US2667436A - Pressure sensitive adhesive coated sheet material - Google Patents

Description

1954 G. J. GOEPFERT ET AL PRESSURE SENSITIVE ADHESIVE COATED SHEET MATERIAL Filed Sept. 21, 1950 INVENTOR GEORGE J. GOEPFERT HGWARD. CAIELD ATTORNEY Patented Jan. 26, i954 UNITED STATES PATENT OFFICE PRESSURE SENSITIVE ADHESIVE COATED SHEET MATERIAL George J. Goepfert and Howard M. Canfield,

Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application September 21, 1950, Serial No. 186,052

9 Claims. (01. 15453.5)

This invention relates to sheet material coated on at least one side with a pressure sensitive adhesive and to a method of making the same. More specifically, it is directed to the production of such material wherein at least a part of the adhesive is provided in the form of a pattern consisting of raised nodules separated by continuous depressed channels formed by applying to the adhesive a sheet of embossed polyethylene.

2 tact with the pressure sensitive adhesive, gas pockets form when the sheet is applied and these pockets develop into blisters or bubbles which make the product unsatisfactory from a commereial standpoint. On the other hand, if the sheet is applied with the ribs outward and if there is the proper combination of tackiness of the pressure sensitive adhesive, thickness of the polyethylene film, depth of embossing of the Products with which this invention are conpolyethylene film, plasticity of the pressure sensicerned are made in numerous forms and used tive adhesive, and pressure applied when the for many purposes. In some instances the mateprotective film is placed on the pressure sensitive rial is wound into rolls in which case it is cusadhesive surface, the pressure sensitive adhesive tomary to treat the back of the sheet material becomes attached to the protective sheet only at to prevent the pressure sensitive adhesive from the parallelograms or rhombs and in addition the sticking to it. In other cases where the sheet pressure sensitive adhesive film takes on a more material is coated on both sides or where it is r less perfect mirror ima e of the prote tiv marketed in special forms such as sheets coated sheet. In such case a substantial portion of the on one side with a non-slip material it is 0115- pressure sensitive adhesive surface consists of tomary to apply a r tective sheet to the pres- 2o raised portions which are adhesively attached to sure sensitive adhesive. One very commonly the parallelogram n th pr t tiv sheet, used form of protective sheeting is Holland cloth, spaced from each other by depressed portions though other such materials have been proposed hich register with the ribs on the p otectiv and used such as a combination of thin paper sheet andprovide channels of substantial crossnd print 1 th or paper coated with shellac. section through which any entrapped gases can Where such sheets are employed it is difficult to escape. apply them to the adhesive surface in such a D p n ing pon the nditi ns, the pattern on manner that they are free from wrinkles. Furthe pressure sensitive adhesive may be practically thermore, these materials are opaque and make a r pr du ion n reverse of the pattern of the it impossible to inspect the pressure sensitive adprotective sheet. If conditions are notideal, the hesive coating after the protective sheet has been reproduction of the parallel g am becomes imapplied. Difiiculties are also experienced from perfect, first bein S ch at h e es of t e excessive sticking of the protective sheet to the raised rhombs of the pressure sensitive adhesive adhesive and many of these sheets which have pproach each other and the channels in the been used are not sufiiciently impervious to air adhesive become correspondingly reduced in ith th lt th t the dh i i improperly area. In the extreme case the pressure sensitive protected against oxidation. If oxidation 00- adhesive Will be Shaped t a r u t o rat er curs the adhesive loses its tack and becomes stiff than a mirror i age of the protective Sh t- In and unsatjsfactory such case the pressure sensitive adhesive con- We have discovered that pressure sensitive ad- Sists of depressed P a-Holo r s d aised ribs. hesive can be very satisfactorily protected by the In o r Wo d in t r m s e P use of pigmented m of polyethylene which tive sheet contactsthe pressure sensitive adhesive has been embossed to prgvide parallelograms OVGI substantially its entire area. Such COIldiwhich lie in substantially the same plane and ti011 is undesirable because it blocks D the which are separated from but attached to each esflape 0f 8 8 a d tends to result in blisters other by raised ribs which are relatively narrow such as are obtained when the embossed film is and shallow. We prefer to emboss with rhombs pp d W th the raised ribs in contact with the which are so formed that the ribs between the ure ensitive adhesive. rhombs form continuous lines extending to the We have further discovered that a Pressure Sides of t protective t. sensitive adhesive film can be produced which is We have further discovered that it is important n the form of raised h m s s p t d y nt the protective sheet be applied with the necting channels on sheet material coated in long rhombs next to the pressure sensitive adhesive Webs by pp y the embossed p tec ve sheet film nd th ib extending t a dl If the to the pressure sensitive adhesive as described, sheets are applied with the ribs downward in conremoving the protective sheet, and winding the.

materia1 into rolls. Such product has the advantages that there is a substantial reduction in the tendency for the pressure sensitive adhesive to stick to the back of the sheet material and that such product can be caused to adhere to other materials without wrinkling or forming blisters. If a sheet iscoated with pressure sensitive adhesive wherein the adhesive is in the form of a substantially smooth film there is a tendency for the sheet to buckle or even to-formblisters when it is attached to some other object. With the improved design of pressure sensitive adhesive obtainable according to this form of our invention such tendency is substantially reduced and it is very easy to spread out the sheet material so that it will be perfectly smooth. If material is applied under considerable pressure the sheet adheres firmly whereas if it is desired to have the sheet attached temporarily this can be done by applying light pressure such that only the rhombs contact the other object and the sheet can be much more easily detached.

We have illustrated'our invention by reference to drawings wherein:

Fig. l is a plan view of a portion of the pressure sensitive adhesive as it is formed according to the preferred embodiment of the invention;

Fig. 2 is'a plan of a piece of sheet material covered with the protective film;

Fig. 3 is a section along the lines 3--3 of Fig. 2;

Fig. 4 is a diagrammatic side elevation of a portion'of a form of apparatus suitable for carry-- ing out one modification of our invention;

Fig. 5 is a diagrammatic side elevation of a portion of a form of apparatus suitable for carrying out another modification of our invention; and

Fig. 6 is a section of the product made according to another embodiment of the invention.

Referring particularly to Fig. 3, the product consists of a backing I which may be paper, cloth, plastic or other suitable sheet material coated on one side with a pressure sensitive adhesive film 2 which is covered by the protective sheet of polyethylene 3. As is illustrated in Fig. l, the pressure sensitive adhesive consists of raised rhombs 4' separated bychannels 5. When the protective' sheet is on the film, as shown in Figs. 2 and 3, the channels 5 register with the openings 5 below the ribs '7 of the protective sheet.

Theembodiment shown in Fig. 6 isslmilar to that shown in Fig. 3 except that the face of the sheet material opposite the one which is coated with the pressure sensitive has a layer of granular material 8 attached to it by an adhesive 9.

In Fig. 4 we have illustrated a form of apparatussuitable for carrying out the process of' one modification of our invention. Referring there'- to, reading from left to right, the apparatus consists of sticks l in a conventional festooning apparatus on which the coated material l [is uspended and from which it travels over a toboggan 12 provided with a suction box I3 connected through opening [4 to a source of suction not shown inthe drawing. The protective sheet material is provided in the form of a roll I over which is hung a drag H, such as a sheet of canvas .or other suitable cloth, to the bottom of which is attached a weight 18. I'he upper end of the drag is adjustably attached to framework I9 so that the area of the drag which contacts the sheet material, and correspondingly the amount of the drag, can be varied. The apparatus'also contains tension rolls 20' and 2! be tween which there is an idler roll 22, counterroll 23, idler roll 2 and wind-up roll 25.

In employment of the apparatus the adhesive coated sheet H is brought down over toboggan l2 and into contact with the polyethylene film 2B. The combination is then threaded around rolls 20, 22, 2 l, 23 and 2E and fastened to wind-up roll 25. Suction is applied to the suction box [3 to assist in effecting tension on the sheet material and tension is also controlled by the tightness of a belt, not shown in the drawings, which drives tension rolls 20 and 2! from the same source of power as is applied to the wind-up roll 25, also not shown in the drawings. The wind-up roll. the'tension, idler'and counterrolls, toboggan and fest'oons are all conventional in the coating industry and the manner in which this form of ap paratus is used is well known in that art.

The apparatus illustrated in Fig. 5 is adapted for the manufacture of sheet material coated with pressure sensitive adhesive wherein the adhesive is in the form of raised rhombs as illustrated in Fig. 1 but no protective sheet is used. That apparatus is similar to the apparatus of Fig. 4 up to the idler roll 24 but differs from the apparatus of Fig. 4 by the provision of an idler roll 2'! and an additional wind-up roll 28. In making this form of product the sheet ma: terial is coated and covered with the protective sheet as in making the product according to the process of Fig. 4 but when the combined sheet reaches roll 2'! the protective sheet is separated from the adhesive coated sheet and pulled up around idler roll 21 and attached to wind-up roll 28.

As stated, we have found that it is necessary to control numerous factors in order to obtain this ideal condition of the pressure sensitive adhesive film. In general we have found that it is desirable to have the pressure sensitive ad-- hesive relatively plastic when the protective sheet is applied. This may be done by having the sheet material warm when the protective sheet is applied as by assembling the protective sheet on the pressure sensitive adhesive film when the product comes from the oven in which the sheet material is heated to remove solvents from the pressure sensitive adhesive coating.

We have also found it necessary to maintain at least a minimum ratio between the depth of embossing of the protective sheet and the thickness of the pressure sensitive adhesive film although this minimum is in turn somewhat dependent upon the pressure applied to the protective sheet when it is placed over the pressure sensitive adhesive film. Furthermore, there is a somewhat critical ratio between the thickness of the polyethylene film and the depth of the embossing.

The thickness of the pressure sensitive adhesive film is usually determined by limitations of the use for which the product is made as well as the kind of sheet material employed. For example, in making a sheet material for nonslip purposes where it is customary to coat the cloth backing on one side with granular material such as abrasive grains to make a product somewhat similar to abrasive cloth and on the other side with pressure sensitive adhesive, it is desirable to employ adhesive films of the order of .005 inch to .008 inch in thickness. On the other hand, where sheets are being made as by coating a sheet of paper with the pressure sensitive adhesive to provide products to be used as labels thepressure sensitiveadhesive filmmay be thin- 5. her. In general we have found that it is necessary to employ adhesive films at least about .003 inch thick in order to obtain satisfactory adhesion although this thickness is determined somewhat by the character of the adhesive used.

Where the pressure sensitive adhesive film is relatively thick the embossing should be correspcndingly deep since we have found that a lightly embossed sheetwhen applied to a thick film is likely to reproduce itself in the film rather than form the desirable mirror image. While we do not wish to be bound by any theories it has been suggested that this mirror image results when conditions are such that the ribs on the protective sheet are pressed against the pressure sensitive adhesive film so lightly that the .resilience of the polyethylene causes the ribs first to become embedded in the pressure sensitive adhesive when the sheet is pressed against the film and then to retract when the pressure is released thereby forming these raised parallelograms in the pressure sensitive adhesive which are spaced between depressed lines matching with the ribs on the protective sheet. In any event, by proper selection of the combination of the characteristics and structure described above along with suitable conditions of temperature and pressure the desirable configuration of the pressure sensitive adhesive film is obtained.

We will now illustrate our invention by specific examples. It is to be understood that the examples are not limitative but are merely descriptive of products and combinations which will result in the product of our invention.

Example 1 A drill cloth of such weight that a piece 32 inches wide contains 2.58 yards per pound, having a count of 72 X 48 and 14s warp was filled with 8 pounds per sandpapermakers ream of 480 sheets 9 x 11 inches of a phenol-formaldehyde resin. The cloth was then coated with 28 pounds per ream of 80 grit silicon carbide attached by a phenol-formaldehyde resin. Methods of making such products are Well known in the abrasive industry and will not be further described since they form no part of this invention. One suitable method, for example, is that described and claimed in U. S. Patent No. 2,184,896.

The back of the cloth was then coated with 6 pounds per ream of a priming adhesive which was heated for 1 hour at 175 F. to remove the solvent and a coating of pressure sensitive adhesive to the extent of 30 pounds wet weight was applied over the priming coat. This was then heated for 2 hours at 175 F. to remove the solvents.

The priming adhesive contained approximately 50% solids suspended in water, the solids being of the following composition:

The pressure sensitive adhesive was a solution containing 30% solids dissolved in gasoline. The solids composition was as follows:

Per cent GRS rubber 45 Staybelite resin 20 Hercolyn 8 Zinc oxide 27' "GRS rubber is a copolymer of butadiene with styrene manufactured according to a Government specification. The Staybelite resin is hydrogenated rosin and the Hercolyn is hydrogenated methyl abietate. Staybelite and Hercolyn are manufactured by Hercules Powder Company.

The pressure sensitive adhesive solution was prepared by milling the solid materials described to obtain a homogeneous mixture and then dissolving this mixture in the gasoline. 35 pounds per ream wet weight were applied which when dried left a film .00. inch thick.

After the solvent had been removed from the pressure sensitive adhesive the product was taken from the drying racks where it was heated in festoon form and was covered with a protective film of pigmented polyethylene which had a molecular weight in the range 15,000 to 25,000 and which had first been formed into a sheet .0055 inch thick and. then embossed in the form of rhombs the sides of which were approximately fi; inch long. The rhombs were formed with the long diagonal lengthwise of the sheet and of such shape that the greater diagonal was twice that of the lesser. The sheet had 11 rhombs to the inch crosswise of the sheet and 5 to the inch lengthwise. The depth of the embossing was approximately .002 inch. Its molecular weight was approximately 20,000 and it contained approximately .2% of a blue dye consisting of a copper salt of a phthalocyanine dye and about 1% of zinc oxide to increase the opacity of the film.

The protective sheet was applied in the apparatus illustrated diagrammatically in Fig. 4. Sufiicient tension was applied to the roll of embossed polyethylene to cause it to feed evenly ethylene film were determined both lengthwise and crosswise on a Scott paper tester in which the jaw was pulled at the rate of 12 inches per minute. Tests were made on strips finch wide with the jaws 1 inch apart at the start. Under these conditions of test the material tested lengthwise stretched 8 inches and broke under a load of 4 pounds. The cross stretch was 6 inches and the cross strength was 3%,; pounds.

Emample 2 lb. rope cylinder paper of a type commonly employed in the abrasive industry was first coated with a priming coat as described in Example 1, then with the pressure sensitive adhesive of Example 1, the wet weight of the pressure sensitive adhesive coat being 20 pounds per ream. When dry this left a film approximately .004 inch thick.

The protective sheet employed was .004 inch thick and had been embossed in the form of rhombs the sides of which were inch long. The rhombs were formed with their long diagonals lengthwise of the sheet and of such proportions that the long diagonals were approximately twice that of the lesser. The sheet had 14 rhombs to the inch crosswise and. 6 to'the inch lengthwise. The depth of the embossing was .0015. inch. A strip tested as described. in Example 1 pulled lengthwise broke under, aload of 41 pounds and. stretched. 4 inches. Crosswise it broke at 3 pounds and stretched 3 inches. It had amolecular weight of approximately 20,00,0and contained approximately 2% of a green. dye consisting of a copper salt of a phthalocyanine dye and about 1% of zinc oxide to increase the opacity of. the film.

The sheet was applied as described. in. Example 1 but was removed in the apparatus illuse trated in Fig. 5 by stripping it from the pressure sensitive adhesive film around; idler roll 2! and wound upon roll 28. The productobtained had the pressure sensitive, adhesive in substantiallythe shape illustrated in ,Fig; 1.v The protective sheet was easily stripped fron'rthe pressure sensitive adhesive and the product was readily unwound from the roll form inwhich. it was prepared.

We have stated that there are certain critical conditions required in order to producetheprodnot of the raised rhombs. ences between various compositions of pressure. sensitive adhesive it is impractical to attempt. to specify the exact conditions for all the various modifications in which the invention may be em ployed. We have given two specific examples and have there described conditions which resulted in the desired configuration of the pressure sensitive adhesive film. Following are statements of the conditions which tend to promote formation of this desired pattern.

1. With increased thickness of pressure-sensitive adhesive it is necessary to increase. the depth of embossing of the protective sheet.

2. For any given plasticity of the pressure sensitive adhesive, which increases-with the temperature, and for any given protective sheet elasticity, there is a maximum pressure'at which-the sheet can be applied to the filmwithout causing a reproduction rather than a mirror image. The pressure should preferably be only. sufiicient to bring out the mirror image as increases in pressure cause first a tendency for closure of the, channels and eventually a reproduction.

3. The embossed film must be applied with the ribs out.

4. The depth of embossing should be about 25-50% of the thickness of the protective sheet.

5. In general the thickness of the protective sheet should not be less than the thickness of the pressure sensitive adhesive film nor more than about .007 inch for pressure sensitive adhesive films of the thickness usually employed.

6. While the desired pattern can be reproduced, by the use of protective sheets embossed with parallelograms, we have found that where the parallelograms are squares there is, some tendency for the formation of blisters, possibly because one-half of the channels run lengthwise of the sheet Whereas when the embossing is in the form of rhombs the channels all extend to the edges. For this reason we prefer to use rhombs and in general have found that it is desirable to have the rhombs with the long diagonals running lengthwise of the film and being approximately twice as long as the short diagonals.

In the specific examples we have described the use of zinc oxide to increase opacity and a, particular green pigment which is sold by the Harmon Color Works of Patterson, Pennsylvania, under the-trade-mark Opaline.-.G1. Pigments Because of the differforthis purpose are well, known and are manu-L factured; by. numerous concerns such as the Du Pont Company and the Imperial Paper and Color Corp. of. Glens Falls, New York. One most common type of pigment is the salt of a phthalocyanine which can be obtained in either a blue or a green color, typical pigments being Du Ponts Monastral Green or Rama-p0 Green, or Harmons Luna Blue and Imperials Red F 1869 and Sherwood A 4436. Other pigments may be used, including both organic and inorganic materials. Where organic pigments are used we employ them in the range of about .05 to 2% andzwhere inorganic pigments are used we may use from about 1% to about 10%. In the examples we have described the use of 1% of zinc oxide to increase the opacity of polyethylene film. The zinc oxide may be omitted or, if some increase in opacity above that imparted by an organic pigment is desired, inorganic pigments either alone or along with organic pigments may also be used.

We have illustrated our invention by reference to two specific examples and have set forth certain principles to be applied in carrying out the invention. We have also set forth a suggested explanation of why this unexpected pattern is formed, It is to be understood that our invention is not restricted to the specific examples and that we are not to be bound by the theories as to why the process results in the product but, rather, that the invention is to be of the scope set forth in the appended claims.

We claim:

1. As a new article of manufacture, sheet material having a film of pressure sensitive adhesive adhesively attached to at least one side, and a protective sheet consisting essentially of pigmented polyethylene embossed to form parallelograms which lie substantially in the same plane and which are separated from but attached to each other by raised ribs adhesively attached to the outer surface of the pressure sensitive adhesive film with the ribs on the outer side, the pressure sensitiveadhesive illm being in large part in the-form of para-llelograms which are separated by channels in which the pressure sensitive adhesive coating is thinner than that of the parallelograms and are attached to the parallelograms on the protective sheet, the channels in the pressure sensitive adhesive and the ribs on the protective sheet forming channels which communicate to the edge of the sheet through which gases which might be entrapped between the pressure sensitive adhesive film and the protective sheet can escape whereby the protective sheet is substantially free from blisters and bubbles.

2. Article as claimed in claim 1 wherein the pressure sensitive adhesive film is about .003 to .008 inch thick and the polyethylene sheet is about .003 to .007 inch thick.

3. Article as. claimed in. claim 2 wherein the depth of the embossing of the protective sheet is about 25-50% of the thickness of the sheet.

4. Article as claimed in claim 3 wherein the parallelograms are rhombs.

5. Article as claimed in claim 4 wherein the thickness of the pressure sensitive adhesive film is about .004 to .007 inch, the thickness of the protective sheet is about .0045 to .0055 inch, the length of each side of the rhombs is approximately g inch and the depth of embossing is about .0015 to .002 inch.

6. Article as claimed in claim 5 wherein only one side of the sheet material is coated with pressure sensitive adhesive and the other side is provided with a coating of granular material.

7. Article as claimed in claim 6 wherein the polyethylene has a molecular weight of about 15,000 to 25,000.

8. Article as claimed in claim 1 wherein only one side of the sheet material is coated with pressure sensitive adhesive and the other side is provided with a coating of granular material.

9. As a new article of manufacture, sheet material comprising a backing having a substantially planar surface and a coating of pressure sensitive adhesive attached to said surface, said coating consisting of a multiplicity of parallelograms separated from each other at their outer surfaces but joined at the surface of the backing by thinner films of the pressure sensitive adhesive, the thinner films being in the form of substantially continuous channels which provide passageways for gases whereby when the pressure sensitive adhesive coated surface is pressed onto another surface to cause attachment thereto the air which might be entrapped between the two surfaces escapes through the channels and the sheet GEORGE J. GOEPFERT. HOWARD M. CANFIELD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,543,283 Falor et a1 June 23, 1925 1,823,278 Martin Sept. 15, 1931 2,156,279 Drew -1 May 2, 1939 2,178,566 Dike et a1 Nov. 7, 1939 2,256,864 Ferguson Sept. 23, 1941 2,264,628 Engert et a1 Dec. 2, 1941 2,292,024 Dreher Aug. 4, 1942 2,485,295 Larson Oct. 18, 1949 2,486,669 Nassimbene Nov. 1, 1949 2,541,498 Calvert Feb. 13, 1951 2,596,377 Derman May 13, 1952 OTHER REFERENCES Precocious Plastic, article published in Modern Plastics for February 1948, page 78.

Claims (1)

1. AS A NEW ARTICLE OF MANUFACTURE, SHEET MATERIAL HAVING A FILM OF PRESSURE SENSITIVE ADHESIVE ADHESIVELY ATTACHED TO AT LEAST ONE SIDE, AND A PROTECTIVE SHEET CONSISTING ESSENTIALLY OF PIGMENTED POLYETHYLENE EMBOSSED TO FORM PARALLELOGRAMS WHICH LIE SUBSTANIALLY IN THE SAME PLANE AND WHICH ARE SEPARATED FROM BUT ATTACHED TO EACH OTHER BY RAISED RIBS ADHESIVELY ATTACHED TO THE OUTER SURFACE OF THE PRESSURE SENSITIVE ADHESIVE FILM WITH THE RIBS ON THE OUTER SIDE, THE PRESSURE SENSITIVE ADHESIVE FILM BEING IN LARGE PART IN THE FORM OF PARALLELOGRAMS WHICH ARE SEPARATED BY CHANNELS IN WHICH THE PRESSURE SENSITIVE ADHESIVE COATING IS THINNER THAN THAT OF THE PARALLELOGRAMS AND ARE ATTACHED TO THE PARALLELOGRAMS ON THE PROTECTIVE SHEET, THE CHANNELS IN THE PRESSURE SENSITIVE ADHESIVE AND THE RIBS ON THE PROTECTIVE SHEET FORMING CHANNELS WHICH COMMUNICATE TO THE EDGE OF THE SHEET THROUGH WHICH GASES WHICH MIGHT BE ENTRAPPED BETWEEN THE PRESSURE SENSITIVE ADHESIVE FILM AND THE PROTECTIVE SHEET CAP ESCAPE WHEREBY THE PROTECTIVE SHEET IS SUBSTANTIALLY FREE FROM BLISTERS AND BUBBLES.

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