CA1242853A - Pressboard and process for its preparation - Google Patents
Pressboard and process for its preparationInfo
- Publication number
- CA1242853A CA1242853A CA000476568A CA476568A CA1242853A CA 1242853 A CA1242853 A CA 1242853A CA 000476568 A CA000476568 A CA 000476568A CA 476568 A CA476568 A CA 476568A CA 1242853 A CA1242853 A CA 1242853A
- Authority
- CA
- Canada
- Prior art keywords
- pressboard
- weight
- floc
- volume
- fibrids
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Paper (AREA)
- Organic Insulating Materials (AREA)
- Casting Or Compression Moulding Of Plastics Or The Like (AREA)
Abstract
TITLE
IMPROVED PRESSBOARD AND PROCESS FOR ITS PREPARATION
ABSTRACT OF THE DISCLOSURE
High temperature resistant pressboard having a desirable combination of compression set values and oil absorption is prepared by a process whereby a low density pressboard is first prepared by forming a wet lap of multiple layers of a waterleaf containing 50-95% by weight water and pressing the wet lap at 100-200°C under a pressure of 10-60 kg/cm2, drying, ultimately at 270-320°C until substantially no further moisture is evolved and finally pressing at 270-320°C under a pressure of 8-350 kg/cm2 and optionally cooling under restraint.
IMPROVED PRESSBOARD AND PROCESS FOR ITS PREPARATION
ABSTRACT OF THE DISCLOSURE
High temperature resistant pressboard having a desirable combination of compression set values and oil absorption is prepared by a process whereby a low density pressboard is first prepared by forming a wet lap of multiple layers of a waterleaf containing 50-95% by weight water and pressing the wet lap at 100-200°C under a pressure of 10-60 kg/cm2, drying, ultimately at 270-320°C until substantially no further moisture is evolved and finally pressing at 270-320°C under a pressure of 8-350 kg/cm2 and optionally cooling under restraint.
Description
3 2~Z~353 TITLE
IMPROVED PRESSBOARD END PROCESS FOR ITS PREPARATION
DESCRIPTION
TECHNICAL FIELD
This inYention relates to an improved aromatic polyamide pressboard having increased resistance to compces6ion combined with relatively : high oil absorption characteristics. the invention al60 relate& to a proce6s for preparing the improved pre6~board.
BACKGROUND OF THE INVENTION
Pressboa~d prepared prom cellulo6ic materials has been known and commeccially used for many year6.
While the cellulosic pre66board is extremely u6eful.
its use at high tempecature it limited by the low thecmal 6tability of cellulo~ic material6.
More cecently. aromatic eolyamide fiber6 US patent 3,063.966 and 3,133,138)~ fibrid~ (U.S.
patent 2,999,708) and paper tU.S. patent 3,756,908) having excellent p~oper~ie6 at high temperature have become known. Pre6sboard compri6ed of aromatic polyamide fiber6 and fibrid6 i6 al60 known and can readily be prepared using the 6ame erocedure~ used in the preparation of cellulo~ic pre~6board.
Aromatic polyamide pre6~board has been found to be u6eful in many aeplication6. For example, it oil filled t~an~former~ it ha been found Jo have a 6uitably high oil absorption which contribute6 to good electrical in6ulating propectie~. However, or 60me u6e6, it i6 nece66ary that the pre6~board not only HT-2400-A 35 have a 6uitably high oil ab60rption but al60 provide ~2~21 3~i;3 resistance to compression so that the pressboard can provide suitable separation of electrically conducting component. It has been found that compaction processes as taught by the prior art either do not provide p~essboard products having adequate re6i6tance to compression, or that they do 60 only by providing a pressboard product which doe6 not have adequate oil absorption.
This invention provide6 an improYed aromatic polyamide pLessboard having a combination of good resistance to compression and adequate oil absorption. This invention also provide6 a process for the preparation of the improved pressboard.
BRIEF DESCRIPTION OF THE INVENTION
This invention provides a high density pres6board comprised of 20-95~ by weight aromatic polyamide fibrids and 80-5% by weight high temperature resistant floc, said pressboard having a calculated void volume of 13 to 28~ by volume of the pre6sboard, a thicknes6 of 0.5 to 50 mm, a mercury intrusion volume at low ~ur~ace~olume ,Vml, of les6 than 0.20 cm /g; a mercury intru6ion volume at high surface/volume, Vmh, of 0.08 to 0.28 cm3/g, a oil absorption by volume in cm3/g. VO, of 0.09 to 0.2B
and by weight 8-24~; and a total aYailable absorption volume in cm3/g, Va, equal to the largest of the values for Vml, Vmh, and VO: the ratio of V
to V~l being ae least 1.1; 6aid pre~board having a compre6sion jet (as hereinafter defined) of greater than 0.12 mm but no moee than O.5 mm. Preferably the pre66board is compri6ed of 50-70% by weight aromatic polyamide fibrid~ and 30-50% by weight high temperature re6i6tant floc. Preferably ehe high temperature re6istant floc consi~t6 of an aromatic polyamide and the pres~board has a density of 1.00 to Zi~5,3 1.20 g/cm3. Preferably 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 bloc and has a thickness of 1 to 10 mm, a density ox 1.02 to 1.17 g/cm3, most preferably 1.10 to 1.15 g/cm3.
The pressboard preferably ha a compres6ion set of 0.12 to 0.35 mm~ most preerably 0.20 to 0.30 mm.
The improved pressboard it prepared by a pcocess whereby an aqueous 61urry having 0.1 Jo 2% by weight total solids compri6ed of 20-95% by weight aromatic polyamide fibrids and 80-5% by weight high temperature re~i6tant floc having a length of 2 to lZ
mm., 6aid acomatic polyamide fibrid6 and high temperature resistant floc having a melting point higher than 3Z0C, the slurry i8 formed into a watarleaf having a water content of 50-95% by weight, the watecleaf i6 combined into multiple layers to form 20 a wet lap, the wet lap is pre66ed at 100 to 200C
under a pressure of 10 to 60 kg/cm2 to form a low density pre~6board having a calculated void volume of 30 to 60% by volume of the pre66board, the low density pres6board is dried, ultimately at 270-320C, until
IMPROVED PRESSBOARD END PROCESS FOR ITS PREPARATION
DESCRIPTION
TECHNICAL FIELD
This inYention relates to an improved aromatic polyamide pressboard having increased resistance to compces6ion combined with relatively : high oil absorption characteristics. the invention al60 relate& to a proce6s for preparing the improved pre6~board.
BACKGROUND OF THE INVENTION
Pressboa~d prepared prom cellulo6ic materials has been known and commeccially used for many year6.
While the cellulosic pre66board is extremely u6eful.
its use at high tempecature it limited by the low thecmal 6tability of cellulo~ic material6.
More cecently. aromatic eolyamide fiber6 US patent 3,063.966 and 3,133,138)~ fibrid~ (U.S.
patent 2,999,708) and paper tU.S. patent 3,756,908) having excellent p~oper~ie6 at high temperature have become known. Pre6sboard compri6ed of aromatic polyamide fiber6 and fibrid6 i6 al60 known and can readily be prepared using the 6ame erocedure~ used in the preparation of cellulo~ic pre~6board.
Aromatic polyamide pre6~board has been found to be u6eful in many aeplication6. For example, it oil filled t~an~former~ it ha been found Jo have a 6uitably high oil absorption which contribute6 to good electrical in6ulating propectie~. However, or 60me u6e6, it i6 nece66ary that the pre6~board not only HT-2400-A 35 have a 6uitably high oil ab60rption but al60 provide ~2~21 3~i;3 resistance to compression so that the pressboard can provide suitable separation of electrically conducting component. It has been found that compaction processes as taught by the prior art either do not provide p~essboard products having adequate re6i6tance to compression, or that they do 60 only by providing a pressboard product which doe6 not have adequate oil absorption.
This invention provide6 an improYed aromatic polyamide pLessboard having a combination of good resistance to compression and adequate oil absorption. This invention also provide6 a process for the preparation of the improved pressboard.
BRIEF DESCRIPTION OF THE INVENTION
This invention provides a high density pres6board comprised of 20-95~ by weight aromatic polyamide fibrids and 80-5% by weight high temperature resistant floc, said pressboard having a calculated void volume of 13 to 28~ by volume of the pre6sboard, a thicknes6 of 0.5 to 50 mm, a mercury intrusion volume at low ~ur~ace~olume ,Vml, of les6 than 0.20 cm /g; a mercury intru6ion volume at high surface/volume, Vmh, of 0.08 to 0.28 cm3/g, a oil absorption by volume in cm3/g. VO, of 0.09 to 0.2B
and by weight 8-24~; and a total aYailable absorption volume in cm3/g, Va, equal to the largest of the values for Vml, Vmh, and VO: the ratio of V
to V~l being ae least 1.1; 6aid pre~board having a compre6sion jet (as hereinafter defined) of greater than 0.12 mm but no moee than O.5 mm. Preferably the pre66board is compri6ed of 50-70% by weight aromatic polyamide fibrid~ and 30-50% by weight high temperature re6i6tant floc. Preferably ehe high temperature re6istant floc consi~t6 of an aromatic polyamide and the pres~board has a density of 1.00 to Zi~5,3 1.20 g/cm3. Preferably 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 bloc and has a thickness of 1 to 10 mm, a density ox 1.02 to 1.17 g/cm3, most preferably 1.10 to 1.15 g/cm3.
The pressboard preferably ha a compres6ion set of 0.12 to 0.35 mm~ most preerably 0.20 to 0.30 mm.
The improved pressboard it prepared by a pcocess whereby an aqueous 61urry having 0.1 Jo 2% by weight total solids compri6ed of 20-95% by weight aromatic polyamide fibrids and 80-5% by weight high temperature re~i6tant floc having a length of 2 to lZ
mm., 6aid acomatic polyamide fibrid6 and high temperature resistant floc having a melting point higher than 3Z0C, the slurry i8 formed into a watarleaf having a water content of 50-95% by weight, the watecleaf i6 combined into multiple layers to form 20 a wet lap, the wet lap is pre66ed at 100 to 200C
under a pressure of 10 to 60 kg/cm2 to form a low density pre~6board having a calculated void volume of 30 to 60% by volume of the pre66board, the low density pres6board is dried, ultimately at 270-320C, until
2~ sub6tantially no further moisture is evolved and finally pces~ed at 8 to 350 kg/cm2 at 270-3~0C.
Preferably the temperature i6 275-300C. Most preferably, the final pre66ing i6 at 275-285C and the pre6~Ure i8 15 to 70 kg/cm2. Pceferably the 30 prefi6board i6 cooled undec re6~raint. Preferably the hiqh temperature resi6tant floc con~ist~ of an aromatic polyamide. Preferably the aromatic polyamide fibrids and the high temperature cesi6tant floc con6i6t of poly~m-phenylene isophthalamide)~
~5 ~2~2~35~
DETAILED DESCRIPTION OF T E INVENTION
Definitions By "aromatic polyamide is meant non~usible polyamides whecein the amide group, i.e., the ., .
- C - N -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 cing of separate aromatic ring radicals. The term "aromatic ring" is defined herein as a carbocyclic ring possessing ee~onance.
By "aromatic polyamide fibrids~ meant small, nongranular, nonrigid ibrous or film-like particle6 of an aromatic polyamide having a melting point higher than 320C. Two of their three dimensions are of the order ox microns. Their smallnes6 and suppleness allows them to be deposited in phy6ically entwined configurations 6uch a 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
Preferably the temperature i6 275-300C. Most preferably, the final pre66ing i6 at 275-285C and the pre6~Ure i8 15 to 70 kg/cm2. Pceferably the 30 prefi6board i6 cooled undec re6~raint. Preferably the hiqh temperature resi6tant floc con~ist~ of an aromatic polyamide. Preferably the aromatic polyamide fibrids and the high temperature cesi6tant floc con6i6t of poly~m-phenylene isophthalamide)~
~5 ~2~2~35~
DETAILED DESCRIPTION OF T E INVENTION
Definitions By "aromatic polyamide is meant non~usible polyamides whecein the amide group, i.e., the ., .
- C - N -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 cing of separate aromatic ring radicals. The term "aromatic ring" is defined herein as a carbocyclic ring possessing ee~onance.
By "aromatic polyamide fibrids~ meant small, nongranular, nonrigid ibrous or film-like particle6 of an aromatic polyamide having a melting point higher than 320C. Two of their three dimensions are of the order ox microns. Their smallnes6 and suppleness allows them to be deposited in phy6ically entwined configurations 6uch a 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.
By "high temperature re6istant floc" is meant short fiber6, typically having a length of 2 to lZ mm and a linear density of 1-10 decitex, made of a material having a melting point higher than 320C, 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 material6 such as mica may also be pre6ent in rela~iYely finely subdivided form.
~.Z4 28~3 By aromatic polyamide floc" i6 meant 6hort fibers cut from fibecs prepared by the proce~e6 described in U.S. patents 3,063,966, 3,133,13B, 3,767,756, and 3,869,430.
Conventional aromatic polyamide pre~sboard may be prepared by feeding an aqueous 61urcy of MPD-I
fibrids and MPD-I floc to a cylinder paper forming machine whereby water is removed and multiple layers of fibrous mateEial having a water content of 50-95%
by weight of the wet sheet it built up to a wet lap of the desired thickness The wet lap it cut f rom the cylinder, laid flat and pressed at 100-200C, under a pressure of 10-60 kg/cm . The resulting conYentional pressboard usually ha a high oil absorption of 20-50% by weight, a den6ity of about 0.7 to 0.9 gem a calculated void volume of about 35 to 50% by volume of the pressboard, mercury intru6ion volume of about 0.30 to 0.50 cm3/g, both at low and high 6urface/volume, a ratio of total available ab60rption volume in cm3/g, Va, to the mercury intru6ion volume at low surface/volume, Vml, of about 1 and a compres6ion 6ee of 0.75 to 205 mm.
However, for 60me uses, 6uch a6 spacers used in oil filled tran6former6, the comp~e~6ion 6et desirably 6hould be not les6 than about 0.12 mm or more than about 0.5 mm while maintaining an oil ab60retion of at lea6t 8~. Pres6board with compce6sion set value6 of lest than about 0.12 mm do not have the combination of compressibility and re6ilience nece~ary to maintain eroPer 6pacing of electrical component in, e.g., t~an6former~.
Pre66board with compre6~ion 6et values greater than 0.5 mm likewise do not maintain proper spacing of components.
2~3 The above desired properties are provided by the product of this invention. It has been found that when a low den6ity pressboard having a calculated void volume of 30 to 60% prepared as described above is further dried, ultimately at a temperature of 270-320C, until substantially no further moisture is evolved and then pressed at 270-320C and a pre6sure of 8 to 350 kg/cm2, preferably followed by cooling under restraint, a pres~boald having the desired properties is obtained. The drying i8 preferably accomplished by step-wi~e increase in temperature.
Moisture evolution is facilitated by application and release of light pressure. In general, the pre6sing is preferably at 275-300C at 15 to 70 kg/cm2 or at least 5 minute but thick product6 may require pressing for longer times. More than one layer ox low density pressboard may be combined during high temperature pressing. In this case, longer pressing times 6hould be employed. Preferably the high temperature pres6ing should be above the glass tran6ition temperature (~g) of the aromatic polyamide comprising the fibridfi which in the case of the prefereed poly(m-phenylene isophthalamide) fibrids i6 about 275C.
It has been found that the proce6s described above, wherein a wet lap i8 formed of multiple layers of waterleaves having a water content of 50-95~ and the wet lap is pressed at 100-200C under a pressure of 10-60 kg/cm2 ts pcepare a low density pressboard 30 having a calculated void Yolume of 30-60%, and the low density pressboard i8 then dried and pres6ed again at 270-320C under a pres6ure of 8-3~0 kg/cm , is essential for obtaining a pressboard product exhibiting good re6i6tance to compression as jell a6 35 adequate oil ab60rption. If the low density ~2~3~3 pressboard has a calculated void volume of less than 30%, the oil ab60rption ox the f inal pres6board product tend6 to be very poor.
The pre6sboard of thi6 invention i8 u~e~ul in clamping rings and in axial and radial 6pacer6 in oil f illed electrical tran6formers.
Product of this invention have a calculated void volume ox 13 to 28~ by volume of the pressboard, mercury intrusion Yolumes at low surface/volume, Vml, of less than 0.20 cm3/g and at high surface~volume, Vmh, of 0.08 to 0.28 cm3/g, an oil ab60rption by volume in cm3~g, VO, ox 0.08 to 0.28 and by weight of 8-24~ and a total available absorption volume in cm3/g, Va, equal to the lS largest of the value for Vml, V~h and VO, the ratio ox Va to Vml being at least 1.1. Pressboard having a calculated void volume of more than 28~ or a ratio of Va to Vml of 1.0 generally exhibit6 poor compres6ion set, while pre~6board having a calculated 20 void volume of le6s than 13~ or Vmh le66 than O.OB
cm3/g generally exhibits poor oil absorption. The product6 of thi6 invention have Va values which are quite different from Vml value6, the ratio of these being at least 1.1 and a6 sigh a 4.
2s TESTS
Density. Dry pre66board it cut into a rectangular 6ample mea6uring at least 10 em x 10 cm (I
in x 4 in), preferably at least 20 cm x 20 cm t8 in x 30 8 in3, making sure that the ~orner6 are cut square 60 ehat the upper and lower faces of the 6ample are of the Rame area and that the dimen~ion6 can be measured accurately. The length and width of the rectangular 6ample are mea6ured to an accuracy of at lea6e 0.25 cm ~5 tO.l in). The thickne~6 of the rectangular sample ox ~2~5,~
pces6board i8 measured in at least ten places 6paced 6ubstantially equally apart around all sides of the pressboard, away from the edges, using a micrometer caliper which contacts the sample with 6urfaces having a diameter of about 0.6 cm (0.25 in) at a pre~6ure of about 0.1 kg/cmZ (about l.Z5 psi), to an accuracy of at least 0.00025 cm (0.1 mil), averaging the ten thickness measurements. The sample of pre~sboard is then weighed to the nearest O.OOol g. The volume of the sample of pressboard Vb is then calculated in cm and the weight i5 divided by the volume to give the density in g/cm3.
Calculated Void Volume. The void volume in cm3, Vv, of a 6ample of the pres~board i6 detecmined from the relationship Vb = Vm V~, or VV = Vb - Vm. where Vb is the volume of the pre6~board in cm3 a6 determined above, Vm i8 the total volume in cm3 of 20 all the materials comprising the pres6board, and Vv is the retaining volume in cm3, which it taken as the void volume. Vm is determined from the weight6 and densitie6 of each of the materials of which the pre6sboard samele it made, calculated a follow6:
V = Wf I , where 1.38 g/cm I
Wf is the weight in g of the aromatic polyamide fibrids in the pressboard 6ample, Wi it the weight in g of the floc (including any other non-fibrid high temperature re6i~tant ma~erial~ in the pre6~board ample, and Pi it the density of the material of which the floc is made tl.38 g~cm3 for MPD-I and 1.44 g~cm3 for polytp-phenyl~ne terephthalamide)~.
35 when there i6 more than one kind of floc (or other ~2428~3 high temperature resistant material such a6 mica), Wi/pi i8 calculated as follow6:
Wi Wl , W2 +, . . Wn Pi Pl P2 Pn 5 where i = 1, ..., n The calculated void volume a6 a percentage volume, Vv, i6 then calculated as follow6:
% Vv =11 m] x loo = V~ ox 100 In the case of a 100% MPD-I pcessboard 6ample having a weight in g of ~b and a volume in cm3 of Vb, and since for this case Ym = Wb 1.38 g a the equation reduces to:
VV =Ll - Wb x 100 Vb~1.38 g/cm3 The calculated void volume it a mea~u~e of all of the voids, both isolated void and interconnected voids, in a sample of pressboard.
Oil Absorption. This test i6 carried out in accordance with the method described by the International Electrotechnical Commi66ion, IEC
Standard, Publication 641-~, First edition (1979), "Specification for pres6board and pce6spaper for electrical purposes, Part 2: Method6 of test," page6 29 and 31 (section 17), publifihed by Bureau Central de la Commi6sion Electrotechnique Internationale Geneva, Switzerland. The result it expre6sed Jo the neare6t 0.1% as a percentage by weight oil ab60rption on the original ma66 of the pres~board 6ample tested. The oil absorption by volume in cm3/g, VO, i6 when calculated by dividing the percentage by weighe oil ab60rption by the den6ity of ehe 6ample of pre~6board. VO values are initially reported to the 28~3 same number of significant ~igure6 as the percentage by weight oil absorption, then rounded to two decimal places.
Compression Set. The pre6sboard to be te6ted 5 i6 cut into rectangular ~trip6 3.8 cm (1.5 in) wide X
5.1 cm (2.0 in) long and a sufficient number of the 6trips are tacked to make a 6tack approximately 5.1 cm (2.0 in) high. The tack of sample6 it placed in an oven for 4~ hr~. at 110C, then taken from the oven and placed in a conventional machine for testing compressive properties, eguipped for constant rate of crosshead movement and having a capacity of at least 10,000 kg (22,000 lb.) (e.g., the Tiniu~ Olsen Universal Testing Machine, Model 60 SDT, Servo-controlled, 60,000 lb. capacity, Super L U~M, made by the Tiniu~ 016en Universal Testing Machine Co., Inc., Easton Rd., Willow Grove, PA 19090 equipped with a Model MM Flat Bed X-Y Recorder manufactured by Houston Instrument6, Inc. and Tiniu6 Olsen Model D-2 and D-4 Deflectomer~ for accurately measuring the deflection ox compre6sed 6ample6 at two different chart magnifications. In carrying out the test, the load i6 applied at the constant rate of 0.5 cm per mix. (0.2 in. per min.) and relea6ed. A load of 680 kg (1,500 lb.), equivalent Jo 35 kg~cm2 (3,448 kPa:
500 p5i), i6 applied Jo the 6tack of samples, and the load it the immediately released to a load of 13S kg (300 lbs.). Thifi load, equivalent to 7 kg/cm~ (690 kPa; 100 p6i), it designated a the bedding pressure, and the load i5 releafied to this bedding pres6ure between each cycle. The stask of ~ample6 ifi next cycled to 1361 kg (3,000 lb~.), equivalent to 70 kg~cm2 (6,B95 kPa: 1,000 psi), returning to the bedding pre66ure. It it then cycled to 2,722 kg (6,000 lb6.), equivalent to 141 kg/cm2 (13,790 kPa;
~24 2,000 psi), retucning to the bedding pre~ure.
Finally it is cycled to 4.082 kg (9,000 lb~.), equivalent to 211 kg/cm2 (20,685 kPa: 3,000 pi and back once more to the bedding pres6ure. The compression set it taken as the lows in height in mm (alternatively in mils) ox 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 reading6 coneinuously plotted on a chart 80 that the entire sequence of cycle it displayed on a graph f or each sample tested.
If the amount of sample material is limited, the 3.~ em 5.1 cm rectangular 6trip6 are 6tacked 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 re6ult to correspond to the result which would be obtained fcom a tack 5.1 cm (2.0 in.) high.
Merc~Ey Intrusion Yolume In this determination a conventional mercury poro6imeter tAminco Mercury 60,000 pig max, Newport Scientific Co., Inc., Silver Spring, MD 20910~ i6 employed to determine the volume of mercury which Jan be forced 25 into the pores, or interconnected void6, of a porou6 6ample. To determine whether the 6urface area of a given weight of the pre6~board ha an effect on the volume of mercury which can be forced into it6 pore6, determination are made both on low æur~ace~volume 30 samples and high ~urface/volume ~6ubdivided) ample of the pres~board.
The nominal weight of each 6ample te6ted it 0.~ g. To prepare the low 6ucfaceivolume and high 6urface/volume 6ample6, an initial sample 61ightly 35 heavier than 0.6 g and preferably rectangular in shape e 11 is cut from the pre~sboard to be tested. The initial sample is then cut down in size ~e.g. with a pair of side-cutter6) in a series of approximately 25 to 35 clean cuts stcaight through the pressboard near its s edges to produce a corresponding number of ~ragment6.
leaving a preferably quadrilateral sample weighing about 0.3 g which is taken as the sample for the low ~urface/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. If the sample it very thin and a jingle piece weighing 0.3 g which will fit in the penetrometer bulb cannoe be preparad, the low ~urface/volume sample is prepared in the form of two or even three eiece~ which will fit in the bulb.
The low sur~ace/volume sample is weighed to the nearest 0.0001 g on glassine paper. A sufficient number of the pres~board fragments, preferably about 25 eO 30, to weigh about 0.3 g are placed on gla~sine paper (preferably they are collected on the glassine paper as they are cut) a6 the high ~urface/volume (subdivided) sample. The su~diYided sample is weighed to the nearest O.OOOl g.
To conduct the determination, a weighed sample iB placed in the open penetrometer bulb, after which the bulb i6 capped and evacuated until the vacuum gauge display6 a pres6ure of 50 microns of mercury or lest. The filling device i6 then tilted backward until it stop i6 reached, Jo thae the eip of the penetrometer it immersed in mercury. The stopcock on the filling device i8 gradually opened to admit air to the 6y8te~ slowly, causing mercuLy to enter the penetrometer bulb, zapping the tube to aid in wetting the sample with mercury. After total weteing ha6 been achieved, the filling device it returned to vertical ~z~
position. The penetLometer is then moved from the vacuum chamber to the pressure chamber.
The pressure is then gradually increa6ed, recording penetrometer reading6 at interval6 as the S pressure increases. The equipment is customarily provided with more than one pressure gauge, e.g.
recording maximum values of about 350 kg/cm (34 spa; S,000 pi) and about 4200 kg/cmZ (414 MPa:
60,000 psi), and if 60 the equipment it 6witched over to the high pressure gauge at the appropriate time a6 the pressure increases. The penetrometer reading at 4200 kg/c~2 (414 MPa, 60,000 psi) i6 recorded at the conclusion of the text. The meccury intrusion volume at 4200 kg/cm2 is determined from the penetrometer reading in accordance with the instcuceion6 provided by the manufacturer of the equipment. For a pacticular 6pecimen of pres6board, mercury intrusion volume value6 in cm3/g (cm3 of mercury at 4200 kg/c~2 pressure per g of pre6sboard) are first determined to four decimal places, then rounded and finally reported Jo two decimal places both for the low 6urface/volume and high 6urface/volume (6ubdivided) 6a~ple6. If de6ired, graph6 of mercury intrusion Yolume values oYer the entire pressure range are constructed, based on the penetrometer reading6 taken at interval6 throughout the te6t. The mercury intru6ion volume at low 6urface/volume it designated by the 6ymbol, Vml, and the mercury intru6io~ volume at high 6urfaoe/volume it de6ignated by the 6ymbol, Vmh Total Available Ab~orDtion Volume. The total available ab60~ption volume, Va, of a pre~6board sample it taken a being equal So the largest of the value6 for Vml, V~h and VO (all ~alue6 prior to rounding) fox the sample. For any given sample of s 13 pressboard, Va is a measure of the volume in cm3 per g of the intecconnected voids in the sample which are accessible to penetration by liquids.
The ratio, Va/Vml, is then calculated, using values of Ya and Vml 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 ox a ~tructu~e of limited oc partial accessibility ox internal voids in the pressboard, a 6eructure associated with good compression resistance of the pressboa~d when the calculated void volume of the pressboard is no more than 28%.
A. _Pceparation of "Standard Pres6board"
Filaments of poly(m-phenylene isophthalamide) (MPD-I) having an inherent visco6ity of 1.5 were dry spun from a solution containing 19~ MPD-I, 70%
dimethylacetamide tDMAc), gt calcium chloride, and 2~ -water. On leaving the drying tower the a~-~pun filaments were given a preliminary wa6h with water Jo thaw they contained about 60t DMAc, 15% calcium chloride, and 100-150S waxer, based on the weight of dry polymer. The filaments were washed and drawn 4X
at 90C in a counter-current extraction-draw process in which the calcium chlsride determined as chloride content and DMAc contene were ceduced to about 0.1 and 0.5%, respectively. The filaments were crystallized immediately after drawing by passing them over hot roll6 at a temperature of about 340C. The filament 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 ox 70 dN/tex (79 gpd~ and an elongation of 34%. the filament6 were cut to floc having a length of 3.4 mm ~0.135 in).
~Z42BS3 Fib~ids of MPD-I having an inherent viscosity of 1.5 were prepared ~ub6tantially a6 described by ~ro~s in U.S. Patent 3,756,908, issued September 4, 1973, column 5 line 34-54, stopping short of the refining step.
An aqueous slurry was prepared containing 1.0 wt. ibid and floc having a composition of 60% of the above MPD-I fibrid~ and 40~ of the above MPD-I
floc. The slurry was held in an agitated vessel and then pumped to a double disc refine (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 lS dams. The plate ox the refine were positioned with a gap of 0.5 mm (20 mil6~ between the rotor and the 6tator plates. The roeor plates were operated at 900 rpm. After passing through the refiner, the filurry was pasted through a second refiner under the tame Z0 operating conditions. After the two passe through the refiners the fib~id~ in the slurcy were well reduced in size and well opened into fib~id films, while the floc fiber were well di6tributed among the ibrids. The 6 lurry made in this way was then diluted ZS to approximately 0.1% by weight solid and fed to a conventional cylinder wet paper-making machine upon which a continuous sheet of wet paper wa6 made and transferred Jo an endle~6 felt, the moi6ture content being adjusted by fiuc~ion and pressure to about 400%
30 based on solids (80~ by weight cod on the wet 6heet). The weight of the olid~ in the wet paper was approximately 36 g/m . The eontinuou~ wee 6hee~ way next delivered to a forming roll, where it was wound continuously on a cylindrical tube until it overlapped about 70 time. A longitudinal cut was then made in the layered paper and the entire thicknes6 of wet lap (wet layered paper) was then removed and placed between the platens of a hot press, the platen6 being maintained at 140C and having been covered with wire 6c~een to facilitate moisture removal. The pre66 way loaded at contact pressure, and the pre6sure was then raised eo and maintained for one hour at 35 kq~cm2 (3450 kPa; 500 psi~ while the platens of the pre66 were maintained at 140C. The product, herein designated as "Standard Pressboard", was a low density aramid pre66board approximately 3.2 mm (lZ6 mils) thick. It was found to have a density of 0.~2 g/cm3, a calculated void volume, % Yv, of 41~ by volume of the pressboard, a co~pre6sion c of 2.13 em (8~ mil6), and an oil absorption of 32.5%. V0 was 0.38 cm3~g, V~l was 0.38 cm3/g (rounded from 0.3791), and Vmh was 0.42 cm3/g (rounded from 0.4197) Va for this Standard Pces6board 6ample wa6 0.42 cm /g and the ratio V /V 1 way 1 1 B. Preparation of ComPression-Resistant Pre66board A 30.5 cm X 30.5 cm (12 in X 12 in) square sheet of the "Standard Pre66board" prepared a6 in Part A above wa6 predried at 150C for at lea6t 2 hour6 and then placed between the platen6 of a flat ere66 tMachine No. 9175-M, Wat60n Stillman Pres6 Divi6ion, Farrel Company, Emhart Machinery Group, 25 Main St., An60nia, Connecticut 06401). With the plateRs preheated to 280C and maintained at that temperature, a pre6~ure of 19.5 kg~cm2 (1910 kPa; 277 p6i) wa6 appl;ed to the "Standard Pre6~board~' for a total of 20 minute, relea6ing the p~e~6ure for a few second and then reapplying it aster a total ox 1. 2, 30 6, 12.
and 16 minute6 to permit e6cape of any trapped ga6es.
After a total of 20 minute6 of hot pce66ing, the pre~sboard wa6 taken out hot, placed in another pre66 285~
at room temperature, and allowed to cool under a pressure ox 2.~ kg/cm2 t276 kPa: 40 psi), jut ~ufficiènt to keep the pressboard flat while cooling.
The product. designated as "Sample lA", was an aramid pre6sboard approximately Z.45 mm (96.5 mil6) thick ~hicknes~ range 2.35-2.53 mm). It was found to have a density of 1.11 g/cm3, a % Vv of 20~, a compre~6ion 6et of 0.30 mm (12 mils), and an oil absorption ox 12.~ . V0 was 0.15 cm /g, Vml 0 way 0.15 cm /~ (rounded from 0.1502), and V was mh 0.17 cm /g (rounded from 0.1700). Va for Sample lA way 0.17 cm /g and the ratio Va/Vml was 1.1.
Another 6heet of predried "Standard Pres6board" way subjected to the same procedure, except that a pressule of 18.5 kg/cm2 (1813 kPa, 263 p6i~ was applied in the press for a total of 20 minutes at 2B0C. The product, designated as "Sample lB", was approximately 2.5 mm (~8.7 mill) thick (thickness range 2. 3a - 2.60 mm). It was found to have a density of 1.08 g/cm3, a S Vv of 2Z%, a compression set of 0~36 mm (14 mils), and an oil ab60rption of 12.19%. V0 way 0.14 cm3/g, Vml way 0.16 cm /g (rounded from 0.1551), and Vmh was 0.17 cm /g (rounded from 0.1743). Va for Sample lB was 0.17 cm /g and the ratio Va/Vml was 1.1.
EXAMPLE Z
Two 46 cm X 122 cm (18 in x 48 in) rectangular sheets of "Standard Press~oard", prepared substantially as described in Paet A of Example 1 but having a thickness of 3.0 mm (llB mils), were aligned in a tack above and below a 46 cm x 122 cm 6heet of 1.6-mm thick "Standard Pres~board", similarly prepared except what proportionately fewer overlap of wet papeL were wound on ehe cylindrical coll in the ~2~3~i,3 ~o~ming step. All of the 6heet6 were predried at 150C just beore worming the tack. The aligned tack was then placed immediately in a hot press having platens oil-heated to 280C (535F) and subjected to three 2-minute cycle of contact pre66ure (3.5 kg/cm2) at 2B0C followed by release of pressure. A one-minute cycle of pre~6ure at 28 kg/cm~ (2758 kPa: 400 p6i) and quick relea6e way hollowed by a one-minute cycle of pre6sure at 35 kg/cmZ and quick Eelease, after which pre66ure wa applied at 35 kg/cmZ for fifteen minute6 while the platens were maintained at 2~00C. The pre6sboard product was taken out hot and placed under contact pressure in a separate press, initially at room temperature and water-cooled to ab60rb the heat of the pressboard, to keep it flay while cooling. The product, designated "Sample 2", wa6 an aramid pressboard approximately 5.3 em thick (210 mils). It was found to have a den6ity of 1.12 g~cm3, a % Vv 20 of 19%, a compre6sion 6et of 0.13 mm (5 mils), and an oil ab60rpt on of 9.3%. V0 wa6 0.11 cm3~g, Vml was 0.09 cm ~g (rounded from 0.0940), and Vmh wa6 0.17 cm ~g (rounded from 0.1665). Va for Sample 2 wa6 0.17 cm ~g and the ratio VaJVml wa6 1.8.
A 46 cm x 81 cm l in x 32 in) rectangular 6heet of 2.1-mm thick pre66board, prepared ~ubstan~ially like the "Standard Pre~6board" ox Part A
30 of Example I, except that proportionately fewer overlap6 of wet paper weee u6ed, a placed without predrying in a pre~6 equipped for electrical heating and water cooling. Initially the pres6 wa6 at 66C
(150F) and contact pres6ure, about 3.5 kg/c~2 (345 35 kPa: 50 psi). the pre~6 wa6 heated over about 20 so minutes under the tame contact pressure. with no interval of pcessure release, to about Z80C (about 535E). The pressure was then increa6ed to 35 kg/cm (3~48 kPa; 500 psi) and maintained at that pressure, with no relea6e of pres~u~e, for 12 ~inute6 while the pres6 way maintained at 280C. The electrical heating way then discontinued and the pre6s was then cooled back down to 66C with circulation of cool water over a 20-minute period while the pressure lO was maintained at 35 kg/~m2. The product, designated "Sample 3", was an aramid pre~board approximately 1.6 em ehick (64 mil6). lt way found to have a density of 1.13 g/~m3, a % V~ of lB~, a compce8sion 8et of 0.13 mm (5 mil6), and an oil absorpt on of 9.32~. V0 way 0.11 cm3/g, Vml was 0.06 cm /g (rounded prom 0.0553), and Vmh was 0.14 cm /g (rounded from 0.1390). V or Sample 3 way a 0.14 cm~/g and the ratio Va/Vml way 2.5.
Square ~heet6 of low density pre66board were preeaced in sub6tantially the 6ame manner as the "Standard Pressboard~' of Part A of Example l, with the following exception6. Fibrids were refined and mixed 2S with f loc at the paper-making machine. Fifty 6hee~6 of wet paper were combined unto a wet lap and the entire wet lap way jut into ~0-cm (8-in) square. In pressing the 6quare~ of wet lap at 140C under a pre~6ure of 35 kg/cm2, the pressure wa6 applied for 30 30 minute6 rather than ona hour. The low density pre~6board 80 formed way 2.1 mm (81 mill thick and had a den6ity of 0.88 g/cm3. It6 % Vv wa6 36~.
The low density pre66board was predried a lZ0C in an oven for four hour6 and then placed between the ~5 platen6 of a flat pre6s preheated to 280~C a6 in a 19 ~4~28~
Part B ox Example I. Low pressure was applied briefly at fiest, with three cycles ox celease of the ~re6sure to permit escape of the trapped gasses followed by reapplication ox the pre6sure. A pressure of 53 kg/cm2 (5171 kPa; 750 psi) was then applied or a contact time of 1 minute, the hot pressboard finally being cooled under r~&traint in a separate press. The product, designated a "Sample 4A", was an aramid pres~board 1.75 mm (69 mils) thick and had a density ox 1.04 gem It6 % Vv was 25%. Vml way 0.15 cm3/g (rounded f rom 0.1542) and V~h was 0.17 cm /g (rounded from 0.1712), The compLession set was 0.20 mm (8.0 mils), the oil absorption was 15.9t by weight of pressboard, and VO was 0.19 cm3/g. For Sample 4A, Va was 0~19 cm /g and the ratio Va/V~l was 1.2.
Other 20-cm square 6heets of low density pres~board were prepared in the tame manner, except that the weight of the 601ids in the wet paper was approximately 60 g/m2, the wet lap was formed from ZO thirty sheets ox wet paper, and in the pressing step the pres6ure was applied for 45 minutes rather than 30 minutes. The low density pres~board was 2.1 mm ~84 mil6) thick and had a density of 0.92 g/cm3. It S
V~ was 33~. The low dansity pre~sboard was p~edried 25 and hot pre6sed in the same manner as Sample 4A, except that the pressure of 53 kg/cm2 wa6 applied for a contact time of 10 mi~ute6. The product, designated as Sample "~B", way an aramid pre~board l.Q em t71 mil6) thick and had a den6ity of 1.15 30 g/cm3. Its % V~ was 17%. Vml was 0.05 cm3/g (rounded prom 0.0486) and Vmh was 0.15 cm /g Srounded from 0.1~52). The compre6sion 6et was 0.147 em (5.8 mils), the oil absorpeio~ wa6 9.7& by weight of pre~board, and VO wa6 0.11 ~m3~g. For Sample 35 4B, Va wa6 0.15 cm /g and the ratio Va/Vml way 3Ø
i,3 EXAMPT,E 5 In a series of experiment, low density pre6~board6 were made which contained varying ratios of MPD-I fibrids and floc. the low density pres~board6 were made in 6ubstan~ially the 6ame manner as the "Standard Pre66board" of Part A of Example 1 with the following exceptions. Fibrid6 were refined and then mixed with floc at the paper-making machine in the proportion6 given below. Wet paper was produced with the weight of the 601ids being approximately 60 g/m2. Thirty sheets of wet paper were combined into a wet lap which was cut into 20-cm (8-in.~ ~quare6 and pre6sed.
In one experiment a mixture of 80S fibrids and 20% floc having a cut length of 0.32 cm t0.125 in) was used. The low density pressboard was prepared under a pressure of 17.6 kg/cm2 (1724 kPa: 250 psi) for 1.5 hr. at a temperature of 140C. It was approximately 2.1 mm (82 mil6) thick and had a density 20 of 0.92 g/cm3. t Vv wa6 33~.
The low density pres6board way dried at lZ0C
for 4 hour6 and pre66ed at 280C~ under low pres6ure at fir6t with brief cycles of release and reapplication of pre66ure, then for 10 min. at 8.8 25 kg/cm2 (862 kPa; 125 pi he product. designated "Sample SA". wa6 an aramid pre66board approximately 1.9 mm (73 mill) thick. had a den6ity of 1.04 g/cm3, a compre~6ion jet of 0.21 mm (a.3 mils), an oil absorption of 13.7% my weigh pre66board, and V0 was 30 0.16 cm3~g. % Vv for sample 5A was calculated a6 25%. Vml wa6 0.10 cm3/g trounded from O.og9o)~
Vmh way al60 0.10 cm /g rounded from 0.0996).
c 21 ~z~
For sample SA Va was 0.16 cm3/g (the large6t of the ml~ V0, and Vmh) and the ratio V /V wa$
1.6.
The procedure or preparing the low density pressboard was repeated, except that a mixture ox 40 fibrids and 60% floc was used and that the pres6ure applied was 35 kg/cmZ (3450 kPa; 500 psi) for a period of q5 minutes at 140C. The low density pres6board was approximately Z.6 mm (103 mils) thick and had a density of 0.78 g/cm3. % Vv was 43%.
The low density pres6board was dried at 120C for 4 hours and pressed at 280C, under low pressure a first with brief cycles of release and reapplication of pressuce, then for 10 min. at a pres6ure of 53 kg/cm2 (5171 kPa3, finally being cooled under ce~traint in a separate pre6~. The product, designated "Sample 5B", was an aramid pres6board approximately 2.0 mm (79 mils) thick, had a den6ity of 1-0? g/cm3, a compression jet of .15 mm (6.0 mil6), an oil ab60rption of 17.1% by weight of pressboard, and V0 was 0.20 cm3/g. % Vv was 26%. Vml wa6 0.17 cm /g (rounded from 0.16B3) and Vmh wa6 0.27 cm /g (rounded from 0.2673). For Sample SB, Va was 0.27 cm /g and the eatio Va/Vml wa6 1.6.
The procedure for preparing the low den6i~y pressboard was repeated again except that a mixture of 20t fibeid6 and 80~ floc was u6ed and that the pre~fiure applied way 35 kg/cm2 for a period of 45 ~inute~ at 140C. The low density pres~board way 30 approximately 3.1 mm (123 mil6) thick and had a den6ity Df 0.70 g/cm3. Vv for this low density pres~board wa6 49~. The low density pressboard was dried a6 de6cribed above and pres6ed at 280C, under low pce~sure a fir6t with brief cycle of release and 35 reapplication of pres6ure, then for 10 min. at 79 2~
,3 kg/c~Z (7763 kPa: llZ5 p6i). The pcoduct, designaeed "Sample 5C", wa6 an ara~id p~essboard applox~ately 2.1 em (84 thick, had a density of 1.03 g/cm3, a compre~slon set of 0.35 mm (13.6 mils), an oil absoLpeion of 12.1~ by weight of pres6board, and Y0 wa6 0.14 cm /g. Vv was 25%. V 1 way 0.16 cm3/q (rounded prom 0.1565) and Vmh wa 0.23 cm Jo (rounded prom 0.2342~. For Sample 5C, Va was 0.23 cm g and ehe ratio Va~Vml was 1.5.
The procedure for preparing the low den6~ty pres~board way repeated once more. except that a mixture of 95~ fibrids and 5% floc way used and that the pre66uLe applied was 17.6 kg/cm2 or a period of 1.5 hr ae 140C. The low density pressboard was approximately 1.9 mm (75 mils) thick and had a density ox 0.90 g/cm3. % Vv way 35~. The low density pre66board was dried a6 de6cribed above and pressed at 280C, undee low pre6~ure at fic6t with brief cycles of eelease and reapplication of pressure, then for 10 min at 8.8 kg/cm2. The product, de6ignated sample 5D~, was a aramid pre6sboard approximately 1.7 mm (68 mils) thick, had a density of 1.06 g~cm3, a co~pres6ion 6et of 0.34 mm ~13.4 ifs an oil ab60~ption of 11.7% by weight of pres6board, and V0 25 way 0.14 cm ~g. t Vv was 23~. Vml wa6 O.OS
cm3~g (rounded from 0.0459) and V~h was O.OB
cm3fg kounded from 0.0~05). For Sample SD, Va - way 0.14 cm /g and the raeio Va/Vml wa6 3Ø
It a serie6 of experiments, low density pre66board6 ba6ed partly on high-eemperature resistant floc6 other than MPD-I flocs were made. The low den6ity pres~board~ were made in sub~tant~ally the 3~ 6a~e wanner as the "Standard Pressboard" of Hart A of ' I
~24ZB53 non-MPD-I bloc way blended with MPD-I floc having a cut length of 0.32 cm (0.125 in.) and the blend of floc6 was mixed at the paper machine with refined fibrids in the proportions given below. Wet paper was 5 produced with the weight of the solid6 being approximately 60 g/m2. Thirty 6heets of wet eaper were combined into a wet lap which was cut into 20-cm (8-in.) squares and pressed undec the condition given in ox. 1, Part A.
In one experiment, a mixture of 60% MPD-I
fibrid6, 20~ MPD-I floc, and 20% commercially available poly(p-phenylene terephthalamide) (PPD-T) floc having a linear den6ity of 1.67 decitex (1.5 denier) and a cut length of 0.32 cm (0.125 in.) wa6 used to ~repa~e an low density pre~6board having a thickness of 2.9 mm (113 mill), a density of 0.83 cm ~g, and a % Vv of 41%. The low den6ity pre~6board was dried at 120C for 4 hour6 and pressed at 280C, under low pre~ure at first wieh brief cycles of release and reapplication of pre66uee, then at 53 kg/cm2 (5171 kPa; 750 psi) for 10 min., the hot pre6sboard finally being cooled under re6traint in a Reparate pre66. The product, de6ignated a6 "Sample 6A" wa6 a pre66board 2.2 mm (~6 mil6) thick having a density of 1.10 g/cm3, a % Vv of 22t, a compres6ion cet of 0.27 mm (lO.B ~il6), an oil ab60cption of 10.8S by weight of pre~6board, and a V0 of 0.13 cm3/g. Vml was 0.08 cm3/g trounded from 0.0787) and Vmh wa6 0.12 cm3/g (rounded from 0.1151). Va for Sample 5A wa6 0.13 cm /g and the ratio Va/Vml wa6 1.6.
In another experiment, a mixture of 60~ MPD-I
~ibrid~, 35~ ~PD-I floc, and So E-gla66 fiber floc having a den6ity of 2.4 g/cm3 a linear den6ity of 3.3 decitex ~3 denier, and a cut length of 0.64 cm c 24 ~24 ;~
(0.25 in) was used to prepare an low density pcessboard having a thickness of 2.2 mm (88 mils), a density ox o.91 cm3/g, and a Vv 36~. The low density pressboard was dried and pressed by the same procedure described above for making Sample 6A, The product, designated as "Sample 6B", was an aramid/glass fiber pressboard 1.8 mm. (71 mils~ thick having a density of 1.15 g/cm3~ a Vv of 20%, a compression 6et of 0.18 mm (7 mils), an oil absorption of 8.6% by weight ox pressboard and a VO of 0.10 cm /g. Vml was 0.06 cm3/g (rounded from 0.0576) and Vmh was 0.14 cm3/g (rounded from 0.14Z4).
V~ for Sample 6B was 0.14 cm3/g and the ratio Va/V~l was 2.5.
Control Sample Out6ide the Invention (1) The procedure of Example 1, Part B, was repeated, except that the pcessure was incLeased to 53 kg/cm2 (5171 kPa; 750 p6i), the press again being ~ain~ained at a eemperature of 280C. This product, desiqnated as "Control 1" had an oil absorption of only 2.03S. It was about 2.2 em (87 ) thick (thickne6s range Z.14-2.31 mm) and had a density of 1.21 q/cm3, a % Vv of 12%, and a compre66ion set 25 of 0.30 mm (12 mils). VO way 0.023 cm3/g, Vml was 0.04 cm /g (counded from 0.0~33), and Vmh was 0.09 c~3/g (rounded from 0.0889). For Control 1, Va was 0.04 cm3/g and the ratio Va~Vml was 2.05.
(~) The procedure for preparing "Standard Pressboard" a6 described it Example 1, Part I, was repeated, except that the platens of the press were heated to 200C and, after loading the preys at contact pressure, the pre66ure wa6 raised Jo and 35 maintained at 60 kg/cm2 (5880 kPa; 850 pi for one c 25 5,~
hour while the platens of the press were maintained at 200C. The product, designated as "Control 2", had a high value of compres6ion 6et of 1.0 mm (40 mill). It had a density ox 1.07 g/cm3, a ~Vv of 22~, and an oil absorption of 9.59%. V0 was 0.11 cm3/g, V
was 0.17 cm /g (rounded from 0.1733 cm3/g~, and V~h wa6 also 0.17 cm3/g (rounded from 0.1723).
For Control 2, Va way 0.17 cm3/g and the ratio Va/Vml was 1Ø
(3A) ~ilament6 of MPD-I were prepared substantially as described by Ross in U.S. Patent 3,756,908, Column 6, lines 11-23. The resulting high modulus filaments were then cut to a floc hazing a length of about 0.64 cm (0.25 in) and then slurried in water to concentration of about 0.3~.
Pibrids of MPD-I were prepared sub6tantially as described in column 5, lines 3~-57 of the same patent. The refined fibrids were then diluted further in water Jo a concentration of about 0.5%, and pas6ed to a mixing "T" along with the above mentioned 61urry of high modulus floc, at a ratio of fibrid to floc of about 1.55 to 1.0 (60% fibrids and 40S floc). The mixture was directed to the headbox of a ~ourdrinier paper-making machine and then to a forming wire for production of a wet 6heet. The wet 6heet way then removed from the wire and pa6~ed through 6eeam heated dryer can6 to reduce the moisture content of the hoe to about 5~ or less. The paper way then wound on a roll for further processing.
The paper waz removed from its roll, cut into 20-cm s8-in) 6quares, and then platen preyed to produce 6a~ples of 2-ply paper 6ub~tantially a de6cribed in column 7, line 6-11, of the 6ame patent. The sample6 of 2-ply paper were pres6ed a 70.3 kg~cm2 (689.5 kPa; 1000 p~1) and 280C for one i ~;~4~
minute. The resulting paper, designated a "Control 3A" had a thickness of about 0.25 mm (lO mils), a density of absut O.B7 g/cm3, and a % Vv of 37% by volume of the paper. Vml was 0.28 cm3/g (rounded from 0.2B42) and Vmh was 0.18 cm3/g (rounded from O.lBl8). The compression set way l.0 mm (40 mils), the oil absorption was 35.3% by weight of paper, and V0 way Of cm3/g. For Control 3A, Va was 0.41 cm /g and the ratio Va/Vml was l.S.
(3B) Filaments of MPD-I were prepared substantially as described by Gross in U.S. Patent 3,756,908, column 5, lines 6B-75, and column 6. line6 1-7, resulting in low modulus filaments which were then cut to a floc having a length of about 0.64 cm ~0.25 in) and s1urried in water to a concentration of 0.2~.
Fibrids of MPD-I were prepared as described above for Control 3A and paper6 were prepared by combining the fibrid and the low modulu6 floc at a ratio of fibrid to floc of 1.5 to l.0 (60~ fibrid and 40% floc) in a wet 20-cm (8-in) squale hand6heet mold (e.g., of the type made by Noble and Wood). Paper made in this way are considered to be e6~entially the 6ame a6 papee~ made on a Fourdrinier paper machine.
The wet 6heets were removed from the lO0 mesh screen of the hand6heet mold and dried on hot sheet dryer6 to reduce the moi6ture content to about 5% or lest. The ~heet6 were then platen posed Jo produce samples of 2-ply paper. They were ere~sed at 70.3 kg~cm2 (689.5 kPa; lO00 p8i) and 260C for one minute.
The resulting paper, designated a6 "Control 3B" had a thickness of about 0.29 mm (ll mil6), a den6ity of about 0.77 g/cm3, and a % Vv of 44t by volume of the paper. Vml way 0.58 cm3~q (rounded from 0.5787) and Vmh wa6 0.38 cm fg (rounded ffom 2~,3 0.3793). The compression et was 1.4 mm (54 mils), the oil absorption was 49.9% by weight of the paper, and V0 was 0.58 cm /g. For Control 3B, Va wa6 0.5a cm3/g and the ratio Va/Vml wa6 1Ø
By "high temperature re6istant floc" is meant short fiber6, typically having a length of 2 to lZ mm and a linear density of 1-10 decitex, made of a material having a melting point higher than 320C, 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 material6 such as mica may also be pre6ent in rela~iYely finely subdivided form.
~.Z4 28~3 By aromatic polyamide floc" i6 meant 6hort fibers cut from fibecs prepared by the proce~e6 described in U.S. patents 3,063,966, 3,133,13B, 3,767,756, and 3,869,430.
Conventional aromatic polyamide pre~sboard may be prepared by feeding an aqueous 61urcy of MPD-I
fibrids and MPD-I floc to a cylinder paper forming machine whereby water is removed and multiple layers of fibrous mateEial having a water content of 50-95%
by weight of the wet sheet it built up to a wet lap of the desired thickness The wet lap it cut f rom the cylinder, laid flat and pressed at 100-200C, under a pressure of 10-60 kg/cm . The resulting conYentional pressboard usually ha a high oil absorption of 20-50% by weight, a den6ity of about 0.7 to 0.9 gem a calculated void volume of about 35 to 50% by volume of the pressboard, mercury intru6ion volume of about 0.30 to 0.50 cm3/g, both at low and high 6urface/volume, a ratio of total available ab60rption volume in cm3/g, Va, to the mercury intru6ion volume at low surface/volume, Vml, of about 1 and a compres6ion 6ee of 0.75 to 205 mm.
However, for 60me uses, 6uch a6 spacers used in oil filled tran6former6, the comp~e~6ion 6et desirably 6hould be not les6 than about 0.12 mm or more than about 0.5 mm while maintaining an oil ab60retion of at lea6t 8~. Pres6board with compce6sion set value6 of lest than about 0.12 mm do not have the combination of compressibility and re6ilience nece~ary to maintain eroPer 6pacing of electrical component in, e.g., t~an6former~.
Pre66board with compre6~ion 6et values greater than 0.5 mm likewise do not maintain proper spacing of components.
2~3 The above desired properties are provided by the product of this invention. It has been found that when a low den6ity pressboard having a calculated void volume of 30 to 60% prepared as described above is further dried, ultimately at a temperature of 270-320C, until substantially no further moisture is evolved and then pressed at 270-320C and a pre6sure of 8 to 350 kg/cm2, preferably followed by cooling under restraint, a pres~boald having the desired properties is obtained. The drying i8 preferably accomplished by step-wi~e increase in temperature.
Moisture evolution is facilitated by application and release of light pressure. In general, the pre6sing is preferably at 275-300C at 15 to 70 kg/cm2 or at least 5 minute but thick product6 may require pressing for longer times. More than one layer ox low density pressboard may be combined during high temperature pressing. In this case, longer pressing times 6hould be employed. Preferably the high temperature pres6ing should be above the glass tran6ition temperature (~g) of the aromatic polyamide comprising the fibridfi which in the case of the prefereed poly(m-phenylene isophthalamide) fibrids i6 about 275C.
It has been found that the proce6s described above, wherein a wet lap i8 formed of multiple layers of waterleaves having a water content of 50-95~ and the wet lap is pressed at 100-200C under a pressure of 10-60 kg/cm2 ts pcepare a low density pressboard 30 having a calculated void Yolume of 30-60%, and the low density pressboard i8 then dried and pres6ed again at 270-320C under a pres6ure of 8-3~0 kg/cm , is essential for obtaining a pressboard product exhibiting good re6i6tance to compression as jell a6 35 adequate oil ab60rption. If the low density ~2~3~3 pressboard has a calculated void volume of less than 30%, the oil ab60rption ox the f inal pres6board product tend6 to be very poor.
The pre6sboard of thi6 invention i8 u~e~ul in clamping rings and in axial and radial 6pacer6 in oil f illed electrical tran6formers.
Product of this invention have a calculated void volume ox 13 to 28~ by volume of the pressboard, mercury intrusion Yolumes at low surface/volume, Vml, of less than 0.20 cm3/g and at high surface~volume, Vmh, of 0.08 to 0.28 cm3/g, an oil ab60rption by volume in cm3~g, VO, ox 0.08 to 0.28 and by weight of 8-24~ and a total available absorption volume in cm3/g, Va, equal to the lS largest of the value for Vml, V~h and VO, the ratio ox Va to Vml being at least 1.1. Pressboard having a calculated void volume of more than 28~ or a ratio of Va to Vml of 1.0 generally exhibit6 poor compres6ion set, while pre~6board having a calculated 20 void volume of le6s than 13~ or Vmh le66 than O.OB
cm3/g generally exhibits poor oil absorption. The product6 of thi6 invention have Va values which are quite different from Vml value6, the ratio of these being at least 1.1 and a6 sigh a 4.
2s TESTS
Density. Dry pre66board it cut into a rectangular 6ample mea6uring at least 10 em x 10 cm (I
in x 4 in), preferably at least 20 cm x 20 cm t8 in x 30 8 in3, making sure that the ~orner6 are cut square 60 ehat the upper and lower faces of the 6ample are of the Rame area and that the dimen~ion6 can be measured accurately. The length and width of the rectangular 6ample are mea6ured to an accuracy of at lea6e 0.25 cm ~5 tO.l in). The thickne~6 of the rectangular sample ox ~2~5,~
pces6board i8 measured in at least ten places 6paced 6ubstantially equally apart around all sides of the pressboard, away from the edges, using a micrometer caliper which contacts the sample with 6urfaces having a diameter of about 0.6 cm (0.25 in) at a pre~6ure of about 0.1 kg/cmZ (about l.Z5 psi), to an accuracy of at least 0.00025 cm (0.1 mil), averaging the ten thickness measurements. The sample of pre~sboard is then weighed to the nearest O.OOol g. The volume of the sample of pressboard Vb is then calculated in cm and the weight i5 divided by the volume to give the density in g/cm3.
Calculated Void Volume. The void volume in cm3, Vv, of a 6ample of the pres~board i6 detecmined from the relationship Vb = Vm V~, or VV = Vb - Vm. where Vb is the volume of the pre6~board in cm3 a6 determined above, Vm i8 the total volume in cm3 of 20 all the materials comprising the pres6board, and Vv is the retaining volume in cm3, which it taken as the void volume. Vm is determined from the weight6 and densitie6 of each of the materials of which the pre6sboard samele it made, calculated a follow6:
V = Wf I , where 1.38 g/cm I
Wf is the weight in g of the aromatic polyamide fibrids in the pressboard 6ample, Wi it the weight in g of the floc (including any other non-fibrid high temperature re6i~tant ma~erial~ in the pre6~board ample, and Pi it the density of the material of which the floc is made tl.38 g~cm3 for MPD-I and 1.44 g~cm3 for polytp-phenyl~ne terephthalamide)~.
35 when there i6 more than one kind of floc (or other ~2428~3 high temperature resistant material such a6 mica), Wi/pi i8 calculated as follow6:
Wi Wl , W2 +, . . Wn Pi Pl P2 Pn 5 where i = 1, ..., n The calculated void volume a6 a percentage volume, Vv, i6 then calculated as follow6:
% Vv =11 m] x loo = V~ ox 100 In the case of a 100% MPD-I pcessboard 6ample having a weight in g of ~b and a volume in cm3 of Vb, and since for this case Ym = Wb 1.38 g a the equation reduces to:
VV =Ll - Wb x 100 Vb~1.38 g/cm3 The calculated void volume it a mea~u~e of all of the voids, both isolated void and interconnected voids, in a sample of pressboard.
Oil Absorption. This test i6 carried out in accordance with the method described by the International Electrotechnical Commi66ion, IEC
Standard, Publication 641-~, First edition (1979), "Specification for pres6board and pce6spaper for electrical purposes, Part 2: Method6 of test," page6 29 and 31 (section 17), publifihed by Bureau Central de la Commi6sion Electrotechnique Internationale Geneva, Switzerland. The result it expre6sed Jo the neare6t 0.1% as a percentage by weight oil ab60rption on the original ma66 of the pres~board 6ample tested. The oil absorption by volume in cm3/g, VO, i6 when calculated by dividing the percentage by weighe oil ab60rption by the den6ity of ehe 6ample of pre~6board. VO values are initially reported to the 28~3 same number of significant ~igure6 as the percentage by weight oil absorption, then rounded to two decimal places.
Compression Set. The pre6sboard to be te6ted 5 i6 cut into rectangular ~trip6 3.8 cm (1.5 in) wide X
5.1 cm (2.0 in) long and a sufficient number of the 6trips are tacked to make a 6tack approximately 5.1 cm (2.0 in) high. The tack of sample6 it placed in an oven for 4~ hr~. at 110C, then taken from the oven and placed in a conventional machine for testing compressive properties, eguipped for constant rate of crosshead movement and having a capacity of at least 10,000 kg (22,000 lb.) (e.g., the Tiniu~ Olsen Universal Testing Machine, Model 60 SDT, Servo-controlled, 60,000 lb. capacity, Super L U~M, made by the Tiniu~ 016en Universal Testing Machine Co., Inc., Easton Rd., Willow Grove, PA 19090 equipped with a Model MM Flat Bed X-Y Recorder manufactured by Houston Instrument6, Inc. and Tiniu6 Olsen Model D-2 and D-4 Deflectomer~ for accurately measuring the deflection ox compre6sed 6ample6 at two different chart magnifications. In carrying out the test, the load i6 applied at the constant rate of 0.5 cm per mix. (0.2 in. per min.) and relea6ed. A load of 680 kg (1,500 lb.), equivalent Jo 35 kg~cm2 (3,448 kPa:
500 p5i), i6 applied Jo the 6tack of samples, and the load it the immediately released to a load of 13S kg (300 lbs.). Thifi load, equivalent to 7 kg/cm~ (690 kPa; 100 p6i), it designated a the bedding pressure, and the load i5 releafied to this bedding pres6ure between each cycle. The stask of ~ample6 ifi next cycled to 1361 kg (3,000 lb~.), equivalent to 70 kg~cm2 (6,B95 kPa: 1,000 psi), returning to the bedding pre66ure. It it then cycled to 2,722 kg (6,000 lb6.), equivalent to 141 kg/cm2 (13,790 kPa;
~24 2,000 psi), retucning to the bedding pre~ure.
Finally it is cycled to 4.082 kg (9,000 lb~.), equivalent to 211 kg/cm2 (20,685 kPa: 3,000 pi and back once more to the bedding pres6ure. The compression set it taken as the lows in height in mm (alternatively in mils) ox 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 reading6 coneinuously plotted on a chart 80 that the entire sequence of cycle it displayed on a graph f or each sample tested.
If the amount of sample material is limited, the 3.~ em 5.1 cm rectangular 6trip6 are 6tacked 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 re6ult to correspond to the result which would be obtained fcom a tack 5.1 cm (2.0 in.) high.
Merc~Ey Intrusion Yolume In this determination a conventional mercury poro6imeter tAminco Mercury 60,000 pig max, Newport Scientific Co., Inc., Silver Spring, MD 20910~ i6 employed to determine the volume of mercury which Jan be forced 25 into the pores, or interconnected void6, of a porou6 6ample. To determine whether the 6urface area of a given weight of the pre6~board ha an effect on the volume of mercury which can be forced into it6 pore6, determination are made both on low æur~ace~volume 30 samples and high ~urface/volume ~6ubdivided) ample of the pres~board.
The nominal weight of each 6ample te6ted it 0.~ g. To prepare the low 6ucfaceivolume and high 6urface/volume 6ample6, an initial sample 61ightly 35 heavier than 0.6 g and preferably rectangular in shape e 11 is cut from the pre~sboard to be tested. The initial sample is then cut down in size ~e.g. with a pair of side-cutter6) in a series of approximately 25 to 35 clean cuts stcaight through the pressboard near its s edges to produce a corresponding number of ~ragment6.
leaving a preferably quadrilateral sample weighing about 0.3 g which is taken as the sample for the low ~urface/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. If the sample it very thin and a jingle piece weighing 0.3 g which will fit in the penetrometer bulb cannoe be preparad, the low ~urface/volume sample is prepared in the form of two or even three eiece~ which will fit in the bulb.
The low sur~ace/volume sample is weighed to the nearest 0.0001 g on glassine paper. A sufficient number of the pres~board fragments, preferably about 25 eO 30, to weigh about 0.3 g are placed on gla~sine paper (preferably they are collected on the glassine paper as they are cut) a6 the high ~urface/volume (subdivided) sample. The su~diYided sample is weighed to the nearest O.OOOl g.
To conduct the determination, a weighed sample iB placed in the open penetrometer bulb, after which the bulb i6 capped and evacuated until the vacuum gauge display6 a pres6ure of 50 microns of mercury or lest. The filling device i6 then tilted backward until it stop i6 reached, Jo thae the eip of the penetrometer it immersed in mercury. The stopcock on the filling device i8 gradually opened to admit air to the 6y8te~ slowly, causing mercuLy to enter the penetrometer bulb, zapping the tube to aid in wetting the sample with mercury. After total weteing ha6 been achieved, the filling device it returned to vertical ~z~
position. The penetLometer is then moved from the vacuum chamber to the pressure chamber.
The pressure is then gradually increa6ed, recording penetrometer reading6 at interval6 as the S pressure increases. The equipment is customarily provided with more than one pressure gauge, e.g.
recording maximum values of about 350 kg/cm (34 spa; S,000 pi) and about 4200 kg/cmZ (414 MPa:
60,000 psi), and if 60 the equipment it 6witched over to the high pressure gauge at the appropriate time a6 the pressure increases. The penetrometer reading at 4200 kg/c~2 (414 MPa, 60,000 psi) i6 recorded at the conclusion of the text. The meccury intrusion volume at 4200 kg/cm2 is determined from the penetrometer reading in accordance with the instcuceion6 provided by the manufacturer of the equipment. For a pacticular 6pecimen of pres6board, mercury intrusion volume value6 in cm3/g (cm3 of mercury at 4200 kg/c~2 pressure per g of pre6sboard) are first determined to four decimal places, then rounded and finally reported Jo two decimal places both for the low 6urface/volume and high 6urface/volume (6ubdivided) 6a~ple6. If de6ired, graph6 of mercury intrusion Yolume values oYer the entire pressure range are constructed, based on the penetrometer reading6 taken at interval6 throughout the te6t. The mercury intru6ion volume at low 6urface/volume it designated by the 6ymbol, Vml, and the mercury intru6io~ volume at high 6urfaoe/volume it de6ignated by the 6ymbol, Vmh Total Available Ab~orDtion Volume. The total available ab60~ption volume, Va, of a pre~6board sample it taken a being equal So the largest of the value6 for Vml, V~h and VO (all ~alue6 prior to rounding) fox the sample. For any given sample of s 13 pressboard, Va is a measure of the volume in cm3 per g of the intecconnected voids in the sample which are accessible to penetration by liquids.
The ratio, Va/Vml, is then calculated, using values of Ya and Vml 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 ox a ~tructu~e of limited oc partial accessibility ox internal voids in the pressboard, a 6eructure associated with good compression resistance of the pressboa~d when the calculated void volume of the pressboard is no more than 28%.
A. _Pceparation of "Standard Pres6board"
Filaments of poly(m-phenylene isophthalamide) (MPD-I) having an inherent visco6ity of 1.5 were dry spun from a solution containing 19~ MPD-I, 70%
dimethylacetamide tDMAc), gt calcium chloride, and 2~ -water. On leaving the drying tower the a~-~pun filaments were given a preliminary wa6h with water Jo thaw they contained about 60t DMAc, 15% calcium chloride, and 100-150S waxer, based on the weight of dry polymer. The filaments were washed and drawn 4X
at 90C in a counter-current extraction-draw process in which the calcium chlsride determined as chloride content and DMAc contene were ceduced to about 0.1 and 0.5%, respectively. The filaments were crystallized immediately after drawing by passing them over hot roll6 at a temperature of about 340C. The filament 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 ox 70 dN/tex (79 gpd~ and an elongation of 34%. the filament6 were cut to floc having a length of 3.4 mm ~0.135 in).
~Z42BS3 Fib~ids of MPD-I having an inherent viscosity of 1.5 were prepared ~ub6tantially a6 described by ~ro~s in U.S. Patent 3,756,908, issued September 4, 1973, column 5 line 34-54, stopping short of the refining step.
An aqueous slurry was prepared containing 1.0 wt. ibid and floc having a composition of 60% of the above MPD-I fibrid~ and 40~ of the above MPD-I
floc. The slurry was held in an agitated vessel and then pumped to a double disc refine (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 lS dams. The plate ox the refine were positioned with a gap of 0.5 mm (20 mil6~ between the rotor and the 6tator plates. The roeor plates were operated at 900 rpm. After passing through the refiner, the filurry was pasted through a second refiner under the tame Z0 operating conditions. After the two passe through the refiners the fib~id~ in the slurcy were well reduced in size and well opened into fib~id films, while the floc fiber were well di6tributed among the ibrids. The 6 lurry made in this way was then diluted ZS to approximately 0.1% by weight solid and fed to a conventional cylinder wet paper-making machine upon which a continuous sheet of wet paper wa6 made and transferred Jo an endle~6 felt, the moi6ture content being adjusted by fiuc~ion and pressure to about 400%
30 based on solids (80~ by weight cod on the wet 6heet). The weight of the olid~ in the wet paper was approximately 36 g/m . The eontinuou~ wee 6hee~ way next delivered to a forming roll, where it was wound continuously on a cylindrical tube until it overlapped about 70 time. A longitudinal cut was then made in the layered paper and the entire thicknes6 of wet lap (wet layered paper) was then removed and placed between the platens of a hot press, the platen6 being maintained at 140C and having been covered with wire 6c~een to facilitate moisture removal. The pre66 way loaded at contact pressure, and the pre6sure was then raised eo and maintained for one hour at 35 kq~cm2 (3450 kPa; 500 psi~ while the platens of the pre66 were maintained at 140C. The product, herein designated as "Standard Pressboard", was a low density aramid pre66board approximately 3.2 mm (lZ6 mils) thick. It was found to have a density of 0.~2 g/cm3, a calculated void volume, % Yv, of 41~ by volume of the pressboard, a co~pre6sion c of 2.13 em (8~ mil6), and an oil absorption of 32.5%. V0 was 0.38 cm3~g, V~l was 0.38 cm3/g (rounded from 0.3791), and Vmh was 0.42 cm3/g (rounded from 0.4197) Va for this Standard Pces6board 6ample wa6 0.42 cm /g and the ratio V /V 1 way 1 1 B. Preparation of ComPression-Resistant Pre66board A 30.5 cm X 30.5 cm (12 in X 12 in) square sheet of the "Standard Pre66board" prepared a6 in Part A above wa6 predried at 150C for at lea6t 2 hour6 and then placed between the platen6 of a flat ere66 tMachine No. 9175-M, Wat60n Stillman Pres6 Divi6ion, Farrel Company, Emhart Machinery Group, 25 Main St., An60nia, Connecticut 06401). With the plateRs preheated to 280C and maintained at that temperature, a pre6~ure of 19.5 kg~cm2 (1910 kPa; 277 p6i) wa6 appl;ed to the "Standard Pre6~board~' for a total of 20 minute, relea6ing the p~e~6ure for a few second and then reapplying it aster a total ox 1. 2, 30 6, 12.
and 16 minute6 to permit e6cape of any trapped ga6es.
After a total of 20 minute6 of hot pce66ing, the pre~sboard wa6 taken out hot, placed in another pre66 285~
at room temperature, and allowed to cool under a pressure ox 2.~ kg/cm2 t276 kPa: 40 psi), jut ~ufficiènt to keep the pressboard flat while cooling.
The product. designated as "Sample lA", was an aramid pre6sboard approximately Z.45 mm (96.5 mil6) thick ~hicknes~ range 2.35-2.53 mm). It was found to have a density of 1.11 g/cm3, a % Vv of 20~, a compre~6ion 6et of 0.30 mm (12 mils), and an oil absorption ox 12.~ . V0 was 0.15 cm /g, Vml 0 way 0.15 cm /~ (rounded from 0.1502), and V was mh 0.17 cm /g (rounded from 0.1700). Va for Sample lA way 0.17 cm /g and the ratio Va/Vml was 1.1.
Another 6heet of predried "Standard Pres6board" way subjected to the same procedure, except that a pressule of 18.5 kg/cm2 (1813 kPa, 263 p6i~ was applied in the press for a total of 20 minutes at 2B0C. The product, designated as "Sample lB", was approximately 2.5 mm (~8.7 mill) thick (thickness range 2. 3a - 2.60 mm). It was found to have a density of 1.08 g/cm3, a S Vv of 2Z%, a compression set of 0~36 mm (14 mils), and an oil ab60rption of 12.19%. V0 way 0.14 cm3/g, Vml way 0.16 cm /g (rounded from 0.1551), and Vmh was 0.17 cm /g (rounded from 0.1743). Va for Sample lB was 0.17 cm /g and the ratio Va/Vml was 1.1.
EXAMPLE Z
Two 46 cm X 122 cm (18 in x 48 in) rectangular sheets of "Standard Press~oard", prepared substantially as described in Paet A of Example 1 but having a thickness of 3.0 mm (llB mils), were aligned in a tack above and below a 46 cm x 122 cm 6heet of 1.6-mm thick "Standard Pres~board", similarly prepared except what proportionately fewer overlap of wet papeL were wound on ehe cylindrical coll in the ~2~3~i,3 ~o~ming step. All of the 6heet6 were predried at 150C just beore worming the tack. The aligned tack was then placed immediately in a hot press having platens oil-heated to 280C (535F) and subjected to three 2-minute cycle of contact pre66ure (3.5 kg/cm2) at 2B0C followed by release of pressure. A one-minute cycle of pre~6ure at 28 kg/cm~ (2758 kPa: 400 p6i) and quick relea6e way hollowed by a one-minute cycle of pre6sure at 35 kg/cmZ and quick Eelease, after which pre66ure wa applied at 35 kg/cmZ for fifteen minute6 while the platens were maintained at 2~00C. The pre6sboard product was taken out hot and placed under contact pressure in a separate press, initially at room temperature and water-cooled to ab60rb the heat of the pressboard, to keep it flay while cooling. The product, designated "Sample 2", wa6 an aramid pressboard approximately 5.3 em thick (210 mils). It was found to have a den6ity of 1.12 g~cm3, a % Vv 20 of 19%, a compre6sion 6et of 0.13 mm (5 mils), and an oil ab60rpt on of 9.3%. V0 wa6 0.11 cm3~g, Vml was 0.09 cm ~g (rounded from 0.0940), and Vmh wa6 0.17 cm ~g (rounded from 0.1665). Va for Sample 2 wa6 0.17 cm ~g and the ratio VaJVml wa6 1.8.
A 46 cm x 81 cm l in x 32 in) rectangular 6heet of 2.1-mm thick pre66board, prepared ~ubstan~ially like the "Standard Pre~6board" ox Part A
30 of Example I, except that proportionately fewer overlap6 of wet paper weee u6ed, a placed without predrying in a pre~6 equipped for electrical heating and water cooling. Initially the pres6 wa6 at 66C
(150F) and contact pres6ure, about 3.5 kg/c~2 (345 35 kPa: 50 psi). the pre~6 wa6 heated over about 20 so minutes under the tame contact pressure. with no interval of pcessure release, to about Z80C (about 535E). The pressure was then increa6ed to 35 kg/cm (3~48 kPa; 500 psi) and maintained at that pressure, with no relea6e of pres~u~e, for 12 ~inute6 while the pres6 way maintained at 280C. The electrical heating way then discontinued and the pre6s was then cooled back down to 66C with circulation of cool water over a 20-minute period while the pressure lO was maintained at 35 kg/~m2. The product, designated "Sample 3", was an aramid pre~board approximately 1.6 em ehick (64 mil6). lt way found to have a density of 1.13 g/~m3, a % V~ of lB~, a compce8sion 8et of 0.13 mm (5 mil6), and an oil absorpt on of 9.32~. V0 way 0.11 cm3/g, Vml was 0.06 cm /g (rounded prom 0.0553), and Vmh was 0.14 cm /g (rounded from 0.1390). V or Sample 3 way a 0.14 cm~/g and the ratio Va/Vml way 2.5.
Square ~heet6 of low density pre66board were preeaced in sub6tantially the 6ame manner as the "Standard Pressboard~' of Part A of Example l, with the following exception6. Fibrids were refined and mixed 2S with f loc at the paper-making machine. Fifty 6hee~6 of wet paper were combined unto a wet lap and the entire wet lap way jut into ~0-cm (8-in) square. In pressing the 6quare~ of wet lap at 140C under a pre~6ure of 35 kg/cm2, the pressure wa6 applied for 30 30 minute6 rather than ona hour. The low density pre~6board 80 formed way 2.1 mm (81 mill thick and had a den6ity of 0.88 g/cm3. It6 % Vv wa6 36~.
The low density pre66board was predried a lZ0C in an oven for four hour6 and then placed between the ~5 platen6 of a flat pre6s preheated to 280~C a6 in a 19 ~4~28~
Part B ox Example I. Low pressure was applied briefly at fiest, with three cycles ox celease of the ~re6sure to permit escape of the trapped gasses followed by reapplication ox the pre6sure. A pressure of 53 kg/cm2 (5171 kPa; 750 psi) was then applied or a contact time of 1 minute, the hot pressboard finally being cooled under r~&traint in a separate press. The product, designated a "Sample 4A", was an aramid pres~board 1.75 mm (69 mils) thick and had a density ox 1.04 gem It6 % Vv was 25%. Vml way 0.15 cm3/g (rounded f rom 0.1542) and V~h was 0.17 cm /g (rounded from 0.1712), The compLession set was 0.20 mm (8.0 mils), the oil absorption was 15.9t by weight of pressboard, and VO was 0.19 cm3/g. For Sample 4A, Va was 0~19 cm /g and the ratio Va/V~l was 1.2.
Other 20-cm square 6heets of low density pres~board were prepared in the tame manner, except that the weight of the 601ids in the wet paper was approximately 60 g/m2, the wet lap was formed from ZO thirty sheets ox wet paper, and in the pressing step the pres6ure was applied for 45 minutes rather than 30 minutes. The low density pres~board was 2.1 mm ~84 mil6) thick and had a density of 0.92 g/cm3. It S
V~ was 33~. The low dansity pre~sboard was p~edried 25 and hot pre6sed in the same manner as Sample 4A, except that the pressure of 53 kg/cm2 wa6 applied for a contact time of 10 mi~ute6. The product, designated as Sample "~B", way an aramid pre~board l.Q em t71 mil6) thick and had a den6ity of 1.15 30 g/cm3. Its % V~ was 17%. Vml was 0.05 cm3/g (rounded prom 0.0486) and Vmh was 0.15 cm /g Srounded from 0.1~52). The compre6sion 6et was 0.147 em (5.8 mils), the oil absorpeio~ wa6 9.7& by weight of pre~board, and VO wa6 0.11 ~m3~g. For Sample 35 4B, Va wa6 0.15 cm /g and the ratio Va/Vml way 3Ø
i,3 EXAMPT,E 5 In a series of experiment, low density pre6~board6 were made which contained varying ratios of MPD-I fibrids and floc. the low density pres~board6 were made in 6ubstan~ially the 6ame manner as the "Standard Pre66board" of Part A of Example 1 with the following exceptions. Fibrid6 were refined and then mixed with floc at the paper-making machine in the proportion6 given below. Wet paper was produced with the weight of the 601ids being approximately 60 g/m2. Thirty sheets of wet paper were combined into a wet lap which was cut into 20-cm (8-in.~ ~quare6 and pre6sed.
In one experiment a mixture of 80S fibrids and 20% floc having a cut length of 0.32 cm t0.125 in) was used. The low density pressboard was prepared under a pressure of 17.6 kg/cm2 (1724 kPa: 250 psi) for 1.5 hr. at a temperature of 140C. It was approximately 2.1 mm (82 mil6) thick and had a density 20 of 0.92 g/cm3. t Vv wa6 33~.
The low density pres6board way dried at lZ0C
for 4 hour6 and pre66ed at 280C~ under low pres6ure at fir6t with brief cycles of release and reapplication of pre66ure, then for 10 min. at 8.8 25 kg/cm2 (862 kPa; 125 pi he product. designated "Sample SA". wa6 an aramid pre66board approximately 1.9 mm (73 mill) thick. had a den6ity of 1.04 g/cm3, a compre~6ion jet of 0.21 mm (a.3 mils), an oil absorption of 13.7% my weigh pre66board, and V0 was 30 0.16 cm3~g. % Vv for sample 5A was calculated a6 25%. Vml wa6 0.10 cm3/g trounded from O.og9o)~
Vmh way al60 0.10 cm /g rounded from 0.0996).
c 21 ~z~
For sample SA Va was 0.16 cm3/g (the large6t of the ml~ V0, and Vmh) and the ratio V /V wa$
1.6.
The procedure or preparing the low density pressboard was repeated, except that a mixture ox 40 fibrids and 60% floc was used and that the pres6ure applied was 35 kg/cmZ (3450 kPa; 500 psi) for a period of q5 minutes at 140C. The low density pres6board was approximately Z.6 mm (103 mils) thick and had a density of 0.78 g/cm3. % Vv was 43%.
The low density pres6board was dried at 120C for 4 hours and pressed at 280C, under low pressure a first with brief cycles of release and reapplication of pressuce, then for 10 min. at a pres6ure of 53 kg/cm2 (5171 kPa3, finally being cooled under ce~traint in a separate pre6~. The product, designated "Sample 5B", was an aramid pres6board approximately 2.0 mm (79 mils) thick, had a den6ity of 1-0? g/cm3, a compression jet of .15 mm (6.0 mil6), an oil ab60rption of 17.1% by weight of pressboard, and V0 was 0.20 cm3/g. % Vv was 26%. Vml wa6 0.17 cm /g (rounded from 0.16B3) and Vmh wa6 0.27 cm /g (rounded from 0.2673). For Sample SB, Va was 0.27 cm /g and the eatio Va/Vml wa6 1.6.
The procedure for preparing the low den6i~y pressboard was repeated again except that a mixture of 20t fibeid6 and 80~ floc was u6ed and that the pre~fiure applied way 35 kg/cm2 for a period of 45 ~inute~ at 140C. The low density pres~board way 30 approximately 3.1 mm (123 mil6) thick and had a den6ity Df 0.70 g/cm3. Vv for this low density pres~board wa6 49~. The low density pressboard was dried a6 de6cribed above and pres6ed at 280C, under low pce~sure a fir6t with brief cycle of release and 35 reapplication of pres6ure, then for 10 min. at 79 2~
,3 kg/c~Z (7763 kPa: llZ5 p6i). The pcoduct, designaeed "Sample 5C", wa6 an ara~id p~essboard applox~ately 2.1 em (84 thick, had a density of 1.03 g/cm3, a compre~slon set of 0.35 mm (13.6 mils), an oil absoLpeion of 12.1~ by weight of pres6board, and Y0 wa6 0.14 cm /g. Vv was 25%. V 1 way 0.16 cm3/q (rounded prom 0.1565) and Vmh wa 0.23 cm Jo (rounded prom 0.2342~. For Sample 5C, Va was 0.23 cm g and ehe ratio Va~Vml was 1.5.
The procedure for preparing the low den6~ty pres~board way repeated once more. except that a mixture of 95~ fibrids and 5% floc way used and that the pre66uLe applied was 17.6 kg/cm2 or a period of 1.5 hr ae 140C. The low density pressboard was approximately 1.9 mm (75 mils) thick and had a density ox 0.90 g/cm3. % Vv way 35~. The low density pre66board was dried a6 de6cribed above and pressed at 280C, undee low pre6~ure at fic6t with brief cycles of eelease and reapplication of pressure, then for 10 min at 8.8 kg/cm2. The product, de6ignated sample 5D~, was a aramid pre6sboard approximately 1.7 mm (68 mils) thick, had a density of 1.06 g~cm3, a co~pres6ion 6et of 0.34 mm ~13.4 ifs an oil ab60~ption of 11.7% by weight of pres6board, and V0 25 way 0.14 cm ~g. t Vv was 23~. Vml wa6 O.OS
cm3~g (rounded from 0.0459) and V~h was O.OB
cm3fg kounded from 0.0~05). For Sample SD, Va - way 0.14 cm /g and the raeio Va/Vml wa6 3Ø
It a serie6 of experiments, low density pre66board6 ba6ed partly on high-eemperature resistant floc6 other than MPD-I flocs were made. The low den6ity pres~board~ were made in sub~tant~ally the 3~ 6a~e wanner as the "Standard Pressboard" of Hart A of ' I
~24ZB53 non-MPD-I bloc way blended with MPD-I floc having a cut length of 0.32 cm (0.125 in.) and the blend of floc6 was mixed at the paper machine with refined fibrids in the proportions given below. Wet paper was 5 produced with the weight of the solid6 being approximately 60 g/m2. Thirty 6heets of wet eaper were combined into a wet lap which was cut into 20-cm (8-in.) squares and pressed undec the condition given in ox. 1, Part A.
In one experiment, a mixture of 60% MPD-I
fibrid6, 20~ MPD-I floc, and 20% commercially available poly(p-phenylene terephthalamide) (PPD-T) floc having a linear den6ity of 1.67 decitex (1.5 denier) and a cut length of 0.32 cm (0.125 in.) wa6 used to ~repa~e an low density pre~6board having a thickness of 2.9 mm (113 mill), a density of 0.83 cm ~g, and a % Vv of 41%. The low den6ity pre~6board was dried at 120C for 4 hour6 and pressed at 280C, under low pre~ure at first wieh brief cycles of release and reapplication of pre66uee, then at 53 kg/cm2 (5171 kPa; 750 psi) for 10 min., the hot pre6sboard finally being cooled under re6traint in a Reparate pre66. The product, de6ignated a6 "Sample 6A" wa6 a pre66board 2.2 mm (~6 mil6) thick having a density of 1.10 g/cm3, a % Vv of 22t, a compres6ion cet of 0.27 mm (lO.B ~il6), an oil ab60cption of 10.8S by weight of pre~6board, and a V0 of 0.13 cm3/g. Vml was 0.08 cm3/g trounded from 0.0787) and Vmh wa6 0.12 cm3/g (rounded from 0.1151). Va for Sample 5A wa6 0.13 cm /g and the ratio Va/Vml wa6 1.6.
In another experiment, a mixture of 60~ MPD-I
~ibrid~, 35~ ~PD-I floc, and So E-gla66 fiber floc having a den6ity of 2.4 g/cm3 a linear den6ity of 3.3 decitex ~3 denier, and a cut length of 0.64 cm c 24 ~24 ;~
(0.25 in) was used to prepare an low density pcessboard having a thickness of 2.2 mm (88 mils), a density ox o.91 cm3/g, and a Vv 36~. The low density pressboard was dried and pressed by the same procedure described above for making Sample 6A, The product, designated as "Sample 6B", was an aramid/glass fiber pressboard 1.8 mm. (71 mils~ thick having a density of 1.15 g/cm3~ a Vv of 20%, a compression 6et of 0.18 mm (7 mils), an oil absorption of 8.6% by weight ox pressboard and a VO of 0.10 cm /g. Vml was 0.06 cm3/g (rounded from 0.0576) and Vmh was 0.14 cm3/g (rounded from 0.14Z4).
V~ for Sample 6B was 0.14 cm3/g and the ratio Va/V~l was 2.5.
Control Sample Out6ide the Invention (1) The procedure of Example 1, Part B, was repeated, except that the pcessure was incLeased to 53 kg/cm2 (5171 kPa; 750 p6i), the press again being ~ain~ained at a eemperature of 280C. This product, desiqnated as "Control 1" had an oil absorption of only 2.03S. It was about 2.2 em (87 ) thick (thickne6s range Z.14-2.31 mm) and had a density of 1.21 q/cm3, a % Vv of 12%, and a compre66ion set 25 of 0.30 mm (12 mils). VO way 0.023 cm3/g, Vml was 0.04 cm /g (counded from 0.0~33), and Vmh was 0.09 c~3/g (rounded from 0.0889). For Control 1, Va was 0.04 cm3/g and the ratio Va~Vml was 2.05.
(~) The procedure for preparing "Standard Pressboard" a6 described it Example 1, Part I, was repeated, except that the platens of the press were heated to 200C and, after loading the preys at contact pressure, the pre66ure wa6 raised Jo and 35 maintained at 60 kg/cm2 (5880 kPa; 850 pi for one c 25 5,~
hour while the platens of the press were maintained at 200C. The product, designated as "Control 2", had a high value of compres6ion 6et of 1.0 mm (40 mill). It had a density ox 1.07 g/cm3, a ~Vv of 22~, and an oil absorption of 9.59%. V0 was 0.11 cm3/g, V
was 0.17 cm /g (rounded from 0.1733 cm3/g~, and V~h wa6 also 0.17 cm3/g (rounded from 0.1723).
For Control 2, Va way 0.17 cm3/g and the ratio Va/Vml was 1Ø
(3A) ~ilament6 of MPD-I were prepared substantially as described by Ross in U.S. Patent 3,756,908, Column 6, lines 11-23. The resulting high modulus filaments were then cut to a floc hazing a length of about 0.64 cm (0.25 in) and then slurried in water to concentration of about 0.3~.
Pibrids of MPD-I were prepared sub6tantially as described in column 5, lines 3~-57 of the same patent. The refined fibrids were then diluted further in water Jo a concentration of about 0.5%, and pas6ed to a mixing "T" along with the above mentioned 61urry of high modulus floc, at a ratio of fibrid to floc of about 1.55 to 1.0 (60% fibrids and 40S floc). The mixture was directed to the headbox of a ~ourdrinier paper-making machine and then to a forming wire for production of a wet 6heet. The wet 6heet way then removed from the wire and pa6~ed through 6eeam heated dryer can6 to reduce the moisture content of the hoe to about 5~ or less. The paper way then wound on a roll for further processing.
The paper waz removed from its roll, cut into 20-cm s8-in) 6quares, and then platen preyed to produce 6a~ples of 2-ply paper 6ub~tantially a de6cribed in column 7, line 6-11, of the 6ame patent. The sample6 of 2-ply paper were pres6ed a 70.3 kg~cm2 (689.5 kPa; 1000 p~1) and 280C for one i ~;~4~
minute. The resulting paper, designated a "Control 3A" had a thickness of about 0.25 mm (lO mils), a density of absut O.B7 g/cm3, and a % Vv of 37% by volume of the paper. Vml was 0.28 cm3/g (rounded from 0.2B42) and Vmh was 0.18 cm3/g (rounded from O.lBl8). The compression set way l.0 mm (40 mils), the oil absorption was 35.3% by weight of paper, and V0 way Of cm3/g. For Control 3A, Va was 0.41 cm /g and the ratio Va/Vml was l.S.
(3B) Filaments of MPD-I were prepared substantially as described by Gross in U.S. Patent 3,756,908, column 5, lines 6B-75, and column 6. line6 1-7, resulting in low modulus filaments which were then cut to a floc having a length of about 0.64 cm ~0.25 in) and s1urried in water to a concentration of 0.2~.
Fibrids of MPD-I were prepared as described above for Control 3A and paper6 were prepared by combining the fibrid and the low modulu6 floc at a ratio of fibrid to floc of 1.5 to l.0 (60~ fibrid and 40% floc) in a wet 20-cm (8-in) squale hand6heet mold (e.g., of the type made by Noble and Wood). Paper made in this way are considered to be e6~entially the 6ame a6 papee~ made on a Fourdrinier paper machine.
The wet 6heets were removed from the lO0 mesh screen of the hand6heet mold and dried on hot sheet dryer6 to reduce the moi6ture content to about 5% or lest. The ~heet6 were then platen posed Jo produce samples of 2-ply paper. They were ere~sed at 70.3 kg~cm2 (689.5 kPa; lO00 p8i) and 260C for one minute.
The resulting paper, designated a6 "Control 3B" had a thickness of about 0.29 mm (ll mil6), a den6ity of about 0.77 g/cm3, and a % Vv of 44t by volume of the paper. Vml way 0.58 cm3~q (rounded from 0.5787) and Vmh wa6 0.38 cm fg (rounded ffom 2~,3 0.3793). The compression et was 1.4 mm (54 mils), the oil absorption was 49.9% by weight of the paper, and V0 was 0.58 cm /g. For Control 3B, Va wa6 0.5a cm3/g and the ratio Va/Vml wa6 1Ø
(4) 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 pre~sboard was prepared by applying a pressure of 35 kg/cm2 (3450 kPa: 500 psi) for a period of 45 minute6 at 140C. The low density pressboard was approximately 1.7 mm (68 mils) thick and had a density of 1.00 g/cm3. % Vv was 2~. The low density pres6board was dried at 120C for 4 hrs and pressed at 280C, under low pres6ure at first with brie cycles of release and Leapplication of pres6ure, then for 5 min a 5.8 kg/cmZ. The product, designated "Control 4", was an aramid pres~board approximately 1.6 mm (62 mil6) thick, had a density of 1.12 g/cm3, a compre66ion set of 0.14 mm (5.5 ~il83, an oil absorption of l by weight of pres6board, and V0 was 0.02 cm3/g. % Vv wa6 19~. Vml wa6 0.01 cm /q (rounded from 0.0141~ and Vmh was 0.02 cm Jg (rounded from 0.0173). For "Control 4", Va way 0,02 cm3~g and the ratio Va~Vml was 1.2.
The properties and void parametec6 foc all of the pre66board 6ample6 prepared a6 described in the example, together with the control 6ample6, are listed in the Table. the "Standard Pre66board"
(abbreviated Std. Pres~board~ sample of Part A ox 30 Example 1. is al80 listed. In the Table, the 6amples are li6ted in descending order according to their calculated void volume, % Vv.
The properties and void parametec6 foc all of the pre66board 6ample6 prepared a6 described in the example, together with the control 6ample6, are listed in the Table. the "Standard Pre66board"
(abbreviated Std. Pres~board~ sample of Part A ox 30 Example 1. is al80 listed. In the Table, the 6amples are li6ted in descending order according to their calculated void volume, % Vv.
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Claims (26)
1. High density pressboard comprised of 20-95% by weight aromatic polyamide fibrids and 80-5%
by weight high temperature resistant floc, 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, Vml, of less than 0.20 cm3/g: a mercury intrusion volume at high surface/volume, Vmh. of 0.08 to 0.28 cm3/g, an oil absorption by volume in cm3/g, Vo, of 0.09 to 0.28 and by weight of 8-24 wt.%; and a total available absorption volume in cm3/g, Va, equal to the largest of the values for Vml, Vmh, and Vo; the ratio of Va to Vml being at least 1.1; said pressboard having a compression set of greater than 0.12 mm but no more than 0.5 mm.
by weight high temperature resistant floc, 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, Vml, of less than 0.20 cm3/g: a mercury intrusion volume at high surface/volume, Vmh. of 0.08 to 0.28 cm3/g, an oil absorption by volume in cm3/g, Vo, of 0.09 to 0.28 and by weight of 8-24 wt.%; and a total available absorption volume in cm3/g, Va, equal to the largest of the values for Vml, Vmh, and Vo; the ratio of Va to Vml being at least 1.1; said pressboard having a compression set of greater than 0.12 mm but no more than 0.5 mm.
2. Pressboard of claim 1 wherein the high temperature resistant floc is an aromatic polyamide floc and the pressboard has a density of 1.0 to 1.20 g/cm3.
3. Pressboard of claim 2 wherein at least a portion of the floc consists of poly(p-phenylene terephthalamide).
4. Pressboard of claim 1 wherein at least a portion of the floc is glass fiber floc.
5. Pressboard of claim 2 wherein the aromatic polyamide fibrids and floc consist essentially of poly(m-phenylene isophthalamide).
6. Pressboard of claim 5 wherein the pressboard is comprised of 50-70% by weight fibrids and 50-30% by weight floc.
7. Pressboard of claim 6 wherein the density is 1.02 to 1.17 g/cm3.
8. Pressboard of claim 7 wherein the density is 1.10 to 1.15 g/cm3.
9, Pressboard of Claim 6 wherein the compression set is greater than 0.12 mm but less than 0.35 mm.
10. Pressboard of Claim 9 wherein the compression set is greater than 0.20 mm but less than 0.30 mm.
11. Process for preparing the high density pressboard of Claim 1 whereby an aqueous slurry having 0.1 to 2% by weight total solids comprised of 20-95%
by weight fibrids of an aromatic polyamide and 80-5%
by weight of high temperature resistant floc having a length of 2 to 12 mm, said aromatic polyamide fibrids and said high temperature resistant floc having a melting point higher than 320°C, the slurry is formed into a waterleaf having a water content of 50-95% by weight of the waterleaf; 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/cm2 to form a low density pressboard having a calculated void volume of 30 to 60% by volume of the pressboard, the low density pressboard is dried, ultimately at 270 to 320°C until substantially no further moisture is evolved and then pressed at 8 to 350 kg/cm2 at 270 to 320°C.
by weight fibrids of an aromatic polyamide and 80-5%
by weight of high temperature resistant floc having a length of 2 to 12 mm, said aromatic polyamide fibrids and said high temperature resistant floc having a melting point higher than 320°C, the slurry is formed into a waterleaf having a water content of 50-95% by weight of the waterleaf; 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/cm2 to form a low density pressboard having a calculated void volume of 30 to 60% by volume of the pressboard, the low density pressboard is dried, ultimately at 270 to 320°C until substantially no further moisture is evolved and then pressed at 8 to 350 kg/cm2 at 270 to 320°C.
12. Process for preparing the high density pressboard of Claim 9 whereby an aqueous slurry having 0.1 to 2% by weight total solids comprised of 20-95%
by weight fibrids of an aromatic polyamide and 80-5%
by weight of high temperature resistant floc having a length of 2 to 12 mm, said aromatic polyamide fibrids and said high temperature resistant floc having a melting point higher than 320°C, the slurry is formed into a waterleaf having a water content of 50-95% by weight of the waterleaf; 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/cm2 to form a low density pressboard having a calculated void volume of 30 to 60% by volume of the pressboard, the low density pressboard is dried, ultimately at 270 to 320°C until substantially no further moisture is evolved and then pressed at 8 to 350 kg/cm2 at 270 to 320°C.
by weight fibrids of an aromatic polyamide and 80-5%
by weight of high temperature resistant floc having a length of 2 to 12 mm, said aromatic polyamide fibrids and said high temperature resistant floc having a melting point higher than 320°C, the slurry is formed into a waterleaf having a water content of 50-95% by weight of the waterleaf; 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/cm2 to form a low density pressboard having a calculated void volume of 30 to 60% by volume of the pressboard, the low density pressboard is dried, ultimately at 270 to 320°C until substantially no further moisture is evolved and then pressed at 8 to 350 kg/cm2 at 270 to 320°C.
13. Process for preparing the high density pressboard of Claim 10 whereby an aqueous slurry having 0.1 to 2% by weight total solids comprised of 20-95% by weight fibrids of an aromatic polyamide and 80-5% by weight of high temperature resistant floc having a length of 2 to 12 mm, said aromatic polyamide fibrids and said high temperature resistant floc having a melting point higher than 320°C, the slurry is formed into a waterleaf having a water content of 50-95% by weight of the waterleaf; 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/cm2 to form a low density pressboard having a calculated void volume of 30 to 60% by volume of the pressboard, the low density pressboard is dried, ultimately at 270 to 320°C until substantially no further moisture is evolved and then pressed at 8 to 350 kg/cm2 at 270 to 320°C.
14. The process of Claim 11 wherein the high temperature resistant floc is comprised of an aromatic polyamide.
15. The process of Claim 12 wherein the high temperature resistant floc is comprised of an aromatic polyamide.
16. The process of Claim 13 wherein the high temperature resistant floc is comprised of an aromatic polyamide.
17. The process of Claim 14 wherein the pressboard is comprised of 50-70% by weight of poly \
(m-phenylene isophthalamide) fibrids and 30-50% by weight of poly (m-phenylene isophthalamide) floc.
(m-phenylene isophthalamide) fibrids and 30-50% by weight of poly (m-phenylene isophthalamide) floc.
18. The process of Claim 15 wherein the pressboard is comprised of 50-70% by weight of poly (m-phenylene isophthalamide) fibrids and 30-50% by wieght of poly (m-phenylene isophthalamide) floc .
19. The process of Claim 16 wherein the pressboard is comprised of 50-70% by weight of poly (m-phenylene isophthalamide) fibrids and 30-50% by wieght of poly (m-phenylene isophthalamide) floc.
20. Process of Claim 17 wherein the low density pressboard is dried, ultimately at 275-300°C, and pressed at 275-285°C and 15 to 70 kg/cm2.
21. Process of Claim 18 wherein the low density pressboard is dried, ultimately at 275-300°C, and pressed at 275-285°C and 15 to 70 kg/cm2.
22. Process of Claim l9 wherein the low density pressboard is dried, ultimately at 275-300°C, and pressed at 275-285°C and 15 to 70 kg/cm2.
23. The process of any one of Claim 11, Claim 12 and Claim 13 wherein the final pressboard is cooled under restraint.
24. The process of any one of Claim 14, Claim 15 and Claim 16 wherein the final pressboard is cooled under restraint.
25. The process of any one of Claim 17, Claim 18 and Claim 19 wherein the final pressboard is cooled under restraint.
26. The process of any one of Claim 20, Claim 21 and Claim 22 wherein the final pressboard is cooled under restraint.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US58960184A | 1984-03-14 | 1984-03-14 | |
| US589,601 | 1984-03-14 | ||
| US69779785A | 1985-02-04 | 1985-02-04 | |
| US697,797 | 1985-02-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1242853A true CA1242853A (en) | 1988-10-11 |
Family
ID=27080604
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000476568A Expired CA1242853A (en) | 1984-03-14 | 1985-03-14 | Pressboard and process for its preparation |
Country Status (11)
| Country | Link |
|---|---|
| EP (1) | EP0156587B1 (en) |
| JP (2) | JPH0762319B2 (en) |
| KR (1) | KR900008535B1 (en) |
| AU (1) | AU578270B2 (en) |
| BR (1) | BR8501096A (en) |
| CA (1) | CA1242853A (en) |
| DE (1) | DE3581099D1 (en) |
| DK (1) | DK115685A (en) |
| ES (1) | ES8607451A1 (en) |
| GR (1) | GR850657B (en) |
| MX (1) | MX167850B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS62191599A (en) * | 1986-02-19 | 1987-08-21 | 静岡県 | Production of inorganic paper |
| JP2543346B2 (en) * | 1986-07-25 | 1996-10-16 | 大福製紙株式会社 | Synthetic paper |
| WO1994016142A1 (en) * | 1993-01-04 | 1994-07-21 | Mishima Paper Co., Ltd. | Aramid paper with high surface smoothness |
| US5320892A (en) * | 1993-02-22 | 1994-06-14 | E. I. Du Pont De Nemours And Company | Tough layered papers with improved surface adhesion |
| CN1078645C (en) | 1999-01-22 | 2002-01-30 | 四川省对外经济贸易总公司 | Special synthetic fiber paper and its production |
| US6312561B1 (en) * | 2000-01-21 | 2001-11-06 | E. I. Du Pont De Nemours And Company | Flame barrier compositions and their use |
| CN102216507A (en) * | 2008-11-14 | 2011-10-12 | 纳幕尔杜邦公司 | Processes for making sheet structures having improved compression performance |
| WO2010056665A1 (en) * | 2008-11-14 | 2010-05-20 | E. I. Du Pont De Nemours And Company | Sheet structures having improved compression performance |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3756908A (en) * | 1971-02-26 | 1973-09-04 | Du Pont | Synthetic paper structures of aromatic polyamides |
| JPS5181862A (en) * | 1975-01-16 | 1976-07-17 | Mitsubishi Rayon Co | |
| JPS5263268A (en) * | 1975-10-23 | 1977-05-25 | Unitika Ltd | Method of manufacture of formed product of aromatic polyamide |
| JPS5316070A (en) * | 1976-07-30 | 1978-02-14 | Teijin Ltd | Sheets |
| JPS5465747A (en) * | 1977-11-04 | 1979-05-26 | Motoo Takayanagi | High molecular composite body |
| JPS5549811A (en) * | 1978-10-03 | 1980-04-10 | Mitsubishi Paper Mills Ltd | Laminated insulating board |
| JPS5596506A (en) * | 1979-01-19 | 1980-07-22 | Tokyo Shibaura Electric Co | Method of fabricating coil insulator of oillfilled electric equipment |
| JPS57183499A (en) * | 1981-05-06 | 1982-11-11 | Mitsui Toatsu Chemicals | Sheet like article |
| JPS59211208A (en) * | 1983-05-16 | 1984-11-30 | Fuji Electric Corp Res & Dev Ltd | Laminated insulator for oil-immersed electric apparatus |
-
1985
- 1985-03-12 BR BR8501096A patent/BR8501096A/en not_active IP Right Cessation
- 1985-03-12 AU AU39755/85A patent/AU578270B2/en not_active Expired
- 1985-03-13 EP EP85301728A patent/EP0156587B1/en not_active Expired - Lifetime
- 1985-03-13 MX MX204608A patent/MX167850B/en unknown
- 1985-03-13 DE DE8585301728T patent/DE3581099D1/en not_active Expired - Lifetime
- 1985-03-13 DK DK115685A patent/DK115685A/en not_active Application Discontinuation
- 1985-03-13 ES ES541208A patent/ES8607451A1/en not_active Expired
- 1985-03-14 CA CA000476568A patent/CA1242853A/en not_active Expired
- 1985-03-14 KR KR1019850001634A patent/KR900008535B1/en not_active IP Right Cessation
- 1985-03-14 JP JP60049461A patent/JPH0762319B2/en not_active Expired - Lifetime
- 1985-03-14 GR GR850657A patent/GR850657B/el unknown
-
1995
- 1995-04-18 JP JP7116494A patent/JP2733456B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| MX167850B (en) | 1993-04-15 |
| KR850006461A (en) | 1985-10-05 |
| JP2733456B2 (en) | 1998-03-30 |
| DE3581099D1 (en) | 1991-02-07 |
| ES541208A0 (en) | 1986-05-16 |
| JPH07324296A (en) | 1995-12-12 |
| EP0156587A1 (en) | 1985-10-02 |
| AU3975585A (en) | 1985-09-19 |
| BR8501096A (en) | 1985-11-05 |
| JPH0762319B2 (en) | 1995-07-05 |
| AU578270B2 (en) | 1988-10-20 |
| DK115685A (en) | 1985-09-15 |
| JPS60209100A (en) | 1985-10-21 |
| KR900008535B1 (en) | 1990-11-24 |
| EP0156587B1 (en) | 1990-12-27 |
| ES8607451A1 (en) | 1986-05-16 |
| DK115685D0 (en) | 1985-03-13 |
| GR850657B (en) | 1985-07-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |