIG. 2. State (1) is the initial state where the sheet-like paper material 9 has been fed to and placed on the upper surface of the cutter 6. The first blank holder 1, second blank holder 2, deep drawing punch 7, and ejector member 8 are located at positions above the sheet-like paper material 9. State (2) shows a blank 9a, or a piece that is going to be processed, punched out from the sheet-like paper material 9. The first and second blank holders 1 and 2 are integrally moved downward so that the cutter 6 punches out a circular blank 9a from the sheet-like paper material 9 in cooperation with the first blank holder 1. At this time, as mentioned above, a constant gap S is maintained between the lower end face 1a of the first blank holder 1 and the upper surface of the die 3 (see FIG. 1), and the lower end face 2a of the second blank holder 2 is located lower by a difference Z than the lower end face 1a of the first blank holder 1, so that the relationship of ST+Z is established, wherein T is the thickness of the sheet-like paper material 9 (see FIG. 1). Therefore, the lower end face 1a of the first blank holder 1 is not in contact with the surface of the sheet-like paper material 9, while the lower end face 2a of the second blank holder 2 is applying a pressure on the surface of the sheet-like paper material 9 as given by the spring 4s. With this pressure being applied to the periphery of the circular blank 9a by the second blank holder 2, the process proceeds to an initial step of deep drawing shown as State (3). In this step, the deep drawing punch 7 and the ejector member 8 are integrally lowered to press a central portion of the blank 9a against the inner circumferential surface of the die 3 to start deep drawing. At first the first blank holder 1 has no bearing on the blank 9a since its lower end face 1a is not in contact with the surface of the blank 9a. As deep drawing advances, however, the outer peripheral portion of the blank 9a is reduced in diameter, causing the blank to wrinkle and the blank surface to warp or causing the blank to increase its thickness, and eventually contacts the lower end face 1a of the first blank holder 1. This contact effectively prevents large wrinkles from being formed during wrinkling.

(13) At this point, the lubricating oil supply felt 10 is in contact with the lower face of the outer peripheral portion of the blank 9a and applying lubricating oil in this region. As deep drawing proceeds, the blank 9a reduces in diameter, and its outer peripheral portion moves from a region under the lower end face 1a of the first blank holder 1 to the region under the lower end face 2a of the second blank holder 2, so that lubricating oil is distributed entirely over the area where the die 3 contacts the blank 9a, to reduce contact friction.

(14) State (4) shows a middle step of the deep drawing process. The punch 7 and the ejector member 8 are integrally lowered further into the die 3 and the side wall of the bottom member is being formed between the punch and die. Deep drawing proceeds, with a constant pressure being applied on the outer peripheral portion of the blank 9a on the upper surface of the die 3 from the lower end face 2a of the second blank holder 2 as given by the spring 4s. It is the major characteristics of the present invention that this pressure provided by the spring 4s is always constant irrespective of the thickness of the blank 9a. In the conventional apparatus wherein the gap between the blank holder and the upper surface of the die was constant, the pressure applied on the outer peripheral portion of the blank 9a varied depending on the variations in thickness of the material of the blank 9a itself or changes of thickness during the process, which caused problems such as rupture or insufficient pressure application. The present invention employs a pressure application mechanism 4, which is the spring 4s in this embodiment, whereby a constant pressure is applied even if the thickness of the blank 9a varies, so that thickness variations are absorbed by displacement of the second blank holder 2. State (5) shows the last step of the deep drawing process. The outer peripheral portion of the blank 9a has come off of the lower end face 2a of the second blank holder 2 and been drawn onto the inner circumferential surface of the die 3 to be the side wall of the bottom member, whereupon the deep drawing is complete. State (6) shows the removal of the pressed paper piece (bottom member in this embodiment) that has been deep drawn from the die. The ejector member 8, which was fitted in the punch 7, separates from the punch 7 and moves downward independently, to eject the pressed paper piece formed inside of the die 3. After deep drawn, the pressed paper piece thus obtained according to the present invention, although not shown, is then inserted into a tubular body member, and the wall portion of the pressed paper piece is joined to the side wall of the body member to produce a paper container.

Examples

(15) A comparison was made of an already commercially available pressed paper piece produced by a conventional method (Conventional product 1), a pressed paper piece formed by the method described in Japanese Patent Application Laid-open No. 2001-270013 (Conventional product 2), and the pressed paper piece made by the production method of the present invention.

(16) Paper stock with a base weight of 200 g/m.sup.2 and laminated on each side with polyethylene was used as the blank, and a paraffin-based adhesive was used during forming. The adhesive is one that is commonly used for paper cups. A spring mechanism was employed for the mechanism that allows displacement of the blank holder relative to the top surface of the die 1 while a constant pressure is being applied to the outer peripheral portion of the blank 9a. The following other conditions were set the same:

(17) [Shared Conditions]

(18) Blank diameter: 065 mm

(19) Blank thickness: T=0.37 mm

(20) Die hole diameter: 47.1 mm

(21) Die shoulder radius: 1.5 mm

(22) Punch outer diameter: 46.0 mm

(23) Pressing speed: about 360 mm/sec

(24) Next, the working conditions of the present invention, Conventional product (1), and Conventional product (2) are shown in Table 1. Wrinkle reducing pressure here refers to the pressure applied from the second blank holder to the blank in an early stage of the processing.

(25) TABLE-US-00001 TABLE 1 Present Conventional Conventional Invention Product (1) Product (2) Wrinkle First Present Absent Integral Reducing Blank Method holder Second Present Present Blank holder Size Of Outer 65 mm 65 mm First Diameter Blank Inner 56.2 mm holder Diameter Size Of Outer 56 mm 56 mm Second Diameter Blank Inner 48 mm 48 mm 48 mm holder Diameter Gap S Between Die 0.38 mm 1.00 mm Upper Surface And First Blank holder Difference Z 0.05 mm Wrinkle Reducing 3.3 MPa 3.3 MPa Pressure

(26) Mechanical properties of deep drawn pieces of paper blank differ depending on the orientation of paper fibers. As the paper is made by flowing pulp through the paper making machine in a predetermined direction, the fibers tend to align themselves with the advancing direction, which is called the grain direction of paper. The sheet-like paper material 9 in the present invention is fed along this grain direction of paper, i.e., along the direction in which the fibers are aligned, and this direction will hereinafter be referred to as MD direction, while the direction orthogonal thereto will be referred to as CD direction. The paper is intrinsically strong in the MD direction as it hardly stretches in this direction, while it can stretch and is easy to break and wrinkle in the CD direction.

(27) In FIG. 3, A is a photograph taken from the CD direction of the pressed paper piece of the present invention. Pictures were taken only from the CD direction, in consideration of the paper characteristics noted above, as wrinkling is more likely to occur in the CD direction. The paper piece has a smooth surface and no wrinkles are visually perceptible. For more detailed evaluation, it was observed with a scanning electron microscope at 50 times magnification.

(28) In FIGS. 3, C, D, and E are microscopic photographs of a side wall cross section at 2 mm height from the bottom (CD_2), a side wall cross section at 5 mm height from the bottom (CD_5), and a side wall cross section at 1 mm height from the upper end (CD_m1), as indicated in diagram B. All the cross sections were observed from the upper end side. No wrinkles are found in CD_2 and CD_5. In CD_m1, although fine dents were perceptible, no folded-over portions were present.

(29) In FIG. 4, A is a photograph taken from the CD direction of Conventional product (1). Wrinkles are visually perceptible. Similar observation revealed that small dents were present in CD_5, which developed into wrinkles in CD_m1 larger than those at the corresponding position of the pressed paper piece of the present invention.

(30) In FIG. 5, A is a photograph taken from the CD direction of Conventional product (2). Large wrinkles are clearly visible. Observation was made similarly except that, instead of CD_m1 as in FIG. 3, the cross section of the side wall at 8 mm height from the bottom (CD_8) was observed, which revealed that large, distinguished wrinkles had formed in all the cross sections.

(31) As shown by the results described above, the pressed paper piece of the present invention not only has a better finished surface but also has much less wrinkling than conventional products, which enables a reliable bond to be formed with another component such as a body member without cavities or the like in the adhesive layer, and so a desirable paper container that can withstand long-life applications can be provided.

INDUSTRIAL APPLICABILITY

(32) Although the invention has been described herein with respect to an example of forming the bottom part of a paper container such as a paper cup, the invention is not limited to the bottom part of two-piece paper containers but may also be applied to one-piece paper containers with side walls of a small height such as paper dishes or paper trays. The pressed paper piece or paper container of the present invention may contain drinks such as milk, milk for use in portions, coffee, or food products such as jam, yogurt, cheese, butter, ice cream, or snack food.