US 3776812 A
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United States Patent 3,776,812 PROCESS FOR MAKING PAPER CONTAINING LATEX WITH CARBOXYL GROUP Hendrik Jongetjes, Heemskerk, Netherlands, assignor to Koninklijke Papierfabrieken Van Gelder Zonen N.V., Amsterdam, Netherlands No Drawing. Continuation of abandoned application Ser. No. 770,791, Oct. 25, 1968. This application Nov. 17, 1971, Ser. No. 199,797
Int. Cl. DZlh 3/40; D21d 3/00 US. Cl. 162168 9 Claims ABSTRACT OF THE DISCLOSURE The preparation of a fibrous bonding agent for nonwoven materials in which a polymer latex containing 0.02- 10 percent carboxyl groups is mixed with an aqueous solution of a cationic polymeric substance at a pH of 6-9. Within sixty minutes, the finely divided particles which are formed are converted into fine, fibrous particles by adjusting the pH of the mixture to 2-4 with stirring and taking care that the final solids content is 0.01- 10 percent by weight. Also, the fiber so produced and the manufacture of non-woven materials using said fibrous binding agent.
This application is a continuation of Ser. No. 770,791, filed Oct. 25, 1968, now abandoned.
The invention relates to a process for the preparation of a fibrous binding agent for non-woven materials, in which a latex of a polymer or copolymer containing carboxyl groups is fiocculated with a water-soluble cationogenic polymer substance.
The term non-woven material is well understood in the art and describes a productwith a self-sustaining, smooth structure, mainly composed of fiber that may or may not be linked together by a binding agent. As fibers to be used for this purpose there may be mentioned, for instance, natural, vegetable and animal fibers modified natural fibers, regenerated natural fibers like rayon fiber, inorganic fibers like asbestos, glass and slag wool, synthetic fibers or mixtures thereof.
For the manufacture of non-woven materials by a wet process from a suspension in water of regenerated cellulose fibers, synthetic fibers or inorganic fibers, it is necessary to add a binding agent to obtain cohesion between the fibers. This cohesion is required during the production of the non-Wovens in order to pass them through the machine when wet. In addition, it is necessary for the nonwovens to be sufiiciently strong for many end uses when they are still wet.
Various processes are known for the binding of the fibers (see 0. Batista, Synthetic Fibers in Paper Making, Interscience Publishers, Inc., New York 1964). Thus, it has been suggested to add fibers to the suspension of fibers, said added fibers having a lower softening temperature than the fibers to be bound, and thus causing the non-woven web to cohere by a subsequent heat treatment. This method has the disadvantage that during the production of the non-Wovens the machine may break down because of the stickiness of the non-Wovens, whereas the structure of the finished non-Wovens is fiat and harsh. In theory it is also possible to sprinkle a solution or dispersion of the binding agent onto the fibrous web when still wet, or to impregnate the wet web with it. That process is diificult to carry out in a paper machine, because thte web, when wet, has too little cohesion for satisfactorily undergoing such a treatment.
A process is often used in which fibrous particles of a polymeric substance are added to the fiber suspension. In US. patent specification 2,988,782 a process has been described in which such finely divided fibrous particles 3,776,812 Patented Dec. 4, 1973 may be obtained by precipitating a synthetic polymer from a solution by means of a liquid, that does not dissolve the polymer, while applying high shear.
In Dutch patent specification 6402888 a process has been described for the preparation of fine particles of a binding agent by precipitation of a latex of an elastic copolymer having free carboxyl groups, with a copolyamide. The precipitate thus obtained is, it is true, an excellent binding agent by itself, but it has no fibrous structure. It is therefore less suitable for the production of non-Wovens with an open structure, because a fair amount of the binding agent is lost with the white water.
In Dutch patent application 6402859 a process for the production of non-Wovens by a Wet process by means of a fibrous precipitate of a latex has been described. The binding agent is prepared by precipitating a latex of an acrylic or a vinylic copolymer, preferably by adding the latex to a solution of a precipitating agent in water. Salts of polyvalent metals, particularly alum, and/or cationic organic compounds, particularly cationic polymers, are mentioned as precipitating agents. Additives may also be added to the latex to be precipitated, for instance, polyacrylic acid and salts thereof or carboxymethyl cellulose. The additive accomplishes the formation of elongated, fibrous, frayed particles. According to the introductory part of the specification there is only a moderate stirring at the precipitation, which causes low shear that has no shearing action on the precipitated particles. According to the Examples I and II an amount of 550 cm. of liquid is stirred, however, with a stirrer having a diameter of 5 cm. at the rate of 1600 r.p.m., undoubtedly causing high shear to occur. It is conceivable that during this process coarse particles will be formed, to begin with, which are mechanically broken down. A disadvantage of this process is that, apart from the complicated way of stirring, the ions of polyvalent metals co-precipitate with the additives. The co-precipitate thus formed has, on the one hand, a detrimental effect on the dehydration speed of the non-woven web in the paper machine. On the other hand this finished non-woven web contains a certain amount of salts and hydrophilic polymers. These unwanted constituents have to be washed away in order to decrease the hydrophilic properties of the non-woven, because it would otherwise have too little strength when wet. The binding agent obtained according to this known process is therefore unsuitable for the production of a proper.non-woven from natural fibers.
It has been found that the disadvantages of the prior art processes are avoided and a highly suitable fibrous binding agent can be obtained when (a) a latex of a polymer having carboxyl groups or a latex containing a polymer having carboxyl groups and one or more polymers without carboxyl groups, the content of carboxyl groups of which amounts to 0.02-10 percent by weight calculated on the total amount of polymer or polymers, is mixed with (b) an aqueous solution of a cationic polymeric substance at a pH of 6-9, and by causing, after sixty minutes at the most, the finely divided particles formed to be converted into fine, fibrous particles by means of adjusting the pH of the mixture to 2-4 with stirring, and taking care that the solids content of the mixture finally amounts to 0.0l-l0 percent by weight. The process is preferably carried out in such a way that the mixture of latex and solution of cationic polymeric substance has a solids content of 0.1-5 percent by weight.
The term a latex of a polymer having carboxyl groups" means an aqueous dispersion of an elastomeric polymer or copolymer into which carboxyl groups have been introduced by methods well known, per se.
The dispersed polymers may be natural polymers, modified natural polymers, synthetic polymers, or copolymers.
Synthetic polymers or copolymers may both be obtained by addition polymerization and polycondensation. Latices of copolymers of butadiene and styrene, of butadiene and acrylonitrile, and of acrylic and methacrylic esters are preferred. The molecular weight of the polymers or copolymers is of no importance. Either the ratio of the monomers in co-polymers is essential. The only requirement is that a latex of an elastomeric polymer or copolymer having carboxyl groups be used.
Typical examples of latices used in the present process are those described in British Pat. No. 824,286 to The B. F. Goodrich Company. This patent describes the preparation of latices of carboxyl-containing elastomers by the copolymerization of an olefinically unsaturated carboxylic acid with a diene. In a similar way latices of polymers having carboxyl groups may be prepared from unsaturated carboxylic acids without using comonomers.
The content of carboxyl groups of the polymer, or mixture of polymers, dispersed in the latex should amount to 0.02- percent by weight. When the content of carboxyl groups is lower, fibrous particles are indeed obtained, but they are less stable both in mechanical and chemical respects. When the content of carboxyl groups is in excess of ten percent by weight there is too much of the cationic flocculation agent required, which would render the process less attractive economically. In addition to this there are at the moment no latices available having a higher content of carboxyl groups. The carboxyl groups must not be esterified, but may be neutralized, for instance, by means of an alkali metal or ammonium ion. Upon acidification to pH 2-4 in the second phase of the process the free carboxyl groups are formed.
It has been found that it is not imperative to use a latex containing only a polymer having carboxyl groups. The latex may also contain one or more polymers without carboxyl groups, i.e., a mixture may be used of a latex of a polymer having carboxyl groups and one or more latices of polymers without carboxyl groups, provided that the content of carboxyl groups, calculated on the total amount of polymers, amounts to 0.02-10 percent by weight.
As examples of basic polymers having carboxyl groups, which may be dispersed in latices to be used as starting material, are mentioned: copolymers of acrylic and methacrylic esters, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyethylene, polypropylene, copolymers of butadiene and styrene, and of butadiene and acrylonitrile.
The polymers or copolymers without carboxyl groups which may be used together with those having carboxyl groups differ from the last-mentioned polymers or copolymers in that a hydrogen atom has been substituted for the carboxyl group. It should be understood, however, that when a polymer or copolymer without carboxyl groups is used it need not be similar to the polymer or copolymer having carboxyl groups which is present in the latex. For instance, a copolymer of butadiene and acrylonitrile having carboxyl groups may be used together with a polyvinyl chloride without carboxyl groups.
The latices may contain anionic and/or non-ionic stabilizing agents. In addition to this the latices may contain additives, like antioxydants, anti-foaming agents, accelerators, etc. Stabilizing agents, antioxydants and accelerators have been described in the book of D. C. Blackley, High Polymer Latices, vol. 1, chapter II, par. 6, 4 and 3 respectively. Suitable anti-foaming agents are those known in the art such as Antifoam A and other compounds on a silicone basis.
Polyamides, polyamines, polyimines or copolymers thereof, which may be cross-linked, for instance with epichlorohydrin, are used as water-soluble cationic polymeric substances by which the polymers of the latex are fiocculated. Particularly suitable are cationic urea-formaldehyde resins and melamineformaldehyde resins and deri at e o s a itline, such d ya d am cle-formaldehyde resins. Cationic modified starch may also be used.
The water-soluble cationic polymers may be prepared according to the process described in US. Pats. Nos. 2,786,823, 2,926,154 and 3,215,654 and in Dutch Pat. No. 110,447.
The cationic polymers used are mostly low molecular weight compounds, which are used in paper making as retention agents or as wet strength agents. Typical examples of such polymers are Kymene 557 (manufactured by Hercules Inc.) and Urecoll K (manufactured by Badische Anilin-und Soda Fabrik A. G. at Ludwigshafen- Rhein, Western Germany).
Three-fifteen percent by weight of cationic polymer calculated on the solids of the latex is preferred. Higher percentages may also be used, however, e.g., up to fifty percent by weight. Flocculation may occur in percentages lower than three percent by weight, but there occurs insufficient cross-linking of the binding agent during the subsequent heat treatment. In this case the water resistance is not sufficient.
The cationic polymeric substances are bound to the polymers of the latex containing carboxyl groups, the carboxyl groups being neutralized by formation of salts with the cationic groups, the flocculate of the polymers thus being formed.
By using the aforementioned cationic polymers as flocculation agents, a binding agent is obtained which imparts an extremely high wet strength to non-woven web on the wire of the paper machine, right at the beginning of the process. That in itself is a great advantage from the viewpoint of workability of the non-woven web in the paper machine before the dryer. In addition to this there occurs a cross-linking reaction during the heat treatment, when the web is dried, between the carboxyl groups of the polymer from the latex and the cationic groups of the flocculating agent. The strength of the non-woven, both when dry and wet, is increased even more by this, and an excellent resistance to washing and dry cleaning is also obtained for this reason.
Due to the satisfactory properties of the binding agent prepared according to the process of the invention, the non-Wovens manufactured according to it are ready for use immediately, without an after-treatment being required.
The process according to the invention is preferably carried out as follows: The latex is put into a mixing vessel provided with a stirrer. The latex is diluted, with stirring, with such an amount of water that the content of solids of the final mixture will have the desired value. While stirring in the normal manner a solution of the cationic polymeric flocculating agent is added to the water, care being taken that the pH of the mixture in the vessel is maintained at about 6-9. An extremely fine pre-flocculate is formed during this mixing. The particle size of the pre-flocculate is generally less than 50 micron and is therefore too small to be used as binding agent for non-wovens.
Not more than sixty minutes after the addition of the cationic flocculating agent, the second phase of the process must be carried out. That is to say that the pH of the liquid has to be adjusted to 2-4 with normal stirring Within sixty minutes. If this is done after a longer period than sixty minutes, there is a danger of agglomeration of the fine particles to coarser particles than do not have the desired fibrous shape.
By decreasing the pH to 2-4, fine fibers are formed from the fine particles of the pre-flocculate, said fibers having a length of 50-500 micron and a ratio between length and width of 2:1 to 10:1, provided care has been taken that the solids content of the mixture amounts to 0.01-10 percent by weight, preferably 0.1-5 percent by weight.
Inorganic acids may be used for decreasing the pH, such as hydrochloric acid, sulfuric acid, and nitric acid. Preferably used, however, are Organic carboxylic acids,
such as acetic acid and formic acid, because these weaker acids decrease the pH more gradually.
The binding force depends i.a. on the surface of the :flocculated binding agent. This surface is greater per unit weight as the particles are smaller. As has been stated, there is a minimum limit to the size of the particles. The range of particle size should be from 50 to 400 microns. The minimum limit depends on the pore size of the nonwoven web to be bound. The size of the particles can be regulated by controlling the conditions during the flocculation, such as pH, concentrations, temperature, etc., within strict limits. Particle size is increased with decreasing pH, increasing concentrations and increasing temperature.
It s also possible to start with an undiluted latex and to flocculate said latex in the way described above and to acidify the mixture afterwards until the pH is 2-4. Subsequently the diluent water is added. The fine fibrous particles are only formed when the mixture has been diluted until a solids content of 0.01-10 percent by weight, preferably 0.1-5 percent by weight, has been obtained. In using this process there is a danger, however, that part of the particles will not be fibrous in shape.
The components may also be added in a reversed order, but again there is the possibility that the fibrous flocculate will have a less even structure and size, which does not improve the strength properties of the non-Wovens manufactured with them. It is also possible to add both the latex, which may or may not have been diluted, and the solution of the cationic polymeric substance, each from a storage vessel, to a mixing vessel where stirring takes place.
The suspension of fibrous particles obtained according to the invention can be used immediately as a binding agent, either by mixing with a suspension of fibers to be bound, or by adding said fibers to the suspension of the binding agent. The fibrous binding agent can, however, also be separated from the suspension, be packed as a moist mass, stored, transported, and subsequently used.
It is surprising that the fibrous flocculate obtained according to the invention will stand up to mechanical forces, changes in pH and chemicals. The formation of the fibers is therefore an irreversible process. Once the fibers have been formed, however, they may be used as binding agent and mixed with any fiber mixture, whatever composition this mixture may have.
Due to the great variety in latices, cationic polymeric fiocculating agents and fibrous compositions for the manufacture of non-Wovens, a large number of final products can be obtained, which are immediately ready for use.
A fibrous binding agent obtained according to the invention has excellent binding properties as compared with natural, regenerated, inorganic and synthetic fibers and mixtures thereof. It is highly suitable for the production in the wet process of non-woven materials having an extremely low base weight (-50 g./m.
The non-woven materials are manufactured from an aqueous suspension of fibers in a paper machine, preferably of the inclined screen type. The fibers may be inorganic fibers such as glass fibers, fibers of cellulose and regenerated cellulose, synthetic fibers such as polyamide, polyester polyacrylic and polypropylene fibers and copolymer fibers. The length of the fibers may vary from 3 to 25 millimeters, the preferred length being about 6 millimeters. The ratio of length to diameter of the fibers should be no more than 500:1.
The concentration of the fibers in the aqueous suspension should be no more than 0.1% by weight. Immediately before the aqueous fiber suspension is dehydrated the binding agent is added to it in an amount of up to 50% by weight, preferably to 35% by weight, calculated on the dry weight of the fibers.
Hand formed sheets of non-woven materials may be manufactured in a similar way in a laboratory sheet forming apparatus.
The invention is further illustrated with reference to the following examples.
EXAMPLE I In a flask with a content of 600 ml., provided with a stirring blade, the following substances are mixed with normal stirring.
440 ml. of water 50 ml. of latex of a copolymer of butadiene and styrene having a weight ratio of butadiene to styrene of about 1:1 and having three percent by weight of carboxyl Yield 500 ml. of suspension of an extremely fine preflocculate, hardly to be seen with the naked eye, having solids content of about five percent.
10 ml. of said suspension is mixed with 1000 ml. of water, the pH of which has been adjusted to three by means of acetic acid.
This causes the fine particles of the pre-flocculate to grow to fibrous particles.
Polyamide fibers (length 6 mm., 1.5 den.) are stirred in water at a concentration of 0.1% by weight in a high speed mixer at 2800 rpm. The suspension obtained is diluted to a total volume of 10 liters in a laboratory sheet forming apparatus. The Ifibres particles of the binding agent prepared in the above-mentioned way are added in an amount of 50% by weight, calculated as dry binding agent on the weight of the dry fibers. After thorough mixing the suspension is sieved while stirring, thus forming a wet fibrous web on the sieve plate. The wet sheet is taken from the sieve plate and dried during 5 minutes at a temperature of C. After drying the non-woven sheet is heated during 2 minutes at a temperature of to C. The non-woven obtained has a basis weight of 50 g./m. The retention of binding agent in the nonwoven appears to be 95-100 percent.
The tensile strength of the non-woven web when dry amounts to 4.8 kg./5 cm. and the elongation at break amounts to 33 percent. The wet strength amounts to 82 percent of the dry strength.
EXAMPLE II In a flask with a content of 600 ml. the following substances are mixed with normal stirring.
475 ml. of water 22 ml. of latex of a polyacrylic ester (Hycar 2671 manufactured by the B. F. Goodrich Company; 50 percent solids, pH 5.7, specific weight 1.06, particle size 2300 angstroms). (This type of latex has been described in US. Pats. Nos. 2,754,280 and 2,931,749.)
3 ml. of a one percent solution of a cationic polyamide cross-linked with epichlorohydrin (Kymene 557 manufactured by Hercules, Inc., pH 5.7).
Yield 500 ml. of suspension of an extremely fine preflocculate having a solids content of about two percent. Upon acidification of this suspension to a pH of 3.5 with acetic acid, a fibrous flocculate is obtained. Twenty-five ml. of the suspension of the flocculate, which contains 0.5 g. of binding agent, are added to a fiber suspension, in which there is 1 g. of staple fibers of regenerated cellulose (length 6 mm., 1.5 den.). A non-woven is manufactured from this fibrous suspension in a laboratory sheet former in the manner described in Example I.
Upon drying the obtained non-woven appears to be flexible and strong. The non-woven can stand up very well to yellowing, washing and dry cleaning.
The retention of binding agent amounts to 97 percent. The tensile strength of the membrane when dry is 4.5 kg./cm. and the elongation at break 28 percent.
7 I claim: 1. A process for the production of non-woven fibrous materials comprising mixing fibers to be bound with a fibrous binding agent to form an aqueous fiber suspension, dehydrating said suspension to form a wet fibrous web and heating the web, said fibrous binding agent being formed by mixing a latex of a polymer having carboxyl group selected from the group consisting of carboxyl group containing butadiene-styrene copolymers, butadiene-acrylonitrile, copolymers, acrylic and methacrylic ester copolymers, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyethylene, polypropylene, and wherein the content of the carboxyl groups amounts from 0.02 to percent by weight calculated on the total amount of polymer with an aqueous solution of a cationic polymer substance selected from the group consisting of polyamides, polyamines, and cationic modified starch wherein the amount of said cationic polymeric substance is from 3 to 50 percent by weight, calculated as solids on the solids of the latex, at a pH of 6 to 9 for a maximum of 60 minutes and converting the finely divided particles into fine fibrous particles by adjusting the pH of the mixture to 2 to 4 with stirring, with the solids content of the mixture being between 0.01 to 10 percent by Weight, wherein the amount of fibrous binding agent calculated as solids on the dry fibrous web is no more than 50 percent by weight.
2. The process of claim 1 wherein the amount of fibrous binding agent is from 15 to percent by weight.
3. The process of claim 1 wherein said fibers are glass fibers.
4. The process of claim 1 wherein said fibers are regenerated cellulose fibers.
5. The process of claim 1 wherein said fibers are selected from the group consisting of polyesters and polyamides.
6. The process of claim 1 wherein said polymer having carboxyl groups is a carboxyl group containing butadienestyrene copolymer.
7. The process of claim 1 wherein said cationic polymer is a cationic urea-formaldehyde resin.
8. The process of claim 1 wherein the pH is adjusted to 2 to 4 by adding a water-soluble organic acid.
9. The process of claim 1 wherein the amount of cationic polymeric substance, calculated as solids on the solids of the latex, amounts to 3 to 15 percent by weight.
References Cited UNITED STATES PATENTS 2,563,898 8/ 1951 Wilson et al 26029.4 UA 2,680,682 6/1954. Dearing l62167 2,905,583 9/1959 Feigley et a1 162l69 X 3,193,446 7/ 1965 Eisenberg 162--169 X ROBERT L. LINDSAY, JR., Primary Examiner US. Cl. X.'R.