Process for producing fibrous board

Abstract

An object of the present invention is to provide a process for producing fiberous board with which fiberous board exhibiting high bending strength and high stiffness at a wide range of heating temperatures and a wide range of compressing and heating times. In the present invention, fiberous board having an initial flexural modulus of at least 300 MPa in three point bending test is obtained by forming a web by correcting sheath-core composite fibers of which a core component is formed from a copolymer of ethylene glycol and terephthalic acid and the sheath component is formed from ethylene glycol, adipic acid, terephthalic acid, isophthalic acid; and/or diethylene glycol. The web is then compressed in a direction of thickness and heated, so that the sheath component softens and melts and the sheath-core composite fibers are melt bonded together and molded into a flat plate shape.

Claims

1. A process for producing a fibrous board having an initial flexural modulus of not less than 300 MPa in a three point bending test, comprising: collecting sheath-core composite fibers, of which the core component is formed from a copolymer of ethylene glycol and terephthalic acid, and the sheath component is formed from ethylene glycol, adipic acid, terephthalic acid and isophthalic acid; and optionally diethylene glycol, to form a web, and then compressing the web in a direction of thickness direction and heating to soften or melt the sheath components so as to bond the sheath-core composite fibers with each other, wherein the web is shaped into a plate to form a fibrous board, and a molar ratio of isophthalic acid:adipic acid:terephthalic acid in the sheath component is within the range of 0.004 to 0.6:1:1 to 10.

2. The process of claim 1, wherein the web is preliminarily heated and sandwiched by a pair of metal plates having normal temperature and then compressed in the direction of thickness.

3. The process of claim 1, wherein the web having normal temperature is sandwiched by a pair of heated metal plates, and then compressed in the direction of thickness.

4. The process according to claim 1, wherein the web is needle punched to have the sheath-core composite fibers three dimensionally interlaced prior to the compressing and heating.

5. The process according to claim 1, wherein the fibrous board has a maximum bending strength of not less than 7.3 MPa in a three point bending test.

6. The process according to claim 1, wherein the sheath-core composite fiber is sheath-core composite continuous filament or sheath-core composite staple fiber.

7. The process according to claim 1, wherein the web is shaped into a plate to form a fibrous board by cooling after the compressing and heating.

8. The process according to claim 1, wherein a weight ratio of core to sheath is 0.3-5:1.

9. The process according to claim 1, wherein the collected web exhibits a mass of at least 150 g/m.sup.2.

10. The process according to claim 1, wherein the compressing is carried out with a surface pressure of 1-500 kg/cm.sup.2 and the heating is carried out at a temperature of 100-200° C.

11. The process according to claim 1, wherein the collected fibers consist of said sheath-core composite fibers, of which the core component is formed from a copolymer of ethylene glycol and terephthalic acid, and the sheath component is formed from ethylene glycol, adipic acid, terephthalic acid and isophthalic acid; and optionally diethylene glycol.

Description

EXAMPLE 1

(1) A copolymer of ethylene glycol and terephthalic acid (a melting point of 260° C.) was prepared as a core component. A copolymer of ethylene glycol, diethylene glycol, adipic acid, terephthalic acid and isophthalic acid (a melting point of 200° C.) was prepared as a sheath component. The diol components contained 99 mole % of ethylene glycol and 1 mole % of diethylene glycol, and the dicarboxylic acids contained 19 mole % of adipic acid, 78 mole % of terephthalic acid and 3 mole % of isophthalic acid. Both of the core component and sheath component were provided into a spinning apparatus having composite spinning holes and then melt spun to obtain a sheath-core composite continuous filament. The sheath-core composite continuous filament had a weight ratio of core component:sheath component=7:3. The filaments were introduced into an air sucker located under the spinning apparatus and rapidly sucked and thinned, followed by open filaments by an art-known opening devise to collect and to accumulate on a moving screen conveyer to obtains filamentous web. The filamentous web was conveyed to a needle punching machine and needle punched at a punch density of 90 punches/cm.sup.2 and a needle depth of 10 mm, to obtain a needle punched nonwoven fabric having a weight of 900 g/m.sup.2.

(2) The resulting needle punched nonwoven fabric was put between a pair of metal plates which had been heated at 200° C. and compressed for 60 seconds therebetween in which a spacer having 3 mm was inserted between the two metal plates. The needle punched nonwoven fabric was taken out from the pair of metal plates and left at room temperature for cooling to obtain a fibous board.

EXAMPLE 2

(3) A fibous board was obtained as generally described in Example 1, with the exception that a pair of metal plates heated at 180° C. was employed instead of those of 200° C.

EXAMPLE 3

(4) A fibous board was obtained as generally described in Example 1, with the exception that a compression time was changed from 60 seconds to 15 seconds.

EXAMPLE 4

(5) A fibous board was obtained as generally described in Example 1, with the exception that a compression time was changed from 60 seconds to 30 seconds.

EXAMPLE 5

(6) A fibous board was obtained as generally described in Example 1, with the exception that a compression time was changed from 60 seconds to 45 seconds.

COMPARATIVE EXAMPLE 1

(7) The copolymer obtained in Example 1 was prepared as core component. A copolymer of ethylene glycol, diethylene glycol, terephthalic acid and isophthalic acid (a melting point of 200° C.) was prepared as sheath component. In the copolymer constituting the sheath component, the diol component contained 99 mole % of ethylene glycol and 1 mole % of diethylene glycol, and the dicarboxylic acid included 80 mole % of terephthalic acid and 20 mole % of isophthalic acid. Both of the core component and sheath component were provided into a spinning apparatus having composite spinning holes and then melt spun to obtain a sheath-core composite continuous filament. The sheath-core composite continuous filament had a weight ratio of core component:sheath component=6:4. The filaments were introduced into an air sucker located under the spinning apparatus and rapidly sucked and thinned, followed by open filaments by an art-known opening devise to collect and to accumulate on a moving screen conveyer to obtains filamentous web. The filamentous web was conveyed to a needle punching machine and needle punched at a punch density of 90 punches/cm.sup.2 and a needle depth of 10 mm, to obtain a needle punched nonwoven fabric having a weight of 900 g/m.sup.2.

(8) The resulting needle punched nonwoven fabric was put between a pair of metal plates which had been heated at 200° C. and compressed for 60 seconds therebetween in which a spacer having 3 mm was inserted between the two metal plates. The needle punched nonwoven fabric was taken out from the pair of metal plat and left at room temperature for cooling to obtain a fibrous board.

(9) [Measurement of Maximum Bending Strength in Three Point Bending Test]

(10) Test pieces having a length direction of 150 mm and a wide direction of 50 mm were obtained from the fibrous boards obtained in Examples 1 to 5 and Comparative Example 1. The test pieces had a thickness of 3 mm±0.4 mm because the spacer having 3 mm was put between the pair of metal plates, but the thickness was considered to be 3 mm with rounding down. Since, in the fibrous board the sheath-core composite filaments tend to be aligned with a mechanical direction (a direction of conveying the fibrous board), highest bending strength can be obtained when the mechanical direction is aligned with the length direction of the test piece. Accordingly, the mechanical direction of the each fibrous board was aligned with the length direction of the each test piece. The test piece was placed on fulcrum points whose distance was 100 mm and a pushing plate went down at a speed of 20 mm/min at the center of the fulcrum points to load on the test piece. A maximum load when the fibrous board was broken was measured and a maximum bending strength was calculated to show in Table 1. The calculation was conducted the following equation: MPa=[6×(maximum load N)×50 mm]/[50 mm×(3 mm).sup.2].

(11) [Measurement of Initial Flexural Modulus (MPa)]

(12) An initial flexural modulus was calculated from an initial slope from a strain-bending load curve obtained by the measuring the maximum bending strength in the three point bending test, and it is shown in Table 1. The calculation was conducted by the following equation:
Initial flexural modulus MPa=[Initial slope×(100 mm).sup.3]/[4×50 mm×(3 mm).sup.3].

(13) TABLE-US-00001 TABLE 1 Maximum bending Initial flexural Example Number strength (MPa) modulus (MPa) 1 9.1 470 2 9.4 550 3 8.7 490 4 11.0 470 5 7.8 440 Comparative 6.8 230 Example 1

(14) When the values of maximum bending strength and initial flexural modulus of the fibrous boards obtained from Examples 1 to 5 and Comparative Example 1 are compared, the fibrous boards of Examples show excellent stiffness in bending strength and excellent flexural modulus, in comparison with the fibrous board obtained in Comparative Example 1. When the values of maximum bending strength and initial flexural modulus of the fibrous boards obtained in Examples 1 to 5 are compared, the fibrous boards having excellent maximum bending strength and excellent initial flexural modulus are obtained even if heating temperature and compressing time are changed in considerable ranges.