SE1851430A1

SE1851430A1 - Method for hydrophobizing a cellulose substrate by utilizing a fatty acid halide

Info

Publication number: SE1851430A1
Application number: SE1851430A
Authority: SE
Inventors: Carl-Magnus Brandén; Raija Bådenlid; Susanne Hansson
Original assignee: Stora Enso Oyj
Priority date: 2018-11-16
Filing date: 2018-11-16
Publication date: 2020-05-17
Also published as: WO2020100101A1; EP3880884A4; CN113227494A; CN113227495A; KR20210100636A; KR20210100635A; US20220010493A1; US20220002949A1; WO2020100097A1; EP3880884A1; EP3880886A1; EP3880886A4; JP2022507555A; JP2022507536A; SE543029C2

Abstract

The present invention relates to a method for hydrophobizing a cellulose substrate, which comprises a first side and a second side, which faces away from the first side, wherein the method comprising the steps of:- drying the cellulose substrate to a dry content above 80%, preferably above 85%;- providing a fatty acid halide in spray form; and- guiding said fatty acid halide in spray form to contact the first side of the cellulose substrate, and at least partially penetrate the cellulose substrate.

Description

lO METHOD FOR HYDROPHOBIZING A CELLULOSE SUBSTRATE Field of invention Method for hydrophobizing of a cellulose substrate, which comprising a first side and a second side, which faces away from the first side.

Background There is a need to increase the hydrophobicity of materials with a cellulose substrate in several fields, in the e.g. textile industry and the paper- and paperboard industry.

Paper- and paperboard are usually treated with sizing agentsto enhance certain qualities, above all to increase theresistance to penetration of water and other liquids into theinternal paper or paperboard. There are two types of sizing: and surface sizing. In internal sizing, chemicals are added to the pulp at the wet end, e.g. ASA or AKD. Common surfacesizing agents include e.g. starch or acrylic co-polymers.US4lO7426 discloses a method for imparting water-repellentcharacteristics to a surface of a cellulose substrate. Theprocess comprising the steps of exposing the surface to avapour phase consisting essentially of aliphatic acid chloride.

A drawback with this method is that mainly the surface of asubstrate that becomes hydrophobic and not the interior of thei.e. substrate. This causes problem with edge wicking, penetration of liquid into the edges of substrate.In WO20l7002005, a method is described where a vaporized fattyacid halide is arranged to penetrate the cellulose substrate.

However, the equipment required to perform the method lO according to WO20l7002005 is very space consuming andtherefore difficult to implement at an existing production site.

An object with the present invention is to provide an improvedmethod for increasing the hydrophobicity of materials with acellulose substrate that e.g. enhances the water repellency and resistance against edge wicking of a cellulose substrate.

Summary of the invention The inventive method for hydrophobizing a cellulose substratecomprising the following steps: - drying the cellulose substrate to a dry content above 80%,preferably above 85%; - providing a fatty acid halide in spray form; and- guiding said fatty acid halide in spray form to contact thefirst side of the cellulose substrate, and at least partially penetrate the cellulose substrate.

Treating a cellulose substrate according to the method of thepresent invention leads to an increase of the hydrophobicityof the material even at its core, and to enhanced waterrepellency thereof, as well as resistance against edge wicking of a cellulose substrate.

Several additional advantages are also achieved thanks to themethod according to the invention. For example: -the spray device can be aimed in differently defineddirections, -the sprayed reagent will have an even distribution over thesurface even if the surface is rough, -calibration of spray dosage enables for avoiding unwanted surplus of reagent on substrate, lO -the amount of reagent can be easily controlled by adjustingthe spray pressure or the number of spray units, and-the spray nozzles/units do not require to large space whichfacilitates installation at an existing on-line production site.

It is to be understood that “spray form” means in the form ofa plurality of liquid droplets or particles, and that thefatty acid halide in spray form may be delivered by means of aprecision device for dispersion of freely flowing liquid fattyacid halide into said spray form. The droplets or particlesmay be in micro scale with sizes ranging from l-900 um indiameter.

According to one aspect of the invention, the method furthercomprises the step of guiding said fatty acid halide in sprayform to contact also the second side of the cellulosesubstrate by vacuum suction, and at least partially penetrate the cellulose substrate.

The cellulose substrate can be in the form of paper- orpaperboard web, or textiles made from cellulose fibres.The paper- or paperboard web may be a single- or multilayerWeb.

According to one aspect of the invention, the method furthercomprises the steps of: - converting said fatty acid halide in spray form intovaporized fatty acid halide; and- guiding said vaporized fatty acid halide to contact thefirst side of the cellulose substrate, and at least partially penetrate the cellulose substrate. lO According to yet another aspect of the invention, thevaporized fatty acid halide is guided to contact also thesecond side of the cellulose substrate, and at least partially penetrate the cellulose substrate.

Conversion of the fatty acid halide spray into vaporized form may be accomplished by applying thermal energy, i.e. heatingthe spray droplets to a point where they enter gaseous state.As an example, heating of the spray can be performed by IRheating. Other heating devices are conceivable, such as e.g. a hot cylinder, microwaves or similar. Vaporizing of fatty acidhalide in spray form requires lower energy consumptioncompared to vaporizing a freely flowing liquid into gas. As abeneficial consequence, the equipment for converting the sprayinto gas can be made space efficient and therefore be fittedat an existing productions line.

According to another aspect of the invention, said guiding ofthe fatty acid halide is performed by vacuum sucking at thesecond side of the cellulose substrate, such that the fattyacid penetrates the cellulose substrate in a predetermineddirection through the cellulose substrate. Such vacuum suctioncan be generated by means of a vacuum box, a rotating vacuumcylinder or any other suitable vacuum generating equipment.Thanks to the method according to the invention, the covalentdegree will be more even throughout the thickness of thematerial compared to e.g. conventional roll coating of freely flowing reagents onto a running substrate.

The covalent degree is the ratio between the grafted fattyacids and the total fatty acids in the substrate, where thegrafted corresponds the reagent that has reacted and the totalamount is this part together with the free fatty acids that only has been physically absorbed to the substrate.

According to another aspect of the invention, said guiding ofthe vaporized fatty acid halide is performed by vacuum suckingat the first side of the cellulose substrate, so that thevaporized fatty acid is guided along the surface of the firstside of the cellulose substrate in a predetermined directionin such a way that the fatty acid is brought into contact withthe cellulose substrate. In one example, “along the surface”means that the vaporized fatty acid is brought to move substantially parallel with the first side of the substrate.

According to yet another aspect of the invention, the drycontent of the cellulose substrate is above 80%, preferably above 85%, even more preferably above 90%. The higher dry content, the better will the result of the subsequenthydrophobizing be. This is due to that the fatty acid halide has a high reactivity towards water. Therefore, presence ofwater may lead to the undesired formation of fatty acids thatare not attached to the substrate.

According to yet another aspect of the invention, the fattyacid halide can be vaporized and comprises an aliphatic chainlength of between 10 - 22 carbon atoms. Said fatty acid ispreferably selected from palmitoyl chloride (C16), (C18) stearoylchloride or mixtures thereof.According to yet another aspect of the invention, the methodfurther comprises a step of heating the cellulose substrate, before and/or after adding the fatty acid halide.

Figures In the following, the invention will be described further with reference to the drawings, wherein: lO Figure l shows a schematic view of the invention according toa first embodiment, where a fatty acid halide in spray form is applied onto a substrate; Figure 2 shows a schematic view of the invention according toa second embodiment, where a fatty acid halide in vaporized form is applied onto a substrate; Figures 3a-b show schematic views of the invention accordingto a third and fourth embodiments, wherein both the first andsecond sides of a substrate are subjected to a fatty acidhalide; and Figure 4 shows a schematic view of the invention according toa fifth embodiment, where a fatty acid halide in vaporized form is applied onto a substrate.

Detailed description The following detailed description illustrates examples ofsetups for performing the method according to the invention,which may serve to illustrate the principles of the inventiveidea in a non-limiting way. a cellulose substrate l, In Figures l-4, comprising a first side and a second side, is generally referred to as “l”. The second side of said substrate l faces away from the firstside. The cellulose substrate, e.g. a paper- or paperboard web l, is dried in a drying step. The drying is performed by anyconventional drying methods suitable for drying a cellulose substrate. A cellulose substrate of a paper- or paperboard webmay for example be dried by drying cylinders. After the drying step, the cellulose substrate l has a dry content above 80%, preferably above 85% and most preferred above 90%. The higher dry content, the better will the result of the subsequent hydrophobizing be.

The cellulose substrate 1 may thereafter be further dried and heated. The heating is preferably performed in a pre-treatmentstep by IR heating 2 as illustrated in Figs. 1-3. The pre-treatment heating step has several advantages. It will minimize unwanted condensation of the gas upon contact withthe substrate, and also lead to that the subsequent hydrophobizing agent will penetrate better through thesubstrate.

Moreover, any remaining water residues can be further dried; the substrate 1 may possibly be dried even up to 95% dry content.

The first side of the dried and heated substrate 1 is thentreated with a fatty acid halide, in spray form or in gas- phase, to hydrophobize the substrate, such that, the substrate becomes hydrophobic. The applied fatty acid halide will atleast partially penetrate the cellulose of said substrate 1and bind covalently to the fibers therein, increasing thewater repellency of the material. In order to enhance thepenetration of the spray or gas through the substrate, thesecond side of the substrate is subjected to a vacuum suction,simultaneously, during the hydrophobizing of the substrate, such that the spray or gas is transported in a predetermineddirection, through the substrate. This enhances thehydrophobicity of the surface as well as the core of the substrate, such that the substrate will be more resistant against in-plane edge penetration.

The fatty acid halide can be any halide that can be vaporized, however palmitoyl chloride, C16 has, in tests, shown to be particularly suitable. During tests a covalent degree of above 60% has been achieved, compared to conventional AKD sizingwhere just a few percentage of covalent binding can bewhich results in low retention, obtained, which thereby leads to e.g. migration problems, stains and machine stops etc.Another advantage with use of spray or gas for applying thefatty acid halide is that it is very position specific andhydrophobicity is only achieved where the spray or gas canaccess the substrate. The reagent will react with theavailable hydroxyl groups forming HCl as a by-product. Thereagent is also highly reactive towards water and the reactionNevertheless, requires dry substrates. there will always be some presence of water whereupon the corresponding, lessreactive, fatty acid also will be formed as an unboundmolecule. It is therefore difficult to achieve 100% covalent degree. Yet, other advantages with the use of a gas-phase reaction is that the gas can be penetrated and guided throughthe substrate more easily, the reaction is faster and loweramount of chemical reagents are needed compared to application of the same reagent in a liquid state.

Figure 1 illustrates an exemplary way of performing the methodaccording to the invention. A dried and heated cellulosesubstrate 1 in the form of a paper- or paperboard is additionally heated and dried with IR heating from an IR heating box 2. The additional IR heating is optional.

Liquid fatty acid halide is stored in a separate tank 3wherefrom it is ejected through a device 5 for dispersing the liquid into a spray 50. Such device 5 (also referred to as “spray device” 5) can for instance be in the form of a spray nozzle used for atomizing the liquid, i.e. breaking up the fluid into droplets 50. In the present example, the droplets are sprayed by means of the device 5 onto the underlying, running substrate 1. The second side of the substrate 1 is at the same time in contact with a rotating cylinder 6, forinstance a heated cylinder that heats the droplets into gaswhereby the atomized fatty acid molecules react moreefficiently with the cellulose of the substrate. It is alsoconceivable that the rotating cylinder 6 is a vacuum cylinderwith holes (not shown in figure), that sucks the droplets in apredetermined direction through the cellulose substrate 1.Thereby, the cellulose substrate 1 will be hydrophobizedthrough the complete thickness of the substrate.

Another option is that the substrate 1 is arranged to enter(not shown), between two nip rolls preferably heated nip rolls, and that the fatty acid halide is sprayed into the niproll junction whereby the spray droplets are converted intogaseous phase by means of the heated roll/s.

Moreover, the HCl by-product and possibly unreacted e.g.palmitoyl chloride and/or unbound C16 can be removed andcollected for handling.

In Figure 2, a second embodiment according to the present invention is schematically shown. Herein, a dried and heatedcellulose substrate 1 in the form of a paper- or paperboard isoptionally further heated and dried with IR heating from an IRheating box 2, as also previously described in connection with Fig. 1.

Liquid fatty acid halide is stored in a separate tank 3 wherefrom it is transferred e.g. via a tube 4 (or other transferring means) to a device 5 for dispersing the liquid into a spray 50. Such device 5 can for instance be in the form of a spray nozzle used for atomizing the liquid, i.e. breaking up the fluid into droplets 50. In the present example, the droplets are sprayed via the device 5 into a heating chamber 7 such as a pressurized heating tank 7. The spray droplets are heated inside said tank 7 to vaporize into gas-phase, and saidgas 70 is thereafter ejected or deposited through a gasspreading device 71 onto the first surface of said substrate1. The second side of the substrate is at the same time inwith holes contact with a rotating vacuum cylinder 6, (not shown in figure), that sucks the gas in a predetermined direction through the cellulose substrate 1. Thereby, thecellulose substrate 1 will be hydrophobized through thecomplete thickness of the substrate. Moreover, the HCl by-product and possibly unreacted e.g. palmitoyl chloride and/orunbound C16 can be removed and collected for handling.

For both exemplified methods shown in Figs. 1-2, it ispossible to firstly treat the first side of the substrate andsubsequently treat the second side of the substrate with anadditional unit facing the second side of the substrate. Suchtreatment of both side ensures that the whole core of substrate will be modified.

Figures 3a - b show a third and fourth embodiment,respectively, wherein both the first and second side of asubstrate 1 are subjected to hydrophobizing by means ofapplication of a fatty acid halide in spray form.

Referring to Fig. 3a, the substrate 1 is firstly subjected to pre-treatment 2 in the form of heating, e.g. IR heating. Adevice 5 for dispersing liquid into spray is positioned downstream of the pre-treatment 2 at the second side 1b of thesubstrate, adjacent to a rotating cylinder 6 and arranged todirect a spray 50 of fatty acid halide onto the surface of thecylinder 6 which, upon rotating further, will deliver thefatty acid halide onto the surface of the second side 1b ofalso the substrate 1. The rotating cylinder 6 may be heated, l0 to such extent that the sprayed droplet transform into gas before touching the substrate. A vacuum box 8 is arranged at the first side la of the substrate l to draw the reagent into the cellulose structure. According to the herein described third embodiment, the substrate l is further hydrophobized in a subsequent downstream step, wherein fatty acid halide 50' is applied also onto the first side la of the substrate l.

Accordingly, as seen in Fig. 3a, a second device 5' for dispersing liquid into spray 50' is positioned adjacent to a second rotating cylinder 6', said device 5' being arranged to direct a spray 50' of fatty acid halide onto the surface of the cylinder 6' which, upon rotating further, will deliver the fatty acid halide onto the surface of the first side la of thesubstrate l. box 8' The rotating cylinder 6' may be heated. A vacuumis arranged in close proximity of the rotatingat the second side lb of the substrate, cylinder, to guide the reagent to at least partially penetrate the substrate l. The skilled person understands that the equipment (e.g. spray device 5, 5'; vacuum box 8, 8'; cylinder 6, 6' etc) areinterchangeable and that it is possible to firstly treat thefirst side la of the substrate l and thereafter the second side lb.

A fourth embodiment according to the invention is seen in Fig.3b, serving the same purpose as in Fig. 3a, namely to treatboth sides of a substrate l to increase the hydrophobicitythereof. In a similar manner as described for Fig. 3a, thesubstrate l is guided through two subsequent hydrophobizingsteps wherein fatty acid halide is applied firstly onto thesecond side lb of the substrate, and secondly onto the first side la thereof. In the first step, a spray device 5 ispositioned adjacent to a second side lb of the runningsubstrate l and is arranged to direct a spray 50 of fatty acid halide directly onto said surface lb. A vacuum box 8 is ll l0 arranged at the first side la of the substrate, opposing the spray device 5, said vacuum box 8 being arranged to draw thefatty acid halide to at least partially penetrate thesubstrate by means of vacuum suction. A downstream rotatingcylinder 6 may be provided, preferably a heated cylinder, topromote the binding of reagent onto the fibers of the cellulose substrate l.

A corresponding, second hydrophobizing step is arranged downstream of the first cylinder 6, wherebyfatty acid halide is applied also onto the first side la ofthe substrate in a corresponding manner as described for the first hydrophobizing step.

The fatty acid halide in the fourth embodiment can beconverted from spray form to gaseous form before being guidedto contact the substrate l.

In Fig. 4, a fifth embodiment according to the present invention is shown. Herein, said guiding of vaporized fattyacid halide 70 is performed by vacuum sucking 8 at the firstside la of the cellulose substrate, so that the vaporizedfatty acid 70 is guided along the surface of the first side laof the cellulose substrate l in a predetermined direction insuch a way that the fatty acid is brought into contact withthe cellulose substrate l. The vaporized fatty acid is therebybrought to move substantially parallel with the first side ofthe substrate.

To characterize the success of the reaction, contact anglemeasurement was utilized to qualitatively analyze how much thecellulose substrate has been hydrophobized by the method. Anun-treated cellulose substrate had before a contact anglearound 40° and after treatment of the inventive method acontact angle of ll0-l30° on both the first side and the second side of the substrate, despite only one surface was in l2 direct contact with the reagent. Contact angles greater than90° (high contact angle) generally means that wetting of thesurface is unfavourable, so the fluid will minimize contact with the surface and form a compact liquid droplet. l3

Claims

lO C L A I M S (l), which which faces away

1. l. Method for hydrophobizing a cellulose substratecomprising a first side and a second side,from the first side, characterized in that the methodcomprising the steps of: - drying the cellulose substrate (l) to a dry content above80%, preferably above 85%; - providing a fatty acid halide in spray form; and- guiding said fatty acid halide to contact the first side ofthe cellulose substrate, and at least partially penetrate thecellulose substrate (l).

2. Method according to claim l, comprising the step of- converting said fatty acid halide in spray form intovaporized fatty acid halide; and- guiding said vaporized fatty acid halide to contact thefirst side of the cellulose substrate, and at least partiallypenetrate the cellulose substrate (l).

3. Method according to claim l or 2, further comprising thestep of guiding said fatty acid halide to contact also thesecond side of the cellulose substrate, and at least partially penetrate the cellulose substrate (l).

4. A method according to any one of the previous claims,wherein said guiding of the fatty acid halide is performed byvacuum sucking at the second side of the cellulose substrate,such that the vaporized fatty acid penetrates the cellulosesubstrate (l) in a predetermined direction through the cellulose substrate (l).

5. A method according to any one of the previous claims, wherein said guiding of the vaporized fatty acid halide is l4 performed by vacuum sucking at the first side of the ce11u1osesubstrate, such that the vaporized fatty acid is guided alongthe surface of the fist side of the ce11u1ose substrate (1) ina predetermined direction whereby the fatty acid is broughtinto contact with the ce11u1ose substrate.

6. Method according to any one of the previous c1aims, whereinthe dry content of the ce11u1ose substrate is above 90%.

7. Method according to any one of the previous c1aims, whereinthe fatty acid comprises an aliphatic chain length of between10 - 22 carbon atoms.

8. Method according to any one of the previous c1aims, wherein the fatty acid is pa1mitoy1 chloride, C16, stearoy1 chloride,

9. C18 or mixtures thereof.9. Method according to any one of the previous c1aims, whereinthe ce11u1ose substrate (1) is a paper- or paperboard web.

10. Method according to c1aim 9, wherein the web (1) is a mu1ti1ayer web.

11. Method according to any one of the previous c1aims,wherein the method further comprises a step of heating the(1), substrate before and/or after adding the fatty acid ha1ide.

12. Method according to c1aim 11, wherein the substrateheating step is performed by IR heating.

13. Method according to any one of the previous c1aims, wherein the vacuum sucking is performed by a vacuum box (11).

14. Method according to any of claims 1-12, wherein the vacuum sucking is performed by a rotating vacuum cylinder (6).

15. Method according to any one of claims 3 - 14, wherein the conversion of said spray form fatty acid halide into vaporized fatty acid halide is performed by IR heating. 16