Modified ethylene butyl acrylate (EBA) copolymer for hot melt adhesives

Abstract

The invention refers to a modified Ethylene Butyl Acrylate (EBA) copolymer for hot melt adhesives comprising between 60% and 80% by weight of EBA with a n-butyl acrylate comonomer content between 20% and 35 wt% and a high melt flow index (MFI), wherein said EBA copolymer is modified with between 20% and 30% by weight of an EVA copolymer with a vinyl acetate comonomer content between 24% and 35 wt% and a melt flow index (MFI) equal to or greater than 500 g / 10 min at 190ºC, according to ISO 1133. The invention also refers to the use of the modified EBA for producing a HMA composition, to said HMA composition, to the method for producing it and to its use to bond substrates a temperature of between 35ºC and 60ºC.

Description

[0001] MODIFIED ETHYLENE BUTYL ACRYLATE (EBA) COPOLYMER FOR HOT MELT ADHESIVES

[0002] DESCRIPTION

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a modified Ethylene Butyl Acrylate (EBA) copolymer for producing hot melt adhesives (HMA) and to the hot melt adhesive (HMA) composition obtained by using said modified EBA copolymer, said HMA showing better tack properties at lower temperatures than conventional Ethylene Vinyl Acetate (EVA) or Ethylene Butyl Acrylate copolymer (EBA)-based hot-melt adhesives.

[0005] BACKGROUND OF THE INVENTION

[0006] Hot melt adhesives (HMAs) and hot melt pressure sensitive adhesives (HMPSAs) are widely used in industry including automotive, electronics, construction, the manufacturing of packaging, labels, tapes, graphics, disposable sanitary and hygienic products, etc. They are 100% solid materials (solvent-free) at room temperature, form strong bonds quickly, do not need drying tunnels and are easy to handle. On cooling, HMPSAs remain tacky and adhesive and with a slight contact pressure at room temperature adhere to all types of substrates (plastic, metal, glass, paper, wood, etc.). These characteristics make HMPSAs very versatile and suitable for a wide variety of applications.

[0007] The main components of HMAs are typically a polymer, tackifier, wax and antioxidant. The polymer imparts the mechanical strength, the tackifier enhances wetting and tack, the wax lowers the melt viscosity, and the antioxidant inhibits or delays the thermal degradation during processing (I. Skeist, "Handbook of Adhesives", Chapman and Hall (1990); J.M. Martin Martinez, "Adhesivos-Vol I", CYTED-Univ. de Alicante (2001)).

[0008] In the state of the art, it is possible to find different patent documents referred to HMAs compositions. In particular, US20110104488 discloses a pressure-sensitive adhesive comprising a crosslinkable polyolefin and at least one tackifier resin, wherein the polyolefin is composed of at least two monomers A and B and of at least one comonomer C amenable to crosslinking, the monomers A and B being selected from the group consisting of a-olefins, vinyl acetate, n-butyl acrylate and methyl methacrylate or, in the case of EPDM, a diene such as 5-ethylidene-2-norbornene, dicyclopentadiene or 5-vinyl-2-norbornene.

[0009] LIS2018282450 discloses amorphous propylene-ethylene copolymers having application as hot melt adhesives. Optionally, it can also comprise a blend of ethylene vinyl acetate and ethylene n-butyl acrylate copolymers.

[0010] CN 113388342 discloses an adhesive composition comprising 10 to 30 parts of ethylene vinyl acetate (EVA), having a vinyl acetate content of 28 wt% and a melt flow index of 3 to 800 and 10 to 20 parts of ethylene butyl acrylate (EBA) having an acrylate content of 33 wt% and a melt flow index of 20 to 100.

[0011] Despite all the advantages associated with the use of HMAs, they also have some limitations, such as their low resistance to solvents and chemical compounds and their limited performance at low and high temperatures.

[0012] In order to overcome these limitations, the present invention provides a new modified Ethylene Butyl Acrylate (EBA) copolymer for producing hot melt adhesives (HMA) showing surprisingly improved properties, particularly when used at low temperatures, as compared with conventional EVA or EBA-based HMA. Specifically, the invention has been developed as a response to a market need for high-flow, high stability adhesives. It is well known in the state of art that EBA copolymers are more thermally stable than EVA copolymers. Surprisingly, it has been found that this new HMA exhibits some properties of a PSA, which are not common in conventional EVA or EBA-based HMA. It is therefore a new modified EBA copolymer particularly suitable for preparing a low viscosity HMA composition. An additional advantage of the invention as claimed is that the new HMA composition prepared with this new modified EBA copolymer shows surprising tack values at low temperatures (30-40°C), which are not obtained when using conventional EVA or EBA-based HMAs.

[0013] DESCRIPTION OF THE INVENTION

[0014] The present invention refers to a modified Ethylene Butyl Acrylate (EBA) copolymer for hot melt adhesives comprising between 60% and 80% and preferably between 70% and 78% by weight of Ethylene Butyl Acrylate with a n-butyl acrylate comonomer content between 20 wt% and 35 wt%, and preferably between 22 wt% and 33 wt% and a high melt flow index (MFI) (equal to or greater than 150 g / 10 min at 190°C and 2.16 kg, according to ISO 1133), wherein said Ethylene Butyl Acrylate (EBA) copolymer is modified with between 20% and 30% and preferably between 22% and 28% by weight of a Ethylene Vinyl Acetate (EVA) copolymer with a vinyl acetate comonomer content between 24% and 35 wt%, preferably between 27% and 33 wt%, and a melt flow index (MFI) equal to or greater than 500 g / 10 min, preferably between 500 and 1200 g / 10 min and more preferably between 600 and 1000 g / 10 min at 190°C and 2.16 kg, according to ISO 1133.

[0015] This new modified Ethylene Butyl Acrylate (EBA) copolymer is characterized by exhibiting excellent thermal stability and in that it can be obtained by an extrusion process of the EBA and EVA copolymers.

[0016] It is also an object of the invention the method for obtaining the modified Ethylene Butyl Acrylate (EBA) copolymer as it has been previously defined characterized in that it comprises an extrusion process of the Ethylene Butyl Acrylate (EBA) copolymer and the Ethylene Vinyl Acetate (EVA) copolymer.

[0017] It is also an object of the invention the use of this modified Ethylene Butyl Acrylate (EBA) copolymer for producing a HMA composition.

[0018] In addition, it is also an object of the invention the HMA composition obtained by using said modified Ethylene Butyl Acrylate (EBA) copolymer, wherein said HMA composition comprises: a) between 30% and 50% and preferably between 35% and 45% by weight of the modified Ethylene Butyl Acrylate (EBA) copolymer which comprises between 60% and 80% and preferably between 70% and 78% by weight of Ethylene Butyl Acrylate with a n-butyl acrylate comonomer content between 20% and 35 wt%, and preferably between 22% and 33 wt% and a high melt flow index (MFI) (equal to or greater than 150 g / 10 min at 190°C and 2.16 kg, according to ISO 1133), wherein said Ethylene Butyl Acrylate (EBA) copolymer is modified with between 20% and 30% and preferably between 22% and 28% by weight of a Ethylene Vinyl Acetate (EVA) copolymer with a vinyl acetate comonomer content between 24 wt% and 35 wt%, preferably between 27 wt% and 33 wt%, and a melt flow index (MFI) equal to or greater than 500 g / 10 min, preferably between 500 and 1200 g / 10 min and more preferably between 600 and 1000 g / 10 min at 190°C and 2.16 kg, according to ISO 1133; b) between 30 wt% and 50 wt% and preferably between 35 wt% and 45 wt% of a tackifier preferably selected from a group consisting of a polyterpene hydrocarbon, a rosin resin, an aliphatic resin (preferably, a C5 aliphatic resin), an aromatic resin (preferably, a C9 aromatic resin), and an aromatically- modified cycloaliphatic hydrocarbon resin; c) and between 15 wt% and 30 wt% of a wax preferably selected from a group consisting of paraffin wax, polyethylene wax and a blend of Fisher Tropsch and microcrystalline waxes. Preferably, the amount of Fisher Tropsch waxes will be comprised between 8 and 16 wt% and more preferably between 10 and 14 wt% and the amount of microcrystalline wax between 5 and 12 wt%, and more preferably between 6 and 10 wt%; and wherein the HMA composition does not comprise polyhydroxyalkanoate.

[0019] In a preferred embodiment of the invention, the HMA composition can further comprise an antioxidant.

[0020] The method for producing the HMA composition comprises a first step of extrusion of the EBA and EVA copolymers and a second step of adding the result of the extrusion process to the mixture of the additional components of the HMA composition.

[0021] It has been demonstrated that this specific combination of EBA / EVA provides a low viscosity and versatile adhesive, suitable for being used in a wide range of applications. It also exhibits excellent compatibility and thermal stability, as well as a PSA behavior and properties comparable to those of conventional EVA / EBA-based HMA.

[0022] In particular, the composition as claimed has shown surprising results in the tack (adhesion) tests. Tack is the property of an adhesive that enables it to form a bond of measurable strength immediately after the adhesive and the substrate are brought into contact under low pressure.

[0023] Surprisingly, the formulation as claimed has shown tack values greater than 200 kPa at relatively low temperatures (in particular, from 30°C to 60°C), which makes it suitable for being used in different applications. This is an important advantage over the alternative EVA or EBA-based HMAs known in the art, which are not able to achieve high tack values at these low temperatures (J.M. Martin Martinez, “Adhesivos- Vol I”, CYTED-Univ. de Alicante (2001)). Thus, it is a further object of the invention the use of the HMA composition in applications that require low application temperatures or that require control of the tack at a range of temperatures close to body temperature and particularly in medical devices (patches, labels, etc.).

[0024] Particularly, the HMA composition according to the invention can be used to bond substrates such as plastic, metal, glass, ceramic, wood, paper, etc.

[0025] FIGURES

[0026] Figure 1 shows the results of the viscosity measurement of a HMA as claimed (continuous line, — ) and a conventional HMA (dashed line, — ). DETAILED DESCRIPTION OF THE INVENTION

[0027] In order to demonstrate the advantages of the composition as claimed, different tests were carried out with a specific embodiment of the invention. In particular, a HMA composition according to the invention was prepared comprising in percentage by weight:

[0028] 39.8% of modified EBA;

[0029] 39.8% of a polyterpene hydrocarbon resin;

[0030] 12.1 % of Fisher T ropsch waxes;

[0031] 7.8% of microcrystalline wax;

[0032] 0.5% of an antioxidant (Irganox® 1010)

[0033] This HMA composition was compared with a conventional EBA-based HMA composition comprising in percentage by weight:

[0034] 39.8% EBA with a n-butyl acrylate content of 35 wt%, and a melt flow index (MFI) of 320 g / 10 min at 190°C and 2.16 kg, according to ISO 1133;

[0035] 39.8% of a polyterpene hydrocarbon resin;

[0036] 12.1 % of Fisher T ropsch waxes;

[0037] 7.8% of microcrystalline wax; and

[0038] 0.5% of an antioxidant (Irganox® 1010)

[0039] Table 1 shows the results of the tack tests, measured in a Texture Analyzer TA.XT2i (Stable Microsystems, Surrey, England). The tack measurement was carried out at different temperatures between 30 and 110 °C, measured using a thermocouple placed in contact with the sample. To carry out the hot tack measurement test, a 3 mm diameter cylindrical stainless steel rod (with a smooth contact surface) with a surface area of 7-1 O'6m2was used, and the following conditions were used: speed of approach of the probe to the surface of the adhesive: 0.1 mm / s force applied to the adhesive surface: 5 N force application time on the adhesive surface: 1 s speed of separation of the probe from the adhesive surface: 1 mm / s.

[0040] Table 1 claimed

[0041] As it is shown in Table 1 , the HMA as claimed achieves high tack values at low temperatures when compared to the tack values obtained when using a conventional HMA.

[0042] An additional test was carried out to compare the viscosity values of a HMA as claimed and a conventional HMA. The measurements were carried out in a DV2TH B equipment at a constant temperature of 160°C, using the SC4-27 spindle. To carry out the test, the sample was introduced into the thermocontainer of the viscometer and the test temperature was selected. When the sample melted, the spindle was introduced into the sample, increasing the speed progressively, avoiding bubbles, until the sample did not present any lumps. After stabilization, the viscosity measurement was made at a certain speed.

[0043] The results are shown in Figure 1. As it can be observed, the HMA as claimed obtains viscosity values similar to the viscosity values achieved with a conventional HMA.

[0044] Additional tests have been carried out to compare the behavior of the HMA composition as claimed with a conventional EBA-based HMA composition. The tests have demonstrated that the HMA composition as claimed has a behavior similar to a conventional EBA-based HMA composition in terms of compatibility, thermal stability and viscosity. It has also shown a balanced performance in terms of traction and adhesion properties to different substrates (aluminum, polypropylene, cardboard or canvas).

Claims

CLAIMS1. Modified Ethylene Butyl Acrylate (EBA) copolymer for hot melt adhesives characterized in that it comprises between 60% and 80% by weight of Ethylene Butyl Acrylate with a n-butyl acrylate comonomer content between 20% and 35 wt% and a high melt flow index (MFI), equal to or greater than 150 g / 10 min at 190°C and 2.16 kg, according to ISO 1133, wherein said Ethylene Butyl Acrylate (EBA) copolymer is modified with between 20% and 30% by weight of a Ethylene Vinyl Acetate (EVA) copolymer with a vinyl acetate comonomer content between 24% and 35 wt% and a melt flow index (MFI) equal to or greater than 500 g / 10 min at 190°C and 2.16 kg, according to ISO 1133.

2. Modified Ethylene Butyl Acrylate (EBA) copolymer according to claim 1 , wherein the amount of Ethylene Butyl Acrylate is between 70 and 78% by weight.

3. Modified Ethylene Butyl Acrylate (EBA) copolymer according to claim 1 or 2, wherein the amount of Ethylene Vinyl Acetate is between 22 and 28% by weight.

4. Method for obtaining a modified Ethylene Butyl Acrylate (EBA) copolymer according to claim 1, characterized in that it comprises a extrusion process of between 60% and 80% by weight of Ethylene Butyl Acrylate with a n-butyl acrylate comonomer content between 20% and 35 wt% and a high melt flow index (MFI), equal to or greater than 150 g / 10 min at 190°C and 2.16 kg, according to ISO 1133, and between 20% and 30% of a Ethylene Vinyl Acetate (EVA) copolymer with a vinyl acetate comonomer content between 24% and 35 wt% and a melt flow index (MFI) equal to or greater than 500 g / 10 min at 190°C and 2.16 kg, according to ISO 1133.

5. Use of a modified Ethylene Butyl Acrylate (EBA) copolymer according to any one of claims 1 to 3 for producing a HMA composition.

6. HMA composition characterized in that it comprises: a) between 30% and 50% by weight of a modified Ethylene Butyl as claimed in any one of claims 1 to 3; b) between 30% and 50 wt% of a tackifier selected from a group consisting of a polyterpene hydrocarbon, a rosin resin; an aliphatic resin, an aromatic resin and an aromatically-modified cycloaliphatic hydrocarbon resin;c) and between 15% and 30 wt% of a wax selected from a group consisting of paraffin wax, polyethylene wax and blend of Fisher Tropsch and microcrystalline waxes; and wherein the HMA composition does not comprise polyhydroxyalkanoate.

7. HMA composition according to claim 6, wherein said HMA composition further comprises an antioxidant.

8. HMA composition according to claim 6 or 7, wherein the amount of Fisher Tropsch waxes is comprised between 8 and 16 wt%9. HMA composition according to any one of claims 6 to 8, wherein the amount of microcrystalline wax is comprised between 8 and 16 wt%10. Method for producing a HMA composition according to claim 6, characterized in that it comprises a first step of extrusion of the Ethylene Butyl Acrylate (EBA) and the Ethylene Vinyl Acetate (EVA) copolymer and a second step of adding the result of the extrusion process to a mixture of between 30% and 50 wt% of the tackifier and between 15% and 30 wt% of the wax.

11. Use of a HMA composition according to any one of claims 6 to 9 to bond at least two substrates selected from a group consisting of plastic, metal, glass, ceramic, wood and paper.

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