CN113227494A

CN113227494A - Method for hydrophobicizing cellulose substrates by using fatty acid halides

Info

Publication number: CN113227494A
Application number: CN201980085694.4A
Authority: CN
Inventors: S.汉森; R.巴登利德; C-M.布兰登
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2018-11-16
Filing date: 2019-11-15
Publication date: 2021-08-06
Also published as: WO2020100097A1; EP3880884A1; CN113227495A; EP3880886A4; US20220010493A1; JP2022507536A; EP3880884A4; WO2020100101A1; SE543029C2; JP2022507555A; SE1851430A1; EP3880886A1; KR20210100635A; US20220002949A1; KR20210100636A

Abstract

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

Description

Method for hydrophobicizing cellulose substrates by using fatty acid halides

Technical Field

A method of hydrophobising a cellulosic substrate, the substrate comprising a first face and an opposing second face.

Background

In some fields (e.g. in the textile industry and in the paper and board industry), there is a need to increase the hydrophobicity of cellulose-based materials.

Paper and board are often treated with sizing agents to improve certain qualities, particularly resistance to penetration of water and other liquids into the paper or board. There are two types of sizing: internal sizing and surface sizing. In internal sizing, chemicals (e.g. ASA, AKD or rosin size) are added to the pulp at the wet end. Common surface sizing agents include, for example, starch or acrylic copolymers.

US4107426 discloses a method of imparting water repellency properties to the surface of a cellulosic substrate. The method includes the step of exposing the surface to a gas phase consisting essentially of an aliphatic acid chloride.

The disadvantage of this method is that mainly the surface of the substrate becomes hydrophobic, not the interior of the substrate. This causes a problem of edge wicking (wrapping), i.e. penetration of liquid into the edges of the substrate.

In WO2017002005, such a method is described: wherein the gasified (vapourized) fatty acid halide is arranged to permeate the cellulose substrate. However, the equipment required to carry out the method according to WO2017002005 occupies a large amount of space and is therefore difficult to implement at existing production sites.

It is an object of the present invention to provide an improved method of increasing the hydrophobicity of a material having a cellulosic substrate, for example to increase the water repellency and resistance to edge wicking penetration of the cellulosic substrate.

Disclosure of Invention

The process of the present invention for hydrophobizing a cellulosic substrate comprises the steps of:

-drying the cellulose substrate to a dry content of more than 80%, preferably more than 85%;

-providing a fatty acid halide in spray form; and

-directing the fatty acid halide to contact a first face of a cellulosic substrate and at least partially penetrate the cellulosic substrate.

Treating the cellulosic substrate according to the method of the present invention results in an increase in the hydrophobicity of the material not only at the surface but also in the core thereof, and in an increased water resistance thereof, as well as the resistance of the cellulosic substrate to edge wicking penetration.

Due to the method according to the invention, several additional advantages are also achieved. For example:

the means for applying the sprayed fatty acid halide to the substrate may be aligned in different defined directions,

the agent (i.e. the fatty acid halide) will have a uniform distribution on the surface, even if the surface is rough,

calibration of the dose makes it possible to avoid an unwanted surplus of reagent on the substrate,

the amount of reagent can be easily controlled by adjusting the pressure or the number of the spraying units, and

the nozzles/units do not require large spaces, which facilitates installation at existing on-line production sites.

It is to be understood that "spray form" means the form of a plurality of droplets or particles, and that the fatty acid halide in spray form can be delivered by a precision device that disperses a free-flowing liquid fatty acid halide into the spray form. The droplets or particles may be micro-sized, ranging in size from 1 to 900 μm in diameter.

According to another aspect of the invention, the fatty acid halide directed to be sprayed also contacts the second side of the cellulosic substrate and at least partially permeates the cellulosic substrate. This can be achieved by vacuum suction.

The cellulosic substrate may be in the form of a paper or paperboard web, a paperboard application, a textile made from cellulosic fibers, or a three-dimensional cellulose-based product (e.g., produced by thermoforming). The paper or paperboard web may be a single layer web or a multi-layer web.

According to another aspect of the present invention, the introducing the fatty acid halide is performed by: vacuum suction is applied at the second side of the cellulose substrate such that the fatty acid halide penetrates the cellulose substrate in a predetermined direction through the cellulose substrate. Such vacuum suction may be generated by a vacuum box, a rotating vacuum drum, or any other suitable vacuum generating device. Due to the method according to the invention the degree of covalency may be more uniform throughout the thickness of the material compared to, for example, conventional roll coating of free-flowing agents onto a running substrate.

The degree of covalent is the ratio between the grafted fatty acids and the total fatty acids in the substrate, where the grafted corresponds to the reagents that have reacted, and the total amount is that portion along with free fatty acids that have only been physically absorbed to the substrate.

According to another aspect of the present invention, the introducing the fatty acid halide is performed by: vacuum suction is applied at the first side of the cellulose substrate such that the fatty acid is directed in a predetermined direction along the surface of the first side of the cellulose substrate in a manner that brings the fatty acid into contact with the cellulose substrate. In one example, "along a surface" means moving the fatty acid a controlled distance (depending on the substrate) substantially parallel to the first face of the substrate.

According to another aspect of the invention, the fatty acid halide is mixed with at least one solvent prior to spraying it onto the substrate. Preferably, the solvent is selected from the group comprising: acetone, ethyl acetate and methyl ethyl ketone. It is preferable that: the solvent (or mixture of solvents) does not contain any OH groups and is miscible with the fatty acid halide, which will help resist clogging and facilitate cleaning of the application system. The use of a solvent also allows the amount of fatty acid halide applied to be minimized and controlled in a better manner.

The boiling point of the solvent should preferably not be too high to ensure that no residual solvent is present in the product, preferably the boiling point is 200 ℃ or less, more preferably 150 ℃ or less, and even more preferably 100 ℃ or less. The boiling point of acetone is 59 ℃; the boiling point of ethyl acetate is 77 ℃ and the boiling point of methyl ethyl ketone is 59 ℃ or less. The addition of a solvent to the fatty acid halide may result in the advantage of improving the penetration of the agent into the substrate.

According to one aspect of the invention, the mixture of fatty acid halide and solvent comprises 0.1 to 20 wt.%, preferably 0.1 to 10 wt.%, more preferably 0.1 to 5 wt.% of solvent based on the total weight of the mixture. If the amount of solvent is too high, the reagent may be too dilute to form a uniform coverage and distribution upon application, and thereby increase the need to add an application unit. This may also pose a higher risk of residual solvent molecules in the final product. If the amount of reagent applied becomes too low, it can have a negative impact on the desired material properties.

According to yet another aspect of the invention, the cellulosic substrate has a dry content of 80% or more, preferably 85% or more, even more preferably 90% or more. The higher the dry content, the better the result of the subsequent hydrophobization will be. This is due to the high reactivity of the fatty acid halide to water. Thus, the presence of water can lead to the undesirable formation of too high amounts of fatty acids that do not adhere to the substrate.

According to yet another aspect of the invention, the fatty acid halide to be sprayed comprises an aliphatic chain length between 10 and 22 carbon atoms. The fatty acid is preferably selected from palmitoyl chloride (C16), stearoyl chloride (C18), or mixtures thereof.

According to yet another aspect of the invention, the method further comprises the step of heating the cellulosic substrate before and/or after the addition of the fatty acid halide.

Drawings

The invention will be further described with reference to the accompanying drawings, in which:

fig. 1 shows a schematic representation of the present invention according to a first embodiment in which a fatty acid halide in spray form is applied to a substrate;

fig. 2 shows a schematic view of the invention according to a second embodiment in which a fatty acid halide in gasified form is applied on a substrate;

3a-b show schematic representations of the present invention according to third and fourth embodiments in which both the first and second sides of the substrate are subjected to fatty acid halide;

fig. 4 shows a schematic view of the present invention according to a fifth embodiment in which a fatty acid halide in vaporized form is applied on a substrate; and

fig. 5 illustrates in a schematic way the hydrophobization of a cellulose substrate, wherein such substrate is in the form of a three-dimensional cellulose-based product.

Detailed Description

The following detailed description illustrates an example of an arrangement (setup) for implementing the method according to the invention, which can be used to illustrate the principles of the inventive concept in a non-limiting manner.

In fig. 1-4, a cellulosic substrate 1 comprising a first side and a second side is generically referred to as "1". In these embodiments, the substrate is in the form of a cellulose-based web, such as a paper web or a paperboard web. The second side of the substrate 1 faces away from the first side. The cellulosic substrate (e.g. paper or paperboard web 1) is dried in a drying step. Drying is carried out by any conventional drying method suitable for drying cellulosic substrates. The cellulosic substrate of the paper or board web may be dried, for example, by means of a drying cylinder. After the drying step, the dry content of the cellulose substrate 1 is 80% or more, preferably 85% or more and most preferably 90% or more. Higher dry content can lead to better subsequent hydrophobization results by obtaining a higher degree of covalency.

Thus, the cellulose substrate 1 may be further dried and heated. As illustrated in fig. 1-3, heating is preferably performed in a pretreatment step by IR heating 2. The pre-treatment heating step has several advantages. It will minimize unwanted condensation of the gas upon contact with the substrate and also result in better penetration of the subsequent hydrophobizing agent through the substrate. Additionally, any remaining water residue may be further dried; the substrate 1 may be dried to even up to 95% dry content.

The first side of the dried and heated substrate 1 is then treated with a fatty acid halide in spray form or in the gas phase to hydrophobize the substrate so that the substrate becomes hydrophobic. This is achieved by means of a device 5 for dispersing liquid fatty acid halide into a spray 50 (also referred to as "spray device" 5) which may directly contact the substrate or become vaporized into a gas phase, wherein such gas contacts the substrate. The spraying means 5 may be in the form of a spray nozzle for atomizing a liquid. By "spray atomization" is meant herein a spray that converts a liquid into fine particles by mixing the liquid with compressed air. The spray nozzle produces an atomized spray when passed through the opening under high pressure and in a controlled manner. Higher pressures will form smaller droplets and a finer spray. Different spraying devices 5 are conceivable.

Another example is electrospray, in which electricity is applied to a liquid flowing from a nozzle (which may have various shapes and configurations), and then a fine droplet is formed that is uniform and charged because the electricity exceeds the surface tension. It may also be due to mechanical deformation. A general advantage of the electrospray process is that it can be performed as one step at low cost, low energy input and good flexibility. Ambient temperature and pressure also play a role.

When the first side of the dried and heated substrate 1 has been treated with fatty acid halides, the applied fatty acid halides will at least partially penetrate the cellulose of the substrate 1 and covalently bind to the cellulose therein, increasing the water repellency of the material. In order to enhance the penetration of the spray or gas through the substrate, the second side of the substrate may be simultaneously subjected to vacuum suction during hydrophobization of the substrate, such that the spray or gas is transported through the substrate in a predetermined direction. This increases the hydrophobicity of the surface and core of the substrate so that the substrate will be more resistant to penetration of the inner edge.

The fatty acid halide is any halide that can be vaporized, however palmitoyl chloride C16 has been shown to be particularly suitable in testing. During the test, degrees of covalency of above 40% and even above 60% have been achieved compared to conventional AKD sizing in which no or only a small percentage of covalent bonding is available (which results in low retention, which thereby leads to e.g. migration problems, stains and machine stops, etc.).

Another advantage of using a spray to apply the fatty acid halide is that it has a very high site specificity and achieves hydrophobicity only where the spray can reach the substrate. The reagent will react with available hydroxyl groups to form HCl as a byproduct. The reagents are also highly reactive with water and the reaction requires a dry substrate. Nevertheless, some water will always be present and the corresponding less reactive fatty acid will be formed as unbound molecule. It is therefore not possible to achieve a degree of 100% covalent. However, other advantages associated with using a gas phase reaction are that the gas can be more easily permeated and directed through the substrate, the reaction can be faster and lower amounts of chemical agents can be required than if the same agent were applied in a liquid state.

Fig. 1 illustrates an exemplary manner of performing the method according to the present invention. The dried and heated cellulose substrate 1 in the form of paper or board is additionally heated and dried with IR heating from an IR heating cabinet 2. Additional IR heating is optional.

The liquid fatty acid halide is stored in a separate tank 3 from which it is sprayed through a device 5 for dispersing the liquid into a spray 50. Such a spraying device 5 may, for example, be in the form of a spray nozzle for atomizing a liquid, i.e. breaking up the fluid into droplets 50. In this example, droplets are sprayed by means of the device 5 onto the first face 1a of the substrate 1 travelling below. Said first face 1a of the substrate 1 is simultaneously in contact with a downstream rotating drum 6, said rotating drum 6 being for example a heated drum, which heats the droplets into a gas, whereby the atomized fatty acid molecules react more efficiently with the cellulose of the substrate. It is conceivable to arrange a plurality of spraying units for the travelling substrate, which are positioned one behind the other in turn, wherein each such unit may comprise one or more nozzles. This will enable the fatty acid to be applied in successive steps, whereby smaller doses can be applied several times instead of the entire amount being applied by one unit at a time. Such procedures may in some cases improve the penetration of the agent in the thickness of the cellulosic web.

It is also conceivable to arrange a rotating vacuum drum (not shown) with holes for the second face 1b of the substrate and downstream of the spraying device 5, which is arranged to vacuum draw the fatty acid halide through the cellulose substrate 1 in a predetermined direction. Thus, the cellulosic substrate 1 may be hydrophobized throughout (throughout) the entire thickness of the substrate.

Another arrangement for applying fatty acid halide is: arranging the substrate 1 into between two nip rollers (not shown), preferably wherein at least one of the rollers is a heated nip roller; and directing the fatty acid halide spray into a nip roll joint (junction), whereby the spray droplets are converted to a gas phase by passing the heated roll or rolls. In this arrangement, the spray may also be directed into contact with a heated roll immediately upstream of the roll joint, whereby the fatty acid halide is vaporized by the heat of the roll and applied to the substrate immediately thereafter, i.e., within seconds or milliseconds.

Yet another arrangement for applying the fatty acid halide is to spray the fatty acid halide directly onto a heated roller arranged to transfer the fatty acid halide to a traveling substrate immediately, i.e., within seconds or milliseconds. Upon contacting the substrate, the heat from the roller will convert the fatty acid halide to a gaseous phase, meaning that vaporization and contact of the fatty acid halide with the substrate occur simultaneously. In such embodiments, the heated roller provides several functions: the function of bringing the fatty acid halide into contact with the substrate, the function of vaporizing the fatty acid halide into a gas phase, and the function of promoting a chemical reaction that covalently binds the fatty acid halide to the substrate. The gasification of the fatty acid halide may be arranged to occur before or while the heated roller contacts the substrate, depending on where the spray is applied to the heated roller. For example, if the spray is directed such that the fatty acid halide hits the heated roll a short distance before the roll contacts the substrate, gasification will occur before contact, whereas in the case where the spray is directed such that the fatty acid halide hits the roll at the nip (nip) between the heated roll and the substrate, gasification will occur simultaneously with contact. If the spray is not totally vaporized, it will still be distributed in a uniform manner over the rollers and then absorbed by the plate in the form of droplets.

In addition, HCl by-product and possibly unreacted, e.g., palmitoyl chloride and/or unbound C16 may be removed and collected for disposal.

In fig. 2, a second embodiment according to the invention is shown by way of example. Here, also as previously described for fig. 1, the dried and heated cellulosic substrate 1 in paper or paperboard form is optionally further heated and dried with IR heating from an IR heating cabinet 2.

The liquid fatty acid halide is stored in a separate tank 3 from which it is transferred, e.g. via a pipe 4 (or other transfer means), to a device 5 for dispersing the liquid into a spray 50. Such means 5 may for example be in the form of a spray nozzle for atomizing the liquid, i.e. breaking up the fluid into droplets 50. In this example, the droplets are sprayed via the device 5 into a heating chamber 7, such as a pressurized heating tank 7. The sprayed droplets are heated in the tank 7 to be vaporized into a gas phase, and the gas 70 is then sprayed or deposited on the first surface of the substrate 1 by a gas distribution device 71. Said first side of the substrate is simultaneously in contact with the rotating cylinder 6. Another vacuum type rotary cylinder may be arranged at the second face 1b of the substrate for sucking gas in a predetermined direction through the cellulose substrate 1. Thus, the cellulosic substrate 1 may be hydrophobized throughout the entire thickness of the substrate. Any HCl by-product and possibly unreacted, e.g., palmitoyl chloride and/or unbound C16 may be removed and collected for disposal.

For both exemplary methods shown in fig. 1-2, the first side of the substrate may be treated first and then the second side of the substrate may be treated with additional units facing the second side of the substrate. This two-sided treatment ensures that the entire core of the substrate will be modified. The use of two or more spray units may be placed in such a way that: which makes a minimum amount of space required and matches existing equipment. By using multiple units, it may also be possible to run the machine at an increased speed.

Fig. 3a-b show a third and fourth embodiment, respectively, in which both the first and second sides of the substrate 1 are subjected to hydrophobization/hydrophobization by applying fatty acid halides in the form of a spray.

Referring to fig. 3a, a substrate 1 is first subjected to a pre-treatment 2 in the form of heating, for example IR heating. A means 5 for dispersing the liquid as a spray is located downstream of the pre-treatment 2, at the second face 1b of the substrate, adjacent the rotating drum 6 and arranged to direct a spray 50 of fatty acid halide on the surface of the drum 6, which drum 6, when rotating, will further deliver the fatty acid halide on the surface of the second face 1b of the substrate 1. The spin basket 6 may be heated, again to the extent that the sprayed droplets are converted to a gas before they reach the substrate. A vacuum box 8 is arranged at the first face 1a of the substrate 1 to draw the reagents into the cellulosic structure. According to a third embodiment described herein, the substrate 1 is further hydrophobized in a subsequent downstream step, wherein also a fatty acid halide 50' is applied on the first face 1a of the substrate 1. Accordingly, as seen in fig. 3a, a second means 5 ' for dispersing the liquid as a spray 50 ' is located adjacent to the second rotating drum 6 ', said means 5 ' being arranged to direct a spray 50 ' of fatty acid halide onto the surface of the drum 6 ', said drum 6 ' upon rotation will further deliver fatty acid halide onto the surface of the first face 1a of the substrate 1. The rotary drum 6' may be heated. A vacuum box 8' is arranged next to the rotating drum at the second side 1b of the substrate to direct the reagent to penetrate the substrate 1 at least partially. The skilled person understands that the respective apparatuses (e.g. spraying means 5, 5 '; vacuum boxes 8, 8 '; drums 6, 6 ', etc.) are interchangeable and can treat first the first side 1a and then the second side 1b of the substrate 1.

A fourth embodiment according to the invention is seen in fig. 3b, which has the same purpose as in fig. 3a, i.e. to treat both sides of the substrate 1 to increase its hydrophobicity. In a similar manner to that described in fig. 3a, the substrate 1 is guided through two successive hydrophobization steps, wherein the fatty acid halide is applied firstly on the second side 1b of the substrate and secondly on its first side 1 a. In a first step, the spraying means 5 is located adjacent the second face 1b of the travelling substrate 1 and is arranged to direct a spray 50 of fatty acid halide onto said surface 1 b. A vacuum box 8 is arranged at the first face 1a of the substrate, opposite the spraying device 5, said vacuum box 8 being arranged to draw the fatty acyl halide at least partially through the substrate by vacuum suction. A downstream rotating drum 6, preferably a heated drum, may be provided to facilitate binding of the reagent to the cellulosic substrate 1. A corresponding second hydrophobization step is arranged downstream of the first drum 6, whereby fatty acid halides are likewise applied to the first side 1a of the substrate in a corresponding manner as described for the first hydrophobization step.

The fatty acid halide in the fourth embodiment may be converted from a spray form to a gaseous form before being directed to the contact substrate 1.

In fig. 4, a fifth embodiment according to the present invention is shown. A pre-treatment step for heating the substrate is described, wherein such heating may be performed by, for example, IR heating. Further, the introduction of fatty acid halides is here carried out by: vacuum suction 8 is performed at the first face 1a of the cellulose substrate such that the fatty acid is directed in a predetermined direction along the surface of the first face 1a of the cellulose substrate 1 in such a way that the fatty acid is brought into contact with the cellulose substrate 1. Thereby causing the fatty acids to move substantially parallel to the first side of the substrate.

Fig. 5 schematically illustrates a method according to the invention, wherein the substrate 10 is a three-dimensional cellulose-based product. Here, the conveyor belt 9 is transporting a plurality of three-dimensional cellulosic products 10 through a unit 11, the unit 11 being arranged to hydrophobize said products by the method of claim 1. The three-dimensional product 11 may be, for example, a preformed paper tray, mug or container, or other type of 3D shaped article made of cellulose. After having passed through unit 11, where the gasified fatty acid halide is brought into contact with the cellulose substrate and at least partially penetrates its thickness, the exiting product 10' has acquired hydrophobic properties.

To characterize the success of the reaction, contact angle measurements were used to qualitatively analyze the extent to which the cellulosic substrate was hydrophobized by the method. The contact angle of the untreated cellulose substrate before treatment by the method of the invention was about 40 °, and the contact angles on both the first and second sides of the substrate after treatment by the method of the invention were 110-. Contact angles greater than 90 ° (high contact angles) generally mean that wetting of the surface is not favoured, so that the fluid will minimise contact with the surface and form compact droplets.

Other modifications and variations will be apparent to persons skilled in the art in view of the above detailed description of the invention. For example, the method according to the invention may be used as a complement to other methods of applying fatty acid halides to a substrate. However, it should be apparent that such other modifications and variations may be practiced without departing from the spirit and scope of the invention.

Claims

1. Process for hydrophobizing a cellulosic substrate (1), the cellulosic substrate (1) comprising a first side and a second side facing away from the first side, characterized in that the process comprises the steps of:

-drying the cellulosic substrate (1) to a dry content of more than 80%, preferably more than 85%;

-providing a fatty acid halide in the form of a spray; and

-directing the fatty acid halide to contact a first face of the cellulosic substrate and at least partially penetrate the cellulosic substrate (1).

2. The method of claim 1, further comprising the steps of: the fatty acid halide is also directed to contact the second side of the cellulosic substrate and at least partially penetrate the cellulosic substrate (1).

3. The process according to any one of the preceding claims, wherein the directing of the fatty acid halide is performed by: vacuum suction is applied at the second side of the cellulose substrate such that the fatty acid penetrates the cellulose substrate (1) in a predetermined direction through the cellulose substrate (1).

4. The process of any one of claims 1-2, wherein the directing the fatty acid halide is performed by: vacuum suction is applied at the first side of the cellulose substrate such that the fatty acid is directed in a predetermined direction along the surface of the first side of the cellulose substrate (1), thereby bringing the fatty acid into contact with the cellulose substrate.

5. The method according to any one of the preceding claims, wherein the cellulosic substrate has a dry content of 90% or more.

6. The method of any preceding claim, wherein the fatty acid comprises an aliphatic chain length of between 10-22 carbon atoms.

7. The process of any one of the preceding claims, wherein fatty acid is palmitoyl chloride C16, stearoyl chloride C18, or a mixture thereof.

8. The method according to any of the preceding claims, wherein the fatty acid to be sprayed is mixed with at least one solvent or a mixture of solvents, wherein the solvent is preferably selected from the group comprising: acetone, ethyl acetate and methyl ethyl ketone.

9. The process according to claim 8, wherein the mixture of fatty acid halide and solvent comprises 0.1-20 wt.%, preferably 0.1-10 wt.%, more preferably 0.1-5 wt.% of the total mixture of solvent.

10. The method according to any of the preceding claims, wherein the cellulosic substrate (1) is a paper web or a paperboard web.

11. The method according to claim 10, wherein the web (1) is a single-layer web or a multi-layer web.

12. The method according to any one of claims 1-9, wherein the cellulosic substrate is a three-dimensional cellulose-based product.

13. The method according to any one of the preceding claims, wherein the method further comprises the step of heating the substrate (1) before and/or after the addition of the fatty acid halide.

14. The method of claim 12, wherein the substrate heating step is performed by IR heating.

15. The method according to any of the preceding claims, wherein vacuum suction is performed through a vacuum box (11).

16. The method according to any one of claims 1-14, wherein vacuum suction is performed by a rotating vacuum drum (6).

17. A cellulose-based product that has been treated by the method according to any one of the preceding claims.