US3509991A - Release sheet and adhesive structure embodying the same - Google Patents

Description

May 5, 1970 A. R. HURsT 3,509,991

RELEASE SHEET AND ADHESIVE STRUCTURE EMBODYING THE SAME Filed April 14, 1969 5f-. 1-gli.

United States Patent O 3,509,991 RELEASE SHEET AND ADHESIVE STRUCTURE EMBODYING THE SAME Alan R. Hurst, Hinsdale, Ill., assignor to Arhco, Inc., a corporation of Illinois Continuation-impart of application Ser. No. 772,118,

Oct. 31, 1968. This application Apr. 14, 1969, Ser.

Int. Cl. C09j 7/02; B32b 7/06; B65d 85/67 U.S. Cl. 206-59 10 Claims ABSTRACT OF THE DISCLOSURE A release sheet is provided which has different release values on each side. Accordingly, a sheet of paper is first coated with a polyethylene or other plastic film, e.g., by extrusion and then both sides are coated with a release agent. Usually the paper is saturated with release agent. The difference in surface texture results in the ability of one release surface to release an adhesive more easily than can the other release surface. This effect does not change significantly with age. The release sheet is useful as a backing for pressure sensitive adhesives to provide a roll of adhesive mass, e.g., in tape form, which can be readily separated from the release paper.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-impart of my copending application Ser. No. 772,118 filed Oct. 3l, 1968 and entitled Release Sheet or Web.

STATEMENT OF THE PRIOR ART Field of the invention This invention relates to release sheets or webs and especially release sheets or webs having differential release on opposite surfaces.

Description of the prior art As set forth in my above identified copending application there is a need for new and better release sheets or webs of simple construction for releasing adhesive layers and especially pressure sensitive adhesive layers for various purposes. Release sheets are used in industry for 'releasing adhesive layers in the manufacture of pressure sensitive adhesive tapes, adhesive labels, cast films and other items of manufacture.

Differential release s the ability of a two-side release coated sheet to provide a different ease of adhesive release from one side as compared with the other side. With the usual use of release agents, such an effect is very difficult to obtain on release sheets and the effect normally does not survive with aging. Release sheets are normally stored in roll form before application of the adhesive and the release Values on both sides tend to become equivalent during such storage.

Pressure sensitive adhesive tapes when manufactured in roll form normally use a carrier substrate having an adhesive receiving non-release surface which is tightly adhered to by the adhesive and a backing surface having release properties so that the tape can be removed from the roll with the adhesive still adhering to the proper surface of the backing. Other useful adhesive materials are nonbacked masses of adhesive which can be used as adhesive caulking material for mounting automobile windows and for like purposes. It is to the non-backed adhesive mass which this patent is directed and where differential release is needed. For many adhesives, no really simple and successful way has been devised for marketing adhesive masses in roll form.

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Various attempts to solve this problem have involved coating a substrate such as a plastic film, a special nonabsorptive paper, or a glassine and the like on both sides with a release coating. At least with plastic films the roll is frequently unpredictable during use since the adhesive can just as often adhere to the reverse surface as to the adhesive receiving surface. On papers, fiber pull can be a problem and this results in fibers contaminating the adhesive mass.

Other attempts have also been made to provide differential release between the two surfaces so that the adhesive will selectively adhere to one of the surfaces when unrolled. Although some success at differential release has been achieved, it is not enough for the purpose of providing a successful non-backed rolled adhesive mass. These attempts have mostly involved differential cure of release coatings on opposite sides of the substrate, or chemical modification of the release coating material on one side of the substrate in an attempt to increase or decrease its release properties. The difference in cure has not been satisfactory because the resulting differential release is too slight and too inconsistent to overcome the problem. The chemical modification of release coating has created difficulties because the backing web, when produced, is normally wound into roll form for storage or shipment before applying the adhesive; so that the two release coatings are in intimate contact with each other and tend to transfer from one to the other creating approximately the same release on both sides of the web.

SUMMARY OF THE INVENTION This invention provides a new and useful simple structure using a plastic film coated paper which is release coated on both sides with release agent. The plastic film is secured to one surface of the paper by extrusion or the like before coating or saturating the surfaces with release agent. A release coating is preferably applied to the exposed surface of the film to improve the iilms release properties to an extent that they exceed the release properties of the exposed coated or saturated paper surface. Pressure sensitive adhesive can be applied to the surface of lower (more diflicult) release properties and the resulting laminate can be rolled into roll form. In use of the adhesive, the laminate is pulled from the roll and the adhesive sticks to the surface to which it was originally applied, e.g., in this case to the surface having lower release properties. The laminate can then be applied with the adhesive surface against a surface desired to be coated with adhesive and the backing is then pulled from the adhesive leaving the adhesive adhering to the surface. This provides a layer of adhesive to which other surfaces or articles can be adhered. In another aspect the structures of the present invention can be used wherever an anti-fiber pull release substrate is desired or wherever differential release is desired on a web in a manufacturing process.

While this invention is susceptible of embodiment in many different forms there `are shown in the drawings and will herein be described in detail specific embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and it is not intended to limit the invention to the embodiments illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged section through a preferred embodiment of the release sheet of this invention showing a mass of adhesive in full lines on one release surface and a mass of adhesive in phantom on the other release surface;

FIG. 2 is an enlarged section similar to FIG. 1 showing another use of the release sheet;

YDESCRIPTION OF THE PREFERRED EMBODIMENTS l Usually the plastic film is polyethylene although other plastic films and especially polyoleiin films can be used in lieu thereof. The purpose of the plastic film is to provide a texture different from that of the paper. The release agent can be any of the well known release agents which are capable of being applied as a liquid and then solidified, e.g by solvent vaporization and/o-r curing, and is preferably a silicone polymer release agent.

Turning to FIGS. 1 and 2', an especially preferred form of relesae sheet is illustrated. The release sheet shown generally at is in combination with a laye-r of pressure sensitive adhesive material shown generally at 11. Release sheet 10 includes a layer of paper 12 having a backing film of polyethylene 14 extruded thereon. The absorbent paper 12 is saturated with a cured release composition, e.g., silicone release agent, shown by stippling 16. A silicone coating 18, having the same degree of cure as silicone 16, covers the exposed surface of the film 14 of polyethylene. `The pressure sensitive adhesive material 11 which is carried by the release sheet 10 consists of a mass of adhesive 20 which is readily releasable from the surface of paperv 12 in the absence of fiber pull because the fibers of paper 12 are highly saturated and coated with release material so that adhesive 20 will not pull fibers from the interstices in the paper 12.

In FIG. 3 another form is shown in which the release layer 10a consists of kraft or other relatively non-absorptive paper 12a which is coated with a layer 16a of silicone, and having the backing film 14 and silicone layer 18'. Silicone layer 16a extends slightly below the paper surface as 4at stippling 16. Additionally, adhesive layer 11a consists of a layer of highly porous or absorptive paper 24 which is vsaturated with a pressure sensitive adhesive as indicated by stippling 26. It should be understood that any of the release sheets 10 and 10a can be substituted for the other in each of the structure of FIG. l through FIG. 3, as can the adhesive layers.

Any of the laminate structures can be rolled up into roll form and FIG. 4 illustrates such a roll 30. The mass of adhesive 11 can then readily be separated from the release sheet 10 for various uses. The illustrated release sheets 10 and 10a can also be used as webs for transporting pressrue sensitive adhesive surfaces in various manufacturing processes, such as the manufacture of label. Additionally, pressure sensitive adhesive surfaces can be applied to and removed from both surfaces of the release sheets or webs where desired during such manufacturing processes.l

The structures of FIGS. 1, 2' and 3 provide excellent differential release between the two release surfaces so that a mass of adhesive can be removed more readily from one surface than from the other surface where such differential release .as is desired. The rolls of combination release sheet and adhesive layer are especially useful with high speed equipment where the manufacturer wants the adhesive to stay with one side or the other of the substrate as it is unwound and do not want the adhesive to transfer back and forth. If the adhesive does transfer back and forth and is soft and unsupported it can distort and become unusable and if it does first from one side of the tape and then to the other it becomes very difficult if not impossible to use because of inconsistency in location of the adhesive layer and mechanical problems created thereby.

Normally, where :a silicone release coating is applied to a substrate, e.g., conventional papers used for this purpose, it forms a surface film which is then cured or dried in a drying oven. In the manufacture of the saturated paper 12 used in this invention, it is possible to use an absorptive 'paper which'is" dipped in or Vcc'aated with a penetrating solu tion of siliconey until saturated. The silicone is then cured, or dried, e.g., in accordance with the manufacturers specifications.

As a more specific example vof the manufacture of the silicone saturated polyethylene film paper laminate, as shown in FIG. 2, a solution of Syl-Off 23 paper coating is prepared by cutting back Syl-Off 23 with a suitable solvent'v (toluene) to a 5% solids content. Syl-Off 23 paper coating is a solution of curable silicone rubber polymer in solventtxylene) and has a silicone content of about 30 weight percent." Dibutyl tin di-2-ethyl hexapnoate (Dow Corning Catalyst 23A) was added as a curng'a'gent or highly solvent absorptive coarse light paper, eg., having a weight of25 pounds per ream or less Which had ybeen previously coated on the opposite with polyethylene by extruding a film of polyethylene on the paper surface. The structure was then delivered throughl :a drying oven at about 350 F. at a residence time of from one-half to two minutes to evaporate the solvent and simultaneously cure the silicone saturated paper and the silicone coating on the polyethylene side. This same structure has also been produced by silicone coating one side at a time. The particular method preferred would depend primarily on the equipment available.

The manufacturer of Syl-Off 23 reports cure temperatures for this silicone polymer ranging from below 250 to 500 F. with the high temperatures causing more complete and faster cure, in general. The cure time also increases the degree of cure somewhat up to about a one and one-half or two minute cure time. Thus, a wide variety of cure temperatures and conditions are available for this silicone polymer and this is also true o-f other silicon compositions.

Where a polyethylene or other plastic backing has been applied to the absorptive paper, e.g., as shown in FIG.3, the silicone is applied to the exposed paper side until the paper is saturated and the combination is cured as a unit. Since the release backing includes thermoplastic material, e.g., polyethylene layer 14, care should be taken not to melt or otherwise ruin the polyethylene layer. In the structure of FIG. 1 the polyethylene layer 14 is shown coated with a thin film of silicone `18 and this can be cured concurrently with the silicone 16 in paper 12. A simple way of saturating the paper and coating the plastic backing is to dip the entire structure in a bath of the silicon solution and then meter off the excess silicone solution. Of course, all ofthe release sheets described herein' can be prepared as a continuous web by running the web through, the silicone coating bath and thence through the drying or curing oven. This is particularly true where a film backing is applied on the paper to give it strength for processing through web handling equipment.

Release sheets 'prepared in accordance with the present invention have lbeen tested for release properties and it has been found that both sides of the release sheets have good release properties. For example, the differential release between opposing surfaces of release sheets of the type shown in FIG. 1 were tested and it was found that the silicone coated polyethylene side gave a release value of 30 grams or less per inch from a heat activated adhesive tape while the silicone saturated paper side had a release value of to 500 gram-s per inch, depending on the type of paper used, using the same heat activated adhesive tape under the same conditions on a Keil tester. Specifically, Where the paper was 20 lbt/ream canliner, the release value was 130 to 150 grams per inch and Where the paper was 60 lb./ream Southern kraft paper the release value was l400 to 500 grams per inch. In each instance this is a fully adequate difference in released properties and provides an excellent differential release sheet. The differential release structures prepared by this invention can have a wide variety of diierential release Values. For use with adhesive saturated paper the release properties can be very low (high Keil release values) because the paper does not distort as much as an unsupported extensible pressure sensitive adhesive mass during peeling of the backing.

When using the differential release structure, the adhesive, e.g. solvent based, may be applied to either the release coated polyethylene surface of the release coated paper surface. When applied to the release coated polyethylene surface and stored in roll form it is found that the adhesive will cling preferentially to the polyethylene side of the release structure when it is unwound, eg., FIG. 4. On the other hand, when the adhesive mass is applied to the paper side of the release structure it will also cling preferentially to that side when it is unwound. Thus, adhesives create a good bond with, and remain on the side to which they are initially applied, even where that side has higher release properties (lower Keil release value).

Air may become trapped in the paper when an adhesive mass is applied to the paper side and this can result in bubbling in the adhesive when it is dried. While this bubbling can be significantly reduced by perforating the polyethylene film, it is a generally accepted practice to apply the adhesive mass to the polyethylene side of the release paper thereby veliminating the source of air bubbles.

Advantageously, the silicone coating material saturating the absorptive paper covers all of the bers of the paper to permit complete release of adhesive without liber pull. The release properties to some extent are related to the type of paper used since smoother papers will provide easier or lower release values while rougher or coarser papers provide higher release values.

The differential release sheets of the present invention have excellent stability with regard to maintaining the difference in release values over long periods of aging, even during storage in roll form. Further, the differential release sheet of this invention has an amazing ability to perform satisfactorily over a wide variety of variables. The present release sheets are able to accommodate variations in adhesive compositions, variations in desired speed of adhesive removal both when the roll is unwound and the release paper is later removed leaving the adhesive mass, variations in angle of separation from the adhesive, variations in use and storage temperatures and variations in the mechanics of removal from the adhesive mass, e.g., from smooth to jerky intermittent removal.

A major advantage of this invention is the provision of a tacky adhesive mass on the release structure and in roll form. In roll form the adhesive mass is between opposite surfaces of the release structure, usually a narrow strip when used in this manner. The lower (more dificult) release value surface retains the adhesive as the strip is peeled from the roll. The exposed adhesive can then be applied to an object and the backing materialcan be peeled off leaving a mass of adhesive on the object. The adhesive mass can be in a Variety of thicknesses from ilm thickness up to one-half to one inch thick or thicker and can be used for such purposes as hanging pictures, putting up wall board and wood paneling, mounting and sealing automobile windshields, Vand caulking and sealing operations and the like. Since the adhesive is pressure sensitive there is no need to provide for evaporation of solvents or curing before a strong bond is formed. Further, the adhesive can be pigmented, provided with fillers, stabilizers, antioxidants and other additives as may be desired for a given application. All percentages given herein are by weight unless otherwise indicated.

I claim:

1. A release sheet consisting essentially of a laminate of an absorbent brous paper layer and a polyolen lm layer of a different texture from said paper layer, and a silicone release agent coating on both exposed surfaces of the laminate, said silicone release agent being cured to the same degree on both surfaces and eliminating fiber pull on release of pressure sensitive adhesive from the exposed paper surface.

2. The release sheet of claim 1 wherein said cured silicone release agent extends throughout the paper layer 'and saturates the paper.

3. The release sheet of claim 2 wherein said polyolen lm and paper layers are bonded to each other before saturation of said paper.

4. The release sheet of claim 2 including a layer of adhesive material on the exposed silicone coating, said release sheet being rolled in roll form.

5. The release sheet of claim 1 wherein the polyolen film is polyethylene ilm which has been extruded on the paper.

6. The release sheet of claim 2 having a layer of adhesive material on the silicone coated polyethylene film.

7. The release sheet of claim 1 including a layer of adhesive material on the exposed silicone coated paper surface, said release sheet being rolled in roll form.

I8. The release sheet and adhesive combination of claim 7 wherein the polyolen film is foraminous for permitting escape of air from the paper layer.

9. The release sheet of claim 1, in roll form including a layer of adhesive material between the silicone coated surfaces.

10. The release sheet of claim 1 including a mass of volatile solvent based adhesive adhering to one of the release coated surfaces.

References Cited UNITED STATES PATENTS 2,829,073 4/ 1958 Williams 117-68.5 XR 2,985,554 5/ 1961 Dickard 161-209 XR 3,050,411 8/ 1962 Keil 117-685 3,111,449 11/1963 Gold et al 11768.5 XR 3,152,030 10/ 1964 Sampson 117-685 XR 3,212,957 10/1965 Linda et al 161-167 3,301,741 1/ 1967 Hendrickson et al. 136-247 XR 3,341,004 9/1967 Hoeglund.

3,403,045 9/ 1968 Erickson et al. 161-208 XR JOHN T. GOOLKA'SIAN, Primary Examiner G. W. MOXON II, Assistant Examiner U.S. Cl. X.R.

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