CN107002301B - Monofilament, helical fabric and method of forming the same - Google Patents

Abstract

The invention discloses the monofilament for the component being particularly useful as in spiral fabrics, are formed by the resin combination comprising thermoplastic polymer, and the thermoplastic polymer has the number-average molecular weight less than 14200g/mol.According to another embodiment, monofilament is formed by the resin combination comprising thermoplastic polymer, and the thermoplastic polymer has the free percent thermal shrinkage less than 1%.According to another embodiment, monofilament is formed by the resin combination comprising thermoplastic polymer, and the thermoplastic polymer has the inherent viscosity less than 0.72dl/g.According to another embodiment, monofilament is formed by the resin combination comprising thermoplastic polymer, and the thermoplastic polymer has the melt viscosity less than 3000P.

Description

Monofilament, helical fabric and method of forming the same

technical field

The present invention relates to a monofilament especially useful as a component in a helical fabric, wherein the monofilament is formed from a resin composition comprising a thermoplastic polymer.

Background technique

Spiral fabrics made from wound polymeric monofilaments are widely used in dryers, conveyors, and other industrial applications. For example, the endless belt of the helical fabric is an important component of the dryer section of a paper machine, which is also referred to as a paper machine cloth (PMC). The paper machine cloth is disclosed, for example, in GB 2141749 A and US 2008/0169039 A1.

The helical fabric may include pivot shafts extending through the cooperating portions of the wound monofilaments and connecting the monofilaments together. Additionally, the helical fabric may be provided with filler elements or filler elements that extend through the central portion of the wound monofilament and serve to control the breathability properties of the fabric as well as support the structural integrity of the fabric. The pivot and/or filling element may likewise be formed of monofilament, preferably elongated rather than coiled monofilament. The wound monofilaments are typically thermomechanically converted into a shaped helical product to form a helical fabric. This thermomechanical method for making helical fabrics generally comprises two heat-setting steps, which are carried out at high temperatures, eg, in excess of 180°C. While the first heat setting step serves to relieve structural stress within the fabric and stabilize the helical shape of the monofilament, the second heat setting step is necessary to stabilize the filling element.

However, heat setting methods are energy and time consuming. For these reasons, there is a need to reduce the energy consumption and production time required to manufacture spiral fabrics.

SUMMARY OF THE INVENTION

For these reasons, an object of the present invention is to provide a monofilament having a low shrinkage rate.

According to a first aspect of the present invention, the objects of the present invention are met by monofilaments especially used as components in helical fabrics, wherein the monofilaments are formed from a resin composition comprising a thermoplastic polymer, wherein the thermoplastic polymer has less than Number average molecular weight of 14200 g/mol.

It has surprisingly been found that monofilaments formed from polymers having this relatively low molecular weight are characterized by exceptionally low shrinkage. In particular, it has been determined that the shrinkage of monofilaments formed from this polymer composition is low enough to eliminate one of the two heat-setting steps in the fabric manufacturing method described above. Omitting one of the heat-setting processes results in significant energy savings and sustainability. Furthermore, this results in a significant reduction in fabric processing time and production costs. Due to the low shrinkage of the monofilaments according to the invention, the monofilaments may even contain recycled polymers. Thus, the present invention can reduce the carbon footprint associated with fabric manufacturing.

According to the present invention, the number average molecular weight is measured by gel permeation chromatography using polystyrene standards.

Particularly good results are achieved when the thermoplastic polymer has a number-average molecular weight of 5000 g/mol to 11000 g/mol.

According to another aspect of the present invention, monofilaments particularly used as components in a helical fabric have a free thermal shrinkage of less than 1%, wherein the free thermal shrinkage is determined as compared to the monofilament length before heat treatment Percent change in filament length after 5 minutes of holding the filament at 177°C in the oven, i.e., where the free thermal shrinkage is (the filament length before holding the filament at 177°C for 5 minutes in the oven minus the filament length in the oven Length of filament after holding filament at 177°C for 5 minutes)/(Length of filament before holding filament at 177°C for 5 minutes in oven). Monofilaments with this low shrinkage, when used as filler yarns and/or pivots in spiral fabrics, offer the possibility to omit a heat setting step during the manufacture of spiral fabrics.

Significantly good results are achieved when the monofilament has a free thermal shrinkage of less than 0.5% and most preferably less than 0.35%.

For some applications, monofilaments that exhibit free thermal shrinkage in the above ranges (<1%, or even <0.5% or <0.35%) are required even under more severe thermal conditions. Thus, according to another aspect of the present invention, monofilaments particularly used as components in helical fabrics have a free thermal shrinkage of less than 1%, wherein the free thermal shrinkage is determined to be relative to the monofilament length prior to heat treatment Compare the percent change in monofilament length after holding the monofilament at 204°C for 5 minutes in the oven, i.e., where the free thermal shrinkage is (the monofilament length before holding the monofilament at 204°C for 5 minutes in the oven minus the Monofilament length after 5 minutes incubation of monofilament in oven at 204°C)/(monofilament length before monofilament incubation in oven at 204°C for 5 minutes).

Since the free thermal shrinkage at 204°C is higher than or at least equal to the free thermal shrinkage at 177°C, a monofilament satisfying the "204°C-condition" can be considered a sub-type of a monofilament satisfying the "177°C-condition" Group.

According to a preferred embodiment of the invention, the thermoplastic polymer in both of the above-mentioned aspects of the invention is polyethylene terephthalate (PET). PET has high dimensional stability, adequate abrasion resistance and low hygroscopicity, and is moreover available at moderate prices. In addition, PET is excellent in tensile properties and processability. Therefore, PET monofilaments are particularly suitable for PMC applications.

According to an alternative embodiment of the present invention, the thermoplastic polymer is polyphenylene sulfide, polyamide, polyolefin or PCTA. The polymers may be advantageous in some applications.

The thermoplastic polymer can be a homopolymer or a copolymer.

In another development of the present invention, it is proposed that the resin composition comprises a hydrolysis stabilizer, which is preferably a monomeric carbodiimide or a polymeric carbodiimide. Preferably, the content of the hydrolysis stabilizer relative to the resin composition is 1-2 wt %. In addition to the hydrolysis stabilizer, the resin composition may contain other additives, such as one or more plasticizers, if desired.

The resin composition may include a thermal stabilizer to minimize thermal degradation.

According to yet another preferred embodiment of the present invention, the monofilament has an annular, oval or rectangular cross-section. Specifically, the cross-sectional shape of the monofilament can be selected according to the type of spiral fabric to be manufactured and the application field of the fabric.

Alternatively, the cross-section of the monofilament may have a "capsule shape", "leaf shape", "concave shape", "UFO shape" or any other suitable shape.

According to yet another preferred embodiment of the present invention, the monofilament has a maximum diameter of 0.005 mm to 5 mm, preferably 0.05 mm to 4 mm. According to the present invention, the term "largest diameter" means the largest dimension in the cross-section of the monofilament. Monofilaments having dimensions falling within this numerical range have been found to be particularly suitable for PMC applications.

Therefore, preferably the monofilament has a linear mass density of at least 50 dtex.

A third aspect of the present invention relates to a monofilament particularly useful as a component in a helical fabric, wherein the monofilament is formed from a resin composition comprising a thermoplastic polymer having a characteristic of less than 0.72 dl/g viscosity. According to the present invention, intrinsic viscosity is measured according to ASTM D4603 using a solvent containing 60% phenol and 40% 1,1,2,2-tetrachloroethane. Because the intrinsic viscosity of a thermoplastic polymer is directly related to its number average molecular weight, the monofilaments according to this aspect of the invention have the same advantages as the above-described monofilaments according to the first and second aspects of the invention.

Remarkably good results were obtained when the thermoplastic polymer had an intrinsic viscosity in the range of 0.35 dl/g to 0.6 dl/g.

A fourth aspect of the present invention relates to a monofilament particularly useful as a component in a helical fabric, wherein the monofilament is formed from a resin composition comprising a thermoplastic polymer having a melt viscosity of less than 3000P, where P indicates poise. Similar to intrinsic viscosity, melt viscosity is a parameter related to the number-average molecular weight of thermoplastic polymers, so the monofilaments according to this aspect of the invention have the same advantages as the above-mentioned monofilaments according to the first to third aspects of the invention .

In another development of the invention, it is proposed that the thermoplastic polymer has a melt viscosity of less than 2000P. Such polymers are capable of forming particularly stable monofilaments.

Furthermore, the present invention relates to a spiral fabric comprising:

- a plurality of wound monofilaments arranged side by side in a cooperating relationship,

- a plurality of elongated pivots extending through the cooperating portions of the wound monofilament, and

- a plurality of filler yarns extending through the central portion of the wound monofilament between adjacent pivots,

wherein the filler yarn and/or the pivot is formed from a resin composition comprising a thermoplastic polymer, and wherein the thermoplastic polymer has a number average molecular weight of less than 14200 g/mol.

This helical fabric is easy to manufacture, cost-effective and stable enough to be used as a drying or conveyor belt in high temperature environments, such as the drying section of a paper machine. It has surprisingly been found that the use of monofilaments formed from relatively low molecular weight polymers enables the omission of one of the two heat setting steps in the fabric manufacturing process. Omitting one of the heat-setting processes results in significant energy savings and sustainability. Furthermore, this results in a significant reduction in fabric processing time and production costs. Due to the low shrinkage of the monofilaments according to the invention, the monofilaments may even contain recycled polymers. Thus, the present invention can reduce the carbon footprint associated with fabric manufacturing.

According to another preferred embodiment of the present invention, the thermoplastic polymer has a number average molecular weight of 5000 g/mol to 11000 g/mol. This molecular weight range has been shown to provide particularly good results.

Alternatively or additionally, the thermoplastic polymer may have an intrinsic viscosity of less than 0.72 dl/g and/or a melt viscosity of less than 3000P.

Furthermore, preferably the filler yarn and/or the pivot has a free heat shrinkage of less than 1%, more preferably less than 0.5% and most preferably less than 0.35%. Filling yarns and/or pivots with this low shrinkage offer the possibility to omit a heat setting step during the manufacture of the spiral fabric.

According to another preferred embodiment of the present invention, the fabric forms an endless belt. This endless belt can be used as a conveyor belt or preferably as a drying belt in a paper machine.

Thus, according to yet another embodiment of the present invention, the fabric has sufficient mechanical and thermal stability for use as a drying belt in a paper machine.

In addition, the present invention relates to a method of forming monofilaments, in particular for use as components in helical fabrics, comprising the steps of:

- providing a resin composition comprising a thermoplastic polymer having a number average molecular weight of less than 14200 g/mol;

- extruding the resin composition through a spinneret to form monofilaments; and

- stretching the monofilament one or more times.

The drawing of the monofilament can be performed according to principles generally known in the art of monofilament manufacturing, except for the use of low molecular weight polymers. Providing a low molecular weight polymeric resin enables the drawing of monofilaments characterized by high thermal stability and exceptionally low shrinkage.

Alternatively or additionally, the thermoplastic polymer may have an intrinsic viscosity of less than 0.72 dl/g and/or a melt viscosity of less than 3000P.

Furthermore, preferably the monofilament has a free thermal shrinkage of less than 1%, more preferably less than 0.5% and most preferably less than 0.35%. Monofilaments with this low shrinkage, when used as filler yarns and/or pivots in spiral fabrics, offer the possibility to omit a heat setting step during the manufacture of spiral fabrics.

In another development of the invention, it is proposed that the resin composition is prepared at least partly from recycled polymer. The use of recycled polymers not only reduces production costs, but also reduces carbon footprint.

According to yet another preferred embodiment of the present invention, the monofilament is drawn one or more times at a total draw ratio of 3.0 to 6.0. The draw ratio is favorable for the mechanical properties of the monofilament.

Remarkably good results were obtained when the monofilament was drawn one or more times in an oven at a temperature of 90°C to 250°C.

According to another aspect, the present invention relates to a method of forming a helical fabric comprising the steps of:

a. Provide multiple winding monofilaments,

b. Arranging the wound monofilaments side by side in a cooperating relationship,

c. extending a plurality of elongated pivot shafts through the cooperating portions of the coiled monofilament,

d. Extending a filling element with a free thermal shrinkage measured in an oven at 177°C for 5 minutes of less than 1%, preferably less than 0.5% and most preferably less than 0.3% through the winding sheet between adjacent pivots the central part of the wire, and

e. The arrangement of the wound monofilament and the pivot shaft is heat-set at elevated temperature, releasing structural stress of the monofilament.

Using filler yarns with low shrinkage to produce helical fabrics provides a more efficient manufacturing method. In particular, the use of low shrinkage filling elements has been found to eliminate the need for a second heat setting step, thus promoting energy savings and sustainability.

In another aspect of the present invention, it may be desirable for the filling element to have even better resistance to free thermal shrinkage. Therefore, it may be useful to replace step d of the above mentioned method with the following steps:

b ^* Extend a filling element with a free thermal shrinkage measured in an oven at 204°C for 5 minutes of less than 1%, preferably less than 0.5% and most preferably less than 0.3% through the winding sheet between adjacent pivots the central part of the wire.

According to another preferred embodiment of the present invention, the filling element is drawn from a resin composition comprising a thermoplastic polymer having a number average molecular weight of less than 14200 g/mol.

Alternatively or additionally, the filling element may be drawn from a resin composition comprising a thermoplastic polymer, wherein the thermoplastic polymer has an intrinsic viscosity of less than 0.72 dl/g and/or a melt viscosity of less than 3000P.

Preferably, the pivots are likewise formed from monofilaments having a free thermal shrinkage of less than 1%, preferably less than 0.5%, most preferably less than 0.3%, wherein the free thermal shrinkage is determined to be the same as that prior to heat treatment Monofilament length compared to the percent change in monofilament length after holding the monofilament in an oven at 177°C for 5 minutes. Furthermore, for special applications, a pivot with higher resistance to free thermal shrinkage may be required. Here, the pivots may be formed from monofilaments having a free thermal shrinkage of less than 1%, preferably less than 0.5% and most preferably less than 0.3%, wherein the free thermal shrinkage is determined to be the same as the monofilament before heat treatment Filament length compared to percent change in monofilament length after holding the monofilament in an oven at 204°C for 5 minutes.

According to another preferred embodiment of the present invention, the filling element extends through the central portion of the wound monofilament between adjacent pivots prior to the step of heat setting the arrangement of the wound monofilament and the pivot at high temperature .

Alternatively, the filling element may extend through the central portion of the wound monofilament between adjacent pivots after the step of heat-setting the arrangement of the wound monofilament and the pivot at high temperature.

Preferably, the arrangement of the wound monofilament and pivot is not subjected to any further heat treatment after the heat setting step.

Furthermore, the present invention relates to the use of the above-mentioned monofilaments for forming helical fabrics.

Description of drawings

Next, the present invention is explained in more detail based on exemplary embodiments with reference to the accompanying drawings, in which:

1A is an enlarged side view of a helical fabric made from wound monofilaments, pivots, and filler yarns;

Figure IB is an enlarged side view of a helical fabric according to an alternative embodiment;

Figure 2 is a plan view of the spiral fabric of Figure 1;

Figure 3 is a perspective view of an endless belt formed from the spiral fabric of Figures 1 and 2; and

4 is a graph showing the correlation between the intrinsic viscosity of a PET solution and the number average molecular weight of PET;

Figures 5a, 5b, 5c and 5d are schematic drawings of various cross-sections of a monofilament according to the present invention.

Detailed ways

In Figures 1A, 1B and 2, a fabric 12 is shown formed from a plurality of wound monofilaments 14 that cooperate with each other in the machine direction MD to form a continuous loop. As shown in FIG. 3 , the fabric 12 is formed to provide an endless belt 20 . At the intersection 16 of the wound monofilament 14, there is an arrangement of pivots 18 extending perpendicular to the longitudinal direction MD. After the interlaced winding monofilament 14 and insertion into the pivot 18, the filling element 10 is inserted to extend perpendicular to the machine direction MD. The filling element 10 shown in FIG. 1A has a circular cross section, whereas the filling element 10 ′ shown in FIG. 1B has a substantially rectangular cross section with slightly rounded corners. In order to stabilize the monofilaments 14 in helical form and to relieve the thermal stress within the monofilaments 14, the fabric 12 is subjected to a heat treatment known as heat setting at temperatures in excess of 180°C.

While monofilaments particularly useful as filler yarns can have standard cross-sectional shapes, such as circular, rectangular (often with rounded corners), or oval, other shapes are possible and may be beneficial for certain applications. Some embodiments are shown schematically in Figures 5a-5d. It should be noted that geometric details such as aspect ratios or radii of the curves are only examples. The true value may be different in actual application.

Figure 5a shows a "capsule shape" with flat top and bottom sides and strongly curved left and right sides. These can be semicircular, for example.

Figure 5b shows a "leaf shape" with curved top and bottom sides. This shape can also be described as the shape of a lens.

Figure 5c shows "concave". Here, the top, bottom and side edges are bent to the inside of the monofilament. The four corners may be pointed, or as shown in Figure 5c, may be rounded.

Figure 5d shows a "UFO shape", where the middle portion is generally circular in Figure 5d, but extends slightly to the left and right, giving the appearance of a UFO in a monofilament cross-section.

Filling elements 10, 10' and pivot 18 are formed from a resin composition comprising a thermoplastic polymer and carbodiimide, as described above and below in the exemplary embodiments.

Example

Different monofilament samples were made based on recycled polyethylene terephthalate (PET). More specifically, the PET monofilament chips were pelletized and the resin composition was prepared from the pelletized PET monofilament chips. The intrinsic viscosity of the resin composition was measured according to ASTM D4603 with a solvent combination of 60% phenol and 40% 1,1,2,2-tetrachloroethane. Monofilaments were prepared by extrusion and then drawn from each resin composition at different draw ratios and at different oven temperatures to have a length of 1 meter. The obtained samples were kept in a closed hot air oven at 177 °C for 5 min under unrestricted conditions. (Alternatively, if heavy duty filaments are desired, the samples can be kept in a closed hot air oven at 204°C for 5 minutes under unrestricted conditions.) After this hot air treatment, the change in length of each sample is measured And from this, the percent free shrinkage is calculated.

Intrinsic viscosity is related to the average molecular weight of PET. The correlation between the intrinsic viscosity and the corresponding molecular weight of the PET solution is shown in Figure 4, which is essentially linear. It should be noted that the intrinsic viscosity is the ratio of the natural logarithm of the relative viscosity of the polymer to the mass concentration, while the intrinsic viscosity is the reduced viscosity or the limit of intrinsic viscosity at infinite dilution of the polymer.

Table 1 shows the properties of two monofilament samples 1 and 2 according to the invention and two comparative examples. From Table 1 it can be deduced that the use of low viscosity PET compositions (which is equivalent to using low molecular weight PET) produces monofilaments with a free shrinkage of less than 1%. This low shrinkage eliminates the need for a second heat setting step in the manufacturing method of the spiral fabric as shown in FIG. 1 .

Table 1: Tensile Properties of Monofilaments

List of reference numbers:

10,10' fill element

12 fabrics

14 monofilament

16 intersection

18 pivot

20 endless belt

MD portrait

Claims (21)

1. one kind is particularly useful as the monofilament of the component in spiral fabrics (12), it is less than wherein the monofilament (10,10', 18) has 1% free percent thermal shrinkage, wherein the free percent thermal shrinkage is confirmed as compared with filament length before the heat treatment The percentage of the variation of filament length after in an oven keeping the temperature monofilament 5 minutes at 177 DEG C, wherein the monofilament (10,10', 18) it is formed by the resin combination comprising thermoplastic polymer, the thermoplastic polymer has 5000g/mol~11000g/ Number-average molecular weight and the thermoplastic polymer within the scope of mol have the inherent viscosity less than 0.72dl/g.

2. monofilament according to claim 1, wherein there is the monofilament (10,10', 18) the freely heat less than 0.5% to receive Shrinkage.

3. monofilament according to claim 2, wherein there is the monofilament (10,10', 18) the freely heat less than 0.35% to receive Shrinkage.

4. monofilament according to any one of claim 1-3, wherein the monofilament (10,10', 18) has less than 1% Free percent thermal shrinkage, wherein the free percent thermal shrinkage is confirmed as compared with filament length before the heat treatment in baking oven In 204 DEG C by monofilament keep the temperature 5 minutes after filament length variation percentage.

5. monofilament according to claim 4, wherein there is the monofilament (10,10', 18) the freely heat less than 0.5% to receive Shrinkage.

6. monofilament according to claim 5, wherein there is the monofilament (10,10', 18) the freely heat less than 0.35% to receive Shrinkage.

7. monofilament according to any one of claim 1-3, wherein the thermoplastic polymer is poly terephthalic acid second Diol ester.

8. monofilament described in any one of claim 1 to 3, wherein the thermoplastic polymer is polyphenylene sulfide, polyamides Amine, polyolefin or PCTA.

9. monofilament according to any one of claim 1-3, wherein the thermoplastic polymer is homopolymer.

10. monofilament according to any one of claim 1-3, wherein the thermoplastic polymer is copolymer.

11. monofilament according to any one of claim 1-3, wherein the resin combination includes hydrolysis stabilizer.

12. monofilament according to claim 11, wherein the hydrolysis stabilizer is that monomer carbodiimide or polymerization carbon two are sub- Amine.

13. monofilament according to any one of claim 1-3, wherein the resin combination includes heat stabilizer.

14. monofilament according to any one of claim 1-3, wherein the monofilament (14) has annular, ellipse or square Shape cross section.

15. monofilament according to any one of claim 1-3, wherein the monofilament (14) has 0.005mm~5mm most Major diameter.

16. monofilament according to claim 15, wherein the monofilament (14) has the maximum gauge of 0.05mm~4mm.

17. a kind of method for forming monofilament described in any one of -16 (10,10', 18) according to claim 1 comprising following Step:

Resin combination comprising thermoplastic polymer is provided,

The resin combination is extruded to form monofilament through spinning head；With

It is one or many to stretch the monofilament (10,10', 18).

18. according to the method for claim 17, wherein the thermoplastic polymer is with 5000g/mol~11000g/ The thermoplastic polymer of number-average molecular weight within the scope of mol.

19. according to the method for claim 17, wherein the resin combination at least partly polymer by recycling Preparation.

20. method described in any one of 7-19 according to claim 1, wherein the monofilament is with total drawing in 3.0~6.0 ranges It stretches more one or many than stretching.

21. method described in any one of 7-19 according to claim 1, wherein the monofilament is in an oven at 90 DEG C~250 DEG C Temperature tensile in range is one or many.