Polytetrafluoroethylene extrusion die and extrusion equipment

Abstract

The invention relates to the technical field of dies, in particular to a polytetrafluoroethylene extrusion die and extrusion equipment. A flat sheet outlet; the extrusion runner is connected between the bar inlet and the sheet outlet, and the extrusion direction of the extrusion runner is from the bar inlet to the sheet outlet; an extrusion line is defined by a virtual connecting line passing through the center of the bar inlet and the center of the sheet outlet; in a first section which passes through the extrusion line and is vertical to the sheet outlet, the size of a first opening of the extrusion runner is strictly reduced along the extrusion direction; in a second section which passes through the extrusion line and is parallel to the sheet outlet, a second opening of the extrusion runner sequentially comprises a widened area and a constant area in the extrusion direction, the size of the second opening in the widened area is strictly increased, and the size of the second opening in the constant area is constant. According to the embodiment of the invention, each part of the bar is uniformly stressed, and the sheet with relatively uniform thickness and density is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of molds, and in particular to a polytetrafluoroethylene extrusion mold and an extrusion device. Background Art

[0002] Expanded polytetrafluoroethylene not only has good corrosion resistance and weather resistance, but is also non-toxic, pollution-free, and resistant to high and low temperatures. It is an ideal sealing material and has been widely used in fields such as aerospace, medicine, and petrochemical industry. Compared with other traditional sealing materials, expanded polytetrafluoroethylene has good flexibility, can fit complex shapes and irregular surfaces, and has the advantages of no need for curing, easy installation, easy disassembly, low density, and reusable.

[0003] Expanded polytetrafluoroethylene mainly includes standard type, high-strength type, and fuel-resistant type. Among them, the standard type is a unidirectional tensile structure, and its tensile strength in the tensile direction is relatively high; both the high-strength type and the fuel-resistant type are bidirectional tensile structures, and their tensile strengths in any direction are equivalent, so the dimensional stability is better and the application is more extensive.

[0004] The polytetrafluoroethylene biaxially stretched film is the basis for producing high-strength type and fuel-resistant type expanded polytetrafluoroethylene materials. The uniformity of the thickness and density of the polytetrafluoroethylene biaxially stretched film plays a fundamental role in the performance of high-strength type and fuel-resistant type expanded polytetrafluoroethylene materials.

[0005] The existing preparation method of polytetrafluoroethylene biaxially stretched film often adopts the rod extrusion and stretching method. Its basic preparation process includes steps such as raw material mixing, preforming, pushing, calendering, degreasing, longitudinal stretching, and transverse stretching. The rod obtained after pushing forms a sheet after calendering. However, during the calendering process, the center of the sheet is subjected to the greatest force and the longest time. Therefore, the closer to the center of the sheet, the greater the thickness and density of the sheet, resulting in non-uniform stretching of the polytetrafluoroethylene film sheet in the subsequent longitudinal stretching and transverse stretching steps, and finally the poor uniformity of the thickness and density of the prepared polytetrafluoroethylene biaxially stretched film. Summary of the Invention

[0006] The purpose of the embodiments of the present invention is to provide a polytetrafluoroethylene extrusion mold and an extrusion device to solve the technical problem of non-uniform thickness and density of the sheet after calendering.

[0007] To achieve the above purpose, in the first aspect, the embodiments of the present invention provide a polytetrafluoroethylene extrusion mold, including:

[0008] A rod inlet;

[0009] A flat sheet outlet;

[0010] An extrusion flow channel connected between the rod inlet and the sheet outlet, and the extrusion direction of the extrusion flow channel is from the rod inlet to the sheet outlet;

[0011] A virtual connection line passing through the center of the bar inlet and the center of the sheet outlet defines an extrusion line;

[0012] In a first cross-section passing through the extrusion line and perpendicular to the sheet outlet, the size of the first opening of the extrusion channel strictly decreases along the extrusion direction;

[0013] In a second cross-section passing through the extrusion line and parallel to the sheet outlet, the second opening of the extrusion channel sequentially includes a widening area and a constant area along the extrusion direction. In the widening area, the size of the second opening strictly increases, and in the constant area, the size of the second opening remains constant.

[0014] In some embodiments, the aspect ratio of the sheet outlet is 50 to 200:1.

[0015] In some embodiments, in the first cross-section, two opposite first side walls of the extrusion channel are symmetric about the extrusion line, and the first side walls are smooth curves protruding towards the extrusion line.

[0016] In some embodiments, in the first cross-section, the angle between the tangent at any point on the smooth curve and the extrusion line does not exceed 5°.

[0017] In some embodiments, in the second cross-section, two opposite second side walls of the extrusion channel are symmetric about the extrusion line. The position corresponding to the widening area of the second side wall is a first straight line, the first straight line forms a preset angle with the extrusion line, and the position corresponding to the constant area of the second side wall is a second straight line, and the second straight line is parallel to the extrusion line.

[0018] In some embodiments, the angle between the first straight line and the extrusion line is 14 to 19°.

[0019] In some embodiments, the length of the projection of the first straight line on the extrusion line is 100 to 160 mm; and / or

[0020] the length of the projection of the second straight line on the extrusion line is 5 to 20 mm; and / or

[0021] the ratio of the projection of the first straight line on the extrusion line to the projection of the second straight line on the extrusion line is 11 to 15.

[0022] In a second aspect, an embodiment of the present invention further provides a polytetrafluoroethylene extrusion device, including:

[0023] A pusher press, the pusher press having a bar outlet;

[0024] The above-mentioned polytetrafluoroethylene extrusion die, the bar inlet is connected to the bar outlet; and

[0025] A calender, the calender has a sheet inlet, the sheet outlet is connected to the sheet inlet, and the calender is used to calender the sheet output from the sheet outlet.

[0026] Compared with the prior art, the beneficial effect of the embodiment of the present invention is that the bar is extruded into a sheet in the extrusion channel, rather than rolling the bar into a sheet through a calender as in the prior art. Compared with the rolling process, the extrusion process of the embodiment of the present invention can ensure uniform stress on each part of the bar, and finally obtain a sheet with relatively uniform thickness and density. Description of the Drawings

[0027] Figure 1 It is a schematic view of the polytetrafluoroethylene extrusion die provided by the embodiment of the present invention observed from the sheet outlet.

[0028] Figure 2 is Figure 1 The sectional view at A-A in

[0029] Figure 3 It is a top view of the second template provided by the embodiment of the present invention.

[0030] In the figure:

[0031] 1. The first template; 11. The first flange;

[0032] 2. The second template; 21. The second flange;

[0033] 3. The positioning pin;

[0034] 4. The fastener;

[0035] 5. The bar inlet;

[0036] 6. The sheet outlet;

[0037] 7. The extrusion channel; 71. The first opening; 72. The second opening; 721. The widened area; 722. The constant area; 73. The first side wall; 731. The smooth curve; 74. The second side wall; 741. The first straight line; 742. The second straight line;

[0038] L. The extrusion line. Detailed Embodiments

[0039] The technical solution of the present invention will be further described below in conjunction with the drawings and through specific embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. In addition, it should be noted that for the convenience of description, only parts related to the present invention are shown in the drawings, not all of them.

[0040] In the present invention, some orientation words are defined. Without contrary explanations, the orientation words such as "upper", "lower", "left", "right", "inner", and "outer" are used for the convenience of understanding, and thus do not constitute a limitation to the protection scope of the present invention.

[0041] In the present invention, unless otherwise clearly specified and defined, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features therebetween. Moreover, the first feature being "above", "over", and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "beneath", and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the horizontal height of the first feature is lower than that of the second feature.

[0042] In the description of the present invention, unless otherwise clearly specified and defined, the terms "connected", "joined", and "fixed" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0043] An embodiment of the present invention provides a polytetrafluoroethylene extrusion device, which includes a press (not shown), a polytetrafluoroethylene extrusion die (hereinafter referred to as the die), and a calender (not shown). The die has a rod inlet 5 and a sheet outlet 6. The rod inlet 5 is connected to the rod outlet of the press, and the sheet outlet 6 is connected to the sheet inlet of the calender.

[0044] When the device is in use, the press axially pushes a cylindrical polytetrafluoroethylene rod into the die. In the die, the rod is extruded into a sheet, and then the sheet enters the calender for orientation.

[0045] It should be noted that during the orientation process, the calender can also further calender the sheet.

[0046] Different from the prior art technical solution in which the rod outlet of the press is directly connected to the inlet of the calender, in this embodiment, a die is provided at the rod outlet of the press, and the rod is extruded into a sheet through the die, so that the obtained sheet has uniform thickness and density, solving the problem that the sheet obtained by calendering the rod by the calender has non-uniform thickness and density.

[0047] It should be noted that the structures of the extrusion press and the calender, as well as the forming method of the polytetrafluoroethylene rod, are all prior arts and will not be elaborated herein.

[0048] The following introduces the specific structure of the mold.

[0049] Figure 1 The figure shows a schematic diagram of the mold observed from the sheet outlet 6. As Figure 1 shown, the mold includes a first template 1 and a second template 2. There is a gap between the lower surface of the first template 1 and the upper surface of the second template 2, so as to form a mold cavity (hereinafter referred to as the extrusion channel 7) between the first template 1 and the second template 2. At the rear end of the mold ( Figure 1 the end inward along the paper surface in the figure) is provided with a rod inlet 5 communicating with the extrusion channel 7. At the front end of the template ( Figure 1 the end outward along the paper surface in the figure) is provided with a sheet outlet 6 communicating with the extrusion channel 7. That is, the rod inlet 5 and the sheet outlet 6 are at opposite ends of the extrusion channel 7, and the rod inlet 5 and the sheet outlet 6 are connected through the extrusion channel 7.

[0050] From Figure 1 it can be clearly observed that the sheet outlet 6 is a horizontally extending flat structure. By "flat" it means that the length of the sheet outlet 6 is much greater than the width. For example, the aspect ratio of the length to the width of the sheet outlet 6 can be 50:1, 100:1, 150:1, 200:1, etc., and the aspect ratio of the length to the width of the sheet outlet 6 can be selected between 50 and 200:1. Thus, when the rod passes through the extrusion channel 7 and is output from the sheet outlet 6, the rod is extruded into a sheet, and the aspect ratio of the sheet is the same as that of the sheet outlet 6, making the sheet also present a flat shape.

[0051] As Figure 1 shown, a semi-circular first flange 11 is provided at the rear end of the first template 1, and a semi-circular second flange 21 is provided at the rear end of the second template 2. The first flange 11 and the second flange 21 are connected to each other to form a complete circular flange, and the mold can be conveniently installed on the rod outlet of the extrusion press through the circular flange.

[0052] Of course, in other embodiments, the flange structure may not be used for installation, and other detachable or non-detachable installation methods may be used, such as welding, interference fit, etc.

[0053] Figure 2 The figure shows Figure 1 the cross-sectional view at A-A in the figure. As Figure 2 shown, the centers of the rod inlet 5 and the sheet outlet 6 are on a horizontally extending straight line. In this embodiment, this straight line is defined as the extrusion line L. The extending direction of the extrusion line L is parallel to the moving direction of the rod. Specifically, in Figure 2In this embodiment, the moving direction of the rod is defined as the extrusion direction. Figure 2 The middle is the direction from left to right along the extrusion line L, that is, the direction from the rod inlet 5 to the sheet outlet 6.

[0054] Figure 2 The cross section shown is a first cross section passing through the extrusion line L and perpendicular to the sheet outlet 6. Figure 2 As shown, in the first cross section, the size of the first opening 71 of the extrusion flow channel 7 is strictly reduced along the extrusion direction. That is, the closer to the rod inlet 5, the larger the size of the first opening 71; the closer to the sheet outlet 6, the smaller the size of the first opening 71. "Strictly reduced" means that the first opening 71 does not remain unchanged or increase at any position of the extrusion flow channel 7 along the extrusion direction.

[0055] In addition, if Figure 2 As shown, in the first cross section, the two opposite first side walls 73 in the extrusion flow channel 7 are symmetrically arranged about the extrusion line L, so that when the rod flows in the extrusion flow channel 7, the upper surface and the lower surface are subjected to the same force, thereby improving the uniformity of thickness and density. Moreover, the first side wall 73 is a smooth curve 731 protruding toward the extrusion line L, rather than an inclined straight line or a broken line formed by connecting multiple straight lines, so that the pressure acting on the upper surface and the lower surface of the rod changes accordingly according to the position of the extrusion flow channel 7, rather than being constant, which is conducive to extruding the rod into a sheet, so that the shape of the sheet becomes stable.

[0056] It should be noted that Figure 2 The angle between the tangent line at any point on the middle smooth curve 731 and the extrusion line L does not exceed 5°. The purpose of this setting is to ensure that the longitudinal force of the sheet is uniform during the extrusion process and the fibers are arranged neatly.

[0057] Figure 3 It is a top view of the second template 2. Figure 3 The cross-section shown is a second cross-section passing through the extrusion line L and parallel to the sheet outlet 6. In the second cross-section, the second opening 72 of the extrusion channel 7 includes a widening area 721 and a constant area 722 in sequence along the extrusion direction. The size of the second opening 72 in the widening area 721 strictly increases, and the size of the second opening 72 in the constant area 722 remains constant.

[0058] Thus, when the bar enters the extrusion channel 7, the upper and lower surfaces of the bar are squeezed by the first side walls 73 at corresponding positions, and there is enough space in the width direction of the bar. Therefore, after being squeezed, the bar can flow in the width direction and gradually fill the widened area 721, causing the bar to be gradually squeezed into a sheet. When the sheet moves to the constant area 722, there is no longer space in the width direction of the sheet and it cannot continue to flow in the width direction. The sheet maintains this width and is output from the sheet outlet 6.

[0059] As Figure 3 shown, in the second cross-section, the two opposite second side walls 74 in the extrusion channel 7 are symmetric about the extrusion line L. The position corresponding to the widened area 721 in the second side wall 74 is the first straight line 741, and the first straight line 741 forms a preset angle with the extrusion line L. For example, the angle can be 14-19°. This range of angles enables uniform lateral filling in the channel during the extrusion process. The position corresponding to the constant area 722 in the second side wall 74 is the second straight line 742, and the second straight line 742 is parallel to the extrusion line L.

[0060] In addition, in this embodiment, the length of the projection of the first straight line 741 on the extrusion line L is 100-160 mm; the length of the projection of the second straight line 742 on the extrusion line L is 5-20 mm; the ratio of the projection of the first straight line 741 on the extrusion line L to the projection of the second straight line 742 on the extrusion line L is 11-15. The purpose of such a setting is to maintain the dimensional stability of the sheet after extrusion.

[0061] As Figure 1 and 3 shown, in this embodiment, the first template 1 is located above the second template 2, and the first template 1 and the second template 2 are separately provided, that is, the first template 1 and the second template 2 can be assembled with each other or separated from each other. Specifically, a positioning pin 3 for positioning and a fastener 4 for fastening are provided between the first template 1 and the second template 2. However, it can be understood that in other embodiments, the first template 1 and the second template 2 can be integrally formed and cannot be disassembled.

[0062] The materials of the first template 1 and the second template 2 can be metal materials that are easy to process, such as 304 stainless steel. The upper surface of the first template 1 and the lower surface of the second template 2 can be mirror-polished to reduce the surface roughness.

[0063] When the mold of this embodiment is in use, the bar enters the extrusion channel 7 from the bar inlet 5. Inside the extrusion channel 7, the bar is gradually squeezed, causing the thickness of the bar to decrease and the width to increase, and then it becomes a sheet and is finally output from the sheet outlet 6.

[0064] To test the effect of this embodiment of the mold, the following comparison was made:

[0065] The polytetrafluoroethylene resin grade used hereinafter is CGF216G, purchased from Zhonghao Chenguang Research Institute of Chemical Industry; the co-extrusion aid grade is IP CLEAN LX, purchased from Idemitsu Kosan Co., Ltd. of Japan.

[0066] Examples:

[0067] (1) The co-extrusion aid and the polytetrafluoroethylene resin are fully mixed at a mass ratio of 0.2:1 and allowed to stand at 55 °C for 30 hours.

[0068] (2) The mixed material is pressed into a blank with a diameter of 60 mm in a pre-pressing machine at 55 °C and 1.0 Mpa.

[0069] (3) The above blank is extruded from the mold by a push press to obtain a sheet with a thickness of 0.75 mm and a width of 105 mm at 60 °C and 5.0 Mpa.

[0070] (4) The above sheet is oriented by a calender at 70 °C at a speed of 5 m / min to obtain an oriented film with a thickness of 0.7 mm and a width of 105 mm.

[0071] (5) The above oriented film is degreased from the co-extrusion aid at 200 °C and longitudinally stretched at 250 °C with a longitudinal stretching ratio of 4.0 times to obtain a longitudinally stretched base film.

[0072] (6) The above longitudinally stretched base film is transversely stretched on a medium-wave radiation heating and width expanding unit with a transverse stretching ratio of 20 times and shaped at 370 °C to prepare a polytetrafluoroethylene biaxially stretched film with a thickness of 0.05 - 0.06 mm.

[0073] (7) The obtained polytetrafluoroethylene biaxially stretched film is wound and sintered through a laminating unit to prepare an expanded polytetrafluoroethylene sheet with a specification of 1000*1000*2 mm. The sheet is sampled in a 9-grid manner with a sampling size of 100*100 mm, and the weight of the sample is weighed with an analytical balance (the result is reserved to two decimal places). The results are shown in Table 1 below:

[0074] Table 1

[0075]

[0076]

[0077] Use R to represent the overall density and thickness uniformity of the biaxially stretched film.

[0078] Among them, R = the lightest sample: the heaviest sample. The larger R is, the better the thickness and density uniformity of the biaxially stretched film.

[0079] In the embodiment, R=10.75 / 11.35=0.947.

[0080] Comparative Example:

[0081] (1) The extrusion aid and polytetrafluoroethylene resin were fully mixed in a mass ratio of 0.2:1 and allowed to stand at 55°C for 30 hours;

[0082] (2) Pressing the mixed material into a 60 mm diameter blank in a pre-pressing machine at 55°C and 1.0 MPa;

[0083] (3) The blank is pushed out on a push press at 60°C and 5.0 MPa to form a PTFE rod with a diameter of 10 mm;

[0084] (4) rolling the above-mentioned polytetrafluoroethylene rod into a 0.3 mm oil-containing base film on a calender at 55° C. and a speed of 15 m / min;

[0085] (5) removing the extrusion aid from the oil-containing base film at 200° C., and longitudinally stretching the base film at 260° C. at a longitudinal stretching ratio of 4.0 times to obtain a longitudinally stretched base film;

[0086] (6) stretching the longitudinally stretched base film in a conventional transverse expansion unit at a transverse stretching ratio of 20 times, and setting the film at 370° C. to prepare a polytetrafluoroethylene biaxially stretched film;

[0087] (7) The polytetrafluoroethylene biaxially stretched film obtained above was rolled and sintered by a film coating unit to obtain an expanded polytetrafluoroethylene sheet with a specification of 1000*1000*2 mm, and the sheet was sampled in a 9-grid manner with a sampling size of 100*100 mm. The sample weight was weighed with an analytical balance (the result was rounded to two decimal places). The results are shown in Table 2 below:

[0088] Table 2

[0089] Number 1 2 3 4 5 6 7 8 9 Weight / g 11.26 11.79 11.00 11.10 10.99 12.35 11.98 11.88 10.42

[0090] In the comparative example, R=10.42 / 12.35=0.844<0.947.

[0091] It can be seen that the R value in the embodiment is larger, so compared with the solution in the prior art, the solution of this embodiment can obtain a polytetrafluoroethylene film with better thickness and uniformity.

[0092] The foregoing is a description of embodiments of the present invention. Through the above description of the disclosed embodiments, those skilled in the art can implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A polytetrafluoroethylene extrusion die, characterized in that, Comprising: A bar inlet (5); A flat sheet outlet (6); An extrusion channel (7) connected between the bar inlet (5) and the sheet outlet (6), the extrusion direction of the extrusion channel (7) being from the bar inlet (5) to the sheet outlet (6); A virtual connection line passing through the center of the bar inlet (5) and the center of the sheet outlet (6) defines an extrusion line (L); In a first cross-section passing through the extrusion line (L) and perpendicular to the sheet outlet (6), the size of the first opening (71) of the extrusion channel (7) strictly decreases along the extrusion direction; In a second cross-section passing through the extrusion line (L) and parallel to the sheet outlet (6), the second opening (72) of the extrusion channel (7) sequentially includes a widening region (721) and a constant region (722) along the extrusion direction. In the widening region (721), the size of the second opening (72) strictly increases, and in the constant region (722), the size of the second opening (72) remains constant.

2. The polytetrafluoroethylene extrusion die according to claim 1, wherein The aspect ratio of the sheet outlet (6) is 50 to 200:

1.

3. The polytetrafluoroethylene extrusion die according to claim 1, wherein In the first cross-section, the two opposite first side walls (73) of the extrusion channel (7) are symmetric about the extrusion line (L), and the first side walls (73) are smooth curves (731) convex towards the extrusion line (L).

4. The polytetrafluoroethylene extrusion die according to claim 3, characterized in that, In the first cross-section, the angle between the tangent of any point on the smooth curve (731) and the extrusion line (L) does not exceed 5°.

5. The polytetrafluoroethylene extrusion die according to claim 1, wherein In the second cross-section, the two opposite second side walls (74) of the extrusion channel (7) are symmetric about the extrusion line (L). The position corresponding to the widening region (721) of the second side walls (74) is a first straight line (741), the first straight line (741) forms a preset angle with the extrusion line (L), and the position corresponding to the constant region (722) of the second side walls (74) is a second straight line (742), and the second straight line (742) is parallel to the extrusion line (L).

6. The polytetrafluoroethylene extrusion die according to claim 5, wherein, The angle between the first straight line (741) and the extrusion line (L) is 14 to 19°.

7. The polytetrafluoroethylene extrusion die according to claim 5, characterized in that, The length of the projection of the first straight line (741) on the extrusion line (L) is 100 to 160 mm; and / or The length of the projection of the second straight line (742) on the extrusion line (L) is 5 to 20 mm; and / or The ratio of the projection of the first straight line (741) on the extrusion line (L) to the projection of the second straight line (742) on the extrusion line (L) is 11 to 15.

8. A polytetrafluoroethylene extrusion device, characterized in that, Comprising: A press, the press having a bar outlet; The polytetrafluoroethylene extrusion die according to any one of claims 1 to 7, the bar inlet (5) being connected to the bar outlet; And A calender, the calender having a sheet inlet, the sheet outlet (6) being connected to the sheet inlet, and the calender being used to calender the sheet output from the sheet outlet (6).

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