CA1038576A

CA1038576A - Method of making microporous elastomeric material

Info

Publication number: CA1038576A
Application number: CA215,385A
Authority: CA
Inventors: Doyle V. Haren; Arthur D. Logan
Original assignee: Dayco Corp
Current assignee: Day International Corp
Priority date: 1973-12-27
Filing date: 1974-12-06
Publication date: 1978-09-19
Also published as: US3928521A

Abstract

ABSTRACT OF THE DISCLOSURE
A method of making a microporous elastomeric material having interconnected cavities and which may be used in an ink dispensing article is provided. The material is made by a particular sequence of steps namely, firstly admixing particles of hydrated magnesium sulfate in an elastomeric matrix material, then curing the elastomeric matrix material and simultaneously causing liberation of water of crystallization from the hydrated magnesium sulfate.
This provides a blowing effect resulting in the formation of interconnecting passages between the particles. Then, there is the steps of leaching the particles from the matrix material, the leaching being achieved in an accelerated manner due to the interconnecting passages.

Description

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This invention relates to a method for making a microporous elastomeric material.
Microporous rubber materials are widely used through~
out industry for various purposes including ink dispensing rollers, pads, and the like. It is well known in industry that microporous materials may be made using procedures ~ which employ non-hydrated soluble salts such as, for example, '7 sodium chloride or sodium nitrate. ~ow~ve`r, ~ such procedures which use non-hydrated salts increase the :7, `i lO overall cost of the microporous material due to the exce991vo ; ` time required and difficulty in removing the particular salt utilized from the rubber material by leaching process. ,~
., , ~. .
l This invention provide~ an improved method of mak-s ing a microporous elastomerlc material and an improved method ~ ~
~ 15 of making an ink dispensing article having such microporous ` ~ ;l material provided as a portion thereo. Such materlal has `~
~i~ interconnected cavities or pores throughout. The present ,~;, - ~ .. .
in~ention, in its broad aspect, provides a method which $ ~ comprises the steps of: admixing particles of hydrated mag- ;- ~
1 20 nesium sulfate in an elastomeric matrix material; curing ; ; ;
,. ::.
j the elastomeric matrix material and sub~tantially simultane- ~ ;
3 ous1y causing liberation of wa~er of crystallization from said hydrated magnesium sulfate which provides a blowing e~ffect resulting in the formation of interconnecting pas~
sages between said particles; and leaching said particles from the matrix material; said leaching being achieved in ;`
an accelerated manner due to said interconnecting passages.
;.: . ; . :
,~ By another aspect of this invention, a method i8 `
y; ~ provided for making an ink-dispensing article comprising the steps of: ~A~ forming a microporous rubber ink-dispensing ~' , . ' . .

i`~ 10385~6 mQter:ial which has interconllected cav:ities, said forming s-tep comprising the steps of: admixing sized part-icles of hydrated magnesium sulfate in a rubber~ma-trix ma-terial; curing the rubber matrix material and substan-tially simul-taneous~y causing libera-tion of wa-ter of crys-tallization Erom said hydrated magnesium sulfa-te, which provides a blowing effect resulting in -the formation of interconnect~
ing passages between said particles; and leaching said par-ticles from said matrix material; said leaching being achieved in an ; ;~
accelerated manner due to said interconnecting passages; and (B) fixing the microporous rubber ink-dispensing material so formed to an associated support means to define said article.
By a variant of one aspec-t of -the invention the fixing step (B) comprises fixing said microporous ma-terial in tubular form ~;
on a ro-tatable suppor-t -to define an ink-dispensing roll.
By a varian-t o:F another aspect oF the invention the ~ixing step (B) colllprises Fixing sa.id microporous material in Elat form on a flat support pla-te to define an ink-d:ispensing pad.
By a variant of a fur-ther aspect of the invention the I admi~ing step comprises -the preparation steps of grinding hydrated ! magnesium sulfate and sizing the ground hydrated magnesium sulfate by passing the ground material through a screen and wherein said admixing step is achieved employing a mechanical mixer.
By a varian-t of a s-till further aspect of -the invention -the admixing s-tep comprises admixing said sized par-ticles of hydra-ted magnesium sulfa-te in an amoun-t so -that they comprise between 40 and 75% of the volume of -the microporous material formed~by said forming ;~
step.
By a Yariant of yet another aspect of the invention said admixing step comprises admixing said sized particles of hydrated magnesium sulfa-te in an amount so that they comprise generally of the

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~r~er of 60% of the void vo:Lume ol the microporous material formed by said forming step.
By a varian-t of a s-till Eur-ther aspect of -the invention ~"
-the admixing step comprises -the prepara-tion s-teps of grinding and sizing hydra-ted magnesium sulfate con-taining 7 molecules of wa-ter oÆ crystallization per molecule of magnesium sulfa-te. ;
By a variant of another aspect of -the invention the i~
preparation steps of grinding and sizing said hydrated magnesium , sulfate comprises grinding and sizing said hydrated magnesium sulfate ;
to provide particles wherein about 95% of said par-ticles pass through a 100 mesh screen and abou-t 81% of said particles pass through a 140 mesh ccreen. I
By a varian-t of a further aspect of the invention the forming s-tep fur-ther comprises the s-tep oE rinsing -the cured and leached rubber material. ~"
By a varlan-t of a still fur-ther aspect of the invention the curing and leaching steps are achieved in a substan-tially simultaneous manner.
By a variant of another aspect of the invention the curing and~leaching s-teps are achieved using hot wa-ter at a ~

temperature in excess of 150F. `
By a varian-t of ye-t ano-ther aspect of the invention the ,~
curing and leaching steps are achieved subs-tantially simultaneously by immersing -the rubber ma-trix material con-taining -the sized par-ticles of hydrated magnesium sulfa-te in a -tank of water which is controlled ~ `
to temperature ranging between 150 and 212F.
By a yariant of a further aspect of the invention the forming step co~prises the further steps of rinsing the microporous -~
rubber ma-terial with tap water a~ room ambient tempera-ture and drying the cured, leached, and rinsed material in an oven a-t a ~ -2a-,:. . . :: . .,. :. . : ., : - , . .

" ~. , ~empera-ture ranging between 300 and 350F, By a variant of a s-till further aspect of the inven-tion the preparation s-teps of grinding and sizing said hydrated magnesium sulfate comprises grinding and sizing said hydrated magnesium sulfate -to provide par-ticles of roughly 100 mesh size.
By a variant oE yet a further aspect oE the invention the sizing step comprises employing a-t leas-t one mechanical screen to achieve said sizing and in which said admixing step comprises admixing said sized particles so -that they comprise generally of the ~;
order of 60% of the void volume of -the microporous ma-terial formed by said forming s-tep. .
In the accompanying drawings:
Fig. 1 is a perspec-tive view illus-tra-ting an exemplary ink-dispensing roll made utilizing the me-thod of an aspec-t of -this invention;
F'ig. 2 is a fragmen-tary perspective view illustrating an exemplary ink-dispensing pad made u-tilizing the method of an aspect of this invention;
ll Fig. 3 is an enlarged fragmentary cross-sec-tional view particularly illustrating the microporous elastomeric material made by the method of an aspect of this invention which comprises the ink-dispensing roll or pad of Figs. 1 and 2 and particularly illustra-ting, in an exaggerated manner, cavities which for convenience of drawing are of roughly equal size interconnec-ted by numerous internal channels which promote leaching;
Fig. 4 is a schematic presentation particularly setting forth method steps which may be employed in making i -2b-,.: : . . ::: :: ,::::: :. :,.: : . . . , . . . : ...................... :
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the microporous elastomerlc ink-dlspensing article provided by the method of an aspect of this lnvention; and ~ .
. Fig. 5 is an enlarged fragmentary cross-sectional .,, ;~
view illustrating elastome,ric ma~rix ma~.erial loaded with :~
hydrated magnesium sulfate prior to curi.ng and,leaching.
Reference is now made t~ Fig. l of the drawing which illustrates an exemplary ink-dispensing article or ~ ~., ;
roll which is designated generally by the reference numeral ;-~
10. The roll lO has a central shaft 11 provided with a . .
10 cylindrical supporting portion 12 which i9 detachably fi~ed .`"~
concentrlcally around ~he shaft ll and an outer tubular microporous elastomeric material in the form of a microporous rubber material 13 i9 fixed against the supporting portion ' `
. 12. The material 13 is msde utilizing the method pf an ,~' '~;".
aspect of this inven'tion and is suitably filled ar satura-ted with ink, or the litce, in accordance with techniques ' :' ~; which are well known in the art and as will be described : . - , ~. . ~ .: . -in more detail subsequently. - ;', ~

-. Another exemplary lnk-dispensing article in the form . ,. '':

~' :20 of a pad is shown in Fig. 2 and such pad is designated gen-; ~ ~erally by the reference numeral 15. The pad employs a ' microporous rubber material which is also designated by the ~' .
, reference numeral 13 and the material 13 is fixed by.a sui~a- '' . ble adhesive means 16 to a comparatively rigid supporting ' ,: -. .
' 25. plate which i8 shown as a metal plate 17 and in accorda~ce : .

with techniques which are well known in the art. . '~
; : ~ ,.- ~ .,. :
. The microporous rubber material or composition 13 .
comprising the ink-dispensing roll 10 and the ink-dispensing ~; ;
pad 15 is illustrated in Fig. 3 and has a plurality o cavi-30 ties 20 which are interconnected by internal passages or .
.

.

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channels 21 generally of clifferent sizes. The cavities 20 have different irregular shapes, determined by the manner in which they are formed, and may be of roughly equal size :~
or different sizes. The microporous material 13 is capable of dispensing ink, or similar substances, in a uniform man-ner and in a manner which is considered superior to previously proposed microporous elastomeric materials.
The unique method according to an aspect of this ;~
invention of making the microporous elastomeric material 13 will now be discribed in detail in connection with Fig.
4 of the drawing. In particular, sized particles of hydrated ~ -magnesium sulfate are provided as indicated at 23 and such particles may be provided by grinding action with the siz-ing being achieved employing a suitable mechanlcal screen, ~ ~ ;
or the l:Lke.
The sized particles are then suitably admixed in an elastomeric matrix material as indicated at 24. Although any known technlque may be employed to achieve the mixing ~t~
~ action, such mixing is preferably achieved by introducing i the si~ed particles together with the elastomeric or rub-ber compound in amechanical mixerto define (as shown in Fig.
5) a loaded rubber matrix material 25, i.e., a rubber matrix , material 26 loaded with sized particles 27 of hydrated mag-1 nesium sulfate.
i~ The loaded material comprised of the rubber mater-25 ial or compound 26 with its sized particles 27 of hydrated -~I magnesium sulfate is then cured and leached as illustrated at 30 and 31 respectively in Fig. 4. During the curing of the elastomeric rubber material-there is a substantially simultaneously liberation of water of crystalli~ation from 30 the hydrated magnesium sulfate which provides a blowing ~ I

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effect resulting in the for~ation of the interconnecting passage~ 21 between the particles of magnesium sulfate.
During the leaching of the particles from the matrlx mater~
ial the leaching is achieved in an accelerated manner due '~
to the numerous interconnecting passages 21 whlch make pO5 sible a more efficient leaching action, thereby completely , to define microporous material 13 having cavi~ies 20 inter~
connected by passages 21.
The cured and leached rubber material with the inter- ~;
connected microporous,cavities defined therein i8 suitably rinsed as indicated at 32 to remove any residual,magnesium sulfate which may be present thereon whereupon any residual ` '~
water is removed from the microporous material 13,by air drying as indicated at 33. The drying process may be accel-erated, i~ desired, by prior removal of exce~s water by mechanical action such,as, for example, by squeezing, or by other suitable means. ' ', , 'Following air drying of the material 13 an ink dis- , , :
,-; pensing article is made and this may be achieved by maki~g ' -~
i ~ 20 a tubular member for the roll lO'which as indicated pre-viously i8 designated by the numeral 13 or a flat member for the pad 15 which i9 also designated by the numeral 13. 'i~
It should be appreciated that the tubular member ~ .
13 of the roll 10 may be made by any suitable technique '~

known in the art, including by ex,trusion thereof in tubular ~; form uslng the loaded material 25 prior to curing and leach~

~, ing or by sultably forming of a flat sheet which is cured, ; leached, and then wrapped in tubular form around the sup~

.
porting portion 12 and fixed thereto. However, regardless ~ '~

of the manner in which the tubular membar 13 iq made or '~ "''" ~

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- .; .

formed it i9 suitably fixed to the supporting rotatable ,~
support or hub portion 12 in accordance with well known techniques to complete the ink-dispensing roll 10.
Similarly, the microporous elastomeric sheet por~ ;
tion 13 is suitably cut to the desired configuration and I ~ ;
!. .
fixed by adhesive means 16 to the support plate 17 using any known technique to define the ink-dispensing pad 15.
Once the microporous material 13 is fixed or bond-ed in position on its associated roll lO or pad 15, ink is loaded therein using any technique which is known in the art.
Depending on the ink used and the detailed character of the elastomeric material, the ink may be heated to a predeter-mined temperature, such-as, for example, 150F, to facili-tate saturatLon thereof in the material 13. Also vacuum and/or pressure may be used to facilitate saturatLon.
Having described the improved method of an aspect _ -of this invention the detailed description will now proceed with details of the size of the particles 27, the extent ~ ",:,-of hydration of the magnesium sulfate, the amount of hydrated magnesium sulfate which may be employed in an elastomeric matrix, and finally specific examples of the method of this invent:lon. In particular, during the step of providing sized particles of hydrated magnesium sulfate the sizing is preferably such that roughly "lOOmesh" particles are provided. What is meant by "100 mesh" will be described in more detail subsequently. The hydrated magnesium sul-fate preferably contains seven molecules of water of cry-stallization per molecule of magnesium sulfate and the for- -mula is written MgS04.7H20. The amount of hydrated magne-sium sulfate which may be used in the microporous material ;
-, .

13 may comprlse between 40 and 75~ of the total volume of the mater:ial 13.
EXAMPLE ' `~
Si~ed particles of "100 mesh" hydrated magnesium sulfate containing 7 molecules of water of crystalliz~tion ' ' per molecule of magnesium sulfate are provided by grinding ~ ~
and sizing is achieved using a mechanical screen. The si~ed = `~ ' particles are thoroughly mixed in a suitable rubber matrix `~
material in amechan:ical mixerto define a loaded.rubber mater~
ial 25. The loaded rubber material 25 is then substantially simultaneously cured and leached in a tank of hot water at a temperature of 168F for a time period of 24 hours. The r residual salt is then r'insed from the cured and leached rubber using ordlnary tap water at room ambient temperature for approximately one minu~e. The cured, leached, and rinsed rubber material is dried in an oven which is controlled at a temperature ranging between 300 and 350F for a length ¦'~'''' of time sufficient to drive off any residual water whereby some post curing may also be provided and the microporous elastomeric material 13 is completed and may be used in the roll 10 or pad 15. ,~'~
'' In the above example, the curing and leaching is ~ ~-achieved in a single step; however, it is to be understood ~ ~
that the curing and leaching may be achieved in separate ~ ~' steps and when thus achieved the curing may be achieved before, or after the leaching step. `
It will also be appreciated that hydrated magnesium sulfate containing other than 7 molecules of water per molecule of magnesium sulfate may be provided. In addition, in those instances where curing and leaching is achieved in a single , ' ~' '.

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step the time required for such ~ingle-step curing and leaching may range between 10 hours and 72 hours as a func~ion of the dimensions of the article being processed and the temperature of the hot water em~ployed~ which may range between 150F and 212F. :
. The material 13 illustrated and described in this disclosure of the method of aspects of lthis invention is -~
: . , cross-hatched in the drawing as a rubber material. Such ,~
rubber material may be either a natural rubber or a synthe- -tic rubber compound. Howe~er, it is to be understood that : .
any suitable elastomeric material may be used to define the .
microporous materis.l produced by the method of aspec~s of this invention.
In this disclogure o~ the invention, "100 mesh" ~ :
particles of hydrated magnesium sulfate have been specifically mentioned; however, it is to be understood that particles :~
of other sizes may be provided. For example, such particles may be as small as 200 mesh size or larger than 100 me~h : ~ :
depending upon the size of the cavities or pores des.ired in the microporous material.: ~
~ Actually, the "100 mesh" particles of magnesium . ~ :
.
sulfate material were chosen for making an ink-disp!ensing article, based on what is considered to be the largest pore : size which will yiela a satisfactory balance between ink ~ : -pickup characterlstics, ink feed to a surface being printed,~
:~ and freedom from so-called "misting" or ink spin-o~f when - ~ running. .
A typical screen analysis for the "100 mesh" par- `:
:~ ticles is presented below where the 100 mesh screen has an .
aperture measuring .0058" square, while the 140 mesh screen 103~
` c ~ `
has an aperture measuring .0041" square. ~ -Particles retained on 80 mesh screen 0% ~ ~;
Particles retained on 100 mesh screen 5.0% ;~
Particles retained on 140 mesh 3creen 13.7%
Particles smaller than 140 mesh screen 81.3Z
, 100.0%

From the above screen analysis, it is seen that ;!~

95% of all the material is smaller than 100 mesh, while :.,:
81.3% is smaller tha~ 140 mesh.
10` As previously mentioned, the amount of hydrated magnesium sulfa~e in the material 13 ~ay comprise 40 to 75%
of the total volume of such material. During actual labors~
. . ~ , ; tory tests it was found that ater the improved leaching ~;
action provlded by the method of an aspect of this invention, about 95% and more o`the soluble materials had in fact been leached out and the re ulting microporous material had an actual void volume of about 61% which will be consider~d as generally of the order of 60%. Void measurements were '~ made indirectly by determining the weight of sampleR before !~ 20 and after leaching and drying. As a crosscheck, the ink pickup o~ each sample was determlned on a weight basis.

~rom this information, ink pickup was converted to a volume ` ~
i, , ` ,' ~ .. .
basi9 and it was found that the volume of ink absorbed was about 58~ oE tha total apparent volume of each sample; i.e., ~` 25 58% of the sampla was void volume that had been filled with

3 - - -~
7' ~ ink. Thi~ compared quite well with the 61X void volume deter~

mined by removal of soluble components and suggests that a smalL portion of tha void v~olume was uninked, due either to ins~fficient soak time or possibly viscosity efEects of !: : 30 the ink.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method of making an ink-dispensing article comprising the steps of, (A) forming a microporous rubber ink-dispensing material which has interconnected cavities, said forming step comprising the steps of, admixing sized particles of hydrated magnesium sulfate in a rubber matrix material, curing the rubber matrix material and substantially simultaneously causing liberation of water of crystalli-zation from said shydrated magnesium sulfate which provides a blowing effect resulting in the formation of interconnecting passages between said particles, and leaching said particles from said matrix material, said leaching being achieved in an accelerated manner due to said interconnecting passages; and (B) fixing the microporous rubber ink-dispensing material so formed to an associated support means to define said article.

2. A method as set forth in claim 1 in which said fixing step (B) comprises fixing said microporous material in tubular form on a rotatable support to define an ink-dispensing roll.

3. A method as set forth in claim 1 in which said fixing step (B) comprises fixing said microporous material in flat form on a flat support plate to define an ink-dispensing pad.

4. A method as set forth in claim 1 in which the admixing step comprises the preparation steps of grinding hydrated magnesium sulfate and sizing the ground hydrated magnesium sulfate by passing the ground material through a screen and wherein said admixing step is achieved employing a mechanical mixer.

5. A method as set forth in claim 1 in which said admixing step comprises admixing said sized particles of hydrated magnesium sulfate in an amount so that they comprise between 40 and 75% of the volume of the microporous material formed by said forming step.

6. A method as set forth in claim 1 in which said admixing step comprises admixing said sized particles of hydrated magnesium sulfate in an amount so that they comprise generally of the order of 60% of the void volume of the microporous material formed by said forming step.

7. A method as set forth in claim 1 in which said admixing step comprises the preparation steps of grinding and sizing hydrated magnesium sulfate containing 7 molecules of water of crystallization per molecule of magnesium sulfate.

8. A method as set forth in claim 7 in which said preparation steps of grinding and sizing said hydrated magnesium sulfate comprises grinding and sizing said hydrated magnesium sulfate to pro-vide particles wherein about 95% of said particles pass through a 100 mesh screen and about 81% of said particles pass through a 140 mesh screen.

9. A method as set forth in claim 7 wherein said forming step further comprises the step of rinsing the cured and leached rubber material.

10. A method as set forth in claim 4 in which said curing and leaching steps are achieved in a substantially simultaneous manner.

11. A method as set forth in claim 10 in which said curing and leaching steps are achieved using hot water at a temperature in excess of 150°F.

12. A method as set forth in claim 1 in which said curing and leaching steps are achieved substantially simultaneously by immersing the rubber matrix material containing the sized particles of hydrated magnesium sulfate in a tank of water which is controlled to temperature ranging between 150° and 212°F.

13. A method as set forth in claim 12 wherein said forming step comprises the further steps of rinsing the microporous rubber material with tap water at room ambient temperature and drying the cured, leached, and rinsed material in an oven at a temperature ranging between 300° and 350°F.

14. A method as set forth in claim 7 in which said preparation steps of grinding and sizing said hydrated magnesium sulfate comprises grinding and sizing said hydrated magnesium sulfate to provide particles of roughly 100 mesh size.

15. A method as set forth in claim 14 in which said sizing step comprises employing at least one mechanical screen to achieve said sizing and in which said admixing step comprises admixing said sized particles so that they comprise generally of the order of 60% of the void volume of the microporous material formed by said forming step.