KR20210100636A - Cellulose-based hydrophobization method by using fatty acid halides - Google Patents

Abstract

The present invention relates to a method for hydrophobizing a cellulosic substrate comprising a first side and a second side opposite the first side, the method comprising the steps of:
- drying the cellulosic substrate to a dry content of at least 80%, preferably at least 85%;
- providing a fatty acid halide in the form of a spray;
- contacting the fatty acid halide in spray form with the first side of the cellulosic substrate and inducing it to penetrate at least partially into the cellulosic substrate.

Description

Cellulose-based hydrophobization method by using fatty acid halides

The present invention relates to a method for hydrophobizing a cellulose substrate, said substrate comprising a first side and an opposite second side.

There is a need to increase the hydrophobicity of cellulosic-based materials in several fields, for example in the textile industry and in the paper- and paperboard industry.

Paper- and paperboard are generally treated with sizing agents to improve certain qualities, inter alia, to increase the resistance to penetration of water and other liquids into the paper or paperboard. There are two sizing types: internal and surface sizing. In internal sizing, chemicals such as 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 for imparting water-repellent properties to the surface of a cellulosic substrate. The process includes exposing the surface to a vapor phase consisting essentially of an aliphatic acid chloride.

A disadvantage of this method is that it becomes primarily hydrophobic and the surface of the substrate rather than the interior of the substrate. This leads to the problem of edge wicking, i.e. liquid penetration into the edge of the substrate.

In WO2017002005, a method is described in which vaporized fatty acid halides are arranged to penetrate the cellulosic substrate. However, the equipment required to perform the method according to WO2017002005 occupies a lot of space, so it is difficult to implement in an existing production site.

It is an object of the present invention to provide an improved method for increasing the hydrophobicity of materials with a cellulosic substrate, for example, which improves the water repellency and resistance of the cellulosic substrate to edge hygroscopic penetration.

The present invention is a cellulose-based hydrophobization method comprising the steps of:

- drying the cellulosic substrate to a dry content of at least 80%, preferably at least 85%;

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

- contacting said fatty acid halide with the first side of the cellulosic substrate and inducing it to penetrate at least partially into the cellulosic substrate.

Treatment of the cellulosic substrate according to the method of the present invention increases the hydrophobicity of the material not only at the surface but also at the center, and improves the water resistance and resistance of the cellulosic substrate to edge moisture absorption.

Several additional advantages are also achieved thanks to the method of the invention. E.g:

- the device for applying the atomized fatty acid halide to the substrate can be aimed in a different defined direction,

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

- volume correction can prevent an excess of unwanted reagents in the substrate;

- the amount of reagent can be easily controlled by adjusting the pressure or the number of spray units,

- Nozzle/unit does not require large space which facilitates installation in existing on-line production site.

It should be understood that "spray form" means in the form of a plurality of droplets or particles, and that the fatty acid halide in the form of a spray can be delivered by a precision device for dispersing the free-flowing liquid fatty acid halide in the form of said spray. The droplets or particles may be micro-scale with sizes ranging from 1-900 μm in diameter.

According to another aspect of the invention, the atomized fatty acid halide is also directed to contact the second side of the cellulosic substrate and at least partially penetrate the cellulosic substrate. This can be done by vacuum suction.

The cellulosic substrate may be in the form of a paper- or paperboard web, a paperboard application, a fabric made of cellulosic fibers, or a three-dimensional cellulosic-based product produced, for example, by thermoforming.

The paper- or cardboard web may be a single- or multi-layer web.

According to another aspect of the present invention, the derivation of the fatty acid halide is performed by vacuum suction on the second side of the cellulosic substrate such that the fatty acid halide penetrates the cellulosic substrate in a predetermined direction through the cellulosic substrate. Such vacuum suction may occur by means of a vacuum box, a rotating vacuum cylinder, or any other suitable vacuum generating equipment. Thanks to the method according to the invention, the degree of sharing can be more uniform throughout the thickness of the material, for example compared to conventional roll coating of a free-flowing reagent on a moving substrate.

Covalentity is the ratio of grafted and total fatty acids in a substrate, where grafted corresponds to the reacted reagent and the total amount is this fraction with free fatty acids physically adsorbed to the substrate.

According to another aspect of the present invention, the induction of the fatty acid halide is performed on the first side of the cellulosic substrate such that the fatty acid is directed in a predetermined direction along the surface of the first side of the cellulosic substrate in such a way that the fatty acid is in contact with the cellulosic substrate. carried out by vacuum suction. In one example, "along the surface" means that the fatty acid moves substantially parallel to the first side of the substrate (according to the substrate) for a controlled distance.

According to another aspect of the present invention, the fatty acid halide is mixed with at least one solvent before being sprayed onto the substrate. Preferably, the solvent is selected from the group comprising acetone, ethyl acetate and methyl ethyl ketone. It is preferred that the solvent (or mixture of solvents) does not contain OH-groups and is also miscible with the fatty acid halide, which will prevent clogging and facilitate cleaning of the application system. The use of solvents also makes it possible to minimize and control the amount of fatty acid halide applied in a better way.

The boiling point of the solvent should preferably not be too high to ensure that there will be no residual solvent in the product, preferably less than 200 °C, more preferably less than 150 °C, even more preferably less than 100 °C. Acetone has a boiling point at 59 °C; Ethyl acetate has a boiling point at 77°C and methyl ethyl ketone has a boiling point below 59°C. Adding a solvent to the fatty acid halide can result in the advantage of improved penetration of the reagent into the substrate.

According to one embodiment of the present invention, the mixture of fatty acid halide and solvent comprises 0.1-20 wt %, preferably 0.1-10 wt %, more preferably 0.1-5 wt % solvent of the total weight of the mixture. If the amount of solvent is too large, the reagent may be too diluted to form a uniform coverage and distribution upon application, increasing the need for an application unit. This can also lead to a higher risk of residual solvent molecules in the final product. If the amount of applied reagent is too low, the desired material properties may be adversely affected.

According to another aspect of the invention, the dry content of the cellulosic substrate is at least 80%, preferably at least 85%, even more preferably at least 90%. The higher the dry content, the better the result of subsequent hydrophobization. This is because the fatty acid halide has a high reactivity to water. Thus, the presence of water can lead to the undesired formation of excessive amounts of fatty acids that are not attached to the substrate.

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

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

In the following, the invention will be further described with reference to the drawings, wherein:
1 shows a schematic diagram of the invention according to a first embodiment in which a fatty acid halide in the form of a spray is applied to a substrate;
2 shows a schematic diagram of the invention according to a second embodiment in which a fatty acid halide in vaporized form is applied to a substrate;
3a-b show schematics of the invention according to third and fourth embodiments in which both the first and second sides of the substrate are exposed to fatty acid halides;
4 shows a schematic diagram of the invention according to a fourth embodiment in which a fatty acid halide in vaporized form is applied to a substrate;
5 shows a schematic manner of hydrophobization of a cellulosic substrate, wherein the substrate is in the form of a three-dimensional cellulose-based product.

details

The following detailed description illustrates examples of settings for carrying out the method according to the invention, which may serve to explain the principles of the inventive idea in a non-limiting way.

1-4 , the cellulosic substrate 1 comprising a first side and a second side is generally referred to as “1”. In this embodiment, the substrate is in the form of a cellulosic based web, such as a paper- or cardboard web. The second surface of the substrate 1 does not face the first surface. A cellulosic substrate, for example a paper- or cardboard web 1 , is dried in a drying step. Drying is carried out by any conventional drying method suitable for drying the cellulosic substrate. The cellulosic substrate of the paper- or cardboard web can be dried, for example, by means of a drying cylinder. After the drying step, the cellulosic substrate 1 has a dry content of at least 80%, preferably at least 85% and most preferably at least 90%. A higher dry content may provide better subsequent hydrophobization results by obtaining higher covalent properties.

The cellulosic substrate 1 can then be further dried and heated. The heating is preferably carried out in the pre-treatment step by IR heating (2) as shown in Figs. 1-3. The pretreatment heating step has several advantages. This will minimize condensation of unwanted gases upon contact with the substrate, and will also allow better penetration of subsequent hydrophobizing agents through the substrate. Moreover, any remaining water residue may be further dried; The substrate 1 can possibly be dried to a maximum of 95% dry content.

The first side of the dried and heated substrate 1 is then treated with a fatty acid halide in the form of a spray or gaseous phase to make the substrate hydrophobic so that the substrate becomes hydrophobic. This is done by means of a device 5 (also referred to as “spray device” 5) for dispersing a liquid fatty acid halide into a spray 50 , the spray being in direct contact with the substrate or vaporizing such gas into a gaseous phase in contact with the substrate. can be The spray device 5 may be in the form of a spray nozzle used for liquid atomization. "Spray atomization" means converting a liquid into a spray of fine particles by mixing a liquid with compressed air. The spray nozzle creates an atomized spray as it passes through the opening in a controlled manner at high pressure. Higher pressure will produce smaller droplets and finer strays. Several different spray devices 5 are conceivable.

Another example is electrospray, in which electrical force is used in a liquid flowing from a nozzle, which can have a variety of shapes and forms, and thereafter the electrical force exceeding the surface tension results in the formation of fine, uniform, charged droplets. This may also be due to mechanical distortion. The general advantages of the electrospray process are that it can be performed in one step with 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) is treated with a fatty acid halide, the applied fatty acid halide at least partially penetrates the cellulose of the substrate (1) and covalently bonds with the cellulose therein, so that the material will increase water repellency. To enhance penetration of the spray or gas through the substrate, the second side of the substrate may be subjected to simultaneous vacuum suction during hydrophobization of the substrate such that the spray or gas is transported through the substrate in a predetermined direction. This will improve the hydrophobicity of the center as well as the surface of the substrate, making the substrate more resistant to in-plane edge penetration.

Fatty acid halide is any halide that can be vaporized, but palmitoyl chloride, C16, has been shown to be particularly suitable in testing. A small percentage of covalent bonds can or cannot be obtained and this results in less retention, such as 40% during testing, compared to conventional AKD sizing which causes migration problems, stains and mechanical hangs, etc. Ideal and even greater than 60% covalentness was achieved.

Another advantage of using a spray to apply a fatty acid halide is that it is highly site specific and hydrophobicity is achieved only where the spray can access the substrate. The reagent will react with the available hydroxyl groups forming HCl as a by-product. The reagent is also very reactive with water and the reaction requires a dry substrate. Nevertheless, there will always be some water and the corresponding less reactive fatty acids will also be formed as unbound molecules. Therefore, it is impossible to achieve 100% commonality. However, other advantages associated with the use of gas phase reactions are that gases can more readily penetrate and be directed through the substrate, reactions can be faster, and require less chemical reagents compared to application of the same reagents in liquid state. that it can

1 shows an exemplary manner of carrying out a method according to the invention. The dried and heated cellulosic substrate 1 in paper- or cardboard form is further heated and dried by IR heating in an IR heating box 2 . Additional IR heating is optional.

The liquid fatty acid halide is stored in a separate tank (3) from which it is ejected through a device (5) for dispersing the liquid into a spray (50). Such a spray device 5 may be, for example, in the form of a spray nozzle used to atomize a liquid, ie to break the fluid into droplets 50 . In this embodiment, droplets are sprayed on the first side 1a of the underlying moving substrate 1 by means of a device 5 . Said first face 1a of the substrate 1 is simultaneously in contact with a downstream rotating cylinder 6, for example a heated cylinder that heats the droplets into a gas whereby atomized fatty acid molecules are more efficiently combined with the cellulose of the substrate. react It is conceivable to arrange multiple atomizing units which are located behind each other in turn with respect to the moving substrate, wherein each such unit may comprise one or a plurality of atomizing nozzles. This will allow the application of fatty acids in successive steps, whereby a smaller dose can be applied several times instead of one unit applying the entire amount at a time. Such procedures may in some cases improve the penetration of reagents in the thickness of the cellulosic web.

A rotating vacuum cylinder with an aperture (not shown) is arranged in relation to the second side 1b of the substrate and downstream of the spray device 5 and to vacuum suck the fatty acid halide through the cellulosic substrate 1 in a predetermined direction. It is also conceivable to be arranged. Thereby, the cellulosic substrate 1 can be hydrophobized through the full thickness of the substrate.

Another arrangement for applying the fatty acid halide is arranged such that the substrate 1 is sandwiched between two pressing rolls (not shown), preferably wherein at least one of the rolls is a heated pressing roll, and the fatty acid halide spray is applied to the pressing roll. It is sent to the junction whereby the spray droplets are converted to the gas phase by the heated rolls. In this arrangement, the spray can also be sent into contact with a heated press roll just upstream of the press 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. .

Another arrangement for fatty acid halide application is that the fatty acid halide is sprayed directly onto a heating roll arranged to transport the fatty acid halide to a moving substrate immediately, ie within seconds or milliseconds. Upon contact with the substrate, the heat of the roll will convert the fatty acid halide to the gas phase, meaning that vaporization occurs as soon as the fatty acid halide comes into contact with the substrate. In such embodiments, the heated roll serves several functions: contacting the fatty acid halide with the substrate, vaporizing the fatty acid halide into the gas phase, and catalyzing a chemical reaction to covalently bond the fatty acid halide to the substrate. Vaporization of the fatty acid halide can be arranged to occur either before the heated roll contacts the substrate, or concurrently with the heated roll contacting the substrate, depending on where the spray is applied on the heated roll. For example, if a spray is sent such that a fatty acid halide hits a heated roll at a short distance before the roll comes into contact with the substrate, vaporization will occur prior to contact, whereas the fatty acid halide will occur in the nip between the roll and the substrate. If the spray is directed to contact the heated roll, vaporization will occur simultaneously with the contact.

Even if not all of the spray vaporizes, it will be dispersed as a uniform material on a roll and then absorbed in the form of droplets by the board.

Moreover, HCl by-products and possibly unreacted eg palmitoyl chloride and/or unbound C16 can be removed and collected for handling.

2 , a second embodiment according to the invention is schematically shown. Here, the dried and heated cellulosic substrate 1 in the form of paper- or cardboard is optionally further heated and dried by means of IR heating in an IR heating box 2 , as also described above with respect to FIG. 1 .

The liquid fatty acid halide is stored in a separate tank ( 3 ) and transported from there to an apparatus ( 5 ) for dispersing the liquid in the spray ( 50 ), for example via a tube ( 4 ) (or other means of transport). Such a device 5 may be, for example, in the form of a spray nozzle used to atomize a liquid, ie break the fluid into droplets 50 . In this example, the droplets are sprayed through the device 5 into a heating chamber 7 , such as a pressurized heating tank 7 . Spray droplets are heated inside the tank 7 to vaporize into a gas phase, and the gas 70 is then ejected or deposited on the first surface of the substrate 1 through a gas diffusion device 71 . Said first side of the substrate is in contact with the rotating cylinder 6 at the same time. Another rotating cylinder of vacuum type may be arranged on the second side 1b of the substrate for sucking gas in a predetermined direction through the cellulosic substrate 1 . Thereby, the cellulosic substrate 1 can be hydrophobized through the full thickness of the substrate. Any HCl by-product and possibly unreacted eg palmitoyl chloride and/or unbound C16 can be removed and collected for handling.

For the two illustrated methods shown in Figures 1-2, it is possible to treat the first side of the substrate first and subsequently treat the second side of the substrate with an additional unit facing the second side of the substrate. Such double-sided treatment ensures that the entire core of the substrate will be denatured. The use of more than one spray unit requires minimal space and can be arranged in such a way that it fits into existing equipment. By using a plurality of units, it is also possible to run the machine at an increased speed.

3A-B show a third and a fourth embodiment, respectively, wherein both the first and second surfaces of the substrate 1 are subjected to hydrophobization by applying a fatty acid halide in the form of a spray.

Referring to FIG. 3A , the substrate 1 is first subjected to a pretreatment 2 in the form of heating, for example IR heating. A device (5) for dispersing the liquid into a spray is located downstream of the pretreatment (2) on the second side (1b) of the substrate, adjacent to the rotating cylinder (6), and dispensing a spray (50) of fatty acid halide into the cylinder (6) ), when the cylinder is further rotated, it will transfer the fatty acid halide to the surface of the second side 1b of the substrate 1 . The rotating cylinder 6 may also be heated to the extent that the atomized droplets are transformed into a gas prior to contacting the substrate. A vacuum box 8 is arranged on the first side 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 a fatty acid halide 50 ′ is also applied to the first side 1a of the substrate 1 . Thus, as shown in Fig. 3a, a second device 5' for dispersing the liquid into a spray 50' is located adjacent to the second rotating cylinder 6', and the device 5' is a fatty acid halide. is arranged to direct a spray 50' of the fluoride to the surface of the cylinder 6', which, when rotated further, will deliver the fatty acid halide to the surface of the first side 1a of the substrate 1 . The rotating cylinder 6' can be heated. The vacuum box 8' is arranged in close proximity to the rotating cylinder on the second side 1b of the substrate to induce the reagents to penetrate at least partially into the substrate 1 . A person skilled in the art will know that the equipment (eg spray apparatus 5, 5'; vacuum box 8, 8'; cylinders 6, 6', etc.) is interchangeable and the first side 1a of the substrate 1 is It is understood that it is possible to process first and then the second side 1b.

A fourth embodiment according to the invention is shown in FIG. 3b , serving the same purpose as in FIG. 3a , ie treating both sides of the substrate 1 to increase hydrophobicity. In a manner similar to that described for FIG. 3A , the substrate 1 is induced through two subsequent hydrophobization steps wherein a fatty acid halide is first applied to the second side 1b of the substrate, and the first side 1a ) is applied second. In a first step, the spraying device 5 is positioned adjacent to the second side 1b of the moving substrate 1 and is arranged such that a spray 50 of fatty acid halide is directed directly to said surface 1b. A vacuum box 8 is arranged on the first side 1a of the substrate, opposite the spraying device 5 , said vacuum box 8 attracting fatty acid halides for penetration into the substrate at least partially by vacuum suction. arranged to pull. A downstream rotating cylinder 6, preferably a heated cylinder, may be provided to facilitate bonding of the reagents to the cellulosic substrate 1 . A corresponding second hydrophobization step is arranged downstream of the first cylinder 6 , whereby the fatty acid halide is also applied to the first side 1a of the substrate in a manner corresponding to that described for the first hydrophobization step do.

In a fourth embodiment the fatty acid halide may be converted from a spray form to a gaseous form before being brought into contact with the substrate 1 .

4 , a fifth embodiment according to the invention is shown. A pretreatment step for heating the substrate is shown, wherein such heating can be effected, for example, by IR-heating. In addition, the induction of the fatty acid halide is such that the fatty acid is induced in a predetermined direction along the surface of the first side 1a of the cellulose substrate in such a way that the fatty acid is in contact with the cellulose substrate 1 in the first It is carried out by vacuum suction (8) on the face (1a). The fatty acids thereby move substantially parallel to the first side of the substrate.

5 shows in a schematic manner a method according to the invention, wherein the substrate 10 is a three-dimensional cellulose-based product. Here, a conveyor belt (9) is transporting the three-dimensional cellulosic product (10) through a unit (11) arranged to hydrophobize said product by the method of claim 1 . The three-dimensional product 11 may be, for example, a prefabricated paper tray, mug or container, or other type of 3D-shaped object made of cellulose. After passing through the unit 11 , wherein the vaporized fatty acid halide contacts the cellulosic substrate and at least partially penetrates the thickness, the exiting product 10 ′ acquires hydrophobic properties.

To characterize the success of the reaction, contact angle measurements were used to qualitatively analyze how hydrophobicized the cellulosic substrate was by the method. The untreated cellulosic substrate had a contact angle of about 40° and had a contact angle of 110-130° on both the first and second sides of the substrate after treatment of the method of the present invention, even though only one surface was in direct contact with the reagent. . A contact angle greater than 90° (high contact angle) generally means poor wetting of the surface, so the fluid will minimize contact with the surface and form dense droplets.

Other modifications and variations will become apparent to those skilled in the art in view of the above detailed description of the invention. For example, the method according to the invention can be used as a complement to other methods of applying fatty acid halides to substrates. It should be evident, however, that such other modifications and changes may be made without departing from the spirit and scope of the present invention.

Claims (17)

A method for hydrophobizing a cellulosic substrate (1) comprising a first side and a second side not facing the first side, characterized in that it comprises the following steps:
- drying the cellulosic substrate 1 to a dry content of at least 80%, preferably at least 85%;
- providing a fatty acid halide in the form of a spray;
- contacting said fatty acid halide with the first side of the cellulosic substrate (1) and inducing it to penetrate at least partially into the cellulosic substrate. The method of claim 1 , further comprising the step of inducing said fatty acid halide to also contact the second side of the cellulosic substrate and to penetrate at least partially into the cellulosic substrate ( 1 ). The method according to any one of the preceding claims, wherein said induction of fatty acid halides is carried out by vacuum suction on the second side of the cellulosic substrate such that the fatty acids penetrate the cellulosic substrate (1) in a predetermined direction through the cellulosic substrate (1). how to be 3. The method according to any one of claims 1 to 2, wherein said induction of fatty acid halide is such that the fatty acid is directed in a predetermined direction along the surface of the first side of the cellulosic substrate (1) whereby the fatty acid is brought into contact with the cellulosic substrate. so as to be carried out by vacuum suction on the first side of the cellulosic substrate. Process according to any one of the preceding claims, wherein the dry content of the cellulosic substrate is at least 90%. A method according to any one of the preceding claims, wherein the fatty acid comprises an aliphatic chain length of 10 - 22 carbon atoms. The method according to any one of the preceding claims, wherein the fatty acid is palmitoyl chloride, C16, stearoyl chloride, C18 or mixtures thereof. Process according to any one of the preceding claims, wherein the fatty acid to be atomized is admixed with at least one solvent or mixture of solvents, said solvent preferably selected from the group comprising acetone, ethyl acetate and methyl ethyl ketone. 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% solvent of the total mixture. Method according to any one of the preceding claims, wherein the cellulosic substrate (1) is a paper- or cardboard web. 11. The method according to claim 10, wherein the web (1) is a single- or multi-layer web. 10. The method according to any one of claims 1 to 9, wherein the cellulosic substrate is a three-dimensional cellulosic based product. The method according to any one of the preceding claims, wherein the method further comprises a step of heating the substrate (1) before and/or after adding the fatty acid halide. 13. The method of claim 12, wherein heating the substrate is performed by IR heating. Method according to any one of the preceding claims, wherein the vacuum suction is carried out by means of a vacuum box (11). 15. The method according to any one of the preceding claims, wherein the vacuum suction is carried out by means of a rotating vacuum cylinder (6). A cellulose-based product treated by a method according to any one of the preceding claims.

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