LAMINAR PACKAGING FOR VOLATILE MATERIALS

Abstract: A laminar package material for packaging of volatile compositions containing solvents with a vapor pressure of from about 90 hPa to about 300 hPa at 20 DEG C, includes a combination of a polyolefin (A), a second polymer (B) serving as a barrier material incompatible with the polyolefin and an alkylcarboxyl-substituted polyolefin serving as a compatibilizer (C).

Description: LAMINAR PACKAGING FOR VOLATILE MATERIALS Technical Field This invention generally relates to packaging materials for volatile materials such as dental adhesives and primers containing materials such as acetone. More particularly, the invention relates to laminar packaging materials. Specifically the invention relates to such a material having a polyolefin layer, a second polymer serving as a barrier material incompatible with the polyolefin layer, and a alkylcarboxyl-substituted polyolefin serving as a compatibilizer . Background of the invention The present invention relates to laminar packaging materials useful in the preparation of containers for dental adhesive systems. The laminar, shaped containers significantly reduce permeability of these packaging materials filled with dental adhesive systems. Such adhesive systems often contain highly volatile components such as acetone and the like. In the containment art, plastics have found increasing use as replacements for glass and metal containers, especially of chemical and pharmaceutical products. The advantages of such plastic packaging include lighter weight, decreased fragility (versus glass) , lower cost and manifold processing. Major disadvantages in the packaging of chemicals and pharmaceuticals are the shortcomings in the barrier properties of common materials, such as polyethylene, polypropylene, poly (ethylene terephthalate) , polycarbonate and polystyrene. To overcome that problem laminar shaped plastic materials which consist of multiple layers of polyolefines such as polyethylene, polycarbonate and polystyrrole have been developed. Polyvinylalcohol and ethylene vinyl alcohol are used for the barrier layers. Because of incompatibility of the polymers, an adhesive polymer often is employed as a compatibilizer. For example, U.S. Pat. No. 5,438,109 discloses barrier materials for reducing the permeability of plastic packaging materials. The barrier material can be formed from polyepoxide and polyamine. Multilayer packaging materials and multilayer containers including the polyamine- polyepoxide barrier material are disclosed. European Patent Specification 0 411 601 discloses plastic articles comprising of a polyolefin, a physical mixture of two polymeric materials incompatible with the polyolefin and an alkylcarboxyl-substituted polyolefin wherein the components of the physical mixture are present in the polyolefin as a multitude of thin overlapping layers. Also disclosed is the use of these laminar articles as a fuel tank for motor vehicles because of better resistance against mixtures of oxygenated compounds and hydrocarbons. FR-A-2 652 303 discloses laminar shaped articles that consist of 3 layers (A/B/A) wherein the compatible agent is incorporated into the polyolefin forming the outer layers (A) and the polyamide forming the core layer (B) . Also disclosed is the use of that laminar article as a container of great dimension. The patent discloses that this kind of container has resistance against permeation of solvents, resistance against shock and resistance against delamination. None of the heretofore known containers have the benefit of utilizing the multilayer plastic material for small packaging units for dental adhesive systems containing a combination of acidic media and solvents with a vapor pressure in the range of 90 hPa to 300 hPa @ 20°C like acetone or ethylacetate . Therefore, a need exists for such a package. Summary of the invention The present invention concerns the use of multilayer plastic containers for packaging of dental adhesive systems containing a combination of acidic media and solvents with high vapor pressure like acetone or ethylacetate . The loss of solvents suitable for dental systems by diffusion through the walls of a conventional plastic container has been found to be unacceptably high from a shelf-life oriented standpoint. There is therefore, a high risk of corrosion due to acidic media present in dental adhesive systems. Dental adhesive systems which use ethanol or water as a solvent do not need a multilayer container, although they could certainly be packaged in such a container. The present invention provides for the use of a multilayer plastic container as a packaging for dental adhesive systems comprising a combination of: (A) a polyolefin (B) a polymer serving as a barrier material incompatible with (A) (C) a polyolefin which is alkylcarboxyl-substituted serving as a compatibilizer wherein the components of (B) are present as the core layer between two outer layers of component (A) . Component (C) may be placed as an adhesive layer between the core layer of component (B) and the outer layer of component (A) (5-layer technique) or component (C) may be present in a physical mixture of component (A) (2- and 3-layer technique) . Detailed description of the invention By the term "packaging material for dental adhesive systems" as used throughout this description is meant that plastic materials are used to form a container suitable to store dental adhesive systems such as "Prime & Bond" available from Dentsply International Inc. The laminate packaging materials of the present invention exhibit a combination of low permeability to solvents with a vapor pressure in the range of from about 90 hPa to about 300 hPa at 20°C like acetone or ethylacetate and a high resistance to corrosion of acidic media. Such solvents are normally an essential part of dental adhesive systems . By the term "low permeability" is meant that the packaging material of the invention looses less than about 0.02, preferably less than 0.01 and most preferably less than 0.005 measured as grams of liquid per centimeters squared permeating a 0.5 mm thick wall over a one year period at 23°C. This low permeability is equivalent to a loss of less than 10% during two years shelf-life at 23° which is tolerable from the customer's point of view. Exceeding loss interferes the function of the stored product. Multilayer packaging materials according to this invention fulfill these requirements if dental adhesive systems containing solvents with a vapor pressure in the range of from about 90 hPa to about 300 hPa @ 20°C are used. Conventional plastic packaging is not capable of storing such dental adhesive systems. Dental adhesive systems incorporating solvents with a vapor pressure lower than about 90 hPa like ethanol or water, normally do not need a laminate container, although such could still be employed if desired. The inventive container is a multilayer plastic material for relatively small containers for dental adhesive systems with a volume capacity of less than 15 ml, preferably less than 10 ml and most preferably less than 8 ml. Such small laminate containers have not been known in the industry. A wide variety of materials may be utilized to form suitable multilayer shaped containers, including those to now be described. The polyolefin (A) used in . preparing the multilayer shaped containers of the present invention includes polyethylene, polypropylene, polybutylene, polystyrene, polycarbonate, related copolymers and the like. Polyethylene is preferred and may be high, medium and low density. High density polyethylene is most preferred from the shelf-life oriented standpoint. The polyolefin is present in amounts of about 30 to 98%, preferably about 40 to 97% and most preferably about 45-95% by weight. Examples of useful polymers for component (B) are polyamides, polyepoxides, polyesters, polyvinylalcohol, copolymers of vinyl alcohol, physical mixtures and reaction products thereof. These polymeric materials are referred to as barrier polymers. The term "physical mixture" is defined in the following way: the at least two barrier polymers are mixed in a suitable container in a "salt and pepper" fashion. The term "reaction products" is defined as two or three different kinds of monomers which make-up the above polymers and which are copolymerized or terpolymerized. Also included is grafting one of the above polymers with another. Each of the above polymers are incompatible with the polyolefine (A) . The polyamides include copolyamides and can be semi- crystalline and amorphous polymers. The polyamides used in the present invention include those semi-crystalline and amorphous resins having a molecular weight of a least about 5000 and commonly referred to as nylons. Examples of polyamides include 6,6-nylon, 6,9-nylon, 6,10-nylon, 6,12- nylon, and polyamides produced by ring opening of lactams, e.g. polycaprolactam, polylauriclactam. It is also useful in the compositions of the present invention to use polyamides prepared by copolymerization of two of the polymers above or terpolymerization of three of the above polymers . Examples of useful polyepoxides are polyglycidyl ethers of aromatic polyols, e.g., polyphenol . Such polyepoxides can be produced, for example, by etherification of an aromatic polyol with epichlorohydrin or dichlorohydrin in the presence of alkali. The aromatic polyol may be, e.g., bis (4-hydroxyphenyl) -2, 2-propane (bisphenol A), bis (4- hydroxyphenyl) -1, 1-ethane, (4-hydroxyphenyl) -1, 1 isobutane, bis (4-hydroxytertiarybutylphenyl) -2, 2-propane, bis (4- hydroxynaphtyl) methane, 4, 4 ' -dihydroxybenzophenone, 1,5- dihydroxynaphtalene and the like. Also suitable as the polyepoxides are polyglycidyl ethers of polyhydric aliphatic alcohols such as 1, 2-ethanediol, 1, 2-propanediol, 1,3- propanediol, 1, 4-butanediol, 1, 5pentanediol diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol and the like. The polyepoxides usually have molecular weights above about 200. Polyesters are well-known and are made by reacting dibasic carboxylic acids with glycols under well known conditions. Examples of carboxylic acids used in preparation of polyesters are terephtalic acid, isophtalic, and the like. Polyvinylalcohol and copolymers of vinyl alcohol containing up to about 10 weight percent of methyl acrylate, methyl methacrylate or other lower alkyl (meth) acrylates or ethylene/vinyl alcohol copolymers containing up to 50 mole percent ethylene, are normally made by polymerizing vinyl acetate alone or copolymerizing it with other monomers followed by saponification to obtain the corresponding polyvinyl alcohol homopolymer or vinyl alcohol copolymer. Component (B) is present in amounts of about 1 to 40, preferably about 5 to 25 and most preferably about 8 to 15 weight percent. Component (C) is an alkylcarboxyl-substituted polyolefin which serves as a compatibilizer and adheres together adjacent layers of the polyolefin and the barrier polymers. Use of the compatibilizer is important, because in its absence the barrier polymer layers making up the multilayer container do not adhere well to the polyolefine matrix (A) and the container does not have useful, mechanical properties. The alkylcarboxyl-substituted polyolefin compatibilizer is a polyolefin which has carboxylic moieties attached thereto, either on the polyolefin backbone itself or . on side chains. By "carboxylic moiety" it is meant carboxylic groups selected from the group consisting of acids, esters, anhydrides, and salts . The compatibilizer can be prepared by direct synthesis or by grafting. An example of direct synthesis is the polymerization of an alpha-olefin with an olefinic monomer having a carboxylic moiety. An example of grafting is the addition of a monomer having a carboxylic moiety to a polyolefin backbone. In the compatibilizer made by grafting, the polyolefin is polyethylene or a copolymer of ethylene and the like. The polyolefine is grafted with an unsaturated carboxylic acid, anhydride, or ester monomer. Examples for suitable unsaturated carboxylic acids, anhydrides, esters and salts include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, the acid anhydrides thereof, metal salts thereof, mono- and diesters thereof as well as glycidyl methacrylate, 2-hydroxy ethyl acrylate, 2-hydroxy ethylmethacrylate, monoethylmaleate, di-n-butylmaleate and the like. Component (C) is present in amounts of about 0.1 to 60.0 weight percent, preferably about 0.5 to 50 weight percent and most preferably about 0.8 to 45 weight percent. Multilayer packaging materials especially designed for dental adhesive systems of the present invention comprise at least one layer of a physical mixture of polyolefine (A) and the compatibilizer (C) and at least one layer of the barrier polymer (B) . In another embodiment of the invention, a laminate comprises a first layer of polyolefine (A) , a second layer of the compatibilizer (C) and a third layer of the barrier polymer (B) . In a preferred embodiment of the invention of a multilayer packaging material for dental adhesive systems, the first layer is a physical mixture of polyolefine (A) and compatibilizer (C) , the second layer is a barrier polymer (B) and the third layer is the same as the first layer (termed the 3-layer technique) . Another preferred embodiment of the invention comprises 3 different kinds of material and 5 layers, polyolefine (A) / compatibilizer (C) / barrier polymer (B) / compatibilizer (C) / polyolefine (A) (termed the 5-layer technique) . The above described multilayer packaging materials for dental adhesive systems may be formed into containers by conventional plastic processing techniques. The structures may be formed by well known lamination or extrusion techniques. Molded containers like bottles and tubes may be manufactured from the above described packaging materials by blow molding the packaging material or by such molding techniques all of which are well-known in the art. Preferred is a technique using coextrusion combined with blow molding of the above packaging material. From a manufacturing point of view the 5-layer coextrusion technique is somewhat inferior to the 3-layer coextrusion technique because of the more complicated installation of 3 extruders in the case of 5-layer technique compared to a number of 2 extruders in the case of 3-layer technique. This situation is intensified because the present invention is intended to use suitable containers for dental adhesive systems having small volumes of less than about 15 ml. Overall these multilayer plastic containers exhibit improved fluid barrier properties toward dental adhesive systems containing solvents with a vapor pressure in the range of from about 90 hPa to about 300 hPa @ 20°C like acetone or ethylacetate compared with those of a single layer of plastic material of the same thickness. The present invention is more particularly described in the following examples which are intended as illustration only since numerous modifications and variations will be apparent to those skilled in the art. Table I shows the weight loss of acetone stored in packaging materials of examples 1-3 and comparative examples 4-5. Table II shows the weight loss of ethylacetate stored in packaging materials of example 1 and comparative example 5. Table III shows values for adhesion on dentine obtained with "Prime & Bond 2.1" stored in bottles of example 1 at a temperature of 48°C over a period of 3 month. The figures indicate a stability of adhesion over a 3 month period confirming the intended utilization of the bottles of example 1 as packaging for dental adhesive systems containing solvents with a vapor pressure in the range of about 90 hPa to about 300 hPa at 20°C. Testing procedures The effectiveness of the barrier was determined by filling the test containers with acetone and ethylacetate 50 to 75 percent of total volume and determining the weight loss at 23 and 37°C over a period of several weeks. For each temperature and solvent, triplicates were run. The bottles were weighed periodically and their weight loss was plotted against time and average steady state weight loss was determined for each run. The average steady state weight loss was extrapolated to a period of one year. The permeability was calculated on the basis of weight loss, average wall thickness and surface area of the container. Example 1 The following compositions were used: Laminar bottles consist of three layers: The first layer is made of a physical mixture of high density polyethylene GF 4750 (Hoechst AG) and compatibilizer ADMER L2100 (Mitsui Petrochemical Ltd.) in the weight ratio of 50:50. The second or core layer is made of ethylene/polyvinylalcohol copolymer EP-F101A (Kuraray Ltd.) making up to 10 percent of wall thickness of the laminate. And the third layer consists of the similar materials as the first layer, such that the layer sequence is A/B/A. The bottles were filled with acetone and ethylacetate . Example 2 : The following compositions were used: Laminar bottles consist of 5 layers in the sequence of: 1. a layer of high density polyethylene GF 4750 (Hoechst AG) , 2. a layer of compatibilizer ADMER, 3. a layer of ethylene/polyvinylalcohol copolymer EP-F101A (Kuraray Ltd.) making up to 10% percent of wall thickness of the laminate, 4. a layer similar to 2. , and 5. a layer similar to 1. The layer sequence is A/B/C/B/A. The bottles were filled with acetone . Example 3 : The following compositions were used: Laminar tubes consist of 5 layers in the sequence of denomination: 1. a layer of high density polyethylene, 2. a layer of compatibilizer, 3. a layer of barrier polymer, 4. a layer similar to 2., and 5. a layer similar to 1. The layer sequence is A/B/C/B/A. The tubes were filled with acetone. Comparative Example 4 : In comparative example A bottles solely made of polypropylene were used. Regularly the bottles were utilized as packaging for "ProBond-Adhesive" (Dentsply) . The bottles were filled with acetone. Comparative Example 5 In comparative example 5 bottles solely made of low density polyethylene were used. Regularly the bottles were utilized as packaging for "Dyract Cem-Liquid" (Dentsply) . The bottles were filled with acetone and ethylacetate. Table I Table I I Table III It is evident therefore, that the objects of a laminar packaging material for volatile materials such as dental adhesives is carried out by the invention as herein described. All possible aspects of the invention beyond the best mode have not been necessarily described, and the scope of the invention shall only be determined by the following claims .

Claims: We claim : 1. A laminar package material for packaging of volatile compositions containing solvents with a vapor pressure of from about 90 hPa to about 300 hPa at 20° C, comprising a combination of a polyolefin (A) , a second polymer (B) serving as a barrier material incompatible with the polyolefin and an alkylcarboxyl-substituted polyolefin serving as a compatibilizer (C) . 2. The laminar plastic material of claim 1 wherein the laminar plastic material is formed into laminar containers using coextrusion combined with blow molding. 3. The laminar plastic material of claim 1 wherein the laminar packaging material is formed into bottles or tubes with a maximum compactly volume of less than about 15 ml. 4. The laminar plastic material of claim 1 having barrier properties exhibiting a permeability towards solvents with a vapor pressure in the range of from about 90 hPa to about 300 hPa at 20°C of less than 0.02 measured as grams per centimeter squared permeating a 0.5 mm thick container over a one year period at about 23°C. 5. The laminar plastic material of claim 1 comprising at least one layer of a physical mixture of polyolefin (A) and the compatibilizer (C) , and at least one layer of the barrier polymer (B) . 6. The laminar plastic material of claim 1 comprising of a first layer of polyolefin (A) , a second layer of the compatibilizer (C) and a third layer of the barrier polymer (B) . 7. The laminar plastic material of claim 1 comprising of a first layer which is a physical mixture of polyolefin (A) and compatibilizer (C) , a second layer which is a barrier polymer (B) and a third layer which is the same as the first layer. 8. The laminar plastic material of claim 1 comprising 5 layers: polyolefine (A) /compatibilizer (C) /barrier polymer (B) /compatibilizer (C) /polyolefine (A) . 9. The laminar plastic material of claim 1 wherein the polyolefin (A) is selected from the group consisting of polybutylene, polyethylene, polypropylene, polystyrene, polycarbonate and related copolymers. 10. The laminar plastic material of claim 1 wherein the polymer serving as a barrier material is selected from the group consisting of polyamides, polyepoxides, polyesters, polyvinylalcohol, copolymers of vinyl alcohol, physical mixtures and reaction products thereof. 11. The laminar plastic material of claim 1 wherein the alkylcarboxyl-substituted polyolefin compatibilizer is a polyolefin which has carboxylic moieties attached thereto, either on the polyolefin backbone itself or on side chains.

Inventors: WILNER RALF, WILNER, RALF
Applicants: DENTSPLY INT INC, DENTSPLY INTERNATIONAL INC.
Application year: 1997
Main classification: C08L23
IPC codes: B32B27, C08J5, C08L23, C08L51, C08L101