AU664654B2 - Thixotropic wood adhesive gel - Google Patents

Description

Pr 1 Thixotropic Wood Adhesive Gel Background Of The Invention Field of the Invention This invention relates to thixotropic, water based, general purpose, polyvinyl acetate, polyvinyl alcohol adhesive gel for porous and semiporous substrates such as paper, card board, cloth and wood.

Background Art Many different general purpose adhesives for adhering porous and semiporous substrates such as paper and wood are available. However, such adhesives have various shortcomings for use in projects which are performed on wall boards and other vertical surfaces such as in a class room by young children such as excessive running when placed on a vertical surface, and difficulty of the dried adhesive: to take a conventional wood stain; to be sanded; or to resist moisture.

This invention provides a thixotropic adhesive gel which can be easily dispensed from a conventional hand held plastic squeeze bottle for wood glue. After being dispensed oo o from the squeeze bottle, the adhesive does not run on vertical surfaces and forms a dry glue line which can be sanded, stained and has resistance to moisture.

The adhesive of this invention comprises polyvinyl acetate as the primary adhesive agent; xanthan gum as a thixotropic thickening agent; polyvinyl alcohol as a tackifying oo o 2o agent; and a combination of both wood flour and glyoxal as water resisting agents for the BLo 4 dried adhesive. Additional conventional ingredients used in adhesive compositions such as defoamers, preservatives, and the like can also be use provided that such ingredients or the quantity thereof do not adversely affect the adhesives. Compatible preservatives are generally added to the gel.

o, 25 The Handbook of Water-Soluble Gums and Resins by R.L. Davidson, 1980 by 0o0 o McGraw-Hill, inc. pages 20-20 discloses partially hydrolysed polyvinyl alcohol as an adhesive and page 20-18 discloses the use of certain gelling agents to control penetration of o 0o" polyvinyl alcohol solutions into porous substrates or to prevent run-off of coating by dipping whereas page 20-19 of that reference discloses the use of an antifoam agent with polyvinyl alcohol. Pages 21-15 and 21-16 of the Handbook reference describe adhesive properties of polyvinylpyrrolidone (PVP). Among other shortcomings, these references do not mention the use of thixotropic agents with polyvinyl alcohol nor proportions of ingredients used in obtaining the advantageous properties of this invention.

Water based polyvinyl acetate emulsions are popular wood glues. The Handbook of Adhesives, Third Edition which is edited by I. Sk< ist: pages 388-390 describes the use of polyvinyl alcohol for imparting wet tack and as a protective colloid for polyvinyl acetate ITFLA' emulsions; pages 394-395 discusses thixotropy, pseudoplasticity and thickening of

TO

i _NA\LIBZ1003MFAR r ~-_-L--YYlii~Xi 2 polyvinyl acetate with various materials; and page 398 describes the use of foam control agents and biocides in such adhesives.

US. 3 442 845 relates to polyvinyl acetate adhesives which, upon drying, are redispersible in cold or hot water. The adhesive compositions of the 845 patent use polyvinyl alcohol, water-soluble gums, and cellulose ethers as anti-coalescing agents for the polyvinyl acetate. Propylene glycol and other polyhydroxy compounds are mentioned as plasticisers for polyvinyl alcohol.

US. 4 251 400 also relates to a polyvinyl acetate adhesive which is redispersible in hot and cold water in the dried film form and which uses polyvinylpyrrolidone and a nonvolatile, water-soluble, plasticiser as the anti-coalescing agent. In addition to the polyvinyl acetate and polyvinylpyrrolidone that patent also mentions the use of polyvinyl alcohol, propylene glycol, as well as water-soluble ethers in the adhesive composition.

European Patent Application Publication Number 0210052 relates to various tubes for dispensing reactive adhesives such as cyanoacrylate at a rate of one or two drops at a time. The patent mentions resilient plastic tube dispensers and broadly states that the adhesive can be thixotropic.

Technical Bulletin DB-15 entitled "KELZAN, Xanthan Gum", of Merck Co.

describes xanthan gum as a thickener and suspending agent for water based systems and promotes its suspending, pseudoplastic (thixotropic), and stability properties.

KELCO XANTHAN GUM, Third Edition, of Kelco a division of Merck Co.

Sshows much the same as the above KELZAN bulletin, and also states that its xanthan gum provides smooth flow under sheer in adhesive formulaions and that this allows the application of high solids.

US. 3 676 174 Uses a mixture of wood flour and plaster of Paris to form a paintable base for moulded articles. In Col. 2, step 5, it discloses a composition of: 1 part plaster of Paris; 1 part of wood flour; and 6 parts fine metal powder. This dry powder is mixed with an equal quantity of polyvinyl acetate solution diluted with water and is used as a coating on clay objects.

US. 2 510 257 discloses an aqueous polyvinyl acetate. emulsion adhesive containing S 30 glyoxal and polyvinyl alcohol. The glyoxal imparts water resistance to the adhesive.

US. 4 638 022 Uses polyvinyl acetate together with pecan shell flour to provide a coating for wood or plastic which accepts conventional wood stains. The composition of this reference appears to be in an organic solvent system.

A commercial product called "Glue Gap 202 GF Filling" of the Garott Wade Company, Inc. which is located at 161 Sixth Avenue, New York, N.Y. is an aqueous polyvinyl acetate emulsion adhesive which contains wood fibres or wood flour. This product is viscous but has little or no thixotropy; also, much of the wood fibre appears to settle easily and requires shaking to disperse the wood fibres.

L_ ANMIR7I(niPArfrt MW-_ I mm p- 3 Summary Of The Invention According to a first embodiment of the present invention there is provided an aqueous thixotropic adhesive gel emulsion comprising, by weight: A. about 40% to 85% of water; B. about 10% to 45% of polyvinyl acetate; C. about 1.5% to 15% of polyvinyl alcohol; D. about 0.1 to 1.5% of xanthan gum; E. about 0.005 to 0.4% of glyoxal; and F. about 2% to 20% of wood flour.

According to a second embodiment of the present invention there is provided an aqueous emulsion of a thixotropic adhesive gel comprising: A. polyvinyl acetate in an amount sufficient to provide an adhesive bond for wood; B. polyvinyl alcohol in an amount sufficient to provide wet tack to the adhesive; C. glyoxal in an amount sufficient to provide water resistance to the adhesive; D. wood flour in an amount sufficient to improve the water resistance imparted by the glyoxal; and E. xanthan gum in an amount sufficient to provide thixotropic properties to the adhesive and a viscosity of about 15 000cps to 350 000cps at low shear while the thixotropic properties allow extrusion of the gel from a S flexible dispenser having a dispensing opening of about 1.85mm in diameter by applying j finger-pressure to the dispenser.

According to a third embodiment of the present invention there is provided a thixotropic, aqueous polyvinyl acetate emulsion adhesive gel which contains polyvinyl alcohol in a quantity sufficient to provide wet tack to the adhesive, from about 0.005% to 0.4% of glyoxal, about 2% to 20% of wood flour, and xanthan gum in a quantity sufficient to provide thixotropic properties to the gel and a viscosity capable of suspending the wood flour and of discharging the gel by applying finger pressure on a flexible plastic bottle having an orifice of 1.85mm in diameter and wherein the quantities are by weight of the S gel.

According to a fnurth embodiment of the present invention there is provided a process for preparing an aqueous emulsion of a thixotropic adhesive gel whi.h comprises I so30 mixing, by weight: A. about 40% to 85% of water; B. about 10% to 45% of polyvinyl acetate; C. about 1.5% to 15% of polyvinyl alcohol; D. about 0.1% to 1.5% of xanthan gum; E. about 0.005% to 0.4% of glyoxal; F. about 2% to 20% of wood flour to form a gel having a thixotropic index of about 1.5 to 7, a low shear viscosity of about 15 000cps to 350 000cps, and a high shear viscosity of about 10 000cps to 50 000cps.

Advantages of the invention include; The adhesive gel will not run when applied to porous and semiporous vertical surfaces and will not spill when used as a general r purpose school glue. The adhesive gel extrudes easily and in a steady stream from a small orifice when a flexible tube or squeeze bottle is finger pressed and reverts to gel when finger-pressure is released. The combination of adhesive gel and small dispenser I^ opening, eg. from about 1.52 to 29.21mm in diameter, minimises or eliminates wrinkling TO r 4 of paper upon drying of the adhesive. The adhesive in a clear resilient plastic dispenser can be viewed within the dispenser as clear which may include a tint of colour. The adhesive gel is preferably crystal clear or has a clear coloured tint and provides a clear dry film. The dry adhesive film is flexible and will not crack on bending. The adhesive gel has a strong wet-tack to hold paper surfaces together while drying. It has a long rate of set so as to permit sliding and positioning of substrates before fibre tearing permanent adhesive bonds are developed. The adhesive gel as well as dried films thereof will launder-out in hot or cold water. (10) The adhesive gel can be tinted easily with non-toxic water-soluble dyes. (11) The adhesive gel is non-toxic and is not an irritant to the skin and eyes as defined in the United States Federal Hazardous Substances Act.

Brief Description of the Drawings Figure. 1 is a side elevation of a flexible tube dispenser containing the adhesive gel of this invention.

Figure. 2 is a plan view of that shown in Figure. 1.

Figure. 3 is a side elevation of a flexible squeeze bottle containing the adhesive gel of this invention.

Figure. 4 is a plan view of that shown in Figure. 3.

Detailed Description Of The Invention Figure. 1 shows a conventional, flexible plastic, low density, polyethylene tube dispenser (10) having a clear hollow tube portion (12) which has a capacity of about and a crimped, closed end The wall thickness of the polyethylene is 0.5mm. The closed end beyond crimp (14) has an extending flap (16) which has a cut out portion (18) so that the dispenser (10) can be hung up and displayed or stored. The dispensing end of tube (12) has a conventional screw threaded dispenser closure cap (22) which can effect opening and closing of orifice (26) by holding cap (22) in place while twisting cap end Dispenser (10) contains adhesive gel (40) of this invention and the adhesive (40) in contact with tube (12) provide a clear appearance when the dispenser is viewed.

Figure. 2 more clearly shows dispenser opening (26) at the end of cap (24).

Figure. 3 shows a clear, conventional, flexible plastic, low density polyethylene squeeze bottle (30) which has a capacity of 120mL. Bottle (30) has neck portion (32) which has an open end with conventional screw threads, not shown. Conventional dispenser closure cap (22) has internal screw threads which mate with those of neck portion Cap (22) can effect opening and closing of orifice (26) by twisting of the cap end (24) with Figures. 1 and 2. Dispenser bottle (30) contains clear gel adhesive The clarity or transparency of the portion of the bottle (30) containing the adhesive (40) is similar to that of Figure. 1.

,sRA Figure, 4 more clearly shows dispenser opening (26) at the end of cap (24).

IN:\L1Z100384:EAR I In place of a flexible plastic tube or squeeze bottle, other dispensers such as deformable, ductile, metal tubes can be used; although such tubes do not provide for clarity.

The preferred polyvinyl alcohol adhesive gels of this invention are clear. The term "clear" is used herein in contrast to opaque. The term "clear" includes transparent, ie., see through, as well as translucent.

The term "water-soluble" as used herein refers to solutions of either solids or liquids which are soluble or miscible in water to provide a solution which is clear at the concentration employed.

The polyvinyl acetate adhesives of this invention are aqueous dispersions, also referred to herein as emulsions, which contain polyvinyl acetate in an amount sufficient to provide an adhesive bond upon drying; polyvinyl alcohol in an amount sufficient to increase the wet tack of the adhesive; glyoxal in an amount sufficient to provide water resistance to the dried adhesive; wood flour in an amount which, together with the glyoxal, acts synergistically to increases water resistance imparted by the glyoxal; and xanthan gum in an amount typically sufficient to provide a thixotropic index of from about 1.5 to 7 when viscosity of the gel at 20rpm is divided into the viscosity of the gel at 2rpm at 25 0 C as measured with an RVF Brookfield viscometer using a number 6 spindle. The wood flour also permits sanding and staining of the dried adhesive.

The gel of this invention has good wet tack properties. It has a slow enough rate of set that permits a sufficient period of time for positioning a second piece of wood such as b' sliding of the second surface over the first before wood fibre tearing adhesive bonds develop between the two substrates which permanently hold the pieces in place.

The water, polyvinyl acetate, polyvinyl alcohol, xanthan gum, glyoxal, and wood flour will generally make up (compose) at least 90%, preferably 95%, and particularly 98% of the adhesive composition.

The Xanthan Gum Xanthan gum is a natural high-molecular weight branched polysaccharide. It functions as a hydrophilic colloid to thicken, suspend, and stabilise water-based systems.

The quantity of xanthan gum used in this invention is that which is sufficient to provide the adhesive gel with the desired thixotropic index and viscosity. Such quantity can vary over a broad range such as that of about 0.1% to 1.5% by weight of the adhesive, and preferably the quantity of xanthan gum will vary from about 0.2% to 0.8% by weight of the adhesive.

Other water soluble thickening agents were tried for use in this invention but were found unsatisfactory due to immiscibility, lack of adequate stability, or they adversely affected water resistance of the dried adhesive. These other thickening agents which were not found suitable include: hydroxyethylcellulose; alginates; the sodium salt of 0 ro N A T B I UI~ 6 carboxymethylcellulose (CMC), and polyvinylpyrrolidone. The superiority of xanthan gum over other hydrophilic gums such as CMC was unexpected. CMC is a preferred hydrophilic gum used as the thickening agent for the polyvinyl alcohol adhesive gels of this application. However, those gels do not contain dispersed polyvinyl acetate, glyoxal or wood flour and only optionally contain xanthan gum as the thickening agent.

The term "thixotropic" as used herein is also meant to cover pseudoplastic. The thixotropic index used in this invention permits extrusion of the gel from a small dispenser opening by use of finger-pressure on a flexible dispenser such as a tube or squeeze bottle.

Due to thixotropy, the adhesive rapidly reverts to a higher viscosity after extrusion from the orifice when force or shear is not being applied. The adhesive gel does not run, when applied to wood in a vertical plane after being extruded through the small orifices of the dispensers used in this invention. By not running, the adhesive fairly stays in place on the area to which it is extruded with minimal spreading unless external force is applied. The minimum spreading can include a slight amount of downward creep due to gravity such as that of less than 38mm and preferably less than 2.54mm. The use of smaller orifices in the dispensers such as those of less than 2.54mm in diameter, eg., 18.5mm in diameter minimise any creep.

o The thixotropic index for the adhesive gel of this invention varies from about 1.5 to 7 S preferably about 1.5 to 5 and particularly 1.8 to 4.0. For the polyvinyl acetate adhesive gels, the thixotropic index for the adhesive gel of this invention varies from about 1.5 to 7 preferably about 2 to 5 and particularly 2.5 to 4.0. For the polyvinyl alcohol adhesive gels, the thixotropic index for the adhesive gel of this invention varies from about 1.5 to preferably about 1.5 to 4 and particularly 1.8 to 2.5. The term "thixotropic index" as used herein is the number obtained by dividing the viscosity reading of the gel at 2rpm in centipoise by the viscosity reading at 20rpm in centipoise by use of an RVF Brookfield viscometer using a number 6 spindle at 25 0

C.

ao° The viscosity readings in this invention are taken after the gel has been at rest eg.

undisturbed, for a period of time such as 12 hours. The adhesive gels of this invention are stable.

o 30 In order to prevent settling of the wood flour in the adhesive and to prevent running after being extruded from a squeeze bottle, the adhesive of this invention has a high viscosity at rest or under lo', 'hear. However, due to its thixotropic properties it will pour out of an open mouth container or flow to a lower level when the container is tipped. This facilitates the discharge of the adhesive from plastic bottle glue dispensers having small openings. On the other hand, a non-thixotropic adhesive or adhesive with little thixotropy at the viscosities used in this invention present difficulties in removal from a plastic bottle having a small orifice and particularly in removal of substantially all of the adhesive.

The polyvinyl alcohol adhesive gels of this invention have a viscosity of about S 000cps to 100 000cps at 25 0 C and preferably about 50 000cps to 90 000cps at 25 0 C as 4q. -lneasured with an RVF Brookfield viscometer by use of a number 6 spindle at 2rpm.

y-

C

j i

I

i 0 o uo o o 0 0 C 008 o 0 0 o a o o o '1 o 7 When measured at 20rpm with an RVF Brookfield viscometer at 25 0 C by use of a number 6 spindle, the viscosity of about 15 000cps to 60 000cps, preferably about 20 000cps to 000cps, provided that the thixotropic index is within the ranges set forth herein.

The polyvinyl acetate adhesive gels of this invention have a viscosity of about 000cps to 350 000cps at 25°C and preferably about 40 000cps to 120 000cps at 25 0 C as measured with an RVF Brookfield viscometer by use of a number 6 spindle at 2rpm.

When measured at 20rpm with an RVF Brookfield viscometer at 25 0 C by use of a No. 6 spindle, the viscosity is about 10 000cps to 50 000cps, preferably about 14 000cps to 000cps, provided that the thixotropic index is within the ranges set forth herein.

Polyvinyl Acetate The adhesive agent used in this invention is principally polyvinyl acetate although polyvinyl alcohol also forms adhesive bonds. The quantity of polyvinyl acetate in the gel is that which is sufficient tc provide an adhesive bond for wood. The quantity of polyvinyl acetate is generally from about 10% to 45% by weight of the adhesive and particularly from about 20% to The polyvinyl acetate can have a molecular weight such as that which is conventional with polyvinyl acetate wood glues, eg., about 30 000 to 200 000. Preferably, the molecular weight of the polyvinyl acetate is from about 30 000 to 100 000 although higher or lower molecular weight resins can be used. It is preferred to use polyvinyl acetate emulsions that are homopolymer dispersions (emulsion) with a total solids content of about 40% to 65 by weight of the polyvinyl acetate emulsion, Polyvinyl Alcohol The term "polyvinyl alcohol" as used throughout the specification and claims in relation to polyvinyl acetate adhesive gels is intended to include both completely 25 hydrolysed and partially hydrolysed polyvinyl alcohols such as those which are useful as emulsifying agents in polyvinyl acetate aqueous emulsions.

The polyvinyl alcohol will preferably be partially hydrolysed and have a molecular weight of about 25 000 to 100 000 and preferably about 40 000 to 80 000. The viscosity of the polyvinyl alcohol can vary over. a wide range such as that of about 5 or 6cps, which is referred to in the art as low viscosity, to 40 to 50cps, which is referred to in the art as high viscosity as measured with an RVF Brookfield viscometer using a number 1 spindle at rpm at 20°C for a 4% aqueous solution. The preferred degree of hydrolysis for the partially hydrolysed polyvinyl alcohol is about 87% to 89%. The partially hydrolysed polyvinyl alcohol is preferred for consumer products in contrast to industrial applications.

The reason for this is that the use of fully hydrolysed polyvinyl alcohol provides to the composition a reduced general stability, eg., a lack of freeze-thaw stability, and exhibits syneresis on standing for a relatively short period of time.

The quantity of polyvinyl alcohol in the gel is that which will increase the wet tack of the adhesive. This can vary over a wide range such as that of from about 1.5% to 15% by 'weight of the adhesive and preferably from about 2.5% to Often, polyvinyl acetate o o lk" I M I _I I m~~P~ emulsions use small quantities of partially hydrolysed polyvinyl alcohol as a protective colloid. The total amount of polyvinyl alcohol in the adhesives of this invention include that which may be used as a protective colloid in the polyvinyl acetate emulsion as well as any further additions such as that for increasing wet tack of the adhesive.

The Glyoxal The glyoxal acts synergistically with the wood flour to provide water resistance to the dried adhesive. The quantity of glyoxal used in this invention is that which is sufficient to provide water resistance to the dried adhesive, Glyoxal, in a quantity of as little as about 0.005% by weight of the adhesive can be sufficient. The quantity of glyoxal will generally vary from about 0.005% to 0.4% by weight of the adhesive, preferably from about 0.01% to 0.2% by weight of the adhesive and particularly from about 0.02% to Larger quantities of the glyoxal can be used but larger quantities adversely affect stability, eg., freeze-thaw stability and promote excessive thickening of the composition on aging. The glyoxal is generally incorporated into the adhesive in the form of an aqueous solution, eg., a 20% to 50% solution of the glyoxal in water.

Plasticisers Optionally, a water soluble plasticiser for the polyvinyl alcohol can also be used in the composition. Such plasticisers soften the polyvinyl alcohol and make the polyvinyl alcohol more flexible, Illustrative of such plasticisers there can be mentioned: alkanes having from 2 to 5 carbon atoms and 2 to 3 hydroxy groups such as: propylene glycol; glycerol; ethylene glycol; and diethylene glycol; although ethylene glycol and diethylene glycol can have some toxic properties. The quantity of the water-soluble plasticiser is that which is sufficient to plasticise the polyvinyl alcohol and will generally vary from about to 3% by weight of the adhesive gel, Although such plasticisers can be used it is S 25 preferred to avoid them when higher water resistance is desired.

Water insoluble plasticisers for the polyvinyl acetate can also be used in the adhesives of this invention. Illustrative of such plasticisers there can be mentioned: butyl benzyl S phthalate; dibutyl phthalate; tricresyl phosphate; and the like, When used, the quantity of the water insoluble plasticiser will generally be less than one percent, eg. from about 0,1% to 0.5% by weight of the adhesive, SWood Flour The quantity of wood flour in the gel is that which is sufficient to improve the water resistance imported by the glyoxal. The quantity of wood flour will generally vary from about 2% to 20% by weight of the adhesive and particularly from about 3% to 15%, even more particularly from 4% to The wood flour, after incorporation and suspension in the glue, can easily pass through an 1.85mm diameter orifice in the compositions of this invention. The wood flour remains suspended in the gel for a prolonged period of time, eg., at least one month without significant settling, and does not interfere with smooth A discharge of the gel from the dispenser orifice, The wood flour is that of finely divided 7 o particles of wood which generally has a particle size (US, Standard Sieve Series) of less I N:\UZ10034;EAn F, pp 9 than auiout 10mesh (2000-tm), and preferably less than 20mesh (850pm). Such wood flour can be that of hardwood, eg., maple, or soft wood, eg., soft pine. The preferred wood flour is that of softwood.

Water The major ingredient in the polyvinyl alcohol adhesive gel of this invention is water, The quantity of water can vary over a broad range such as that from about 70% to 93 by weight of the adhesive gel, preferably 75% to 93% and particularly from about 80% to by weight thereof.

The total quantity of water for the polyvinyl acetate adhesive gels of the invention includes water from the polyvinyl acetate emulsion used in making the adhesive, if the polyvinyl acetate is incorporated in the adhesive as an aqueous polyvinyl acetate emulsion.

The total quantity of water includes additional quantities of water added in the preparation of the adhesive as well as that carried by the component ingredients, The quantity of water will generally vary from about 40% to 85% by weight of the adhesive, preferably 45% to 16 75% and particularly 50% to The Defoamer Conventional water-soluble defoamers are generally used in the adhesives of this invention, Such defoamers include silane defoamers and polyalkoxylated polyethers eg., butoxy polyoxyethylene-propoxyl propylene glycol. The quantity of the defoamer is that which maintains density of the gel, prevents excessive foam in the manufacturing process, and facilitates filling of the dispensers with the gel, Generally, the quantity of the defoamer varies from about 0.05% to 0,35% by weight of the gel composition.

The Dispenser The dispenser for the thixotropic adhesive gel can be a conventional, flexible, low 25 density polyethylene squeeze bottle such as one having a capacity of 120mL. Illustratively, the 120mL plastic squeeze bottle used for ELMER'S SCHOOL GLUE of Borden, Inc. is S; suitable. Such dispensers are shown in Figures 1 to 4 hereof. Finger-pressure between the thumb and forefinger or the thumb and fingers is used to dispense the gel from the dispenser squeeze bottle on to a substrate such as wood, The dispenser cap orifice (26) has a diameter of about 1.52 to 2,92mm, preferably 1.78 to 2,54mm and particularly about S1,78 to 2,0mm, The use of a rectangular slit of approximately 1.6mm wide and 7.94mm long as found in many wood glue dispensers is also suitable, The thixotropic gel adhesive o (40) flows out of the cap orifice (26) in a steady stream on being finger-pressed due to its thixotropic properties in spite of its high viscosity in the undisturbed state, The area of 3s such dispenser opening is from about 7,1 to about 77,5mm 2 When applied to a substrate in the vertical plane, the gel does not run and has a Sminimum amount of creep due to the thixotropic properties of the gel. Any such creep is generally less than 3,8mm and more often less than 2,54mm, Due to the ability of the I thixotropic gel to be applied through a small dispenser opening, a thin glue line can be k P..4 r ovided on a first substrate such as construction paper which minimises the amount of INALIZ1003 4:EAR r 00O r p adhesive as well as wrinkling of paper upon drying. When a second substrates such as a second piece of construction paper is pressed over the first piece in order to be adhered thereto, the high tack of the gel holds the second substrate in place on the vertical surface.

The slow rate of set permits a prolonged period of time for positioning the second substrate such as by sliding of the second surface over the first before fibre tearing adhesive bonds develop between the two substrates which permanently hold the pieces in place.

A preferred method for manufacture of the polyvinyl acetate adhesive gel of this invention is as follows: Water is added to a tank equipped with a mixer and the mixer is started. Polyvinyl alcohol and xanthan gum are sprinkled into the mixture. An antifoam agent is then added and mixing is continued until the polyvinyl alcohol is "wet-out" and softened. The mixing is continued and the temperature is raised to 85 0 C to 90 0 C until a smooth homogeneous mixture is obtained. The mixture is then cooled to about 75°C with continued mixing and a polyvinyl acetate aqueous emulsion is added such as an emulsion containing about 50% of the polyvinyl acetate emulsified with about 3% of polyvinyl 1is alcohol and the remainder being water. Mixing is continued and the temperature is lowered to about 50°C and then glyoxal, wood flour and any preservatives are added.

Mixing is continued until the mixture is smooth and homogeneous, In order that those skilled in the art may more fully understand the invention presented herein, the following examples are set forth, All parts and percentages-in the examples, as well as elsewhere in this application, are by weight, unless otherwise specifically stated, The viscosity measurements referred to herein are by use of an RVF Brookfield viscometer with a number 6 spindle at 25 0 C unless otherwise specifically stated, The term "low shear" refers to the viscosity measurements at 2rpm whereas "high shear" refers to viscosity measurements taken at Procedure For Determining Wet Tack This procedure uses blocks of Grade 1 and Grade 2 white pine with each block being long, 19mm high and 45mm wide. The grain of the wood is parallel to the length of the block and the sides which are 19amm high and 50mm long are planed and smooth.

Such sides are referred to herein as test sides, Each test side therefor provides a surface of 19,7cm 2 A series of tests are performed with the above described blocks of wood with two blocks being required for each test. In each test an eye screw is placed in the centre of one of the test sides of each block, Gel adhesive is then placed on the opposite side of the eye screw of one of the test blocks so that it covers the entire 19,7cm 2 of surface. The test side of the second block opposite the second block eye screw and the side of the first block having the glue thereon are pressed against each other in sliding relationship while being placed in register so that the edges of one block do not extend beyond thle edges of the other, A scale is attached to the eye screw of the first block whereas a weight is attached I to tilhe eye screw of the second block, The scale is then lifted upwardly by the operator and X 11. r l INAuZlodao4XAnI 11 the two blocks are lifted vertically so as to lift the weight. Thus, the operator lifts the scale by hand which in turn lifts the first block through the eye screw. This in turn lifts the second block due to the wet tack of the adhesive which in turn lifts the weight which is attached to the second block eye screw. This test is repeated with clean blocks of wood and the weight is increased each time until the adhesive between the two blocks fails to lift the second block and its attached weight. The last weight which was lifted in this test is referred to as the quantity of wet tack or simply wet tack of the adhesive. This test measures the wet tack in a direction which is perpendicular to the adhered surfaces. In spite of the lengthy description of this test, it can be performed, and for reliability is performed, rapidly by the operator. The glue, when the wet track is measured between the blocks of wood is very close to the physical and chemical condition of the glue when it left the jispenser orifice. The wet tack is a measure of what is often referred to as the grabbing power of the adhesive, A minimum amount of wet tack is needed when gluing on substrate to another in a vertical plane, otherwise, the substrate which is not held in place but rather depends on the wet glue for positioning would slip off of the vertical surface of the first substrate, The wet tack of the gel of this invention preferably varies from about 2 to over 90g.cm 2 and preferably from about 38 to 75g.cm- 2 Procedure For Determining Rate Of Set Determinations for the rate of set are performed on a white paper pad. A glue line is placed on smooth white paper of a 13,97 x 21.59mm paper pad, The single glue line is placed in about the middle of the pad parallel to the length of the paper. This glue is then spread evenly by the use of a No. 22, WIRE-CATOR which is supplied by the Leneta Company. The WIRE-CATOR is also referred to as a wire wrap rod. The WIREo CATOR draws down a uniform thickness of film from the single glue line. Use of the No, 22 WIRE-CATOR draws down a glue line to a thickness of 1.5 mil.

A second sheet of the same paper has one of its narrow ends raised so that it can be grasped by the fingers. The second sheet is pressed over the first sheet. The two pieces are then slowly pulled apart by lifting the raised end of the second sheet and holding the first sheet down in place. The time that it takes to encounter fibre tearing bond is the rate of set. The preferred rate of set for the gels of this invention is from about 16 seconds to o 35 seconds and preferably from about lS to 32 seconds.

The values for both the wet tack and rate of set recited herein are obtained at and a relative humidity of 35 Example 1 This example shows the composition and properties of a polyvinyl acetate adhesivc gel of this invention.

I7AO|f) i ff[ IN:\LIbZIO0384:EAh Ehh. r- 11

I

Ingredient Parts By Weight Deionised water 54.6 Polyvinyl Acetate 33.5 Polyvinyl alcohol 1 Wood Flour 2 6.2

KELZAN-S

3 Glyoxal 4 0.04

DEFOAMER

5 0..26 Ethyl parahydroxybenzoate 0.1 Benzoflex 9-886 0.2 Propylene Glycol 0.6 1 Partially hydrolysed polyvinyl alcohol.

o 2 Pine wood flour No. 14020 of American Wood Fibres, Inc.

3 A dispersible grade of xanthan gum sold by Merck Co.

0 4 As a 40% solution of glyoxal in water 5 5 DEFOAMER 622 which is a monofunctional polyalkoxylated polyether defoamer I supplied by the Thomas W. Dunn Corp of Ridgefield, N, J.

6 A plasticiser for polyvinyl acetate which is sold by Velsicol Chemical Corp. of Chicago, Ill.

The adhesive of Example 1 was easily dispensed with finger-pressure from a resilient plastic four ounce polyethylene bottle having a cap with an orifice of about 1.85mm diameter. After being dispensed on to a piece of pine wood held vertically, it formed a uniform, thin, horizontal bead of adhesive which did not run and formed wood fibre tearing adhesive bonds between two pieces of wood on drying. The gel can be dispensed in a steady stream through the dispenser orifice. It had a thixotropic index of about about 24 hours after it was manufactured and a viscosity of 115 000cps at a spindle speed o of 2rpm and a viscosity of 32 500cps at a spindle speea of 20rpm when measured at 25 0

C

S" with an RVF Brookfield viscometer with an No. 6 suindle. Subsequent viscosity measurements by use of the same method and equipment were as follows: after standing for about 2 days a viscosity of 117 500cps at 2rpm and a viscosity of 33 000 cps at after 3 days from manufacture, a viscosity of 135 000cps at 2rpm and 34 500cps at Example 2 This example provides another formulation having the advantageous properties of this invention.

~c r F L= 1*F tI 0 0 04 o; 0 0 4 000 0 I I n(0 0 0 *i K r~- (D Ingredient Parts By Weight Water 55 53 Polyvinyl Acetate 33.5 Partially Hydrolysed Polyvinyl Alcohol KELZAN-S, Xanthan Gum 1 0.4 Glyoxal 2 0.07 Pine Wood Flour 3 KATHON LX 1.5%4 0.1 SKANE M8 5 0.1 COLLOIDS 5816 0.3 1 A product of Merck Co.

2 Diluted in water 3 Pine wood flour No. 14020 of American Wood Fibres, Inc.

4 A microbicide product of Rohm and Haas 5 5 A microbicide product of Rohm Haas Company 6 Defoamer product of Rh6ne-Poulenc As with Example 1, the adhesive dispensed easily form a 1.85mm diameter orifice of a plastic dispenser bottle and a bead of the adhesive when dispensed on a vertical surface did not run. After manufacture the adhesive had a viscosity at 2rpm of 80 000 to 10 000cps at 2rpm spindle speed at 25 C and a viscosity of 22 000 to 26 000cps at "Orpm spindle speed at 25 0 C for a thixotropic index of 3.5. After 2 days from manufacture the viscosity at 2rpm was 89 000cps and 24 000cps at 20rpm for a thixotropic index of 3.3.

After two weeks from manufacture the viscosity at 2rpm was 85 000cps and the viscosity at 20rpm was 25 000cps. All viscosity measurements were made by use of an RVF 15 Brookfield viscometer with a number 6 spindle at 25 0

C.

Example 3 A polyvinyl acetate adhesive gel was prepared with a composition the same as that of Example 1 except that 1.20 of hydroxyethylcellulose was used as the thickening agent and about 0.7% less water was used so as to balance the additional hydroxyethylcellulose.

It was found that the hydroxyethylcellulose was incompatible in the product since it quickly separates from the mixture leaving the mixture watery and with non-uniform clumping throughout.

Example 4 A polyvinyl acetate adhesive gel was prepared with the same composition as Example 1 except that 1.65% of polyvinylpyrrolidone and 0.60% of carboxymethylcellulose were used as the thickening agents. Again, proportionately less water was used to make up for the increased amount of thickening agent. The viscosity of the gel showed rapid deterioration and was not suitable for use in this invention.

S

p.- 4 14 Example A polyvinyl acetate adhesive gel was prepared with the identical ingredients as that of Example 1 except that 0,6% of carboxymethylcellulose(CMC) was used in place of of the xanthan gum and the quantity of water was decreased by 0.1% to compensate for the lower amount of thickener. This formulation was unsatisfactory because the viscosity deteriorated. Thus, the initial viscosity at 2rpm was 145 000cps and at 10rpm it was 000cps. Ten rpm speed was used as the higher speed because the viscosity could not be read on the instrument scale at 20rpm due to the high viscosity. After 2 days from the date of manufacture the viscosity was down to 45 000cps at 2rpm and 27 000 cps at After one week from the date of manufacture, the viscosity was 25 000cps at 2rpm and 17 5000 at 20rpm. Two weeks after the time of manufacture, the viscosity was 15 000cps at 2rpm and 20 500cps at 20rpm. The viscosity measurements were made in the same manner as in Example 2. It can be seen that both the viscosity and the thixotropic index deteriorated rapidly with the use of CMC as the thixotropic agent.

Example 6 This example shows the synergistic effect of glyoxal and wood flour for attaining water resistance of the dried polyvinyl acetate adhesive gel of this invention.

Four samples of adhesive gels were used in this Example. Sample 4 was the adhesive gel of Example 2 above. The composition of Sample 1 was the same as that of Example 2 except that it contained neither glyoxal nor wood flour without any other change in the formulation. The composition of Sample 2 was the same as Example 2 except that it contained no wood flour without any other change in the formulation. The composition of Sample 3 was the same as that of Example 2 except that it contained no glyoxal without any other change in the formulation. Each of the samples were drawn down with a No. 34 wire wrap rod to about a 50mm width band of adhesive film on a glass plate. The drawn down adhesives were permitted to dry by standing at 24°C and relative humidity for 6 days before proceeding with the following tests.

Two series of tests were performed. In the first series, a drop of deionised water was placed on each of the drawn down adhesives and the time it took for each film to blush (slight white discolouration) was measured. Film with longer times for discolouration is film which is more resistant to water. Immediately after discolouration was noted, the area of film under the drop of water was rubbed with the finger. Easy dispersibilty of the film under the drop of water indicates poor water resistance whereas difficulty in dispersibility of the affected area under the drop of water indicates better water resistance. In this series of tests the time for the film to blush was: 2 seconds for Sample 1; 9 seconds for Sample 2; 3 seconds for Sample 3; and 35 seconds for Sample 4. In this series of tests, rubbing of the film area under the drop of water showed: easy dispersion for Sample 1; some dispersion of Sample 2; easy dispersion of Sample 3; and no dispersion of Sample 4, _IILnlna~~ pp. S.e second series of tests, a drop of water was permitted to stay on each of the samples until the area under the water turned opaque (an opaque white or off-white coloration). For the film area under the drop of water, it took: 1 minute to become opaque for Sample 1 and the film was easily dispersed in water with finger rubbing; 2 minutes to become opaque for Sample 2 and there was some dispersion of the film with finger rubbing; 1 minute .o become opaque for Sample 3 and the film was readily dispersed with the finger rubbing; 45 to 60 minutes to become opaque for Sample 4 and the film did not disperse with finger rubbing but instead broke away in large fragments.

It was also observed that the drop of water for Sample 4 in both series of tests showed "beading" which was not shown in the other samples. Beading is an indication of a hydrophobic surface as opposed to a hydrophilic surface.

It can be seen from Example 6 that the glyoxal and wood flour in the compositions of this invention act synergistically to increase water resistance of the dried adhesive.

Example 7 15 This example can provide another formulation having the advantageous properties of this invention.

a 41 a O rp 0 0 0 0"o 0000 0 0 4 Ingredient Parts By Weight Water 66.0 Polyvinyl Acetate 22.0 Partially Hydrolysed Polyvinyl Alcohol Wood Flour 5.6 Xanthan Gum Glyoxal 0.1 Defoamer 0.3 0 oO Example 8 This example can provide another formulation having the advantageous properties of this invention.

Ingredient Parts By Weight Water 60.0 Polyvinyl Acetate 20.0 Fully Hydrolysed Polyvinyl Alcohol Wood Flour 15.4 Xanthan Gum 1,2 Glyoxal 0.2 Defoamer 0.2

Claims (30)

1. An aqueous thixotropic aihesive gel emulsion comprising, by weight: A. about 40% to 85% of water; B. about 10% to 45 of polyvinyl acetate; C. about 1.5% to 15% of polyvinyl alcohol; D. about 0.1 to 1.5% of xanthan gum; E. about 0.005 to 0.4% of glyoxal; and F. about 2% to 20% of wood flour.

2. The gel of claim 1 wherein the thixotropic index is from about 2 to 5.0 and the quantity of wood flour is sufficient to provide staining and sanding properties to the dried adhesive.

3. The gel of r1aim 1 containing from about 0.05% to 0.3% by weight of a water- soluble defoamer.

4. The gel of claim 1 comprising, by weight, about: 15 A. 45% to 75% water; So B. 20% to 40% of polyvinyl acetate; C. 2.5% to 7% of polyvinyl alcohol; SD. 0.2% to 0.8% of xanthan gum; E. 0.01% to 0.2% of glyoxal; and F. 3% to 15% of wood flour, The gel of claim 1 wherein at least 95 by weight, of the gel is composed of water, polyvinyl acetate, partially hydrolyzed polyvinyl alcohol, xanthan gum, glyoxal, and wood flour. S° 6. The gel of claim 1 which has a viscosity of 15 OO0cps to 350 000cps at Low o a 25 Shear.

7. The gel of claim I which has a thixotropic index of about 1,5 to 7.

8. The gel of claim 7 which contains from about: 45 to 75% water; 20% to o, o polyvinyl acetate; 2.5% to 7% of polyvinyl alcohol; 0.2% to 0.8% of xanthan gum; 0.02% to 0,1% of glyoxal; and 4% of 8% of wood flour,

9. The gel of claim 8 wherein at least 98% thereof is composed of: water, polyvinyl acetate, polyvinyl alcohol; glyoxal; wood flour; and xanthan gum. An aqueous emulsion of a thixotropic adhesive gel comprising: A, polyvinyl acetate in an amount sufficient to provide an adhesive bond for wood; B, polyvinyl alcohol in an amount sufficient o provide wet tack to the adhesive; C. glyoxal in 3b an amount sufficient to provide water resistance to the adhesive; D. wood flour in an amount sufficient to improve the water resistance imparted by the glyoxal; and E. xanthan gum in an amount sufficient to provide thixotropic properties to the adhesive and a viscosity of about 15 000cps to 350 000cps at low shear while the thixotropic properties allow extrusion of the gel from a flexible dispenser having a dispensing opening of about F, 3',85mm in diameter by applying finger-pressure to the dispenser. V C P R"W UJ A r 17

11. The gel of claim 10 wherein the polyvinyl acetate is from 20% to

12. The gel of claim 10 or claim 11 wherein the quantity of polyvinyl alcohol is at least 1.5% by weight of the gel.

13. The gel of any one of claims 10 to 12, wherein the quantity of wood flour is sufficient to provide staining and sanding properties to the dried adhesive.

14. The gel of any one of claims 10 to 13 wherein: the quantity of xanthan gum is sufficient to provide a thixotropic index of from about 1.5 to 7 when viscosity of said gel at 20rpm is divided into the viscosity at 2rpm of said gel at 25 0 C as measured with an RVF Brookfield viscometer using a number 6 spindle,

15. The gel of claim 14 wherein the thixotropic index is from about 2 to

16. The gel of any one of claims 10 to 15 which has a viscosity of 15 000cps to 350 000cps at low shear.

17. The gel of any one of claims 10 to 16 containing from about 0.05% to 0.3% by weight of a water-soluble defoamer,

18. The gel of any one of claims 10 to 17 wherein upon extrusion from the dispensing opening, the gel forms a bead which does not run when applied in a horizontal S*line on wood in a vertical plane.

19. The gel of claim 10 which comprises, by weight: about 10% to 45% of polyvinyl acetate; about 40% to 85% water; about 1.5% to 15% of polyvinyl alcohol; about 0.1% to 1.5% of xanthan gum; about 0.005% to 0.4% of glyoxal; and about 2% to of wood flour. The gel of claim 19 wherein the quantity of water is from about 45 to 75

21. The gel of claim 19 or claim 20 which contains about 0.005 to 0.4% of glyoxal, 25 22. The gel of claim 10 comprising, by weight, about: A. 45% to 75% water; B. to 40% of polyvinyl acetate; C. 2.5% to 7% of polyvinyl alcohol; D. 0.2% to 0.8% of xanthan gum; E. 0,01% to 0.2% of glyoxal; and F. 3% to 15% of wood flour. oo 23. The gel of claim 22 wherein at least 95%, by weight, of the gel is composed of 0 04 water, polyvinyl acetate, partially hydrolysed polyvinyl alcohol, xanthan gur, glyoxal, and wood flour. i 24. The gel of claim 10 which contains from about 0.2% to 0.8% of xanthan gum; 0.02% to 0.1% of glyoxal; and 4% to 8% of wood flour. The gel of claim 24 wherein at least 98% thereof is composed of: water; polyvinyl acetate; polyvinyl alcohol; glyoxal; wood flour; and xanthan gum.

26. A thixotropic, aqueous polyvinyl acetate emulsion adhesive gel which contains polyvinyl alcohol in a quantity sufficient to provide wet tack to the adhesive, from about 0.005% to 0.4% of glyoxal, about 2% to 20% of wood flour, and xanthan gum in a quantity sufficient to provide thixotropic properties to the gel and a viscosity capable of suspending the wood flour and of discharging the gel by applying finger pressure on a r 18 flexible plastic bottle having an orifice of 1.85mm in diameter and wherein the quantities are by weight of the gel.

27. The gel of claim 26 wherein the quantity of polyvinyl alcohol is from 1.5% to

28. The gel of claim 26 or claim 27 wherein the quantity of polyvinyl alcohol is about 2.5% to 7%.

29. The gel of any one of claims 26 to 28 wherein the quantity of glyoxal is about 0.01% to 0.2%. The gel of any one of claims 26 to 29, wherein the quantity of wood flour is about 3% to

31. The gel of claim 30 wherein the wood flour is that of soft pine wood.

32. The gel of any one of claims 26 to 31, wherein and the quantity of xanthan gum is from 0.1% to

33. An aqueous emulsion of a thixotropic adhesive gel substantially as hereinbefore S 15 described with reference to any one of the Examples but excluding the comparative examples.

34. A process for preparing an aqueous emulsion of a thixotropic adihesive gel which comprises mixing, by weight: A. about 40% to 85% of water; B. about 10% to of polyvinyl acetate; C. about 1.5% to 15% of polyvinyl alcohol; D. about 0.1% to 1.5% of xanthan gum; E. about 0.005% to 0.4% of glyoxal; F. about 2% to 20% of wood flour to form a gel having a thixotropic index of about 1.5 to 7, a low shear viscosity of S about 15 000cps to 350 000cps, and a high shear viscosity of about 10 000cps to 000cps. The process of claim 34 which comprises mixing: A. 45% to 75% water; B. 20% to 40% of polyvinyl acetate; C. 2.5% to 7% of polyvinyl alcohol; D. 0.2% to 0.8% of xanthan gum; E. 0.01% to o.2% of glyoxal; and F. 3% to 15% of wood flour to form said gel having a thixotropic index of about 2 to 5, a low shear viscosity of 40 000cps to 120 000cps and a high shear viscosity of 14 000cps to 35 000cps.

36. The process of claim 35 wherein by weight 0.02% to 0.1% of glyoxal is employed.

37. The process of claim 36 wherein the quantity of wood flour is from 4% to 8%.

38. The process of claim 37 wherein at least 95% of the mixture is c'mposed of water, polyvinyl acetate, polyvinyl alcohol, xanthan gum, glyoxal, and wood flour.

39. The process of any one of claims 35 to 38 wherein the polyvinyl alcohol is partially hydrolysed. A process for preparing an aqueous emulsion of a thixotropic adhesive gel substantially as hereinbefore described with reference to any one of the Examples but excluding the comparative examples. 41, An adhesive gel prepared by the process of any one of claims 34 to FjINZLIU1O384XAb iL F, 19

42. An adhesive gel of claim 41 wherein the dried adhesive is sandable and stainable. Dated 4 August, 1995 Borden Inc. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 4$I 0I* o ':XU 004^ o P "Y pr -I Thixotropic Wood Adhesive Gel Abstract A water based thixotropic adhesive gel is disclosed which comprises; an aqueous emulsion of polyvinyl acetate in an amount sufficient to form adhesive bonds on wood; partially hydrolysed polyvinyl alcohol in an amount sufficient to provide wet tack of the adhesive; glyoxal in an amount sufficient to provide water resistance to the adhesive; and wood flour in an amount sufficient to increase the water resistance imparted by the glyoxal and to provide sanding and staining properties to the adhesive; and xanthan gum in an amount sufficient to provide a thixotropic index and viscosity allowing extrusion of the gel from a flexible dispenser having a dispensing opening of about 1.851mm in. diameter by applying finger-pressure to the dispenser while, upon extrusion,.:4le gel forms a bead which does not run when applied in a horizontal line on wnod in a vertical plane. A further water based thixotropic adhesive gel is disclosed which comprises water; partially hydrolysed polyvinyl alcohol, or wherein a portion of the polyvinyl alcohol is replaced with polyvinylpyrrolidone; a water-soluble high viscosity thickening agent polymer which is compatible with the polyvinyl alcohol and which imparts thixotropic properties to the gel; a water-soluble plasticiser for the polyvinyl alcohol; and a water- soluble defoamer in proportion of ingredients so that the viscosity of the adhesive will break down when a flexible tube or squeeze bottle dispenser is finger-pressed and have a sufficiently low viscosity to allow for easy extrusion from an orifice having a diameter of about 1.5 to 3,8mm. When pressure is released, after the desired amount of adhesive has flown out of the dispenser, the adhesive quickly reverts to very close to its original gel state so that it will not run on a vertical surface on porous and semiporous surfaces such as paper, An article of manufacture is also provided whereby the adhesive gel containing the above ingredients is in a flexible dispenser from which the adhesive can be dispensed by finger-pressure. A conventional, flexible plastic, low density, polyethylene tube dispenser (10) has a clear hollow tube portion (12) which has a capacity of about 90mL and a crimped, closed end The wall thickness of the polyethylene is 0,5mm, The closed end beyond crimp (14) has an extending flap (16) which has a cut out portion (18) so that the dispenser can be hung up and displayed or stored. The dispensing end (20) of tube (12) has a conventional screw threaded dispenser closure cap (22) which can effect opening and 4 closing of orifice (26) by holding cap (22) in place while twisting cap end Dispenser contains adhesive gel (40) of this invention and the adhesive (40) in contact with tube (12) provide a clear appearance when the dispenser is viewed. JFigure. 1 IN\LIBCI00181: GSA I