Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
  • D21H13/10—Organic non-cellulose fibres
  • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H13/26—Polyamides; Polyimides
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H5/00—Special paper or cardboard not otherwise provided for
  • D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
  • D21H5/1272—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of fibres which can be physically or chemically modified during or after web formation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/48—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials
  • H01B3/52—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials wood; paper; press board

Definitions

• This invention relates to an improved aromatic polyamide pressboard having increased resistance to compression combined with relatively high oil absorption characteristics.
• the invention also relates to a process for preparing the improved pressboard.
• Pressboard prepared from cellulosic materials has been known and commercially used for many years. While the cellulosic pressboard is extremely useful. its use at high temperature is limited by the low thermal stability of cellulosic materials.
• aromatic polyamide fibers U.S. patents 3.063.966 and 3.133.138
• fibrids U.S. patent 2.999.788
• paper U.S. patent 3.756.908 having excellent properties at high temperatures
• Pressboard comprised of aromatic polyamide fibers and fibrids is also known and can readily be prepared using the same procedures used in the preparation of cellulosic pressboard.
• Aromatic polyamide pressboard has been found to be useful in many applications. For example, in oil filled transformers it has been found to have a suitably high oil absorption which contributes to good electrical insulating properties. However, for some uses. it is necessary that the pressboard not only have a suitably high oil absorption but also provide resistance to compression so that the pressboard can provide suitable separation of electrically conducting components. It has been found that compaction processes as taught by the prior art either do not provide pressboard products having adequate resistance to compression, or that they do so only by providing a pressboard product which does not have adequate oil absorption.
• This invention provides an improved aromatic polyamide pressboard having a combination of good resistance to compression and adequate oil absorption. This invention also provides a process for the preparation of the improved pressboard.
• This invention provides a high density pressboard comprised of 20-95% by weight aromatic polyamide fibrids and 80-5% by weight high temperature resistant floe. said pressboard having a calculated void volume of 13 to 28% by volume of the pressboard. a thickness of 0.5 to 50 mm, a mercury intrusion volume at low surface/volume .V ml , of less than 0.20 cm 3 / g; a mercury intrusion volume at high surface/volume. V mh . of 0.08 to 0.28 cm 3 /g, an oil absorption by volume in cm 3 /g. V o , of 0.09 to 0.28 and by weight 8-24%: and a total available absorption volume in cm 3 /g.
• V a equal to the largest of the values for V ml , V mh , and V o : the ratio of V a to V ml being at least 1.1: said pressboard having a compression set (as hereinafter defined) of greater than 0.12 mm but no more than 0.5 mm.
• the pressboard is comprised of 50-70% by weight aromatic polyamide fibrids and 30-50% by weight high temperature resistant floc.
• the high temperature resistant floc consists of an aromatic polyamide and the pressboard has a density of 1.00 to 1.20 g/cm 3 .
• the aromatic polyamide fibrids and high temperature resistant floc consist essentially of poly(m-phenylene isophthalamide)(MPD-I).
• the pressboard preferably is comprised of aromatic polyamide fibrids and floc and has a thickness of 1 to 10 mm, a density of 1.02 to 1.17 g/cm 3 . most preferably 1.10 to 1.15 g / cm 3 .
• the pressboard preferably has a compression set of 0.12 to 0.35 mm, most preferably 0.20 to 0.30 mm.
• the improved pressboard is prepared by a process whereby an aqueous slurry having 0.1 to 2 % by weight total solids comprised of 20-95% by weight aromatic polyamide fibrids and 80-5% by weight high temperature resistant floc having a length of 2 to 12 mm., said aromatic polyamide fibrids and high temperature resistant floc having a melting point higher than 320°C, is prepared; the slurry is formed into a waterleaf having a water content of 50-95% by weight the waterleaf is combined into multiple layers to form a wet lap; the wet lap is pressed at 100 to 200°C under a pressure of 10 to 60 kg/cm 2 to form a low density pressboard having a calculated void volume of 30 to 60% by volume of the pressboard; and the low density pressboard is dried, ultimately at 270-320°C, until substantially no further moisture is evolved and finally pressed at 8 to 350 kg/cm 2 at 270-32 0°C .
• the temperature is 275-300°C.
• the final pressing is at 275-285°C and the pressure is 15 to 70 kg/cm 2 .
• the pressboard is cooled under restraint.
• the high temperature resistant floc consists of an aromatic polyamide.
• the aromatic polyamide fibrids and the high temperature resistant floc consist of poly(m-phenylene isophthalamide).
• aromatic polyamide nonfusible polyamides wherein the amide group, i.e.. the radical where R is hydrogen or a 1-6 carbon alkyl group, of each repeating unit is linked through the nitrogen atom and the carbon atom to a carbon atom in the ring of separate aromatic ring radicals.
• aromatic ring is defined herein as a carbocyclic ring possessing resonance.
• aromatic polyamide fibrids small, nongranular. nonrigid fibrous or film-like particles of an aromatic polyamide having a melting point higher than 320°C. Two of their three dimensions are of the order of microns. Their smallness and suppleness allows them to be deposited in physically entwined configurations such as are commonly found in papers made from wood pulps. Fibrids can be prepared by precipitating a solution of the aromatic polyamide into a coagulant such as in apparatus of the type disclosed in U.S. patent 3,018.091.
• high temperature resistant floc short fibers, typically having a length of 2 to 12 mm and a linear density of 1-10 decitex. made of a material having a melting point higher than 320°C. such as aromatic polyamides. aromatic polyamide-imides. aromatic polyimides, polybenzimidazoles. etc.. or inorganic materials such as glass, ceramic materials, alumina, etc. Other high temperature resistant materials such as mica may also be present in relatively finely subdivided form.
• aromatic polyamide floc short fibers cut from fibers prepared by the processes described in U.S. patents 3.063.966. 3.133.138. 3,767,756, and 3.869.430.
• Conventional aromatic polyamide pressboard may be prepared by feeding an aqueous slurry of MPD-I fibrids and MPD-I floc to a cylinder paper forming machine whereby water is removed and multiple layers of fibrous material having a water content of 50-95% by weight of the wet sheet is built up to a wet lap of the desired thickness.
• the wet lap is cut from the cylinder, laid flat and pressed at 100-200°C. under a pressure of 10-60 kg/cm 2 .
• the resulting conventional pressboard usually has a high oil absorption of 20-50% by weight, a density of about 0.7 to 0.9 g/cm . a calculated void volume of about 35 to 50% by volume of the pressboard.
• mercury intrusion volume of about 0.30 to 0.50 cm 3 /g. both at low and high surface/volume, a ratio of total available absorption volume in cm 3 /g. V . to the mercury intrusion volume at low surface/volume.
• V ml . of about 1 and a compression set of 0.75 to 2.5 mm.
• the compression set desirably should be not less than about 0.12 mm or more than about 0.5 mm while maintaining an oil absorption of at least 8%.
• Pressboard with compression set values of less than about 0.12 mm do not have the combination of compressibility and resilience necessary to maintain proper spacing of electrical components in, e.g.. transformers.
• Pressboard with compression set values greater than 0.5 mm likewise do not maintain proper spacing of components.
• a low density pressboard having a calculated void volume of 30 to 60% prepared as described above is further dried, ultimately at a temperature of 270-320°C, until substantially no further moisture is evolved and then pressed at 270-320°C and a pressure of 8 to 350 kg/cm 2 , preferably followed by cooling under restraint, a pressboard having the desired properties is obtained.
• the drying is preferably accomplished by step-wise increase in temperature. Moisture evolution is facilitated by application and release of light pressure.
• the pressing is preferably at 275-300°C at 15 to 70 kg/cm 2 for at least 5 minutes but thick products may require pressing for longer times.
• More than one layer of low density pressboard may be combined during high temperature pressing. In this case. longer pressing times should be employed.
• the high temperature pressing should be above the glass transition temperature (T ) of the aromatic polyamide comprising the fibrids which in the case of the preferred poly(m-phenylene isophthalamide) fibrids is about 275°C.
• the pressboard of this invention is useful in clamping rings and in axial and radial spacers in oil filled electrical transformers.
• Products of this invention have a calculated void volume of 13 to 28% by volume of the pressboard. mercury intrusion volumes at low surface/volume. V ml , of less than 0.20 cm 3 /g and at high surface/volume. V mh , of 0.08 to 0.28 cm /g. an oil absorption by volume in cm3/g. V . of 0.08 to 0.28 and by weight of 8-24% and a total available absorption volume in cm 3 /g. V . equal to the largest of the values for V ml . V mh and V o , the ratio of V a to V ml being at least 1.1.
• Pressboard having a calculated void volume of more than 28% or a ratio of V a to V ml of 1.0 generally exhibits poor compression set. while pressboard having a calculated void volume of less than 13% or V mh less than 0.08 cm 3 /g generally exhibits poor oil absorption.
• the products of this invention have V a values which are quite different from V ml values, the ratio of these being at least 1.1 and as high as 4.
• Dry pressboard is cut into a rectangular sample measuring at least 10 cm x 10 cm (4 in x 4 in), preferably at least 20 cm x 20 cm (8 in x 8 in), making sure that the corners are cut square so that the upper and lower faces of the sample are of the same area and that the dimensions can be measured accurately.
• the length and width of the rectangular sample are measured to an accuracy of at least 0.25 cm (0.1 in).
• the thickness of the rectangular sample of pressboard is measured in at least ten places spaced substantially equally apart around all sides of the pressboard. away from the edges, using a micrometer caliper which contacts the sample with surfaces having a diameter of about 0.6 cm (0.25 in) at a pressure of about 0.1 kg/cm 2 (about 1.25 psi).
• the sample of pressboard is then weighed to the nearest 0.0001 g.
• the volume of the sample of pressboard V b is then calculated in cm 3 and the weight is divided by the volume to give the density in g/cm 3 .
• V b is the volume of the pressboard in cm 3 as determined above.
• V m is the total volume in cm of all the materials comprising the pressboard.
• V v is the remaining volume in cm 3 , which is taken as the void volume.
• V m is determined from the weights. and densities of each of the materials of which the pressboard sample is made. calculated as follows: where W f is the weight in g of the aromatic polyamide fibrids in the pressboard sample. w i is the weight in g of the floc (including any other non-fibrid high temperature resistant material) in the pressboard sample.
• the calculated void volume as a percentage volume, % V v is then calculated as follows: In the case of a 100% MPD-I pressboard sample having a weight in g of W b and a volume in cm 3 of V b . and since for this case the equation reduces to:
• the calculated void volume is a measure of all of the voids, both isolated voids and interconnected voids, in a sample of pressboard.
• the pressboard to be tested is cut into rectangular strips 3.8 cm (1.5 in) wide X 5.1 cm (2.0 in) long and a sufficient number of the strips are stacked to make a stack approximately 5.1 cm (2.0 in) high.
• the stack of samples is placed in an oven for 48 hrs. at 110°C. then taken from the oven and placed in a conventional machine for testing compressive properties, equipped for constant rate of crosshead movement and having a capacity of at least 10,000 kg (22.000 lb.) (e.g.. the Tinius Olsen Universal Testing Machine. Model 60 SDT. Servo-controlled. 60.000 lb. capacity.
• Super L UTM made by the Tinius Olsen Universal Testing Machine Co.. Inc.. Easton Rd.. Willow Grove.
• PA 19090 equipped with a Model MM Flat Bed X-Y Recorder manufactured by Houston Instruments. Inc. and Tinius Olsen Model D-2 and D-4 Deflectomers for accurately measuring the deflection of compressed samples at two different chart magnifications).
• the load is applied at the constant rate of 0.5 cm per min. (0.2 in. per min.) and released.
• a load of 680 kg (1.500 lb.). equivalent to 35 kg/cm 2 (3.448 kPa: 500 psi). is applied to the stack of samples, and the load is then immediately released to a load of 136 kg (300 lbs.). This load. equivalent to 7 kg/cm 2 (6 9 0 kPa: 100 psi). is designated as the bedding pressure.
• the stack of samples is next cycled to 1361 kg (3.000 lbs.), equivalent to 70 kg/cm 2 (6.895 kPa: 1.000 psi). returning to the bedding pressure. It is then cycled to 2,722 kg (6.000 lbs.), equivalent to 141 kg/cm2 (13.790 kPa; 2,000 psi), returning to the bedding pressure. Finally it is cycled to 4,082 kg (9.000 lbs.). equivalent to 211 kg/cm 2 (20.685 kPa: 3.000 psi). and back once more to the bedding pressure.
• the compression set is taken as the loss in height in mm (alternatively in mils) of the stack of samples, as measured by the deflectometer. upon the return to the bedding pressure after the final cycle. It is preferred to have the deflectomer readings continuously plotted on a chart so that the entire sequence of cycles is displayed on a graph for each sample tested.
• the 3.8 cm X 5.1 cm rectangular strips are stacked to a lesser height, preferably at least 2.55 cm (1.0 in.) high, and the deflection after the final cycle is multiplied by the appropriate factor to scale the result to correspond to the result which would be obtained from a stack 5.1 cm (2.0 in.) high.
• a conventional mercury porosimeter (Aminco Mercury 60,000 psig max. Newport Scientific Co.. Inc.. Silver Spring, MD 20910) is employed to determine the volume of mercury which can be forced into the pores, or interconnected voids, of a porous sample.
• a conventional mercury porosimeter (Aminco Mercury 60,000 psig max. Newport Scientific Co.. Inc.. Silver Spring, MD 20910) is employed to determine the volume of mercury which can be forced into the pores, or interconnected voids, of a porous sample.
• determinations are made both on low surface/volume samples and high surface/volume (subdivided) samples of the pressboard.
• the nominal weight of each sample tested is 0.3 g.
• an initial sample slightly heavier than 0.6 g and preferably rectangular in shape is cut from the pressboard to be tested.
• the initial sample is then cut down in size (e.g. with a pair of side-cutters) in a series of approximately 25 to 35 clean cuts straight through the pressboard near its edges to produce a corresponding number of fragments. leaving a preferably quadrilateral sample weighing about 0.3 g which is taken as the sample for the low surface/volume measurement.
• This low surface/volume sample should be of such shape that it will fit intact in the penetrometer bulb (sample chamber) of the porosimeter. if at all possible.
• the low surface/volume sample is prepared in the form of two or even three pieces which will fit in the bulb.
• the low surface/volume sample is weighed to the nearest 0.0001 g on glassine paper.
• a sufficient number of the pressboard fragments, preferably about 25 to 30. to weigh about 0.3 g are placed on glassine paper (preferably they are collected on the glassine paper as they are cut) as the high surface/volume (subdivided) sample.
• the subdivided sample is weighed to the nearest 0.0001 g.
• a weighed sample is placed in the open penetrometer bulb. After which the bulb is capped and evacuated until the vacuum gauge displays a pressure of 50 microns of mercury or less.
• the filling device is then tilted backward until its stop is reached. so that the tip of the penetrometer is immersed in mercury.
• the stopcock on the filling device is gradually opened to admit air to the system slowly, causing mercury to enter the penetrometer bulb. tapping the tubes to aid in wetting the sample with mercury. After total wetting has been achieved, the filling device is returned to vertical position. The penetrometer is then moved from the vacuum chamber to the pressure chamber.
• the pressure is then gradually increased. recording penetrometer readings at intervals as the pressure increases.
• the equipment is customarily provided with more than one pressure gauge, e.g. recording maximum values of about 350 kg/cm 2 (34 MPa: 5,000 psi) and about 4200 kg/cm 2 (414 MPa: 60.000 psi), and if so the equipment is switched over to the high pressure gauge at the appropriate time as the pressure increases.
• the penetrometer reading at 4200 kg/cm 2 ( 4 14 MPa: 60.000 psi) is recorded at the conclusion of the test.
• the mercury intrusion volume at 420 0 kg/cm 2 is determined from the penetrometer reading in accordance with the instructions provided by the manufacturer of the equipment. For a particular specimen of pressboard.
• mercury intrusion volume values in cm 3 /g (cm 3 of mercury at 4200 kg/cm 2 pressure per g of pressboard) are first determined to four decimal places, then rounded and finally reported to two decimal places both for the low surface/volume and high surface/volume (subdivided) samples. If desired, graphs of mercury intrusion volume values over the entire pressure range are constructed, based on the penetrometer readings taken at intervals throughout the test.
• the mercury intrusion volume at low surface/volume is designated by the symbol.
• v ml and the mercury intrusion volume at high surface/volume is designated by the symbol. V mh .
• the total available absorption volume, V a of a pressboard sample is taken as being equal to the largest of the values for V ml , V mh and V 0 (all values prior to rounding) for the sample. For any given sample of pressboard. V a is a measure of the volume in cm 3 per q of the interconnected voids in the sample which are accessible to penetration by liquids.
• V a /V ml The ratio, V a /V ml . is then calculated. using values of V a and V ml prior to rounding in making the calculation. In reporting the ratio, it is rounded to one decimal place.
• a value of this ratio equal to or greater than 1.1 is indicative of a structure of limited or partial accessibility of internal voids in the pressboard. a structure associated with good compression resistance of the pressboard when the calculated void volume of the pressboard is no more than 28%.
• the filaments were crystallized immediately after drawing by passing them over hot rolls at a temperature of about 340°C.
• the filaments so produced had a linear density of 2.2 decitex (2.0 denier). a tenacity of about 3.7 dN/tex (4.2 g/denier). an initial modulus of 70 dN/tex (79 gpd) and an elongation of 34%.
• the filaments were cut to floc having a length of 3.4 mm (0.135 in).
• An aqueous slurry was prepared containing 1. 0 Wt. % fibrids and floc having a composition of 60% of the above MPD-I fibrids and 40% of the above MPD-I floc.
• the slurry was held in an agitated vessel and then pumped to a double disc refiner (Beloit Jones Model 3000 20-inch Double Disc refiner, made by the Jones Division of the Beloit Corporation. Dalton. Massachusetts 01226). equipped with refining discs containing narrow bars and channels with surface dams.
• the plates of the refiner were positioned with a gap of 0.5 mm (20 mils) between the rotor and the stator plates. The rotor plates were operated at 900 rpm.
• the slurry was passed through a second refiner under the same operating conditions. After the two passes through the refiners the fibrids in the slurry were well reduced in size and well opened into fibrid films. while the floc fibers were well distributed among the fibrids.
• the slurry made in this way was then diluted to approximately 0.1% by weight solids and fed to a conventional cylinder wet paper-making machine upon which a continuous sheet of wet paper was made and transferred to an endless felt. the moisture content being adjusted by suction and pressure to about 400% based on solids (80% by weight based on the wet sheet). The weight of the solids in the wet paper was approximately 36 g/m 2 .
• the continuous wet sheet was next delivered to a forming roll. where it was wound continuously on a cylindrical tube until it overlapped about 70 times.
• a longitudinal cut was then made in the layered paper and the entire thickness of wet lap (wet layered paper) was then removed and placed between the platens of a hot press, the platens being maintained at 140°C and having been covered with wire screen to facilitate moisture removal.
• the press was loaded at contact pressure, and the pressure was then raised to and maintained for one hour at 35 kg/cm 2 (3450 kPa: 500 psi) while the platens of the press were maintained at 140°C.
• the product, herein designated as "Standard Pressboard”. was a low density aramid pressboard approximately 3.2 mm (126 mils) thick.
• V a for this Standard Pressboard sample was 0.42 cm 3 /g and the ratio V a /V ml was 1.1.
• a 30.5 cm X 30.5 cm (12 in X 12 in) square sheet of the "Standard Pressboard" prepared as in Part A above was predried at 150°C for at least 2 hours and then placed between the platens of a flat press (Machine No. 9175-M. Watson Stillman Press Division. Farrel Company. Emhart Machinery Group. 25 Main St.. Ansonia. Connecticut 06401). With the platens preheated to 280°C and maintained at that temperature. a pressure of 19.5 kg/cm 2 (1910 kPa: 277 psi) was applied to the "Standard Pressboard" for a total of 20 minutes, releasing the pressure for a few seconds and then reapplying it after a total of 1. 2. 3. 6. 12.
• Example 1A was an aramid pressboard approximately 2.45 mm (96.5 mils) thick (thickness range 2.35-2.53 mm). It was found to have a density of 1.11 g/cm 3 , a % V v of 20%, a compression set of 0.30 mm (12 mils), and an oil absorption of 12.71%.
• V o was 0.15 cm 3 /g
• V ml was 0.15 cm 3 /g (rounded from 0.1502).
• V mh was 0.17 cm 3 /g (rounded from 0.1700).
• V a for Sample 1A was 0.17 cm3/g and the ratio V a /V ml was 1.1.
• Example 1B Another sheet of predried "Standard Pressboard" was subjected to the same procedure. except that a pressure of 18.5 kg/cm 2 (1813 kPa: 263 psi) was applied in the press for a total of 20 minutes at 280°C.
• the product, designated as "Sample 1B”. was approximately 2.5 mm (98.7 mils) thick (thickness range 2.38 - 2.60 mm). It was found to have a density of 1.08 g/cm 3 . a % V of 22%. a compression set of 0.36 mm (14 mils), and an oil absorption of 12.19%. V o was 0.14 cm 3 / g.
• V ml was 0 .16 cm 3 /g (rounded from 0.1551). and V mh was 0.17 cm 3 /g (rounded from 0.1743).
• V a for Sample 1B was 0.17 cm 3 /g and the ratio V a /V ml was 1.1.
• the aligned stack was then placed immediately in a hot press having platens oil-heated to 280°C (535°F) and subjected to three 2-minute cycles of contact pressure (3.5 kg/cm 2 ) at 280°C followed by release of pressure.
• a one-minute cycle of pressure at 28 kg/cm 2 (2758 kPa; 400 psi) and quick release was followed by a one-minute cycle of pressure at 35 kg/cm 2 and quick release, after which pressure was applied at 35 kg/cm 2 for fifteen minutes while the platens were maintained at 280°C.
• the pressboard product was taken out hot and placed under contact pressure in a separate press, initially at room temperature and water-cooled to absorb the heat of the pressboard. to keep it flat while cooling.
• Example 2 The product, designated "Sample 2", was an aramid pressboard approximately 5.3 mm thick (210 mils). It was found to have a density of 1.12 g/cm 3 , a % V v of 19%, a compression set of 0.13 mm (5 mils), and an oil absorption of 9.3%.
• V was 0.11 cm 3 /g.
• V ml was 0.09 cm 3 /g (rounded from 0.0940), and V mh was 0.17 cm 3 /g (rounded from 0.1665).
• V a for Sample 2 was 0.17 cm 3 /g and the ratio V a /V ml was 1.8.
• a 46 cm x 81 cm (18 in x 32 in) rectangular sheet of 2.1-mm thick pressboard was placed without predrying in a press equipped for electrical heating and water cooling. Initially the press was at 66°C (150°F) and contact pressure, about 3.5 kg/cm 2 (345 kPa: 50 psi). The press was heated over about 20 minutes under the same contact pressure, with no intervals of pressure release, to about 280°C (about 535°F). The pressure was then increased to 35 kg/cm 2 (3448 kPa: 500 psi) and maintained at that pressure.
• Example 3 was an aramid pressboard approximately 1.6 mm thick (64 mils). It was found to have a density of 1.13 g/cm3, a % V v of 18%, a compression set of 0.13 mm (5 mils), and an oil absorption of 9.32%.
• V o was 0.11 cm 3 /g
• V ml was 0.06 cm 3 /g (rounded from 0.0553)
• V mh was 0.14 cm /g (rounded from 0.1390).
• V for Sample 3 was 0.14 cm 3 /g and the ratio V a /V ml was 2.5.
• Square sheets of low density pressboard were prepared in substantially the same manner as the "Standard Pressboard" of Part A of Example 1. with the following exceptions. Fibrids were refined and mixed with floc at the paper-making machine. Fifty sheets of wet paper were combined into a wet lap and the entire wet lap was cut into 20-cm (8-in) squares. In pressing the squares of wet lap at 140°C under a pressure of 35 kg/cm . the pressure was applied for 30 minutes rather than one hour. The low density pressboard so formed was 2.1 mm (81 mils) thick and had a density of 0.88 g/cm 3 . Its % V v was 36%.
• the low density pressboard was predried at 120°C in an oven for four hours and then placed between the platens of a flat press preheated to 280°C as in Part B of Example 1. Low pressure was applied briefly at first. with three cycles of release of the pressure to permit escape of the trapped gasses followed by reapplication of the pressure. A pressure of 53 kg/cm 2 (5171 kPa; 750 psi) was then applied for a contact time of 1 minute, the hot pressboard finally being cooled under restraint in a separate press.
• the product, designated as "Sample 4A”. was an aramid pressboard 1.75 mm (69 mils) thick and had a density of 1.04 g/cm 3 . Its % V v was 25%.
• V ml was 0.15 cm 3 /g (rounded from 0.1542) and V mh was 0.17 cm /g (rounded from 0.1712).
• the compression set was 0.20 mm (B.O mils), the oil absorption was 15.9% by weight of pressboard. and V o was 0.19 cm 3 /g.
• V a was 0.19 cm 3 /g and the ratio V a /V ml was 1.2.
• Sample 4B was an aramid pressboard 1.8 mm (71 mils) thick and had a density of 1.15 g/cm 3 . Its % V v was 17%. V ml was 0.05 cm 3 /g (rounded from 0.0486) and V mh was 0.15 cm 3 /g (rounded from 0.1452). The compression set was 0.147 mm (5.8 mils), the oil absorption was 9.7% by weight of pressboard. and V o was 0.11 cm 3 /g. For Sample 4B, V a was 0.15 cm 3 /g and the ratio V a /V ml was 3.0.
• low density pressboards were made which contained varying ratios of MPD-I fibrids and floc.
• the low density pressboards were made in substantially the same manner as the "Standard Pressboard" of Part A of Example 1 with the following exceptions.
• Fibrids were refined and then mixed with floc at the paper-making machine in the proportions given below.
• Wet paper was produced with the weight of the solids being approximately 60 g/m 2 . Thirty sheets of wet paper were combined into a wet lap which was cut into 20-cm (8-in.) squares and pressed.
• the low density pressboard was dried at 120°C for 4 hours and pressed at 280°C, under low pressure at first with brief cycles of release and reapplication of pressure, then for 10 min. at 8.8 kg/cm 2 (862 kPa: 125 psi.)
• the product, designated "Sample 5A” was an aramid pressboard approximately 1.9 mm (73 mils) thick, had a density of 1.04 g/cm 3 , a compression set of 0.21 mm (8.3 mils). an oil absorption of 13.7% by weight pressboard. and V o was 0.16 cm /g. % V v for sample 5A was calculated as 25%.
• V ml was 0.10 cm /g (rounded from 0.09 9 0).
• V mh was also 0.10 cm 3 /g (rounded from 0.0 996 ).
• V a was 0.16 cm 3 /g (the largest of the values for V ml , V o , and V mh ) and the ratio V a /V ml was 1.6.
• the procedure for preparing the low density pressboard was repeated, except that a mixture of 40% fibrids and 60% floc was used and that the pressure applied was 35 kg/cm 2 (3 4 50 kPa: 500 psi) for a period of 45 minutes at 140°C.
• the low density pressboard was approximately 2.6 mm (103 mils) thick and had a density of 0.78 g/cm 3 . % V was 43%.
• the low density pressboard was dried at 120°C for 4 hours and pressed at 280°C, under low pressure at first with brief cycles of release and reapplication of pressure, then for 10 min. at a pressure of 53 k g / cm 2 (5171 k P a). finally being cooled under restraint in a separate press.
• Example 5B The product. designated "Sample 5B". was an aramid pressboard approximately 2.0 mm (79 mils) thick, had a density of 1.02 g/cm 3 , a compression set of .15 mm (6.0 mils). an oil absorption of 17.1% by weight of pressboard. and V o was 0.20 cm 3 /g. % V v was 26%. V ml was 0.17 cm 3 /g (rounded from 0.1683) and V mh was 0.27 cm 3 /g (rounded from 0.2673). For Sample 5B. V a was 0 .27 cm 3 /g and the ratio V a /V ml was 1.6.
• the procedure for preparing the low density pressboard was repeated again, except that a mixture of 20% fibrids and 80% floc was used and that the pressure applied was 35 kg/cm 2 for a period of 45 minutes at 140°C.
• the low density pressboard was approximately 3.1 mm (123 mils) thick and had a density of 0.70 g/cm 3 % V v for this low density pressboard was 49%.
• the low density pressboard was dried as described above and pressed at 280°C, under low pressure at first with brief cycles of release and reapplication of pressure, then for 10 min. at 79 kg/cm 2 (7763 kPa; 1125 psi). The product, designated "Sample 5C".
• V a was 0.23 cm 3 /g and the ratio V a /V ml was 1.5.
• the procedure for preparing the low density pressboard was repeated once more. except that a mixture of 95% fibrids and 5% floc was used and that the pressure applied was 17.6 kg/cm 2 for a period of 1.5 hr at 140°C.
• the low density pressboard was approximately 1.9 mm (75 mils) thick and had a density of 0.90 g/cm 3 . % V v was 23%.
• the low density pressboard was dried as described above and pressed at 280°C. under low pressure at first with brief cycles of release and reapplication of pressure, then for 10 min at 8.8 kg/cm 2 .
• the product designated "Sample 5D".
• V a was 0.14 cm 3 /g and the ratio V a /V ml was 3.0.
• low density pressboards based partly on high-temperature resistant flocs other than MPD-I flocs were made.
• the low density pressboards were made in substantially the same manner as the "Standard Pressboard" of Part A of non-MPD-1 floc was blended with MPD-I floc having a cut length of 0.32 cm (0.125 in.) and the blend of flocs was mixed at the paper machine with refined fibrids in the proportions given below.
• Wet paper was produced with the weight of the solids being approximately 60 g/m 2 . Thirty sheets of wet paper were combined into a wet lap which was cut into 20-cm (8-in.) squares and pressed under the conditions given in Ex. 1. Part A.
• the low density pressboard was dried at 120°C for 4 hours and pressed at 280°C, under low pressure at first with brief cycles of release and reapplication of pressure, then at 53 kg/cm 2 (5171 kPa: 750 psi) for 10 min., the hot pressboard finally being cooled under restraint in a separate press.
• the product, designated as "Sample 6A” was a pressboard 2.2 mm (86 mils) thick having a density of 1.10 g/cm 3 . a % V v of 22%, a compression set of 0.27 mm (10.8 mils), an oil absorption of 10.8% by weight of pressboard. and a V o of 0.13 cm 3 /g.
• V ml was 0.08 cm 3 /g (rounded from 0.0787) and V mh was 0.12 cm 3 /g (rounded from 0.1151).
• V a for Sample 6A was 0.13 cm 3 /g and the ratio V a /V ml was 1.6.
• V ml was 0.06 cm 3 /g (rounded from 0.0576) and V mh was 0.14 cm 3 /g (rounded from 0.1424).
• V a for Sample 6B was 0.14 cm 3 /g and the ratio V a /V ml was 2.5.
• Example 1 The procedure of Example 1. Part B. was repeated, except that the pressure was increased to 53 kg/cm 2 (5171 kPa: 750 psi), the press again being maintained at a temperature of 280°C.
• This product. designated as "Control 1" had an oil absorption of only 2.03%. It was about 2.2 mm (87 mils) thick (thickness range 2.14-2.31 mm) and had a density of 1.21 g/cm 3 , a % V v of 12%. and a compression set of 0 . 3 0 mm (12 mils).
• V was 0.023 cm 3 /g
• V ml was 0.04 cm 3 /g (rounded from 0.0433).
• V mh was 0.09 cm 3 /g (rounded from 0.0889).
• V a was 0.04 cm 3 /g and the ratio V a /V ml was 2.05.
• V o was 0.11 cm 3 /g
• V ml was 0.17 cm /g (rounded from 0.1733 cm /g)
• V mh was also 0.17 cm3/g (rounded from 0.1723).
• V a was 0.17 cm 3 /g and the ratio V a /V ml was 1.0.
• Fibrids of MPD-I were prepared substantially as described in column 5. lines 34-57 of the same patent.
• the refined fibrids were then diluted further in water to a concentration of about 0.5%. and passed to a mixing "T" along with the above mentioned slurry of high modulus floc. at a ratio of fibrid to floc of about 1.55 to 1.0 (60% fibrids and 40% floc).
• the mixture was directed to the headbox of a Fourdrinier paper-making machine and then to a forming wire for production of a wet sheet.
• the wet sheet was then removed from the wire and passed through steam heated dryer cans to reduce the moisture content of the sheet to about 5% or less.
• the paper was then wound on a roll for further processing.
• the paper was removed from its roll, cut into 20-cm (8-in) squares, and then platen pressed to produce samples of 2-ply paper substantially as described in column 7, lines 6-11. of the same patent.
• the samples of 2-ply paper were pressed at 70.3 kg/cm 2 (689.5 kPa: 1000 psi) and 280°C for one minute.
• the resulting paper, designated as "Control 3A" had a thickness of about 0.25 mm (10 mils), a density of about 0.87 g/cm . and a % V v of 37% by volume of the paper.
• V ml was 0.28 cm 3 /g (rounded from 0.2842) and V mh was 0.18 cm 3 /g (rounded from 0.1818).
• the compression set was 1.0 mm (40 mils), the oil absorption was 35.3% by weight of paper, and V o was 0.41 cm 3 /g.
• V a was 0.41 cm 3 /g and the ratio V a /V ml was 1.5.
• Fibrids of MPD-I were prepared as described above for Control 3A and papers were prepared by combining the fibrid and the low modulus floc at a ratio of fibrid to floc of 1.5 to 1.0 (60% fibrid and 40% floc) in a wet 20-cm (8-in) square handsheet mold (e.g.. of the type made by Noble and Wood). Papers made in this way are considered to be essentially the same as papers made on a Fourdrinier paper machine. The wet sheets were removed from the 100 mesh screen of the handsheet mold and dried on hot sheet dryers to reduce the moisture content to about 5% or less. The sheets were then platen pressed to produce samples of 2-ply paper. They were pressed at 70.3 kg/cm 2 (689.5 kPa: 1000 psi) and 260°C for one minute.
• Control 3B The resulting paper, designated as "Control 3B” had a thickness of about 0.29 mm (11 mils), a density of about 0.77 g/cm3, and a % V v of 44% by volume of the paper.
• V ml was 0.58 cm /g (rounded from 0.5787) and V mh was 0.38 cm 3 /g (rounded from 0.3793).
• the compression set was 1.4 mm (54 mils), the oil absorption was 49.9% by weight of the paper. and V o was 0.58 cm 3 /g.
• V a was 0.58 cm 3 /g and the ratio V a /V ml was 1.0.
• Example 5 The procedure of Example 5 for preparing Sample 5D was repeated, using a mixture of 95% fibrids and 5% floc, except that the low density pressboard was prepared by applying a pressure of 35 kg/cm 2 (3450 kPa: 500 psi) for a period of 45 minutes at 140°C.
• the low density pressboard was approximately 1.7 mm (68 mils) thick and had a density of 1.00 g/cm 3 . % V v was 28%.
• the low density pressboard was dried at 120°C for 4 hrs and pressed at 280°C. under low pressure at first with brief cycles of release and reapplication of pressure, then for 5 min at 8.8 kg/cm 2 .
• Control 4 The product, designated "Control 4", was an aramid pressboard approximately 1.6 mm (62 mils) thick. had a density of 1.12 g/cm 3 , a compression set of 0.14 mm (5.5 mils), an oil absorption of 1.4% by weight of pressboard. and V o was 0.02 cm 3 /g. % V v was 19%. V ml was 0.01 cm 3 /g (rounded from 0.0141) and V mh was 0.02 cm 3 /g (rounded from 0.0173). For "Control 4". Va was 0,02 cm 3 /g and the ratio V a /V ml was 1.2.

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• 1985
  • 1985-03-12 BR BR8501096A patent/BR8501096A/pt not_active IP Right Cessation
  • 1985-03-12 AU AU39755/85A patent/AU578270B2/en not_active Expired
  • 1985-03-13 EP EP85301728A patent/EP0156587B1/de not_active Expired - Lifetime
  • 1985-03-13 MX MX204608A patent/MX167850B/es unknown
  • 1985-03-13 DE DE8585301728T patent/DE3581099D1/de not_active Expired - Lifetime
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  • 1985-03-13 ES ES541208A patent/ES8607451A1/es not_active Expired
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• 1995
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