Ethylene-vinyl acetate copolymer pellet

Abstract

To provide ethylene-vinyl acetate copolymer pellets having reduced blocking and bridging that arise during production, transportation, processing, and storage.SOLUTION: Pellets are composed of a resin composition containing a lubricant and an ethylene-vinyl acetate copolymer, in which the melt flow rate is 1500 g / 10 min or more as measured at 190°C under a load of 21.18 N in accordance with JIS K6924-1, and the vinyl acetate content is 25 mass% or more as measured in accordance with JIS K6924-1. The pellets have silicone adhered to their surfaces.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to ethylene-vinyl acetate copolymer pellets and a method for producing the same. [Background technology]

[0002] Ethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated as EVA), especially EVA with a high content of constituent units derived from vinyl acetate (hereinafter sometimes abbreviated as VAc content), has a low softening point and is therefore often used as the main raw material for hot melt adhesives. Hot melt adhesives are used in increasing amounts year by year because they have a short hardening time after application and are solvent-free.

[0003] However, in the case of EVA with a high vinyl acetate content, due to its low softening point, pellets are prone to sticking together, i.e., blocking, even at around room temperature. This blocking can reduce productivity during the pellet manufacturing process and during pellet storage. For example, during the pellet manufacturing stage, pellets may stick to each other or to the manufacturing equipment, making stable production impossible. In addition, when molding using pellets, pellets may stick together inside the hopper, forming clumps that make it difficult to remove them from inside the hopper (bridging). Furthermore, when pellets are stored, they may form clumps that make it impossible to remove them from the packaging, hindering stable production.

[0004] As a method for improving such bridging and blocking of pellets, a method of coating the surface of pellets with inorganic substances such as talc and silica, polyolefin fine powder, polyethylene wax, and their dispersions or surfactants, a method of adding higher fatty acids to the pellets, and the like have been proposed. These methods include a method of coating pellets with an aqueous slurry of polyolefin fine powder (see, for example, Patent Document 1), a method of coating pellets with a surfactant (see, for example, Patent Document 2), a method of mixing higher fatty acids or their salts with pellets (see, for example, Patent Document 3), and a method of adding an additive selected from the group consisting of N,N'-ethylenebisoleamide, N,N'-ethylenebiserucamide, N,N'-diersyladipimide, and N,N'-dioleyldipimide (see, for example, Patent Document 4). However, the method of Patent Document 1 has a problem that during storage of resin pellets with a low softening point, the powder is buried, causing blocking, and depending on the amount of adhesion, the physical properties of the resin are deteriorated. The method proposed in Patent Document 2 had a problem that blocking occurred during storage because the coating peeled off when the pellets came into contact with walls during air transport or packaging. The methods proposed in Patent Documents 3 and 4 had a problem that the bleeding speed of the additive was insufficient, so the obtained pellets had low slip properties and were poor in preventing bridging. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 3,528,841 [Patent Document 2] JP 2002-293946 A [Patent Document 3] Japanese Patent Application Publication No. 56-136347 [Patent Document 4] Japanese Patent Application Publication No. 57-200434 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide EVA pellets which are suppressed from undergoing blocking and bridging during production, transportation, processing and storage. [Means for solving the problem]

[0007] As a result of intensive research aimed at solving the above-mentioned problems, the inventors have discovered that pellets made of a resin composition containing a lubricant and an ethylene-vinyl acetate copolymer having specific properties, and having silicone adhered to the surface, can suppress blocking and bridging that occurs during production, transportation, processing, and storage, and have thus completed the present invention.

[0008] That is, the embodiments of the present invention are as follows [1] to [5]. [1] A pellet comprising a resin composition containing a lubricant and an ethylene-vinyl acetate copolymer having a melt flow rate (hereinafter referred to as MFR) of 1,500 g / 10 min or more, measured according to JIS K6924-1 at 190°C and a load of 21.18 N, and a vinyl acetate content of 25% by mass or more, measured according to JIS K6924-1, and having silicone adhered to the surface. [2] The pellet according to the above [1], wherein the lubricant is at least one selected from the group consisting of fatty acid amides, fatty acid esters, fatty acid triglycerides, waxes and fatty alcohols. [3] The pellet according to the above [1] or [2], wherein the amount of the lubricant blended is 0.1% by mass or more and 1% by mass or less in the ethylene-vinyl acetate copolymer pellet. [4] The pellet according to any one of the above [1] to [3], wherein the amount of the silicone attached is from 0.001% by mass to 0.1% by mass. [5] A method for producing resin pellets according to any one of the above [1] to [4], comprising the steps of melting a resin composition comprising a lubricant and an ethylene-vinyl acetate copolymer having a melt flow rate of at least 1500 g / 10 min, as measured in accordance with JIS K6924-1 at a temperature of 190°C under a load of 21.18 N, and having a vinyl acetate content of at least 25 mass %, as measured in accordance with JIS K6924-1, and extruding the resin composition from an extruder, and cutting the extruded molten resin composition into pellets while cooling it with cooling water containing silicone. Effect of the Invention

[0009] The ethylene-vinyl acetate copolymer pellets according to one embodiment of the present invention can suppress blocking and bridging that occurs during production, transportation, processing, and storage. [Brief description of the drawings]

[0010] [Figure 1] 1 shows a pellet manufacturing apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below.

[0012] The pellets according to one embodiment of the present invention are made of a resin composition containing a lubricant and an ethylene-vinyl acetate copolymer having an MFR of 1500 g / 10 min or more, measured according to JIS K6924-1 at a temperature of 190° C. and a load of 21.18 N, and a vinyl acetate content of 27 mass % or more, measured according to JIS K6924-1, and having silicone adhered to the surface.

[0013] The ethylene-vinyl acetate copolymer may be any ethylene-vinyl acetate copolymer that is generally called an ethylene-vinyl acetate copolymer. There is no particular limitation on the method for producing EVA, and EVA may be obtained by any method, such as a tubular method or an autoclave method. Here, the vinyl acetate content of EVA measured according to JIS K6924-1 is 25% by mass or more, and preferably 27% by mass or more, since pellets with excellent adhesiveness can be obtained when hot melted. In addition, the MFR of EVA measured according to JIS K6924-1 at a temperature of 190°C and a load of 21.18N is 1500g / 10min or more, and since pellets with a low softening point and good processability can be obtained when hot melted, the MFR is preferably 2000g / 10min or more. In addition, EVA is preferably an EVA with a melting point of 50°C or more and 60°C or less, since it becomes a hot melt with excellent handling properties.

[0014] The silicone may be any silicone that is generally called silicone, and examples of silicone include polysiloxanes having a repeating unit represented by the following formula (1), because they reduce adhesion to pipes, silos, etc. during the EVA production process and provide pellets with reduced blocking between pellets. The repeating units of formula (1) may be the same structural formula or different types. Examples of the silicone include dimethyl polysiloxane and methyl phenyl polysiloxane, which may be used alone or in combination of two or more types.

[0015] [ka]

[0016] (In the formula, R1 and R2 each independently represent a monovalent hydrocarbon group.) Examples of R1 and R2 include alkyl groups such as methyl and ethyl groups, aryl groups such as phenyl and tolyl groups, and cycloalkyl groups such as cyclohexyl and cyclobutyl groups.

[0017] In addition, since silicone is more easily attached to EVA pellets and pellets free of blocking can be obtained, it is preferable that silicone contains a surfactant, and examples of such surfactants include polyoxyethylene alkylphenyl ether surfactants, sorbitan fatty acid ester surfactants, etc. As a product containing such silicone and a surfactant, for example, FORTIS (registered trademark) EC9052 manufactured by Nalco Japan LLC is commercially available.

[0018] The amount of silicone adhering to the pellets is preferably 0.001% by mass or more and 0.1% by mass or less, and more preferably 0.003% by mass or more and 0.01% by mass or less, since EVA pellets with less adhesion to pipes, silos, etc. during the pellet production process can be obtained and have excellent processability. Here, the amount of silicone adhering to the pellets is a value obtained by converting the weight concentration of silicon measured by high-frequency inductively coupled plasma atomic emission spectrometry of the pellets that have been incinerated and then melted in an alkali to form a solution, into the weight concentration of silica.

[0019] The lubricant in the present invention may be any lubricant that is generally called a lubricant, and among them, fatty acid amides, fatty acid esters, fatty acid triglycerides, waxes, and fatty alcohols are preferred, since they have excellent bleeding resistance from EVA and provide EVA pellets with little blocking when the pellets are stored in paper bags, flexible containers, silos, etc., and fatty acid amides are particularly preferred. The molecular weight of the lubricant is preferably 588 or more, since they provide excellent bleeding resistance from EVA. Examples of fatty acid amides having a molecular weight of 588 or more include ethylene bisoleic acid amide and ethylene biserucic acid amide. Examples of ethylene bisoleic acid amide include Slipax (registered trademark) O manufactured by Mitsubishi Chemical Corporation, and examples of ethylene biserucic acid amide include Slipax (registered trademark) R manufactured by Mitsubishi Chemical Corporation. These may be used alone, or two or more may be used in combination.

[0020] The amount of the lubricant to be blended is preferably 0.1% by mass or more and 1% by mass or less, and more preferably 0.2% by mass or more and 0.5% by mass or less, in order to obtain EVA pellets with less blocking and excellent processability.

[0021] The resin composition may contain, within the scope not impairing the effects of the present invention, ethylene-α-olefin copolymers such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-hexene copolymers and ethylene-octene copolymers, ethylene-acrylate copolymers, ethylene-methacrylate copolymers, etc. Furthermore, the resin composition may contain antistatic agents, light stabilizers, ultraviolet absorbers, nucleating agents, antioxidants, flow improvers, release agents, colorants, inorganic neutralizing agents, hydrochloric acid absorbers, filler conductive agents, chain extenders, hydrolysis inhibitors, etc.

[0022] The pellet manufacturing method according to one embodiment of the present invention includes a step of melting a resin composition, extruding the resin composition from an extruder, and cutting the extruded molten resin composition into pellets while cooling it with cooling water containing silicone. EVA obtained by a tubular method, an autoclave method, or the like is melted using an extruder such as a twin-screw extruder or a single-screw extruder, and then solidified and cut into pellets. The shape of the pellets may be spherical or cylindrical.

[0023] Methods for pelletizing include an underwater cutting method in which the molten resin is cut while being cooled in cooling water, a hot cutting method in which the molten resin is cooled with water, and a strand cutting method in which the molten resin is cut after being cooled with water. Of these, the underwater cutting method is preferred because it has excellent productivity and produces pellets with little blocking.

[0024] Silicone is preferably added to cooling water since it provides pellets with excellent adhesion to the pellet surface. The temperature of the cooling water is preferably 5°C or higher and 20°C or lower, since this provides excellent adhesion of silicone to the pellets and excellent cutting properties.

[0025] The method for adding the lubricant is not particularly limited, and examples thereof include a method in which the EVA and the lubricant are mixed in advance and kneaded in the extruder, and a method in which the lubricant is added by a side feed or the like in the middle of the extruder. EXAMPLES

[0026] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples. In the examples and comparative examples, the following ethylene-vinyl acetate copolymers, lubricants, and silicones were used. <Ethylene-vinyl acetate copolymer> EVA(1)(MFR2200g / 10min, density 939kg / m 3 , vinyl acetate unit content 28% by mass, melting point 52°C) <Lubricant> Lubricant (1): Ethylene bis oleamide (molecular weight 588.99, manufactured by Mitsubishi Chemical Corporation, trade name Slipax O) Lubricant (2) Ethylene bis erucamide (molecular weight 705.25, manufactured by Mitsubishi Chemical Corporation, trade name Slipax R) <Silicone> Silicone: FORTIS (registered trademark) EC9052A (manufactured by Nalco Japan Co., Ltd.) [Examples 1 to 3] When EVA pellets are produced in a pellet production line in which EVA molten resin is pelletized using a hot-cut pelletizer as shown in Figure 1, the pellets are separated from a water slurry consisting of pellets, fine resin powder, and pellet cooling water, and the remaining fine resin powder and pellet cooling water are filtered to recirculate the pellet cooling water to the pelletizer, EVA and a lubricant are mixed in a predetermined ratio shown in Table 1, and silicone is added to the cooling water. The EVA is obtained using a known high-pressure polymerization method, and has an MFR of 2200g / 10min as measured according to JIS K6924-1 at a temperature of 190°C and a load of 21.18N, and a vinyl acetate content of 28% by mass as measured according to JIS K6924-1. [Comparative Example 1] Granulation was carried out in the same pellet production line as in Example 1, except that silicone was not added to the cooling water. [Comparative Example 2] The EVA was pelletized in the same pellet production line as in Example 1, except that no lubricant was added to the EVA. <Measurement of silicone adhesion amount on pellet surface> The produced pellets were weighed on a platinum plate and burned with a gas burner. The residue obtained by burning the pellets was incinerated in an electric furnace at 650°C for 1 hour, and then 0.5g of sodium tetraborate and 0.3g of sodium carbonate were added to the incinerated material. The platinum plate containing the mixture of the incinerated material, sodium tetraborate, and sodium carbonate was alkali-fused in an electric furnace at 950°C for 1 hour. After adding 4ml of 20% hydrochloric acid, the mixture was diluted to 100mL with purified water, and then the amount of Si was quantified by inductively coupled plasma emission spectrometry, and the value obtained by converting it to SiO2 was taken as the amount of silicone attached to the pellet surface. The evaluation results are shown in Table 1.

[0027] [Table 1]

[0028] <Blocking and bridging suppression effect> The occurrence of bridging was confirmed in the silo of the pellet production line. It was evaluated according to the following criteria.

[0029] ◯: No blocking or bridging occurred.

[0030] ×: Blocking such as blockage of the pneumatic transport pipe or bridging in the silo occurred. <Blocking evaluation during storage> 100 g of the prepared pellets were placed in a wooden box with an inner diameter of 60 x 60 x 60 mm and covered with release paper, and a load of 7 kg was placed on it. The pellets were left at 35°C for 48 hours, and then at 23°C for 24 hours. After the specified time had passed, the pellets were taken out of the wooden box and checked for the presence or absence of aggregation. Evaluation was based on the following criteria.

[0031] ○: No blocking occurred during storage.

[0032] ×: Blocking occurred during storage, forming aggregates.

[0033] ─: Blocking and bridging occurred on the production line, making it impossible to produce pellets.

[0034] [Table 2]

[0035] As shown in Table 2, by using a lubricant and silicone in combination, bridging and blocking did not occur on the production line, and no blocking occurred during storage of the obtained pellets. [Explanation of symbols]

[0036] 1; Extruder 2. Pelletizer (hot cut type) 3. Centrifugal dehydrator 4;Tank 5; Partial filtration device 6,7;Pump

Claims

1. A pellet comprising a resin composition containing a lubricant and an ethylene-vinyl acetate copolymer having a melt flow rate of 1,500 g / 10 min or more as measured in accordance with JIS K6924-1 at a temperature of 190° C. and a load of 21.18 N or more and a vinyl acetate content of 25 mass % or more as measured in accordance with JIS K6924-1, and having silicone adhered to the surface.

2. 2. The pellet according to claim 1, wherein the lubricant is at least one selected from the group consisting of fatty acid amides, fatty acid esters, fatty acid triglycerides, waxes, and fatty alcohols.

3. 2. The pellet according to claim 1, wherein the amount of the lubricant blended is 0.1% by mass or more and 1% by mass or less in the ethylene-vinyl acetate copolymer pellet.

4. 2. The pellet according to claim 1, wherein the amount of the silicone attached is from 0.001% by mass to 0.1% by mass.

5. 5. A method for producing pellets according to claim 1, comprising the steps of melting a resin composition comprising a lubricant and an ethylene-vinyl acetate copolymer having a melt flow rate of 1500 g / 10 min or more, as measured in accordance with JIS K6924-1 at a temperature of 190° C. and a load of 21.18 N, and a vinyl acetate content of 25% by mass or more, as measured in accordance with JIS K6924-1, and extruding the resin composition from an extruder, and cutting the extruded molten resin composition into pellets while cooling it with cooling water containing silicone.

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