WO1991017201A1

WO1991017201A1 - Water-resistant latexes, adhesives and laminates

Info

Publication number: WO1991017201A1
Application number: PCT/US1991/002606
Authority: WO
Inventors: Ashok C. Makati; Robert T. Iwamasa
Original assignee: The Dow Chemical Company
Priority date: 1990-05-08
Filing date: 1991-04-16
Publication date: 1991-11-14
Also published as: AR245744A1; EP0528867A4; CA2083847A1; FI925973A; EP0528867A1; FI925973A0; AU7855091A

Abstract

The present invention relates to water-resistant latexes and a process for their preparation, and to water-resistant adhesives based upon these latexes and a process for the preparation of the adhesives. The adhesives can be used to prepare laminates with improved water resistance. A blend of low pKa and high pKa acids is utilized in the instant invention to facilitate stabilization by the fugitive base ammonium hydroxide prior to stripping. Reduction of metal ion electrolytes in these materials greatly improves their water resistance without resorting to the use of nonaqueous systems for the preparation of the latex.

Description

WATER-RESISTANT LATEXES, ADHESIVES AND LAMINATES

The present invention relates to water resistant latexes and a process for the preparation thereof. Typical applications for such latexes include adhesives, binders and coatings whether used in combination with a filler or without a filler.

Latexes are typically prepared with additives which are thought to contribute to undesirable water sensitivity in various latex applications. This problem in various latex systems has prompted the development of

10 solvent-based systems having less sensitivity to water. These solvent based systems generally are more costly than aqueous systems, all other factors being equal. Nonaqueous solvent based systems have the additional ,,- disadvantage that solvent emissions into the environment from these systems increasingly is a problem.

U.S. Patent Number 4,972,018 discloses the use of ammonia-based latexes in a latex based adhesive _Q composition containing ammonium zirconium carbonate for the enhancement of hot, green bond adhesive properties of paperboard and corrugated board. U.S. Patents Number 4,721,748 and 4,668,730 disclose the use aqueous _c- ammonium hydroxide as a fugitive alkali in the preparation of colloid stabilized latex adhesives. U.S. Patent Number 4,626,567 relates to a water-resistant clear and colored acrylic latex sealant. U.S. Patent Number 4,425,291 relates to a method for the production of more water-resistant foamed elements from a waterglass containing natural latex dispersion. U.S. Patent Number 4,340,524 discloses water-resistant latex sealants. U.S. Patent Number 3,966,661 discloses a continuous process for the preparation of carboxylated latexes in a two reactor system which possibly uses ammonium based ingredients.

It would be desirable to produce a water-based latex for use in systems where water resistance is important, where the constituents of the latex do not compromise the water resistance of the system.

An important embodiment of the present invention is a process for preparing latexes which comprises:

(a) emulsion polymerizing one or more monomers selected from monoethylenically unsaturated carboxylic acid monomer, monovinyl aromatic monomer, aliphatic conjugated diene monomer, acrylate monomer, vinylidene halide monomer and vinyl halide monomer to form a polymeric latex in the presence of a stabilizing amount of a surfactant in either an acid form or an ammonium salt form and optionally a sodium salt surfactant in an amount not to exceed 0.3 parts per hundred parts monomer, and (b) stabilizing the polymer prior to stripping with ammonium hydroxide.

Another embodiment of the instant invention is a process for preparing an adhesive which comprises:

(a) emulsion polymerizing one or more monoethylenically unsaturated carboxylic acid monomers with a group of one or more comonomers

to form a polymeric latex in the presence of:

(i) a stabilizing amount of a surfactant in an acid form or an ammonium salt form 5 ^J and optionally a sodium salt surfactant in an amount not to exceed 0.3 parts per hundred parts monomer, and

(ii) an initiating amount of ammonium 0 persulfate and optionally potassium or sodium persulfate in an amount of up to 1.75 parts per 100 parts monomer; and

(b) stabilizing the polymer prior to stripping 5 with ammonium hydroxide; and

(c) adding a wetting agent to the latex to form an adhesive in an amount of from 0.5 to 6.0 weight percent based on the total weight of the adhesive.

Other aspects of the invention include the latex and the adhesive produced by the processes of this invention, and a laminate prepared with the adhesive of this invention. The invention additionally includes the use of specific monoethylenically unsaturated carboxylic acid monomers, such as acrylic, fumaric and itaconic acids to impart stability to the latex when ammonium hydroxide is used as the neutralizing agent.

Although the instant invention provides a general process for the preparation of latexes suitable for use in water-resistant applications, such as water resistant adhesives, another important aspect of the invention is a process for preparing latexes which comprises:

(a) emulsion polymerizing one or more monoethylenically unsaturated carboxylic acid monomers with a group of one or more comonomers to form a polymeric latex in the presence of a stabilizing amount of a surfactant in either an acid form or an ammonium salt form and optionally a sodium salt surfactant in an amount not to exceed 0.3 parts per hundred parts monomer, and

(b) stabilizing the polymer prior to stripping with ammonium hydroxide.

The comonomer group is one of groups (i) through (vi):

(i) one or more monovinyl aromatic monomers and one or more aliphatic conjugated diene monomers;

(ii) one or more monovinyl aromatic monomers, one or more aliphatic conjugated diene monomers and one or more acrylate monomers;

(iii) one or more monovinyl aromatic monomers _- and one or more acrylate monomers;

(iv) one or more acrylate monomers;

(v) one or more vinylidene halide and one or more butadiene monomers; and

10

(vi) one or more vinyl halide monomers,

Another important embodiment of the instant invention is a process for preparing an adhesive which 15 comprises:

(a) emulsion polymerizing one or more monoethylenically unsaturated carboxylic acid monomers with a group of one or more 20 comonomers

to form a polymeric latex in the presence of:

(i) a stabilizing amount of a surfactant in an acid form or an ammonium salt form

25 and optionally a sodium salt surfactant in an amount not to exceed 0.3 parts per hundred parts monomer, and

(ii) an initiating amount of ammonium

30 persulfate and optionally potassium or sodium persulfate in an amount of up to 1.75 parts per 100 parts monomer; and

-._£.. (b) stabilizing the polymer prior to stripping with ammonium hydroxide; and (c) adding a wetting agent to the latex to form an adhesive in an amount of from 0.5 to 6.0 weight percent based on the total weight of the adhesive.

The comonomer group is one of groups (i) through (vi):

(iii) one or more monovinyl aromatic monomers and one or more acrylate monomers;

(iv) one or more acrylate monomers;

(v) one or more vinylidene halide and one or more butadiene monomers; and

(vi) one or more vinyl halide monomers.

Typical monomers that could be employed to produce homopolymer or copolymer latexes to be used in a system of the present invention, include monovinyl aromatic monomer, aliphatic conjugated diene, acrylate monomer, a vinylidene halide or vinyl halide monomer, vinyl esters of carboxyl acids containing from 1 to 18 carbon atoms, such as vinyl acetate or vinyl stearate, methacrylonitrile and acrylonitrile. Optimally a monoethylenically unsaturated carboxylic acid monomer is used. Crosslinking agents such as divinylbenzene and ethylene glycol dimethacrylate could also be used.

Representative latex compositions include styrene/butadiene copolymers; vinyl acetate homopolymer and copolymers; vinylidene chloride/butadiene copolymers; vinylidene chloride copolymers; vinyl chloride copolymers; styrene/acrylate and methacrylate copolymers; and acrylate and methacrylate homopolymers and copolymers. Typical preferred examples of latexes which can be employed in adhesives of the present invention are styrene-butadiene latexes and carboxylated styrene-butadiene latexes similar to those disclosed in U.S. Patent 4,396,453, which is hereby incorporated by reference.

The term "monovinyl aromatic monomer", as used herein, is meant to include those monomers with a radical of the formula:

R

I

CH₂=C-

(wherein R is hydrogen or a lower alkyl such as an alkyl having from 1 to 4 carbon atoms) attached directly to an aromatic nucleus containing from 6 to 10 carbon atoms, including those wherein the aromatic nucleus is substituted with alkyl or halogen substituents. The preferred monomers are styrene and vinyltoluene.

The term "aliphatic conjugated diene", as used herein, is meant to include compounds such as 1 ,3-butadiene, 2-methyl-1 ,3-butadiene, piperylene ( 1 ,3-pentadiene) , and other hydrocarbon analogs of 1 ,3-butadiene. "Vinylidene halides" and "vinyl halides" suitable for this invention include vinylidene chloride and vinyl chloride, which are highly preferred. Vinylidene bromides and vinyl bromide can also be employed.

The term "acrylate", as used herein, is meant to include the acrylate or methacrylate monomers. Additionally, the acrylates can include acids, esters, amides, and substituted derivatives thereof. Generally, the preferred acrylates are C-_]-CQ alkyl acrylates or methacrylates. Examples of such acrylates include butyl acrylate, 2-hexyl acrylate, tert-butyl acrylate, methylmethacrylate, butylmethacrylate, hexylmethacrylate, isobutylmethacrylate, and isopropylmethacrylate. The preferred acrylates are butyl acrylate and methylmethacrylate.

The term "monoethylenically unsaturated carboxylic acid monomer", as used herein, is meant to include those monocarboxylic monomers such as acrylic acid, and methacrylic acid; dicarboxylic monomers such as itaconic acid, fumaric acid, maleic acid, and their monoesters. The comparatively higher pKa acids are acrylic and methacrylic acid and the relatively lower PKa value acids are itaconic, fumaric and maleic. The most practical acids and therefore the most preferred monomers for incorporation into the latex polymers are acrylic, itaconic, and fumaric.

The amount of monoethylenically unsaturated carboxylic acid monomer typically present in a latex particle can vary from 1.0 to 8.0 parts based on total monomer present in the particle. The preferred amount of monoethylenically unsaturated carboxylic acid monomer present in a latex particle is from 1.0 to 3.0 parts based on total monomer present in the particle. The optimal amount of acid will vary depending on the type of acid utilized and the properties the latex is meant to impart in a given end use. However, a more preferred amount of acid present is 2.5 parts based on total monomer present in the particle.

The most preferred copolymer latexes of the present invention are prepared as carboxylated styrene/butadiene, carboxylated acrylate and carboxylated styrene/acrylate latexes in various ratios.

The typical optimum ratios for these latex monomers are: (1) for carboxylated styrene/butadiene, 20/80 to 65/35 by weight and (2) for styrene/acrylate latexes, depending on the acrylate chosen, 10/90 to 50/50 by weight.

Many emulsion polymerization processes utilize salt forms of surfactants which cause water-sensitivity in the resultant latex, such as potassium and sodium salt surfactants; the most common are sodium salt surfactants which significantly contribute to the stability of the latex system but are thought to cause water-sensitivity in the resultant latex.

The present process calls for use of volatile salt forms of surfactants such as ammonium salt surfactants or surfactants in the acid form which are thought to decrease the sensitivity of the resultant latex without sacrificing the stability of the latex system. The present process will yield water-resistant latexes in the presence of sodium salt surfactants, so long as the amount of sodium salt surfactant does not exceed 0.50 parts based on one hundred parts monomer. Preferably the amount of sodium salt surfactant will not exceed 0.30 parts based on one hundred parts monomer.

Any non-sodium salt or non-potassium salt surfactant which does not inhibit water-resistance properties in the resultant latex, can be used in the present invention. One example of such a surfactant is an ammonium salt of dodecyl sulfonated phenyl ether.

The acid form of the surfactant or the ammonium salt surfactant can typically be present in an amount sufficient to stabilize the latex which is dependent on the polymerization variables for preparing the latex. A stabilizing amount is therefore known in the art as being typically dependent on the types and amounts of initiators, desired latex particle size and acid monomer used in the polymerization. An amount of ammonium salt surfactant which can be considered a stabilizing amount is in the range of from 0.1 to 3.0 parts based on one hundred parts monomer. The ammonium salt surfactant can also be a post-additive to the latex prior to stripping the latex.

Sodium hydroxide is also a typical polymerization additive as well as post-additive; the presence of sodium hydroxide is also thought to inhibit the water-resistance of the resultant latex. However, when neutralizing the latex, the sodium hydroxide is advantageously thought to sufficiently ionize carboxyl groups of high pKa carboxylic acid monomers which thereby impart stability to the latex. Combining high PKa acid monomers with lower pKa acid monomers enables ammonium hydroxide to be substituted for sodium hydroxide for neutralization to increase the water- resistance of the latex without sacrificing the end use benefits of using high pKa acid monomers. For example, where acrylic acid, which is a high pKa acid, is used as a carboxylic acid monomer for the latex, itaconic acid can be incorporated as well without sacrificing the benefits of using the acrylic acid monomer and without sacrificing ionization of the carboxyl groups.

The most practical high PKa acid for use as a 0 carboxylic acid monomer is acrylic acid and the most practical lower pKa acids are itaconic and fumaric acids. If acrylic acid is incorporated as a carboxylic acid monomer of the latex and ammonium hydroxide is used as the pre-stripping additive, itaconic or fumaric acid 5 will be preferred acids to use in combination with acrylic acid. The ratio of acrylic acid to itaconic acid will be in the range of from 16 to 1 to 2.0 to 1. The ratio of acrylic acid to fumaric acid will also 0 typically be in the range of from 16 to 1 to 5 to 1. A mixture of itaconic and fumaric can also be mixed with the acrylic acid in similar ratios.

The conventional post-additive neutralizing _- agent in the art is sodium hydroxide. In the present process the post-additive neutralizing agent will be ammonium hydroxide rather than sodium hydroxide. The ammonium hydroxide will typically be post-added to bring the pH of the system up to stabilize the latex; such an 0 amount is typically dependent on the type and amount of acid monomer incorporated in the system, but is typically in the range of from 0.3 to 3.5 parts based on one hundred parts monomer. Preferably the range is from 0.3 to 1.0 parts when about 3 parts of carboxylic acid 5 monomer is used and from 1. 0 to 3.5 parts when between 3 and 8 parts of acid monomer is used based on one hundred parts monomer.

Similarly, typical polymerization processes - utilize initiators, such as sodium and potassium persulfate, which are also thought to contribute to the water-sensitivity of a latex prepared from such processes. The present invention provides for the use of ammonium persulfate as the optimal initiator for 10 emulsion polymerizing water-resistant latexes. An initiating amount of ammonium persulfate initiator is that amount conventionally know in the art which is necessary to begin polymerization of the monomers during the polymerization process. Such an amount is typically

15 in the range of from 0.2 to 3.0 parts and is optimally in the range of from 0.25 to 2.0 parts based on total parts monomer.

Initiators such as sodium or potassium

20 persulfate can be present in the polymerization process but optimally should not exceed a level of greater than 1.75 parts based on one hundred parts monomer.

The Latex as an Adhesive

25 The latex of the present invention can be utilized as a water-resistant adhesive and can be combined with a suitable wetting-agent to enhance such adhesive properties. Examples of such wetting-agents

30 are non-surfactant or non-detergent type wetting-agents conventionally known in the art such as diols and other polyols. The most preferred wetting-agents are the diol based wetting-agents.

-,_- Typically, such wetting agents are used in amounts of from 0.5 to 6.0 weight percent based on the total weight of the adhesive. The more preferred range of wetting agent present in the adhesive is from 1 to 4 and the most preferred range of wetting agent in the adhesive is from 2 to 4 weight percent based on total weight of the adhesive.

The term "laminate" as used herein, is meant to include structures which are manufactured by lamination, using the present latex system as the laminating adhesive. A laminate structure is typically comprised of substrates which are laminated to the same or different substrate. The film laminate structure is typically comprised of films which are laminated to each other by coating the primary film or web with the present adhesive. The secondary web is then laminated to the primary web after the adhesive is dried.

The term "substrate" means any solid material having a surface which can be adhered to a complimentary surface of the same or different substrate with the present latex and a diol based wetting agent acting as an adhesive formulation. The term substrate is inclusive of any type of naturally occurring and synthetic solid materials. Representative examples of such solids and their forms include the following: plastic, plastic film, paper, paperboard, fabrics, wood, glass, ceramic, metal, foil, metallized plastic film, or most any other solid in the form of a film, sheet, board or block.

The term "plastic substrates" is inclusive of all conventional plastic substrates, for example, polyolefin films, such as polypropylene and polyethylene, as well as polyester film or polyamide film, or metallized polyester or polypropylene films.

Plastic substrates generally have low energy surfaces and are difficult to adhere to other substrates. Therefore, the surfaces are normally activated by flame oxidation, corona discharge, and chemical etching or primer coatings in an attempt to improve adhesion.

The Preparation of the Polymeric Latex

The polymeric latex is prepared by conventional emulsion polymerization techniques. Water and a seed latex are introduced into a reactor equipped with lab pumps to deliver monomer and aqueous feeds. The reactor is purged with nitrogen and heated. Over a four hour period is added two monomer streams and a third stream containing water, the ammonium salt aqueous surfactant and ammonium persulfate (or equivalent initiator(s) for producing water-resistant latex). Following the addition of the monomer streams and aqueous streams, the reaction mixture is sustained at a heated temperature for one additional hour and then cooled. The resulting latex will be neutralized with ammonium hydroxide to a pH of at least 6. The latex is then stripped to remove unreacted monomer.

The peel adhesion for plastic film to plastic film is measured by a T-Peel test (ASTM D-1876-72) on an Instron.

Although as specified some of the latexes in the following examples are prepared without added surfactant present, these latexes are vulnerable to instability and are prepared without surfactant for purposes of comparison. The practice of the process would conventionally entail the use of surfactant as someone familiar with latex preparation would recognize

Further, the latexes from the following Examples 1-6 are prepared using approximately 0.7 parts of sodium persulfate initiator based on 100 parts monomer.

Example 1

A styrene/butadiene/acrylic acid (in about a 50/50 ratio with about 2 parts acid) latex is prepared according to a conventional recipe, however, no surfactant is used in the recipe and ammonium hydroxide is used as the neutralizing agent for the example latex. Five parts of a diol based wetting-agent is added to the ammonium neutralized latexes. The comparative latex is made similarly but with surfactant: 1.0 part sodium salt of dodecyl sulphonated phenyl ether. Both the example and comparative example formulations are diluted with water to 34 percent solids and evaluated as film laminating adhesives. The formulated adhesives are coated to film using conventional gravure coating methods to give coat weights approximately 1 to 1.5 lbs. per 3000 sq. ft. of film. The coated film is dried in a forced air oven. The adhesive coated film is laminated to secondary film under pressure and heat. The laminates are cut in 1 inch strips and exposed to 100°F and 100 percent relative humidity environment for a week. The humid peel adhesion is determined using Instron T-peel test (ASTM D-1876 -72) at 12 inches/minutes.

Laminate 1 is prepared by drawing the adhesive down a corona treated polypropylene film (available from Hercules as Hercules B-523) and is laminated to the polypropylene side of a polyvinylidene chloride treated 70 gauge polypropylene film (available from Mobil as Mobil 70 PXS). Laminate 2 is prepared by coating the adhesive on metallized polyester film and laminating to the ethylene vinyl acetate side of a ethylene vinyl acetate/Surlyn* coextruded film (*DuPont trademark). Laminate 3 is prepared by coating the polyvinylidene chloride side of a polyvinylidene chloride/oriented polyethylene terephthalate film and is laminated to the ethylene vinyl acetate side of an ethylene vinyl acetate/Surlyn* coextruded film (*DuPont trademark).

The results are shown in Table 1. The examples having any sodium salt surfactant present, whether by being prepared in the presence of the surfactant or by post-addition of surfactant, show significantly less tolerance to the peel adhesion test which measures the strength of the bond the adhesive forms thereby indicating that the stronger bonds are exhibited by the laminates which have no sodium salt of dodecyl sulphonated phenyl ether present.

TABLE I

As is shown in the Table I, a minor amount of a sodium salt of dodecyl sulphonated phenyl ether surfactant will yield water-resistant adhesive bonds, however, the bond is not as strong as one prepared without the sodium salt of dodecyl sulphonated phenyl ether. If more than a minor amount of the sodium salt of dodecyl sulphonated phenyl ether is added the water- resistance of adhesive is not acceptable as shown in the Comparative Example 1.

Example 2

This example compares the effect of using conventional sodium salt of dodecyl sulphonated phenyl ether as a surfactant and an ammonium salt of dodecyl sulphonated phenyl ether as a surfactant.

The latex of Example 2 is prepared similarly to the latex of Example 1, however, an ammonium salt of dodecyl sulphonated phenyl ether is used as a ' surfactant. The latex of Comparative Example 2 is also prepared similarly the latex of Example 1, however, using a sodium salt of dodecyl sulphonated phenyl ether as a surfactant at approximately 0.5 parts based on 100 parts monomer. Although the Comparative Example 2 only uses a minor amount of sodium salt of dodecyl sulphonated phenyl ether, and the latexes are ammonium hydroxide neutralized, the adhesive properties of the Comparative Example 2 are not as desirable as those exhibited by Example 2 prepared with the ammonium salt of dodecyl sulphonated phenyl ether surfactant.

Laminate 1 is prepared by drawing the adhesive 0 down a corona treated polypropylene film (available from Hercules as Hercules B-523) and is laminated to the polypropylene side of a polyvinylidene chloride treated 70 gauge polypropylene film (available from Mobil as _t- Mobil 70 PXS). Laminate 2 is prepared by coating the adhesive on metallized polyester film and laminating to medium density polyethylene film.

The laminates were allowed to cure at 100°F for 0 18 hours. The laminates are cut in 1 inch strips and dry peel adhesion is then measured. The 1 inch strips are exposed to 100°F 100 percent relative humidity for five days for the humid peel adhesion evaluation. The humid peel adhesion is determined using Instron T-peel 5 test (ASTM D-1876-72) at 12 inches/minutes. TABLE II

The data in Table II demonstrate the large delta between the bond strength of a latex adhesive prepared with an ammonium salt surfactant and a latex adhesive prepared with a sodium salt surfactant. The sodium salt surfactant latex does not have the desirable bond strength of the ammonium salt surfactant latex.

The data in Table II demonstrate that this effect is even greater for a laminate prepared with a metal film, Laminate 2, than for a laminate prepared with a plastic film, Laminate 1.

Example 3

This example demonstrates the effect of the type of neutralizing agent on humid peel adhesion strength. The latex is prepared similarly to the latex of Example 1. The latexes are prepared without surfactant and neutralized according to the schedule in Table III. The adhesive is formulated from the latex and four parts of a diol wetting agent and diluted to 34 percent solids. Laminate 1 is prepared by drawing the adhesive down a corona treated polypropylene film (available from Hercules as Hercules B-523) and is laminated to the polypropylene side of a polyvinylidene chloride treated 70 gauge polypropylene film (available from Mobil as Mobil 70 PXS). Laminate 2 is prepared by coating the adhesive on metallized polyester film and laminating to medium density polyethylene film.

The laminates are allowed to cure at 100°F for 18 hours. The laminates are cut in 1 inch strips and dry peel adhesion is then measured. The 1 inch strips are exposed to 100°F 100 percent relative humidity for five days prior to the humid peel adhesion evaluation. The humid peel adhesion is determined using Instron T-peel test (ASTM D-1876-72) at 12 inches/minutes.

Results are shown in Table III. TABLE III

Table III illustrates that by having both a sodium salt as a surfactant and a sodium hydroxide neutralizing agent present in the latex, the humid adhesive bond strength is unacceptable, therefore the latex water-resistance of the adhesive is unacceptable.

Example 4

A series of ammonium hydroxide neutralized latexes are prepared similarly in composition to the latex of Example 1, without surfactant present.

However, the acid component ratios of acrylic acid and itaconic acid are varied according to the schedule in Table IV. These latexes are diluted to approximately 36 percent solids. Three parts of a diol wetting agent is also added to the latexes.

The laminates are prepared by drawing the adhesive down a corona treated polypropylene film (available from Hercules as Hercules B-523) and laminated to the polypropylene side of a polyvinylidene chloride treated 70 gauge polypropylene film (available from Mobil as Mobil 70 PXS).

The laminate is prepared by drawing the adhesive down a corona treated polypropylene film (available from Hercules as Hercules B-523) and is laminated to the polypropylene side of a polyvinylidene chloride treated 70 gauge polypropylene film (available from Mobil as Mobil 70 PXS).

The laminates were allowed to cure at 100° F for 18 hours. The laminates are cut in 1 inch strips and dry peel adhesion is then measured. The 1 inch strips are exposed to 100° F 100% relative humidity for five days prior to the humid peel adhesion evaluation. The humid peel adhesion is determined using Instron T-peel test (ASTM D-1876-72) at 12 inches/minutes. The results are shown in Table IV.

TABLE IV

Table IV shows the Acrylic Acid modified latex retains the optimum bond strength as shown in the Dry/Humid ratio column. However, the use of acrylic acid alone in combination with volatile bases, such as ammonium hydroxide rather than sodium hydroxide, can render the latex vulnerable to instability. Itaconic Acid alone exhibits the least desirable bond strength retention. The various combinations of acrylic and itaconic yield acceptable bond strength retention and can retain stability even when neutralized with ammonium hydroxide.

Example 5

Similarly to Example 4, a series of latexes are prepared varying the ratios of acrylic acid to fumaric acid. These latexes are formulated and evaluated similarly to Example 4. The laminate is prepared by drawing the adhesive down a corona treated polypropylene film (available from Hercules as Hercules B-523) and is laminated to the polypropylene side of a polyvinylidene chloride treated 70 gauge polypropylene film (available from Mobil as Mobil 70 PXS).

The laminates were allowed to cure at 100°F for 18 hours. The laminates are cut in 1 inch strips and dry peel adhesion is then measured. The 1 inch strips are exposed to 100°F 100 percent relative humidity for five days prior to the humid peel adhesion evaluation. The humid peel adhesion is determined using Instron T-peel test (ASTM D-1876-72) at 12 inches/minutes. The results are shown in Table V.

TABLE V

The results can be similarly compared to the results in Example 4. Fumaric Acid has a lower PKa to acrylic and therefore, does not perform as well as the pure acrylic acid modified latex as shown in Example 4.

Example 6

A latex with the monomer composition of methyl methacrylate/butyl acrylate/acrylic acid (that is a 20/80 ratio with approximately 2 parts total acid) is prepared without surfactant present and neutralized in the presence of ammonium hydroxide. A comparative adhesive is similarly formulated but with 1.0 part sodium salt of dodecyl sulphonated phenyl ether. Both the latexes are than formulated with 3 parts of a diol wetting agent and evaluated as described in Example 4. The results are shown in Table VI.

Laminate 1 is prepared by drawing the adhesive down a corona treated polypropylene film (available from Hercules as Hercules B-523) and is laminated to the polypropylene side of a polyvinylidene chloride treated 70 gauge polypropylene film (available from Mobil as Mobil 70 PXS). Laminate 2 is prepared by coating the adhesive on metallized polyester film and laminating to medium density polyethylene film.

The laminates were allowed to cure at 100°F for 18 hours. The laminates are cut in 1 inch strips and dry peel adhesion is then measured. The 1 inch strips are exposed to 100°F 100 percent relative humidity for five days prior to the humid peel adhesion evaluation. The humid peel adhesion is determined using Instron T-peel test (ASTM D-1876-72) at 12 inches/minutes. The results are shown in Table VI.

TABLE VI

As is shown in Table VI, the retention of adhesive bond strength for the comparative latex having 1.0 parts of post-added sodium salt surfactant is unacceptably low. The latex prepared without surfactant performs acceptably.

Example 7

This example compares the effect of using conventional sodium persulfate as an initiator and an ammonium persulfate as an initiator. The latex of Example 7 is prepared similarly to the latex of Example 1. Laminate 1 is prepared as described in Example 1 by coating the adhesive on metallized polyester film and laminating adhesive to the ethylene vinyl acetate side of a ethylene viny acetate/Surlyn* coextruded film (* Dupont trademark).

The laminates were allowed to cure at 100°F for 18 hours. The laminates are cut in 1 inch strips and dry peel adhesion is then measured. The 1 inch strips are exposed to 100°F 100 percent relative humidity for five days prior to the humid peel adhesion evaluation. The humid peel adhesion is determined using Instron T-peel test (ASTM D-1876-72) at 12 inches/minutes. The results are shown in Table VII.

The latex prepared with ammonium persulfate initiator exhibits higher desirable peel adhesion than the latex prepared with sodium persulfate.

TABLE VII

Claims

CLA I MS :

1. A process for preparing latexes which comprises:

(a) emulsion polymerizing one or more monomers selected from monoethylenically

,. unsaturated carboxylic acid monomer, monovinyl aromatic monomer, aliphatic conjugated diene monomer, acrylate monomer, vinylidene halide monomer and vinyl halide monomer to form a polymeric

10 latex in the presence of a stabilizing amount of a surfactant in either an acid form or an ammonium salt form and optionally an alkali metal salt surfactant in an amount not to exceed 0.3 parts per

15 hundred parts monomer, and

(b) stabilizing the polymer prior to stripping with ammonium hydroxide.

0 2. A process for preparing latexes which comprises:

(a) emulsion polymerizing one or more monoethylenically unsaturated 5 carboxylic acid monomers with a group of one or more comonomers to form a polymeric latex in the presence of a stabilizing amount of a surfactant in either an acid form or an ammonium salt form and optionally an alkali metal salt surfactant in an amount not to exceed 0.3 parts per hundred parts monomer, and

(b) stabilizing the polymer prior to stripping with ammonium hydroxide.

3. The process of Claim 2, wherein the comonomer group is one of groups (i) through (vi):

(iv) one or more acrylate monomers;

(v) one or more vinylidene halide and one or more butadiene monomers; and

(vi) one or more vinyl halide monomers.

4. The process of Claim 2 wherein the monoethylenically unsaturated carboxylic acid monomer is selected from the group consisting of (i) a mixture of acrylic acid and fumaric acid; (ii) a mixture of acrylic and itaconic acid and (iii) a mixture of acrylic acid, fumaric acid and itaconic acid.

5. The process of Claim 3 wherein the emulsion polymerizing monomers are selected from the group consisting of: (i) monovinyl aromatic monomer, aliphatic conjugated diene monomer and monoethylenically 0 unsaturated carboxylic acid monomer and the monovinyl aromatic monomer is styrene and the aliphatic conjugated diene monomer is butadiene; (ii) acrylate monomer and monoethylenically unsaturated carboxylic acid monomer and the acrylate is selected from methylmethacrylate; 5 butyl acrylate; 2-ethylhexyl acrylate; (iii) monovinyl aromatic monomer, acrylate monomer and monoethylenically unsaturated carboxylic acid monomer and the monovinyl aromatic monomer is styrene, and the acrylate monomer is 0 butyl acrylate.

6. The process of Claim 2 wherein the amount of monoethylenically unsaturated carboxylic acid monomer present in the latex is from 1 to 8 parts based on total _J- monomer present in the particle.

7. The process of Claim 6 wherein the monoethylenically unsaturated carboxylic acid monomer is a mixture of acrylic acid and itaconic acid present in a 0 ratio in the range of from 16 to 1 to 2 to 1 or a mixture of acrylic and fumaric acid, wherein the ratio of acrylic acid to fumaric acid will be in the range of from 16 to 1 to 5 to 1.

5 8. The process of Claim 6 wherein the monoethylenically unsaturated carboxylic acid monomer is a mixture of acrylic acid, fumaric acid and itaconic acid wherein the ratio of acrylic acid to fumaric acid/itaconic acid will be in the range of from 16 to 1 to 2 to 1.

9. A process for preparing an adhesive which comprises:

(a) emulsion polymerizing one or more monomers selected from monoethylenically unsaturated carboxylic acid monomer, monovinyl aromatic monomer, aliphatic conjugated diene monomer, acrylate monomer, vinylidene halide monomer and vinyl halide monomer to form a polymeric latex in the presence of:

(i) a stabilizing amount of a surfactant in an acid form or an ammonium salt form and optionally an alkali metal salt surfactant in an amount not to exceed 0.3 parts per hundred parts monomer, and

(ii) an initiating amount of ammonium persulfate and optionally potassium or sodium persulfate in an amount of up to 1.75 parts per 100 parts monomer; and

(b) stabilizing the polymer prior to stripping with ammonium hydroxide; and

10. A process for preparing an adhesive which _j- comprises:

to form a polymeric latex in the presence of:

(i) a stabilizing amount of a surfactant in an acid form or an -* ammonium salt form and optionally an alkali metal salt surfactant in an amount not to exceed 0.3 parts per hundred parts monomer, and 0 (ii) an initiating amount of ammonium persulfate and optionally potassium or sodium persulfate in an amount of up to 1.75 parts per 100 parts monomer; and 5

(b) stabilizing the polymer prior to stripping with ammonium hydroxide; and

(c) adding a wetting agent to the latex to 0 form an adhesive in an amount of from 0.5 to 6.0 weight percent based on the total weight of the adhesive.

11. The process of Claim 10, wherein the comonomer group is one of groups (i) through (vi): (i) one or more monovinyl aromatic monomers and one or more aliphatic conjugated diene monomers;

- (ii) one or more monovinyl aromatic monomers, one or more aliphatic conjugated diene monomers and one or more acrylate monomers;

10 (iii) one or more monovinyl aromatic monomers and one or more acrylate monomers;

(iv) one or more acrylate monomers;

15 (v) one or more vinylidene halide and one or more butadiene monomers; and

(vi) one or more vinyl halide monomers.

20 12. A latex prepared by the process of Claim 1,

13- An adhesive prepared by the process of Claim 9.

_P5 14. A laminate prepared with the adhesive of

Claim 9.

30

35