JPH025469B2 - - Google Patents

Description

Detailed Description of the Invention The present invention performs single-sided coating and double-sided coating of polytetrafluoroethylene (sometimes abbreviated as PTFE) coated fabric, particularly fabric (sheet-like base material structure). The present invention relates to a method for producing a PTFE-coated cloth suitable for

More specifically, the present invention can advantageously overcome troubles such as the occurrence of unfavorable phenomena such as sagging, muddy cracks, and foaming on the other side of the cloth, and requires extremely high skill. Moreover, a desired uniform single-sided coating and double-sided dissimilar coating layers can be easily and efficiently formed with excellent handling and workability without requiring delicate technical methods unsuitable for industrial implementation. The present invention relates to an improved method of making polytetrafluoroethylene coated fabrics.

In particular, the present invention provides an orifice opening of a slit applicator for applying a coating composition comprising an aqueous dispersion of polytetrafluoroethylene (PTFE) to a heat-resistant fabric in contact with a vertically rising surface of the heat-resistant fabric. and the amount of the PTFE aqueous dispersion coating composition having a viscosity of 50 to 2000 centipoise and a concentration of 30 to 60% by weight applied to the heat-resistant fabric,
The coating composition is applied to the heat-resistant cloth from the orifice by controlling the liquid level ΔH from the slit-shaped opening of the orifice to the coating composition liquid level by keeping it in the range of 1.5 to 15 mm. The present invention relates to a method for producing a polytetrafluoroethylene-coated fabric, which comprises coating the fabric with polytetrafluoroethylene.

Polytetrafluoroethylene coated fabric has high mechanical strength and excellent dimensional stability.
It has many of the excellent properties of PTFE, such as heat and cold resistance, electrical properties, chemical resistance, and even non-stick properties.

For this reason, it can be used as a conveyor belt for sticky materials and high or low temperature items, and as a base for printed circuit boards.
It can be used as a peeling sheet for rubber and plastics, or as a protective curtain against chemicals, etc.
It is used in many industrial fields such as electricity and chemistry. Methods for producing such PTFE-coated fabrics include heat-resistant fabrics such as glass fiber, carbon fiber, "Kevlar", "Nomex", etc.
A heat-resistant woven fabric such as (DuPont's fully aromatic polyamide fiber) is immersed in a bath of an aqueous polytetrafluoroethylene dispersion, the cloth is impregnated with polytetrafluoroethylene and coated, and then dried. A method is used in which PTFE is thermally bonded to cloth by firing.

Although the above method is an excellent method for coating both sides of a cloth, it is not possible to coat one side or coat different types of both sides.

When coating one side using this method,
One method is to bring one side of the cloth into contact with the liquid surface of the bath, and then pull the cloth out of the liquid surface while the PTFE adheres to the surface of the cloth, but before it has penetrated to the back side of the cloth due to capillary action in the cloth. It will be done.

However, coating one side of fabric, especially thin fabric, by such a method requires very delicate and highly skilled techniques, and therefore polytetrafluoroethylene dispersions, which tend to penetrate easily, are not normally used; A thickener is added to the dispersion to create a composition that is less likely to penetrate. Isopropanol, surfactants, etc. are used as thickeners, and the viscosity thereof is generally adjusted to a range of 500 to 20,000 centipoise.

If the viscosity of the composition increases, the phenomenon of permeation into the fabric will be reduced, but on the other hand, there are problems in that the handling of the liquid (composition) becomes worse and the amount of polytetrafluoroethylene that adheres to the fabric increases. This is not only economically disadvantageous, but also causes deterioration of the condition of the coated surface, such as sagging, muddy cracks, and foaming.

According to the research conducted by the present inventors, when applying a coating composition made of an aqueous PTFE dispersion to a heat-resistant sheet-like substrate structure, the coating composition made of an aqueous PTFE dispersion is applied to a heat-resistant cloth. The orifice opening of the slit applicator is positioned in contact with the vertically rising surface of the heat-resistant fabric, and the PTFE aqueous dispersion coating composition has a viscosity of 50 to 2000 centipoise and a concentration of 30 to 60% by weight. The coating amount on the heat-resistant cloth is determined by the liquid level height △H from the slit opening of the orifice to the liquid level of the coating composition.
controlled by keeping it in the range of 1.5-15mm,
By applying the above-mentioned coating composition to the heat-resistant cloth through the orifice, it is possible to prevent the occurrence of undesirable phenomena such as inconvenient permeation and leaching to other surfaces of the cloth, sagging, muddy cracks, and foaming on the coated surface. The troubles can be advantageously overcome and the desired uniform single-sided coating and double-sided dissimilar coating layers can be easily and efficiently obtained without requiring delicate technical methods that require great skill and are unsuitable for industrial implementation. It has been found that an improved method for producing a polytetrafluoroethylene coated fabric that can be efficiently formed with improved handling and workability can be provided.

Furthermore, according to the method of the present invention, the above-mentioned problems in single-sided coating, which were difficult to solve with conventional methods, are solved, and even when double-sided coating is performed, it is possible to coat both sides with different types, for example, with different coatings on both sides of the cloth. It has been found that this method has the advantage that it is easy to produce products with characteristics such as coatings with different colors or different types of fillers.

Accordingly, an object of the present invention is to provide a method for producing a PTFE-coated fabric suitable for coating one side of a heat-resistant fabric and coating both sides of a heat-resistant fabric with a different type.

The above objects and many other objects and advantages of the present invention will become more apparent from the following description.

According to the method of the present invention, a coating composition comprising an aqueous PTFE dispersion is applied to a heat-resistant cloth using a slit.
Position the orifice opening of the applicator against the vertically rising surface of the heat-resistant fabric until the viscosity
50-2000 centipoise and concentration 30-60% by weight
The PTFE aqueous dispersion coating composition is applied to the heat resistant fabric. At this time, according to the method of the present invention, the
The amount of the PTFE aqueous dispersion coating composition to be applied to the heat-resistant cloth is determined by adjusting the liquid level ΔH from the slit opening of the orifice to the coating composition liquid level from 1.5 to
The coating composition is applied onto the heat resistant fabric through the orifice in a controlled manner by maintaining a range of 15 mm.

The aqueous PTFE dispersion coating composition having a viscosity of 50 to 2000 centipoise and a concentration of 30 to 60% by weight used in the method of the present invention is, for example, a commonly commercially available or used composition having a viscosity of 30 to 60% by weight and a viscosity of 10% by weight. It can be obtained by adjusting the viscosity to 50 to 2000 centipoise by adding a thickener to an aqueous PTFE dispersion of about 30 centipoise.

Thickeners used for the above-mentioned viscosity adjustment can be selected and used as appropriate, such as hydrophilic organic liquids such as ethanol, isopropanol, and acetone, and nonionic surfactants, which are conventionally used as thickeners for polytetrafluoroethylene aqueous dispersions. Preferred thickeners used in the present invention include water-soluble polymers such as polyacrylic resins and polyalkylene oxide resins. A viscous PTFE aqueous dispersion coating composition can be easily obtained. The thickener used for adjusting the viscosity as described above is not limited to one type, and multiple types can be used in combination as appropriate. Furthermore, if necessary, colloidal alumina,
It is also possible to add PKT fibrous potassium titanate or the like to make a low-viscosity, non-penetrating coating composition, and such a composition is extremely useful especially when coating thin bare fabrics. A coating composition prepared by adding glass balloons or glass beads to the above coating composition is effective for closing gaps in woven fabrics, and can be used, for example, as a coating composition for polytetrafluoroethylene-coated glass fiber woven fabrics for awnings. Useful. Furthermore, other additives such as pigments, fillers, adhesive strength enhancers for coatings, etc. can also be added as appropriate. Further, in the present invention, PTFE includes not only a homopolymer of tetrafluoroethylene but also a copolymer containing tetrafluoroethylene as a main component and a comonomer copolymerizable with the same. Examples of such comonomers include the formula CF ₂ =
Perfluoroolefins represented by CFRf, perfluoro(alkyl vinyl ethers) represented by CF ₂ =CFORf, and CH ₂ =CHRf
Examples include perfluoroalkyl ethylenes represented by the following formula, and perfluoroalkyl vinyl ethers represented by CH ₂ =CHORf (wherein Rf has 1 to 7 carbon atoms).

In the present invention, heat-resistant fabrics made of inorganic and organic fibers and arbitrary combinations thereof can be used as the heat-resistant fabrics on which the above-mentioned PTFE aqueous dispersion coating composition is applied. For example, glass fiber, rock wool, carbon fiber, asbestos fiber,
Heat-resistant inorganic fibers such as metal fibers; heat-resistant organic fibers such as polyimide fibers, aromatic polyamide fibers, aromatic polyester fibers; woven fabrics derived from any combination of these materials;
Examples include knitted fabrics, non-woven fabrics, and similar sheet-like structures. These heat resistant fabrics are made of PTFE
The coating layer can be selected and utilized as appropriate, with the aim of not causing significant deterioration of physical properties due to deformation, thermal decomposition, etc. under the firing process conditions of about 350 to about 500° C. in which the coating layer is fused to these base fabrics.

Next, one embodiment of the method of the present invention will be illustrated in more detail using the accompanying drawings.

1 is a schematic layout of an apparatus illustrating an example of carrying out the method of the invention, and FIG. 2 is a schematic diagram of a modification of a slit applicator suitable for use in carrying out the method of the invention. FIG.

In Figure 1, the heat-resistant cloth 5 rising vertically
The orifice 2 opening of the coater 1 of the slit applicator is positioned in light contact with the surface of the heat-resistant fabric so as to be able to run upwards, and the coating consisting of the aqueous PTFE dispersion in the coater 1 is placed in contact with the surface of the fabric. The composition 3 flows out from the opening of the orifice 2 and is applied onto the surface of the heat-resistant cloth. In the example shown in the figure, the heat-resistant cloth 5 is shown rising almost perpendicularly to the horizontal direction, but it may also be run at an appropriate inclination to the horizontal direction within the range that can be applied. In general, it may be inclined to either the left or the right with respect to the vertical direction as long as no undesirable phenomenon such as sagging occurs. In the present invention, the term "vertically rising" includes such a mode of rising with an inclination within an allowable range. Further, the opening of the orifice 2 of the coater 1 does not need to be in contact with the heat-resistant cloth 5 in its entirety, but may be in partial contact with the heat-resistant cloth 5. sex cloth 5
There is no problem even if they are close to each other with a slight gap between them so as not to overflow downward from the opening portion facing the . In the present invention, the term ``locating the opening of the orifice 2 in contact with the vertically rising surface of the heat-resistant cloth'' includes such a permissible close state.

In the method of the present invention, the coating composition 3 is applied to the surface of the upward traveling heat-resistant cloth 5 in the above-mentioned state. The liquid level height ΔH from the center line of the opening to the liquid level of the coating composition is controlled by keeping it within the range of 1.5 to 15 mm. This value of liquid level height corresponds to a liquid pressure of approximately 0.002 to 0.02 Kg/cm ² .
If the liquid level height △H is too high, exceeding approximately 15 mm, PTFE
The coating composition 3 consisting of an aqueous dispersion is applied to the heat-resistant cloth 5
There is a risk of overflowing downward from the area where the opening of the orifice 2 faces, or leakage to the back side in the case of single-sided coating. When ΔH is low, it becomes difficult to uniformly apply the coating composition 3 to the surface of the heat-resistant cloth 5 that is traveling upward.
In the method of the present invention, the amount of coating is controlled by maintaining the liquid level height within the above range ΔH.

The liquid level height △H can be changed as appropriate depending on various factors such as the type and viscosity of the coating composition made of the aqueous PTFE dispersion used, the type and surface condition of the heat-resistant coating fabric, but the above △ It is changed as appropriate under conditions that satisfy the H range. For example, bare cloth
When applying a single-sided coating to a fabric, it is generally preferable to keep it at about 3.5 mm or less; if ΔH is set too large, the coating composition 3 will reach the back side of the fabric due to capillary action.
may leach out, defeating the purpose of single-sided coating. For example, in the case of double-sided coating, △H should be approximately 7
It is preferable to keep it below mm. The reason that double-sided coating allows for a larger ΔH than single-sided coating is that the composition is allowed to penetrate into the fabric to a certain extent. However, if ΔH is made larger than 7 mm, the composition may spill out from the back side of the cloth, which is not preferable. Furthermore, when a coated cloth or a non-porous cloth is coated instead of the bare cloth as exemplified above, the above-mentioned permeation phenomenon will not be a problem, and ΔH can be made even larger. Depending on the above-mentioned factors, the liquid level height ΔH can be appropriately selected within the range of 1.5 to 15 mm.

In the method of the present invention, the above-mentioned liquid level height ΔH is
Appropriate selection of the viscosity and concentration of the coating composition consisting of the PTFE aqueous dispersion is a combined parameter with controlling the coating amount by maintaining the liquid level height △H appropriately in the range of 1.5 to 15 mm. It is also important. The present invention provides a PTFE aqueous dispersion coating composition having a viscosity of 50 to 2000 centipoise, preferably an upper limit of 1500 centipoise or less, more preferably an upper limit of about 1000 centipoise or less, and a concentration of 30 to 60% by weight. things are used.

The use of PTFE aqueous dispersion coating compositions with too high a viscosity, e.g., compositions with viscosities greater than 10,000 centipoise, increases the coverage of the composition on the fabric, which is economically disadvantageous and is often excessive. Problems such as muddy cracks, foaming and sagging occur due to the adhesion of a large amount of the composition. These problems are particularly likely to occur when coating thick bare fabrics, coated fabrics, non-porous fabrics, etc. with the composition.

On the other hand, coating compositions with a viscosity lower than 50 centipoise, such as commercially available aqueous polytetrafluoroethylene dispersions without added thickeners (viscosity 10 to
(approximately 20 centipoise) have very good permeability into fabrics, which often causes problems when coating one side of thin, bare fabrics. Therefore, it is important to adjust the viscosity of the coating composition used in the present invention to a range of 50 to 2000 centipoise, and it is preferable to use a coating composition having a viscosity of 1500 centipoise or less.

Furthermore, in addition to thickeners, colloidal alumina,
DKT fibrous coating compositions containing potassium titanate and the like have low viscosity and low permeability into fabrics, so they can be used more effectively when coating thin fabrics. In such compositions
It can also be used at viscosities of 500 centipoise or less, or even 300 centipoise or less.

In the embodiment shown in FIG. 1, the amount of the PTFE aqueous dispersion coating composition 3 applied to the heat-resistant cloth 5 can be controlled by keeping the liquid level height ΔH in the range of 1.5 to 15 mm. , by adjusting the liquid amount of the composition 3 supplied from the supply tank 7 to the coater 1, for example, using a pot 6, and discharging an excess amount of the composition 3 through the discharge pipe 4, ΔH can be maintained at a desired approximately constant level. It can be done by keeping it at the level. In this embodiment, the liquid level height ΔH can be determined by the difference between the position of the top opening of the discharge pipe 4 and the position of the orifice 2 of the coater 1. (not shown).
Such control of the amount of application by adjusting the liquid level height ΔH can be performed in an automatic manner, if desired.
For example, a liquid level detection means may be provided and this and the Kotoku 6 may be linked using an automatic control system.
Alternatively, these and the vertical movement of the discharge pipe 4 may be linked using an automatic control system. The aqueous PTFE dispersion coating composition discharged through the discharge pipe 4 is stored in a storage tank 8 and returned to the supply tank 7 by a pump 9 so that it can be reused.

As described above, while traveling vertically
The heat-resistant cloth 5 coated with the PTFE aqueous dispersion coating composition is guided, for example, to a drying furnace 10 and a firing furnace 11 provided in its traveling path, and a coating in which PTFE is firmly fused to the heat-resistant cloth 5 is produced. A cloth can be formed. In addition, 12 and 13 in the figure are guide rolls of the heat-resistant cloth 5. Furthermore, the method of the present invention can be applied to double-sided coating, for example, as shown by the dotted line in the figure,
A coater 19 is provided on the back side in the same manner as described above, and the coating composition is applied also on the back side in the same manner as described above, and is similarly passed through the drying furnace 10 and the firing furnace 11 to be firmly fused to both sides. A coated fabric with a coated PTFE layer can be obtained. At this time, for example, by changing the color tone of the coating composition applied to each side, it is also possible to produce coated fabrics with different colors on the front and back sides all at once.

Furthermore, when carrying out the method of the present invention, contact between the vertically rising surface of the heat-resistant cloth 5 and the opening of the orifice 2 of the slit applicator is made such that the lower opening of the orifice 2 is located in contact with the heat-resistant cloth 5. The upper part of the opening can be positioned slightly away from the heat-resistant cloth 5 with a certain clearance,
This is preferable in that it makes it easy to adjust the thickness 17 of the PTFE aqueous dispersion coating composition applied to the heat-resistant cloth 5. An example is shown in FIG.
In the example shown in FIG. 2, the coater 1 is rotatably provided in the direction of the arrow a in the figure with a horizontal central axis X parallel to the surface of the heat-resistant cloth 5 as the rotation axis, and In the running direction of the heat-resistant cloth 5 shown in
It can be adjusted so that the cloth 5 and the opening lower part 15 of the orifice 2 are in contact with each other and the opening upper part 14 of the orifice 2 is positioned a little apart. Thus, the opening surface of the orifice 2 is positioned with a slight inclination to the heat-resistant cloth 5 at the angle shown in the figure. Therefore, by appropriately adjusting the angle, the gap 16 can be made larger or smaller as desired, and as a result, the thickness 17 of the PTFE aqueous dispersion coating composition applied to the heat-resistant cloth 5 can be reduced. can be easily adjusted to the desired thickness. At this time, the above coater 1
The passage 18 leading the composition from the supply tank 7 to the coater 1 can be constructed of a flexible material for rotation. A portion of the discharge pipe 4 may also be constructed from a similar material.

Thus, according to the method of the present invention, various contamination problems in the conventional method, such as undesirable seepage to other surfaces of the fabric, and occurrence of undesirable phenomena such as sagging, muddy cracks, and foaming on the coated surface, can be avoided. The troubles can be advantageously overcome and the desired uniform single-sided coating and double-sided dissimilar coating layers can be easily and efficiently obtained without requiring delicate technical methods that require great skill and are unsuitable for industrial implementation. It is possible to efficiently produce a polytetrafluoroethylene coated fabric with improved handling and workability.

Further, for the polytetrafluoroethylene coated fabric obtained by the method of the present invention, especially the single-sided coated fabric, an adhesive may be applied to the side where the heat-resistant fabric 5 such as glass fiber or carbon fiber is exposed. Therefore, it can be easily adhered to a desired part of another desired article.

Such ease of adhesion makes the double-sided coated fabric extremely advantageous for a variety of applications. For example, adhesion to a conveyor belt surface can provide chemical resistance, non-stick properties to the belt, and adhesion to a heat sealer prevents the sealer from adhering to hot melted plastics. Also, adhesion to the lower surface of an article gives it sliding properties;
Allows easy movement of goods. In addition, by adhering or wrapping it around printed circuit boards, electric wires, etc., it is also possible to make various electrical devices with high electrical insulation and durability.

Hereinafter, an example of implementing the method of the present invention will be illustrated in more detail.

Example 1 Water-soluble acrylic resin (trade name: "Acrisol") was added to 100 parts by weight of a 60% polytetrafluoroethylene aqueous dispersion (trade name: "Teflon" 30).
Add and mix 0.65 parts by weight of ASE60) to prepare a coating composition with a viscosity of 875 centipoise, and use the apparatus shown in Figure 1 to coat one side of a glass fiber woven fabric with a width of 450 mm with polytetrafluoroethylene. Ta.

In other words, the coating speed was 2 m/min, and the ΔH of the apparatus was set to 3 mm.

The temperature of the drying oven is gradually raised from 260℃ to 330℃, and the maximum temperature of the firing oven is
The temperature was set at 480℃.

The resulting polytetrafluoroethylene-coated glass fiber woven fabric was free from cracks and foaming, and no penetration of polytetrafluoroethylene into the back surface (uncoated surface) of the woven fabric was observed. The thickness of the polytetrafluoroethylene coating was about 100 microns.

[Brief explanation of drawings]

1 is a schematic layout of an apparatus illustrating an example of carrying out the method of the invention, and FIG. 2 is a schematic diagram showing a modification of a slit applicator suitable for use in carrying out the method of the invention. FIG.

Claims (1)

[Claims] 1. The orifice opening of the slit applicator for applying a coating composition consisting of an aqueous dispersion of polytetrafluoroethylene (PTFE) to a heat-resistant cloth is positioned in contact with the vertically rising surface of the heat-resistant cloth, and the viscosity is increased. 50 to 2000 centipoise and concentration
The amount of the PTFE aqueous dispersion coating composition of 30 to 60% by weight to be applied to the heat-resistant cloth is determined by the liquid level height ΔH from the slit-shaped opening of the orifice to the liquid level of the coating composition. A method for producing a polytetrafluoroethylene coated fabric, comprising applying the coating composition to the heat-resistant fabric through the orifice while controlling the thickness to be within a range of 1.5 to 15 mm.