JPS60252708A - Spinneret for melt spinning of thermoplastic polymer - Google Patents

Abstract

PURPOSE:To uniformize the viscosity of the molten polymer near the spinneret, and to improve the filtering efficiency, by placing a porous plate which generates Joule heat by electrical current nearly parallelly to the surface of the spinneret opposite to the extrusion side interposing a gap therebetween. CONSTITUTION:The molten polymer supplied to the upper block 2 is passed through the porous plate 4 to obtain molten liquid having low impurity content and having uniform temperature by the filtering and heating actions of the plate, and the liquid is extruded through the nozzle 6' of the spinneret 6. The porous plate 4 is electrified through the terminals 5 using a slider for voltage control and a transformer for voltage transformation, and the required amount of Joule heat is generated. The porous plate is e.g. a laminate manufactured by sintering three sheets of stainless mesh.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a melt spinneret device for thermoplastic synthetic fibers.

b. Prior art In general, the melt spinning process for thermoplastic synthetic fibers consists of a chip drying process to prevent a decrease in molecular weight due to hydrolysis, a melting process in which the chips are heated and melted to form a melt, which is then supplied in a fixed amount, and a melt that is supplied in a fixed quantity. An r-filtration step for removing foreign matter in the liquid, a discharge step for discharging the r-filtered melt from the pores to form a trickle, a cooling step for solidifying the discharged melt trickle with a cooling air stream, and a melt It also serves as a pulling mechanism to stretch and thin the trickling stream during the cooling and solidification process.

A conventional melt spinneret device has a structure in which a P material and a spinneret are housed in a metal block maintained at a constant temperature, and includes the above-mentioned r-passing process and discharge process.

In order to spin as many fibers as possible with such a spindle device, it would be sufficient to make one spindle large and arrange many pores at high density, but the temperature of the polymer at each pore As the pore density increases, it becomes equal.

As it becomes increasingly difficult, the number of pores is limited to the order of several thousand at most, even in fiber spinning, which seeks to spin a large number of fibers.

Conventionally, the basic idea of temperature uniformity in spinneret equipment is to increase the heat capacity of the entire spinneret equipment, including the f-material and the spinneret, as much as possible (to maintain temperature uniformity throughout the equipment, and to reduce the flow rate inside the equipment). This idea attempts to equalize the temperature of the melt.However, this approach not only increases the size of the entire device and increases thermal energy loss, but also creates a contradiction in that the area of the die itself cannot be made very large. The reason for this is that with a cap that maintains temperature simply by heat conduction, the larger the area, the greater the influence of the cooling air, which tends to cause an uneven temperature drop. A uniform temperature drop makes melt discharge in the pores of the nozzle uneven, and causes knealing and yarn breakage phenomena, which is unfavorable in terms of process stability and quality control.In order to prevent uneven temperature drop on the nozzle surface, By attaching a cross-sectional plate to a part of the surface of the cap, or more aggressively,
There is also an attempt to preheat and install a heat insulating board, as described in Japanese Patent Publication No. 47-8169. However, attaching some type of heat insulating material to the spindle itself in this way means that the area in which the pores are arranged is reduced, so it is not suitable for the purpose of spinning a large number of fibers.

On the other hand, the conventional melt spinneret 1jtij also has problems with regard to thermal decomposition of the polymer. Generally, when thermoplastic polymers are melted, more or less thermal decomposition occurs. The higher the melting temperature and the longer the time, the more intense thermal decomposition occurs, so it is desirable to melt at the lowest possible temperature and spin in a short time to prevent thermal decomposition. However, in conventional spinning equipment, when melting at low temperatures, crystallized parts and high molecular weight parts within the polymer are not completely melted and become mixed as unplasticized particles, and the melt viscosity is too high, resulting in problems such as melt fracture phenomena. Since abnormal flow occurs and spinning stability decreases, the temperature in the melting process is set high, ignoring some thermal decomposition.
In the spinneret device, efforts are focused exclusively on removing foreign substances such as thermal decomposition products and maintaining the optimum spinning temperature.

As one successful example of solving the above two problems, there is a melt spinning apparatus described in Japanese Patent Application Laid-Open No. 58-91804, which was previously proposed by the present inventors.

This device generates Joule heat by directly applying electricity to a mesh-like spinneret, which has a pore density several tens to hundreds of times higher than that of conventional spinnerets, thereby directing cooling air to the surface of the spinneret. It maintains a constant temperature against spraying. That is, in this device, the temperature of the cap itself is detected by a temperature measuring element, and this is fed back to the voltage regulator to increase or decrease the amount of current, thereby controlling the temperature of the cap to a constant temperature. This solves problem 1. Furthermore, the second problem has basically been solved by a method that can be called an instant melting method. That is, in the melting step, the polymer is melted at the minimum temperature that allows a constant flow supply, and the optimum spinning temperature is instantaneously raised by y in the spinneret. According to this equipment, even if the optimum spinning temperature is a temperature that is commonly considered dangerous for thermally decomposing the polymer, the temperature is raised for only a few seconds at most, so the risk of decomposition reactions is extremely small. Become.

However, in the apparatus described in Japanese Patent Application Laid-open No. 88-91804, it is difficult to use a conventional ordinary spinneret. This is because the conventional cap is approximately 10 meters thick, which is not only too thick to generate Joule heat, but also
This is because the shape is complicated, so it is difficult to maintain a uniform temperature throughout the cap.

According to the results of the inventor's intensive research to improve the invention described in JP-A No. 58-91804, it was found that a mesh-like spinneret with relatively thick slits was used. In the case of instant melting, the heating time is so short that the temperature of the polymer passing through the center of the slit may not be raised sufficiently, and depending on the type of polymer, it may take several minutes to several tens of minutes. There are many polymers that hardly decompose even if they are melted at the optimum temperature for spinning, so if the dangerous range is within a short range of several seconds to tens of seconds, there are many polymers that hardly decompose even if they are melted at the optimum temperature for spinning. However, it was found that non-uniformity of the melting temperature can be prevented by providing a melting time within an allowable range.

C.Object of the Invention The first object of the present invention is to equalize and stabilize the temperature of the molten polymer near the spinneret and to break it when producing a large number of synthetic fiber bundles from a thermoplastic polymer by the melt spinning method. It is an object of the present invention to provide a melt spinneret device that reduces troubles such as yarn and knealing.

A second object of the present invention is to provide a spinneret device that can provide good spinning stability even when the polymer temperature during the melting process is kept to a minimum in order to suppress thermal decomposition of the thermoplastic polymer as much as possible. There is a particular thing.

A third object of the present invention is to provide a more advanced fiber aggregate manufacturing apparatus as proposed by the present inventors and described in Japanese Patent Application Laid-Open No. 58-91804.

Other objects of the invention will become apparent from the description below.

d Structure of the Invention According to the research of the present inventor, the object of the present invention is to provide a perforated plate having a diameter of 5 so that Joule heat is generated at a temperature higher than the melting point of a thermoplastic polymer when energized, to reduce the melting weight of a spinneret. It is installed in the vicinity of the direction opposite to the discharge side of the coalescence, separated from the spinneret surface in y-parallel, and the molten polymer passing through the perforated plate is heated and immediately supplied to the spinneret surface for melt spinning. It has been found that this can be achieved by a thermoplastic polymer melt spinneret device characterized by:

In the spinneret device of the present invention, a temperature measuring element is installed between the perforated plate and the spinneret to detect the temperature of the molten thermoplastic polymer, and the amount of current applied to the perforated plate is controlled based on the temperature. It is even more advantageous to do so.

The melt spinneret device of the present invention will be explained in more detail below.

In the spinneret device of the present invention, the perforated plate has the function of generating Joule heat and melting the thermoplastic polymer when energized, so it is advantageous that the porous plate is formed of a conductor having a resistivity of 2 to 200 μΩ. . Therefore, this perforated plate has the effect of heating the molten polymer passing through the slits of the perforated plate to a desired constant temperature since Joule heat is generated by controlled energization.

This perforated plate is preferably one in which the cross section perpendicular to the current direction is uniform and the porous structure is substantially the same in any cross section; such a perforated plate allows the polymer to pass through any pores. If the original temperature is the same, then y
They have the advantage of being heated to the same temperature at the same rate.

Preferred examples of such perforated plates include wire mesh with a mesh size of 10 to 500 or a lamination of a plurality of wire meshes, and
It is a sintered metal with a diameter of ~150 μm or a punching plate with a hole diameter of 0.3 to 3 m and a porosity of 10 to 40 mm, which has a large number of fine through holes, and has a heating filtration effect on the polymer. . Among these, particularly preferred are 1
It is a perforated plate made of one or more wire meshes.

In the perforated plate of the present invention, unplasticized particles or abnormally high viscosity arms (for example, spherulites formed in the raw material solid polymer or abnormally high molecular weight polymer) in the polymer that is melted and supplied to the perforated plate In order to slowly pass through the slits of the perforated plate,
It is heated sufficiently and melts, thus reducing the viscosity and exhibiting good fluidity. On the other hand, a portion that is sufficiently melted from the beginning and has a low viscosity quickly passes through the slits of the perforated plate without being heated much. In any case, the polymer passing through the perforated plate will be subjected to a microscopic viscosity-uniforming effect. Furthermore, foreign substances such as thermally degraded polymers and side reaction products caused by heating are retained and heated within the perforated plate, change into stable carbides, and remain within the perforated plate. Thus, since the perforated plate of the present invention has the above-mentioned functions and actions, it has an extremely good r-perturbation rate, and has a simple and simple structure without the need to make it complicated and dense like the r-material in conventional spinning equipment. Therefore, f overpressure also becomes small.

As described above, the spinneret device of the present invention has a porous plate heated by energization, which is installed in the vicinity of the side opposite to the discharge side of the molten polymer and parallel to the spinneret surface. Not only can a molten polymer heated to a constant temperature be constantly supplied to the tube, but it also has the effect of preventing the temperature of the die surface from decreasing due to the cooling air.

That is, in a conventional cap device, that is, a cap device without a perforated plate, the temperature of the cap and its support body decreases or fluctuates due to the cooling air, which causes a decrease or fluctuation in the temperature of the polymer near the cap, and A vicious cycle is repeated in which the polymer whose temperature has decreased comes into contact with the mouthpiece and promotes the drop or fluctuation of the mouthpiece temperature, but in the mouthpiece device of the present invention, the polymer having a much larger heat capacity than the cooling air (for example, air) is used. In addition to the temperature of the polymer near the cap, which is always supplied to the cap at a constant temperature regardless of the temperature of the cap or its support, the temperature of the cap does not drop or fluctuate, or even if it occurs, it is extremely becomes smaller.

Further, the spinneret device of the present invention has an effect of preventing thermal decomposition during melt spinning at a temperature dangerous for thermal decomposition, and is therefore extremely industrially advantageous. The reason for this is that during the polymer melting process, the polymer is heated to a temperature at which there is no risk of thermal decomposition, and then the temperature is rapidly raised to a dangerous temperature for thermal decomposition using a perforated plate that is heated with electricity.
This is because it can be easily supplied to the die immediately without giving the time required for thermal decomposition.

Particularly, according to the spinneret device of the present invention, the supply time of the instantaneously heated polymer to the spinneret as described above can be controlled by controlling the distance (d) between the perforated plate and the spinneret. It is possible to change it appropriately.

In the spinneret device of the present invention, the distance between the perforated plate and the spinneret (
d) is preferably in the range of 2 to 20 nt, preferably 3 to 15+ nt, and the thickness of the cap is advantageously in the range of 0.3 to 3 nt, preferably 0.2 to 2 nt. .

The thermoplastic polymers that can be melt-spun using the spinneret apparatus of the present invention are broader than the range of polymers commonly applied in known melt-spinning processes, and may include a large number of different polymers. can. An example is shown below.

(1) Polyolefin or polyvinyl polymer; For example, polyethylene, polypropylene, polybutylene,
Polystyrene, polyvinyl chloride, polyvinyl acetate, polyacrylonitrile napolyacrylate, or mutual copolymers thereof.

(11) Polyamide: Aliphatic polyamide such as polye-cabulactam, polyhexamethylene adivamide, and polyhexamethylene sebamide.

For example, polyparaphenylene isophthalamide.

Aromatic polyamides such as polyparaphenylene isophthalamide, polyparaphenylene terephthalamide, and polymetaphenylene terephthalamide.

(iii) polyester; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, diphenyl dicarboxylic acid, naphthalene dicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, sepatic acid, decane dicarboxylic acid; Alicyclic 1 dicarboxylic acids such as hydroterephthalic acid are used as the dibasic acid component, and ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, decamethylene glycol dediethylene glycol, 2,2-dimethylpurpanediol, etc. A polyester or a wholly aromatic polyester having as a glyfur component an aliphatic glycol such as aliphatic glycol such as cyclohexane dimetatool, an aromatic aliphatic glycol such as xylylene glycol, or an aromatic dihydroxy compound such as resorcinol or hyde-1 quinone.

These polyesters or wholly aromatic polyesters may also contain a component of oxycarboxylic acid such as p-oxybenzoic acid. The above-mentioned dibasic acid component or glycol component may be contained in the above-mentioned polyester or wholly aromatic polyester singly or in combination of two or more.

Particularly preferred examples include polyethylene terephthalate pipes, polytetramethylene terephthalate, polytrimethylene terephthalate, U.S. Pat. Polyester elastomer described in No. 3,036 or US Pat.
, No. 990, No. 3,036,991 and No. 3,6.
Fully aromatic polyesters and other polymers described in No. 37,595, etc. Polycarbonates using polyether sulfone, polyphenylene sulphide, and various bisphenols in addition to the polymers (1) to (iiO) described above; Poly 7 cetal; each pole polyurethane; polytetrafluoride diethylene t polytrifluorochloroethylene, polyvinylidene difluoride.

polytetrafluoroethylene-propylene hexafluoride copolymer, polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene-ethylene copolymer, polytetrafluoroethylene-bu p-pyrene copolymer, The above-mentioned fluorine-containing thermoplastic polymers such as polyvinyl fluoride or polytrifluorochloroethylene-ethylene copolymer may be used alone (or may be a mixture of two or more types). The polymer may contain a softening agent, a viscosity increasing agent, etc. in order to increase plasticity and melt viscosity.The polymer may also contain a pre-an stabilizer, which is usually used as an additive for fibers, Pigments, heat stabilizers, flame retardants, lubricants, matting agents, etc. may be contained.

Furthermore, the polymer is not necessarily limited to a linear polymer, but may be a partially crosslinked three-dimensional polymer that exhibits fiber-forming properties at least temporarily.

Further, a part of a soluble liquid medium may be contained in the melting chamber, and an inert gas or a gas generating agent may be added.

Among the thermoplastic polymers described above, polyvinyl chloride, polyvinyl acetate, polyacrylonitrile, polyacrylic acid ester.

JJ tl ＾ Turtle〕 ＃ζノ 、-II Noteill
When melted, some polyfluorinated ethylene and various aromatic polyamides undergo decomposition and crosslinking in a short period of time, making continuous production of fibers by melt spinning impossible with conventional methods. Although difficult, the use of the apparatus of the present invention makes it possible to spin these polymers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus of the present invention will be explained in detail below by way of examples together with the accompanying drawings.

Example 1 FIG. 1 is a sectional view of a spinneret device showing one embodiment of the device of the present invention, including a polymer melt supply port, an upper block 2. Patsukin 3. Perforated plate 4, current-carrying terminal 5. Base 6. It is composed of a temperature measuring body 7 and a lower block 8.

A thermoplastic polymer melt melted in a melting process using an extruder or the like is metered into the upper block 2 from a melt supply 1''1 by a metering pump. The melt supplied into the upper block eventually passes through the perforated plate 4,
At this time, it is subjected to overheating and heating to become a molten liquid with a constant degree of thirst with few foreign substances, which is immediately supplied to the mouthpiece 6 and pores 6'.
is discharged to the outside. The discharged molten liquid trickle is cooled by external cooling air and is stretched out by a pulling device and solidified into fibers.

The porous plate 4 is installed so that it can generate the necessary Joule heat by being energized by an ordinary AC power supply via a voltage dispensing slider and a voltage conversion transformer 5. The perforated plate has substantially uniform material and structure along its surface so that Joule heat is generated uniformly over its entire surface.
It is desirable that the structure and shape of the cross section be uniform.

In this example, one of the preferred materials for such a perforated plate is used.
A three-ply sintered laminate of stainless steel wire mesh was used.

Furthermore, in order to increase the transient efficiency of this laminate, as shown in FIG. # of (4-c)
It has an r@ structure.

The shape of the cap is usually circular, but in the device of the present invention, it is preferable to have a rectangular shape like the above-mentioned perforated plate, so in this example,
The entire apparatus shown in FIG. 1 was a box-shaped rectangular parallelepiped, the nozzle 6 was rectangular, and the spinning area was 600 m long and 30 m wide.

Regarding the pores of the spindle, in order to spin as many fibers as possible from one spindle, circular nozzle-shaped pores with a diameter of 0.3 mm are arranged in a 60' staggered pattern with a hole spacing of 1.5 m. It was set at 8,000.

As shown in FIG. 1, the perforated plate 4 and the cap 6 are installed close to each other, and are located in the middle between them.

A temperature measuring element 7 is installed. The temperature measuring element 7 detects the temperature of the melt that has passed through the perforated plate 4, feeds it back to the energization amount control device, operates the voltage adjustment slider, controls the amount of energization to the perforated plate, and adjusts the temperature of the melt. can be held constant.

Therefore, in order to accurately control the melting temperature near the spinneret, which is most important for spinning, it is preferable that the distance (d) between the perforated plate and the spinneret be as close as possible; Taking into consideration the uniform flow of , then d = 8 m.

The above apparatus was prepared, and polyethylene terephthalate having an intrinsic viscosity of 0.65 measured with a 30°0 O-proprophenol solution was supplied as a melt at 285°0 to the above apparatus, and the temperature was increased to 287°C. An attempt was made to extrude the material at a speed of 800 m/min and spin it at a speed of 800 m/min. That is, the melt supplied at 285'O was raised by 2°0 using the perforated plate 4 which was electrically heated, and then supplied to the nozzle and discharged.

As a result, the density of pores and the total number of pores in the five spindles were much higher than the normal spinneret pressure, so even though cooling air was blown directly under the spinnerets to prevent the fibers from adhering to each other, spinning was not possible. was in extremely good condition. For comparison, when the power supply to the perforated plate was stopped, yarn breakage and knealing began to occur frequently over time, and spinning became impossible after about 1 hour. At that time, the temperature of the melt between the perforated plate and the cap was 268'0.

Embodiment 2 FIG. 3 is a sectional view of a spinneret device showing another example of the apparatus of the present invention, in which the melt supply port 10. Lower boot stock 20. It is composed of a gasket 30°, a perforated plate 409, a conductive terminal 50-a for the metal, a conductive terminal 50-b for the perforated plate, a base 60, and a temperature sensing element 70. The thermoplastic polymer melt melted in the melting process of Ex-F Ruder etc. is transferred from the melt supply port 10 to the lower boot tank 20 by a metering pump.
A fixed amount will be supplied within the period. The melt supplied into the lower block is supplied to the upper part (in the direction opposite to the direction of movement) through a number of nozzles 80, and eventually passes through the perforated plate 40, but at this time it is subjected to over-effect and heating. The melt becomes a constant temperature melt containing few foreign substances, is immediately supplied to the die 60, and is extruded to the outside through the slit of the die 60.

The spinneret 60 in this embodiment is approximately the same as the spinneret described in JP-A-58-91804, proposed by the present inventors. That is, the base is
It has a large number of closely spaced pores with a porosity expressed by the following formula % () of approximately 10% or more, and the partition member surrounding the large number of slits is free from conductors that can generate Joule heat. It is what it is.

The molten liquid Kff discharged onto the nozzle as it is will only form a continuous liquid surface on the nozzle and will not form fibers at all, but as described in Japanese Patent Application Laid-open No. 5B-91804,
When the molten liquid is drawn upward while blowing a strong cooling air on the surface of the die, the continuous molten liquid is converted into a fibrous stream and a large number of fibrous bundles are obtained. The electric current of this cooling wind is much stronger than that of ordinary melt-spinning.

Caution is required.

In this embodiment, a 70-mesh stainless steel wire mesh is used as the perforated plate, and the lead, energization, and control method are the same as in the first embodiment.

The spinneret 60 of this embodiment is a mesh-like spinneret, and is preferably made of a wire mesh, an etched metal porous plate, a punched metal plate, etc. as described in JP-A-58-91804. Adopts mesh plain weave stainless steel wire mesh. The fiber forming area in one die has a length of 600 mm and a width of 30 mm, which is exactly the same as the perforated plate 40.

A suitable voltage is applied to this mesh-like base 60 from a terminal 50-a from a power source similar to that of the porous plate 40, and the temperature is set so that Joule heat is generated.

The distance d between the perforated plate 40 and the cap 60 is 1'0, and a temperature measuring element 70 is installed in the middle between the two to detect the temperature of the melt and adjust the amount of current flowing through the perforated plate. .

With the above apparatus prepared, polymotylene terephthalate having an intrinsic viscosity of 1.00 measured with a 0-10 phenol solution at 30°O was supplied as a melt at 270°0 to the melt supply port IO. An attempt was made to spin approximately 450,000 fibers by raising the temperature to 310'O, the optimum temperature for spinning, using a perforated plate 40 heated by electricity, and holding the temperature for 15 seconds.

As a result, the comparison, spinning, and thread tension were extremely good compared to the method that does not use any perforated plate.

In addition, when the intrinsic viscosity of the obtained fiber was measured, it was 0.98, which indicates that the degree of decomposition is extremely low compared to the value of 0.87 for the fiber obtained by melting at 310'O from the beginning. I understand.

According to the apparatus K of the invention as described above, it is possible to stably melt-spun a large number of fibers from one spinneret apparatus, with fiber density and total number of fibers per 1 d of spinneret reaching several times to several tens of times that of conventional apparatuses. .

Furthermore, the apparatus of the present invention can take measures to prevent thermal decomposition without sacrificing spinning stability compared to conventional melt spinning devices. Not only plastic polymers but also polymers whose degree of thermal decomposition is too high at the optimum viscosity for stable melt spinning can be melt-spun with a low degree of decomposition.

Further, according to the apparatus of the present invention, it is possible to supply the polymer to one die IT with the polymer melting temperature at a minimum during the melting process, and to raise the temperature to the required strength immediately before the die, resulting in a large energy saving effect.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a spinneret device showing one embodiment of the device of the present invention. 1 is a melt supply port, 2 is an upper pull, 3 is a gasket, 4 is a perforated plate, 5 is a through W terminal, 6 is a base, 7 is a temperature measuring element, and 8 is a lower pull. FIG. 2 is an enlarged cross-sectional view of a sintered wire mesh laminate showing a specific example of the perforated plate 4 shown in FIG. 4-IL is 30 mesh wire mesh,
4-b is a 70-mesh wire mesh, and 4-c is a 100-mesh wire mesh. FIG. 3 is a cross-sectional view of a spinneret apparatus showing another embodiment of the apparatus of the present invention. IO is the melt supply port, 20 is the lower pull, 30 is the packing, 40 is the perforated plate, 50-& is the current-carrying terminal for the base, 50-b is the current-carrying terminal for the perforated plate, 60 is the base, and 70 is the temperature measuring element. be.・・・”〆′

Claims (1)

[Claims] 1. A porous plate that generates Joule heat at a temperature higher than the melting point of the thermoplastic polymer when energized is placed near the spinneret in the opposite direction from the molten polymer discharge side. Melt spinning of a thermoplastic polymer, characterized in that the molten polymer passing through the perforated plate is heated and immediately supplied to the spinneret surface for melt spinning. Base device. 2. Item 1, in which a temperature measuring body is installed between the perforated plate and the spinneret to detect the temperature of the molten thermoplastic polymer, and the amount of current applied to the perforated plate can be controlled based on the temperature. The described melt spinneret apparatus. 3. The melt spinneret device according to item 1 or 2, wherein the perforated plate is composed of one or more wire meshes. 4. The spinneret has a large number of closely spaced pores with a porosity expressed by the following formula % () of about 10% or more, and the partition member surrounding the large number of slits absorbs Joule heat. 4. A melt spinneret device according to any one of claims 1 to 3, characterized in that the melt spinneret device is comprised of a conductor configured to generate electricity.