SE543029C2 - Method for hydrophobizing a cellulose substrate by utilizing a fatty acid halide - Google Patents

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 said method comprising the steps of:- drying the cellulose substrate (1) to a dry content above 80%, preferably above 85%;- providing a fatty acid halide in spray form;- converting said fatty acid halide in spray form into vaporized fatty acid halide; and- guiding said vaporized fatty acid halide 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 BY ÜTILEZING A FÅTT? ÅCIÛ HÄLIDÉ 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 fatty acid halide is arranged to penetrate the cellulose substrate. lO However, the equipment required to perform the methodaccording 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; ~ converting said fatty acid halide in spray form intovaporized fatty acid hal;*e, and - guiding said vaporized fatty acid halide Å off tocontact the first 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 defined directions, lO -the sprayed reagent will have an even distribution over thesurface even if the surface is rough, -calibration of spray dosage enables for avoiding unwantedsurplus of reagent on substrate, -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 which facilitates 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 vaporized fatty acid halide "L to contact also the second side of the cellulose substrate 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 multilayer Web. .finw- enx "å lO ff vw. 1 r' ë-lfw- " l l »w- r “ « w-r- -1 « lLJ. 1 , J- v.. , - ”LJ- 4 b. . »LL 4 .,._ k ,f n. , ._ f. b. ML k4._.,L._v % r ' l -l f 111 % ,^ JJ .L. A..J.-_ JL).

I ., ,~ ï-'n , 4-, “A+ »f ,J~1»-~.~ ~ _, 4- .J~ +.«\. 1 «\~ ~q~ n rlq L \J _/_L.\,\._. vi! W V.. vtLlm/LJLJ. V4.. .Aflyt \J\.. ~ '_ V..¿¿\/ 4; I v '._,_L I \.. 1» f» =-r L. 1 ' »w 1 wa “ 111. L,Lv. k ...,_A._ \ 4.1 , ._L4 J, 41. , u, LL J 4.1. . ,Å..L-f' r l'11“ L %-v-»- J 4 l r l*J l J JL I J JJ.. A. i JJ 1 L l l kx» J 1. L.f J» +~ f! - : l« ! 1 -.J» -~4~. ._ J. J. J _, ._ .L. W J x. LA. _. I. k, J 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 halide penetrates the cellulose substrate in apredetermined direction through the cellulose substrate. Suchvacuum suction can be generated by means of a vacuum box, arotating vacuum cylinder or any other suitable vacuumgenerating equipment. Thanks to the method according to theinvention, the covalent degree will be more even throughoutthe thickness of the material compared to e.g. conventionalroll coating of freely flowing reagents onto a running substrate. lO |15 The covalent degree is the ratio between the grafted fatty acid halides and the total fatty acid halidgs in the substrate, where the grafted corresponds the reagent that hasreacted and the total amount is this part together with thefree fatty acid halides that only has been physically absorbedto 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 halide is guided along the surface of thefirst side of the cellulose substrate in a predetermineddirection in such a way that the fatty acid halide is broughtinto contact with the cellulose substrate. In one example,“along the surface” means that the vaporized fatty acid halideis brought to move substantially parallel with the first sideof 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 acidhalides that are 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 lO - 22 carbon atoms. Said fatty acid halideis preferably selected from palmitoyl chloride (C16), (Cl8) stearoyl chloride or mixtures thereof. lO 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: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 according to a third and fourth embodiments, wherein both the first andsecond sides of a substrate are subjected to a fatty acidhalide; andFigure 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 inventive idea in a non-limiting way. lO In Figures l-4, a cellulose substrate l, 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 firsta paper- or paperboard web side. The cellulose substrate, e.g.l, is dried in a drying step. The drying is performed by anyconventional drying methods suitable for drying a cellulosesubstrate. A cellulose substrate of a paper- or paperboard webmay for example be dried by drying cylinders. After the dryingstep, the cellulose substrate l has a dry content above 80%,preferably above 85% and most preferred above 90%. The higherdry content, the better will the result of the subsequent hydrophobizing be.

The cellulose substrate l may thereafter be further dried and heated. The heating is preferably performed in a pre-treatmentstep by IR heating 2 as illustrated in Figs. l-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 subsequenthydrophobizing agent will penetrate better through the any remaining water residues can be substrate. Moreover, further dried; the substrate l may possibly be dried even up to 95% dry content.

The first side of the dried and heated substrate l 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 land 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 predetermined direction, through the substrate. This enhances thehydrophobicity of the surface as well as the core of thesubstrate, 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 above60% has been achieved, compared to conventional AKD sizingwhere just a few percentage of covalent binding can be which 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 reactionrequires dry substrates.

Nevertheless, there will always be some presence of water whereupon the corresponding, less reactive, fatty acid halide also will be formed as an unbound molecule. 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. 'ctrate 1. The outline shown in Figure 1 ii mot U ínvention, but is shown for improved underst«nding of the concept. ¿trf :Qing the ifthci io ord? ..« A dried and heated cellulose substrate 1 inthe form of a paper- or paperboard is additionally heated anddried with IR heating from an IR heating box 2. The additional IR heating is optional. T Liquid fatty acid halide is stored in a separate tank 3wherefrom it is ejected through a device 5 for dispersing the(also referred to as liquid into a spray 50. Such device 5 “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 dropletsare sprayed by means of the device 5 onto the underlying,running substrate 1. The second side of the substrate 1 is atthe same time in contact with a rotating cylinder 6, forinstance a heated cylinder that heats the droplets into gaswhereby the atomized fatty acid halide 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 enterbetween two nip rolls (not shown), 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 heated cellulose 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 liquidinto 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 7such as a pressurized heating tank 7. The spray droplets areheated 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 a l0 substrate l are subjected to hydrophobizing by means of application of a fatty acid halide in spray form.

Referring to Fig. 3a, the substrate l is firstly subjected to pre-treatment 2 in the form of heating, IR heating. A e.g.device 5 for dispersing liquid into spray is positioneddownstream of the pre-treatment 2 at the second side lb 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 lb ofthe substrate l. The rotating cylinder 6 may be heated, alsoto such extent that the sprayed droplet transform into gasbefore touching the substrate. A vacuum box 8 is arranged atthe first side la of the substrate l to draw the reagent intothe cellulose structure. According to the herein describedthird embodiment, the substrate l is further hydrophobized ina subsequent downstream step, wherein fatty acid halide 50' isapplied also onto the first side la of the substrate l. a second device 5' for Accordingly, as seen in Fig. 3a, 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 vacuum is arranged in close proximity of the rotating cylinder, at the second side lb of the substrate, 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. ll l0 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 acidhalide directly onto said surface lb. A vacuum box 8 isarranged at the first side la of the substrate, opposing thespray 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 thecellulose 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 presentHerein, invention is shown. acid halide 70 said guiding of vaporized fattyis performed by vacuum sucking 8 at the firstside la of the cellulose substrate, so that the vaporized fatty acid halide 70 is guided along the surface of the first side la of the cellulose substrate l in a predetermined l2 lO direction in such a way that the fatty acid halide is broughtinto contact with the cellulose substrate l. The vaporizedfatty acid halíde is thereby brought to move substantiallyparallel with the first side of the 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 llO-l30° on both the first side and thesecond side of the substrate, despite only one surface was indirect 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 (14)

1. C L A I M S 1. Method for hydrophobizing a cellulose substrate (1), whichcomprising a first side and a second side, which faces awayfrom the first side, characterized in that the methodcomprising the steps of: - drying the cellulose substrate (1) to a dry content above80%, preferably above 85%; - providing a fatty acid halide in spray form; and - converting said fatty acid halide in spray form into vaporized fatty acid halide; - guiding said vaporized fatty acid halide to contact thefirst side of the cellulose substrate, and at least partially penetrate the cellulose substrate (1). f) MI 4- rÃ| fifimnvvJ-Änm 4- m1 -x-Äm 'l n vvnA-wÅn-Ãnrv -l-ln m4- v\ -F L.. Lrvpixvvl uLL/px/Lvliiixj pv \_,4_u.|..1.u. 4., x., iuyriuiixg pxxx., ut, tJ 4.-F.L nnnx-r v-i-Ävw/v n-w-Érluvxivvipiiia uuiu rvau-Ãnlånrv n-wÅrJ x--r-ww väv fl F-x-I-í-xv -wm-É/J lfxfi-l-IÅ +- f~< vwi-fwm-I- -l-'ln 'fiuiuilxxj uumu vutJx/Lippvl Lucy] uL/.Lu 1.1.u_|__Lvl\., cv x/vlipupt. LLM..v~ Å -F +lmm m "I 1111 n nnlfin-F-v--w-i- -xvxrl -x-f- 1 -xn-i- -x +-'.1_ ut v.l_ L.11\_, px/.Lmumvup uuuquptupb, uxiu UL. .Lpuap u L, H|..| -wïïwvu_|__|__y 'U gå. Method according to claim 1-er-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 (1). É4. 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 (1) in a predetermined direction through the cellulose substrate (1). gå. A method according to any one of the previous claims,wherein said guiding of the vaporized fatty acid halide isperformed by vacuum sucking at the first side of the cellulosesubstrate, such that the vaporized fatty acid is guided alongthe surface of the fist side of the cellulose substrate (1) ina predetermined direction whereby the fatty acid is brought into contact with the cellulose substrate. âê. Method according to any one of the previous claims, wherein the dry content of the cellulose substrate is above 90%. É4. Method according to any one of the previous claims,wherein the fatty acid comprises an aliphatic chain length of between 10 - 22 carbon atoms. 1%. Method according to any one of the previous claims,wherein the fatty acid is palmitoyl chloride, C16, stearoyl chloride, C18 or mixtures thereof. §9. Method according to any one of the previous claims,wherein the cellulose substrate (1) is a paper- or paperboard web. 219. Method according to claim §9, wherein the web (1) is a multilayer web. 1Q11. Method according to any one of the previous claims,wherein the method further comprises a step of heating thesubstrate (1), before and/or after adding the fatty acidhalide. 11

2. Method according to claim 121, wherein the substrateheating step is performed by IR heating. lêê. Method according to any one of the previous claims, wherein the vacuum sucking is performed by a vacuum box (ll). l§4. Method according to any of claims l-liê, wherein the vacuum sucking is performed by a rotating vacuum cylinder (6). líë. Method according to any one of claims 2% - l§4, whereinthe conversion of said spray form fatty acid halide into vaporized fatty acid halide is performed by IR heating.