DE2312423A1 - METHOD OF PRODUCING FIBRILS SUITABLE FOR PAPER MANUFACTURING - Google Patents

Description

Method of producing for papermaking

suitable fibrils

For this application, the priority will be from March 13, 1972 U.S. Patent Application Serial No. 234 321 claimed.

The invention relates to improvements in a method for producing fibrils from polymers of high molecular weight as well as improvements in paper made from such fibrils. In particular, relates the invention is based on an improvement of the method for Production of fibrils from polyolefins, especially linear polyethylene, of very high molecular weight, which results in that paper or other fleece-like structures in which these fibrils are incorporated have improved properties exhibit. In particular, the invention relates to a modification of the method for producing pibrils from polyolefins, especially linear polyethylene, of very high molecular weight, according to which the polyethylene before the production of the Fibrils is mixed with an additional polymer and the pibrils are then made from this polymer mixture and processed into paper with improved properties. The fibrils produced according to the invention can be omitted aqueous dispersion to form cohesive, self-supporting

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Process leaves and can therefore be used to Paper and other nonwoven-like products with improved properties according to known papermaking methods to manufacture. '·

In recent years, there has arisen in the art a need for better paper which is synthetic fibers contains. There are already several. Synthetic paper pulp Fibers and methods are known by which such paper can be made. These known paper stocks are " has been successful for quite limited and special uses. But since those contained in these papers Synthetic fibers are very dissimilar in structure to natural paper pulp fibers, these material compositions have become in the great majority of cases where a product is required that has the essential properties of the paper and also has some properties that cannot be found on natural paper proven. Such a paper is supposed to be an improved one Flexibility and both in the wet and in the dry state a high tensile strength and bursting strength can be produced easily and economically.

The synthetic hydrophobic fibers that are in the first place have been developed for textile applications Nowadays also used for the development of numerous specialty papers and other non-woven fiber products that are not traditionally associated with the paper industry Related. Special effort is put on the manufacture of paper and paper-like webs made of these polymer fibers have been used, either for their end use in unconverted form in special paper or for combination with other materials, e.g. in the production of laminates. For these end uses was it advantageous for obvious reasons, such as ease of availability and economy, the well-known, conventional papermaking

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to operate systems and processes.

The patents ..... (patent application P 22 52 758.8) and ..... (patent application P 22 57 586.6) adhere to processes for generating Clay I-fibrils of high quality to the subject that are particularly suitable for the production of paper and other fleece-like products in the paper machine. The invention concerns amendments to those proposed in the cited patents Pibril and papermaking processes aimed at improving the paper obtained in this way or other Aiming nonwoven product. '.

In the older procedures mentioned above, the fibrils are removed from a solution of a very high molecular weight polyolefin such as polyethylene or polypropylene, in particular from a solution of linear polyethylene, produced by subjecting the solution to shear, so that the polymer molecules contained in it are oriented, Immediately thereafter, the dissolved polymer is on a purely thermal Ways out of the solution are precipitated by quickly placing the solution in a cooling bath or with the help of other coolants is cooled. Solutions of polyolefins in suitable solutions are best suited for the production of this type of pibrils liquid hydrocarbons. The cooling of these oriented solutions is usually carried out under conditions under which no shear takes place at temperatures which are considerably below the precipitation temperature of the polymer solution, and in the process, solvent-swollen fiber masses are formed. These fiber masses are then usually processed into librils in a series of operations. Usually the excess solvent is first separated from the fiber mass, then the fiber mass is cut into pieces cut to the desired length, and the cut or chopped fiber paste is processed by grinding or refining to individual pibrils for making paper or other fleece-like products processed in the paper machine according to conventional paper-making processes. To

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In the processes of the patents mentioned, the pibrils are made from a single polymer "or the solution of a single polymer made in hydrocarbons.

Although the papers or other non-woven products, which are manufactured from the m-glasses produced according to these older processes are of good quality, it has been shown that the sheets of paper in some of their physical oil properties are still in need of improvement. The invention is therefore based on the object of synthetic Polymers according to the process of the above-mentioned patents to produce paper that have better physical properties than the paper obtained according to the earlier patents. In particular, they should be made from purely synthetic pibrils Paper sheets are produced that have better tensile strength, burst strength and cold strength than those made from the J-fibrils produced according to the cited patents Sheets of paper.

It has been found that paper or other nonwoven-like Products of high quality, which have better properties than those. Products made by the processes of the above Patents are available, can be made by using the hot hydrocarbon solution of the polyolefin to which the pibrils to be embedded in the paper are produced, a second polymer is added before the production of the librils. As a result of the addition of only small amounts of this second polymer, sheets of paper are obtained from the pibrils produced in this way of higher tensile strength, bursting strength, ductility and cold strength, which generally have a higher quality grade exhibit. The second polymer, which according to the invention is added to the starting polymer solution, is a Homopolymer of styrene, which is a much lower one Molecular weight than the linear polyethylene from which the pibrils are made. The polystyrene can Hydrocarbon solution before pibril generation in amounts of about 5 to 35 percent by weight, based on the linear

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High molecular weight polyethylene, can be added to give the desired properties to the paper to be made from the fibrils to give improved properties. For this purpose, about 10 to 25 percent by weight of polystyrene is preferably used, based on linear polyethylene, too.

For a better understanding of the invention, reference is made to the method according to patent ..... (patent application P 22 52 758.8) taken. In the process according to this patent, the polymer from which the fibrils are produced is first used should, dissolved in a dissolving vessel, the contents of which are stirred by a stirrer. Located at the bottom of the stirrer paddles or blades, and the stirrer will, by one The motor located outside the dissolving vessel is set in rotation. The solvent contained in the dissolving vessel for As described in the patent mentioned, the polymer should be an inert liquid, the polymers should be of high molecular weight dissolves at elevated temperatures. Some of the solvents preferred according to the invention are luminous oil, gasoline, Tetrahydronaphthalene, xylenes, chlorinated solvents and like that. Preferably, however, the solvent consists of hydrocarbons of moderately high boiling point that are capable of are to dissolve olefin polymers of high molecular weight (especially linear polyethylene) at elevated temperatures. Particularly essentially aliphatic hydrocarbons with a boiling range of about 155 to 180 ° C. are preferred. The solvent is fed to the dissolving vessel through a line and is usually preheated to about 135 ° G. The polymer to be dissolved in the solvent should have a high molecular weight to have; in particular, a high molecular weight polyolefin such as polyethylene or polypropylene is used.

The polymer is preferably a linear ethylene polymer of very high molecular weight. Particularly preferred are according to the invention for the production of improved fibrils olefin polymers of very high molecular weight,

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which have an inherent viscosity of at least 3.5, as the following examples explain. The inherent The viscosity of the polymer is defined by the following equation:

Inherent viscosity =

Herein "t means the all time or transit time of the polymer solution by the "viscometer, t means the fall time of the solvent, and c "means the concentration of the polymer in the solvent. The inherent viscosities specified here are based on solutions of 0.05 g of polymer 100 ml of decahydronaphthalene determined at 135 ° G.

The ethylene or other olefin polymer is in the hydrocarbons at elevated temperature, in general in the range of 14-0. up to 160 G, dissolved after it is in the dissolving vessel has been fed through a feed line. In the dissolving vessel, the Polyäthylehlosung, which is about 0.25 to 3> 0 percent by weight of polymer contains, constantly from the stirrer kept moving. Tor preferably has the solution · in that Dissolving vessel has a concentration of 0.5 to 2.5 percent by weight of polyethylene. These polymer concentrations are, however not necessarily; they are just preferred. The olefin polymer concentrations in solution; should not be based on the percentage by weight, but according to the desired Adjust the viscosity of the solution. Fm the desired fibrils to obtain, should as much olefin polymer to the solvent be added that the resulting solution, be .- .. correct at 145 ° G, a viscosity of about 50 to 30,000 cP having. The polymer solution can also contain stabilizers included, which -increased the decomposition of the polymer in these Prevent temperatures. Such stabilizers are, for example, "Ionol", "Santonox R" and dilauryl thiodipropionate. . . ,.

The polymer solution is taken from the dissolving vessel by a Pump disconnected through white line.

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With the procedure according to patent ..... (patent application P 22 52 758.8) is the polymer solution through a line fed to a centrifugal spinning device or hammer mill. The hot polymer solution becomes the effect of the centrifugal spinning device exposed, merging into a fiber mass swollen by solvent. After the passage the swollen fiber mass with the associated liquid solvents falls through the device through the bottom outlet out of the device.

During operation, it flows into the outer or circumferential area the centrifugal spinning device through a line cooled liquid in order to form the fiber mass from the polymer solution to assist in their passage through the centrifugal spinning device. The spinning device assigned led chilled liquid can be any nonsolvent for the polymer dissolved in the dissolving vessel, but is preferably the same liquid as that in the dissolving vessel is used to dissolve the polymer. The possibility of dissolving the olefin polymer in the dissolving vessel and for Cooling to use the same liquid in the spinning device is given because there are many solvents these polymers do not dissolve at lower temperatures. This way, with the solvent recovery associated difficulties avoided. If the cooled solvent supplied to the device is from the same source comes like the solvent supplied to the dissolving vessel, it is first passed through a cooler, where it is heated to 10 ° C or is cooled underneath.

The product discharged from the bottom or outlet of the spinning device is a fiber mass swollen by solvent, which still contains liquid solvent and coolant and is fed to a press through an outlet line. In the press is the swollen fiber mass from most of the liquids, such as solvents and coolants, which, as mentioned above, can consist of the same substance,

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separates. The separation takes place by pressing out the fiber mass in the press, and this process can be in or outside the press a filtration through a. Sieve upstream where the major part of the liquids is already separated from the fiber mass. The separated liquids flow out the press and, if the same hydrocarbons are used as the solvent and coolant, through recirculated a line for reuse. The fibrils are still slightly swollen in the form of a mass of fibers Condition from the press through an outlet line into a grinder or similar refiner for the further treatment carried out

When using polyethylene, an alcohol such as isopropanol is fed into the grinder to remove the other To support treatment, finishing and removal of excess or additional solvent from the fiber mass. In addition to helping to remove additional solvent from the pulp, the alcohol also acts as a Suspending agents for the fibrils in the milling device. The fiber mass swollen by solvent becomes fibrils of the desired length, e.g. from 1 to 5 mm, for use in the manufacture of paper or other web-like products cut in the paper machine. The grinding device can be a mixer, a disk mill, a Hollander or be a 'similar refiner. The grinding process should take as long as the solvent-swollen fibers se is broken up into a multitude of individual fibrils. .

If necessary, the treatment can be carried out in the grinding device Perform in a medium other than an alcoholic medium. For this you can use e.g. acetone, hydrocarbons, especially aliphatic hydrocarbons, and the like use. Any liquid in which the olefin polymer is present can be used as a refining and suspending agent does not dissolve, even in the polymer solvent

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is soluble, even that used in the dissolving process step Polymer solvent itself - if the milling process is carried out at sufficiently low temperatures will. As already mentioned, this is possible because many of these solvents have lower polyolefins Temperatures do not dissolve. The grinding process carried out in the refiner sometimes takes place in a medium other than an alcoholic medium, e.g. in hydrocarbons and especially in aliphatic hydrocarbons, because it is indicated under certain circumstances, a non-aqueous or for fleece formation to use an organic medium, e.g. hydrocarbons. In such cases it is beneficial to work with fibrils, which have already been ground or refined in a medium consisting of hydrocarbons. Such a system. (using hydrocarbons) is technically an option for areas where there is not enough water for the conventional papermaking is available, or where there is contamination from aqueous liquids cannot be admitted. Slurries in hydrocarbons have been found to be very solid receives handmade paper sheets.

When the fibrils in an aqueous or essentially If aqueous papermaking processes are to be used, the refinement in the grinding device should reduce the solvent content of the fibrils to less than 5 percent by weight. As shown, however, surprisingly has that you get a better and stronger paper when the fibrils still contain some solvent, the solvent should cannot be completely removed. In this sense, it was found that the paper finally obtained was significant has better properties when the fibrils from which it is made have been grafted to the point that they are contain less than 5 percent by weight, but preferably greater than about 0.25 percent by weight of residual solvent. This refining of the fibrils to a residual solvent content of

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less than 5 percent by weight can be achieved with the help of a downstream Steam treatment take place «

I ^{1 For} the last stage of the process, the product consisting of fibrils, alcohol or other suspending and refining agents and, to a certain extent, the solvent used to dissolve the polymer is conveyed from the grinding device into a filter for final separation or filtration, When separation or filtration occurs, the product exits the filter through a solids outlet and now consists of the improved fibrils or non-rigid particles according to the invention. A mixture of alcohol or other suspending agent and a certain but smaller amount of solvent flows out of the filter through a liquid outlet. This liquid flows through an alcohol cleaner, which in the patent ..... (patent application P 22 52 758.8) is referred to as isopropanol cleaner, because in this embodiment of the invention, polyethylene is used as the material for the fibrils and isopropanol as a suspending agent and finishing aid. The cleaned isopropanol is fed back from the cleaner through a circuit line for further use in the isopropanol supply. The solvent, which is separated from the isopropanol in the cleaner, flows out of the cleaner into a solvent circulation line and thus returns to the solvent supply. If necessary, the product discharged from the filter can be treated with steam or washed with water in order to remove alcohol residues therefrom. This additional process step is not absolutely necessary, but it is necessary if the fibrils are to be processed by a papermaking process "which uses a purely aqueous medium. If the refining and milling has been carried out in hydrocarbons, it may at this point of the process, it may be advantageous or necessary to treat the fibrils with steam in order to drive off most of the remaining hydrocarbons therefrom.

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According to the invention, paper sheets or the like can non-woven products, the better "properties and a have a higher quality than the previously available paper sheets or fleece-like products made from iT glasses produced by the method of the earlier patent mentioned above. According to the invention becomes the starting hydrocarbon solution of the only one Polyolefins a second polymer before the production of the pibrils added. This second polymer has a lower molecular weight than the polyolefin and is relatively small amounts added to produce a surprising improvement in many of the physical properties of the product to achieve the egg glasses produced paper. This according to the invention added second polymer is a homopolymer of styrene and is used in amounts of about 5 to 35, preferably from about 10 to 25 percent by weight, based on the amount of polyolefin, especially linear polyethylene of high molecular weight, dissolved in the hydrocarbon solution of the polyolefin.

The polystyrene can be desolate to the hydrocarbons after heating them, at the same time as or before the addition, or after the linear polyethylene has been dissolved will.

Example 1 (comparative example)

In this example, pibrils are made according to the procedure

according to patent (patent application P 22 52 758.8) without the

the object of the invention forming improvement produced and for the production of paper in a paper machine Noble and Wood used. The physical properties of the paper are determined and are given below. This example serves only as a comparative example in order to demonstrate the improvement achieved according to the invention.

A stainless steel vessel equipped with a stirrer is filled with 3.0 l of aliphatic hydrocarbons (boiling point -

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■ range 155-180 ° C) "charged, the 0.018 g of a mixture equal parts by weight of "Ionol", "Santonox R" and dilauryl thiodipropionate contained as an oxidation retarder. The mixture of solvent and oxidation retarder is a.uf 150 ° G heated and then with 15.0 g linear polyethylene from ho-hem Molecular weight (inherent viscosity 13 »33) added.

The slurry is kept at 150 g while stirring kept, Ms the polyethylene has completely gone into solution and causes a generation of fibrils according to the above "The method described has formed a suitable. solution. This solution is then in a centrifugal spinning device, such as that described in patent ..... (patent application P 22 52 758.8)

• Hammer mill, transferred, the rotor of which rotates at a speed of 11 140 rpm. I ¹ Suitable for papermaking

• Librillas are made according to the other procedural steps in accordance with the patent ..... (patent application P 22 52 758.8) generated. Refining takes place in the Waring mixer with isopropanol. A slurry of the librilles is fed to the headbox of a Hoble and Wood paper machine, in which it is "traditionally hand-scooped paper sheets are made will. Various physical properties are determined on the paper sheets obtained in this way; the results can be found in the table below.

Example 2

The procedure is as in Example 1, but with the addition of polystyrene to the hot starting solution of the polyethylene in the hydrocarbons.

The vessel described in Example 1 has a value of 3.0. 1 of the solvent specified in Example 1 charged, which ■ contains the same amount of the same antioxidant mixture. The solvent is heated to 150 ° G. As soon as that Mixture of solvent and oxidation retarder this temperature 1.5 g of polystyrene (commercially available "Dow Styron" 666 ") are added and this is brought into solution

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The polystyrene solution obtained is mixed with 15.0 g of linear polyethylene of high molecular weight (inherent viscosity 13.33). This mixture is heated to 150 ° C. with stirring held "until the polyethylene has completely dissolved and a suitable solution for the production of fibrils has been found with a polystyrene content of about 10 percent by weight, based on linear polyethylene. Those produced from this solution by following the procedure of Example 1 Fibrils are used to make handmade paper sheets in the Noble and Wood paper machine. The physical properties of these paper sheets are also given in the table below.

Example 3

The procedure is as in Example 2, but with the addition of 3.0 g of the same polystyrene. The solution of Polyethylene and polystyrene thus contain 20 percent by weight of polystyrene, based on the linear polyethylene. The properties of the paper produced from these fibrils according to Examples 1 and 2 can also be found in the following Tabel.

example

Characteristic* m 1 2 3 Basis weight, g / m 78.59 78.84 86.80 Tensile strength, kg / 15 mm 1.66 3.09 3.49 Tear length (tensile factor), 1391 2461 2568 Stretching, fo 4.54 30.90 27.00 Burst strength according to Mullen, g / cm ² 977 2615 2580 Burst factor according to Mullen 13.4 32.06 31.17 Tear resistance after Elmendorf, g / sheet 205.3 204.0 258.0 Tear factor to Elmendorf 248.3 248.3 287.4 Folding resistance, cycles' until it breaks 14.3 > 10,000 > 10,000 Opacity, tfo 81.1 84.5 82.2 Brightness, $ 75.2 .74.3 76.4

* Tappi test standard T220 M-60

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As the table shows, the addition of a small one achieves this Amount of polystyrene τοη relatively low molecular weight to the starting solution of linear polyethylene of high molecular weight in hydrocarbons improvements. in many physical properties of the off the fibrils made of paper. Particularly noteworthy are the improvements in tensile strength, such as they result from the increase in the tear length, as well as the improvement in the bursting strength according to Mullen, in the • folding strength and in the stretch. .

Example 4 .

Example 2 is used with the difference that 2.5 g of polystyrene are dissolved in 2.0 l of the hydrocarbons given in Example 1. The. A solution of polystyrene in hydrocarbons is admixed with 10.0 g of the linear high molecular weight polyethylene used in Example 2 and heated until a solution suitable for producing fibrils by the method of Example 1 is formed, which is 25 percent by weight of polystyrene on linear polyethylene; contains. After the further process steps of Example 1, pibrils are then produced, from which hand-scooped paper sheets in a paper machine according to Noble and. Wood, also according to Example 1, can be produced. These paper sheets are similar to those of Examples 2 and 3 and show the same improved properties according to the invention.

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Claims (6)

Gulf Research. & Development Company S-492 claims 1. Process for producing paper-making suitable High molecular weight polymer fibrils, "in which an olefin polymer having an inherent viscosity of at least 3.5 in hot hydrocarbons dissolved to a hot olefin polymer solution, the hot olefin polymer solution to orient the polymer molecules subjected to shear, then by bubbling the solution through an at a temperature substantial cooling zone kept below the precipitation temperature of the solution while maintaining the orientation of the polymer molecules in the solution the polymer in the form of a solvent swollen fiber mass precipitated, an essential part of the Separated polymer solvent from the fiber mass, the I fiber mass by grinding in a polymer which does not dissolve and liquid soluble in the polymer solvent is comminuted into a number of fibrils and the fibrils be separated from the non-dissolving liquid, characterized in that the hot hydrocarbon solution of the olefin polymer before the production of the fibrils is polystyrene in amounts of about 5 to 35 percent by weight, based on the olefin polymer added. 2. The method according to claim 1, characterized in that linear polyethylene is used as the olefin polymer. 3. The method according to claim 2, characterized in that linear polyethylene with an inherent viscosity of at least 5.0 in a concentration in the hydrocarbons - 15 30984 9/0804 substances from about 0.25 "to 5.0 percent by weight will work. 4. The method according to claim 3, characterized in that one works with a solution, the linear polyethylene of an inherent viscosity of at least 10.0 in concentrations from about 0.25 to 3.0 weight percent and polystyrene in amounts from about 10 to 25 weight percent based on linear polyethylene, contains. 5. Fibril produced according to claims 1 to 4. 6. Paper, characterized in that it is produced from a plurality of pibrils produced according to claims 1 to 4 has been. - 16 - 3096A9 / 060