US2929738A - Method of coating glass fiber yarns - Google Patents

Description

,March 22, 1966 Filed Feb. 11, 1959 TE PERATURE c s. BATESON ET AL METHOD OF COATING GLASS FIBER YARNS' 2 Sheets-Sheet l SYDNEY BA r650 JAN C/IRYS'TAM x ATTOQ/VE March 22, 1960 s, BATESON ET AL 2,929,738

METHOD OF COATING GLASS FIBER YARNS Filed Feb. 11, 1959 2 Sheets-Sheet 2 INVENTORS SYDNEY enriso/v 4 JAN CHRYSTMA/V METHOD OF COATING GLASS FIBER YARNS Sydney Bateson, (lshawa, Ontario, and Jan Chrystman, Rexdale, Ontario, Canada, assignor to Pittsburgh Plate Glass Company, Allegheny County, Pa.

Application February 11, 1959, Serial No. 798,571

4 Claims. (Cl. 117-103) The present invention relates to a method of coating 21 base material with a plastisol and it has particular relation to a method of applying a plastisol to a strand of glass fibers so that each individual filament making up the strand is coated with the liquid and a uniform overal coating is applied to the strand.

Glass fiber yarns coated with a plastisol are now being woven. in large quantities into insect screening. The plastisols used are dispersions of a high molecular weight polymer such as polyvinyl chloride in a liquid plasticizer. Small amounts of other materials such as coloring pigments or dyes are also present in the dispersions. The glass 'fiber yarns which are preferably employed are known to the trade as 75l/0 and 1504/2. glass fiber yarns. A 75-1/0 yarn contains approximately 7,500 yards to the pound and is composed of a single strand made up of 204 individual glass filaments, each of said filaments having an average diameter in the neighborhood of .0005 inch. A 150-1/2 glass fiber yarn is made up of two continuous filament strands twisted andplied together, each strand containing approximately 15,000 yards to the pound and being made up of 204 individual glass filaments having an average diameter in the neighborhood of 0.00038 inch.

The outside diameter of the two yarns is about the same. It is preferred to employ the T75-l/0 yarn be cause it is much less expensive than the 150-l /2 yarn. On the other hand, the 150-1/2 yarn is much more susceptible to coating with the plastisol because it is relatively free from fuzm'ng and consequent contamination of the plastisol during the coating operation. The fuzzing is brought about by the shearing oil of broken ends of individual filaments of the yarn as the yarn passes through the plastisol. As the fuzzing progresses, the broken ends build up in number in the plastisol and clog the various types of dies or other equipment used in the coating process. Thus, it is an object of this invention to provide a'method of coating glass fiber yarns, particularly 751 yarns with a plastisol without the occurrence of fuzzing during the coating operation.

In the application of a plastisol to a glass fiber yarn, it is important that the plastisol penetrate the yarn and flow around and coat the-individual filaments making up the yarn. The plastisol coating on the individual filaments acts as a lubricant for each individual filament to prevent breakage of the filaments caused by abrading on each other. A further object of the invention is to provide a method of coating and impregnating a glass fiber yarn so that the individual filaments are coated with the plastisol.

A conventional method of applying a-plastisol to a glass fiber yarn involves passing the yarn through a bath of the plastisol to pick up an excessive amount of the plastisol and thereafter passing the coated yarn through a die or a pair of matchinggrooved rollers. The use 'of grooved rollers has been found preferable to attain the desired impregnation of the plastisol on-the yarn. When iv ly h stam n ,Pl $i 1 er a e Patented Mar. 22, 1960 required, the usual practice is to make several passes of the yarn through the plastisol and dies.

When the yarn has been coated with the plastisol, it is subjected to sufficient heat, about 150 to 200 C. for polyvinyl chloride dispersions, to fuse the plastisol into a solid coating. This heating may be accomplished by the use of radiant heaters or other conventional heating systems. It has been noticed that during the heating of the plastisol there is a tendency for it to flow just prior to fusion and form irregular knobs or bumps along the yarn. This is highly undesirable for it is of the utmost importance that theyarn be uniformly coated. Any irregularities in yarn diameter show up glaringly when the yarn is woven into screening. Thus, a further object of the invention is to produce a yarn of uniform diameter throughout its length and free from any irregularities such as knobs or bumps along the yarn.

It has been found that the choice of the plastisol to be employed is of prime importance in achieving the production of a satisfactory product at high rates of production. Further, it has been found that the property of viscosity of the plastisol is of great importance. In order to obtain adequate impregnation and prevent fuzzing, it is desired that the viscosity of the plastisol be as low as possible. The viscosity of a plastisol may be decreased by increasing the amount of the plasticizer and by using certain types of plasticizer and in some instances volatile solvents may be added to produce a material of low viscosity. When volatile components are addedto a plastisol, it is then known as an organosol and ordinarily organosols are not .not satisfactory for use in the high speed coating of a glass fiber yarn. This is because of the extremely slow rate at which the organosol must be heated to fusion in order to allow the volatile components to be removed without the formation of blisters in the coating. Thus, the use of an organosol does not lend itself to high speed coating of glass fiber yarn.

Although use of a plastisol of low viscosity is desirable to achieve impregnation and prevent fuzzing, there are several disadvantages in using low viscosity plastisols. First, the low viscosity plastisol is more subject to the formation of bumps or knobs on the yarn for it will not remain in place on the yarn during the preliminary heating after the coated yarn has been passed through the dies and prior to fusion. Secondly, the final properties of plastisols having low room temperature viscosities are not as satisfactory as those having higher room-temperature viscosities. The lower viscosity plastisol coated yarns do not have as good tensile strength or abrasion resistance. Also, their weathering properties are not as good. The plasticizer is caused to migrate to the surface of the yarn when his subjected to ultra-violet radiations. The moisture resistance of a yarn coated with a lower viscosity plastisolis also poorer.

In accordance with the present invention, a method has been provided whereby a plastisol having a relatively high viscosity and providing the yarn with the desired physical characteristics maybe utilizedto thoroughly impregnate the yarn and produce a yarn free from irregular bumps and knobs thereon. This method makes use ofthe physical property of plastisols wherein the viscosity of the plastisol-dropssteadily upon heating untilit reaches a minimum viscosity whereupon further rise in temperature of the plastisol causes it to fuse and its viscosity to rise rapidly. It has been found-that -the, minimum viscosity of a plastisol prior to ,fusion is roughly One-half of the viscosityof the plastisol at room temperature. The present invention involves heating the plastisol for application to the yarnsothat the plastisol is applied at a viscosity much lower than its normal -r oom temperature viscosity. The heating of the plastisol and pr sa i 9 th at sti lat e .v rsim vhe 3 1 accomplished in a number of ways. For example, the plastisol may be heated and then contacted with the yarn. A further method involves using'heated dies or heated grooved a rollers" and" applying" the plastisol *to' the rollers so that it is heated just prior to and'as it is being brought into contact with the yarn. f.

' The invention may be further described in conjunction with the drawing in whichr Fig. 1 is a graph illustrating the effector temperature on the viscosity of a plastisol;

Fig. 2 is a diagrammatic elevation of apparatus suitable for practice of the invention; and

Fig. 3 is a plan view of a portion of the apparatus shown in Fig. 2 taken along lines III-Ill of Fig. 2.

As stated, a property of plastisols is that during the heating and fusing process, the viscosity of the plastisol decreases from room temperature to a minimum and then rises rapidly. This is shown in the graph in Fig. 1 of the drawings. The ordinate of the graph is viscosity in centipoises and the abscissa is temperature in degrees C. The various curves show the viscosity properties of the following materials:

(1) A plastisol containing 66 parts by weight of dioctyl sebacate per 100 parts by weight of polyvinyl chloride particles having a particle size of about 0.03 to 0.05 micron.

(2) A plastisol containing 67 parts by weight of diisooctyl phthalate per 100 parts by weight of polyvinyl chloride.

(3) A plastisol containing 65 parts by weight of 50/50 mixture of dioctyl sebacate and dioctyl adipate per 100 parts by weight of polyvinyl chloride.

sheaves f of broken ends of the yarn and fuzzing occurs thereby contaminating the bath and requiring its frequent replacement. This is especially the case with 75-1/0 yarns where broken ends are much more prevalent than with other types of yarns, for example 150-1/2 yarns where broken ends created during manufacture are tucked in during the twisting and plying operations. Valve 27 in the fiow'line from the reservoir controls'the flow of plastisol to the rollers. The flanges 24 prevent any overflow of plastisol from dripping over the sides of the coating roller and also help to maintain a supply of the plastisol at the grooves 22.

The coated and impregnated yarn is then passed through a heating chamber 30 open at both the top and bottom. The lower portion of the heating chamber contains radiant heaters 32. Air rises by convection in the chamber and heats the yarn prior to entering the chamber and I heats the rollers 18 and 20. The heated rollers in turn It can be seen from the graph that the viscosity of i the various plastisols decreases roughly by about onehalf as the plastisol is heated from room temperatures to a temperature approximating 50 to 60 C. where it reaches a minimum. As the temperature of the plastisol is raised slightly above this minimum viscosity point, the viscosity of the plastisol rises very rapidly as it begins to fuse.

Results of various experiments have shown that plastisols having viscosities above 8000 at the time of application do not provide proper penetration for a high speed, i.e. 100 to 600 or more feet of yarn per minute, application of plastisol to glass fiber yarns. On the other hand, it has been found that 'plas'tisols having viscosities above 8000 centipoises and up to 16,000 or more centipoises at room temperature provide the yarn with the best coating as far as tensilestrength, abrasion resistance and weathering is concerned when fused to the yarn. Thus, by applying the plastisol at its minimum viscosity in accordance with the teachingv of the present invention, these higher room temperature viscosity plastisols may be used.

Apparatus suitable for practice of the invention is shown in Fig. 2 of the drawing. Glass fiber yarn 10 from a suitable package 12 passes through a twin disc tension compensator 14 over an idler pulley 15 vertically downward between rollers 18 and 20. Roller 20 has peripheral grooves 22 and edge flanges 24. The rollers are spring-loaded (not shown) so as to press against each other and roller 18 has its extremities fitted snugly inside and against the inner sides of the flanges 24 on the roller 20.- The grooves 22 in the rollers are approxim atelyin the shape of a horseshoe with the open end of the-groove facing the roller 18. The dimensions of the groove may vary and may be for example 0.02 inch acrossthe opening, 0.02 inch deep and having a radius of curvature at the inner portion of 0.01 inch.

As the yarn 10 passes through groove 22, plastisol 25 dropped from a reservoir 26 is forced into and around the yarn 10. It has been found that applying the plastisol inthis manner is preferred to passing the yarn through a bath ofplastisol and then through a die. When the yarnis first passed through a bath of plastisol, shearing heat the plastisol dripped thereon so that it is at a tem perature approximating its minimum viscosity at the time it is forced into and around the glass yarn.

The plastisol is fused in place on the yarn as it passes between the radiant heaters 32. The coated yarn then passes out of the bottom of the chamber 30 past a blower 34 which blows air across the heated and fused plastisol coated yarn to cool it. The coated yarn then passes over idler pulleys 36 and 38 through a suitable traverse 40 to a cylindrical tube 42 upon which it is wound. The tube 42 is mounted on a weighted spindle 43 which moves vertically in slots 45 of guides 46. The tube 42 and yarn wound thereon rest on rubber roller 48 which is driven at a constant speed by means of suitable driving means (not shown). The roller 48 in turn drives tube 42 which is resting on it. This method of indirect package drive insures a constant linear yarn speed throughout the coating operation irrespective of the increasing diameter of the yarn package collected on tube 42. A con stant linear speed of yarn travel as well as a'constant tension has been found to be desirable to insure uniformity of application of a plastisol to the yarn.

The operation of the apparatus shown in Figs. Q and 3 may be further described with respect to the application of the plastisol represented by curve 1 on the graph shown in Fig. 1 to a 75-1/0 glass fiber yarn traveling through the apparatus at about 500 feet per minute. The peripheral speed of the rollers 18 and 20 is 50 feet per minute but may vary between about 5 to 30 percent of the speed of the yarn. 1

The rollers 18 and 20 are heated to a temperature of about C. by air rising from the chamber 30 and the rollers in turn heat the plastisol as it is dripped onto roller 20 and subsequently carried into contact with roller 18. The temperature of the plastisol in the grooves 22 as it is applied to the yarn is about 60 C. The plastisol may be preheated in the reservoir 26 if desired to supplement the heat provided by the rollers 18 and 20.

After being coated and impregnated with the plastisol, the yarn is heated to a temperature of about C. to fuse the plastisol on the yarn as it passes between the radiant heaters. By this operation approximately 1 pound of plastisol is applied to a pound of the 75-l/0 yarn and the finished yarn has a diameter of about .013 inch and a tensile strength of about 10.5 pounds per square inch. 1

The invention has been described with respect to the use of dispersions of polyvinyl chloride in a suitable liquid plasticizer. The description of such dispersions is illustrative only and it is intended that dispersions of other resins in the form of plastisols be applied to glass fiber yarn in accordance with the teachings of this in: vention.

The resinous materials are more generally known as dispersion resins and they may be produced by emulsion polymerization. They are fine powders of a fusibleresin or a resin which will coalesce when heated." Thermo plastic resins are preferred for use in the practice of the invention but thermosetting resins may be employed if they are in the A or B stage of polymerization or if they will readily fuse or coalesce in the form they are used upon the application of heat. Suitable thermoplastic resins include polyvinyl acetate and copolymers thereof with polyvinyl chloride, polyvinyl alcohol, polyethylene, polymers of acrylic acid and esters thereof such as methyl methacrylate, polystyrene, cellulose esters and ethers, vinylidene chloride and various copolymers of these resins. Suitable thermosetting resins in the state set forth above include phenol formaldehyde, aminoformaldehydes such as urea formaldehyde and melamine formaldehyde, epoxy resins such as polymers of epichlorohydrin and bis-phenol, silicones, alkyds and allyl esters such as allyl carbonates.

The plasticizers which may be used in combination with the above resins are well known in the plastics art and include numerous esters such as esters of phthalic acid, adipic acid, succinic acid, sebacic acid and others, sulfonamides and phosphates. Small percentages of coloring pigments such as aluminum flake or dies may be incorporated in the dispersions to provide yarns of different color and appearance.

The present invention has provided a method for uniformly coating and impregnating glass fiber yarns, particularly 75-1/0 yarns with plastisols at high speeds. The terms high speed or high rate of speed as used in the specification and claims are intended to mean speeds of the order of 100 to 600 or more feet per minute and are used to distinguish the coating process from those coating processes in which the base to be coated is stationary or moving very slowly. It is desired, of course, that the yarn be moving as fast as possible in order to make the process as economical as possible. The actual speed of coating is governed by the limitations of the particular coating equipment and its ability to apply the plastisol and heat it to fusing temperature immediately after its application to the yarn. For example, the longer the length of the heating chamber 30, the faster the yarn can be coated and moved through the chamber.

These plastisol coated yarns are free from knobs and bumps and have uniform diameter throughout, high tensile strength, abrasion resistance and good weathering properties. The invention has provided means for using a wider selection of plastisols than previously available for high speed coating and has permitted the production of thicker coatings than normally producible at any speed without resort to multiple passes of the yarn through coating apparatus.

Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details be limiting upon the scope of the invention except insofar as included in the accompanying claims.

This application is a continuation-in-part of our copending application Serial No. 507,934, filed May 12,

. 1955, now abandoned.

We claim: 1. A method of applying a smooth, uniform coating of a plastisol to a glass fiber yarn which is moving at a high rate of speed which comprises coating and impergnating the yarn which is at room temperature with a smooth, uniform coating of a plastisol which is heated just prior to its application to the yarn to a temperature above room temperature which approximates the temperature at which the plastisol is at its minimum viscosity and heating the plastisol on the yarn immediately after its application to the yarn to a temperature suificient to fuse the plastisol on the yarn in the form of a smooth, uniform coating.

2. A method of applying a smooth, uniform coating of a plastisol to a glass fiber yarn moving at a high rate of speed which comprises coating and impregnating the yarn which is at room temperature with a smooth, uniform coating of a plastisol which is heated just prior to its application to the yarn to a temperature of 50 to 60 C. and heating the plastisol on the yarn immediately after its application to the yarn to a temperature sufiicient to fuse the plastisol on the yarn in the form of a smooth, uniform coating.

3. A method of applying a dispersion of a resin comprising essentially polyvinyl chloride particles dispersed in a plasticizer therefor to a glass fiber yarn moving at a high rate of speed which comprises coating and impregnating the yarn which is at room temperature with a smooth, uniform coating of a dispersion of the resin which is heated just prior to its application to the yarn to a temperature above room temperature which approximates the temperature at which the plastisol is 'at its minimum viscosity and heating the dispersion on the yarn immediately after its application to the yarn to a temperature sufficient to fuse the polyvinyl chloride particles to each other and to the yarn in the form of a smooth, uniform coating.

4. A method of applying a dispersion of a resin comprising essentially polyvinyl chloride particles dispersed in a plasticizer therefor to a glass fiber yarn moving at a high rate of speed which comprises coating and impregnating the yarn which is at room temperature with a smooth, uniform coating of a dispersion of the resin which is heated just prior to its application to the yarn to a temperature of 50 to 60 C. and heating the dispersion on the yarn immediately after its application to the yarn to a temperature sufficient to fuse the polyvinyl chloride particles to each other and to the yarn in the form of a smooth, uniform coating.

References Cited in the tile of this patent UNITED STATES PATENTS 509,213 Friedlander Nov. 21, 1893 1,196,914 Weiss Sept. 5, 1916 2,083,132 Williams et a1 June 8, 1937 2,245,708 Patton June 17, 1941 2,362,397 Pearce Nov. 7, 1944 2,426,413 Pollett Aug. 26, 1947 2,431,745 Flanagan Dec. 2, 1947 2,439,051 McGill Apr. 6, 1948 2,491,102 Frowde Dec. 13, 1949 2,647,296 Shive Aug. 4, 1953 2,723,210 Biefeld Nov. 8, 1955

Claims (1)

1. A METHOD OF APPLYING A SMOOTH, UNIFORM COATING OF A PLASTISOL TO A GLASS FIBER YARN WHICH IS MOVING AT A HIGH RATE OF SPEED WHICH COMPRISES COATING AND IMPREGNATING THE YARN WHICH IS AT ROOM TEMPERATURE WITH A SMOOTH, UNIFORM COATING OF A PLASTICOL WHICH IS HEATED JUST PRIOR TO ITS APPLICATION TO THE YARN TO A TEMPERATURE ABOVE ROOM TEMPERATURE WHICH APPROXIMATES THE TEMPERATURE AT WHICH THE PLASTICOL IS AT ITS MINIMUM VISOCITY AND HEATING THE PLASTISOL ON THE YARN IMMEDIATELY AFTER ITS APPLICATION TO THE YARN TO A TEMPERATURE SUFFICIENT TO FUSE THE PLASTICOL ON THE YARN IN THE FORM OF A SMOOTH, UNIFORM COATING.

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