A kind of PTFE expanded board and preparation method thereof

Abstract

The present invention belongs to the technical field of polytetrafluoroethylene materials, and specifically relates to a PTFE expanded board and a preparation method thereof. The PTFE expanded board is formed by sequentially stretching, laminating, sintering and hot pressing of a PTFE composite base film; the PTFE composite base film is a sandwich composite structure, wherein the middle interlayer is an unmodified PTFE layer, and both sides of the interlayer are modified PTFE layers; and the unmodified PTFE layers are respectively embedded in the modified PTFE layers on both sides; the PTFE composite base film is obtained by multi-layer co-extrusion, calendering and deoiling of a PTFE blank having a three-layer composite structure; the middle layer in the three-layer composite structure of the PTFE blank is an unmodified PTFE dispersion resin material layer, and both sides of the middle layer are modified PTFE dispersion resin material layers. The obtained PTFE expanded board does not have a delamination phenomenon, greatly improves the interlayer peeling strength of the PTFE expanded board, and solves the problem of poor interlayer adhesion of the PTFE expanded board in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of polytetrafluoroethylene materials, and specifically relates to a PTFE expanded plate and a preparation method thereof. Background Art

[0002] In the field of materials science and engineering, multilayer composite membranes are an important material and are widely used in various industrial and living fields. Among them, polytetrafluoroethylene (PTFE) is widely used to prepare multilayer composite membranes due to its excellent chemical stability, high temperature resistance and low friction, and the composite membranes are made into expanded boards by lamination. However, during the lamination process, due to the high melt viscosity of pure PTFE, the bonding effect between pure PTFE layers is not ideal, which leads to low interlayer peeling strength, affecting the performance of the final product. In previous studies, interlayer bonding was generally achieved by adding adhesives. Commonly used adhesives are generally two types, one is fluorine oil, that is, dissolving fluorinated surfactants in solvents, such as sodium perfluorooctane sulfonate and perfluorotriethylamine; the other is fluorinated polymer emulsions, such as PTFE emulsions, PFA emulsions and FEP emulsions. However, this type of method has obvious disadvantages. The introduced substances may affect the overall structure of the expanded board, thereby affecting its use. At the same time, if the ineffective components in the adhesive cannot be removed in time, the membrane surface will turn yellow, affecting the appearance and performance.

[0003] Patent CN111152533B mixes polytetrafluoroethylene, polytetrafluoroethylene modified material, fiber material, titanium dioxide and organic solvent in proportion, and adds one or more of glass fiber or carbon fiber. During the preparation process, the polytetrafluoroethylene microporous membrane is subjected to surface plasma treatment to prepare a multifunctional expanded polytetrafluoroethylene sheet, but no solution is proposed for the interlayer bonding force of the multilayer composite membrane. In addition, since the polytetrafluoroethylene modified material itself is easy to break when stretched and has low tensile strength, stretching the resin mixture obtained after mixing with unmodified polytetrafluoroethylene resin will affect the stretching effect of the unmodified polytetrafluoroethylene, resulting in a decrease in its tensile strength.

[0004] Patent CN113334670A is composed of a number of base films and filling films arranged at intervals; the filling film is arranged in the middle layer, and the base film is arranged on both sides of the filling film; the base film is a biaxially stretched PTFE film material, and the filling film is a thermoplastic polymer film material. However, due to the high melt viscosity and low friction of the unmodified PTFE itself, the PTFE film and the thermoplastic polymer film are simply compounded by heat pressing, and the interlayer peeling strength is relatively low.

[0005] Patent CN114181481B is formed by laminating unmodified PTFE stretch film and modified PTFE stretch film at intervals and hot pressing. Although the addition of modified PTFE film avoids direct hot pressing of unmodified PTFE film and improves the interlayer adhesion to a certain extent, due to the high melt viscosity and low friction of unmodified PTFE itself, the adhesion between modified PTFE film and unmodified PTFE film is still insufficient. In addition, modified PTFE itself has poor fiber-forming property, is not easy to stretch into film, and is prone to breakage. Therefore, the selection of modified PTFE in this patent is narrower, which indirectly increases the processing cost.

[0006] In addition, the patent also discloses a method of first mixing the modified resin with the unmodified resin, then calendering it into a composite film, and finally obtaining a composite expanded board by laminating the composite film. That is, it is equivalent to mixing the modified material into the unmodified material, and relying on the low melt viscosity of the modified material to improve the interlayer adhesion. However, since the modified material is not completely in contact on the lamination surface, the improvement of adhesion is limited. At the same time, the modified material and the unmodified material are mixed for stretching, which also sacrifices some tensile strength to a certain extent. Summary of the invention

[0007] In order to solve the problems of poor interlayer bonding and low peeling strength of PTFE multilayer expanded sheets in the prior art, the present invention provides a multilayer PTFE expanded sheet with high peeling strength and a preparation method thereof. The obtained PTFE expanded sheet does not have a delamination phenomenon, greatly improves the interlayer peeling strength of the PTFE expanded sheet, and solves the problem of poor interlayer bonding of PTFE expanded sheets in the prior art.

[0008] The technical solution of the present invention is:

[0009] A PTFE expanded plate is formed by sequentially stretching, laminating, sintering and hot-pressing a PTFE composite base film.

[0010] The PTFE composite base tape membrane is a sandwich composite structure, wherein the middle sandwich is an unmodified PTFE layer, and both sides of the sandwich are modified PTFE layers; and the unmodified PTFE layer is respectively embedded in the modified PTFE layers on both sides.

[0011] The PTFE composite base tape membrane is obtained by multi-layer co-extrusion, calendering and deoiling of a PTFE blank with a three-layer composite structure.

[0012] The middle layer in the three-layer composite structure of the PTFE blank is an unmodified PTFE dispersion resin material layer, and both sides of the middle layer are modified PTFE dispersion resin material layers; wherein the layer thickness ratio of modified PTFE dispersion resin material layer: unmodified PTFE dispersion resin material layer: modified PTFE dispersion resin material layer is 1: (1-4): 1. When the PTFE blank is formed by a common cylindrical preforming mold, the layer thickness here refers to the maximum layer thickness, that is, the thickness of the material layer at the diameter.

[0013] The present invention has found that the PTFE composite membrane obtained by extrusion in the form of mixed resin in the prior art has the following problems: first, the fiberization degree of the modified PTFE dispersed resin and the unmodified PTFE dispersed resin is different, the fiberization degree of the modified PTFE dispersed resin is weaker, and the fiber strength is also lower, which leads to a lower strength of the material extruded by the mixed resin when stretched. Secondly, the mixed resin material is stretched to obtain a single-layer film, and the single-layer film is not a completely modified material with low melt viscosity. Therefore, when laminating and compounding, the laminated surface is not entirely in contact with the modified PTFE dispersed resin material, so the improvement of the bonding force is limited.

[0014] The PTFE expanded board described in the present invention is formed by stretching, stacking, sintering and hot pressing a PTFE composite base film in sequence, and the PTFE composite base film used is obtained by multi-layer co-extrusion, calendering and deoiling of a PTFE blank with a three-layer composite structure. Among them, the layer thickness ratio of modified PTFE dispersion resin layer: unmodified PTFE dispersion resin layer: modified PTFE dispersion resin layer is 1: (1-4): 1. In such a design, first, the middle layer is a single unmodified PTFE dispersion resin, which has a better degree of fiberization and higher strength, and plays a major role in strength. Then, both sides are single pure modified PTFE dispersion resin materials, which make the adhesion better during lamination. At the same time, the present invention has found that, based on the above-mentioned structural design, according to the material layer thickness ratio, the interlayer peeling strength and tensile strength of the PTFE expanded board can achieve the effect of synchronous synergistic improvement.

[0015] In the present invention, the PTFE expanded board has a layer thickness ratio of the modified PTFE dispersion resin material layer: the unmodified PTFE dispersion resin material layer: the modified PTFE dispersion resin material layer of 1:2:1.

[0016] In the present invention, the PTFE expanded sheet has an interlayer peeling force of 2.0-2.5 N / mm and a tensile strength of 40-51 MPa.

[0017] In the present invention, the PTFE expanded sheet has a thickness of 1-15 mm and a density of 0.5-1.5 g / cm 3 .

[0018] In the present invention, the SSG of the unmodified PTFE dispersion resin in the PTFE expanded sheet is 2.120-2.300, and the extrusion pressure at a compression ratio of 400:1 is 30-50 MPa; the SSG of the modified PTFE dispersion resin is 2.135-2.185, and the melt viscosity is 4.0×10 8 Pa s-3.0×10 10 The modifier monomer of the modified PTFE dispersion resin is chlorotrifluoroethylene, perfluoroalkoxy vinyl ether or hexafluoropropylene.

[0019] The preparation method of the above-mentioned PTFE expanded sheet comprises the following steps:

[0020] (1) Ingredients: Unmodified PTFE dispersion resin A and modified PTFE dispersion resin B are mixed with auxiliary oil respectively and then aged to obtain paste material A and paste material B.

[0021] (2) Preforming: The paste material A and the paste material B obtained in step (1) are respectively added into a cylindrical preforming mold with double partitions; wherein the double partitions are symmetrically distributed along the central axis of the cylindrical preforming mold, and the distance between each partition and the central axis is 1 / 3R-2 / 3R, where R is the radius of the cylindrical preforming mold. The double partitions here are movable, that is, two partitions are inserted into the existing preforming mold according to the requirements to ensure that the raw materials are not mixed.

[0022] The double partitions divide the inner space of the cylindrical preforming mold into three spaces along the axial direction, and the paste material A is added to the middle space, and the paste material B is added to the spaces on the other two sides respectively; at the same time, the paste material A and the paste material B are added to the same level. The tops of the added materials are at the same height, which can ensure that the PTFE blank formed during extrusion is always a three-layer composite structure.

[0023] After the feeding is completed, the partition is pulled out and pre-molded to obtain a PTFE blank with a three-layer composite structure, wherein the middle layer is an unmodified PTFE dispersion resin material layer and the two sides are modified PTFE dispersion resin material layers.

[0024] (3) Extrusion and calendering: The PTFE blank obtained in step (2) is subjected to multi-layer co-extrusion in a flat die with a compression ratio of 40-100, and then calendered and deoiled to obtain a PTFE composite base tape membrane. During extrusion, the direction of the dividing line between the unmodified PTFE dispersion resin material layer and the modified PTFE dispersion resin material layer in the PTFE blank should be consistent with the length direction of the flat die to ensure that the extruded material still maintains a three-layer composite structure during flat die extrusion.

[0025] (4) Stretching: The PTFE composite base film obtained in step (3) is stretched at 200° C.-300° C. to obtain a PTFE composite film.

[0026] When single longitudinal stretching is performed, the stretching ratio is 5-15 times.

[0027] When biaxial stretching is performed, the longitudinal stretching ratio is 5-10 times, and the transverse stretching ratio is 3-8 times.

[0028] (5) Sintering: The obtained PTFE composite membrane is rolled onto a stainless steel roller under a tension of 1.5-2.5N; at this time, the inner modified PTFE dispersion resin layer of the PTFE composite membrane is in direct contact with the outer modified PTFE dispersion resin layer, so that the bonding parts of the sintered PTFE composite membrane are all the bonding between the modified PTFE dispersion resin layers, which has a better bonding effect and further improves the interlayer bonding force. Then, sintering is performed at 350℃-400℃ for 5-80min.

[0029] (6) Hot pressing: The sintered PTFE composite film is cut open along the axial direction of a stainless steel roller, and then hot pressed at a pressure of 0.8-3.0 MPa, a hot pressing time of 1-120 s, and a temperature of 100-300°C to obtain the PTFE expanded sheet.

[0030] In the present invention, in the method for preparing the PTFE expanded board, the aging temperature in step (1) is 30-35° C. and the aging time is 16-30 hours.

[0031] In the step (2), the preforming temperature is 20-25° C., the preforming pressure is 1.0-2.0 MPa, and the preforming time is 2-10 min.

[0032] In the method for preparing the PTFE expanded board of the present invention, in step (2), the distance between each partition and the central axis is 1 / 2R, where R is the radius of the cylindrical preforming mold.

[0033] In the present invention, in the method for preparing the PTFE expanded sheet, in step (1), the amount of auxiliary oil added to the paste material A is 22%-28% of the mass of the unmodified PTFE dispersion resin A; the amount of auxiliary oil added to the paste material B is 22%-28% of the mass of the modified PTFE dispersion resin B. The auxiliary oil is an isoparaffin solvent oil. Preferably, the isoparaffin solvent oil is Isopar M.

[0034] In the present invention, in the method for preparing the PTFE expanded sheet, the thickness of the PTFE composite membrane obtained in step (4) is 0.03-0.15 mm. Preferably, the thickness of the PTFE composite membrane is 0.06-0.09 mm.

[0035] The beneficial effects of the present invention are as follows: the PTFE expanded sheet of the present invention is formed by sequentially stretching, laminating, sintering and hot pressing a PTFE composite base film. The PTFE composite base film is a sandwich composite structure, wherein the middle sandwich is an unmodified PTFE layer, and both sides of the sandwich are modified PTFE layers; and the unmodified PTFE layers are respectively embedded in the modified PTFE layers on both sides. The PTFE composite base film is obtained by multi-layer co-extrusion, calendaring and de-oiling of a PTFE blank having a three-layer composite structure.

[0036] This design allows the layers to be completely composited together without stratification, and the interlayer peeling force can reach 2.0-2.5N / mm; at the same time, the tensile strength can also reach 40-51MPa, achieving the effect of simultaneously improving the interlayer peeling force and tensile strength of the PTFE expanded board. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the SEM image of the longitudinal section of the PTFE expanded sheet obtained in Example 1.

[0038] Figure 2 This is the SEM image of the longitudinal section of the PTFE expanded board obtained in Comparative Example 5.

[0039] Figure 3 It is a schematic top view of the preforming mold structure of the present invention.

[0040] Among them, 1 is a separator, 2 is an unmodified PTFE dispersion resin layer, and 3 is a modified PTFE dispersion resin layer. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0042] 1. Determination of tensile strength and elongation at break: The tensile strength of expanded polytetrafluoroethylene board is tested according to GB / T1040-92, with three groups of samples for each test and the average value is taken.

[0043] 2. Density determination: According to GB1033-1970 "Plastic specific gravity test method", add a small amount of wetting agent to the distilled water during the test.

[0044] 3. Peel strength test: Peel strength is tested according to the national standard GB / T 2791-1995.

[0045] 4. The unmodified PTFE dispersion resin and modified PTFE dispersion resin used in the specific implementation manner are both commercially available products.

[0046] Example 1

[0047] The PTFE expanded sheet is formed by sequentially stretching, laminating, sintering and hot pressing a PTFE composite base film. The PTFE composite base film is a sandwich composite structure, wherein the middle sandwich is an unmodified PTFE layer, and both sides of the sandwich are modified PTFE layers; and the unmodified PTFE layers are respectively embedded in the modified PTFE layers on both sides.

[0048] The PTFE composite base tape membrane is obtained by multi-layer co-extrusion, calendering and deoiling of a PTFE blank with a three-layer composite structure; the middle layer in the three-layer composite structure of the PTFE blank is an unmodified PTFE dispersion resin material layer 2, and both sides of the middle layer are modified PTFE dispersion resin material layers 3.

[0049] The layer thickness ratio of the modified PTFE dispersion resin layer: the unmodified PTFE dispersion resin layer: the modified PTFE dispersion resin layer is 1:2:1.

[0050] The SSG of the unmodified PTFE dispersion resin in the PTFE expanded sheet is 2.171, and the extrusion pressure at a compression ratio of 400:1 is 38 MPa; the SSG of the modified PTFE dispersion resin is 2.150, and the melt viscosity is 1.04×10 10 Pa·s.

[0051] The preparation method of the PTFE expanded sheet comprises the following specific steps:

[0052] (1) Ingredients: Unmodified PTFE dispersion resin A and modified PTFE dispersion resin B were mixed with auxiliary oil Ispor M respectively and aged at 35°C for 20 h to obtain paste A and paste B; wherein the amount of Ispor M added to paste A was 26% of the mass of unmodified PTFE dispersion resin A; and the amount of Ispor M added to paste B was 26% of the mass of modified PTFE dispersion resin B.

[0053] (2) Preforming: The paste A and the paste B obtained in step (1) are respectively added into a cylindrical preforming mold having double partitions; wherein the double partitions are symmetrically distributed along the central axis of the cylindrical preforming mold, and the distance between each partition 1 and the central axis is 1 / 2R, where R is the radius of the cylindrical preforming mold.

[0054] The double partitions divide the inner space of the cylindrical preforming mold into three spaces along the axial direction. Paste A is added to the middle space, and paste B is added to the spaces on the other two sides respectively; at the same time, it is ensured that paste A and paste B are added to the same level.

[0055] After the feeding is completed, the partition is pulled out and pre-molded for 10 minutes at 25° C. and a pressure of 2.0 MPa to obtain a PTFE blank with a three-layer composite structure having an unmodified PTFE dispersion resin material layer 2 as the middle layer and modified PTFE dispersion resin material layers 3 on both sides.

[0056] (3) Extrusion and calendering: The PTFE blank obtained in step (2) is subjected to multi-layer co-extrusion in a flat-mouth mold with a compression ratio of 52.3, and then calendered and deoiled to obtain a PTFE composite base tape membrane.

[0057] (4) Stretching: The PTFE composite base film obtained in step (3) is subjected to a single longitudinal stretching at 300° C. with a stretching ratio of 5 times to obtain a PTFE composite film with a thickness of 0.08 mm.

[0058] (5) Sintering: The obtained PTFE composite membrane was rolled onto a stainless steel roller under a tension of 2.0 N. The thickness of the PTFE composite membrane roll was 16.2 mm. The membrane was then sintered at 380° C. for 30 min.

[0059] (6) Hot pressing: The sintered PTFE composite film was cut open along the axial direction of the stainless steel roller, and then hot pressed for 120 seconds at a pressure of 0.8 MPa and a temperature of 300°C to obtain a PTFE expanded sheet with a thickness of 5.4 mm.

[0060] Example 2

[0061] The PTFE expanded sheet is formed by sequentially stretching, laminating, sintering and hot pressing a PTFE composite base film. The PTFE composite base film is a sandwich composite structure, wherein the middle sandwich is an unmodified PTFE layer, and both sides of the sandwich are modified PTFE layers; and the unmodified PTFE layers are respectively embedded in the modified PTFE layers on both sides.

[0062] The PTFE composite base tape membrane is obtained by multi-layer co-extrusion, calendering and deoiling of a PTFE blank with a three-layer composite structure; the middle layer in the three-layer composite structure of the PTFE blank is an unmodified PTFE dispersion resin material layer 2, and both sides of the middle layer are modified PTFE dispersion resin material layers 3.

[0063] The layer thickness ratio of the modified PTFE dispersion resin layer: the unmodified PTFE dispersion resin layer: the modified PTFE dispersion resin layer is 1:2:1.

[0064] The SSG of the unmodified PTFE dispersion resin in the PTFE expanded sheet is 2.148, and the extrusion pressure is 47 MPa at a compression ratio of 400:1; the SSG of the modified PTFE dispersion resin is 2.174, and the melt viscosity is 6.27×10 8Pa·s.

[0065] The preparation method of the PTFE expanded sheet comprises the following specific steps:

[0066] (1) Ingredients: Unmodified PTFE dispersion resin A and modified PTFE dispersion resin B were mixed with auxiliary oil Ispor M respectively and aged at 35°C for 20 h to obtain paste A and paste B; wherein the amount of Ispor M added to paste A was 27% of the mass of unmodified PTFE dispersion resin A; and the amount of Ispor M added to paste B was 27% of the mass of modified PTFE dispersion resin B.

[0067] (2) Preforming: The paste A and the paste B obtained in step (1) are respectively added into a cylindrical preforming mold having double partitions; wherein the double partitions are symmetrically distributed along the central axis of the cylindrical preforming mold, and the distance between each partition 1 and the central axis is 1 / 2R, where R is the radius of the cylindrical preforming mold.

[0068] The double partitions divide the inner space of the cylindrical preforming mold into three spaces along the axial direction. Paste A is added to the middle space, and paste B is added to the spaces on the other two sides respectively; at the same time, it is ensured that paste A and paste B are added to the same level.

[0069] After the feeding is completed, the partition is pulled out and pre-molded for 10 minutes at 25° C. and a pressure of 2.0 MPa to obtain a PTFE blank with a three-layer composite structure having an unmodified PTFE dispersion resin material layer 2 as the middle layer and modified PTFE dispersion resin material layers 3 on both sides.

[0070] (3) Extrusion and calendering: The PTFE blank obtained in step (2) is subjected to multi-layer co-extrusion in a flat-mouth mold with a compression ratio of 52.3, and then calendered and deoiled to obtain a PTFE composite base tape membrane.

[0071] (4) Stretching: The PTFE composite base film obtained in step (3) is first longitudinally stretched at 280°C with a stretching ratio of 10 times, and then transversely stretched at 300°C by 8 times to obtain a PTFE composite film with a thickness of 0.04 mm.

[0072] (5) Sintering: The obtained PTFE composite membrane was rolled onto a stainless steel roller under a tension of 2.0 N. The thickness of the PTFE composite membrane roll was 17.6 mm. The membrane was then sintered at 350° C. for 60 min.

[0073] (6) Hot pressing: The sintered PTFE composite film was cut open along the axial direction of the stainless steel roller, and then hot pressed for 120 seconds at a pressure of 2.0 MPa and a temperature of 300°C to obtain a PTFE expanded sheet with a thickness of 5.6 mm.

[0074] Example 3

[0075] The PTFE expanded sheet is formed by sequentially stretching, laminating, sintering and hot pressing a PTFE composite base film. The PTFE composite base film is a sandwich composite structure, wherein the middle sandwich is an unmodified PTFE layer, and both sides of the sandwich are modified PTFE layers; and the unmodified PTFE layers are respectively embedded in the modified PTFE layers on both sides.

[0076] The PTFE composite base tape membrane is obtained by multi-layer co-extrusion, calendering and deoiling of a PTFE blank with a three-layer composite structure; the middle layer in the three-layer composite structure of the PTFE blank is an unmodified PTFE dispersion resin material layer 2, and both sides of the middle layer are modified PTFE dispersion resin material layers 3.

[0077] The layer thickness ratio of the modified PTFE dispersion resin layer: the unmodified PTFE dispersion resin layer: the modified PTFE dispersion resin layer is 1:2:1.

[0078] The SSG of the unmodified PTFE dispersion resin in the PTFE expanded sheet is 2.182, and the extrusion pressure at a compression ratio of 400:1 is 32 MPa; the SSG of the modified PTFE dispersion resin is 2.160, and the melt viscosity is 1.18×10 10 Pa·s.

[0079] The preparation method of the PTFE expanded sheet comprises the following specific steps:

[0080] (1) Ingredients: Unmodified PTFE dispersion resin A and modified PTFE dispersion resin B were mixed with auxiliary oil Ispor M respectively and aged at 35°C for 20 h to obtain paste A and paste B; wherein the amount of Ispor M added to paste A was 24% of the mass of unmodified PTFE dispersion resin A; and the amount of Ispor M added to paste B was 24% of the mass of modified PTFE dispersion resin B.

[0081] (2) Preforming: The paste A and the paste B obtained in step (1) are respectively added into a cylindrical preforming mold having double partitions; wherein the double partitions are symmetrically distributed along the central axis of the cylindrical preforming mold, and the distance between each partition 1 and the central axis is 1 / 2R, where R is the radius of the cylindrical preforming mold.

[0082] The double partitions divide the inner space of the cylindrical preforming mold into three spaces along the axial direction. Paste A is added to the middle space, and paste B is added to the spaces on the other two sides respectively; at the same time, it is ensured that paste A and paste B are added to the same level.

[0083] After the feeding is completed, the partition is pulled out and pre-molded for 10 minutes at 25° C. and a pressure of 2.0 MPa to obtain a PTFE blank with a three-layer composite structure having an unmodified PTFE dispersion resin material layer 2 as the middle layer and modified PTFE dispersion resin material layers 3 on both sides.

[0084] (3) Extrusion and calendering: The PTFE blank obtained in step (2) is subjected to multi-layer co-extrusion in a flat-mouth mold with a compression ratio of 52.3, and then calendered and deoiled to obtain a PTFE composite base tape membrane.

[0085] (4) Stretching: The PTFE composite base film obtained in step (3) is longitudinally stretched at 280° C. with a stretching ratio of 10 times to obtain a PTFE composite film with a thickness of 0.06 mm.

[0086] (5) Sintering: The obtained PTFE composite membrane was rolled onto a stainless steel roller under a tension of 2.0 N. The thickness of the PTFE composite membrane roll was 20.5 mm. The membrane was then sintered at 400° C. for 5 min.

[0087] (6) Hot pressing: The sintered PTFE composite film was cut open along the axial direction of the stainless steel roller, and then hot pressed for 120 seconds at a pressure of 3.0 MPa and a temperature of 200°C to obtain a PTFE expanded sheet with a thickness of 6.2 mm.

[0088] Example 4

[0089] The difference between the PTFE expanded board preparation method described in Example 1 and the PTFE expanded board preparation method described in Example 1 is that the step (4) stretching of the PTFE composite base tape membrane obtained in step (3) is first longitudinally stretched at 280°C with a stretching ratio of 5 times, and then transversely stretched at 300°C by 3 times to obtain a PTFE composite membrane with a thickness of 0.03 mm.

[0090] The rest is the same as in Example 1.

[0091] Example 5

[0092] The difference from the PTFE expanded board described in Example 1 is that in the PTFE expanded board described in this example, the layer thickness ratio of modified PTFE dispersion resin material layer: unmodified PTFE dispersion resin material layer: modified PTFE dispersion resin material layer is 1:1:1.

[0093] The difference from the PTFE expanded board preparation method described in Example 1 is that in the step (2) preforming of the PTFE expanded board preparation method described in this example, the distance between each partition and the central axis is 1 / 3R, and R is the radius of the cylindrical preforming mold.

[0094] The rest is the same as in Example 1.

[0095] Example 6

[0096] The difference from the PTFE expanded board described in Example 1 is that in the PTFE expanded board described in this example, the layer thickness ratio of modified PTFE dispersion resin material layer: unmodified PTFE dispersion resin material layer: modified PTFE dispersion resin material layer is 1:4:1.

[0097] The difference from the PTFE expanded board preparation method described in Example 1 is that in the step (2) preforming of the PTFE expanded board preparation method described in this example, the distance between each partition and the central axis is 2 / 3R, and R is the radius of the cylindrical preforming mold.

[0098] The rest is the same as in Example 1.

[0099] Comparative Example 1

[0100] The difference from the PTFE expanded board described in Example 1 is that in the PTFE expanded board described in this comparative example, the layer thickness ratio of modified PTFE dispersion resin material layer: unmodified PTFE dispersion resin material layer: modified PTFE dispersion resin material layer is 1:6:1.

[0101] The difference from the PTFE expanded board preparation method described in Example 1 is that in the step (2) preforming of the PTFE expanded board preparation method described in this comparative example, the distance between each partition and the central axis is 3 / 4R, and R is the radius of the cylindrical preforming mold.

[0102] The rest is the same as in Example 1.

[0103] Comparative Example 2

[0104] The difference from the PTFE expanded board described in Example 1 is that in the PTFE expanded board described in this comparative example, the layer thickness ratio of modified PTFE dispersion resin material layer: unmodified PTFE dispersion resin material layer: modified PTFE dispersion resin material layer is 1:0.67:1.

[0105] The difference from the PTFE expanded board preparation method described in Example 1 is that in the step (2) preforming of the PTFE expanded board preparation method described in this comparative example, the distance between each partition and the central axis is 1 / 4R, and R is the radius of the cylindrical preforming mold.

[0106] The rest is the same as in Example 1.

[0107] Comparative Example 3

[0108] The difference from the PTFE expanded sheet described in Example 1 is that the modified PTFE dispersed resin in the PTFE expanded sheet described in this comparative example has an SSG of 2.156 and a melt viscosity of 3.1×10 8 Pa·s.

[0109] The rest is the same as in Example 1.

[0110] When the above-mentioned PTFE expanded sheet is prepared and stretched, many defects such as filaments and cracks appear on the surface, resulting in uneven stretching. In addition, the sheet will stick to the stretching roller, causing entanglement and failure to stretch.

[0111] Comparative Example 4

[0112] The difference from the PTFE expanded sheet described in Example 1 is that the modified PTFE dispersed resin in the PTFE expanded sheet described in this comparative example has an SSG of 2.177 and a melt viscosity of 4.3×10 10 Pa·s.

[0113] The rest is the same as in Example 1.

[0114] Comparative Example 5

[0115] This comparative example adopts the method of alternately laminating two films in patent CN114181481B.

[0116] The specific steps are as follows:

[0117] (1) Mixing: Unmodified PTFE dispersion resin A with SSG of 2.171 and extrusion pressure of 38 MPa at RR400 was mixed with 26%wt Ispor M additive oil, and PTFE dispersion resin A with SSG of 2.150 and melt viscosity of 1.04×10 10 After the modified PTFE dispersion resin B with a weight of 28%wt Isopar M was mixed and aged for a certain period of time, two pastes were obtained.

[0118] (2) Preforming: The paste materials in step (1) are added into preforming molds without partitions for preforming to form blanks.

[0119] (3) Extrusion and calendering: The blank obtained in step (2) is extruded through a circular die at a compression ratio of 100, and then calendered and deoiled to obtain a base film.

[0120] (4) Stretching: The base film obtained in step (3) was uniaxially stretched 5 times at 300°C to obtain an unmodified film (thickness 0.09 mm) and a modified film (thickness 0.08 mm).

[0121] (5) Sintering: The stretched unmodified membrane and modified membrane were alternately stacked layer by layer under a tension of 2.0 N and rolled onto a stainless steel roller to obtain a multilayer composite membrane with a thickness of 15.7 mm. The membrane was then sintered in an oven at 380°C for 30 min.

[0122] (6) Hot pressing: The sintered multilayer film was cut open along the axial direction of the roller, and then hot pressed at a pressure of 0.8 MPa and a temperature of 300°C for 3 minutes to obtain a PTFE multilayer expanded sheet. At this time, the expanded sheet has a thickness of 6.1 mm.

[0123] Comparative Example 6

[0124] This comparative example adopts a method of preparing an expanded board by mixing unmodified PTFE resin A and modified PTFE resin B in proportion.

[0125] The specific steps are as follows:

[0126] (1) Mixing: Unmodified PTFE dispersion resin A with SSG of 2.171 and extrusion pressure of 38 MPa at RR400 and SSG of 2.150 and melt viscosity of 1.04×10 10 The modified PTFE dispersion resin B with a weight of 27% by weight was mixed evenly in a ratio of 39:61, and then mixed with 27% by weight Isopar M auxiliary oil, and then aged for a certain period of time to obtain a mixed paste.

[0127] (2) Preforming: Add the paste in step (1) into a preforming mold without a partition to perform preforming to form a blank.

[0128] (3) Extrusion and calendering: The blank obtained in step (2) is extruded through a circular die at a compression ratio of 100, and then calendered and deoiled to obtain a base film.

[0129] (4) Stretching: The base film obtained in step (3) was uniaxially stretched 5 times at 300° C. to obtain a mixed film (thickness 0.08 mm).

[0130] (5) Sintering: The mixed film obtained in step (4) was rolled onto a stainless steel roller under a tension of 2.0 N. The obtained composite film had a thickness of 13.5 mm. The composite film was then sintered in an oven at 380° C. for 30 min.

[0131] (6) Hot pressing: The sintered multilayer film is cut open along the axial direction of the roller, and then hot pressed at a pressure of 0.8 MPa and a temperature of 300°C for 3 minutes to obtain a PTFE multilayer expanded sheet. At this time, the expanded sheet has a thickness of 6.3 mm.

[0132] Comparative Example 7

[0133] The difference from the PTFE expanded board preparation method described in Example 1 is that during the sintering in step (5) of the PTFE expanded board preparation method described in this comparative example, the sintering is carried out at 300° C. for 30 minutes.

[0134] The rest is the same as in Example 1.

[0135] Comparative Example 8

[0136] The difference from the PTFE expanded board preparation method described in Example 1 is that in step (6) of the PTFE expanded board preparation method described in this comparative example, hot pressing is performed at 380° C. and 3.5 MPa for 5 minutes during hot pressing and shaping.

[0137] The rest is the same as in Example 1.

[0138] Due to the excessively high hot pressing temperature and pressure, the edge of the expanded board becomes shrunk and transparent, and the expansion effect almost disappears, making it no longer usable as an expanded board.

[0139] The thickness, density, tensile strength and peel strength of each expanded board obtained in Examples 1-6 and Comparative Examples 1, 2 and Comparative Examples 4-7 are summarized in Table 1 below.

[0140] Table 1 Thickness, density, tensile strength and peel strength of each expanded board

[0141]

[0142] It can be seen from the data in Table 1 that the interlayer peeling force and tensile strength of the PTFE expanded board described in the present invention are simultaneously improved.

Claims

1. A PTFE expanded sheet, characterized in that: The expanded plate is made of a PTFE composite base film through sequential stretching, lamination sintering and hot pressing. The PTFE composite base tape membrane is a sandwich composite structure, wherein the middle sandwich is an unmodified PTFE layer, and both sides of the sandwich are modified PTFE layers; and the unmodified PTFE layer is respectively embedded in the modified PTFE layers on both sides; The PTFE composite base film is obtained by multi-layer co-extrusion, calendering and deoiling of a PTFE blank with a three-layer composite structure; The middle layer of the three-layer composite structure of the PTFE blank is an unmodified PTFE dispersion resin material layer, and both sides of the middle layer are modified PTFE dispersion resin material layers; Wherein, the layer thickness ratio of the modified PTFE dispersion resin layer: the unmodified PTFE dispersion resin layer: the modified PTFE dispersion resin layer is 1:(1-4):1; The interlayer peeling force of the PTFE expanded sheet is 2.0-2.5N / mm; the tensile strength is 40-51MPa; The SSG of the unmodified PTFE dispersion resin in the PTFE expanded sheet is 2.120-2.300, and the extrusion pressure at a compression ratio of 400:1 is 30-50 MPa; the SSG of the modified PTFE dispersion resin is 2.135-2.185, and the melt viscosity is 4.0×10 8 Pa s-3.0×10 10 Pa·s; The modifier monomer of the modified PTFE dispersion resin is chlorotrifluoroethylene, perfluoroalkoxy vinyl ether or hexafluoropropylene.

2. The PTFE expanded sheet according to claim 1, characterized in that: The layer thickness ratio of the modified PTFE dispersion resin layer: the unmodified PTFE dispersion resin layer: the modified PTFE dispersion resin layer is 1:2:

1.

3. The PTFE expanded sheet according to claim 1, characterized in that: The PTFE expanded sheet has a thickness of 1-15 mm and a density of 0.5-1.5 g / cm 3 .

4. The method for preparing the PTFE expanded sheet according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Ingredients: Unmodified PTFE dispersion resin A and modified PTFE dispersion resin B are mixed with auxiliary oil respectively and then aged to obtain paste material A and paste material B; (2) Preforming: Add the paste material A and the paste material B obtained in step (1) into a cylindrical preforming mold having double partitions, respectively; wherein the double partitions are symmetrically distributed along the central axis of the cylindrical preforming mold, and the distance between each partition and the central axis is 1 / 3R-2 / 3R, where R is the radius of the cylindrical preforming mold; The double partitions divide the inner space of the cylindrical preforming mold into three spaces along the axial direction, and the paste material A is added to the middle space, and the paste material B is added to the spaces on the other two sides respectively; at the same time, it is ensured that the paste material A and the paste material B are added to the same level; After the feeding is completed, the partition is pulled out and preformed to obtain a PTFE blank with a three-layer composite structure, wherein the middle layer is an unmodified PTFE dispersion resin material layer and the two sides are modified PTFE dispersion resin material layers; (3) Extrusion and calendering: The PTFE blank obtained in step (2) is subjected to multi-layer co-extrusion in a flat die with a compression ratio of 40-100, and then calendered and deoiled to obtain a PTFE composite base tape membrane; (4) Stretching: stretching the PTFE composite base film obtained in step (3) at 200° C.-300° C. to obtain a PTFE composite film; When a single longitudinal stretch is performed, the stretching ratio is 5-15 times; When biaxial stretching is performed, the longitudinal stretching multiple is 5-10 times, and the transverse stretching multiple is 3-8 times; (5) Sintering: The obtained PTFE composite membrane is rolled onto a stainless steel roller under a tension of 1.5-2.5N; and then sintered at 350°C-400°C for 5-80min; (6) Hot pressing: The sintered PTFE composite film is cut open along the axial direction of a stainless steel roller, and then hot pressed at a pressure of 0.8-3.0 MPa, a hot pressing time of 1-120 s, and a temperature of 100-300°C to obtain the PTFE expanded sheet.

5. The method for preparing the PTFE expanded sheet according to claim 4, characterized in that: In step (1), the aging temperature is 30-35°C and the aging time is 16-30h; In the step (2), the preforming temperature is 20-25° C., the preforming pressure is 1.0-2.0 MPa, and the preforming time is 2-10 min.

6. The method for preparing the PTFE expanded sheet according to claim 4, characterized in that: In the step (2), the distance between each partition and the central axis is 1 / 2R, where R is the radius of the cylindrical preforming mold.

7. The method for preparing the PTFE expanded sheet according to claim 4, characterized in that: In the step (1), the amount of auxiliary oil added to the paste A is 22%-28% of the mass of the unmodified PTFE dispersion resin A; the amount of auxiliary oil added to the paste B is 22%-28% of the mass of the modified PTFE dispersion resin B.

8. The method for preparing the PTFE expanded sheet according to claim 4, characterized in that: The thickness of the PTFE composite membrane obtained in step (4) is 0.03-0.15 mm.

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