FR2647692A1 - GAUFRABLE FILTERING FABRIC - Google Patents

Abstract

A thermoformable breathable coherent filter fabric is disclosed. This filter cloth contains a mixture of glass wool fibers and chopped twisted glass fibers and a thermoformable polymer binder at a temperature of 93.3 to 176.7 degree (s) C (200 to 350 degree (s) F) and capable of undergoing crosslinking by heating to a temperature above 137.8 degree (s) C (280 degree (s) F). The fabric can be embossed in the dry state without cracking or splitting. The filter cloth according to the invention is particularly intended to form an air filter.

Description

GAUFRABLE FILTERING FABRIC

  The present invention relates to a coherent breathable filter fabric comprising glass fibers and a binder and to be embossed and gathered to form a

air filter.

  Air filters in the form of sheets or gathered fabrics made of glass fibers are used in different installations because of their high surface area to volume ratio. To achieve maximum efficiency, it is important to maintain during use an adequate distance between adjacent gathers; this is achieved by means of a separating piece or separate separating element which is added to the filter, or by practicing in the sheet or the fabric itself embossings or deformations, for example corrugations, which serve maintain a distance between adjacent folds

after the frown.

  Mathews et al. Previously proposed in U.S. Patent No. 3,035,965 to form a glass fiber paper of diameter less than 2.5, and coated with a thermoplastic polymer; however, this paper was devoid of cut twisted fibers of larger diameter. In U.S. Patent No. 4,418,774, Powell discloses a composite nonwoven of glass fibers and textile fibers with a thermoplastic binder. In U.S. Patent No. 4,428,677, Klein discloses an air filter which comprises small diameter glass fibers, textile fibers and a thermoplastic binder. In GB-A-874383 (1961), Buckman discloses a scrunched air filter having embossed spacers consisting of filter paper impregnated with synthetic resin. Bulletin N.815 E of Flanders Filter Inc. (1987) also describes a corrugated and corrugated air filter. It is believed that it has been common practice to make such embossing or deformation

  during the formation of the fabric or leaf, while that

  it is still in the wet stage of a flat-table paper machine. Attempts to emboss the fabric or sheet after drying have not been successful because the fabric or sheet tends to crack or crack which destroys its cohesion and effectiveness. Since most filter manufacturers do not fabricate the filter cloth or filter sheet themselves, however, they wish to have embossing with a variety of patterns and spacings in order to adapt the fabric to the specially designed gathered filters. For individual applications, there is a demand for a filter cloth or filter sheet uniform, with a dry surface and smooth, consisting of glass fibers, and which can be embossed or deformed by means of a simple and inexpensive apparatus such as that a pair of cylinders

  embossing having the desired configuration.

  It has now been found that a dry sheet of glass fiber filter material having certain critical characteristics can be easily embossed in the wet state without cracking or fragmentation by simple heating at a temperature between 93.3 and 176.7. C (200 and 350 F) and passage between embossing rolls. The sheet is a coherent, thermoformable, breathable filter fabric which comprises a glass fiber blend consisting essentially of (1) 5 to 35% by weight of cut twisted fibers having an average length of 3 to 19 mmn and a average diameter of 6 to 20 μm, and (2) glass wool constituting the complement and having an average fiber length of 0.1 to 5 mm and an average fiber diameter of 0.2 to 6 μm, at the same time a thermoplastic polymeric binder capable of crosslinking by heating at a temperature of 137.8 C (280 F) or more, the amount of binder being from 2 to 30% by weight based on the total of the blend of glass and binder, said fabric having a thickness of 0.3 to 1 mm (0.012 to 0.040 inches), a tensile strength in the direction of travel of the sheet in the machine (DM) from 700 to 4377, 5 N / m width (4 to 25 psi) and tensile strength in the perpendicular direction from 350 to 2101 N / m in width (2 to 12 psi). width) as well as a base weight of from 6.25 to 15.65 kg / m2 (40 to 100 lb / 3000 sq.ft). In a preferred embodiment, the sheet has an elongation of at least 2% without cracking or fragmentation upon embossing at 93.3 C (200 F) on a protuberance having a circular segment-shaped cross-section having a height of 2 mm and a width of 8.5 mm, and it maintains a permanent elongation of at least 1.0% in the embossed portion after said embossing even when it is subsequently heated to 137.8 C (280 F ) or more to accelerate or complete the crosslinking, then cooled to the

ambient temperature.

  v. Preferably, the fiber mixture consists essentially of 8 to 15% by weight of cut twisted fibers, the balance being glass wool, and the amount of binder is between 3 and 6% by weight. Also preferably, the filter cloth has a basis weight of 8.6 to 11.7 kg / m 2 (55 to 75 lb / 3000 sq.ft.) and it maintains a permanent elongation of 1 to 5% in the portion

  embossed after crosslinking and cooling.

  In another embodiment, said fiber mixture consists of (1) 8 to 15% by weight of cut twisted fibers which have an average length of 6 to 13 mm, (2) glass wool constituting the complement and having a average length of fiber from 1 to 3 mm, the amount of binder constituting 3 to 6% by weight, said fabric has a thickness of 0.3 mm to 1 mm, a rigidity of Gurley in the direction of movement of the fabric in the machine (DM) of 1500 mg or more, and it maintains a permanent elongation of 1 to 5% in the embossed portion after crosslinking and

cooling.

  In other preferred embodiments, the glass fiber mixture contains 8 to 15% by weight of cut twisted fibers which have an average length of 6 to 13 mm, the binder composition constitutes 3 to 6% by weight of the total , the fabric has a basis weight of 8.6 to 11.7 kg / m 2 (55 lb / 3000 sq.ft.), a Gurley rigidity of at least 1500 mg, and it retains, after embossing at 93 , 3 C (2000F) on a protuberance having a circular segment-shaped cross-section having a height of 2 mm and a width of 8.5 mm, a permanent elongation of 1 to 5% even when it is then heated to 137.8 ° C (280 F) or more to accelerate or complete the crosslinking, then cooled to room temperature. Streaking on the dry fabric to facilitate folding to form creases is preferably performed on the unheated fabric prior to heating and embossing. Some degree of crosslinking of the binder may occur during the embossing step, depending on the temperature at which the fabric is heated and the time required for the embossing step; further cross-linking may occur by additional heating after embossing and / or even after obtaining the fabric under

gathered form.

  Other features of the fabric will appear in

the following description.

  The glass fibers of the fabric comprise a blend of two types or classes of fibers, namely chopped glass fibers and glass wool having the dimensions and proportions mentioned above. Fibers of this type are readily obtainable from a variety of sources. The mixture can be prepared using conventional techniques and equipment. A dry blend can be used, but it is preferable to use a wet mix in which the fibers are dispersed in an aqueous medium in a drummer or pulper or in a high shear mixing pan, preferably with the addition of a acid to facilitate and promote the separation of glass fibers. The binder necessary to impart to the product the cohesion and other necessary physical properties may be mixed with the fiber mixture during or after the preparation of the mixture. In a preferred embodiment, the fiber blend is first formed into a fabric or sheet on a flat-bed paper machine, after which the fabric or sheet is saturated with an aqueous binder dispersion. The excess water is then removed by suction sufi'la flat-bottomed paper machine and the fabric or sheet is dried in the manner

  usual on heated dryer cylinders.

  The binder is in the form of a thermoplastic material such as a vinyl or vinylidene polymer or copolymer which is capable of crosslinking when heated to a temperature of 137.8 C (280 F) or higher. The crosslinking ability can be achieved by incorporating a crosslinking agent capable of reacting with residual vinyl groups or other reactive moieties such as carboxyl groups in the thermoplastic polymer or copolymer, or by blending with the polymer or vinyl or vinylidene copolymer of a second resin or polymeric material capable of undergoing crosslinking

  when heated, such as urea resin

  formaldehyde, a melamine-formaldehyde resin, a phenol-formaldehyde resin, an epoxy resin or the like. For best results it is desirable for the thermoplastic binder to have a glass transition temperature (Tg) of + 10 ° C. to + 50 ° C. and to be able to retain its thermoplasticity when heated to a temperature of up to 137 ° C. 8 C (280 F). Suitable binders or crosslinkable products include copolymers of vinyl chloride, vinylidene chloride, vinyl acetate, acrylic esters, acrylonitrile, and the like; the crosslinking ability is provided by comonomers which have pendant carboxyl groups, for example, or by mixtures with a urea-formaldehyde resin or other thermosetting materials. The crosslinking can be activated by heating at a high temperature of at least 137.8.degree.

(280 F).

  The following examples are intended to illustrate the

  nature of the invention without limiting its scope.

  A mixture of cut twisted glass filaments or fibers (diameter 6.5 μm) and flame-blown glass microfibers or wool (diameter 0.65-2.7 μm) was prepared from the following constituents: Dimeter LoQnur nominal nominal glass pm pm code 104 0.4 0.2-1 code 106 0.65 0.5-0.8 code 110 2.7 0.8-1.2

DE 1/2 "636 6.5 12.5

  Codes 104, 106 and 110 denote glass microfibers produced by Manville Corp. from 475 borosilicate glass. DE 1/2 "636 fibers are manufactured by Owens-Corning from a conventional E glass. Three different fiber blends are prepared according to parts by weight Fiberglass A to C code 104 4.4 2.5 8.4 code 106 70.5 60.6 46.3 code 110 15.7 17.4 36

DE 1/2 "636 9.4 9.5 11.3

  The fibers were mixed to form a suspension at a solids level of 5% in water adjusted to pH 2.7 with sulfuric acid. The suspension was formed in a high shear mixing tank. After the initial dispersion and mixing, the suspension was diluted to 2% by weight and metered into the headbox of a flat-table paper machine in which it was further diluted to a in solids of about 0.1 to 0.5% to ensure uniform fiber distribution. After the initial formation of a fiber mat on the fabric of the flat-table paper machine, each of the blends A and B was saturated with an aqueous dispersion containing 3 to 5% by weight of binder. a mixture of 30 parts by weight of a copolymer of vinylidene chloride and acrylic ester (GEON 660X14) having a glassy tradition temperature (Tg) of 14 C, and 70 parts by weight of a copolymer of chloride of vinyl and acrylic ester (GEON 460X47) having a glass transition temperature of 46 C, both copolymers having inherently reactive self-crosslinking amide functional amide groups activated at a temperature of 137.8 ° C (280 ° C). Such copolymers are available from BF Goodrich Co. The excess binder and water was removed on the fabric of the Fourdrinier paper machine and the fiberglass and binder fabric was removed. been dried from the fa habitual lesson on steam-heated drying cylinders. Thus, three different tissues with three different basis weights of 8.6, 9.7 and 10.9 kg / m 2 were prepared.

(55, 62 and 70 lb / 3000 sq.ft.).

  Mixture C was also treated as described above except that the binder consisted of 15 parts by weight of GEON 660X14 and 85 parts by weight of GEON 460X47; the resulting fabric had a base weight of 10.9 kg / m2

(70 lb / 3000 sq.ft.).

  The characteristics of the four tissues were as follows: Procedure Fiber Blend

A B C D

  binder,% wt. TAPPI T 413-80 * 5.5 5.5 5.5 5.4 basis weight TAPPI T 41079 kg / m2 8.6 9.7 10.9 10.9 lb / 3000 sq.ft. 55 62 70 70 caliber, TAPPI T 411-76 mm 0.48 0.56 0.63 0.63 in. 0.019 0.022 0.025 0.025 tensile (DM) ** TAPPI T 494-70 N / m wide 1400 1926 2276 1681 lb / in.de width 8.0 11, 0 13.0 9.6 elongation **

  (DM),% TAPPI T 494-70 1.6 1.6 1.5 1.1

  pulling (DP) ** TAPPI T 494-70 N / m width 963 1400 1751 1191 lb / in. width 5.5 8.0 10.0 6.8 lengthening **

  (DP),% * TAPPI T 494-70 1.9 1.9 2.2 1.4

  rigidity of Gurley (DM), mg TAPPI T 543-84 1800 2600 3400 2967 * TAPPI is an organization that publishes standard tests used in the paper industry; the letter "T" and the number that follows it identify the operating mode

  standardized that is used to perform the test.

** at 22.2 OC (72 "F).

  Each sheet could be heated by infrared rays to a temperature of 148.9 C (3000 F), then quickly introduced while still hot between two polyurethane embossing rolls, to undergo cracking or splitting an embossing on a rib or protuberance having a cross section-shaped cross-section of 2 mm in height: t of 8.5 mm in width. Each sheet could also be streaked and folded to form gathers of about 2.54 cm to 23 cm in height, the opposite sides of the gathers being kept at a distance from each other by the embossings with a gathers density of 4 to 12 cm. gathers for 2.54 cm. After the deformation and embossing steps, the fabric temperature was raised to over 280 F (137.8 C) to cause crosslinking of the binder and thereby improve rigidity and stiffness.

  shape retention characteristics of the filter cloth.

  In each finely gathered and folded filter, the distance between the gathers was maintained under different conditions and the different filters showed high air filtration efficiency, as shown by the following test results:

A B C D

Air resistance man H20

(ASTM F-778-82) 38 38 46 34.5

DOP penetration,%

  (ASTM D2986-71) * 0.005 0.009 0.001 0.015

  * ASTM standard using dioctylphthalate (DOP) In general, when embossed and fully crosslinked, the products of the present invention have an air resistance (ASTM F-778-82) of 0.5 to 70 mm H20 and a DOP penetration (ASTM D2986-71) of 0 to 99%. When the binder content of the product according to the invention is less than 7%, the filters constructed with a suitable sealing material can successfully pass the standardized test UL 900, class 1 (standard established by Underwriters Laboratories,

and accepted in the industry).

  1 1 1. A thermoformable, breathable, coherent filtering fabric, characterized in that it comprises: a glass fiber mixture consisting essentially of (1) 5 to 35% by weight of cut twisted fibers having an average length from 3 to 19 mm and an average diameter of 6 to 20 μm, and (2) glass wool constituting the complement and having an average fiber length of 0.1 to 5 mm and an average fiber diameter of 0.2 at 6 μm, and a thermoplastic polymeric binder capable of crosslinking by heating at a temperature of 137.8 C (280 F) or more, the amount of binder being from 2 to 30% by weight based on the total of the mixture of fiberglass and binder, said fabric having a thickness of 0.3 to 1 mm (0.012 to 0.040 inches), a tensile strength in the direction of travel of the sheet in the machine (DM) from 700 to 4377, 5 N / m wide (4 to 25 psi) and tensile strength in the perpendicular direction (DP) 350 to 2101 N / m in width (2 to 12 lb / in. width) and a basis weight of 6.25 to 15, 65 kg / m2 (40 to 100

lb / 3000 sq.ft).

  2. thermoformable filter fabric according to claim 1, characterized in that it has an elongation of at least 2% without cracking or fragmentation when embossing at 93,30C (200CF) on a protuberance having a shaped cross-section. of a circle segment having a height of 2 mm and a width of 8.5 mm, and in that it retains a permanent elongation of at least 1.0% in the embossed portion after the crosslinking and cooling at

Room temperature.

  3. thermoformable filter fabric according to claim 1 or 2, characterized in that said fiber mixture consists essentially of 8 & 15% by weight of cut twisted fibers, the balance being made of glass wool, and the amount of binder being included

between 3 and 6% by weight.

  The thermoformable filter fabric according to claim 2, characterized in that it has a basis weight of 8.6 to 11.7 kg / m 2 (55 to 75 lb / 3000 sq.ft.) and maintains a permanent elongation of 1 to 5% in the embossed part after

  crosslinking and cooling.

  Filter fabric according to claim 1, characterized in that said fiber mixture consists of (1) 8 to 15% by weight of cut twisted fibers which have an average length of 6 to 13 mm, (2) glass wool constituting the complement and having an average fiber length of 1 to 3 mm, the amount of binder constituting 3 to 6% by weight, and in that said fabric has a thickness of 0.3 mm to 1 mm, a rigidity of Gurley in the machine moving direction (DM) of 1500 mg or more, and retains a permanent elongation of 1 to 5% in the

  embossed portion after crosslinking and cooling.