JP2002267018A - Resin-coated rubber gasket and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin-coated rubber gasket and its manufacturing method free of deterioration or elution of the rubber and suitable for a plate type heat- exchanger, in particular used in the food industries. SOLUTION: The rubber gasket is formed in a consolidated structure from a cotton-form core rubber 7 consisting of a rubber compound chiefly containing rubber and a reinforcing filler and a resin sheet 6 covering the surfaces of the core rubber, wherein the resin sheet 6 ranges not only over the oversurface and side faces of the rubber gasket 5 but also its undersurface, and therewith a covering part 6' is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gasket used to prevent fluid leakage in a wide range of fields such as piping and equipment, and more particularly to a heat exchange between fluids in the food industry and the chemical industry. The present invention relates to a gasket for a plate-type heat exchanger used in a method and an improvement of a method for producing the gasket.

[0002]

2. Description of the Related Art Generally, a plate-type heat exchanger comprises a plurality of rectangular heat transfer plates 1 having holes serving as fluid passages 3 at four corners of a heat transfer surface 2 as shown in FIG. The gasket 5 has a laminated structure. By changing the shape of the gasket 5, two kinds of fluids alternately pass through the heat transfer surface 2 on the heat transfer plate 1 and exchange heat through the heat transfer plate 1. And is widely used in the food and chemical industries. The gasket 5 used in the plate heat exchanger is mounted in the groove 4 on the outer periphery of the heat transfer plate 1 and plays an important role for sealing between two kinds of fluids and between the fluid and the outside. An elongated rubber molded product having a polygonal cross section is often used.

The gasket 5 is generally formed by cross-linking a rubber compound containing rubber and carbon black as main components. The types of rubber used include ethylene propylene rubber (EPM and EPDM) and acrylonitrile butadiene rubber. (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), fluorine rubber (FKM), and the like are properly used depending on the type and temperature of the fluid.

In the food industry, short-time sterilization at a high temperature has become the mainstream, and the temperature of the internal fluid has been reduced to 15%.
The temperature rises to about 0 ° C in many cases, and a cleaning chemical such as an acid is used as a fluid for cleaning the inside of the heat exchanger. In No. 5, the separation of carbon black due to the deterioration of the rubber, the elution of components in the rubber, and the like are observed, which may be a problem. So, in recent years,
Gaskets coated with a fluororesin which has high heat resistance and chemical resistance and does not cause deterioration or elution have been used, and the present inventors have developed a rubber and reinforcing filler as shown in FIG. Core rubber 7 made of a rubber composition mainly composed of: a resin sheet 6 covering the surface of the core rubber
(Japanese Patent Application No. 11-2402).
03).

[0005]

However, the resin-coated rubber gasket as described above is used by mounting it in a groove corresponding to the shape of the gasket as shown in FIG. Was limited to the upper side and the upper side.

On the other hand, some types of plate heat exchangers have a structure in which a part or all of the heat transfer surface where the gasket is installed has no groove. In such a case, the gasket described above is used. As shown in FIG. 12, there is a possibility that the rubber portions on the lower side and the lower side of the gasket come into contact with the fluid, and the components in the rubber elute.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and maintains a predetermined value of tensile strength, elongation and compression set even when used under high temperature or under chemicals. It is an object of the present invention to provide a gasket which is free from deterioration and eluted matter and is particularly suitable for a plate heat exchanger used in the food industry, irrespective of the shape of a groove in a plate.

[0008]

In order to achieve the above object, the present invention provides a linear core rubber comprising a rubber composition mainly composed of rubber and a reinforcing filler such as carbon black; In a resin-coated rubber gasket in which a resin sheet covering the surface of the core rubber is integrated, the gist is that the resin sheet extends around the lower surface in addition to the upper and side surfaces of the rubber gasket. Further, in order to achieve the same object, the present invention provides a sheet made of resin,
In a method for producing a resin-coated rubber gasket, in which a rubber composition mainly composed of an uncrosslinked rubber and a reinforcing filler is brought into contact with the rubber composition, a pressure is applied at the crosslinking temperature of the rubber. The gist of the present invention is to attach a coating mold that covers a part of the gasket so that the resin flows to the lower surface in addition to the upper and side surfaces of the gasket.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a resin-coated rubber gasket of the present invention (hereinafter, simply referred to as "gasket") in correspondence with FIG. 10 showing a conventional gasket. FIGS. 2A and 2B are cross-sectional views illustrating a method of manufacturing a gasket according to the present invention.

As shown in the figure, a gasket 5 according to the present invention comprises a linear core rubber 7 made of a rubber composition mainly composed of rubber and a reinforcing filler such as carbon black;
In a resin-coated rubber gasket in which the resin sheet 6 covering the surface of the core rubber is integrated, the resin sheet 6
Has a covering portion 6 'which extends to the lower surface in addition to the upper and side surfaces of the rubber gasket. In addition, it is also possible to use silica as a reinforcing filler. As shown in FIG. 2A, the gasket 5 is provided with a lid (here, a coating die 10) that does not completely hide the opening surface of the cavity of one die (here, the lower die 9). A resin sheet 6a is stretched so as to cover the resin sheet, an adhesive is applied on the resin sheet 6a, and a rod-shaped body 7 made of a rubber composition mainly composed of uncrosslinked rubber and carbon black is formed.
a, and then, as shown in FIG. 3B, the other mold (here, the upper mold 8) is mounted, and the molds 8, 9 are maintained at the rubber crosslinking temperature and at a predetermined pressure. Press. By this heat molding, the rod-shaped body 7a is formed into a predetermined cross-sectional shape with cross-linking, and at the same time, the resin sheet 6a is integrally joined to the surface thereof. Covered by Reference numeral 6 'denotes a covering portion that covers a part of the rubber portion on the lower surface. Then, the molds 8 and 9 are removed, and the excess resin sheet 6a is removed, whereby the gasket 5 shown in FIG. 1 is obtained. If necessary, the gasket 5 may be subjected to secondary crosslinking using an oven.

In the above description, the type of the coating die 10 is not particularly limited. For example, as shown in FIG. As shown in FIG. 4, an example in which the coating die 10 is incorporated in a part of the lower die 9 can be used.

In the above description, a fluororesin sheet is used as the resin sheet, and the type thereof is not particularly limited. For example, polytetrafluoroethylene (PTFE) and tetrafluoroethylene / perfluoroalkylvinyl ether copolymer are used. Coalescence (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), polyvinylidene fluoride (PVD)
F), an ethylene / tetrafluoroethylene copolymer (E
TFE), polychlorotrifluoroethylene (PCTF
E) and the like. In addition, as the resin to be used, any resin-based material such as general-purpose plastics such as polyethylene and polypropylene can be applied in addition to the fluorine-based resin. The thickness is 0.01 mm or more in consideration of chemical resistance, sealability and moldability.
A sheet in the range of 0.5 mm is used, but is preferably 0,5 mm.
05 mm to 0.25 mm. This is because if the thickness of the sheet is too thin, the fluororesin sheet 6a is stretched at the time of integral molding in FIG. This is because the work of fitting into the groove becomes difficult, and the resin sheet 6 is easily deformed due to stress relaxation and leaks easily.

Further, it is preferable to apply an appropriate surface treatment to the surface of the resin sheet 6a on which the rods 7a are placed.
As the treatment liquid, for example, in the case of a fluororesin sheet,
A complex compound solution obtained by adding sodium metal to a solution of naphthalene in tetrahydrofuran can be used. Thereby, the adhesiveness between the fluororesin sheet 6 and the core rubber 7 can be further improved. Also, the resin sheet 6
As the adhesive applied to a, for example, in the case of a fluororesin sheet, an organosiloxane can be used. This adhesive need not be applied to the entire surface of the fluororesin sheet 6a, but may be applied along the groove of the cavity of the mold 9. In the joint portion between the core rubber 7 of the gasket 5 and the fluororesin sheet 6, the joining strength is particularly low at the bent portion of the core rubber 7, and therefore, the cavity of the mold 9 corresponding to the bent portion of the core rubber 7. By applying the adhesive along the groove, the peeling of the fluororesin sheet 6 at this portion can be suppressed.

On the other hand, the kind of the rubber composition forming the core rubber 7 is not particularly limited, and is appropriately selected according to the use conditions. For example, when used for a gasket for a plate heat exchanger, ethylene propylene rubber (EP
M, EPDM), acrylonitrile butadiene rubber (N
BR), hydrogenated acrylonitrile butadiene rubber (H
NBR), fluoro rubber (FKM) and the like can be used, but resins generally used for sealing materials such as thermoplastic elastomers can also be used. Can be.

As a type of carbon black which is a typical reinforcing filler, carbon black used as a usual rubber reinforcing agent such as MT, FEF, SRF and HAF type can be used. In order to obtain good values of elongation, compression set, and the like, it is desirable to use a finer particle size than HAF. As the cross-linking agent, those conventionally used for this type of gasket may be used, but in particular, when applied to a plate heat exchanger in the food industry, it is preferable to use a peroxide-based cross-linking agent. . Further, a known co-crosslinking agent may be used in combination.
If necessary, other additives conventionally used for this type of gasket may be added. The composition of the rubber composition containing these is not limited, and is appropriately selected according to the required physical properties.

[0016]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. (Example 1) As shown in FIG. 2 (a), a lid (coating die) 10 is attached to a molding die (lower die) 9 so that the entire opening surface of the cavity is not hidden, and the PTFE resin is 1500 mm thick.
× 500 mm, formed into a sheet having a thickness of 0.2 mm, and a pin hole for positioning was formed in a fluororesin sheet 6a having one surface treated with a complex compound solution obtained by adding metallic sodium to a tetrahydrofuran solution of naphthalene, Coating die 10 so that the surface treatment surface faces molding die (upper die) 8.
Is stretched so as to cover a part of the cavity opening surface of the molding die (lower die) 9 on which the adhesive (organo) is attached along the groove shape of the cavity on the surface treatment surface of the fluororesin sheet 6a. After the application of siloxane), a rod 7a formed by extruding an uncrosslinked rubber composition comprising EPDM rubber, a peroxide-based crosslinking agent (dicumyl peroxide), and carbon black into a rod is placed, and then FIG. After pressurizing with the upper die 8 and heating at 170 ° C. for 20 minutes as shown in (b), the molded product is taken out of the dies 8 and 9, excess burrs are cut off, and furthermore, it is heated at 170 ° C. for 2 hours in an oven. Gasket 5 whose cross section is shown in FIG.
Was prepared.

(Embodiment 2) As shown in FIG.
A coating die 1 having a semi-cylindrical convex portion 11 having a radius of 0.8 mm for forming a groove for dispersing stress in a TFE coated portion.
A gasket 5 having a cross section shown in FIG. 6 was produced in the same manner as in Example 1 except that 0 was used. Reference numeral 6 'denotes a covering portion that covers a part of the lower rubber portion.

(Embodiment 3) As shown in FIG. 7, a semi-cylindrical convex portion having a radius of 0.8 mm for attaching a groove for dispersing stress to a rubber portion on a lower surface of a molding die (upper die) 8 is shown. A gasket 5 having a cross section as shown in FIG. 8 was produced in the same manner as in Example 1 except that 11 was attached.

Comparative Example 1 A gasket 5 having a cross section as shown in FIG. 10 was produced in the same manner as in Example 1 except that the coating mold was not used.

Table 1 shows the results of a test in which the gaskets of Examples 1 to 3 and Comparative Example 1 were set on a plate having no groove and whether or not the lower rubber portion was in contact with the fluid.

[0021]

[Table 1]

As can be seen from Table 1, each of the gaskets of Examples 1 to 3 is better than that of Comparative Example 1 without contact with the fluid. Further, the gaskets of the second and third embodiments in which a groove is formed on the lower surface of the gasket also have an effect that the stress concentrated at the boundary between the fluororesin and the rubber is dispersed by the groove.

Although the present invention has been described in detail,
The present invention is not limited to the above, and various modifications are possible. For example, in a gasket having a groove on the lower surface, the cross-sectional shape of the groove is arc-shaped. However, it is needless to say that the shape can be changed to another shape, and the groove is linear, but can be curved. Further, the present invention can be suitably used not only as a gasket for a plate-type heat exchanger, but also as various other sealing materials, particularly as a sealing material exposed to high temperatures or chemicals.

[0024]

As described above, according to the present invention, the rubber portion of the gasket can be used even in a plate heat exchanger having a structure in which some or all of the heat transfer surface gasket installation portion has no groove. Since there is no contact with the fluid, there is no deterioration or elution of rubber, and it is possible to provide a gasket particularly suitable for a plate heat exchanger used in the food industry.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a fluororesin-coated rubber gasket according to the present invention.

FIG. 2 is a configuration diagram of a molding die for explaining a method of manufacturing a fluororesin-coated rubber gasket according to the present invention.

FIG. 3 is a configuration diagram of another mold for explaining a method of manufacturing a fluororesin-coated rubber gasket according to the present invention.

FIG. 4 is a configuration diagram of another mold for explaining a method of manufacturing a fluororesin-coated rubber gasket according to the present invention.

FIG. 5 is a configuration diagram of another mold for explaining a method of manufacturing a fluororesin-coated rubber gasket according to the present invention.

FIG. 6 is a sectional view showing another embodiment of the fluororesin-coated rubber gasket according to the present invention.

FIG. 7 is a configuration diagram of another mold for explaining a method of manufacturing a fluororesin-coated rubber gasket according to the present invention.

FIG. 8 is a sectional view of a fluororesin-coated rubber gasket showing another embodiment of the present invention.

FIG. 9 is a diagram showing an example of a plate heat exchanger.

FIG. 10 is a cross-sectional view of a conventional fluororesin-coated rubber gasket.

FIG. 11 is a cross-sectional view showing contact with a fluid when a conventional fluororesin-coated rubber gasket is used in a groove.

FIG. 12 is a cross-sectional view showing contact with a fluid when a conventional fluororesin-coated rubber gasket is used without entering a groove.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat transfer plate 2 Heat transfer surface 3 Fluid passage 4 Groove 5 Gasket 6 Fluororesin sheet 6 'Coating part which covers a part of lower surface of core rubber 6a Fluororesin sheet 7 Core rubber 7a Bar-shaped rubber composition Body 8 Mold (upper mold) 9 Mold (lower mold) 10 Coating mold 11 Semi-cylindrical 12 Fluid

Claims (3)

[Claims] 1. A rubber gasket in which a linear core rubber made of a rubber composition containing rubber and a reinforcing filler as main components, and a resin sheet covering the surface of the core rubber are integrated. A resin-coated rubber gasket, characterized in that the resin sheet extends around the lower surface in addition to the upper and side surfaces of the rubber gasket. 2. The resin-coated rubber gasket according to claim 1, wherein the resin sheet is a fluororesin. 3. A resin-coated rubber gasket which is pressure-formed at a crosslinking temperature of said rubber in a state where a sheet made of a resin is brought into contact with a rubber composition mainly composed of an uncrosslinked rubber and a reinforcing filler. 3. The method of manufacturing a resin-coated rubber gasket according to claim 1, wherein a resin is wrapped around the lower surface in addition to the upper surface and side surfaces of the gasket by attaching a coating die covering a part of the rubber lower surface to the mold.