EP0162564A2

EP0162564A2 - Fiber for insulating material, non-woven fabric, wadding structure and net-like fiber sheet

Info

Publication number: EP0162564A2
Application number: EP85302536A
Authority: EP
Inventors: Makoto Yoshida; Shunichi Takeda; Kiyoshi Ikeda
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 1984-05-24
Filing date: 1985-04-11
Publication date: 1985-11-27
Also published as: EP0162564A3

Abstract

@ Disclosed is a fiber for a heat insulating material which contains 1-30 wt.% of a metal or metal oxide powder and has an emissive power of not more than 0.3 and an average particle size of 1-100 µm. The fiber preferably has a flatness of at least 2 in the cross-section or is a sheath-core type composite fiber, the sheath component containing a larger amount of the metal or metal oxide powder than the core component. The fiber may be used as a non-woven fabric or a wadding structure. It also may be used in the form of a net-like fiber sheet.

Description

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a fiber for a heat insulating material. More particularly, it relates to a fiber for a heat insulating material which contains a finely divided metal or metal oxide having a low emissive power. It also relates to a non-woven fabric, a wadding structure and a net-like fiber sheet, which are composed of metal or metal oxide-containing fibers.
A web or non-woven fabric formed from the fiber of the present invention or a web or non-woven fabric formed from a mixture containing the fiber of the present invention has an excellent heat insulating property and can satisfy various requirements for heat insulating materials. Such a web or non-woven fabric is useful as a wadding for a sleeping mat or mattress, a coverlet, a foot warmer, sportswear, casual wear or the like.

(2) Description of the Related Art

Various methods have been tried to utilize metals for improving the heat insulating effect in bedding and automobile interior materials, but most of these known methods utilize the technique of vacuum deposition of metals. For example, there has been proposed a coverlet for a foot warmer, which comprises a metal-vacuum-deposited non-woven fabric formed by piling a thin sheet having a metal vacuum-deposited on the surface thereof on a thin web layer and needle-punching the assembly to cause parts of fibers of the thin web layer to project to the metal-vacuum-deposited surface of the thin sheet and to integrate both the sheet and layer with each- other-, a fiber web layer which is piled on the metal-vacuum-deposited non-woven fabric so that the metal-vacuum-deposited surface is located on the outer side, and a fabric for covering both the metal-vacuum-deposited non-woven fabric and the fiber web layer (see Japanese Examined Utility Model Publication (Kokoku) No. 58-10916).
The metal-vacuum deposited non-woven fabric has a problem in that the vacuum-deposited metal is easily separated from the fabric. As a means for overcoming this defect, there has been proposed a process for preparing an aluminum-vacuum-deposited polyester fabric having an excellent durability, which comprises vacuum-depositing aluminum on a polyester fiber fabric and then applying 0.3 to 3% by weight of a composition comprising a copolymer composed mainly of isophthalic acid or a derivative thereof, neopentyl glycol, and polyalkylene glycol, and having a softening point of 60°C to 130°C, onto the fabric (see Japanese Unexamined Patent Publication No. 58-136891).
Each of these known techniques is based on the idea that escape of heat to the outside or intrusion of heat from the outside is prevented as much as possible by utilizing vacuum deposition of a metal.
However, the above-mentioned conventional techniques utilizing the metal-vacuum-depositing process have the following problems.

(1) Since the metal-vacuum-depositing treatment is carried out in a vacuum and a metal is vacuum-deposited in a thickness sufficient to reflect heat rays, the preparation process is discontinuous and lengthy. Thus, continuous production is impossible and it is difficult to enhance productivity.
(2) Since the metal is applied onto a substrate in the vacuum deposition process, even if the above-mentioned structure disclosed in Japanese Examined Utility Model Publication No. 58-10916 is adopted, the vacuum-deposited metal-is gradually separated by rubbing or friction or by repeated washing or scrubbing. Namely, the durability is poor.
(3) Where the durability is increased by coating the surface of a vacuum-deposited metal with a resin, as taught in Japanese Unexamined Patent Publication No. 58-136891, the combination of the vacuum-deposited metal layer and the surface-coating resin stiffens the heat insulating material and the softness property is degraded. Moreover, as pointed out above, the vacuum-deposited metal is readily separated from the fabric during repeated washing or scrubbing. In addition, the vacuum-deposited metal reduces the vapor permeability and thus the fabric becomes discomfortable to wear.

SUMMARY OF THE INVENTION

Under this background, it is a primary object of the present invention to provide a fiber characterized in that (1) continuous production is possible, (2) it has an excellent and durable heat insulating effect, (3) the fiber can be formed into a heat insulating material having a good softness property and a good vapor permeability, and (4) the fiber can be formed into a thin heat insulating material.
It is another object of the present invention to provide a non-woven fabric, a wadding structure or a net-like fiber sheet, which is composed of the above-mentioned fiber.
In accordance with one fundamental aspect of the present invention, there is provided a fiber for a heat insulating material which contains 1 to 30% by weight of a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average particle size of 1 to 100 µm. Although the fiber may have a circular cross-sectional shape, it is preferable that the fiber has an irregular cross-sectional shape. It is more preferable that a flatness of the sectional shape of the fiber be at least 2.
In accordance with another fundamental aspect of the present invention, there is provided a composite fiber for a heat insulating material which comprises a sheath component containing 1 to 40% by weight of a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average particle size of 1 to 100 µm and a core component having a metal or metal oxide fine powder content lower than that of the sheath component.
In accordance with still another fundamental aspect of the present invention, there is provided a non-woven fabric for a heat insulating material which is composed of a web containing at least 10% by weight of a fiber containing 1 to 30% by weight of a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average particle size of 1 to 100 um and having fiber bonding points of an adhesive component. It is preferred that the metal or metal oxide fine powder should have a non-spherical shape.
In accordance with still another fundamental aspect of the present invention, there is provided a wadding structure comprising a fabric covered with a web containing at least 5% by weight of a fiber containing 1 to 30% by weight of a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average particle size of 1 to 100 pm.
In accordance with still another fundamental aspect of the present invention, there is provided a net-like fiber sheet for a heat insulating material, which is obtained by spreading a net-like fiber sheet obtained by extruding a melt of a thermoplastic resin containing a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average diameter of 1 to 100 pm and a blowing substance from a slit die, or a laminate of two or more of these net-like fiber sheets in the lateral direction at an expansion ratio A satisfying the requirements represented by the following formulae:
and
wherein m is the tensile strength (g/d) of the net-like fiber sheet as measured in the longitudinal direction, with the proviso that when m is larger than 1 g/d, m is regarded as being equal to 1, and! is the average distance (mm) between adjacent bonding points in the net-like fiber sheet, wherein the average distance between adjacent bonding points in the net-like fiber sheet is 1 to 50 mm, the tensile strength of the net-like fiber sheet in the longitudinal direction is at least 0.05 g/d, and the average diameter of the fiber of the net-like fiber sheet is 1 to 100 µm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, it is indispensable that the emissive power of the fineⁱpowder of the metal or metal oxide be not more than 0.3 (see page 202 of the Handbook of Chemical Engineering, 4th edition, compiled by the Chemical Engineering Association, Japan). If the emissive power is not more than 0.3, the heat ray emitting or absorbing capacity is low, and therefore, where the fine powder of the metal or metal oxide is contained in the fiber polymer, almost no absorption or emission of heat by heat rays is caused and the heat insulating property is increased. On the other hand, if the emissive power exceeds 0.3, absorption and emission of heat rays through the fine powder of the metal or metal oxide contained in the fiber polymer is increased and the heat insulating effect is reduced.
Fine powders of any metals and metal oxides having an emissive power of not more 0.3 can be used in the present invention. From the view point of easy availability and handling, there is preferably used at least one member selected from fine powders of aluminum, copper, nickel, brass, iron, titanium, and oxides thereof. If the light weight characteristic is taken into consideration, aluminum is most preferred. These metals and metal oxides may be used alone or in the form of a mixture of two or more of them.
The shape of the fine powder of the metal or metal oxide is not particularly critical. However, in view of the heat ray blocking effect, a non-spherical shape such as a linear, rod-like, or thin leafy shape is preferred. Among these, a thin leafy shape such as a long and thin leafy, scaly or irregular cloudy shape is especially preferred. The term "scaly" means that the ratio of the largest diameter (L) to the smallest diameter (D) in the fine powder particle is at least 3, wherein L and D are determined on the three-dimensional particle.
It is preferred that the average particle size of the metal or metal oxide fine powder be 1 to 100 µm, though the preferred average particle size differs to some extent according to the single filament denier of the fiber used. When a fiber composed of fine-denier single filaments is used for a heat insulating material, a metal or metal oxide fine powder having an average particle size not larger than 40 µm, especially not larger than 20 µm, is used. If the average particle size exceeds 100 µm, problems such as the formation of fluffs and yarn breakage readily occur. If the average particle size is smaller than 1 um, the heat ray reflecting effect is drastically degraded.
The content of the metal or metal oxide fine powder is preferably 1 to 30% by weight based on the weight of the fiber. If the content of the metal or metal oxide fine powder is lower than 1% by weight, the heat insulating property is unsatisfactory. If the content of the metal or metal oxide fine powder is higher than 30% by weight, the fiber-forming property is reduced and the physical properties of the obtained fiber are unsuitable.
Where the metal or metal oxide fine powder is contained in a core-sheath type composite fiber, the content of the metal or metal oxide fine powder in the sheath component of the fiber is adjusted to 1 to 40% by weight, preferably 1 to 30% by weight. Since the reflection of heat rays is performed by the sheath portion of the fiber, it is preferred that the metal or metal oxide fine powder is not contained in the core component of the fiber, but the core component may contain the metal or metal oxide fine powder at a content lower than in the sheath component, so far as production of a core-sheath composite fiber is possible.
The metal or metal oxide fine powder is incorporated in a polymeric substance before formation of a fiber. As the fiber of the polymeric substance that can be mixed in the molten state before formation of a fiber with the metal or metal oxide fine powder, there can be mentioned a polyester fiber, a polyamide fiber and a polypropylene fiber. Furthermore, as the fiber of the polymeric substance that can be mixed in the state of a solution (dope) before the formation of a fiber, there can be mentioned a cellulose fiber, an acetate fiber, a wholly aromatic polyamide fiber, and a polyacrylonitrile fiber.
It is preferred that the metal or metal oxide fine powder be contained in the fiber in such a state that the metal or metal oxide fine powder is predominantly present in the peripheral portion of the fiber section. If the flatness (the ratio of the longest diameter to the shortest diameter in the fiber section; longest diameter/shortest diameter) of the sectional shape of the fiber is at least 2, the metal or metal oxide fine powder tends to be located predominantly in the peripheral portion of the section of the fiber at the spinning step. Accordingly, in this case, there can be obtained a metal or metal oxide fine powder-containing fiber in which the metal or metal oxide fine powder is predominantly present in the peripheral portion of the section of the fiber. Therefore, it is preferred that the flatness of the sectional shape of the fiber be at least 2.
If a fiber having a flatness of at least 2 is used for a heat insulating sheet, the heat insulating property is enhanced over that of a fiber having a circular section because of the difference of the sectional shape of the fiber.
Also a core-sheath type composite fiber has a structure suitable for distributing the metal or metal oxide fine powder predominantly in the peripheral portion of the fiber. In view of the physical properties of the core-sheath type composite fiber, the reflecting effect by the metal or metal oxide fine powder in the sheath portion, and the yarn-forming performance, it is preferred that the sheath/core ratio in the sheath-core type composite fiber be from 1/5 to 5/1, more preferably from 1/2 to 3/1.
If the fiber having such a core-sheath two-layer structure is used, the amount of the metal or metal oxide fine powder used can be reduced and the good fiber characteristics can be retained by the core portion. Accordingly, degradation of the physical properties of the fiber by incorporation of the metal or metal oxide fine powder, for example, reduction of the strength or Young's modulus, can be minimized.
An appropriate mixture of the metal or metal oxide fine powder and the fiber-forming polymeric substance is prepared, and when this mixture is melt-spun or a solution of the mixture is wet-spun or dry-spun according to customary procedures, a metal or metal oxide fine powder-containing fiber can be obtained. A fiber having a flatness of at least 2 and a core-sheath type composite fiber may be prepared according to conventional processes.
The single filament denier is not particularly critical, but where the fiber of the present invention is used for a heat insulating material, it is preferred that the single filament denier be 0.5 to 20, especially 2 to 12. If the single filament denier is less than 0.5, fluffing or breakage is readily caused in the yarn-forming process. If the single filament denier exceeds 20, the heat insulating effect by incorporation of the metal or metal oxide fine powder becomes insufficient and the fiber per se becomes rough and hard.
The metal or metal oxide fine powder-containing fiber of the present invention may be used alone or in combination with other fiber for a heat insulating material. Where the metal or metal oxide fine powder-containing fiber of the present invention is used in combination with a fiber free of such fine powder, a web may be formed by mixing both the fibers, or this web or a web composed solely of the metal or metal oxide fine powder-containing fiber of the present invention may be laminated, needle-punched or quilted with a web of other fiber, whereby an integrated non-woven fabric for a heat insulating material can be obtained.
Furthermore, a heat insulating material may be formed according to a method in which a low-melting-point fiber or low-melting-point powder is mixed into a web or an adhesive is applied to a web by dipping or spraying, and the web is subjected to a heat treatment or a heat-pressing treatment to form bonding points among fibers of the web and integrate the fibers with one another, whereby a heat insulating material is prepared. The heat insulating material obtained according to this method has an excellent strength, dimensional stability, and durability.
In the formation of a heat insulating material by combining the metal or metal oxide fine powder-containing fiber of the present invention with other fiber, the kind of the fiber to be combined with the fiber of the present invention is not particularly critical. A natural fiber, a semi-synthetic fiber, a synthetic fiber or an inorganic fiber can be -appropriately selected and used according to the intended use.
When a non-woven fabric for a heat insulating material is prepared by using the metal or metal oxide fine powder-containing fiber of the present invention, it is necessary to incorporate the fiber of the present invention in an amount of at least 5% by weight, preferably at least 10% by weight, based on the weight of the non-woven fabric. If the amount of the fiber of the present invention is smaller than 5% by weight, a satisfactory heat insulating effect cannot be obtained. Incorporation of the fiber of the present invention may be accomplished by fiber mixing, lamination of webs, and lamination of sheets. A web composed of staple fibers or a web composed of filaments may be used.
A web composed solely of the metal or metal oxide fine powder-containing fiber of the present invention or a web composed of a mixture containing the fiber of the present invention may be formed into a wadding structure by covering the web with a fabric such as a non-woven fabric, a knitted fabric or a woven fabric directly or after the web is integrated by needle punching or quilting.
The metal or metal oxide fine powder-containing fiber of the present invention may be in the form of a net-like fiber sheet obtained by extruding a thermoplastic resin containing the above-mentioned metal or metal oxide fine powder and a blowing substance blown in the molten state from a slit die. This embodiment will now be described.
In this embodiment, the above-mentioned net-like fiber sheet or a laminate of two or more of the above-mentioned net-like fiber sheets is spread in the lateral direction at an expansion ratio A satisfying the requirements represented by the following formulae (1) and (2):
and
wherein m is the tensile strength (g/d) of the net-like fiber sheet as measured in the longitudinal direction, with the proviso that when m is larger than 1 g/d, m is regarded as being equal to 1, and is the average distance (mm) between adjacent bonding points in the net-like fiber sheet, whereby a net-like fiber sheet for a heat insulating material is obtained. In this embodiment, the starting net-like fiber sheet has an average distance between adjacent bonding points of 1 to 50 mm, a tensile strength in the longitudinal direction of at least 0.05 g/d, and an average diameter of the fiber of 1 to 100 µm.
By the passage "the sheet is spread in the lateral direction" we mean that the net of the sheet is expanded in the direction perpendicular to the longitudinal direction. The spreading is carried out usually by gradually expanding the sheet in the lateral direction, for example, by using a pin tenter gripping both side edges of the sheet. When the sheet is spread, the sheet is overfed in the longitudinal direction.
The above-mentioned net-like fiber sheet is usually obtained by extruding a thermoplastic resin containing the metal or metal oxide fine powder and a substance blown in the molten state from a slit die and winding the extrudate at a draft ratio of 10 to 300, preferably 20 to 200. This sheet has the characteristics described below.
The thermoplastic resin constituting the net-like fiber sheet has a melting point of 70°C to 350°C, preferably 90°C to 300°C. As the thermoplastic resin, there can be mentioned (i) homopolymers and copolymers derived from monoethylenically unsaturated monomers such as ethylene, propylene, styrene, acrylic acid esters, vinyl acetate, acrylonitrile, and vinyl chloride, (ii) polyesters formed from at least one dicarboxylic acid component (or a lower alkyl ester thereof) selected from, for example, phthalic acids (such as phthalic acid, isophthalic acid, terephthalic acid, and alkyl nucleus substitution products thereof), aromatic dicarboxylic acids having 8 to 15 carbon atoms, such as naphthalene-dicarboxylic acid, and aliphatic and alicylic dicarboxylic acids having 6 to 30 carbon atoms, and at least one glycol component selected from aliphatic and alicyclic glycols having 2 to 12 carbon atoms and aromatic dihydroxyl compounds having 6 to 15 carbon atoms, polyesters formed from hydroxycarboxylic acids (or lower alkyl esters thereof) having 4 to 12 carbon atoms, and mutual copolymer polyesters of these polyesters, (iii) polyamides formed from, for example, aliphatic dicarboxylic acids having 4 to 12 carbon atoms and aliphatic or aromatic diamines having 4 to 15 carbon atoms, polyamides formed from amino acids (or lactams) and mutual copolymers of these polyamides, (iv) polyacetals, and (v) various polyurethanes.
A substance which is converted to a gas when the molten resin is extruded from a slit die is used as the blowing substance. The resin per se may have a gas-generating property or may contain a gas-generating substance. For example, there may be adopted (a) a method in which a substance which is gaseous at normal temperatures, such as nitrogen gas or carbon dioxide gas, is kneaded into a thermoplastic resin to be melt-extruded, (b) a method in which a substance which is liquid at normal temperatures but is gasified at the melt-extruding temperature of a thermoplastic resin, such as water, is kneaded into a thermoplastic resin, (c) a method in which a substance with generates a gas by decomposition, such as a diazo compound or sodium carbonate, is incorporated into a thermoplastic resin, and (d) a method in which a polymer which reacts with a certain thermoplastic resin (such as a polyester or a polyamide) to generate a gas, such as a polycarbonate, is kneaded into such a thermoplastic resin.
In any method, when the thermoplastic resin is extruded in the molten state from a slit die, it is sufficient if a gas is generated from the die simultaneously with the extrusion of the resin. It is preferred that the above-mentioned blown substance and the metal or metal oxide fine powder be sufficiently kneaded with the thermoplastic resin. If this kneading is not sufficient, it is difficult to obtain a uniform net-like fiber sheet having desirable properties.
It is preferable that the content of the metal or metal oxide fine powder in the net-like fiber sheet is from 1 to 40% by weight. It is preferred that the metal or metal oxide fine powder be contained in the fiber in such a state that the fine powder is arranged in parallel to the extrusion direction of the net-like fiber sheet. For example, when a thermoplastic substance containing a scaly metal or metal oxide fine powder and a blown substance is extruded from a cylindrical slit, it is preferred that the scaly metal or metal oxide fine powder be arranged in parallel to the extrusion direction in the cylindrical slit. This structure can be formed by extruding the thermoplastic substance through a slit die for a core-sheath structure. If this two-layer structure is formed, the amount of the metal or metal oxide fine powder used can be reduced, and the physical properties of the net-like fiber sheet can be maintained at high levels by the inner layer portion (core portion) free of the metal or metal oxide fine powder. Therefore, degradation of the properties of the net-like fiber sheet by incorporation of the metal or metal oxide fine powder, such as reduction of the strength or elongation, can be controlled to a very low level. Of course, a heat insulating effect can be attained even if the metal or metal oxide fine powder is contained throughout the section of the net-like fiber sheet, but in order to maintain good characteristics in the net-like fiber sheet and obtain a high heat insulating effect, it is preferable to adopt a two-layer structure as described above.
An embodiment of the process for preparing the above-mentioned net-like fiber sheet will now be described.
A thermoplastic resin containing a fine powder of a metal or metal oxide is extruded from a heating extruder having a vent port in an intermediate portion while an inert gas such as nitrogen is forced into the extruder from the intermediate vent port. The thus-extruded resin contains therein the inert gas in the form of minute bubbles. The gas-containing molten thermoplastic resin is extruded in the compressed state through a slit die. The slit clearance of this slit die is preferably about 20 µm to about 1 mm, more preferably 50 to 500 µm. The pressure at this extrusion is at least 10 kg/cm²G, preferably at least 30 kg/cm²G. If the extrusion pressure is lower than 10 kg/cm²G, it is difficult to obtain a sheet having uniform meshes and, in an extreme case, a product resembling foamed film is obtained.
The resin extruded from the die is promptly cooled. Since this cooling is a factor for determining the mesh size, it is preferred that the cooling be carefully controlled. For example, if a net-like fiber sheet having a large mesh size is desired, the cooling rate is low. In contrast, if a small mesh size is desired, the cooling rate is increased. This cooling is preferably accomplished by blowing air against the extrudate, and the mesh size is adjusted by controlling the air feed rate. Furthermore, cooling can be accomplished, for example, by using a liquid such as water or by placing the extrudate in contact with a cooled solid.
The extruded resin is taken up at a sufficient speed. If the take-up speed is insufficient, the obtained net-like fiber sheet is poor in strength or, in an extreme case, a product resembling a perforated film is obtained. The draft ratio is ordinarily 10 to 300, preferably 20 to 200. By the term "draft ratio" referred to herein is meant the ratio of the take-up speed to the linear speed of the resin passing through the die. Where spreading is carried out while the extrudate is taken up, the speed is converted to the value obtained when spreading is not effected.
As means for adjusting the mesh size of the net-like fiber sheet, there may be adopted a method of controlling the melt viscosity of the resin. For example, the melt viscosity is controlled by varying the temperature condition, controlling the polymerization degree of the resin, incorporating a plasticizer, or adopting these means in combination. Among these, a method of varying the temperature condition is simplest and most preferred.
The process for the preparation of the net-like fiber sheet of the present invention is not limited to the above-mentioned embodiment. Furthermore, there may be adopted, for example, a process in which a thermoplastic resin containing a fine powder of a metal or metal oxide is melted together with a substance capable of generating a gas by thermal decomposition and the melt is extruded from a slit die, and a process in which an inert gas is kneaded into a thermoplastic resin containing a fine powder of a metal or metal oxide in the molten state by using a gas kneader and then the melt is extruded from a slit die. In these processes also, it is preferred that the extrudate be cooled and taken out in the same manner as described above.
The net-like fiber sheet in the present invention is characterized in that (1) the average distance between adjacent bonding points is 1 to 50 mm, (2) the tensile strength in the longitudinal direction is at least 0.05 g/d, and (3) the average diameter of the fiber is 1 to 100 µm.
The net-like fiber sheet satisfying all of the above-mentioned requirements (1), (2), and (3) can be spread at a high expanding ratio very easily to give a uniform net-like fiber sheet.
In the present invention, "the average distance between adjacent bonding points", "the tensile strength in the longitudinal direction" and "the average diameter of the fiber" are determined according to the following methods.

(1) Average Distance (ℓ) between Adjacent Bonding Points

One net-like fiber sheet is spread at a ratio of 2 in the lateral direction and all of the distances between adjacent points included in 10 cm² are measured. The average distance (1) is calculated according to the following formula:

Average distance (ℓ) between adjacent points
wherein ℓ: is the measured distance and n is the number of measured distances.

(2) Tensile Strength (m) in Longitudinal Direction

The net-like fiber sheet is cut in the longitudinal direction so that the total denier of each cut sheet is about 10,000. Twists are given to the cut sheet at a twist number of 1 twist per cm. The sheet is pulled at a chuck distance of 5 cm and a grip separating rate of 5 cm/m. The tensile strength (m) is calculated by dividing the maximum stress by the denier. When two or more sheets are laminated, the laminate is cut in the longitudinal direction and the measurement is carried out in the same manner as described above.

(3) Average diameter (d) of Fiber

A straight line is drawn at a right angle to the fiber axes. By using a 400 magnification microscope, the diameters of 10 to 25 fibers present on the straight line are measured. The above procedure is repeated on several samples. Thus, the diameters of 100 fibers as a whole are measured and the average value is calculated.
The above-mentioned properties (1), (2),and (3) of the net-like fiber sheet are determined according to the above-mentioned measuring methods. If the average distance between adjacent bonding points is shorter than 1 mm, the number of the bonding points becomes too large, and a large expansion ratio and a uniform net-like fiber sheet cannot be obtained. If the average distance between adjacent points exceeds 50 mm, when the sheet is spread, it is very difficult to form a uniform sheet. It is more preferable that the distance between adjacent bonding points be 2 to 40 mm.
The net-like fiber sheet has a tensile strength in the longitudinal direction of at least 0.05 g/d, preferably at least 0.1 g/d. If the tensile strength in the longitudinal direction is lower than the above-mentioned range, spreading becomes substantially difficult and it is almost impossible to obtain a net-like fiber sheet having a practically sufficient high strength.
Even if the above-mentioned requirements (1) and (2) of the average distance between adjacent bonding points and the tensile strength in the longitudinal direction are satisfied, an intended net-like fiber sheet cannot be obtained if the average diameter of the fiber is outside the range of from 1 to 100 µm. If the average diameter of the fiber is smaller than 1 µm, it is almost impossible to obtain a net-like fiber sheet having a stable strength. If the average diameter of the fiber is larger than 100 µm, a uniform net-like fiber sheet having a good softness cannot be obtained.
The net-like fiber sheet satisfying the above-mentioned requirements (1), (2), and (3), or a laminate of two or more of these net-like fiber sheets is spread in the lateral direction at an expansion ratio (A) of at least 2, which ratio satisfies the requirement represented by the following formula (I):
wherein m and ± are as defined above.
If the expansion ratio in the lateral direction is too high or too low and outside the above-mentioned range, a uniform net-like fiber sheet cannot be obtained.
By spreading the net-like fiber sheet, meshes are expanded in the lateral direction. This can be accomplished, for example, by a method in which the net-like fiber sheet is spread in the lateral direction while gripping both ends of the sheet or a method in which the net-like fiber sheet extruded from an annular slit is expanded in the radial direction of the cylindrical slit. There is especially preferably adopted a method in which a plurality of sheets are laminated and the laminate is expanded while gripping both ends of the laminate. The method for spreading the sheet in the lateral direction while gripping both ends will now be described. Of course, similar conditions may be adopted for the method for expanding the sheet in the radial direction.
Where the net-like fiber sheet is spread in the lateral direction, it is preferred that the sheet be overfed at a ratio of 1.3 to 3 in the longitudinal direction. This overfeeding influences the orientation angle of the fiber. If the overfeed ratio is too high, a sheet oriented in the lateral direction is obtained. The optimum expansion ratio depends on the overfeed ratio, and if the overfeed ratio is about 3, the optimum expansion ratio is 3 m.1 to 5 m·ℓ according to the above definition. If the overfeed ratio is about 1.3, an expansion ratio of 1 m·ℓ is preferred. It is possible to intentionally set the overfeed ratio, and this is preferred. However, overfeeding may be naturally effected in some cases. For example, where the length in the longitudinal direction is shortened when a net-like fiber sheet having a definite length is spread in the lateral direction.
It is preferred that spreading be carried out while taking the above-mentioned overfeeding into consideration. For example, where both ends of the sheet are gripped by a pin tenter, the net-like fiber sheet is fed by a feed roller having a peripheral speed higher than the speed of the pin tenter and the sheet is caused to abut against the pin in the folded state. The thus- overfed net-like fiber sheet is spread in the lateral direction. Any method in which the sheet is spread while gripping only both ends of the sheet as mentioned above and a method in which the sheet is divided into several zones in the lateral direction can be adopted as means for spreading the sheet in the lateral direction, so far as the above-mentioned expansion ratio is attained and the sheet is uniformly expanded.
The above-mentioned net-like fiber sheet alone or a laminate of two or more of these sheets may be spread. Where a laminate is spread, it is preferred that the number of the laminated sheets be 2 to 2000, more preferably 10 to 1000.
By this spreading treatment, a uniform net-like fiber sheet can be obtained. This net-like fiber sheet is valuable as a non-woven fabric as it is or after needle punching, stitch bonding or quilting.
The metal or metal oxide fine powder-containing fiber for a heat insulating material according the present invention has the following advantages.

(1) The fiber of the present invention is in striking contrast with a conventional metal-vacuum-deposited non-woven fabric in that a fine powder of-a metal or metal oxide is contained in the fiber per se, and the fiber of the present invention can be continuously prepared as in case of a conventional metal powder- free fiber for a heat insulating material.
(2) Since the fiber of the present invention is different from a conventional metal-vacuum-deposited fiber for a heat insulating material in that a metal or metal oxide fine powder is contained in the fiber per se, the heat insulating property is high and is permanently constant, and the durability such as the washing resistance is high.
(3) In the case of a conventional metal-vacuum-deposited non-woven fabric, stiffness occurs and softness is reduced because of the presence of the vacuum-deposited metal. This disadvantage is obviated in the case of the metal or metal oxide fine powder-containing fiber of the present invention.
(4) Since the heat insulating effect of the fiber of the present invention is high, the thickness of the non-woven fabric can be reduced. Accordingly, a product having a practical heat insulating property can be obtained even if the non-woven fabric is formed into a laminate, and this product has an excellent drape characteristic and packing property.

The present invention will now be described in detail with reference to the following examples that by no means limit the scope of the invention. All of "part" and "%" are by weight unless otherwise indicated.

Example 1

Polyethylene terephthalate obtained according to a customary procedure was melt-mixed with a thin leafy fine powder of aluminum having an average particle size of 3.5 µm in an amount of 10% based on the polymer. The mixture was extruded from a spinneret having a rectangular extrusion orifice having a width of 0.3 mm and a length of 1.2 mm to obtain a filament bundle according to a customary procedure. When the section of the obtained fiber was observed by a microscope, it was found that the flatness of the fiber was 3.5 and that the fine powder of aluminum was predominantly present in the peripheral portion of the fiber section of the flat yarn and only a very small amount of the fine powder of aluminum was present in the central portion of the fiber section. When a filament bundle similarly obtained by using a spinneret having a circular extrusion orifice having a diameter of 0.4 mm was observed, it was found that the flatness of the fiber was 1.0 and the fine powder of aluminum was present at substantially the same densities in both the perpheral portion and central portion of the fiber section of the obtained yarn having a circular section.

Examples 2 through 11 and Comparative Examples 1

through 6

Various metal fine powder-containing fibers were obtained in the same manner as described in Example 1 except that copper, nickel, brass, titanium, iron or aluminum or nickel oxidized at 600°C was used instead of the aluminum fine powder used in Example 1. These fibers were crimped and cut into a size of 1 mm to obtain metal or metal oxide fine powder-containing staple fibers.
A web was formed by mixing 90 parts of the thus-obtained staple fiber with 10 parts of an adhesive staple fiber comprising a sheath composed of a low-melting-point polyester copolymer and a core composed of polyethylene terephthalate and having a fineness of 4 denier and a fiber length of 51 mm and then treating the mixture by a carding machine. The web was needle-punched and was then heat-treated at 150°C for 10 minutes to obtain a non-woven fabric for a heat insulating material having heat-fuse-bonded portions formed by the adhesive fiber.
The heat insulating characteristics (heat conductivity) arid other properties of the thus-obtained non-woven fabrics for heat insulating materials are shown in Table 1.

Example 12

A core-sheath type polyethylene terephthalate fiber having a fineness of 6.1 denier and containing a fine powder of aluminum only in the sheath portion was obtained by melt spinning at 285°C through a concentric double spinneret by feeding ordinary polyethylene terephthalate in the core portion and polyethylene terephthalate containing 20% of a non-spherical fine powder of aluminum having an emissive power of 0.04 and an average particle size of 8.2 pm in the sheath portion and adjusting the sheath/core weight ratio to 2/1. The fiber was drawn, heat-treated, subjected to a stuffing crimping treatment, and heat-treated. Then, the fiber was cut into a length of 51 mm to obtain a core-sheath type crimped staple fiber containing the fine powder of aluminum only in the sheath portion. A web was prepared by mixing 90 parts of the staple fiber with 10 parts of a polyethylene terephthalate crimped staple fiber having a fineness of 4.0 denier and a fiber length of 47 mm and then treating the mixture by a carding machine. The web was needle-punched and heat-treated at 150°C for 10 minutes to obtain a heat insulating material. The basis weight, thickness and heat conductivity (heat insulating property) of the obtained heat insulating material are shown in Table 2.

Example 13

An aluminum fine powder-containing core-sheath type polyethylene terephthalate crimped staple fiber was obtained in the same manner as described in Example 12. A web was prepared by mixing 90 parts of the staple fiber with 10 parts of a heat-adhesive polyester staple fiber comprising a core of polyethylene terephthalate and a sheath of a low-melting-point polyester copolymer having a melting point of 130°C and having a fineness of 4.0 denier and a fiber length of 51 mm and then treating the mixture by a carding machine. The web was needle-punched and heat-treated at 150°C for 10 minutes to obtain a heat insulating material having the staple fibers fusion-bonded. The properties of the obtained heat insulating material are shown in Table 2.

Examples 14 through 22 and Comparative Examples 7

through 12

The procedures of Example 12 were repeated in the same manner except that the kind, shape, and average particle size of the metal or metal oxide fine powder, the metal or metal oxide fine powder content in the sheath or core portion of the core-sheath type fiber, the sheath/core weight ratio, the fineness of the metal or metal oxide fine powder-containing fiber, and the basis weight and thickness of the heat insulating material (non-woven fabric) were changed as indicated in Table 2. The heat insulating characteristics (heat conductivity) of the thus-obtained heat insulating materials are shown in Table 2.
As is seen from the results of Examples 12 through 22 and Comparative Examples 7 through 12 shown in Table 2, a heat insulating material formed by using as the main component a core-sheath type fiber containing a metal or metal oxide fine powder having an emissive power of not more than 0.3 only in the sheath portion or a core-sheath type fiber containing a metal or metal oxide fine powder at a higher content in the sheath portion than in the core portion has a much higher heat insulating property than a heat insulating material formed by using a fiber not containing a metal or metal oxide fine powder at all. Furthermore, this heat insulating material has a good drape characteristic and a good washing resistance and also has practically satisfactory physical properties. On the other hand, in a heat insulating material prepared by using as the main component a core-sheath type fiber containing metal or metal oxide fine powder having an emissive power exceeding 0.3 only in the sheath portion or a core-sheath type fiber in which the content of a metal or metal oxide fine powder is lower than 1% in the sheath portion, the effect of improving the heat insulating property was insufficient.
Where a metal or metal oxide fine powder having an emissive power of not more than 0.3 is incorporated into the sheath portion at a content exceeding 40% or the average particle size of the metal or metal oxide fine powder exceeds 100 µm, fluffing and breaking are often caused at the step of spinning a sheath-core type fiber and thus production of a yarn is difficult.

Examples 23 through 28 and Comparative Examples 13

through 16

A predetermined amount of a non-spherical fine powder of aluminum, copper, nickel, brass or iron having an average particle size shown in Table 3 was incorporated into 100 parts of polypropylene prepared according to a customary procedure. The mixture was melt-kneaded at 230 to 270°C in a melt extruder and melt-extruded through a nozzle having many circular orifices according to a customary procedure to obtain a filament bundle. The filament yarn was doubled, drawn, heat-set, subjected to a stuffing crimping treatment, heat-set, and then cut into a length of 51 mm to obtain a crimped staple fiber containing the non-spherical fine powder of the respective metal. The diameter of the fiber was as shown in Table 3.
A web was formed by mixing 85 parts of the staple fiber with 15 parts of an ES fiber (supplied by Chisso K.K.) having a fineness of 3 denier and a fiber length of 64 mm as an adhesive fiber and treating the mixture by a carding machine. The web was needle-punched and heat-treated at 145°C for 10 minutes to obtain a non- woven fabric for a heat insulating material having heat-fuse-bonded portions formed by the adhesive fiber. The heat insulating property of the obtained non-woven fabric is shown in Table 3. The non-woven fabric had a much higher heat insulating property than that of a non- woven fabric not containing the non-spherical metal fine powder. The non-woven fabric had a good drape characteristic and a good washing resistance and practically acceptable physical properties.
A non-woven fabric formed by using a fiber having a non-spherical powder content of lower than 1% had no substantial heat insulating property-improving effect over a non-woven fabric formed by using a fiber not containing a non-spherical fine powder. Where the content of the metal fine powder exceeded 30%, or where the average particles size of the metal fine powder was larger than 40 µm, fluffing and breaking were often caused at the yarn-preparing step.

Example 29

A non-woven fabric for a heat insulating material was prepared in the same manner as described in Example 23 except that a mixture comprising 5 parts of an aluminum powder having an average particle size of 8.2 um and 5 parts of a copper powder having an average particle size of 9.5 µm was used as the non-spherical metal fine powder.
This non-woven fabric had an excellent heat insulating property the same as the products obtained in Examples 23 through 28, and had a good drape characteristic, a good washing resistance, and practically acceptable physical properties. The obtained results are shown in Table 3.

Example 30 and Comparative Example 17

A non-woven fabric was prepared in the same manner as described in Example 21 except that 10 parts of a spherical copper fine powder having an average particle size of 8 µm was used as the metal fine powder.
The obtained non-woven fabric had a satisfactory drape characteristic, washing resistance, and physical property.
Separately, a non-woven fabric was prepared in the same manner as described in Example 23 except that 10 parts of a non-spherical fine powder of a chromium-nicke: alloy having an average particle size of 8.3 µm was used as the metal fine powder. The heat insulating property of the non-woven fabric was low.
The obtained results are shown in Table 3.
Examples 31 through 33 and Comparative Examples 18

and 19

A non-woven fabric was obtained by mixing the same polypropylene staple fiber as obtained in Example 24, this fiber having an average particle size of 26.2 µm and contained 13% of the aluminum fine powder having an average particle size of 10.2 am, as shown in Table 2, with a polyethylene terephthalate fiber having a fineness of 6 denier, a fiber length of 51 mm, and a fiber diameter of 24 µm, and the above-mentioned ES fiber as the adhesive fiber at a mixing ratio shown in Table 4. Then, the web-forming and needle punching operations and the heat treatment were carried out in the same manner as described in Example 23 and shown in Table 2. The obtained results are shown in Table 4. When the mixing ratio of the staple fiber containing the aluminum powder was higher than 10% the non-woven fabric had a high heat insulating property, good drape characteristic and washing resistance, and practically acceptable physical properties. In contrast, when the mixing ratio of the aluminum powder-containing staple fiber was lower than 10%, the effect of improving the heat insulating property was low.
Examples 34 through 43 and Comparative Examples 20

through 26

A filament bundle was obtained by mixing 100 parts of polyethylene terephthalate obtained according to a customary procedure with a predetermined amount of a metal or metal oxide powder having an average particle size shown in Table 5, which was selected from aluminum copper, nickel, brass, titanium, iron, and aluminum and nickel oxidized at 600°C, melt-kneading the mixture at 285°C in a melt extruder, extruding through a nozzle having many circular orifices, and carrying out melt- spinning according to a customary procedure. The filament yarn was doubled, drawn, heat-set, subjected to stuffing crimping, heat-set, and then cut into a length of 51 mm to obtain a crimped staple fiber having the fine powder of the respective metal or metal oxide. The fiber diameter was as shown in Table 5.
A web was prepared by treating the staple fiber singly or in combination with a predetermined amount, shown in Table 5, of a polyethylene terephthalate staple fiber having a fineness of 6 denier, a fiber length of 51 mm and a circular section, by a carding machine. The obtained web was covered with a plain weave fabric having a basis weight of 120 g/m² and consisting of a mix-spun yarn of cotton and polyethylene terephthalate staple fibers, and was sewn to obtain a wadding structure.
For comparison, a wadding structure was similarly prepared by using only a polyethylene terephthalate staple fiber having a fineness of 6 deniner.
The heat insulating property and other properties of the wadding structure are shown in Table 5.
The wadding structure containing a metal or metal oxide fine powder having an emissive power of not more than 0.3 had a much higher heat insulating property than that of the wadding structure not containing a metal or metal oxide fine powder or containing a metal or metal oxide powder having an emissive power exceeding 0.3. The wadding structure containing a metal or metal oxide fine powder had a good drape characteristic comparable to that of the wadding structure not containing a metal or metal oxide fine powder, and therefore, this wadding structure was practically satisfactory in wearing comfortability and touch. Furthermore, in this wadding structure, the metal or metal oxide fine powder was not separated upon washing and reduction of the heat insulating property by washing was not caused. However, if the metal or metal oxide fine powder content was lower than 1%, the effect of improving the heat insulating property was insufficient. If the content of the metal or metal oxide fine powder exceeded 30% or the average particle size of the metal or metal oxide fine powder exceeded 100 µm, fluffing and breaking were often caused at the yarn-forming step and the yarn could not be stably formed. When a mix-spun fiber comprising the fiber containing a metal or metal oxide fine powder having an emissive power of not more than 0.3 and the fiber not containing a metal or metal oxide fine powder was incorporated in an amount of at least 5%, a high heat insulating property could be obtained. If a metal or metal oxide fine powder having an average particle size smaller than 1 µm was used, the handling property of the fine powder was bad and the heat insulating property of the obtained wadding structure was insufficient.

Example 44

(A) A mixture of 100 parts of polypropylene containing 10% of a scaly aluminum fine powder having an average particle size of 10.2 um and 1 part of talc was continuously fed into an extruder provided with a gas blow-in opening having an inner diameter of 30 mm. While nitrogen gas was introduced into the extruder through the gas blow-in opening under a pressure of 50 kg/cm², the mixture was extruded through a circular slit die having a slit clearance of 250 µm and a diameter of 140 mm. At this extrusion step, the temperature in the vicinity of the feed portion of the cylinder was 240°C, the temperature in the zone ranging from the vicinity of the gas blow-in opening to the tip end of the cylinder was 300°C, and the die temperature was 280°C. The feed quantity and the gear pump arranged between the cylinder and die were controlled so that the extrusion rate was 45 g/min. The polymer extruded from the die was promptly cooled by air maintained at 25°C and was taken up at a take-up speed of 80 m/min to obtain a net-like fiber sheet. Net-like fiber sheets prepared in the above-mentioned manner from four nozzles of the above-mentioned extruding apparatuses were piled together and the laminate was wound on a bobbin. Winding was performed while compressing the sheet obtained in the cylindrical form into a plane shape having a width of 20 cm. The wound laminate comprised eight net-like fiber sheets.
The thus-obtained net-like fiber sheet had 20000 denier as a whole and the tenacity was 3.1 kg. The tensile strength was 0.15 g/d, calculated from these values. Microscope observation indicated that the average diameter of the fiber was 36 um. When one net-like fiber sheet was peeled and spread in the lateral direction at an expanding ratio of 2, it was found that the average distance between adjacent bonded points was 16.5 mm. The value obtained by multiplying the tensile strength by the average distance between adjacent bonded points was 2.5.

(B) By using a pin tenter, a laminate formed by piling 84 of the laminates of the net-like fiber sheets obtained in (A) above was spread. This pin tenter comprised two rows of pins arranged in an unfolded fan-shaped configuration with an inlet width of 160 mm. The pin tenter was disposed so that the spread laminate was cut at a point where the distance between the rows of pins reached 1280 mm (the expansion ratio was 8). The net-like fiber sheet obtained in (A) was fed to the inlet of the pin tenter at a speed 1.8 times the pin speed (the overfeed ratio was 1.7), and both ends of the sheet were stuck on the pins and the sheet was spread. The sheet was cut at the point where the distance between the pin rows was 1280 mm, whereby a net-like fiber sheet was obtained.
(C) The net-like fiber sheet obtained in (B) above was treated for 30 seconds in a hot air drier maintained at 160°C to obtain a bulky non-woven fabric. The physical properties of the non-woven fabric are shown in Table 6. The obtained net-like fiber sheet had a reduced unevenness and was homogeneous. The sheet had a good drape characteristic and washing resistance, and practically acceptable physical properties.

Examples 45 through 50

Net-like fiber sheets were prepared in the same manner as described in (A) of Example 44 by using various metal fine powders (aluminum, copper, nickel, brass and iron) alone or incombination. The physical properties of net-like fiber sheets obtained in the same manner as described in (B) and (C) of Example 44 at various expansion ratios are shown in Table 6.
The thus-obtained net-like fiber sheets were uniform and had a good heat insulating property the same as the product of Example 44, and these net-like fiber sheets had a good drape characteristic and washing resistance, and practically acceptable physical properties.

Comparative Examples 27 through 30

A sheet was prepared in the same manner as described in Example 44 except that the metal fine powder was not incorporated. The sheet exhibited a poor heat insulating property.
A net-like fiber sheet was prepared in the same manner as described in Example 44 except that polypropylene containing 10% of a fine powder of a chromium-nickel alloy having an average particle size of 10.2 pm as the metal fine powder was used. The sheet exhibited a poor heat insulating property.
The net-like fiber sheet obtained in (A) of Example 44 was spread by the same pin tenter as used in (B) of Example 44. Spreading was carried out in the same manner as described in (B) of Example 44 except that the sheet was cut at a point where the distance between the pin rows was 320 mm (the expansion ratio was 2). The thus-obtained net-like fiber sheet had an extremely uneven basic weight, as shown in Table 6.
When the cutting position was changed to a point where the distance between the pin rows was 2080 mm (the expansion ratio was 13), partial breaking was caused before the sheet reached the cutting point, and the product was apparently uneven.

Comparative Example 31

A net-like fiber sheet was prepared in the same manner as described in (A) of Example 44 except that the slit clearance was changed to 1 mm and the extrudate was taken out at a take-up speed of 40 m/min from the die. The thus-obtained net-like fiber sheet had an average diameter of the fiber of 150 um, an average distance between adjacent bonded points of 12.2 mm, and a tensile strength of 0.1 g/d.
From the appearance, it was found that unevenness of the thickness was extreme, and the product was not suitable for a heat insulating material.

Comparative Examples 32 and 33

Net-like fiber sheets differing in the average distance between adjacent bonded points and the tensile strength were prepared in the same manner as described in (A) of Example 44 except that the take-up speed and the feed rate of cooling air were changed. The physical properties of the thus-obtained net-like fiber sheets, the state at the spreading step, and the measurement results are shown in Table 6. Where the average distance between adjacent bonded points was short, a uniform net-like fiber sheet could not be obtained by spreading. If the tensile strength was low, breaking was caused at the spreading step or a uniform net-like fiber sheet could not be obtained. The product had no ' practical utility as a heat insulating material.

Examples 51 through 54

Net-like fiber sheets were prepared in the same manner as described in (A) of Example 44 except that a polymer, shown in Table 7, which contained 10 or 35% of a scaly fine powder of aluminum having an average particle size of 10.2 µm was used and the melting temperature, gas blow-in opening temperature, die temperature, extrusion rate, take-up speed, and cooling speed were changed. Spreading was carried out in the same manner as described in (B) and (C) of Example 44. The characteristic properties of the thus-obtained net-like fiber sheets are shown in Table 7. Each of the net-like fiber sheets had a high heat insulating property and good drape characteristic and washing resistance, and practically acceptable physical properties. The obtained results are shown in Table 7.

Comparative Example 34

A net-like fiber sheet could not be obtained in the same manner as described in Example 44 by using polypropylene containing 1% of a scaly square foil of aluminum (the maximum size was 1 mm) and 9% of a scaly fine powder of aluminum.

Comparative Examples 35 and 36

Net-like fiber sheets were prepared in the same manner as described in Example 44 by using polypropylene containing 0.5 or 63% by weight of a non-spherical fine powder of aluminum. The obtained results are shown in Table 7. When the aluminum powder content in the polymer was 0.5%, a high heat insulating property was not obtained. When the aluminum powder content in the polymer was 63%, a net-like fiber sheet could not be obtained even though experiments were conducted under various conditions.

Example 55 and Comparative Example 37

A polyethylene terephthalate tow having a single filament fineness of 1.7 denier and a total fineness of 330,000 denier was crimped at a rate of 8 crimps per inch and then heat-set at 180°C. Then, the tow was spread into a sheet form. The entire sheet was impregnated with an emulsion type adhesive comprised of an ethyl acrylate/butyl acrylate (50:50) copolymer at a pickup of 7% by weight. The impregnated sheet was dried at 100°C to obtain a sheet composed of filaments arranged in parallel and having a basis weight of 30 g/cm .
Thereafter, the sheet was spread at an expansion ratio of 13.5 in the lateral direction by using a pintenter while the sheet was overfed at an overfeed ratio of 1.8, whereby a filament nonwoven fabric (a') was obtained. The filament nonwoven fabric (a') had a basis weight of 4 g/c_m ².
A mixture of 90% of polypropylene containing 10% of a scaly aluminum fine powder having an average particle size of 15 µm and an emissive power of 0.04, and 10% of nylon-6, was melt-extruded by using an extruder provided with a slit die while a heated nitrogen gas was forced into the molten mixture. The extrudate from the slit die was quenched and taken up, while being drafted, to obtain a continuous filamentary net strand having a basis weight of 1.7 g/m² which had numerous discontinuous cracks extending along the filament length. Eight filamentary net strands were piled together and the laminate, thus-obtained, was spread in the lateral direction at an expansion ratio of 14.4 while the laminate was fed at an overfeed ratio of 1.8, to obtain a net-like fiber sheet (b'). The net-like fiber sheet (b') had a basis weight of 1.7 g/m² and was composed of filaments continuously forming nets and having an average single filament diameter of 40 µm.
Four nonwoven fabrics (a') and five net-like--fiber sheets (b') were piled to obtain a laminate sheet having a laminar structure of (b')/(a')/(b')/(a')/(b')/(a')/ (b')/(a')/(b'). The laminate sheet was heat-pressed by using a pair of smooth-finished heat-pressing rolls, the surfaces of which were maintained at 160°C, to obtain a composite net-like sheet (d') containing an aluminum fine powder and having a basis weight of 24.5 g/m². The microscope observation indicated that the filaments constituting the filament non-woven fabric (a') were embraced by the filaments constituting the net-like fiber sheet (b'). The composite net-like sheet (d') had a smooth surface and almost no fluff and exhibited a good abrasion resistance.
For comparison, a net-like fiber sheet (e') was prepared in a manner similar to that employed for the preparation of the net-like fiber sheet (b'), except that a mixture of 90% of polypropylene containing no aluminum fine powder and 10% of nylon-6. The net-like fiber sheet (e') had a basis weight of 1.7 g/m² and was composed of filaments having an average single filament diameter of 38 µm.
Four non-woven fabrics (a'), which were the same as those mentioned above, and five net-like fiber sheets (e^l) were piled in the same manner as mentioned above to obtain a laminate sheet. The laminate sheet was heat-pressed to obtain a composite net-like sheet (f') containing no aluminum fine powder and having a basis weight of 24.5 g/m2. The composite net-like sheet (f') was of a similar configuration to the composite net-like sheet (d') and had a smooth surface and almost no fluff, and exhibited a good abrasion resistance.
In order to determine heat insulating properties, each of the composite net-like sheets (d') and (f') was irradiated with far infrared rays having a peak wavelength of 3 pm at a temperature of 20°C and a relative humidity of 65% RH by using an aluminum sheathed heater maintained at about 700°C. The temperature of the non-irradiated side surface of each sheet was measured by using a heat flow meter "Shotherm HFM" (trademark, supplied by Showa Denko K.K.) to determine the heat flow rate Q[kcal/m²/hr]. The heat flow rates as determined on the composite net-like sheets (d') and (f') were 220 kcal/m²/hr and 265 kcal/m²/hr, respectively. This result shows that the composite net-like sheet (d') containing an aluminum fine powder had enhanced heat insulating properties over the composite net-like sheet (f').

Examples 56 through 61 and Comparative Example 38

Using each of the thermoplastic polymers shown in Table 8 and a scaly aluminum fine powder having passed through a sieve having a mesh size No. 35 (i.e., having an average particle size of 13 µm) and an emissive power of 0.04, a filament bundle was prepared as follows. A mixture of each polymer and 5%, based on the weight of the mixture, of the aluminum fine powder was melt-kneaded and extruded by using an extruder having an inner diameter of 50 mm and provided with a plain weave metal net having a 20 mesh size (made by Nippon Filcon K.K.) as a spinneret. The aluminum- containing polymer was extruded through the metal net while an electric current of 100 amperes was applied to the metal net at a voltage of 2 volts, thereby making the metal net self-heat- generating. The filamentary extrudate was quenched by blowing cooling air against the extrudate by using a cooling device provided with an air injection nozzle and located in close vicinity to the metal net. The cooling air was blown against the extrudate so that the air passes through the extrudate at a velocity of 7 m/sec. The resulting filament bundle was taken up at a speed of 8 m/min. The filament bundle was drawn at a temperature shown in Table 9 and at a draw ratio of 2 and then subjected to a stuffing crimping treatment whereby the filament bundle was crimped at a rate of 10 crimps per inch. The crimped filament bundle was cut into staple fibers having a 64 mm length. The scanning electron microscope observation indicated that the cross-section of the staple fiber was non-circular and varied along the fiber length.
For comparison, staple fibers were prepared in the same manner as mentioned above except that the aluminum fine powder was not incorporated.

Table 8

Polyethylene: high density grade, m.p. 131°C, supplied by Ube Industries Ltd.
Polypropylene: fiber grade, m.p. 167°C, supplied by Ube Industries Ltd.
Nylon-6: intrinsic viscosity n = 1.3, m.p. 223°C, supplied by Teijin Ltd.
Polybutylene terephthalate: intrinsic viscosity n = 1.1, m.p. 223°C, supplied by Teijin Ltd.
Polyethylene terephthalate: intrinsic viscosity n = 0.71

An oiling agent (Efusol 301, trademark, supplied by _Matsumoto Yushi K.K.) was applied to each of the staple fibers containing an aluminum fine powder and the staple fibers containing no aluminum fine powder at a pick-up of 0.3%, and then dried. The staple fibers are carded to obtain a web having a basis weight of 250 g/m². Thermal conductivity of the web was measured by sandwiching the web with spacers so that the web thickness was 1 cm. The results are shown in Table 9.
As seen from Table 9, the webs containing an aluminum fine powder have a lower thermal conductivity and a better heat retaining property than the web not containing aluminum fine powder.

Claims

1. A fiber for a heat insulating material, which contains 1 to 30% by weight, based on the weight of the fiber, of a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average particle size of 1 to 100 µm.

2. A fiber according to claim 1 wherein the flatness of the fiber, which is defined as the ratio of the longest diameter to the shortest diameter in the fiber cross-section, is at least 2.

3. A fiber according to claim 1 wherein said metal or metal oxide is selected from the group consisting of aluminum, copper, nickel, brass, iron, titanium, and oxides thereof.

4. A fiber according to claim 1 wherein said metal or metal oxide is of a scaly shape.

5. A fiber according to claim 1 which has a fineness of 0.5 to 20 denier.

6. A fiber according to claim 1 which is a sheath-core type composite fiber, the sheath component containing 1 to 40% by weight, based on the weight of the fiber, of the metal or metal oxide powder, and the content of the metal or metal oxide powder in the sheath component being larger than that in the core component.

7. A fiber according to claim 6 wherein said metal or metal oxide is selected from the group consisting of aluminum, copper, nickel, brass, iron, titanium, and oxides thereof.

8. A fiber according to claim 6 wherein said metal or metal oxide is of a scaly shape.

9. A non-woven fabric for a heat insulating material, which is composed of a web containing at least 10% by weight of a fiber containing 1 to 30% by weight of a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average particle size of 1 to 100 µm and having fiber bonding points formed by an adhesive component.

10. A non-woven fabric according to claim 9 wherein said metal or metal oxide is selected from the group consisting of aluminum, copper, nickel, brass, iron and oxides thereof.

11. A non-woven fabric according to claim 9 wherein said metal or metal oxide is of a non-spherical shape.

12. A non-woven fabric according to claim 9 wherein said metal or metal oxide is of a scaly shape.

13. A non-woven fabric according to claim 9 wherein said fiber has a flatness of at least 2, or has a sheath-core type composite structure, the sheath component containing a larger amount of the metal or metal oxide powder than the core component.

14. A wadding structure comprising a web covered with a fabric, said web comprising at least 5% by weight of a fiber containing 1 to 30% by weight of a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average particle size of 1 to 100 pm.

15. A wadding structure according to claim 14 wherein said metal or metal oxide is selected from the group consisting of aluminum, copper, nickel, brass, iron, titanium and oxides thereof.

16. A wadding structure according to claim 14 wherein said metal or metal oxide is of a scaly shape.

17. A wadding structure according to claim 14 wherein said fiber has a flatness of at least 2, or has a sheath-core type composite structure, the sheath component containing a larger amount of the metal or metal oxide powder than the core component.

18. A net-like fiber sheet for a heat insulating material, which is obtained by spreading a net-like fiber sheet obtained by extruding a melt of a thermoplastic resin containing a fine powder of a metal or metal oxide having an emissive power of not more than 0.3 and an average diameter of 1 to 100 pm and a blowing substance from a slit die, or a laminate of two or more of said net-like fiber sheets in the lateral direction at an expansion ratio A satisfying requirements represented by the following formulae:

and

wherein m is the tensile strength (g/d) of the net-like fiber sheet as measured in the longitudinal direction, with the proviso that when m is larger than 1 g/d, m is regarded as being equal to 1, and & is the average distance (mm) between adjacent bonding points in the net-like fiber sheet, wherein the average distance between adjacent bonding points in the net-like fiber sheet is 1 to 50 mm, the tensile strength of the net-like fiber sheet in the longitudinal direction is at least 0.05 g/d, and the average diameter of the fiber of the net-like fiber sheet is 1 to 100 µm.

19. A net-like fiber sheet according to claim 18 wherein said metal or metal oxide is selected from the group consisting of aluminum, copper, nickel, brass, iron, titanium, and oxides thereof.

20. A net-like fiber sheet according to claim 18 wherein said metal or metal oxide is of a scaly shape.

21. A net-like fiber sheet according to claim 18 wherein the longest diameter of said metal or metal oxide powder is not larger than 100 µm.

22. A net-like fiber sheet according to claim 18 wherein the content of a metal or metal oxide powder is 1 to 40% by weight based on the weight of the net-like fiber sheet.

23. A net-like fiber sheet according to claim 18 wherein fibers constituting the net-like fiber sheet are of sheath-core type composite structure, the sheath component containing a larger amount of the metal or metal oxide powder than the core component.

24. A net-like fiber sheet according to claim 18 wherein said net-like fiber sheet is obtained by extruding said thermoplastic resin melt and taking up at a draft ratio of 10 to 300.

25. A net-like fiber sheet according to claim 18 wherein said thermoplastic resin has a melting point of 70 to 350°C.