MX2008008387A - Porous membrane - Google Patents

Abstract

A new acoustic insulating sheet material comprises in laminar assembly a) a primary sound absorbing sheet, and b) a dense porous membrane that i) has an air-flow resistance of about 5000 rayls or less and ii) has an Acoustic Value Ratio as defined herein of at least 3000. Preferably, the membrane is about 200 micrometers or less in thickness, and more preferably is about 150 micrometers or less in thickness. Also, the Acoustic Value Ratio is preferably at least 7,000. The described membrane can also be used alone to acoustically insulate a space, e.g., by mounting it in planar array over an air gap and in position to attenuate noise from a noise source.

Description

MEMBRANE POROSA FIELD OF THE INVENTION This invention relates to thin porous membranes used for acoustic insulation, often in combination with another generally thicker membrane, for insulation.

BACKGROUND OF THE INVENTION Some acoustic insulation tasks are best performed with a combination of a relatively thick primary fibrous sheet and a thinner secondary sheet or membrane (the term "membrane" here means a thin sheet). In combination, the primary sheet and the membrane reduce noise better than the primary sheet by itself; for example, the inclusion of the membrane can often improve the reduction of noise at lower power intervals. In addition, the membrane can provide physical protection to the primary sheet. The membranes can also be used by themselves, mounted in a flat arrangement on an air space (ie, with the film stretched in a flat or curved part over the air gap or the air gap).

When they are placed in a room or other room in which you want to reduce the noise, with a thick air separation Ref.: 194197 appropriate behind the membrane, the membrane works to absorb sounds in the room. An insulation composed of a thick primary insulating sheet and a secondary membrane-like sheet are described, for example, in Thorn et al., U.S. Pat. No. 6,376,396, which describes as membrane-like sheet a compacted non-woven fabric in two sequential operations-a first step of mechanical compaction (such as by stacking with needles or entangled thread) and a second stage of compaction by heat and pressure with presses or calenders. The increased sound absorption is claimed to occur as a result of the second compaction. Another description of the prior art is Tilton, Patent Application Publication of E.U.A. No. US 2004/0002274 To which it describes construction panels, ceiling tiles or similar building components in which a decorative fabric is previously used to cover the exterior of the building component which is replaced by a densified oriented face of fibers of polyester. The densified oriented layer, which is printed with aesthetically pleasing graphics or other signs, is said to reduce costs and also provide improved insulation properties. See also Vanbemmel et al., U.S. Patent. No. 6,720,068, which focuses on a product multilayered or laminated useful as insulation that absorbs sound for automobiles. Recognizing the need for insulation that is cheap, thin and lightweight, the patent discloses a product that comprises a support layer - an open cell foam or a thinly compacted nonwoven fibrous fabric - coated with an extremely thin layer of microfibres. (Col 2, 11. 7-9). The microfiber coating "reaches a thickness of only 0.2 to 1.0 mm, and in particular of 0.3 to 0.7 mm and has a weight per unit area of 20 to 200 g / m2, and in particular of 30 to 100 g / m2" (Col 1, 11. 62-64). There is no specific example of similar description in the patent of a laminate of Vanbemmel's invention. Another commercial form of insulation uses a membrane-like sheet comprising a multi-layered sheet with a spunbond-spin-blown (SMS) spunbonded laminate bonded by heat and pressure and assembled in combination with a primary insulating sheet. A disadvantage of each of the insulation composites described above is that in order to add desired levels of sound insulation to the composite material, the membrane-like secondary sheet is sufficiently thick and heavy enough to add undesirable weight and weight to the composite material. general insulation packaging.

SUMMARY OF THE INVENTION By means of the present invention a new membrane is provided which is of lower cost and often of simpler construction in comparison with the previous membranes and at the same time offers an insulation performance at least equal. A preferred membrane comprises a highly identified non-woven fibrous web, for example a fabric prepared by compacting a non-woven initial sheet material with a very thin thickness, preferably less than 200 micrometers. The new membranes are dense but retain an effective porosity to attenuate the sound; Generally, the porosity is sufficient so that the specific airflow resistance of the membrane is no more than about 10,000 rayls and a wider utility is no more than 5000 rayls (the industry commonly refers to "resistance to flow"). specific air "simply as" resistance to air flow "and this practice will be followed in the present, the same property is sometimes referred to as" acoustic resistance ", for example when focusing on sound isolation, the same test procedure Subsequently described herein is used to measure both air flow resistance and acoustic resistance, the units for the property due are reported in the present in rayls in the ms system, other units used in the industry include Ns / m3 and Pa »s / m). We have found that useful membranes can be defined by summarizing the characteristics of density, thickness and porosity in a new relationship, called acoustic value relation, which relates the solidity (a dimensional fraction that establishes the proportion of the volume of the membrane occupied by the solid constituents of the membrane), porosity (ie resistance to airflow or acoustic resistance) in rayls and the thickness of the membrane, as follows: _,. ,,. , (porosity in rayls) (solidity) Relation of acoustic value = thickness in millimeters We have found that a porous membrane that shows an acoustic value ratio (AVR) of at least 3000 makes possible a high quality acoustic insulation performance, and at the same time adds little cost and weight to the general insulation material. Preferably, the acoustic value ratio is at least 7,000. In addition, the membrane is preferably no greater than about 150 micrometers in thickness; in other words, surprisingly they are useful and desirable thin membranes. A membrane as described can be used in a laminar assembly with a primary sheet that absorbs the sound to prepare surprisingly effective sound insulation. In addition to its use in a composite insulation, a membrane as described may function to provide sound attenuation on its own when distributed in a flat arrangement with a separation of air or air spaces behind the membrane.

BRIEF DESCRIPTION OF THE FIGURES Figures 1-9 are graphs of sound absorption coefficients versus frequency for representative membranes of the invention and of comparative fabrics.

DETAILED DESCRIPTION OF THE INVENTION A fibrous web is preferably used as the initial sheet material for the preparation of a membrane of the invention. Any of a variety of conventional well-known shapes of fabric may be used including spunbond fabrics (generally comprising melt-bonded fibers that are cooled, stretched, collected on a shaping surface in a random isotropic manner such as a cloth. loose entangled and then joined by calendering or by means of air connection); meltblown fabrics (which are formed by extruding a fluid thermoplastic polymer through a row of holes in a die into an air stream of high speed where the extruded polymer streams are attenuated into fibers of generally fine diameter - often averaging 10 micrometers or less in diameter - and transported to a collector where the fibers are collected as a coherent tangled fabric); fabrics linked by spinning (generally dry stretched fabrics that have been hydroentangled); short fiber fabrics loaded or laid in the air; woven fabrics; fabrics laid wet and combinations of said fabrics; the fabrics are often in a self-supporting form but may also be loose and only become self-supporting during the densification of fabrics used to prepare a membrane of the invention. The membranes of the invention can also be prepared from other porous sheet materials such as open-cell or cross-linked foams. In general, any porous thermoplastic sheet material is a candidate for use as an initial sheet material for preparing a membrane of the invention. An initial sheet material for use in the invention can generally be heat-swellable. Generally, any thermoplastic polymeric material that can be formed into fibers or another useful fabric form can be used. More typically, the selected polymers are those commonly selected in fiber formation such as polyethylene, polypropylene, terephthalate - - polyethylene, nylon and urethanes. Elastic materials are useful and offer advantages in conformation adequacy, flexibility and susceptibility to molding. Combinations of materials can be used, including combinations of polymers as well as polymeric materials within which additives, such as pigments or dyes, have been combined. In addition, the initial sheet material may include bicomponent fibers such as core-sheath or two-component fibers side by side ("bicomponent" herein includes fibers with two or more components). Different materials such as fibers of different materials can be combined so that a combined fabric is prepared. For example, short fibers can be combined into meltblown fibers in the manner described in the U.S.A. No. 4,118,531; or particulate material can be introduced and can be retained within a fabric in the manner described in the US patent. No. 3,971,373; or microteles as described in the patent of E.U.A. No. 4,813,948 can be combined in one fabric. Fabrics that are a combination of thermoplastic fibers and other fibers such as wood pulp fibers can also be used, although the introduction of non-thermoplastic material is generally less desirable. Although the invention can be advantageously carried out with a fabric comprising a unitary layer unique, an initial sheet material for use in the invention may also be constituted by more than one layer. For example, SMS fabrics (spunbonded / meltblown / spunbonded) can be used as well as fabrics that combine other fibrous layers, for example layers that differ according to the fiber diameter used in the layers, for This way provide fiber diameter or porosity graduations. A membrane of the invention is typically prepared by densifying an initial sheet material with a calender under heat and pressure. Well-known calendering procedures can be used. Usually, the rolls of calender have a smooth surface, but rolls with bas-relief projections can be used, for example to obtain points of attachment to a cloth or sheet. Sufficient heat and pressure are used to compact the sheet causing deformation and / or melting of sheet material, but heat conditions that can cause the sheet material to flow to completely cover the pores should be avoided. The stretching or heating of a sheet can be used to reopen closed openings by superposition or to enlarge narrow overlapping openings. A membrane of the invention can be adjusted to better attenuate particular intervals of frequency by adjusting the degree of porosity remaining in the membrane after calendering. For example, a membrane that has a resistance to air flow of 5000 to 6000 rayls can better attenuate sounds that have a frequency of 400-1000 Hertz. To have a greater effectiveness over a wider and higher frequency range, the porosity of the calendered or densified membrane will better have an airflow resistance of less than about 2000 or even about 1000 or less. As a corollary to thinness, a membrane of the invention also generally has a low basis weight, ie, preferably about 100 grams per square meter or less and more preferably about 50 grams per square meter or less. A main criterion when selecting an initial material is to obtain a good continuity or uniformity of the finished membrane. Often good membrane properties can be obtained regardless of the diameter of the fibers in an initial sheet material. However, microfiber fabrics can be sold, for example, from fabrics of initial material in which the average of microfibers of 10 micrometers or less in diameter, such fabrics are usually meltblown fabrics. The diameter of the fiber can be determined using a visually real measured diameter such as, for example, scanning electron micrograph (SEM).

Another measurement of fiber diameter is the "effective fiber diameter" (EFD) measured by a method as described in the US patent. No. 5,298,694 (col 2, lines 35-43 and col 12, lines 33-39). For ease of description, the EFD measurements are used in the examples herein. An advantage of the invention are the low cost initial materials that can be used to obtain useful membrane properties. The primary sound absorbing sheet used in the laminate assembly with a membrane of the invention can generally be any of the known sound insulating sheet materials and preferably includes a fabric comprising microfibers and corrugated short fibers combined therein, as it is described, for example, in the US patent No. 5,298,694. Other useful absorbent sheet materials include open cell foams. Generally, the products of the invention are marketed as a membrane by themselves or as sheet articles comprising a membrane laminate assembly and a primary sound absorbing sheet. However, the products of the invention can also be marketed in other ways, for example as a membrane molded article and a primary insulating sheet shaped for a particular application.

Test procedure The tests that define the fabrics of the invention and measure its performance are as follows. Specimen strength is determined by dividing the bulk density of a specimen (usually a fibrous web) by the density of the materials that make up the specimen (cloth). The apparent density of a cloth specimen is determined by first measuring the weight and thickness of a fabric section of 10 cm per cm. The specimen thickness is evaluated as prescribed in the ASTM D 5729 standard test method, modified by using a mass of 150 grams to exert a pressure of 2.9 kPa / m2 (0.4213 pounds / inch2) on the face of each sample. When the sample size is limited to something less than the recommended size in ASTM D 5729, the mass at the pressure foot is appropriately reduced to maintain a loading force of 2.9 kPa / m2 (0.4213 1 fiber / inch2). The specimens are first preconditioned at 22 +/- 5eC in an atmosphere of 50% +/- 5% relative humidity. By dividing the weight of the specimen in grams between the sample area, in square centimeters, the basis weight of the specimen is obtained, which is reported in g / m3. The apparent density of the fabric is determined by dividing the basis weight between the specimen thickness and reported as g / m3. Solidity is a dimensionless fraction that represents the proportion of solids contained in a specimen given, calculated by dividing the apparent density of the specimen by the density of the material constituting the specimen (the density of a polymer can be measured by standard or conventional means if the supplier does not specify the density of the material). The resistance to air flow is evaluated as described in the standard test method ASTM C 522. The specific airflow resistance values, r, are reported as mks rayl (Pa-s / m). Samples are prepared by die cutting a circular sample of 13.33 cm (5.25 inches) in diameter. If the edges are slightly compressed from the die cutting operation, the edges should return to their original or natural thickness before testing. The preconditioned samples are placed in a specimen holder and the pressure difference is measured in a frontal area of 100 cm2. The sound absorption of the acoustic materials is determined by the test method described in ASTM designation E 1050-98, entitled "Impedance and Absorption Using A Tube, Two Microphones and A Digital Frequency Analysis System" (Impedance and absorption using a tube, two microphones and a digital frequency analysis system). The preconditioned samples are tested using a 29-millimeter diameter tube. The 1/3 octave band sound absorption coefficients from 160 to 6300 hertz are the that are reported. For examples 9-11 the samples are tested using a 63 mm diameter tube. The 1/3 octave band sound absorption coefficients are reported from 100 to 3150 hertz.

Examples 1-8 A variety of membranes of the invention are prepared and tested, as summarized in Tables 1-3 and in the graphs of the data in Figures 1 to 8. The initial sheet material for each of the membranes in the examples is the following: For Example 1, nylon fabric joined by spinning (# G066380 supplied by Western Nonwovens). For Example 2, spin-linked polypropylene fabric (# 83149006-01 supplied by BBA Nonwovens). For Example 3, spun-bonded PET fabric (polyethylene terephthalate - Reemay Fabric, supplied by BBA Nonwovens). For Example 4, melt blown polypropylene fabric containing fibers averaging 8 micrometers in diameter (EFD); the average tdiameter of the microfibers is less than about 10 microns. For Example 5, a polyurethane fabric blown by fibers having an average diameter (EFD) of 20 microns.

- For Example 6, a fabric composed of 65% by weight of meltblown polypropylene fiber that averages (EFD) 8 microns in diameter and 35% by weight of "Easy Street" cotton short fibers Veratec. - For Example 7, spin-linked fabric comprising 95% by weight of denier composite fibers of denier 3.4 Kurraray W102, each fiber comprises approximately 50% PET and 50% nylon and 5% by weight two-component fiber " Melty "2 KoSa denier corrugated type 254. - For Example 8, a carded fabric containing polypropylene fibers of 38 millimeters (1.5 inches) in length of denier 1.9 type 196 supplied by Fiver Vision. The initial sheet materials described are calendared between two smooth rolls under the conditions as summarized in Table 2. The tests are performed on the finished membranes of the invention and initial sheet materials alone and on the membrane in combination with a coating material. thicker carded web sheet (20 mm thick) which is not generally used for sound insulation to illustrate the improvement obtained by combining said web material with a membrane of the invention (the web is a 85 weight percent combination) of denier corrugated fibers 2 and 15% by weight of fibers of the components "Melty" denier 2 corrugated with a latex binder applied at a weight of 7 g / m2. The results for air flow resistance and fabric fastness are presented in Table 1 for the initial sheet material and in Table 3 for the completed membrane. The sound absorption measurements for the various test samples are presented in Figures 1-8. In these figures, the frequency in hertz is plotted on the axis of the abscissa and the sound absorption coefficient is plotted on the axis of the ordinates. Figure 1 represents the data for the test fabrics of Example 1, Figure 2 for Example 2 and so on up to Figure 8 and Example 8. Each of Figures 1-8, Figure A is for the material of initial sheet measured with an air gap of 20 millimeters. Graph B is for the calendered membrane of the invention measured with an air gap of 20 millimeters and the graph C is for a laminar assembly of the calendered membrane of the invention and a thicker fabric of 20 millimeters described in the above. In Figure 1, the D graph is data for the thicker fabric alone. There is no graph A in figure 8 because the sound absorption in the initial non-calendered sheet material of said sample was not measured.

- Examples 9-11 Examples 9-11 are prepared from polypropylene SMS (spunbond / meltblown / spunbond) having a basis weight of 17 grams / square meter (0.5 oz / yd2) supplied by First Quality Nonwovens (FQN) as SM1700008. The fabric described is calendered between two plain steel rolls using different conditions for each of Examples 9-11 as set forth in Table 2. Measurements and tests were carried out on the initial sheet material and the completed membrane and the results are presented in Tables 1 and 3. Sound absorption measurements were made on the test membranes in combination with useful acoustic insulating sheet materials (Thinsulate ™ acoustic insulation supplied by 3M, then TAI, and as described in U.S. Patent No. 5,298,694) which is composed of 55 weight percent meltblown fibers and 35 weight percent short corrugated fibers. For a further comparison, sound absorption measurements were made in a laminar assembly (Comparative Example Cl) comprising a commercial fabric with a weight of 51 grams per square meter (SMS fabric of polypropylene available from Kimberly Clark as SM150) and acoustic insulating sheet material supplied by 3M (TAI). An additional description of the SMS fabric of Comparative Example Cl and the TAI fabric are presented in Table 1. The sound absorption measurements are presented in Fbira 9, where the graph A is for the TAI fabric alone; the graph B is for a laminar assembly of the initial non-calendered sheet material and the TAI fabric; Figure C is for a laminar assembly of the completed calendered membrane of Example 11 and the TAI fabric; and the graph D is for the comparative example Cl. In reviewing the test results it is noted that for an improvement over the broad spectrum of frequencies, as illustrated especially by Examples 2, 3 and 8 as well as Examples 9-11 the airflow resistance of the completed membrane is less than 1500 rayls and even less than 1000 rayls, suggesting a desired range of airflow resistance for such broad spectrum improvement. From a separate starting point, the weight of the membrane in Examples 2, 3 and 8 is less than 50 g / m2 and in Example 9-11 it is less than 20 g / m2 and the thickness is less than 100 microns and in five cases is less than 50 micrometers; and the acoustic value ratio is 7,000 or greater and in several examples is 10,000 or greater.

- - TABLE 1 TABLE 2 TABLE 3 It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

1. - -
2. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. An acoustic insulating sheet material characterized in that it comprises in a laminate assembly a) a primary sound absorbing sheet, and b) a dense porous membrane which i) has an air flow resistance of about 10,000 rayls or less, and ii) has an acoustic value ratio as defined herein of at least 3000. 2. The sheet material according to claim 1, characterized in that the membrane has a thickness of about 200 microns or less.
3. 3. The sheet material according to claim 1 or 2, characterized in that the membrane has a flow resistance of. air of 5000 rayls or less.
4. 4. The sheet material according to any of claims 1 to 3, characterized in that the membrane has a thickness of 150 micrometers or less.
5. 5. The sheet material according to any of claims 1 to 4, characterized in that the membrane has an acoustic value ratio of at least 10,000.
6. 6. The sheet material in accordance with - - any of claims 1 to 5, characterized in that the membrane has an air flow resistance of about 2000 rayls or less.
7. 7. A method for acoustically isolating a space, characterized in that it comprises mounting in a flat arrangement on an air gap and in position to attenuate noise from a noise source, a dense porous self-sustaining membrane having an airflow resistance of about 5000 rayls or less and an acoustic value ratio of at least 3000.
8. 8. The method according to claim 7, characterized in that the membrane has a thickness of approximately 150 micrometers or less. The method according to claim 7 or 8, characterized in that the membrane has an acoustic value ratio of at least 7,000. The method according to any of claims 7 to 9, characterized in that it comprises the additional step of assembling a spongier fibrous nonwoven sheet material in the laminate assembly with the membrane.