US2375414A - Manufacture of rubber treated fiber - Google Patents

Description

Patented May 8, 1945 Clark (3. Heritage, Cloquet, Minn., asslgnor to Wood Conversion Company, Cloquet, Minn, a

corporation of Delaware No Drawing. Application May.22, 1940, Serial No. 336,577

2 Claims.

suspension in water) by a high speed rotary disk or like means. The present invention is directed to the use of rubber or like dispersions with or without other agents, to treat the fibers as they are so formed by that process, and not after they are formed. t also relates to the subsequent treatments of the so-treated fiber for uses for which the fiber is particularly adapted by such treatment.

One object of the invention is to introduce dispersed rubber or the like to the grinding elements along with the raw material to be or being defibered.

A particular object of the invention is to add aqueous emulsions of rubber or like material to wood or the like to be or being defibered in a gaseous atmosphere.

Another object 01' the invention is to dry the treated fiber so produced directly, whereby all the solid substances of ,the rubber dispersion and of the wood are preserved.

Still another object of the invention is to provide a highly useful fiber for bulk insulation as mats, which are felted either with or without a binder, mechanically, pneumatically or other- Wise.

A particular object of the invention is to use a treating agent which does not add an odor to the fiber.

Various other and ancillary objects and advantages of the invention will become apparent from the following description and explanation of the invention.

Reference is first made to the U. S. Asplund Patents No. 2,145,851, No. 2,008,892 and No.

. 2,047,170. relating respectively to a machine, the

process of said machine, and the use of a sir-e in such process and machine. The said patents are more particularly directed to the preparation of wood fiber for making fiber board. To these ends, the fiber is discharged from the machine, directly into water, and such operation masks a defect in the machine product which is troublesome in some uses 01' the fiber.

As set forth in the copending application Serial o. 227,338, filed August 29, 1938, of which the present application is a continuation in part, the fiber need not be put into water, or wetted. For certain' uses it is dried directly from the moist condition which results from disintegration in a high pressure steam chamber. The moisture content based on the discharged moist fiber may vary from 40% to 60% and commonly is about The drying is preferably done in ovens heated to about 250 F. more or less, the temperature be- .ing not critical, but chosen to effect drying for the conditions of loading the conveyor therethrough including its speed.

The directly-dried fiber is highly efficient as an insulating fiber to be packed into spaces, particularly in refrigerators. So used, it is customary to bale the dry fiber, ship it to the point of use, break the bales and loosen the fiber, and then pack the fiber into its ultimate position.

The fiber s0 handled from the drier, ls dusty to an undesirable degree. The dust is not only lost from the bulk, but it is a hazard to workmen and to machinery. As much as 5% of the original wood may be present as fiying dust, as a result of the necessary defibering action to attain a fiber free from chips, slivers and like coarser bundles of fiber, all of which lower the insulating efiiciency of the product.

When such fiber is pneumatically conveyed or packed, the presence of dust is a disadvantage to this type of use. Such process may involve filters, or filtration, and the dust may be too concentrated locally, giving poor thermal efilciency. Also, there are practical limitations in the amount of force that may be used to felt fibers by a, pneumatic system. One effect of treatment according to the present invention is a lowering of the resistance of the fiber to felting, whereby better felting for a given force is a desirable result.

The present invention shows that when rubber or rubber-like substance in highly dispersed form, such as an aqueous latex emulsion, or a rubber solution, is added to the raw material to be defibered, such as wood chips, 9. more useful product results. The amount of solid so added may be controlled to vary many properties of the fiber as will later be shown. However, a small quantity may be added without greatly changing many of those qualities which are considerably altered by larger amounts. Such smaller amount is quite efi'ective, however, to minimize the dustiness of the product from the drier, and at other stages, and to alter the felting and other compressive properties. A specimen of latex-treated fiber which has a given content of dustbefore baling,

' has a lessenedcontent of dust after being baled.

It appears that the act of compressing bonds loose dust or treated dust to the treated fibers to lessen fibers.

the dustiness. The terms dust, flying dust" and dustiness are herein used to signify the same condition. The ,dust is considered to be the fine particles which are free to fioat in the air away from the mass when it is in a loose flufiy condition, and is distinguished from the fibers or fines which are held in a felted aggregate from which the dust may float away. The dust, may be broken fibers, particles, and even ultimate Not all the ultimate fiber content of a mass of fibers becomes flying dust. A mass of fibers serves as a matrix capable of retaining ultimate fibers. From any matrix 'of fibers, that portion of it which is capable-of leaving the matrix and of being carried off in the air, to appear as dust, is considered to be the dust content, or to indicate the dustiness. Obviously, it is not a clear cut fraction or component of the mass, being dependent upon the size and density of the matrix, as well as upon the characteristics of the matrix to hold or release the dust. The rubber treatment of the present invention affects the characteristics of the matrix so that it exhibits less dustiness. After balin'g, the same fine particles may be present as before'baling, but they are 'not free to fioat away, and are therefore 'not dust.

'Many methods may be develo'pedto determine dust content. The method must be some standard operation upon the fiber which gives reproducible results with specimens of the same batch, in order that the dustiness of different batches may be compared. One such method is described in the copending application of Anway Serial No. 290,999, filed August 19, 1939, now U. S. Patent 2,324,126, issued July 13, 1943.

As an example of the effect of a small amount of latex on fiber, the following table shows jack pine fiber made in the Asplund machine under conditions to produce the same coarseness modulus (particle size distribution as determined by Wet screening the fibers to isolate fractions thereof). The differences in properties gi'ven below may not be charged to difference in the composition of fiber, due to the sizes of the components, but may be charged to experimental errors in determining them, and to the latex. Many experiments show that the difference in dust content and improved felting qualities are due to the latex.

Table 1 0.9% latex solids Numbers 3-202-46 and 47- Steam pressure, lbs/sq. in Compressive pro ertics:

Free footage in board feet per lb. 0.. Specific elasticity (at 315 board fer-L per lb.) in lbs. per sq. ft Absolute elasticity Specific felting (at 3.15 board feet per 1b.) in lbs. per sq. it Absolute feltlug, an index Coefficient of sliding friction, an index Thermal conductivity (ll. t. u./hr./s(1. fl../ "F, inch) Friability, uuindex Dust,pcrecnt impact resistance, board-feet pcr ll Fractionation, per cent content:

lstfraction I '1'. 2nd fraction... lits ll 3rd fraction 4th fraction Past 4th fraction. Coerscness modulus I 5 sun;

In the above table, the differences are due to the latex only, the Specimens having been made under the same conditions of operation at substantially the same time. The properties designated compressive properties may be interpreted in terms of differences actually observed in using the fibers.

Oneuse of such fiber is inthe pneumatic process of packing them into refrigerator spaces, as set forth in my application Serial No. 294,212, filed September 9, 1939. According'to such process fibers are introduced to a blower fan which forces them in air suspension through a conduit into selected inlets to a space to be packed. Selected outlets are provided, preferably with filters to release the air. In this process there is an air force exerted on the fibers, and fibers are deposited in felted relation. The density of the felt increases with increase of air pressure, other conditions being the same. The property designatedspecific felting means that at a density of 3.15 board feet per pound, the fiber with latex is less resistant to felting, or felts with more ease at a given pressure applied to felt it than fiberwithout latex. Since increase of pressure in a pneumatic system is somewhat involved by economic and mechanical factors, the effect is obtained by treating with latex to improve the fibers for a given mechanical outfit. The benefits from reduced dustare also highly desirable in operating the same system. The compressive properties" may be determined as set forth in the application of Anway, Serial No. 313,920, filed January 15,

-Friability, dust and permanence to heat" These properties may be determined according to the process described in 'said An'way Patent No. 2,324,126. This involves a standardized pounding of the fiber to create and measure dust formed. It incidentally gives by amathematical intercept, an indication of original dust content. By heating fiber for 24 hours at 150 C. and again measuring friability, a ratio of friabilities before and after heating, is found as a measure of permanence to heat.

Friability" is expressed as a mathematical term which is the slope of the straight line obtained by plotting horizontally, the minutes" of pounding time, and vertically, the ratio of fiber loss of original specimen to remnant of the original specimen.

The free-footage is determined as one of the "compressive properties," and is an extrapolated value defined as the natural density of the fiber-at zero compression. The. table shows that the treated fiber is naturally less-bulky.

In giving references to other applica 'ons for letters patent herein, it is to be understood that these are not given as essential to the present disclosure, or for amplifying it, but; only v for the purposeof associating the several inventions into arelated group.

In the foregoing Table 1. the 9%" solids from the rubber latex reduce the original d'ustiness from In said patent under the sub-title- 2.8% to 1.0%. After baling the 1% of dust is reduced materially, depending upon baling pressure. Smaller percentages of latex give results to a proportionate degree,and the preferred content is from .9% to 1%. Additional quantities. are not proportionately effective to reduce the dust, but they alter the various properties of the fiber above listed. Hence, where it is desired so to change these properties, more latex may be added.

Each substance used to treat fibers has its specific effect upon different properties, which effects may be determined only by the tedious. task of actually running the defibrator machine with a series of treatments by each material indifferent quantities, and then tediously determining the various properties. This has been done with latex, and other materials, of which A and B are indicated, merely for the purpose of showing. the specificity of materials. Under the subtitles of the property measured, given below, are given specific efiects'of increased contents of latex, of A, and of B. However. these elfects'must not be considered as absolute to the degree that they may be compared with the data in Table 1, for the reasons given in the next paragraph.

In Table 1 it is to be noted particularly that the fiber masses compared have the same coarseness modulus so that the differences in the properties cannot be attributed to differences in particl -size distribution. A change in the coarseness modulus also effects properties enumerated in Table 1. It has also been determined that with the same coarseness modulus, the actual distribution of sizes may change. It has also been determined that two different sizes of defibrator machines yielding fibers having the sam coarseness modulus will give fibershaving different properties, for example different dustiness. The manner in which treating agents affect the properties of the fiber are not always the same in different sizes of machines. The materials A and B, above referred to and latex have been compared by using a machine of size different from the size used for the fibers of Table 1. Also the fibers produced in the following comparisons have not a constant coarseness modulus and lie generally in the range from 225 to 250. Therefore, some of the effects, and apparent discrepancies may be due in part to a variation in particle size. However, sufficient variations are evident to show that the materials A and B, and latex, act specifically. Such showing is the purpose of the following comparisons.

Coefii cient of sliding friction Increase of l atex markedly decreases the property. For example one series showed it to vary one series reduced it from 118. to 85 by a usage from 4% to being not very effective below Absolute elasticity Free footage Use of latex tends to reduce this property.

Material A drops the free-footage. One series showed a drop from 7.2 to 4.7 in usage from zero to Material B also drops the free footage. For example, one series showed it to drop from 8 to 7.4 in a usage up to 15%.

In the same way other properties may be compared with thematerials: latex, material A, and

. material B, said materials A and B, being the subject matter for other applications for letters patent, inasmuch as they are of different nature and each has its specific effects.

Modifying ingredients Agents to vulcanize the rubber solids may be added without indication of any great change in the dust-reducing function. Accelerators, anti-oxidant compounds, and other materials commonly used in association with rubber are contemplated herein as modifying agents. These may be present in the dispersion with the rubber, or added separately.

Fire-proofing agents Preservatives Agents to prevent decay, mould and insect attack may be added with the latex. For exfrom .884 to 5712 by an increase up to 10% solids of latex.

Material A increases the property. Specifi cally, a series showed it to change from 1.09 to 2.57 when used up to 40% of A.

Material B increases the property. Specifically, one series showed it to increase from .852 to 1.40 up to 8%, and then to decrease again thereafter.

Specific elasticity Latex increases the property. Specifically, one

series showed it to increase from 153 to 182 by increase of latex solids to 8%.

Material A lowers the property. one series showed it to be lowered from 267 to 19.5 by usage of A up to 40%.

Material B lowers the property. Specifically,

Specifically interior.

ample, tetrachlorphenol and pentachlorphenol or their sodium salts may be used, as described in Serial No. 345,610, filed July 15, 1940. Alkalis may also be used without destroying the func- V tions of the latex.

Pneumatic felting moisture from the insulation. For this reason I there are vents from the fiber to the refrigerator Use of any fiber carrying an odorous treating agent in such a vented box, will odorize the food in the refrigerator. Thus, some rubber emulsions will give a so-called rubber odor, but latex is one which is free from odor. This is also true of the fiber made from non-vulcanizing rubber cement solutions.

Where odor is not a requirement to be considered, dispersions, preferably as water-emul sions of rubber or rubber derivatives may be used, and are to. be considered within the broad scope of the invention under the term ,rubber dispersion." Solutions of rubber or'the like in organic volatile solvents are useful, but; owing to the loss of volatile solvent in'process, the aqueous emulsions are the preferred dispersions. Where fiber is dried in an oven at high temperature solvent vapors create a fire-hazard. Hence aqueous dispersions are preferred. By the term rubber,/ it is intended to comprehend rubber latex, rubberlike products derived from natural rubber, the synthetic rubbers, and other balata-like substances.

In practice, the emulsion is employed as the preferred means initially to produce a fine dispersion of the rubber. What happens to the emulsion in the machine isnot known, except that the solid content is distributed onto the fiber discharged. The emulsion may be mixed with wood chips entering the pressure chamber of the Asplund machine. The wood is out of the machine as fiber in about 60 seconds more or less after it enters the pressure chamber. The entry of wood into the machine is rapidly intermittent, and for all practical purposes it may beconsidered as being fed to the machine at a constant rate. The emulsion is also fed at a constant rate in the proportion desired for the treatment. The emulsion may enter with the feed, or it may be injected into the pressure chamber or directly to the grinding means independently of the feed of wood or other vegetable matter, and in the chamber be distributed onto the wood by the grinding means. Byinjecting it into the chamber it mixes with the wood or the like before the latter contacts the defibering means. By. injecting it to the grinding elements, it contacts the vegetable matter prior to completion of the defibering action.

Latex emulsions are obtainable commercially in high concentrations of from 40% to 60% solids. In practice, to insure greater dispersion of low usages of the rubber, the solid are kept below 50%, such as at 40% or 30%. In diluting concentrated commercial latex emulsions, it is desirable to add an alkaline stabilizer. Thus in diluting 100 lbs. of latex emulsions having 60% solids, to one of 40% solids 2 lbs. of 26 ammonia (concentrated) solution is added. The water introduced is slight in comparison to the water which may I enter with the wood, but where large amounts of .latex are employed a control of water in the wood may beefiected if compensation is desired. Such compensation may be important.

Where the fiber is desirably dried directly from the machine, rather than being taken up in water, a lowered watercontent makes the discharged fiber more fluffy or bulky, and hence easier and less costly to dry, giving a more useful insulating fiber. For example where jack pine wood with 131% moisture (based on dry weight of wood), is used with a 40% latex emulsion, 2 parts by weight of the emulsion is used to 100 parts by weight of dry wood.

The fiber is dried directly toan insulating fiber. Theconditionof the wood is also a considerable factor. To get the same dust-reducing benefit with oldjack pine as with green jack pine, more latex is required. But the old wood dries so much easier that the oven may be kept at 49 F. lower. Thus, basing percentages on dry wood content, a comparison shows:

Table 2 Year old Green jack jack pine pine Per cent latex (40% solids) 3. 63 2. Per cent dust 2 2. l. Dryer temperature. 203 252 Per cent chip moisture 5 102.9 Per cent water added with wood 5 Table 3 illustrates the invention comparing a control or untreated fiber, with others produced under the same conditions, one using rubber latex, and another using rubber cement solution. Rough green jack pine wood is run through the 'Asplund defibrator set and operated without change to produce fiber from chips of the wood. The discharged fiber is designated 8-131-107. Then 30% latex is added tothe chips to add .75% rubber solids based on dry wood weight. The discharged fiber is designated S-131-106. Then the latex is changed is add an 8% rubber cement solution in benzol, to add 375% rubber solids based on dry weight of wood. The fiber is designated S131-105. This fiber is dried, and evaluated as to particle size distribution, impact resistance, compressive properties, dust content, friability and permanence to heat, as recorded in Table 3.

Table 3 [Rough jack pine wood chips] Item Untreated Latex Cement Sample 3-131 1U! 106 105 (Join ressive properties:

ree footage 9. 57 9. 52 9. 75

Specific elasticity (K a) 160 117 135 Absolute clasticlltz' (M x 343 3 323 Specific felting r) 20. 2 3i. 2 38. 5

Absolute felting (M l") 249 234 241' Coefficient sliding friction l 1 l Coarseness modulus. 172 198 205 Impact resistance 3. 82 3. 3. 73 1 Acidity (pH)..- 4. 05 4. 2o 4. so Friability U093 U052 002B Permanence to heat 366 .258 162i .lercent dust (by screening) 3. 9 1. 9 2. 4

- vention isclaimed as practically limited, and also as a process independent of the Asplund machine.

I claim:

. 1. The method of making dry vegetable fibers suitable for; forming loosely felted fiber mats, which comprises subjecting vegetable matter to be reduced to fiber to -the defibering action of mechanical defibering and mixing means in a gaseous atmosphere, and in the presence of a non-suspending and a fiber-moistening amount of water, introducing dispersed rubber to the vegetable matter prior to completion of the defibering and distributing said rubber into the loosening the compacted fibers the loosened fibers are less dusty than the fibers prior to said compacting.

2. The method of making dry wood fibers suitable for forming loosely felted lignocellulose fiber mats, which comprises subjecting wood to be reduced to fiber to the action of a high-speed rotary element having a defibering and mixing action, in an atmosphere of steam at a temperature Patent No. 2,575,1nh.

elevated above 212' F. and at which lignin in the lignocellulose becomes softened to permit easy defibration, and in the'abs'ence of a suspending amount of water, introducing dispersed rubber to said material prior to completion of defibration and distributing said rubber into the fiber mass as the fiber is being finally formed, whereby moist rubber-sized fibers are formed including a quantity of dust-forming particles incidentally formed with said fibers, drying said moist rubher-sized fibers to remove moisture and provide dry fibers, said rubber serving to bind some dustiorming particles to fibers to limit the dustiness of said dry fibers, and compacting the dry fibers whereby residual free dust particles are caused to adhere to the rubber-sized fibers, whereby upon loosening the compacted fibers the loosened fibers are less dusty than the fibers prior to said compacting.

CLARK C. HERITAGE.

CERI'IF ICATE OF CORREC 'II ON.

i b y 8, 9 5- GLARK C, HERITAGE.

It s r y l' that error appears in the printed-specification of the above numbered patent requiring correction as follows: Page 2, second column, line 69, after "herein" .and before the comma insert the Words -or patents --affects--- page first column, line 51, for "effects" line 57, after the syllable "arty" and before the period inread 7 sort designated coefficient' of sliding friction, whi h is one of the com- I Pressive P p line 69, after "pr p y" and before the 'period insert "designated specific elasticity, which is one of the compressive properties--;

and second column, line 5, after "property" and before the comma insert "designated absolute elasticity, which is one of the compressive propertiesinsert the following paragraph,

, page 14., second column, line '65, before "I claim:''

"The present application is a 'continuation-in-part of my prior application, Serial No. 227,358, filed August 29, 19 and abandoned. August as, 19L 2.-

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of September, A. v

(Seal) Leslie Frazer First Assistant Commissioner of Patents.

loosening the compacted fibers the loosened fibers are less dusty than the fibers prior to said compacting.

2. The method of making dry wood fibers suitable for forming loosely felted lignocellulose fiber mats, which comprises subjecting wood to be reduced to fiber to the action of a high-speed rotary element having a defibering and mixing action, in an atmosphere of steam at a temperature Patent No. 2,575,1nh.

elevated above 212' F. and at which lignin in the lignocellulose becomes softened to permit easy defibration, and in the'abs'ence of a suspending amount of water, introducing dispersed rubber to said material prior to completion of defibration and distributing said rubber into the fiber mass as the fiber is being finally formed, whereby moist rubber-sized fibers are formed including a quantity of dust-forming particles incidentally formed with said fibers, drying said moist rubher-sized fibers to remove moisture and provide dry fibers, said rubber serving to bind some dustiorming particles to fibers to limit the dustiness of said dry fibers, and compacting the dry fibers whereby residual free dust particles are caused to adhere to the rubber-sized fibers, whereby upon loosening the compacted fibers the loosened fibers are less dusty than the fibers prior to said compacting.

CLARK C. HERITAGE.

CERI'IF ICATE OF CORREC 'II ON.

i b y 8, 9 5- GLARK C, HERITAGE.

It s r y l' that error appears in the printed-specification of the above numbered patent requiring correction as follows: Page 2, second column, line 69, after "herein" .and before the comma insert the Words -or patents --affects--- page first column, line 51, for "effects" line 57, after the syllable "arty" and before the period inread 7 sort designated coefficient' of sliding friction, whi h is one of the com- I Pressive P p line 69, after "pr p y" and before the 'period insert "designated specific elasticity, which is one of the compressive properties--;

and second column, line 5, after "property" and before the comma insert "designated absolute elasticity, which is one of the compressive propertiesinsert the following paragraph,

, page 14., second column, line '65, before "I claim:''

"The present application is a 'continuation-in-part of my prior application, Serial No. 227,358, filed August 29, 19 and abandoned. August as, 19L 2.-

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of September, A.

(Seal) Leslie Frazer First Assistant Commissioner of Patents.