WO2000023285A1

WO2000023285A1 - Photo album page adhesive with color stability

Info

Publication number: WO2000023285A1
Application number: PCT/US1999/024096
Authority: WO
Inventors: Kiem H. Dang; Marilee M. Reski
Original assignee: H.B. Fuller Licensing & Financing, Inc.
Priority date: 1998-10-22
Filing date: 1999-10-18
Publication date: 2000-04-27

Abstract

The present invention relates to a photograph album page for releasably mounting photographs. The album page has at least one mounting surface and a transparent cover sheet wherein the mounting surface comprises a stain-free adhesive material coated thereon. The adhesive comprises from about 20 wt-% to about 98 wt-% of the adhesive of at least one latex and from about 2 wt-% to about 20 wt-% of the adhesive of at least one hiding agent. The adhesive releasably secures photographs between the mounting surface and the transparent film.

Description

PHOTO ALBUM PAGE ADHESIVE WITH COLOR STABILITY

Field of the Invention This invention relates to a photographic album page adhesive which has improved color stability with time.

Background of the Invention

Photo album pages having a coating of a releasable pressure sensitive adhesive have been used for many years. Typically, these photo album pages comprise one substrate coated with the releasable adhesive and a second substrate which is a transparent face sheet.

These pages are designed to snuggly, yet removably hold photographs in place.

Natural latex (1,3-butadiene, 2-methyl) based adhesives have been used for coating photo album pages but discoloration or yellowing of the photo album page due to exposure to elevated temperatures or ultraviolet light is an undesirable characteristic which occurs upon use of such adhesives.

Synthetic based adhesives, such as acrylic type latex, have also been used for releasable coatings on photo album pages but there are several problems associated with these systems as well which include low heat resistance and lack of a smooth peeling characteristic. The harder quality of these synthetic acrylic type latex adhesives causes the peel to be zippery and noisy which is undesirable to manufacturers of magnetic photo albums and to the end user as well.

U.S. Patent No. 5,569,503 issued October 29, 1996 to Piotroski teaches a mounting substrate for displaying items such as photos which utilizes synthetic latex based adhesive which consists of a solid phase including an aliphatic acrylic elastomer and a liquid phase including an aliphatic alkene glycol and water, for use in mounting the photos. The solid phase also contains an inorganic oxide filler selected from the group consisting of aluminum oxide, calcium oxide, titanium oxide and silicon dioxide, with the preferable filler being silicon dioxide. See column 2 lines 5 to 8, lines 62 to 67 and column 3 lines 1 and 2. The elastomer may be selected from the group consisting of methyl, butyl, propyl and isopropyl acrylate elastomers. The liquid phase of the adhesive is comprised of an aliphatic alkene glycol and water. The glycol may be selected from the group consisting of methylene, ethylene, propylene and isopropylene glycol.

Piotroski states at column 1 lines 8 to 14 that "previous photo album adhesives that use organic latex could not provide a uniform and solid adhesive coverage on the substrate page and that other problems inherent in latex-based adhesive photo pages are discoloration, photo damaging and loss of adhesiveness or blocking after a period of time." Piotroski further goes on to state at lines 25 to 29 that "the development of transparent pocket sheets are evidence of the problem that is inherent in the latex-based adhesive pages, namely they lose their adhesiveness, photos fall out of the album or blocking takes place." Hence, the adhesive of Piotroski, it is taught, overcomes the problems associated with the latex-based adhesives.

The synthetic latex based adhesives of the prior art have not been able to meet all of the criteria needed for a photographic album adhesive, namely heat resistance, resulting in the lack of commercial success. Additionally, the present applicants have found that various plasticizers utilized in latex based adhesives have migrated causing staining of the mounted items, such as photographs.

Hence, industry would find advantage in a mounting adhesive that overcomes these problems.

Objects of the Present Invention

It is an object of the present invention to provide an improved adhesive composition for releasably mounting flat items, especially photographs.

The present inventors have now found a unique combination of ingredients which overcomes the aforementioned problems through the use of an adhesive comprising a latex and certain inorganic pigments. A synthetic latex may be added to a natural latex to modify the characteristics of the natural latex based adhesive. These compositions exhibit improved adhesiveness and blocking resistance over 100% natural latex based compositions, high heat resistance and superior color retention over time making them ideally suited for use as photographic album page adhesives. Summary of the Invention

The present invention relates to a mounting substrate for releasably mounting flat items said mounting substrate comprising an adhesive coated mounting surface and a transparent cover sheet wherein said mounting surface comprises a stain- free adhesive material coated thereon said adhesive comprising from about 20 wt-% to about 98 wt-% of the adhesive of at least one latex and from about 2 wt-% to about 20 wt-% of the adhesive of at least one hiding agent. The adhesive releasably secures photographs between the mounting surface and a transparent film. It has been found to be preferable to the present invention to utilize a combination of a natural latex and a synthetic latex in order to achieve superior properties.

The hiding agents preferably have a refractive index of greater than 2.0 and more preferably greater than about 2.5. The preferable hiding agent is titanium dioxide.

The present invention further relates to a photograph album page for releasably mounting photographs. The album page has at least one mounting surface and a transparent cover sheet wherein the mounting surface comprises a releasable adhesive material coated thereon. The adhesive comprises from about 20 wt-% to about 98 wt-% of the adhesive of at least one latex and from about 2 wt-% to about 20 wt-% of the adhesive of at least one hiding agent. The adhesive releasably secures photographs between the mounting surface and the transparent film.

The photograph album page may further have a pair of opposed mounting surfaces, each mounting surface having a transparent cover sheet wherein said mounting surfaces each comprise a releasable adhesive material coated thereon for releasably securing said photographs to said mounting surface. The adhesive is of the repositionable variety having a target peel strength and exhibits no adhesive transfer. Furthermore, the adhesive has excellent adhesion to polymeric film materials and exhibits peels on such materials that are smooth and non- zippery.

The photograph album page is improved in that the adhesive exhibits excellent color retention over time even with elevated temperatures or ultraviolet light. Detailed Descriptions of the Preferred Embodiments

The adhesive of the present invention comprises at least one latex. The latex can include a natural latex, a synthetic latex and mixtures thereof, preferably a natural latex. These compositions are typically supplied in water at about a 50-75% solids emulsion and may more typically be supplied as 50-65% solids emulsions. These emulsions are then useful in the present adhesive from about 20%) to about 98% by weight of the composition. An example of a useful natural latex (1,3-butadiene, 2-methyl) homopolymer is Alcantex Latz®, a 62% solids emulsion available from Alcan Rubber and Chemical Co. in New York, NY.

The present invention may also comprise a synthetic latex. These are aqueous dispersions of water-insoluble latex polymer prepared by emulsion polymerization which is well known in the art. See D.C. Backey, Emulsion Polymerization (Wiley, 1975). Any monomer mixture which yields water-insoluble polymer latex which is dispersible in water may be used to prepare the latex polymers of the present invention. For example, vinyl acetate, which itself has appreciable water solubility as a monomer, may be employed as homopolymers of vinyl acetate which are water-insoluble. Useful monomers include vinyl acetate, and acrylic monomers such as the alkyl esters of acrylic acid and methacrylic acid including the (C,-C₈)alkyl esters of acrylic acid and the (C,-C₈)alkyl esters of methacrylic acid, such as methyl methacrylate, methyl acrylate, ethyl acrylate, ethyl methacrylate, n- butyl methacrylate w-butyl acrylate, 2-ethylhexyl acrylate, w-octyl acrylate, sec-butyl acrylate, isobutyl methacrylate, and cyclopropyl methacrylate.

Minor amounts of alpha, beta-ethylenically unsaturated monomers with appreciable water solubility, such as acrylic acid, methacrylic acid, itaconic acid, citraconic acid, acrylamide and methacrylamide, may also be used in preparing the emulsion polymers useful in the present invention. It is well known in the art that the copolymerization of such water-soluble monomers with water-insoluble monomers often confers desirable properties upon the resultant copolymer including long-term latex stability, dispersibility, increased adhesion to specific substrates and so forth. Acidic monomers which may be used in preparing the emulsions employed in the present invention are alpha, beta-monoethylenically unsaturated acids such as maleic, fumaric, aconitic, crotonic, citraconic, acryloxyproprionic and higher oligomers of acrylic, methacrylic and itaconic acids. Further examples of acidic monoethylenically unsaturated monomers which may be copolymerized to form the water-insoluble addition polymers of the present invention include partial esters of unsaturated aliphatic dicarboxylic acids and in particular, the alkyl half esters of such acids. Examples of partial esters are alkyl half esters of itaconic acid, fumaric acid and maleic acid wherein the alkyl group contains 1 to 6 carbon atoms including methyl acid itaconate, butyl acid itaconate, ethyl acid fumarate, butyl acid fumarate and methyl acid maleate.

Another way of describing these monomers may be unsaturated carboxylic acids including itaconic acid, citraconic acid, crotonic acid mesaconic acid, maleic acid, fumaric acid and so forth and the ,β-unsaturated dicarboxylic acid esters of the dicarboxylic acids described above including aromatic esters, cycloalkyl esters, alkyl esters, hydroxyalkyl esters, alkoxy alkyl esters and so forth.

The emulsion polymers may contain alpha, beta-ethylenically unsaturated aromatic monomers including styrene, vinyl toluene, 2-bromo-styrene, o-bromo-styrene, p-chloro- styrene, o-methoxy styrene, p-methoxy-styrene, allylphenol ether, allyltolyl ether and alphamethyl-styrene. It is preferable to the present invention, for some embodiments, to utilize aromatic type synthetic latex rather than aliphatic latex, either alone or in combination with a natural latex. Styrene-butadiene synthetic latex, for instance, is a preferable latex for use in the present invention.

The emulsion polymers may contain polar or polarizable nonionogenic hydrophilic monomer including acrylonitrile, methacrylonitrile, cis- and trans-crotonitrile, alpha- cyanostyrene, alpha-chloroacrylonitrile, ethyl vinyl ether, isopropyl vinyl ether, isobutyl vinyl ether, butyl vinyl ether, diethylene glycol vinyl ether, decyl vinyl ether, vinyl acetate, hydroxyalkyl(meth)acrylates, such as 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl methacrylate, butanediol acrylate, 3-chloro-2-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and vinyl thiols such as 2-mercaptopropyl methacrylate, 2-sulfoethyl methacrylate, methyl vinyl sulfide and propyl vinyl sulfide.

The synthetic latex polymers may also contain monomeric vinyl esters in which the acid moiety of the ester is selected from the aromatic and (C,-C₈) aliphatic acids including formic, acetic, propionic, w-butyric, w-valeric, palmitic, stearic, phenyl acetic, benzoic, chloroacetic, dichloroacetic, gamma-chloro butyric, 4-chlorobenzoic, 2,5-dimethyl benzoic, o-toluic, 2,4,5-trimethoxy benzoic, cyclobutane carboxylic, cyclohexane carboxylic, l-(p- methoxyphenyl)cyclohexane carboxylic, l-(p-tolyl)-l-cyclopentane carboxylic, hexanoic, myristic and p-toluic acids. The monomer mix may also include multifunctional monomers such as allyl methacrylate, divinyl benzene, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,3-butylene glycol dimethacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate and so forth.

Examples of suitable vinyl monomers may include ethylene, propylene, butylene, isobutylene, hexene, vinyl acetate, vinyl esters of versatic acids, vinyl chloride (Haloflex® from ICI Chemical Co.), acrylonitrile, acrylamide, methacrylamide, vinylidene, chloride, oleic acid, linoleic acid, 1,3-butadiene, isoprene, norbornene, cyclopentadiene and the like. Examples of suitable vinyl aromatic monomers, with which the present invention's monomers can be polymerized, include styrene, α-methylstyrene, vinyltoluene, ethylstyrene, isopropylstyrene, p-hydroxystyrene, p-acetoxystyrene, and p-chlorostyrene. Acrylic copolymers comprising alkyl esters of acrylic and methacrylic acid with minor amounts of acrylic and methacrylic acid or vinyl acrylic polymers comprising vinyl containing monomers or polymers in combination with softer acrylic monomers may be preferable to the present invention. Ethylenically unsaturated monomers which are commonly used are butyl acrylate, methyl methacrylate, ethyl acrylate and mixtures thereof. The polymer often comprises at least 50%) of an ester of acrylic or methacrylic acid. Vinyl/acrylic types of polymers often include ethylenically unsaturated monomers such as vinyl acetate and butyl acrylate or 2-ethylhexyl acrylate where generally at least 50% of the polymer is comprised of vinyl acetate. It is preferable that these acrylic latex or aliphatic acrylic latex polymers be used in combination with a natural latex. The acylic based elastomers have been found to decrease tack which may be detrimental to the ability of the adhesive to hold items on a mounting substrate.

Other ingredients may be used in the monomer composition including free radical catalysts to initiate polymerization, emulsifying agents to protect particles from agglomeration and buffers to maintain a desired pH during polymerization. Conventional emulsion polymerization techniques may be used to prepare the synthetic latex polymers useful in the present invention. The monomers may be emulsified with an anionic or nonionic dispersing agent at a concentration of about 0.5% to about 10% of the total monomer weight. Acidic monomers, being water-dispersible, serve as dispersing agents which aid in emulsifying the other monomers used. A polymerization initiator or catalyst of the free radical types include ammonium or potassium persulfate and they may be used alone or in conjunction with an accelerator, such as potassium metabisulfite or sodium thiosulfate. The initiator and accelerator, commonly referred to as catalysts, may be used in proportions of 0.5% to 2% each based on the total weight of the monomers to be copolymerized. Thermal and redox processes may be used. The polymerization temperature may be from room temperature to 90°C, or more as is conventional. Batch, gradual addition, continuous and multiple stage processes may be used.

Examples of emulsifiers which are suited to the polymerization process of emulsions used in the present invention include alkaline metal and ammonium slats of alkyl, aryl alkyaryl and aralkyl sulfonates, sulfates and polyether sulfates; the corresponding phosphates and phosphonates; and alkyoxylated fatty acids, esters, alcohols, amines, amides; and alkylphenols.

Chain transfer agents, including mercaptans, polymercaptans and polyhalogen compounds are often desirable in the polymerization mixture to control polymer molecular weight.

Copolymers which have been found to be particularly suited to the present invention include vinyl acetate acrylic, vinyl acetate ethylene and styrene-butadiene rubber. These polymers are used to enhance or depress tack levels. Vinyl acetate acrylic is preferably used in combination with a natural latex, while styrene-butadiene rubber may be used alone or in combination with a natural latex. This also depends on the level of tack required. With lower tack levels, it is more difficult to mount items without worry that they will later release from the adhesive coated mounting surface. The amount of tack desired will depend on the end user. This may also vary with coating thickness and application.

If used in combination with natural latex, these synthetic latexes are suitable from 0% to about 50% by weight of the adhesive composition, preferably from about 1 wt-% to about 50 wt-% and most preferably from about 5% to about 30% by weight of the adhesive composition. These latex products are typically supplied as emulsions at about 40%> - 70%> solids. Specific examples of suitable synthetic latex include WB-0531, an acrylic emulsion, sold by the H.B. Fuller Co. in St. Paul, MN; WB-3250, an acrylic emulsion available from the H.B. Fuller Co. in St. Paul, MN; PD-2044, a vinyl acrylic copolymer available from the H.B. Fuller Co.; Airflex® 440H, an ethylene vinyl acetate emulsion available from Air Products and Chemicals in Allentown, PA; and Butofan NS 144, a styrene/butadiene emulsion available from BASF Corp., Dispersions and Paper Chemicals in Charlotte, NC.

Applicants have found that the most useful hiding agent to the present invention has a refractive index of preferably greater than about 2.0, more preferably greater than about 2.25, even more preferably greater than about 2.5 and most preferably greater than about 2.7. Preferably, the hiding agent utilized is titanium dioxide. These hiding agents may be supplied as either solids or as emulsions and are available from various sources. There are different grades of titanium dioxide which are available including the rutile grade (refractive index = 2.71) and the anatase grade (refractive index = 2.56). The higher refractive index invokes more "hiding power" which conceals the discoloration or yellowing of the adhesive or coating. These titanium based hiding agents are useful from about 2% to about 20% of the composition, preferably from about 3% to about 15%> by weight of the composition and most preferably from about 3% to about 10% by weight of the composition. In some instances, it has been found that levels of titanium dioxide between about 8 wt-% and 9 wt-% are a maximum in that no further benefit may be seen from higher levels. The paper used also has white pigment and will produce values for yellowness index. Once the color of the adhesive composition equals that of the paper, there is no need to further increase the level of titanium dioxide. These values are based on the solid weight of the hiding agent and not the emulsion. An example of a suitable hiding agent is Tiona® RCL-535 (refractive index 2.71) titanium dioxide available from Millennium Inorganic Chemicals in Hunt Valley, MD. Many available grades of titanium dioxide are available from Millennium under the tradename of Tiona® . A synthetic hiding agent which is less useful to the present invention, but is more useful in combination with the preferred hiding agents, is sold under the tradename of Ropaque® (OP-62) which is a synthetic styrene/acrylic surfactant stabilized emulsion available from Rohm & Haas Co. in Philadelphia, PA. The resultant adhesive blend when using this particular hiding agent alone was found to have a less white appearance when the adhesive is in film form and it also did not conceal the yellowing when the adhesive was exposed to UN light. It is surmised that this particular product is less useful because the refractive index is less than 2.0.

Other fillers may be used in combination with the preferred hiding agents. These fillers are less useful when used alone. The present inventors have found them to be insufficient to conceal the yellowing of the adhesive. These fillers may be inorganic oxides and sulfides including those of aluminum, ammonium, barium, calcium, magnesium, silicon, zinc and mixtures thereof. Specific examples include calcium carbonate, barium sulfate, barium sulfate-zinc sulfide, aluminum oxide, calcium silicate and silicon dioxide. Silicon dioxide has a refractive index from about 1.41 to about 1.49. Talcs, clays, silicas, starch and synthetic microspheres may also be useful to the present invention. Zinc oxide is often used as an antioxidant but in the present invention it was found to increase discoloration or yellowing. Calcium carbonate (limestone) is available from ECC International in Atlanta, GA and has a refractive index of about 1.63. Silicon dioxide has a refractive index from about 1.41 to about 1.49. Various additives may also be utilized in the present invention including stabilizers, preservatives, defoamers, thickeners, ultra-violet light absorbers, antisettling agents, surfactants and mixtures thereof. Useful defoamers include Foamaster® VF, an oil based defoamer available from Henkel Corporation and Antifoam® FG-10, a silicone defoamer available from Dow Corning. Useful thickeners include Alcogum® 296-W, a 2-propenoic acid homopolymer sodium salt available from Alco Chemical Co. and Νopco® DSX-1515, a urethane ethyoxylate available from Henkel Corp. Some plasticizers may be detrimental to the present invention in that they may cause staining and discoloration of both the album page and the photographic paper or staining of other items which may be mounted in scrap books or memory albums. Texanol®, an ester alcohol solvent available from Eastman Chemical Co. in Kingsport, TN, was found to cause discoloration of the photographic paper even in very small amounts of less than 5 wt-%. Aliphatic alkene glycols may undesirably soften the adhesive, lowering heat resistance and may increase the possibility that the photographs or other mounted items are stained due to plasticizer migration. It has been found, therefore, that it is preferable to use an aliphatic alkene glycol-free adhesive as well as an ester alcohol-free adhesive. Plasticizers which have a tendency to migrate less, for instance, those with higher molecular weights than those previously mentioned, may be useful to the present invention. It is preferable to the present invention to utilize plasticizers in small amounts to insure good heat resistance and stain-free substrates.

The adhesives of the present invention have excellent color retention as measured by yellowness index using a Minolta Chromameter. Preferably, the adhesive composition will have a yellowness index of less than about 22 and preferably less than about 20 at 70 hours or more and even more preferably will have a yellowness index of less than about 22 and more preferably less than about 20 at 140 hours or more and most preferably will have this yellowness index at greater than about 160 hours when exposed to ultraviolet radiation. The resultant water based emulsion preferably has a viscosity of about 500 cPs to about 5000 cPs and more preferably from about 1000 to about 3000 cPs.

These emulsions are useful as adhesives or coatings for releasably mounting articles on display surfaces. These surfaces have also been referred to in the industry as adhesive coated mounting substrates. A clear film material is laminated over the top of these mounting substrates for displaying flat items including photographs, newspaper articles, occasion cards, postcards and so forth. These clear films are generally plastic or polymeric in nature and may be, for instance, polyethylene, polyester(e.g. Mylar®) or polypropylene (i.e. biaxially oriented polypropylene film). Often, these mounting surfaces are found in photograph albums or other books used for keeping memorabilia. The adhesive is generally coated on a single-sided, or more commonly, a dual-sided substrate where both sides of the substrate are coated with adhesive and the transparent film is laminated to both sides. The adhesive may be coated on the whole substrate or page, or may be coated on the edges of a page. The latter may be more common for mounting one item versus coating the whole page which also operates to secure each item to the mounting substrate or page of the photo album. There are many other variations of the present invention and it is not intended that the invention be limited by these specific examples. The compositions of the present invention have been found to be especially advantageous for these mounting substrates because of the lack of yellowing or discoloration which has occurred with aging. These mounting pages are generally white in nature and it is aesthetically unappealing when the adhesive composition yellows. This often is especially noticeable around the edge of the photograph.

The compositions of the present invention have further been found to be especially suited for use in mounting photographs in that there is no staining of the photographic paper. This may occur from the use of solvents, for instance. The resultant compositions are therefore, stain-free. In other words, none of the adhesive ingredients migrate which may cause staining of the items placed on the mounting substrate or of the mounting substrate itself. Plasticizer migration is one such cause of staining. This is most notably seen on the mounting substrate around the edges of mounted items such as photographs and on the items themselves. Staining of photographic paper is a common phenomenon with the use of certain plasticizers. These compositions may be applied using any standard coating equipment, lamination equipment or variations thereof.

The compositions of the present invention have a smooth, soft peel which lacks any zippery or noisy quality. If a peel is not smooth, it will be found that the adhesive will release a substrate, such as a transparent cover sheet for a photograph album, in a zippery fashion. This will make an undesirable sound as the transparent page is pulled away from the adhesive coated mounting surface. The peel value should also not increase with time making it harder, or impossible to remove the items from the mounting substrate. It is also undesirable that the adhesive decrease greatly in peel value, especially to the point where the items would release from the mounting substrate. Preferably, the peel will remain more similar to the initial peel upon aging. Initial peel values as measured using a 180° peel value method, are preferably from about 5 grams per linear inch (about 2 g/linear cm) to about 200 g/linear inch (about 80 g/linear cm). Re-Seal peel values as measured according to the peel test method found in the following Test Methods section, is preferably from about 2 g/linear cm to about 80 g/linear cm. However, Applicants have noted a decrease in peel value upon re-seal. This peel value is preferably no less than about 40% of the original peel value, more preferably no less than 50% of the original peel value, even more preferably no less than about 55%, even more preferably no less than about 65% of the original peel value and most preferably no less than about 70% of the original peel value. The range is preferably from about 3 g/linear cm to about 60 g/linear inch and more preferably from about 2 to about 80 g/linear cm.

TEST METHODS

1. Yellowness Index

Drawdowns were made at a 5 mil (.13 cm) thickness using a drawn down square on a "multipurpose" white paper (approximately 178 grams per meter squared). The samples were allowed to dry overnight at room temperature. They were then placed in a ultraviolet chamber at about 60°C.

A Minolta CR-331 Chromameter was then used to measure the reflected color or the "yellowness." A white sheet of paper was placed under the sample in order to prevent any effect from the black bench tops. "Yellowness" index is calculated using the following formula:

Y.I = 70*a + 175*b / 0.98041*L where (a, b, L) are determined by the Chromameter.

2. Peel Testing A 5 mil (.13 cm) thick drawdown of each composition was prepared on 192 g/m² multipurpose white paper. A sheet of 8.5" x 11 " (21.6 cm x 27.9 cm) paper was cut in half and 3" (7.6 cm) drawdowns were made on the 4.25" x 11" (10.8 cm x 27.9 cm) paper. Each drawdown was allowed a 20 second open time before placing a 4.5" x 11" (11.4 cm x 27.9 cm) polyester film over the coating of adhesive. A 15 lb

(6.8 kg) roller was then used to laminate the pieces together. The final lamination was then placed in a 105°F (41°C) oven for two hours for conditioning. The samples were then placed in a chamber at 55% relative humidity and 23°C under a load of 4 lbs (1.8 kg) for 2 hours. The samples were then cut into 1" x 4" (2.5 cm x 10.2 cm) strips and were tested for initial 180° peel values. An Instron type of peel tester was utilized which involved clamping the polyester (Mylar®) strips to an electronic balance while the paper strip was clamped to a jack screw which pulled at a uniform rate of approximately 10'Vminute (25.4 cm/minute). The electronic balance then collects gram force data 10 times per second which is recorded via a computer. A minimum of 3 runs are performed for each composition. Note that the samples must be free of air pockets in order to get the most accurate peel values. Reseal peel values were obtained by resealing the polyester to the adhesive coated paper and then repeating the 180° peel test.

Photo Graph Staining/Blocking

A wire-wound no. 18 drawdown is used to make a coating of adhesive on 192 g/m² multipurpose white paper (8.5" x 11"). The coating is allowed an open time of 20 seconds at which time a 2" x 3" (5.1 cm x 7.6 cm) piece of Kodak® photograph paper is placed in the center of the coated sheet of paper. Polypropylene film is then laminated over the top of the photograph paper and to the coated white paper with a 15 lb (6.8 kg) roller. The finished laminate is conditioned overnight at room temperature and then placed in an ultraviolet chamber for 1 week. The samples are then visually inspected for staining and discoloration along the edges of the photograph paper. The samples are also checked for removability from the substrate. EXAMPLES

Examples 1-14 and Comparative Examples A and B

Table I

In addition to the above ingredients, approximately 0.5%> defoamer and 1.0% thickener was added to each of the compositions. The numbers not in parenthesis indicate the actual weight, in grams, that was added to each composition.

Table I, above, shows the effects of adding increasingly higher amounts of titanium dioxide to natural latex. The samples were tested as found in Test Method No. 1 and were tested after 72 hours in a UV chamber at a temperature of 60°C. An acceptable color is not achieved until approximately 2.5 wt-%> of titanium dioxide is added to the natural latex. An optimum color is reached at about 3.5 wt-% of titanium dioxide according to the present invention. Comparative Examples C-L Table II

The samples were made just as in Table I and the samples were also tested as in

Table I. As can be seen from the data, the color never reaches an acceptable level, even at 10 wt-% calcium carbonate.

Examples 15-20 and Comparative Example M Table III

* Comparative example M and examples 15, 17, 19 and 20 have 0.60 grams of ammonium hydroxide. Examples 17 and 19 have 0.8 grams of ammonium hydroxide. Each example also has about 0.5 wt-% defoamer and 1.0 wt-% thickener.

Table IV

* PB = paperboard only. No adhesive coating. The examples were each tested for "yellowness" index as described in Test Method

No. 1. Each sample was tested for yellowness index initially and then after 24, 48, 72, 144 and 168 hours. As shown in the Table IV, Comparative Example M, with no titanium dioxide, initially shows an acceptable yellowness index but after 48 hours of exposure to UV rays, it is no longer acceptable. At 3.0 wt-%> of titanium dioxide, the sample maintains an acceptable yellowness index through 168 hours. At about 8.5 wt-%> titanium dioxide, the yellowness index is equal to that of the paperboard only (having no adhesive) and hence no further benefit will be seen from increasing the level of titanium dioxide further in this study. Paperboard has been found to vary in yellowness index and this result cannot be used for other studies.

Examples 21-23 and Comparative Examples N-P Table V

Table VI

*PB = paperboard only. No adhesive coating.

Comparative Examples N-P and examples 21-23 illustrate compositions having a synthetic latex as well as a natural latex. Three different synthetic latexes have been utilized. The comparative examples have no titanium dioxide while examples 21-23 have approximately 7.5% titanium dioxide. As can be seen in Table VI, the compositions without titanium dioxide have unacceptable "yellowness" indices between 48 and 72 hours while those containing the titanium dioxide are still acceptable even at 168 hours.

Table VII

Examples 24-25 and Comparative Example Q

Peel Data

Table VII illustrates peel values which are acceptable to the present invention. Titanium dioxide did not adversely affect the re-seal peel.

Claims

Claims:

1. An improved mounting substrate for releasably mounting flat items comprising a substrate, and coated on at least one surface of said substrate is a stain-free adhesive, said adhesive comprising from about 20 wt-%> to about 98 wt-%> of the adhesive of at least one latex and from about 2 wt-%> to about 20 wt-%> of the adhesive of at least one hiding agent.

2. The mounting substrate of Claim 1 further comprising a transparent cover sheet releasably attached to said adhesive coated surface.

3. The mounting substrate of Claim 1 or 2 wherein said at least one latex is selected from the group consisting of natural latex, synthetic latex and mixtures thereof.

4. The mounting substrate of Claim 3 wherein said adhesive comprises from about 1 wt-%) to about 50 wt-%> of said synthetic latex.

5. The mounting substrate of Claim 3 wherein the synthetic latex comprises a polymer comprising at least one monomer selected from the group consisting of vinyl, ethylene, vinyl acetate, esters of acrylic acid, esters of methacrylic acid, styrene, butadiene and mixtures thereof.

6. The mounting substrate of Claim 3 wherein said synthetic latex comprises at least one polymer selected from the group consisting of vinyl acetate ethylene, vinyl acetate acrylic, styrene-butadiene and mixtures thereof.

7. The mounting substrate of Claim 1 or 2 wherein said hiding agent has a refractive index of less than about 3.

8. The mounting substrate of Claim 1 or 2 wherein at least one of said hiding agents is titanium dioxide.

. The mounting substrate of Claim 1 or 2 wherein said adhesive has a yellowness index of less than about 22.

10. The mounting substrate of Claim 1 or 2 wherein said adhesive further comprises a filler selected from the group consisting of inorganic based fillers, clays, talcs, silicas, synthetic microspheres, starch and mixtures thereof.

11. The mounting substrate of Claim 1 or 2 wherein said adhesive further comprises a component selected from the group consisting of antioxidants, preservatives, defoamers, plasticizers, ultra-violet light absorbers, antisettling agents, surfactants and mixtures thereof.

12. The mounting substrate of Claim 1 or 2 wherein said mounting substrate comprises two opposed mounting surfaces.

13. A photograph album page for releasably mounting photographs thereon, said album page having a mounting surface, and coated on at least one surface of said substrate is a staining-free adhesive comprising from about 20 wt-%> to about 98 wt-%> of the adhesive of at least one natural latex and from about 2 wt-% to about 20 wt-%> of the adhesive of at least one hiding agent.

14. A photograph album page for releasably mounting photographs of claim 13 further comprising a transparent cover sheet releasably attached to said adhesive coated surface.

15. The photograph album page of Claim 13 or 14 wherein said adhesive further comprising from about 1%> to about 50%> of at least one synthetic latex emulsion.

16. The photo album page of Claim 15 wherein said synthetic latex emulsion comprises a polymer comprising at least one monomer selected from the group consisting of vinyl, ethylene, vinyl acetate, esters of acrylic acid, esters of methacrylic acid, styrene, butadiene and mixtures thereof.

17. The photo album page of Claim 15 wherein said synthetic latex emulsion comprises at least one polymer selected from the group consisting of vinyl acetate ethylene, vinyl acetate acrylic, styrene-butadiene and mixtures thereof.

18. The photo album page of Claim 13 or 14 wherein said hiding agent has a refractive index of less than about 3.

19. The photo album page of Claim 13 or 14 wherein said hiding agent is titanium dioxide.

20. The photo album page of Claim 13 or 14 wherein said adhesive has a yellowness index of less than about 22.

21. The photo album page of Claim 13 or 14 wherein said adhesive further comprising a filler selected from the group consisting of inorganic based fillers, clays, talcs, silicas, synthetic microspheres, starch and mixtures thereof.

22. The photo album page of Claim 13 or 14 wherein said adhesive further comprising a component selected from the group consisting of antioxidants, preservatives, defoamers, plasticizers, ultra-violet light absorbers, antisettling agents, surfactants and mixtures thereof.

23. The photograph album page of Claim 13 or 14 wherein said album page has a pair of opposed mounting surfaces.