WO2005019301A1

WO2005019301A1 - Polypropylene glycol modified polyester fibers

Info

Publication number: WO2005019301A1
Application number: PCT/IB2004/003066
Authority: WO
Inventors: Ivo Edward Ruzek
Original assignee: Ivo Edward Ruzek
Priority date: 2003-08-25
Filing date: 2004-07-23
Publication date: 2005-03-03
Also published as: DE10340380A1

Abstract

Disclosed are block co-polyester fibers which provide permanent wet ability and moisture absorption characteristics due to their exceptional fine structure and wF:ich, therefore, can be formed into extraordinary comfortable fabrics. The block co-polyester is characterized by a basic polymer skeleton of polyethylene terephtalate chains where a pert of the constituting glycol units is exchanged by blocks of polypropylene glycol, whereby the portion of polypropylene glycol blocs is as low as possible but still sufficient, that the required beneficial wicking properties in the final web can be reached.

Description

POLYPROPYLENE GLYCOL MODIFIED POLYESTER FIBERS

Field of the invention

The present invention relates to fibers made from block co-polyesters containing blocs of polypropylene glycol and providing exceptionally good moisture management characteristics and that can be formed into extraordinary comfortable fabrics. Further this invention relates to textile or nonwovens fabrics made out of the said block co-polyester.

Background of the invention

Polyester fibers are the most valuated synthetic fibers available at the market place. They combine highly appreciated properties, like specific strength allowing a way to lightweight fabrics, with excellent elastic recovery and limited water retention. Therefore, a polyester fabric resist wrinkles and creases, retain its shape in garments, resist abrasion, dry quickly and require minimal care. Nevertheless, the lake of reasonable water absorption will be f equently considered as negative, however advantageous it might be from the point of view of the capability to dry fast. This is particularly the case when textile or nonwovens fabrics have to be formed only from polyester fibers. Organoleptic and tactile properties of such polyester textile fabrics can eventually be improved by changes of the geometry of polyester fibers. Polyester continuous filament yarns can achieve acceptable characteristics of appearance, hand and comfort by texturizing. Substantial positive changes in textile properties and behavior of polyester fibers have been achieved by use of microfibres, which means fibers with a diameter of less than 10 mμ or titer of less than 1 dtex. The exceptionally good esthetics of polyester microfibres will be up to some extend limited by serious problems in their processing. Except others, they are difficult to dye, because of their high orientation and crystallinity.

When polyester staple fibers are used an improvement in organoleptic properties can be mostly reached by their blending with other fibers, either natural, like cotton, wool, linen etc., or cellulosic man made fibers (viscose). All the fibers used in blended yarns mentioned above have certain advantages and disadvantages, which are mostly different to advantages and disadvantages of polyester fibers. Therefore it is possible to optimize the characteristics of blended textile fabrics by choosing the right ratio of the components.

Cotton is perhaps most widely used component in blended polyester fabrics. It is formed almost entirely of pure cellulose. Supreme quality cotton provides fibers of a length up to 50 mm; poor quality types can be as short as 10 mm and less. An average quality would have fibers of about 25 mm. Mature cotton fibers are characterized by their convulsions. They are formed by twisted ribbons with thickened edges. Cotton is lightweight, absorbs moisture easily and quickly and provides a favorable texture, or hand in yarns and textile fabrics. Low strength characteristics, particularly when wet and lack of elastic recovery are the most disadvantageous properties of cotton. Textile fabrics and garments made of pure cotton require frequent laundering and pressing.

Therefore, blend of cotton with polyester fibers can provide optimized properties in term of the final textile fabrics. Nevertheless, the need to improve organoleptic properties of polyester fibers continues. As the basic properties of polyester fibers are consequence of their fine structure, of the rigidity of their molecular skeleton, many efforts are focused on chemical modification of the basic molecular chain. In the more than 60 years old history of polyester fibers the ways of chemical modifications, as they have been published, mostly in form of patents, are numberless. Of particular interest are, of course, such modifications, which can positively influence moisture absorption and moisture transport in polyester fabrics. One of the recently followed ways used polyethylene glycol as modification substrate. Thanks to the two terminal hydroxyl-groups, polyethylene glycol can be incorporated in the polyester molecular chain. Due to the multiple ether oxygen atoms, which behave as polar groups, polyethylene glycol can reduce surface tension and improve wet ability. A further change in polyester structure can be achieved by additional incorporating of a chain branching agent who helps to further open the rigid skeleton of polyethylene terephtalate. Branum discloses a precise description of this way in terms of the composition of such modified co-polyesters as well as in terms of their manufacturing in the USP 6,509,091 at al., which is here incorporated entirely herein by reference.

As discussed in the USP 6,509,091, the improved wicking that may be achieved in polyester fibers by incorporating polyethylene glycol eventually in combination with a branching agent is advantageous particularly in nonwoven fabrics. Such nonwoven fabrics made of polyethylene glycol modified polyester can be used in several personal care products, like diapers, sanitary napkins and similar. In this regard disposable diapers and other personal care products formed of nonwovens synthetic fabrics are extremely popular and in developed countries they essentially replaced cloth diapers at the market place. This is so not only because nonwoven fabrics enable use of modern technologies and therefore offer an attractive cost structure, but also because nonwoven fabrics provide superior performance. For example continued enhancements to nonwoven fabrics include weight reduction, aesthetic improvements and, of particular relevance to diapers, increase the number of urine impacts an article can endure before requiring disposal.

For many years, synthetic fibers and preferably polyester fibers represented the major component in nonwovens fabrics for disposable personal care products. Such man-made fibers are cost effective and are modifiable to deliver arrange of desired properties. For example denier, crimp, staple length, polymer chemistry and fiber finish chemistry can all be modified to meet specific end-use requirements. In this regard coarser deniers are used to increase bulk, cut length can be optimize for various web formation techniques, and fiber finishes are modified to offer processing advantages, as well as end-use performance.

In the contemporary diaper, the primary function of the polyester nonwoven layer (absorption and distribution layer) is to spread urine from the impact spot to the entire area of the absorption core. This helps to keep the surface of the diaper topsheet essentially dry and makes the diaper available to accept the moisture from the next urine impact. This extends the duration that an absorption product can be used before disposal. The absoφtion and distribution layers are often chemically treated to facilitate this kind of moisture movement. Such chemical treatment of the fiber surface are typically not capable to permit unlimited multiple use, as they are, even when specially formulated, more or less washed out.

In same way this are the moisture management properties, which are required in wipes. Today the wipes are regularly made by hydroentangling of carded webs. Because of not sufficient moisture management properties it is in most cases necessary to use blends of cellulosic fibers, either cotton or viscose, and polyester fibers. Substantial improvement of moisture management properties of polyester fibers would help to reduce or fully abandon the need for blending polyester with cellulosic fibers. Because the cellulosic fibers are much more expensive as polyester fibers, such improvement of the properties of polyester fibers would help to control manufacturing cost of wipes, the probably most rapidly growing segment of all nonwoven fabrics.

Therefore, to substantially improve moisture management properties and this, possibly, independent on the duration of this their function remains a continuing need.

Object and Summary of the Invention

It is an object of this invention to provide a polypropylene glycol modified block co-polyester fiber, that has exceptional good moisture management characteristics and that can be formed into exceptionally comfortable fabrics.

It is another object of this invention to provide polypropylene glycol modified block copolyester composition that is particularly suitable for such fibers.

Further it is an object of this invention to provide methods of preparing polypropylene glycol modified block copolyester fibers that can be formed into exceptionally comfortable fabrics.

It is still an other object of this invention to provide polypropylene modified block copolyester fiber that can be processed using conventional melt spinning equipment, despite such fibers have superior properties in terms of wicking, drying, soft hand and static dissipation properties.

Finally it is an object of this invention to provide textile and nonwovens fabrics providing exceptional moisture management properties, be it formed out of staple fibers or of continuous filaments. Such textile and nonwovens fabrics are especially useful in textile and industrial (protective) apparels, in absorbent personal products, such as wipes, disposable diapers, training paints and adult incontinence products, in sanitary napkins or even in durable products with improved appearance, performance and aesthetics.

Detailed Description

The present invention comprises polypropylene glycol modified block co-polyester and block co-polyester fibers made out of it. Those fibers provide exceptional moisture management characteristics and they can be formed in exceptionally comfortable textile and / or nonwovens fabrics. The block co-polyester out of which the fiber as well as finally the fabrics will be formed, includes basic polyester blocs of polyethylene terephtalate in amount sufficient to maintain basic physical properties of the block copolyster fibers, like strength properties and dimensional stability substantially similar to those of conventional, unmodified polyethylene terephtalate fibers. Further, the co-polyester also includes blocks of polypropylene glycol having an average molecular mass lower than 4000 g/mol in a complementary amount which is sufficient for the block co-polyester fiber to achieve wicking properties which are substantially superior to those of conventional, unmodified polyethylene terephtalate fibers. Furthermore, the block co-polyester fiber has an intrinsic viscosity (IV) of at least about 0.62.

An essential aspect of this invention is that the polypropylene glycol modified block copolyester composition is particularly suitable for fibers. This is why it includes blocks of polyethylene terephtalate in amount sufficient for fibers made out of those co-polyester compositions to possess basic physical properties, such as strength properties and dimensional stability substantially similar to those of conventional, unmodified polyethylene terephtalate fibers. The co-polyester composition also contains blocks of polypropylene glycol of an average molecular mass of less than 4000 g/mol in an amount necessary for a fiber made of those compositions to achieve wicking properties, which are substantially superior to those of conventional, unmodified polyethylene terephtalate fibers. Hence, the weight fraction of polypropylene terephtalate blocs in those co-polyester compositions is between 2 and 20 %. Depending on the end use of such modified bloc- co-polyester fibers the actual weight fraction could be optimized by using the skill of fiber chemist. For many purposes, the optimal and most preferred weight fraction of polypropylene glycol blocs would lay in a range of 10 to 13 %.

Depending on the technology used there is several ways how to add the polypropylene glycol to the basic polyethylene terephtalate. Thereby it has to be understood, that polypropylene glycol represent a pre-polymer of particular kind, which contains two terminal hydroxyl groups and which, therefore, can react with end groups of the basic polyethylene terephtalate and, hence, which can be by esterification (or by trans-esterification respectively) incorporated in the basic polyester skeleton, either as end block, or s intermediate block. As polyesters as polycondensates, are "living polymers in which, particularly under melted conditions, trans-esterification always are taking part, the polypropylene glycol block would not be stationary fixed at a particular place in the basic polyester skeleton.

The USP 6,509,091 [BRANUM, at al.] mentioned above deals with co-polyesters modified by polyethylene glycol (PEG) and by jointly added branching agent capable to cause a particular level of cross linking of the linear polyester molecules.

Polyethylene glycol (PEG) is strictly linear polymer with simple chains, therefore very flexible and adaptable in any fine polymer structure. Just in difference, the basic chain of polyethylene terephtalate (PETP) is as well a linear polymer, but in its structure very rigid, due to the presence of rigid aromatic rings of terephtalic acid connected by very short members of mono ethylene glycol (MEG). The very rigid chains of PETP are capable to form easily crystalline or semi-crystalline structures in the polymer, which, among others are the reason for high density of PETP. Except of that, it is the rigid structure of PETP, which supports many of positive properties of this polymer and fibers made of it. The insertion of longer very flexible molecular chain of PEG has strong impact on the structure of such copolyester. However, the very flexible and very adaptable molecular chains of PEG require the use of either relatively high portion or the use of long chain PEG. In both cases, the PEG would have negative impact on the polycondensation process in those co-polyesters. It would be difficult to manufacture co-polyester at a sufficient level of Intrinsic Viscosity or melt viscosity. This is the reason for use of cross linking or branching agent. In some cases it will be necessary to subject the primary co-polyester from the polymerization in a second step to solid state polymerization.

It is the advantage of the use of polypropylene glycol according to this invention, that it ca avoid the necessity of any branching agent. Even if polypropylene glycol is as well a linear polymer, there are the methylene side groups which reduce its flexibility. This is the reason, why, using PPG, a desired level of disturbance of the rigid structure of the PETP can be reached with reduced portion of the modification agent. In that way it is possible to limit the negative impact of the modification on melt viscosity and spinning properties without using any branching agent.

In one embodiment, the polypropylene glycol could be added jointly with other major constituents - terephtalic acid (or dimethyl terephtalate respectively) and ethylene glycol at the beginning of the reaction and it can be incorporated during the whole process of polycondensation. In an other embodiment it could be added to the reaction product of the first step, i. e. of esterification (or trans-esterification respectively) and take part during the pre-polycondensation and following final polycondensation. In these cases the conditions of the regular process provide a sufficient mixing, so that no any special care has to be taken. It is obvious, that the above embodiments are particularly suitable for bulk and continuous manufacturing of such block co-polyester.

In an other embodiment it is possible to add the polypropylene glycol at the end of the final polycondensation. This would allow higher flexibility and more frequent change in the production program. In such case it is necessary to take special care of a proper mixing of the two components, where the basic polyester mass has high melt viscosity, whereby the other one has rather much lower viscosity. A proper mixing can be eventually achieved by means of static mixers embodied into the pipeline. After the proper mixing, sufficient residential time and a proper vacuum condition for the chemical reaction are required. However, more advantageous is the use of twin screw extruders (e. g. Werner Pfleiderer) with very good mixing effect and with the possibility to install a proper vacuum zone supporting polycondensation and incorporating of the polypropylene glycol blocks into the polyester skeleton chain. In still next embodiment it is possible to use such twin screw extruder for both melting of polyester solid chips and adding the polypropylene glycol modificator. Even in this case it is necessary to assure a sufficient residential time and other conditions (vacuum) to provide the incorporating by polycondensation.

In still other embodiment it is how ever possible to simply add the polypropylene glycol in desired portion to the polyester polymer, solidify the blend and provide a solid state after polycondensation.

It will be understood, that those having an ordinary skill in he art can decide what option would be the most appropriate for each particular case and how the details of each preferred option can be arranged and adjusted.

The capability to achieve the required optimal combination properties in the block copolyester by relatively small portion of PPG is both an advantage in the practicing of the technology and an advantage in the economy of such modification.

It is further and advantage to use PPG of low degree of polymerization rather than such of a high degree of polymerization. Such types of PPG with medium degree of polymerization (MW of about 500 g/mol) provide higher impact on the wet ability and wicking properties, than PPG of high degree of polymerization. This is due to the special kind of activation of etheric bonds in PPG which would decrease with growing length of the polymer chain.

The present invention allows the manufacturing of block co-polyesters which comprise the basic chain of PETP and blocks made of PPG. The portion of PETP remains high enough to assure the co-polyester fibers to possess dimensional stability and strength substantially similar to those of conventional PETP fibers. Thereby, the portion of PPG has to be sufficient to provide in the co-polyester fibers wet ability and wicking properties, dissipation of static charge and other properties allowing to describe them as moisture management, that are superior to those of conventional polyester fibers.

The term fibers as used in this description includes any possible embodiment as continuous filaments, partially oriented filaments, fully drawn yarn, texturized continuous filaments, staple fibers, textile or nonwoven fabrics and even spunbonded nonwoven materials made of continuous filaments.

The terms Intrinsic Viscosity and Melt Viscosity will be used in conventional meaning. Their measurement will be made according to usual and internationally accepted procedures.

In the production of a block co-polyester according to this invention will be used, as usual, ethylene glycol (Mono Ethylene Glycol, MEG), pure terephtalic acid (PTA), or eventually its dimethyl ester, (Dimethyl Terephtalate, DMT) and Polypropylene Glycol (PPG) as modification agent. Further, there will be used catalysts and additives (e. g. stabilisers) well known to such of technical skill.

From chemical point of view, PPG is a glycol of particular kind. It is capable to take part on the esterification process of terephtalic acid and becomes part of the polymer chain of the resulting PETP. Under the conditions of the polymerization represents PPG a component, which does not change in terms of its characteristics, particularly its degree of polymerization or molecular mass. Otherwise, is the molecular mass of PPG, which is basically responsible for many of its properties as well as for its impact in the co-polyester. Particularly important is to respect the fact, that with the increasing degree of polymerization the activity of the terminal hydroxyl groups in PPG will be reduced. This will negatively impact its capability to participate on esterification reactions. Therefore, PPG of medium molecular mass of400 to 1000 will be preferred.

The weight portion of the PPG can be between 3 and 20 %. Preferred will be portions between 4 an 10 %.

The characterization of the block co-polyester requires information about both the molecular mass of the PPG used as well as its weight portion.

Claims

1. Block co-polyester formulation comprising polyethylene terephtalate skeleton chains in a portion necessary to achieve dimensional stability properties in final products as fibers and related fabrics substantially similar as such, which can be achieved in analogous conventional unmodified polyethylene terephtalate products;

Blocks of polypropylene glycol necessary to achieve beneficial wicking properties that are superior to those of conventional analogous unmodified polyethylene terephtalate products, whereby the blocks of polypropylene glycol have an average molecular mass lower than 4000 g/mol; wherein said blocks are substantially incorporated in said basic skeleton formed by polyethylene terephtalate.

2. A block co-polyester formulation according to claim 1, wherein tiie intrinsic viscosity of the block co-polyester is at least 0.62 dl/g.

3. A block co-polyester formulation according to claim 1, wherein the intrinsic viscosity of the block co-polyester is at least 0.65 dl/g.

4. A block co-polyester formulation according to claim 1 , wherein the intrinsic viscosity of the block co-polyester is at least 0.70 dl/g.

5. A block co-polyester formulation according to claim 1 , wherein die intrinsic viscosity of the block co-polyester is at least 0.80 dl/g.

6. A block co-polyester chip formed from block co-polyester according to claims 1 to 4.

7. Modified co-polyester fiber which can be formed into extraordinary comfortable textile fabrics, made from a block co-polyester formulation comprising polyethylene terephtalate skeleton chains in a portion necessary to achieve dimensional stability properties substantially similar to conventional unmodified polyethylene terephtalate fibers; blocks of polypropylene glycol necessary to achieve beneficial wicking properties that are superior to those of conventional , unmodified polyethylene terephtalate fibers, whereby the blocs of polypropylene glycol have an average molecular mass lower than 4000 g/mol; wherein said blocks of polypropylene glycol are substantially incorporated in said basic skeleton formed by polyethylene terephtalate.

8. A co-polyester fiber according to claim 6, wherein the intrinsic viscosity of the block co-polyester is at least 0.65 dl/g.

9. A co-polyester fiber according to claim 6, wherein the intrinsiς viscosity of the block co-polyester is at least 0.70 dl/g.

10. A co-polyester fiber according to claim 6, wherein the intrinsip viscosity of the block co-polyester is at least 0.80 dl/g.

11. A co-polyester fiber according to claims 6 to 9, wherein the weight fraction of the polypropylene glycol is between 2 and 20 %.

12. A co-polyester fiber according to claims 6 to 9, wherein the weight fraction of the polypropylene glycol is between 8 and 16 %.

13. A co-polyester fiber according to claims 6 to 9, wherein the weight fraction of the polypropylene glycol is between 10 and 13 %.

14. A bi-component fiber, wherein at least one of both components will be formed from block co-polyester according to claims 6 to 9.

15. A spun yarn formed from block co-polyester according to claims 6 to 13.

16. A continuous filament yarn formed from block co-polyester according to clams 6 to 13.

17. A fabric formed from block co-polyester according to claims 6 to 15.

18. A nonwoven fabric formed from block co-polyester according to claims 6 to 13.

19. A nonwoven fabric formed from block co-polyester according to claims 6 to 13, wherein said co-polyester fibers comprise staple fibers.

20. A nonwoven fabric formed from block co-polyester according to claims 6 to 13, wherein said co-polyester fibers comprise co-polyester filaments.

21. A nonwoven fabric formed from block co-polyester according to claims 6 to 13, wherein said nonwovens fabric is a melt spunlaid nonwovens fabric.

22. A nonwoven fabric formed from block co-polyester according to claims 6 to 13; wherein said nonwoven fabric is a melt-blown nonwoven fabric.

23. A multiplies fabric formed from block co-polyester according to claims 5 to 13, comprising any combination of individual plies as according to claims 16 to 21

24. A method of manufacturing of block co-polyester fibers that can be formed into extraordinary comfortable fabrics, comprising: incorporating polypropylene blocks into a skeleton chain of polyethylene terephtalate in a melt phase to form a block co-polyester of a intrinsic viscosity of at least 0.65 dl/g, wherein the polypropylene glycol is present in a portion sufficient to achieve beneficial wicking properties and still providing substantially similar dimensional stability as conventional unmodified polyethylene terephtalate; wherein the polypropylene glycol has an average molecular mass of less than about 4000 g/mol; thereafter spinning the block co-polyester formulatioη into any form of fibers.