FI85738C - Cloth with warp yarns of melt extrudable polyphenylene sulfide and synthetic industrial fabric - Google Patents

Description

85738

Kuivatuskanaas. 5 This patent application is a continuation in part of U.S. Patent Application 06/605825, filed May 1, 1984, entitled "Dryer Fabric Having Warp Strud Made of Melt Extrudable Polyethylene Sulfide and Synthetic Polyvinyl Sulfide". sulphide ".

This invention relates to fabrics made of synthetic materials and particularly, but not exclusively, suitable for use in high temperature drying sections of paper machines.

Drying fabrics have increasingly been made of monofilament fibers because such fabrics are easier to keep clean and thus maintain their drying performance and because they are essentially non-absorbent. These fabrics have a normally woven structure, but in recent years an alternative nonwoven structure - so-called "spiral fabrics" assembled from a large number of 20 helical coils joined together by hinge pins - has become popular. DE Patent 2,419,751 and U.S. Patent 4,481,079 disclose this type of fabric. The main material used in such fabrics, whether woven or spiral, is polyester with less frequent use of polyamides. Unfortunately, materials in both of these groups decompose at high temperatures, which disadvantage prevents their use in high-temperature paper machine applications. High temperature space applications are those where the operating temperature is: 30 about 150 ° C or higher.

Some woven fabric manufacturers have resorted to NOMEX or KEVLAR (registered trademarks) to overcome the harsh conditions prevailing in such high temperature applications. Since neither polymer 35 is melt-extrudable, the monofilaments made therefrom are impractical, and thus these materials are used in the form of composite multifilaments 2,85738, often in resin coatings. U.S. Patent No. 4,159,618 discloses a monofilament-like composite fiber suitable for this purpose, but even these composite materials are deficient in that they lose their tensile strength when exposed to moist or dry heat (see U.S. Patent No. 9). 618 Tables 1-3).

With respect to another property of drying fabrics, it is highly desirable that such fabrics be torsionally resistant, i.e., have inherent dimensional stability and retain this property so that they do not skew throughout their life in the paper machine. Woven fabrics made using a monofilament of circular cross-section and conventional materials such as polyester are generally, although they have the desired and already mentioned advantage of purity and non-absorbency, deficient in torsional strength due to the minimum weft and weft of each fiber. U.S. Patent No. 4,290,209 discloses the use of warp yarns of rectangular cross-section with a flattening ratio of about 2: 1, whereby the resulting fabric has excellent torsional strength and surface smoothness properties as well as better permeability and modulus of elasticity. However, none of these improved fabrics are suitable for high temperature applications because of the inherent nature of the polymers normally used. :: tends to break down and lose strength.

U.S. Patent 4,359,501 discloses the following. In applications where the temperature is high, 30 industrial fabric consisting of melt-extrudable polyaryl ether ketone monofilament fibers. . fibers. However, the main disadvantage of this material is that it is so expensive that the woven end product is not subject to certain pa- * *; 35 inherited from the factories economically attractive.

3 85738 The present invention seeks to solve these problems.

In general, the present invention relates to a drying fabric suitable for use in the drying section of a paper machine, wherein at least the machine direction components of the fabric are made of polyphenylene sulfide or a mixture of polyphenylene sulfide and heat resistant polyamide 66 having a polyamide 66 content of up to about 20% by weight. monofilaments.

The invention also relates to a drying fabric according to claim 9 suitable for use in a drying section and to a synthetic industrial fabric according to claim 10.

In a preferred embodiment of the invention, about 6% by weight of heat-resistant polyamide 66 is blended with the polyphenylene sulfide.

In another preferred embodiment, the drying fabric consists of a large number of interwoven warp and weft yarns, of which at least the warp yarns are monofilaments made of polyphenylene sulfide or a mixture of polyphenylene sulfide and heat-resistant polyamide 66.

In another preferred embodiment, the drying fabric consists of a large number of helical coils connected by hinge pins, at least the helical coils being made of polyphenylene sulfide or a mixture of polyphenylene sulfide and heat-resistant polyamide 66.

In another preferred embodiment, the drying gas consists of a large number of helical coils connected by hinge pins, of which at least the helical coils are made of polyphenylene sulfide or a mixture of polyphenylene sulfide and heat-resistant polyamide 66, and the helical coils are rectangular with the longitudinal axis of the rectangle in the plane of the fabric.

Figure 1 is a schematic diagram of a typical drying section used in a paper machine; 4 85738 Fig. 2 is an enlarged cross-sectional view of a plain weave drying fabric consisting solely of monofilaments using flattened warp yarns; Fig. 2Δ is a partial cross-sectional view taken along section line A-A of Fig. 2; Fig. 3 is an enlarged cross-sectional view of a double woven drying fabric using flattened warp yarns made of monofilaments alone, using four weft arms and each warp arm raised and lowered once per pattern run; Fig. 3A is a partial cross-sectional view taken along section line A-A of Fig. 2; Fig. 4 is an enlarged cross-sectional view of a flattened warp yarn; Fig. 5 is a plan view of a portion of flattened spirals assembling a helical drying fabric; and Fig. 5A is an enlarged cross-sectional view of the spiral dirt fabric viewed in the machine direction along section line A-A of Fig. 5.

Referring to Figure 1, there is shown schematically a typical drying section of a paper machine (not shown). The upper level drying cylinders are generally denoted by the number 10 and the lower level by the number 11. The paper web 13 passes serpentinely over the upper and lower drying cylinders, as shown in Fig. 25. The endless top fabric 14 holds the paper web 13 tightly against the top cylinders 10 as it passes partly around the first top cylinder, around the felt roll 15,: partly around the remaining top cylinders 10, and between the others; Passing around the rollers therein then passing around the turntable 16, the guide roller 24 and the tensioning roller 23. ·. : and then over the other swivel rollers 16 before passing over the first drying cylinder again and ending the revolution. Correspondingly, the endless lower fabric 18 holds the paper web 13 tightly against the lower drying cylinders 11 as it passes around these and intermediate lower felt rollers 19 and over the pivot rolls 21, the tension roll 25, the guide roll 5 85738 26 and the other pivot rolls 21 as shown.

Polyphenylene sulfide is a linear high molecular weight polymer / containing repeating units having the structure -s ~ ^ · 10 and commercially available under the registered trademark RYTON from Phillips Chemical Corporation. The pure polyphenylene sulfide used in this invention is priced at a fraction of the price of the material of U.S. Patent 4,359,501, but is instead easily extrudable. It also lacks the "toughness" required for industrial weaving.

We have found that polyphenylene sulfide in monofilament form is much more resistant to hydrolytic degradation than polyester fibers commonly used in drying fabrics. Table 1 shows the test results as a percentage of the residual tensile strength when the polyphenylene sulphide filament and the polyester monofilament filament of the same size were exposed to saturated steam at a temperature of 25,130 ° C in a pressure vessel (measuring pressure 1.7 bar) for 8 days.

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Table 1 Residual tensile strength as a percentage 130 ° C saturated steam 5 turns Polyphenylene Polyethylene terep through nisulfide talalate 0 100% 10C% 1 123 95 10 2 137 3 130 66 4 35 7 134 0 15 8 132

Table 2 shows the test results obtained with the same materials when exposed to saturated steam at a temperature of 150 ° C.

20 Table 2 Residual tensile strength as a percentage of saturated steam at 150 ° C via polyphenylene-polyethylene terephthalate sulfide_allate_ 0 100% 100% / 7 1 125 64;: v 2 us o 30 3 132 6 123: T; 9 H4 12 122 -y lo J.25 7 85738

It is observed that in these accelerated tests, the strength of the polyphenylene sulfide fiber not only was maintained but actually improved, whereas instead the strength of the polyester fiber decreased rapidly and collapsed. This exceptional preservation of hydrolysis resistance even after prolonged exposure makes polyphenylene sulfide a significant candidate material for use in paper machine drying fabrics, especially in high temperature applications.

Unfortunately, this material is only difficult to extrude into the size of a monofilament form commonly used in drying fabrics. Also during weaving, pure material is susceptible to frequent frequent warp breaks due to lack of toughness and is prone to abrasion in the weft of the weaving machine and the ham-15 ends of the railing, all of which make pure polyphenylene sulfide a difficult material for heavy industrial weaving.

The addition of heat-resistant polyamide 66 to polyphenylene sulfide prior to extrusion has alleviated these problems. Experiments with a blend kit have confirmed the following important results: 1. The addition of polyamide 66 serves as a processing aid, making commercial extrusion of the blend a more useful method.

‘. 25 2. "Toughness" is greatly improved. For example, with the addition of 6% by weight of heat-resistant polyamide 66, the measured knot strength increased sevenfold. This property is determined by drawing a thread containing a common simple knot and drawing the resulting load-elongation curve. The area below the curve is a measure of knot strength.

· "'· 3. Full resistance to hydrolytic decomposition # is maintained.

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Table 3 Residual tensile strength in percent 150 ° C saturated steam

Polyphenic- 94% polyphenylene- Polyethylene- 5 interchangeable sulphide via nitereftate fidi_6% polyamide 66 tile_ 0 1CC% 100% 100% 1 120 100 64 10 2 119 - 0 5 122 101 6 119 104 9 120 93 15 12 11C 107 19 126 109 4. Tensile strength is not reduced by the addition of polyamide to pure polyphenylene sulfide.

20 5. Subsequent pilot plant weaving and commercial weaving using a large number of drying fabric designs, including those requiring high weaving stresses v and high weft counts, confirms that the mixture containing polyphenylene sulfide and 6% polyamide. . ·. The use of drying fabrics in warp yarns reduces warp breakage and abrasion to an acceptable level.

. . 6. Increasing the proportion of polyamide 66 from 6% to 20% improves the toughness of the monofilament, but reduces the abrasion resistance.

30 The way in which the additive improves the toughness while maintaining the hydrolysis resistance is not fully known, • · *::: but successful monofilaments are characterized in that they contain the additive in discrete small stretched spheres with a longitudinal axis parallel to *: * 35 with monofilament shaft. These separate spheres are not attached to each other or to the outer boundary surface of the monofilament and are thus protected from the harsh environmental conditions prevailing during the final use of the filament. We have found that in order to preserve the additive as separate spheres, the melt viscosity of the additive must be higher than the melt viscosity of the polyphenylene sulfide at the extrusion temperature and the amount of the additive must be limited. Another factor to consider when selecting an additive is that the additive must not decompose during extrusion after being briefly exposed to the temperature required to melt the polyphenylene sulfide, which is 285-10105 ° C. Some additives that meet the above requirements do not form spheres because they are chemically incompatible with polyphenylene sulfide and react inappropriately.

In our blending experiments to date, we have found that heat-resistant polyamide 66 is the only additive suitable for polyphenylene sulfide that makes the resulting monofilament tough while maintaining its hydrolysis resistance. Other materials that are also capable of imparting the same property to the mixture may be found. Some of the 20 factors that are important in the selection of additives are: higher viscosity than polyphenylene sulfide viscosity at extrusion temperature, chemical compatibility and resistance to thermal decomposition during extrusion.

All types of drying fabrics containing machine direction monofilaments benefit from this invention in terms of hydrolysis resistance. Three preferred structures using rectangular machine direction components are described below, but the invention is not limited to these structures.

Figures 2 and 2A show a plain weave drying fabric 30, which is a typical example of a single ply drying fabric used in the paper industry. In Figures 2 and 2A, 31 indicates the following warp yarns made of polyphenylene sulphide or a mixture of polyphenylene sulphide and polyamide 66 10 85738 and flattened to be approximately rectangular in cross-section, and 32 successive weft yarns. In this structure, every second warp yarn 31 passes over the first weft yarn 32, under the second weft yarn, 5 over the third, and so on. Correspondingly, the adjacent warp yarn passes under the first weft yarn, over the second, under the third, and so on.

Figures 3 and 3A show four double weft drying fabrics 40, a type of drying fabric commonly used in the paper industry, using four weft arms and each nip arm once per pattern run. In Figures 3 and 3A, chapters 41, 42, 43 and 44 denote successive warp yarns made of polyphenylene sulfide or a mixture of polyphenylene sulfide and polyamide 66 and flattened to be approximately rectangular in cross section. The weft is divided in pairs into two layers and numbered from 48 to 57 as shown in the figure. In this woven structure, the warp yarn 41 passes over the copper 50-51 of the weft-20, respectively, between the next pair 52-53, the third. under pair 54-55, between fourth pair 56-57 and so on] / onwards. The next warp yarn 42 passes between the first pair of weft yarns 50-51, under the second pair, between the third pair and over the fourth pair. Respectively, in the order 25, the third and fourth warp yarns 4 3 and 44 are woven, starting under and between the first weft yarn pair, in this order.

Figure 4 shows a cross-section made of polyphenylene sulphide or a mixture of polyphenylene sulphide and polyamide. 30 warp yarns of approximately rectangular cross-section. Such yarns can be made by rolling round monofilament strands or by cutting the film into ore or preferably by melt extrusion through a die of a certain shape. The preferred • ·. ·· * shown in Figure 4. In the 35th embodiment, the flatness ratio a: b is 2: 1, and in the case of woven drying fabrics it is preferably between 1.5: 1 and 2.5: 1.

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Figures 5 and 5A show a helical drying felt 60 consisting of a large number of helical S-helices 61 connected by hinge pins 63 to adjacent z-helices 62. The designations "SM" and "Z" indicate the direction of the thread in accordance with the general practice in the textile industry. The coils 61 and 62 are twisted from a filamentary material made of polyphenylene sulfide or a polyphenylene sulfide-polyamide blend that is approximately rectangular in cross-section at a flatness ratio a: b of 2: 1, as shown in this preferred embodiment. In this structure, the flatness ratio can be between 1.1: 1 and 2.5: 1.

The warp drying fabric 15 of the present invention preferably has a warp number of about 10 to 30 threads / cm. Warp yarns are made of polyphenylene sulfide or a mixture of polyphenylene sulfide and polyamide 66. The dimensions of the main axis of the flattened warp yarns according to the invention vary between 0.318 and 1.270 mm. As far as the weft is concerned, it is not intended to limit the material used to monofilaments. Since the weft yarns in the fabric according to the invention cannot withstand loading, other materials resistant to high temperatures and stable to hydrolytic decomposition, for example a combination yarn and incorporating asbestos or glass-25 fiber, can be used.

In spiral structures in the drying fabric of the invention: another embodiment, helical coils made of polyphenylene sulfide or a mixture of polyphenylene sulfide and heat-resistant polyamide 66 are used, wherein the proportion of polyamide 66 is at most 20% by weight. The hinge pins can be made of the same material or alternatively of other heat-resistant materials, such as the already mentioned composite materials.

In the preferred embodiments described above, 35 monofilaments of rectangular cross-section are used, but also monofilaments of circular cross-section and 12,88738 other shapes may be used, provided that they are made of the material according to the invention. We have found that woven fabrics made from warp yarns of rectangular cross-section made of pure polyphenylene sulphide 5 or (in a different test) made of a mixture of polyphenylene sulphide and 6% polyamide 66 warp yarns are more resistant to torsion than in the manufacture of which polyester in the form of a monofilament has been used as a warp material. The invention can thus be used to improve the torsional strength of fabrics made of round monofilaments, which normally causes inconvenience.

The present invention encompasses all obvious modifications of the preferred embodiments of the examples set forth herein, provided that such modifications are within the scope of the appended claims.

• · · • ·

Claims (15)

1. A cloth suitable for the drying part of a paper machine, characterized in that the edible ink cloth components running in the machine direction are monofilaments made of polyphenylene sulfide or a mixture of polyphenylene sulfide and heat-resistant polyamide 66, wherein the proportion of said polyamide 66 is not more than about 20% by weight. Drying cloth according to claim 1, characterized in that about 6% by weight of heat-resistant polyamide 66 is mixed in said polyphenylene sulfide. Drying cloth according to claim 1, characterized in that said components in the machine direction are made of gill yarns in the woven cloth. Cloth according to Claim 3, characterized in that said gill nets are flattened gill nets which, in their cross-section, are at least rectangular, the longitudinal axis of the rectangle being in the plane of said canvas. 5. A cloth according to claim 4, characterized in that said woven cloth contains flattened gill yarns which, in their cross-section Λ C 3, are in the rectangular section, the flattening ratio being 1.5: 1 - 2.5: 1st 6. A cloth according to claim 1, characterized in that said components in the machine direction consist of a large number of threaded rods joined together by helical spirals. 7. A cloth according to claim 6, characterized in that the monofilament at said helical spirals is seen in the machine direction to its cross-section in a substantially rectangular manner, the longitudinal axis of the rectangle being in the plane of said web. 85738 8. A cloth according to claim 7, characterized in that the flattening ratio of said rectangular cross-section. is 1.1: 1 - 2.5: 1. 9. A cloth suitable for use in a drying part, characterized in that at least the fabric components of the machine are made of monofilament made from a mixture of polyphenylene sulfide and such additive which gives the monofilament toughness while retaining polyphenylene. Of the sulphide is naturally pourable against hydrolysis and exhibits a higher melt viscosity than the polyphenylene sulphide at extrusion temperatures and which is resistant to thermal decay at extrusion temperatures and chemically matches with the polyphenylene sulphide. 10. Synthetic industrial fabric consisting of a large amount of interconnected gutter and wrap monofilament fibers containing polyphenylene sulfide, characterized in that heat-resistant polyamide 66 is blended into said polyphenylene sulfide, the proportion of which in the mixture is at most about 20% by weight. 11. Monofilaments made from a mixture of polyphenylene sulfide and such an additive which imparts toughness to the monofilament without substantially weakening its hydrolysis resistance, characterized in that said additive is added to polyphenylene sulfide from 1 to 20% by weight and said additive exhibits a higher viscosity in extrusion temperatures than the polyphenylene sulfide and is resistant to the decay occurring during the extrusion and chemically matches the polyphenylene sulfide. Monofilament according to claim 11, characterized in that said additive is heat-resistant polyamide 66. Monofilament according to claim 12, characterized in that the proportion of heat-resistant polyamide 66 is about 6% by weight of the proportion of polyphenylene sulphide. 85738 Monofilament according to claim 11, characterized in that it is flat in its cross-section and substantially rectangular in that the axle ratio is 1.1: 1-3: 1. Monofilament according to claim 14, characterized in that the shaft ratio is about 2: 1. 10 15 20 25 30 35