Patent Grant
9364985
The present invention relates to a process for producing free-flowing, agglomeration resistant amorphous poly-alpha-olefin based adhesive pellets and the adhesive pellets manufactured from this process.
Hot melt adhesives are often formed and packaged into solid blocks, e.g., pellets, chubs, pillows, and blocks. Solid blocks are preferred over powder for there is less risk associated with inhalation during loading and unloading, and convenience associated with storing and shipping them. It is also desirable for the adhesives to be provided in a form that can be stored and thereafter automatically transported and fed into the application devices in an application site. Free-flowing, agglomeration resistant free-flowing pellets are desirable to decrease disruption for end-use operators.
Conventional techniques to pelletize soft and tacky plastic materials, as described in U.S. Pat. No. 5,041,251, include extruding and cutting the materials in a cooling fluid, and the pellets remain in the cooling fluid for at least several hours to days. The pellets are separated from the cooling fluid and dusted with wax powder to impart nontackiness. Waxes typically have high crystallinity, and thus aid in free flowing.
Amorphous poly-alpha-olefin (APAO) based adhesives have low crystallinity, are inherently soft and tacky, and tend to agglomerate (block) into a huge mass at elevated temperatures. Agglomerated adhesives disrupt end-use operations because agglomerated mass must be forcibly re-dispersed. To prevent such agglomeration, APAO based adhesives are typically packaged in drums or as individual chubs, blocks and pillows with a protective packaging; or transported in cooled, insulated rail cars. Due to the above limitations, pellet adhesives are typically formed from high crystalline adhesives, such as ethylene vinyl acetates and high crystalline olefin based adhesives, and not from APAO based adhesives.
There is a need in the art for producing pellets of amorphous poly-alpha-olefin based adhesives in a faster throughput that resists agglomeration. The current invention fulfills this need.
The invention provides processes for preparing agglomeration resistant adhesive pellets composed of amorphous poly-alpha-olefin polymers. The process includes (a) extruding the adhesive through an orifice of a die plate immersed in a cooling fluid, which has a temperature, T1, of less than about 45° F. (7.2° C.); (b) cutting the adhesive into a plurality of pellets in the cooling fluid; (c) solidifying the pellets in a recrystallization fluid, T2, which is higher than T1 by at least 30° F., for at least 30 minutes; and (d) separating the pellets from the recrystallization fluid and drying the pellets.
The resultant pellets are free-flowing and non-blocking, and can be stored and transported at temperatures of below 120° F. for prolonged time without agglomerating together.
Applicants have discovered that recrystallizing the pellets at a temperature range of about 25 to about 40° C. (77-104° F.) significantly increases the speed of adhesive recrystallization by from days to several hours. Applicants have also discovered that the resultant pellets have higher hardness characteristics than conventionally formed pellets by a factor of at least three folds.
The process for preparing agglomeration resistant pellet particles and pellet particles made from such process are described. The process yields pellets particles resistant to agglomeration, even at elevated storage and transportation temperatures, i.e., up to 120° F. Furthermore, the process yields pellet particles resistant to compression that may lead to caking into huge mass.
Certain adhesive composition have tendency to agglomerate in elevated storage and transportation temperatures, e.g., 120° F. Such adhesive composition comprises various components, and the majority is based on polymers such as polyolefins or styrenic block copolymers, such as SBS, SIS, SIBS, and blends thereof. As used herein, polymers represent homopolymers, copolymers, terpolymers or interpolymers.
Any adhesive that has a cold crystallization temperature, regardless of the crystalline or amorphous structure, may be utilized in the adhesive. It is preferable for the adhesive to comprise from about 30 wt % to about 90 wt % of an alpha-olefin polymer. In one embodiment, the polymer is greater than 50%, preferably 60% amorphous morphology. Polymers with amorphous morphology have a low degree of structural order, and this lacks of organization results in no visible crystallinity. In another embodiment, the polymer is greater than 30%, preferably 50% semi-crystalline morphology. Polymers with semi-crystalline morphology consist of both crystalline domains and amorphous domains. Preferably, the semi-crystalline polymer contains less than 30% percent crystallinity.
Polyolefins polymers include copolymers of C2 to C12. In one embodiment, polyolefin comonomer is composed of ethylene, propylene, butene, hexane, 4-methyl-1-pentene and/or 1-octene. Exemplary alpha-olefins are selected from the group consisting of ethylene, butene, pentene-1,2-methylpentene-1,3-methylbutene-1, hexene-1,3-methylpentene-1,4-methylpentene -1,3,3-dimethylbutene-1, heptene-1, hexene-1, methylhexene-1, dimethylpentene-1, trimethylbutene-1, ethylpentene-1, octene-1, methylpentene-1, dimethylhexene-1, trimethylpentene-1, ethylhexene-1, methylethylpentene-1, diethylbutene-1, propylpentane-1, decene-1, methylnonene-1, nonene-1, dimethyloctene-1, trimethylheptene-1, ethyloctene-1, methylethylbutene-1, diethylhexene-1, dodecene-1, and hexadodecene-1.
Polyolefins also include high density polyethylene, low density polyethylene, very low density polyethylene, linear low density polyethylene, or ethylene higher alpha-olefin copolymers; polypropylenes, including soft polypropylene, random copolymers, impact copolymers, or heterophasic polypropylene and thermoplastic vulcanized or TPV-based polypropylene; polybutenes, including poly 1-butene homopolymers and copolymers or polyisobutylene; octene, ethylene-propylene monomer or EPM, ethylene-propylene-diene monomer or EPDM and mixtures thereof.
Exemplary diene comonomer units include divinyl benzene, 1,4-hexadiene, 5-1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 1,3-cyclopentadiene, 1,4-cyclohexadiene, and dicyclopentadiene.
In a preferred embodiment, the polyolefin is a comonomer of ethylenes, propylenes and butenes.
The adhesive further comprises additional components, e.g., a tackifier. In one embodiment, the adhesive comprises from about 10 to about 50 wt % of a tackifier, based on the total weight of the adhesive. Exemplary tackifiers include natural and modified resins, polyterpene resins, phenol-modified hydrocarbon resins, aliphatic and aromatic hydrocarbon resins, hydrogenated hydrocarbons, hydrogenated resins and hydrogenated resin esters and rosins. Examples for rosins and its derivatives include wood rosin, tall oil, colophonium, gum rosin, wood rosin, rosin ester resins including its esters, hydrogenated or dehydrogenated forms; terpene resins include for example natural and synthetic terpenes, polyterpenes and terpenesters; aromatic or mixed aliphatic-aromatic tackifying resins, like polymers from cyclopentadiene, dicyclopentadiene; styrene resins, like copolymers from styrene, alpha-methyl styrene, vinyl toluene, methoxy styrene, tertiary butyl styrene, chlorostyrene; aliphatic resins from monomers 1,3-butadiene, cis-1,3-pentadiene, trans-1,3-pentadiene, 2-methyl-1,3-butadiene, 2-methyl-2-butene and other co-polymerizable monomers or aliphatic petroleum hydrocarbon resins.
Preferably, the tackifier has a softening point from about 80° C. to 150° C. (ring and ball method, measured by ASTM E28-58).
Optionally, waxes in quantities of 0 to about 10 wt % by weight can be added to the adhesive. The wax may be of natural or synthetic origin. Suitable natural waxes are vegetable waxes, animal waxes, mineral waxes or petrochemical waxes. Suitable chemically modified waxes are hard waxes, such as montan ester waxes, sarsol waxes, etc. Suitable synthetic waxes are polyalkylene waxes and polyethylene glycol waxes. Preferred waxes are petrochemical waxes, such as petrolatum, microwaxes and synthetic waxes, particularly polyethylene (PE) waxes, polypropylene (PP) waxes, optionally PE or PP copolymers, Fischer-Tropsch resins, paraffin waxes or microcrystalline waxes.
Additionally, up to about 10 wt % of a plasticizer can be added to the adhesive. Suitable plasticizers are medicinal white oils, naphthenic mineral oils, phthalates, adipates, polypropylene, polybutene, polyisoprene oligomers, hydrogenated polyisoprene and/or polybutadiene oligomers, benzoate esters, vegetable or animal oils and derivatives thereof.
The adhesive may further comprise components such as fillers, antioxidants, adjuvants, adhesion promoters, natural waxes, synthetic waxes, oils, low molecular weight polymers, block, antiblock, pigments, processing aids, UV stabilizers, neutralizers, lubricants, surfactants nucleating agents, oxidized polyolefins, acid modified polyolefins, and/or anhydride modified polyolefins. Additives are combined with other adhesive components as individual components, in master batches, or combinations thereof. The selection and the properties are known to the person skilled in the art. They are added to the adhesive in quantities of typically up to about 3 wt % and preferably about 0.1 to about 2 wt %.
Preferably, the adhesive is a soft, semi-pressure sensitive adhesive, which has a needle penetration number of (i) 8 to 50 dmm after 1 hrs conditioning at 25° C., (ii) 10 or to 45 inch/mm after 4 hrs conditioning at 25° C., (iii) 10 to 40 dmm after 24 hrs conditioning at 25° C. More preferably, the adhesive has a needle penetration number of (i) 15 to 40 dmm after 1 hrs conditioning at 25° C., (ii) 15 or to 40 dmm after 4 hrs conditioning at 25° C., (iii) 10 to 30 dmm after 24 hrs conditioning at 25° C.
Unlike highly crystalline adhesives, high content APAO adhesives do not have a recrystallization temperature upon cooling. Such APAO based adhesives have cold crystallization temperature, and any adhesives that have a cold crystallization temperature may be utilized in the described process to form non-blocking, free flowing pellets. While there are various methods known in the art to determine the cold crystallization temperature (Tc), the Tc values reported herein are determined by Differential Scanning calorimeter (DSC). The adhesive is first heated to above its melting temperature to remove any prior heating history, and then cooled to below its glass transition temperature (Tg). The slow crystallization rate of APAO based adhesive keeps the adhesive in an amorphous state during the cooling DSC scan. As the amorphous adhesive is slowly heated to above its glass transition temperature in a second heating DSC scan, the amorphous regions of the adhesive has sufficient kinetic energy and freedom of motion to arrange themselves into a crystalline form. The exothermic peak observed in the second heating scan is determined as the cold crystallization temperature. While not being bound to any specific theory, it is believed that cold crystallization increases the crystallinity of the adhesive and therefore enhances the hardness and strength of the adhesive.
In a preferred embodiment, the cold crystallization temperature of the adhesive ranges from about 82 to about 104° F. (about 28 to about 40° C.).
The process for preparing agglomeration resistant particles comprises melting an amorphous adhesive at an elevated temperature, and then cutting the adhesive into a plurality of pellets either in a cooling fluid or immediately immersed in the cooling fluid. The equipment may be set up so the die plate is immersed in the cooling fluid or just above the cooling fluid. In one embodiment, the adhesive is extruded through an orifice of a die plate directly in the cooling fluid.
The cooling fluid has a first temperature, T1, of less than about 45° F. (7.2° C.). The lower limit depends on the fluid, e.g., for water, the lower limit of the cooling fluid is about 33° F. (0.5° C.), and must be above the freezing point of the cooling fluid. The cooling fluid comprises water, glycol, liquid nitrogen, compressed carbon dioxide or the like. The cooling fluid may further comprise antiblock compositions that inhibit particle blocking, i.e., caking, agglomerating, aggregating and/or sticking, when at least partially coated on the surface of particles in a sufficient amount. Antiblock compositions include powders, silicones, surfactants, waxes, polymers, and combinations thereof.
Antiblock compositions include organic or inorganic compounds such as those selected from the group consisting of talc, mica, calcium carbonate, finely divided or fumed silica, organic acids, metal organic esters, cellulose derivatives, alumina trihydrate, marble dust, cement dust, clay, feldspar, alumina, magnesium oxide, magnesium hydroxide, antimony oxide, zinc oxide, barium sulfate, aluminum silicate, calcium silicate, titanium dioxide, titanates, chalk, polymers such as polyethylene, polypropylene, polystyrene, and combinations thereof. The antiblocking compositions may be employed in any form; however, powders are generally preferable.
Typically, once the pellets are cut, they are transported away from the orifice to prevent from interfering with the continuous extrusion/pelletizing process. The pellets may be transported away from the orifice by various means known in the art, e.g., gravity feed, process water flow, and the like. As known to those skilled in the art, depending upon the size and speed of the pelletizer, the process water flow varies from about 35 gpm to about 350 gpm.
The pellet adhesives are then recrystallized/solidified in a recrystallization fluid having a second temperature, T2. Depending on the adhesive, the recrystallization fluid temperature can vary. In one embodiment, the recrystallization fluid has a T2 range of about 77 to about 105° F. (about 25 to about 41° C.). In a preferred embodiment, recrystallization fluid has a T2 range of about 82 to about 104° F. (about 28 to about 40° C.).
In contrast to conventional techniques that shock or decrease the overall temperature of the pellets to force recrystallization, the present process exposes the pellets to higher recrystallization temperature to speed up the solidification process. In the preferred process, the pellets remain in the recrystallization fluid with the specified T2 for a minimum of about 30 minutes, preferably at least 100 minutes.
The pellets harden and recrystallize in the recrystallization fluid at speeds at least three times faster than the conventional process, and the pellets have sufficient hardness or sufficient low deformation after about 40, preferably 120 minutes, in the recystallization fluid.
The recrystallization fluid comprises water, glycol, liquid nitrogen, compressed carbon dioxide, and the like. The recrystallization fluid may also include antiblock compositions.
The recrystallized pellets are then separated from the recrystallization fluid and dried. After drying, the recrystallized pellets are, optionally, dusted and coated with dry antiblock compositions.
The shape of the pellets can be varied according to the manufacturing process. They can have the form of small pillows, preferably a spherical form like balls, or in another preferred embodiment they form a cylindrical shape. In such case the dimensions are different in each direction, for example in one direction 25 mm with a diameter of 2 to 10 mm. The form of the pellets is not required to be regular, e.g., a spherical form can be compressed or stretched, rods can be symmetrical or have a non regular form as long as the size of the granulates is not too large. The form will be influenced by the manufacturing process, for example the pellets are squeezed, cut and separated to give a partly round form. It is possible but not preferred to mix different forms and sizes of the pellets. Another aspect of the invention is related to the size of the pellets. In one embodiment, the pellets have a weight greater than about 5 mg, and less than about 200 mg each, preferably less than about 100 mg most preferred less than about 80 mg. Smaller particle size increases the flowing properties of the material.
In general, polymers that comprise primarily amorphous or semicrystalline morphology produced in conventional manner typically yield soft pellets. The soft pellets tend to agglomerate upon long term storage and elevated temperature. The pellets according to the invention show free flowing properties at a temperature up to 120° F. This free flowing property remains stable also after storage at elevated temperature.
While conventional process hold the pellets in the cooling fluid to force recrystallization, the present process solidifies the pellets at a temperature at least 30° F. greater than the cooling fluid. Surprisingly, this present process increases the speed of the adhesive solidification by at least a factor of three. Furthermore, the adhesive pellets made from the present process have percent deformation values that are at least three times lower than the pellets made from the conventional method, even only after recrystallizing for about 120 minutes.
The following examples are provided to describe the invention in further detail. These examples, which set forth a preferred mode presently contemplated for carrying out the invention, are intended to illustrate and not to limit the invention.
The adhesive samples were conditioned at 25° C. for various times and then the needle penetration values were measured in accordance with ASTM D1321 with a penetrometer. The results are shown in Table 1.
Samples A, B and C have higher needle penetration values than comparative samples D and E, indicating that Samples A, B and C are softer than the firmer comparative samples D and E. Comparative samples D and E can be readily pelletized due to their low needle penetration values. It is typically understood in the art that softer or semi-pressure sensitive adhesives are more difficult to produce non-blocky pellets.
The cold crystallization temperatures of the adhesives were determined by Differential Scanning calorimeter (DSC), and are summarized in Table 2. Each adhesive was melted at 10° C./min up to 180° C., then cooled at 10° C./min to −50° C. and held at −50° C. for 10 minutes. The adhesive was then re-heated at 3° C./min until 180° C. Using the DSC Universal V4.5A TA Instrument software, the cold crystallization peak (Tc) was determined to be the peak exothermic temperature of the second DSC heating.
The resultant curve, cooling and second heating for Sample A and Sample E are shown in
Adhesive Pellets were produced by a pilot pelletizer with the following process:
Time sweep curve of pellets recrystallized/solidified in various T2 temperatures were tested. Dynamic Time Sweep program in ARES M was run for each pellet samples. The pellet samples were heated at application temperature (150° C.) between two parallel plates and rapidly cooled to designated recrystallization/solidification temperature (40, 80, 85, 90, 100 or 105° F.) and was held at for 24 hours (hrs). Frequency of 10 rad/sec is applied with constant strain of 1.0% and the modulus was recorded over the time. Tan delta value against time is shown in
As shown in
Based on the Time Temperature Sweep test, the residence time it took to achieve Tan Delta=1 is summarized in Table 3.
As shown in Table 3, solidifying the Sample A at temperatures at or above 80° F. decreased the holding time to reach Tan Delta=1 by at least 20%. Moreover, increasing the T2 to above 85° F. and lower than 105° F., maximizes the speed of the solidification process.
Sample A pellet hardness was examined by measuring the percent deformation of pellets solidified in various T2 fluid temperatures. Pellet deformation was examined by measuring the initial diameter (d0) with a modified micrometer (with magnets and steel). A weight of 70 g was place on the pellet for one minute and then the new diameter (d1) was measured. The percent difference, (d0−d1)/d0×100%, was calculated for at least twelve pellet samples and the percent deformation against recrystallization fluid temperatures are shown in
Also, as shown in
Blocking was measured by placing about 950 g weight evenly distributed on top of about 200 g of pellets made from Sample A solidified in various temperatures. The entire set-up was then transferred to 120° F. oven for 24 hrs. The set-up was then removed and cooled to room temperature (about 20° C.). The pellets were then visually and manually observed. A rating of “fail” was given if the adhesive was blocked, and a rating of “pass” was given to adhesive that was completely unblocked.
Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.
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