WO2003046099A1

WO2003046099A1 - Water-based adhesive compositions

Info

Publication number: WO2003046099A1
Application number: PCT/NZ2002/000265
Authority: WO
Inventors: Allan James Easteal; Kaluachchi Gamage Karnika De Silva
Original assignee: Auckland Uniservices Limited
Priority date: 2001-11-30
Filing date: 2002-12-02
Publication date: 2003-06-05
Also published as: AU2002365368A1

Abstract

A series of aqueous based adhesive compositions including poly(vinyl acetate) with a rubber latex are described. At least some cross-linking is preferred, and a tackifing agent is also preferred. The adhesives are water-resistant and heat-resistant adhesives suitable for use with (for example) wood, having little coloration in exposed joints. Significant and long-lasting wet strength is obtained. Versions for use in conjunction with paper products can act as releasable adhesives. Coating versions (in conjunction with paper and cardboard) are also prepared for the printing and packaging industries.

Description

WATER-BASED ADHESIVE COMPOSITIONS

This invention relates to generally to compositions for water based adhesives, and more particularly to compositions including poly(vinyl acetate) and one or more latex(es).

BACKGROUND

An ideal adhesive would include stability and strength properties as well as being cheap to produce, non-toxic, and easy to use. The ideal strength properties of an adhesive would result in substrate bonding which is maintained over a long period depending on the existing physical and chemical environmental factors. The desired strength of bonding can range from very high, for constructional adhesives to very low, for removable paper labels and the like.

Ideally the materials involved in preparation of the adhesive are cheaply and readily available, such as renewable materials.

Safety issues surrounding an adhesive include the absence of possibly carcinogenic materials both in the adhesive as manufactured, and in use. For example the continued slow release of aldehydes from urea-formaldehyde glues used in particle boards in housing, has been at issue in New Zealand's "sick building syndrome". Similarly, the presence of skin cancer promoting substances in isocyanates is a known safety problem. In addition safety can be an issue for cyanoacrylates if inadvertently splashed into a person's eyes.

Stability of the adhesive prior to use is clearly desirable. For commercial purposes the adhesive should have a long shelf life. A recognised difficulty with the shelf life of adhesives is seen for example with conventional re-sealable mailing envelopes, which seal adhesive dries over a relatively short period of time in storage.

It is therefore an object of the present invention to provide a set of aqueous- based contact adhesive compositions having desirable stability, strength, safety and environmental properties for use in bonding and coating a variety of substrates such as wood; metal, such as cold-rolled steel, galvanized steel, and aluminium; fabric; paper; foam; plastic, such as poly(vinyl chloride), polystyrene, polyethylene, polypropylene, and fibreglass or the like or to at least provide the public with a useful choice.

DEFINITIONS

The following terms used throughout the specification are to be understood in light of their following definitions.

The term "contact adhesive" refers to a film of adhesive which is applied to at least a portion of a surface of a first substrate and at least a portion of a surface of a second substrate, the films of adhesive on each substrate then being dried and subsequently brought into contact under pressure so as to form an immediate, durable bond between the adhesive films of each substrate.

"Water based or aqueous" means that the adhesive comprises a water component.

The term "drying" means the substantial removal of water from the adhesive composition through evaporation, heating or vacuum drying.

"Substantially water resistant" means that an adhesive bond formed between two contact adhesive films as defined above is substantially resistant to the effects of boiling water on the strength of the contact adhesive bond.

The term "activator" is the term given to agents that are added to rubbers or emulsions of rubbers to help initiate their curing.

The term "accelerator" is the term given to agents that are added to rubbers or emulsions of rubbers to accelerate their curing. Such accelerators include an organic dithiocarbamate, disulphide or thiozole, such as zinc diethyldithiocarbamate, tetramethyl thiuram disulphide, mercaptobenzothiozole and the like. The term "prevulcanized" is the term used to describe the production of producing a vulcanised latex or rubber product whereby the latex or rubber is dried or cured from a liquid state.

Abbreviations

The following abbreviations as used throughout the specification are intended to refer to the following terms

NR - Natural Rubber latex

NRx, Nc - Cross-linked natural rubber

PVA - Poly(vinyl acetate) [NB: poly(vinyl alcohol) is not a subject of this specification].

PVA ALK - Poly(vinyl acetate) emulsion, alkalised with 22% aqueous ammonia solution to give 1.1% ammoniated PVA emulsion.

Under the specific examples outlined in the detailed description, codes like PALK(8)NR(2) mean 8 parts by volume of PVA alk., 2 parts of natural rubber, and so on, where the following abbreviations are to mean

P - poly(vinyl acetate)

NR- Natural Rubber

A - AQL - Polychloroprene latex (Aquastik 1120/ Neoprene 115 from Du Pont/Dow)

R1- Epoxy resin (Europox 710)

R2 - SE 780 (Akzo Nobel Snowtack tackifing agent) R3 - SE 790 (Akzo Nobel Snowtack tackifing agent)

TA- Tetraethylenepentamine

NC- crosslinked NR

AC- crosslinked polychloroprene latex (AQL)

PALK - alk. PVA - is a poly(vinyl acetate) emulsion, alkalised with 22% aqueous ammonia solution to give 1.1 % ammoniated PVA emulsion

PC - crosslinked and alkalised PVA

N - alk. NR

STATEMENT OF INVENTION

In a first broad aspect this invention provides a water based adhesive composition, including (a) at least one poly(vinyl acetate); and

(b) at least one latex; wherein in use the adhesive composition, after drying, is substantially water-resistant.

Preferably the poly(vinyl acetate) adhesive has been subjected to a cross-linking treatment.

Optionally the composition includes an effective amount of at least one water based tackifying agent capable of promoting adhesion; preferably in the form of an aqueous dispersion, and selected from a range including rosin acids, rosin esters, terpene phenolic resins, other hydrocarbon resins, and coumarone indene resins.

Preferably the tackifying agent is present in an amount of about 1 % to about 50% by volume, based on the wet weight of the total adhesive component. More preferably the tackifing agent is used at about 40% by volume based on the wet weight of the total adhesive component.

Preferably the latex of the adhesive composition includes at least one latex selected from a range including: natural rubber latex; modified natural rubber latex; compounded natural rubber latex; modified, crosslinked natural rubber latex; polychloroprene rubber latex and modified polychloroprene rubber latex.

Preferred modified rubbers include those having unsaturated chains such as styrene or methyl methacrylate bonded onto groups such as butadiene including at the C4 or C10 sites.

Preferably the modified natural rubber is compounded, prevulcanized, or grafted natural rubber.

Preferably the compounded natural rubber includes at least one component suitable to at least partially crosslink natural rubber; the further component being selected from an activator, an accelerator, an antioxidant and a crosslinking agent; and mixtures thereof.

Preferably the prevulcanized natural rubber includes a component suitable to at least partially crosslink natural rubber the further component being selected from an activator, an accelerator, an antioxidant and a crosslinking agent; and mixtures thereof with/without other suitable ingredients before blending with other latexes.

Preferably, the cross linking agent is a zirconium salt in an alkaline medium, such as zirconium nitrate.

Preferably, the activator is an inorganic oxide, such as zinc oxide.

Preferably, the accelerator is an organic dithiocarbamate, disulphide, thiozole and the like, such as zinc diethyldithiocarbamate, tetramethyl thiuram disulphide, mercaptobenzothiozole and the like. Preferably, the antioxidant is a phenolic or amine compound or a blend thereof. More preferably, the antioxidant is Antioxidant 2246, Wingstay L, Vanox MBPC, Vulkanox BKF, 4020, SKF, MB 2 or SP.

Preferably the grafted natural rubber is further modified by the grafting of polar polymers on to natural rubber to increase polarity. Preferably the polar polymer is selected from the range including poly(methyl methacrylate) and styrene.

Preferably preservatives including biocides are included so that degradation of the adhesive composition due to bacterial or fungal attack is reduced.

Preferably (in the case of polychloroprene) additional acid acceptors such as zinc oxide dispersions or aqueous epoxy resins are included so that degradation of the adhesive composition due to release of hydrochloric acid from the polychloroprene rubber is minimised.

Preferably (in the case of polychloroprene and a natural rubber with poly(vinyl acetate)), it is preferred that the natural rubber ranging from about 10% to about 40% by volume is blended with poly(vinyl acetate) first before polychloroprene is added.

Preferably the modified poly(vinyl acetate) has become modified by a cross- linking procedure, and a preferred cross-linking procedure includes use of a zirconium salt; more preferably zirconium nitrate in an alkaline medium.

Preferably the modified polychloroprene has been modified by a cross-linking procedure and stabilised with zinc oxide or an epoxy resin.

Preferably the natural rubber is a stable aqueous emulsion preserved with a low ammonia biocide composite system, or any other suitable preservative system.

Preferably the adhesive compositions as previously described in this section further include a tackifing agent, the tackifing agent comprising one or more items selected from a range including a water soluble rosin or modified rosin acid, ester, terpene phenolic resin, other hydrocarbon resin or coumarone indene resin.

Preferably the water based adhesive has a composition including poly(vinyl acetate), natural rubber, cross-linked polychloroprene rubber, and a tackifing agent.

More preferably at least one of the PVA and the natural rubber is cross-linked.

Even more preferably the invention provides a preferred boiling-resistant, strong adhesive having the composition of "PC(8)/AC(1)/NC(1 )/R2" according to the terminology used herein.

In a further aspect the invention provides a method of bonding at least one substrate; the method comprising the steps of: a) applying a water based adhesive composition as defined above to at least a portion of a surface of at least one substrate, b) allowing the adhesive composition to at least partially dry; and c) contacting the adhesive applied surface of the substrate to another surface.

In a related aspect the invention provides a water based adhesive suitable for bonding two layers of paper of compositions as previously described in this section; wherein any one layer of adhesive on a substrate of paper is capable of adhering to a second layer of adhesive on a substrate of paper so that the adhesive can be used with self-sealing envelopes. In another related aspect the invention provides a water based adhesive; the adhesive being a removable type suitable for use with removable paper labels; the adhesive being resistant to degradation so that a long shelf life can be expected.

In a further related aspect the invention provides a water based releasable adhesive suitable for the manufacture of a range of easily peelable protective coatings; comprising an outer protective layer selected from a range of materials including paper, polyethylene, bubble pack, polypropylene and the like, the layer being provided with an inner coating of a releasable composition according to the invention, so that the protective coating may be attached to a delicate surface such as glass, stainless steel as on televisions, computer screens, microwave ovens, refrigerators etc in order to protect the surface from scratching during transport and before use.

In a further aspect there is provided a method of applying a water resistant coating to at least one substrate; the method comprising the steps of: a) applying a water based adhesive composition as defined above, to at least a portion of a surface of a substrate, and b) allowing the adhesive composition to dry on the substrate.

Preferably the method further includes the step printing on said adhesive composition, said composition being capable of accepting printable compositions while still exhibiting an effective amount of moisture and water transmission resistance. Preferably the composition includes, as a water barrier, at least one substance selected from a range including silicone, Additive 84, Additive 85, and Oratan 2001 , and preferably the substance is incorporated at up to 20% by weight. (These are commercial additive samples from Rohm and Haas and Dow Corning Chemical Companies).

In a related aspect the invention provides a water based adhesive composition suitable for the coating of least one surface of a cardboard including the types of cardboard known as kraft and corrugated boards with a composition according to this invention; the composition being capable of accepting printable compositions yet exhibiting an effective amount of moisture and water transmission resistance between an interior of a box and an exterior.

In a further aspect the invention provides a water-resistant chipboard, the chipboard being substantially comprised of fragments of wood bonded together with a water based adhesive as previously described in this section, thereby forming a structural component.

In a still further aspect this invention provides a transparency sheet including a dye-receptive or printable layer, the dye-receptive layer comprising water based adhesive composition including a poly(vinyl acetate) adhesive together with at least one member of a range including a synthetic latex particularly polychloroprene latex and natural rubber latex.

Further aspects of the present invention will become apparent from the following detailed description and figures of the invention, which is provided by way of example and is not to be taken in any way as limiting the scope or extent of the invention.

Fig 1 : shows graphically the performance of trials 90-99 during a boiling test. (see Example 5, table 8)

Fig 2: shows graphically the performance of trials 120-129 during a boiling test, (see Example 5, table 8)

DETAILED DESCRIPTION

By way of introduction, the invention is based on poly(vinyl acetate) (PVA) modified natural rubber emulsions providing water-resistant and heat-resistant adhesives. The invention originated from experiments intended to enhance the properties of known PVA adhesives. The blends were prepared using commercially available emulsions and other components as follows.

PVA emulsion - Viscopol 6624 (ex Nuplex Chemicals) Natural rubber latex (NR) (RLA Polymers NZ) Aquastik 1120 or Neoprene 115 (Dupont Dow or Henkel NZ Ltd). Tackifying Resins Emulsions - SE 780 (R2), and SE 790 (R3) (EKA

Chemicals) Epoxy Resin - Europox 710

The emulsions were modified and/or crosslinked as stated below before mixing.

The invention also provides an adhesive composition including poly(vinyl acetate) together with modified natural rubber, another synthetic rubber, or their combinations. Such natural and synthetic rubbers include

(a) those having unsaturated chains attached to units such as butadiene, wherein examples of such natural and synthetic rubbers have chains such as styrene or methyl methacrylate conjugated at C4 or C10 sites on dienes;

(b) commercially available modified general-purpose latexes, wherein examples of such natural and synthetic rubbers are commercially available under the tradenames MEGAPOLY latex (rubber latexes grafted with methyl methacrylate in order to increase the polarity and thereby the adhesion of the adhesive compositions). MG 30 is a low polarity compound with 30% PMMA, and MG 49 is a high polarity compound, with 49% PMMA. Other, related compounds can be synthesised. These compositions would give transparent, tough and semi-reinforced films.

Preferred components of the adhesive compositions of the present invention

1 PALK - PVA emulsion was alkalised with 22% industrial grade ammonia solution to give 1.1% ammoniated PVA emulsion.

2 Ammoniated, crosslinked PVA - (denoted as PC in formulations) - alkalised PVA was crosslinked using a 0.3 m/l aq. Zr(NOg)₄ solution. 1.5 ml of this solution was added to 100 ml of alkalised PVA emulsion to effect crosslinking in the system. 3 NR - NR latex (with -45% dry rubber content) was alkalised using 22% industrial grade aqueous ammonia solution. 4% ammonia solution

(relative to latex) was added to alkaline NR latex. 4 NRx - Crosslinked NR latex. In some instances crosslinked NR with an antioxidant was used to improve heat resistant properties. The formulation used to crosslink NR was as follows in Table 1. Table 1. Formulation of crosslinked NR

Component Parts ; by weight

NR latex 100

ZDC 0.5

ZnO 0.5

TMTD 0.5

Antioxidant 1

Note: ZDC = zinc diethyldithiocarbamate TMTD = tetramethylthiuram disulphide

Antioxidant = a phenolic or amine antioxidant

5 Polychloroprene (Neoprene 115) (AQL) - AQ latex was modified using

10% epoxy resin, Europox 710. 6 Tackifying resins were used without any modification.

Optionally the adhesive composition of the present invention can also contain at least one water based tackifying agent to promote adhesion, preferably in an amount of about 1 % to about 50% by volume based on the wet weight of the total adhesive component though preferably about 40% by volume based on the wet weight of the total adhesive component. Suitable tackifing agents for use in the contact adhesives of the invention include rosin acids, rosin esters, terpene phenolic resins, hydrocarbon resins, and coumarone indene resins. The tackifier will generally be used in the form of an aqueous dispersion. One advantage of a tackifing agent is to provide an instant first attachment.

Samples were mixed using simple blending techniques.

EXAMPLE 1 : Contact adhesive suitable for use on self-sealing envelopes:

The formulation outlined in Table 2 below allowed the making of paper envelopes of the type where two lips, each coated with adhesive, are able to form a good bond only with other similarly coated lips. The storage life appears to be good. (Conventional self-seal envelopes lose bond strength in less than a year).

Table 2: Typical formulation of contact adhesive

Component Parts by volume

NR 80

PALK. 20

R3 25

Standard 80 gsm photocopy paper was coated with adhesive samples prepared according to the formulations in Table 3. The strength of the bond produced by making contact between two such coated papers was determined as the force per unit area of coated paper required to separate the two coated paper surfaces immediately after the bond was formed, and after ageing. The results are given in Table 3.

Table 3. Peel strength of adhesives.

^a NR:PVA:tackifing agent (parts by volume); the tackifing agent used was

Snowtack SE 790G from Eka Chemicals (NZ) Ltd. ^b after accelerated ageing at 60°C for one week.

⁰ Natural rubber latex currently used in manufacture of self-sealing envelopes. EXAMPLE 2:

Adhesive for self-sticking note pads similar to the "3M Post-it ™ "type

Adhesive prepared according to the formulation in Table 4 below was applied as a coating to the surface of standard photocopy paper and the coated paper pressed onto surfaces of paper, glass, wood, plastic and metal. The reversible performance as self-sticking note pads was assessed qualitatively as at least equivalent to the performance of "3M Post-it " type note pads. No quantitative tests were carried out.

Table 4: Formulation of adhesive for self-sticking note pads

component parts by volume

NR _* 40

PALK _*

10

R3 _*

50

Triton X-100 _* 1

NR 15 water 1

* These components were pre-mixed, before addition of the remaining components.

EXAMPLE 3:

Contact adhesive for bubble wrap-film

An adhesive prepared according to the preparation outlined in Table 5 was coated onto the flat surface of bubble wrap film. The coated film could be stuck onto a glass surface and peeled away again later without leaving a residue on the glass surface. The coated bubble-wrap film can be used for example to protect architectural glass, picture frame glass, computer screens, TV screen, stainless steel metal surfaces of refrigerator doors and the like during transportation, storage, and shipment. Table 5: Formulation of adhesive suitable for use as bubble wrap film

component parts by volume

NR 80

PALK. 20

R3 10

EXAMPLE 4:

Printable water vapour barrier coating for paper and paperboard

This aspect of the invention is applicable to cardboard boxes and the like where there is a desire to provide both a barrier against the ingress or egress of water, and to provide a substrate on which printing can be applied. The transparency is an advantage. This aspect of the invention provides a one-coat system whereas some prior art sealants require a primer layer to be followed by at least one other. A typical formulation intended by this aspect is outlined in Table 6 below.

Table 6: Typical formulation

component parts by volume

PALK 40

NR 10

AC 10 water 20

The formulations listed in Table 7A were applied as a 10-15 μm thick coating to standard photocopy paper and the water vapour transmission of the coated paper was determined in accordance with American Society for Testing Materials standard specification ASTM E96-95 for an exposure time of three days. The results of the water vapour^'transmission properties of these formulations are given in Table 7A: The abbreviations WVT refers to water vapour transmission (mass of water vapour transmitted per m² per day) and WVTR is water vapour transmission rate, which takes into account coating thickness. Table 7A: Water vapour transmission data for PVAc/NR emulsion coatings

Sample Formulation WVT/g m^"2 d^"1 WVTR/g m^"1 d^"1

1 C1¹ + 25% M² 142.9 26.6

2 C2³ 339.6 57.4

3 N + S⁴ + water (1 :1 :1 ) 516.2 48.1

4 C3⁵ + 15% R⁶ 272.3 47.7

5 C3 + 15% D1⁷ 292.4 49.1

6 C3 + 15% D2⁸ 253.4 39.9

7 N + S + water (2:1 : 4) 330.9 53.7

8 C3 240.0 39.7

9 N + S + water (1 :1 : :2) 548.3 78.5

10 C2 diluted 903.3 120.5

1 C1 = PC(8)/AC(1)/N(1)/R2

M = commercial material (#2200) from Michelman Inc. ³ C2 = PC(8)/AC(1)/N(1)

S = dilutable water repellent silicone emulsion 520 from Dow Corning ⁵ C3 = PC(8)/AC(1)/N(2)

R = commercial material (Oratan 2001) from Rohm & Haas

D1 = commercial material (Additive 85) from Dow Corning ⁸ D2 = commercial material (Additive 84) from Dow-Corning

Parts by volume are in parentheses in Samples 3, 7 and 9.

In a further series of experiments the formulations listed in Table 7B were applied as a 10-15 μm thick coating to standard 80 gsm photocopy paper and the water vapour transmission of the coated paper determined in accordance with standard specification ASTM E96-95 for an exposure time of three days at 50% relative humidity at 23°C with the results given in Table 7B. Table 7B: Water vapour transmission data for PVA/NR emulsion coatings

Sample Formulation Coat weight g m WVT/g m^"2 d^"1

1 C1 11 216

2 C2 10 96

3 C3 14 98

4 C4 10 120

5 C5 9 192

6 C6 8 148

7 C7 9 144

8 C8 6 121

9 C9 7 123

10 C10 9 141

C1 = P(1 )/N(5)

C2 = P(1 )/N(5)/M(1 )

C3 = C1(1 )+ water (0.03)

C4 = P(1)/N(6)

C5 = P(1)/MG1(5)/N(1 ) C6= P(1)/MG2(5)/N(1)

C7 = C1(1 )/APS(0.004)

C8 = C2(1 )/APS(0.004)

C9 = C6(1 )/APS(0.004)

C10 = C4(1 )/APS(0.004)/Talc(0.015) MG1 = Poly(methyl methacrylate)-grafted NR latex with 40% total solids

MG2 = Poly(methyl methacrylate )-grafted NR latex with 50% total solids

APS - Ammonium persulphate

Parts by volume are in parentheses.

All of the samples in Table 7B are wax-free except for sample C2 which may contain some waxy material. All of the samples except sample C2 show good printability. EXAMPLE 5:

Wood Bonding Performance Tests And Results For PVA Based Emulsion

Adhesives

A range of formulations (90-99 and 120-129) was used, as indicated in Tables 8 and 9. Shear strength of wood joints was determined in accordance with the ISO 9020 standard. Wood blocks (at 12 per cent moisture content) were glued at room temperature (~20°C) and kept under compression (20 kg cm^-2) for 24 hours, then left under the same conditions (but without compression) for 3-7 days. Their shear strength was evaluated in the dry condition.

Water resistance of adhesives was tested as follows. Glued wood blocks were immersed in water at room temperature for 6 weeks, then dried in an oven at 60°C for 48 hours prior to shear strength determination. (Note that this procedure does not follow the ISO or ASTM standards)

Boiling water tests were carried out according to the JAS-lll Standard: the glued blocks were immersed in boiling water for three hours, then dried at 60°C for 24 hours. The treatment comprising immersion in boiling water for three hours then drying at 60°C for 24 hours was repeated prior to shear strength determination for those glued blocks that were intact after the first treatment.

Table 8: Wood Bonding Performance Tests

Notes

Parts by volume in parentheses in the description column.

_? Columns W = maximum load kg cm ,

Columns F = Proportion (%) of wood failure (the glue was stronger than the wood).

* Samples 91 , 96, 99, 122, 123, 124, 125, 128 survived the second treatment

The other samples (except 97, 98 and 120) showed weakening but not complete separation at the glue line. Samples 97, 98, 120 separated in boiling water within about 1 hour.

** Glue joints weakened upon boiling were pressed together and left in an oven at 60°C for 48 hrs before testing

By way of interpretation, note that for those samples where the wood, not the glue, gave way, the force involved is about 150-180 kg cm-2. The most promising compositions appear to be those with the highest remaining strength after boiling. Samples 91 , 96, and 125 were good; with 125 being the "best" according to these tests. EXAMPLE 5A: (see also Figs 1 and 2)

Wood bonding performance tests during extended boiling.

Boiling water test

The boiling water test was conducted by continuous boiling of glued wood blocks,, which gave good relative results for water and heat resistance. The wood blocks were subjected to two boiling cycles. First the glued wood blocks were boiled for 3 hr, dried in an air circulated oven at 60°C for 48 hr and re-boiled for 4 hr. The results are presented in Table 9 and in bar charts in Figs 1 and 2, where the height of each bar corresponds to the time to a point of failure. Only a few samples passed both the 3 and then the 4 hour boiling tests.

Water resistance test

The samples were immersed in water at room temperature for 6 weeks with the following results:

The samples showed excellent resistance to water immersion for 6 weeks. Samples 97, 98, 120, 124 and 125 showed creamy appearance at the joints within 2- 3 weeks but the joints were intact.

Although uncompounded polychloroprene latex generally has good mechanical and storage stability, the adhesive composition may require the incorporation of additional acid acceptors such as zinc oxide dispersions or aqueous epoxy resins to minimize the degradation of the adhesive composition due to release of hydrochloric acid from the polychloroprene rubber. Table 9 - Variants Of Wood Adhesive.

Parts by volume in parentheses.

P - Poly(vinyl acetate) NR- Natural Rubber R1- Epoxy resin (Europox 710)

R2 - SE 780 R3 - SE 790 AC- crosslinked AQL

PC - crosslinked alkalised PVA NC- crosslinked NR A - AQL - Aquastik 1120/

Neoprene 115

PALK - alkalised PVA N - alkalised NR TA- Tetraethylenepentamine In Table 9 "pass" in column 3 signifies that the adhesive joint between the wood blocks remained intact after immersion for three hours in boiling water and drying at 60°C for 48 hours. "Pass" in column 4 signifies that the adhesive joint remained intact after subsequent immersion for 4 hours in boiling water. The times recorded in column 3 and column 4 are the times after which the adhesive joint failed during immersion in boiling water.

Sample 90, sample 95, sample 121 and sample 122 coagulated after standing at ambient temperature for 1 week.

EXAMPLE 6:

Particle Boards Using Natural Rubber/ Pva Adhesives

A number of processes to consume wood chips and convert them into boards rely on forming a matrix of mutually adherent chips set into a solid mass. The non-toxic and waterproof nature of adhesives according to this invention permit the manufacture of a water-resistant version of particle board, useful for bathrooms and shower floors as well as other areas likely to be exposed to water. In particular, the traditionally employed adhesive in particle board is likely to release trace amounts of potentially toxic formaldehyde over an extended period and there is a good deal of consumer resistance in some societies to the risk of exposure to this gas.

EXAMPLE 7: Grafted Natural Rubbers In PVA Adhesives

By way of a yet further variation the present invention also provides adhesive compositions including modified natural rubber, another synthetic rubber, or their combinations with PVA. Preferably, such natural and synthetic rubbers have unsaturated chains derived from units such as butadiene or have units derived from C4 to C10 conjugated dienes, such as styrene or methyl methacrylate. Natural rubber is commercially available as modified general-purpose latex. For example, modified latex is available under the tradenames MEGAPOLY latex, as MG 49, and as MG 30 (rubber latexes grafted with methyl methacrylate to increase the polarity and thereby the adhesion of the adhesive compositions. These compositions would give relatively transparent, tough and semireinforced films.

The adhesive compositions of the present invention provide the following advantages

1 The compositions provide an effective contact adhesive for a variety of substrates. The compositions provide a user-friendly alternative to existing adhesives because they are water based and do not employ organic solvents, which may be toxic and expensive.

2 The compositions are inexpensive to produce because they lack exotic materials.

3 One aspect of the invention provides adhesive compositions suitable to manufacture self sealing envelopes and self sticking note pads similar to the commercially available and popular "3M Post-it ™ "Note Pads.

4 Another aspect of the invention provides a set of heat and water resistant, water-based contact adhesive compositions suitable for the outdoor wood products manufacturing industry.

5 A further aspect of the invention provides coating compositions for application on a variety of films including bubble pack, polyethylene, polypropylene and the like which may be used as easily peelable removable protective coatings to prevent scratching or damage of various surfaces including glass, stainless steel and the like.

6 The invention also provides coating compositions for application on variety of surfaces such as paper and cardboard to provide printable, yet water and moisture resistant coatings.

7 The waterproof properties, and the transparency of the glue line after bonding of the compositions of the present invention should allow extensive use in construction of wood laminates particularly in applications where glue lines are traditionally visible.

8 A longer shelf life than current materials used for resealable envelopes is an advantage over existing materials. 9 The capability of the compositions of the present invention to accept ink is useful in product labelling, and may be extended for example to manufacture of audiovisual transparencies, as a printable coating over a "Mylar" sheet.

10 The non-toxic and waterproof nature of the adhesive compositions of the present invention permit the manufacture of water-resistant particle board, useful for bathrooms and shower floors as well as other areas likely to be exposed to water.

Finally, it will be understood that the scope of this invention as described and/or illustrated within this provisional specification is not limited to the preferred embodiments described herein for illustrative purposes. Those of skill will appreciate that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the invention as set forth.

Claims

1 A water based adhesive composition, including (a) at least one poly(vinyl acetate); and (b) at least one latex; wherein in use the adhesive composition, after drying, is substantially water-resistant.

2 The composition according to claim 1 wherein the poly(vinyl acetate) is cross linked.

3 The composition according to claim 1 or claim 2 wherein the at least one latex is selected from one or more of the following; a natural rubber latex, a modified natural rubber, a compounded natural rubber latex, a modified, cross linked natural rubber latex, a polychloroprene rubber latex and a modified polychloroprene rubber latex.

4 The composition according to claim 3 wherein the modified natural rubber includes unsaturated chains.

5 The composition according to claim 4 wherein the unsaturated chains of the modified natural rubber includes styrene or methyl methacrylate groups.

6 The composition according to claim 5 wherein the styrene or methyl methacrylate groups are further bonded to butadiene groups.

7 The composition according to any one of claims 3 to 6 wherein the modified natural rubber is a compounded, a prevulcanized, or a grafted natural rubber.

8 The composition according to claim 7 wherein the compounded modified natural rubber includes one or more further components to at least partially cross link the natural rubber the further components being selected from an activator, an accelerator, an antioxidant and a cross linking agent.

The composition according to claim 7 wherein the prevulcanized natural rubber includes one or more further components adapted to at least partially cross link the prevulcanized natural rubber the further components being selected from an activator, an accelerator, an antioxidant and a cross linking agent.

The composition according to claim 8 or claim 9 wherein the cross linking agent is a zirconium salt in an alkaline medium.

The composition according to claim 10 wherein the zirconium salt is zirconium nitrate.

The composition according to any one of claims 8 to 11 wherein the activator is an inorganic oxide.

The composition according to claim 12 wherein the inorganic oxide is zinc oxide.

The composition according to any one of claims 8 to 13 wherein the accelerator is an organic dithiocarbamate, disulphide, thiozole and the like.

The composition according to claim 14 wherein the accelerator is zinc diethyldithiocarbamate, tetramethyl thiuram disulphide, mercaptobenzothiozole and the like.

The composition according to any one of claims 8 to 15 wherein the antioxidant is a phenolic or amine compound or a blend thereof.

The composition according to claim 16 wherein the antioxidant is Antioxidant 2246, Wingstay L, Vanox MBPC, Vulkanox BKF, 4020, SKF, MB 2 or SP. 18 The composition according to claim 7 wherein the grafted natural rubber is further modified by the grafting of one or more polar polymers on to natural rubber to increase polarity.

19 The composition according to claim 18 wherein the polar polymer is selected from poly(methyl methacrylate) and styrene.

20 The composition according to any one of claims 7 to 19 wherein the natural rubber is in a stable aqueous emulsion.

21 The composition according to claim 19 wherein the aqueous emulsion is preserved with a biocide.

22 The composition according to any one of claims 3 to 21 wherein the polychloroprene rubber latex and the modified polychloroprene rubber latex further include one or more acid acceptors to stabilise said composition.

23 The composition according to claim 22 wherein the one or more acid acceptors is selected from a zinc oxide dispersion or an aqueous epoxy resin.

24 The composition according to any one of claims 3 to 23 wherein about 10% to about 40% by volume of the natural rubber latex is blended with the poly(vinyl acetate).

25 The composition according to claim 24 wherein the natural rubber latex is blended with the poly(vinyl acetate) before any polychloroprene is added to the composition.

26 The composition according to any one of claims 1 to 25 wherein the composition further includes an effective amount of at least one water based tackifying agent.

27 The composition according to claim 26 wherein the water based tackifying agent is an aqueous dispersion. 28 The composition according to claim 26 or claim 27 wherein the water based tackifying agent is selected from one or more of a rosin acid, a rosin ester, a terpene phenolic resin, a hydrocarbon resin, and a coumarone indene resin.

29 The composition according to any one of claims 26 to 28 wherein the tackifying agent is present in an amount of about 1 % to about 50% by volume, based on the weight of the composition.

30 The composition according to claim 29 wherein the tackifying agent is present in an amount of about 40% by volume, based on the weight of the composition.

31 The composition according to any one of claims 1 to 30 further includes, as a water barrier, at least one substance selected from a range including silicone, Additive 84, Additive 85, and Oratan 2001.

32 The composition according to claim 31 wherein the water barrier is present in the composition at up to 20% by weight of the total composition.

33 The composition according to any one of claims 1 to 32 further including at least one preservative.

34 The composition according to claim 33 wherein the preservative is a biocide.

35 The composition according to claim 21 or claim 34 wherein the biocide is a fungicide or a bactericide.

36 A method of bonding at least one substrate; the method comprising the steps of: b) applying a water based adhesive composition as defined in any one of claims 1 to 34, to at least a portion of a surface of at least one first substrate, b) allowing the adhesive composition to at least partially dry on the first substrate; c) contacting the adhesive applied surface to a second substrate surface; and d) forming an adhesive bond between the first and second substrates.

37 The method according to claim 36 wherein said first substrate is selected from wood; metal including cold-rolled steel, galvanized steel, and aluminium; fabric; paper; foam; plastics including poly(vinyl chloride,) polystyrene, polyethylene, polypropylene, and fibreglass.

38 The method according to claim 36 or 37 further including the steps of applying and at least partially drying an adhesive composition as defined in any one of claims 1 to 34 to at least a portion of the second surface of a substrate.

39 The method according to claim 36 or claim 37 wherein said adhesive composition is selected so as to achieve a reversible or releasable adhesive bond when said first substrate is selected from paper, polyethylene, bubble pack and polypropylene.

40 The method according to claim 39 wherein the second substrate is paper when the first substrate is paper.

41 The method according to claim 36 wherein when the first substrate is selected from polyethylene, bubble pack and polypropylene and the second substrate has a delicate surface such as a glass or stainless steel surface, which is readily scratched.

42 A method of applying a water resistant coating to at least one substrate; the method comprising the steps of: a) applying a water based adhesive composition as defined in any one of claims 1 to 34, to at least a portion of a surface of a substrate, and b) allowing the adhesive composition to dry on the substrate. 43 The method according to claim 42 wherein said substrate is selected from wood; metal including cold-rolled steel, galvanized steel, and aluminium; fabric; paper; paperboard; corrugated boards, kraft cardboard; foam; plastics including poly( vinyl chloride,) polystyrene, polyethylene, polypropylene, and fibreglass.

44 The method according to claim 43 wherein said substrate is selected from paperboard, corrugated card and kraft cardboard.

45 The method according to any one of claims 42 to 44 further including the step of printing on the dry water resistant coating on the substrate.

46 A method of bonding at least one first wood substrate to a second wood substrate; the method comprising the steps of: a) applying a water based adhesive composition as defined in any one of claims 1 to 34, to at least a portion of a surface of the first wood substrate, b) allowing the adhesive composition to at least partially dry on the first wood substrate; c) contacting the adhesive applied surface to the second wood substrate surface; and d) forming a transparent adhesive bond between the first and second wood substrates.

47 The method according to claim 46, wherein the adhesive composition includes poly(vinyl acetate), natural rubber, cross-linked polychloroprene rubber, and a tackifing agent.

48 The method according to claim 47 wherein the PVA and the natural rubber is cross-linked.

49 The method according to any one of claims 46 to 48 wherein the composition includes 8 parts by weight of cross linked poly(vinyl acetate), 1 part by weight of cross linked polychloroprene latex; 1 part by weight of cross linked natural rubber and two parts by weight of a tackifing agent "(PC(8)/AC(1)/NC(1)/R2)".

50 A method of making a water-resistant structural chipboard component, the chipboard being substantially comprised of fragments of wood bonded together with a water based adhesive composition including poly(vinyl acetate), natural rubber, cross-linked polychloroprene rubber, and a tackifing agent.

51 The method according to claim 50 wherein the PVA and the natural rubber is cross-linked.

52 The method according to claim 50 or claim 51 wherein the composition includes 8 parts by weight of cross linked poly(vinyl acetate), 1 part by weight of cross linked polychloroprene latex; 1 part by weight of cross linked natural rubber and two parts by weight of a tackifing agent "(PC(8)/AC(1)/NC(1)/R2)".

53 A transparency sheet including a dye-receptive or printable layer, the dye- receptive layer comprising a water based adhesive composition including a pόly(vinyl acetate) component together with at least one member selected from a synthetic latex and/or a natural rubber latex.

54 The transparency sheet according to claim 53 wherein the synthetic latex is polychloroprene latex.