METHOD OF IMPROVING BLOCK RESISTANCE OF ADHESIVE COMPOSITIONS

Abstract: A method is disclosed for improving the block resistance of adhesive compositions containing at least one polyamide resin including the steps of: (1) forming an adhesive composition containing a polyamide resin which is the reaction product of: (a) an acid component of from: (i) about 10 to about 80 equivalent % of a polymeric fatty acid; and (ii) about 10 to about 95 equivalent % of a dicarboxylic acid; and (b) a substantially equivalent amount of an amine component of from: (i) about 60 to about 95 equivalent % of a cycloaliphatic diamine; and (ii) greater than about 0 to less than about 20 equivalent % of ethylenediamine; and (2) applying said adhesive composition to a first substrate; and (3) adhering said first substrate to a second substrate at a heat seal temperature less than about 300 DEG F.

Description: METHOD OF IMPROVING BLOCK RESISTANCE OF ADHESIVE COMPOSITIONS RELATED APPLICATIONS This application is a continuation-in-part application of Serial Number 08/489,996 filed on June 12, 1995. FTELD OF THE INVENTION This invention relates to a method of improving the block resistance of adhesive compositions containing polyamide resins, especially when stored under elevated pressures and temperatures for extended periods of time, without detrimentally increasing the softening points of the compositions. BACKGROUND OF THE INVENTION Polyamide resins are useful for preparing adhesive compositions. Generally, the adhesive composition containing the polyamide resin is applied to a substrate in molten form and cooled, or from solution, emulsion or dispersion and permitted to dry. The adhesive composition containing polyamide resin is then "activated" by heating the adhesive composition to a temperature, referred to as the "heat seal temperature," which must be about or above the softening point of the polyamide resins. One of the problems these adhesive compositions containing polyamide resins suffer is poor block resistance which occurs after the adhesive composition is applied to a first substrate but before the adhesive composition is activated for use when the first substrate is contacted with a second substrate. "Block" or "blocking" as used herein, refers to the undesirable bonding or adhesion between the adhesive and one or more substrates prior to the activation of the adhesive. The blocking generally occurs during the storage of the coated substrate in stacked or rolled form, often under elevated pressures and/or temperatures for extended periods of time. Efforts have been made to improve the block resistance of the adhesive compositions containing polyamide resins. However, much of this effort has had the detrimental effect of increasing the softening point of the polyamide resin to a temperature greater than the heat seal temperature applied in a particular application, which is typically less than about 300°F. For example, PCT/US94/09971 discloses a polyamide resin having flexibility, high strength and low tack containing the condensation product of: (1) an acid component containing: (a) non-linear polymerized fatty acids; and (b) optionally, at least one acid selected from the group consisting of linear dicarboxylic and monocarboxylic acids; and (2) an amine component containing from: (a) about 10 to about 70 equivalent % of a piperazine-containing amine; (b) about 30 to about 90 equivalent % of 1,2-diaminopropane; and (c) optionally, about 0.5 to about 10 equivalent % polyetherdiamine. Many of these compositions, while providing good adhesive properties at temperatures less than a heat seal temperature of about 300°F, exhibit poor block resistance. I have unexpectedly discovered that by using select polyamide resins, including the substitution of ethylenediamine for the 1,2-diaminopropane of the polyamide resins of PCT/US94/09971, 1 was able to improve the block resistance of adhesive compositions without increasing the softening point of the adhesive compositions containing the polyamide resin to a temperature greater than a heat seal temperature of about 300°F. SUMMARY OF THE INVENTION The present invention is directed to a method of improving the block resistance of adhesive compositions containing at least one polyamide resin including the steps of: (1) forming an adhesive composition containing a polyamide resin which is the reaction product of: (a) an acid component of from: (i) about 10 to about 80 equivalent % of a polymeric fatty acid; and (ii) about 10 to about 95 equivalent % of a dicarboxylic acid; and (b) a substantially equivalent amount of an amine component of from: (i) about 60 to about 95 equivalent % of a cycloaliphatic diamine; and (ii) greater than about 0 to less than about 20 equivalent % of ethylenediamine; and (2) applying said adhesive composition to a first substrate; and (3) adhering said first substrate to a second substrate at a heat seal temperature less than about 300T. DETAILED DESCRIPTION OF THE INVENTION The compositions useful in the method of the present invention include the reaction products of an acid component with a substantially equivalent amount of an amine component. As used herein, "equivalent %" values are determined as follows: The total number of free acid groups in the acid component added to the polymerization reaction is set equal to 100 equivalent %. The equivalent percent of amine component is then based on that of acid component; i.e., the total number of free amine groups in the amine component added to the polymerization reaction is expressed as a percentage of the total number of free acid groups. Acid Component The acid component of the polyamide composition useful in the method of the present invention contains: (a) at least one polymeric fatty acid; and (b) at least one dicarboxylic acid. Polymeric Fatty Acid The term "polymeric fatty acid" or "dimer acid," as used herein, refers to complex mixtures of polymerized acids obtained from fatty acids. The term "fatty acids," as used herein, refers to saturated, ethylenically unsaturated and/or acetylenically unsaturated aliphatic carboxylic acids which can be naturally-occurring, synthetic or semi-synthetic. Polymeric fatty acids useful in the method of the present invention include those polymeric fatty acids derived from oleic acid and linoleic acids, such as those present in commercial tall oil fatty acids. The polymeric fatty acids useful in the method of the present invention include non¬ linear polymeric or oligomeric fatty acids made from addition polymerization of unsaturated tall oil fatty acids. Preferably, the polymeric fatty acids are formed from a high percentage of dimer acid, particularly hydrogenated (saturated) dimer acid, to provide desirable physical properties such as color, thermal and oxidative stability. Preferred fatty acids include: (a) about 0-10% by weight C 18 monobasic acids (monomer); (b) about 60-95% by weight C 3ei dibasic acids (dimer); and (c) about 1-35% by weight C 54 and higher polybasic acids (trimer). The relative ratios of monomer, dimer, trimer and higher polymer in unfractionated "dimer acid" depend upon the nature of the starting material and the conditions of polymerization and distillation. Methods for the polymerization of polymeric fatty acids are described, for example, in U.S. Patent 3,157,681, the disclosure of which is incorporated herein by reference in its entirety. The dimer content is also controlled by the fractionation conditions used to reduce the monomer, trimer and higher polymer components. The acid component contains from about 10 to about 80 equivalent % of a polymeric fatty acid. Preferably, the acid component contains greater than about 10 to less than about 80 equivalent % of a polymeric fatty acid, such as, for example, about 15 to about 75 equivalent % of a polymeric fatty acid, about 20 to about 70 equivalent % of a polymeric fatty acid, about 30 to about 60 equivalent % of a polymeric fatty acid, about 35 to about 55 equivalent % of a polymeric fatty acid, about 35 to about 45 equivalent % of a polymeric fatty acid. More preferably, the acid component contains about 40 equivalent % of a polymeric fatty acid. Dicarboxylic Acid Dicarboxylic acids useful in the method of the present invention include aliphatic, cycloaliphatic and aromatic dicarboxylic acids, and include the corresponding anhydrides, esters and acid chlorides. Preferably, the dicarboxylic acids contain from about 2 to about 24 carbon atoms. More preferably, the dicarboxylic acids contain from about 6 to 16 carbon atoms. Even more preferably, the dicarboxylic acids contain from about 8 to 14 carbon atoms. Most preferably, the dicarboxylic acids contain from about 10 to 12 carbons. Aliphatic dicarboxylic acids useful in the method of the present invention include, for example, oxalic, glutaric, malonic, adipic, succinic, pimelic, suberic, azelaic, sebacic and dodecanedioic acids and mixtures thereof. Cycloaliphatic dicarboxylic acids useful in the method of the present invention include, for example, cyclohexane dicarboxylic acids, such and 1,3- and 1,4-cyclohexane dicarboxylic acids and mixtures thereof. Aromatic dicarboxylic acids useful in the method of the present invention include, for example, phthalic, isophthalic, terephthalic and naphthalene dicarboxylic acids and mixtures thereof. The acid component contains from about 10 to about 95 equivalent % of a dicarboxylic acid. Preferably, the acid component contains greater than about 10 to less than about 95 equivalent % of a dicarboxylic acid, such as, for example, about 15 to about 90 equivalent % of a dicarboxylic acid, about 20 to about 85 equivalent % of a dicarboxylic acid, about 25 to about 80 equivalent % of a dicarboxylic acid, about 30 to about 75 equivalent % of a dicarboxylic acid, about 40 to about 70 equivalent % of a dicarboxylic acid, about 45 to about 65 equivalent % of a dicarboxylic acid. More preferably, the acid component contains about 60 equivalent % of a polymeric fatty acid. Amine Component The acid component of the polyamide composition useful in the method of the present invention contains: (a) at least one cycloaliphatic diamine; and (b) ethylenediamine; Cycloaliphatic Diamine Cycloaliphatic diamines useful in the method of the present invention include piperazine and derivatives thereof, including l,2-di(l-piperazinyl)propane, l,3-di-(l-piperazinyl)propane, 1,2- di-(l-piperazinyl)ethane, l,4-di-(l-piperazinyl)butane, and N-hydroxyethylpiperazine. In preferred embodiments, the cycloaliphatic diamine compound has the formula: wherein each of R,, R R 3 and R 4 is hydrogen or alkyl of 1 to about 4 carbon atoms. Preferably, each of R„ Rj, R 3 and R, is independently hydrogren. Exemplary alkyl groups include, for example, methyl, ethyl, propyl, including n-propyl and i-propyl, and butyl, including n-butyl, i- butyl, t-butyl and sec-butyl. The amine component contains from about 60 to about 95 equivalent % of a cycloaliphatic diamine. Preferably, the amine component contains greater than about 60 to less than about 95 equivalent % of a cycloaliphatic diamine, such as, for example, about 70 to about 95 equivalent % of a cycloaliphatic diamine, about 80 to about 95 equivalent % of a cycloaliphatic diamine, about 85 to about 95 equivalent % of a cycloaliphatic diamine. More preferably, the amine component contains about 95 equivalent % of a cycloaliphatic diamine. Ethylenediamine The amine component contains from greater than about 0 to less than about 20 equivalent % of ethylenediamine. Preferably, the amine component contains from about 2 to about 15 equivalent % of ethylenediamine. More preferably, the amine component contains about 10 equivalent % of ethylenediamine. Preparation of the Polyamide Resins The compositions useful in the method of the present invention include the reaction products of an acid component with a substantially equivalent amount of an amine component. Preferably, the relative quantities of the acid component and amine component are selected such that substantially equivalent numbers of reactive carboxyl and amine groups are present in the reaction mixture to produce a neutral or balance polyamide resin. Slight excesses of the acid component or amine component can be used. Slight excesses of carboxyl or amine are acceptable, but this ratio is preferably maintained between about 0.9: 1 to about 1:1.1. The polyamide resins which are arnme-terminated can be combined with an epoxy resin to form a curable thermoset adhesive composition. The techniques and general methods for polymerizing the acid component and the amine component of the polyamide resins useful in the method of the present invention are well known and described, for example, in U.S. Patents 3,377,303, 4,343,743 and 4,485,233, the disclosures of which are incorporated herein by reference, in their entirety. The adhesive compositions containing the polyamide resins useful in the method of the present invention may optionally contain other additives, such as, for example, fillers, reinforcing agents, coupling agents, colorants, odorants, other comonomers, resins, tackifiers, plasticizers, lubricants, stabilizers, antistatic agents, and the like. The polyamide resins of the present invention may be in the form of a hot melt, or in the form of a resin in solution, emulsion or dispersion (including an aqueous dispersion). Method of the Invention The present invention is directed to a method of improving the block resistance of adhesive compositions containing at least one polyamide resin including the steps of: (1) forming an adhesive composition containing a select polyamide resin described herein above; (2) applying said adhesive composition to a first substrate; and (3) adhering said first substrate to a second substrate. The select polyamide compositions described herein are useful in a method of improving the block resistance of an adhesive composition into which it is incorporated without detrimentally increasing the softening point of the adhesive composition above a heat seal temperature of 300°F. The first substrate and second substrate may be the same or different and may be any material for which adhesive compositions containing polyamide resins are typically used, such as, for example, polyvinyl chloride, polypropylene, polyester, polyurethane, polycarbonate, polystyrene, wood, glass, paper and the like. The adhesive composition containing polyamide resin may be applied to the first substrate by conventional means, including the steps of: (1) coating all or any part of one surface of the first substrate with the adhesive composition of the present invention; (2) either cooling the adhesive composition if it is applied from a hot melt or drying the adhesive composition if it is applied from solution, emulsion or dispersion. After the adhesive composition containing polyamide resin has been applied to the first substrate, then the first substrate may be adhered to the second substrate by: (1) contacting the surface of the first substrate coated with the adhesive composition containing the select polyamide resin to the second substrate; and (2) activating the adhesive composition containing the select polyamide resin by increasing the temperature to at least the heat seal temperature. The polyamide resins useful in the method of the present invention have been selected to produce an adhesive composition having a softening point less than or equal to the heat seal temperatures of from about 175°F to about 300°F, preferably from about 175°F to about 250°F, and most preferably from about 175°F to about 200°F. The period of time necessary to activate the adhesive composition depends upon the select polyamide resin, the heat seal temperature applied and pressure applied. Typically, the period of time necessary to activate.the adhesive composition ranges from about 1 second to about 1 minute, however, preferably the period of time ranges from about 1 to about 10 seconds. To ensure substantially permanent bonding between the first and second substrate, it is preferable to apply pressure. The amount of pressure which needs to be applied depends upon the select polyamide resin, the heat seal temperature applied and time that such temperature has been applied. Generally, the amount of pressure is from about 10 to about 100 pounds/inch 2 . The invention is further described in the following examples, which illustrate the method of the present invention. These examples are intended to be illustrative only, and are not to be construed as limiting the scope of the invention. EXAMPLES Example 1 — Preparation of Polyamide Resins Adhesive compositions and comparative adhesive compositions (designated with "C" suffix) were prepared from polyamide resins in the form of an aqueous dispersion formed from the reactants (all values in equivalent %) listed in Table 1 with softening points as measured on a Mettler FP90 Central Processor and a Mettler PF83 HT Dropping Point Cell with a softening point ring at a rate of 1.5°C/minute as listed in Table 2. Table 1 Sample Polymeric Sebsdc Oodecanedioc Piperaztne Ethykne 1,2-Dfatmmo Number Fatty Acid* Add Add diamine propane Adhesive 1 40 - 60 93 2 - Adhesive 2C 40 - 60 93 - 2 Adhesive 3 40 - 60 85 10 - Adhesive 4C 40 _ 60 85 _ 10 Adhesive SC 40 - 60 75 20 — Adhesive 6C 40 — 60 75 _ 20 Adhesive 7 40 60 85 10 _ Adhesive 8 50 - 50 93 10 - •Note The polymeric fatly acid utilized was Dimer- 14 available from Union Camp Corporation (Wayne, New Jersey) having a composition of 0.4 weight % monomer/95.6 weight % dιmer/4.08 weight % trimer and higher polymer. Table 2 Sample Number Softening Point CO Softening Point (*F) Adhesive 1 112 233.6 Adhesive 2C 105 221 Adhesive 3 118 244.4 Adhesive 4C 102 215.6 Adhesive SC 158 316.4 Adhesive 6C 103 217.4 Adhesive 7 <130* <266* Adhesive 8 100 212 *Note: The softening point of Adhesive 7 was estimated not measured. Example 2 — Preparation of Coated Substrate Adhesive compositions and comparative adhesive compositions prepared from polyamide resins in the form of an aqueous dispersion of Example 1 were coated on samples of 5 mil thick polyvinyl chloride ("PVC") and air-dried overnight at room temperature. Example 3 - T-Peel Testing The adhesive-coated samples of PVC prepared according to Example 2 were heat sealed to uncoated PVC at varying temperatures (225°F, 250°F, 275°F and 300°F) for a dwell time of 3 seconds and at 50 pounds/inch 2 . T-peel adhesion tests were conducted on the Adhesive Samples using the Instron Series IV Automated Materials Testing System, at a peel rate of 12 inches/minute and at room temperature. The results are shown in Table 3 with units of pounds linear inch (with higher numbers indicating better adhesion). Table 3 Sample Heat Seal Temperature (°F) Number 225 250 275 300 Adhesive 1 3.4 4.1 6.2 — Adhesive 2C 0.1 0.2 0.7 .. Adhesive 3 — 3.4 4.1 6.2 Adhesive 7 ~ 3.7 4.2 4.8 Adhesive 8 2.7 4.6 4.1 — Table 3 shows that those adhesives within the scope of the invention have better adhesion to the second PVC than the adhesives outside the scope of the invention. Example 4 — Block Resistance Testine The adhesive-coated samples of PVC prepared according to Example 2 were applied to uncoated PVC at room temperature with the adhesive sandwiched between the two layers of PVC. The layered samples were placed in a Carver Press under 1000 pounds/inch 2 pressure overnight at room temperature. Block resistance testing was conducted by carefully peeling apart the layered samples both listening for any cling and observing any adhesive transfer from the coated PVC to the uncoated PVC. The samples were rated according to Table 4. The results are shown in Table 5. Table 4 Rating Noise Transfer blocking hear clinging/noise upon see transfer of adhesive separation from coated PVC to coated PVC slight blocking hear clinging/noise upon see no transfer of adhesive separation from coated PVC to coated PVC non-blocking hear no clinging/noise upon see no transfer of adhesive separation from coated PVC to coated PVC Table 5 Sample Number Observed Blocking Adhesive 1 no blocking Adhesive 2C blocking Adhesive 3 no blocking Adhesive 4C blocking Adhesive 5C not tested — softening point too high Adhesive 6C blocking Table 5 shows that those adhesives within the scope of the invention have improved blocking relative to the adhesive outside the scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. A method of improving the block resistance of adhesive compositions containing at least one polyamide resin, comprising the steps of: (1) forming an adhesive composition containing a polyamide resin which is the reaction product of: (a) an acid component of from: (i) about 10 to about 80 equivalent % of a polymeric fatty acid; and (ii) about 10 to about 95 equivalent % of a dicarboxylic acid; and (b) a substantially equivalent amount of an amine component of from: (i) about 60 to about 95 equivalent % of a cycloaliphatic diamine; and (ii) greater than about 0 to less than about 20 equivalent % of ethylenediamine; and (2) applying said adhesive composition to a first substrate; and (3) adhering said first substrate to a second substrate at a heat seal temperature less than about 300°F. 2. The method of claim 1 wherein said polymeric fatty acid is present at a level of about 30 to about 60 equivalent %. 3. The method of claim 1 wherein said polymeric fatty acid is present at a level of about 40 equivalent %. 4. The method of claim 1 wherein said dicarboxylic acid is present at a level of about 30 to about 75 equivalent %. 5. The method of claim 1 wherein said dicarboxylic acid is present at a level of about 60 equivalent %. 6. The method of claim 1 wherein said cycloaliphatic diamine is present at a level of about 80 to about 95 equivalent %. 7. The method of claim 1 wherein said cycloaliphatic diamine is present at a level of about 95 equivalent %. 8. The method of claim 1 wherein said ethylenediamine is present at a level of about 2 to about 15 equivalent %. 9. The method of claim 1 wherein said ethylenediamine is present at a level of about 10 equivalent %. 10. The method of claim 1 wherein said dicarboxylic acid is an acid selected from the group consisting of sebacic acid and dodecanedioic acid. 11. The method of claim 1 wherein said cycloaliphatic diamine is an amine selected from the group consisting of piperazine and piperazine derivatives 12. The method of claim 1 wherein said cycloaliphatic diamine is an amine having the formula: wherein each of R l5 Rj, R > and R is a moiety selected from the group consisting of hydrogen and alkyl of 1 to about 4 carbons. 13. The method of claim 1 wherein said heat seal temperature is less than about 250°F. 14. The method of claim 1 wherein said heat seal temperature is less than about 200°F.

Inventors: ABEYWARDENA PALITHA KITHSIRI, ABEYWARDENA, PALITHA, KITHSIRI
Applicants: ABEYWARDENA PALITHA KITHSIRI, UNION CAMP CORP, ABEYWARDENA, PALITHA, KITHSIRI, UNION CAMP CORPORATION
Application year: 1996
Main classification: C08L77
IPC codes: C09J177