Papermaking using modified sheet silicates as microparticles
Use of sheet silicates containing amino groups, sulphonic acid groups and/or mercapto groups as microparticles in papermaking, in particular for paper retention and/or drainage.
The invention relates to the use of modified sheet silicates for papermaking, modified sheet silicates per se and processes for their preparation.
In papermaking, microparticle systems are used for improving retention, drainage behaviour and formation (this is understood as meaning the “uniformity” or “degree of flocculation” of paper). These may be both organic and inorganic in nature. They are preferably used in combination with cationic polymers.
Preferably used inorganic microparticles are sheet silicates and silica sols.
In contrast to the organic microparticle systems which exhibit their full effect also in an acidic medium, inorganic microparticle systems based on sheet silicates or silica sol have the disadvantage that they achieve their optimum effect only in a neutral or alkaline medium.
It was an object of the present invention to provide sheet silicates as microparticles for papermaking, which improve the prior art, in particular when used at relatively low pH for accelerating the drainage and improving the retention.
Surprisingly, it has now been found that sheet silicates which are modified with substituted hydroxyalkylsilanes achieve this object.
The invention therefore relates to a process for making paper, wherein the paper retention and/or drainage step is done in the presence of a microparticle which is a sheet silicates containing amino groups, sulphonic acid groups and/or mercapto groups.
In the context of this Application, “acid group” is also understood as meaning salts thereof, in particular alkali metal salts, such as sodium and potassium salts, alkaline earth metal salts, such as magnesium and calcium salts, or ammonium salts.
Preferred sheet silicates are those which were modified with a silane which has, bonded to a silicon atom, a group of the formula I and/or II and/or III
—B—(SO3M)p— (I),
—B—(SH)p— (II),
—B—(NH2)p (III),
in which
- B denotes a (p+1)-valent bridge member,
- p is a number from 1 to 3 and
- M represents hydrogen, alkali metal, in particular Na, Li or K, alkaline earth metal, in particular Mg or Ca, or ammonium.
- B is particularly preferably bivalent, i.e. p represents 1. B preferably represents a linear or branched alkylene group optionally interrupted by one or more oxygen atoms and having 1 to 15 C atoms, a cycloalkylene group having 5 to 8 carbon atoms or a unit of the formulae
B very particularly preferably represents —(CH2)n— in which n=1 to 6, in particular 3.
Sheet silicates having sulphonic acid groups, in particular those of the formula I, particularly preferably those of the formula Ia
—(CH2)3—SO3M (Ia)
are preferably used, M having the abovementioned meaning.
The sheet silicate according to the invention is preferably used in combination with cationic polymers, in particular those from the group consisting of the polyethyleneimines, polyamidoamines, polyacrylamides, polyvinylamines, starch or guar flour, which may optionally be furthermore modified and which may be used individually or in any desired mixture with one another.
Linear or branched compounds having a molecular weight greater than 0.5 million g/mol, in particular of 500 000 to 2 million g/mol, preferably of 700 000 to 1.5 million g/mol, may be mentioned as preferred polyethyleneimines.
Linear or branched compounds having a molecular weight greater than 0.5 million g/mol, in particular of 500 000 to 2 million g/mol, preferably of 700 000 to 1.5 million g/mol, may be mentioned as preferred polyamidoamines.
Preferred polyacrylamides may be both linear and branched. Their molecular weight may be from 2 million to 30 million Dalton, preferably from 2.5 million to 15 million Dalton.
Cationic starches based on potatoes, tapioca, maize, wheat or rice may be mentioned as preferred starch derivatives. They preferably have a degree of substitution of from 0.005 to 0.15, particularly preferably a degree of substitution from 0.02 to 0.08. The starches may optionally also be partially degraded.
The invention furthermore relates to sheet silicates containing sulphonic acid groups and/or mercapto groups and having a sulphur content, based on SiO2 of the sheet silicate, of 0.02 mmol to 1000 mmol, preferably 0.2 mmol to 400 mmol. 1 mmol to 200 mmol are particularly preferred. Here, the amounts are based on 100 g of sheet silicate (mmol/100 g).
Otherwise, the abovementioned preferred ranges are applicable. The sheet silicates according to the invention and having such a sulphur content are preferred in particular when they have a radical of the formula —(CH2)3—SO3M, in which M has the above meaning and in particular represents H or Na.
The invention furthermore relates to a process for the preparation of the sheet silicates according to the invention, which is characterized in that a sheet silicate which is free of SH and SO3M groups and in which M has the above meaning
- a) is reacted with mercapto compounds
for the optional introduction of the SH groups and - b) is reacted with a compound containing SO3M groups or
- b1) is reacted with a compound containing a functional group and the functional group itself is converted into an SO3M group, in particular the mercapto compound obtained according to a) is oxidized, or
- b2) is reacted with a compound containing a functional group and the sheet silicate thus derivatized is further reacted with a compound containing SO3M groups
for the optional introduction of the sulphonic acid groups,
the reaction having been carried out in an aqueous medium having a water content of at least 75% by weight in at least one of the stages a), b), b1) or b2), based on the respective reaction mixture.
The variants a), b) and b1) are particularly preferred.
The compound of the formula III
(CH3)qSi(OR)m(OH)p—(CH2)n—SO3M (III)
in which
- m and p each denote a number from 0 to 3,
- q is 0 or 1
- and the sum of q and m and p is 3,
- n is 1 to 15, preferably 1 to 6, in particular 3,
- M has the above meaning and
- R represents C1-C3-alkyl, in particular methyl or ethyl,
may preferably be mentioned as a compound containing SO3M groups.
Compounds of the formula III which correspond to the formula IIIa
(CH3)qSi(OH)p—(CH2)3—SO3M (IIIa),
in which
- M, p and q have the abovementioned meaning, in particular p represents 3 and q represents 0,
are particularly preferred.
Compounds of the formula IV which correspond to the formula
(CH3)qSi(OH)p—(CH2)3—NH2 (IV),
in which
- p and q have the abovementioned meaning, in particular p represents 3 and q represents 0,
are also particularly preferred.
The unmodified forms are used as the basis for the modified inorganic sheet compounds according to the invention and are then modified. They may be both synthetic and naturally occurring sheet compounds. They include, for example, the sheet silicates or clay minerals or clay mineral-containing allevardite, amesite, beidellite, bentonite, fluorohectorite, fluorovermiculite, mica, halloysite, hectorite, illite, montmorillonite, muscovite, nontronite, palygorskite, saponite, sepiolite, smectite, stevensite, talc, vermiculite and synthetic talc types and the alkali metal silicates maghemite, magadiite, kenyaite, makatite, silinaite, grumantite, revdite and the hydrated forms thereof and the associated crystalline silicic acids. In addition, other inorganic sheet compounds, such as hydrotalcites, double hydroxides and heteropolyacids, may be used.
The invention also relates to a process for the preparation of the modified sheet silicates. In the process according to the invention, they are preferably prepared in aqueous solution.
The process for the preparation of the compounds according to the invention is preferably distinguished by the fact that inorganic sheet compounds which have cation exchange capacities between 10 and 200 meq/100 g, preferably 50-150 meq/g and alkali metal or alkaline earth metal ions as opposite ions are used. These sheet compounds are preferably modified in aqueous dispersions or in dispersions in mixtures of water and polar, water-miscible solvents. The modification is preferably effected in silane concentrations of 0.01 to 90%, preferably 0.1 to 40%, very particularly preferably 0.1 to 35%. The modification is carried out at temperatures between 0° C. and 150° C. It can be carried out either at atmospheric pressure or at elevated pressure. A reaction at normal pressure at temperatures between 15° C. and 80° C. is preferred, very particularly preferably at 15° C. to 50° C. The modification can be carried out at a pH between pH 1 and pH 11. A pH range between 3 and 10.5 is preferred.
The modification is preferably effected at solids contents of sheet silicate in the dispersion of 0.001 to 10% by weight, preferably 0.1 to 5% by weight, particularly preferably 0.1 to 3% by weight.
The modification can be effected both in a separate step and shortly before use in papermaking. The ratio of silane to sheet compound preferably corresponds to 0.002-5 times the cation exchange capacity of the sheet compound used. The modified sheet silicates according to the invention are therefore preferably distinguished by a content of silanes of the formulae I to IV of 0.02 mmol to 1000 mmol, preferably 0.2 mmol to 400 mmol. 1 mmol to 200 mmol are particularly preferred. Here, the amounts are based on 100 g of sheet silicate (mmol/100 g).
The silanes used can be substituted both by alkoxy groups and by hydroxyl groups. The use of trihydroxysilyl compounds which were prepared by hydrolysis of the trialkoxysilanes is preferred. The hydrolysis can be carried out in a one-pot process during the modification or in a separate step.
The invention furthermore relates to a papermaking process which is characterized in that the sheet silicate according to the invention and a cationic polymer are added in any desired sequence to an aqueous fibre suspension and then sheet formation, including drainage and drying of the sheet, is carried out. Such processes are described, for example, in U.S. Pat. No. 5,643,414.
The sheet silicates according to the invention are distinguished by substantially improved efficiency in the drainage rate and the retention, in particular in combination with cationic polymers of low charge density.
EXAMPLES Example 110 g of an ethanolic solution containing 50% by weight of a silane of the formula Si(OCH3)3—(CH2)3—SH are added dropwise to 100 ml of water with vigorous stirring at room temperature. During this procedure, the pH is kept above pH 10 by titration with NaOH. After stirring for one hour at room temperature, the ethanol is distilled off.
80 g of an aqueous solution of Si(OH)3—(CH2)3—SH, which optionally may already be aggregated via hydrogen bridges, are obtained.
Example 2100 g of a solution according to example 1 are oxidized by dropwise addition of hydrogen peroxide. A solution of a silane of the empirical formula Si(OH)3—(CH2)3—SO3H, which may optionally already be aggregated via hydrogen bridges, is obtained.
Example 310 g of an ethanolic solution containing 50% by weight of a silane of the formula Si(OCH3)3—(CH2)3—NH2 are added dropwise to 100 ml of water with vigorous stirring at room temperature. After stirring for one hour at 20 to 40° C., the ethanol is distilled off.
80 g of an aqueous solution of Si(OH)3—(CH2)3—NH2, which optionally may already be aggregated via hydrogen bridges, are obtained.
Example 4583 g of water are initially taken with 541.2 g of 35% strength hydrogen peroxide at 50° C. In the course of 4 hours, 375.9 g of 97% strength 3-mercaptopropyltrimethoxysilane are metered in. Stirring is then continued for a further 2 hours. The pH is adjusted to 2.8 with 50% strength NaOH. The methanol formed during the reaction is distilled off at 50° C. and 130 mbar. Adjustment to a solids content of 25% is then effected with water.
Example 5200 g of a 0.5% strength (w/w) dispersion of a commercial sheet silicate (bentonite) (prepared by weighing in 1 g of this bentonite per 199 g of water and shaking for 12 h at 20° C.) in demineralized water are mixed with a 20% strength (w/w) solution of 3-sulphopropylhydroxysilane in 10% strength NaOH and shaken for 1 week at room temperature (cf. also table 1).
The suspension thus obtained was then washed with demineralized water in a 200 ml ultrafiltration cell over a 25 nm filter (Millipore, USWP 09025) with permanent stirring until the conductivity had decreased to a value of ˜8 μS/cm. The filtration pressure was 4 bar. In the clear filtrate, the pH and the conductivity were measured as a measure of the progress of washing.
The wash process was terminated at conductivities of 20-30 μS/cm (starting from >2000 μS/cm) and a pH of 7-8 (starting from a pH>11). 15-20 wash steps were required for this purpose.
The solids content of the dispersions was determined after the last wash step by means of a drying balance, and the solids content was adjusted back to the original value by adding water.
The efficiency of the compounds from examples 1 to 5 was determined in a known manner by determining the drainage rates in a Mütek DFS 03 apparatus, wire 60/017.
In each case a commercially available, modified sheet silicate not according to the invention served as a standard. Its efficiency was set at 100%.
Carrying Out the Drainage Test
In order to achieve optimum differentiation and comparability between the individual test series, an automated metering and stirring profile is maintained. An apparatus from Mütek (DFS 03) (Dynamic Filtration System) is used for the test. With this apparatus, it is possible, inter alia, to specify stirring profiles as a function of time and to shear the initially introduced substance at up to 1500 rpm.
A paper stock suspension comprising long and short fibre pulp with added GCC (ground calcium carbonate, such as, for example, Hydrocarb® 50 from Omya) was used as a model system for the tests (56% of bleached short fibre pulp, 24% of bleached long fibre pulp and 20% of HYDROCARB® 50). The consistency was 0.5%. As a reference system, a polyacrylamide having a cationicity of 20 mol % and a Brookfield viscosity of 3.91, measured as a 0.1% strength solution in 1 molar NaCl at 60 rpm, was combined with the microparticles. The active substance content of the commercial product was 40% by weight. For measuring the drainage (and the retention) using the DFS 03, the polyacrylamide is used in a concentration of 0.075% by weight (calculated as commercial product) and the microparticles in a concentration of 0.4% by weight (calculated as active substance), based in each case on the paper stock.
For measuring the drainage using the DFS 03, in each case 1 l of stock is initially taken with stirring (500 rpm) and a 0.1% strength solution of the polyacrylamide, which was prepared as described below, is metered in after 20 s. Stirring is then continued for a further 10 s at 500 rpm, and the stirring speed is then increased to 1000 rpm for 20 s. After this phase, the stirring speed is reduced again to 500 rpm and at the same time the microparticle suspension (concentration 0.5% by weight) is added. After stirring for 15 s at 500 rpm, the valve under the wire is opened and the drainage time for a 600 g quantity of water is measured. The drainage time of the zero sample was about 60 s.
Weights Taken:
0.4 g of the polyacrylamide is sprinkled into 99.6 g of water (tap water) with stirring, stirred for 15 minutes (magnetic stirrer 300 rpm) and then allowed to stand for 0.5 h for swelling (switch off stirrer).
The solution is then made up to 400 g (0.1% strength solution) and stirred at 500 rpm for about 2.5 h until everything has completely dissolved.
The increase in efficiency, based on the drainage time of a bentonite not modified according to the invention is obtained as follows:
Increase in efficiency=E(mB)0/EmB·100 [%]
in which
- E(mB)0 is the drainage time [sec] of a bentonite not modified according to the invention
- EmB is the drainage time [sec] of the bentonite modified according to the invention
The following increases in efficiency were obtained:
In contrast to example 6, unpretreated crude bentonites were used in example 7.
In each case 1 g of the crude bentonites 1 to 4 is dispersed in each case in 180 ml of water and stirred overnight with
- 7a. 0.1 mmol of trihydroxysilylpropanesulphonic acid/100 g of solid
- 7b. 1 mmol of trihydroxysilylpropanesulphonic acid/100 g of solid
- 7c. 10 mmol of trihydroxysilylpropanesulphonic acid/100 g of solid
- 7d. 100 mmol of trihydroxysilylpropanesulphonic acid/100 g of solid as an aqueous solution according to example 2 at room temperature and a pH of 7.
The solution is then made up with water to 200 ml.
The efficiency of crude bentonite thus modified was tested as described in example 6 by determining the drainage rate, except that the bentonite is used in a concentration of 0.26%, based on stock. The increase in efficiency was calculated as the ratio of the deviations of the drainage time of the bentonite modified according to the invention and of the crude bentonite from pure polyacrylamide. The following factor is obtained for the increase in efficiency.
Increase in efficiency(ΔEmB/ΔEB)=ΔEB/ΔEB=(E0−EmB)/(E0−EB)
- E0: Drainage time [sec] with pure polyacrylamide (bentonite-free)
- EmB: Drainage time [sec] with bentonite modified according to the invention
- EB: Drainage time [sec] with crude bentonite
In the case of crude bentonite 1 for example, the following drainage times were obtained:
From the difference between the drainage time of 56.6 sec with the use of pure polyacrylamide and the drainage time of 50.3 sec with addition of crude bentonite 1, an acceleration of 6.3 seconds is obtained.
From the difference between the drainage time of 56.6 sec with the use of pure polyacrylamide and the drainage time of 25.8 sec with addition of crude bentonite 1 modified with 0.1 mmol/100 g of sulphosilane, on the other hand, an acceleration of 31 seconds is obtained. An acceleration of drainage by the factor 4.9 was calculated therefrom. The effect of the other bentonites was determined analogously.
The modification of the bentonites is carried out as in example 7 and the testing of the drainage rate as in example 8, except that the trihydroxysilylpropylamine from example 3 is used for the modification.
The following acceleration factors of the drainage times are obtained:
Preparation of an aqueous solution of 3-mercaptotrihydroxysilane:
1 l of water is initially introduced at 40° C. 19.6 g of 3-mercaptotrimethoxysilane are added dropwise in 4 hours. The methanol formed is distilled off at atmospheric pressure. The pH is then adjusted to 12.8 with 20 ml of 50% strength sodium hydroxide solution. A clear aqueous solution is obtained.
Example 11The modification of the bentonite is carried out as in example 7 and the testing of the drainage rate as in example 8, except that the trihydroxysilylpropyl mercaptan from example 10 is used for the modification.
Example 12The efficiency of the crude bentonites thus modified was tested as described in example 6 by determining the drainage rate, except that the bentonite is used in a concentration of 0.26%, based on stock. In comparison with the corresponding crude bentonite accelerations of the drainage rate by the following factors are obtained: (Crude bentonite=1)
The drainage rates were increased by the following factors:
Claims
1. A process for making paper, wherein the paper retention and/or drainage step is done in the presence of a microparticle which is a sheet silicates containing amino groups, sulphonic acid groups and/or mercapto groups.
2. The process according to claim 1, wherein in that the sheet silicates are modified with a silane which has, bonded to a silicon atom, a group of the formula I and/or II and/or III —B—(SO3M)p— (I), —B—(SH)p— (II), —B—(NH2)p (III), in which
- B denotes a (p+1)-valent bridge member,
- p is a number from 1 to 3 and
- M represents hydrogen, alkali metal or ammonium.
3. The process according to claim 1, wherein the sheet silicate, contains at least 0.02 mmol, based on 100 g of solid sheet silicate of an alkylsilane of the general formula (CH3)qSi(OR)m(OH)p—CH2)n—X in which
- X denotes SO3M, SH or NH2 and
- m and p each denote a number from 0 to 3,
- q is 0 or 1 and
- the sum of q and m and p is 3,
- n=1 to 15,
- M represents an element from the group consisting of the alkali metals, alkaline earth metals or ammonium,
- R represents C1-C3-alkyl.
4. The process according to claim 1, wherein the sheet silicate is of the montmorillonite type or of the sheet silicate type containing montmorillonite, contains at least 0.02 mmol, based on 100 g of solid montmorillonite, of an alkylsilane of the general formula (CH3)qSi(OR)m(OH)p—CH2)n—X in which
- X denotes SO3M, SH or NH2 and
- m and p each denote a number from 0 to 3,
- q is 0 or 1 and
- the sum of q and m and p is 3,
- n=1 to 15,
- M represents an element from the group consisting of the alkali metals, alkaline earth metals or ammonium,
- R represents C1-C3-alkyl, in particular methyl or ethyl.
5. The process according to claim 1, wherein the sheet silicate contains at least 0.02 mmol, based on 100 g of solid sheet silicate, of an alkylsilane of the general formula Si(OH)3—(CH2)3—X in which
- X denotes SO3M, SH or NH2.
6. The process according to claim 1, wherein the sheet silicate comprises sheet silicates or clay minerals or clay mineral-containing allevardite, amesite, beidellite, bentonite, fluorohectorite, fluorovermiculite, mica, halloysite, hectorite, illite, montmorillonite, muscovite, nontronite, palygorskite, saponite, sepiolite, smectite, stevensite, talc, vermiculite and synthetic talc types and the alkali metal silicates maghemite, magadiite, kenyaite, makatite, silinaite, grumantite, revdite and the hydrated forms thereof and the associated crystalline silicic acid and other inorganic sheet compounds.
7. A sheet silicate containing sulphonic acid groups and/or mercapto groups and having a sulphur content, based on SiO2 of the sheet silicate, of 0.02 mmol to 1000 mmol, based in each case on 100 g of sheet silicate (mmol/100 g).
8. A sheet silicate according to claim 7 containing sulphonic acid groups and/or mercapto groups and having a sulphur content, based on SiO2 of the sheet silicate, of 0.2 mmol to 400 mmol, based in each case on 100 g of sheet silicate (mmol/100 g).
9. Inorganic sheet silicate compounds wherein they contain at least 0.02 mmol, based on 100 g of solid sheet, of an alkylsilane of the general formula (CH3)qSi(OR)m(OH)p—(CH2)n—X in which
- X=SO3M, SH or NH2 and
- m and p each denote a number from 0 to 3,
- q is 0 or 1 and
- the sum of q and m and p is 3,
- n is 1 to 15,
- M represents an element from the group consisting of the alkali metals, alkaline earth metals or ammonium,
- R represents C1-C3-alkyl.
10. The inorganic sheet silicate compound according to claim 9 which is of the montmorillonite type or of the sheet silicate type containing montmorillonite.
11. The sheet compounds according to claim 9, wherein they contain at least 0.02 mmol, based on 100 g of solid sheet, of an alkylsilane of the general formula Si(OH)3—(CH2)3—X in which
- X has the meaning stated in claim 7.
12. Sheet silicate compounds according to claim 9, wherein the unmodified forms are used as a basis of the inorganic sheet compounds modified according to the invention, it being possible for these to be both synthetic and naturally occurring sheet compounds, such as the sheet silicates or clay minerals or clay mineral-containing allevardite, amesite, beidellite, bentonite, fluorohectorite, fluorovermiculite, mica, halloysite, hectorite, illite, montmorillonite, muscovite, nontronite, palygorskite, saponite, sepiolite, smectite, stevensite, talc, vermiculite and synthetic talc types and the alkali metal silicates maghemite, magadiite, kenyaite, makatite, silinaite, grumantite, revdite and the hydrated forms thereof and the associated crystalline silicic acids and other inorganic sheet compounds.
13. Modified sheet silicate compound according to claim 9, wherein the zeta potential thereof is equal to or greater than the zeta potential of the unmodified sheet compound.
14. Modified compounds according to claim 7 to 9, wherein the colloidal stability is increased in comparison with the unmodified samples.
15. A process for making paper, wherein the paper retention and/or drainage step is done in the presence of a microparticles which is a inorganic sheet silicates according to claim 7 or 9.
16. A process for the preparation of the compounds according to claim 7 or 9, wherein inorganic sheet compounds which have cationic exchange capacities between 10 and 200 meq/100 g and alkali metal or alkaline earth metal ions as opposite ions are used and these sheet compounds are used in aqueous dispersions or dispersions in mixtures of water and polar solvents having mass concentrations <30%, and aqueous silane solutions (corresponding to 1-6) having mass contents of <20% are added to these dispersions, the ratio of silane to sheet compound corresponding to 0.02 to 5 times the cationic exchange capacity of the sheet compound used and the preparation temperatures being between 0 and 100° C. and the pH of the dispersions being between 1 and 10.
Type: Application
Filed: Sep 21, 2005
Publication Date: Oct 12, 2006
Inventors: Karlheinrich Meisel (Odenthal), Bernd Hauschel (Leverkusen), Carlos Moreno Montoya (Leverkusen), Arno Nennemann (Bergisch Gladbach)
Application Number: 11/231,382
International Classification: D21H 17/09 (20060101); D21H 23/76 (20060101); D21H 17/68 (20060101); D21H 17/69 (20060101); D21H 21/10 (20060101);
