KR910005013B1 - Low Density Nonwoven Aramid Sheet and Manufacturing Method Thereof - Google Patents

Abstract

A low density abrasion-resistant non woven aramid sheet made by expanding a dried, wet-laid sheet of fibrids and fibres, which has self-bonded regions made with heat and pressure. The re-wet sheet is heated dielectrically to expand the interior of the non densified portions without substantially roughening or disrupting their surface skin. The sheet may be used in upholstered furniture, especially in aircraft seat cushions and similar applications.

Description

Low Density Nonwoven Aramid Sheet and Manufacturing Method Thereof

The present invention relates to an improved low-density nonwoven sheet composed of aramid fibrids and short aramid fibers, having low porosity, softness and surface abrasion resistance, and a method for producing the same.

As is known from EP-A-73,668, low density (less than 0.16 g / ml) nonwoven sheet structures consisting of aramid fibers and fibrids are useful for heat dissipation and sound insulation among other nonwovens. These low-density materials are rapidly dried to form a tacky low-density sheet having a plurality of paper-like layers of film components that form a macroscopic cell with evenly expanded sheet thickness without drying at all. It is prepared from a wet integrated sheet of expanded fibrid-fiber mixture. Although the tensile strength, surface integrity, and structure of known sheets are sufficient for many applications, other applications are those which have strength and surface abrasion resistance and less porosity than those obtained from sheets produced by wet dense non-drying processes. in need. Drying these known wet dense sheets, such as by passing through a soft heated can or roll, can provide a smoother, more dense sheet to give a stronger and tougher sheet material. In contrast, previous attempts to expand such dry sheets to the lower densities required for some applications have not been successful.

Thus, one object of the present invention is a method of expanding a wet integrated fibrid-fiber nonwoven aramid sheet after it has been dried once. Another object of the present invention is a low density sheet structure composed of aramid fibers and aramid fibrids with improved tensile strength, surface continuity, surface integrity and surface wear resistance. Still another object of the present invention is a sheet structure having sufficient flexibility and fire resistance, which is used as a fire-blocking sheet in applications where a thin, flexible and light weight fire resistant material is required and in upholstery furniture.

Under appropriately selected conditions, the paper-based nonwoven sheet of the wet dense aramid fibrid / fiber mixture is dried, wetted and then expanded to provide a new low density sheet structure that is soft on the outside and dense and skin-like. Has a uniformly expanded portion; If necessary, the expanded portion has a sponge-like to open instrument shape (air filled) internal structure; This sheet structure has low water resistance porosity.

The product of the present invention is a low density nonwoven sheet structure consisting essentially of a mixture of 30 to 90% by weight aramid fibrids and supplementally 70 to 10% by weight aramid short fibers, defined by self-bonded and compressed areas and There is an expanded portion consisting of a chamber formed by two surface layers on the opposite, dense and smooth skin of the bleed and fibers (the two surface layers surround the less dense interior), the sheet having at least about 10 seconds of drip pores. Porosity low enough to provide drip porosity test time.

The inflated portion is preferably discontinuously defined by compressed regions arranged in cut lines. Cutting of the compressed linear region has been found to improve both the expansion uniformity within the expanded portion of the sheet structure and the degree of expansion under certain conditions.

The product of the present invention is substantially improved in abrasion resistance as compared to the products of the prior art, which are manufactured by the wet integrated non-dry expansion method. The abrasion resistance of the improved product is at least 1000, preferably 2000 times, until fracture, as measured by the Tabber Abrasion Test.

The term "short fibers" and "floc" as used herein and in the prior art are used interchangeably with respect to the short fibers commonly used in the manufacture of wet dense paper sheets. Typically, the length of the fibers suitable for such applications is less than about 2.5 cm, most preferably less than about 0.68 cm. Suitable linear density of the fiber is 0.55 to 11.1 dtex, preferably 1.0 to about 3.5 dtex. For maximum strength and resistance to shrinkage, short fibers are preferably cut from highly stretched, heat stabilized filaments. As used herein, the term “fibrid” refers to both synthetic, micro, non-granular, flexible, fibrous or film-like particles, as described, for example, in the above-mentioned European Patent Application and US Patent No. 2,999,788. to be.

Although fibrids and fibers are specific aramid polymers, it is preferred that the fibrids and at least some of the short fibers consist of poly (m-phenylene isophthalamide), i.e., MPD-I. For better fire resistance, in particular to protect against “break-open” when exposed to flames, a portion of the short fibers is treated with poly (p-phenylene terephthalamide), ie PPD-T. It is preferable to make. The same weight mixture of PPD-T and MPD-I fibers has a good balance of wear resistance and fire resistance, which is a mixture of 20% by weight of each fiber type and 60% by weight fibrids. In order to improve performance and compatibility in making sheet structures, the PPD-T fibers can be pulped to increase the fibril properties of the PPD-T fibers as is known in the art.

In addition, the present invention forms a soft wet integrated sheet of aramid material, compresses a pattern of non-expandable compressed regions into sheets to define the expandable portions between the regions, and permits dielectric heating of the patterned sheet wetted with water. A method of producing an expanded nonwoven sheet of aramid fibrids and short aramid fibers comprising the step of rapidly evaporating water to produce a very expanded portion of the sheet, wherein the wet dense sheet is heat dried to Water evaporates to provide a dry sheet with a smooth surface; By forming a pattern of non-expandable compressed regions with heat and pressure to produce an inflated laminated sheet structure consisting of at least one layer of dry sheets, the material itself is compressed in the compressed region over the thickness of the laminated sheet structure defining the expandable portion. Bonding; Stress-bending the dry sheet with a wet or saturated pattern sheet structure by stress-bending in the presence of water; An improvement is that the wet sheet is dielectric heated to rapidly evaporate water and expand the interior of the expandable portion of the patterned sheet without destroying the surface of the sheet. When the sheet structure made for expansion consists of only a single layer of dry sheet, expansion occurs more rapidly if the thickness of the dry sheet is at least 15 mils, preferably at least 20 mils.

Wet dense sheets are suitably dried without calendering under tension on heated cans or rolls, as known in the art of papermaking.

In order to avoid the expansion of the sheet structure in the compressed region, it is desirable to use an ultrasonic device which is formed by heat and high pressure and which acts as a heat source through the ultrasonic vibration of the sheet material.

It is desirable to add a dielectric coupling agent to water to heat more rapidly because it is difficult to expand such sheets after they have been dried once.

In addition, the sheet is mechanically operated or stress-flexed in the presence of water to dry it more efficiently and quickly to saturate it with water prior to expansion of the laminated sheet material, or facilitates penetration and impregnation of water therein. For example, this is accomplished by passing a sheet through a water bath with a sinusoidal wave path on a 90 ° edge, that is, less than 1/16 in radius. If stress-flexion acts on the dry sheet, as a result of this the sheet should get wet. This stress-flexion not only reduces the time required for water to penetrate the sheet, but also increases the impregnation of the water to provide a more cellular internal structure in the expanded portion.

A very surprising feature of the present invention is that once dried, a portion of the sheet can be expanded without actually destroying the surface of the sheet. Thus, it is possible to produce a sheet that is much softer and has less pore surface than the previous sheet produced by expanding the wet aggregated non-dried sheet. Even more surprising is the ability to adjust the internal characteristics of the inflated part as mentioned earlier. These internal properties are characterized by the area between the compressed regions (the larger the area, the more open and less sponge-like the interior), the tensile bending of the dry sheet prior to expansion to provide more cellular sponge interior, and the ability of the dielectric coupling of water in the sheet. (Eg increased by the presence of surfactants or dissolved ionized salts). It depends on various factors, including the strength of the electric field during dielectric expansion, the rate at which the sheet passes through the heating zone (retention time), the thickness of the sheet being expanded, and the number of separation sheet layers used to produce the sheet. do. Another possibility involves laminating an undried nonwoven sheet between two dry sheets before forming a compressed region if the sheet can be inflated to provide a dense outer skin to provide a cellular-filled structure inside. .

Of course, the tensile strength of the obtained expanded sheet depends on the thickness or basis weight of the expanded sheet. For example, a sheet typically having a basis weight of about 60 oz / yd ² (200 g / m ² ) and a thickness of about 23 mils (0.58 mm) has a tensile strength of at least about 10 in-lbs (11.53 kg-cm). The best tensile strength and wear resistance can be provided by heat setting the sheet at a temperature sufficient for the polymer material to crystallize in the sheet.

The sheet moistened with tap water prior to expansion absorbs at least 75% by weight of the dry sheet; However, the impregnation amount is preferably about 140%. Water containing a dielectric coupling agent can reduce the impregnation percentage needed to improve swelling. Typically, a sheet having a basis weight of about 6Oz / yd ² (200 g / m ² ) may be soaked with tap water for about 50 seconds to obtain about 140% water impregnation and provide good expandability. However, if the amount of water impregnation is reduced and lowered, a product having excellent expansion can be obtained by spraying water containing up to 5% by weight of the dielectric coupling agent on the surface of the sheet so that the water content is less than 50%.

Also, as noted, the stress bending described above can reduce the time it takes for water to penetrate the sheet and reduce the percentage of water needed for good expansion. In addition, stress bending can be used to increase expansion to the sheet even at low water concentrations.

The sheet can be suitably patterned into the compressed region to uniformly control the expansion in the longitudinal as well as transverse directions during the process of inflating the sheet. The patterning and spacing of the portions can be varied to achieve the desired degree of expansion.

It is evident that the present invention provides a wide range of shape change possibilities that depend on factors such as the design or pattern of the compressed region and the properties of the sheet being expanded. Other materials, such as mica, can be incorporated into the sheet without disturbing the sheet's performance or desired use.

Suitable heated embossing rolls, plates and the like can be used to form the compressed area, but ultrasonic embossing or bonding devices are preferred. Anvils in the ultrasonic device can be designed into a moderately raised portion, which provides the desired pattern as the sheet passes through the device. Ultrasonic binders provide binding conditions more than 4000 psi at 275 ° C., uniformly and easily, which has been found to be efficient. Suitable patterns include diamonds, squares, rectangles, circles, and other geometric shapes. In individual patterns of small lupus, ultrasonic bonding seems to facilitate the expansion of small segments. It is preferred that the compressed region consists only of a fraction, for example 20% or less of the sheet total surface area.

When the adhesive tape is used on the surface and then peeled off, it is evident that the toughness and the integrity of the sheet surface of the present invention are increased in resistance to loss of material. This can be measured quantitatively with the Tape Pull Test as described herein, with the loss of material of the sheet of the invention less than 4 mg / cm ² . In such a test the compressed area is preferably free of material loss. In general, the smaller the surface area of each expanded portion in wear resistance, the better the performance in the test. Thus, preferred sheet structures of the present invention are discontinuous in the expanded portion, and the surface area of the expanded portion is in the range of about 0.1 to about 25 cm ² , respectively.

In sheets containing short fiber mixtures of MPD-I and PPD-T, the fire resistance of the sheet increases as the amount of PPD-T fibers increases, but wear resistance tends to decrease.

Preferred sheets of the present invention have a smooth, two-dimensional expanded portion of the surface (actually filaments are loose and irregular in the visible surface compared to normal paper), can give a certain degree of gloss, and are irregular, woven and woolen. It is distinguished from the surface of the sheet | seat manufactured by the well-known non-drying process which has many hairs and has many pores.

Products of the present invention, in particular those containing mixtures of poly (m-phenylene isophthalamide) and poly (p-phenylene terephthalamide) fibers, have increased strength and wear resistance compared to undried expansion sheets and thus have When used as a fire protection layer, wear life is increased, for example when used as floor carpets and especially as seat cushions in aircraft.

In general, the larger the surface area of the bulged portion, the more openings are created inside the center. Abrasion resistance and part-to-part uniformity degrade as the area increases, especially as the bulging portion with surface area on each side of the sheet larger than about 4 in ² increases.

Other uses of the products of the present invention include thermal, lining in protective clothing and resistance to fire, heat and sound. Other uses are readily apparent from the physical and chemical properties of these low weight sheets.

Known ultrasonic coupling devices, due to their simplicity and efficiency, can be used to provide a desirable compression pattern with a straight geometry, such as diamond or square. Particularly preferred is a pattern made by two substantially parallel groups of lines with a distance between the lines in each group of at least about 1 cm (3/8 inch) and no more than about 2.5 cm (1 inch). Ultrasonic bonding to form patterns on dry sheets not only has high pattern applicability, but also provides more effective self-bonding to prevent delamination or blow-apart of compressed areas under conditions necessary for the expansion process.

The compressed area should suitably be at least about 0.5 mm wide and about 1 mm long and should be cut by spaced blocks of approximately equal length along the linear direction. A compact portion of about 1 mm can be used. The cutting improves the expansion control from part to part along and across the inflated sheet.

The present invention provides an aramid expanded sheet product having a wear resistance of 3 to 10 times or more as compared to a sheet prepared by a known non-drying process.

이온 계면활성제, 세틸베타인 계면활성제 또는 이온염(예를들면, 황산 나트륨)등의 유전커플링제를 사용하여 가장 우수한 결과를 수득한다.Another advantage of the process of the present invention over the non-drying process of the prior art is the improved productivity that can achieve expansion with smaller amounts of water (eg, 5 times or less than the wet sheet process). Woolite

The best results are obtained using dielectric coupling agents such as ionic surfactants, cetylbetaine surfactants or ionic salts (eg sodium sulfate).

In this regard, the adiabatic performance can be improved by tensile-bending the sample before or after the wetting process to promote the development of internal cellular structures, but the tensile strength is weakly lost.

Dry sheets for use in the process of the present invention for producing improved products can be produced using known papermaking devices and techniques taught in US Pat. Nos. 3,756,908 and EP 73,668.

[Test Methods]

[Drip Porosity Test]

This test measures the time elapsed for a special aqueous sodium chloride solution to penetrate the expanded sheet product. Elapsed time is a measure of the density and porosity of the product surface. Products with dense surfaces and low porosity are permeable and retain solution for a long time.

)이며 직경이 6.4cm(2.5in)인 입이 넓은 항아리(＂Mason＂ home-canning jar)를 시험에 사용한다. 항아리의 바닥에 지름이 대략 0.16cm(0.0625in)인 통풍구(通風口)를 뚫는다. 중앙부위의 구멍이 6.4cm(2.5in)인 통상적인 스크류-톱 환상 캡(링)(screw-top annular cap)(ring)을 가진 항아리를 제공한다. 시험을 시작하기 위해, 통풍구를 막고 항아리에 염수(鹽水 : 0.9wt% Nacl) 600ml를 채운다. 팽창된 제품의 원형 표본 샘플을 스크류-톱 환상 캡에 맞도록 적절하게 잘라 중앙 부위의 구멍을 완전하게 밀폐한다. 환상 캡에 알맞고 중앙부위의 구멍의 크기가 캡과 동일한 환상가스켓(예를들면, 고무 가스켓)을 환상 샘플의 위 아래에 얹어 방수시일(water-tight seal)을 만든다 : 샘플과 가스켓은 캡의 내부에 놓는다 : 캡을 항아리에 대하여 나사못으로 단단하게 고정시켜서 항아리의 상단이 캡의 중앙 구멍을 덮고 있는 샘플과 완전히 밀접하게 한다. 거울위에 대략 20.3cm(8in)로 쌓은 유리판 위에서 구멍이 막힌 항아리를 뒤집는다. 구멍이 뚫리는 순간에 스톱워치(stopwatch)를 작동시킨다. 용액이 샘플에 침투하는 것을 거울로 관찰한다. 용액이 샘플을 침투하여 유리판이 젖을 때 침투는 빠르며, 이를 쉽게 관찰할 수 있다. 때때로 유리의 표면에서 약간의 응축(엷은 ＂안개＂)이 관찰된다 : 그러나, 응축이 나타나는 것이 용액이 샘플을 침투한 것이라고는 생각되지 않는다. 구멍이 뚫리는 순간에서 유리판이 젖기까지의 경과시간을 기록한다. 항아리를 뒤집었을 때 용액이 곧바로 샘플에 침투할 경우, 이때의 시간을 0초로 기록한다. 각각의 시험표본의 임의로 선택한 세 개의 샘플에 대한 경과시간을 기록하고 표본에 대한 결과로서 세 개의 경과시간에 대한 평균을 기록한다.Capacity is 0.95ℓ (1gt) and height is 12.4cm (

And a 6.4 cm (2.5 in) wide mouth jar (Mason® home-canning jar). Drill a vent (通風口) with a diameter of about 0.16cm (0.0625in) at the bottom of the jar. A jar is provided with a conventional screw-top annular cap with a central hole of 2.5 inches. To begin the test, cover the vents and fill the jar with 600 ml of brine (0.9 wt% Nacl). A circular specimen sample of the inflated product is appropriately cut to fit the screw-top annular cap to completely seal the hole in the center area. A water-tight seal is made by placing an annular gasket (eg a rubber gasket) on the top and bottom of the annular sample that is suitable for the annular cap and has the same center hole size as the cap. Place in: Screw the cap firmly against the jar so that the top of the jar is completely in contact with the sample covering the center hole of the cap. Overturn the clogged jar on a glass plate approximately 20.3 cm (8 in) above the mirror. Start the stopwatch at the moment the hole is drilled. Observe the mirror's penetration of the solution into the sample. When the solution penetrates the sample and the glass plate gets wet, the penetration is fast and can be easily observed. Sometimes some condensation is observed on the surface of the glass: however, it is not believed that the appearance of condensation has penetrated the sample. Record the elapsed time from the moment the hole is drilled to the glass plate getting wet. If the solution immediately penetrates the sample when the jar is turned over, record the time as 0 seconds. Record the elapsed time for three randomly selected samples of each test sample and record the average of the three elapsed time as results for the sample.

[Tape pull test]

Tape pool delamination is a measure of the amount of adhesive material adhered to an adhesive tape by squeezing it with an adhesive material and removing it from the surface of a completely dry expanded product. The amount of adhesive material adhered to the tape is a direct measure of the integrity and toughness of the surface. The amount of adhesive material adhered to the tape of the rough structure is small, while the amount of adhesive material adhered to the tape of the soft, less dense structure is high.

For testing purposes, one side of the product to be tested is defined as side A and the other side as side B. If the machine direction can be known or inferred, the line defined by the MD line is drawn in the machine direction, otherwise it is drawn in any direction. The machine direction refers to the direction already set in a conventional papermaking machine. The difference between the A side and the B side is the result of the fiber coating: the side where the wire is formed is different from the exposed side. The line defined by the TD (horizontal direction) line is drawn perpendicular to the MD line on the A plane. Eight specimens 2.5 cm (1 inch) wide and 15.2 cm (6 inch) long are cut out of the inflated product, four pieces in one pair parallel to the MD line and the other four pieces The jaws are parallel to the TD line, then the embossed area in the sample pieces is minimized to the extent possible and the four pieces cut in each direction are cut in the same pattern so that all pieces cut in the given direction are similar to each other.

brand 810Magic Transparent Tape). ASTM 시험 D-3330-76(180˚박리접착시험 : 180°Peel Adhesion Test)에서 테이프는 강철에 대하여 279g/cm(25oz/in)의 접착력을 시험한다. 폭이 동일한 샘플조각을 한쪽 끝에서 이보다 0.6cm(0.25inch) 짧은 다른쪽 끝까지 덮고, 이 자체를 테이프 뒷면에 포개어 두께가 길이 약 0.6cm(0.25in)의 두배인 탭(tab)을 접착제 표면안에 제공한 다음, 조각의 끝부분을 서로 접착하여 테이프에 도달하지 않게 한다. 각각의 MD 및 TD조에서 4개의 샘플중에서, 테이프를 각 조중에서 2개 샘플의 A면에 사용하고 탭은 이들 두 샘플의 반대편 끝에 있으며, 테이프를 각 조중에서 2개 샘플의 B면에 사용하고 탭은 이들 두 샘플의 반대편 끝에 있다. 이미 각각의 테이프를 적용한 샘플을 11.5MPa (166psi)의 압력으로 열반(熱盤)사이에서 가압한다.The tape used for the test is a transparent tape with a width of 2.5 cm (1 inch) and adhesive applied only on one side. (3MCo. Sotch

brand 810 Magic Transparent Tape). In ASTM Test D-3330-76 (180 ° Peel Adhesion Test), the tape is tested for adhesion of 279 g / cm (25 oz / in) to steel. Cover the same width of the sample piece from one end to the other end, which is 0.6 cm (0.25 inch) shorter than the other, and lay it on the back of the tape so that a tab twice as thick as about 0.6 cm (0.25 in) in the adhesive surface After providing, the ends of the pieces are glued together so that they do not reach the tape. Of the four samples in each MD and TD bath, the tape is used on the A side of two samples in each tank and the tab is on the opposite end of these two samples, and the tape is used on the B side of the two samples in each tank. The tab is at the opposite end of these two samples. Samples with each tape already applied are pressurized between nirvana at a pressure of 11.5 MPa (166 psi).

The full width of the tab at the end of the tape was tested while firmly gripping the full width of the tab at the end of the sample piece to the lower jaw of the tensile tester (Instron® Model 1130 with a load cell of 500 g). Grip firmly with the clamp attached to the upper jaw of the. The tensile tester is then operated to bring the jaw apart at a rate of 30.5 cm (12 inches) / min. Stop the machine when the tape is completely off the sample.

Accurately cut a 12.7 cm (5 inch) piece from the piece of tape that has fallen and weigh it to 0.01 g. Measure the average weight of clean pieces 12.7 cm in length and then subtract the weight of the stripped pieces 12.7 cm in length to determine the weight of the surface adhesive material removed in each test procedure.

The average of eight samples measured eight times per sheet of test is reported in milligrams per square centimeter.

[Taber wear test]

This test is based on ASTM Test Method D-1175-64T (page 283) using a CS-10 grit size friction wheel with a 500 g / wheel load on the specimen (Rotary Platform, Double Head Method). Do according to. The failure that occurs when the size of the hole that passes completely through the sheet can be measured. Record the results as the number of breaks. Preferred products of the present invention withstand up to 1000 or more times before being destroyed, and have low wear resistance as a final product, but are satisfactory. Seat Wear Test (Boeing's Squirmin Herman ＂Seatwear Life Test)

This test is based on an interior lining formed from the expanded sheet product being tested and a conventional sheet cushion fabric [eg, wool / nylon (90/10) sheet having a basis weight of 441 g / m ² (13 oz / yd ² ). -Cover fabric; and a conventional airplane seat cushion having a polyurethane foam composition surrounded by an outer lining formed of the same. The expanded sheet product is sewn into the seat-cover fabric, and the seat cover is made so that it can be easily peeled off when examining the expanded sheet product, for example, a zipper is attached to take out the seat cushion when necessary.

The seatware-testing device shown in Figure 2 of Sally A. Hasselbrack's article `` Textiles is Ready When You Are '' in the May 1982 issue of Textile World. Test the seat cushion with. The wear-testing device is made of soft rubber, weighs 64 kg (140 lb) and is shaped like a human buttocks, and is wrapped in a pant-like cover made of 100% polyester 2-bar tricoat knitted fabric. It includes weight. At 2 minutes, the seat tester was contacted with the seat cushion for 1 minute 40 seconds and cushioned for 20 seconds. While in contact with the cushion, the seat tester is shaken with a 25 degree arc at 13.5 times / min while rotating the cushion into a 35 degree arc at 18 times / min. Stop the test and check the lining by periodically removing the seat cushion fabric with the inner lining attached. Determination of breakage of the inner lining that occurs when the size of the hole that completely passes the lining can be observed. After 50 hours of testing, if the lining is complete, the expanded sheet product is considered to have passed the test.

Example 1

This embodiment describes a method for producing the expanded sheet of the present invention and a method for producing a flameproof airplane seat cushion from the expanded sheet.

All aramid paper for making expanded sheets is conventionally manufactured using a commercial Fourdrinier paper-making machine. A fibrid of about 0.5% by weight poly (m-phenylene isophthalamide) (MPD-I) in tap water is fed to one inlet of the mixed tea tube. 2.2 decitex (2 denier) MPD-I flocs, 0.64 cm (0.25 in) in length (pulpized flocs with about 0.35% by weight in Canadian water and a Canadian Standard Freeness of 450 to 575) / length A 50/50 slurry of poly (p-phenylene terephthalamide) (PPD-T) of 4 mm (average length 0.5 to 8 mm) is fed to the other inlet of the mixed tube tube. The weight ratio of fibrid-floc-pulp is 60/20/20. The effluent is sent to a head box and then to the place where the wire is formed. The completely dried sheet is wound on a cylindrical Fuji roll by passing the sheet formed over a steam-heated drying can whose surface temperature is maintained at 140 ° C. with an exposure time of 2 minutes. The process is carried out with a paper machine to provide a dry sheet having a basis weight of about 200 g / m ² (about 6 oz / yd ² ) and a thickness of 0.58 mm (23 mil).

The sheet wound on the Fujiroll is unwound and ultrasonically embossed through an ultrasonic embossing station, where each sheet is embossed between the ultrasonic horn and the anvil. The horn used (Eagle Road, Danburg, Conn, Branson Co.) has an impact surface of 15.2 cm (6 in) in length and 1.3 cm (0.5 in) in width. The horn with the sheet in between is 1.9mm (0.075in) long, 0.64mm (0.025in) wide, 1.9mm (0.075in) spaced, and is surrounded by a rectangular projection on a plane perpendicular to the anvil's axis. A line is exerted on a patterned rotating anvil (drum) with a length of 15.2 cm (6 in), a surface speed of about 10 to 13 ft / min and a diameter of 7.6 cm (3 in). The machine vibrates at a frequency of 20,000 times / sec and creates pressure between the horn and the anvil using a horn with air pressure set at 20-30 psi on the machine. In the present embodiment, two different anvils are used, one of which has a 1.3 cm (0.5 in) spaced side of the protrusion and the other of which has a surface of 2.5 cm (1 inch) spaced apart. Emboss two sheets individually on each anvil and pass them between the horn and the anvil for as long as necessary to cover the entire sheet in one direction (each passage parallel to the previous passage at appropriate intervals) and then each Make two pairs of square sheets of length 1.3 cm (1/2 inch) or 2.5 cm (1 inch).

Four embossed sheets are sequentially wetted in a tank of tap water with 1% by weight of an ionic surfactant. The contact time is 23 seconds and the speed is 61 cm / min (2 ft / min), passing the sheet into the tank. A wet sheet containing at least about 120% water is passed through a tank with a 20 kw dielectric heater operating at 27 MHz to expand the dielectric sheet. The sheet is passed between a set of electrodes 122 inches (48 inches) long and spaced 5 to 8 cm (2 to 3 inches) apart.

The sheet has a discontinuous expansion portion defined by a dense square pattern cut linearly, with each expansion portion extending from a less dense central portion to a dense two skin-like surface layer through a denser cell sponge or lamination portion. It consists of a chamber formed by two opposing skin-like surface layers that are dense and smooth surrounding the interior where the density of the material increases to the outside. Sheets with a larger pattern have expanded portions with more internal holes.

The sizes of the embossed patterns are different and the two dielectrically expanded sheets are heat treated, while the other two are not heat treated. The heat setting is carried out on a Bruckner frame at 260 ° C. for 3 minutes under minimum tension. Four sheets obtained were determined as follows:

Test item A-Embossed square 1.3 cm: not heat-set.

Test item B-Square embossed on each side 1.3cm: Heat setting.

Test Item C-Embossed square 2.5cm: Not heat-setting.

Test item D-square embossed on each side 2.5cm: Heat fixation.

Four sheets prepared as described above were sewn as liners inside the wool / nylon (90/10) sheet cover fabric having a basis weight of 441 g / m ² (13 oz / yd ² ). A conventional airplane seat cushion with an embossed inflated sheet is prepared as a liner surrounding the polyurethane foam composition which uses the lined fabric to make the seat cushion. When a seat cushion made of four test item sheets is tested by a seat wear test, the cushion made of each test item passes the test (after 50 hours of testing, no breakdown of the protective expansion sheet occurs). Item B does not interfere with the test after 100 hours. Mock seat cushions made from individual test items also pass Boeing's OSU thermal relaxation test at 5 watts / cm ² (polyurethane foam is not wound up by the flame for at least 30 seconds). Another characteristic of the expansion sheet of the four test items is listed in the table:

Although not the sheet of the present invention, three comparable expansion sheets of the same 60/20/20 composition [Canada standard freeness of 300 to 425 and a length of PPD-T fiber of 2 mm (average 0.5 to 4 mm) rather than 4 mm are Except that it is an expanded sheet that has not been dried, and the wet sheet is compressed by pressing a diamond pattern (4.45 cm x 1.91 cm and 2.5 cm continuous densified lines) embossed by a machine at room temperature. Shall be. The expanded sheet has a three-dimensional surface that is very roughly woven with the naked eye. An unexpanded expansion sheet wets immediately in the drip porosity test (0 seconds) and breaks in 500 times in the fiber wear test. The two heat set expansion sheets (heat set at 260 ° C. for 30 seconds and 3 minutes) represent 1 second and 650 times, 0 seconds and 700 times in the same test, respectively, which are all inferior in this test as compared to the sheet of the invention. Do. The results of the tape pools for the three items are 5.79, 5.79 and 6.3 mg / cm ^2, respectively. In a typical seat wear test, the first one failed as the lining, the second barely passed, and the third passed. However, even if the third pass the test, the bulk and drapeability are impaired due to heat setting.

Example 2

This example illustrates a method of making the sheet of the invention from two separate sheets of aramid paper bonded to each other and then expanded.

Aramid paper for the production of these expanded products has a length of 0.64 cm (0.25 in.) And a conventional pod linear paper machine from about 55% MPD-I fibrid and about 45% MPD-I 2.2 decitex (2 denier) flocs. To manufacture. After the wet sheet is formed in the machine, it is passed through a drying can maintained at a temperature range of 85 to 115 ° C. for low basis weight paper and 110 to 140 ° C. for high basis weight paper, in order to dry the paper. Fit your time. Paper does not calendar.

In one embodiment, the width is 0.3 m (1 ft), the length is 0.6 m (2 ft), the basis weight is 40.7 g / m ² (1.2 oz / yd ² ), and the actual measured thickness is 0.10 mm (4 mil) (nominal Two fully dried aramid paper sheets, typically 5 mils thick, are transferred together with the ultrasonic embossing table described in Example 1. One on the sheet and the other on the sheet is embossed with ultrasound to adhere to each other in dense parts with a 1.3 cm (0.5 in) cut square pattern on one side.

중량%의 이온 계면활성제(＂woolite＂)를 가한 수돗물 탱크에 엠보싱된 시이트를 통과시켜 적신다. 습윤 시이트를 유전 팽창시킨다. 부드럽고 조밀하며 거친 2개의 스킨으로 형성된 기구상 챔버와 팽창부분으로 한정되는 엠보싱된 압축영역에서 생성된 제품은 우수한 접착보전성을 유지한다. 습윤 및 유전 팽창에 대한 작동조건은 체류시간과 자장(field)이 증가한 것을 제외하고 실시예 1에 기술한 것과 유사하다.

Wet the embossed sheet through a tap water tank to which weight percent of ionic surfactant was added. The wet sheet is dielectrically inflated. The product produced in the embossed compression zone defined by the mechanical chamber formed by the soft, dense and coarse two skin and the inflated portion retains good adhesion integrity. The operating conditions for wetting and dielectric expansion are similar to those described in Example 1 except that the residence time and field increased.

In another embodiment, two aramid paper sheets of different thicknesses and completely dried are ultrasonically bonded together. One sheet is 0.25 mm (10 mil) thick and has a basis weight of 81.4 g / m ² (2.4 oz / yd ² ). The other sheet is 0.38 mm (15 mil) thick and has a basis weight of 129.9 g / m ² (3.8 oz / yd ² ). Both sheets are embossed, bonded, wetted, and dielectrically expanded ultrasonically as described above. The resulting product is similar to that produced above: however, the development of internal cells or laminated structures in the inflation portion on the inner surface of the skin layer is observed in this thick sheet.

The products produced in the two embodiments are defined as follows:

Test item II-A: 4mil sheet bonded to 4mil sheet.

Test item II-B: 10 mil sheet bonded to 15 mil sheet.

The characteristics of the expansion sheet are as follows:

Example 3

%인 수돗물의 용액에 침지시키면서 황동블럭(brass block)의 90°변부를 잡아당겨 시이트에 응력을 가한다. 여러번 응력을 가한 후(8회), 시이트를 1분동안 기계의 방향과 동일한 방향으로 액체속에 2회 침지시킨다. 벨트속도 3.0ft/min에서 3.0in 이격된 한조의 전극이 갖춰진 85MHz RF 가열기로 시이트를 유전가열한다. 생성된 제품은 쉽게 팽창하여 균일하고 불연속적인 팽창부분을 형성하는데, 이는 조밀하고 부드러우며 스킨상의 표면층이 내부보다 덜 조밀하다.The 23 mil dry sheet, which is actually identical to the MDP-I composition of Example 2, is embossed in a rectangular pattern (1/2 inch and 1.0 inch) using ultrasonic waves. ＂Woolite＂

The sheet is stressed by pulling the 90 ° edge of the brass block while immersing in a solution of tap water of%. After several stresses (8 times), the sheet is immersed twice in the liquid in the same direction as the machine direction for 1 minute. The sheet is dielectrically heated with an 85 MHz RF heater with a set of electrodes spaced 3.0 inches apart at a belt speed of 3.0 ft / min. The resulting product easily expands to form a uniform and discontinuous expanded portion, which is dense and soft and the surface layer on the skin is less dense than the interior.

Claims (22)

Essentially, it consists of a mixture of 30 to 90% by weight of aramid fibrids and supplementally 70 to 10% by weight of aramid short fibers, defined by self-bonded and compressed areas and facing and dense of fibrids and fibers, There is an expanded portion consisting of a chamber formed by two surface layers on the soft skin, where the two surface layers surround the less dense interior, and have a porosity that provides a time of at least about 10 seconds in the drip porosity test. Low enough low density nonwoven sheet structure. The sheet structure of claim 1, having a basis weight of less than about 7 oz / yd ² and at least 1,000 wear resistances until fracture in a fiber wear test. 2. The sheet structure according to claim 1, wherein the compressed region has surface integrity, and there is almost no loss of material even when visually irradiated in a tape pull test. The sheet structure of claim 1, wherein the compressed region defines a discontinuously expanded portion and is arranged in a cut linear pattern. The sheet structure of claim 4, wherein the discontinuously expanded portions each occupy a surface area of the sheet within the range of about 0.1 to about 25 cm ² . 6. The sheet structure of claim 5, wherein the surface integrity is sufficient so that the loss of material in the tape pull test is less than 4 mg / cm ² . The sheet structure according to claim 1, wherein at least part of the short fibers and fibrids are made of poly (m-phenylene isophthalamide). 8. The sheet structure of claim 7, wherein about 10-30% by weight of the sheet consists of short fibers of poly (p-phenylene terephthalamide). 8. The sheet structure of claim 7, wherein the weight ratio of fibrids, short fibers of MPD-I, and short fibers of PPD-T is 60/20/20, respectively, and the PPD-T fibers are pulped. The sheet structure of claim 1, wherein the material density inside the expanded portion increases from the less dense central portion to the surface layer and the dense sponge-like bubble portion increases to become more dense at the skin-like surface layer. 2. The sheet structure of claim 1, wherein the expanded portion consists essentially of a dense skin-like surface layer and an open interior with little fibrid / fibrous material in the mechanical structure. The sheet structure of claim 11, wherein the surface layer is derived from separate sheets of fibrids and fibers, and the sheets self-bond together together in the compressed region. The sheet structure of claim 12, wherein the sheet weight is less than about 3 oz / yd ² . Forms a soft wet integrated sheet of aramid material, compresses a pattern of non-expandable compressed regions into sheets to define the expandable portions between the regions, and rapidly heats the water by dielectric heating the patterned sheet wetted with water. A method of making an expanded nonwoven sheet consisting of aramid fibrids and short aramid fibers comprising the steps of creating a very expanded portion in a process comprising the steps of: Providing a pattern of non-expandable compressed regions with heat and pressure to produce an inflated laminated sheet structure consisting of at least one dry sheet in a compressed region over the thickness of the laminated sheet structure defining the expandable portion. Self-adhesive material High: stress-bend and saturate the patterned sheet structure with water: dielectrically heat the stressed wet sheet to rapidly evaporate water and break the interior of the expandable portion of the patterned sheet without destroying the surface of the sheet. An improved method of making an expanded nonwoven sheet, characterized by expansion. The method of claim 14, wherein at least some of the short fibers and fibrids are poly (m-phenylene isophthalamide). The method of claim 15, wherein the inflatable portion defined by the compressed region is discontinuous and occupies a surface area of about 0.1 cm ² to 25 cm ² , respectively. The method of claim 16, wherein the compressed regions are arranged in a truncated linear pattern and occupy less than about 50% of the sheet surface. The method of claim 14, wherein the compressed region is formed with an ultrasonic device. 15. The method of claim 14 wherein a sheet of dry sheet having a thickness of at least about 20 mils is used. 15. The method of claim 14, wherein the laminated sheet structure consists of two wet integrated dry sheets each having a thickness of at least about 4 mils. The method of claim 14, wherein the sheet structure is stressed during drying. The method of claim 14, wherein the sheet structure is stressed in the wet state.