GB2282609A - Method for degumming silk fabrics and apparatus therefor - Google Patents

Abstract

A method and apparatus for degumming a silk fabric to remove sericin. A degumming solution is heated in a kier (1) to 120 - 130 DEG C and the silk fabric is immersed in the heated solution for 30 - 60 minutes. The kier comprises a body (2) containing a degumming chamber (7) and a pair of heat exchanger chambers (8) communicating at their top and bottom portions with the degumming chamber. A lid (3) seals the kier and an intake/exhaust pipe (4) filled with a valve (5) is used to control the pressure. In the heat exchanger chambers are two pairs of heat exchanger pipes and steam discharge pipes having upwardly directed nozzles, each pair being provided one above the other. Steam or cooling water can be supplied to the heat exchanger pipes to control the temperature. The top and bottom of the kier body are in communication through a circulation pipe (14) which includes a pump (15) and a heat exchanger (16). <IMAGE>

Description

METHOD FOR DEGUMMING SILK FABRICS AND APPARATUS THEREFOR This invention relates to a method for degumming silk fabrics and an apparatus therefor.

Generally, silk fabrics are subjected to degumming treatment to remove sericin contained in the silk at the rate of about 25 % and thus to impart the fabrics elegant luster and feeling to the touch or to make possible smooth dyeing and printing.

In degumming silk fabrics9 they were heretofore immersed in boiled water under normal pressure for 6 - 10 hours. This method is thus inefficient. Further, due to the long time required for degumming, the fabrics tend to suffer damages such as fluffing and bending. Another problem of this method is that the consumption of energy and degumming agent is large and thus uneconomical.

An object of this invention is to solve the above problems and to substantially shorten the time required for degumming.

According to this invention, there is provided a method for degumming a silk fabric comprising the steps of heating a degumming solution contained in a degumming kier to 120 - 130 C and immersing a silk fabric in the degumming solution for 30 - 60 minutes for degumming the fabric.

From another aspect of the invention, there is provided an apparatus for degumming silk fabrics comprising a degumming kier having a lid, an intake/exhaust pipe having an intake/exhaust valve for opening and closing the pipe, the degumming kier having a degumming chamber and a pair of heat exchanger chamber communicating at top and bottom portions thereof with the degummming chamber, two pairs of heat exchanger pipes and steam discharge pipes having nozzles for discharging steam upwards, each pair being provided one over the other in the respective heat exchanger chambers, a circulation pipe through which the bottom and top of the kier body communicate with each other, and a pump and a heat exchanger provided in the circulation pipe.

As described above, with the degumming method according to this invention, silk fabrics can be degummed in a very short time. Because of the short degumming time, fabrics are less likely to be damaged.

With the degumming apparatus of this invention, the degumming solution is heated by the steam supplied into the heat exchange pipes and the steam discharged through the nozzles of the steam discharge pipes. The steam discharged through the nozzles also serves to form a convective motion of the degumming solution. Thus, the degumming solution can be heated to a predetermined temperature in a very short period of time.

Since a silk fabric is degummed making use of the convection of the degumming solution, it can be degummed uniformly over the entire area.

Further, after degumming, the degumming solution is supplied into the circulation pipe, where the degumming solution is cooled by means of the heat exchanger provided in the circulation pipe. Thus, the temperature and pressure in the kier body can be reduced effectively. This in turn makes it possible to take out the degummed silk fabric efficiently in a short time without damaging it.

Other features and objects of the present invention will become apparent from the following description taken with reference to the accompanying drawings, in which: Fig. 1 is a vertical sectional front view of one embodiment of the degumming apparatus according to this invention; and Fig. 2 is a vertical sectional side view of the same.

(1) Degumming Method It is well-known that sericin contained in silk threads immersed in a degumming bath dissolves in the water as the water temperature rises. In order to examine the relation between the solubility of sericin and the water temperature in the degumming bath, silk threads were immersed in a degumming bath filled with a degumming solution not containing chemicals (that is, plain water) and kept at 100 - 130cm for 10 - 30 minutes and the rate of reduction in the weight of silk threads was measured. The results are shown in Table 1.

The test results shows that the degumming solution temperature has a great influence on the rate of reduction in the weight of silk threads. At the solution temperature of 1100C or under, sericin remains in the silk threads.

If it is 1200C or over, however, the rate of weight reduction increases to 24 - 25 %, which is a normal level.

No significant increase in the weight reduction rate was observed even when the solution temperature was increased to 130eC or over. This means that the ideal degumming temperature is between 120 and 130 CC.

On the other hand, the degumming time has to be 20 minutes or longer. But if the degumming time is shorter than 30 minutes, no uniform degumming is possible. For smooth degumming, the degumming time has to be 30 minutes or longer. If the degumming time is too long, however, the silk threads will begin to melt. Thus, the degumming time should be between 30 and 60 minutes.

Sericin in the silk threads can be dissolved sufficiently by immersing the threads in plain water kept at high temperature. No chemicals are necessary to add.

But, in order to increase the whiteness of the silk fabric and to completely remove any fats and oils from the fabric, conventional chemicals such as soap and surface-active agents may be added.

For example, 2 g/Z of soap, 1 g/2 of hydrosulfite and 1 g/2 of an anionic or nonionic surface-active agent may be added.

Soap and surface-active agent serve to remove fats and oils and thus to improve the feeling of the fabric and also to improve its whiteness due to their high detergency.

Hydrosulfite serves to increase the whiteness of the fabric.

Now, reference is made to the quality of degummed silk fabrics. High-temperature degumming is most effective in degumming fabrics having their wefts twisted strongly, such as crepes. This is because, in a conventional degumming method, the degumming solution cannot infiltrate sufficiently into the strongly twisted threads, so that the sericin in these threads can be dissolved only at a very slow pace. This leads to a difference in the rate of weight reduction between the wefts and the warps. If the degumming time is increased in order to increase the rate of weight reduction of the wefts, not only will the warps tend to be damaged but they will be degummed excessively.

This will make it difficult to dye the fabric uniformly and also lower the feeling of the fabric.

But high-temperature degumming is free of these problems. Namely, the difference in the rates of weight reduction between the wefts and the warps is kept small while the fabric is protected against damage. Crepes can be degummed in an ideal condition.

Besides the fact that the wefts and warps can be degummed uniformly, sericin scarcely remains in the silk threads after degumming and fibroin is kept free of damage.

Thus, the fabric can be dyed beautifully. The fabric thus dyed is more vivid in color tone than those obtained with a conventional method. Also a relatively deep color is obtainable.

Table 2 shows the high-temperature degumming method according to the present invention in comparison with a typical conventional degumming method.

(2) Degumming Apparatus As shown in the figures, a degumming kier 1 comprises a keir body 2 and a lid 3. By closing the lid 3, the kier body 2 is sealed.

An intake/exhaust pipe 4 is connected to the upper part of the degumming kier 1. The intake/exhaust pipe 4 is opened and closed by an intake/exhaust valve 5.

A pair of partitioning plates 6 are provided in the kier body 2 at both sides thereof, kept apart a predetermined distance from side plates of the kier body 2.

The partitioning plates 6 divide the interior of the kier body 2 into a degumming chamber 7 and a pair of heat exchanger chambers 8. Each heat exchanger chamber 8 communicates at its peripheral part with the degumming chamber 7.

In each heat exchanger chamber 8, a zigzag heatexchanger pipe 9 and steam-discharging pipe 10 are provided one over the other. While heating a degumming solution filling the kier body 2, steam is supplied to the heatexchanger pipe 9. When the degumming solution is heated above a predetermined temperature, cooling water is now supplied to the pipe 9, cooling the degumming solution to the predetermined temperature.

A plurality of nozzles 11 are formed in the steamdischarging pipe 10. The steam supplied into the pipe 10 is discharged upwards through the nozzles 11.

A drain pipe 12 is connected to the bottom of the kier body 2. A cooling water supply pipe 13 is provided in the kier body 2 at its upper part. The pipe 13 and the bottom of the kier body 2 are connected together by means of a circulation pipe 14.

A pump 15 and a heat exchanger 16 are provided along the circulation pipe 14.

The heat exchanger 16 has a cooling water pipe 19.

The degumming solution in the circulation pipe 14 is cooled by the heat exchange with the cooling water supplied into the cooling water pipe 19.

A silk fabric 17 to be subjected to degumming treatment is set in the kier body 2, while being hung on a frame 18. In degumming the silk fabric 17, after filling the kier body 2 with a degumming solution, the lid 3 is closed to hermetically seal the interior of the kier. In this state, steam is supplied into the heat-exchanger pipes 9 and the steam-discharging pipes 10.

By supplying steam into the heat-exchanger pipes 9, the temperature of the pipes 9 rises. By the heat exchange with the heat-exchanger pipe 9, the degumming solution is heated.

On the other hand, the steam supplied into the steamdischarge pipe 10 is discharged through the nozzles 11, thus directly heating the degumming solution. The steam discharged through the nozzles 11 serves to form a convection of the degumming solution. Thus, the degumming solution can be heated extremely effectively.

The silk fabric is degummed with the temperature of the degumming solution kept at 120 - 1300 C. Since the degumming solution is in convective motion all the while, the fabric is degummed uniformly.

After degumming the fabric for 30 - 60 minutes, the supply of steam is stopped, the pressure in the kier body 2 is lowered and the silk fabric 17 is taken out. If the intake/exhaust valve 5 is opened in order to release and lower the pressure, the pressure in the kier body will drop so sharply that the degumming solution will evaporate instantly, thus causing a sharp fall in the solution level.

Thus, the silk fabric 17 will float up to the surface of the degumming solution and degumming residues that are drifting on the surface of the degumming solution will adhere to the fabric.

Also, the fabric may be bent when it floats up due to the sharp drop in the pressure in the kier body 2.

Thus, when reducing the pressure in the kier body 2, the degumming solution in the kier body 2 is fed into the circulation pipe 14 by driving a pump 15, the degumming solution is cooled by means of the heat exchanger 16 provided in the circulation pipe 14 and the solution thus cooled is returned to the kier body 2 via the cooling water supply pipe 13.

When the degumming solution cools down to a predetermined temperature, the intake/exhaust valve 5 is opened gradually to further reduce the pressure in the kier body 2. When the pressure in the kier body decreases to a predetermined value, the lid 3 is opened to take out the silk fabric 17.

[Table 1]

Temperature Time Weight Temperature Time Weight (C) (min) reduction ( C) (min) reduction rate (%) rate (%) 10 7.49 10 23.56 100 20 7.44 1 2 0 20 24.23 30 7.87 30 24.92 10 17.42 10 24.75 1 1 0 20 19.41 1 3 0 20 24.71 30 20.41 30 24.03 Silk threads... four 24-denier threads (double-twisted) Immersion bath ratio of 1 : 30 [Table 2]

Method Conventional degumming High-temperature degumming method method according to the Condition present invention Rough degumming Liquid after main degumming is used. None Bath ratio 1 : 30 100 C 2 hours Main degumming Bath ratio 1 : 30 Bath ratio 1 : 30 Drug concentration Drug concentration Needle-like marseilles soap Needle-like marseilles soap ......... 6 g/ 2 ......... 2 g/ g Hydrosulfite... 2 g/ Q Hydrosulfite... 1 g/ Q 18 Be sodium silicate... 4 g/ l Peletex TP... 2 g/ l Peletex TP... 1 gI 100 C 3 hours 120 xC 40 minutes Washing with hot 100 xC 1 hour 100 C 30 minutes water Result of test Weight reduction 25.1 % 25.1 % rate Weight reduction 28.4 % 26.0 % rate (%) (warp) Weight reduction 21.8 % 24.2 % rate (%) (weft) Whiteness 82.4 % 82.9 % Strength (warp) 58.8 kg 63.3 kg Strength (weft) 22.4 kg 24.0 kg Ductility (warp) 27.6 % 37.2 % Ductility (weft) 26.6 % 33.4 % NOTE) Weight reduction rate: After the sample had been naturally dried, it was left in the thermostatic humidistatic chamber until the amount became constant, and then it was obtained by use of the following formula.

Weight Pre-degumming weight - Post-degumming weight reduction= x100 rate Pre-degumming weight Whiteness: Whiteness index was denoted by the reflectance on the wavelength of 465 mm.

Ductility: The sample piece (3 mm X 10 cm) was measured by Autograph S-100 (Shimadzu Seisakusho) with a tensile speed of 150 mm/min.

Claims (4)

1. A method for degumming a silk fabric comprising the steps of heating a degumming solution contained in a degumming kier to 120 - 130 0C and immersing a silk fabric in said degumming solution for 30 - 60 minutes for degumming the fabric.

2. An apparatus for degumming silk fabrics comprising a degumming kier having a lid, an intake/exhaust pipe having an intake/exhaust valve for opening and closing said pipe, said degumming kier having a degumming chamber and a pair of heat exhanger chamber communicating at top and bottom portions thereof with said degumming chamber, two pairs of heat exchanger pipes and steam discharge pipes having nozzles for discharging steam upwards, each pair being provided one over the other in said respective heat exchanger chambers, a circulation pipe through which the bottom and top of said kier body communicate with each other, and a pump and a heat exchanger provided in said circulation pipe.

3. A method for degumming a silk fabric, substantially as herein described with reference to the accompanying drawings.

4. Apparatus for degumming silk fabrics, substantially as herein described with reference to the accompanying drawings.