EP0399053A1

EP0399053A1 - Polyester composite mono-filament for screen gauze

Info

Publication number: EP0399053A1
Application number: EP89913175A
Authority: EP
Inventors: Yoshimitsu Itou; Mototada Fukuhara; Akira Kishiro
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 1988-12-05
Filing date: 1989-12-04
Publication date: 1990-11-28
Anticipated expiration: 2009-12-04
Also published as: WO1990006384A1; EP0399053A4; EP0399053B1; DE68926617D1; KR910700366A; ATE138983T1; KR950007817B1; DE68926617T2

Abstract

The polyester composite mono-filament for a screen gauze in accordance with the present invention is a sheath-core composite yarn using a polyester having a low glass transition point as a sheath component. The area ratio of the core-sheath is 70:30 - 95:5, the strength at break of the mono- filament is at least 6 g/d and a modulus at elongation of 10 % is at least 3.5 g/d. The composite mono- filament of the present invention is excellent in weavability, dimensional stability and strength, has less occurrence of scum and therefore makes it possible to produce a screen gauze having high printing accuracy.

Description

Technological Field

The present invention relates to a polyester composite monofilament suitable for a mesh fabric used for screen printing. In more detail, the present invention relates to a polyester composite monofilament suitable for obtaining a bolting cloth with high mesh and high modulus used in the fields wherein high accuracy is required such as electronic circuits.

Background Technology

As bolting cloths for printing, in the past, mesh fabrics consisting of a natural fiber such as silk or an inorganic fiber such as stainless steel fiber have been widely used. Recently, mesh fabrics namely bolting cloths consisting of nylon and polyester having flexibility, durability and dimensional stability, have been used in many cases. Above all, bolting cloths consisting of polyester monofilaments have been widely used as they are little influenced by water and are inexpensive in comparison with nylon .
However, in the field of printing of electronic circuits, it has been required, year by year, more strict accuracy.
Up to the present, as a polyester monofilament with low elongation causes a large amount of scum, it has been recognized that weaving is impossible by using the mono- filament with low elongation. However, requirements by the printing industry becomes more severe than before and a mesh fabric with a fine denier and a high mesh, namely, with a high weave density is required. Tension applied on a filament during weaving is not necessarily proportional to its denier and high tenacity per monofilament is needed. The thinner the denier is, a product with higher breaking strength is needed. Therefore, to improve printing accuracy, it is necessary to have a bolting cloth with high strength, high modulus and fine mesh.
Generally speaking, to produce a polyester filament with high strength and high modulus, the draw ratio in the manufacturing process of the original fiber is raised at a high level. Thus the obtained filament has a highly oriented and highly crystallized structure. However, in the manufacturing process of the bolting cloth, a fabric with an extremely high density is woven at a high speed. Therefore, the warp filament.is repeatedly exposed to a strong friction with a reed etc., and part of the surface of the filament is thereby scraped and beardlike or powdery scum is easily generated. Especially, as orientation and crystallization become higher, this tendency is enhanced and as the result, it becomes necessary to stop weaving temporarily and to clean the weaving machine. This action not only spoils productivity but also causes unevenness of weaving at this part, which results in a defect of a product. Even when it is not necessary to clean, part of the produced scum is woven into the fabrics and this results in a defect of printing in case of precise printing. It is therefore an extremely important object of this invention for the original filament with high strength to prevent scum from generation.
Up to now, a number of technologies for improvement have been proposed to reduce scum. For example, in Japanese Patent Laid-Open No. 16948/1980, it was proposed that a high elongation original filament with a breaking elongation of 38-60% was used as a warp. However, using a high elongation filament means that the draw ratio is set lower at the manufacturing process of the original filament and it becomes inevitably difficult to obtain a fabric with a high modulus as the final product. Namely, it means that in this conventional technology, such characteristics as high strength and high modulus are sacrificed to prevent scum from generation. Therefore, according to the above mentioned patent, if making thinner denier is attempted to obtain a higher mesh fabric, tenacity becomes insufficient and weaving processability is remarkably spoiled and as the result, it is difficult to obtain a bolting cloth with a high mesh for precise printing. As the result, it should be a problem to be solved how a high modulus filament can be woven while occurrence of scum is suppressed.
In addition, in Japanese Patent Laid-Open No. 276048/ 1987, and International Patent Laid-Open No. W088/06103, a composite filament wherein such a polymer as nylon having good adhesiveness with emulsions and resins for pattern making and being durable to scraping was used as the sheath was proposed. Development of scum can be prevented in case of nylon in comparison with polyester, because of its toughness for scraping, but there exists a defect that nylon exhibits higher moisture absorption and poor dimensional stability. In the precise printing, dimensional stability after a fabric is set and fixed on a frame and storage time, plate making (forming of a printing pattern) and the process to printing, is extremely important. If nylon is used, even it is a part of the composite filament, it is easily influenced by temperature and humidity and the tention imparted to .the fabric tends to be relaxed. Especially, if the atmosphere in the workshop is not strictly controlled, the influence becomes larger. Therefore, by said technology, weaving characteristics can be improved but accuracy of precise printing cannot be improved.
In addition, in Japanese Patent Laid-Open No. 276048/ 1987 and International Patent Laid-Open No. W088/06103, it is described that a polyester with a low viscosity is used as a sheath component, but no practical example is described. On the contrary, a polyester with a low viscosity is not generally used as a raw material for a monofilament for a bolting cloth. A polyester with a low viscosity means generally a polyester with a low degree of polymerization and is easily crystallized by the heat during drawing. Thus obtained monofilament exhibits poor toughness and is brittle. Therefore, when a sheath-core type composite monofilament wherein a polyester with a low viscosity is used as a sheath, the polyester with a low viscosity is scraped by friction during weaving a fabric and scum is produced. Therefore, the sheath-core type composite monofilament wherein a polyester with a low viscosity is used as the sheath component is not suitable for bolting cloth for screen printing.
The present invention is to provide a polyester composite monofilament suitable for precise printing, with good dimensional stability, good weaving characteristics and reduced scum.
Namely, the purpose of the present invention is to provide a polyester composite monofilament with high tenacity and high modulus suitable for fine denier and high mesh fabrics.

Disclosure of the Invention

This invention relates to a polyester composite monofilament for a bolting cloth for screen printing characterized by a polyester composite monofilament consisting of a polyester wherein

(a) glass transition temperature (Tg) of a polyester forming a sheath is 35 - 73°C and is lower than the glass transition temperature (Tg) of a polyester forming a core,
(b) the area ratio of the core to the sheath is in the range of 70:30 - 95:5, and
(c) breaking strength of said monofilament is 6 g/d or higher and modulus at 10% elongation is 3.5 g/d or higher.

A feature of the polyester composite monofilament for a bolting cloth of the present invention is high tenacity per monofilament against tension applied in the weaving process.
Required tenacity of the monofilament depends on the type of a weaving machine to be used and the number of rotation during weaving and when the tenacity is about 50 g/filament or higher, problems during weaving are practically dissolved. Namely, if the breaking strength is 6 g/d or higher, a monofilament with a denier of about 9 d can be provided and furthermore, if it is 7 g/d or higher, it becomes possible to make the denier thinner down to 7 d. Therefore, it is necessary to make the breaking strength of the monofilament to be 6 g/d and preferably 7 g/d or higher. The higher the breaking strength of the monofilament the better the result is, and when a polyethylene terephthalate is used as the core component, the purpose of the present invention can be achieved by the breaking strength of about 10 g/d or lower.
On the other hand, even if a high mesh fabric consisting of a high tenacity monofilament is used, if it is deformed by a stress applied by squeeze during printing, a high printing accuracy cannot be kept. For this purpose, a monofilament with a high modulus is needed. The modulus of the monofilament means the stress produced in the filament at 10% elongation. Namely, it is a value obtained by dividing tenacity at 10% elongation in the S-S curve of the original filament by its denier. It is necessary to make this modulus 3.5 g/d or larger and more preferably, 3.8 g/d or larger. The higher the modulus of the monofilament is, the better the result is and when a polyethylene terephthalate is used as the core component, the purpose of the present invention can be achieved by the modulus of about 10 g/d or lower.
To achieve high breaking strength and high modulus like this, it is essential for the original filament to be drawn at high draw ratio during the manufacturing process. As the result, a filament with a low elongation is obtained, however, by applying the technology of the present invention, it becomes possible to perform sufficient weaving even if a filament with low elongation with which it was impossible up to now is used. Namely, it is possible to make the elongation of the monofilament lower than 33% . Of course, it is not preferable in the sense of easy handling of the filament that the elongation is extremely low and an elongation of 10% or larger is preferable and 15% or larger is more preferable.
On the other hand, if one attempts to achieve high breaking strength and high modulus on polyester, development of scum during weaving is accordingly enhanced. This is because, in polyester fibers highly oriented and crystallized by drawing, the strength increases in the direction along the fiber axis as the result, on the contrary the fiber becomes accordingly brittle and weak against bending, shearing and scraping. Since high strength and high modulus are required as the final product, the fiber itself should have said mechanical characteristics. Under these conditions, it is the most important object of the present invention is to prevent development of scum.
The feature of the present invention is how good weaving properties can be kept for the monofilament with such a high breaking strength, a high modulus and a low elongation. In the present invention, this problem has been solved by making the monofilament to be a sheath-core type monofilament.
It was found from the study of the present inventors that a copolyester with a low Tg hardly produces scum. Generally speaking, low Tg means that the mobility of molecular chains in amorphous parts is high and it is regarded as not glassy state but rubbery state. Namely, the polymer is soft and is hardly scraped against friction. The effect of scum suppressing becomes remarkable when Tg of a polyester is 73°C or lower.
If suppression of said scum only is the purpose of the present invention, the lower the Tg is, the better the effect is, but on the other hand, when Tg is close to room temperature, dimensional stability during application is decreased and it is not suitable for application in the field of precise printing, which is the target of the present invention. Therefore, in the polyester composite monofilament of the present invention, Tg of the polyester suitable for precise printing should be 35 - 73°C and more preferably 45 - 65°C.
A polymer having such a Tg can be obtained by copolymerizing a crystalline polyester with a monomer increasing flexibility of the molecular chain or a monomer or a polymer with a relatively low molecular weight hardly producing steric hindrance. For example, in case of polyethylene terephthalate, as the suitable copolymers, dicarboxylic acids such as isophthalic acid, adipic acid, dimer acid and sebacic acid, a compound of a general formula R₁O(C_nH_2nO)_mR₂ (wherein ^R ₁ and ^R ₂ are each H or an alkyl group having 1 to 4 carbon atoms; n is an integer of 2-5; m is an integer of 2-250), for example, low molecular weight glycols such as diethylene glycol, butane diol and neopentyl glycol, polyalkylene glycols such as polyethylene glycol and polytetramethylene glycol can be cited.
As the amount of copolymerized moiety, it is not indiscriminately determined but it depends on the type of selected copolymer and it should be properly decided in such a way that the Tg of obtained polymer shows 35 - 73°C. ô,
In addition, generally speaking, a polymer with a low degree of polymerization (a low viscosity) is easily crystallized by heating in comparison with a polymer with a high degree of polymerization (a high viscosity), exhibits poor toughness and a tendency to becoming brittle. Therefore, as the sheath component of the present invention, it is preferable that a polymer with a high degree of polymerization with an inherent viscosity [η] of 0.60 or larger and being spinnable is used.
A copolyester with a low Tg is generally soft, but on the contrary, it is difficult to make breaking strength, modulus and elongation higher by using this copolyester and therefore, it is impossible to obtain a filament satisfying the mechanical characteristics of the monofilament of the present invention as it is. In the present invention, on this point, this problem can be solved by employing a composite structure wherein a polymer with a lower Tg was used for only the sheath component. Namely, the polymer scraped by the friction against a reed and a guide bar is the polymer on the surface. Therefore, it is enough to use a polymer with a low Tg on the surface. Mechanical characteristics such as breaking strength, modulus and elongation should depend on the polymer forming the core.
Based on such a conception, it is necessary to set the ratio of the core to be relatively higher and as the result, it is necessary that the area ratio of the core to the sheath is at least 70:30 or more and preferably 80:20 or more.
In the present invention, both the core and the sheath are made of polyesters and peeling on the interface of the composite scarcely occurs, but if the sheath becomes too thin, so-called composite disarrangement such as exposure of the core polymer on part of the fiber surface tends to occurs. It may result in the decrease in the effect for suppressing the development of scum and therefore, the limitation of the area ratio should be 95:5.
Namely, if the area ratio is in the range of 70:30 - 95:5, good composite arrangement could be ensured and suppression of the development of scum is possible. It is preferable that the thickness of the sheath is at most 5u. or thinner. As the polyester constituting the core of the present invention, taking the cost etc. into consideration, polyethylene terephthalate used in larger quantities in clothing and industrial applications is most preferable, but a polyester with a high rigidity consisting of l,2-bis(phenoxy)ethane-4,4'-dicarboxylic acid or 2,6-naphthalene-dicarboxylic acid and ethylene glycol and a liquid crystal polyester of whole aromatic can be used. In any case, Tg of these polyesters should be higher than that of the polymer constituting the sheath and it is preferable that the Tg is practically 78°C or higher. Within this range, if necessary, the third component can be incorporated or copolymerized.
In addition, the following structure can be used as the polyester composite monofilament of the present invention.
One of the preferable morphology is a concentric circle structure wherein the center of a core and the center of a sheath coincide. It is not preferable that if the core is eccentric, crimps or curls are produced caused by a little difference in thermal and mechanical characteristics of polymers constituting the core and the sheath.
Another preferable morphology is a islands-in-a-sea type structure wherein a plurality of cores (islands) are surrounded with a sheath (a sea). The advantage of an islands-in-a-sea type structure like this is exhibited when a polyethylene terephthalate with higher degree of polymerization, for example, an inherent viscosity [n] of 0.75 or higher or a liquid crystalline polyester, which easily provides a high modulus filament as cores is used. These polyesters provides high strength and high modulus, but on the other hand, they lacks flexibility and hardly follow the bent structure of warp and weft when a high mesh fabric is prepared.
To solve said problem, the denier of the constituted filament is made thinner. Those fibers with thin denier are flexible even their moduli are high and easily follow the deformation during weaving. However, if a simple assembled body of multi-filaments is used, the fiber bundle becomes flat in a fabric and it is difficult to ensure a large dimension of the opening when a screen fabric is made thereof. As the result, it becomes necessary to give a twist to the filament for improving the weaving characteristics and it results in making the process more complex and giving an insufficient uniformity of opening. Therefore, in this case, it is preferable to prepare a structure wherein a plurality of cores are surrounded with a sea.
To realize effectively said purpose, the denier of a single filament constituting an island is preferably 3 d or thinner, more preferably 1 d or thinner and it is preferable that thinner filaments are more flexible. It is necessary that the number of filaments constituting the islands is at least 5 or larger. If the number of islands becomes small, it becomes difficult to ensure the ratio of the sea component to the island component as described- before and as the result, it results in setting the volume ratio of the sea component large to realize an uniform composite and the feature of high strength and high modulus is hardly exhibited. 100 or more is possible as the number of the islands, but too many number only results in making the spinning nozzle too complicated and up to about several dozens should be enough for achieving the purpose of the present invention.
It is preferable that the crosssectional shape of the monofilament should be round. The reason is that if the shape is a deformed crosssection, halation occurs when a photosensitive emulsion is cured to give a bad influence to printing accuracy in some cases. Another reason is that comparing with the round crosssection, the filament with a deformed crosssection exhibits poor straightness and hardly provides a screen with a uniform opening.
As the practical method for obtaining the composite monofilament of the present invention, any conventional well-known composite spinning method can be applied. Namely, polymers forming each the core and the sheath are independently melted and metered and both are joined together at the rear face of a spinneret so as to form a sheath-core structure and extruded from the same nozzle to obtain the composite monofilament.
Practical methods for obtaining an islands-in-a-sea type composite filament are, for example, a conventionally known spinning method for preparing a laterally-arranged polymer disclosed in Japanese Patent Publication No. 26723/1972. Namely, the islands-in-a-sea type composite filament is obtained by melting and metering separately two polymers constituting respectively a sea component and an island component, feeding them respectively in the same spinning pack, forming each independently a sheath-core composite flow at the first stage, joining together each sheath-core flow at the second stage and extruding a multi-core islands-in-a-sea type composite flow from a nozzle, but the method is not necessarily restricted by this method. Anyhow, it is preferable that a plurality of ultrafine filaments form each independently an island and a structure wherein the islands are surrounded by a polymer forming a sea is formed. In the present invention, as it is not the purpose to dissolve the sea component and to obtain the bundle of the ultrafine filaments, it is allowable that islands are partly joined together a little. However, too many joinings of flows reduce the effect of making the filament ultrafine and the filament lacks flexibility. Joinings of flows should be avoided as much as possible by taking the design of the nozzle into consideration in accordance with the viscosity of the polymer to be used.

Best Embodiment for Practicing the Present Invention

The effect of the present invention will be practically explained in more detail by Examples hereinbelow but the present invention will not be restricted thereby. Evaluations in these Examples were performed by the following methods.
Tg:
10 mg of a powder of the polymer were sampled. The measurement was performed by using a differential scanning calorimeter (manufactured by Perkin-Elmer Co., Ltd: Type DSC-4) while the temperature was elevated at a speed of 16°C/min. By a peak in the course of temperature elevation, the glass transition temperature Tg (°C) was obtained by using the data treating system of Perkin-Elmer Co., Ltd.
Evaluation of scum:
A mesh fabric was woven by means of a Sulzer type weaving machine at the number of rotation of the weaving machine of 350 rpm. Observing the degree of contamination of a reed, when it was judged that continuous weaving became impossible, the weaving machine was stopped and the reed was washing. The weaving period up to this time was defined as a reed washing cycle (m). The shorter this washing cycle was, the more the development of scum was.
Modulus of a fabric:
A tenacity-elongation curve of a fabric was obtained by means of the labeled strip method described in JIS L1068-1964 using a tensile tester with a constant speed stretching under a testing condition with a width of a test sample of 5 cm, a clamped distance of 20 cm and a extension speed of 20 cm/min and the tenacity (kg) at 10% elongation was defined as the modulus of the fabric.

Example 1

A polyethylene terephthalate (A) with an intrinsic viscosity [n] of 0.80 was prepared as a core component of a composite monofilament. Tg of this polymer was 79°C. On the other hand, as a sheath component, a polymer (B) with an intrinsic viscosity [nj of 0.67 made by incorporating 8 wt.% of polyethylene glycol with a molecular weight of 1,000 when a polyethylene terephthalate was polymerized, was prepared. Tg of this polymer was 58°C.
A composite monofilament wherein the polymer A was the core and the polymer B was the sheath spun at 1,000 m/min by means of a conventional well-known composite spinning method at a spinning temperature of 295°C. In this case, the composite ratio of the core to the sheath was 90:10 at the area ratio. Drawing of the obtained undrawn monofilament was performed at various draw ratio by using a pair of hot rolls each heated at 90°C and 140°C to obtain drawn monofilaments with a denier of 8 denier. Said monofilaments were woven, finished and treated to obtain high mesh bolting cloth with a mesh of 300. Drawing condition, characteristics of the original filaments and the results of evaluation on the obtained fabric were shown in Table 1.
In the experiment No.l, as the breaking strength of the monofilament was low, filament, breakages occurred during weaving. In the experiment No.2, as the modulus of the monofilament was low, a fabric with a low modulus was obtained and it exhibited bad printing accuracy. In the experiments Nos.3, 4 and 5, even the monofilaments exhibited high strength and high modulus, development of scum was little. High modulus and high mesh bolting cloth were obtained and it was possible to perform highly precise printings with a line width of 80 µm by using said cloth.

Example 2

According to the method shown in Example 1, sheath-core composite filaments with a monofilament denier of 7 denier wherein a polyethylene terephthalate (A) with an intrinsic viscosity of 0.75 was used as the core component and copolyesters with a different Tg were respectively used as the sheath components and the core-sheath area ratios were different each other, were obtained. High mesh fabric with a mesh of 360 mesh were obtained by weaving said monofilaments, finishing and treating them. The results of evaluation on scum on each composite filament were shown in Table 2. In this table, the dimensional stability was determined by observing the degree of distortion of a printed pattern after printing on 3,000 pieces was finished and by marking less distortion as good and more distortion as poor.
In the experiment No.6, as the content of the copolymerized component was small, Tg of the copolyester was high and scum was developed during weaving. In the experiment No.10, as the Tg was too low and therefore, dimensional change during printing was large and distortion of printed pattern of the printed matter was large and as the result, it was judged that the bolting cloth provided bad printing accuracy. In the experiment No.13, as a copolymerized component with a high Tg was used, Tg of the copolyester was accordingly high and scum was generated during weaving. In the experiment No.14, as the area ratio of the core component was small, the filament had low elongation and scum was generated. In the experiment No.15, as the area ratio of the sheath component was small, the effect of suppressing the development of scum became little and scum was generated. Experiments Nos.7, 8, 9, 11 and 12 were examples of the present invention and even though the original filaments exhibited high strength and high modulus, no scum was generated. The obtained high mesh fabric were plain gauzes with high modulus and highly precise printing with a line width of 70 µm was possible.

Example 3, Comparative ;Example 1

Properties of a plain gauze woven with a composite monofilament with a sheath made of nylon and a core made of polyester (Comparative Example 1) and those of a plain gauze woven with a polyester composite monofilament of Experiment No.4 in Example 1 were compared with each other.
A composite monofilament with a denier of 8 denier was obtained in accordance with Example 1 by using a nylon polymer with [n] =1.2 and Tg = 41°C as the sheath and a polyethylene terephthalate with an intrinsic viscosity [η] = 0.80 and Tg = 79°C. Strength, elongation and modulus of the obtained filament were 6.5 g/d, 32% and 3.5 g/d respectively. In the same way as the filament of Experiment No.4 in Example 1, bolting cloth of 330 mesh were prepared. Both samples exhibited good weaving properties.
Said fabrics were each set on a making-up frame with a size of 44 cm and tensions of the fabrics were measured with time. The atmosphere was kept usually at 20°C and 65% RH and after 7 days, they were exposed in an high temperature and high humidity atmosphere such as 40°C and 80% RH and stabilities of tensions of the fabrics were evaluated. Tensions of the fabrics were measured in terms of N/cm by using TENSION METER-40D manufactured by HINRICH MANTEL Co., Ltd. The results were shown in Table 3.
The fabric made of the composite monofilament wherein nylon was the sheath component (Comparative Example 1) exhibited large initial change and large dependence on temperature and moisture, which showed that it was unstable. On the other hand, the fabric using the composite monofilament of the present invention (Example 3) exhibited small initial change and small dependence on temperature and moisture, which showed that it was stable.

Example 4 ,

A polyethylene terephthalate with an intrinsic viscosity [n] of 0.8 was prepared by an ordinary method as an island component of a composite monofilament. Tg of this polymer was 79°C. On the other hand, as a sea component, a polymer with an intrinsic viscosity [n] of 0.64 made by incorporating 10 wt.% of polyethylene glycol with a molecular weight of 1,000 when a polyethylene terephthalate was polymerized, was prepared. Tg of this polymer was 56°C.
Composite spinning was performed by meas of a well known method for obtaining a laterally-arranged polymer to obtain a monofilament with a ratio of the sea to the island of 10:90, having 16 independent islands and with a total denier of 10 denier. Strength, modulus at 10% elongation and elongation of this monofilament were 6.5 g/d, 5.3 g/d and 32% respectively. This monofilament showed very much flexibility. A fabric with 315 mesh was woven and according to the result of evaluation of scum, even though this was a high strength polyester monofilament like this, washing cycle of reed was 1,000 m. When continuous weaving was performed, no washing of the weaving machine was necessary for a long time and a bolting cloth with excellent quality was obtained efficiently.

Comparative Example 2

By using the polyethylene terephthalate used in Example 4 for the island component with an intrinsic viscosity [n] = 0.8 a monofilament with a denier of 10 was prepared by means of an ordinary method. The strength of the filament was made 6.5 g/d by adjusting spinning and drawing conditions so as to be able to compare directly with Example 4. The obtained monofilament had a modulus at 10% elongation of 5.5 g/d and an elongation of 33% respectively. Even though both monofilaments had the same denier, the monofilament of Example 4 exhibited hard feeling. Evaluation of scum showed that a large amount of scum was accumulated only after 80 m and continuous weaving was impossible.

Example 5

To compare Tg of the sea component with the development of scum, islands-in-a-sea type monofilaments were obtained by using polymers shown in Table 4 as sea components in accordance with Example 4. The composite ratio in this Example was 15:85 and the monofilaments consisted of 24 islands.
Characteristics and evaluation results on the obtained filaments were shown in Table 4. In addition, dimensional stability shown in Table 4 was obtained by comparing printing accuracy after printing 1,000 times.
In the experiment Nos. A and H, as Tg of the copolymer used as the sea component was too high, a larger amount of scum was produced in evaluation of scum and the reed washing cycle was extremely short and stable weaving for a long time was difficult. In the experiment E, as Tg of the copolymer was too low, dimensional stability of the fabric obtained was poor and the printing accuracy was no good. The experiment Nos. B, C, D, F and G were high strength and high modulus polyester monofilaments of the present invention, which exhibited long reed washing cycle during weaving and the obtained fabric had high strengths and high moduli and excellent dimensional stabilities.

Example 6

A polymer copolymerized with adipic acid with Tg of 63°C and an intrinsic viscosity [n] = 0.67 was prepared. A composite monofilament was obtained in accordance with Example 1. In this case, for comparison, the composite ratio of the sea to the island and the number of island component were changed as shown in Table 2. The obtained results were shown in Table 2.
In addition, dimensional stability shown in the Table was obtained by comparing printing accuracy after printing for 1,000 times.
In the Experiment No. I, strength of the obtained monofilament was low and a trouble such as filament breakage occurred during weaving. In the Experiment No. J, as the strength was low, when the fabric was set under stretching, it was easily broken. In the Experiment No. M, as the ratio of the sea was 3, which was too small, no suppression effect on occurrence of scum existed and the reed washing cycle was accordingly short. In the Experiment No. 0, as the area ratio of the sea component was 35, which was too large, strength of the obtained monofilament was low and filament breakage occurred during weaving and it was impossible to weave a fabric.
Experiment Nos. K, L and N were high strength and high modulus polyester monofilaments of the present ivnention. These monofilaments exhibited little generation of scum during weaving and the obtained fabrics had high strengths and high moduli and excellent dimensional stabilities.

Industrial Application Field

In a polyester composite monofilament of the present invention, by using a copolyester which does not generate scum, has a low glass transition point and is soft as the sheath component suppressing development of scum and a polyester exhibiting enhanced mechanical characteristics of the.monofilament as the core component, even the monofilament provides high strength, high modulus and low elongation, the problem which is the development of scum during weaving can be solved. As the result, a bolting cloth consisting of a monofilament, with a fine denier and having a high mesh, a high tenacity and a high modulus can be obtained and it is possible to perform with good accurracy a highly precise printing without dimensional change during printing and with a line width of 100 um or smaller.

Claims

1. A polyester composite monofilament for bolting cloth for screen printing characterized by a composite monofilament consisting of a polyester wherein

(a) glass transition temperature (Tg) of a polyester forming the sheath is 35 - 73°C and is lower than the glass transition temperature of a polyester forming the core,

(b) the area ratio of the core to the sheath is in the range of 70:30 - 95:5, and

(c) braking strength of said monofilament is 6 g/d or higher and modulus at 10% elongation thereof is 3.5 g/d or higher.

2. A polyester composite monofilament for bolting cloth according to Claim 1 characterized by said composite monofilament wherein it is substantially a concentric circle type sheath-core structure.

3. A polyester composite monofilament for bolting cloth according to Claim 1 characterized by said composite monofilament wherein the core component is polyethylene terephthalate and the sheath component is a copolyester wherein polyethylene terephthalate is a main component.

4. A polyester composite monofilament for bolting cloth according to Claim 4 characterized by said sheath component being a copolyester wherein at least one selected from dimer acid, adipic acid, sebacic acid and a compound of the following general formula is copolymerized with polyethylene terephthalate.

R₁O(C_nH_2nO)_mR₂

wherein R₁ and R₂: one selected from H or an alkyl group having 1 to 4 carbon atoms,

n: an integer of 2 - 5,

m: an integer of 2 - 250.

5. A polyester composite monofilament for bolting cloth according to Claim 1 wherein said composite monofilament is less than 9 denier.

6. A polyester composite monofilament for bolting cloth according to Claim 1 characterized by said composite monofilament wherein number of the core is 5 or more and the denier of each individual core is 3 d or smaller.