METHOD FOR FORMING A HOT FUSION ADHESIVE
Field of the Invention This invention relates to a method for forming a hot melt adhesive, particularly a hot melt adhesive that reacts to moisture; a hot melt adhesive that reacts to moisture manufactured by the method; and a method for joining substrates, such as structural components, using the adhesive. More particularly this invention relates to a method for forming an isocyanate-functional hot melt adhesive which reacts to moisture by first forming a hydroxyl-functional prepolymer from a polyol selected from the group including polyester polyols, polyether polyols and mixtures of the same and a polyisocyanate and subsequently form the hot melt adhesive which reacts to moisture from the hydroxyl functional prepolymer, a polyol selected from the group including polyester polyols, polyether polyols and a polyisocyanate. BACKGROUND OF THE INVENTION Hot melt adhesives are desirable for rapid solidification and for the absence of aqueous medium or solvent that provides fluidity to other types of adhesives. Hot melt adhesives that
they react to moisture which on the basis of a urethane containing an isocyanate group can be designed to produce a relatively low melt viscosity for easy handling and application; the reaction with moisture increases the final properties of the adhesive. The U.S. Patent No. 5,939,499 discloses a hot melt polyurethane adhesive composition which is a two component system, ie a mixture of an isocyanate functional prepolymer based on a polyether polyol, a polyester polyol or mixtures thereof and a thermoplastic elastomer polyether polyester. SUMMARY OF THE INVENTION The problem confronted by the inventor is the provision of an alternative method to form a hot melt adhesive that reacts to moisture that combines both precursors, polyester and optionally low cost polyether in a single effective composition that functions as a pressure sensitive adhesive before hardening and as a strong bonding adhesive after hardening of moisture. Preferably the process can be carried out in a sequential manner in a single reactor. According to a first aspect of the present invention there is provided a method for forming a hot melt adhesive that reacts to moisture including a) forming a reactivating hydroxy-functional prepolymer
first components including a polyol selected from the group including polyether polyols, polyester polyols and mixtures thereof and a polyisocyanate, the total proportion of OH / NCO groups of the first components being on an equivalent basis of 1.05 to 3.0; b) mixing second components including the hydroxyl functional prepolymer, a polyol selected from the group including polyester polyols, polyether polyols and a polyisocyanate, the weight ratio of the hydroxyl functional prepolymer to the crystalline polyester polyol being 9/1 to 1/9 and the ratio of NCO / OH groups of the second components being on an equivalent basis from 1.5 to 2.2; and e) reacting or allowing the mixture to react. According to a second aspect of the present invention there is provided a hot melt adhesive that reacts to moisture formed by the method of the first aspect of the present invention. According to a third aspect of the present invention there is provided a method for bonding substrates including forming a hot melt adhesive that reacts to moisture by the method of the first aspect of the present invention; heat the hot melt adhesive at a temperature of 90 ° C to 140 ° C; applying the hot melt adhesive heated to a first substrate in the presence of moisture; contact the fusion adhesive in
hot applied with a second substrate; and cooling or allowing the adhesive to cool. DETAILED DESCRIPTION OF THE INVENTION The composition of this invention is a hot melt adhesive composition reactive to moisture. By "reactive to moisture" it means here that the composition contains isocyanate groups which are capable of reacting with water desirably to effect an increase in the molecular weight of the adhesive composition and / or to effect the degradation of the adhesive in order to increase the properties of the adhesive. hardness of the adhesive subsequent to contact with water. By "hot melt" it means here that the adhesive may be a solid, semi-solid or viscous mass that can be heated advantageously to provide a liquid adhesive of a viscosity suitable for application and adhesion to substrates. By "open time" means here the time between the application of the adhesive to a first substrate and the contact of the applied adhesive with a second substrate. The method for forming a hot melt adhesive that reacts to the moisture of the present invention includes forming a hydroxyl-functional prepolymer by reactivating first components that include a polyol selected from the group including polyether polyols, polyester polyols, and mixtures thereof. and a polyisocyanate, the proportion of OH / NCO groups being
first components' on an equivalent basis of 1.05 to 3.0. The polyether polyol and the polyester polyol which can be used to form the hydroxyl functional prepolymer can be independently selected from crystalline, semi-crystalline or amorphous polyols; In general, increasing the crystalline polyol content increases the production of bond strength and decreases the open time. The polyols preferably have an average molecular weight ("MW") measured by gel permeation chromatography, from 250 to 8,000, more preferably from 250 to 5,000. Suitable polyester polyols include those formed from diacids or their monoester, diester or anhydride counterparts and diols. The diacids may be saturated C4-C12 aliphatic acids, including branched, unbranched or cyclic materials and / or C8-C5 aromatic acids. Suitable examples of suitable aliphatic acids include, for example, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, 1,12 -dedecanodioic, 1,4-cyclohexanedicarboxylic and 2-methylpentanedioic acids. Examples of suitable aromatic acids include, for example, acids, terephthalic, isophthalic, phthalic, 4,4'-benzophenone dicarboxylic acid and 4,4'-diphenylamino dicarboxylic acid. The diols can be branched C2-C? 2 diols, not
branched or cyclic aliphatic diols. Examples of suitable diols include, for example, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,3-butanediol, hexanediols, 2-methyl-2, -pentanediol. , cydohexane-1,4-dimethanol and 1,12-dodecanediol. Suitable polyether diols include polyoxy-C2-C6-alkylene polyols, including branched and unbranched alkylene groups. Examples of suitable polyether diols include, for example, polyethylene oxide, poly (1,2- and 1,3-propylene oxide), poly (1,2-butylene oxide) and random or block copolymers of ethylene oxide and 1,2-propylene oxide. . To form the functional hydroxyl prepolymer, at least one polyisocyanate, i.e., an isocyanate containing at least two isocyanate groups is used. Suitable polyisocyanates include, for example, aromatic, aliphatic, cycloaliphatic polyisocyanates and combinations thereof, such as, for example, m-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate. , 1,4-cyclohexane diisocyanate, hexahydrotoluene diisocyanate, 1,5-naphthalene diisocyanate, l-methoxy-2,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 4,4'-biphenylene diisocyanate, 3, 3'-dimethoxy-4,4'-biphenyl diisocyanate, 3,3'-diethyl-4,4'-biphenyl diisocyanate, 3,3'- dimethyl-4,4'-biphenylmethane diisocyanate, isophorone diisocyanate, 4,4 ', 4"-triphenylmethane triisocyanate, polymethylene polyphenylene polyisocyanate, 2,4,6-toluene triisocyanate and 4,4'-dimethyl-diphenylmethane tetraisocyanate or prepolymers they have Mn less than 2000 and they contain at least two isocyanate groups. A mixture of 4,4'-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate is preferred. The hydroxyl functional prepolymer is formed by reactivating the first components including a polyol selected from the group including polyether polyols, polyester polyols and mixtures thereof and a polyisocyanate, the OH / NCO group ratio of the first components on an equivalent basis it is from 1.05 to 3.0. The first components contain less than 1% water, preferably less than 0.1% water by weight based on the total weight of the components. The first components can be mixed by conventional means, preferably in a dry inert atmosphere and reactivated, preferably at a temperature of 80 ° C to 120 ° C. Optionally, a catalyst such as, for example, a tertiary amine or a tin base catalyst can be mixed with the components at a level less than 0.3% by weight based on the total weight of the mixed components. The method for forming a hot melt adhesive that reacts to the moisture of the present invention
it includes mixing second components comprising the hydroxyl functional prepolymer, a polyol selected from the group including polyester polyols, polyether polyols and a polyisocyanate, the weight ratio of the hydroxyl functional prepolymer being to the crystalline polyester polyol from 9/1 to 1/9 and the proportion of NCO / OH groups of the second components on an equivalent basis is from 1.5 to 2.2, preferably from 1.8 to 2.1; and reacting or allowing the mixture to react. The hydroxyl-functional prepolymer has been described above. The polyol can be crystalline, semi-crystalline or amorphous and can be selected from those polyols described and exemplified in the foregoing and can (be) the same (s) or different (s) from the polyol (s) (is) used to form the hydroxyl-functional prepolymer. A polyol which is a crystalline polyester polyol is preferred. The at least one polyisocyanate can be selected from those polyisocyanates described and exemplified above and can (be) the same (s) or different (s) of the polyisocyanate (s) used to form the prepolymer. The proportion of NCO / OH groups of all the second mixed components taken on an equivalent basis is from 1.5 to 2.2, preferably from 1.8 to 2.1, in order to provide an adhesive composition with an excess of isocyanate groups. Higher levels
of the NCO / OH ratio would result in higher than desired levels of free isocyanate monomer and lower levels of the NCO / OH ratio would result in higher application viscosity than desired. The second components contain less than 1% water, preferably less than 0.1% water, by weight based on the total weight of the components. The second components can be mixed by conventional means, preferably in a dry inert atmosphere and reactivated, preferably at a temperature of 80 ° C to 120 ° C, preferably for a sufficient time to react substantially all of the hydroxyl groups. Optionally, a catalyst, such as, for example, a tertiary amine or a tin base catalyst can be mixed with the components at a level less than 0.3% by weight based on the total weight of the components mixed either before, during or after the reaction to form the adhesive composition. The hot melt adhesive of this invention, which is an NCO-functional adhesive, is stored, preferably in a dry inert atmosphere, until its use. The hot melt adhesive can be formulated by mixing therein additional conventional ingredients such as fillers, pigments, adhesives, plasticizers, rheology modifiers, thermoplastic acrylic resins, etc., taking into account the reactivity of
the NCO-functional groups that desirably is maintained. In the method for joining substrates of the present invention, the hot melt adhesive which reacts to moisture is heated to a temperature of 80-140 ° C, preferably at a temperature of 100 ° C to 130 ° C, in order to of achieving a suitable viscosity for transporting the adhesive, such as in pumping or gravity feed, to the application equipment and for applying the adhesive to a first substrate in the presence of moisture. The application of the adhesive can be effected by conventional means such as, for example, a hot spray applicator, hot bead applicator, hot nozzle and hot roller coater, to form a continuous or discontinuous film of adhesive, as want. The adhesive can typically be applied at a level of 3.7 to 18.6 kg / square meter (4-20 g / square foot) even when in the cases where one of the substrates is a fabric it can be applied at a level as low as 1-40. g / square meter. It is contemplated that the moisture, ie, the water, which is anticipated to effect the reaction with the NCO-functional groups with which the final cohesive force of the applied adhesive is increased, may be, for example, a result of environmental humidity, artificially controlled or controlled humidified air, a vapor of water droplets or a spray of liquid water that contacts the applied adhesive. Is contemplated
in addition that the mixture can be increased by other reactive ingredients of the NCO-functional group such as, for example, amines. In alternative embodiments, the reactive hot melt adhesive can be applied to a substantially dry first substrate in the absence of contact with moisture and stored either in the absence of moisture for subsequent use or contacting a second substrate in the presence or absence of moisture. Then, the applied adhesive is contacted with a second substrate to provide a laminated structure. The laminated structure thus formed is optionally subjected to applied pressure such as passing it between rolls typically under a pressure of 10 to 100 pounds per linear inch depending on the hardness and deformability of the substrate to effect increased contact of the substrate with the adhesive and the laminated construction. it is then cooled or allowed to cool. In another embodiment the adhesive can be applied simultaneously or sequentially to both surfaces of the first substrate whose adhesive is then simultaneously or sequentially bonded to two additional surfaces, which may be the same or different. It is further contemplated that the laminated structure may subsequently be joined to another substrate (s) using the same or different adhesive before or after the process described herein. The first and second substrates that are going to join in
The method of this invention may be the same or different and include, for example, metal, wood, consolidated wood products, paper, woven or non-woven fabrics and plastics, which may have smooth or structured surfaces and are provided in the form of rolls. , sheets, films, metal ribbons, etc. These include, for example, mahogany veneered wood, impregnated paper, extruded polystyrene foam, expanded polystyrene foam, reinforced glass fiber polyester, polyester fabric, high or low pressure laminate, veneered wood, aluminum, steel, PVC and industrial plastics. The following examples are presented to illustrate the invention and the results obtained by the test procedures. Abbreviations MDI = diphenylmethane diisocyanate FRP = reinforced glass fiber plastic EXAMPLE 1. Preparation of the hot melt adhesive composition reactive to moisture of the invention by the method of this invention. A container with a gas inlet tube, thermometer, agitator, vacuum and heating jacket was arranged. The polyols were preheated overnight at 75-85 ° C to facilitate handling. 1755 g of polyol of hexanediol adipate (Rucoflex S105P110 with a hydroxyl no.
= 110; M.W. = 1000; RUCO Polymer, New York, NY), 2421 g of polyether polyol (PPG 1025, MW = 1000; PPG Ind., Pittsburgh, PA) and 3 g of phenolic antioxidant (Irganox 245; Ciba Geigy Corp., New York, NY) to the reaction vessel and the temperature was raised to 105 ° C with stirring. After 30 minutes at 105 ° C and a vacuum of 20 mm of mercury, the temperature was lowered to 90 ° C. 844 g of a 98/2 mixture of 4,4-MDI and 2,4-MDI (Bayer Inc., Pittsburgh, PA) were added and the temperature was maintained at 100-105 ° C for one hour with stirring and under nitrogen . 3631 g of hexanediol adipate (a crystalline polyester polyol) (Rucoflex S105P55 with a hydroxyl no = 55, MW = 2000) and 15 g of vinyl trimethoxysilane (Silquest A-171; OSI Specialties, Div. Of Witco Corp. New) were added. York, NY) and the reaction temperature rose to 103-105 ° C; Vacuum of 20 mm of mercury was applied for 30 minutes and the temperature dropped to 90 ° C. 1324 g of MDI was added; and exotherm was observed and the reaction temperature was maintained at 100-105 ° C under nitrogen for one hour. During the last 40 minutes, the agitation speed was reduced and 200-300 mm of vacuum Hg was applied. After a one hour wait, 1 g of benzoyl chloride and 6 g of JEFFCAT DMDEE were added. The mixture was continued for additional 30-40 minutes under nitrogen. At this time the reaction product was emptied into a container which was then protected in dry nitrogen and
seal. The product had a viscosity at 127 ° C (260 ° F) = 11,000 cps (28 Spindles at 10 rpm). (1 Spindle = 15,120 yards)
EXAMPLE 2. Evaluation of hot melt adhesive that reacts to moisture. The adhesive of Example 1 was heated to 130 ° C and applied to a first substrate on the visible cover. After a period of time (here "open time") the adhesive contacted the second substrate in the presence of ambient humidity and the compound was passed through a guide roller at a pressure of 50-100 pounds per linear inch. The substrates used were lauan wood about 1/8 inch thick; aluminum charging initiator; and FRP. Plane traction was determined by the method of ASTM C-297 using an Instron Model 4502 at a header speed of 0.05 inches per minute. The coating cut was determined by the ASTM method D-1002 using an Instron Model 4502 at a header speed of 0.05 inches per minute. The stabilized specimens were subjected to three cycles of heat and cold according to ASTM D-1183 and were then conditioned for one week at room temperature before being tested.
Table 2.1. Traction in Plane-Substrates FRP / Wood 3 Stabilized cycles (Extension-11.1 g / square foot) Open Time (min) Plane Pull (PSI) Type of cut
1 254 wood 100% 3 204 wood 100% 5 202 wood 100%
Table 2.2. Coating Cut-FRP Substrates / Wood 3 stabilized cycles (Extension 11.1 g / square foot) Open Time (min) Coating Cut (psi) Cut Type 1 348 wood 100%
3 316 wood 100%
255 wood 100%
Table 2.3. Traction force in plane at various temperatures -As substrates / wood (open time = 2 min., Extension 11.1 g / square foot) Temperature Plane traction (psi) Type of Cutting
-40 C (-40F) 251 wood 100% (75 F) 137 wood 100% (180 F) 100 wood 100%
Table 2.4. Coating cutting force at various temperatures - Al Substrates / Wood (Open time = 2 min,; Extension 11.1 g / square foot) Temperature Coating Cutting (psi) Cutting Type
-40 C (-40F) 122 wood 100% (75 F) 140 wood 100% (180 F) 172 wood 100%
Table 2.5. Coating cutting force at various temperatures - FRP / Wood substrates (Extension 11.1 g / square foot) Open time Open time Open time = 1 min = 3 min = 5 min Temperature Cutting Cutting Cutting Coating Coating Coating (psi) ( psi) (psi) - 40 C (-40F) 187 140 270 (75 F) 181 431 455 (180 F) 151 208 250 Note: All cuts were 100% wood cuts. It was observed that the applied adhesive is aggressively adherent. The fresh strength of the laminates was acceptable in all. The method for joining substrates of this invention including the hot melt adhesive that reacts to the moisture of this invention formed by
The method of this invention provides a useful level of adhesive performance.