EP0622479A2

EP0622479A2 - A monofilament made from a blend of a polyester having a polyhydric alcohol component of 1,4-cyclohexanedimethanol, and a polyamide

Info

Publication number: EP0622479A2
Application number: EP94106271A
Authority: EP
Inventors: Herbert D. Stroud, Jr.; Paul R. Cadmus
Original assignee: Hoechst Celanese Corp
Current assignee: Teijin Monofilament Germany GmbH
Priority date: 1993-04-26
Filing date: 1994-04-22
Publication date: 1994-11-02
Anticipated expiration: 2014-04-22
Also published as: BR9401568A; DE69411444D1; CA2119678A1; DE69411444T2; EP0622479B1; ATE168144T1; EP0622479A3; FI941916A0; JPH0711114A; FI941916A

Abstract

The present invention is directed to a monofilament made from a blend of a polyester having a polyhydric alcohol of 1,4-cyclohexane-dimethanol, and a polyamide. Additionally, the blend may include a polyolefin. This blend is useful as an article of paper making machine clothing used in forming, pressing, or drying sections of a paper making machine when the blend is in the form of a fiber structure. The blends usefulness stems from its dry-heat strength and hydrolysis resistance.

Description

Field of the Invention

The present invention is directed to a monofilament made from a blend of a polyester having a polyhydric alcohol component of 1,4-cyclohexanedimethanol, and a polyamide. This invention is particularly useful as an article of paper making machine clothing used in the forming, pressing, or drying sections of a paper making machine when the blend is in the form of a fiber structure.

Background of the Invention

Paper is composed of cellulosic fibers that are formed into a sheet. A paper making machine consists of three main sections: the forming section, the pressing section, and the drying section.
In the forming section, the cellulosic pulp slurry or furnish is injected onto a forming fabric which is a long, woven mesh belt. As the forming fabric moves along through the forming section, some of the water in the slurry drains through the fabric and a paper web is formed. As this paper web leaves the forming section, it is composed of about 80% water and about 20% solids. For many years, forming fabrics were woven from metal wires and had a life of about one week on a paper machine. This short life was due to metal fatigue and abrasion caused by contacting the machine parts in the forming section. In the 1960's, experiments were begun to replace the metal fabrics with woven, synthetic, monofilament yarn fabrics. Today, polyester monofilament is the yarn of choice for this application and typical fabric life is about 60-120 days.
After leaving the forming section, the paper web moves into the pressing section where a high compressive force is exerted by a pair of press rolls to remove more water from the paper web. The press fabric serves as cushioning and water removing media between the press rolls. As the paper leaves the pressing section, the paper web contains about 60% water and 40% solids.
Traditionally, press fabrics were made of 100% wool due to its resilience and water absorbency. However, synthetics have been developed with good resilience that have longer life than woolen felts. Fabrics of choice today consist of a base fabric, woven from polyamide monofilaments into which polyamide fibers have been needlepunched to form a felt. Typically life of press felts is 30-60 days.
The drying section consists of large, steam-heated cylinders that dry the paper web to a level of about 6% moisture. A dryer felt or fabric is needed to hold the paper in contact with the dryer cylinders. Originally, these fabrics were made from cotton, but as paper making developed, higher speed and temperature shortened the life of the cotton dryer felts.
Many different fibers and yarns have been used to develop better-performing dryer felts so as to improve the efficiency of the paper making process. Presently, the predominant yarn used in the manufacture of dryer fabrics is polyester monofilament. See, Luciano, B., Albany International Fabric Facts, Volume 38, No. 4-6. Dryer fabrics made from polyester monofilament operating at normal temperatures (300° to 350°F) last about one year.
In order to improve profitability, paper makers desire to increase speeds of the paper making machines. To sufficiently dry the paper at increased throughput, additional heat is used in the dryer section and perhaps in other sections of the paper machine as well.
Elevated temperatures tend to adversely affect the hydrolysis resistance of polyester yarns. For this reason manufacturers of dryer fabrics have looked at other fibers and yarns in an effort to increase fabric life at higher temperatures.
Moreover, if a fabric has to be replaced at other than scheduled maintenance cycles due to failure or damage, the downtime cost to the paper maker can be significant. For this reason, it is desirable to manufacture dryer fabrics that will run with longer and more predictable times under increased heat and speed conditions.
As we move into the next century, an ever increasing emphasis is being put on using recycled paper in the making of new paper. In the U.S., Federal and state laws are being passed which require a certain amount of recycled paper to be used in each pound of paper manufactured. For the environmentalist this is a good law, however, for the paper makers this law poses new challenges because the recycled paper has a high level of contaminants. Contaminants include wood pulp residues, inorganic residues (such as clays and titanium dioxide), adhesives from mailing labels, stickers from hot-melt adhesives, non-paper films, and printing inks. These contaminants may either stick to the paper making fabrics or be carried on through the paper machine in the paper sheet. If these contaminants cannot be easily removed, the fabrics will become plugged and the quality of the paper will decrease to the point that the fabric must be replaced. Due to the ease of cleaning, fabrics made from 100% monofilaments are desired. See: Luciano, B., Ibid.
One solution is to use polyphenylene sulfide (PPS) monofilaments in the manufacture of dryer felts. PPS has very good hydrolysis resistance, but unfortunately, the polymer is difficult to extrude into monofilaments and is quite expensive. Also, PPS monofilaments are very brittle which can cause problems on the paper machine. An example of a PPS monofilament is found in U.S. Patent No. 5,162,151, which is incorporated herein by reference.
Another fiber solution to the harsh environment of the paper making process is the use of poly(2-methyl-1,5-pentylene) terephthalamide. See U.S. Patent No. 5,162,152, which is incorporated herein by reference. Yet another fiber solution is the use of a copolymer of terephthalic acid, isophthalic acid, and 1,4-dimethylocyclohexane (also referred to as 1,4-cyclohexanedimethanol). See: U.S. Patent No. 5,169,499, which is incorporated herein by reference.
Accordingly, there is a need in the paper making industry to develop new fibers for use in paper making clothing.

Summary of the Invention

One embodiment of the present invention is directed to a monofilament made from a blend of a polyester having a polyhydric alcohol of 1,4-cyclohexane-dimethanol, and a polyamide. This blend is useful as an article of paper making machine clothing used in forming, pressing, or drying sections of a paper making machine when the blend is in the form of a fiber structure. The blends usefulness stems from its dry-heat strength and hydrolysis resistance. Another embodiment of the present invention is directed to a monofilament made from a blend of a polyester having a polyhydric alcohol of 1,4-cyclohexanedimethanol, a polyamide, and a polyolefin. This blend, as the foregoing, is useful as an article of paper making machine clothing and its usefulness stems from the those mentioned in regard to the foregoing product in addition to it greater ability to be formed into a spiral fabric.

Description of the Invention

The inventive blends disclosed herein include a polyester having a polyhydric alcohol component of 1,4-cyclohexanedimenthanol, and a polyamide. The blend may include about 70 to about 95 percent by weight of the polyester and about 5 to about 20 percent by weight of the polyamide. The blend preferably includes about 85 to about 95 percent by weight of the polyester and about 5 to about 10 percent by weight of polyamide. Additionally, the blend may include a hydrolysis stabilizing agent. The hydrolysis stabilizing agent may comprise about 0.5 to about 5 percent by weight of the blend, preferrably it comprises about 1.0 percent by weight of the blend. The blend may also include a thermo-oxidative stabilizing agent. The thermo-oxidative stabilizing agent may comprise about 0.05 to about 10 percent by weight of the blend, preferrably it comprises about 5 percent by weight of the blend.
The inventive blends disclosed herein also include a polyester having a polyhydric alcohol component of 1,4-cyclohexanedimenthanol, a polyamide, and a polyolefin. The blend may include about 70 to about 95 percent by weight of the polyester, and about 5 to about 20 percent by weight of the polyamide, and about 1 to about 6 percent by weight of the polyolefin. The blend preferably includes about 85 to about 95 percent by weight of the polyester, and about 5 to about 15 percent by weight of polyamide, and about 1 to about 3 percent by weight of the polyolefin. Additionally, the blend may include a hydrolysis stabilizing agent. The hydrolysis stabilizing agent may comprise about 0.5 to about 5 percent by weight of the blend, preferably it comprises about 1.0 percent by weight of the blend. The blend may also include a thermo-oxidative stabilizing agent. The thermo-oxidative stabilizing agent may comprise about 0.05 to about 10 percent by weight of the blend. If used, it preferrably comprises about 5 percent by weight of the blend.
The term "monofilament", as used herein, is directed to any single filament of a manufactured fiber usually of a denier higher than 14. The term "shaped article", as used herein, is directed to articles which are made by extrusion or molding techniques, including, but not limited to, fibers, films, injection molded articles, and blow molded articles.
The term "polyester having polyhydric alcohol component of 1,4-cyclohexanedimethanol", as used herein, is directed to, but not limited by the polyester material disclosed and claimed in U.S. Patent No. 2,901,466, which is incorporated herein by reference. The polyfunctional acid component may be selected from, but is not limited to, the group of: isophthalic acid; terephthalic acid; derivatives of isophthalic acid; derivatives of terephthalic acid; and combinations thereof. These polyester may be referred to as polycyclohexlandymethanol terephthalate (PCT)-a polyester from the condensation reaction of cyclohexanedimethanol (CHDM) and terephthalatic acid or its derivatives, or PCTA - the condensation product of CHDM, terephthate acid and isothalic acid. Each of the foregoing products are commercially available from the Eastman Chemical Co., of Kingsport, TN under the tradename Eastman 3879 (the PCT product) and "KODAR" THERMX Copolyester Type 13319 (the PCTA product). The PCTA material is preferred. The fiber processability of these materials may be improved by the addition of a minor portion of polyethylene terephthalate. See: British Patent Specification No. 1,040,470 incorporated herein by reference.
The term "polyamide", as used herein, is directed to any of the known polyamide polymers. The polyamide appears to improve the dry-heat strength and hydrolysis resistance of the yarns made from the blend. Exemplary polyamides include, but are not limited to: nylon 6; nylon 6,10; nylon 6,12; nylon 11; nylon 12; nylon 4,6; nylon 6,T; nylon 6,6; and combinations thereof. Nylon 6,6 is preferred. The foregoing nylon materials are commercially available from the Engineering Plastic Division of the Hoechst Celanese Corporation, Summit, NJ.
The term "polyolefin", as used herein, is directed to any of the known polyolefin polymers. The polyolefin appears to improve the ability of the fiber to be formed into a spiral yarn. Exemplary polyolefins include, but are not limited to: polyethylene, polypropylene, polyoctene and copolymers thereof. A copolymer of ethylene/octene is preferred. These materials are commercially available from Dow Chemical Company, Atlanta, GA under the tradename of "ASPUN".
The term "hydrolysis stabilizing agent", is used herein, refers to an "endcapping agent". Endcapping agents are used to prevent degregation of the polyester polymer. This particular form of degradation results from hydrolysis. Exemplary hydrolysis stabilizing agents include the class of chemicals known as carbodiimides. A preferred carbodiimide is known chemically as 2,6-diisopropylphenyl carbodiimide. Such carbodiimides are commercially available under the tradename "STABAXOL", "STABAXOL P", "STABAXOL P-100" from the Rhein Chemie GmbH of Rheinau, Federal Republic of Germany and "CARBO D" from BASF of Parsippany, NJ. "STABAXOL I" and "CARBO D" are preferred.
The term "thermo-oxidative stabilizing agent", as used herein, refers to a material added to prevent degredation of the polyester when subjected to hot dry heat. The preferred material is sold under the commercial name of "KODAR" THERMX 13319 L0001 from the Eastman Chemical Co. of Kingsport, TN.
The polyolefin-containing alloy monofilaments, disclosed herein, are particularly suited for spiraling end uses. Spiraling end uses refer to, for example, fabrics, made from spiraled monofilaments, that may be used in conveyor belts, lay belts, dryer fabrics for paper machines and the like. Spiraled fabrics refer to the following, for example: A monofilament is passed through a spiraling machine in order to make an oval shaped spiral. In this spiraling machine, the monofilament is heated and then wrapped around a mandrel of a specific shape. As new monofilament comes into the spiraling machine and is spiraled, the cooled monofilament wrapped around the mandrel is pushed off the end of the mandrel. These spiraled monofilament coils are then meshed together and a pintle yarn is passed through the intermeshed coils to form an interlocked structure. An entire fabric is constructed by building up the number of coiled structures that are fastened together by pintle yarns. In the open space between the pintle yarns, it is possible to insert an additional monofilament in order to control the air permeability of the fabric. After the fabrics are made, they are heat set in order to fix their dimensional stability. A fabric made from spiraled coils is attractive because it costs less than a woven fabric of similar dimensions. It is also possible to repair a defect in the fabric made from spiraled monofilaments by removing the pintle yarns on either side of the defect, removing the defective portion of the fabric, and inserting a new section in place of the part that was removed. See generally, U.S. Patent No. 4,423,543 which discusses spiral fabrics, and which is incorporated herein by reference.
Other details and aspects of the invention are more fully described in the examples set forth hereinafter. Weights are given as weight percent unless otherwise noted.

EXAMPLES

In the following examples, the manufacture of the present invention (without polyolefins) is illustrated, and a physical property and performance comparison of the present invention to other materials is made. The components and weight percentages of the tested blends are identified in TABLE 1.
The polyester resins are dried to remove moisture. The moisture content of the dried resins should be less than 0.007%. The resins are then transferred into an oxygen free hold vessel located above a three heated zone, single screw extruder. The resins are gravity fed into the extruder. Other components of the blend are added by including the polyamide resins, of the blend are added by metering devices when the resins are gravity fed into the extruder. While in the extruder, all components of the blend are melted and intimately mixed. The set temperatures for each zone are given in TABLE 2. The blend is then melt spun through a spin die or spinnerette to produce monofilaments having a diameter of 0.50 mm. The spin die temperature and blend temperature at extrusion are given in TABLE 2. After leaving the spin die, the monofilaments are quenched in a water bath located beneath the spin die. After quenching, the monofilaments are drawn and heat set. The heat setting occurs in an oven located in the third draw zone. The draw ratios and heat set oven temperatures are given in TABLE 2.
The physical properties of the foregoing monofilaments are given in TABLE 3. "Denier" was calculated by weighing one meter lengths of the monofilament. "Hot air shrinkage" was calculated by placing a sample (one meter in length, coiled into a loop of about 10-11 cm in diameter) into a forced hot air oven set at 200°C for 15 minutes, then removing the sample from the oven, letting the sample cool and finally measuring the length of the sample. "Relative elongation at one gram per denier" (Rel. Elong. @ 1G/D); "elongation at break" (Elong @ Break); and "tenacity" are measured using an Instron Tensile Tester Model #4201 set with a 500mm gauge length, a cross head speed of 500 mm/minute, and using flat faced clamps (the monofilament running over the top of the top clamp to below the bottom of the bottom clamp). "Loop strength" and "knot strength" are measured using the Instron setup noted above, the exceptions being: for "loop" - two monofilaments are joined by intersecting loops; and for "knot" - the monofilament is tied with an overhand knot. "Abrasion cycles to failure" was measured by utilizing a squirrel cage apparatus to abrade weighted monofilament samples. The squirrel cage (diameter 8 3/8 inches; with fifteen 0.2024 inch Precision Brand Product Ind. T302 stainless steel spring tempered wire equally spaced about the periphery of the cage). The squirrel cage is rotated at 60 revolutions per minute. The monofilaments are draped over the squirrel cage from a bar located above top dead center of the cage and weighted with either 50 grams (monofilament diameter less than 0.50mm) or 100 gram (monofilament diameter 0.50mm or more). The results are reported as the number of cycles lapsed at the moment of monofilament breakage.
In TABLE 4, "hydrolysis resistance" of the examples is set forth. The hydrolysis resistance is measured as the percent strength retention as a function of days in a hydrolysis pot. Samples (about one meter in length) are coiled into 3 inch diameter loops. Samples are needed for the initial and each sample day. Samples are placed on a rack inside a consolidated sterilizer autoclave. The autoclave is set to 15 psi and 250°F (121°C) for continuous operation with a 60 minute exhaust time (cool down cycle). On days when samples are to be tested, the autoclave is cooled down and samples are removed and allowed to cool and equilibrate for one day prior to Instron testing. Samples for future test days are reheated in the autoclave as discussed above. Measurement of the "load to break" on samples is performed on an Instron Tensile Tester Model #4201, gauge length-500mm, cross head speed-500 mm/min, and using flat, leather faced clamps. The percent strength retention is calculated against the initial load to break.

In TABLE 5, "dry heat strength" of the examples is set forth. The dry heat strength is measured as the percent strength retention as a function of days in a forced air circulation oven. Samples (about one meter in length) are coiled into 3 inch diameter loops. Samples are needed for the initial and each sample day. Samples are hung from a steel sample holder located eight inches from the top of the inside of the chamber of the forced air circulation oven. The oven is set at a temperature of 175°C for continuous operation. Samples are removed on test days and allowed to cool. Measurement of the "load to break" on samples is performed on an Instron Tensile Tester Model #4201, gauge length-500mm, cross head speed 500mm/min, and using flat, leather faced clamps. The percent strength retention is calculated against the initial load to break.

TABLE 1

SAMPLE	A	B	C	D	E	F	G	H	I
% polyester (CHDM)¹	100	90	99	95	94	89	84	79	74
% polyamide²	-	10	-	-	-	5	10	15	20
% hydrolysis stabilizer ³	-	-	.9	-	.9	.9	.9	.9	.9
% thermo-oxidative stabilizer⁴	-	-	-	5	5	5	5	5	5

Notes: 1. Polyester (CHDM) - "KODAR" THERMX copolyester type 13319 by Eastman Chemical Co., Kingsport, TN.
2. Polyamide - nylon 6,6 by Engineering Plastics Division, Hoechst Celanese Corporation, Summit, NJ.
3. Hydrolysis stabilizer - Stabaxol® 1 by Rhein Chemie GmbH, Rheinau, Federal Republic of Germany.
4. Thermo-oxidative stabilizer - "PCTA 13319 L0001" by Eastman Chemical Co., Kingsport TN.

In the following example, the manufacture of the present invention (with polyolefin) and its physical properties are illustrated. The components and weight percentages of the tested blends are as follows: PCTA (THEMRX 13319) - 87%, Nylon (N186 from Hoechst Celanese) - 10%, polyolefin (ASPUN 6830A, ethylene-1-octene copolymer with 0.1% maleic anydride and 0.05% calcium sterate) - 2%; and hydrolysis stabilizing agent (BASF Carbo D)-0.9%.
The polyester resins are dried to remove moisture. The moisture content of the dried resins should be less than 0.007%. The resins are then transferred into an oxygen free hold vessel located above a three heated zone, single screw extruder. Zone 1 was heated to 299°C, Zone 2 to 305°C, and Zone 3 to 305°C. The resins are gravity fed into the extruder. Other components of the blend, including the polyamide resins and polyolefin resins, are added by metering devices when the resins are gravity fed into the extruder. While in the extruder, all components of the blend are melted and intimately mixed. The blend is then melt spun through a spin die or spinnerette to produce monofilaments having a diameter of 0.70 mm. The spin die temperature was 310°C and blend temperature at extrusion was 327°C. After leaving the spin die, the monofilaments are quenched in a water bath located beneath the spin die. After quenching, the monofilaments are drawn and heat set. The heat setting occurs in an oven located in the third draw zone. The draw ratios are, respectively, 3.2, 1, 1, and heat set oven temperature was 155°C.

The physical properties of the foregoing monofilaments are given in TABLE 6. The test procedures are the same as previously discussed above.

TABLE 6

Denier	4254	4254
Rel. Elong. @ 1G/D (%)	4.7	4.2
HAS @ 200°C (%)	12.5	12.6
Tenacity (G/D)	2.21	2.38
Loop (G/D)	1.83	1.68
Knot (G/D)	1.58	1.42
Elong. @ Break (%)	26.7	26.6
Diameter (mm)	0.709	0.71

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims

A shaped article comprising a blend of a polyester having a polyhydric alcohol component of 1,4-cyclohexanedimethanol, and a polyamide.
An article of paper machine clothing used in the forming, pressing or drying sections of a papermaking machine, said article comprising a fiber structure, said fiber structure being a blend of a polyester having a polyhydric alcohol component of 1,4-cyclohexanedimethanol, and a polyamide.
The blend according to claims 1 or 2 further comprising a polyolefin.
The blend according to claims 1 or 2, wherein said polyester comprises about 70 to about 95 percent by weight of said blend and said polyamide comprises about 5 to about 20 percent by weight of said blend.
The blend according to claims 1 or 2, wherein said polyester comprises about 85 to about 95 percent by weight of said blend and said polyamide comprises about 5 to about 10 percent by weight of said blend.
The blend according to claims 1 or 2, further comprising a hydrolysis stabilizing agent, said hydrolysis stabilizing agent comprising from about 0.5 to about 5 percent by weight of said blend.
The blend according to claim 6 wherein said hydrolysis stabilizing agent comprises a carbodiimide.
The blend according to claim 7 wherein said hydrolysis stabilizing agent comprises about 1 percent by weight of said blend.
The blend according to claims 1 or 2, further comprising a thermo-oxidative stabilizing agent, said thermo-oxidative stabilizing agent comprising from about 0.05 to about 10 percent by weight of said blend.
The blend according to claim 9 wherein said thermo-oxidative stabilizing agent comprises about 5 percent by weight of said blend.
The blend according to claims 1, or 2, or 3 wherein said polyamide is selected from the group consisting of: nylon 6, nylon 6,10; nylon 6,12; nylon 11; nylon 12; nylon 4,6; nylon 6,T; nylon 6,6; and combinations thereof.
The blend according to claim 12 wherein said polyamide is nylon 6,6.
The blend according to claims 1, or 2, or 3, wherein said polyester having a polyhydric alcohol component of 1,4-cyclohexanedimethanol further comprises a polyfunctional acid selected from the group consisting of: isophthalic acid; terephthalic acid; derivatives of isophthalic acid; derivatives of terephthalic acid; and combinations thereof.
The blend according to claim 3, wherein said polyester comprises about 70 to about 95 percent by weight of said blend, said polyamide comprises about 5 to about 20 percent by weight of said blend and said polyolefin comprises about 1 to about 6 percent by weight of said blend.
The blend according to claim 3, wherein said polyester comprises about 85 to about 95 percent by weight of said blend, said polyamide comprises about 5 to about 15 percent by weight of said blend, and said polyolefin comprises about 1 to about 3 percent by weight of said blend.
The blend according to claims wherein said polyolefin is selected from the group consisting of: polyethylene polypropylene, polyoctene, copolymers thereof and combinations thereof.