Classifications

• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M15/00—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment
  • D06M15/19—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment with synthetic macromolecular compounds
  • D06M15/21—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D06M15/263—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds of unsaturated carboxylic acids; Salts or esters thereof
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S516/00—Colloid systems and wetting agents; subcombinations thereof; processes of
  • Y10S516/01—Wetting, emulsifying, dispersing, or stabilizing agents
  • Y10S516/07—Organic amine, amide, or n-base containing

Definitions

• This invention relates to a process for stiffening of textiles, which are subjected to repeated laundering, with a stitiening agent which is applied to the fiber and is insoluble in cold or hot water as well as in neutral-reacting washing agent solutions, that is, under the conditions of so-called fine laundering, but still soluble in alkaline-reacting washing solutions even after ironing.
• the stiffening agent consists of dispersions of water-insoluble copolymers of the polyvinyl ester containing free carboxyl groups, said dispersions having been prepared in the presence of protective colloids and possibly emulsifiers.
• aqueous dispersions of polyvinyl acetate may be used for finishing and stiffening of textiles.
• these stiffening compositions have the property that they are not, or only to a minor extent, removed from the fiber during laundering and that, therefore, a distinct stiffening eifect is still present after several launderings. Consequently, wash-resistant finishes based on polyvinyl acetate are often used as initial or permanent finishes.
• Such polyvinyl acetate dispersions are not only used as initial finishes, but also as stiffening agents for household textiles which are subjected to repeated launderings. Since the synthetic resin impregnation is not, or only to a very minor extent, removed from the fiber during laundering, the textile material once treated does not require a subsequent treatment with highly dilute dispersions until after a certain number of launderings in order to maintain the desired degree of stiflness.
• the advantage of the high wash-resistance of such permanent stiifeners is, on the other hand, connected with substantial disadvantages. It has been found that soil adheres more firmly to textiles finished with the permanent stifleners than to textiles treated with starch compositions.
• aqueous alkaline solution of copolymers of vinyl acetate and unsaturated polymerizable acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid or fumaric acid
• acrylic acid, methacrylic acid, crotonic acid, maleic acid or fumaric acid as in initial finish for textiles, for 'instane as a halt stiffener.
• These copolymers are used not only in aqueous alkaline solution in the form of their alkali metal salts, but also in the form of their free acids, namely dissolved in organic solvents, especially in lower alkanols.
• relatively highly concentrated solutions with a solids content above 5% by weight must be used, and the treatment of the textile material must in most cases be repeated several times.
• the dispersions used in accordance the present invention also have a particle diameter between 7 and 0.1 preferably 0.5 to 4
• Customary protective colloids for highly concentrated, highly viscous dispersions based on copolymers of vinyl acetate with copolymerizable carboxylic acids are particularly polyvinyl alcohol and partially saponified polyvinyl acetate.
• relatively large amounts of such protective colloids are required for a sufiicient stabilization of the dispersions.
• copolymer dispersions with improved storage stability are obtained by adding only a part of the polyvinyl alcohol or partially saponified polyvinyl acetate to the monomer mixture at the beginning of the polymerization, and adding the major amount of protective colloid to the finished dispersion subsequent to the polymerization.
• Such particularly cold-stable, viscous dispersions to which the high polyvinyl alcohol content imparts a high tackiness and which are therefore of particular interest in the field of adhesives, have been suggested for use also as textile finishing agents, such as sizing agents.
• the synthetic resin films produced from these dispersions are relatively soft, and because of this property the soiling tendency of the textile material treated therewith is increased.
• the large amounts of polyvinyl alcohol reduces the water-stability of the finish, so that it swells considerably in water or fine washing solutions and is partially removed from the fiber.
• the customary ironing temperatures which lie above 100 C., a partial cross-linking of the synthetic resin film on the fiber takes place.
• cross-linking has the effect that the synthetic resin film substantially loses its alkali solubility and can no longer be removed from the fiber to a sufiicient degree. For this reason such copolymer dispersions have no advantages over the known permanent stifieners based on homopolymeric polyvinyl acetate.
• an object of this invention to provide a method for providing a stiffening finish for textiles which is relatively permanent under neutral conditions but removable under alkaline conditions.
• a further object is to provide a method for stiffening textiles wherein the finishing agent is not adversely affected by heat of ironing or soil.
• alkali-soluble dispersions which do not contain polyvinyl alcohol but instead other water-soluble high polymers, such as copolymers'of acrylamide or cellulose products, as a protective colloid produce fibers which do not cross-link upon being heated to temperatures which occur during normal ironing, but instead completely retain their alkali-solubility.
• hydroxyethyl cellulose for instance, also contains hydroxyl groups.
• the subject matter of the present invention is a process for stiffening of textiles, which are subjected to repeated landering, with a stiffening agent which is applied to the fiber and is insoluble in cold or hot water as Well as in neutral-reacting washing agent solutions, that is, under the conditions of so-called fine laundering, but still soluble in alkaline-reacting washing solutions even after ironing.
• the stiffening agent consists of dispersions of water-insoluble copolymers of the polyvinyl ester containing free carboxyl groups, said dispersions having been prepared in the presence of protective colloids and possibly emulsifiers.
• the preparation of the dispersion is effected, for example, according to copending application Ser. No. 277,436, that is, by polymerizing vinyl esters together with an unsaturated polymerizable monocarboxylic acid, such as acrylic acid, methacrylic acid, crotonic acid, or a similar dicarboxylic acid, such as maleic acid, fumaric acid or itaconic acid, as well as their semi-esters, in the presence of a protective colloid and possibly an emulsifier as well as in the presence of a water-soluble peroxide-catalyst.
• an unsaturated polymerizable monocarboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, or a similar dicarboxylic acid, such as maleic acid, fumaric acid or itaconic acid, as well as their semi-esters, in the presence of a protective colloid and possibly an emulsifier as well as in the presence of a water-soluble peroxide-cata
• the content of unsaturated carboxylic acids in the copolymer should advantageously not be less than 2 and no more than 10 mol percent, preferably 3 to 7 mol percent, since the polymers with a lesser acid content have an insufficient alkali solubility, and those with a higher acid content have an un desirable swelling property in water;
• Suitable vinyl esters are those whose acyl radicals contain 2 to 4 carbon atoms, that is, vinyl acetate, vinyl propionate, vinyl butyrate, as well as mixtures thereof. It is preferred to use copolymers of vinyl acetate.
• the dilspersions contain as protective colloids high molecular substances which are soluble in water, such as polyacrylamide, copolymers of acrylic acid amide or methacrylic acid amide with acrylic acid esters, copolymers of acrylic acid amide with N-substituted acrylic acid amides or water-soluble cellulose derivatives, such as hydroxyethyl cellulose.
• the protective colloids are employed in an amount of 0.5 to 7%, preferably 1.0 to 5%, based on the molecular content.
• dispersions which contain as protective colloids water-soluble copolymers of acrylamide and lower N- alkylacrylamides with a chain length of 2 to 6 carbon atoms.
• Such dispersions are characterized by an unusually high storage stability at a protective colloid content of only 0.5 to 3%, based on the vinyl acetate copolymer.
• water-soluble protective colloids possess certain surfactive properties, such as the copolymers of acrylamide and N-tert.-butylacrylamide, it is possible to forego the concurrent use of emulsifiers, or only very small quantities thereof are required.
• emulsifiers are ionic and nonionic emulsifiers, such as fatty alcohol sulfates, fatty alcohol glycol ethers and sulfonic acid esters and phosphoric acid esters thereof. It is further possible to add to the above described synthetic resin dispersions certain additional substances, such as ironing assistants, wetting agents, optical brighteners, and the like, prior to their application as stiffening agents in order to achieve certain additional effects in use.
• the dispersions are diluted with water to a solids content of 0.055% by weight, preferably 0.15 to 1% by weight. Higher concentrations produce only a small increase and are not in general required for household laundering.
• the starting composition may for example be composed as follows:
• stiffening compositions may be employed in the same manner as the commercial permanent stiffeners based on synthetic resins.
• the textile material to be treated is immersed into the dilute dispersion and is all-owed to remain therein for some time.
• the textile material be agitated during the treatment.
• the application of the stiffening composition to the fabric may easily be followed by means of the retrogression of the turbidity in the solution.
• the degree of turbidity at the same time gives a clue as to what extent the bath is already exhausted and whether a fresh stiffening agent must possibly be added thereto.
• the correspondingly diluted dispersions may also be sprayed onto the textile material. Subsequent to the treatment, the textile pieces are freed from excess moisture by wringing or centifuging, and are then ironed as usual.
• the textiles treated in accordance with the present invention exhibit varying degrees of stiffness, depending on the concentration of the dispersion. Even at high concentrations the stiffened fabrics remain elastic and retain a pleasant feel without being tacky.
• the stiffening effect is equally resistant against repeated treatment with cold and hot water as well as neutral fine Washing solutions as well as against mechanical stress.
• the synthetic resin stiffness may, however, also be completely removed by a normal alkaline washing treatment, possibly by boiling under alkaline conditions. In this manner the disadvantageous consequences of an excessively frequent application or excess dosage of the stiffening agent, but especially the above described graying and yellowing effects of the treated fabrics, can be substantially avoided.
• a laundry stiffener which is simple to use is made available particularly to the private consumer, and he may leave it on the fiber or also completely remove it during cleaning of the textiles, depending on the requirements.
• Example I For the preparation of the synthetic resin dispersion pursuant to copending application Ser. No. 277,436 the procedure was as follows: 6 gm. of a protective colloid (copolymer of 50% acrylamide and 50% tert.-butylacrylamide) were dissolved in 225 cc. of water, and 1.4 gm. of sodium lauryl sulfate as well as 18 gm. of a emulsifier solution were added thereto. The emulsifier was produced by addition of 8 mols ethylene oxide to coconut fatty alcohol and subsequent reaction with phosphorous pentoxide in a molar ratio of 2:1. 10% of a mixture of 279 gm. of vinyl acetate and 9.6 gm.
• a protective colloid copolymer of 50% acrylamide and 50% tert.-butylacrylamide
• the dispersion thus obtained was divided into three parts, each of which was diluted with water to a solids content of 0.15%, 0.3% and 0.5%, respectively.
• Previously washed pieces of linen and cotton fabric were introduced into these dispersions and were agitated from time to time.
• the solution ratio was gm. of fabric per 1 liter of solution.
• After ten minutes the textile samples were withdrawn from the solution, wrung out, and after a short period of drying, were ironed in a slightly moist state.
• those treated in the 0.15% solution exhibited a distinct degree of stiffening, those treated in the 0.3% solution a medium degree of stiffening, and those treated in the 0.5% solution a high degree of stiffening.
• Example II A dispersion with a solids content of 50%, a viscosity of 16,000 cp. (25 C.) and an acid number of 15.5 was prepared by a method analogous to that described in Example I, using the following materials:
• Example I 6 gm. of the protective colloid used in Example I, 18 gm. of the emusifier used in Example I,
• Example 111 In a manner analogous to that described in Example I, a low viscosity dispersion was prepared from:
• the dispersion formed a clear solution in dilute alkalies. Textiles were also stiffened with this dispersion in the manner described in Examples I and II; the synthetic resin stiffener was resistant against neutral washing agents, but it could be removed again from the textile material with the aid of alkaline washing solutions.
• Example IV For purposes of comparison with the stiffening agents according to the present invention, a commercial 50% high polymeric polyvinyl acetate dispersion having a viscosity of 8,000 cp. (25 C.) was diluted with water to a solids content of 0.3%. Linen and cotton fabrics were treated with this dispersion in the same manner as indicated in Examples I and II. The samples exhibited the same degree of stiffening as those treated in accordance with the present invention, but the stiffness could not be removed either by fine washing or by prolonged boiling under alkaline conditions.
• Example V In a further comparative test, a copolymer dispersion containing polyvinyl alcohol was used.
• the dispersion was prepared under the exclusion of air by adding dropwise a mixture of 341 gm. of vinyl acetate and 10.5 gm. of crotonic acid to a solution of 11 gm. of polyvinyl alcohol (saponification number in 225 gm. of water at 70 C.
• the polymerization was initiated by the addition of 1. 8 gm. of potassium persul-fate dissolved in a small amount of water and was carried to completion after four hours of stirring and heating as described in Example I.
• about 60% dispersion with a viscosity (according to Epprecht) of about 1500 cp. (25 C.) was obtained, which was found to be less storagestable and especially not cold stable in comparison to the dispersions described in Examples I and H.
• this dispersion was diluted to a solids content of about 50% with a solution of 45 gm. of the above mentioned polyvinyl alcohol in gm. of Water subsequent to the polymerization.
• the dispersion whose viscosity (according to Epprecht) was now 6500 cp. (25 C.), was found to be adequately storage-stable and cold-stable.
• Ttextile samples were treated in the above described manner with the dispersions diluted to a solids content of 0.5 and certain degree of stiffness was also achieved therewith.
• the stiffening composition stabilized with additional polyvinyl alcohol was found to be less water-resistant and could be removed by repeated neutral fine washing.
• the resin in both cases could no longer be removed from the fiber to a major extent by an alkaline was-hiig process.
• the polymer adhering to the washed textile samples had substantially lost its stiffening effect.
• Example VI In a third series of tests the dispersions prepared according to Examples I and III as well as the dispersions of Example V prepared with polyvinyl alcohol were applied to cleaned glass plates.
• the synthetic resin films which had been dried at room temperature, formed a clear solution within two to three hours in a 1% sodium hydroxide solution at 20 C.
• Another series of samples was heated for ten minutes in a drying chamber to 100 110 C. and the solubility was again investigated in a 1% sodium hydroxide solution at room temperature as well as at the boiling point in a 1% aqueous crystalline soda solution. The following results were obtained:
• the films of the dispersions according to Examples I and III also formed a clear solution within the same period of time in a 1% sodium hydroxide solution at 20 C. after the heat treatment. While the polyvinyl alcohol-containing films of Example V swelled, they remained films even after two days of standing. Upon boiling in a 1% soda solution the films made from the dispersions according to Examples I and III completely dissolved within 10 to 15 minutes, whereas the resin containing the polyvinyl alcohol remained undissolved after 30 minutes.
• Process for providing a stiffening finish to textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions which comprises treating said textile with aqueous dispersions of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and copolymerizable carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group Consisting of water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an amount from about 0.5 to 7% by weight, which is sub stantially free of reactive vinyl alcohol groups.
• Process for providing a stiffening finish to textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions which comprises treating said textiles with aqueous dispersions of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and copolymerizable carboxylic acids hav ing from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group consisting of water-soluble copolymers of acrylamide with N-allcyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an 0 amount from about 1 to 5% by weight, which is substantially free of reactive vinyl alcohol groups.
• Process for providing a stifiiening finish to textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions which comprises treating said textiles with aqueous dispersions of copolymers containing free carboxyl.
• dispersions prepared from vinyl esters of alkanoic caids of 2 to 4 carbon atoms and 2 to 10 mol percent copolymerizable semiesters of unsaturated carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group consisting of water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an amount from about 0.5 to 7% by weight, which is substantially free of reactive vinyl alcohol groups.
• protective colloids selected from the group consisting of water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an amount from about 0.5 to 7% by weight, which is substantially free of reactive vinyl alcohol groups.
• Process for providing a stiffening finish to textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions which comprises treating said textiles with aqueous dispersions of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and 3 to 7 mol percent copolymerizable semiesters of unsaturated carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group consisting of water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an amount from about 0.5 to 7% by weight, which is substantially free of reactive vinyl alcohol groups.
• Process for providing a stiffening finish to textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions which comprises treating said textiles with aqueous dispersions of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and copolymerizable carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids which are water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical, in an amount from about 1 to 5 percent by weight, which is substantially free of reactive vinyl alcohol groups.
• a stiffening agent for textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions, which comprises an aqueous dispersion of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and copolymerizable carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group consisting of water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to '6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an amount from 0.5 to 7% by weight, which is substantially free of reactive vinyl alcohol groups.
• stiffening agent of claim 9 containing in addition emulsifiers.
• a stiffening agent for textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions, which comprises an aqueous dispersion of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and copolymerizable carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group consisting of Water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an amount from about 1 to 5% by weight, which is substantially free of reactive vinyl alcohol groups.
• a stiffening agent for textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions, which comprises an aqueous dispersion of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and 2 to mol percent copolymerizable semiesters of unsaturated carboxylic acids having from one to two carboXyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group consisting of water-soluble copolymers of acrylamide with N-alkyl acrylarnides having from 2 to 6 carbon atoms in the alkyl radical and water-soluble hydroxyethyl cellulose in an amount from about 0.5 to 7% by weight, which is substantially free of reactive vinyl alcohol groups.
• a stiffening agent for textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions, which comprises an aqueous dispersion of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and 3 to 7 mol percent copolymen'zable semiesters of unsaturated carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids selected from the group consisting of water-soluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the'alkyl radcal and water-soluble hydroxyethyl cellulose in an amount from about 0.5 to 7% by weight, which is substaantially free of reactive vinyl alcohol groups.
• a stiffening agent for textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions, which comprises an aqueous dispersion of copolymers containing free carboxyl groups prepared from vinyl esters of alkanoic acids of 2 to 4 carbon atoms and copolymerizable carboxylic acids having from one to two carboxyl groups in the molecule, said dispersions having been prepared in the presence of protective colloids which are watersoluble copolymers of acrylamide with N-alkyl acrylamides having from 2 to 6 carbon atoms in the alkyl radical, in an amount from about 1 to 5 percent by weight, which is substantially free of reactive vinyl alcohol groups.
• the stiffening agent of claim 9 diluted with water to a solids content of about 0.05 to 5 percent.
• the stiffening agent of claim 9 diluted with water to a solids content of about 0.15 to 1 percent.
• a stifiening agent for textiles wherein the finish is stable against neutral washing agent solutions but soluble in alkaline washing agent solutions, which comprises an aqueous dispersion having a content of (a) from about 40 to percent of copolymers containing free carboxyl groups prepared from vinyl acetate and 2 to 10 mol percent copolymerizable carboxylic acids having from one to two carboxyl groups in the molecule, (b) from about 1 to 5 percent of a water-soluble copolymer of acrylamide and N-butylacrylamide in a ratio of 1:3 to 3:1, and (c) from 0 to 1 percent of emulsifiers.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
• Detergent Compositions (AREA)
• Compositions Of Macromolecular Compounds (AREA)

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Citations (4)

• 1963
  • 1963-04-11 DE DE19631444073 patent/DE1444073A1/de active Pending
  • 1963-05-02 US US277434A patent/US3311576A/en not_active Expired - Lifetime
  • 1963-12-31 NL NL63302924A patent/NL148125B/xx not_active IP Right Cessation
• 1964
  • 1964-04-10 DK DK652465AA patent/DK107933C/da active
  • 1964-04-10 AT AT315464A patent/AT249629B/de active
  • 1964-04-10 CH CH458764A patent/CH435200A/de unknown
  • 1964-04-10 DK DK180564AA patent/DK107222C/da active
  • 1964-04-10 BE BE646375D patent/BE646375A/xx unknown
• 1974
  • 1974-12-31 NL NL7417061A patent/NL7417061A/xx unknown

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