Free-flowing pellets containing pressure sensitive adhesives

Abstract

The present invention provides a hot melt adhesive in the form of a pellet comprising: (i) a core consisting of a hot melt pressure sensitive adhesive having a softening point of 60 to 150°C, and (ii) an outer shell consisting of a coating composition comprising: (A) a thermoplastic styrenic block polymer, wherein the thermoplastic styrenic block polymer has a styrene content of 15 to 50%, (B) a wax present in an amount ranging from about 20% to about 50%, by weight of the coating composition (ii), (C) a plasticizer, (D) an antioxidant, and (E) optionally a slip additive, (F) tackifier in an amount ranging from 0% to 5% by weight of the coating composition, and wherein the outer shell (ii) completely coats the core (i).

Description

FREE-FLOWING PELLETS CONTAINING PRESSURE SENSITIVE ADHESIVES[1] The invention relates to hot melt adhesives provided in the form of free-flowing pellets.[2] Thermoplastic adhesives, especially hot melts, can be manufactured and packaged as disclosed in EP 0469564. According to this document a hot melt adhesive is formed as a separate portion, solidified and thereafter this portion is surrounded by a plastic packaging material. The plastic packaging material shall be meltable with the adhesive. The range of the pillow-shaped portions disclosed is from about 100 g to about 4 kg.[3] In order to reduce the tendency of the individual pillows to stick and adhere to each other, it is known to coat them with a separating, anti-stick substance, as disclosed in US 5373682 and US 7328547. US 5373682 discloses a method by pumping or pouring molten hot melt adhesive in liquid form into a cylindrical plastic tube of plastic film made by a low density polyethylene or a polyethylene vinyl acetate polymer containing up to 10 % by weight vinyl acetate. The sizes of the plastic tube range from about three inches to 18 inches in length and are not free flowing. In US 7328547, the anti-stick substance is disclosed as film forming material containing at least 25% wax. The adhesive can be manufactured for example in a co-extrusion process. No specific form of the adhesive as delivered is disclosed.[4] EP 0957029 discloses a process to manufacture coated portions of an adhesive by co-extrusion. The polymer is provided in molten form and during the extrusion process an outward coating is applied. No information of specific compositions of the adhesive or coating material is provided.[5] EP 1196509 discloses a method to form granulated hot melt adhesives. This granulate is cooled to a non sticky form. Thereafter the adhesive material is coated with an ingredient of such adhesive in a liquid form which is non sticky as solid material and shall form an outside coating on such granulates. Such granulates a disclosed as free flowing.[6] US 6238732 discloses a process to manufacture pellets of a pressure sensitive adhesive whereby the pellets are covered with coating of a non-blocking ingredient of theadhesive. As components to form the coating, powders or solutions and dispersions are disclosed.[7] US 10,544,295 discloses a non-tacky film-forming polymer composition (cover material), and tacky hot melt adhesives in the form of pellets which are coated with the polymer composition and producible by coextruding the hot melt adhesive and the cover material. The film-forming composition comprises 5 to 40 % by weight of at least one Fischer Tropsch wax having a melting point of > 95 ° C. and 30 to 70 % by weight of at least one metallocene-catalyzed polyolefin having a softening point of > 95° C and a melt flow index (MFI) (230° C, 2.16 kg) of <1000 and >300 g / 10 minutes.[8] The prior art teaches the possibility to coat larger portions of a hot melt adhesive with a plastic coating. Such coatings are required for packaging pressure sensitive adhesives which by way of their use shall provide permanent tacky surfaces. Only with such non-sticky coating the adhesive material can be transported in single portions.[9] The coating materials as disclosed in the prior art are selected so that they can be mixed with the adhesive and do not negatively impact the adhesive property of the adhesive. In case of a powdery coating material this is easy to apply. But for use of portions, it is required that this coating shall not be damaged during transportation. In case of defects of the shell, the portions will adhere to one another and the portions have to be separated before further processing. Also in case of elevated temperature during transportation and storage, it has been noted that coatings are not stable when manufactured of a powder sticking at the surface of the adhesives, and so the portions, blocks or pillows will stick together. So such coatings which are made by application of a powder on the surface of an adhesive do not provide really continuous coatings, and they are not stable against friction during the handling and transportation process.

[0010] If the materials are coated with films of a thermoplastic polymer, the stability of such coat is higher. But the manufacturing process is complex. As disclosed in the prior art, the packaging process provides pillows or blocks which are handled manually. An automatic feeding process of smaller portions to a melting device is not possible.

[0011] Coating of smaller particles is disclosed by using as coating a liquid dispersion which shall form a solid layer on the surface of the particles. This puts a strong limitationon the process, as only specific coating materials can be used based on the requirement of having a liquid coating as solution or dispersion. The coating process in a liquid form as dispersion is energy consuming. The solvent has to evaporate to get a non sticky surface and the parts have to be moved so that no clogging appears during this step.

[0012] As the adhesive is handled manually, larger portions of the adhesive are preferred. Such forms of packaging have the disadvantage that a supply of smaller amounts to the application device is not possible. So the actual molten amount of an adhesive in a melting tank to maintain a steady supply of adhesive is relatively large, which leads to thermal stress of the adhesive melt.

[0013] Another disadvantage of smaller packaged adhesive portions is based on the form. The relationship of shell volume and core volume requires a higher amount of shell material. So the adhesive after being molten will contain a larger amount of film forming material stemming from the shell of the portions. This may negatively impact the properties of the adhesive.

[0014] Consequently, there is a need for a supply of hot melt adhesives in the form of pellets which shall be supplied in bulk form and can be processed by automatic feeder systems, and which have improved properties in terms of better end-sealing of the pellets and a better resistance of oil migration from the core adhesive.SUMMARY OF THE INVENTION

[0015] The inventers of the present invention have discovered a novel coating composition that can form a protective outer shell to completely coat tacky hot melt adhesives thereby forming pellets. The coating composition creates a more flexible outer shell than the traditional polyolefin-based coatings, so provides a better end-sealing of the pellets and a better resistance of oil migration from the core adhesive. The present invention provides a non-tacky coating composition which forms an outer shell to protect the tacky hot melt adhesive in the core through a co-extrusion process. This coating composition enables tacky adhesives to be packed into millimetre size pellets (also known as chubs, or microchubs) which are vacuum feedable through an automated feeding system.

[0016] According to one aspect of the present invention, there is provided a hot melt adhesive (1) in the form of a pellet comprising:(i) a core consisting of a hot melt pressure sensitive adhesive (2) having a softening point of 60 to 150°C, and(ii) an outer shell consisting of a coating composition comprising:(A) a thermoplastic styrenic block polymer in an amount ranging from about 30% to about 60%, by weight of the coating composition (ii), wherein the thermoplastic styrenic block polymer has a styrene content of 15 to 50%,(B) a wax present in an amount ranging from about 20% to about 50%, by weight of the coating composition (ii),(C) a plasticizer present in an amount ranging from about 15% to about 40%, by weight of the coating composition (ii),(D) an antioxidant present in an amount ranging from about 0.2% to about 2%, by weight of the coating composition (ii),(E) optionally a slip additive present in an amount ranging from about 1% to about 10%, by weight of the coating composition (ii), and(F) tackifier in an amount ranging from 0% to 5% by weight of the coating composition, and wherein the outer shell (ii) completely coats the core (i).

[0017] According to another aspect of the present invention, there is provided a coextrusion process for preparing a hot melt adhesive (1) as defined herein, comprising simultaneously extruding the core consisting of the hot melt pressure sensitive adhesive (i), and the coating composition such that the coating composition completely covers the core (i) to form the outer shell.

[0018] According to another aspect of the present invention, there is provided the use of a hot melt adhesive (1) as defined herein in an automated operated feeder, preferably in a vacuum operated feeder.

[0019] According to another aspect of the present invention, there is provided the use of a hot melt adhesive (1) as defined herein as a pressure sensitive adhesive.

[0020] Further advantages of the present invention include a positive impact on sustainability: the process required to prepare the pellets can be altered depending on exactly the need of the customer. Therefore, if a smaller batch is required, just that amount can be made, and no excess produced.

[0021] Throughout the specification, unless otherwise specified, references to softening point refer to the softening point of a material as measured according to the Mettler Cup and Ball method defined in ASTM D6090.DETAILED DESCRIPTION

[0022] The term “coated pellet” shall include particles of small size showing a symmetrical or unsymmetrical form, having a weight of up to 10g each. The size is less than 20 mm in either direction the lower limit is more than 1 mm. The coated pellets according to the invention are free flowing at a temperature of less than 45°C. Under free-flowing it is understood that a bulk of pellets will be flowing under influence of the gravity through a perpendicular tube at ambient temperature. The pellets are flowing, preferably with no clogging, sticking or blocking within a reasonable time period. The temperature of pellets and tube is the same and is equal or less than 45°C. A suitable test procedure involves:

[0023] Placing 1 kg coated pellets in an oven at 45°C for 6 hours.

[0024] After this period the coated pellets are removed from the oven, cooled to ambient temperature (about 20°C) and poured into the top of a testing tube device (a perpendicular tube device with a dimension of 10 cm in diameter and 30 cm in height, the tube being closed at the bottom end of the tube) for flowing properties.

[0025] Placing a weight of 2 kg on top of the bulk of coated pellets in the tube for 30 minutes.

[0026] After 30 minutes, removing the weight from the top of the coated pellets and removing the closure at the end of the tube to allow the coated pellets to flow from the bottom of the tube into a void or a bucket below the tube.

[0027] Measuring the time taken for the coated pellets to flow out of the tube at ambient temperature (about 20°C).

[0028] The coated pellets are considered passing the free-flowing test if, after being aged at 45°C for 6 hours, the time taken for coated pellets to flow out of the test tube device is no more than 3 minutes, preferably no more than 2 minutes, more preferable no more than 1 minute.Thermoplastic Styrenic Block Polymer

[0029] Component (A) in the coating composition is a thermoplastic styrenic block polymer in an amount ranging from about 30% to about 60%, by weight of the coating composition (ii), wherein the thermoplastic styrenic block polymer has a styrene content of 15 to 50%.

[0030] The inventors surprisingly found that coatings incorporating thermoplastic styrenic block polymers having the defined styrene content completely coat the core adhesives, and exhibit the favorable properties defined herein, for example the creation of a more flexible, yet non-tacky, outer shell when applied to the core adhesive. The styrene content is 15 to 50%, preferably 20 to 45%, yet more preferably 25 to 45% and most preferably 30 to 45%.

[0031] A variety of suitable thermoplastic materials meeting the above requirements can be used in the coating composition. Examples include styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), styrene-butadiene butylene-styrene (SBBS) (i.e. a partially hydrogenated styrene-butadiene-styrene copolymer), styrene-(ethylene- butylene)-styrene (SEBS), styrene-(ethylene-propylene)-styrene (SEPS), and styrene- block-isobutylene-block-styrene (SIBS). These polymers may be used alone or as mixtures thereof.

[0032] Preferably, the thermoplastic styrenic block copolymer in the coating composition is a partially or fully hydrogenated styrenic block copolymer, or mixtures thereof. Preferably, the thermoplastic styrenic block polymer (A) is fully hydrogenated. Most preferred is SEBS.

[0033] Suitable polymers are, for example, available from Kraton polymers, TSRC Corporation, Versalis SpA, LCY Elastomers LP and Ningbo Jinhai Chenguang Chemical Corporation.

[0034] Typical SIS grades include:Kraton D1165 (30% styrene), Kraton D1126 (21% Styrene) from Kraton,- Vector 4211 (30% styrene), 4411 (44% styrene) from TSRC JH8291 (30% styrene) from Jinhai

[0035] Typical SEBS grades include:Kraton G1652 (29% styrene), Kraton G1726 (30% Styrene, 70% diblock) from KratonGlobaprene 9550 (30% styrene), Globalprene 9552 (30% styrene) from LCY

[0036] Typical SBBS grades include:- Tuftec P1500 (30% styrene) from AsahiWax

[0037] Component (B) in the coating composition is a wax present in an amount ranging from about 20% to about 50%, by weight of the coating composition (ii),

[0038] 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, sasol waxes, vinyl acetate modified waxes such as AC-400 (available from Honeywell), maleic anhydride modified waxes such as Epolene C-18 (available from Westlake Chemical) and AC-575A and AC-575P (available from Honeywell) and oxidized EVA waxes such as Licowax® 371 FP (available from Clariant). Suitable synthetic waxes are polyalkylene waxes and polyethylene glycol waxes. Preferred waxes are polyolefin waxes, such as petrolatum, microwaxes and synthetic waxes, particularly polyethylene waxes, polypropylene waxes, optionally PE or PP copolymers, Fischer-Tropsch resins, paraffin waxes or microcrystalline waxes. Available Fischer-Tropsch waxes include H1 wax and Seration 1820 wax from Sasol, polyolefin waxes include polyethylene waxes Licocene 4201, Licocene 3101, etc. from Clariant, Polywax 1000 from NLICERA, AC8, AC9 from Honeywell, L-C 103NC, 104NC from LION Chemical.

[0039] Preferably, the wax component (B) is at least one Fischer-Tropsch wax; and or / one polyethylene wax. The wax component (B) may be at least one Fischer-Tropsch wax; and or / one polyethylene wax and at least one further wax (a wax that is not a Fischer-Tropsch wax or a polyethylene wax). The Fischer-Tropsch wax suitably has a DSC melting peak at about 80-110°C measured at 10°C / min heating rate in accordance with ASTM 3418. The polyethylene wax suitably has a DSC melting peak at about 115- 130°C measured at 10°C / min heating rate in accordance with ASTM 3418.

[0040] Preferably, the wax component (B) comprises at least a FT wax, and optionally at least one other wax, which is preferably a polyethylene wax.Plasticizer

[0041] Component (C) in the coating composition is a plasticizer present in an amount ranging from about 15% to about 40%, by weight of the coating composition (ii).

[0042] 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.

[0043] Further examples of plasticizer include hydrogenated plasticizers like oils or oligomers of polybutene. Also, monohydric or polyhydric alcohols with a molecular weight of 1000 to 6000 g / mol may also be used, for example polyalkylene glycols. Another group of suitable plasticisers are esters, including, for example, liquid polyesters and glycerol esters, such as glycerol diacetate and glycerol triacetate as well as neopentyl glycol dibenzoate, glyceryl tribenzoate, pentaerythritol tetrabenzoate and 1,4- cyclohexanedimethanol dibenzoate. Also plasticizers based on aromatic dicarboxylic acid esters can be used, for example the esters of phthalic acid, isophthalic acid or terephthalic acid. Also esters of sulfonic acids are used as plasticiser. Fatty acids are also suitable plasticizers. Such components are commercially available.Antioxidant

[0044] Component (D) in the coating composition is an antioxidant present in an amount ranging from about 0.2% to about 2%, by weight of the coating composition (ii).

[0045] Antioxidants suitable for use include phosphites, phenols, sterically hindered phenols of high molecular weight, polyfunctional phenols, sulfur- and phosphorus- containing phenols. Suitable compounds in the context of the invention are, for example, hydroquinone, hydroquinone methyl ether or phenothiazine. The selection and the properties are known to the person skilled in the art.Slip Additive

[0046] Component (E) in the coating composition is a slip additive and it is an optional one. When it is present, the slip additive (E) is present in an amount ranging from about1% to about 10%, by weight of the coating composition (ii). In an alternative embodiment, there is no slip additive (E) in the coating composition (ii). When present, the slip additive is different to the wax (B).

[0047] Slip additives are used to reduce the friction between outer shell coating surfaces. This also improves the free-flow ability of the pellets. Most commonly suitable for use are fatty acid amides, including their primary and secondary amides. Specifically, unsaturated fatty acid amides such as erucamide and oleamide are preferred slip additives for the outer shell coating. Available slip additives include Erucamide, Crodamide E, Crodamide ER, Crodamide VRX, Crodamide OR, Crodamide BR, Crodamide SR from CRODA Polymer Additives.Tackifier

[0048] Component (F) in the coating composition is a tackifier and it is an optional one. When present, component (F) is a tackifier in an amount ranging from more than 0% to 5% by weight of the coating composition.

[0049] The inventors have surprisingly found that the coating composition need not contain any tackifier, and advantageously contains essentially no tackifier. In this context, “essentially no tackifier” means either 0% of tackifier in the coating composition by weight of the coating composition, or at most 0.5wt% of tackifier in the coating composition by weight of the coating composition, preferably at most 0.2wt% of tackifier in the coating composition by weight of the coating composition. It will be understood by the skilled person in the context of the present invention that the core (i) defined herein may comprise a tackifier, and that the coating composition (ii) is essentially free of tackifier.

[0050] When present, tackifying resins useful in the adhesive materials of the invention comprise natural and modified resins, polyterpene resins, phenol-modified hydrocarbon resins, aliphatic and aromatic hydrocarbon resins, hydrogenated hydrocarbons, hydrogenated resins and hydrogenated rosin esters and rosins.

[0051] 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 fromstyrene, alphamethyl 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-polymerisable monomers or aliphatic petroleum hydrocarbon resins.

[0052] Thus, the coating composition can be advantageously formulated and used to form an outer shell over a core adhesive.

[0053] The outside shell of the pellets is made by the coating composition defined herein and is preferably not tacky at ambient temperature at 25°C, preferably up to 45°C. Tackiness was assessed using the tackiness test detailed in the Examples section.

[0054] The coating composition preferably has a melting point of 130°C to 160°C, more 140°C to 160°C.

[0055] The coating composition of the shell and the PSA of the core are compatible. So they shall form a homogenous mixture, which is stable as a melt. Typically, the coating composition (ii) has a softening point which is equal to or higher than the melting point of the adhesive material of the core (i).

[0056] The outer shell coating composition has a viscosity of about 1,500 to about 5,000 cps at 180°C, measured in accordance with ASTM 3236-88 (Standard Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials).Core (i)

[0057] The pellets defined herein include a core consisting of a hot melt pressure sensitive adhesive (2), typically having a softening point of 60 to 150°C. PSA-type hot melt adhesives are generally known to the skilled person for example based on styrene block copolymers as disclosed in EP 0451920 or EP 1493794, acrylate type adhesives according to WO 02 / 010307, polyolefin type adhesives according to DE 19944225, EVA type adhesives disclosed in DE 102006054196.

[0058] Suitably, the core (i) comprises at least one suitable polymer as the base polymer. For example the base polymer can be a thermoplastic polymer, such as a styrenic block copolymer, including hydrogenated, unhydrogenated and partially hydrogenated including SIS, SBS, SEBS, SEPS, SBBS, SIBS, etc.; a metallocene catalyzed polyolefin copolymer,for example polyethylene, polypropylene, polybutene and copolymers thereof; a Ziegler- Natta catalyzed amorphous poly-a-olefin (APAO) such as atactic propylene and propylene copolymers with ethylene, butene, hexane, and octane, or ethylene or propylene homopolymers or copolymers and mixtures of the polymers; ethylene vinyl acetate copolymer; an acrylate, an alkyl acrylate or methacrylate (e.g., ethyl acrylate, ethyl methacrylate, ethyl n-butyl acrylate, butyl acrylate, butyl methacrylate, and combinations thereof; a thermoplastic polyester; a thermoplastic polyamide; a thermoplastic polyurethane; and combinations thereof.

[0059] The hot melt pressure sensitive adhesive core (i) may also include one or more of a wax, a tackifier, a plasticizer and an oil. Specific ingredients may be selected from those described above in relation to the outer shell (ii), as well as from well-known ingredients in these functional categories.

[0060] As will be evident from the present disclosure, the nature of the hot melt pressure adhesive (2) of the core (i) is not so limited, and the formulation and preparation of such an adhesive is well within the common general knowledge of the skilled person, based on the desired properties of the overall pellet of adhesive. For example, the core may include (in addition to the base polymer) a wax, a tackifier, a plasticizer and an oil. Alternatively, the core may also include (in addition to the base polymer) a wax, a tackifier and a plasticizer. Alternatively, the core may also include (in addition to the base polymer) a tackifier and an oil. Alternatively, the core may also include (in addition to the base polymer) a tackifier.

[0061] Any suitable tackifier which is conventionally used in the preparation of PSAs may be incorporated into the core PSA adhesive. Explicit reference may be made to the depiction of the state of the art in the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, 1989) or any PSA related literatures.

[0062] In addition, other typical auxiliaries and additives can be incorporated in a suitable PSA material. Examples are stabilizers, light stabilizers and / or adhesion promotors. Their function is to protect the polymers against decomposition during processing, storage or use. The selection and the properties are known to the person skilled in the art. They are added to the adhesive material in quantities of typically up to 3 wt.-% and preferably about 0.1 to 2 wt.-%. The adhesive compositions can additionally contain other compatible polymers, fillers, pigments, dyes, oils, fragrances and other conventional additives.

[0063] The adhesive of the core (i) is a hot melt pressure sensitive adhesive. Such adhesives retain the ability to form a serviceable bond to an adherend under light pressure at room temperature. More particularly, such reactive or non-reactive adhesive compositions will demonstrate cold flow under finger pressure at room temperature.Pellets

[0064] The coating composition is selected to form a coating or film having a non-tacky surface and shall form a barrier against the environment.

[0065] As disclosed herein, the outer shell of the pellets is made from a different composition including different polymers than the PSA material in the core. The outer shell shall have a thickness of about 2 to 200 pm, preferably 10 to 100 pm particularly more than 20 pm. This is dependent on the size of the pellets.

[0066] If the amount of coating composition is too large in relation to the amount of PSA in the core, the properties of the adhesive will decrease. In other words, the core of the pellet is formulated as a PSA such that the end of use of the pellet is as a PSA. When the outer shell has the thickness described above, the pellet itself can be used as a PSA because the pellet exhibits the PSA properties of the core composition. If the outer shell does not cover the whole surface or is too thin, the stability of the flowing properties of the adhesive pellets is not ensured. The amount of coating composition is typically up to 12 wt-% relative to the weight of the pellet, preferably about 1 to 10 wt-%,

[0067] The outer shell (ii) completely coats the core (i). In other words, the outer shell forms a continuous coating, and no core material is exposed. Such coating can be achieved by heating the coating composition above the melting temperature. This can be performed by application of a powdered material being heated after coating above the melting temperature of the coating or preferably by co-extrusion and application of the coating composition as a melt.

[0068] The pellet of the present invention suitably has one or more of the following characteristics:1) it weighs less than 10g;2) it has a diameter of less than 20 mm in any dimension;3) it has a cylindrical, spherical, or pillow-like shape; and4) it is free-flowing at a temperature below 45°C.

[0069] The lower limit of the diameter in any dimension is preferably more than 1 mm, more preferably more than 3 mm.

[0070] The shape of the pellets can be varied according to the manufacturing process. They can have the form of small pillows or microchubs, a spherical form like balls, or of cylindrical shape. In such case the dimensions are different in each direction, for example in one direction 20 mm with a diameter of 2 to 10 mm in another direction. 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.

[0071] The weight of each pellet may be less than 8g, suitably less than 5g. Smaller particle size increases the flowing properties of the material.

[0072] The pellets according to the invention show free flowing properties at a temperature up to 45°C. The test procedure is as defined above.

[0073] A preferred method for manufacturing the pellets defined herein is the co-extrusion process. In such a co-extrusion process, the core adhesive to be packaged is melt blended in a mixer and then squeezed or extruded through an appropriately sized orifice in a die while still at a temperature above or very close to the softening point of the adhesive material. The orifice and die may be of any conventional configuration and generally is such as to provide either a slot like or cylindrical like configuration for the adhesive composition as it is pumped through the orifice. The temperature of the die must be maintained above the melting point of the core adhesive composition, and is typically in the range of 100° C to 150° C. In co-extrusion, the coating composition for the shell is then simultaneously extruded from the die to surround the core adhesive to be packaged and thus forms an outer shell which surrounds completely the adhesive to be packaged. Co-extrusion techniques are well known in the art, and suitable equipment for co-extrusion processes are known to a person skilled in the art.

[0074] As known, since the materials being extruded at elevated temperatures, the coextrusion process typically occurs under water or is immediately immersed to water so that the core adhesive and coating composition that surrounds the core adhesive begins to cool immediately after being extruded from the die. Thereafter, the core adhesive covered by the coating composition is allowed to cool either in a water bath or in a refrigerant medium such as chilled glycol, liquid nitrogen, compressed carbon dioxide or the like, or under ambient conditions so that the wrapped adhesive is sufficiently cooled for handling. The coated adhesive will be pinched mechanically preferably after cooling to a more solid form into pellets of desired size, shape, or weight. By this process it is essential that the separating step also covers the cut section of the pellets completely with a coat. Accordingly, the temperature of the pellet at this step has to be selected so that the coating composition can still be stretched and cover the whole surface. Otherwise, a long term stability of the flowing properties of the pellets is not secured.

[0075] It is also possible to manufacture the pellets by a co-extrusion process whereby the softening point of the coating composition is higher or equal to the softening point of the core adhesive.

[0076] Very small amounts of anti-blocking additives such as micronized FT waxes, micronized PE waxes, etc. may be further added optionally to the coated pellets after cooling to enhance lubricity and flow behaviour of the pellets. The amount of the optional anti-blocking additive is typically less than about 1500 ppm. The particle size (D90) of the micronized FT wax is less than 50 pm, preferably less than 20 pm.

[0077] The pellets may be further packaged after cooling in a container, box, or bag for transportation. The container can be made of mechanically stable material so that large amounts of such pellets can be handled. Page

[0078] The pellets can be supplied in bulk form, e.g. as container or as supersac bag. The content of the container can be discharged by known means on the processing site. After discharging the pellets it can be transported by the known devices, e.g. screws, belt conveyors and other systems. Preferably the pellets can be transported by pressurised gas e.g. air or by vacuum for example in a vacuum feeder system. In such processing mechanical friction is provided to the surface of the pellets. So the transport of the pellets according to the invention is possible without clogging in the transportation system and sticking of the pellets.Use

[0079] The present invention defines a hot melt adhesive (1) in the form of a coated pellet. Such adhesives are used as pressure sensitive adhesives; the pressure sensitive nature of the pellet arising from the pressure sensitive nature of the core adhesive.

[0080] Another aspect of the invention is the use of coated pellets as defined herein in automated supply operations of an application device. During further processing at the customer’s site a portion of the materials can be discharged from the packaging container and transported to the melting device. This transportation can be performed by known devices preferably by a vacuum feeder. In the melting tank the materials in the pellet are molten and can be pumped to the application devices for example nozzles or rolls.

[0081] As the pellets each have a small volume, it is possible to feed the adhesive in smaller portions to the melting device. So, even with a small amount of adhesive pellets to be processed in the melting tank, an automatically operating feeder system is possible. No manual feeding of the melting tank is required. The amount of adhesive can be easily metered by known methods and devices. If only low amounts of pellets are fed in the melting tank, the melting process can be accelerated. The stock of molten material can be reduced. A degradation process of the adhesive during melting can thus be reduced.

[0082] The invention may also be defined by one or more of the following statements.Statement 1. a hot melt adhesive (1) in the form of a pellet comprising:(i) a core consisting of a hot melt adhesive pressure sensitive (2) having a softening point of 60 to 150°C, and(ii) an outer shell consisting of a coating composition comprising:(A) a thermoplastic styrenic block polymer in an amount ranging from about 30% to about 60%, by weight of the coating composition (ii), wherein the thermoplastic styrenic block polymer has a styrene content of 15 % to 50%,(B) a wax present in an amount ranging from about 20% to about 50%, by weight of the coating composition (ii),(C) a plasticizer present in an amount ranging from about 15% to about 40%, by weight of the coating composition (ii),(D) an antioxidant present in an amount ranging from about 0.2% to about 2%, by weight of the coating composition (ii),(E) optionally a slip additive present in an amount ranging from about 1% to about 10%, by weight of the coating composition (ii), and(F) tackifier in an amount ranging from 0% to 5% by weight of the coating composition, and wherein the outer shell (ii) completely coats the core (i).Statement 2. A hot melt adhesive (1) according to statement 1, wherein the thermoplastic styrenic block copolymer (A) is a partially hydrogenated thermoplastic styrenic block copolymer.Statement 3. A hot melt adhesive (1) according to statement 1, wherein the thermoplastic styrenic block copolymer (A) is a fully hydrogenated thermoplastic styrenic block copolymer.Statement 4. A hot melt adhesive (1) according to statement 1, wherein the thermoplastic styrenic block copolymer (A) is a styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene ethylene-propylene-styrene block copolymer (SEPS), SBBS (styrene- butadiene-butylene-styrene copolymer, or SIS (styrene-isoprene-styrene copolymer).Statement 5. A hot melt adhesive (1) according to statement 1, wherein the thermoplastic styrenic block copolymer (A) is a combination of two or more of styrene-ethylene- butylene-styrene block copolymer (SEBS), styrene ethylene-propylene-styrene block copolymer (SEPS), SBBS (styrene-butadiene-butylene-styrene copolymer and SIS (styrene-isoprene-styrene copolymer).Statement 6. A hot melt adhesive (1) according to statement 1, wherein the thermoplastic styrenic block copolymer (A) is a combination of styrene-ethylene-butylene-styrene block copolymer (SEBS) and at least one styrene ethylene-propylene-styrene block copolymer (SEPS), SBBS (styrene-butadiene-butylene-styrene copolymer or SIS (styrene-isoprene- styrene copolymer).Statement 7. A hot melt adhesive (1) according to statement 1, wherein the thermoplastic styrenic block copolymer (A) is a styrene-ethylene-butylene-styrene block copolymer (SEBS).Statement 8. A hot melt adhesive (1) according to any preceding statement, wherein the wax (B) is a Fischer-Tropsch wax, a polyethylene wax, a polypropylene wax, an oxidized EVA wax, or a mixture thereof.Statement 9. A hot melt adhesive (1) according to any preceding statement, wherein the wax (B) is a mixture of a Fischer-Tropsch wax and at least one other wax.Statement 10. A hot melt adhesive (1) according to any preceding statement, wherein the thermoplastic styrenic block polymer (A) is present in an amount ranging from about 20% to about 45%, by weight of the coating composition (ii).Statement 11. A hot melt adhesive (1) according to any preceding statement, wherein the wax (B) is present in an amount ranging from about 25% to about 50%, by weight of the coating composition (ii).Statement 12. A hot melt adhesive (1) according to any preceding statement, wherein the wax (B) is present in an amount ranging from about 30% to about 45%, by weight of the coating composition (ii).Statement 13. A hot melt adhesive (1) according to any preceding statement, wherein the plasticizer (C) is present in an amount ranging from about 15% to about 30%, by weight of the coating composition (ii).Statement 14. A hot melt adhesive (1) according to any preceding statement, wherein the tackifier (F) is present in an amount less than 3% by weight of the coating composition (i).Statement 15. A hot melt adhesive (1) according to any preceding statement, wherein the tackifier (F) is present in an amount less than 2% by weight of the coating composition (i).Statement 16. A hot melt adhesive (1) according to any preceding statement, wherein the tackifier (F) is present in an amount less than 1% by weight of the coating composition (i).Statement 17. A hot melt adhesive (1) according to any preceding statement, wherein the coating composition (ii) is essentially free from tackifier (F).Statement 18. A hot melt adhesive (1) according to any preceding statement, wherein the components (A), (B), (C), (D), (E) and (F) total 100% by weight of the coating composition (ii).Statement 19. A hot melt adhesive (1) according to any preceding statement, wherein the outer shell (ii) is not tacky at a temperature below 45°C.Statement 20. A hot melt adhesive (1) according to any preceding statement, wherein the hot melt adhesive pressure sensitive (2) of the core (i) is styrenic block copolymer-based, polyolefin-based, EVA-based, PLA-based, polyurenthane-based, or acrylic polymer- based.Statement 21. A hot melt adhesive (1) according to any preceding statement, wherein the pellet has one or more of the following characteristics:1) it weighs less than 10g;2) it has a diameter of less than 20 mm in any dimension;3) it has a cylindrical, spherical, or pillow-like shape; and4) it is free-flowing at a temperature below 45°C.Statement 22. A co-extrusion process for preparing a hot melt adhesive (1) as defined in any preceding statement, comprising simultaneously extruding the core (i) consisting of the hot melt adhesive pressure sensitive (2), and the coating composition such that the coating composition completely covers the core (i) to form the outer shell.Statement 23. Use of a hot melt adhesive (1) as defined in any one of statements 1 to 21 in an automated operated feeder, preferably in a vacuum operated feeder.EXAMPLES

[0083] The following illustrative embodiments provide non-limiting examples of the present invention.Test procedures

[0084] Preparation of test strips (1.1)1. Oven preheated to 180°C; Hotplate preheated to 130°C2. Sample and 250 pm squeegee heated in oven for min. 3 h or until sample is molten3. 40 x 10 cm PET-Foil placed on hotplateHeated squeegee placed on PET-Foil with 250 pm opening facing the hot surface 20 g sample filled in squeegee funnel Squeegee pulled slowly and evenly across length of the PET-Foil Squeegee removed at the end of the foil PET-Foil with coating removed from hotplate Coating cooled down for min. 5 h

[0085] Tackiness test (1.2) Coating from 1.1 cut in 5 cm wide pieces 2 pieces stacked coating sides facing Stack of 2 pieces forming 1 sample 2 samples weighed down with 1 kg rectangular metal weight covering whole samples Weighed down samples tempered at room temperature, 45 °C, 50 °C and 55 °C for 24 hours separately for each tackiness trial Weights removed from samples and cooled down at room temperature (21 °C) for minimum 3 hours Testing performed by manual separation of coatings and visual evaluation defined in 1.4

[0086] Tackiness test after oil exposure (1.3) Coating from 1.1 cut in 10 cm wide pieces Strong paper tissue soaked in Primol 352 and Nyflex 223 respectively and placed on plastic trays Coating pieces placed on oil-soaked tissue with sample side fully touching the tissue Coating pieces soaked for 24 h Coating pieces removed from oil tissues and residual oil removed with fresh paper tissues Coating pieces cut in two 5 cm pieces and stacked sample sides facing together 2 coating pieces forming 1 sample 2 samples weighed down with 1 kg rectangular metal weight covering whole samples Weighed down samples tempered at 50 °C for 3 days10. Samples cooled down at room temperature with weights removed for min 3 h11. Testing performed by manual separation of coatings and visual evaluationEvaluation of prepared samples (1.4)

[0087] Two coatings from one sample are separated manually and assessed regarding visual defects and the force which is needed to separate them. The following criteria shown in Table 1 are taken into account while evaluating the coating separation of outer shell coatings and adhesive coatings:Table 1 Evaluation Criteria of Tackiness Test (1.2) and Tackiness Test after oil exposure(1.3)

[0088] The coating compositions in Table 2 were prepared according to the test procedure above. Outer shell coating approaches which passed the Tackiness Test were considered of good quality. The viscosity, softening point, tackiness test and under influence of oil were carried out according to the procedures above.Table 2 Outer Shell Coating Formulations and Test ResultsCompatibility test

[0089] Sample 1 from the above was used to prepare pellets using various core adhesives A to F, as shown in Table 3.

[0090] Compatibility was tested by visual means. The coating was added in an amount of 5wt% relative to the weight of the pellet overall, with the remainder of the pellet i.e. 95wt% by weight of the pellet being the core adhesive. The coating and core compositions weremixed and filled in glass jars. The samples were put in the oven for 6 hours at 160°C. After 6 hours, the samples were visually assessed for compatibility, taking into consideration viscosity, phase separation and no noticeable defects, for example colour change.Table 3 Core Adhesive Compatibility TestExample B,C,D,F = Polyolefin basedExample A, E = Styrene-block-Copolymer based

[0091] Thus, it can be seen that a wide range of pellets based on different core PSAs and exhibiting good compatibility can be prepared in accordance with the present invention.Free-flowing test

[0092] Pellets were tested using the following procedure:Placing 1 kg coated pellets in an oven at 45°C for 6 hours- After this period the coated pellets are removed from the oven, cooled to ambient temperature (about 20°C) and poured into the top of a testing tube device (a perpendicular tube device with a dimension of 10 cm in diameter and 30 cm in height, the tube being closed at the bottom end of the tube) for flowing properties.Placing a weight of 2 kg on top of the bulk of coated pellets in the tube for 30 minutes.- After 30 minutes, removing the weight from the top of the coated pellets and removing the closure at the end of the tube to allow the coated pellets to flow from the bottom of the tube into a void or a bucket below the tubeMeasuring the time taken for the coated pellets to flow out of the tube at ambient temperature, (about 20°C).

[0093] Core adhesives A, C and D from Table 3 were used to prepare coated pellets using Sample 1 from Table 2 and an olefin based outer shell coating for free-flowing test, as shown in Table 4. The olefin based outer shell coating was prepared according to the disclosure in US 10,544,295 (sample E3 in Example 1).

[0094] The coated pellets were considered passing the free-flowing test if, after being aged at 45°C for 6 hours, the time taken for coated pellets to flow out of the test tube device was no more than 3 minutes.Table 4 Pellets Free-flowing Test Results

[0095] It will be appreciated that the invention may be modified within the scope of the appended claims.

Claims

CLAIMS1. A hot melt adhesive (1) in the form of a pellet comprising:(i) a core consisting of a hot melt pressure sensitive adhesive (2) having a softening point of 60 to 150°C, and(ii) an outer shell consisting of a coating composition comprising:(A) a thermoplastic styrenic block polymer in an amount ranging from about 30% to about 60%, by weight of the coating composition (ii), wherein the thermoplastic styrenic block polymer has a styrene content of 15 % to 50%,(B) a wax present in an amount ranging from about 20% to about 50%, by weight of the coating composition (ii),(C) a plasticizer present in an amount ranging from about 15% to about 40%, by weight of the coating composition (ii),(D) an antioxidant present in an amount ranging from about 0.2% to about 2%, by weight of the coating composition (ii),(E) optionally a slip additive present in an amount ranging from about 1% to about 10%, by weight of the coating composition (ii), and(F) tackifier in an amount ranging from 0% to 5% by weight of the coating composition, and wherein the outer shell (ii) completely coats the core (i).

2. A hot melt adhesive (1) according to claim 1 , wherein the thermoplastic styrenic block copolymer (A) is a partially or fully hydrogenated thermoplastic styrenic block copolymer.

3. A hot melt adhesive (1) according to claim 1 , wherein the thermoplastic styrenic block copolymer (A) is a styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene ethylene-propylene-styrene block copolymer (SEPS), SBBS (styrene-butadiene- butylene-styrene copolymer, SIS (styrene-isoprene-styrene copolymer) or a combination thereof, and is preferably a styrene-ethylene-butylene-styrene block copolymer (SEBS).

4. A hot melt adhesive (1) according to claim 1 or 2, wherein the wax (B) is a Fischer- Tropsch wax, a polyethylene wax, a polypropylene wax, an oxidized EVA wax, or a mixture thereof, preferably the wax (B) is a mixture of a Fischer-Tropsch wax and at least one other wax.

5. A hot melt adhesive (1) according to any preceding claim, wherein the thermoplastic styrenic block polymer (A) is present in an amount ranging from about 20% to about 45%, by weight of the coating composition (ii).

6. A hot melt adhesive (1) according to any preceding claim, wherein the wax (B) is present in an amount ranging from about 25% to about 50%, by weight of the coating composition (ii), preferably in an amount ranging from about 30% to about 45%, by weight of the coating composition (ii).

7. A hot melt adhesive (1) according to any preceding claim, wherein the plasticizer (C) is present in an amount ranging from about 15% to about 30%, by weight of the coating composition (ii).

8. A hot melt adhesive (1) according to any preceding claim, wherein the tackifier (F) is present in an amount less than 3% tackifier by weight of the coating composition (i), preferably in an amount less than 2%, more preferably less than 1% by weight of the coating composition (i).

9. A hot melt adhesive (1) according to any preceding claim, wherein the coating composition (ii) is essentially free from tackifier (F).

10. A hot melt adhesive (1) according to any preceding claim, wherein the components (A), (B), (C), (D), (E) and (F) total 100% by weight of the coating composition (ii).

11. A hot melt adhesive (1) according to any preceding claim, wherein the outer shell (ii) is not tacky at a temperature below 45°C.

12. A hot melt adhesive (1) according to any preceding claim, wherein the hot melt adhesive pressure sensitive (2) of the core (i) is styrenic block copolymer-based, polyolefin-based, EVA-based, PLA-based, polyurenthane-based, or acrylic polymer- based.

13. A hot melt adhesive (1) according to any preceding claim, wherein the pellet has one or more of the following characteristics:5) it weighs less than 10g;6) it has a diameter of less than 20 mm in any dimension;7) it has a cylindrical, spherical, or pillow-like shape; and8) it is free-flowing at a temperature below 45°C.

14. A co-extrusion process for preparing a hot melt adhesive (1) as defined in any preceding claim, comprising simultaneously extruding the core (i) consisting of the hot melt adhesive pressure sensitive (2), and the coating composition such that the coating composition completely covers the core (i) to form the outer shell.

15. Use of a hot melt adhesive (1) as defined in any one of claims 1 to 13 in an automated operated feeder, preferably in a vacuum operated feeder.

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