A method for preparation of a cushion material

Abstract: The cushion material according to the invention is prepared by mixing (A) polyester fibers having a fineness of 4 to 30 denier and a cut length of 25 to 150 mm with (B) core-sheath type conjugated fibers having a fineness of 2 to 20 denier and a cut length of 25 to 76 mm in a weight ratio of 95 ∼ 40 : 5 ∼ 60, the sheath component of said conjugated fibers having a melting point lower than that of the core component of said conjugated fibers and said polyester fibers with a difference of 30°C or more. In the cushion material, cubically and continuously interconnected portions of the fibers are adhered by fusion of the sheath portion of the above core-sheath type conjugated fibers. The cushion material having a thickness of 10cm or more and a good quality can be stably prepared by combining far-infrared ray or hot air flow heating and steaming in the heat-treatment.

Description: This invention relates to a method for preparation of cushion material using conjugated fibres. Various cushion materials made of polyester fibres have been developed. There are usually prepared by using two types of polyester fibres having different melting points with respect to each other or using core-sheath type conjugated fibres, and heat-treating in a hot air circulating oven to melt the component having a low melting point. In this procedure, the hot air is passed through the interior of webs. In the preparation of a relatively low density cushion material (i.e. cushion material having a density not higher than 0.01 g/cm²) unevenness in density occurs in the direction of thickness of the cushion material due to air pressure. In the preparation of a high density cushion material, it is difficult for the hot air to pass through the webs and thus the thickness of cushion material which can be prepared is restricted. Furthermore, since the heating mechanism is mainly convection and conduction, the loss in energy is disadvantageously high. In Japanese Laid-Open Patent Publication No. 223,357 of 1987, there has been proposed a method for the preparation of a cushion material by using far-infrared radiation as the heat source to overcome such disadvantages. In its Examples, a use of core-sheath type conjugated fibres having sheath of a low melting substance is disclosed. The heating mechanism of this method is radiation and the energy in the far-infrared long wave region is absorbed in the fibre material and causes internal heating by molecular vibration and thus the heat-fusable fibres in the webs are efficiently melted. Hence, no unevenness in density in the hot air circulating oven arises and also the process can be carried out at low temperature in a short period to give good workability. However, the method is disadvantageous in that, when the web is thick it is difficult to melt the interior. Furthermore, Japanese Laid-Open Patent Publication No. 311,050 of 1983 discloses a product in which interconnections are fused by melting low-melting fibres with steaming. In this case, the interconnections can be fixed by melting the low-melting fibres without adhesives and consequently a product having a good cushioning property can be obtained in a relatively stable condition, but it has problems in workability. Voluminous products having no strain by compression set cannot be obtained. FR-A-2 307 071 discloses a cushion material which consists of (A) polyester fibres having a fineness of 6.7 dtex and a cut length of 50 mm and (B) core-sheath type conjugated fibres having a fineness of 13.3 dtex and a cut length of 49 mm in a weight ratio of 50/50, the sheath component having a melting point lower than that of the core component and said polyester fibres (A) with a difference of 30°C or more, whereby cubically and continuously interconnected portions of said fibres (A) are adhered by fusion to the sheath component of fibre (B). The cushion material exhibits wide variations in density, for example variations of ± 10% or more. Thus, the methods of heat treatment for the preparation of the cushion material have both merits and demerits. Also they cannot provide voluminous products having no strain by compression set. An object of the present invention is to provide a method for preparation of a voluminous cushion material comprising polyester fibres and which has a high quality and little strain by compression set so that it can be used as mats for beds. The inventors have found that the above object can be attained by using specific conjugated fibres and combining the advantages of heating by using far-infrared radiation or a hot air flow with heating by steaming. Summary of the Invention In accordance with the present invention there is provided a method for preparation of a cushion material, comprising mixing (A) polyester fibres having a fineness of 4 to 33 dtex (4 to 30 denier) and a cut length of 25 to 150 mm with (B) core-sheath type conjugated fibres having a fineness of 2 to 22 dtex (2 to 20 denier) and a cut length of 25 to 76 mm in respective amounts by weight of 95 ∼ 40 and 5 ∼ 60 per 100 parts by weight in total of the fibres (A) and (B) to prepare card webs, the sheath component of said conjugated fibres having a melting point 30°C or more lower than that of the core component of the conjugated fibres and the polyester fibres. adhering temporarily the card webs by heating with far-infrared radiation or with a hot air circulating heater to melt the sheath component of the conjugated fibres, laminating the temporarily adhered webs, introducing the laminated webs in a steam vessel, evacuating the vessel to a pressure not higher than 10⁵Pa (750 mm Hg), and introducing steam of at least 9.8 x 10⁴Pa (1 kg/cm²) pressure into the vessel to heat-treat the laminated webs and to mutually adhere web layers of the laminated webs. The above-described method enables a cushion material which has a thickness of at least 10 mm and a density of 0.003 ∼ 0.15 g/cm³, the scattering of the density being not greater than ± 5%, to be stably obtained. Detailed Description of the Invention Among the polyester fibres used as (A), there are included general fibres made of polyethylene terephthalate, polyhexamethylene terephthalate, polytetramethylene terephthalate, poly-1,4-dimethylcyclohexane terephthalate, polyhydrolactone or their copolymerized ester and conjugated fibres prepared by conjugate spinning. Side-by-side type conjugated fibres comprising two polymers having a different heat shrinkage percentage with respect to each other are preferred, because they form spiral crimps to give a cubic structure. Especially, hollow yarns having a hollowness of 5 to 30% are preferably used. As the core-sheath type conjugated fibers (B), conjugated fibers prepared by using common polyester fiber component as the core and low-melting polyester, polyolefin, polyamide or the like as the sheath may be used. However, the difference between the melting points of the core component and sheath component must be at least 30°C. The sheath of the core-sheath type conjugated fibers (B) is preferably of a low-melting polyester. Such a polyester is generally obtained as a copolymerized polyester. Among the dicarboxylic acids used for producing the copolymerized polyester, there are exemplified aliphatic dicarboxylic acids such as adipic acid and sebacic acid, aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid and naphthalene dicarboxylic acid, alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid and the like, and among the diols used for producing the copolymerized polyester, there are exemplified aliphatic diols and alicyclic diols, such as hexanediol, diethylene glycol, polyethylene glycol and paraxylene glycol and the like. Further, an oxyacid such as parahydroxy benzoic acid may be used to produce the copolymerized polyester. As the polyesters, there are exemplified those prepared by the copolymerization of terephthalic acid and ethylene glycol together with isophthalic acid and 1,6-hexanediol, and the like. According to the present invention, it is preferred to use hollow conjugated fibers as the main fibers (A) in the cushion material as described above, because the fibers in the web interconnect irregularly and fuse with the low-melting component of the core-sheath type conjugated fibres at the interconnections to give a cubic structure and thus a product of very low repeated compression set is prepared. The present invention provides a cushion material which has a thickness of not less than 10 mm and a density of 0.003 to 0.13 g/cm³ and a scattering range of density of not greater than ± 5% and which cannot be prepared by conventional methods. It is prepared by not only using a specified ratio of the core-sheath type conjugated fibers comprising a low-melting component as the sheath for melt-bonding between fibers but also using a special method of heat treatment as follows. Thus, according to the present invention the cushion material is prepared by a method of laminating and heat treating by two steps in which the fibers (A) and (B) are mixed together and the surface of the resultant card webs is tentatively fused with far-infrared radiation or with a hot air circulating oven and then the fused webs are laminated according to the defined density and thickness and the laminate is fed into a steam vessel and the vessel is evacuated to a pressure of 10⁵ Pa (750 mm Hg) or less and then steam of at least 1 kg/cm² is introduced into the vessel to heat-treat the laminate. By such a method of laminating and heat-treating by two steps, even the inner layer of the cushion material is melt-adhered uniformly and a product of total good feeling and of excellent appearance can be prepared efficiently. For example, a thick cushion material having a thickness not less than 10 mm, especially not less than 30 mm, can be easily prepared with a desired density, the scattering range of which is within ±5%. Also, a cushion material having a hardness of not lower than 10 g/cm² can be prepared stably. In the present invention, other fibers may be mixed as the third component. Also, at least part of the fibres used in the present invention may be replaced by latent-crimping polyester conjugated fibres, antibacterial polyester fibres containing an antibacterial agent such as antibacterial zeolite or flame-retarding fibres. Especially, in the case an antibacterial agent is milled in the sheath portion of the core-sheath type conjugated fibres (B), the sheath portion is rendered molten by the heat treatment and at the same time the antibacterial agent spreads over the whole cushion material and adheres to it to show high effect. Detailed Description of the Preferred Embodiments The following examples serve to illustrate the invention in more detail although the invention is not limited to the examples. Example 1 (A) 80 weight % of hollow conjugated polyester fibres having a hollowness of 16.1 % (fineness: 14 dtex (13 denier), cut length: 51 mm, melting point: 257 °C) prepared by conjugating side by side a polyethylene terephthalate having a relative viscosity of 1.37 and a polyethylene terephthalate having a relative viscosity of 1.22 in a ratio of 1:1 and (B) 20 weight % of core-sheath type conjugated fibers (fineness: 4 dtex (4 denier), cut length: 51 mm) containing a polyethylene terephthalate having a melting point of 257°C as the core and a copolymerized polyester (terephthalic acid/isophthalic acid=60/40) having a melting point of 110°C as the sheath were mixed together in a hopper feeder and carded and then made into a web having a weight of 350 g/cm² with a cross layer method. The web was passed through a far-infrared heater at 130°C continuously to give a melt-adhered web. The resultant web was cut into sheets 1 m wide and 2 m long and 10 sheets of the cut web were laminated and placed between two stainless steel plates and pressed to a thickness of 10 cm and fed into a steam oven. Air in the steam oven (and in the web laminate in it) was evacuated with a vacuum pump to a pressure of 10⁵ Pa (750 mm Hg) and then steam of 3 kg/cm² was fed to the steam oven and the laminate was heat-treated at 132°C for 10 min. Steam in the oven was evacuated again with a vacuum pump to give a cushion material 100 cm wide, 200 cm long and 10 cm thick having a density of 0.035 g/cm³ in which the webs were melt-adhered into a whole mass in the oven. The resultant cushion material gas cut into 8 sheets each 50 cm square and then cut into three equal parts to the direction of thickness. Distribution of density and hardness, repeated compression and compression set of each portion were measured in accordance with JIS K 6401. The results are shown in Tables 1 and 2 together with the test results for conventional cushion materials prepared by hot air circulation ( Comparative Examples 1 and 2 ). From the measured values shown in Tables 1 and 2, it can be found that the cushion material prepared by the method according to the present invention has a hardness and a density focused within a definite range in any portion and is low in compression set and has a uniform excellent quality. Compression test Sample Compression hardness Pa(kg/cm²) Compression set (%) Repeated compression set (%) Resilience (%) Example B 6.37 x 10³ (0.065) 9.6 6.5 57 D 6.07 x 10³ (0.062) 9.4 6.5 55 E 6.17 x 10³ (0.063) 9.4 6.6 57 G 6.47 x 10³ (0.066) 9.7 6.4 58 Comp.Ex.1 5.68 x 10³ (0.058) 15.6 16.8 33 2 5.19 x 10³ (0.053) 17.4 18.3 34 *1) The designations for samples in Examples are same as in Table 1. *2) In Comparative Examples, the test was carried out by piling up three sheets of the sample having a thickness of 33 mm. Test method 1. Surface hardness Nine positions were measured by using a F type harness meter and their average is shown. 2. Density The volume and the weight of the sample were measured and the density was calculated by the following equation. D = W V where D: Apparent density ( g/cm³ ) W: Sample weight ( g ) V: Sample volume ( cm³ ) 3. Compression hardness ( in accordance with JIS K 6401 ) A sample of 150 x 150 mm was placed between two parallel compression plates and compressed to 3.53 x 104 Pa (0.36 Kg/cm ) at a rate of not higher than 10 mm/sec. and the thickness at that time was measured to give the initial thickness and then the sample was further compressed to 25 % of the initial thickness and stood for 20 sec. and the load was read to give the hardness. 4. Compression set A sample of 150×150 mm was placed between two parallel compression plates and compressed to 50 % of the initial thickness and fixed and then stood at room temperature for 40 hours and then the compression plates were removed and the sample was stood for 30 min. and the thickness was measured. where C: Compression set ( % ) t₀: Initial thickness of the sample ( mm ) t₁: Thickness of the sample after the test ( mm ) 5. Repeated compression set A sample of 150×150 mm was placed between two parallel compression plates and repeatedly compressed for 80,000 times to 50 % of the sample thickness at room temperature at a rate of 60 times per min. and then the sample was removed and stood for 30 min. and the thickness was measured and the set was calculated by the same equation as in the above 4. 6. Resilience ( JIS K 6401-1980 ) A sample specimen of a side of not less than 100 mm and a thickness of not less than 50 mm was placed on a horizontal platform and a 5/8 common steel ball specified in JIS B 1501 ( Steel ball for ball bearing ) was freely dropped from the height of 460 mm over the surface of the sample onto it and the resilient height was measured. The test was repeated on the different three or more sites of the sample and the average value was shown. where R: Resilience ( % ) D₀: Drop distance 460 ( mm ) D₁: Resilient height ( mm ) Example 2. (A) 75 weight % of regular polyester fibres (fineness: 15 denier, cut length: 64 mm, melting point: 257 °C) and (B) 25 weight % of core-sheath type conjugated fibres (fineness: 3 dtex (3 denier), cut length: 51 mm) containing a polyethylene terephthalate having a melting point of 257 °C as the core and a copolymerized polyester (terephthalic acid/isophthalic acid=60/40) having a melting point of 110°C as the sheath were mixed and carded. Then the obtained webs were laminated and moulded in the same manner as in Example 1 to give laminates having a density of 0.01g/cm³ to 0.04 g/cm³ as shown in Table 3. The flame resistance of the laminates was measured by a method according to the standard test for flame-retarded products in Japan Flame Retardant Association. The results are shown in Table 3. density (g/cm³) maximum carbonized length (mm) average carbonized length (mm) judgement Example 2 0.01 90 79 acceptable 0.02 85 79 acceptable 0.03 80 74 acceptable 0.04 72 69 acceptable Comp. Ex. 0.01 113 105 acceptable 0.03 96 92 acceptable *1) In Comparative Examples, the test was carried out by piling up three sheets of the sample having a thickness of 33 mm. Example 3 (A) 50 weight % of hollow conjugated polyester fibres having a hollowness of 16.4 % (fineness: 14 dtex (13 denier), cut length: 51 mm) prepared by conjugating side by side a polyethylene terephthalate having a relative viscosity of 1.37 and a polyethylene terephthalate having a relative viscosity of 1.22 in a ratio of 1:1 and 32 weight % of disinfecting hollow fibres (fineness: 14 dtex (13 denier), cut length: 64 mm) consisting of polyethylene terephthalate compounded with metal ion comprising zeolite solid perticles which have antibacterial properties, and 18 weight % of core-sheath type conjugated binder fibres (fineness: 3 denier, cut length: 51 mm) were mixed and carded according to the general method. With the resultant web, a cushoning material having a width of 100 cm, a length of 200 cm, a thickness of 10 cm and a density of 0.035 g/cm² was obtained in the same manner as in Example 1. The antibacterial activity of the cushoning material was measured with use of a germ, Klebsiella pueumeniae, by Shake Flask Method decided in Sanitary Finishing Conference for Textures. The results are shown in Table 4. Sample antibacterial fibre density (g/cm³) colony number decreasing ratio of the germ before shaking after shaking Example Upper layer 32 % 0.035 2.0x10⁴ 300 98.5 % Mid. layer 140 99.3 % Lower layer 240 98.8 % Comparative Example - 0.033 2.0x10⁴ 1.8x10⁴ 10.0 % Blank Test - 2.0x10⁴ 2.0x10⁴ 0 % As described above, the present invention can provide a cushion material of high quality, which has a uniform density and a very low compression set regardless of thickness.

Claims: A method for preparation of a cushion material, comprising: mixing together (A) polyester fibres having a fineness of 4 to 33 dtex and a cut length of 25 to 150 mm and (B) core-sheath type conjugated fibres having a fineness of 2 to 20 dtex and a cut length of 25 to 76 mm in respective amounts by weight of 95 40 and 5 60 per 100 parts by weight in total of the fibres (A) and (B) to prepare card webs, the sheath component of said conjugated fibres having a melting point at least 30°C lower than that of the core component of said conjugated fibres and said polyester fibres, adhering temporarily the card webs by heating with far-infrared radiation or with circulating hot air to melt the sheath component of the conjugated fibres, laminating the temporarily adhered webs, introducing the laminated webs into a steam vessel, evacuating the vessel to a pressure not higher than 10⁵Pa (750mm Hg), and introducing steam of at least 9.8 x 10⁴Pa (1 kg/cm²) pressure into the vessel to heat-treat said laminated webs and to mutually adhere the webs together. A method according to claim 1, wherein said polyester fibres (A) are side-by-side type conjugated fibres consisting of two polymers having different heat shrinkage percentages with respect to each other. A method according to claim 1 or 2, wherein the fibres comprise antibacterial fibres.

Inventors: MASUDA YUGORO, NOHARA SABURO, MASUDA, YUGORO, NOHARA, SABURO
Applicants: KANEBO LTD, KANEBO LTD.
Application year: 1989
Main classification: D04H1
IPC codes: D04H1, B68G1