CA2026427A1 - Synthetic resin plastic suspension or dispersion for use as a fusion adhesive - Google Patents

Abstract

ABSTRACT

This is the description of an adhesive used in the form of a watery suspension or dispersion which is painted or otherwise applied to the selected substrate, the water is either removed or the suspension is dried, and finally the bonding is attained through the application of heat. The suspension is made by subjecting acetic-acid vinyl ester, alpha-olefinic unsaturated systems and similar compounds as well as other substances to a suspension polymerization in water.

Description

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SYNTHETIC RESIN_PLASTIC SUSPENSION
~ OR DISPERSIQ~EQ~_~5~ FUSIO~ A_HESIVE

-~ The invention concerns a water plastic 5 suspension or dispersion which can be used as a meltable ;
adhesive.
There are different systems among adhesives.
Dispersions and suspensions for adhesive and sealing applications usually contain polyvinyl alcohol or derivatives of cellulose as protective colloids; these substances are not meltable. Also the polymers which contain these protective colloids are practically not meltable, or their melting point is in the range of the decomposition temperature, so that a reversible change of condition is not possible.
The dry films of dispersions containing `~
protective colloids develop at best only a slight surface taak after being heated.
With the appropriate formulations and the use of 2~0 ~emulsifiers,~ finely~dispersed synthetic plastic resin ;dispers~ions with low polymerization grade can be obtained which are meltable, but at temperatures just above room temperature, the coatings made from these dispersions are 'not block- and~tack free.
2~5 ~ They have poor heat resistance and exposed to higher temperatures. ~hese products have a very low ;-viacosity after melting. With these types of coatlngs or ` films, porous substrates cannot be glued together since these polymers will soak into the substrates at temperatures above the activating/melting temperature.

From the point of view of Hotmelt adhesives, these adhesives are by definition meltable and contain for instance EVA, resins and waxes.
The melt viscosity and blocking properties can be sufficiently regulated by adjusting the formulation.
However, because of the polymer structure of these types of products a broad softening range is obtained so that the heat resistance of such an application (glued as described - in DIN 53 254) does not exceed a temperature of 70--80- C.
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lOTheoretically it would be possible to overcome these disadvantages by using EVAs with a very low melt flow index. In practice however it is not possible to apply such highly viscous polymers as hotmelt adhesives in the desired thickness of < 200 ~m. This eliminates these lS products for the majority of uses because of their low heat ~ resistance. Hotmelt adhesives must be heated and melted in .~ vessels for a long period of time during their manufacture for optimum homogenization of the raw materials -, and -i before application - in order to attain optimum processing 20 properties. These procedures often lead to the thermal -~
degradatlon of these systems. -~;
Hotmelt adhesives based on fatty acid polyamides - i.e. the condensation products oP dimerized, higher unsaturated fatty acids and diamines or saturated ~` 25 polyesters - i.e. the condensation products of aromatic ,~ ,and/or aliphatic dicarboxylic acids and glycols and/or -~
other diols - will improve the heat stability, with ~; appropriate adjustment of the formulation, by approximately 15^C however, the high price of these products limits their ~ -use to exceptional cases, and the application technique becomes too complicatedj since at the required higher working temperatures the adhesives tend to degrade more rapidly on the use of a protective gas is necessary. `
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In systems based on solvents, the dissolution with organic solvents makes it possible to manufacture the desired coatings for later use, however the use of organic solvents makes this procedure so expensive, that it is only used in exceptional cases. Also the use of solvents should be avoided at all cost for environmental reasons, particularly since not just the application procedure is ....
very expensive - i.e. the protective measures to avoid explosion.
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The purpose of the present invention is to if~ propose an adhesive which does not have these disadvantages, does not require expensive devices for its manufacture and processing, and which can be handled and used in an environmentally safe manner.
These problems are solved with the meltable adhesive described in the claims.
According to the invention the application is ,~; made out of the watery phase, which is simpler and less expensive than the application in the molten or dissolved phase.
The watery synthetic plastic resin suspension or disperaion has the following advantages:
The suspension contains water and not an environmentally hazardous solvent.
- The applied and dried coating is tack- and block free at room temperature.
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he polymer can be molten to a mass with real measurable rheological properties by means of a heated ~; press or also in small melting containers.

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, - The melting range can be adjusted according to the monomer compound and the degree of polymerization.
- The synthetic plastic resin of the dispersion does not soak into porous absorbent substrate when applied because the size of the particles is controlled, but instead remains in the area where it is needed for the gluing process.
- The adhesive provides heat resistance values which cannot be attained with conventional hotmelt adhesives.
- The adhesive does not need to endure long temperature exposure during the manufacturing process and during the application, as is the case with hotmelt adhesives, and therefore does not tend to degrade.
;~ 15 The suspension/dispersion forms a tack- and `~block free coating at room temperature after it is applied ;
to any smooth, absorbent or non-absorbent substrate after the water in the mixture has been separated or evaporated.
; When heated, the coating melts forming a sticky, highly viscous liquid with very good cohesion and adhesion.
The molten adhesive film is a genuine molten mass with a viscosity, depending on the formulation of between 50,000 -1,000,000 mPas at approximately 220- C. The melt flow indexes of the water-free polymers, depending on the ~; 25 formulation and according to DIN 53 735 are between 0.1 to 400 g/10 min. The gluing process, the properties attained ; during the gluing process only take place because of physical processes (change of state), which does not exclude that if reactive monomers are used, a chemical reaction like polymerization could take place. According to the known procedure of the suspension of polymerization, the monomers are emulsified in water with the alpha- -olefinic unsaturated compounds under the effect of shearing stresses, and are polymerized with the help of a monomer soluble initiators.
The following can be used as olefinic unsaturated compounds: vinyl esters or organic carboxylic acid whose carbon structure contains 1-20 C-atoms; esters of acrylic or methacrylic acid with C1- to C20 alcohols, alipathic or preferably aromatic alpha-beta unsaturated hydrocarbons, mono and/or di-esters of the cis or trans-dibutene acid, alpha-beta unsaturated carboxylic acids as well as their derivatives. Preferred are acetic acid, `~:
` propionic acid, isononic aci~, dodecane acid vinyl ester, styrene, vinyl toluene, cis-dodecane acid butyl ester, acrylic acid or crotonic acid.
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lS In addition to the mentioned alpha-olefinic unsaturated compounds, also polyfunctional monomers can be used, which allow a partial cross-linking in polymers.
The following are examples of that type of monomers: Esters from unsaturated carboxylic acids with alcohols which contain functional groups, such as glycidyl alcohol, several function alcohols such as ethylene- -~
propylene or butylene glycol, vinyl and allyl compounds as well as modlfied acryl amides.
Dispersing agents, sometimes also called 2S suspension stabilizers, are used in the manufacture of the plastic resin suspension, some for instance based on fine, insoluble, mostly inorganic substances such as kaolin, talcum, bentonite, montmorillonite, metal hydroxides or phosphates, or based on highly molecular, organic substances which are water soluble but not soluble in monomers - i.e. cellulose derivatives, starch ether, polyvinyl alcohols or their co-polymers, polyacrylic acid or of poly-methacryIic acid salts and their derivatives, butylene acid derivatives, polyvinyl pyrrolidine or their co-polymers, polystyrene or its co-polymers, as well as different condensation resins.
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In order to increase stability, and to control the size of the particles, modulators and surface active ~;
substances are added such as alkaline salts of alkane and alkylaren sulphonic acids, alkaline salts of alkyl sulphates with long alkyl groups, alkaline salts of fatty acis, ethoxilated products of the above mentioned surface active substances, succinic acid derivatives, ethoxilated fatty amines.
The molecular weights of the polymers can be regulated by means of regulators such as aldehydes, ketones, thiols, terpenes or cyclo-alipathic enol ether. -The monomer soluble catalysts used are peroxides - -~
or azo compounds.
; In addition to being influenced by the dispersing agent, the size of the forming beads can also be influenced by the stirring speed and by the geometry of the r~eartor~vessel The size of the particles varies according - ;-to~the application between 0.5 ~m and up to several mm.
Depending~on the variation one can obtain polymers which tend~to~phaae~separation or products which resemble stable finely dispersed dispers1ons~
The suspension/dispersion prepared by means of polymerization can be used directly for the gluing and coating applications. Compounding with thixotropic agents ~-or othor bin~dlng substances is also possible. -The~suspension resulting directly from the ~` ~ polymerization or the prepared suspension can be applied by means of a coating bar, by roller application, with low pressure~or roller machines, using nozzle application by ` spraying or dipping or also using a transfer process, to ~;~
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any smooth, absorbent or non-absorbent sur~aces such as pl~stic foils, paper, sheets impregnated with synthetic resins, wood or chip board substrates; fleece made ~f synthetic or natural fibres; foam materials, e.g. based on PE, PUR, PVC - or to metals.
~ ecause the particle size is adjusted during the polymerization process, the synthetic plastic resin soaks only to a small extent into any eventual absorbent substrate. After the drying or the removal of the water a synthetic resin film remains with low cohesion and adhesion. The water can be removed by evaporation, e.g.
through a change of state, for instance in a drying tunnel, or by means of a suction procedure similar to a filtration ; procedure. Contrary to the systems known to this date, ~- lS after the application and drying a block free coating is obtained. After heating the polymer with tempered presses, hot rollers, calenders or heated air, the previously block free surface melts forming an adhesive of high cohesion and good adhesion. As long as the adhesive remains in liquid state the coated substrate can be glued to other parts/surfaces simultaneously, or immediately after the heating procésses.
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EXAMPLE
650 g deionized water is placed in a 1.5 1 laboratory vessel which can be heated or cooled, and which i equipped with a condenser, an agitator and an apportioning device, and 9.0 g of polyacrylic acid - a 50%
paste in 60 crystal oil (molecular weight 2,800,000) is added while stirring vigorously. After 10 minutes of homogenization the mixture is brought to a pH value of 7 .~ ~
~-~ with concentrated ammonia.
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In another mixing container 220 g of acetic acid vinyl ester are mixed with gO g of acrylic acid butyl-ester, 0.6 g of dibenzoyl peroxide and 15 g of ethoxilated fatty amine C1gH37N-(CH2CH20-)x, yHr where x+y= 20 (molecular weight 1149) are dissolved in the monomers. The monomer mixture is pre-emulsified in the reactor in the above mentioned watery solution at room temperature and under vigorous stirring. After adding another 0.1 g of dibenzoyl peroxide, the mixture is heated to the point of slight reflux while stirring, 0.1 g dibenzoyl peroxide are added to the reaction mixture three times at intervals of 2 hours each time. After the completion of the reflux (approximately 6 hours~ the mixture is left for 1 hour at 80 C for the final polymerization of the preparation, while ~ 15 heat is being supplied from an outside source. In order to `- -~ adjust the pH-value, 2 ml of concentrated ammonia added after the suspension polymer has cooled down. A synthetic ~ -~ plastic resin suspension is obtained which has a solid -~-`~ content of approximately 28%, a viscosity of approximately 1000 mPas, a neutral pH-value, and which tends to precipitate. However, the precipitate may be stirred again resulting in a preparation with the same properties. The ~` homogenized mixture can be applied onto paper foil with a 200;~m spiral coating bar. After the water had dried up, ; 2S the coatlng remained totally block free following a test commonly conducted in this industry which consists of the following: 10 round, coated, dry foil cutouts each with a surface of 100 cm2 are stacked on each other for 72 hours under a load of 5 kg. After the weights were removed the ; ~ ~ 30 fi ~ were not sticky or glued together.
y means of tempered presses the coated foils can be pressed onto an absorbent or non absorbent substrate with their;coated sides facing the substrate, at a ~` ~ temperature of 160-C and a press time of 3 seconds. During this procedure the coating melts and the foil is glued to `,'' ~ ,~4~ ,. ' ~ S~

the substrate, showing excellent adhesion, cohesion and heat resistance.
: Coated, dried plastic films or separated, dried suspension polymers will melt in an oven at a temperature S of 250 C forming a liquid flowing mass.
~: A viscosity of 800,000 mPas at 220 C was :~ determined using the Thermosel ~VT Brookfield viscosimeter. ::

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Claims (2)

1. Water synthetic plastic resin suspension or dispersion of homo-, co-, or terpolymers containing alpha-olefinic monomers mixed with protective colloids and surface active substances to be used as meltable adhesives, characterized by the fact that the following mixture:

48 - 98 Weight - % acetic acid vinyl ester 0 - 50 Weight - % other alpha-olefinic unsaturated systems 1 - 10 Weight - % dispersing agents 0 - 10 Weight - % protective colloids 1 - 10 Weight - % surface active substances are polymerized in a watery suspension procedure, and that the suspension can be used as such.

2. Meltable adhesives according to claim 1, characterized by the fact that the synthetic plastic resin suspension can be applied to surfaces by painting, spraying, pressing, wiping, dipping or by using the transfer procedure, forming a block free meltable adhesive after the water has dried up or has been absorbed.