阅读说明：本技术 包含芳族聚酰胺浆粕的纸和由其制造的摩擦纸 (Paper comprising aramid pulp and friction paper made therefrom ) 是由 M.阿夫沙里 于 2018-10-29 设计创作，主要内容包括：公开了一种纸,其包含60重量％至99重量％的芳族聚酰胺纤维浆粕和1重量％至40重量％的在纤维表面上的聚乙烯吡咯烷酮涂层,所述涂层既不以化学方式也不以静电方式结合到所述纤维上。还描述了一种包含所述纸和树脂涂层的摩擦纸复合物。(Paper comprising 60 to 99 weight percent aramid fiber pulp and 1 to 40 weight percent polyvinylpyrrolidone coating on the surface of the fiber, the coating being neither chemically nor electrostatically bound to the fiber is disclosed. A friction paper composite comprising the paper and a resin coating is also described.)

1. A paper, comprising: 60 to 99 weight percent aramid fiber pulp based on the total weight of the paper, the fiber pulp comprising fibers; and from 1 to 40% by weight, based on the total weight of the paper, of polyvinylpyrrolidone present as a coating on the surface of the fibers, the coating being neither chemically nor electrostatically bound to the fibers.

2. The paper of claim 1 comprising 80 to 98 weight percent aramid fiber pulp and 2 to 20 weight percent polyvinylpyrrolidone.

3. The paper of claim 1 comprising 80 to 95 weight percent aramid fiber pulp and 5 to 20 weight percent polyvinylpyrrolidone.

4. The paper of claim 1 comprising 80 to 90 weight percent aramid fiber pulp and 10 to 20 weight percent polyvinylpyrrolidone.

5. The paper of claim 1 having a ratio of tensile strength to average gurley of 300cc of at least 4.0 MPa/s.

6. The paper of claim 1 consisting of or consisting essentially of 60 to 99 weight percent aramid fiber pulp and 1 to 40 weight percent polyvinylpyrrolidone.

7. The paper of claim 1, further comprising aramid floe, the floe comprising fibers, the floe being present in an amount of 1 to 30 weight percent based on the total weight of the paper, wherein the polyvinylpyrrolidone is present as a coating on the surfaces of the aramid fiber pulp fibers and the aramid floe fibers, and wherein the aramid fiber pulp does not exceed 98 weight percent based on the total weight of the paper.

8. The paper of claim 1, further comprising a combination of aramid floe and aramid fibrids comprising fibers, the combination of aramid floe and aramid fibrids being present in an amount of 1 to 30 weight percent based on the total weight of the paper, wherein the polyvinylpyrrolidone is present as a coating on the surfaces of the aramid fiber pulp fibers and the aramid floe fibers and the aramid fibrids, and wherein the aramid fiber pulp does not exceed 98 weight percent based on the total weight of the paper.

9. The paper of claim 1 or 7, further comprising a filler or friction modifying particles.

10. The paper of claim 9, wherein the filler or friction modifying particles are one or more of: silica, diatomaceous earth, graphite, alumina, metal oxides, metal nitrides, or metal carbides.

11. The paper of claim 7 consisting of, or consisting essentially of, 60 to 98 weight percent aramid fiber pulp based on the total weight of the paper, 1 to 30 weight percent aramid floe based on the total weight of the paper, and 1 to 20 weight percent polyvinylpyrrolidone based on the total weight of the paper.

12. A composite comprising 40 to 95 weight percent of the paper of claim 1 and 5 to 60 weight percent of a resin, wherein the resin is a phenolic resin, a silicone resin, a polyimide, or a combination thereof.

13. The composite of claim 12 comprising 60 to 90% by weight of the paper of claim 1 and 10 to 40% by weight of the resin.

14. A composite comprising 40 to 95 weight percent of the paper of claim 7 and 5 to 60 weight percent of a resin, wherein the resin is a phenolic resin, a silicone resin, a polyimide, or a combination thereof.

15. The composite of claim 14, comprising 60 to 90 wt% of the paper of claim 7 and 10 to 40 wt% of the resin.

Background

The invention relates to a base paper comprising aramid pulp and polyvinylpyrrolidone. The paper may be used as a friction material when coated with a resin.

U.S. patent No. 5,532,059 to Lee discloses a fibrous pulp of a combination of poly (p-phenylene terephthalamide) and poly (vinyl pyrrolidone) and a method of making the same. The process involves carrying out a poly (p-phenylene terephthalamide) polymerization reaction in the presence of poly (vinyl pyrrolidone), and the product is an improved pulp with increased fibrils without fiber stalks.

U.S. patent No. 3,036,950 to Martin describes a method of depositing a water-dispersible resin on pulped cellulose pulp fibers comprising first dispersing polyvinylpyrrolidone into an aqueous slurry of the fibers and then dispersing the resin into the slurry, the polyvinylpyrrolidone being added in an amount of at least about 0.05% by weight based on the dry weight of the pulp fibers.

U.S. Pat. No. 6,139,688 to Ramachandran teaches a coated aramid fiber wherein the coating is a small amount of chitosan and the coated fiber can be used to make improved friction paper.

There is a continuing need to provide a paper for use in friction applications in which the tensile strength of the paper can be increased without increasing or minimally increasing the porosity of the paper.

Disclosure of Invention

The present invention relates to a paper comprising: 60 to 99 weight percent aramid fiber pulp, the fiber pulp comprising fibers; and 1 to 40% by weight of polyvinylpyrrolidone present as a coating on the surface of the fiber, the coating neither being chemically nor electrostatically bound to the fiber.

The invention further relates to a friction material composite made from the paper.

Detailed Description

While the present invention is susceptible of embodiment in various forms, the following description of several embodiments is provided with the understanding that the present disclosure is to be considered an exemplification of the invention, and is not intended to limit the invention to the specific embodiments illustrated. Headings are provided for convenience only and should not be construed as limiting the invention in any way. Embodiments shown under any heading or any section of the disclosure can be combined with embodiments shown under the same or any other heading or section of the disclosure.

Any combination of the elements described herein, in all possible variations thereof, is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Definition of

As used herein, the term "paper" is used in its normal sense and refers to a nonwoven sheet prepared using conventional wet-laid papermaking processes and equipment. In the context of the present disclosure, paper is also referred to as "base paper".

As used herein, a "friction paper" is a composite comprising a base paper as described above and a resin coating.

By "pulp" is meant particles of aramid material having stems and fibrils extending from the stems, wherein the stems are generally columnar and about 10 to 50 microns in diameter, while the fibrils are hair-like members attached to the stems having a diameter of only a fraction of a micron or a few microns and a length of about 10 to 100 microns. In papermaking, it is important that the fibrils on the pulp act as hooks or fasteners to hold adjacent particles in the paper and provide integrity to the paper structure. The pulp used herein has a surface area of 0.5 to 20 square meters per gram. Aramid pulp can be made, for example, by refining aramid floe or as described in U.S. patent No. 5,202,184.

Floes generally include staple fibers made by cutting continuous filament fibers into short lengths without significant fibrillation. Although the length of the staple fibers can be almost any length, examples of suitable ranges are 1mm to 12mm for the reinforcing fibers and 5mm to 800mm for the staple fibers spun into a yarn. Typically, the surface area of the floe is about 0.08 to 0.6 square meters per gram. Staple fibers suitable for use in the present invention are the reinforcing fibers disclosed in U.S. patent No. 5,474,842 to Hoiness.

As used herein, the term "fibrids" refers to very finely divided polymeric products of small, film-like, substantially two-dimensional particles having a length and width of about 100 to 1000 microns and a thickness of about 0.1 to 1 micron.

In the context of the present application, the term aramid includes polymers in which at least 85% of the amide (- -CONH- -) linkages are directly attached to two aromatic rings. Additives may be used with the aramid; and it has been found that up to as much as 10 percent by weight of other polymeric materials can be blended with the aramid or that copolymers can be used having as much as 10 percent of other diamines substituted for the diamines of the aramid or as much as 10 percent of other diacid chlorides substituted for the diacid chlorides of the aramid. Para-aramid is an exemplary polymer in the fibers of the present invention, and poly (p-phenylene terephthalamide) (PPD-T) is the preferred para-aramid. Another suitable aramid-type fiber is an aromatic copolyamide-based fiber, such as one prepared by reacting terephthaloyl chloride (TPA) with a combined mixture of p-phenylenediamine (PPD) and 3, 4' -diaminodiphenyl ether (DPE), for example, in a molar ratio of 50/50. Another suitable fiber is a fiber formed by: two diamines, p-phenylenediamine and 5-amino-2- (p-aminophenyl) benzimidazole, undergo polycondensation with their terephthalic acid derivatives or anhydride derivatives or acid chloride derivatives or isomers of the foregoing. Another fiber type is an aromatic copolymer derived from the copolymerization of para-phenylenediamine, 5(6) -amino-2- (p-aminophenyl) benzimidazole, and terephthaloyl dichloride.

Paper

In the context of the present disclosure, paper is also referred to as base paper.

In one embodiment, the paper comprises: 60 to 99 weight percent of an aramid fiber pulp, such as para-aramid fiber pulp, comprising fibers; and 1 to 40 weight percent of a polyvinylpyrrolidone (PVP) coating on the surface of the fiber, the coating neither chemically nor electrostatically bonded to the fiber.

In another embodiment, the paper comprises: 80 to 98 weight percent aramid fiber pulp, such as para-aramid fiber pulp; and 2 to 20 wt.% of a polyvinylpyrrolidone (PVP) coating.

In another embodiment, the paper comprises: 80 to 95 weight percent aramid fiber pulp, such as para-aramid fiber pulp; and 5 to 20 wt.% of a polyvinylpyrrolidone (PVP) coating.

In yet another embodiment, the paper comprises: 80 to 90 weight percent aramid fiber pulp, such as para-aramid fiber pulp; and 10 to 20 wt.% of a polyvinylpyrrolidone (PVP) coating.

In yet another embodiment, the paper further comprises 1 to 30 weight percent aramid floe, such as para-aramid floe. Alternatively, the paper further comprises 1 to 20 weight percent aramid floe, such as para-aramid floe, or 1 to 10 weight percent aramid floe, such as para-aramid floe.

Paper can also be made using a combination of aramid floe and aramid fibrids, where the fibrids serve to hold the floe and other paper components together.

The paper may further comprise components such as fillers or friction modifying particles. Exemplary fillers include silica, diatomaceous earth, graphite, and alumina. Exemplary friction modifying particles include metal oxides, nitrides, carbides, and mixtures thereof. The friction modifying particles may have at least one dimension less than 1 micron.

One method of applying PVP to aramid pulp is by adding PVP to an aqueous slurry of pulp and other fibrous materials, forming paper and drying the paper. However, other methods may be used.

The paper may be made on any suitable paper machine using techniques well known in the art.

Preferably, the paper has a ratio of tensile strength to average Gurley (Gurley) air permeability of 300cc value of at least 4.0MPa/s or at least 4.3 MPa/s.

Friction paper

The friction paper as described herein is a composite comprising a base paper as described above and a resin coating.

In one embodiment, the friction paper comprises 40 to 95 weight percent base paper and 5 to 60 weight percent resin.

In another embodiment, the friction paper comprises 60 to 90 weight percent base paper and 10 to 40 weight percent resin.

Friction paper resin

The resin component of the friction paper may be a phenolic resin, a modified phenolic resin, a silicone resin, a polyimide, or a combination thereof.

Silicone resins useful in the present invention include, for example, heat-curable silicone sealants and silicone rubbers. Another useful resin is an epoxy-modified phenolic resin that contains from about 5 to about 25 weight percent, and preferably from about 10 to about 15 weight percent, of an epoxy compound, with the remainder (excluding solvents and other processing aids) being phenolic resin.

As is known in the art, a resin is impregnated onto and into a base paper, which is then cured by heat and pressure to form the final shape of the friction paper. The paper may be impregnated using conventional techniques such as dip coating and surface coating.

Industrial applicability

The present invention may be used as a high energy friction material for use with clutch plates, drive belts, brake shoes, synchronizer rings, friction discs, or system plates.

Some embodiments disclosed herein are set forth in the following clauses, and any combination of these clauses (or portions thereof) may be made to define an embodiment. For example, if the compositions described in the examples can vary according to additional features or claim elements, it is to be understood that other compositions described in other examples can also vary according to the same additional features or claim elements. For example, clause 1a discloses an embodiment wherein the aramid fiber pulp in the paper as recited in clause 1 is para-aramid fiber pulp; similarly, for any other embodiment that discloses a paper or composite comprising (or consisting of or consisting essentially of) aramid fiber pulp, there is another embodiment wherein the paper or composite comprises (or consists of or consists essentially of) para-aramid fiber pulp. Generally, for any embodiment in which the compositions described herein (such as paper or composites) comprise or consist essentially of aramid fiber pulp or aramid floe or aramid fibrids, there is another corresponding embodiment that comprises or consists essentially of para-aramid fiber pulp or para-aramid floe or para-aramid fibrids. Furthermore, the methods of utilizing the compositions described herein can also be varied by such compositional variations.

Clause 1: a paper, comprising: 60 to 99 weight percent aramid fiber pulp based on the total weight of the paper, the fiber pulp comprising fibers; and from 1 to 40% by weight, based on the total weight of the paper, of polyvinylpyrrolidone present as a coating on the surface of the fibers, the coating being neither chemically nor electrostatically bound to the fibers.

Clause 1 a: in one embodiment, the aramid fiber pulp in the paper of clause 1 is para-aramid fiber pulp.

Clause 2: the paper of clause 1 or 1a, comprising 80 to 99 weight percent aramid fiber pulp or para-aramid fiber pulp and 1 to 20 weight percent polyvinylpyrrolidone. In one embodiment, the paper of clause 1 or 1a comprises 80 to 98 weight percent aramid fiber pulp or para-aramid fiber pulp and 2 to 20 weight percent polyvinylpyrrolidone.

Clause 3: the paper of clause 1 or 1a, comprising 80 to 95 weight percent aramid fiber pulp or para-aramid fiber pulp and 5 to 20 weight percent polyvinylpyrrolidone.

Clause 4: the paper of clause 1 or 1a, comprising 80 to 90 weight percent aramid fiber pulp or para-aramid fiber pulp and 10 to 20 weight percent polyvinylpyrrolidone.

Clause 4 a: in one embodiment, there is provided a paper comprising: an aramid fiber pulp or para-aramid fiber pulp, the fiber pulp comprising fibers; and polyvinylpyrrolidone present on the surface of the fiber as a coating that is neither chemically nor electrostatically bound to the fiber; wherein the weight ratio of aramid fiber pulp or para-aramid fiber pulp to polyvinylpyrrolidone is from 60: 40 to 99: 1; or 80: 20 to 99: 1; or from 80: 20 to 98: 2; or from 80: 20 to 95: 5; or from 80: 20 to 90: 10.

Clause 5: the paper of any of the preceding clauses having a ratio of tensile strength to average gurley permeability 300cc value of at least 4.0 MPa/s. In one embodiment, the ratio of tensile strength to average Gurley air permeability 300cc value is at least 4.3 MPa/s.

Clause 6: the paper of clause 1, consisting of or consisting essentially of 60 to 99 weight percent aramid fiber pulp and 1 to 40 weight percent polyvinylpyrrolidone.

Clause 6 a: the paper of clause 1, consisting of or consisting essentially of 80 to 98 weight percent aramid fiber pulp and 2 to 20 weight percent polyvinylpyrrolidone.

Clause 6 b: the paper of clause 1, consisting of or consisting essentially of 80 to 95 weight percent aramid fiber pulp and 5 to 20 weight percent polyvinylpyrrolidone.

Clause 6 c: the paper of clause 1, consisting of or consisting essentially of 80 to 90 weight percent para-aramid fiber pulp and 10 to 20 weight percent polyvinylpyrrolidone.

Clause 7: the paper of clause 1, further comprising aramid floe, such as para-aramid floe, the floe comprising fibers, the floe being present in an amount of 1 to 30 weight percent based on the total weight of the paper, wherein the polyvinylpyrrolidone is present as a coating on the surfaces of the aramid fiber pulp fibers and the aramid floe fibers, and wherein the aramid fiber pulp does not exceed 98 weight percent based on the total weight of the paper. In one embodiment, the aramid fiber pulp and the aramid floe are para-aramid fiber pulp and para-aramid floe.

Clause 7 a: the paper of clause 1, further comprising aramid floe, the floe comprising fibers, the floe being present in an amount of 1 to 20, or 5 to 20, weight percent based on the total weight of the paper, wherein the polyvinylpyrrolidone is present as a coating on the surfaces of the aramid fiber pulp fibers and the aramid floe fibers, and wherein the para aramid fiber pulp does not exceed 98 weight percent based on the total weight of the paper. In one embodiment, the aramid fiber pulp and the aramid floe are para-aramid fiber pulp and para-aramid floe.

Clause 7 b: in one embodiment, there is provided the paper of clause 4a, further comprising aramid floe. In one such embodiment, the aramid floe is present in an amount of 1 to 30 wt.%, or 1 to 20 wt.%, or 5 to 20 wt.%, based on the total weight of the paper. In one embodiment, the aramid floe is para-aramid floe.

Clause 8: the paper of clause 1, further comprising a combination of aramid floe and aramid fibrids comprising fibers, the combination of aramid floe and aramid fibrids being present in an amount of 1 to 30 weight percent, or 1 to 20 weight percent, or 5 to 20 weight percent based on the total weight of the paper, wherein the polyvinylpyrrolidone is present as a coating on the aramid fiber pulp fibers and the surfaces of the aramid floe fibers and the aramid fibrids, and wherein the aramid fiber pulp is not more than 98 weight percent based on the total weight of the paper. In one embodiment, the aramid fiber pulp and the aramid floe and the aramid fibrids are para-aramid fiber pulp and para-aramid floe and para-aramid fibrids.

Clause 8 a: in some embodiments, the paper of clause 4a further comprises a combination of aramid floe and aramid fibrids. In one such embodiment, the combination of aramid floe and aramid fibrids is present in an amount of 1 to 30 weight percent, or 1 to 20 weight percent, or 5 to 20 weight percent, based on the total weight of the paper. In one embodiment, the aramid fiber pulp and the aramid floe and the aramid fibrids are para-aramid fiber pulp and para-aramid floe and para-aramid fibrids.

Clause 9: the paper of any of the preceding clauses further comprising a filler or friction modifying particles.

Clause 10: the paper of clause 9, wherein the filler or friction modifying particle is one or more of: silica, diatomaceous earth, graphite, alumina, metal oxides, metal nitrides, or metal carbides.

Clause 10 a: the paper of clause 9, wherein the filler is one or more of: silica, diatomaceous earth, graphite, or alumina.

Clause 10 b: the paper of clause 9, wherein the friction modifying particles are one or more of: a metal oxide, a metal nitride, or a metal carbide.

Clause 11: the paper of clause 7, consisting of or consisting essentially of 60 to 98 weight percent aramid fiber pulp based on the total weight of the paper, 1 to 30 weight percent aramid floe based on the total weight of the paper, and 1 to 20 weight percent polyvinylpyrrolidone based on the total weight of the paper. In one embodiment, the aramid fiber pulp and the aramid floe are para-aramid fiber pulp and para-aramid floe.

Clause 11 a: the paper of clause 7, consisting of or consisting essentially of 60 to 93 weight percent aramid fiber pulp based on the total weight of the paper, 5 to 20 weight percent aramid floe based on the total weight of the paper, and 2 to 20 weight percent polyvinylpyrrolidone based on the total weight of the paper. In one embodiment, the aramid fiber pulp and the aramid floe are para-aramid fiber pulp and para-aramid floe.

Clause 12: a composite comprising 40 to 95 weight percent of the paper of clause 1 and 5 to 60 weight percent of a resin, wherein the resin is a phenolic resin, a silicone resin, a polyimide, or a combination thereof.

Clause 13: the composite of clause 12, comprising 60 to 90 weight percent of the paper of clause 1 and 10 to 40 weight percent of the resin.

Clause 14: a composite comprising 40 to 95 weight percent of the paper of clause 7 and 5 to 60 weight percent of a resin, wherein the resin is a phenolic resin, a silicone resin, a polyimide, or a combination thereof.

Clause 15: the composite of clause 14, comprising 60 to 90 weight percent of the paper of clause 7 and 10 to 40 weight percent of the resin.

The invention is further defined in the following examples, in which all parts and percentages are by weight unless otherwise indicated. It should be understood that these examples, while indicating preferred embodiments of the invention, are given by way of illustration only and are not to be construed in any way as limiting. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Test method

The average caliper of the base and friction papers was measured at 5 points on the paper samples according to ASTM D645M-97(2007) using a Thwing-Albert ProGage instrument.

The average thickness of the friction paper was measured by a thickness meter model ID-C1128 from Sanfeng Corporation (Mitsutoyo Corporation), and the thickness at the breaking point of the paper sample was used.

The areal weight of the base paper and friction paper was measured according to ASTM D646-13.

The areal weight of the friction paper was calculated by dividing the measured weight by the area (21 cm. times.9 cm) immediately after curing.

The porosity and air permeability of the base paper and friction paper were measured according to ASTM D726-94 using a Genuine Gurley 4320 Gurley air permeability tester 4110 (Gurley Precision Instruments, Troy, NY) of Troy, N.Y.. Each sample was placed in the holder of an air permeability apparatus and air was forced through 0.1 square inch or 0.645cm of the sample at a pressure of 0.304(kPa)²And then recalculated to 1 square inch or 6.45cm by software². 300cc (cm)³) The time (in seconds) required for the air to pass through the sample is recorded as the gurley air permeability, in units of (s/300 cm)³Or s/300cc), referred to herein as the gurley permeability 300cc value. Values are reported as the average of 5 tests per sample. The machine also calculates porosity. Qualitatively, the relationship between porosity and air permeability is that the higher the porosity, the higher the air permeability, but it should be noted that the air permeability reported here refers to the time (in seconds) it takes 300cc of air to pass through the sample. The shorter (smaller) the time, the higher the air permeability; thus, time in seconds is actually inversely proportional to air permeability.

Tensile strength values were measured for both base and friction papers according to ASTM D828-16. Values are reported as the average of 8 tests per sample.

Examples of the invention

The following examples are given to illustrate the invention and should not be construed as limiting the invention in any way. All parts and percentages are by weight unless otherwise indicated. Examples prepared according to the invention are indicated by numerical values. The control or comparative examples are indicated by letters. Data and test results relating to the comparative examples and examples of the present invention are shown in tables 1 and 2.

The pulp used in all examples was a para-aramid commercially available from DuPont, DuPont DE Nemours and Company, Wilmington, DE, Wilmington, Del.D. having a denier per filament of 2.25merge 1F892。

The flocs are para-aramid fibers having a cut length of 3mm, also commercially available from DuPontmerge 1F570。

PVP is available under the trade name Sokalan from BASF, Florham, NJ. Grade K30P.

Preparation of base paper for comparative example A

Para-aramid pulp was added to water while stirring to provide a 2% slurry of para-aramid pulp. The slurry was filtered through a filter bag and the wet cake was pressed in a flat press at 100psi for 1 minute at ambient temperature to complete dewatering. The paper is not dried.

7.46 grams of para-aramid pulp was added to 2.5 liters of water to form a second slurry, which was then fed onto a screen on a laboratory paper machine. The paper formed was not pressed further but dried at 300+/-20 ℃ for 5 minutes.

The dried paper had an average thickness of 0.72mm and an areal weight of 168g/m²(gsm, g/m) and a porosity of83.8 percent. The paper was tested for air permeability and tensile strength, with the results shown in table 1.

Preparation of base paper of example 1

It was prepared in a similar manner to comparative example a, except that after the para-aramid pulp was added to make a slurry, PVP was also added while stirring in an amount such that the weight of the added PVP was 5% of the weight of the added para-aramid pulp. The pressure, time and temperature were the same as in comparative example a.

The dried paper had an average thickness of 0.69mm and an areal weight of 170g/m²And a porosity of 82.9%. The paper was tested for air permeability and tensile strength, with the results shown in table 1.

Preparation of base paper of example 2

It was prepared in a similar manner to comparative example a, except that after the para-aramid pulp was added to make a slurry, para-aramid floe was added while stirring in an amount such that the weight of the para-aramid floe added was 20% of the weight of the para-aramid pulp added, and PVP was also added while stirring in an amount such that the weight of the PVP added was 5% of the weight of the para-aramid pulp added. The pressure, time and temperature were the same as in comparative example a.

The dried paper had an average thickness of 0.76mm and an areal weight of 164g/m²And a porosity of 85.1%. The paper was tested for air permeability and tensile strength, with the results shown in table 1.

TABLE 1

Preparation of Friction paper

To test the efficacy of base paper as a friction material, the base paper was dipped into a phenolic resin. The resin was type PR54562 (30% solution) in methanol solvent, available from Sumitomo Bakelite, NA (Novi, MI, USA), Sumitomo Bakelite, Nuwei, Mich. After impregnation, the paper is removed and the excess resin is drained off. The paper was air dried for 30 minutes and then dried in an oven at 100 ℃ for 15 minutes. The resin content of the paper is measured by mass percent concentration. The paper was then placed between glass plates and the resin was cured at 165 ℃ for 10 minutes and then post-cured in an oven at 165 ℃ for 5 hours. The resin content in the coated paper was determined by comparing the relative weights of the paper before and after resin coating.

Comparative example B was made from the base paper of comparative example a. Examples 3-8 were made similarly to comparative example B, except that during the base paper manufacture, PVP was added in the amounts shown in table 2 as described in example 1.

For each type of friction paper, the average physical properties of the 7 samples were determined and are summarized in table 2.

Tensile tests were performed on 120mm by 10mm friction paper samples with a chuck distance of 60 mm. The thickness was measured at three points along the sample and the thickness closest to the break point was used in the calculation. The test was carried out at ambient temperature (about 23 ℃) at a rate of 1mm per minute. The highest and lowest tensile values were excluded and the average tensile strength was determined from the remaining five samples (table 2 below).

TABLE 2

The conventional wisdom is that as the porosity of paper increases, the tensile strength decreases. For friction paper, it is desirable to have increased tensile strength without compromising porosity. It was unexpectedly and surprisingly found that the addition of PVP to the base paper pulp resulted in such an increase in the tensile value of the friction paper while maintaining an acceptable level of porosity. The addition of PVP at about 10 wt.% appears to provide the best tensile properties.