TECHNICAL FIELD

The present invention relates to a hot melt adhesive composition, and more particularly, to a hot melt adhesive composition which has reduced stringing, is clear and is superior in thermal stability.

BACKGROUND ART

Hot melt adhesives are being widely used in various applications, such as packaging, bookbinding and woodworking, due to, for example, their high setting speed, good economical efficiency and freeness from solvents. However, hot melt adhesives string during use, soiling peripheral machineries

(e.g., a case packing machine and a printer in the case of a corrugated board packaging line), adhering to the packages to diminish the value of the packages, and affecting (causing the malfunctioning of) the devices such as a sensor.

A typical application procedure for hot melt adhesives includes a nozzle coating. In this procedure, stringing is generated even after the OFF signal, due to delay in response by the nozzle cavity or mechanical shielding (spring back). This stringing becomes more remarkable when the distance between the nozzle and the article to which the adhesive is applied is long, when the line speed is high or when the melt viscosity of the hot melt adhesive is high. Therefore, when the stringing occurs, the operator must stop the application lines and remove the strings.

Many attempts have been made to reduce the stringing of hot melt adhesives. For example, Japanese Patent Application KOKAI Publication No. H07-331221 discloses reducing the stringing by incorporating a specified amount of a specified low molecular weight ethylene/unsaturated carboxylic acid copolymer into a hot melt composition containing specified amounts of a base polymer such as an ethylene/vinyl acetate copolymer or an ethylene/(meth)acrylate copolymer and a tackifying resin. However, this hot melt adhesive composition tends to sag, and is poor in cohesion force, leading to insufficient bonding strength.

Japanese Patent Application KOKAI Publication No. Hl 1-61067 discloses blending a specified fumed silica into a hot melt composition containing a specified ethylene/unsaturated ester copolymer, a tackifying resin and a wax, in order to reduce the stringing. Japanese Patent Application KOKAI Publication No. 2003-238920 discloses incorporating a specified amount of a polyethylene into a composition two specified ethylene/unsaturated ester. Japanese Patent Application KOKAI Publication No. 2004-2634 discloses incorporating, into a base resin such as an ethylene/vinyl acetate copolymer or an ethylene/acrylate ester copolymer, a resin incompatible with the base resin as colloidal particles. However, these hot melt adhesive composition lack clarity, have poor thermal stability, and gel or carbonize during a long period of use, causing clogging of the applicator and bringing about application failure.

[Patent Document 1] Jpn. Pat. Appln. KOKAI Publication No. H07-331221 [Patent Document 2] Jpn. Pat. Appln. KOKAI Publication No. Hll-61067 [Patent Document 3] Jpn. Pat. Appln. KOKAI Publication No. 2003-238920

[Patent Document 4] Jpn. Pat. Appln. KOKAI Publication No. 2004-2634 DISCLOSURE OF THE INVENTION

OBJECT OF THE INVENTION

Therefore, an object of the present invention is to provide a hot melt adhesive composition which has significantly reduced stringing, and is superior in thermal stability and clarity.

SUMMARY OF THE INVENTION

The present inventors have conducted extensive studies in an attempt to produce a hot melt adhesive composition which is substantially non-stringy, and superior in thermal stability and clarity. During the studies, they have paid attention to ethylene/α-olefin copolymers such as those described in U.S. Patent No. 6,107,430. The ethylene/α-olefin copolymers can afford hot melt adhesive compositions superior in thermal stability. The present inventors have found that the object can be achieved by adding, to the ethylene/α-olefin copolymer (first component), a specific polymer,

which is incompatible with the copolymer, but can significantly reduce the stringing of the copolymer, i.e., an ethylene/(meth)acrylic acid ester copolymer (second component) and a third component which is compatible with the first and second components, in specified amounts. The present invention is based on these findings. Thus, according to an aspect of the present invention, there is provided a hot melt adhesive composition comprising: a first component comprising at least one ethylene/C3 - C20 α-olefin copolymer; a second component comprising at least one ethylene/(meth)acrylic acid ester copolymer in an amount of about 6 to about 12 parts by weight per 100 parts by weight of the first component; and a third component comprising at least one tackifying resin, in an amount of about 50 to about 200 parts by weight per 100 parts by weight of the first component, the third component being compatible with the first and second components.

DETAILED DESCRIPTION OF THE INVENTION

A hot melt adhesive composition according to the present invention contains (1) a first component comprising at least one ethylene/C3 - C20 α-olefin copolymer, (2) a second component comprising at least one ethylene/(meth)acrylic acid ester copolymer, and (3) a third component compatible with the first and second components.

The ethylene/Cβ - C20 α-olefin copolymer constituting the first component is a copolymer of ethylene with at least one C3 - C20 α-olefin (for example, propylene, isobutylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-l-pentine, and 1-octene). The α-olefin is preferably a C4 - C20 α-olefin, and is more preferably a Cg - Cg α-olefin, with 1- octene being most preferred. It is preferable that the ethylene/α-olefin copolymer contains about 20 to about 40 mol% of a C3 - C20 α-olefin. The hot melt adhesive composition of the present invention can be used in various applications, including packaging, bookbinding and woodworking. Generally, the ethylene/α-olefin copolymer preferably has a melt index of about 5 to about 2500 g/10 min., and preferably has a melt index of about 150 to about 2500 g/10 min. for packaging applications.

The ethylene/α-olefin copolymers used in the present invention as well as their preparation method are described in, for example, U.S. Patent No. 6,107,430. Ethylene/ 1-octene copolymers are commercially available from Dow Chemical under the trade name, "AFFINITY". Examples include AFFINITY EG 8185 (melt index: 30.00 g/10 min.), AFFINITY EG 8200G (melt index: 5.00 g/10 min.), AFFINITY GA 1900 (melt index: 1000.00 g/10 min.), AFFINITY GA 1950 (melt index: 500.00 g/10 min.), and AFFINITY PT 1409 (melt index: 6.00 g/10 min.). These ethylene/ 1-octene copolymers have a 1-octene content of 35-37 mol %. The ethylene/α-olefin copolymers can be used singly or in combination. The second component of the hot melt adhesive composition of the invention is a polymer incompatible with the first component, i.e., the ethylene/α-olefin copolymer, and significantly reduces the stringing. The second component comprises a copolymer of ethylene with at least one (meth)acrylic acid ester, i.e., an ethylene/(meth)acrylic acid ester copolymer. It should be noted that the term "(meth)acrylic acid ester" is a generic term for an acrylic acid ester and a methacrylic acid ester. The (meth)acrylic acid ester is preferably a Ci - Cg alkyl (for example, methyl, ethyl, propyl and butyl) ester of (meth)acrylic acid, with C\ - C4 alkyl ester of (meth)acrylic acid being more preferred. It is most preferred that the (meth)acrylic acid ester is ethyl acrylate or methyl methacrylate. The ethylene/(meth)acrylic acid ester copolymer contains (meth)acrylic acid ester in an amount of, preferably about 5 to about 35 mol %, more preferably about 20 to about 35 mol %. Further, the ethylene/(meth)acrylic acid ester copolymer preferably has a melt index of about 20 to about 400 g/10 min. Such ethylene/(meth)acrylic acid ester copolymers are commercially available. Examples include an ethylene/ethyl acrylate copolymer sold under the tradename of EVAFLEX-EEA A 704 (melt index: 275g/10 min.; ethyl acrylate content: 25 mol %) and A 709 (melt index: 25g/10 min.; ethyl acrylate content: 34 mol %) by DuPont-Mitsui Polychemicals Co. Ltd.; ethylene/ethyl acrylate copolymers sold under the tradename of DPDJ-9169 (melt index: 20 g/10 min.; ethyl acrylate content: 20 mol %), the tradename of NUC-6070 (melt index: 250 g/10 min.;

ethyl acrylate content: 25 mol %) and the tradename of NUC-6940 (melt index: 20 g/10 min. ; ethyl acrylate content: 35 mol %) by Japan UniCar Co. Ltd.; and ethylene/methyl methacrylate copolymers sold under the tradename of ACRYFT CM5021 (melt index: 450 g/10 min. ; methyl methacrylate content: 28 mol %), the tradename of ACRYFT CM5022 (melt index: 450g/10 min. ; methyl methacrylate content: 32 mol %) and the tradename of ACRYFT CM5023 (melt index: 150 g/10 min. ; methyl methacrylate content: 28 mol %) by Sumitomo Chemical Co., Ltd. Ethylene/(meth)acrylic acid ester copolymers can be used singly or in combination.

The third component of the hot melt adhesive composition of the present invention is compatible with the first and second components described above, and serves to make the hot melt adhesive composition clear. The third component contains at least one kind of tackifying resin.

In the present invention, the term "compatible with" refers to a "clear" state that a mixture of two or more components molten by heating to an application temperature (usually 160 to 180°, typically 180°) does not exhibit any phase separation of the components, and transmits visible light therethrough, even after allowed to stand for several hours. The term "clear state" is defined as a state that when the molten mixture is put in a flat-bottomed glass sample bottle up to a level of 10 cm (height), with the bottle being placed on a news paper sheet, letters on the news paper under the bottle can be read by eye when viewed from right above the molten mixture.

The third component can be provided by one kind of tackifying resin, or by a combination of a first tackifying resin that is compatible with the first component (ethylene/α-olefin copolymer) and a second tackifying resin that is compatible with the second component (ethylene/(meth)acrylic acid ester copolymer). In the latter case, the first and second tackifying resins can be provided by petroleum resins. More specifically, the first tackifying resin preferably comprises a fully hydrogenated petroleum resin, more preferably a petroleum resin having a hydrogenation degree of about 95% or higher. The second tackifying resin preferably comprises a partially

hydrogenated petroleum resin, or more preferably a partially hydrogenated petroleum resin having a hydrogenation degree of about 60 to about 70%. Petroleum resins are synthetic resins prepared by polymerizing an unsaturated petroleum fraction. Typical examples of the raw materials for these resins include C4 to C5 fractions (such as 1-butene, isobutylene, butadiene, pentene, isoprene, piperidine and 1,3-pentadiene), and C9 to Cio fractions (such as vinyltoluene, indene, α-methylstyrene and cyclopentadiene), by-produced in naphtha decomposition and having a high saturation degree. The petroleum resins include aliphatic petroleum resin, alicyclic petroleum resin, aromatic petroleum resin and a copolymerized petroleum resin of an aliphatic component and aromatic component. The aliphatic petroleum resin is a resin obtained by polymerizing the C4 to C5 portions mentioned above. The alicyclic petroleum resin is a resin obtained by cyclization dimerization of the acyclic diene component in the C4 to C5 fractions and polymerizing thus obtained dimeric monomers, or polymerizing cyclopentadiene. The aromatic petroleum resin is a resin obtained by polymerizing the C9 to C 10 fractions mentioned above. The copolymerized petroleum resin of an aliphatic component and aromatic component is a resin obtained by polymerizing the C4 to C5 fractions mentioned above with the C9 to Ci Q fractions mentioned above. The partially and fully hydrogenated petroleum resins are commercially available. For example, partially hydrogenated C5 aromatic petroleum resins are available from Idemitsu

Kosan under the tradenames of IMARV S-100 (softening point: 100°), and IMARV S-110 (softening point: 110°). Fully hydrogenated C5 aromatic petroleum resins are available from Idemitsu Kosan under the tradenames of IMARV P-90 (softening point: 90°), IMARV P-100 (softening point: 100°), IMARV P-125 (softening point: 125°), and EVIARV P-140 (softening point: 140°).

The hot melt adhesive composition of the present invention contains the second component (ethylene/(meth)acrylic acid ester copolymer) in an amount of about 5 to about 12 parts by weight per 100 parts by weight of the first component (ethylene/Cβ to C20cr°l ^e fi ⁿ copolymer). If the amount of the second component is

less than about 5 parts by weight per 100 parts by weight of the first component, the stringing cannot be sufficiently suppressed. On the other hand, if the amount of the second component exceeds about 12 parts by weight per 100 parts by weight of the first component, the clarity or transparency of the resultant hot melt adhesive composition is insufficient. The amount of the second component is preferably about 7 to about 10 parts by weight per 100 parts by weight of the first component.

The amount of the third component (tackifying resin) is about 50 to about 250 parts by weight per 100 parts by weight of the first component. If the amount of the third component is less than about 50 parts by weight per 100 parts by weight of the first component, the resultant hot melt adhesive composition becomes elastic and lacks adhesiveness. On the other hand, if the amount of the second component exceeds about 250 parts by weight per 100 parts by weight of the first component, the resultant hot melt adhesive becomes brittle. In the case where the third component is provided by a combination of the first tackifying resin and the second tackifying resin, the amount of the first tackifying resin is preferably about 40 to about 150 parts by weight with respect to 100 parts by weight of the first component, and the amount of the second tackifying resin is preferably about 10 to about 50 parts by weight, per 100 parts by weight of the first component. The amount of the first tackifying resin is preferably about 70 to about 120 parts by weight per 100 parts by weight of the first component, and the amount of the second tackifying resin is preferably about 20 to about 40 parts by weight per 100 parts by weight of the first component.

The hot melt adhesive composition of the present invention may contain wax in addition to the first to third components, in order to lower the viscosity of the adhesive composition, thereby suppressing the crystallization of the composition and to adjust service life of the composition.

Various types of wax that are generally used in hot melt adhesives can be used. Examples include synthetic waxes such as Fischer-Tropsch waxes, polyethylene waxes, polypropylene waxes, atactic polypropylene waxes and ethylene/vinyl acetate copolymer; petroleum waxes such as paraffin waxes, purified paraffin waxes and

microcrystalline waxes; and natural waxes such as Japan wax, carnauba wax and beeswax. Preferably, the waxes used have a melting point of about 60 to about 120°. These waxes are commercially available.

In the hot melt adhesive composition of the present invention, the wax is 5 preferably contained in an amount of about 30 to about 85 parts by weight per 100 parts by weight of the first component.

The hot melt adhesive composition of the present invention can contain an antioxidant. Various types of antioxidant that are generally employed for hot melt adhesives can be used. Examples include hindered phenol antioxidants (e.g. o IRGANOX 1010, and 1076 available from Ciba Specialty Chemicals), and phosphite antioxidant (e. g., IRGAFOS 168 available from Ciba Specialty Chemicals).

Further, the hot melt adhesive composition of the present invention can contain a liquid tackifying resin and/or a process oil. Examples of the liquid tackifying resin include MARUKACLEAR H available from Maruzen Petrochemical, and REGALITE 5 RlOlO available from Eastman Chemical. Examples of the process oil include paraffin oil PW-90 and naphthene oil 371 -N.

In the above descriptions, the amount of each component of the hot melt adhesive composition of the present invention is expressed with reference to the weight of the first component. However, in another embodiment, the amount of each o component of the hot melt adhesive composition can be specified with reference to the total amount of the hot melt adhesive composition. In this case, the hot melt adhesive composition of the present invention preferably contains about 20 to about 60% by weight of the first component, about 1 to about 10% by weight of the second component, about 20 to about 60% by weight of the third component, 0 to about 40% 5 by weight of the wax and 0 to about 1 % by weight of the antioxidant. More preferably, the hot melt adhesive composition of the present invention preferably contains about 25 to about 50% by weight of the first component; about 2 to about 4% by weight of the second component; about 20 to about 50% by weight of the first tackifying resin, about 5 to about 20% by weight of the second tackifying resin; about 10 to about 30% by

weight of the wax; and 0 to about 1% by weight of the antioxidant.

EXAMPLES

Examples of the present invention will now be described; however, the invention is not limited to these examples. Examples 1 to 6 and Comparative Examples 1 to 5

A hot melt adhesive composition having the compositions specified in TABLE 1 below was prepared.

In TABLE l:

AFFINITY GA 1950 (TM) is an ethylene/ 1-octene copolymer available from Dow Chemical (melt index: 500.00 g/10 min.; 1-octene content: 35-37 mol %), and is a first component of the invention: ACRYFT CM5021 (TM) is an ethylene/methyl methacrylate copolymer available from Sumitomo Chemical (melt index: 450 g/10 min.; methyl methacrylate content: 28 mol %), and is a second component of the invention;

EEA A704 is an ethylene/ethyl acrylate copolymer available from Mitsui DuPont Polychemical 1 (melt index: 275 g/10 min.; ethyl acrylate content: 25 mol %), and is a second component of the invention;

IMARV P125 IMARV P-125 is a fully hydrogenated C5 aromatic petroleum resins available from Idemitsu Kosan (softening point: 125°; average molecular weight by VPO: 880), and is a first tackifying resin of the invention;

IMARV S-100 is a partially hydrogenated C5 aromatic petroleum resins available from Idemitsu Kosan (softening point: 100°; average molecular weight by VPO: 700), and is a second tackifying resin of the invention;

BARECO PX-100 is a Fischer-Tropsch wax (melting point: 98°) available from Baker Petrol ite; and

IRGANOX 1010 is a hindered phenol antioxidant available from Ci ba Specialty Chemicals.

Each hot melt adhesive composition was measured for the following properties in the following manner. The results are shown also in TABLE 1.

Initial Viscosity (unit: mPa ^• s)

Using Brookfield Model RVF Viscometer and a thermocell, the initial viscosity of the composition is measured at 180° with No. 21 spindle.

Viscosity After Heat Aging (unit: mPa ^• s)

100 g of the hot melt adhesive is placed in a 225-cc glass jar and the jar is covered with aluminum and capped. Then, the jar is placed in an oven and heated at 180° for one week, at which the viscosity is measured in the same manner as in the

initial viscosity described above.

Viscosity Change Rate (%) After Heat Aging

The viscosity change rate is calculated according to the following equation: { [(viscosity after heat aging) - (initial viscosity)] / (initial viscosity)} x 100 5 Initial Clarity (Compatibility Test

A flat-bottomed glass sample bottle having a volume of 110 cc is placed on a news paper sheet (not particularly limited, but usually the font is in Mincho-tai having a size of 3 mm), and the hot melt adhesive sample molten at an application temperature of 180°is put in the bottle up to a level of 1 cm. Then, letters on the o news paper under the bottle are read by eye from above the adhesive sample. When the letters are readable, the adhesive sample is added to a level of another 1 cm, and the letters are read similarly. This operation is repeated to an adhesive level of 10 cm or more. When the letters are readable even at a level of 10 cm, the sample is judged as clear. The highest level (cm) of the molten adhesive sample where the 5 letters could be read is reported. Incidentally, in the case where bubbles are present in the sample when the sample is put in the bottle, the sample bottle containing the sample is heated again to 180° to expel the bubbles, and then the sample is subjected to the measurement. Adhesion Test o Using an adhesion strength test apparatus available from JT Toshi, the hot melt adhesive is applied on a K-liner corrugated cardboard piece at an application temperature of 180° and in an application amount of 3 g/m. Then, the cardboard piece is adhered to another K-liner corrugated cardboard piece at an open time of 2 seconds and a pressure of 7.8 kPa. The adhered corrugated cardboard pieces is put in a 5 thermostat held at -20°, -10°, 5°, 23°, 50° or 60° for 12 hours or more, and under these atmospheres, the two pieces are forcibly peeled by hand. The ratio (%) of the broken cardboard piece portion area to the entire adhered area is measured. If the ratio is 80% or more, the adhesive composition is judged as passing the test at that temperature.

Stringing Test

The stringing property of the hot melt adhesive is evaluated basically by the method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-2634, except that the number of shots is set at 100, the temperature of the tank, hose and nozzle is set at 180° or 170°, the nozzle diameter is set at 20/1000 inches and the pump pressure is set to 0.3 or 0.2 MPa. The amount of the adhesive composition fallen on the pan is measured and the form of the fallen adhesive composition is observed. In TABLE 1 , with respect to the form of the fallen adhesive, "D" means drops only, "S" means strings only, "DS" means almost drops with slight strings, and "SD" means almost strings with slight drops. Thus, if the form of the fallen adhesive is "D", the adhesive is fully free from stringing. If the form of the fallen adhesive is "DS", the adhesive is substantially free from stringing.

As seen from the results in TABLE 1, the hot melt adhesive composition of the present invention is superior in adhesivity, exhibits good thermal stability (low in viscosity change before and after heat aging), is superior in clarity and is substantially free from stringing.

What is claimed is: