CH699926B1 - Corrosion resistant lining laminate. - Google Patents

Abstract

A lining laminate for corrosive media, in particular for hydrofluoric acid, comprises a sealing layer (2) of a fluoropolymer and a lamination (4) applied on one side of the sealing layer, the latter consisting of a fabric which is partially embedded in the sealing layer and partially protruding. The knitted fabric is formed from a fully fluorinated polymer, in particular from PTFE.

Description

Technical area

The invention relates to a corrosion-resistant lining laminate according to the preamble of claim 1 and a method for its production.

State of the art

For the storage and transport of corrosive or aggressive media, it is known to line containers and pipes with an inner layer of a chemical-resistant plastic, in particular of a fluoroplastic. For example, in DE-OS 1 936 118 such a container is described, which is formed by a mechanically or chemically roughened fluoroplastic body with a shell arranged around it made of glass fiber reinforced epoxy or polyester resin. However, it has been found that the bond strength of such roughened surface arrangements is partially inadequate.

Furthermore, chemical-resistant lining laminates are known for use in corrosive environments, comprising a layer of a fluoroplastic with a one-sided embedded adhesion promoter in the form of a knitted fabric or fabric. The adhesion promoter is intended to attach the laminate with the aid of an adhesive system to a structure to be lined, such as a steel container or another part of the plant. For example, commercial web-shaped lining laminates of tetrafluoroethylene-perfluoroalkylvinylether copolymer (also referred to as "perfluoroalkoxy" or PFA) are known, which are equipped with a lamination in the form of a glass fiber knitted fabric by default (eg the product "Symalit <®> PFA" from Quadrant EPP AG in Lenzburg, Switzerland). But other lining laminates such as e.g. Symalit® FEP and Symalit® MFA with fiberglass knitted lamination and Symalit <®> ECTFE and Symalit® PVDF with synthetic knit lamination are commercially available.

The fields of application of such lining laminates include chlorine electrolysis and sodium chlorate production, but also other applications in which severe corrosion protection is necessary.

However, it has been found that the above-mentioned linings, especially in the presence of hydrofluoric acid in the process under certain conditions (depending on the concentration, temperature, pressure) have only a limited life, i. E. After a certain life of, for example, 2 to 3 years, the lining can partially detach from the container wall, since the glass-knitted lamination loses its inherent strength by the permeable hydrofluoric acid.

Presentation of the invention

The object of the invention is to provide an improved lining laminate, which is particularly useful in contact with hydrofluoric acid and granted a longer service life with proper processing. Further objects of the invention is to specify a method for producing the lining laminate according to the invention.

These objects are achieved according to the invention by the characterizing features of claim 1 and by the manufacturing method according to claim 4.

The lining laminate according to the invention comprises a sealing layer of a fluoropolymer and a lamination applied on one side of the sealing layer, wherein the lamination is a partially embedded and partially protruding knitted fabric made of a fully fluorinated polymer in the sealing layer.

The measures according to the invention initially have the consequence that the lamination is resistant to aggressive media and in particular hydrofluoric acid and accordingly the lining laminates can be used with far improved service life for hydrofluoric acid. While other fibers which would be chemically resistant to hydrofluoric acid (e.g., carbon fibers or ECR glass fibers) are not knitable and thus obtainable only as sheetlike, non-drapable fabrics, the present invention provides lamination with three-dimensional formability or stretchability. Thus, the inventive liner laminate can also be used for deep-drawn parts. It will be appreciated that, depending on the configuration of the container or component to be lined, the lining is made, if necessary, from a plurality of blanks of the lining laminate, which are welded together.

It is known that all liquid and gaseous media diffuse into any plastic in a certain amount and permeate through it over time. The time until incipient permeation and the permeation rate are influenced by many factors. The most important are: medium (molecular size, polarity, concentration), temperature gradient, pressure gradient, thickness of the plastic layer. It is also known that hydrofluoric acid, after penetrating the fluoroplastic layer, chemically attacks the usually used laminates made of polyester or glass fiber knit. The concomitant disintegration of the liner results in a highly undesirable decrease in composite adhesion between the liner laminate and backing material, which may later result in delamination of the liner from the vessel wall. In contrast, the knitted fabric formed from a fully fluorinated polymer is not attacked, resulting in a comparatively longer life of the container.

The inventive liner laminate can be used both as an inner liner in a steel lining as well as inner liner in a fiberglass dual-laminate construction.

According to a second aspect of the invention, there is provided a method of making a liner laminate by continuously compressing respective webs of the fluoropolymer and the fabric at temperatures above the softening range of the fluoropolymer.

Preferred embodiments of the invention are defined in the dependent claims.

Basically come as a material for the sealing layer, various thermoplastic fluoroplastics in question. Advantageously, the fluoroplastic is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter also: PFA). The knitted fabric used for the lamination of a fully fluorinated polymer is preferably made of polytetrafluoroethylene (hereinafter also: PTFE), in particular of a PTFE yarn, since PTFE has a very good chemical resistance to almost all chemicals, especially against hydrofluoric acid.

Brief description of the drawings

Embodiments of the invention are described below with reference to the drawings, in which: <Tb> FIG. 1 <sep> a section of a lining laminate, in perspective view; <Tb> FIG. 2 <sep> a section of the lining laminate of FIG. 1, in a vertical sectional view; <Tb> FIG. FIG. 3 shows a detail of a container equipped with the lining laminate of FIG. 1, in a vertical sectional view; FIG. and <Tb> FIG. FIG. 4 shows a section of a dual-laminate construction with a lining laminate of FIG. 1 and a support structure made of glass-fiber-reinforced plastic, in a vertical sectional view.

Ways to carry out the invention

The lining laminate shown in Figs. 1 and 2 comprises a sealing layer 2 made of a fluoropolymer and a liner 4 applied on one side thereof. As the fluoropolymer for the sealing layer, in particular, a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) is used. The lamination is formed by a partially embedded in the sealing layer and partially protruding knit of a fully fluorinated polymer such as PTFE.

The liner serves as an adhesion layer to attach the liner laminate to a container or to reinforce it with a fiber reinforced vinyl ester resin to a dual laminate construction. This is explained in more detail in FIGS. 3 and 4.

As can be seen from Fig. 3, for attaching the lining laminate to the inner wall Wi a container wall W, first the lamination 4 with a suitable adhesive, for example, with an epoxy adhesive E, occupied. In this case, the fabric 4 is impregnated with the adhesive E. Thereafter, the liner 4 is pressed against the inner wall Wi and held until the adhesive has cured. It is understood that the inner wall is pretreated according to the adhesive system used, so for example roughened and degreased.

4 shows a dual laminate in which the lining 4 of the lining laminate according to the invention is bonded to a layer G of a glass-fiber-reinforced polyester or vinyl ester resin.

Such a plant part (container, pipe, reactor, etc.) can be filled with a corrosive medium M such as hydrofluoric acid. Even if small amounts of hydrofluoric acid penetrate through the sealing layer 2 over time, the lining 4 remains undamaged and can further serve as an adhesive layer in which the epoxy adhesive or reinforcing resin is anchored.

The production of the lining laminate is preferably carried out by continuous pressing. In this process, a melt layer of the fluoropolymer provided as the sealing layer and an equally wide web of the fully fluorinated polymer knit are combined in a calender and rolled between the heated calender rolls to form a lining laminate.

Examples

The lining laminates were produced in webs of 10 m length and 1.25 m width with a thickness of 1.5 to 2.8 mm. As a lamination, a knit fabric of fibrillated PTFE yarn having a denier of 880 dtex was used.

In the production of the liner laminate by the extrusion process, the PFA plastic melt (processing temperature to 380 ° C) of the lining laminate, which is provided by the extruder, was fed via a slot die to the nip of a calender with roll temperatures of up to 280 ° C. The fabric also came from the roll to the nip and was embedded in the plastic melt resp. compressed (splitting forces up to 2000 N / cm).

Alternatively, the preparation according to the pressing process would be considered. In this case, an already produced film is heated on one side until it can either be pressed between rolls or on a double belt press with the Kaschiergut.

Claims (4)

A corrosion-resistant liner laminate comprising a fluoropolymer sealing layer (2) and a liner (4) applied to one side of the sealant layer, the liner being a partially embedded and partially protruding fabric in the sealant layer, characterized in that the fabric is made from a fully fluorinated polymer is formed. 2. The lining laminate according to claim 1, wherein the sealing layer is formed of perfluoroalkyl vinyl ether copolymer (PFA). 3. Lining laminate according to claim 1 or 2, wherein the knitted fabric of polytetrafluoroethylene, in particular in the form of yarn, is formed. A method of producing a liner laminate according to claim 1, wherein respective webs of the fluoropolymer and the fabric are continuously pressed together at temperatures above the softening range of the fluoropolymer.