EP4116474A1

EP4116474A1 - Ultra-light silk fabric and method for its production

Info

Publication number: EP4116474A1
Application number: EP22182502.9A
Authority: EP
Inventors: Antonio REZZONICO
Original assignee: Mantero Seta SpA
Current assignee: Mantero Seta SpA
Priority date: 2021-07-06
Filing date: 2022-07-01
Publication date: 2023-01-11
Also published as: IT202100017822A1

Abstract

The invention relates to a fine silk fabric made by using an extremely thin silk thread for both weft and warp (1a, 1b, 5a, 5b), with a very large number of twists.

The extreme fineness of this thread makes it possible to obtain a fabric commonly referred to as chiffon, but having fineness, softness and lightness characteristics much superior to those of prior-art silk fabrics, which, on average, were normally created with counts twice as high. The raw count of the thread used to obtain the fabric is within a range from a minimum of 7-9 denier to a maximum of 13-15 denier, singly stranded, twisted with a high number of twists ≥ 2,500 turns/m.

Description

The present invention relates to a fabric made of fine natural silk and to a manufacturing method for producing it on a loom.
In particular, the thinness of the fabric according to the invention is compared with that of ordinary silk fabrics commonly available on the market.
Indeed, as is known, the standard base thread count which is generally processed in silk mills for making either derived silk yarns (single-stranded and multi-stranded) and fabrics, is 20/22 denier; the 13/15 thread count can also be found on the market, but it is seldom used, normally in 2 or more plies (twisted thread).
This type of silk thread is processed by means of established looms and techniques, to obtain silk fabrics having the well-known and much appreciated features of this material, such as glossiness, lightness and smoothness.
In this context, in the textile and/or clothing industry the need is felt (by the Applicant and others) for a thin silk fabric having improved lightness and softness characteristics in comparison with the silk fabrics currently known in the art.
To the Applicant's knowledge, this need has not been fulfilled yet, in that no fabrics exist which are produced using threads having a count which is, for example, half the most widespread 20/22 denier count.
This is due to the fact that a lower count reduces the mechanical properties of the yarn, so much so that it can no longer be processed using normal silk weaving processes and looms.
When the latter operate at usual speeds for threads having a count of 20/22 denier, they would inevitably subject any threads with a lower count (particularly warp threads) to strains and friction caused by the pulling force and by the abrasive action exerted by the loom comb during the beating phase, which would result in high risks of breakage.
In light of the above considerations, it can therefore be stated that the technical problem underlying the present invention is to provide a fine silk fabric which, while being very light and soft, can be processed by means of looms and used as a base for printing and/or piece-dyeing, or anyway for any other purpose allowed by known silk fabrics.
The idea for solving this problem is that, in order to be able to create such a fabric and attain the desired main peculiarities of softness and lightness, it is necessary to start from the very origin of the spinning process, i.e. the silk reeling process (unwinding the filament from the cocoons produced by silkworms).
The reference thread count taken into consideration for this invention is, preferably, 9/11 denier, i.e. thinner than half the base count normally produced in silk mills.
In order to spin such a thread count, it is important to accurately select the cocoons produced by silkworms to choose those which appear to be the best ones as concerns formation, colour and evenness.
The reeling process is carried out by working only 4/5 cocoons, compared with the usual 8/9 that are commonly unwound to obtain the 20/22 denier base thread count normally produced at industrial level.
These features make it possible to design a specific process for producing a natural thread which is as thin as possible and to obtain therefrom the fabric of the present invention. In particular, the toughness of the fibre permits spinning such a fine thread count, which will then be able to withstand the next reeling, winding, doubling and twisting phases, even with a high number of turns.
In accordance with the invention, in order to produce this fine silk fabric, the twisting of the thin thread occurs in two successive steps, so as to prevent the thread from undergoing excessive strains and avoid the risk of breakage.
Preferably, the first twisting step is carried out using the single strand process, on double-twist twisting machines.
In addition to increasing the thread's toughness, the twisting so made gives the thread a regular, round and compact appearance, which is the same appearance that will be found in the finished fabric.
In accordance with a preferred embodiment, this first twisting step is carried out with a number of twists ≥ 2,500 turns per metre in both directions (right-hand twist and left-hand twist). These and other features of the invention are specifically set out in the claims appended to this description.
Such features and the effects deriving therefrom, as well as the results and the advantages of the invention, will become more apparent in light of the following description of one possible, non-exclusive embodiment thereof, which is provided herein merely by way of non-limiting example with reference to the annexed drawings, wherein:

Fig. 1 schematically shows a step of processing chain or warp filaments in the process according to the invention;
Figs. 2 and 3 schematically show further steps of processing warp filaments in the process according to the invention;
Fig. 4 schematically shows a processing step of woof or weft filaments in the process according to the invention;
Figs. 5 (a)-(b) are macro-magnified photographic images comparing a known silk thread with a silk thread according to the invention, respectively in the raw state (a) and after degumming (b);
Fig. 6 shows a comparison between the fabric made from silk threads according to the process of the invention and a fabric of the type which is normally produced using traditional-count thread.
Fig. 7 shows the fabric made from silk threads according to the process of the invention before and after the dissolution and degumming steps.

With reference to the above-listed drawings, for simplicity's sake there will be described herein after the main processing steps of the method according to the invention, with reference to filament pairs.
However, this should not be understood in a limiting manner and those skilled in the art will be able to produce a fabric according to the invention, by applying the teaching disclosed herein.
For making the fine silk fabric according to the invention, the base thread hank obtained after spinning 4/5 silk cocoons is first wound on reels and then subjected to the first twisting step with a number of twists ≥ 2,500 turns per metre, in both directions (right-hand twist and left-hand twist).
The reference count taken into consideration for this invention is 9/11 denier, i.e. thinner than half the standard base count normally produced in silk mills.
In order to spin such a count, it is important to accurately select the cocoons produced by silkworms and to choose those which appear to be the best ones as concerns formation, colour and evenness.
The reeling process is carried out by working only 4/5 cocoons, compared with the usual 8/9 that are commonly unwound for the 20/22 denier base count normally produced.
As is known, a cocoon is formed in nature by 2 drools secreted by the silkworm's glands (sericteria).
As they come in contact with air, the two drools coagulate and adhere to each other under the action of sericin, thus forming a single thread (filament) which is used by the silkworm to build up its cocoon.
The average count of the filament, which forms the cocoon and is approximately 1 km long, is 2.4 denier; therefore, in order to obtain the desired final count of 9/11 denier, only 4/5 cocoons need to be subjected to the reeling step (unwinding the filament from the cocoons) in the silk mill.
It must be reminded that the variable number of cocoons is due to the different sizes that each filament secreted by silkworms may have in nature, as well as to the different sizes of the drooling between the beginning and the end of its secretion during the cocoon formation process.
Therefore, in order to obtain a regular desired final thread count, during the reeling process the machine constantly checks the thickness of the bundle of filaments and modulates the number of processed cocoons to compensate for the different degrees of fineness that may be found in nature.
In accordance with the invention, the twisting process is carried out in two separate steps, at least as concerns the warp thread, i.e. discriminating between the warp and weft threads.
In fact, since the filaments are very thin, if a single twist in excess of 3,000 turns per meter were applied to the warp threads, subsequently it would not be possible to subject them to the second twisting for coupling them with the supporting water-soluble thread.
The subdivision of the process according to the invention into two steps depends on, among other parameters, the final number of turns to be obtained and the initial yarn count, but it can be stated that, preferably, approximately 65-75 % of the twisting operation is carried out in the first step, while the remaining 35-25 % is carried out in the second step.
It must nevertheless be pointed out that it is also possible to envisage more than two separate filament twisting steps for processing the fabrics.
In the example considered herein, a final twisting of 3,700 turns per metre of threads having a count of 9/11 denier is to be obtained.
In this case, a first twisting step at 2,500 turns per metre is performed in both directions (right-hand twist and left-hand twist) by carrying out a traditional single strand twisting process on double-twist twisting machines, on a thread whose fineness results in an extremely low production yield in terms of weight (kg).
In addition to further increasing the thread's toughness, the twisting of a single thread having such a count gives the thread a regular, round and compact appearance, which is the same appearance that will be found in the finished fabric.
This step of the production process is schematically illustrated in Figure 1, which shows two filaments 1a, 1b of the chain or warp of the fabric arranged side by side; the figure shows the twisting directions, respectively left-handed for the thread 1a and right-handed for the thread 1b.
In the second step of the production process according to the invention, two different intended uses should be considered for the 9/11 denier thread obtained from the above-described first step: for the warp or for the weft.
As is known, the thread that will be used for chain or warp will be subjected to greater strains, especially during the loom weaving step.
Therefore, it will have to be processed differently than the thread to be used for weft, so that it will be able to withstand either the beaming step (sectional warping) and the delicate comb beating step during the subsequent weaving phase.
In order to overcome this obstacle, in accordance with the invention the thread 1a, 1b intended to be used for warp is, during this second processing step, twined with a thread of water-soluble synthetic fibre 2a, 2b. An example of such a fibre that can be used for the present invention is the one commercially known as "Solvron".
This special synthetic yarn, obtained by dry spinning of polyvinyl alcohol (PVA), has properties of prompt solubility by simple immersion in hot or boiling water, without requiring the use of any chemicals. Other synthetic or natural water-soluble fibres having similar properties may however be used.
Anyway, regardless of the water-soluble material employed for the thread 2a, 2b, it should preferably be a continuous thread having good mechanical properties to withstand the high number of twists and the strains induced by the twisting process.
Such properties permit a uniform and intimate association between the thread 2a, 2b and the corresponding silk thread 1a, 1b, resulting in effective support of the silk thread during the next processing step.
This step of associating the natural thread with the water-soluble synthetic thread differs from the techniques currently known in the art in that:

the natural thread is a continuous-filament thread of pure silk;
the count of the natural thread is 4 times thinner than the minimum count used so far (8 Dtex vs 33 Dtex);
the single silk strand is twisted at ≥ 2,500 turns/m;
the association with the synthetic thread is made with a number of twists ≥ 500 turns/m.

The association between the two fibres (silk thread and water-soluble thread) is made with a medium-to-high number of twists in the range of 500 to 1,000 turns/m, depending on the initial count of the silk in use; it must be done in the same direction as the first twist given to the single silk strand (2,700 turns/m) to further increase its value in the final silk thread.
The resulting final twist of the 9/11 silk thread will therefore be given by the twists made during both steps of the production process: first twisting of the silk thread at 2,700 turns/m and second twisting to associate the silk thread with the water-soluble thread at 500 to 1,000 turns/m. The final result will be, therefore, a thread 3a, 3b composed of silk 1a, 1b and water- soluble thread 2a, 2b, extra twined with the silk fibre at 3,600 turns/m.
In this case as well, the second twisting is carried out by working in both left and right direction (S/Z), as shown in Figures 2 and 3.
The composite filament 3a, 3b thus obtained can then be used as the warp thread of an intermediate semi-finished fabric, wherein the weft consists of a silk thread 5a,5b, which can advantageously be used in the next stages of the production process.
This intermediate semi-finished fabric and the final fabric will be further discussed below.
As is known, when subjected to these twists, yarns increase their own instability due to the reaction that the thread exerts upon itself to return to its initial state (nervousness or elastic effect), which results in difficult processing without causing the formation of holes and hence lack of linearity.
In order to stabilize this new condition of the thread, the latter is normally subjected to an autoclave treatment under specific conditions of temperature and humidity with saturated steam (4-hour cycle at 70°C); such conditions will fix the new state acquired during the twisting stage, so that the thread can then undergo the next processing steps.
However, this important step cannot be performed on the silk thread 1a, 1b associated with the water- soluble fibre 2a, 2b, because the latter could not withstand the fixing temperature and would dissolve, thus jeopardizing all the work carried out up to this point.
To overcome this problem, the twist fixing phase is divided into two steps: in the first step only the silk thread 1a, 1b is fixed after the first twisting, the latter being the one causing the highest reaction force due to the exerted twisting action (≥ 2,500 turns/m), whereas in order to stabilize the thread 3a, 3b after the second step of association with the water- soluble fibre 2a, 2b, which step determines, at any rate, a further need for fixing, it is necessary to find a correct balance between added twist and count difference between the two fibres 1a, 1b and 2a, 2b.
These two factors must be balanced to keep the resulting paired thread 3a, 3b stable.
The water-soluble synthetic thread 2a, 2b used for this association has a count which is three times higher than that of 9/11 denier silk; this difference, combined with the balance found in the association twist, helps exerting a predominant force that can keep the resulting thread 3a, 3b stable.
At the same time, the final count of the chain thread must be sufficient to withstand the stresses induced by the comb during the weaving process and must be coherent with the centimetre reductions and the related reed plan of 2 threads per tooth; these preferred technical specifications are both conceived to obtain the expected results from the fabric made in accordance with the invention.
Thread counts, twists, reductions and comb passing are, therefore, some of the most important elements that lead to the final result of the fabric of the present invention.
The silk thread 5a, 5b having a count of 9/11 denier used for weft needs no reinforcement, and therefore does not undergo the second step of association with the supporting water-soluble fibre.
This is due to the smaller strains to which it is subjected, compared with the same thread 1a to be used for warp.
During the weaving process it will nevertheless be necessary to take into account the extreme fineness of the thread 5a, 5b, using looms with properly adjusted clamps and reducing the weaving speed to around 250 to 320 strokes/minute.
This component must therefore be already treated during the first twisting step, by applying thereto the desired final twists of 3,600 turns/metre, in both directions S/Z just like the chain thread.
The chain (or warp) components 1a, 1b and the weft components 5a, 5b are all twisted in both directions (S twist and Z twist), as schematically shown in Figures 1 and 4.
However, unlike the warp threads, the weft threads 5a, 5b can be twisted in one step, directly up to values in excess of 3,000 turns/m or even 3,600 turns/m and more.
On the loom, they will be regularly balanced by alternating them, whether 1/1 or 2/2, for the purpose of maintaining, as is normally done for all fabrics of this kind, proper stability in both orthogonal directions.
Some construction variants are nonetheless possible, wherein the fabric is balanced by mutually opposing the two twists in the two directions (e.g. single S twist for warp and single Z twist for weft), and some variant embodiments are also possible wherein a single weft twist is woven on a balanced chain.
This latter construction will give as a result the classic crepon effect of silk fabrics of this type, but still with the peculiar fineness and lightness of the fabric of the present invention.
Once the chain thread 1a, 1b has been prepared in association with the water-soluble fibre, the beaming process is carried out, preferably with sectional warps, which offer better control over the thread tension and parallelism parameters.
During this step, the correct balance of the twist associating the 9/11 count silk thread 1a, 1b with the water-soluble synthetic thread 2a, 2b is verified, which twist, as aforesaid, must make the resulting thread stable.
Moreover, the water-soluble synthetic thread 2a, 2b, being very slippery, must not slip over itself while passing through the two combs (lifter and reducer) of the warping machine. Should this happen, tangles would form on account of breakage of the single fibres composing the thread, which would then cause the silk thread to break on the loom, since it will no longer receive proper and regular support from the synthetic fibre.
The base fabric 10', i.e. the intermediate semi-finished one, and the main fabric 10 to be produced with the process described herein, are a "square" orthogonal fabric, i.e. a fabric built with the same centimetre reductions in both warp and weft directions, with a taffeta weave. This aspect also contributes to giving the finished fabric 10, i.e. after all ennobling treatments, better orthogonal stability and better resistance of the threads to slipping in both directions (the threads slipping on the weft threads, and vice versa).
It is nevertheless possible to create fabrics with different reductions, depending on the desired final result, which is also related to the initial thread count of the silk in use and to the desire to obtain, by means of different weaves, wavy and/or unbalanced effects such as "seersaker" or "barre".
The invention can also be applied to jacquard looms, from which it will be possible to obtain customized interlaced patterns and ratios up to full fabric height through the use of large-format jacquard.
What is important and binding for the purposes of the present invention is the construction of fabrics through the use of spun silk having counts and construction feature falling within the ranges stated herein, i.e. very fine silk threads that are the peculiar feature of the present invention.
To provide a visual indication of this situation, Fig. 5 shows macro-magnified photographic images comparing a 20/22 denier silk thread F commonly used in the industry, with a 9/11 denier silk thread 1a according to the invention, respectively in the raw state (a) and after degumming (b).
An example of a process for producing the fabric according to the invention comprises the following operating parameters:

RAW SILK THREAD: TD 9/11
SUPPORTING SYNTHETIC FIBRE: DTEX 31/9
WARP REDUCTION: 56 threads/cm
WEFT REDUCTION: 56 insertions/cm
REED PLAN: 2 threads/tooth
WEAVE: taffeta

Once the raw fabric has been obtained, a clearing step is carried out, which is the activity that starts the actual ennobling phase.
The first operations that need to be carried out is dissolving the water-soluble fibre which was used as a support for the chain silk thread; this is achieved with a thermal shock, by soaking the fabric in a hot-water bath already brought to a temperature of 80°C, with a bath ratio of 1/30 w/w, for a time of approximately 20 minutes.
All this is done while adequately stirring the bath, preferably with continuous overflowing. Then the actual silk clearing step is started via a traditional cycle, following a star pattern. Finally, the fabric is rinsed with a new bath of clean water (classic method).
As is known, the silk clearing cycle determines a 25% weight loss due to dissolution of the sericin component that is naturally present in the thread: this weight reduction causes the yarn count, which is reduced by the same percentage, to become 6.7-8.2 denier, which is the final fineness of the ennobled fabric 10 ready to be packaged.
The resulting fabric 10 has those features of lightness and softness initially searched for by the invention, and is now ready to be used as a base for printing and/or piece-dyeing and/or finishing works.
The final yarn count of the finished fabric 10 will thus preferably show a variance from a minimum value of 5.5 denier to a maximum value of 11.5 denier, depending on the initial raw count, which values fall within the range previously stated herein; such a reduction comes from the removal of the sericin component that was naturally present on the thread, achieved during the fabric degumming phase (75% fibroin, 25% sericin and other substances).
Figure 6 shows a comparison between the fabric 10 produced starting from raw silk threads 1a, 1b having a count of 9/11 denier in accordance with the process of the invention and a fabric T of the type normally produced using the traditional silk count of 20/22 denier.
Figure 7 shows a similar comparison between the intermediate fabric 10' produced starting from raw silk threads 1a, 1b having a count of 9/11 denier in accordance with the process of the invention (reference (a)) and the final fabric 10 obtained after the dissolution and degumming phases (reference (b)).
In a possible variant of these constructional solutions, clearing step is not carried out and the process stops after the step of dissolving the water-soluble synthetic component, in order to use the fabric as organza, i.e. a crude silk fibre having the peculiarity of keeping a rigid and crisp handle which is typical of non-cleared fabrics; in this case as well, the fabric will differ from normal organza for the structure and, most importantly, the fineness of the thread employed, which will characterize its final touch.
For both applications, whether as a printing base or as a piece-dyeing base, every single step of the process must be appropriately considered; suitable modifications will have to be made to the standard cycles, trying to apply all the necessary precautions to the production processes.
This will be useful to properly control the movements of the fabric in the machine as well as to ensure proper handling of such a light, soft and volatile fabric, so as to be able to meet the requirements at the basis of the invention.
All of the above-described features of the invention fall within the scope of the following claims.

Claims

Fine natural silk fabric, comprising a plurality of threads (1a, 1b, 5a, 5b) arranged according to a weft and warp, characterized in that the warp threads (1a, 1b) and/or the weft threads (5a, 5b) have a raw count of between 7 denier and 15 denier.
Fabric according to claim 1, wherein the twist of the threads (1a, 1b, 5a, 5b), at least the warp threads (1a, 1b), is greater than 3,000 turns per metre (turns/m), and preferably greater than 3,500 turns/m.
Fabric according to claims 1 or 2, wherein the twist of the warp threads (1a, 1b) and/or of the weft threads (5a, 5b) is a single stranded twist.
Fabric according to any one of claims 1 to 3, wherein the twist of the warp threads (1a, 1b) and/or the weft threads (5a, 5b) is carried out in left-hand (S) and right-hand (Z) directions.
Fabric according to any one of the preceding claims, wherein the twists are balanced in both warp and weft directions.
Fabric according to any one of the preceding claims, comprising a centimetre reduction in the warp threads (1a, 1b) and/or the weft threads (5a, 5b) comprised between 40 and 60 threads/cm.
Fabric according to any one of the preceding claims, wherein the warp threads (1a, 1b) are associated with a water-soluble synthetic thread (2a, 2b) made of composite filaments (3a, 3b).
Fabric according to any one of the preceding claims, characterized in that it is cleared of the sericin component.
Fabric according to any one of claims 1 to 7, of the organza type obtained by interrupting the processing before clearing the silk and after dissolving a water-soluble synthetic thread (2a, 2b) supporting the warp threads (1a, 1b).
Fabric according to any one of the preceding claims, comprising unbalanced twists to obtain crepon effects.
Process for manufacturing a fine silk fabric (10, 10') according to any one of the preceding claims, comprising the steps of:
a) spinning silk from a reduced number of cocoons compared with the spinning standard, so as to obtain a spun silk (1a, 1b; 5a, 5b) with a raw count between 7-9 denier and 13-15 denier;

b) performing a first twisting of the warp spun silk (1a, 1b), with twists ≥ 2,500 turns/m;

c) performing a second twisting of the warp spun silk (1a, 1b) with water-soluble synthetic fibres (2a, 2b) to obtain a composite thread (3a, 3b);

d) warping the silk thread (1a, 1b) twined with the water-soluble thread (2a, 2b);

e) weaving (flat or jacquard);

f) dissolving the water-soluble fibre component (2a, 2b) within the fabric by soaking in a hot water bath.
Process according to claim 11, further comprising at least one or more of the following steps:
g) clearing the silk fabric;

h) preparing for printing and/or dyeing;

i) printing and/or dyeing;

1) ennobling;

m) packaging the finished fabric.
Process according to claim 11 or 12, comprising a step of twisting the woof or weft spun silk (5a, 5b), with twists ≥ 3,000 turns/m.
Process according to any one of claims 11 to 13, wherein the twists of the warp threads (1a, 1b) and/or the weft threads (5a, 5b) are made in both left-hand and right-hand (S/Z) directions.
Process according to any one of claims 11 to 14, wherein the twists of the warp threads (1a, 1b) and/or of the weft threads (5a, 5b) are single stranded.
Process according to any one of claims 11 to 15, wherein the water-soluble synthetic fibre thread (2a, 2b) used in association with the silk thread is a thread commercially known as Solvron.
Process according to any one of claims 11 to 16, wherein the fabric (10) is made by interlaced weaves or Jacquard weaves.