JPH03101804A - Embossable filter web - Google Patents

Abstract

PURPOSE: To form a thermoformable filter by manufacturing a web obtd. by compounding a glass fiber mixture of a specific compsn. and a thermoplastic polymer binder which crosslinks at a temp. above 280 deg.F at a specific ratio. CONSTITUTION: A glass fiber blend is prepd. by mixing 5 to 35 wt.% chopped strand fibers 5 having an average fiber length of 3 to 19 mm and an average fiber diameter of 6 to 20 μm and 95 to 65 wt.% glass wool having an average fiber length of 0.1 to 5 mm and an average fiber diameter of 0.2 to 6 μm. The thermoformable air permeable coherent filter web is manufactured by such glass fiber blend and the thermoplastic polymer binder which is 2 to 30 wt.% (with web) and is crosslinked by heating at a temp. above 280 deg.F. Thermosetting web has a characteristic value of tensile strength of 4 to 25lb/in width at a thickness of 0.012 to 0.040in.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a formable breathable cohesive filter web comprising glass fibers and a binder that is adapted to be embossed and pleated to form an air filter.

Shirred sheet or web glass fiber air filters are desirably used in a variety of settings because of their high surface area to volume ratio. For maximum efficiency, it is important to maintain sufficient spacing between adjacent pleats during use. This spacing may be achieved by a separate spacing or separator element added to the filter, or by helping to maintain the spacing between adjacent pleats after pleating.
This is accomplished by applying embossing or deformations, such as shallow depressions, to the sheet or web itself.

Previously, U.S. Pat. No. 3. of Mathews et al. 0 3 5
．． In 965, it was proposed to form a glass fiber paper coated with a thermoplastic polymer, less than 2.5 microns in diameter, but without the larger diameter chopped strand fibers. Po
U.S. Patent No. 4 to Well et al. 3 1 8. 7 7
No. 4 describes a composite nonwoven web of glass fibers and textile fibers with a thermoplastic binder.

Klein U.S. Patent No. 4. 2 8 6. 9 7
No. 7 describes air fibers containing small diameter glass fibers, textile fibers and thermoplastic binders.

Buckman British Patent No. 87 4. 3 8 3
No. (1961) describes a pleated air filter with an embossed baser made of synthetic resin-impregnated filter paper. Flanders Filter Inc. The Bull
Letin No. 815E (1987) also describes a pleated air filter with shallow recesses. It is believed that it was customary to carry out such embossing or deformation during the warm stage of the Fourdrinier machine when forming webs or sheets.

Attempts to emboss the sheet or web after drying have been unsuccessful because the web has a tendency to crack or split, thus impairing its cohesiveness and effectiveness. Although most filter manufacturers or fabricators do not manufacture their own filter sheet or web materials, they use a variety of embossing methods to fit the web into individually designed pleated filter structures to suit specific applications. There is a need for a uniform dry smooth surface web or sheet that can be embossed or otherwise deformed with simple and inexpensive equipment, such as a pair of embossing rolls, having the desired pattern.

However, a dried sheet of glass fiber filter material with certain critical property values can be dried without easily cracking or splitting by heating it to a temperature below 200-350°C and passing it through an embossing roll. I found that it embossed easily in the condition. The sheet essentially has (1
) Chopped strand fibers with an average fiber length of 3-19 mm and an average fiber diameter of 6-20 μm
A glass fiber blend consisting of (2) 35% by weight of glass wool with an average fiber length of 0.1 to 5 mm and an average fiber diameter of 0.2 to 6 μm was prepared by adding 28% by weight of glass fibers.
1. A thermoformable breathable cohesive filter web comprising a thermoplastic polymeric binder capable of crosslinking when heated to temperatures below 0 or more, wherein the amount of binder is relative to the total amount of glass fiber blend and binder. 2～
30% by weight, and the web is 0.012 to 0.040
in thickness, tensile strength (MD) from 4 to 25 lb/in width
and a thermoplastic filter web having a tensile strength (CD) of 2 to 12 °C b/in width and a basis weight of 40 to 100 l b/30 00 ft''.

In a preferred embodiment, the sheet has a height of 2 mm and a height of 8. It exhibits an elongation of at least 2.0% when embossed at 200°F on a boss having a cross-section in the form of a circular segment with a width of 5 mm, and after this embossing is subsequently heated to below 280°C to cross-link and A permanent elongation of at least 1.0% is retained within the embossment even as cooling to room temperature is developed or completed.

In other preferred embodiments, the glass fiber blend comprises 8-15% by weight chopped strand fibers, and the chopped strand fibers are 6-13 mm.
, the binder composition is 3-6% by weight of the total, the web has a basis weight of 55-75°Cb/3000ft' and a Gurley stiffness of at least 1500mg, and a height of 2mm and 8. After embossing at 200'F onto a boss having a cross section in the shape of a circular segment with a width of 5 mm, subsequent heating to 280°F or above and cooling to room temperature allowed crosslinking to develop or complete. A permanent elongation rate of 1 to 5% is maintained.

Dry web scoring to facilitate folding for pleating is preferably performed on the unheated web prior to heat embossing.

Depending on the heating temperature of the web and the duration of the embossing step, some binder crosslinking may occur during the embossing step. Thus, additional crosslinking can occur by further heating after embossing and/or even after collection of the pleated web.

Other properties of the Web will be apparent from the following description.

The glass fibers in the web include a blend of two fibers, one being chopped glass fibers and the other being glass wool having the dimensions and proportions described. Such fibers are readily obtained from a variety of sources. Blends may be prepared by conventional procedures and equipment. Although dry blending can be used, the fibers are disrupted in an aqueous medium in a beater or pulper or high shear mixing vat, preferably with the addition of an acid or a temperature that facilitates separation of the glass fibers. Preferably, wet blending is used. During or after preparation of the blend, binders required to provide the necessary cohesiveness and other physical properties to the product can be combined with the fiber blend. In a preferred embodiment, the fiber blend is first
The web or sheet is then saturated with an aqueous dispersion of binder, the excess water is suctioned off on a Fourdrinier machine, and the web or sheet is dried in a heated dryer in a conventional manner. Dry with water.

The binder is in the form of a thermoplastic such as a vinyl or vinylidene polymer or copolymer that crosslinks when heated to temperatures below 280°C. This crosslinking ability is
Urea which crosslinks vinyl or vinylidene polymers or cobolimers upon heating by adding a crosslinking agent which reacts with other reactive moieties such as residual vinyl or carboxyl groups in the thermoplastic polymer or cobolimer. by blending with another resin or polymeric material such as mono-formaldehyde resin, melamine-formaldehyde resin, phenol-formaldehyde resin, epoxy resin, etc. For best results,
It is preferred that the thermoplastic binder material has a glass transition temperature (Tg) of +10°C to +50°C and retains thermoplasticity upon heating to temperatures below 280°C. Suitable binders or crosslinking substances include cobolymers such as vinyl chloride, vinylidene chloride, vinyl acetate, acrylic acid esters, acrylonitrile, etc., the crosslinking ability of which may be determined, for example, by cobolymers with side carboxyl groups or with urea-formaldehyde or others. and the crosslinking is effected by blending with a thermoset of at least two
The vine is activated by heating it to a high temperature of 80°C or higher.

The specific examples below are intended to be illustrative of the essence of the invention and are not intended to limit its scope.

Example 1 Chopped strand glass filament or fiber (6.5 μm diameter) and flame blown glass microfiber or wool (0.65-27 μm diameter)
A blend was prepared from the following ingredients: Nominal diameter Nominal length Glass fiber μm mm Code 10
4 0.4 0.2~1 code 10
6 0.65 0.5~0.8 code 110 2.7 0.8~1.2D
EI/2″ 636 6,5 12.
5 codes 104, 106 and code 110 are Man
Glass microfibers made from type 475 borosilicate glass by D.
EI/2"636 is manufactured from conventional E glass by Owens-C: orning. Three fiber blends were prepared in the following parts by weight;
Δ Dan Dan code 10
4 4.4 2.5 8.4 code 106 70.5 60.6 46
．． 3 code 110 15.7 17.4
36DE 1/2" 636 9.4
9,5 11.3 Blend the fibers and pH 2.5 with sulfuric acid. A slurry was formed at a solids level of 5% in water prepared in Example 7. The slurry was formed in a high shear mixing vat. After initial dispersion or blending, the slurry is diluted to 2% by weight and metered into a Fourdrinier headbox where it is further diluted to a solids content of approximately 0.1-0.5% to ensure uniform fiber distribution. did. Fourdrin
After initial formation of the fiber mat on the ier screen, each of Blends A and B was prepared with a binder content of 3 to 5.
% by weight of the aqueous dispersion. The binder is 14
30 parts by weight of vinylidene chloride/acrylic ester cobolimer (GEON 660
It consisted of a mixture of parts by weight. Both cobolimers are
It is endowed with unique thermoreactive self-crosslinking amide functional side groups that are activated at temperatures below 280°C. Such a cobolimer is B
．． F. Goodrich Co. Obtained from. Excess binder and water were removed on a Fourdrinier screen and the glass fiber binder web was dried in a conventional manner on a steam heated dryer. Thus, 5
Three webs were prepared with three basis weights: 5, 62, and 70 b/3000 ft'.

Fiber Blend C was also treated as described above, but the binder consisted of 15 parts by weight of GEON 660x 14 and 5 parts by weight of GEON 460x 578.

The resulting web had a basis weight of 70 lb/3o00 ft2.

The characteristic values of the four types of webs were as follows: Part by weight
TAPPI T413-80 5.5 5.5
5.5 5.4%” TAPPIT49
4-70 1.6 1.6 1.5
1.1%” TAPPIT494-70
1.9 1.9 2.2 1.426
00 2967 072 Each seat can be infrared heated to under 300 horse degrees,
It can then be quickly passed through a pair of polyurethane embossing rolls when warm, thus producing a 2 mm high, wide, 8. It was possible to embossing on ribs or bosses having a cross section in the form of a circular segment of 5 mm. Each sheet was also scored or folded to form pleats of lin to about 9 inches in height, and the opposing sides of the pleats were held apart by embossing with a pleat density of 4 to 12 pleats per inch. . Following the scoring and embossing steps, the temperature of the web was raised above 280°C to effect crosslinking of the binder, thus increasing the stiffness and shape retention properties of the filter web. In each case, the finished crimped and folded filter material maintained interfold spacing at various conditions in degrees Fahrenheit and exhibited high air permeability as shown by the test results below. When the bangu content of the product of this invention is greater than 7% °F, filters made with suitable sealants may be
Able to pass L900, grade l.

Claims (5)

[Claims] 1. Essentially (1) an average fiber length of 3 to 19 mm and 6 to
Glass fibers consisting of 5-35% by weight of chopped strand fibers with an average fiber diameter of 20 μm and the remaining weight % of glass wool with an average fiber length of 0.1-5 mm and an average fiber diameter of 0.2-6 μm. a thermoformable breathable cohesive filter web comprising a blend and a thermoplastic polymer binder capable of crosslinking upon heating to a temperature of 280° F. or higher, wherein the amount of the binder is the sum of the glass fiber blend and the binder. 2 to 30% by weight of the amount, and the web has a thickness of 0.012 to 0.040 inches, 4
~25 lb/in wide tensile strength (MD) and 2-12
tensile strength (CD) of lb/in width and 40-100l
Thermoformable filter web having a basis weight of b/3000ft^2. 2. Further, the web has an elongation rate of at least 2.0% without cracking or cracking during embossing at 200°F onto bosses having a circular segment-shaped cross section with a height of 2 mm and a width of 8.5 mm. and retaining a permanent elongation of at least 1.0% in the embossing after crosslinking and cooling to room temperature.
Thermoformable filters as described in Section. 3. the fiber blend consists essentially of (1) 8-15% by weight of chopped strand fibers and the remainder by weight of glass wool, and the amount of binder is 3-6% by weight;
Thermoformable filter web according to claim 1 or 2. 4. Thermoformable filter web according to claim 2, wherein the web has a basis weight of 55 to 75 lb/3000 ft^2 and retains a permanent elongation of 1 to 5% in the embossing after crosslinking and cooling. . 5. The fiber blend consists essentially of (1) chopped strand fibers having an average fiber length of 6 to 13 mm;
(2) the remaining weight percent glass wool having an average fiber length of 1 to 3 mm, the amount of binder being 3 to 6 weight percent, and the web having a thickness of 0.012 to 0.030 inches; The thermoformable filter web of claim 1 having a Gurley stiffness (MD) of at least 1500 mg and retaining a permanent elongation of 1 to 5% in the embossing after crosslinking and cooling.