MXPA96002779A

MXPA96002779A - Adhesive mixtures of packaging with controlled barrier properties

Info

Publication number: MXPA96002779A
Application number: MXPA/A/1996/002779A
Authority: MX
Inventors: Milton Lambert Robert; Dale Sherman Henry
Original assignee: Morton International Inc
Priority date: 1995-07-27
Filing date: 1996-07-15
Publication date: 1998-04-01

Abstract

A top-grade barrier latex adhesive component of an acrylic / chlorinated vinyl or acrylic / chlorinated vinyl / vinyl material and an acrylic latex barrier adhesive component of acrylic / vinyl lower grade are mixed in relative proportions and used to adhere the films of the low grade barrier material such as the polyolefin films, thus providing an adhesive layer of controlled barrier properties to the g

Description

"ADHESIVE MIXTURES OF PACKAGING WITH CONTROLLED BARRIER PROPERTIES TO GAS" The present invention is directed to mixtures of adhesive components, in particular mixtures of acrylic adhesive components or acrylic / vinyl latex, one of whose latex adhesive components is formed from a considerable portion of chlorinated vinyl monomers. The mixture of adhesive components provides packaging material with controlled gas barrier properties.

BACKGROUND OF THE INVENTION For many types of food packaging applications, such as packing meats and cheeses, it is desirable that the packaging material transmit as little gas as possible. For these purposes, high gas barrier materials such as a film or coatings of nylon, ethylene / vinyl alcohol, or polyvinylidene chloride can be employed. On the other hand, certain foods, particularly fruits and vegetables, can maintain their freshness for longer if the packaging material provides some gas transmission. Fruits and legumes, even when harvested, continue respiratory functions for a prolonged period of time, and packaging is preferably provided to allow the product to breathe. Everyone is well acquainted with nylon mesh bags, where citrus fruits are commonly sold, allowing porous bags, a full exposure of the fruit to the atmosphere. If the citrus fruits were packed in air-tight bags, a rapid breakdown would occur. Harvested fruits emit gases, particularly ethylene oxide, which accelerates fruit rot. The packaging of air-tight fruits would, of course, result in the accumulation of the concentrations of these gases. In fact, it is known that fruits are genetically programmed to produce these gases. A fruit, after all, is a vehicle for the seed of regeneration of the species, and if the fruit is not eaten and the seed is transported by an animal, the rot of the fruit is necessary for the seed to develop in a plant . Likewise, vegetables continue a certain respiratory function after harvesting, even when generally less than fruit. Research has shown that different fruits and vegetables have different respiration requirements, each fruit or vegetable can have a longer shelf life in the packaging of specific gas barrier properties, so there is a need for producers of the packaging material are capable of adjusting the gas barrier property of the packaging material, in accordance with specific packaging applications.A proposed approach to adjusting the gas barrier properties is to vary the thickness or thickness of the film or the specific layers of a film laminate The manufacturers of packaging materials, particularly multilayer film laminates, have difficulty with this approach since it is difficult from the point of view of both material handling and considerations of adjustment of the apparatus and changing the thicknesses of the film layer from a packaging application The present invention is directed to mixtures of adhesive components, the proportions of which can be easily adjusted, to provide controlled gas barrier properties.

SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, there is provided a blend of a first higher grade barrier latex adhesive component comprising a polymer formed of monomers consisting of acrylic monomers and chlorinated vinyl monomers and optionally other vinyl monomers , and a second adhesive component of lower grade barrier latex comprising a polymer formed of acrylic monomers and optionally, vinyl monomers, including chlorinated vinyl monomers. The gas barrier property of the film formed entirely of the superior grade barrier latex adhesive component, has an oxygen transmission rate (OTR) of at least 775 cubic centimeters of 02 / square meter / day, preferably at least 1550 cubic centimeters of 02 / square meter / day and especially preferably 3100 centimeters cubic of 02 / square meter / day less than a film formed entirely of the minor grade barrier adhesive component. At present, the OTRs are based on a coating weight of 5.71 kilograms per 1000 square meters, this being a common coating weight. The polymer of the first latex adhesive component comprises between about 5 percent and about 95 percent of the combined weight of the polymers of the first and second latex adhesives, and the polymer of the second latex adhesive component comprises between about 95 percent and about 5 weight percent of the combined weight of the polymers of the first and second latex adhesives, whereby, the gas barrier properties of the film formed from the latex adhesive mixture is intermediate to a film formed of any of the first or of the second latex adhesive component alone. Another aspect of the invention is a method for producing a multilayer laminate with an adhesive layer having controlled gas barrier properties, by adhering two or more layers of film having low gas barrier properties, with a latex adhesive which It has greater gas barrier properties. The composition of the latex adhesive is prepared using an appropriate amount of a first latex adhesive component having superior grade barrier properties and an appropriate amount of a second latex adhesive component having lower grade barrier properties in order to provide an adhesive layer with an OTR varying from that of the barrier latex adhesive component of higher grade to that of the lower grade barrier latex adhesive component.

DETAILED DESCRIPTION OF CERTAIN PREFERRED MODALITIES Herein, the gas barrier properties of an adhesive layer are described in terms of its oxygen transmission rate (OTR) based on a coating weight of 5.71 kilograms per 1000 square meters. Although other gases, such as CO2, ethylene and ethylene oxide are also factors for the freshness of the food product, the rate of transmission of these gases will generally vary in the direction of that in which the rate of oxygen transmission varies. The gas barrier property of a multilayer packaging laminate (2 or more layers) depends, of course, not only on the gas barrier property of the adhesive layer or layers but also on the gas barrier properties of the layers. layers of film as well as the adhesive. However, the present invention is applicable mainly to laminates wherein all the film layers have insufficient gas barrier properties relative to that to be provided by the adhesive layer. More particularly the invention is directed to multilayer laminates formed from sheets of polyolefins such as polyethylene and polypropylene. The polyolefins have insufficient gas barrier properties, typically having OTR within the range of 775 to 7750 cubic centimeters of 02 / square meter / day / .025 millimeter. These sheets may be of the same or different polymers. In the present, therefore, the gas barrier property is discussed with regard only to that of the adhesive layer provided by the latex adhesive applied to a coating weight of 5.71 kilograms per 1000 square meters. The producer of the packaging material will also have to dose the gas barrier properties of the film layers, by adapting the packaging to specific applications. The terms "higher grade barrier" and "lower grade barrier" as used herein to describe the latex adhesive components, are relative terms having one adhesive component gas barrier properties significantly greater than the other. The optimum OTR for most fruits and legumes ranges from about 775 to about 4650, particularly from about 1085 to about 3488 cubic centimeters of 02 / square meter / day, and the invention is primarily aimed at providing OTR within these scales even when the OTR may be varied through any scale to which the latex adhesive components of the type described herein are capable. Suitable acrylic monomers to form both the higher grade barrier and lower grade barrier adhesive components include, but are not limited to, acrylic acid, methacrylic acid and alkyl esters of 1 to 12 carbon atoms of acrylic and methacrylic acid. The top-grade barrier latex adhesive component is also formed in part from chlorinated vinyl monomers, such as vinyl chloride and preferably vinylidene chloride. It is believed that large chlorine molecules contribute to lend density to the packaging of the polymer and thus to improved gas barrier properties. Vinylidene chloride is preferred to vinyl chloride to form the superior latex barrier latex adhesive component because it contains two chlorine molecules and is a liquid, as opposed to gaseous vinyl chloride, at room temperatures. Any or both of the adhesive components may also contain copolymerizable vinyl monomers such as vinyl acetate. The top-grade barrier latex adhesive component polymer is typically formed from about 40 percent to about 95 weight percent vinylidene chloride and / or vinyl chloride, preferably from about 50 percent to about 95 percent by weight. percent vinylidene chloride and / or vinyl chloride. The higher grade barrier latex adhesive component is formed from about 5 percent to about 60 percent acrylic monomer (s), preferably from about 5 percent to 50 percent by weight. The adhesive component of higher grade barrier latex can also be formed from up to about 55 weight percent of a copolymerizable vinyl monomer. The higher grade barrier latex adhesive component does not need to contain acid functionality, but up to about 5 percent of a monomer having carboxylic acid functionality can be formed. Although not required, the higher grade barrier latex component may have hydroxyl functionality such as that provided by the hydroxyethyl acrylate. Preferably, between about 2 percent and about 15 percent by weight of the monomer used to form the higher grade barrier latex component has hydroxyl functionality. It is believed that the hydroxyl functionality improves the adhesive properties. The polymer of the higher grade barrier latex adhesive has a weight average molecular weight ranging from about 25 thousand to about 200 thousand. The polymer of the lower grade barrier latex adhesive component is formed mainly of acrylic monomers, ie from about 50 percent to 100 percent acrylic monomers. the rest is formed of copolymerizable vinyl monomers such as vinyl acetate. As with the higher grade barrier latex adhesive component, the polymer of the lower grade barrier adhesive component can be formed, in part, from vinylidene chloride and / or vinyl chloride, but the proportion is considerably less than in the superior grade barrier adhesive component. The lower grade barrier latex adhesive component does not need to contain acid functionality, but up to about 10 weight percent of a monomer having carboxylic acid functionality can be formed. Although not required, the lower grade barrier latex component may have hydroxyl functionality such as that provided by hydroxyethylene acrylate. Preferably, the hydroxyl value of the adhesive component of the lower grade barrier latex is formed from about 2 percent to about 10 percent by weight of a monomer having hydroxyl functionality. The polymer of the lower grade barrier latex adhesive has a weight average molecular weight ranging from about 20 million to about 100 million. In addition to the polymer, both the higher grade barrier latex adhesive component and the lower grade barrier latex component include surfactants in amounts sufficient to emulsify the polymers and maintain an aqueous emulsion of the polymers. The surfactants are typically anionic surfactants and / or nonionic surfactants. Some useful anionic surfactants include Rhodocal (R >; DS-10 and Arosol (R) MA-80. Some useful nonionic surfactants include CO 660 Igepal (R) and TritonW 405. In both of the lower grade barrier adhesive components as the higher grade barrier adhesive component, the surfactant is typically used at about 0.1 percent. to about 5 weight percent, based on the weight of the polymer. The latex adhesive components are formed by any conventional means to form latex polymers. More conveniently, the latex adhesive components are formed by conventional emulsion polymerization in aqueous media whereby a latex is formed in situ. The latex adhesive components can also be commercially available latex adhesives, as long as two latex adhesives are available which individually form adhesive layers having sufficiently different gas barrier properties. In the application, a producer of the packaging material will be supplied with two adhesive components that individually form adhesive layers with different OTRs that cover the OTR scale required for multiple packaging applications. Although for some packaging needs only the higher grade barrier adhesive component or the lower grade barrier component can be used to provide the desired gas barrier property, intermediate gas barrier properties are obtained by mixing appropriate amounts of two components latex adhesives. In general, one or the other of the components must be used at least about 5 percent (based on the total polymer content of the two components) to have a significant change in the gas barrier properties of the other component. . The gas barrier that is provided by the mixtures of the two components is usually linear. In any case, for any given mixture of two known components, a gas barrier curve can be predetermined. These curves prove to be quite reproducible. Therefore, a manufacturer of the packaging material when changing from one packaging application to another, each having different optimal gas barrier requirements, needs only to dose the different relative amounts of the two components. Because the gas barrier properties of the adhesive layer are variable, film type, film thickness and coating weight do not need to be changed when moving from one packaging application to another. Latex components of the type used in accordance with the present invention are found to have good compatibility with one another. This is not always the case when mixing different latexes. Coagulation is often a problem with mixed latexes, to a latex of the same general type. The latex components of the type used in accordance with the present invention form homogeneous adhesive layers with no tendency to separate into separate phases. This compatibility is believed to be responsible for achieving a highly predictable, essentially linear relationship between the relative amounts of the two latex adhesive components and the gas barrier properties of a film formed from the blend. Another advantage of the system of the present invention is that the gas barrier properties of a film that is formed, even when dependent on the relative amounts of the higher grade barrier and lower grade barrier components, tends to be relatively independent of the coating weight. The coating weights of the adhesives are typically between about 3.26 and about 8.15 kilograms per 100 square meters, with a very typical coating weight of 5.71 kilograms per 1000 square meters. However, achieving an exact coating weight consistency is difficult to obtain and the weight of the coating can vary up to 20 percent in either direction during a rolling process. Within the normal scale of coating variations, the gas barrier properties of the adhesive layer that is formed tend to be fairly uniform. The packaging laminates are formed from polymer sheets and the latex adhesive in conventional manners, typically a dry-bonded lamination process. The aqueous emulsion is applied to a film, dried to form an adhesive layer and then brought into contact with the other film. The solids of the adhesive components and the final adhesive mixture can vary from about 35 percent to about 60 percent solids, with a typical amount of 46 percent solids. For reasons of simplification, it is preferred that each of the adhesive components before mixing be about the same level of solids so that the mixture has a similar solids level, regardless of the relative proportions of the two components. The invention will now be described in greater detail through specific Examples.

EXAMPLE 1 A higher grade barrier latex adhesive component was prepared from the following mixture of monomer and redox mixture: MONOMER MIX% by weight Monomer 60 vinylidene chloride 30 hydroxy 2-ethylhexyl methacrylate 15 REDOX COMPONENTS Parts / 100 of Monomer 0.10 ammonium persulfate 0.20 hydrogen peroxide (35%) 0.27 erythorbic acid The following is the protocol for preparing the superior latex barrier latex adhesive component. The following solutions are prepared. 1. Gafac (R> Re96 ?! 10.0 grams deionized water 89.1 grams I-anionic surfactant This solution is neutralized to a pH of 6.5 to 6.8 with deionized water 3.6 grams aqueous ammonia 1.9 grams 2. deionized water 107.0 grams Aerosol < R) A-1962 (97%) 12.2 grams Igepal < R) CO 8873 (70%) 6.3 grams ^ anionic surfactant - ^ nonionic surfactant To prepare the pre-emulsion the following deionized water is charged 743.7 grams sodium salt of SEM (5%) 888.1 grams solution 1 104.6 grams solution 2 125.5 grams deionized water 82.4 grams Mix well, and under stirring add the following, hydroxyethylacrylate 450.5 grams 2-ethylhexyl acrylate 889.2 grams vinylidene chloride 3115.8 grams Stir until a stable pre-emulsion is formed. CHARGE OF THE REACTOR The following solutions are prepared: 3. ammonium citrate, dibasic 6.6 grams deionized water 8.9 grams 4. Igepal < R) CO 887 (70%) 15.8 grams deionized water 26.8 grams 5. Aerosol (R) A-196 (97%) 3.9 grams deionized water 26.8 grams 6. Erythorbic acid 10.2 grams deionized water 935.9 grams 7. hydrogen peroxide (35) %) 18.7 grams deionized water 267.4 grams To load the container the following is added: deionized water 2050.0 grams solution 3 15.5 grams ammonium persulfate 4.5 grams solution 4 42.6 grams solution 5 30.7 grams deionized water 71.3 grams The reator is heated to a temperature of 46 ° at 48 ° C and added: hydrogen peroxide (35%) 4.5 grams Charged in the reactor; pre-emulsion (seed loading) 128.4 grams Mix and stabilize the temperature at 46o-48 ° C; then activator loading (solution 6) is started, to be added through 11.6 hours. After 15 minutes, the pre-emulsion feed starts at 35.5 grams / 10 minutes. After 10 minutes, the feed is increased to 70.6 grams per minute.

After 20 minutes, the rate is increased to 107.0 grams per minute (approximate addition time 450 minutes) After 105 minutes the initiating charge (solution 7) is started at 6 grams per 10 minutes (approximate addition time, 450 minutes) . When the pre-emulsion is finished, the lines are washed with 64.2 grams of deionized water. After the rinse is completed, the following are added to the container; 8. Deionized water 17.8 grams hydrogen peroxide (35%) 1.2 grams After rinsing: deionized water 8.9 grams The temperature is maintained from 46 ° to 48 ° C for 30 to 35 minutes, and then heated to temperature of 64 ° C at 67 ° C. At the temperature of 64 ° to 67 ° C the following is added: deionized water 8.9 grams hydrogen peroxide (35%) 1.2 grams rinse with deionized water 10. deionized water 17.6 grams erythorbic acid 3.6 grams rinse with deionized water 8. grams Keep temperature at 64 ° C at 67 ° C for one hour. Then cool to 27 ° C to 30 ° C. The pH is adjusted from 2.0 to 2.5 with aqueous ammonia, increments of 5.0 grams are added. It is filtered and the materials are checked which must meet the following criteria: Solids from 44.0 to 46.0% pH from 2.0 to 2.5 Weight / 3.785 liters 4.54 kilograms viscosity 350.0 centipoises maximum This adhesive component if used only to form a film at a weight of coating of 5.71 kilograms per 1000 square meters has an OTR of 1159 cubic centimeters of 02 / square meter / day.

Example 2 A lower grade barrier latex adhesive component is prepared from the following monomer mixture:% by weight MONOMERICA MIXTURE 71 butyl acrylate 17 vinyl acetate 6 hydroxy ethylacrylate 6 acrylic acid AGENTS REDOX parts / 100 mixture monomeric COMPONENT 0.44 ammonium persulfate 0.03 hydrogen peroxide (35%) 0. 38 Erythorbic Acid The following is the protocol for preparing the lower grade barrier adhesive component. Pre-emulsion To a mixing tank the following materials are added water deionized 1114.6 grams sodium borate 13.9 grams Triton X 4054 (70%) 108.0 grams Aerosol A-196 (97%) 23.0 grams sodium salt of SEM (5%) 470.9 grams butyl acrylate 3435.7 grams vinyl acetate 651.3 grams hydroxy ethylacrylate 280.7 grams acrylic acid 280/7 grams deionized water (for rinsing) 87.5 grams ^ nonionic surfactant Mix until a stable pre-emulsion is formed. Reactor charge deionized water 1949.8 grams sodium borate .6 grams Triton X 405 (70%) 5.6 grams Aerosol A-196 (97%) 0.6 gram 1% iron solution 4.6 grams Heat the reactor at 50 ° C to 53 ° C. While the reactor is heating prepare the following solutions. 1. deionized water 31.9 grams ammonium persulfate 9.3 grams 2. deionized water 243.7 grams ammonium persulfate 11.1 grams 3. deionized water 493.2 grams erythorbic acid 17.4 grams With the reactor at a temperature of 50 ° C to 53 ° C, a pre -stable emulsion, and three solutions: A. Load solution 1 into reactor B. Begin adding solution 3 through 8 hours. C. Begin adding the pre-emulsion through 7 hours. Thirty minutes after starting the pre-emulsion, begin adding solution 2 through 6.5 hours. Keep during the addition, the temperature at 50 ° C to 53 ° C.

Just before the end of the pre-emulsion and solution 2, prepare the following solution. 4. deionized water 29.0 grams hydrogen peroxide (35%) 5.2 grams When the addition of the pre-emulsion is completed and solution 2 begins adding the solution 4 to the container through 30 minutes. When the addition of solution 4 is complete, solution 3 should last another thirty minutes. When all solutions are exhausted, keep the temperature from 50 ° C to 53 ° C for one hour. Cool to room temperature and check the materials. Adjust the solids as required with deionized water; add as required. Physical Properties of White solids: from 49.0 to 51.0% pH: from 2.0 to 3.0 viscosity: 350.0 centipoises maximum weight / 3.785 liters 3.95 kilograms This adhesive component is used only to form a film at 5.71 kilograms per 1000 square meters of coating weight, and has an OTR of 3720 cubic centimeters of 02 / square meter / day.

Example 3 The latex adhesive components of Examples 1 and 2 were mixed in various proportions (proportions based on the polymer content of each component). The blends were used to laminate two polyethylene films. The OTRs of the films provided by the mixtures are described in the following table: % by weight of Component OTR (cubic centimeters of barrier of higher degree of 0 ^ / 100 me / day) 90 1752.- 80 2589.- 70 3069.-

Claims

CLAIMS;

1. An aqueous latex adhesive forming composition comprising a mixture of A) a first latex adhesive component comprising a polymer formed of a monomer mixture comprising between about 40 percent and about 95 percent by weight of vinylidene chloride, vinyl chloride or mixtures thereof, between about 5 percent and about 60 percent by weight of acrylic monomers and from 0 percent to about 55 percent by weight of copolymerizable vinyl monomers plus a surfactant in sufficient quantity to maintain an emulsion of the polymer, and B) a second latex adhesive component comprising a polymer formed between about 50 weight percent and 100 weight percent acrylic monomer, the remainder being a copolymerizable vinyl monomer, plus a sufficient amount of a surfactant to maintain an emulsion of the polymer the first component A) latex adhesive has a rate of oxygen transmission, at least about 775 cubic centimeters of 02 / square meter / day less than that of the second component B) latex adhesive, the first and second latex components are mixed so that the polymer of the first latex adhesive component comprises between about 5 percent and about 95 percent of the total polymer of the first and second latex adhesive components and the polymer of the second latex adhesive component comprises between about 95 percent and about 5 percent by weight of the total polymer of the first and second adhesive components of the latex.

A composition according to claim 1, wherein the first adhesive component A of the latex has an oxygen transmission rate of at least about 1550 cubic centimeters of 02 / square meter / day less than the second adhesive component B of latex.

3. A composition according to claim 1, wherein the first latex adhesive component A) has an oxygen transmission rate of at least about 3100 cubic centimeters of 02 / etro square / day less than that of the second component B ) latex adhesive.

A composition according to claim 1, wherein when coated at a coating weight of 5.71 kilograms / 1000 square meters and dried, it provides an adhesive layer having an oxygen transmission rate of between about 775 and about 3100 cubic centimeters of 02 / square meter / day.

A composition according to claim 1, wherein when coated at a coating weight of 5.71 kilograms / 1000 square meters and dried an adhesive layer is provided having an oxygen transmission rate of between about 775 and about 3488 cubic centimeters of 02 / square meter / day.

6. A method for producing a laminate comprising first and second sheets of polymeric material adhered with an adhesive layer of controlled oxygen transmission rate, the method comprising providing a first acrylic-based aqueous latex adhesive component capable of forming a film with a first oxygen transmission regime when applied to a coating weight of 5.71 kilograms per 1000 square meters. providing a second acrylic-based aqueous latex adhesive component capable of forming a film with a second oxygen transmission rate when applied to a coating weight of 5.71 kilograms per 1000 square meters, the first oxygen transmission regime is at least about 775 cubic centimeters of 02 / etro square / day less than the second oxygen transmission rate, mix a portion of the first component with a portion of the second component in relative proportions according to the oxygen transmission rate that is requires to form a mixture of the adhesive composition, and adhere the first sheet to the second sheet with the adhesive composition mixture.

7. A method according to claim 6, wherein the first and second sheets are polyolefins.

A method according to claim 6, wherein the first oxygen transmission rate is at least about 1550 cubic centimeters of 02 / square meter per day, lower than the second oxygen transmission rate.

9. A method according to claim 6, wherein the first oxygen transmission rate is at least about 3100 cubic centimeters of 02 / square meter / day less than the second oxygen transmission rate.

10. A method according to claim 6, wherein the adhesive mixture when applied to a coating weight of 5.71 kilograms / 1000 square meters and dried, provides an adhesive layer having an oxygen transmission rate of between about 775 and approximately 4650 cubic centimeters of 02 / square meter / day. A method according to claim 6, wherein the adhesive mixture when applied to a coating weight of 5.71 kilograms / 1000 square meters and dried, provides an adhesive layer having an oxygen transmission rate of between approximately 1085 and approximately 3488 cubic centimeters of 02 / square meter / day.