Method of producing joint sheet and the joint sheet

Abstract: A joint sheet (7) used as a gasket or packing member for automobiles, ships and the like consists of a first layer (7a) made from a given composition, a second layer (7b) made by mixing finely pulverized scrap pieces of previous joint sheet having a given particle size with a composition for the formation of joint sheet similar to said given composition and a third layer (7c) of the same joint sheet similar to the first layer.

Description: This invention relates to a method of producing a joint sheet of a type used as the material for a gasket or packing for automobiles, ships, various machineries and equipment and the like. US-A-5 292 579 discloses how a joint sheet is produced by inserting a composition for the formation of the joint sheet, comprising inorganic fibers or organic fibers or a mixture thereof, a rubber material, rubber additives and a filler, between a pair of rollers comprising a hot roller and a cold roller to heat and roll the composition, laminating the composition on the hot roller in the form of a sheet, and then peeling off the laminated sheet from the hot roller. Next, the resulting joint sheet is punched out in a shape to be used as packing. However, when the joint sheet is punched out in the form of a packing piece, a great amount of scrap material in the form of punched pieces corresponding to 60-70% of the joint sheet is created, so that there are problems that the material yield is low and the cost is increased. It is, therefore, an object of the invention to alleviate the aforementioned problems and to provide a joint sheet and a method of producing the same. According to a first aspect of the invention, there is provided a method of producing joint sheets comprising the steps of:- kneading a composition 1 for the formation of one joint sheet; feeding the composition between a pair of rollers comprising a hot roller 2 and a cold roller 3; heating and rolling the composition; and removing the resulting sheet from the rollers to obtain said one joint sheet 7, characterised by the steps of:- finely pulverizing scrap material recovered from a previous joint sheet into particles by means of a grinder; and including the resulting particles in the said composition 1 prior to formation of the sheet so that the composition is partly reclaimed, and wherein the reclaimed composition for the formation of joint sheet comprises not more than 50 weight % of particles, and the scrap material is pulverized into particles having a particle size of not more than 1.4 mm, and wherein a first composition not containing said particles is fed between the pair of rollers 2,3, to form a first layer 7a on the hot roller 2, then said reclaimed composition including said particles is fed between the pair of rollers 2,3 to form a second layer 7b on top of the first layer 7a, and a third composition also not containing particles is fed between the pair of rollers 2,3 to form a third layer 7c upon the second layer so that the joint sheet 7 is a laminate of said three layers, said compositions comprising inorganic fibers or organic fibers or a mixture thereof, a rubber material, rubber additives and a filler. According to a second aspect of the invention, there is provided a joint sheet consisting of a first layer made from a first composition for the formation of joint sheets, a second layer made by finely pulverizing scrap material obtained from a previous joint sheet into particles having a particle size of not more than 1.4 mm by means of a grinder and which are included in a second, reclaimed, composition for the formation of joint sheet in an amount of not more than 50 weight%, and a third layer made from a third composition for the formation of joint sheet, the compositions comprising inorganic fibers or organic fibers or a mixture thereof, a rubber material, rubber additives and a filler. The term "scrap material" used herein is understood to include redundant scraps of the composition from the formation of the sheet, defective goods, a fragment produced at a cutting step, in addition to pieces produced in the punching of the sheet. As mentioned above, according to the invention, since pieces of the joint sheet produced in the conventional punching of the joint sheet into the form of packing can be reused, not only is the material yield improved and the cost decreased, but also industrial wastes are reduced. Furthermore, each of the first and third layers in the joint sheet according to the invention form an outer face which is made from a joint sheet material not including the pulverized scrap material of a joint sheet, so that the seal surface is smooth and even and consequently sufficient sealing performance can be developed. The invention will be described with reference to the accompanying drawings, wherein: Fig. 1 is a schematic view illustrating a method of producing a joint sheet; Fig. 2 is a partially enlarged sectional view of a known sheet laminate laminated on a hot roller; Fig. 3 is a partially enlarged sectional view illustrating an embodiment of the joint sheet according to the invention laminated on the hot roller; and Fig. 4 is a graph showing the relation between the amount of scrap material added and the tensile strength of the resulting joint sheet. According to the invention, a composition 1 for the formation of the joint sheet comprising inorganic fibers or organic fibers or a mixture thereof, a rubber material, rubber additives and a filler, which is kneaded, for example, in an agitator, is inserted between a pair of rollers comprising a hot roller 2 and a cold roller 3 (see Fig. 1), whereby the composition 1 is heated and rolled to laminate the composition 1 on the hot roller 2 in the form of a sheet 4. The laminated sheet 4 is peeled off from the hot roller and punched out into a shape to be used as packing. Then, scrap material comprising punched pieces of the joint sheet which do not form the packing are finely pulverized into particles having a particle size of not more than 1.4 mm by means of a grinder and added to the composition mentioned above in an amount of not more than 50 weight% to produce a subsequent joint sheet according to the invention. In Fig. 1, numeral 5 labels a guide for recovering a solvent such as toluene or the like disposed above the cold roller 3, and numeral 6 indicates a solvent recovering vessel. Fig. 2 is a partially enlarged sectional view of the conventional sheet laminate 4 laminated on the hot roller 2, in which numeral 4a is a first layer of the sheet laminate and number 4b a second layer thereof. Fig. 3 is a partially enlarged sectional view of a reclaimed joint sheet 7 of three layer construction according to one aspect of the invention laminated on the hot roller 3, in which numeral 7a is a first layer, number 7b a second layer and numeral 7c a third layer. For the inorganic fiber, use may be made of glass fiber, rock wool, various ceramic fibers, carbon fiber and metal fiber. For the organic fiber, use may be made of aromatic polyamide fiber, fibrillated aromatic polyamide fiber, polyamide fiber, polyolefine fiber and the like. These inorganic fibers and organic fibers may be used alone or in admixture thereof. In the case of the mixture of the inorganic fiber and organic fiber, the mixing ratio of the inorganic fiber to the organic fiber is preferably about 1 : 1 - 4 : 1 in weight ratio. Furthermore, these fibers are preferably compounded into the joint sheet in an amount of about 10-60 weight%. For the rubber material, use may be made of nitrile rubber (NBR), styrene-butadiene rubber (SBR), isoprene rubber (IR), chloroprene rubber (CR), ethylene-propylene rubber (EPM), fluororubber (FPM), silicone rubber (SI) and the like. The rubber material is preferably compounded into the joint sheet in an amount of about 10-30 weight%. For the rubber additives, a vulcanizing agent such as sulfur, zinc oxide, magnesium oxide or the like may be used, and a vulcanization accelerator such as thiazole compound, polyamine compound, sulfenamide compound, guanidine compound or the like may be used. The rubber additives can be compounded into the joint sheet in an amount of about 0.5-10 weight%. For the filler, use may be made of clay, talc, barium sulfate, sodium bicarbonate, graphite, calcium carbonate, carbon black, diatomaceous earth, mica, aluminium sulfate, alumina hydrate, magnesium carbonate and the like. The filler can be compounded into the joint sheet in an amount of about 10-70 weight%. An example of a first composition for the first layer 4a shown in Fig. 2 is shown as follows. Fibrillated aromatic polyamide fiber 15 weight% NBR 12 weight% Rubber additives 3 weight% Filler 70 weight% Toluene 0.4 l per kg of the above mentioned mixture An example of a second composition for the second layer 4b shown in Fig. 2 is shown as follows. Fibrillated aromatic polyamide fiber 10 weight% Glass fiber 10 weight% NBR 18 weight% Rubber additives 2 weight% Filler 60 weight% Toluene 0.4 1 per kg of the above mentioned mixture The above first and second compositions are used to produce a joint sheet as follows. At first, the first composition is inserted between the hot roller 2 heated to 120-150°C and the cold roller 3 maintained at 30-50°C. When the thickness of the first composition reaches 10-20% of the thickness of the desired sheet, the second composition is added onto the first composition to form a sheet laminate shown in Fig. 2. In this case, pressure between the rollers 2, 3 is maintained at about 20-40 bar. Thereafter, the sheet laminate is subjected to a vulcanization treatment at an ambient temperature of 100-150°C in a drying furnace for 30-60 minutes. The thus obtained joint sheet is subjected to punching and used as a packing member. According to the invention, the scrap material from punching the above joint sheet is charged into a grinder, where it is finely pulverized at 5000 rpm into particles having a particle size of not more than 1.4 mm and added to a composition such as those mentioned above for reuse. In the joint sheet according to the invention, the amount of scrap material added is in practice to be not more than 50 weight%. An example of a composition for the formation of the reclaimed joint sheet containing 10 weight%, 30 weight% or 50 weight% of scrap material is shown as follows. Scrap Material 10 weight% 30 weight% 50 weight% Fibrillated aromatic polyamide fiber 18 weight% 6.5 weight% 4 weight% Glass fiber 18 weight% 6.5 weight% 4 weight% NBR 18 weight% 18 weight% 18 weight% Rubber additives 2 weight% 2 weight% 2 weight% Filler 52 weight% 37 weight% 22 weight% Toluene 0.4 l per kg of the above mentioned mixture. Moreover, an embodiment of the reclaimed joint sheet 7 shown in Fig. 3 is shown as follows: Layer First Layer (7a) Second Layer (7b) Third Layer (7c) Fibrillated aromatic polyamide fiber 15 weight% 6.4 weight% 10 weight% Glass fiber - 6.4 weight% - NBR 12 weight% 15 weight% 18 weight% Rubber additives 3 weight% 2 weight% 2 weight% Filler 70 weight% 40.2 weight% 70 weight% Scrap material - 30 weight% - Toluene 0.41 l per kg of the above mentioned mixture. The above compositions can be used to produce a reclaimed joint sheet as follows. At first, the composition for the first layer 7a is inserted between the hot roller 2 heated to 120-150°C and the cold roller 3 maintained at 30-50°C. When the thickness of the composition reaches 10-20% of the thickness of the desired sheet, the composition for the second layer 7b is inserted between the hot roller and the cold roller. When the thickness of the composition on top of the first layer reaches to 70-80% of the thickness of the desired sheet, the composition for the third layer 7c is inserted between the hot roller and the cold roller to form a joint sheet. In this case, a pressure between the rollers 2, 3, is maintained at about 20-40 bar. Thereafter, the sheet laminate may be subjected to a vulcanization treatment at an ambient temperature of 100-150°C in a drying furnace for 30-60 minutes. In the present invention, the reason why the particle size in the fine pulverization of the scrap material is limited to not more than 1.4 mm is due to the fact that when the particle size exceeds 1.4 mm, the particle size as an additive becomes too coarse and lowers the quality of the reclaimed joint sheet. Further, the reason why the amount of the scrap material added is limited to not more than 50 weight% is due to the fact that when the amount exceeds 50 weight%, the quality of the reclaimed joint sheet is degraded. That is, when the scrap material is added in an amount of more than 50 weight% adhesion of the composition to the cold roller is caused in the formation of the sheet and the quality of the resulting reclaimed joint sheet is frequently degraded. Also, as shown in Figure 4, when the amount of scrap punched pieces, added exceeds 50 weight%, the tensile strength falls below a satisfactory value of about 80 kgf/cm 2 . As mentioned above, according to the invention, scrap material comprising punched pieces of the joint sheet after the punching of the joint sheet as packing can be reused, so that not only the material yield is improved and the cost is decreased, but also industrial wastes are reduced. Further, each of the first and third layers in the reclaimed joint sheet according to the invention is made from a joint sheet containing no scrap material, so that the seal surface of the joint sheet becomes smooth and even, and hence sufficient sealing performance can be developed.

Claims: A method of producing joint sheets comprising the steps of:- kneading a composition (1) for the formation of one joint sheet; feeding the composition between a pair of rollers comprising a hot roller (2) and a cold roller (3); heating and rolling the composition; and removing the resulting sheet from the rollers to obtain said one joint sheet (7), characterised by the steps of:- finely pulverizing scrap material recovered from a previous joint sheet into particles by means of a grinder; and including the resulting particles in the said composition (1) prior to formation of the sheet so that the composition is partly reclaimed, and wherein the reclaimed composition for the formation of joint sheet comprises not more than 50 weight % of particles, and the scrap material is pulverized into particles having a particle size of not more than 1.4 mm, and wherein a first composition not containing said particles is fed between the pair of rollers (2,3), to form a first layer (7a) on the hot roller (2), then said reclaimed composition including said particles is fed between the pair of rollers (2,3) to form a second layer (7b) on top of the first layer (7a), and a third composition also not containing particles is fed between the pair of rollers (2,3) to form a third layer (7c) upon the second layer so that the joint sheet (7) is a laminate of said three layers, said compositions comprising inorganic fibers or organic fibers or a mixture thereof, a rubber material, rubber additives and a filler. A method of making a packing piece by forming a joint sheet by the method of claim 1 and punching it out to shape, wherein punched out pieces constitute said scrap material. A joint sheet consisting of a first layer (7a) made from a first composition for the formation of joint sheets, a second layer (7b) made by finely pulverizing scrap material obtained from a previous joint sheet into particles having a particle size of not more than 1.4 mm by means of a grinder and which are included in a second, reclaimed, composition for the formation of joint sheet in an amount of not more than 50 weight %, and a third layer (7c) made from a third composition for the formation of joint sheet, the compositions comprising inorganic fibers or organic fibers or a mixture thereof, a rubber material, rubber additives and a filler. A joint sheet according to claim 3, wherein the inorganic fiber is selected from glass fiber, rock wool, various ceramic fibers, carbon fiber and metal fiber, and the organic fiber is selected from aromatic polyamide fiber, fibrillated aromatic polyamide fiber, polyamide fiber and polyolefine fiber. A joint sheet according to claim 3 or 4, wherein the compositions comprise a mixture of inorganic fiber and organic fiber in a ratio of inorganic fiber to organic fiber of about 1 : 1 - 4 : 1 in weight ratio. A joint sheet according to claim 3, 4 or 5, wherein the joint sheet contains 10-60 weight % of the inorganic fibers or the organic fibers or the mixture thereof as the case may be. A joint sheet according to any one of claims 3 to 6, wherein the rubber material is selected from nitrile rubber, styrene-butadiene rubber, isoprene rubber, chloroprene rubber, ethylene-propylene rubber, fluororubber and silicone rubber and compounded into the joint sheet in an amount of 10-30 weight %. A joint sheet according to any one of claims 3 to 7, wherein the rubber additives are selected from a vulcanizing agent and a vulcanization accelerator, and compounded into the joint sheet in an amount of 0.5-10 weight %. A joint sheet according to any one of claims 3 to 8, wherein the filler is selected from clay, talc, barium sulphate, sodium bicarbonate, graphite, calcium carbonate, carbon black, diatomaceous earth, mica, aluminum sulphate, alumina hydrate and magnesium carbonate, and compounded into the joint sheet in an amount of 10-70 weight %. A packing piece comprising a joint sheet according to any one of claims 3 to 9, punched out to shape.

Inventors: FUJIWARA KEN, HOSHI MASAMICHI, NAKANO HIROYUKI, TATEMICHI YOSHIHIKO, TOMIZAWA TSUTOMU, FUJIWARA, KEN, HOSHI, MASAMICHI, NAKANO, HIROYUKI, TATEMICHI, YOSHIHIKO, TOMIZAWA, TSUTOMU, FUJIWARA, KEN, C/O NIPPON LEAKLESS INDUSTRY CO.LTD, HOSHI, MASAMICHI, C/O NIPPON LEAKLESS IND.CO. LTD, NAKANO, HIROYUKI, C/O NIPPON LEAKLESS IND. CO. LTD
Applicants: HONDA MOTOR CO LTD, NIPPON LEAKLESS INDUSTRY CO LT, HONDA GIKEN KOGYO KABUSHIKI KAISHA, NIPPON LEAKLESS INDUSTRY CO., LTD.
Application year: 1995
Main classification: B32B25
IPC codes: B29K105, C09K3, F16J15, B29D7, B29B17, B29B11, B32B25, B29K21