CA1086916A - Acrylic adhesive for bonding vinyl coatings - Google Patents

Abstract

ACRYLIC ADHESIVE FOR BONDING VINYL COATINGS
ABSTRACT OF THE DISCLOSURE
The specification discloses noncracking perma-nent adhesives which utilize mixtures of phenolic resins and methacrylate resins having a Mw greater than about l00,000 and preferably about 400,000 for bonding plasti-cized vinyl resin coverings, e.g., PVC, to hard polymeric substrate surfaces such as ABS, etc. Also, it is preferable that the vinyl resin covering contain plasticizers which are no more than limited in compatibility with the adhesive.
It is theorized that the adhesive mixture prevents migration of plasticizer from the plasticizer-containing vinyl resin covering into the adhesive and eventually into the polymeric substrate.

Description

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BACKGROUND OF THE INVENTION
1 Vinyl resins have been used to coat or cover a wise variety of materials. Most materials such as acrylonitrile-,butadiene-styrene (hereinafter referred to as ABS) may be coated with a vinyl resin without the use of the adhesive materials simply by dipping or spraying the material being coated with the resin coating. How-ever, vinyl resin coverings particularly on materials like ABS are likely to be nonpermanent, in that a good bond between the materials is not formed. Within a short time after coating, peeling and cracking, etc., of the polymeric surface results. Further, if the coating or covering is to be used on surfaces which are subject to frictional contact, e.g., rubbing, etc., the covering or coating slips.
Several attempts have been made to securely bond vinyl resin coverings to various materials. Systems involving preheating of the material being coated, baking of the covering, etc., have all been used with!~nly limited success. Presently, vinyl resins which are utilized in coverings are available as dispersions or suspensions. The vinyl resin is usually in the form of a paste dispersion or elastomers in a plasticizer ~plastisol) and paste dispersions of such elastomers in a plasticizer and a volatile liquid (organisols).
These materials have been particularly difficult to

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1 permanently adhere to surfaces, e.g., polymeric surfaces.
In the use of such systems, it has been necessary to apply the vinyl resin dispersions only after the surface to which they are being applied has been treated with a primer. Various primers, e.g., vinyl butyral wash primer, have been utilized to aid in bonding of the vinyl resin dispersion. Among several disadvan-tages of known primers for vinyl resin include:
insufficient adherence to permit forming andstamping operations subsequent to coating; the requirement of critical preheating of surfaces and curing of primer and/or coatings; a decreased adherency with aging; and cracking and breaking of the polymeric substrate. It is theorized that the cracking of the polymeric substrate is caused to great extent by migration of the plasticizer from the cured resin dispersions through the primer into the substrate.
The prior art has attempted to alleviate these problems by use of primers comprising various mixtures of acrylic resins. One such mixture comprises acrylic and epoxy resins. Such mixtures have been useful particularly where the surface to which the vinyl dispersion is being bonded is metallic. However, such mixtures do not adequately bond vinyl resin d;spersions to polymeric materials, e.g., ABS~ Further, they do not eliminate cracking and breaking of polymeric substrate by plasticizer, if the vinyl resin comprises plasticizer.
SUM~ RY OF THE INVENTION
In accordance with the present invention, it has been found that strong and permanent adhesives useful for bonding vinyl resin coverings to surfaces, can be made

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1 by employing mixtures of phenoliic resins and metha-crylate resins having a ~w greater than about 100,000, preferably about 400,000. Also~ preferably, the methacrylate resin is a lower a]Lkyl methacrylate, most preferably, a methyl methacrylate.
If the adhesive is used with vinyl resin coverings, contains plasticizer, and the plasticizer is no more than limited in compatibility with the resins, such superior bonding results, particularly on polymeric suraces, as to show a synergistic combination.
The adhesive preferably comprises from about 1 per cent to about 95 per cent ~all per cent are by weight resin solids) phenolic resin and rom about 5 per cent to about 99 per cent methacrylate resin, more preferably from about 50 per cent to about 80 per cent phenolic resin and from abou~ 20 per cent to about 50 per cent methacrylate resin, and most preferably from about 60 per cent to about 70 per cent phenolic resin and rom about 30 per cent to about 40 per cent metha-crylate resin.
When the covering comprises plasticizer~
preferably the plasticizer is no more than limited in compatibility with the resin, i.e., pllthalate plasticizers It ls theorized that the polymeric mixtures of this invention act as efficient permanent adhesives for plasticizer-containing coverings because they resist migration of the vinyl coating plasticizer.
DESCRIPTION OF THE PREFERRFD EMBODIME~T
The noncracking adhesives of this invention for bonding vinyl coverings to polymeric surfaces com-prise mixtures of phenolic resin and methacrylate resins.

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1 Phenolic resins usefu:L with this invention must be thermosetting and are obtained by the conden-sation of phenol or substituted phenols with aldehyde such as formaldehyde, actaledehyde, and urfural. Among phenolic resins which are particularly useful with this invention are: phenol-formald0hyde resins such as DS-9-2816 sold by Jamestown Finishes, Inc., Jamestown, New York.
The methacrylate resins of this invention have a Mw greater than 100,000, more preferably, about 400,000. Preferably, the methacrylate resin is a Cl to C4 lower alkyl, most pre~erably a methyl methacrylate resin.
Weight average molecular weight, ~w is defined as:
~w = ~

where Mi is the molecular weight of particles of chain length i, and Ni is the number of particles of chain length i. Since highly polymeric resins are composed of mixtures o macramolecules, the higher the ~w, the greater the number of longer chained macramolecules in the resin.
Examples of methacrylate resins whlch are useful with this invent~on include those taught by U. S. 3,150,118 which are Cl to C4 lower alkyl metha-crylate/l~weT alkyl acrylate copolymers. An example of a particularly useul methacrylate resin having ~w about 400,000 is a copolymer of methyl methacrylate and normal or isobutyl acrylate wherein the methyl methacrylake comprises from about 40 to 75 wt. per cent of the copolymer and the normal or isobutyl acrylate comprises rom about - ~ .

~ 6 1 20 to about 50 wt. per cent of the copolymer. A com-mercially available version of this resin is AcryloidTM
55D~2 sold by Rohm and Haas Company, Philadelphia, Pennsylvania.
If plasticizers are used in the vinyl coverings used in conjunction with this invention, they may be either highly compatible (primary) or limited in com-patibility (secondary) with the phenolic and methacrylate resin adhesive mixture. However, if the plasticizer utilized in the vinyl coating is no more than limited in compatibility with the resins, the adhesive mixture shows such superior bonding, i.e., craze or cracking resistance particularly on polymeric surfaces, characteristics as to show a synergistic combination. Useful plasticizers include adipate and sebacate esters, polyols, e.g., ethylene glycol and its derivatives, and caster oil.
Most preferred plasticizers having no more than limited compatibility with the resins include phthalate esters, i.e., diisodecyl phthalate and/or epoxy tallate, and those comprising metallic solids, i.e., liquid cadmium barium zinc stabilizer, sold by Argus Chemical Corp., Brooklyn, New York. Least preferred plasticizers having high compatibility with the resins include phosphates, i.e., tricresyl phosphate.
It is theorized that the phenolic resin either macrascopically or molecularly sufficiently reacts witnin the methacrylate resin matrix actually surrounding the long chained methacrylate resin molecules, as to provide a barrier which is virtually inpenetratable by the poly-vinyl resin plasticizers. This barrier effect is particularly noted where the plasticizer is no more than limited in .

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1 compatibility with the resins.
The resins are commercially available as solutions which contain -from about 1 to about 20 weight per cent solids in various solvents. When applying the adhesive to the surface being covered with the vinyl resin ~spersion, it is preferred that the commercially available resins after being formed into the adhesive mixture be mixed with an organic solvent. The amount of solvent utilized depends on among other things, the atmospheric temperature, pressure, and humidity. However, it is preferred that the solvent-to-adhesive mixture be between about 10:1 and 1:10 by volume, preferably the ratio is about 1:1 by volume.
Though many solvents are suitable, the organic solvent used preferably comprises blends or mixtures of alkyl and aryl ketones, aromatic hydrocarbons, and alcohols. Useful alkyl ketones include methylethyl, methylisobutyl and diisobutyl ketones and diacetone alcohol. Among aromatic hydrocarbons useful with this invention are toluol and high flash naphtha. Alcohols include 2-methoxy ethynol, alkyl CellusolveTM, etc.
The adhesive mixture of this invention preferably comprises from about 1 per cent to about 95 per cent phenolic resin, and from about 5 per cent to about 99 per cent methacrylate resin, more preferably, the mixture comprises from about 50 per cent to about 80 per cent phenolic resin, and from about 20 per cent to about 50 per cent methacrylate resin and most prefera-bly the mixture comprises from about 60 per cent to about 70 per cent phenolic resin, and from about 30 per cent to about 40 per cent methacrylate resin ~all p ,f . ... ..
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~ 8 ~ ~ 6 l per cent by weight resin solids).
Various agents may be added by those skilled in the art to control adhesion kinetics, e.g., curing agents. Curing agents useful with this adhesive in-clude polyfunctional amines and acid anhydrides. Examples o-f poly-functional amines include diethylene triamine, trethylene tetramine, tetraethlene petamine, and phenylenediamine-meta. Examples of acid anhydrides include maleic, dichloromaleic and phthalic anhydrides.
Any of the commercially available vinyl resins are useful with this invention. Suitable vinyl covering polymers include copolymers of vinyl chloride and vinyl acetate. Examples of suitable vinyl materials include Vinylite~ YHH and QYNL sold by Union Carbide and Carbon Corporation. However, as above discussed, the nature of the plasticizer contained in the resin is of great importance.
Example I
Adhesives are formulated by intermixing varying amounts of a commercially available phenolic resin solu-tion, DS-9-2816 (15% solids), sold by Jamestown Finishes, Inc., Jamestown, New York, and a methacrylate resin, having a Mw of about 400,000 AcryloidTM, 55D42 (8% solids), sold by Rohm and Haas Company, Philadelphia, Pennsylvania.
The adhesive is spray or dip coated on an ABS molded surface which is subsequently covered by injection molding the following material over the ABS substrate:
Parts Polyvinyl chloride resin (QYNL) . . . . . . 100 Diisodecyl phthalate . . . . . . . . . . . . 91 Epoxy Phthalate. . . . . . . . . . . . . . . 8 .~, .

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6~6 1 (continued) Parts CaCO3 . . . . . . . . . . . . . . . . . . . . 20 Stearic Acid. . . . . . . . . . . . . . . . . 1/4 BaCdZn Chelator Stabilizer . . . . . . . . . 2-1/2 The composite is then tested as to the adherence of the vinyl coating to the ABS before and after aging.
The adhesive strength of the resulting bond is given in pounds per inch width. The PVC covering has a Durometer rating of 70 and thus itself tears at around 50 pounds per inch of width. The following table summarizes the results of these tests:
adhesive strength*
Parts Parts in lbs./inch of width methacrylate phenolic resin resin solution solution (8% solids) (15% solids)

4 1 51-57 *In all cases, the vinyl coating tore before adhesive failed.
Example 2 ABS Cycolac TTM tensile bars coated with only methacrylate resin (55D42) and coated with a 1:2, metha-crylate (55D42) to phenolic resin (DS-9-2816), adhesive mixture were strained to 0.8 per cent over a 15-1/2 inch diameter wooden drum. Various plasticizers contained in g '': .: - ,.

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1 vinyl coverings are painted onto the adhesive-covered surface of the ABS until the surface crazed. The ~ollowing table sets forth the results of these tests:

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' 1 As seen in this example, the phosphate plasticizer 9 which is highly compatible with the adhesive resin mixture acts to penetrate the resin and attack the ABS substrate rapidly as compared to the other limited incompatibility plasticizers showing the synergistic combination of resins and preferred plasticizers. ..
As various changes could be made in the above methods and products without denarting from the scope of the invention, it is in~ended that all matter contained in the above description shall be interpreted ~.
illustrative and not in a limiting sense.

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Claims

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

A method for adhering a vinyl resin covering con-taining plasticizer consisting of substantially only phthalate esters to a polymeric substrate of a material forming a hard substrate surface, comprising coating said polymeric substrate with an adhesive comprising a mixture of from about 1 wt.
per cent to about 95 wt. per cent phenolic resin solids and from about 5 wt. per cent to about 99 wt. per cent methacrylate resin solids, said methacrylate resin having a weight average molecular weight of about 400,000; followed by molding said vinyl resin onto said coated polymeric substrate.

The method of claim 1 wherein said methacrylate resin employed is a C1 to C4 lower alkyl methacrylate.

The method of claim 2 wherein said lower alkyl methacrylate employed is methyl methacrylate.

The method of claim 2 wherein said methacrylate resin employed is a C1 to C4 lower alkyl methacrylate/lower alkyl acrylate copolymer.

The method of claim 4 wherein said copolymer employed is a copolymer of methyl methacrylate and normal or isobutyl acrylate wherein the methyl methacrylate comprises from about 40 to about 75 wt. per cent of the copolymer and the normal or isobutyl acrylate comprises from about 20 to about 50 wt.
per cent of the copolymer.

The method of claim 1 wherein said plasticizer comprises diisodecyl phthalate.

The method of claim 1 wherein said adhesive employed is comprised of a mixture of commercially available resin solutions containing from about 1 to about 20 wt. per cent resin solids and is dissolved in an organic solvent before said adhesive is applied to the surface being coated with said vinyl resin coating wherein the solvent-to-adhesive mixture is between about 10:1 and 1:10 by volume.

The method of claim 7 wherein said solvent-to-adhesive mixture employed is about 1:1 by volume.

The method of claim 7 wherein said solvent employed is selected from a group comprising alkyl and aryl ketones, aromatic hydrocarbons, and alcohols.

The method of claim 1 wherein said adhesive employed includes curing agents.

The method of claim 10 wherein said curing agent is selected from a group comprising polyfunctional amines and acid anhydrides.

The method of claim 1 wherein said polymeric sub-strate employed comprises rigid polyvinyl chloride.

The adhesive of claim 1 wherein said polymeric substrate employed comprises acrylonitrile-butadiene-styrene (ABS).

The method of claim l wherein said adhesive employed comprises a mixture of from about 50 wt. per cent to about 80 wt. per cent phenolic resin solids and from about 20 wt. per cent to about 50 wt. per cent methacrylate resin solids.

The method of claim 1 wherein said mixture employed comprises from about 60 wt. per cent to about 70 wt. per cent phenolic resin solids and from about 30 wt. per cent to about 40 wt. per cent methacrylate resin solids.

An article comprising a vinyl resin covering of a material suitable for molding onto a substrate and con-taining plasticizer consisting of substantially only phthalate esters; a polymeric substrate of a material forming a hard substrate surface to which said vinyl resin covering is ad-hered and an adhesive bonding said vinyl resin covering to said polymeric substrate, said adhesive comprising a mixture of from about 1 wt. percent to about 95 wt. percent phenolic resin solids and from about 5 wt. percent to about 99 wt. per-cent methacrylate resin solids, said methacrylate resin having a weight average molecular weight of about 400,000.

The article of claim 16 wherein said methacrylate resin is a C1 to C4 lower alkyl methacrylate.

The article of claim 17 wherein said lower alkyl methacrylate is methyl methacrylate.

The article of claim 17 wherein said methacrylate resin is a C1 to C4 lower alkyl methacrylate/lower alkyl acrylate copolymer.

The article of claim 19 wherein said copolymer is a copolymer of methyl methacrylate and normal or isobutyl acrylate wherein the methyl methacrylate comprises from about 40 to about 75 wt. percent of the copolymer and the normal or isobutyl acrylate comprises from about 20 to about 50 wt.
percent of the copolymer.

The article of claim 16 wherein said plasticizer comprises diisodecyl phthalate.

The article of claim 16 wherein said adhesive is comprised of a mixture of resin solutions containing from about 1 to about 20 wt. percent resin solids and is dis-solved in an organic solvent before said adhesive is applied to the surface being coated with said vinyl resin coating wherein the solvent-to-adhesive mixture is between about 10:1 and 1:10 by volume.

The article of claim 22 wherein said solvent-to-adhesive mixture is about 1:1 by volume.

The article of claim 22 wherein said solvent is selected from a group comprising alkyl and aryl ketones, aromatic hydrocarbons, and alcohols.

The article of claim 16 wherein said adhesive includes curing agents.

The article of claim 25 wherein said curing agent is selected from a group comprising polyfunctional amines and acid anhydrides.

The article of claim 16 wherein said polymeric surface comprises rigid polylvinyl chloride.

The article of claim 16 wherein said polymeric surface comprises acrylonitrile-butadiene-styrene.

The article of claim 16 wherein said adhesive comprises a mixture of from about 50 wt. percent to about 80 wt. percent phenolic resin solids and from about 20 wt.
percent to about 50 wt. percent methacrylate resin solids.

The article of claim 16 wherein said adhesive mixture comprises from about 60 wt. percent to about 70 wt.
percent phenolic resin solids and from about 30 wt. percent to about 40 wt. percent methacrylate resin solids.

The article of claim 16 wherein said phthalate is an epoxy tallate.