Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1999-11-15
2001-07-10
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
Reexamination Certificate
active
06258309
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for preparing polyester fibers which are superior in water absorbency when compared to those of cotton and wool.
2. Description of the Prior Art
Polyester fibers are usually prepared mainly from terephthalic acid or aromatic dicarboxylic acid, such as 2,6-naphthalenedicarboxylic acid, or their ester derivatives, and ethylene glycol through polycondensation.
Polyester fibers are superior in mechanical properties and thermal resistance, but poor in water absorbency, when compared to natural fibers, such as regenerated cellulose, because polyester fibers have a structure of high crystallinity and few water-affinitive groups, e.g., hydrophilic groups in their molecules. The term “water absorbency” as used herein means the extent to which fiber mass, such as filaments, strands, textile fabrics, knitted goods, non-woven fabrics and the like, absorbs water. Where water absorbency is needed, the use of polyester fibers may cause a problem.
For this reason, active research has been directed to the development of polyester fibers which are of excellent water absorbency while retaining their physical properties.
For example, U.S. Pat. No. 3,329,557 and U.K. Pat. No. 956,833 disclose that polyester can be blended with hydrophilic polyalkylene glycol before spinning. The polyester fibers thus obtained, however, show fairly deteriorated physical properties in addition to not reaching a satisfactory level of water absorbency.
Korean Pat. Publication No. 93-6779 discloses a polyester with an organic compound having polyalkylene or polyamine as a main chain. Disclosed in Korean Pat. Publication No. 86-397 is a polyester mixed with the eluting agent ROSO
3
M (wherein R is an alkyl group containing 1-30 carbon atoms or an alkylaryl group containing 7-40 carbon atoms and M is an alkaline metal or an alkali earth metal) and spun and the fibers are made porous by elution treatment with an aqueous alkaline solution. These polyester fibers are significantly improved in water absorbency, but suffer from a significant disadvantage of being expensive. The additives are highly priced and additional processes increased the high production cost.
It is also known that polyester fibers are provided with hydrophilicity by addition with colloidal silica particles. This causes likewise an increase in production cost.
It is also known that polyester fibers are provided with hydrophilicity by addition with colloidal silica particles. This causes likewise an increase in production cost.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the above problems encountered in the prior art and to provide a method for preparing polyester fibers which show excellent water absorbency as well as physical properties.
It is another object of the present invention to provide a method for preparing polyester fibers, which does not significantly increase the production cost.
In one embodiment of the present invention, there is a method for preparing polyester fibers of excellent water absorbency, in which inorganic particles are added at an amount of 0.01-50 weight %, based on the total weight of the fibers, at a suitable addition time from polyester polymerization to a stage before spinning. In one aspect, the addition time is selected from a polyester polymerization stage, a stage in which polyester is flowed under pressure to a spinneret, and a stage in which polyester is melt-extruded to chips. In another aspect of the embodiment, the inorganic particles are selected from the group consisting of calcium oxide particles, magnesium oxide particles, manganese oxide particles and mixtures thereof and range in size from 0.01 to 50 &mgr;m.
DETAILED DESCRIPTION OF THE INVENTION
Polyester is usually prepared from polycarboxylic acid and polyhydric alcohol. For the polyester fibers of the present invention, aromatic dicarboxylic acid or its ester derivatives are employed. Examples of the aromatic dicarboxylic acid useful in the present invention include isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, phthalic acid, adipic acid, sebacic acid, and mixtures thereof. As the polyhydric alcohol, ethylene glycol is mainly used, together with a small amount of other alcohols, such as propylene glycol, butanediol, 1,4-cyclohexanediol and neopentylglycol.
If necessary, additives such as thermal stabilizers, anti-blocking agents, antioxidants, antistatic agents, UV absorbents, etc, may be used in preparing polyester fibers.
In accordance with the present invention, inorganic particles are used in preparing polyester fibers, in order to endow the polyester fibers with high hydrophilicity. The inorganic particles are selected from the group consisting of calcium oxide particles, magnesium oxide particles, manganese oxide particles, and mixtures thereof.
As for the addition time of the inorganic particles during the preparation of polyester fibers, it may be selected from a polyester polymerization stage, a stage in which polyester is flowed under pressure to a spinneret, and a stage in which polyester is melt-extruded to chips.
In the polyester polymerization stage, the inorganic particles are preferably added at the time just after completion of the esterification step, or at the time of the polycondensation step. In this regard, the inorganic particles to be added must not contain moisture lest the reaction is inhibited.
After being polymerized through polycondensation, polyester is transferred under pressure to a spinneret in order to spin polyester fibers. In the course of this transfer, calcium oxide particles, magnesium oxide particles, manganese oxide particles or mixtures thereof may be added. In this connection, some of the polymer is drawn from the transfer pipe, added with the inorganic particles, and returned to the remaining polymer in the pipe.
When the polyester polymerized is transferred to an extruder to produce polyester chips, the inorganic particles are fed directly. The inorganic particle-containing polyester chips can be used in the present invention, alone or in combination with other polyester chips.
Typically, calcium oxide particles can be obtained from calcium carbonate ores. First, calcium carbonate ores are pulverized to small pieces and baked at about 1,000° C. in a furnace to separate calcium oxide and carbon oxide. Calcium carbonate particles are advantageous in that they are easily obtained and low-priced owing to simple manufacturing processes. When encountered with water, calcium oxide is readily converted into calcium hydroxide (Ca(OH)
2
). Accordingly, this high hydrophilicity of calcium oxide enables the polyester fibers to have excellent water absorbency. This mechanism of improving water absorbency is true of magnesium oxide and manganese oxide.
Preferably, the inorganic particles range, in size, from 0.01 to 50 &mgr;m. For example, when inorganic particles with a size less than 0.01 &mgr;m are used, a great improvement is not brought about in the water absorbency. On the other hand, inorganic particles greater than 50 &mgr;m readily cause fiber cutting upon spinning processes or after-treatment processes. The inorganic particles are preferably used at an amount of about 0.1-50 weight %, based on the weight of the polyester. For example, the amount smaller than 0.1 weight % gives a trace contribution to the improvement in water absorbency while the amount greater than 50 weight % deleteriously affects the physical properties of the polyester.
As mentioned above, the inorganic particles must not contain water nor impurities, otherwise, deterioration is found in the spinnability and after-treatment process. Further, because the presence of inorganic particles in polyester is a direct factor to abrade the physical properties of the polyester, it is preferred that the inorganic particles be as pure as possible.
A better understanding of the present invention may be obtained in light of the following examples which are set forth, but are not to be construed
Jo Deog Jae
Kim Yeon Soo
Harrison & Egbert
Saehan Industries Incorporation
Tentoni Leo B.
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