JPH021652B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a perfluorocarbon copolymer film and a method for producing the same. Melt processable perfluorocarbon copolymers such as those made from tetrafluoroethylene/perfluoro(alkyl vinyl ether), tetrafluoroethylene/hexafluoropropylene and tetrafluoroethylene/hexafluoropropylene/perfluoro(alkyl vinyl ether) copolymers. Coalescing films are well known in the art. These copolymers are melt extruded through an orifice to form a film and then rapidly cooled. Such films are useful for chemical shielding, polishing release surfaces and specialty items. However, these films have the disadvantage of excessive creep, ie, excessive deformation under mild loading over long periods of time, and extremely low tensile modulus. Additionally, perfluorocarbon copolymers have traditionally been extruded into a tube, blown to approximately double the diameter of the tube to increase the strength of the film, and then heat-shrinked, for example, around processing rolls. It has been attempted to provide such rolls with a low-friction protective surface.
However, when such films are heated, they tend to expand in a direction perpendicular to the direction of stretch produced by blowing, and therefore such perpendicular directions are necessary to hold the film taut. It is not practical for heat shrinking around rectangular surfaces where directional tension is required. Also, U.S. Pat. No. 3,770,711 tests a tetrafluoroethylene/hexafluoropropylene copolymer film up to about 40% and a tetrafluoroethylene/perfluoro-(propyl vinyl ether) copolymer film up to about 40% in a tensile tester.
It describes uniaxial stretching up to 250%. However, these films expand in the direction perpendicular to the stretch when heated, as seen below. According to the present invention, there is provided a perfluorocarbon copolymer film that shrinks in one direction when the degree of shrinkage is measured by heating, but does not expand in a direction perpendicular to the first direction. Furthermore, the tensile modulus of the film measured in the vertical direction remains comparable to the modulus measured in the first direction, and the creep resistance measured in the vertical direction shows a considerable improvement. These physical properties are unpredictable. In a preferred embodiment, the present invention provides a polymer having a shrinkage of 0 to 10% in a direction perpendicular to the stretching direction (hereinafter referred to as the "transverse direction") when heated for 2 minutes to a temperature about 50° C. below the crystalline melting point of the polymer; Shrinkage in the stretching direction (hereinafter referred to as “longitudinal direction”) is at least 20%
and preferably has a transverse tensile modulus greater than 70% of the longitudinal tensile modulus at room temperature and a transverse creep resistance that is at least twice as improved as that of the unstretched film. The present invention relates to a processable perfluorocarbon copolymer film. Also provided are methods of making these films. FIG. 1 illustrates one drawing device useful in practicing the present invention. FIG. 2 illustrates another stretching device useful in practicing the present invention. Perfluorocarbon copolymers useful in the practice of this invention include tetrafluoroethylene and at least one
It includes melt processable copolymers formed by copolymerization with certain perfluorinated ethylenically unsaturated comonomers. Some useful comonomers have the formula R _f −(CF ₂ −) _o CF=CF ₂ or R _f −O−(CF ₂ −) _o CF=CF ₂ or R _f −(CF ₂ −) _o O−CF = CF ₂ or R _f −O−(CF ₂ −) _o ′O−CF=CF ₂ or a mixture thereof, (where n is a base number from 0 to 10, n′ is a base number from 1 to 10, , Rf is perfluorinated alkyl of 1 to 8 carbon atoms or ω-hydroperfluorinated alkyl of 1 to 8 carbon atoms). R _f is preferably perfluorinated alkyl of 1 to 8 carbon atoms. A preferred class of comonomers is perfluoro(alkyl vinyl ether) comonomers in which the alkyl group has 1 to 18 carbon atoms [these have the formula R _f
-(CF ₂ -) _o O-CF=CF ₂ and can also contain multiple ether groups and cyclic ethers], α-perfluoroalkene comonomers having 3 to 18 carbon atoms [these are Formula R _f − (CF ₂ −) _o
CF=CF ₂ ], or any combination of these comonomers forming a copolymer from more than one of these comonomers. Most preferred is tetrafluoroethylene and 5-15% hexafluoropropylene or 0.4
Copolymers formed by copolymerization with ~5% perfluoro(alkyl vinyl ether) to form dipolymers, or combinations of these comonomers to form terpolymers (where percentages of comonomers are molar %). These copolymers generally have 1
It has a specific melt viscosity of ^{1.times.10.sup.3} to ^{1.times.10.sup.7} poise and is therefore melt processable (ie, can be made into articles by melting and molding). Of course, the crystalline melting point of each of these copolymers depends on the amount of comonomer present; generally speaking, the greater the amount of comonomer present, the lower the crystalline melting point. These copolymers also have a second-order transition temperature of 85-100°C (both the crystalline melting point and the second-order transition temperature are measured using conventional differential calorimetry; the melting point is the peak of the endotherm in the scan). . The preparation of these copolymers is disclosed in U.S. Pat.
It is well known as detailed in No. 3528924. The copolymers used in this invention may also contain minor amounts of other reactive comonomers, including those that are not perfluorinated. These are usually added to modify the processability of the polymer. The formation of perfluorocarbon copolymer films is also well known in the art. Generally speaking, the polymer is extruded from an orifice in the molten state and is well quenched to a temperature below its melting point. The extrusion orifice can be such that the film produced is a flat sheet or a tube. Film thickness is generally determined before stretching.
0.5-100 mils and about 0.05-20 mils after stretching. When drawing a tubular film in accordance with the present invention, the tube can first be folded flat or cut open into a flat sheet. The film that is subjected to the stretching process described herein is a film that has not been substantially stretched.
In other words, this film is “as it is”.
It is a film of low modulus and low strength. Typically, these films have a modulus of approximately 500 MPa in the transverse and longitudinal directions, and exhibit a dimensional stability of approximately ±2.0% in both directions (negative Dimensional changes indicate expansion). The method of the invention can best be described by reference to the accompanying drawings. In FIG. 1, the perfluorocarbon film 1 is rolled around a portion of its circumference in contact with a roll 2, around a portion of its circumference in contact with a roll 3, and then placed under tension into some conventional winding means. be transported. Rolls 2 and 3 are arranged parallel to each other, and in order to effect uniaxial stretching in the hand-stretching zone 4, the circumferential driving speed of roll 2 is slower than that of roll 3, and the difference in these circumferential speeds is due to the fact that the film is less stretched than the unstretched film. The film should be stretched from about 2.5 times its length to the breaking point of the film. The break point for many of the films included in this invention is approximately 4.5 times the length of the unstretched film. Of course, multiple rolls can also be used for carrying out this stretching. To prevent film 1 from slipping on rolls 2 or 3, the film is rolled under pressure, for example by partially wrapping the film around rolls 2 and 3 as seen in FIG. be brought into contact with Alternatively, conventional nip rolls can be used to press film 1 onto one or both of the rolls. To achieve the desired stretching, the film should be at least about 40°C above the second order transition temperature of the polymer;
and must be heated to a temperature not higher than about 80°C. Preferably, this stretching temperature is 145°~
The temperature is 155℃. The film is required to be at the stretching temperature when it enters the stretching zone 4. Heating can be carried out, for example, by heating the roll 2 or by enclosing the drawing device shown in FIG. 1 in an oven. In order to impart shrinkage properties to the film as a result of stretching, the film must be held under tension until it cools below the second order transition temperature of the polymer. This can be achieved by applying conventional cooling means between the roll 3 and the winding means or by applying conventional cooling means between the roll 3 and the winding means.
This is achieved by allowing the cooling system to act as a cooling means. As is common with stretched films, the edge-most portions of the film have a non-uniform thickness relative to the rest of the film. Such edge portions, or "beads", are generally trimmed prior to wrapping the wound film. In FIG. 2, which shows another drawing device used in the method of the invention, the perfluorocarbon film 1' passes in contact with and over roll 2', passes in contact with and over roll 3', and under tension. It is then transferred to conventional winding means. In this case too, rolls 2' and 3' are arranged parallel to each other, and the peripheral speed of roll 2' is lower than that of roll 3' in order to uniaxially stretch the film 1' in the stretching zone 4'. In this apparatus, the film is heated to the drawing temperature by a radiant heater 5'. An important aspect of the invention is the ratio of the width of the film to be stretched to the length of the stretching zone, where the length of the stretching zone is defined as the length of the portion of the film that is then being stretched; Medium stretch zone 4
and the length of the film at 4'. The result of this ratio being too low is a film that contracts in the direction of stretch but expands in the direction perpendicular to stretch when reheated, as will be seen below.
For purposes of this invention, the ratio of film width to stretch zone length should be greater than about 3, and preferably greater than about 10. of course,
If a partially wrapped stretching device as shown in Figure 1 is used, the distance between these rolls must be greater than the thickness of the film in order for the film to pass between them. It only requires Another important aspect of the present invention is the degree of uniaxial stretching. A perfluorocarbon film that is originally stretched by less than about 2.5 times its length (less than about 2.6 times its length in the case of tetrafluoroethylene/hexafluoropropylene copolymers) is heated in a direction perpendicular to the stretch. It has a tendency to expand. If a perfluorocarbon film is intended to be stretched more than about 4.5 times its unstretched length, the film will break at some point. In the film of the present invention, the tensile modulus in the direction perpendicular to the stretching, i.e., the transverse direction (TD), increases with the stretching ratio, and when the uniaxial stretching as described above is completed, the tensile modulus in the direction of stretching, i.e., the longitudinal direction (LD), increases with the stretching ratio. Stays greater than 70% of the modulus. Such results are surprising since it has previously been found that uniaxial stretching generally does not substantially alter the transverse tensile modulus. Furthermore, the films of the present invention exhibit 0-10% transverse shrinkage and at least 20% longitudinal shrinkage when heated for 2 minutes to a temperature about 50 DEG C. below the crystalline melting point of the polymer. In contrast, stretched perfluorocarbon films produced by prior art methods
Due to the small ratio of the film width to the length of the stretching zone used therein, it expands in the transverse direction when heated to temperatures similar to those mentioned above. In the past, too much creep has also been detrimental to the performance of as-cast perfluorocarbon films. Although it would be expected that uniaxial stretching would improve tensile creep resistance in the stretching direction, the uniaxial stretching of the method of the present invention
A surprising result after 150% stretching is a two-fold improvement in the transverse tensile creep resistance of the perfluorocarbon film (all creep progress measurements reported herein are made at room temperature). That is, the degree of creep progress is ASTM D-
674 for 1000 hours under a load of 10 MPa or less than that of the as-molded film. The lack of lateral expansion and, in most cases, lateral contraction of the films of the present invention allows them to fit around window casings, around cooking surfaces, over dome-shaped frames, etc. , and heat shrinks, causing the film to become taut. The high transverse tensile modulus complements the well-known low friction, durability of these fluorocarbon polymers, making the film resistant to deformation-induced strain, warping, and warping. Finally, the two-way creep resistance of the films of the present invention reduces the need for structural support for these films. Generally, the films of the present invention can be used as carriers, electrically insulating,
Useful as a chemical barrier, thermal barrier, physical barrier, structural member, or manufacturing aid in the following applications: wire bundling, wire insulation, membrane switches, motor slots, flat cables, flexible printed circuits, capacitors. , strain gauges, under-carpet wiring, transformers, ultra-high voltage cables, cable connection tapes, etc.; electrets; tamper-resistance seals for outdoor use such as meters for utility equipment; and other tamper-resistance seals; substitute for mica;
Microwave lenses/windows (furnaces/radomes); tubes (spiral-wound, laminated, sealed);
Gaskets; diaphragms; heat exchangers; chemical reactors; linings; conduits; expansion joints; bladders; sight glass covers; regulating pond liners; flange safety cover; spill control swim bladder; protective fabric; bursting disc; anti-stick/corrosion-resistant surface or coating; pump; windows and glazing; lighting lenses; solar rays (glazing/reflector/absorber);
Coated film substrates; skylights; construction panels; reflective films (metallized and laminated); greenhouses; photovoltaic covers; sewage treatment enclosures; protective laminations (i.e. documents, signatures, decals, labels); release films; metalized supports Belts; cooking/heating equipment (UV, IR, electromagnetic); anti-icing surfaces; roll covers; solar sails; drafting films; high heat source shielding (light bulbs, flames, etc.); chemical services; pressure sensitive tape substrates; belts; Lid (capliner); magnetic recording film substrate; punch tape substrate; interior surface (protection and decoration); yarn (slit film);
Bandages; packaging (chemicals, pharmaceuticals, sterilization, etc.); roll feather carriers; enclosures (glove boxes,
Oxygen tents, etc.); Office machinery (ribbon shields, etc.); Equipment adjustment printed panels; Roofing;
Cross-ply sheet; air-blocking curtain; oven lining. The invention will be better understood by reference to the examples. The test method for determining the amount of shrinkage in a film is as follows: Six 10 cm x 2.5 cm samples are cut from the material, three along the stretch direction and three perpendicular to it. They are placed in an oven approximately 50° C. below the crystal melting point for 3 minutes without restraint. After removal and air cooling, the sample is measured in its long dimension. The shrinkage ratio is calculated in two directions and the results are averaged for each direction (negative shrinkage indicates expansion). Example A 0.25 mm (10 mil) thick film of tetrafluoroethylene/1.1 mol% perfluoro(propyl vinyl ether) copolymer (crystalline melting temperature 305°C, specific melt viscosity 20×10 ⁴ poise at 372°C) and tetrafluoroethylene Fluoroethylene/7% hexafluoropropylene copolymer (crystal melting temperature 275℃, specific melt viscosity
0.25mm (10mil) thick at 372℃ (30 x 10 ⁴ poise)
films (both produced by melt extrusion onto a quenching drum) at 150°C.
The film was stretched by passing it through the stretching apparatus shown in FIG. The film width stretching zone length ratio was 17. The following results were obtained (0% stretch indicates as-extruded or as-molded film). The film width was 12 inches and the stretch zone was 0.69 inches.

[Table] *** Comparative example where test data could not be obtained A film of the same tetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer as in Example 1 was prepared with a ratio of film width to length of the stretched zone of 0.9. was stretched under the conditions of the example.
Here, the stretch zone length was 13.68 inches and the film width was 12 inches. Expansion in the transverse direction (TD) was demonstrated as shown below: Table % Stretching % TD Shrinkage 150 -13.0 200 -6.6 250 -3.6 300 -2.0 350 -0.82 ^* *The film breaks above 350% elongation.

[Brief explanation of drawings]

FIG. 1 is a drawing for explaining one stretching device useful in carrying out the present invention, and FIG. 2 is a diagram for explaining another stretching device. In the figure, 1, 1'... film, 2,
3, 2', 3'... Roll, 4, 4'... Stretching zone.

Claims (1)

[Claims] 1. When heated for 2 minutes at a temperature 50°C lower than the crystalline melting point of the copolymer, the shrinkage in the first in-plane direction of the film is 0 to 10%, and the shrinkage in the first direction in the same plane is 0 to 10%; A melt processable perfluorocarbon copolymer film having a shrinkage of at least 20% in a second direction perpendicular to the first direction. 2. A copolymer having a transverse shrinkage of 0 to 10% and a longitudinal shrinkage of at least 20% when heated for 2 minutes at a temperature 50° C. below the crystalline melting point of the copolymer. Melt processable perfluorocarbon copolymer film. 3. The film of claim 2 having a transverse tensile modulus greater than 70% of its longitudinal tensile modulus. 4. The film according to claim 3, which exhibits a degree of creep that is one-half or less than the degree of creep of the as-produced film. 5. The melt-processable perfluorocarbon copolymer comprises repeating units of tetrafluoroethylene and at least one other perfluorinated ethylenically unsaturated comonomer.
The film according to item 1 or 4. 6 The other perfluorinated ethylenically unsaturated comonomer has the formula R _f −(CF ₂ −) _o CF=CF ₂ or R _f −O−(CF ₂ −) _o CF=CF ₂ or R _f −(CF ₂ −) _o O−CF=CF ₂ or R _f −O−(CF ₂ −) _o ′O−CF=CF ₂ or a mixture thereof, (where n is a base number from 0 to 10, and n′ is 1 ~10, and Rf is perfluorinated alkyl of 1 to 8 carbon atoms or ω-hydroperfluorinated alkyl of 1 to 8 carbon atoms) Claim 5 The film mentioned. 7 The other perfluorinated ethylenically unsaturated comonomer has the formula R _f −(CF ₂ −) _o CF=CF ₂ , where R is a perfluorinated alkyl of 1 to 8 carbon atoms, and n is 0. 6. The film according to claim 5, which has a radix of 10 to 10. 8. The other perfluorinated ethylenically unsaturated comonomer has the formula R _f -( _CF2- ) _oO -CF= _CF2 , where Rf is a perfluorinated alkyl of 1 to 8 carbon atoms, and n is a base number of 0 to 10). 6. The film according to claim 5, wherein: 9. The film of claim 7, wherein the comonomer has the formula _CF3 -CF= _CF2 . 10 The comonomer has the formula CF ₃ -CF ₂ -CF ₂ -O-CF
9. The film according to claim 8, having = _CF2 . 11 At least two other perfluorinated ethylenically unsaturated comonomers are present and have the formula
CF ₃ −CF=CF ₂ and CF ₃ −CF ₂ −CF ₂ −O−CF=
A film according to claim 5 having CF ₂ . 12 By uniaxially stretching a substantially unstretched film of a melt-processable perfluorocarbon copolymer,
When heated at a low temperature for 2 minutes, the shrinkage of the film in a first direction in the plane is 0-10%, and the shrinkage in a second direction perpendicular to the first direction in the same plane is at least 10%. 20% perfluorocarbon copolymer film, comprising: (a) a pair of adjacent parallel rolls in which the peripheral drive speed of one roll is slower than that of the other roll; (b) contacting the unstretched film under pressure against low speed driven rolls and in the stretching zone between the pair of rolls the film is at least as fast as the secondary transformation rate of the copolymer; About 40℃ higher, but 80℃
(c) heating the film to a temperature of no higher than: the pair of rolls are positioned such that the film width to stretching zone length ratio is at least 3; The film is fed from the roll to a high-speed drive roll and brought into contact under pressure, and the difference in peripheral drive speed between the two rolls is such that the film is 2.5 times the length of the unstretched film between the two rolls and the film breaks. and then (d) holding the film under tension while cooling the film below the second order transition temperature of the copolymer. 13. The method of claim 12, wherein in step (c) the film is stretched between 2.5 and 4.5 times the length of the unstretched film. 14. The method of claim 13, wherein the rolls are positioned such that the ratio of film width to length of the stretching zone is at least 10. 15. Claim 12, wherein the melt-processable perfluorocarbon copolymer comprises repeating units of tetrafluoroethylene and at least one other perfluorinated ethylenically unsaturated comonomer;
The method according to item 13 or 14. 16 The other perfluorinated ethylenically unsaturated comonomer has the formula R _f −(CF ₂ −) _o CF=CF ₂ or R _f −O−(CF ₂ −) _o CF=CF ₂ or R _f −(CF ₂ −) _o O−CF=CF ₂ or R _f −O−(CF ₂ −) _o ′O−CF=CF ₂ or a mixture thereof, (where n is a base number from 0 to 10, and n′ is 1 -10, and Rf is perfluorinated alkyl of 1 to 8 carbon atoms or ω-hydroperfluorinated alkyl of 1 to 8 carbon atoms. Method described. 17 The other perfluorinated ethylenically unsaturated comonomer has the formula R _f −(CF ₂ −) _o CF=CF ₂ , where R is a perfluorinated alkyl of 1 to 8 carbon atoms, and n is 0 16. The method according to claim 15, wherein: 18 The other perfluorinated ethylenically unsaturated comonomer has the formula R _f −(CF ₂ −) _o O-CF=CF ₂ , where R is a perfluorinated alkyl of 1 to 8 carbon atoms, and n is a radix of 0 to 10) The method according to claim 15. 19. The method of claim 17, wherein the comonomer has the formula _CF3 -CF= _CF2 . 20 The comonomer has the formula CF ₃ -CF ₂ -CF ₂ -O-CF
19. The method of claim 18, wherein = _CF2 . 21 At least two other perfluorinated ethylenically unsaturated comonomers are present and have the formulas _CF3 -CF= _CF2 and _CF3 - _CF2 - _CF2- O-CF
= CF ₂ . The method according to claim 15.