US3075260A - Stereotype mat - Google Patents

Description

Jan. 29, 1963 F. J. s'rANczAK ETAL STEREOTYPE MAT 2 Sheets-Sheet 1 Filed May 9, 1955 Jan. 29, 1963 F. J. sTANczAK ETAL 3,075,260

STEREOTYPE MAT Filed May 9, 1955 2 Sheets-Sheet 2 United States Patent O 3,075,260 STEREOTYPE MAT Frank J. Stanczak, Easton, Pa., and Richard A. Wolterding, Neenah, Wis., assignors, by mesne assignments, to Kimberly-Clark Corporation, a corporation of Delaware Filed May 9, 1955, Ser. No. 507,113 10 Claims. (Cl. 22-55) The present invention relates generally to stereotype mats and is particularly concerned with an improved cornposite stereotype mat and backing and with certain methods for manufacturing such products. This application is a continuation-in-part of our copending application Serial No. 349,352, filed April 17, 1953, now Patent 2,936,797, issued May 17, 1960.

In the usual process for making a stereotype mat, a paperboard mat or flong, as it is sometimes called, is laid, over a lockup containing the type, engravings, and other printing elements which are to be reproduced in the stereotype plate. then subjected to heavy pressure, suicient to press the mat into the face of the lockup and provide a reproduction of the printing elements in the face of the mat. During the pressing operation, a molding combination of cork, felt, or other suitable materials is positioned intermediate the mat and the pressure element.

Following the pressing operation, the mat may be dried by a process which includes placing the imprintedv mat in a curved former and dryer, sometimes termed the scorcher. This forming and drying operation achieves several desirable results. Since the actual printing plate is made by casting molten type metal against the curved mat as a matrix, it is necessary that the mat be completely dried prior to the casting operation and that it be sufficiently hard and rigid to resist the casting pressure. In addition, it is the current practice in various printing industries to shrink stereotype mats quite substantial amounts in order to reduce the size of the printed image and the amount of paper required in the printing operation. These two functions, i.e., the preparation of the mat for the casting operation and the controlled shrinkage of that mat are accomplished during the drying operation.

The usual dryer for forming the mat receives the mat against a curved, foraminous surface, which is connected to a source of reduced pressure in order that the moisture and other vapors liberated during the heating operation will be drawn off through the back of the mat. When using a high shrink mat, it is normally desirable for the drying to be done in two steps, in the first of which the mat is heated while still fiat to drive off some of the moisture and, in the second step, the mat is formed into a curved shape in the dryer mentioned above and is heated under vacuum conditions to drive olf the remaining moisture through the back of the mat. In this Way, the maximum shrinkage of the mat is achieved. In a low-shrink or a non-shrink mat the pre-drying step prior to placing the mat in the former is generally not required.

Since the forming and casting operations involve quite substantial pressures, it has been found necessary to provide some means for preventing buckling or yielding of the mat in the nonprinting areas, and particularly those areas which are of substantial dimensions. In practice, the most common means for packing or backing the mat consists in attaching thin strips of paper felt along the rear surface of the mat in those areas of the mat which have rather large nonprinting areas. This hand packing is usually done after the mat has been molded and, if a pre-drying step is used, between the first drying and the final drying against the curved former. Reinforcement of nonprinting areas too small to be packed with felt The lockup with the mat in position is` 3,075,260 Patented Jan. 29, 1963 strips is sometimes accomplished by running the point of a pencil on the back side of the mat in those areas to form nonplanar areas in the face of the mat which will resist buckling more eectively.

Packing operations of the type mentioned above constitute a very serious problem in the newspaper field. Mat packing is inherently time consuming and costly and, of even greater importance, it must be done shortly before press time, when every minute is vital. Many of the pages of the newspaper cannot be completed in the lock-` up until a few minutes before press time, either because it is desi-red to cover last minute developments or because of the time necessary to complete the stereoplates that make up portions of the pages. Consequently, when such pages are finally closed, and there may be many such pages in a large newspaper, it is necessary that the stereotype mat be promptly finished so that the plates for the presses can be cast and installed. At this point, the necessity heretofore for hand packing each of the mats has been a serious deterrent to prompt completion of such mats. The hand packing operation is time consuming and requires the services of skilled workmen who must use considerable judgment in selecting the areas to be packed and in applying the packing material properly, in

order to render the packing effective for its intended purpose. Consequently, this type of packing represents a very substantail proportion of the time and cost involved in producing stereotype plates. Pages must be closed an appreciable length of time in advance of the time set for operation of the press, and skilled workmen who might be otherwise engaged are required for the hand packing operation.

In the conventional process, the mat must be packed prior to the final forming and drying operation, and the presence of the packing strips on the back of the mat during this operation creates further serious problems in the production of satisfactory stereotype plates. Particularly when the packed stereotype mats are subjected to the heat in the former and dryer, the packing shrinks at a different rate and in a different amount than does the mat. In those areas where a large amount of packing has been applied, the unequal shrinkage and/or slippage between the mat and the packing due to the heat of the dryer may cause the strips to overlap printing areas or otherwise distort the mat. In addition, the packing strip with its adhesive layer does not permit free passage of moisture and other vapors, and incomplete drying and irregular shrinkage of the mat often occurs in heavily packed areas. These deficiencies in hand packed mats are particularly emphasized in color printing wherein registration of the several mats bearing the same imprint or reproduction is important. A slight variation in the manner of packing the several mats required for a single reproduction in color may seriously affect the registration of material reproduced from such mats.

There is, therefore, a very great existing need for an improved steretotype making procedure, and especially for an improved mat packing means which will not impede the free passage of moisture and other vapor through the back of the mat during drying and which will shrink substantially to the same degree as the mat. This material should also be flexible both before and after drying, since the mat is subjected to considerable bending during use and must remain flexible during the treatment in the former and dryer, as well as atthe time of the subsequent pressure yduring ltherolling and pressing of the mat, poor definition of the printing characters and a rough surface on the face of the printing Will result. The desirable mat backing material should also be adaptable for use in conventional `mat forming equipment and withV conventional technique.

The present invention Yhas for its principal 'object the provision of stereotype making procedures and materials capable of meetingthe above stated requirements. A more specific object of the invention is the provision of an improved, composite stereotype mat and backing which can be used without any need for subsequent packing of the non-printing areas, while maintaining the Vnormal vapor permeability necessary to the'nal forming of the mat. A further object is to provide such a composite mat wherein the shrinkage characteristics are compatible with existing stereotype mat products of the shrinkage type.

Another object of the invention is to provide a backing material suitable for use in conjunction with known stereotype mats, which is completely moldable and bo-ndable with the mat to resist the molding pressures, and so that it can resist the pressures encountered during the forming and drying operation so as to be properly set to provide a unitary mat element having adequate strength and rigidity to withstand the pressures produced during the casting operation. Y

Still another object of the invention is to provide a ethod for the production of a nished stereotype matrix, whichmethod is considerably faster in operation and more economicalV than the conventional process of hand packing-stereotype mats now in use.

The various features of the invention and the specific manner in which the objects of the invention are accom-V plished will be made apparent in the following description and the accompanying drawings of certain illustrative embodiments of the invention.

In the drawings:

FIGURE l is a view, in perspective of a portion of a lookup or other printing element illustrating one manner inwhich the mat, the backing, and the blanket are arranged in the practice of the invention;

FIGURE 2 is a View in perspective of a composite mat unit in accordance with the invention with theV backingV already attached;

FIGURE 3 is a fragmentary view in elevation of the assembly during pressing or molding of the mat about the printing form and is` illustrative ofone method which may be used;`

FIGURE 4 is an enlarged cross-section view of a portion of the backed mat after its removalV from the moldiris press; Y

FIGURE 5 is a fragmentary view of the backed mat during itsformation in the dryer; and

FIGURE 6 is aside elevational View of the backed mat in theform in .which it is received in a casting box.

Inl the practice of the present invention, a paperboard mat of the type newV commonly used is provided with a backing consistingiof a plurality of plies of creped, cellulosic tissues having dispersed therein a thermally rigidiablebinder, exemplified in the 'preferred embodiment of this invention by'various thermosetting resins. A material of this type has beenfound to be properly moldable iu'that it iscapa'ble ofV taking a permanent set in the printing areas of the mat, but still retains its resiliency so as to provide the` desired bulk inthe portions overlying the nonprinting areas of the mat. Further advantages stem from the fact that the backing material, after hardening of the binder, has a substantially increased tensile and,.of more importance,.a substantially increased compressivel strengtha desirable feature during the casting operation, but the mat is still quite iiexible so that it can conform to the' curved surface of the casting box. One of the more remarkable characteristics of the backing whenapplied to a conventional stereotype mat is the fact that the shrinkage ofthe combined mat and backing which fitakes place during scorching is very nearly the same as the unpacked mat itself.

The material which we employ for the backing has found extensive use in the manufacture of filters and for various other purposes. The material and its method of preparation are described in Catlin and Wollwage U.S. Patent No. 2,554,814, issued May 29, 1951. As described in that patent, the preferred material consists of a plurality of plies of thin, creped, cellulosic tissue having an air-dry basis weight before creping within the range from about 5 to 10 pounds per standard ream of 480 sheets, each 24 by 36 inches, and having a crepe ratio generally in the range Hfrom 2.0 to 3.0, and containing a bonding agent in stated amounts.

The bonding agents which we prefer to use are liquid phenol formaldehydes. Other thermosetting resins such as urea-formaldehyde resins, melamine-formaldehyde resins, and resorcinal-formaldehyde resins, low pressure resins of the unsaturated polyester type (eg. diallyl phthalate), and a mixture of such thermosetting resins may also be used. Y

It is important that the resins employed be curable at a fairly rapid rate. Most desirably, the resins should be curable at temperatures and times employed in conventional equipment for scorching stereotype mats. With the present invention the linal drying and forming takes about three minutes and cures the resin at aboutV 350 F. It will be apparent, however, that this temperature and time might be varied without any undue inconvenience or serious loss of time.

It is not essential that the resin impregnant be completely water soluble, as the resin can be introduced into the creped tissue sheets in solvents other than water or as a suspension of resin particles in water. In some instances, it is preferable to use a nonaqueous liquid vehicle, asthere is less danger of reducing the bulk of the creped tissue than in the case of an aqueous vehicle. However, it is important that the impregnant be rendered sufficiently tacky by Water to provide adequate adhesion between the several sheets and between the backing and the mat or flong. In this respect, it is believed that best results can be obtained with resins having a water tolerance or dilutability of from L() part of water to 1.0 part of resin to 1.0 part of resin to 7.0 parts of water, by weight, in accordance with the standard dilutability testsused in the art. Y

The resin content in the impregnated product may vary depending upon the physical properties desired and the resin used. In general, for our purpose the product should contain from about l5 percentrto 75 percent by Weight of resin, with 40 to 50 percent being a particularly satisfactory range. The percentage values mentioned are on the weight of the finished product on a volatile-free basis. After impregnation and drying, the volatile content Aof the impregnated multi-ply material preferably should Vnot exceed about 15 percent by weight, on a bone dry basis, as impregnatedwebs having higher volatile contents are hardl to handle Y and become sticky. A volatile content of from 5 to 9 percent appears to provide the Vbest results, although `volatile contents of substantially lesser percentages may be satisfactory in certain instances where the flexibility of the impregnated web is not'important and where an adhesive is to be used for joining; theweb to thefstereotype mat. content of the material is determined by heating a sample for 10 minutes at 160 C., and measuring the weight loss. 'Iltis loss, expressed as a percentage of the original weight, represents the volatile content.

Perhaps a more sensitive and more accurate test for deter-mining a proper condition for the resin in the multiply backing material after impregnation and drying, if a water soluble resin is employed, is with reference to the Water solubility of the resin. Expressed in this manner, it is preferable that the resin in the web after impregnation and drying be from 15 to 75 percent water soluble The volatile i'n distilled water at 25 C. A water solubility of about 35% appears to provide the best results, but a considerable lower solubility, or even no water solubility, may be satisfactory if exibility is not important and an adhesive is used for joining the web to the stereotype mat.

In a specific example, the backing was prepared by superposing twelve sheets of creped tissue made from chemical pulp, each individual sheet having a drier basis weight of 5.9 pounds per standard ream of 480 sheets, 24 by 36 inches, and a crepe ratio before impregnation of approximately 2.3. Thus the basis weight of the creped material was approximately 13.5 pounds per standard ream. The superposed sheets were impregnated by passage through a bath, aqueous or otherwise, containing the resinous bonding agent. The excess liquid was removed by passing the wet superposed sheets through felt covered squeeze rolls using only such pressure as would not change the structural characteristics of the multi-ply product or its individual plies. The impregnated sheets were then dried by a current of hot air at a temperature of about 245 F. to 325 F. The volatile content of the impregnated backing material at this stage was approximately ll percent by weight. Material prepared in this manner can be readily heat treatedto cure the resin dispersed throughout the plies of the material.

As normally practiced, the process of the present invention involves applying a relatively moist paperboard mat or llong of conventional type to the upper surface of a lockup containing the printing elements to be reproduced, while at the same time providing a multi-ply backing sheet of paper of the type described over the paperboard mat. This backing sheet may be integral with the mat or separate therefrom. Suliicient pressure is then applied to the assembly by conventional procedures, which may involve the use of a pressure pad or cushion, to produce a reproduction of the printing elements in the face of the mat. By this operation, the raised printing areas in the lockup become depressed areas in the face of the mat and the nonprinting areas in the lockup become raised areas in the mat.

After pressing, the mat and its associated backing are removed as a unit, and subjected to a drying operation in one or more steps. Drying of the mat serves to eliminate substantially -all of the moisture in the mat so that the moisture does not interfere with the casting operation, while forming the mat for casting. Further, the drying and forming operation in connection with shrink-type mats serves to reduce the size of the mat to the particular dimensions required in the stereotype plate. During the drying process, the temperature is maintained at a sufliciently high value to set the resin in the backing to elfect polymerization to such a degree that the resin no longer exhibits any substantial plastic flow under the temperatures and pressures of plate cast- In FIGURE l, reference numeral indicates generally a printing form including the usual heavy metal chase 11 for containing the various components of the form, including the usual locking wedges of quoins (not shown) for holding the printing elements in place in the case. Substantially ush with the level of the chase 11 is an arrangement of printing elements which may include type slugs 12, each of which contains raised type faces 13 and engraving 14 separated from the type 12 by means of a spacer 16 and a second set of type 17 with its raised type faces 18. A paperboard mat 19, which ordinarily contains from about l0 to 40 percent by weight of freeV moisture is shown superposed over the printing form. Paperboard mats of this type commonly vary in thickness from about .024 to .040 inch. The mats are selected by a given newspaper primarily on the basis of their shrinkage characteristics. Mats of the type now most generally used shrink considerably upon drying, depending in part upon their relative moisture content. This shrinkage occurs to the greatest degree transversely of the mat, at right angles to the machine direction of thev bers. The shrinkage in the lengthwise direction is ordinarily about half of what it is in the cross direction.

ln newspaper work, it is common to use mats which provide from about one-half to about one and one-fourth inches in cross-wise shrinkage for a mat measuring about fifteen and nine-sixteenths inches wide and twenty-one and three-quarter inches long between the limits of the type area. In choosing a mat for the process of this invention where only one drying step is used, it may be desirable to allow for a slight decrease in shrinkage Vover that ordinarily anticipated, so that where a given mat may have a characteristic shrinkage of one and oneeighth inches, it will shrink about one inch when combined with the backing material described. Where a conventional pre-drying step is employed, however, substantially all of the rated shrinkage in a given mat will be achieved by the end of the iinal drying step.

Disposed immediately over the mat 19, and coextensive ltherewith is a pad or multi-ply sheet 21 composed of a plurality of bonded plies of creped cellulosic tissue or wadding impregnated with an unset thermosetting resin, as previously described. For a mat having a thickness of .024 to .040 inch and a moisture content of l0 to 40 percent, the initial thickness of the wadding pad should be in the range of from about .030 to .100 inch. This is equivalent to a sheet of from 6 to 20 plies of resin impregnated tissue, as described, having a basis weight per standard ream of about to 300 pounds and containing 40 percent of resin on a bone dry basis. It may be desirable to use a non-impregnated tissue ply above the resin impregnated plies to avoid adherence between the backing and the molding combination.

Above the wadding pad 21 is a compressible cushion or molding combination 22 which may comprise a sheet of yieldable material such as cork, or mixtures of cork and synthetic rubber and/or fabric. In this respect it should be noted that the molding combination fairly well regulates the pressure that is applied to the stereotype mat during the molding operation. The pressure on the mat will vary considerably between the printing and nonprinting areas because of the type `of molding cornbination selected and because of the space areas land depths available in the lookup. Consequently, it will be seen that the molding combination is a matter of choice depending largely on the space-depth desired in the mat and on the particular type of mat being used.

One example, of the numerous molding combinations which could be employedincludes a sheet .070 inch thick consisting of a cork composition with a fabric facing, in combination with a fiberboard sheet having a thickness of .090 inch. However, we have found that the molding combination can be eliminated in some cases.

In the practice of the invention by the use of the ma-l terials described in the foregoing, it will generally be found that good adhesion is produced -between the mat and the plies of the backing material. This is especially Atrue when the backing material contains a moisture sensitive resin and when the volatile content of the mat material is greater than about 4.0 percent.

In certain instances, however, it has been found desirable to provide an additional layer of adhesive between the mat and the backing. This adhesive may be ofsuch nature that it adheres the mat and the backing prior to the molding operation, or the adhesive may be applied in such manner that it joins the mat and the backing only during the molding and/or drying operations. For example, an adhesive may be applied to the mat or to the backing, or to both, or the adhesive may consist of a separate film or an impregnated carrier sheet adapted for insertion into the lay-up assembly between the mat and the backing.

The adhesive coating 20a is preferably a uniform film of a moisture sensitive adhesive material, such as sodium acrylate, .Methocel, a methyl cellulose sold by Dow Chemical Co. or polyvinyl alcohol, in order that it will 35cm-eee.

be' tacky during the' formation of the combined mat and backing' when the moisture in the mat is drawn into the backing', ,or it may be a pressure sensitive material which will bond the backing to the mat during the molding operation. Further, the adhesive should be moisture permeable,l so that it does not act as a barrier to the moisture in the mat 19a asV this moisture seeks to penetrate the backing 21a? The adhesive selected for joining. the mat to the backing should preferably be one which is suciently tacky to provide a good bond between the mat and the backing during the molding of the composite stereotype mat. Otherwise, the subsequent drying operation might de form the hacking as it receives moisture from the mat and cause uneven shrinkage' of 4the two resulting in their getting out ofregister with eachother.

If desired, a film or carrier sheet may be used for thc adhesive lm v29u. However, in such instance it is desirable that the carrier sheet be capable of distortion in order to conform withV the mat and backing. For this reason a' soft tissue or a non-woven fabric might be used.

ItV is possible that by using an added adhesive layer, asdescribed above, a somewhat smaller amount of resin might be used in the backing, since this resin content is no longer relied on for adhering the backing to the mat in the manner previously described. It is also possible that it may be desirable in certain instances to use a heated pressure roll in the molding operation, in order to better set the adhesive and thereby improve the hond- -ing between the mat and backing.

With reference now particularly to FIGURES, it is seen that. the printing form 1d with the mat, backing, and blanket in place is set on the table 23 and passed between the nip'of pressure rolls 24 and 26. One or both of the rolls 2d and Ztris made vertically adjustable to compensate for different thicknesses of printing forms. The pressures of molding used in our process are substantially the same as those used presently in molding stereotype mats. Itis difficult to measure the exact pressure employed, as the contacting areas of roll to which the pressure is applied cannot be` ascertained accurately. However, it'. is generally accepted that the molding pressures 'required lfor good reproductionV are on the order of: 2,000to 4,030 pounds per square inch over `theV printing areas and maybe considerably higher.

The'use of aroller moldingl'm'achine comprising a chase-supporting bed and a pair of rotatable pressurev rolls is by far the most common method of molding mats, but the process of the present invention is equally applicable to molding procedures invoiving the use of direct pressure with flat platens. I

As pressure is applied to theassembly shown in FIG- URE 3, themat i9 is compressed into the spaces be-Y tween the raised printing characters and k*forms a sharply deiined reproduction of the printing characters contained in the lookup or form 16. The porous backing 2i is also capable of absorbingy any moisture expressed from the mat 19. The' backing 2i is considerably more compressible than the mat 19 and, as a result of the pressing, the thickness of the backing 2i is considerably reduced over the printing areas. Under ordinary molding pressures, the' thickness may be reducedy by a factor of four or-ve times over the' printing areas, so that a backing originally .05() inch in thicknessV may-end up as a compressedV backingof about .01() inch, whereas in the nonprinting areas .the bulk is compressed toabout .040 inch, thereby providing a space depth between the level of the non` printing areasl and the base of the printing areas of about .030`vinch.` Thus ino-ne operation the mat is molded and completely packed simultaneously and more rapidly than is possiblein a hand packing operation. Furthermore, with the described invention, the molded depth retention in half tone areas is better than ina hand packed mat.

The backing material is such that its face is able to conform accurately to the contour of the back of' the"- mat i9 duringV application of pressure. AAt the same time the backing .becomes quite securely bonded to vthe back of the mat i9 over the areas of the4 mat subiectedjto high molding pressures. In ins'tauceswhere the glue line or adhesiye oating'pZtla' isnotrelied onto b'ond the backing to the mat, this bonding is effected either because of the adhesive properties ,of the resin contained in the backr ing, or it may be partly ldue to agmechanical' locking of the printing areas at the back of the' matin the collapsed arcas' of the backing immediately overlying theseareas of the mat. With the use of the adhesive coating' 20a the pressure on the mat duringv the molding operation causes the back tov be bonded to the mat. With a moisture sensitive adhesive this bonding is effected by the expression of moisture in the mat toward the adhesivey to thereby render the latterV suciently tacky to bond the hacking tothe mat.

K A portion of the backed mat after removal from the molding apparatus is illustrated in enlarged form in FGURE 4.' mat 19 is depressed in c'onforrnityvto the shape of the lookup, as seen at 28 and 29, depending on the pressure, molding combination, and the space areas and depths available in the original lookup. l

in the nonprinting areas, as for example in.- the area 29, the remarkableresiliency, of the backing 2i causes the backing-to recover much of its original vthickness after removalVV of the molding pressure',` vas indicated Vat numeral 33;. Yet in the areas above the printing surfaces, such as the area 31, Vthe backing takes amore permanent set but still retains a high degree ofhiiexibility` and moisture permeability. The-result is that the backed` mat produced by the molding operation has a generally` planar rear surface 35 which may b e readily conformedto the surface of the dryer. Further, the backing material is packedy into those small nonprinting areas that a hand packer does not even touch in the ordinary processk of stereotype matv forming. Consequently, lthere is pro` vided by the backing a proper arrangement of bulkfor resisting collapsing of the mat during subsequent steps in the formation of the tinished stereotype matrix.

Afterthe remoyal from the molding apparatus, the composite mat and backing is then ready for drying and for setting of the resin. For the manufacture of curved stereotype plates, rthe mat 19 and its backingrZl are given a uniform curvature by introducing the mat into a conventional dryer'assembly illustrated in FIGURE 5. The particular dryer illustrated in the drawings consists of an asbestos covered drum 34 in which a plurality of heating elements 36 are disposed beneathy the asbestos surface. A cover or chamber 37 having arperfrorated inner face 38 ishinged tothe base 34 at 'a hinge 39. The backed mat is held against the inner face 33 by applying a vacuum to the back of the composite mat through the perforations in the face 38; The cover is also heatedV by means of spaced heating elements 40 contained therein. As previously stated, the multi-ply pad of resin-.impregnated tissue sheets mayV include one unimpregnated ply on theupper surface thereof.V K

The Avacuum applied to theVmat-holds the mat in con-Y tact with the face tand spaces the face of the mat slightly from the rasbesto-s covered 1surfaceof the base 34 when the cover 37 is in its closed position. Thus the vacuum serves not only to hold the mat in position but, also, forms the back of the mat in a smooth surface so as to provide a uniformly curved reference surface for the mat. The temperature at the base of the scorcher is ordinarily on the order of 250 to 400 F. As the heat is applied, the moisture is driven from the mat and this moisture passes through the porous backing material and is there-Y upon vented. Itis important that the resin selected should not become cured` or rigid until substantially all of the desiredvshrinkage of the mat and backing has taken place. Consequently, the resin should be one which will become As seen in that drawing, the face of theV g cured throughout at a temperature somewhere near the upper range of the scorcher temperature which will prevail throughout the mat when` essentially all of the moisture has been drawn therefrom. The resins mentioned above have these characteristics and mats packed with these types of dispersed resin products do not evidence any tendency to crack or warp during casting of the stereotype plate.

Where only one drying step is used, a treatment time of 2 to 5 minutes at temperatures of 300 F. to 400 F. will suiiice to drive olf the moisture and set the resin sufficiently under moisture conditions normally prevailing in that mat. The control of shrinkage is facilitated by operating at a lower vacuum, on the order of one and onehalf inches of mercury during the first minute or two and then increasing it to a value of 5 to 6 inches of mercury when substantially all of the moisture has been driven off. And, as previously mentioned, substantially all of the moisture is driven oft before the resin in the backing is set and, therefore, such resin content does not intefere with the shrinkage of the mat and backing as a unit. Where a pre-drying step is employed in conjunction with a final drying and forming, times of about 40 to 80 seconds at temperatures of about 150 to 250 F. may be employed to initiate shrinkage of the composite mat without substantial setting of the resin. In this latter respect, it should be noted that there are definite advantages in some instances in utilizing a pre-drying step before finally forming the mat. The pre-drying operation helps to rigidify the backing so that it is better able to resist the vacuum pressure in the final dryer and prevent an undesirable collapsing of the uncured mat under such pressure. Further, this pre-drying of the mat and backing is an aid in providing better space-depth characteristics in some instances.

The resin in the backing should be cured suliiciently during the final drying operation to a point wherein it will resist collapse under the temperatures and pressures encountered in the casting of the stereotype plate. Our experience indicates that in the case of a phenol-formaldehyde resin a cure of at least 85 percent should be achieved. Expressed alternatively, the resin extractibles in the sheet should not exceed about 15 percent. The extractibles content can be readily determined by the standard A.S.T.M. test (13494-41) which involves taking a known weight of typical sample of the cured sheet material in finely comminuted form, and placing this sample in a Soxhlet apparatus where it is extracted with hot acetone for a period of four hours. The acetone is then evaporated under controlled conditions and the sample removed, so that the residue constitutes the extractible materials which have been dissolved by the acetone.

Upon removal of the backed mat from the scorcher, the mat is ready for insertion in the casting box. The final form of the mat is illustrated in FIGURE 6 of the drawings and includes the paperboard mat 19 having a casting face i9b of concave shape and the backing 21 in which the thermosetting resin has become set and rigidified by the heat treatment in the dryer. Composite mats of this type have been found to adequately resist collapse under type casting pressures on the order of l5 to 25 pounds per square inch.

The process described can be very conveniently carried out on conventional stereotype forming equipment with little or no change in the present procedures or equipment and, when so used, it realizes most important savings in time and labor as well as producing an improved mat and, consequently, a better printing plate.

There are a number of factors which should be considered in the practice of the invention in order to achieve the best results in the molding of the composite mat and backing. These include (l) the degree of creping in the individual unimpregnated tissue plies constituting the backing material; a crepe ratio of between 1.3 and 2.5 is preferred, (2) the amount of stretch in the backing after l@ impregnating and drying should be between 20% and 60% in the machine direction, based on the original length of the sample of backing, (3) the resin content in the backing, which is preferably 40 to 50 percent by dry weight of the finished product on a volatile free basis, but which may be within a range of 15 to 75 percent and still be effective in certain instances, (4) the thickness or bulk of the backing, preferably .030 to .100 inch before the composite mat is formed in the case of newspaper mats, (5) the Water solubility of the resin in the backing after impregnation and drying which is desirably about 35%, in the event a water soluble resin is used,

(6), the percentage of volatiles in the backing after the composite web is formed, indicated above as being preferably no greater than 15 percent of the resin content, with a range of from 5 to 9 percent being desired for most practical uses, (7) the type of molding combination employed, and (8) whether a single or multiple step, nonshrink or shrinkage process is desired in forming the stereotype mat or matrix. It will be understood of course, that the thickness of the mat will be largely a matter of convenience. While all of the above mentioned factors play a part in providing the improved stereotype mat made possible by this process, a proper balancing within the various ranges disclosed herein should be achieved to obtain the finest quality reproduction.

The foregoing discussion has dealt primarily with the backing of curved stereotype mats of the high shrink type now commonly employed in newspaper work. The numerous advantages of the new combination can also be realized in related fields. As previously indicated, the mat and backing can be pressed between flat platens, and the resulting backed mat after curing of the resin and shrinkage of the mat can be employed for making flat castings. Alternatively, the molding, curing, and shrinkage may be part. of the same operation, by employing heated, perforated platens in the fiat molding press.

For another example, advertising agencies distribute the so-called ad mats to numerous newspapers throughout the country. These mats are commonly of the noshrink type and are intended to provide a mold for receiving a iiat casting of metal or for direct casting in newspaper work. The casting is then inserted into a newspaper page lockup along with the remaining printing elements, and a high shrinkage mat is then molded on this lockup. The described backing can also be employed as a backing for the no-shrink type mat. In this type of application, the resin in the backing is convenienty cured at the time the mat is molded by using heated platens in a direct pressure molding assembly, and the mat and its attached backing may then be distributed to the various newspapers.

Another field in which mats of little or no shrinkage are commonly employed is that of color reproduction. Normally, color printing systems include a series of as many as four printing rolls, one for each of colors desired, so that a plurality of stereotype plates must be provided for each printed page. In this field, it is essential that there be perfect registry between the printing surfaces, soit is common practice to use a no-shrink mat for preparing each of the plates. Because of its inherent ability to con-.` form exactly to the mat during drying the backing material of the present invention has especial utility in the manufacture of such mats.

It will be evident that various modifications can be made in the disclosed examples without departing from the scope of the present invention.

1. The method of making a stereotype mat which comprises applying onto a printing form a relatively moist paperboard mat having a moisture content in the range from 10 to 40 percent by weight and -a multi-ply backing superimposed thereon, said backing comp-rising a moldable sheet containing a plurality of plies of creped tissue having an unset thermosetting resin dispersed therein, the

1 i resin content` in said backing to 75 percent by weight of said sheet on a dry basis, said backing sheet having a volatile content in the range from 5 to 15 percent by weight on a bone dry basis, applying suliicient pressure to the resulting assembly to form an impression of the p-rinting areas of said printing form into said mat, removing said assembly from said printing form, drying said backing and said mat while applying a re-V duced pressure Vat the rear of said backing so that the moisture in said mat is vented through said backing, and heating said mat and said backing under conditions suiiicierit to cure the resin in said backing to withstand the pressures encountered in stereotype casting.

2,. The method of making a stcreotype'mat which comprises applying onto a printing form a relatively moist paperboard mat having a moisture content in the range from to 40 percent by weight and a multi-ply backing superimposed thereon, said backing comprising a moldable sheet containing a plurality of plies of creped tissue having an unset thermosetting resin dispersed therein, the resink content in said backing sheet constituting from to 75 percent by weight of said sheet on a dry basis, said backing sheet having a volatile content in the range from 5 to 15 percent by weight on a bone dry basis, applying suilicient pressure to the resulting assembly to form an impression of the printing areas of said printing form into said mat, removing said assembly from said printing form, drying said backing and said mat so that the moisture in said mat is expelled, and heating said mat and said backing under conditions sufficient to cure the resin in said backing to withstand the pressures encountered in stereotype casting.

3. The method of making ak stereotype mat which comprises applying onto a printing form a .relatively moist paperboard mat having a moisture content in the range from l0 to 40 percent by weight and multi-ply backing superimposed thereon, said backing comprising a moldable, moisture-permeable sheet containing a plurality of plies of creped, cellulosic tissue having an unset thermosetting resin dispersed therein, said backing sheet containing from 15 to 75 percent by weight of said resin on a dry basis, said backing sheet having a volatile content in the range troni 5 to lSpercent by weight on a bone dry basis, applyingy suilicient pressure to the resulting assembly to form an impression of the printing areas of said printing form onto said mat, removing said assembly from said printing form, drying said mat and said backing under conditions suicient to permit shrinkage of said mat and backing to a predetermined degree, and heating said mat and' said backing at temperatures sufficient to cure the resin in said backinv.

4. The method lof making a stereotype mat which comprises` applying onto a printing form a paperboard mat having a free'moisturecontent in the range from 15 to 40 percent by Weight and Va multi-ply backing sheet or pad superimposed thereon, said backing comprising a plurality of plies of creped paper bonded together by an unset thermosetting composition distributed through. said plies and having an initial thickness in the range of from about 0.030 to 0.100 inch and being moisture permeable, the resin content in said backing material constituting from 15 to 75 percent by-weight of said backing material, said backing sheet having a volatile content in the range from 5 to 15 percent by weight on a bone dry basis, applying sufficient pressure to said mat andy said backing while in superimposed relation over said form to form an impression of said form in saidmat, removing said mat and backing material as an assembly from said printing form, and thereafter drying said mat and said backing at a temperature sufficient to dry said mat into a substantially moisture-free Kcondition and'to cure the resinous composition in said backing material.

5; The method of making a stereotype mat which cornprises impregnating la Vplurality of plies of creped, cellulosic tissue with an unset thermosetting resinous compo sheet constituting from 15' sition dispersed in a liquid vehicle, drying the impregnated material to provide a laminated, moisture-permeable backing material having resin particles dispersed therein in sufficient quantities to provide a resin content of from l5 to 75 percent by weight in said backing material, said backing material having a volatile content in the range from 5 to l5 percent by weight on a bone dry basis, superimposing said backing over a paperboard mat with `an adhesive film therebetween, said paperboard mat having a moisture content from 10 to 40 percent by weight, laying the resulting backed mat over a series of printing elements with the paperboard portion thereon in contact with said element, applying suiicient pressure to make an impression of said printing elements in said paperboard, removing said backed mat from said printing elements, and thereafter drying said backed mat by the application thereto of heat, While simultaneously removing moisture vapor from said mat through said backing material, at a temperature suilcient to dry the backed mat to cure the resin in said backing material sufficiently to withstand the pressures encountered in stereotype casting.

6. A stereotype matrix comprising a molded iiong and a molding blanket secured thereto and providing a backing for said flong, said molding blanket including a cured thermosetting resin impregnated fibrous sheet, the free surface of said ong having the printing matter molded therein and the contacting surfaces of said blanket and said ilong being contoured in the non-printing areas, the free surface of said molding blanket being flat.

7. A sterotype matrix comprising a molded ong and a molding blanket in juxtaposition, and a Vquantity of adhesive between said flong and said molding blanket adherring said molding blanket to said ong, said molding blanket including a sheet of fibrous material impregnated with a cured phenolic resin, the free surface of said ong having printed matter molded therein and the contacting surfaces of said sheet and said flong being contoured in the non-printing areas, and the free surface of said molding blanket being flat.

8. A stereotype matrix comprising a molded flong and a molding blanket in juxtaposition, and a layer of adhesive between said flong and said molding blanket adhereing said molding blanket to said ong, said molding blanket consisting substantially of a layer of paper sheet material impregnated with a cured phenolic resin, the free surface of said flong having printed matter molded therein yand the contacting surfaces of said blanket and said ong being contoured in the non-printing areas, the free surface of said molding blanket being ilat.

9. A stereotype matrix comprising a molded ong and a molding blanket in juxtaposition, and a layer of adhesive between said ong and said molding blanket adhering said molding blanket to said iiong, said molding blanket consisting substantially of a layer of paper sheet material impregnated with a cured phenol formaldehyde resin, the free surface of said ilong having printing matter molded ytherein and the contacting surfaces of said blanket and said Hong being contoured in the non-printing areas, the free surface of said molding blanket being flat.

l0. A stereotype matrix comprising a molded flong and a molding blanket in juxtaposition, and a layer of adhesive between said flong and said printing blanket adhering said molding blanket to said ong, said molding blanket consisting substantially of a layer of paper sheet material. having a maximum thickness of between about 0.035 inch `and about 0.040 inch and impregnated with a cured phenol formaldehyde resin, the resin constituting about 50% by Weight of the impregnated sheet, the free surface of said flong having printing matter molded therein and the contacting surfaces of said blanket and said ong being contoured in the non-printing areas, the free surface of said molding blanket being flat.

(References on feilowing page) References Cited in the file of this patent UNITED STATES PATENTS Annand May 27, 1909 Baekeland July 17, 1917 5 Novotny Nov. 22, 1921 Schroger Jan. 27, 1925 Hole Aug. 27, 1929 Cochran et a1 May 29, 1934 Matuschke et a1. May 26, 1936 10 Morgan etal. Feb. 9, 1937 14 Catlin Mar. 15, 1938 Rowe Mar. 14, 1944 Baker Dec. 27, 1949 Catlin et a1 May 29, 1951 Germain Mar. 4, 1952 Richardson Mar. 1, 1955 Schaum NOV. 27, 1956 FOREIGN PATENTS Germany June 11, 1928

Claims (2)

1. THE METHOD OF MAKING A STEREOTYPE MAT WHICH COMPRISES APPLYING ONTO A PRINTING FROM A RELATIVELY MOIST PAPERBOARD MAT HAVING A MOISTURE CONTENT IN THE RANGE FROM 10 TO 40 PERCENT BY WEIGHT AND A MULTI-PLY BACKING SUPERIMPOSED THEREON, SAID BACKING COMPRISING A MOLDABLE SHEET CONTAINIG A PLURALITY OF PLICES OF CREPED TISSUE HAVING AN UNSET THERMOSETTING RESIN DISPERSED THEREIN, THE RESIN CIONTENT IN SAID BACKING SHEET CONSTITUTING FROM 15 TO 75 PERCENT BY WEIGHT OF SAID SHEET ON A DRY BASIS, SAID BACKING SHEET HAVING A VOLATILE CONTENT IN THE RANGE FROM 5 TO 15 PERCENT BY WEIGHT ON A BONE DRY BASIS, APPLYING SUFFICIENT PRESSURE TO THE RESULTING ASSEMBLE TO FORM AN IMPRESSION OF THE PRINTING AREAS OF SAIID PRINTING FORM INTO SAID MAT, REMOVING SAIID ASSEMBLE FROM SAID PRINTING FORM, DRYING SAID BACKING AND SAID MAT WHILE APPLYING A REDUCED PRESSURE AT THE REAR OF SAID BACKING SO THAT THE MOISTURE IN SSID MAT IS VENTED THROUGH SAID BACKING, AND HEATING SAID MAT AND SAID BACKING UNDER CONDITIONS SUFFICIENT TO CURE THE RESIN IN SAID BACKING TO WITHSTAND THE PRESSURES ENCOUNTERED IN STEREOTYPE CASTING.

6. A STEREOTYPE MATRIX COMPRISING A MOLDED FLONG AND A MOLDING BLANKET SECURED THERETO AND PROVIDING A BACKING FOR SAID FLONG, SAID MOLDING BLANKET INCLUDONG A CURED THERMOSETTING RESIN INPREGNATED FIBROUS SHEET THE FREE SURFACE OF SAID FLONG HAVING THE PRINTING MATTER MOLDED THEREIN AND THE CONTACTING SURFACE OF SAID BLANKET AND SAID FLONG BEING CONTOURED IN THE NON-PRINTING AREAS, THE FREE SURFACE OF SAID MOLDING BLANKET BEING FLAT.

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