JP4616658B2 - Non-woven - Google Patents

Description

  The present invention relates to a non-woven fabric, and more particularly to a non-woven fabric made of short fibers made of polyethylene naphthalate and having excellent tear strength and heat resistance.

  Conventionally, development of a nonwoven fabric having heat resistance has been demanded in various fields. For example, non-woven fabrics are widely used in the fields of heat insulating materials, electrical insulating materials, filters, medical materials, building materials, etc., but heat resistance is required in some of these fields. Development demands are increasing.

  One direction to obtain a heat resistant nonwoven is to use a heat resistant polymer as the material. Nonwoven fabrics using polyethylene naphthalate, which is one of heat-resistant polymers, have already been proposed. Patent Document 1 proposes a non-woven fabric in which a web obtained by mixing polyethylene naphthalate fibers and fibers from a polymer having latent adhesiveness is heat-bonded. In this nonwoven fabric, the fiber used as the adhesive component is typically a fiber from a polyethylene terephthalate copolymer, and its melting point is considerably low. Therefore, this nonwoven fabric is affected by the melting point of the adhesive component, and the original heat resistance of polyethylene naphthalate is not utilized.

  Patent Document 2 proposes a nonwoven fabric that is substantially made of polyethylene naphthalate fiber, has an average fiber diameter of 0.1 to 10 μm, and is excellent in vertical and horizontal tensile strength. However, this non-woven fabric is specifically manufactured by a jet spinning (melt blow) method, and the fiber diameter is non-uniform, thin, and extremely fine. However, the strength of the fiber cannot be said to be sufficiently high. It also affects the tear strength of the nonwoven fabric. Moreover, since this nonwoven fabric is based on jet spinning, it is difficult to provide nonwoven fabrics having various types of characteristics.

  Furthermore, Patent Documents 3 and 4 describe a non-woven fabric for heat-sensitive stencil paper, which is obtained by making a paper sheet of stretched short fibers and unstretched short stretched fibers of polyethylene terephthalate and thermocompression bonding with a calendar. However, as shown in these references, a non-woven fabric obtained by pressure bonding with a metal / elastic roll-type calender pressing machine under conditions of a metal roll surface temperature of 215 ° C. and a linear pressure of 20 kg / cm is shown. ing. However, according to our research, nonwoven fabrics molded under such conditions are still insufficient in terms of tear strength, and there are limits to the applications that can be applied in terms of practicality.

JP 50-18773 A JP-A-4-146251 JP 2000-118162 A JP 2000-118163 A

  An object of the present invention is to provide a non-woven fabric having excellent heat resistance and greatly improved tear strength.

  According to the studies by the present inventors, the object of the present invention is a nonwoven fabric comprising a polyethylene naphthalate drawn short fiber and a polyethylene naphthalate unstretched short fiber, and both the short fibers are thermocompression-bonded. It was found that the non-stretched short fiber DSC peak temperature measured in (1) was achieved by a nonwoven fabric characterized by being 270 ° C. or higher.

  According to the present invention, a nonwoven fabric excellent in heat resistance and having significantly improved tear strength is provided. Moreover, since the nonwoven fabric of this invention also has high intensity | strength and can fully be practically used even if it is thin, the effect in terms of weight reduction of a nonwoven fabric is exhibited.

In the present invention, the nonwoven fabric is composed of polyethylene naphthalate drawn short fibers and polyethylene naphthalate unstretched short fibers, and both fibers are thermocompression bonded.
In the nonwoven fabric of the present invention, unstretched polyethylene naphthalate short fibers substantially act as an adhesive component, and the resulting nonwoven fabric has strength and excellent heat resistance.

  Polyethylene naphthalate constituting both of the above fibers, specifically, polyethylene-2,6-naphthalate or copolymer polyethylene-2,6-naphthalate containing a third component of 5 mol% or less. In general, polyethylene-2,6-naphthalate is obtained by combining naphthalene-2,6-dicarboxylic acid or a functional derivative thereof with ethylene glycol or a functional derivative thereof in the presence of a catalyst under suitable reaction conditions. Synthesized. In this case, a copolymerized or mixed polyester is synthesized by adding one or more appropriate third components before the completion of the polymerization of polyethylene-2,6-naphthalate. a) Compounds having two ester-forming functional groups; for example, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, and dimer acid; cyclopropanedicarboxylic acid, cyclobutanedicarboxylic acid, hexahydroterephthalic acid, etc. Alicyclic dicarboxylic acids; aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, naphthalene-2,7-dicarboxylic acid, diphenyldicarboxylic acid; diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethanedicarboxylic acid, 3 , Sodium 5-dicarboxybenzenesulfonate, etc. Carboxylic acid; oxycarboxylic acid such as glycolic acid and p-oxyethoxybenzoic acid; propylene glycol, trimethylene glycol, diethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentylene glycol, p-xylene glycol, 1,4-cyclohexane Dimethanol, bisphenol A, p, p-diphenoxysulfone 1,4-bis (β-hydroxyethoxy) benzene, 2,2-bis (p-β-hydroxyethoxyphenyl) propane, polyalkylene glycol, p-phenylenebis An oxy compound such as (dimethylsiloxane), or a functional derivative thereof; a compound having a high polymerization degree derived from the carboxylic acid, oxycarboxylic acid, oxy compound or functional derivative thereof; or (b) one Compounds having a stealth-forming functional group, such as benzoic acid, benzoylbenzoic acid, benzyloxybenzoic acid, methoxypolyalkylene glycol, etc. (c) Compounds having three or more ester-forming functional groups, such as glycerin, pentaerythritol, trimethylol Propane and the like are also substantially linear and can be used to some extent.

  The polyethylene naphthalate having an intrinsic viscosity [η] of 0.45 to 1.0 is used. The intrinsic viscosity [η] referred to in the present specification is a value obtained by dissolving a polymer in a mixed solvent of phenol and orthodichlorobenzene (mixing ratio 6: 4) and measuring the viscosity at 35 ° C. When the intrinsic viscosity [η] exceeds 1.0, the melt viscosity becomes abnormally high and melt spinning becomes difficult, and when [η] is less than 0.45, a fiber having a desired high melting point and good physical properties is obtained. Since it cannot be obtained, it is inappropriate.

The drawn short fibers in the present invention are preferably highly oriented with a birefringence Δn of 0.20 or more, more preferably 0.20 to 0.36, and even more preferably 0.30 to 0.35. The density is preferably 1.350 to 1.365 g / cm ³ .

  The unstretched short fibers are preferably 0.01 or less, more preferably 0.008 or less, and still more preferably 0.008 or less as Δn. Since the fiber orientation is low as described above, the adhesive strength with the drawn short fiber becomes strong and the fiber is less likely to fall off, which is preferable. Moreover, it is preferable that a density is 1.325-1.340.

  Even if the fiber diameters of the drawn short fibers and the undrawn short fibers constituting the nonwoven fabric of the present invention are too large, the uniformity of the nonwoven fabric is poor and it is particularly difficult to make a thin film paper. On the other hand, if the fiber diameters of the drawn short fibers and the undrawn short fibers are too small, the strength required for a nonwoven fabric cannot be obtained. Therefore, the fiber diameter of the drawn short fiber and the undrawn short fiber is preferably 5 to 50 μm, and more preferably 10 to 30 μm.

The drawn short fiber and the undrawn short drawn fiber may have any cross-sectional shape, but the undrawn short fiber is preferably flat, and in this case, the portion corresponding to the major axis of the cross section is within the above fiber diameter range. Is particularly preferred.
Further, both the drawn short fibers and the undrawn short fibers are more preferably short fibers of about 1 to 15 mm.

  The nonwoven fabric of the present invention is a nonwoven fabric composed of the above-mentioned stretched short fibers and unstretched short fibers, and both fibers are thermocompression bonded. In the present invention, the DSC of unstretched short fibers measured with the nonwoven fabric is used. It is important that the peak temperature is 270 ° C. or higher, preferably 271 ° C. or higher.

  When thermocompression bonding the above two fibers in forming a nonwoven fabric, a calender roll or the like is used. For example, a metal roll with a metal / elastic roll calender press as described in the example of JP-A-2000-118163 is used. In a nonwoven fabric obtained by pressure bonding under conditions of a surface temperature of 215 ° C. and a linear pressure of 20 kg / cm, the DSC peak temperature of unstretched fibers is less than 270 ° C., the tear strength is significantly reduced, and the heat resistance is also lowered. .

The cause of this is not clear, but the crystallization of unstretched short fibers has a great influence on the tear strength of the nonwoven fabric. In addition to the fact that both short fibers are sufficiently fused, It is presumed that crystallization is sufficiently advanced. Moreover, it is considered that some fine structure change occurs at the peak temperature of the DSC, and it has been found that there is a phenomenon in which the tear strength of the nonwoven fabric is remarkably improved.
Further, the DSC peak temperature of the drawn short fibers is preferably 277 ° C. or higher, more preferably 278 ° C. or higher. At this time, the tear strength of the nonwoven fabric tends to be higher.

  When the above-mentioned unstretched short fibers and stretched short fibers are measured by DSC of the nonwoven fabric, if there is a difference between the peak temperatures, they appear as two peaks, the low temperature side is unstretched short fibers, and the high temperature side is stretched It appears as the peak temperature of short fibers. Furthermore, the present invention includes a case where the peak temperature of the undrawn short fibers is shifted to the high temperature side so that the DSC peak of the drawn short fibers overlaps.

  In the present invention, if the mixing ratio of the drawn short fibers is too low, the strength becomes low, and it is difficult to obtain the strength required for insulating paper. On the other hand, if the mixing ratio of unstretched fibers is too low, the adhesion is insufficient and the surface smoothness is insufficient. Therefore, in the nonwoven fabric of the present invention, the mixing ratio of drawn short fibers and undrawn short fibers is preferably in the range of 90:10 to 30:70, and more preferably in the range of 80:20 to 50:50.

If the basis weight of the nonwoven fabric of the present invention is too large, it is difficult to handle. Conversely, if the basis weight is too small, the strength is insufficient, which is a problem. Therefore, the basis weight of the nonwoven fabric of the present invention is preferably 10 to 300 g / m ² , more preferably 20 to 200 g / m ² .

  The thickness of the nonwoven fabric of the present invention is too thick even if it is too thick, and the heat treatment efficiency is deteriorated. Conversely, even if it is too thin, it is prone to wrinkles because it is weak. Therefore, the thickness of the nonwoven fabric of the present invention is preferably 0.2 to 6 mm, more preferably 0.4 to 4 mm.

The tear strength of the nonwoven fabric of the present invention is 0.1 cN / (g / m ² ) or more, and the tear strength sufficient as an electric insulating paper, a heat insulating material, and a filter is maintained.

  The nonwoven fabric of the present invention may be mixed with the third component in a range that does not impair the tear strength, heat resistance, and other basic performances. As such a third component, natural fibers, polyvinyl alcohol-based, aramid-based synthetic fibers, and the like can be used.

The nonwoven fabric of this invention demonstrated above can be manufactured by the following method, for example.
First, the unstretched fiber can be obtained by forming the above-described polyethylene naphthalate into a chip shape, melt spinning by a conventional method, and cutting it into a predetermined length. In addition, the drawn monofilament is made of the above-mentioned polyethylene naphthalate in a chip shape, etc., melt-spun by a conventional method, drawn, and further subjected to heat treatment as necessary, and then cut to a predetermined length. Can be obtained by:

  In the present invention, polyethylene naphthalate may be added to flame retardants, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, organic lubricants such as pigments, fatty acid esters and waxes, or antifoaming agents such as polysiloxane, as necessary. An agent or the like can be blended.

  The obtained drawn short fibers and undrawn short drawn fibers are mixed and dispersed in water with a pulper or a beater so as to have a predetermined ratio, and then made with a circular net, short net or long net paper machine, and then a thermal calendar. Raw cotton is obtained by pressure bonding.

  In the nonwoven fabric of the present invention, as described above, when the DSC peak temperature of the unstretched short fibers is set to 270 ° C. or higher and the peak temperature of the drawn short fibers is expressed to 277 ° C. or higher, the calender roll is used. The surface temperature of the roll is 160 ° C. to 300 ° C., and the linear pressure is 50 to 250 kg / cm. Specifically, even if the roll surface temperature is as low as 160 ° C., the DSC peak temperature can be expressed at 270 ° C. or higher as long as the linear pressure is 240 kg / cm or higher. On the other hand, when the surface temperature of the calender roll is as high as 260 ° C., the DSC peak temperature can be expressed by setting the linear pressure to 50 kg / cm or more.

The measurement methods in the examples are as follows.
(1) DSC peak temperature The DSC peak temperature is measured with a differential calorimetric analyzer manufactured by Perkin Elmer Co., Ltd. at a heating rate of 10 ° C./min.
(2) Fiber birefringence is measured using a polarizing microscope Levex type compensator under white light.
(3) Nonwoven fabric strength and elongation Measured according to JIS L 1096 with a constant speed elongation type tensile tester.
(4) Tear Strength of Nonwoven Fabric According to JIS L 1096, the tear strength was measured with a constant-speed elongation type tensile tester, and the value obtained by dividing the tear strength by weight.

[Example 1]
(Manufacture of drawn short fibers)
A polyethylene naphthalate chip having an intrinsic viscosity of 0.64 was melted at 300 ° C., discharged at 295 ° C. through a die having 1000 holes, and wound at a speed of 600 m / min. Next, this undrawn yarn was drawn in 95 ° C. warm water at a magnification of 3.5 times, subjected to a tension heat treatment at 200 ° C., and then a relaxation heat treatment at 150 ° C. A drawn fiber was obtained and cut into 5 mm to obtain drawn short fibers.

(Manufacture of unstretched short fibers)
A polyethylene naphthalate chip having an intrinsic viscosity of 0.64 is melted at 300 ° C., discharged through a die having a pore number of 1000 at 295 ° C., wound at a speed of 1000 m / min, an average fiber diameter of 8 μm and a birefringence of 0.1. 01 undrawn fiber was obtained, and this was cut into 5 mm to obtain undrawn short fibers.

(Paper making)
The drawn short fibers and undrawn short fibers were sufficiently mixed and dispersed in a pulper at a weight ratio of 65:35, and then heated and dried with a circular paper machine at a speed of 9 m / min and a Yankee dryer surface temperature of 130 ° C. The paper weight per unit area was 10 g / m ² .

  Subsequently, the metal roll was calendered with a metal / elastic roll calendering machine under conditions of a metal roll surface temperature of 260 ° C. and a linear pressure of 60 kg / cm to obtain a nonwoven fabric having a thickness of 1 mm. When the DSC of this nonwoven fabric was measured, a peak temperature of undrawn short fibers was observed at 271 ° C, and a peak temperature of drawn short fibers was observed at 279 ° C. The results are shown in Table 1. The tear strength, strength, and elongation of the nonwoven fabric all indicate physical properties in the length direction of the nonwoven fabric.

[Example 2 and Comparative Examples 1 and 2]
A nonwoven fabric was obtained in the same manner as in Example 1 except that the calendar conditions for papermaking were changed as shown in Table 1. The results are shown in Table 1.

  According to the present invention, a short fiber nonwoven fabric having excellent heat resistance and high tear strength is provided. Therefore, it can be advantageously used for non-woven fabric applications that require heat resistance and tear strength, such as heat insulating materials, electrical insulating paper, and various filters.

Claims (4)

  A nonwoven fabric comprising polyethylene naphthalate drawn short fibers and polyethylene naphthalate undrawn short fibers, and both short fibers are thermocompression bonded, and the DSC peak temperature of the undrawn short fibers measured with the nonwoven fabric is 270 ° C. or higher. A nonwoven fabric characterized by being.   The nonwoven fabric according to claim 1, wherein the DSC peak temperature of the drawn short fibers measured with the nonwoven fabric is 277 ° C or higher. The nonwoven fabric according to claim 1 or 2, having a tear strength of 0.1 cN / (g / m ² ) or more.   Polyethylene naphthalate short fibers having a birefringence (Δn) of 0.22 or more and low orientation polyethylene naphthalate short fibers having a birefringence (Δn) of 0.01 or less are mixed. The nonwoven fabric according to any one of claims 1 to 3, which is finely bonded and thermocompression bonded.