EP0685008B1 - Paper-machine felt - Google Patents

Abstract

PCT No. PCT/EP94/03337 Sec. 371 Date Aug. 14, 1995 Sec. 102(e) Date Aug. 14, 1995 PCT Filed Oct. 10, 1994 PCT Pub. No. WO95/16810 PCT Pub. Date Jun. 22, 1995The invention relates to postcondensed paper machine felts comprising a polyamide base fabric and a polyamide coating needled thereon, the paper machine felts having a relative solution viscosity in sulfuric acid in accordance with the DIN 53,727 standard of 5 or more. The invention further relates to a method of increasing the molecular weight of paper machine felts which comprises impregnating the paper machine felts with a solution of postcondensation catalysts, followed by drying and thermally postcondensing the felts below the melting point of the polyamide in a solid phase by the exclusion of oxygen.

Description

The invention relates to the subject matter specified in the claims.

The invention particularly relates to a post-condensed paper machine felt made of a polyamide base fabric and a needled polyamide cover layer.

The invention further relates to a method for increasing the molecular weight the aforementioned paper machine felts.

Paper machine felts usually consist of a base fabric to which a pre-needled nonwoven is needled. In principle, it is also here possible to use spunbonded webs instead of dry-laid nonwovens.

DE-A-40 27 063 describes a process for the production of special high molecular polyamide fibers described by post-condensation. The disadvantage of these post-condensed fibers is that they process poorly because they are very stiff due to their high molecular weights.

More energy must therefore be used for carding and needling and this increased energy expenditure also increases the Risk of fiber damage during processing.

It must also be taken into account that post-condensed fibers in the felt can hardly be fixed again, i.e. Tensions in the fiber built up during processing cannot be completely eliminated will. This favors so-called fiber shedding, i.e. working out Larger fiber fragments or even whole fibers from the felt.

Post-condensed fibers also have practically no thermal shrinkage more. The felts can change during the fixing process, which is also important for the Basic tissue is necessary, no longer pre-compress. This can cause that fiber anchoring is not optimal.

It is therefore an object of the invention to provide paper machine felts which a high chemical resistance, a higher air permeability and a have better abrasion resistance.

This task is accomplished by the post-condensed paper machine felt Claim 1 and solved by the method according to claim 6.

Advantageous embodiments of the invention are in the subclaims contain.

First of all, it is not self-evident for the person skilled in the art that there is a difference in quality between a paper machine felt made of post-condensed fibers according to the prior art and a post-condensed paper machine felt according to the invention exists.

However, it is to be expected that the simultaneous post-condensation of the Basic fabric made of monofilaments and / or multifilaments a certain Advantage arises. Usually, however, is the durability of the base fabric no problem.

However, it was found that, surprisingly, tests on the Felt test press (see also Table 1 below) significant Differences between standard felts and the post-condensed ones according to the invention Paper machine felts result. The post-condensed according to the invention Felt shows a significantly smaller change in air permeability post-condensed during the test compared to the felt Fibers, but the final value is similar for both felts. This is for papermaking is advantageous because the running-in time is shortened and the Felt properties change less during runtime.

It was also surprising to find that the two felts were too clearly differentiate in terms of fiber loss.

Overall, it was found that, surprisingly, an inventive one post-condensed paper machine felt the required good resistance against chemicals and abrasion if it has a solution viscosity of at least 5, measured at 20 ° C (according to DIN 53 727) in Has sulfuric acid.

The polyamide threads of the post-condensed according to the inventive method Paper machine felts consist in particular of aliphatic or partially aromatic polyamide or copolyamide, the aliphatic based on ω-aminocarboxylic acids, Lactams or aliphatic diamines and aliphatic Dicarboxylic acids with 4 to 12 carbon atoms, and the partially aromatic aliphatic monomers based on 4 to 12 carbon atoms. Here are polyamide 4, polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyamide 612, polyamide 1212, polyamide 10T and Polyamide 1 2T preferred.

Inorganic phosphorus compounds, preferably salts or esters of phosphorous acid or orthophosphoric acid or the acids themselves, are used as post-condensation catalysts, H ₃ PO ₄ , H ₃ PO ₃ , Na ₂ HPO ₄ .12 H ₂ O, Na ₂ HPO _3. 5H ₂ O and NaH ₂ PO _{4 are} particularly preferred. The textile fabrics are impregnated, the catalyst content of the preferably aqueous solution being at most 0.5% by weight, preferably 0.1 to 0.3% by weight, particularly preferably 0.2% by weight, based on the amount of textile to be condensed , is. The post-condensation is carried out at temperatures from 160 to 200 ° C., preferably at 170 to 190 ° C., in an inert gas atmosphere or in vacuo for 5 to 48 hours, preferably 6 to 24 hours, particularly preferably 8 to 12 hours.

In a particularly advantageous embodiment of the process according to the invention, the textile fabric is treated with aqueous solutions of H ₃ PO ₄ or H ₃ PO ₃ in quantities of 0.2% by weight, based on the quantity of textile to be condensed, at 180 ° C. in vacuo for 8 hours post-condensed.

The paper machine felt according to the invention made of polyamide threads has 20 ° C a relative solution viscosity, measured as a 1% solution in 98% sulfuric acid (DIN 53 727), of at least 5, preferably at least 6, particularly preferably at least 6.5, very particularly preferably at least 7. The polyamide threads are in particular those made from ω-aminocarboxylic acids or lactams with 4 to 12 carbon atoms or from aliphatic Diamines and aliphatic dicarboxylic acids with 4 to 12 carbon atoms. Here are polyamide 4, polyamide 6, polyamide 11, polyamide 12, Polyamide 46, polyamide 66, polyamide 610, polyamide 612 and polyamide 1212 prefers.

Another embodiment comprises partially aromatic polyamides or copolyamides from aliphatic monomers with 4 to 12 carbon atoms and aromatic monomers with 6 to 12 carbon atoms, in particular Polyamide 10T and polyamide 12T.

A particular advantage of the invention is that it is made of easy to process first low-viscosity polyamide threads without fiber damage in a known per se Way a textile structure can be produced, its molecular weight then according to the invention by post-condensation to a relative Solution viscosity in sulfuric acid is increased by at least 7, whereby at the same time increases the crystallinity and fixes the shape of the textile fabric becomes.

The following examples show embodiments of the invention without to limit them to that.

example 1 Post-condensation of a paper machine felt

A piece of paper machine felt measuring 1 x 0.5 m, consisting of a base fabric made of polyamide 6 monofilament (ηrel = 3.4 ± 0.1) and one needled fleece as a cover layer made of polyamide 6 fibers (Grilon® TM26R, ηrel = 3.4 ± 0.1, measured as a 1% solution in 98% sulfuric acid according to DIN 53 727 at 20 ° C) with an aqueous solution of phosphorous Impregnated acid (0.2 wt .-%, based on the felt weight). After Air drying was done in a laboratory autoclave for 16 hours Vacuum condensed at 180 ° C. The solution viscosity of this post-condensed Paper machine felt was 10.5 ± 0.5 in sulfuric acid.

Example 2

A paper machine felt with the dimensions 2 x 0.2 m consisting of one Base fabric made of polymide 6-thread (monofilament) (ηrel = 3.4) and a needled Fleece as cover layer made of polyamide 6 fibers (Grilon® TM262R, 17th dtex, 90 mm) was with an aqueous solution of phosphorous acid (0.24%) impregnated at 98 ° C for 30 minutes in a dyeing autoclave. The felt was then dried at 60 ° C. for 18 hours. The post-condensation was carried out in a vacuum oven at 180 ° C. for 16 Hours. The analysis data of this sample (sample 2) are in the Tables 1 and 2 listed.

Comparative examples

Sample 3 consists of a felt made of TM262R.

Sample 4 consists of a felt made of TM262R, the fibers being post-condensed (30 minutes, 98 ° C; 16 hours, 180 ° C, vacuum) relative viscosity of the fibers 7.8.

Test conditions

Three felts were made according to the scheme in Figure 1 for the tests. Samples 3 and 4 were considered standard felts and felt 2 was as follows treated:

The felt was in a dyeing autoclave at 98 ° C for 30 minutes with 0.24% impregnated acid solution. After that it is at 60 ° C for 18 Hours. The post-condensation was carried out in a vacuum oven performed at 180 ° C for 16 hours (see Example 2).

Analyzes and results

The relative viscosities of the fibers and the monofilaments were measured in 1% sulfuric acid. sample Fibers Monofilament gray Monofilament white 3rd Standard felt η _rel = 3.3 3.4 3.4 2nd Post-condensation felt η _rel = 6.6 7.3 8.11 4th Standard felt from post-condensed fibers η _rel = 7.8 3.4 3.4

Felt test press

The felts were tested on the FTP-EMS felt test press.

In the test, a test felt of 2 x 0.2 m is clamped in two collets. The collets are connected to each other by a rope under the machine connected and pulled back and forth during the test. The test consists of the partial steps, pressure test, pressure test with high pressure shower and abrasion test. During the pressure test, the felt is pushed back and forth using a pair of pressure rollers moved here (Fig. 2a). Throughout the test before and after the press nip the felt is constantly wetted. The line pressure of the pair of printing rollers can can be set between 0 and 300 kN / m. As a measure of compaction of the felt, the thickness and the air permeability are different Press passes determined.

During the pressure test with a high-pressure shower (high-pressure shower), the felt is pressed before and after the press nip with an oscillating high pressure shower (water pressure 40 bar) wetted (Fig. 2b). The influence of the high-pressure shower is assessed visually and the worked-out fibers, which are collected in a filter weighed.

In the abrasion test with ceramic strips, a "ceramic strip imitation roller" is used (Fig. 3). There are gaps in the transverse direction on this roller milled out so that the remaining webs take the form of squeegees to have. During the test, the felt pattern is pulled under the high-speed cable Abrasive roller pulled back and forth. The behavior of the felts against Abrasion becomes microscopic and by measuring the amount of fiber rubbed off judged.

Test procedure

A. Wash and fix.

B. 100 x printing rollers (DW) at 150 kg / cm line printing.

C. + 2700 x DW = 2800 x DW

D. 200 x high pressure shower (HD) with 40 bar water pressure and pressure rollers at 150 kg / cm.

E. + 800 x HD = 1000 HD.

F. 500 x abrasion roller.

Treatments A to F are carried out in succession on a test specimen. Then felt thickness, air permeability and fiber loss measured in comparison to the untreated sample.

Results

Table 1 shows the results of the samples processed with the felt test press to find.

The thickness of the post-condensed felt (sample 2) changes at least as a result of the test run. Sample 2 has the greatest thickness after the test.

The air permeability of the standard felts (samples 3 and 4) is higher compared to the post-condensed felt (sample 2) both in the unfixed and in the fixed state.

The change in air permeability due to the treatment on the felt test press is lowest in the post-condensed felt (sample 2), i.e. Sample 2 has the most uniform properties over the entire test cycle.

At 30 g / m ² (sample 3) or 26 g / m ^{2, the} fiber loss of the comparative felts is significantly higher than that of the post-condensed felt (sample 2, 21 g / m ² ).

Claims (12)

1. Postcondensed paper machine felt comprising a polyamide batt on a polyamide base, characterized in that the paper machine felt has a DIN 53 727 relative solution viscosity in sulphuric acid of at least 5.
2. Paper machine felt according to Claim 1, having a relative solution viscosity in sulphuric acid of at least 6, preferably at least 6.5, particularly preferably of at least 7.
3. Paper machine felt according to Claim 1 or 2, characterized in that the polyamide is an aliphatic polyamide or copolyamide derived from ω-aminocarboxylic acids or lactams having 4 to 12 carbon atoms, preferably polyamide 4, polyamide 6, polyamide 11 or polyamide 12.
4. Paper machine felt according to Claim 1 or 2, characterized in that the polyamide is an aliphatic polyamide or copolyamide derived from aliphatic diamines and aliphatic dicarboxylic acids having 4 to 12 carbon atoms, preferably polyamide 46, polyamide 66, polyamide 610, polyamide 612 or polyamide 1212.
5. Paper machine felt according to Claim 1 or 2, characterized in that the polyamide is a partly aromatic polyamide or copolyamide derived from aliphatic monomers having 4 to 12 carbon atoms and aromatic monomers having 6 to 12 carbon atoms, preferably polyamide 10T or polyamide 12T.
6. Process for raising the molecular weight of paper machine felts according to any one of Claims 1 to 5, characterized in that the paper machine felt is impregnated with a solution of postcondensation catalysts, subsequently dried and then thermally postcondensed in the solid phase in the absence of oxygen at below the melting point of the polyamide.
7. Process according to Claim 6, characterized in that the postcondensation catalysts used are inorganic phosphorus compounds, preferably phosphorous acid, orthophosphoric acid, their salts or esters, particularly preferably H₃PO₄, H₃PO₃, Na₂HPO₄·12H₂O, Na₂HPO₃·5H₂O or NaH₂PO₄.
8. Process according to Claim 7, characterized in that the postcondensation catalysts are applied to the paper machine felt in the form of aqueous solutions.
9. Process according to Claim 7, characterized in that the catalyst quantity used is not more than 0.5% by weight, preferably 0.1 to 0.3% by weight, particularly preferably 0.2% by weight, based on the paper machine felt quantity to be postcondensed.
10. Process according to any one of the preceding Claims 6 to 9, characterized in that the postcondensation is carried out at temperatures of 160 to 200°C, preferably at 170 to 190°C, in an inert gas atmosphere or vacuo.
11. Process according to any one of the preceding Claims 6 to 10, characterized in that the postcondensation is carried out over a period of 5 to 48 hours, preferably 6 to 24 hours, particularly preferably 8 to 12 hours.
12. Process according to any one of the preceding Claims 6 to 11, characterized in that the paper machine felt is postcondensed at 180°C in vacuo with aqueous solutions of H₃PO₄ or H₃PO₃, 0.2% by weight, based on the paper machine felt quantity to be postcondensed, for 8 hours.

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