Hot Melt Adhesive Compositions

The present invention relates to thermofusible, or "hot-melt", adhesive compositions. The thermofusible adhesive compositions of the present invention comprise: a.) at least one substantially amorphous poly(alpha-olefin), and b.) at least one copolymer of ethylene and an alkyl (meth)acrylate.

Thermofusible, or "hot-melt", adhesives are solid at room temperature. It suffices to melt them by heating between 150 and 200.degree. C., setting occurring by cooling.

The main constituents of a thermofusible adhesive are: a base copolymer, a tackifying resin, waxes, stabilizers, and optionally fillers.

Polyolefins, copolymers thereof, polyamides, and so on, may be used as the base copolymer. The base copolymer constitutes the core of the hot melt. It provides and determines its general properties, in particular, cohesion, thermal behavior, and stability.

The tackifying resin imparts better hot adhesive power to the thermofusible adhesive, and thus better adhesion at the application temperatures.

The waxes make it possible to control the viscosity and to modify the rheological curve of the base polymer as a function of the temperature.

The stabilizers are antioxidants or anti-UV agents. They increase the resistance to ageing of the mixture.

The plasticizers modify the cold properties of the hot-melt and in particular the flexibility of the adhesively bonded joint.

U.S. Pat. No. 4,816,306 of the prior art describes thermofusible adhesives composed of:

a. 35 to 45% by weight of the ethylene/n-butyl acrylate copolymer;

b. 35 to 55% of a tackifying resin;

c. 10 to 20% of a wax with a high melting point.

Application JP 60 096676 KOKAI published on May 30, 1985 describes thermofusible adhesives consisting of:

A 100 parts of polymers:

Aa 25 to 75% of an ethylene copolymer,

Ab 75 to 25% of an ethylene/unsaturated carboxylic acid ester copolymer, and

B 25 to 200 parts of a tackifying resin;

at least one of the polymers A being grafted with an unsaturated carboxylic acid or a derivative and the viscosity of these adhesives being, at 180.degree. C., less than 50 Pascal seconds.

The examples show that Aa is chosen from ethylene-propylene or ethylene-butene rubbers and Ab is an ethylene/ethyl acrylate copolymer, at least one being grafted with maleic anhydride.

The quality of the adhesion obtained is measured by the SAFT test according to ASTM D 4498, which measures the cohesion limit temperature at shear, and by the T peeling test according to ASTM 1876-72.

New thermofusible adhesive compositions have now been found which are stronger in the SAFT test and in the T peeling test and which do not require grafting.

The present invention is a thermofusible adhesive composition comprising:

a at least one essentially amorphous poly(alpha-olefin),

b at least one copolymer of ethylene and an alkyl (meth)acrylate,

the cloud point of the composition being below 170.degree. C.

The essentially amorphous poly(alpha-olefins) are referred to as "APAOs" hereinafter. APAOs of the compositions of the invention advantageously have at least one of the following characteristics:

viscosity at 190.degree. C. between 3000 and 50,000 mPa s,

softening temperature (bead and ring, ASTM D 28) between 80 and 160.degree. C.,

needle penetration (0.1 mm) of 4 to 21,

density at 23.degree. C. between 0.85 and 0.9 g/cm.sup.3,

viscosity index (J) between 40 and 95 cm.sup.3 /g,

molecular weight MW between 30,000 and 75,000,

intrinsic viscosity (100 ml/g) between 0.4 and 0.9.

The substantially amorphous poly(alpha-olefin) a of the invention is preferably made from the alpha-olefins ethylene, propylene, butene, and hexene. In accordance with the present invention, the substantially amorphous poly(alpha-olefin) may be an ethylene/propylene, propylene/butene, or ethylene/hexene copolymer. However, ethylene/propylene/butene copolymers with a high butene content, ethylene/propylene/butene copolymers with a high propylene content, or butene homo- or copolymers are preferred.

The alkyl group of the alkyl (meth)acrylate of the copolymer b may be linear, branched or cyclic, and may have up to 20 carbon atoms. Isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and propyl (meth)acrylate are illustrative. n-Butyl acrylate is preferred. The copolymer b may contain 20 to 45% by weight of alkyl (meth)acrylate, and preferably 26-40%.

The compositions of the invention are prepared by simple mixing of the various products a and b in the molten state.

In order to measure the cloud point, the composition of the invention is heated to 180.degree. C.; it is stirred until homogenized, a thermometer is inserted into the composition and time is allowed for the temperature to stabilize. The temperature at which the composition remaining on the end of the thermometer begins to cloud is noted. The value read corresponds to the cloud point.

The cloud point measures the compatibility of the various components of the thermofusible adhesive.

Homogenous compositions are thus obtained, they are easier to prepare and may be stored. They are also easier to use, there is no risk of separation of the constituents or of blocking of the equipment during use.

The Applicant has discovered that most of the essentially amorphous poly(alpha-olefins) and of the copolymers b are compatible and thus the cloud point is below 170.degree. C. A person skilled in the art may easily choose the proportions of a and b and the various properties of the products a and b in order to obtain a cloud point below 170.degree. C. It would not be departing from the scope of the invention to add a small amount of a crystalline polyolefin or poly(alpha-olefin) to the composition of the invention, provided that the cloud point of the composition is below 170.degree. C.

The proportions of a and b may vary within a wide range. Good results are obtained with weight proportions of 60 parts to 20 parts of a per 20 to 80 parts of b. 30 to 50 parts of (a) per 8 to 20 parts of (b) are preferably used.

The cloud point is advantageously below 165.degree. C.

The compositions of the invention may also comprise tackifying resins, waxes, plasticizers and stabilizers.

As regards the tackifying resins, those of low polarity and free of any unsaturation, such as polyterpene resins, terpene resins, essentially aliphatic hydrocarbon resins and esterified and hydrogenated colophony resins, are advantageously used. The terpene resins are, for example, those derived from alpha-pinene, beta-pinene or dipentene. The essentially aliphatic hydrocarbon resins result from the catalytic or thermal polymerization of petroleum fractions rich in olefins and diolefins.

The Applicant has discovered that the tackifying and breaking elongation properties of the thermofusible adhesive of the invention are increased by these tackifying resins; however, the breaking forces are decreased.

As regards the waxes, polyethylene waxes, microcrystalline waxes or Fisher-Tropsh waxes advantageously used; they lower the viscosity and modify the open time and the setting time.

The open time denotes the time required for the thermofusible adhesive to pass from the liquid form to the more or less solid form which no longer allows the adhesive bonding. The setting time denotes the time taken for the assembly to become integral.

The room temperature, the temperature of the support, that of the thermofusible adhesive and the amount of adhesive deposited may modify the open time.

As regards the plasticizers, aliphatic or naphthenic oils may be used.

Anti-UV stabilizers and antioxidants are also added.

A person skilled in the art can readily determine the possible amounts of tackifying resin, of waxes, of plasticizers and of stabilizers as a function of the desired adhesion properties or the desired viscosity; the open time, and the nature and surface state of the materials to be adhesively bonded.

The amount of poly(alpha-olefin) a and of copolymer b may be from 100 parts per 50 to 200 parts of the tackifying resin, waxes plasticizers and stabilizers altogether.

The Applicant has discovered that the tackifying resins, the waxes and the plasticizers mentioned above were compatible with the compounds a and b of the invention. Thermofusible adhesives having a cloud point below 170.degree. C. are thus obtained. The Applicant has noted that the compounds a and b were particularly compatible, and hence compositions consisting only of the products a and b have a cloud point very much below 170.degree. C.

A person skilled in the art can advantageously select the products a and b such that the cloud point of the composition consisting of a and b alone is below 100.degree. C. and preferably between 30 and 75.degree. C.

Thus, by adding the tackifying resin, the waxes and the plasticizers, an adhesive having a cloud point below 170.degree. C. is obtained.

Thermofusible adhesives were prepared from the following products:

The weight content of comonomers was determined by infrared.

The characteristics of the copolymer P, Q and R are as follows:

All the formulations of these thermofusible adhesives are stabilized with 3,000 ppm of Irganox 1010.

Hence, the following are examples of thermofusible adhesives and the corresponding evaluations. The weight proportions are indicated in the corresponding columns of the table. - BROOKFIELD VISCOSITY AT 10 T PEELING CREEP AT OLEFINIC BEAD RING REV/MIN ALU/ALU 50.degree. C. AMORPHOUS ETHYLENIC TACKIFYING TEMPERATURE mPa s SAFT (N/cm) ALU/ALU COPOLYMER A COPOLYMER B RESIN PLASTICIZERS CLOUD POINT .degree. C. A7 .degree. C. AT 23.degree. C. (MINUTES) EXAMPLES 40% 10% 30% 20% .degree. C. ASTM D 28 ASTM 3236 ASTM 4498 ASTM 1876 LOAD 500 g 1 Q I J N >190 49 2200 56 8 5 2 Q B J N 140 54 2600 59 8.4 5.30* 3 Q I K N >190 48 2300 54 7.2 5 4 Q B K N 140 55 2550 58 7.8 5.30* 5 Q I L N >190 49 2320 54 7 5 6 Q B L N 150 55 2500 57 7.5 5.30* 7 R I J N >190 47 2320 55 7.6 4 8 R B J N 160 51 2420 58 8.1 5 9 R I K N >190 48 2300 53 7.5 4 10 R B K N 160 52 2450 56 8 5 11 R I L N >190 47 2400 52 7.7 4 12 R B L N 160 52 2580 55 8.2 5 13 P A M O 140 70 2370 55 8 5 14 P B M O 160 49 2500 55 8 5 15 P C M O 160 48 2520 55 8.5 5 16 P D M O 160 48 2420 55 8 5 17 P E M O 158 48 2200 56 7.6 5 18 P F M O 163 47 2280 53 7.3 4.30* 19 P G M O >190.degree. C. 45 2020 50 6.2 4 INCOMPATIBLE 20 P H M O >190.degree. C. 44 2050 49 6.8 4 INCOMPATIBLE 21 P I M O >190.degree. C. 44 2150 51 6.9 4 INCOMPATIBLE