Free-flowing pellets containing pressure-sensitive adhesive

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 from 60°C to 150°C, and (ii) an outer shell consisting of a coating composition comprising: (A) a thermoplastic styrenic block polymer, wherein the styrene content of the thermoplastic styrenic block polymer is from 15% to 50%, (B) a wax in an amount of 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) a tackifier in an amount of from 0% to 5% by weight of the coating composition, and wherein the outer shell (ii) completely coats the core (i).

Description

[0001] This invention relates to hot melt adhesives provided in the form of free-flowing pellets.

[0002] Thermoplastic adhesives, particularly hot melt adhesives, can be manufactured and packaged as disclosed in EP 0469564. According to this document, the hot melt adhesive is formed into separate portions, cured, and then surrounded by a plastic packaging material. This plastic packaging material should be meltable together with the adhesive. The disclosed pillow-shaped portions range from about 100 g to about 4 kg.

[0003] To reduce the tendency of individual pillow-shaped objects to stick and adhere to each other, it is known to coat them with a release agent, as disclosed in US 5373682 and US 7328547. US 5373682 discloses a method of pumping or pouring a molten hot-melt adhesive in liquid form into a cylindrical plastic tube containing a plastic film made of low-density polyethylene or a polyethylene vinyl acetate polymer containing up to 10% by weight of vinyl acetate. The plastic tube is in the range of about 3 inches to 18 inches in length and is not free-flowing. In US 7328547, the release agent is disclosed as a film-forming material containing at least 25% wax. The adhesive can be manufactured, for example, in a co-extrusion process. The specific form of the delivered adhesive is not disclosed.

[0004] EP 0957029 discloses a method for manufacturing a coated portion of an adhesive by co-extrusion. The polymer is provided in molten form, and an external coating is applied during the extrusion process. No information is provided regarding the specific composition of the adhesive or coating material.

[0005] EP 1196509 discloses a method for forming granular hot melt adhesive. The granules are cooled to a non-sticky form. Thereafter, an adhesive material is coated with an adhesive component in liquid form, which is non-sticky as a solid material, and an outer coating is formed on the granules. The granules are disclosed to be free-flowing.

[0006] US 6238732 discloses a method for manufacturing pressure-sensitive adhesive granules, wherein the granules are coated with a coating of an anti-blocking component of the adhesive. Powders or solutions and dispersions are disclosed as components forming the coating.

[0007] US 10,544,295 discloses a non-adhesive film-forming polymer composition (covering material) and a granular viscous hot melt adhesive, the granular viscous hot melt adhesive being coated with the polymer composition and formed by co-extruding the hot melt adhesive and the covering material. The film-forming composition comprises 5% to 40% by weight of at least one Fischer-Tropsch wax with a melting point >95°C and 30% to 70% by weight of at least one metallocene-catalyzed polyolefin having a softening point >95°C and a melt flow index (MFI) (230°C, 2.16 kg) ≤1000 and ≥300 g / 10 min.

[0008] Existing technology has demonstrated the possibility of coating larger portions of hot melt adhesives with a plastic coating. Such a coating is necessary for packaging pressure-sensitive adhesives, which should provide a permanently tacky surface. Only with this non-tacky coating can the adhesive material be transported in single-part form.

[0009] The coating materials disclosed in the prior art are chosen so that they can be mixed with the adhesive without negatively affecting the adhesive properties. This is easy to apply for powder coating materials. However, for the use of parts, the coating must not be damaged during transport. If the shell is defective, the parts will adhere to each other and must be separated before further processing. Also, it has been noted that coatings made from powder adhering to the adhesive surface are unstable during transport and storage at elevated temperatures, causing the parts, lumps, or pillow-like structures to stick together. Therefore, coatings made by applying powder to the adhesive surface do not provide a truly continuous coating, and they are unstable against friction during handling and transport.

[0010] If the material is coated with a film of thermoplastic polymer, the coating offers greater stability. However, the manufacturing process is complex. As disclosed in the prior art, the packaging process involves manually operated pillow-shaped or block-shaped containers. Automated feeding of smaller portions into the melting device is not feasible.

[0011] A method for coating smaller particles using a liquid dispersion as a coating is disclosed, wherein the liquid dispersion is intended to form a solid layer on the particle surface. This imposes significant limitations on the method because only specific coating materials can be used based on the requirement of having a liquid coating as a solution or dispersion. Coating methods using dispersions in liquid form are energy-intensive. The solvent must evaporate to obtain a non-sticky surface, and parts must be moved to prevent clogging during this step.

[0012] Since the adhesive is applied manually, larger quantities are preferred. A disadvantage of this packaging method is that smaller quantities cannot be supplied to the application device. Therefore, the actual amount of adhesive melted in the melting tank to maintain a stable supply is relatively large, leading to thermal stress in the adhesive melt.

[0013] Another disadvantage of smaller packaged adhesive components is based on their form. The relationship between shell volume and core volume requires a larger amount of shell material. Therefore, the molten adhesive will contain a larger amount of film-forming material from the shell component. This can negatively impact the adhesive's performance.

[0014] Therefore, it is necessary to supply hot melt adhesives in granular form, which should be supplied in bulk and can be handled by an automated feeding system, and have improved properties in terms of better end-sealing of the granules and better prevention of oil migration in the core adhesive. Summary of the Invention

[0015] The inventors of this invention have discovered a novel coating composition that can form a protective shell to completely coat a viscous hot melt adhesive, thereby forming granules. The coating composition forms a more flexible shell than conventional polyolefin-based coatings, thus providing better end-sealing of the granules and better prevention of oil migration from the core adhesive. This invention provides a non-viscous coating composition that forms a shell via co-extrusion to protect the viscous hot melt adhesive in the core. This coating composition enables the viscous adhesive to be packaged into millimeter-sized granules (also known as chubs or microchubs) that can be vacuum-fed via an automated feeding system.

[0016] According to one aspect of the invention, a hot melt adhesive (1) in granular form is provided, comprising: (i) A core composed of a hot melt pressure-sensitive adhesive (2) with a softening point of 60°C to 150°C, and (ii) A housing composed of a coating composition comprising: (A) A thermoplastic styrene-based block polymer, comprising about 30% to about 60% by weight of the coating composition (ii), wherein the styrene content of the thermoplastic styrene-based block polymer is 15% to 50%. (B) Wax, comprising about 20% to about 50% by weight of the coating composition (ii). (C) A plasticizer, comprising about 15% to about 40% by weight of the coating composition (ii). (D) An antioxidant, comprising about 0.2% to about 2% by weight of the coating composition (ii). (E) An optional slip additive, present in an amount of about 1% to about 10% by weight of the coating composition (ii), and (F) Tackifier, comprising 0% to 5% by weight of the coating composition. and The outer shell (ii) completely coats the core (i).

[0017] According to another aspect of the invention, a co-extrusion method for preparing a hot melt adhesive (1) as defined herein is provided, comprising simultaneously extruding a core (i) composed of a hot melt pressure-sensitive adhesive and a coating composition such that the coating composition completely covers the core (i) to form the shell.

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

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

[0020] A further advantage of this invention includes a positive impact on sustainability: the method required to prepare the pellets can be modified according to the exact needs of the customer. Therefore, if a smaller batch is required, only that amount can be produced without excess.

[0021] Throughout this specification, unless otherwise stated, the softening point referred to is the softening point of the material as measured by the Mettler cup-ball method as defined in ASTM D6090. DETAILED DESCRIPTION The term "coated granules" should include granules of small size, in symmetrical or asymmetrical form, each weighing at most 10g. The dimension in any direction is less than 20mm, with a lower limit greater than 1mm. The coated granules according to the invention are free-flowing at temperatures below 45°C. It should be understood that free flow means the granule pile flows through a vertical pipe under the influence of gravity at ambient temperature. The granules flow within a reasonable timeframe, preferably without blockage, adhesion, or clogging. The temperature of the granules and the pipe are the same and equal to or below 45°C. Suitable testing procedures involve: Place 1 kg of coated granules in an oven at 45°C for 6 hours.

[0023] After this period, the coated granules are removed from the oven, cooled to ambient temperature (approximately 20°C), and poured into the top of a test tube device (a vertical tube device with a diameter of 10 cm and a height of 30 cm, which is closed at the bottom) to test flow performance.

[0024] Place a 2kg weight on top of the coated pellet pile in the tube for 30 minutes.

[0025] After 30 minutes, remove the weight from the top of the coated granules and remove the closure at the end of the tube to allow the coated granules to flow out from the bottom of the tube and into the gap or bucket below the tube.

[0026] Measure the time required for the coated granules to flow out of the tube at ambient temperature (approximately 20°C).

[0027] If, after aging at 45°C for 6 hours, the time required for the coated granules to flow out of the test tube device does not exceed 3 minutes, preferably not more than 2 minutes, and more preferably not more than 1 minute, then the coated granules are considered to have passed the free flow test.

[0028] Thermoplastic styrenic block polymers Component (A) in the coating composition is a thermoplastic styrene-based block polymer, and its content is about 30% to about 60% by weight of the coating composition (ii), wherein the styrene content of the thermoplastic styrene-based block polymer is 15% to 50%.

[0029] The inventors have surprisingly discovered that coatings incorporating thermoplastic styrene-based block polymers with a defined styrene content completely coat the core adhesive and exhibit advantageous properties as defined herein, such as forming a more flexible yet non-sticky shell when applied to the core adhesive. The styrene content is 15% to 50%, preferably 20% to 45%, more preferably 25% to 45%, and most preferably 30% to 45%.

[0030] A variety of suitable thermoplastic materials that meet the above requirements can be used in the coating composition. Examples include styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), styrene-butadiene-butene-styrene (SBBS) (i.e., partially hydrogenated styrene-butadiene-styrene copolymer), styrene-(ethylene-butene)-styrene (SEBS), styrene-(ethylene-propylene)-styrene (SEPS), and styrene-block-isobutylene-block-styrene (SIBS). These polymers can be used alone or as mixtures thereof.

[0031] Preferably, the thermoplastic styrene block copolymer in the coating composition is a partially or fully hydrogenated styrene block copolymer, or a mixture thereof. Preferably, the thermoplastic styrene block polymer (A) is fully hydrogenated. Most preferably, it is SEBS.

[0032] Suitable polymers are available from companies such as Kraton polymers, TSRC Corporation, Versalis SpA, LCYElastomers LP and Ningbo Jinhai Chenguang Chemical Corporation.

[0033] Typical SIS levels 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.

[0034] Typical SEBS ratings include: - Kraton G1652 (29% styrene), Kraton G1726 (30% styrene, 70% diblock), from Kraton. - Globalprene 9550 (30% styrene), Globalprene 9552 (30% styrene), from LCY.

[0035] Typical SBBS levels include: - Tuftec P1500 (30% styrene), from Asahi.

[0036] Waxes Component (B) in the coating composition is wax, and its content is from about 20% to about 50% by weight of the coating composition (ii).

[0037] Waxes can be of natural or synthetic origin. Suitable natural waxes are plant waxes, animal waxes, mineral waxes, or petrochemical waxes. Suitable chemically modified waxes are hard waxes, such as montan ester waxes, sasolwaxes, 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 polyolefin waxes and polyethylene glycol waxes. Preferred waxes are polyolefin waxes, such as petrolatum, microcrystalline waxes, and synthetic waxes, particularly polyethylene waxes, polypropylene waxes, optional PE or PP copolymers, Fischer-Tropsch resins, paraffin wax, or microcrystalline waxes. Available Fischer-Tropsch waxes include H1 wax and Seration 1820 wax from Sasol, and polyolefin waxes include polyethylene waxes such as Licocene 4201 and Licocene 3101 from Clariant, Polywax 1000 from NUCERA, AC8 and AC9 from Honeywell, and LC 103NC and 104NC from LION Chemical.

[0038] Preferably, wax component (B) is at least one Fischer-Tropsch wax; and / or a polyethylene wax. Wax component (B) may be at least one Fischer-Tropsch wax; and / or a polyethylene wax and at least one other wax (a wax that is not a Fischer-Tropsch wax or a polyethylene wax). Fischer-Tropsch waxes suitably have a DSC melting peak of about 80°C–110°C, measured according to ASTM 3418 at a heating rate of 10°C / min. Polyethylene waxes suitably have a DSC melting peak of about 115°C–130°C, measured according to ASTM 3418 at a heating rate of 10°C / min.

[0039] Preferably, wax component (B) comprises at least one FT wax, and optionally at least one other wax, preferably a polyethylene wax.

[0040] Plasticizers Component (C) in the coating composition is a plasticizer, and its content is about 15% to about 40% of the weight of the coating composition (ii).

[0041] Suitable plasticizers include pharmaceutical white oil, naphthenic mineral oil, phthalates, adipates, polypropylene, polybutene, polyisoprene oligomers, hydrogenated polyisoprene and / or polybutene oligomers, benzoates, vegetable or animal oils and their derivatives.

[0042] Further examples of plasticizers include hydrogenated plasticizers such as oils or oligomers of polybutene. Additionally, mono- or polyols with molecular weights from 1000 g / mol to 6000 g / mol, such as polyalkylene glycols, can also be used. Another class of suitable plasticizers are esters, including, for example, liquid polyesters and glyceryl esters, such as glyceryl diacetate and glyceryl triacetate, as well as neopentyl glycol dibenzoate, glyceryl tribenzoate, pentaerythritol tetrabenzoate, and 1,4-cyclohexanedimethyl dibenzoate. Plasticizers based on aromatic dicarboxylic acid esters, such as esters of phthalic acid, isophthalic acid, or terephthalic acid, can also be used. Esters of sulfonic acids can also be used as plasticizers. Fatty acids are also suitable plasticizers. These components are commercially available.

[0043] Antioxidants Component (D) in the coating composition is an antioxidant, and its content is about 0.2% to about 2% by weight of the coating composition (ii).

[0044] Suitable antioxidants include phosphites, phenols, high molecular weight sterically hindered phenols, polyfunctional phenols, and sulfur- and phosphorus-containing phenols. Suitable compounds in the context of this invention include, for example, hydroquinone, hydroquinone monomethyl ether, or phenothiazine. Their selection and properties are known to those skilled in the art.

[0045] Slip additives Component (E) in the coating composition is a slip additive, and is optional. When present, the slip additive (E) is present in an amount of about 1% to about 10% by weight of the coating composition (ii). In an optional embodiment, the slip additive (E) is not present in the coating composition (ii). When present, the slip additive is different from wax (B).

[0046] Slip additives are used to reduce friction between shell coating surfaces. This also improves the free-flowing ability of the granules. Fatty acid amides, including their primary and secondary amides, are most commonly used. Specifically, unsaturated fatty acid amides such as erucamide and oleamide are preferred slip additives for shell coatings. Available slip additives include Erucamide, Crodamide E, Crodamide ER, Crodamide VRX, Crodamide OR, Crodamide BR, and Crodamide SR from CRODA Polymer Additives.

[0047] Tackifiers Component (F) in the coating composition is a tackifier, and is optional. When present, component (F) is a tackifier, and its content is greater than 0% to 5% by weight of the coating composition.

[0048] The inventors have surprisingly discovered that the coating composition does not need to contain any tackifier, and is advantageously substantially free of tackifier. In this document, “substantially free of tackifier” means that the tackifier content in the coating composition is 0% of the weight of the coating composition, or that the tackifier content in the coating composition is at most 0.5% by weight, preferably at most 0.2% by weight. In the context of this invention, those skilled in the art will understand that the core (i) as defined herein may contain a tackifier, and that the coating composition (ii) is substantially free of tackifier.

[0049] When present, the tackifying resins used in the adhesive materials of the present invention include natural and modified resins, polyterpene resins, phenol-modified hydrocarbon resins, aliphatic and aromatic hydrocarbon resins, hydrogenated hydrocarbons, hydrogenated resins, and hydrogenated rosin esters and rosin.

[0050] Examples of rosin and its derivatives include wood rosin, tall oil, rosin, rosin gum, wood rosin, rosin ester resins (including their ester, hydrogenated or dehydrogenated forms); terpene resins including, for example, natural and synthetic terpenes, polyterpenes and terpene esters; aromatic or mixed aliphatic-aromatic tackifying resins, such as polymers derived from cyclopentadiene and dicyclopentadiene; styrene resins, such as copolymers of styrene, α-methylstyrene, vinyltoluene, methoxystyrene, tert-butylstyrene, and chlorostyrene; aliphatic resins derived from monomers 1,3-butadiene, cis-1,3-pentadiene, trans-1,3-pentadiene, 2-methyl-1,3-butadiene, 2-methyl-2-butene and other copolymerizable monomers, or aliphatic petroleum hydrocarbon resins.

[0051] Therefore, the coating composition can be advantageously formulated and used to form a shell on a nuclear adhesive.

[0052] The outer shell of the granules is made of the coating composition defined herein and is preferably non-sticky at an ambient temperature of 25°C, preferably at up to 45°C. The stickiness is evaluated using the stickiness test detailed in the Examples section.

[0053] The melting point of the coating composition is preferably 130°C to 160°C, more preferably 140°C to 160°C.

[0054] The coating composition of the shell and the PSA of the core are compatible. Therefore, they form a homogeneous mixture that is stable as a melt. Typically, the softening point of the coating composition (ii) is equal to or higher than the melting point of the binder material of the core (i).

[0055] The viscosity of the shell coating composition at 180°C is from about 1,500 to about 5,000 cps, as measured according to ASTM 3236-88 (Standard Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials).

[0056] Nuclei (i) The granules defined herein include a core consisting of a hot melt pressure-sensitive adhesive (2) with a softening point typically between 60°C and 150°C. PSA-type hot melt adhesives are generally known to those skilled in the art, such as those based on styrene block copolymers as disclosed in EP0451920 or EP 1493794, acrylate-type adhesives according to WO 02 / 010307, ​​polyolefin-type adhesives according to DE19944225, and EVA-type adhesives disclosed in DE 102006054196.

[0057] Suitablely, the core (i) comprises at least one suitable polymer as the base polymer. For example, the base polymer may be a thermoplastic polymer, such as a styrene-based block copolymer, including hydrogenated, unhydrogenated, and partially hydrogenated copolymers, including SIS, SBS, SEBS, SEPS, SBBS, SIBS, etc.; metallocene-catalyzed polyolefin copolymers, such as polyethylene, polypropylene, polybutene, and copolymers thereof; Ziegler-Natta-catalyzed amorphous poly-α-olefins (APAO), such as atactic propylene and copolymers of propylene with ethylene, butene, hexane, and octane, or homopolymers or copolymers of ethylene or propylene and mixtures thereof; ethylene-vinyl acetate copolymers; acrylates, alkyl acrylates, or alkyl methacrylates (e.g., ethyl acrylate, ethyl methacrylate, ethyl n-butyl acrylate, butyl acrylate, butyl methacrylate, and combinations thereof); thermoplastic polyesters; thermoplastic polyamides; thermoplastic polyurethanes; and combinations thereof.

[0058] The hot melt pressure-sensitive adhesive core (i) may also include one or more of waxes, tackifiers, plasticizers, and oils. Specific ingredients may be selected from those described above with respect to the housing (ii), as well as ingredients well known from these functional categories.

[0059] It is apparent from this disclosure that the properties of the hot-melt pressure-sensitive adhesive (2) of the core (i) are not limited thereto, and the formulation and preparation of such adhesive, based on the desired performance of the entire adhesive granule, are entirely within the scope of common knowledge to those skilled in the art. For example, the core may include (in addition to the base polymer) waxes, tackifiers, plasticizers, and oils. Optionally, the core may also include (in addition to the base polymer) waxes, tackifiers, and plasticizers. Optionally, the core may also include (in addition to the base polymer) tackifiers and oils. Optionally, the core may also include (in addition to the base polymer) tackifiers.

[0060] Any suitable thickener commonly used in the preparation of PSA can be incorporated into the nuclear PSA binder. See Donatas Satas's "Handbook of Pressure Sensitive Adhesive Technology" (Van Nostrand, 1989) or any other PSA-related literature for a description of the prior art.

[0061] In addition, other typical auxiliaries and additives can be incorporated into suitable PSA materials. Examples include stabilizers, light stabilizers, and / or adhesion promoters. Their function is to prevent the polymer from decomposing during processing, storage, or use. Their selection and properties are known to those skilled in the art. They are typically added to the adhesive material in amounts of up to 3% by weight, preferably about 0.1 to 2% by weight. The adhesive composition may also contain other compatible polymers, fillers, pigments, dyes, oils, fragrances, and other conventional additives.

[0062] The adhesive of the core (i) is a hot-melt pressure-sensitive adhesive. Such adhesives retain the ability to form a usable bond with the substrate under slight pressure at room temperature. More specifically, such reactive or non-reactive adhesive compositions exhibit cold flow when pressed with a finger at room temperature.

[0063] Pellets Select a coating composition to form a coating or film with a non-sticky surface and to create a barrier against the environment.

[0064] As disclosed herein, the outer shell of the pellets is made of a different polymer composition than the PSA material in the core. The thickness of the outer shell should be about 2 to 200 µm, preferably 10 to 100 µm, and particularly greater than 20 µm. This depends on the size of the pellets.

[0065] If the amount of coating composition is too large relative to the amount of PSA in the core, the adhesive performance will be reduced. In other words, the core of the granules is formulated as a PSA so that the granules are ultimately used as a PSA. When the shell has the thickness described above, the granules themselves can be used as a PSA because the granules exhibit the PSA properties of the core composition. If the shell does not cover the entire surface or is too thin, the stability of the flow properties of the adhesive granules cannot be guaranteed. The amount of coating composition is typically up to 12% by weight, preferably about 1% to 10% by weight relative to the weight of the granules.

[0066] 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. This coating can be achieved by heating the coating composition above its melting temperature. This can be done by applying a powder material and then heating the powder material above the melting temperature of the coating after coating, or preferably by co-extrusion and applying the coating composition as a melt.

[0067] The pellets of the present invention suitably have one or more of the following characteristics: 1) Its weight is less than 10g; 2) Its diameter in any dimension is less than 20mm; 3) It has a cylindrical, spherical, or pillow-like shape; and 4) It flows freely at temperatures below 45°C.

[0068] The lower limit of the diameter in any dimension is preferably greater than 1 mm, and more preferably greater than 3 mm.

[0069] The shape of the granules can vary depending on the manufacturing method. They can be in the form of small pillows or microchubs, spheres such as balls, or cylinders. In this case, the dimensions differ in each direction, for example, 20 mm in one direction and 2 to 10 mm in diameter in another. The shape of the granules does not need to be regular; for example, spheres can be compressed or stretched, and rods can be symmetrical or have irregular shapes, as long as the particle size is not too large. The shape will be affected by the manufacturing method, such as extruding, cutting, and separating the granules to give a partially circular shape. It is possible, but not preferred, to mix granules of different shapes and sizes.

[0070] The weight of each pellet can be less than 8 g, and appropriately less than 5 g. Smaller particle size increases the flow properties of the material.

[0071] The granules according to the invention exhibit free-flow properties at temperatures up to 45°C. The test procedure is as defined above.

[0072] A preferred method for preparing the granules as defined herein is co-extrusion. In this co-extrusion method, the core binder to be packaged is melt-blended in a mixer and then extruded or extruded through an orifice of appropriate size in a die while still at a temperature above or very close to the softening point of the binder material. The orifice and die can be of any conventional construction and typically provide a slit-like or cylindrical structure as the binder composition is pumped through the orifice. The temperature of the die must be maintained above the melting point of the core binder composition and is typically in the range of 100°C to 150°C. In co-extrusion, a coating composition for the shell is then simultaneously extruded from the die to surround the core binder to be packaged, thereby forming a shell that completely surrounds the binder to be packaged. Co-extrusion technology is well known in the art, and suitable equipment for co-extrusion methods is known to those skilled in the art.

[0073] As is known, co-extrusion methods are typically carried out underwater or immediately immersed in water because the material is extruded at elevated temperatures, allowing the core binder and the coating composition surrounding the core binder to begin cooling immediately after being extruded from the die. Subsequently, the core binder, coated with the coating composition, is cooled in a water bath or in a cooling medium such as chilled glycol, liquid nitrogen, compressed carbon dioxide, or under ambient conditions, ensuring the coated binder is sufficiently cooled for processing. The coated binder is preferably mechanically kneaded into pellets of the desired size, shape, or weight after cooling to a more solid form. In this method, the separation step must also completely cover the cut cross-section of the pellets with the coating. Therefore, the temperature of the pellets in this step must be selected so that the coating composition can still be stretched and cover the entire surface. Otherwise, the long-term stability of the pellet's flow properties cannot be guaranteed.

[0074] Granules can also be produced by co-extrusion, whereby the softening point of the coating composition is higher than or equal to that of the core binder.

[0075] Very small amounts of anti-blocking additives, such as micronized FT wax or micronized PE wax, may optionally be further added to the coated granules after cooling to enhance the lubricity and flow behavior of the granules. 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 µm, preferably less than 20 µm.

[0076] The granules can be further packaged in containers, boxes, or bags for transport after cooling. The containers can be made of mechanically stable materials to handle large quantities of such granules.

[0077] The granules can be supplied in bulk, for example, as containers or as supersac bags. The contents of the containers can be discharged at the processing site by known methods. After discharge, the granules can be transported by known means, such as screw conveyors, belt conveyors, and other systems. Preferably, the granules can be transported by pressurized gas such as air or by vacuum, for example, in a vacuum feeder system. In this processing, mechanical friction is provided to the surface of the granules. Therefore, the transport of granules according to the invention can be carried out without blockage or granule sticking in the transport system.

[0078] Use This invention defines a hot melt adhesive (1) in the form of coated granules. This adhesive is used as a pressure-sensitive adhesive; the pressure-sensitive properties of the granules are derived from the pressure-sensitive properties of the core adhesive.

[0079] Another aspect of the invention is the use of coated granules, as defined herein, in the automated supply operation of an application device. During further processing at the customer site, a portion of material can be discharged from a packaging container and transported to a melting device. This transport can be carried out using known devices, preferably a vacuum feeder. In the melting tank, the material in the granules is melted and can be pumped to the application device, such as a nozzle or roller.

[0080] Because each granule has a small volume, the binder can be fed into the melting unit in smaller portions. Therefore, an automated feeder system is possible even when only a small amount of binder granules needs to be processed in the melting tank. Manual feeding of the melting tank is unnecessary. The amount of binder can be easily measured using known methods and apparatus. Feeding only small amounts of granules into the melting tank accelerates the melting process. Inventory of molten material can be reduced. Therefore, the degradation of the binder during the melting process can be minimized.

[0081] The present invention may also be defined by one or more of the following statements.

[0082] Statement 1, a hot melt adhesive in granular form (1), comprising: (i) A core composed of a hot melt pressure-sensitive adhesive (2) with a softening point of 60°C to 150°C, and (ii) A housing composed of a coating composition comprising: (A) A thermoplastic styrene-based block polymer, comprising about 30% to about 60% by weight of the coating composition (ii), wherein the styrene content of the thermoplastic styrene-based block polymer is 15% to 50%. (B) Wax, comprising about 20% to about 50% by weight of the coating composition (ii). (C) A plasticizer, comprising about 15% to about 40% by weight of the coating composition (ii). (D) An antioxidant, comprising about 0.2% to about 2% by weight of the coating composition (ii). (E) An optional slip additive, present in an amount of about 1% to about 10% by weight of the coating composition (ii), and (F) Tackifier, comprising 0% to 5% by weight of the coating composition. and The outer shell (ii) completely coats the core (i).

[0083] Statement 2, the hot melt adhesive (1) according to Statement 1, wherein the thermoplastic styrene block copolymer (A) is a partially hydrogenated thermoplastic styrene block copolymer.

[0084] Statement 3, the hot melt adhesive (1) according to Statement 1, wherein the thermoplastic styrene block copolymer (A) is a fully hydrogenated thermoplastic styrene block copolymer.

[0085] Statement 4. The hot melt adhesive (1) according to Statement 1, wherein the thermoplastic styrene block copolymer (A) is styrene-ethylene-butene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), SBBS (styrene-butadiene-butene-styrene copolymer) or SIS (styrene-isoprene-styrene copolymer).

[0086] Statement 5, the hot melt adhesive (1) according to Statement 1, wherein the thermoplastic styrene block copolymer (A) is a combination of two or more of styrene-ethylene-butene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), SBBS (styrene-butadiene-butene-styrene copolymer) and SIS (styrene-isoprene-styrene copolymer).

[0087] Statement 6. The hot melt adhesive (1) according to Statement 1, wherein the thermoplastic styrene block copolymer (A) is a combination of at least one of styrene-ethylene-butene-styrene block copolymer (SEBS) and styrene-ethylene-propylene-styrene block copolymer (SEPS), SBBS (styrene-butadiene-butene-styrene copolymer) or SIS (styrene-isoprene-styrene copolymer).

[0088] Statement 7. The hot melt adhesive (1) according to Statement 1, wherein the thermoplastic styrene block copolymer (A) is a styrene-ethylene-butene-styrene block copolymer (SEBS).

[0089] Statement 8. The hot melt adhesive (1) according to any of the preceding statements, wherein the wax (B) is Fischer-Tropsch wax, polyethylene wax, polypropylene wax, oxidized EVA wax or a mixture thereof.

[0090] Statement 9. The hot melt adhesive (1) according to any of the preceding statements, wherein the wax (B) is a mixture of Fischer-Tropsch wax and at least one other wax.

[0091] Statement 10: The hot melt adhesive (1) according to any of the preceding statements, wherein the content of the thermoplastic styrene block polymer (A) is about 20% to about 45% by weight of the coating composition (ii).

[0092] Statement 11: The hot melt adhesive (1) according to any of the preceding statements, wherein the content of said wax (B) is about 25% to about 50% of the weight of said coating composition (ii).

[0093] Statement 12, the hot melt adhesive (1) according to any of the preceding statements, wherein the content of said wax (B) is about 30% to about 45% by weight of said coating composition (ii).

[0094] Statement 13, the hot melt adhesive (1) according to any of the preceding statements, wherein the content of said plasticizer (C) is about 15% to about 30% by weight of said coating composition (ii).

[0095] Statement 14. The hot melt adhesive (1) according to any of the preceding statements, wherein the content of the tackifier (F) is less than 3% by weight of the coating composition (i).

[0096] Statement 15: The hot melt adhesive (1) according to any of the preceding statements, wherein the content of the tackifier (F) is less than 2% by weight of the coating composition (i).

[0097] Statement 16. The hot melt adhesive (1) according to any of the preceding statements, wherein the content of the tackifier (F) is less than 1% by weight of the coating composition (i).

[0098] Statement 17. The hot melt adhesive (1) according to any of the preceding statements, wherein the coating composition (ii) is substantially free of tackifier (F).

[0099] Statement 18. A hot melt adhesive (1) according to any of the preceding statements, wherein components (A), (B), (C), (D), (E) and (F) total 100% by weight of the coating composition (ii).

[0100] Statement 19. The hot melt adhesive (1) according to any of the preceding statements, wherein the housing (ii) is non-sticky at temperatures below 45°C.

[0101] Statement 20: The hot melt adhesive (1) according to any of the preceding statements, wherein the hot melt pressure-sensitive adhesive (2) of the core (i) is based on a styrene block copolymer, a polyolefin, an EVA, a PLA, a polyurethane, or an acrylic polymer.

[0102] Statement 21. The hot melt adhesive (1) according to any of the foregoing statements, wherein the granules have one or more of the following characteristics: 1) Its weight is less than 10g; 2) Its diameter in any dimension is less than 20mm; 3) It has a cylindrical, spherical, or cushion-shaped form; and 4) It flows freely at temperatures below 45°C.

[0103] Statement 22. A co-extrusion method for preparing a hot melt adhesive (1) as defined in any of the preceding statements, comprising simultaneously extruding a core (i) composed of a hot melt pressure-sensitive adhesive (2) and a coating composition such that the coating composition completely covers the core (i) to form the shell.

[0104] Statement 23, Use of the hot melt adhesive (1) as defined in any one of Statements 1 to 21 in an automatically operated feeder, preferably in a vacuum-operated feeder.

[0105] Examples The following exemplary embodiments provide non-limiting examples of the present invention.

[0106] Test procedures Preparation of test strips (1.1) 1. Preheat the oven to 180°C; preheat the hot plate to 130°C.

[0107] 2. Heat the sample and 250 µm scraper in an oven for at least 3 hours or until the sample melts.

[0108] 3. Place the 40 × 10 cm PET film on the hot plate.

[0109] 4. Place the heated squeegee on the PET film with the 250 µm opening facing the heated surface.

[0110] 5. Fill the 20g sample into the scraper funnel.

[0111] 6. Slowly and evenly pull the scraper along the length of the PET film.

[0112] 7. Remove the scraper at the end of the membrane.

[0113] 8. Remove the coated PET film from the hot plate.

[0114] 9. Allow the coating to cool for at least 5 hours.

[0115] Viscosity test (1.2) 1. Cut the coating from 1.1 into 5 cm wide slices.

[0116] 2. Stack the two pieces together with the coated sides facing each other.

[0117] 3. Stack the two pieces together to form a sample.

[0118] 4. Press down on the two samples with a 1 kg rectangular metal weight that covers the entire sample.

[0119] 5. The compressed samples were each conditioned for 24 hours at room temperature, 45°C, 50°C, and 55°C for each viscosity test.

[0120] 6. Remove the weights from the sample and allow it to cool at room temperature (21°C) for at least 3 hours.

[0121] 7. Testing is performed by manually separating the coating and visually evaluating it, as defined in 1.4.

[0122] Viscosity test of oil after exposure (1.3) 1. Cut the coating from 1.1 into 10 cm wide slices.

[0123] 2. Soak the tough paper towels in Primol 352 and Nyflex 223 respectively, and place them on a plastic tray.

[0124] 3. Place the coated sheet on an oil-soaked paper towel, ensuring the sample side is fully in contact with the paper towel.

[0125] 4. Soak the coated sheet for 24 hours.

[0126] 5. Remove the coated sheet from the oiled paper towel and wipe away any remaining oil with a fresh paper towel.

[0127] 6. Cut the coated sheet into two 5 cm pieces and stack them with the sample sides facing each other.

[0128] 7. Combine the two coated sheets to form a sample.

[0129] 8. Press down on the two samples with a 1 kg rectangular metal weight that covers the entire sample.

[0130] 9. The compressed sample was conditioned at 50°C for 3 days.

[0131] 10. Remove the weights and allow the sample to cool at room temperature for at least 3 hours.

[0132] 11. Test by manually separating the coating and performing a visual evaluation.

[0133] Evaluation of prepared samples (1.4) The two coatings from a single sample were manually separated, and visual defects and the force required to separate them were evaluated. When evaluating the separation of the housing coating and the adhesive coating, the following criteria shown in Table 1 were considered: Table 1 Evaluation criteria for viscosity test (1.2) and viscosity test after oil exposure (1.3)

[0134] The coating compositions in Table 2 were prepared according to the test procedures described above. Shell coating methods that pass the viscosity test are considered of good quality. Viscosity, softening point, viscosity tests, and tests under the influence of oil were performed according to the procedures described above.

[0135] Table 2. Shell Coating Formulation and Test Results

[0136] Compatibility testing Using Sample 1 from above, granules were prepared with various core binders A to F, as shown in Table 3.

[0137] Compatibility was tested visually. The coating was added at 5% by weight relative to the total weight of the granules, with the remaining 95% by weight of the granules serving as the core binder. The coating and core composition were mixed and placed in glass jars. The samples were placed in an oven at 160°C for 6 hours. After 6 hours, the compatibility of the samples was visually evaluated, taking into account viscosity, phase separation, and the absence of obvious defects such as color change.

[0138] Table 3. Nuclear adhesive compatibility test

[0139] Examples B, C, D, and F = Based on polyolefins Examples A and E = Based on styrene block copolymers Therefore, it can be seen that a wide range of granules based on different nuclear PSAs and exhibiting good compatibility can be prepared according to the present invention.

[0140] Free flow test Use the following procedure to test the pellets: - Place 1 kg of coated granules in an oven at 45°C for 6 hours.

[0141] - After this period, the coated granules are removed from the oven, cooled to ambient temperature (approximately 20°C), and poured into the top of a test tube device (a vertical tube device with a diameter of 10 cm and a height of 30 cm, which is closed at the bottom) to test flow performance.

[0142] - Place a 2 kg weight on top of the coated pellet pile in the tube for 30 minutes.

[0143] - After 30 minutes, remove the weight from the top of the coated granules and remove the closure at the end of the tube to allow the coated granules to flow out from the bottom of the tube and into the gap or bucket below the tube.

[0144] - Measure the time required for the coated granules to flow out of the tube at ambient temperature (approximately 20°C).

[0145] Coated granules were prepared using the core binders A, C, and D from Table 3. Free-flow tests were performed using Sample 1 from Table 2 and the olefin-based shell coating, as shown in Table 4. The olefin-based shell coating was prepared according to the disclosure in US 10,544,295 (Sample E3 in Example 1).

[0146] If the coated granules are aged at 45°C for 6 hours and the time required for them to flow out of the test tube device does not exceed 3 minutes, then the coated granules are considered to have passed the free flow test.

[0147] Table 4 Results of Granule Free Flow Test

[0148] It should be understood that the present invention can be modified within the scope of the appended claims.

Claims

1. A hot melt adhesive in granular form (1), comprising: (i) A core composed of a hot melt pressure-sensitive adhesive (2) with a softening point of 60°C to 150°C, and (ii) A housing composed of a coating composition comprising: (A) A thermoplastic styrene-based block polymer, comprising about 30% to about 60% by weight of the coating composition (ii), wherein the styrene content of the thermoplastic styrene-based block polymer is 15% to 50%. (B) Wax, comprising about 20% to about 50% by weight of the coating composition (ii). (C) A plasticizer, comprising about 15% to about 40% by weight of the coating composition (ii). (D) An antioxidant, comprising about 0.2% to about 2% by weight of the coating composition (ii). (E) An optional slip additive, present in an amount of about 1% to about 10% by weight of the coating composition (ii), and (F) Tackifier, comprising 0% to 5% by weight of the coating composition. and The outer shell (ii) completely coats the core (i).

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

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

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

5. The hot melt adhesive (1) according to any one of the preceding claims, wherein the content of the thermoplastic styrene block polymer (A) is about 20% to about 45% by weight of the coating composition (ii).

6. The hot melt adhesive (1) according to any one of the preceding claims, wherein the content of said wax (B) is about 25% to about 50% by weight of said coating composition (ii), preferably about 30% to about 45% by weight of said coating composition (ii).

7. The hot melt adhesive (1) according to any one of the preceding claims, wherein the content of said plasticizer (C) is about 15% to about 30% by weight of said coating composition (ii).

8. The hot melt adhesive (1) according to any one of the preceding claims, wherein the content of the tackifier (F) is less than 3% by weight of the coating composition (i), preferably less than 2% by weight of the coating composition (i), and more preferably less than 1%.

9. The hot melt adhesive (1) according to any one of the preceding claims, wherein the coating composition (ii) is substantially free of tackifier (F).

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

11. The hot melt adhesive (1) according to any of the preceding claims, wherein the housing (ii) is non-sticky at temperatures below 45°C.

12. The hot melt adhesive (1) according to any one of the preceding claims, wherein the hot melt pressure-sensitive adhesive (2) of the core (i) is based on a styrene block copolymer, a polyolefin, an EVA, a PLA, a polyurethane, or an acrylic polymer.

13. The hot melt adhesive (1) according to any one of the preceding claims, wherein the granules have one or more of the following characteristics: 5) Its weight is less than 10g; 6) Its diameter in any dimension is less than 20mm; 7) It has a cylindrical, spherical, or cushion-shaped form; and 8) It is free-flowing at temperatures below 45°C.

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

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

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