Self Releasable Nonmoisture Activated Wall Covering

Abstract

A wall covering, such as wallpaper, having a coating of dry, encapsulated adhesive on the back surface which is made tacky by the application of heat and/or pressure in the absence of moisture, and a method of manufacturing wallpaper which includes applying the encapsulated adhesive in the paper making machine or in a separate coating operation.

Description

This invention relates to wall covering having a dry adhesive on its working surface which does not require moistened adhesive at the time of its application to a wall surface, and a method of manufacture thereof. The adhesive material may be applied to the working surface at any stage during manufacture but for economic reasons it may be preferable to apply the adhesive to the working surface before the converter prepares the decorative surface.

Accordingly, a primary object of the invention is to provide a wall covering which does not require a moistened adhesive at the time of its application to a wall surface.

Although the invention is applicable to a wide variety of wall coverings it will be described as applied to wallpaper. It should be understood, however, that upon suitable modification the invention can be adapted for use with cloth, wood veneer, plastic or combinations thereof.

Another object is to provide a wallpaper as above described, or at least the base stock therefor, which can be manufactured either entirely on existing paper making machines utilizing presently known methods of coating application whereby extensive modifications of the paper making machines and processes can be avoided, or, alternatively, partially on an existing paper making machine followed by a coating operation separate from the paper making machine, in which event very little or no modification need be made in the paper making machine.

Another object is to provide a wallpaper as above described which may be easily applied by a paper hanger and in which the undesirable pattern matching problem common to wallpapers which require moistened adhesive during application is eliminated.

Another object is to provide a wallpaper as above described which can be made tacky by the application of heat or pressure, or a combination of both heat and pressure, but which is sufficiently insensitive to the temperatures and pressures encountered in the manufacture, shipment and storage processes to resist premature activation.

Another object is to provide a wallpaper as above described which has the characteristic of being self releasable so that it may be easily removed after a period of years. If a heat activatable adhesive is used, it will only be necessary to reapply heat to strip the paper from the wall or other base surface to which it has been applied.

Other objects and advantages of the invention will become apparent from the following description wherein a preferred embodiment is described in detail.

The invention is illustrated more or less diagrammatically in the accompanying figures wherein:

FIG. 1 is a section of a conventional paper making machine which has been slightly modified to carry out the invention;

FIG. 2 is a diagrammatic view of an air knife coater; and

FIG. 3 is a section of a conventional paper making machine in which an air knife coater has been incorporated.

Like reference numerals will be used to refer to like parts throughout the following description of the invention.

Wallpaper stock is currently manufactured by making a base stock in a conventional manner on a paper making machine. The base stock is then subjected to a conversion process which may include printing, coating, and/or embossing operations. In the case of prepasted wallpaper, which is considered to be adhesive coated wallpaper which is moisture activated, adhesive materials are placed on the working surface of a moving web of paper, generally during the conversion process and after the coating, printing and/or embossing operations. If the adhesive materials are applied from a liquid solution thereof the liquid carrier is dried to yield a dry backing. The paper hanger activates the adhesive material by applying moisture to the working surface of the paper just prior to its placement on a wall surface.

In the process which is included in this invention adhesive material containing an activating agent in encapsulated form is applied to the back or working surface of a moving web of paper. The paper hanger activates the dry adhesive on the paper by the application of heat and/or pressure in the absence of moisture. Under certain conditions, as in humid climates or when it is expected that the paper will be subjected to artificially created humid conditions, it may be preferable to moisten the paper just prior to application to ensure against buckling and cockling at high relative humidities. It should be understood, however, that the moisture, if used, is for the purpose of, in effect, prestretching the paper, and not for the purpose of activating the adhesive. Even if moisture is used, however, the paper will be far easier to handle and apply than conventional prepasted wallpaper which requires moisture to make the adhesive sticky or tacky.

It is quite possible to apply the adhesive material at any point in the manufacture of the finished product, including a point in time subsequent to the final printing or embossing, that is, during the conversion process. Since the application of the adhesive is one of the less expensive operations in the entire process it is preferred, however, to apply the adhesive material early in the manufacturing process.

Accordingly, in one embodiment of the invention encapsulated adhesive material is applied to the working surface of the moving web of paper at a station in the conventional paper making machine, preferably at a location just ahead of the dryer. This mode of application is illustrated in FIG. 1 wherein a portion of the paper making process is diagrammatically illustrated.

A moving web of paper is indicated generally at 10. The web, at the left edge of FIG. 1, is approaching a conventional breaker stack 11 which consists of a number of rolls. At the time the paper reaches the breaker stack it may be moving at a lineal speed of from 400 to 2,000 feet per minute and may have a moisture content of about 20 percent to 5 percent.

As the web 10 leaves the breaker stack it passes under a guide roller 12 and then three additional guide rollers 13, 14 and 15 which are so positioned as to guide the web downwardly into a coating station indicated generally at 16 at which, as illustrated in the drawing, the coating is applied directly to the aforesaid back or working surface of the paper.

After passing through the coating station 16 the web enters a drier section indicated generally at 17. In order to provide sufficient time for the setting of the coating station, a drying roll 18 is placed a convenient distance from the coating station, which in this instance is somewhat below the conventional drying rolls 19, 20, 21, 22 and 23. This arrangement is desirable because the wire side of the web to which the coating has been applied comes into direct contact with the surface of a drying roll in the dryer section and enough time must be provided to dry the coating sufficient to avoid sticking. It will be noted that by virtue of the illustrated arrangement of rolls the coated working surface does not come into contact with a roll until it reaches roll 19 in the cluster of five rolls in the dryer section.

After passing through the dryer section the web direction is changed by idler roll 24 and the web then passes through a conventional calendar section 25 and leaves the machine.

It is, of course, possible for the coated web to go immediately into the conversion process but it will be understood that usually the stock will be coiled in roll form and shipped to the converter.

The coating station 16 consists essentially of a supporting roll 28 which may be approximately 36 inches in diameter, and carries a rubber cover 29. A small roll is indicated at 30, the small roll being approximately 12 inches in diameter. The small roll is mounted in adjustably positionable bearings 31 and is driven by variable speed driving means 32. A separate speed controller for motor 32 is indicated at 33 whereby roller 30 may be separately controlled as to speed, direction of rotation, radial movement toward and away from the supporting roll 28, and the pressure to be applied to the web. Preferably the diameter of the small roller 30 is small enough to minimize the area of contact with the web yet large enough to apply pressure evenly throughout its length and form, with the web and end pans of customary design (not shown), a space for a pool of coating.

A coating is continually supplied to the pool formed between the rollers and end pans by a conventional supply means. A header 34 having openings through which the coating material is discharged into the pool may be utilized for example. Preferably the coating is continuously supplied to the pool area, the rate of supply being controlled to accommodate web speed, paper absorption, and desired coating weight. Small roll 30 is preferably positioned to engage the supporting roll 28 above the horizontal plane passing through the axis of the supporting roll. The nip is thus placed into proper position with respect to the space requirement of an existing paper making machine, the angle at which the web travels toward the supporting roll, and the angle at which the web must leave the supporting roll. The web must come into supporting contact with the roll 28 before it enters the pool of coating and it should leave the supporting roll 28 as close as practical after passing through the nip in order to prevent the coating from being absorbed through the web and deposited on the roll. Furthermore, it is desirable to start the setting and drying of the coated web at the earliest moment because the coated working surface of the web comes into bearing contact with dryer roll 19. For a more complete description of a suitable mode of applying the coating to the working surface reference is made to U.S. Pat. Nos. 3,146,159 and 3,231,418. It will be understood, as described in those patents, that the speed of roll 30 is preferably suitably less than that of roll 28, and may be as low as 10 percent of the speed of the web.

The amount of dry adhesive material which is coated on the working surface of the web may vary. Preferably about 16 to 18 pounds of adhesive material per 3,000 square feet of paper should be employed.

In the event only a portion of the desired coating may be feasibly applied at coating station 16, a second coating may be employed.

Under certain circumstances a greater or lesser amount of adhesive may be employed. It may be desirable for example to place a preliminary or barrier coating of latex and kaolin clay or other material compatible with the adhesive and the paper on the web to reduce the coat weight of adhesive required. The precoat serves the additional function of preventing soak-through of the liquid adhesive coating. The employment of such a precoat may make possible the reduction of the weight of adhesive required to about 10-15 pounds per 3,000 square feet. This is an important economic advantage since the adhesive material is relatively expensive at the present time.

A barrier coating composition of 81/4 parts kaolin clay, 11/4 parts styrene butadiene latex and 1/2 part starch made at 53 percent solids and having a viscosity of 3,400 centipoises may be used. The ratios can be changed somewhat, or functionally equivalent materials substituted in whole or in part, so long as satisfactory holdout characteristics are obtained. About 8 to 10 pounds of barrier coating per 3,000 sq. ft. of paper will efficiently seal the web and reduce strike in of the subsequent adhesive coating. When a barrier is applied, another coating station 16 followed by dryers could be placed in the paper making machine of FIG. 1 just ahead of the illustrated coating station.

If desired, the adhesive coating may be applied off the machine by an air-knife coater, and such a variant is indicated in FIG. 2. The entering web 40 passes between a pair of rolls 41, 42, the bottom roll 42 being a dip roll which picks up coating 43 from pan 44 and applies it to the bottom of the web. The web then passes around the backing roll 45 where an air jet 46 blows off the excess coating. For a more complete description of an air-knife coater, reference is made to U.S. Pat. No. 3,341,351. The coating weight can be controlled by the solids and viscosity of the coating as well as the air pressure or velocity of air applied to the jet 46. The paper is then passed around a direction changing roll 47 and is then carried through a tunnel dryer 48 in which high velocity heated air is used to dry the paper. A pair of pull rolls are indicated at 49, 50.

The series of rolls 51-55 are used to chill the surface of the paper. Cold water is circulated through rolls 51, 52 and 54 to reduce the temperature of the paper. It has been found that this chilling operation reduces the tendency of the coated paper to block or stick to adjacent layers of paper when it is wound up into a roll. This same chilling technique might be used advantageously by the wallpaper converter if embossing is required should sticking present a problem when an embosser is used. In this event the chilling rolls would be installed between the festoon dryer and the embosser.

In FIG. 3, both a barrier coating station 16 and an air-knife coater, indicated generally at 39, for applying adhesive have been incorporated into a paper making machine. In this embodiment three direction changing rolls 36, 37 and 38 are employed to correctly orient the barrier coated web 40 preparatory to entering the coater. It will be understood that while this embodiment has the advantage of completing the manufacture in one run through the machine, it has the disadvantage of losing production of the entire machine should a malfunction occur only in the air-knife coater. Accordingly, the technique used will depend to some extent on the performance reliability of the equipment and other factors.

The adhesive material applied in coating station 16 is preferably of the encapsulated type. Thus, encapsulated adhesive materials in a suitable liquid carrier such as water are coated at the coating station 16, and the carrier is evaporated in the dryer section 17.

The adhesive material may be either of the heat or pressure activated type, or a combination of both types. If a heat activated type is employed the adhesive should not be activatable, or tackifiable, at a temperature below about 175.degree. F. since the paper is subjected to temperature up to this value during the paper making process. The theoretical upper limit of the heat activatable temperature range is of course the scorching temperature of the paper which will vary from paper to paper. For wallpaper stock an appropriate temperature range would be about 190.degree. to slightly above 200.degree..

Methods of formulation of encapsulated adhesives are illustrated and described in greater detail in the Green, et al. U.S. Pat. No. 2,800,457, and the Green U.S. Pat. 2,800,458 to which reference is made for a further description.

In this connection, a heat activatable capsular adhesive formulation containing 39.4 percent solids by weight and having a Brookfield viscosity of 60 c.p. with the No. 1 spindle at 60 r.p.m. may be prepared following the teachings of the aforesaid patents. Specifically, only about 10 percent to about 20 percent of the dry particles need be encapsulated. The encapsulated material should include about one-third of the solid plasticizer which may, for example, be di-octyl phthalate, although more than one plasticizer may be used if desired. The dry latex, which may be a ter-polymer, for example an acetate acrylic, and the remainder of the plasticizer need not be encapsulated. Such a formulation was applied to hanging paper stock and the the following observed:

a. When applied at the rate of 181/3 pounds per ream (24 .times. 36 .times. 500) on 433/4 lb./ream hanging paper stock and heat activated the stock was found to adhere very satisfactorily to a latex painted wall, 13 lb./ream bond paper, wall board and Masonite. Block tests run at 106.degree. F. and 1.5 psi were completely block free, and there was only "light pick" at 8 psi.

b. When a lower coat weight of about 13 lb./ream was employed and application was made with a house-hold flat iron good adhesion was achieved.

The above adhesive had substantially no open tack time. This however is permissible because a paper hanger does not need to slide the paper on the wall surface to ensure pattern match since there is no distortion of the paper due to the presence of excess moisture. A tack time of varying lengths of time may be provided however, if desired, and it is contemplated that periods of up to 6 minutes may be provided, though as a practical matter one-half minute or less may be quite adequate.

Alternately, a heat activatable capsular adhesive formulation may be used which is similar to the one described above except that it may contain about 50 percent solids by weight. Again, only about 10 percent to about 20 percent of the dry particles need be encapsulated. The encapsulated material should include about one-third of the solid plasticizer.

It should also be understood that other modifications may optionally be employed. For example, in the event the adhesive coated paper exhibits a tendency to curl, a roll 30 may be used having a textured surface, a suitable example being disclosed in co-pending application Ser. No. 547,887 which is assigned to the assignee of this application. It will be understood that a continuous film of adhesive has a different expansion and contraction capability than the paper base stock. Use of such a textured roll would result in the application of essentially a noncontinuous film of adhesive which would overcome the tendency to curl. Such a noncontinuously coated roll would have the additional beneficial effects of reducing the coating weight necessary, and allowing the paper to "breath" after it is applied to a wall.

Another feature which may optionally be used if advantageous is a spray, applied just prior to winding, to prevent blocking in the rolls of finished paper. The spraying step may conform in all pertinent particulars to the conventional Oxidry process, or the Ortman-McCain hydrosol process, both of which are widely employed in offset printing to prevent sheets sticking together, and ink smearing.

Yet another feature which may optionally be used if advantageous is a breaker bar. By passing the paper having the dried adhesive film thereon over a breaker bar the film is fractured by the placement of minute cracks therein. This will be particularly helpful when a continuous adhesive film has been formed because the cracks permit the surface to breathe, i.e., since the surface is not completely sealed the tendency to curl with changes in relative humidity would be reduced or eliminated. If desired the breaker may be inserted in a rewinder operation wherein the rolls are slit to the size required by the customer instead of after the drying operation.

The coated paper may be applied by either radiant or conductive heat. A flat metal applicator may be used to apply conductive heat. If a heated roller is employed it should preferably be flattenable in order to insure a more even application of heat. Any conveniently constructed applicator may be employed, such as a hot plate followed by a roller.

One outstanding advantage of the present invention is particularly apparent during the application process, especially when the paper is exposed to a dry environment such as the southwestern states. In such an environment the paper hanger need merely place the paper, in a dry condition, on the wall surface by a preliminary tacking operation such as touching the applying instrument to one or two places near the ceiling of the room. Since no moisture is used the paper does not stretch and an exact pattern match can be achieved. As soon as the pattern match is established the applying instrument is merely passed back and forth over the surface of the paper. In humid environments, moisture may be applied to ensure prestretching of the paper, but addition of moisture for this purpose does not create the usual difficulties associated with prepasted wallpaper.

From the standpoint of application to a wall surface it will be apparent that heat activated adhesive may be more desirable from the standpoint of ease of release from the wall when a change of paper is desired.

However, a paper having an encapsulated adhesive which is activatable by a combination of heat and pressure may be very advantageous under certain conditions. The adhesive selected for such an application should however take into account the temperatures and pressures encountered in paper making, converting, storage, and shipment. Thus, even if one of the two activating conditions is present, the adhesive will not tackify because the other condition is absent. A heat and pressure activated adhesive which requires a temperature of around 175.degree. F. and minimum pressure of about 5 psi will be quite feasible, and these conditions may be readily produced by the paper hanger at the time of application to a wall surface.

It should further be noted that it is not necessary to encapsulate all components of the adhesive material. Only the adhesive or only the plasticizer may be encapsulated and in many instances this may be the preferred mode since at the present time partially encapsulated adhesives are less costly than fully encapsulated adhesives. Furthermore, the percent of solids used may vary, depending on the particle size required and other factors. At the present time it is contemplated that the percent of solids may vary from about 20 percent to 50 percent.

One of the greatest advantages of wall covering made as above described is its ability to be stripped from the receiving surface after placement thereon. Further, the ability to strip an already applied wall covering is not time restricted to any substantial degree. Thus, the applier, who may for example be a home owner as contrasted to a professional paper hanger, may decide a few minutes or a few years after the covering has been applied that it does not appear aesthetically pleasing due to any one of a number of factors, such as misjudging seam placement or improper measurements during initial application, or a desire to change patterns after the passage of time. To strip the covering it is only necessary to reapply heat and/or pressure to the exposed surface. The application of the proper medium will retackify the adhesive, and then the covering can be easily stripped from the wall or receiving surface. The stripping does not require any intentionally added moisture.

From the foregoing it will at once be understood that the invention may be practiced with variations which are obvious to those having ordinary skill in the art. Accordingly, the scope of the invention should be limited not by the scope of the aforegoing exemplary description but solely by the scope of the hereinafter appended claims.

Claims

I claim:

1. A decorative wallpaper, said decorative wallpaper including

a conventional, flexible hanging base stock,

a preliminary coating applied to the working surface of said hanging base stock,

said preliminary coating consisting of a composition containing kaolin clay and latex,

a final coating of adhesive material in dry form applied over the preliminary coating,

said adhesive material being partially encapsulated in unbroken capsules,

said adhesive material further being tackifiable by the application of heat or pressure, or a combination of heat and pressure, in the absence of moisture.

2. The decorative wallpaper of claim 1 further characterized in that the partially encapsulated adhesive is heat activatable.