US3523818A - Recording instrument resinous film - Google Patents

Description

Aug. l1', 1970 J. BLUMENTHAL RECORDING INSTRUMENT RESINOUS FILM Filed Dec. 11, 1967 www mv www INVENTOR. JOHN BLUMENTHAL ATTORNEYS United States Patent O 3,523,818 RECORDING INSTRUMENT RESINOUS FILM John Blumenthal, Wickliffe, Ohio, assignor to Clevite Corporation, a corporation of Ohio Filed Dec. 11, 1967, Ser. No. 689,526 Int. Cl. B44d 5/02; C08b 21 /08 U.S. Cl. 117-138.8 12 Claims ABSTRACT OF THE DISCLOSURE A method of making a matte-finished film comprising This invention relates, as indicated, to a matte-finished liquid receptive surface on a resinous film, such as a polystyrene film, which is improved particularly in respect of its abrasive character, and in more specific embodiments of the invention, a combined lubricated and abrasive matte-finished liquid-receptive surface on such a resinous film.

This invention also relates to a process for producing such surfaces on resinous films of improved ink receptivity as well as impro-ved surface characteristics for operation particularly with balanced hydrostatic inking systems.

Matte-finished ink-receptive resinous films are known. A typical example of such lms, and the method of producing the same, is disclosed in Pat. No. 3,311,497.

Poly (alkenyl-aromatic) resinous films may be well adapted for use with a balanced hydrostatic inking system, such as that taught in Re. Pat. No. 25,692. Such hydrostatic inking systems have numerous advantages. For example, such inking systems supply ink to the pen independently of gravitational forces whereby the device will operate in any position and will operate under severe acceleration forcesA Moreover, the device employing such a recording system is substantially independent of temperature and altitude effects. Still further, pen recorder devices of the type described in Pat. Re. 25,692 do not throw ink when the pen is moving at high speed. When the proper type of ink is employed, the ink will not dry and clog the pen. In these systems, ink is positively delivered to the tip of the pen independently of capillary forces and virtually independently of centrifugal forces on the pen tip whereby the quantiy of ink delivered to the pen tip is in effect metered in accordance with the amount of ink deposited on the moving record medium. Inks which will dry rapidly are known and have been used but pose a problem because of clogging of the pen point. Consequently, it has been found desirable to utilize in such hydrostatic inking systems a relatively nondrying ink in co-operation with an absorbent surface such as provided by a matte-finished ink-receptive resinous film of the type above described.

Such a system is itself not without problems, and it is to the improvement of such systems that the present invention is primarily directed.

The relatively nondrying inks which are used are of the ball-point pen type. This ink is quite similar to ballpoint pen ink in that it comprises a dye dissolved in glycol, three being about 50` percent dye which means that a modest amount of the ink will last a very long time in comparison to the substantially non-viscous liquid inks in comparison to the substantially nonviscous liquid inks ice which are fed by capillary attraction through a pen. These inks have recently undergone some improvement for entirely different purposes which improse a limitation on hydrostatic recording inking systems. The dyes tend to be fugitive and the demands of legal and banking institutions have forced `modification of ball-point pen inks to overcome this problem. This is believed to have been done by the inclusion of very finely divided absorptive pigments, such as carbon black, -which renders the ink more abrasive than heretofore which results in pen tip wear.

When such improved ball-point pen type inks are sought to be used in hydrostatic inking systems utilizing a resinous recording medium such as polystyrene film, an unusual phenomenon is observed. The combined effect of ink moving radially outwardly from an arc of the tubular tip of approximately 270 degrees and the motion of the medium upon which the trace is recorded causes a peculiar type of wear resulting in the formation of a minute heel on the inking pen tip. This wear and formation of the heel is occasioned by the abrasive nature of the compositions of currently available nondrying inks. It has been found, for example, that in a normal test run for a period as short as ten minutes, such a step or heel can be formed on the bottom surface of the tubular pen tip. This small heel is enough to destroy the necessary seal between the tubular tip of the pen and the recording medium. Ink flows laterally under the hydrostatic pressure, and instead of a quick-drying trace on a polystyrene matte-finished recording surface, such as described in the aforesaid U.S. Pat. No. 3,311,497, excessive amount of ink under pressure is supplied, feathering occurs, and the trace is readily smeared on handling.

This problem can be obviated, it has been found, by depositing simultaneously with the formation of the matte finish, an abrasive pigmentary material in a predetermined distribution density upon the matte-finished surface of the resinous film. This is accomplished by the relatively simple means of dispersing in the solvent-diluent swelling system a very finely divided pigmentary material such as a refractory metal oxide, carbide or nitride. The distribution density of these particles adhered on the ink-receptive surface of the film and which in the preferred cases are less than micron size, provides an amount sufficient to yield a surface abrasive to a metallic pen tip and is preferably within the range of from 10 108 to 5 101o particles per square inch of matte- .'finished chart medium.

It has also been found that improved results can be secured by an improved matte-finishing composition 0f the type hereinafter more particularly described and method of forming the matte surface on a resinous film.

Another problem which has been encountered with systems embodying the matte-finished resinous film and balanced hydrostatic inking system is that which is known as slip-stick action. Such a condition results when the pen tends to chatter on the surface, and the seal between the tubular inking tip and the resinous film recording medium is broken. Such slip-stick action can be substantially eliminated by the inclusion in the matte-finishing composition of a small amount of an organic lubricant, such as stearic acid, castor oil, paraffin wax, or the like.

Thus, in the most preferred embodiments of this invention, there are provided at once on the improved resinous recording media of the present invention, abrasive means to impart a controlled amount of wear on the tubular tip of the inking pen suffiicent to prevent formation of a heel or remove any heel that has previously formed, but not so much as to wear away the tip at an excessive rate, and lubricating means to prevent slip-stick action in recording, a rather paradoxical combination of effects. Various aspects of this invention may be better 3 understood by having reference to the annexed drawings wherein:

FIG. 1 is a schematic diagram showing the mechanical and electrical components of a balanced hydrostatic writing system.

FIG. 2 is a greatly enlarged sectional view showing the tubular tip of the pen on the recording medium.

FIG. 3 is a still more greatly enlarged plan view of the tip of a tubular pen showing the area of wear.

FIG. 4 is a fragmentary side view of the tip shown in FIG. 3 showing the heel caused by the combined effects of a moving recording medium and flow of a pigment-containing ink.

The terms matte-finished, etched, open-pored and open-celled are used herein to denominate the surface resulting when a stressed resinous film is treated with a solvent-diluent containing swelling agent and dried.

Briefly stated, then, the present invention is in an etched or matte-finished resinous film having adhered to the surface thereof particles of an abrasive material preferably in a distribution density of from l l08 to 5 101 particles per square inch, said particles having a particle size less than about one micron and said particles preferably, although not essentially, being white in color. Still further, this invention provides an improved surface treating solution or dispersion characterized by the presence therein of:

(a) A relatively low-boiling or volatile solvent for the resinous film;

(b) A diluent or nonsolvent for the resinous lm having a relatively lower evaporation rate with respect to butyl acetate than the solvent;

(c) From about one to about live percent by weight of an ester of cellulose which is readily wet by the ink, such as cellulose acetate, cellulose nitrate, cellulose acetate-butyrate, cellulose nitrate-acetate, cellulose acetatepropionate, etc.;

(d) A polymeric acrylic ester resin, such as polymethyl methacrylate, polymethyl ethacrylate, etc., the ratio of the cellulose ester to the acrylic ester being in the range of from 1:1 t0 4:1, respectively, to improve hardness of the matte surface and physical strength under the pen tip as well as adhesion of the cellulosic resin to the resinous substrate; and

(e) From about 0.05 to about 0.1 percent by weight of the entire composition of particulate refractory metal oxide, carbide or nitride, the particle size being less than about one micron.

The foregoing composition may also include about 0.05 to about .5 percent `by Weight of the entire composition of an organic lubricant material such as stearic acid, parain wax, caster oil, or the like.

|Referring now more particularly to the annexed drawings, there is shown in FIG. 1 and oscillographic pen recorder system comprised of one or more inking pens 10 each having a tubular tip 11 formed of strainless steel or the like, with the tip 11 forming a seal with the record tmedium 12 which is plastic, as has previously been discussed.

The record member 12 is driven past the tip 11 of the pen 10 by a motor 15, and a microswitch 16 is positioned under the recording medium 12 where it is engaged and held closed by the medium. When the supply of recording medium is exhausted, switch 16 opens and releases the pressure on the ink-feed system, as Will be explained in connection with the electrical circuit.

The pen 10 is actuated by a pen motor 18 which receives its electrical signal from a source 19, as is known to the art. Ink is supplied from a manifold 20 through flexible tube 21, and is supplied to the manifold 20 through flexible tube 22. In the tube 22 there is a solenoid operated shut-olf valve 25 which normally is closed. The ink supply is contained in a can 26 which has a check valve and pressure regulator 27 at its lower end, the can 26 being connected to the shut-olf valve 25 by the tube 22. The ink within the can 26 is maintained under pressure by gas therein, or the pressure may be established of maintained by a pump or by a spring-loaded piston. If a gas-pressurized can is used the ink should be in the bottom thereof, or the can should have an internal diaphragm separating the gas from the ink so that it will feed all of the ink out of the can independently of the position of the can. In certain other embodiments of hydrostatically operated Systems, pressure on the ink is varied in accordance with chart and/or writing speed.

The electrical circuit `for the system includes a power supply 30, a circuit 31 to the motor 15 for driving the paper 12, a circuit 32 to the microswitch 16 and a circuit 33` to the solenoid actuated shut-olf valve 25. An operator-actuated switch 35 is located in the circuit so that when it is closed and the microswitch 16 is closed, the valve 25 is energized and opens to apply pressure from container 26 through the system to the pen tip 11, and the paper-advancing motor 15 starts. When switch 35 is opened, the motor stops and valve 25 closes, shutting off the pressure from the supply 26. When this happens, pressure in the manifold 20 and in the tube 21 and pen 10 drops to a modest value. -Due to the location of the microswitch 16, if the supply of record medium becomes eX hausted, the circuit opens stopping motor 1S and closing the valve 25.

It will be seen that the modification of the system which has been described provides a balanced hydrostatic inkwritng system for writing on a moving record medium 12. The system includes a pen which has a tubular tip 11 whose entire periphery, as shown in FIG. 2, is effectively sealed against the surface of the record medium. The system also includes the motor 15 as a drive means for driving the record medium and the pen motor '18 is provided as a means for moving the pin tip across the record rnedium during a recording operation. A supply of ink within the can 26 is provided, and it is connected to the pen by means of regulator 27, tube 22, valve 25, tube 22, manifold 20, and tube 21. The can 26 is included in a pressure means for applying pressure to the ink during a writing operation to force the ink through the pen tip and against the record medium. A bias means 28 is provided for biasing the tip of the pen against the record medium with sufficient force that the ink pressure is insuliicient to break the effective `seal at the pen tip.

In FIG. 3 is a plan view of the surface of the-tip 1-1 which is in contact with the record medium. The crosshatched area indicated by the numeral 40 is slightly recessed due to wear caused by abrasive pigment particles contained within the ink. The ink moves olf the trailing edge 41 and out the lateral portions 42 and 43\ by the normal swinging action of the pen in combination with the movement of the record medium. 'Ihe remaining area 43 is a heel because the surface of the polymeric or resinous record medium in the normal case causes no wear on this portion of the tip. The curved edges 44 and 45 of the heel are due to the radius arm of the pen. FIIG. 4 shows the worn areas 42 and 41 in the tip 11. The shoulder 44 displaces the trailing edge of the pen slightly from the surface and impairs the seal which must be maintained between the pen and the recording medium -for most satisfactory reproduction.

With the improved recording medium of the present invention, even defective tubular tips 11, the defect in which is such a heel 43, is actually lapped by the recording medium and after a period of use is a better tubular tip than was originally applied to the record medium. The wear is now even and the entire face of the tubular tip 11 lies within a single plane, or sufficiently so to maintain the desired seal.

The record media of the present invention are swellable solid poly (alkenyl-aromatics), such as polystyrene, lm having a thickness of from 70.5 to l0 mils, and preferably from 0.5 to 2 mils. It is desirable for best results that the poly (alkenyl-benzene) film be oriented in at least one direction, and preferably biaxially oriented. The pro cedure for orientation of such poly (alkenylbenzene) films is well known, and conventional procedures and apparatus are utilized for such purposes. lIn general, the poly (alkenyl-benzene) is extruded through an annular orifice at substantial wall thicknesses, for example onesixteenth inch, and while still in the soft or plastic condition, the tubular extrudate is drawn in an axial direction by a drawing device so as to elongate the tube and cause a reduction in the wall thickness. This accomplishes orientation in an axial direction. Simultaneously, aitpressure may be applied to the interior of the tube in the process of being drawn so as to expand the diameter thereof quite substantially to effect a transaxial orientation of the polymer and effect still further reduction in the thickness of the wall. This is an example of biaxial orientation. It appears that the higher the degree of orientation of the poly (alkenyl-aromatic), the finer and more suitable is the :resulting matte finish when the film is treated in accordance herewith. Specific examples of poly (alkenyl-aromatic) compounds include the thermoplastic homopolymers and copolymers of styrene, alpha-methyl styrene, alkyl substituted styrene such as vinyl toluene, and di-vinyl benzene, and the several monoand di-chloro styrenes and the like may be used in accordance herewith.

Thin films, formed in the foregoing manner and slit along an element of the resulting tube to form a flat sheet, are clear, transparent and have a glossy surface. The preferred material for use in accordance herewith is biaxially oriented polystyrene film 1.5 to 2 mils thick. Such a preferred material exerts a pull in either direction (along which the film is oriented) of at least about 250 lbs. per square inch as measured by the ASTM D-l504 tensile test.

It has been found that the clear poly (alkenyl-benzene) film may be treated with a variety of solvent-diluent compositions to create a matte surface layer lwhich is white and opaque in appearance and capable of being marked with a variety of inks. A number of such solvent-diluent compositions is disclosed in the aforementioned Pat. No. 3,311,497. Best results are secured, however, with rather specific solvent-diluent compositions which tend to yield very much finer porous or open-celled laye-r on the surface to produce the matte finish. iin general, these systems are characterized by the presence therein of a ketone and a (l1-C3 alcohol. The ketone is a solvent for the poly (alkylene-benzene), and the alcohol is a diluent which is somewhat slower evaporating than the ketone. Considering the evaporation rate of butyl acetate as l, the e'vaporation rate of methyl ethyl ketone relative thereto is about 4.6 and that of iso-propyl alcohol is 1.7 and their respective boiling points are about 1 C. apart.

A basic constituent in our treating compositions is a solvent-diluent blend including a solvent for the poly (alkylene-benzene) and a diluent for the active solvent which is a nonsolvent for the poly (alkylene-benzene). The rblend consists, firstly, of at least one solvent that exhibits someactivity toward the poly (alkylene-benzene) film, e.g., polystyrene film, and secondly, at least one diluent that is less -volatile than the former and does not attack or soften the film. These requirements are satisfied, for example, by a mixture of methyl ethyl ketone and isopropyl alcohol respectively, which is the solvent-diluent combination we prefer to use.

The ratio of the more volatile active solvent to the less volatile diluent must Ibe so adjusted, that the resultant blend exhibits at least a slight activeness toward the film When it is applied thereto. In the case of the methyl ethyl ketone, isopropyl alcohol mixture, the threshold of activeness occurs at a ratio of about 1:1 by volurne.

With other solvent-diluent combinations, Very different ratios will satisfy this criterion. For example, the threshold of activeness is obtained at a ratio of about 8:1 by volume with acetone and methyl alcohol respectively.

When solvent-diluent mixtures that satisfy the stated criteria are metered onto an oriented poly (alkylenebenzene) film and then removed by evaporation, the surface layer of the film undergoes a transformation characterized by the formation of a porous open-celled structure. The mechanism causing the transformation is believed to be as follows:

(1) The essentially active solvent-diluent mixture in contact with the stressed film, and in conjunction with said stresses, produces a network of minute fissures, probably by a process akin to crazing.

(2) As evaporation commences, the more Volatile active solvent leaves the film at a greater rate than does the less volatile diluent, and a point is reached Where the mixture loses its solvent action with respect to the poly (alkylene-'benzene). At this stage the solvent mixture serves to prevent the porous and softened poly (alkylene-benzene) layer from collapsing and fusing into a nonporous film.

(3) At most, only minute traces of active solvent are retained in the plastic in the final stages of evaporation, and the porous structure becomes strong enough to remain as the end product.

Yet another consideration enters into the choice of active solvents, namely that of solvent release. In general, solvents for which the plastic has great tolerance will be released very slowly by the plastic. This prolongs the period in which the plastic is plasticized and tacky. Thus, in order to still obtain a final porous structure, it becomes necessary to use a significantly slower evaporating diluent, or a much higher percentage of diluent, or both.

When using solvents to which poly (alkylene-benzene) has extreme tolerance with the attending slow release, e.g. aromatic hydrocarbons and halogenated aliphatic hydrocarbons, the resultant porous layer formed by the treatment will have a icoarser structure, and will persist to a greater depth. Examples of such solvents are: toluene, xylene, and 1,1,1-trichloroethane.

Conversely, treating mixtures based on solvents for which the poly (alkylene-benzene) has a low tolerance such as the aliphatic carbonyl compounds containing 3 to 6 carbon atoms require less diluent, less differential volatility, or both. They also typically give shallower porous layers with finer structures. Examples of such solvents are acetone, methyl ethyl ketone, and ethyl acetate, in ascending order with respect to coarseness of the pores they produce.

Suitable combinations of solvents and diluents are set forth below:

7 EXAMPLE 7 Parts by vol. Methyl ethyl ketone 4 Isopropyl alcohol 4 Methyl isobutyl ketone 1 Many other combinations of solvents and diluents may be used with some success although the foregoing combinations represent the best examples. The solvents, or ketones, and aromatic solvents are selected on the basis that in any solvent-diluent combination, one ingredient must be able to swell or dissolve the poly (alkylene-benzene) while the other, the diluent, must not attack the plastic and possess a slower evaporation rate than the former.

In general, the depth of the porous layer formed ranges from 0.1 to 0.5 mil. No better way other than ink reception is known for measuring the fineness of the discontinuity which results upon treating the surface of a poly (alkylene-benzene) film with the solvent-diluent mixtures of this invention. Actual application of ink from a hydrostatically balanced inking system is the best test. Observation is made with respect to the tendency to smear or not to smear immediately after application by rubbing ones nger over the inked surface. In such tests, a ball-point pen type ink is used.

The matte should, when treated under normal atmospheric conditions in accordance herewith, be of fine, uniform, porous structure. If heat is used in the drying step, the etch is less deep but the etched layer on the substrate appears, in general, to be better adhered thereto. yIn general, the drying air temperature for best results is in the range of 82 F. to 88 F., or slightly above ambient air temperature. As the drying zone or tunnel becomes cooler, adhesion tends to fall off and the etch is less deep. There is a maximum in the etch depth-drying temperature curve. By controlling the temperature during the entire cycle of the etching process and supplying heat to the system to offset the heat loss due to evaporation the ineness of the matte, its depth, and its adhesion to the substrate may be optimized. Optimum conditions for any given installation must be arrived at by trial-anderror methods within the framework of the foregoing.

The solvent-diluent system is preferably utilized at room temperature, i.e. about C. Generally the higher the solvent-diluent temperature, the deeper the etch. The poly (alkylene-benzenes) are poor solvent releasers and tend to stay tacky. The diluent tends to keep the soft mass separated so that it cannot collapse again into a smooth clear film. The effect of the orientation is to serve as a mechanical force to cause disturbance of the surface upon swelling and aid in the release of solvent through the provision of cracks or fissures and voids through which the solvent can escape.

The solvent-diluent mixtures of the present invention are also characterized by the presence therein of resin solids to the extent of about 2 to` 4 percent by weight. In the preferred instances, a plurality of resins is used. For most purposes, a mixture of two resinous materials is found to be most satisfactory.

Resins are chosen on the basis of wettability by glycolbased dye inks, and are included in the mix to enhance the ink receptivity of the nal product.

Glycol inks are extremely slow drying by evaporation, and resistance to smearing usually depends on absorption by the medium upon which they are used. Much higher absorption rates can be built into the porous poly alkylene-benzene) layer if the solvent-diluent mixture chosen for the treatment also acts as a poor solvent for the particular resin dissolved therein, so that the resin itself fails to form a continuous lm when dried. Thus, the treating composition becomes in itself a blush lacquer. Most cellulosics are satisfactory for this purpose. Cellulose acetate butyrate is preferred.

When such a mixture of solvents and resin is metered onto oriented poly (alkylene-benzene) lm and the solvents then caused to evaporate, the resin addition nally assumes an extremely iine porous form which is superimposed upon and mingled with the relatively coarser spongy structure that formed more or less concurrently as a result of the action of the solvent mixture on the lm. By these means it is possible to attain ink absorption speeds that are competitive to the more effective coated papers that have found use as chart media with the aforesaid balanced hydrostatic inking system.

The blush coat formed by the cellulose acetate butyrate is, by itself, physically weak, and does not bond well to the poly (alkylene-benzene) substrate. In a practical treating composition these defects are largely overcome by adding a quantity of a second resin. The latter performs an adhesive function, and tends to toughen the final product.

The second resin is an acrylic-type resin which is used to improve the adhesion and cohesion of the system. It is not affected by the ink. The ratio of the ink receptivity improving resin to the cement-type resin is in the range from about 1:1 to 4:1 by weight. These proportions may be varied to obtain the drying and adhesion desired with a particular ink.

An indicated above, slip-stick action may be prevented by the inclusion in the solvent-diluent systems of the present invention of a lubricant material. The amount of such lubricant material should be in the range of from 0.05 percent to about .5 percent by weight of treating mixture. Generally, 0.2 percent by Weight is sufficient. Specic examples of materials which may be used as lubricants include stearic acid, oleic acid, ricinolcic acid, castor oil, paraffin wax, mineral oil, etc. Excessive amounts of the lubricant adversely affect the ink and its dryability. If too little of the lubricant is included, there is no effect on the undesirable property of slip-stick action. Where slip-stick action is not a burdensome problem, this ingredient can be omitted from the composition.

Also, as indicated above, the solvent-diluent systems of the present invention include, as an essential ingredient, a fine abrasive material. The amount of such abrasive material ranges from about 0.005 to about 0.1 percent by weight, and generally 0.015 percent by weight will be found to be satisfactory. This provides a distribution concentration on the polystyrene or poly (alkylene-benzene) yfilm of abrasive material Within the range of 1 108 to 5 X 1010 particles per square inch of matte-finished surface for satisfactory control of heel formation Without undue tip Wear. Suitable materials include the refractory metal oxides, carbides and nitrides, such as titanium dioxide, silicon dioxide, zirconium oxide, aluminum oxide, beryllium dioxide, silicon carbide, etc. These materials are generally hard pigmentary materials and have, desirably, an individual particle size of 1 micron or less and preferably 1A micron or less. In some cases, pigment particle agglomeration may occur without observable adverse effect on the achievement of the desired abrasive effect.

When the foregoing ingredients are mixed together, there results a somewhat cloudy solution, and the abrasive material has a tendency to settle on standing. However, provision of agitation means for containers of the treating material will be found sufficient to maintain the abrasive material in suspension. Ordinarily, the agitation provided simply by pumping the iluid in a circulatory manner from a reservoir into the dip trough on the coating machine will provide sufficient agitation to maintain the abrasive material in suspension.

As indicated above, the suspension is applied to the poly (alkylene-benzene) lm by means of a supply roller dipping into a supply vessel and then contacting the surface of the film passing, thereover. The thickness of the applied coating of solvent-diluent composition is metered by means of a Mayer rod Wound with 8-mi1 to 25-mil wire. Ordinarily, a #14 to a #16 Mayer rod is used. Thus, in production, an excess is applied to the lm and within a minimum amount of time after application to the film, it is metered by passing over the Mayer rod. Ordinarily, the time lapse is preferably less than .5 second and generally less than 0.1 second after application. lf the contact time with an excess of the solvent-diluent mixture is too long, the surface tends to become corrugated. Thereafter, the film passes over rollers to allow a contact time of the metered solvent-diluent film with the poly (alkylene-aromatic) film for a period of from l to 20 seconds. Thereafter, the surface is contacted with a jet of air which may be at ambient temperature or at a temperature of up to about 150 F. to compensate for the cooling effect of the solvent on evaporation. Infrared radiationmay be utilized to improve the solvent-diluent release from the surface of the film. The structure of the matte finish is substantially set in the first few seconds.

EXAMPLE 8 The following is a typical procedure for producing an ink-receptive surface on oriented polystyrene film, consistent with the requirements in a hydrostatically balanced inking system:

g. cellulose acetate butyrate 18 g. poly (methyl methacrylate) 980 ml. methyl ethyl ketone 800 ml. isopropyl alcohol (anhydrous) 100 ml. methyl isobutyl ketone 3.8 g. stearic acid The resins are dissolved separately in methyl ethyl ketone. The solutions are then combined and the remaining solvents are subsequently added. The titanium dioxide and stearic acid are dispersed in a smaller quantity of the mixture and finally stirred into the master batch. The treating mixture is metered onto oriented polystyrene film with a v#14 Mayer rod and dried in an air current at near room temperature.

The back side of the film is also treated to render it porous. This is done to further opacify the film, and also to give it greater compliance to the pen tip for improved sealing.

In the solvent-diluent mixture used in the back side treatment there is again dissolved a resin, this time to impart wettability by a subsequently applied anti-static coating, which typically consists of a polyelectrolyte in an alcohol, water solution.

The following is a practical back side treating recipe:

500 ml. methyl ethyl ketone 350 ml. isopropyl alcohol 30 g. cellulose acetate butyrate (alcohol soluble butyrate) The treating mixture is metered onto the back side of the film with a #24 Mayer rod, and dried in an air stream at near room temperature.

To the surface resulting from the above treatment a coating is applied that will provide some electrical conductivity -for the prevention' of charge accumulation through triboelectrification. The following is an antistatic coating composition which is preferred.

15 ml. Calgon conductive polymer 261 (60% polymer in H2O) 15 ml. methanol 270 ml. ethyl alcohol The mixture is metered onto the pretreated film with a smooth rod on a Mayer rod coater.

In an alternate method the anti-static agent is included directly in the treating mixture, i.e. in the composition used to create the porosity. With this procedure, the choice of anti-static agent is limited to those that are soluble in the solvents used in the treating composition. The anti-static agent used in this manner should be free of water since the presence of even small amounts of water in the mix can prevent the formation of the porous layer. The following recipe has been employed with success:

30 g. cellulose acetate butyrate 23 g. quaternary ammonium derived antistat 500 ml. methyl ethyl ketone 350 ml. isopropyl alcohol The treating mixture is metered onto the back side of the oriented polystyrene film with a #24 Mayer rod, and dried in an air stream at near room temperature.

Drying of the film is carried out over a period of from 1 to 5 minutes utilizing ambient air or irradiation or a combination of both to improve the drying and the setting of the matte surface. After completion of the drying, the material is rolled up on a product roll and is ready for use. sequentially with the completion of the drying operation, there may be applied a printed grid by conventional printing means directly to the surface of the matte-finished poly (alkylene-benzene) film. With the grid applied, the product is now ready for use in recording instruments. This product, it is found, has an exceptionally good ink receptivity, and the ink dries to touch almost immediately upon applicaiton and independently of the speed with which the pen travels relative to the recording medium. No slip-stick effect is noted, and the dilfculty encountered with the abrasive ball-point pen type inks is completely obviated by the use of a coating composition of the solvent-diluent type which applies a very thin layer of abrasive pigmentary material to the surface of the polystyrene or poly (alkylene-benzene) film. The resinous ingredients coact not only to cement the matte surface to the plastic substrate, but also coact in the matte surface to improve the adhesion of the particulate material thereto to provide the desired abrasive surface on the plastic recording medium film. Also they act in the final product to improve ink receptivity. The formation of the heel on the pen tip entirely disappears when recording media produced in accordance with the present invention are employed. As a matter of fact, tubular inkapplying tips which have become roughened by use with abrasive inks against plastic surfaces not treated in accordance with the present invention may be reconditioned by running them for a relatively short period of time in contact with recording media surfaces produced in accordance herewith.

The invention has been described above in a preferred embodiment. Modifications of this preferred embodiment may, of course, be made to impart still further advantages to the recording media of the present invention. For example, instead of treating a single surface of the poly (alkylene-benzene) film as above illustrated, both sides may be so treated to provide a whiter recording medium. Also, the handling of such films frequently induces static charges of electricity which are often undesirable and render the recording medium diiiicult to handle.

Under certain circumstances it has been found desirable to treat the recording media of the present invention with an antistatic composition to improve the handling characteristics of the recording medium and the behavior of the ink on the matte surface. As has been indicated above, the surface which results upon treatment of the poly (alkenyl-benzene) film with the swelling agents above-described results in the provision of a matte surface containing very tine pores or pits remarkably uniformly distributed over the surface. These pits or pores may also be used as reservoirs to retain an antistatic agent usually applied in the presence of a resinous material which will adhere to such a surface.

Alternative procedures are available for conferring such antistatic properties upon the recording media of this invention. A preferred treatment involves a preliminary treatment with a matte surface forming composition which is the same as or similar to one of the solvent-diluent compositions above referred to, for example those given in Examples l through 7, and those given in Example 8. While it is not necessary to have the resin components in swelling agents used for surface treatment of the reverse side which is to be subsequently given an antistatic treatment, such compositions may, of course, be used. Preferably, the procedure is to rst produce a matte surface on the reverse side of the recording medium from that which is intended to be the ink-receptive surface. This has a dual purpose. The matte surface is somewhat spongy and provides a resiliency in the recording medium film which improves the ride of the recording pen tip. Secondly, it provides interstices or pores which become reservoirs for the antistatic agent.

The second step is to retreat the reverse side with an antistatic composition which is preferablyan aqueous a1- coholic solution of a polymeric antistatic agent such as a quaternary ammonium compound, or with an alkali metal salt of a sulfonated poly (alkylene-henzene), e.g. sodium salt of sulphonated polystyrene (see U.S. Pat. No. 3,027,- 275). Those compositions which are aqueous solutions and contain methanol will not of themselves cause any swelling or matte formation on the surface of polystyrene.

An alternative procedure is to include the antistatic agent with the swelling composition as in the aforementioned Pat. No. 3,027,275 It has been found that the water which normally accompanies certain of these antistatic agents is intolerable in the solvent-diluent system and ad versely alects the results which are obtained, even to the point of no etch being obtained.

Thus, there has been provided an improved matte-tinished ink-receptive poly (alkenyl-benzene) recording ilm for use with hydrostatic or pressurized recording devices where the ink is supplied to the recording surface under a positive pressure.

What is claimed is:

1. The method of making a matte-finished poly (alkenyl-benzene) recording medium lm receptive to an ink containing abrasive particles which comprises the steps of:

(a) metering onto at least one surface of an oriented poly (alkenyl-benzene) film a solvent-diluent composition comprising:

(1) a low boiling solvent for the poly (alkenylbenzene) lm;

(2) a diluent, non-solvent for said film having a lower evaporation rate than said solvent; the ratio of solvent and diluent being suilicient to attack the film when applied thereto;

(3) from about 1% to 5% by weight of the entire solventdiluentcomposition of an ester of cellulose;

(4) a polymeric acrylic ester resin; the ratio of cellulose ester to acrylic ester being in the range of from 4:1 to 1:1, respectively;

(5) from about 0.05 to about 0.1% by weight of the entire solvent-diluent composition of particulate abrasive material, the particle size being less than about 1 micron;

(b) allowing the solvent-diluent composition to remain in contact with said lm for from 1 to 20 seconds at room temperature; and

(c) drying the lm by moving air at a temperature of from room temperature up to 150 F. whereby the surface is given a matte inish receptive to ink and particles of said particulate abrasive material are adhered to said surface.

2. The method of claim 1 wherein the composition metered onto said surface also includes from 0.05% to 0.5 of an organic lubricant material.

3. A composition for producing a matte linish on an oriented poly (alkenyl-benzene) lm comprising:

(a) a low boiling solvent for a poly (alkenyl-benzene) film;

(b) a diluent, nonsolvent for said lm having a lower evaporation rate than said solvent; the ratio of solvent and diluent being suicient to attack the lm when applied thereto;

(c) from about 1% to 5% by weight of the entire solvent-diluent composition of an ester of cellulose;

(d) a polymeric acrylic ester resin; the ratio of cellulose ester to acrylic ester being in the range of from 4:1 to 1:1, respectively;

(e) from about 0.05 to about 0.1% by weight of the entire solvent-diluent composition of particulate abrasive material, the particle size being less than about 1 micron.

4. A composition in accordance with claim 3 also including from 0.05 to 0.5% of an organic lubricant material.

5. A composition in accordance with claim 3 wherein the abrasive material is a refractory metal oxide.

6. A composition in accordance with claim 3 wherein the low boiling solvent is a C3 to C5 aliphatic ketone.

7. A composition in accordance with claim 6 wherein the solvent is methyl ethyl ketone.

8. A composition in accordance with claim 3 wherein the diluent is a C1 to C3 monohydric alcohol.

9. A composition in accordance with claim 3 wherein the cellulose ester is cellulose acetate-butyrate.

10. A composition in accordance with claim 3 wherein the acrylic ester is poly (methyl methacrylate).

11. A composition in accordance with claim 3 wherein the abrasive material is titanium dioxide.

12. A composition in accordance with claim 11 wherein the solvent is lmethyl ethyl ketone; the diluent is isopropyl alcohol; the cellulose ester is cellulose acetatebutyrate; and the acrylic resin is poly (methyl methacrylate).

References Cited UNITED STATES PATENTS 2,536,657 1/1951 Reese.

2,617,748 11/1952 Bjorksten et al. 260-17 2,702,255 2/ 1955 Yaeger 260--17 2,964,423 12/1960 Van Stappen.

3,027,275 3/ 1962 Park.

3,115,420 12/1963 Centa et al.

3,311,497 3/ 1967 Park.

WILLIAM D. MARTIN, Primary Examiner I. E. MILLER, J R., Assistant Examiner U.S. Cl. X.R.

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