JP2005272744A - Ethylene/vinyl acetate copolymer and hot-melt adhesive composition comprising the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ethylene/vinyl acetate copolymer suitable for a hot-melt adhesive composition having both heat resistance and cold resistance. <P>SOLUTION: The ethylene/vinyl acetate copolymer satisfies the following requirements (a)-(c): (a) the melt flow index (MI) is 0.5-5,000 g/10 min and the vinyl acetate (VAc) content is 2-25 mol%; (b) the branch number (B: mol%) expressed in terms of the sum of the mol% of the vinyl acetate content and the mol% of alkyl branches having a carbon number of two or more satisfies formula (1); and (c) when the branch number of the component having a weight average molecular weight Mw of not less than 100,000 g/mol contained in the ethylene/vinyl acetate copolymer is measured, the branch number (Bh: mol%) in the high-molecular weight range expressed in terms of the sum of the mol% of the vinyl acetate content and the mol% of alkyl branches having a carbon number of two or more satisfies formula (2): 1+(100-Bh)/Bh>100/([VAc]+0.4). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ethylene / vinyl acetate copolymer and a hot melt adhesive composition comprising the same. More specifically, the present invention relates to an ethylene / vinyl acetate copolymer suitable for a hot melt adhesive composition having both heat resistance and cold resistance.

  In the hot melt adhesive, a thermoplastic resin is used as a main component, and depending on the type of the thermoplastic resin, it is called a polyolefin, polyester or polyamide hot melt adhesive. Also, a hot resin mainly composed of a thermoplastic elastomer using as a main component a styrene block copolymer such as styrene / butadiene / styrene block copolymer (SBS) or styrene / isoprene / styrene block copolymer (SIS). Melt adhesives are also known. Among these, polyolefin-based hot melt adhesives, particularly hot melt adhesives in which a tackifier resin and a wax are blended with an ethylene / vinyl acetate copolymer (hereinafter referred to as EVA), are inexpensive and have a main component. A hot melt adhesive that can be applied to a wide range of applications can be prepared by changing the vinyl acetate content, molecular weight, and formulation of an EVA, so it is widely used in fields such as packaging, bookbinding, and plywood / woodwork bonding. in use. Hot melt adhesives have various performance requirements, such as heat-resistant adhesiveness, heat-resistant creep resistance, cold-resistant adhesiveness, low-temperature flexibility, optimum melt viscosity, solidification speed, etc. In addition, hot melt adhesives suitable for various applications have been devised by optimizing the types and blending ratios of tackifying resins, waxes and the like. In packaging applications, the demand for the solidification rate has become stricter year by year as the production rate increases.

  A problem that has been pointed out in the past for EVA hot melt adhesives is the compatibility between heat resistance and cold resistance. Generally, EVA hot melt adhesives have problems with heat-resistant adhesion, and when storing items such as corrugated cardboard packages adhered in summer in warehouses, problems such as opening due to softening of the adhesive layer may occur. . On the other hand, when heat resistance is improved, the problem that cold-resistant adhesiveness is inferior occurs. In other words, heat resistance and cold resistance are contradictory characteristics in EVA hot melt adhesives. Generally, hot melt adhesives with high heat resistance are inferior in low temperature characteristics, and it is a problem to achieve both heat resistance and cold resistance. It was one.

  Many studies have been made to solve this problem. There has been proposed a hot melt composition having improved heat resistance while maintaining cold resistance by using a paraffin wax having a specific melting point and viscosity range (see, for example, Patent Documents 1 and 2). In addition, an adhesive composition having heat resistance and cold resistance has been proposed by using a specific tackifying resin in EVA having a vinyl acetate content of 30% by weight or more and limiting the blending composition (for example, patents). Reference 3). However, the methods described in Patent Documents 1 to 3 are aimed at overcoming the above-mentioned problems by making full use of blending techniques, and the structure of EVA has not been optimized.

  As a technology relating to a hot melt composition that defines the structure of EVA, a composition comprising EVA having higher crystallinity than conventional EVA, a tackifying resin, and Fischer-Tropsch wax has been proposed (for example, see Patent Document 4). .) Furthermore, a hot melt composition using a combination of two types of EVA having different molecular weights and different vinyl acetate contents with improved crystallinity as a base polymer has been proposed (see, for example, Patent Document 5). Further, a technology relating to a hot melt composition comprising EVA, which is a combination of EVA having a low molecular weight and low vinyl acetate content and EVA having a high molecular weight and high vinyl acetate content and high crystallinity, has been proposed ( For example, see Patent Document 6.) However, in each of the methods described in Patent Documents 4 to 6, since EVA having a high crystallinity and a high melting point is used as a constituent component, the heat resistant adhesive property is improved as compared with the conventional EVA, but vinyl acetate, Like vinyl acetate, the number of branches including alkyl branches that inhibit crystallization is reduced, so that the cold resistance, particularly the low temperature flexibility, is inferior to the conventional EVA.

  In addition, a technique relating to a hot melt composition containing EVA whose crystallinity of a high molecular weight component is enhanced by increasing the branching degree distribution of EVA has been proposed (see, for example, Patent Document 7). However, in the method described in Patent Document 7, it is necessary to use various EVAs with a specified number of branches in order to increase heat resistance.

JP-A-7-247468

JP-A-11-323278 JP 2001-59078 A JP 7-242867 A Japanese Patent Laid-Open No. 10-130606 JP-A-10-130436 JP 2003-002923 A

  The present invention has the same excellent heat resistance as that of conventional hot-melt adhesives (hereinafter referred to as heat-resistant grades) with improved heat resistance, and has significantly improved cold resistance over heat-resistant grades. It is an object of the present invention to provide an EVA and hot melt adhesive composition that can be applied to an adhesive.

  As a result of intensive investigations to solve the above problems, the present inventors have found that a hot-melt adhesive composition in which an ethylene / vinyl acetate copolymer with a controlled composition distribution has excellent heat resistance and excellent cold resistance is obtained. As a result, the present invention has been completed.

That is, the present invention relates to an ethylene / vinyl acetate copolymer that satisfies the following requirements (a) to (c) and a hot melt adhesive composition comprising the same.
(A) The melt flow index (MI) at 190 ° C. and a load of 2.16 kg is 0.5 to 5000 g / 10 minutes, and the vinyl acetate (VAc) content is 2 to 25 mol%.
(B) the number of branches (B: mol%) represented by the sum of mol% of vinyl acetate content and mol% of alkyl branches having 2 or more carbon atoms satisfies the following formula (1);

（ｃ）エチレン・酢酸ビニル共重合体に含まれる重量平均分子量Ｍｗが１０００００ｇ／ｍｏｌ以上の成分の分岐数を測定したとき、酢酸ビニル含量のモル％と炭素数２以上のアルキル分岐のモル％との和で表される高分子量域の分岐数（Ｂｈ：モル％）が下記（２）式を満足する。
１＋（１００−Ｂｈ）／Ｂｈ＞１００／（［ＶＡｃ］＋０．４） （２）
以下に本発明を詳細に説明する。

(C) When the number of branches of a component having a weight average molecular weight Mw of 100,000 g / mol or more contained in the ethylene / vinyl acetate copolymer is measured, mol% of vinyl acetate content and mol% of alkyl branches having 2 or more carbon atoms; The number of branches (Bh: mol%) in the high molecular weight range represented by the sum of the formulas satisfies the following formula (2).
1+ (100−Bh) / Bh> 100 / ([VAc] +0.4) (2)
The present invention is described in detail below.

  The EVA of the present invention has a vinyl acetate content of 2 to 25 mol%, preferably 5 to 20 mol%. When the vinyl acetate content is more than 25 mol%, EVA becomes amorphous and does not exhibit sufficient strength. When the vinyl acetate content is less than 2 mol%, the crystallinity is improved and the cold resistance is lowered.

  The EVA of the present invention has an MI in the range of 0.5 to 5000 g / 10 minutes, preferably 10 to 4000 g / 10 minutes, and more preferably 50 to 2000 g / 10 minutes. When MI is larger than 5000 g / 10 minutes, the strength of EVA is extremely lowered and the adhesive strength as a hot melt composition is not expressed. When MI is smaller than 0.5 g / 10 minutes, the viscosity during processing increases. Workability is reduced.

Further, the number of branches represented by the sum of the vinyl acetate content in EVA and the mol% of alkyl branches having 2 or more carbon atoms satisfies the above formula (1). In general, as the vinyl acetate content increases, alkyl branching decreases. The vinyl acetate content in EVA and the alkyl branch having 1, 2, 4 and 5 or more carbon atoms can be measured by ¹³ C-NMR. C. A report by Randall (JMA-REV. MACROMOL. CHEM. PHYS., C29 (2 & 3), pages 201-317 (1989)) can be referred to. Since the vinyl acetate content and the alkyl branch having 2 or more carbon atoms inhibit EVA crystallization and contribute to a decrease in elastic modulus, low temperature flexibility is improved. On the other hand, an alkyl branch having 1 carbon atom (methyl branch) has a lower inhibitory effect on crystallization than other branches. For this reason, the sum of the vinyl acetate content and the alkyl branch having 2 or more carbon atoms correlates well with the crystallinity of EVA. Alkyl branching in EVA can be controlled by polymerization conditions such as polymerization temperature, pressure, or type of chain transfer agent. Compared with conventional polymerization conditions, by increasing the polymerization pressure and using a large amount of alkane, alcohol, ketone or aldehyde as a chain transfer agent, alkyl branching in EVA is reduced and crystallinity is improved. Therefore, EVA which reduces alkyl branching and does not satisfy the formula (1) has a high melting point, and the heat resistance of the hot-melt adhesive composition is improved, but the low-temperature flexibility is lowered. On the other hand, the cold resistance of the hot melt adhesive composition containing many alkyl branches and satisfying the formula (1) is good.

  Furthermore, the EVA of the present invention is characterized in that it has a branch number that satisfies the requirement (c). As a method of fractionating a high molecular weight fraction having a weight average molecular weight Mw of 100,000 g / mol or more contained in EVA, a solubility difference using a method using preparative size exclusion chromatography (SEC) or a mixed solution of a good solvent and a poor solvent is used. A method of sorting according to the above can be used. When the fractionated weight average molecular weight Mw in EVA has a branching number satisfying the formula (2) in a high molecular weight fraction of 100,000 g / mol or more, a high crystalline component exists in the high molecular weight region. The heat resistance of the composition is improved.

  Those satisfying the above requirement (b) but not satisfying the requirement (c) are excellent in cold resistance but insufficient in heat resistance. On the other hand, those not satisfying the requirement (b) and satisfying the requirement (c) are excellent in heat-resistant adhesiveness but are insufficient in cold resistance. Therefore, the hot melt adhesive composition based on EVA having a branch number that satisfies the requirements (b) and (c) at the same time can achieve both heat resistance and cold resistance.

  The EVA production method of the present invention can be produced by high pressure radical polymerization in which ethylene and vinyl acetate are copolymerized using a commonly used radical initiator such as an azo initiator or a peroxide initiator. . In this case, the polymerization pressure is preferably 130 to 250 MPa, and the polymerization temperature is preferably 140 to 210 ° C. Among the high-pressure radical polymerization methods, since the number of branches is affected by the temperature distribution of the reactor, it is preferable to perform polymerization by generating a temperature distribution above and below the reactor, in which case the temperature at the top is the bottom It is the temperature of the 70% portion of the vertical diameter, and the lower temperature is the temperature of the 30% portion of the vertical diameter from the bottom, the upper temperature is 180-210 ° C, and the lower temperature is 140-175 ° C. It is preferable that it is the range of these.

  As the tackifier resin used in the present invention, those already used in general for hot melt adhesives can be used, for example, aliphatic hydrocarbon resins and alicyclics, which are collectively referred to as petroleum resins. Examples include aromatic hydrocarbon resins, aromatic hydrocarbon resins, terpene resins containing α-pinene or β-pinene, rosin resins, hydrogenated rosin resins, styrene resins, coumarone / indene resins, etc. Is done.

  The blending ratio of the EVA and the tackifying resin is not particularly limited as long as the characteristics required as a hot melt adhesive are satisfied, and can be varied widely. However, when considering the general blending ratio, EVA100 The amount of tackifying resin is 20 to 150 parts by weight, preferably 60 to 120 parts by weight with respect to parts by weight.

  In the hot melt adhesive composition of the present invention, a wax can be blended, and the wax is not limited at all, but petroleum wax such as paraffin wax, microcrystalline wax and sazol wax; Natural waxes such as wood wax, carnauba wax, beeswax; synthetic waxes such as Fischer-Tropsch wax, crystalline polyethylene wax, crystalline polypropylene wax, EVA wax; acid-modified polyethylene wax, acid-modified polypropylene wax, acid-modified EVA wax, etc. Examples thereof include modified waxes. Wax is added for the purpose of imparting fluidity to hot-melt blends, controlling set time or open time, and imparting heat resistance. There is an upper limit on the amount possible. Usually, the blending amount in the hot melt adhesive composition is preferably 40% by weight or less, more preferably 30% by weight or less.

  The viscosity of the hot melt adhesive composition can be appropriately selected depending on the purpose of use. The viscosity varies with the formulation, ie, the molecular weight of EVA, the viscosity of the tackifying resin, the viscosity of the wax, and the blending ratio of these formulations.

  If necessary, the hot melt adhesive composition of the present invention may contain various stabilizers such as pigments, dyes, antioxidants, oils, plasticizers, inorganic fillers, and the like.

  The manufacturing method of the hot melt adhesive composition of the present invention can be manufactured by a known method, that is, by mixing the respective blending components under melting. Although the melting temperature in that case does not have a restriction | limiting in particular, 160-230 degreeC is preferable, More preferably, it is 180-200 degreeC. On the other hand, a known method such as an extruder, an open roll mill, a Banbury mixer, a kneader, a kneader ruder, or a melt mixing tank can be used as the mixing method.

  The hot melt adhesive composition of the present invention can be used for conventionally known applications, that is, for bonding paper, polyester film, metal, plywood, cloth, thermoplastic resin, thermoplastic elastomer, rubber and the like.

  The bonding method of the hot melt adhesive composition of the present invention is not particularly limited. Conventional equipment for hot melt adhesives can be used. Nozzle type hot melt applicators, spray type hot melt applicators, flat nozzle type hot melt applicators, roll type coaters, extrusion type coaters Etc. are exemplified.

  By using the ethylene / vinyl acetate copolymer having a controlled branch number according to the present invention, a hot melt adhesive composition having both heat resistance and cold resistance can be provided.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention does not receive a restriction | limiting at all by these Examples. In addition, the analysis, the test method, and raw material resin which were used in the Example and the comparative example are as follows.

1. Analysis method The vinyl acetate content and the number of branches were calculated by a conventional method by measuring ¹³ C-NMR (400 MHz ¹³ C-NMR measuring device manufactured by JEOL) using ethylene / vinyl acetate copolymer as a heavy chloroform solution. The molecular weight of the fractionated EVA was measured by the following system.

GPC measuring device 8010 (model number) manufactured by Tosoh Corporation
Column: TSKgel GMH-HR-H × 2
Eluent: THF
Flow rate: 1 ml / min Temperature: 40 ° C
Molecular weight-Standard sample: Monodispersed polystyrene Detector: Differential refractometer Sample injection amount: 100 microliters Test Method (2-1) Synthesis of Hot Melt Adhesive Composition EVA 40 g, petroleum resin (Tosoh Corporation: 120HS) 40 g, wax (Sazol Wax: Sasol, H1) 20 g, antioxidant (phenolic antioxidant) Agent: 0.3 g of Irganox 1010 (manufactured by Ciba Specialty Chemicals) was placed in a 300 ml beaker, melted in an oven at 180 ° C., and stirred uniformly to obtain a hot melt adhesive composition.

(2-2) Heat-resistant adhesive test: T peel test The hot-melt adhesive composition obtained in (2-1) was subjected to a heat-resistant adhesive test described in the Japan Adhesive Industry Association Standard hot melt adhesive test method. Corrugated cardboard test pieces were prepared according to the method A test piece preparation. A load of 300 g was applied to the test piece, and the time until the cardboard was peeled off under a constant temperature environment was measured and used as a heat resistance index. In this test, the temperature is first maintained at 60 ° C. for 250 minutes, then heated to 65 ° C. at a rate of 5 ° C./minute, held for 250 minutes, further heated to 70 ° C. at 5 ° C./minute, and maintained at 70 ° C. The environment was used.

(2-3) Low-temperature characteristics: low-temperature flexibility After hot-pressing the hot melt adhesive composition obtained in (2-1) at 160 ° C., a sheet having a thickness of 1 mm is prepared (1.0 cm × 12 cm) to obtain a test piece. A sample gripped by a bending tester was put in a low-temperature thermostat, and when the sample reached a predetermined temperature, a 180-degree bending test was performed, and the lowest temperature at which the sample did not break was defined as cold resistance.

3. Synthesis of EVA Using a 6 liter autoclave reactor, ethylene and vinyl acetate monomer were premixed at a mixing weight ratio of 0.725 to 0.275 and supplied at a flow rate of 200 kg / hour, reaction pressure 160 MPa, residence time Under the conditions of 78 seconds and a production rate of 20 kg / hour, 0.1 kg / hour of peroxide was supplied as an initiator to polymerize EVA. Table 1 shows the polymerization conditions of the produced EVA1-4 and various physical properties of the obtained EVA1-4. In addition, the raw material gas temperature of Table 1 is the temperature of ethylene and vinyl acetate mixed gas.

４．ＥＶＡの分別
高分子量域の分岐数を求めるために以下の通りＥＶＡの分別を行った。恒温槽に設置された直径１０ミクロンのガラスビーズを充填した金属製円筒管（直径２．５ｃｍ、高さ６０ｃｍ）に、５ｇのＥＶＡ１を５０ｃｃの熱ヘキサンに溶解させ、充填した。恒温槽内を−１０℃に冷却した後、２−プロパノール（ＩＰＡ）で円筒管の溶媒を置換しＥＶＡ１を析出させた。５０℃に昇温した後、ＩＰＡとヘキサンとの混合溶媒を順次組成を変え６００ｃｃずつ流し、各組成の溶出溶液をエバポレーターで濃縮し分別物を得た。分別条件及び分別結果を表２に示す。この分別結果より、式（３）を用いて高分子量域の分岐数（Ｂｈ：モル％）を求めた。なお、ＥＶＡ２〜４もＥＶＡ１と同様に分別を行い、高分子量域の分岐数を求めた。これらの結果を表３に示す。

4). EVA fractionation In order to determine the number of branches in the high molecular weight region, EVA fractionation was performed as follows. 5 g of EVA1 was dissolved in 50 cc of hot hexane and filled in a metal cylindrical tube (diameter 2.5 cm, height 60 cm) filled with glass beads having a diameter of 10 microns placed in a thermostatic bath. After the inside of the thermostatic bath was cooled to −10 ° C., the solvent in the cylindrical tube was replaced with 2-propanol (IPA) to precipitate EVA1. After the temperature was raised to 50 ° C., the composition of the mixed solvent of IPA and hexane was changed in order and 600 cc was flown at a time, and the elution solution of each composition was concentrated with an evaporator to obtain fractions. Table 2 shows the classification conditions and the classification results. From this fractionation result, the number of branches in the high molecular weight region (Bh: mol%) was determined using Equation (3). In addition, EVA2-4 was fractionated similarly to EVA1, and the number of branches in the high molecular weight region was determined. These results are shown in Table 3.

式（３）中のＢｉはＭｗが１０００００ｇ／ｍｏｌ以上の各成分の分岐数、ｆｉは各成分の分取量（％）である。

Bi in the formula (3) is the number of branches of each component having Mw of 100,000 g / mol or more, and fi is the fraction (%) of each component.

実施例１
ＥＶＡ１を用い、（２−１）に従いホットメルト接着剤組成物を合成し、（２−２）および（２−３）に従い耐熱接着性および低温特性試験を行った。その結果を表４に示す。

Example 1
Using EVA1, a hot-melt adhesive composition was synthesized according to (2-1), and heat-resistant adhesiveness and low-temperature characteristics tests were conducted according to (2-2) and (2-3). The results are shown in Table 4.

Comparative Example 1
Using EVA2, a hot-melt adhesive composition was synthesized according to (2-1), and heat-resistant adhesiveness and low-temperature characteristics tests were conducted according to (2-2) and (2-3). The results are shown in Table 4.

Comparative Example 2
Using EVA3, a hot-melt adhesive composition was synthesized according to (2-1), and heat-resistant adhesiveness and low-temperature characteristics tests were conducted according to (2-2) and (2-3). The results are shown in Table 4.
Comparative Example 3
Using EVA4, a hot-melt adhesive composition was synthesized according to (2-1), and heat-resistant adhesiveness and low-temperature characteristics tests were conducted according to (2-2) and (2-3). The results are shown in Table 4.

表４から明らかなように比較例１に用いたＥＶＡ２は分岐数が多く式（１）を満足し耐寒性に優れるものの、式（２）を満足せず耐熱性が不十分である。比較例２に用いたＥＶＡ３は式（１）を満足し耐寒性に優れるものの、式（２）を満足せず耐熱性が不十分となる。また比較例３に用いたＥＶＡ４は式（２）を満足し耐熱性が良好であるものの、式（１）を満足せず耐寒性は悪くなる。これに対して、実施例１に用いたＥＶＡ１は式（１）と式（２）を満足し、耐熱接着性に優れかつ、耐寒性も優れる。

As is clear from Table 4, EVA2 used in Comparative Example 1 has a large number of branches and satisfies formula (1) and is excellent in cold resistance, but does not satisfy formula (2) and has insufficient heat resistance. EVA3 used in Comparative Example 2 satisfies the formula (1) and is excellent in cold resistance, but does not satisfy the formula (2) and has insufficient heat resistance. EVA4 used in Comparative Example 3 satisfies the formula (2) and has good heat resistance, but does not satisfy the formula (1) and deteriorates cold resistance. On the other hand, EVA1 used in Example 1 satisfies the formulas (1) and (2), has excellent heat-resistant adhesiveness, and excellent cold resistance.

Claims (3)

An ethylene / vinyl acetate copolymer that satisfies the following requirements (a) to (c):
(A) The melt flow index (MI) at 190 ° C. and a load of 2.16 kg is 0.5 to 5000 g / 10 minutes, and the vinyl acetate (VAc) content is 2 to 25 mol%.
(B) the number of branches (B: mol%) represented by the sum of mol% of vinyl acetate content and mol% of alkyl branches having 2 or more carbon atoms satisfies the following formula (1);

(C) When the number of branches of a component having a weight average molecular weight Mw of 100,000 g / mol or more contained in the ethylene / vinyl acetate copolymer is measured, mol% of vinyl acetate content and mol% of alkyl branches having 2 or more carbon atoms; The number of branches (Bh: mol%) in the high molecular weight range represented by the sum of the formulas satisfies the following formula (2).
1+ (100−Bh) / Bh> 100 / ([VAc] +0.4) (2) A hot melt adhesive composition comprising a tackifier resin blended with the ethylene / vinyl acetate copolymer according to claim 1. A hot melt adhesive composition comprising the hot melt adhesive composition according to claim 2 and a wax.