Background of the Invention (1) Field of the Invention:

This invention is directed to the manufacture of very short inorganic glass fibers and mineral wool fibers with low shot content in a controlled range of aspect ratios. Aspect ratio may be defined as the ratio of fiber length to fiber diameter and is expressed as a dimensionless number. Shot is generally formed from cooled slag which has failed to"be fully attenuated in the mineral wool manufacturing process. The short glass or •mineral wool fibers can be used as reinforcing agents in plastics.

Description of the Prior Art Mineral wool fibers have been manufactured for a long time and are well known in the art. There are two commercial methods in current use for making mineral wool fibers. One of these methods is performed on an appara¬ tus which uses a single dish-shaped rotor with steam attenuation to form the fibers. The rotor may be in a vertical or horizontal plane. Typical apparatus of this type is shown in the following U. S. patents: No. 3,022,538, issued on February 27, 1962 to C. B. Setterberg, No. 2,328,714, issued on September 7, 1943 to D. C. Drill, and No. 2,944,284, issued on July 12, 1960 to W. T. Tillotson et al. The other conventional method uses multiple rotors which hurl a molten stream of liquid melt against their outer rims in _/ sequence to form the mineral wool fibers. Typical apparatus of this type is

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shown in the following U. S. Patents: No. 3,045,279-W. K. Hesse, issued July 24, 1962; No. 2,991,499-H. E. Holcomb, issued July 11, 1961, and No. 2,561,843-J. E. Coleman, issued July 24, 1941.

It should be noted that while- some of these pat¬ ents disclose apparatus for separating shot from fibers, none of them disclose a method of producing a very short mineral wool fiber. Rather the teachings of disclosures are directly opposed to that of shortening the fiber. Generally, these fibers are used in the form of long fibers which can be intertwined to form a nonwoven mat or held together by a binder to form a rigid board. Under these prior art conditions, it is desirable to have the fibers relatively long.

More particularly, mineral wool fibers have heretofore been used as heat insulation material in paper- enclosed batts, as reinforcing agents in spray-on heat insulation, or as fibers in rigid acoustical panels and tiles. For all of these applications, there is no need to shorten the length of the fibers as they are formed. In fact, it is generally preferred that the fibers be as long as possible with a large aspect ratio.

In many applications, efforts have been made to separate shot from mineral wool fibers.

Conventionally an air elutriation method is used to separate shot from fibers. This method usually has a stream of air which moves the fibers in an upward arc. It is well known that the shot particles have a much higher weight-to-length ratio than the fibers which are generally long and slender. The air stream not only separates the shot from the fibers because of the difference in response of the shot and the fibers but the air also, to some exte breaks some of the shot away from the fibers to which it i attache .

In addition, the fibers and shot may be separate by using water as the separating medium. However, this la ter method requires an additional drying step, which makes the process less attractive than air elutriation.

a molten mass has long been known. Generally, a mass of glass marbles are melted in a heating unit and fine fila¬ ments of glass are extruded through small holes in the bot¬ tom of the heating unit. These filaments are then collected on spools or in an unwoven mat. Often the filaments are accumulated into bundles which are held together by a binder to give added strength. It is also known to cut or chop the fibers into shorter lengths.

It has also long been known to use defibrating or refining apparatus for reducing wood or cellulosic chips to individual fibers. In the defibrating or refining appara¬ tus, wood chips are rubbed against one another until the result is a mass of long individual cellulose fibers which then can be felted into paper or fiberboard. However, in the process, it is desirable to keep the fibers as long as- practicable, as very short fibers are useless for making paper or fiberboard.

The short fibers of the present invention when mixed with resin enhance the physical properties of the resultant filled resin. It is, however, desirable to maxi¬ mize this enhancement and to also produce filled resins with improved resistance to moisture.

Summary of the Invention

The present invention is directed to a novel pro¬ cess in which inorganic glass or mineral wool fibers are shortened to within a limited range of lengths in a continu¬ ous process.

It is an object of the present invention to pro¬ vide a novel method for separating shot from mineral wool fibers.

^'■ -It is another object of the present invention to- provide a novel method for making glass or mineral wool fibers within a relatively _, narrow range of aspect ratios.

It is yet another object of the present invention to provide a novel method for making mineral wool fibers with a minimum of shot in a continuous process.

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Still another object of the present invention, is to provide a novel method for improving the physical pro¬ perties of resins filled with short shot-free fibers.

Yet another object of the present invention is to provide a novel method for improving the physical pro¬ perties of resins filled with short shot-free fibers when such resins are exposed to moisture.

Detailed Description of the Invention The novel process of the present invention may be described with reference to known machinery with, in some instances, novel applications of the known machinery. For purposes of illustration, the invention will be described in terms of mineral wool fibers although it can be used for reduction of glass iber also. The known machinery comprises a mineral wool manufacturing facility such as those disclosed in the above cited patents. The mineral wool fibers and.associated shot are then placed into a refiner so that the individual fibers are separated from their attached shot and the fibers are reduced in length to a range of shorter fibers within a narrow range of aspect ratios. Following the refining step, the mass of shortened fibers and shot are put through an air class¬ ifier where the shot is separated from the fiber and the useful short fibers are removed for packing. The shot is then also packaged and, if desired, can be recycled as part of the starting material for mineral fiber produc¬ tion.

For purposes of this invention it will be assumed that the mineral wool fibers have been made using the multiple rotating disc apparatus shown in the Holcomb patent. The fibers are of multiple lengths with a general distribution of from about 0.5 inches to 36 inches. The shot content was from approximately 25% to 50% of the total weight of the combined shot and fibers. .Some of the shot will be individual particles, and some will still - be attached- to the end of the fibers. In the material

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fiber was 5 microns with a distribution of diameters from 1 micron to 15 microns. The aspect ratios of the unre- fined mineral wool fibers varied from about 10 to 10 . While the fibers are individualized, they nonetheless are in the form of a tangled, unwoven mat or mass of fibers.

The mineral wool fibers thus described were sent through a refiner. For convenience the conventional refiner used was one manufactured and sold by Sprou -Waldron Company, Type No. L9479, Design B. A Sprout-Waldron refiner is well known in the cellulose fiber field, although its use in mineral wool fiber field is new. The Sprout-Waldron refiner consists of a Chamber with a central infeed opening having a fixed plate and a rotatable plate. The plates are generally circular in shape and have facing ribs. The plates can be adjusted relative to each other so as to establish a fixed distance or gap between their faces. A suitable power source is connected to rotatable plate to impart rotation thereto.

As is well known, the mass of fibers and shot are introduced into one end of the refiner and are moved in a spiral path from the center of the facing plates to the outer edge of the plates by the relative rotation of one plate with respect to the other. The fibers and shot are moved outwardly until the fibers emerge in shortened form at the output end of the refiner and the shot emerges relatively unaffected. Other types of disc or plug refin¬ ers may also be used. A plug refiner has a conical plug and complementary outer shell configuration and the fibers are moved with a forward linear force component in a rotating helical fashion from input to output.

The feature to be here emphasized is the fact that there- is a continuous process for reducing the length - of the fiber and removing the shot therefrom.

In the case of the invention, the gap was varied from almost entirely closed to an opening of about 0.140 inches or 3556 microns. The following Table I shows the relationship between the gap opening, the aspect ratio,

and the percent shot passing through a 30 mesh (U. S .

Sieve) screen. Table I shows the effect of two differen feed rates for the mineral wool fiber into the Sprout- Waldron refiner.

Table I .

Aspect Ratio vs. Plate Gap 1 #/Sec. Feedrate

Weight % Shot Gap (inches) Aspect Ratio (L/D) (Passing a 30-Mesh Scr

.010 42 28

.020 43 32

.040 44 25

.050 48 32

.065 64 32

.070 68 31

.100 75 33

2 #/Sec. Feedrate

.030 31 25 .055 48 •34 .070 71 38 .090 80 39 .100 100 37

• Ϊ30 142 38

From this table, it can be seen that there is direct relationship between the aspect-ratio and the siz of the gap opening.

The amount of shot passing a 30-mesh screen as percent by weight of the sample is relatively constant despite gap size opening.

It is thus seen that for a desired aspect rati of mineral fibers, a refiner can be prepared with a fixe gap opening and the fibers fed through the refiner in a continuous manner.

There is a relationship between the feed rate the mineral wool fiber into the refiner and the aspect ratio of the fibers for a given gap size. It has been found that gap size significantly larger than those show will not be effective in reducing fiber length.

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While applicants don't wish to be held to any scientific explanation for the action in the refiner, it appears that there are two actions involved. The shot is broken away from the ends of the fibers so that almost all of the shot is reduced to individual particles and the fibers are shortened by the action of the refiner. It is felt that the refiner does not act in the manner of a chop¬ per or guillotine, but rather causes the brittle fibers to break against each other much in the manner that strands of thin, dry spaghetti will break if forced against each other. The average length of the fiber is in the order of about 1/5 that of the gap size.

While a Sprout-Waldron refiner has been used as the device to break the shot away from the fiber and to reduce the fiber length to a narrow range of aspect ratios, the actual separation of shot and fibers may be accomplished by using an air classifier. An air classifier capable of proper separation is described in U. S. Patent No. 3,615,009, issued on October 26, 1971 of which Walter J. Norton is the inventor. This is commercially available from The Georgia Marble Company of Atlanta, Georgia. The air classifier is designed so that an airstream is recirculated through the system to separate finer particles from coarser ones. The finer particles are drawn through a particle separator which allows fine particles to pass through while rejecting coarse particles. There is a centrifugal separa¬ tor into which the finer particles are drawn with the stream of air and these particles are removed from the system. The air classifier can be easily adjusted to accept particles of a given range of sizes and reject longer and smaller ones. In this device the mineral wool fibers which have a large aspect ratio are separated from the shot, and the shot con¬ tent drops to below 1% by weight compared to the 25 to 50% in the mineral wool, as formed.

While the Georgia Marble air sifter has been found to be most acceptable, other air separators which are capable of separating particles of different aspect ratios can be used. Air elutriation is a known method of separa-

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ting particles of different weight to surface ratios. Ob ously, the weight to surface ratio of generally round par cles is vastly different from that of particles having a much larger aspect ratio (length to diameter) . Thus the type of separator is not critical to this invention. How ever, a suitable separator must be selected to accomplish the separation.

While the emphasis of the invention thus far ha been the separation of shot from mineral wool fibers and breaking of the fibers into shorter lengths, the concept breaking fibers can be applied also to such brittle fiber as glass fibers. It has been found that glass fibers can broken into shorter lengths and have a narrow range of aspect ratios when subjected to the process of the presen invention. Even a glass fiber mat often has between abou 7% to 14% of shot, as commercially produced.

The inorganic fibers produced with the narrow range of aspect ratios of about 30 to about 140 will be referred to as short fibers.

It has also been discovered that the short fibe of the present invention can be advantageously modified b reacting them with a silane in general and in particular silane of the formula:

R-Si(OH) ₃ wherein R is selected from the group consisting of: amino-alkylene, amino-alkylene-amino-alkylene, vinyl, acryloxy, ethacrylox , epoxy-cyclohexyl-alkylene, glycidoxy-alkylene, and ercapto-alkylen . The above-described alkylene radicals generally have 1 to carbon atoms and preferably have 2 to 6 carbon atoms.

The alkoxy silanes useful in the present invent can be used as such but are preferably hydrolyzed to the corresponding hydroxy silanes by well known procedures.

alkoxy silane is simply mixed with a stoichiometric amount of water at room temparature. The reaction is exothermic and cooling is employed to maintain the reaction mixture at about 0° to 40°C. The reaction is complete when the reaction mixture clarifies. Examples of suitable alkoxy silanes include among others vinyltriethoxysilane, vinyl- tris (2-methoxy-ethoxy) silane, gamma-methacryloxy- propyltrimethoxy-silane, garama-aminopropyl- trimethoxysilane, n-beta-(aminoethyl)-gamma-aminopropyl- tri ethoxy-silane, beta-(3,4-epoxy-cyclohexyl) ethyl- trimethoxysilane, gamma-glycidoxy-propyltrimethoxy-silane, gamma-mercaptopropyl-trimethoxysilane. Examples of suit¬ able hydroxy silanes are the corresponding hydroxy silanes. Gamma-aminopropyl-trihydroxy-silane is the preferred hydroxy silane because of its reactivity.

The short fibers can be reacted with the silane in any convenient manner but are generally ^" reacted by charging the short fibers isito a blender' equipped with a spray system. The silane is then sprayed onto the short fibers by means of the spray system while the blender is in operation. Widely varying temperatures are possible but the reaction is preferably carried out at 10 to 110°C. Ambient temperature is preferred. A solvent can be pre¬ sent or absent but is preferably absent. The silane can be reacted with the short fibers at widely varying ratios but the silane generally comprises from 0.01 to 2 and pre¬ ferably 0.05 to 1 weight percent of the mixture. At much lower ratios the treated short fibers do not exhibit pro¬ perties sufficiently different from untreated short fibers. Higher ratios are possible but uneconomical.

The treated short fibers are incorporated into the resin in the same manner as employed in connection with conventional fillers. The treated short fibers can comprise widely varying proportions from less than five to over ninety-five weight percent of the filled resin.

The effect of surface treating the short inor¬ ganic fibers with silanes was investigated. Property en¬ hancements resulted from the surface treatment. The

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change in properties after water conditioning was studie for surface treated short fibers as well as untreated short fibers. The net effect of incorporating short fibers into a general purpose nylon 6,6 such as Zytel 10 (DuPont Company, Basking Ridge, New Jersey)-, and into a general purpose polybutyleneterephthalate such as Celanese J-105 (Celanese Plastics, Summit, New Jersey) , was to achieve significant reinforcement of the resins. The short inorganic fibers used for this work had an average fiber diameter of 5 to 6 microns and an average aspect ratio of 46. The short fibers were incorporated into the resin with percentages of short fibers of 33 percent and 50 percent by weight.

The invention is further illustrated by the fo lowing examples in which all parts and percentages are b weight unless otherwise indicated. These non-limiting examples are illustrative of certain embodiments designe to teach those skilled in the art how to practice the ^• invention and to represent the best mode contemplated fo carrying out the invention. Example 1

The procedure for obtaining test specimens was initially to dry the nylon 6,6 for 3 hours at 175° F (79° C) . The short fibers and nylon 6,6 were well blend by using a 12-inch Henschel mixer for 30 seconds prior t compounding in a Brabender 3/4-inch single-screw extrude A standard nylon screw was used in the extruder. The ex truder was controlled at 540° F (282° C) on the rear and front sections and 520°F (271° C) on the die. The com¬ pounded material was chipped and then injection-molded b using a 1-oz. Newbury Industries machine. Injection temperatures ranged from 520° to 580°F (271° to 304°C) d pending on the loading of the short fibers. The die was ^' heated to 200°F for all samples. Test bars were produce for unfilled nylon, nylon filled with 33 weight percent short fibers, nylong filled with 50 weight percent short fibers. Samples were tested immediately after molding o kept in a desiccator until they could be tested. The

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- consistent with. ASTM test procedures. The physical and thermal properties of nylon reinforced with silane -treated short. fibers are to be found in Table II. Example 2

Test bars were produced as in Example 1. Samples were-water. treated prio -to -testing.by immersion in 122° F (50° C) water for 16 hours and then tested imme¬ diately. This was done to evaluate the effects of fiber- • resin interaction with and without silane treatment of the water conditioning. Tests were carried out using unfilled nylon and nylon dilled with 33 weight percent short fibers. The results of the water conditioning tests are to be found in Table III. Example 3

The procedure of Example 1 was followed using a general purpose polybutylene terephthalate instead of the nylon 6,6. Test results are to be found in Table IV. Example 4

The procedure of Example 3 was repeated using polybutyleneterephthalate resin reinforced with 33 weight percent short fibers. The test results are to be found in Table V.

The physical properties for various resins fil¬ led with reinforcing short fibers can be enhanced when the resin and reinforcer are chemically bound by using a silane such as ga ma-aminopropyl-trihydroxy-silane. The results of treating the nylon resin filled with short fibers with a silane are shown in Table II. It can be seen that at both short fiber content levels of 33 weight percent and 50 weight percent the silane enhanced the properties markedly. It is especially noteworthy that at a 50 percent loading all composite properties were im¬ proved over those of unfilled nylon or nylon filled with untreated short fibers. In short, a true reinforcement of the resin was observed at this level.

In normal usage, materials such as nylon are e posed to atmospheric moisture. This results in a pick-u of water and subsequent change in physical properties. The compounded materials were therefore water conditione to give some indication of the relative changes that might be expected. The method of water conditioning was chosen as a convenient means of quickly observing change As a result, no attempt was made to equalize total water absorption. The results are shown in Table III. The dr as-molded, samples were used for comparisons. The speci¬ mens with surface-treated short fibers retained a higher percentage of the original, dry sample measurement.

Tables IV and V are similar to Tables II and I except that a general purpose polybutyleneterephthalate (PBT) was substituted for the nylon 6,6. The silane use for the surface-treatment of the resin filled with treat short fiber was gamma-aminopropyl-trihydroxy-silane in a the tests whose results are recorded in Tables II throug V inclusive.

Short fibers have been shown to be an effectiv reinforcing agent when incorporated into a general purpo resin with enhancement of physical and thermal propertie when a surface treatment with silane is applied to the fibers. The increased fiber-matrix chemical bonding was responsible for greater retention of physical strengths when the components were subjected to a moist environmen The surface treatment with silane may be recommended for long term maximum retention of properties.

In summary, the invention pertains to a novel process for treating glass or mineral wool fibers to create short silane treated fibers within a limited rang of aspect ratios.

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Table II

PHYSICAL AND THERMAL PROPERTIES OF A GENERAL PURPOSE NYLON 6,6 ^; REINFORCED WITH SURFACE-TREATED SHORT FIBERS

33 wt. % short fibers 50 wt. % short fibers

Property Unfilled Untreated Treated Untreated Treated

Tensile Strength (psi) 9 ₈ 940 9,580 12,700 9,030 16,590

Tensile Modulug (psi) 294,000 473,000 495,000 548,000 608,000

Izod Impact Strength , 0.75 0.53 0.59 0.63 0.77 (ft,-lb/in.notch)

H Flexural Strength (psi) 11,480 15,260 17,700 14,900 24,000

Flexural Mo ulus (psi) 181,000 793,000 731,000 1,163,000 1,230,000

Heat Distortion Temperature 352 394 ^' 400 430 454 (°F @ 264 psi)

Table III

EFFECT OF WATER.CONDITIONING OF NYLON 6,6 REINFORCED WITH SHORT FIBERS

33 wt. . % short fibers

Property Unfilled Untreated Surfac Treate

Tensile Strength (psi) Dry* 9,940 9,580 12,700 Wet** 6,330 5,340 8,700

Tensile Modulus (psi) Dry 294,000 473,000 495,000 Wet 165,000 347,000 335,000

Izod Impact Strength Dry 0.75 0.53 0.59 (ft. -lb. /in. notch) Wet 2.06 0.91 1.20

Flexural Strength (psi) Dry 11,480 15,260 17,700 Wet 6,280 8,300 11,400

Flexural Modulus (psi) Dry 181,000 793,000 731,000

Wet 180,000 391,000 433,000

* Dry: Tested as molded

** ^' Wet: Tested after a 16-hour soak in 50 °C distilled wat

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Table IV

PHYSICAL AND THERMAL PROPERTIES OF A GENERAL PURPOSE PBT REINFORCED WITH SURFACE-TREATED SHORT FIBERS

33 wt. % short fibers 50 wt. % short f

Property Unfilled . Untreated Treated Untreated Tre

Tensile Strength (psi) 7,340 7,790 10,220 8,180 10

Tensile Modulus (psi) 259,000 441,000 508,000 589,000 634

Izod Impact Strength 0.34 0.47 ■ 0.48 0.57 0. (£t„-lb./in..notch) .

Flexural Strength (psi) 9,520 11,750 14,440 11,900 17,

Flexural Modulus (psi) 330,000 815,000 799,000 1,280,000 1,270,

Heat Distortion-JTemperature 1 16655 359 354 ^' 386 ^' 38 (°F @ 264 psi)

Table V

EFFECT OF MATER CONDITIONING OF ^• PBT REINFORCED ^' WITH SHORT FIBERS

33 wt. % short fibers

Surface-

Property Unfilled Untreated Treated ^"

Tensile Strength (psi) Dry* 7,340 7,790 10,220 Wet** 6,960 ' 6,300 7,650

Tensile Modulus- (psi) Dry 259,000 441,000 508,000 Wet 246,000 392,000 441,000

Izod Impact Strength Dry 0.34 0.47 0.48 (ft.-lb./in. notch) Wet 0.46 0.31 0.36

Flexural Strength (psi) Dry 9,520 11,750 14,440 Wet 8,270 8,670 11,840

Flexural Modulus (psi) Dry 330,000 815,000 799,000 Wet 283,000 640,000 679,000

- * Dry: Tested as molded.

** Wet: Tested after a 16-hour soak in 50 ^β C distilled water.