GB2199039A - Pressure-sensitive adhesives - Google Patents

Description

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1 - 1 "PRESSURE-SENSITIVE ADHESIVES" This invention relates to pressure-sensitive adhesives having acrylic polymers combined with a selected class of aromatic hydrocarbon resins.

Pressure-sensitive adhesives of an acrylic type are known for their high transparency and superior ageing resistance, and therefore, have found wide application not only to tapes suitable for wrapping, aesthetic and masking purposes, labels, seals, stickers and the like, but also for interior decoration work. Certain tackifiers are used to this end to provide the desired adhesive characteristics.

Rosin and terpene resins are in common use as tackifiers. Petroleum hydrocarbon resins have also been proposed as tackifiers. These hydrocarbon resins, however, are not well compatible with acrylic polymers and are also inadequate as regards adhesivity and hence do not warrant commercial application..

It has now been found that pressure-sensitive acrylate adhesives of superior physical properties can be obtained by the addition of selected tackifiers of a hydrocarbon resin type. These tackifiers are easy to derive from aromatic distillates readily available from petroleum and coal tar.

The adhesives according to the invention are applicable in a solution or aqueous emulsion form.

It is thus a primary object of the invention to provide improved pressuresensitive adhesives which are economically feasible and highly capable of exhibiting excellent tackiness, adhesion and cohesion characteristics.

k According to the invention, there is provided a pressure-sensitive adhesive comprising an acrylic polymer and a hydrocarbon resin having a hydroxyl number of 40 - 130 and a softening point of 60 0 - 150 0 C. The adhesives of the invention can be applied in solution or in the form of an aqueous emulsion.

Hydrocarbon resins suitable for the purpose of the invention may be obtained by polymerizing one or more of either or both aromatic petroleum and coal tar fractions distilling at from 140 0 to 240 0 C with one or more phenols in the presence of a Friedel-Crafts type catalyst. The resulting reaction mixture can conveniently be after-treated to decompose the catalyst with an alkaline material and also to remove unreacted oils and low polymers, whereby a pure polymerizate is obtained.

Petroleum fractions useful in the invention include cracked oils produced upon thermal cracking of naphtha, kerosine, light oil and the like. Coal tar fractions used herein include heavy gas oils produced from coke ovens. Both fractions have a boiling point in the 0 0 range of 140 - 240 C. Contained in each such fraction are usually aromatic olefins having a carbon number of 8 - 10 and including styrene, alkylstyrenes, indene, alkylindenes, coumarone and the like, the olefins content being 35 percent by weight.

Eligible phenols include, for example, phenol, cresol, xylenol, t-butyl phenol, and nonyl phenol. These phenols may be used alone or in combination.

The amount of the phenol to be added may be in the range of 5 to 40 parts, preferably 10 - 30 parts, by weight based on 100 parts by weight of the petroleum and/or coal tar fractions. This range should be observed to attain a desired range of hydroxyl numbers as later described.

Catalysts useful in the reaction of the petroleum and/or coal tar fractions with a phenol or phenols include, for example, boron trifluoride, aluminium chloride, boron trifluoride-phenol complexes, and boron trifluoride-dialklyl ether complexes. The amount of the catalyst to be added should usually be in the range of 0.05 - 5 percent, preferably 0. 1 - 3 percent, by weight of the total petroleum and/or coal tar fractions.

Reaction temperature and time may be at from -10 0 to +80 0 C for about 10 minutes to 5 hours. After completion of the reaction, the catalyst may be decomposed with sodium hydroxide, sodium carbonate, or a similar alkali, followed by removal of unreacted oils and low polymers as by evaporation or distillation.

Importantly, the hydrocarbon resins contemplated under the invention should have a hydroxyl number in the range of 40 - 130, preferably 50 120, and a softening point in the range of 600 150 0 C, preferably 80 0 130 0 C.

Smaller hydroxyl numbers than 40 would invite insufficient compatibility with the polyacrylate base and inadequate adhesion. Greater hydroxyl numbers than 130 would improve these qualities, but conversely make the resulting tackifier objectionably colourable and less productive.

Lower softening points than 600C would induce reduced cohesion, whilst higher softening points than 150 0 C would fail to give adequate tackiness and sufficient adhesion.

- U In the practice of the invention, the tackifier may be blended with a base polymer selected from acrylic polymers. -The amount of the tackifier to be used may be in the range of 3 - 70 parts, preferably 5 - 50 parts, by weight based on 100 parts 5 by weight of the base polymer.

Eligible base polymers may be polymeric acrylic esters in common use as base polymers for pressure-sensitive adhesives. Examples of the base polymers include homopolymers of acrylic esters, copolymers of different acrylic esters and copolymers of acrylic esters with ethylenically unsaturated comonomers. The choice of the base polymer depends upon the particular field of application. Particularly preferred is a base polymer resulting from copolymerizing more than 30 percent by weight of one or more acrylic esters having an alkyl group of 1 - 8 carbon atoms with less than 70 percent by weight of one or more ethylenically unsaturated comonomers. The above acrylic esters when polymerized become self-adherent in nature. Preferred are acrylic esters having an alkyl group of 4 - 8 carbon atoms, specific examples of which include methyl acrylate, ethyl acrylate, n-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, hexylethyl acrylate, octyl acrylate, and 2- ethylhexyl acrylate.

Ethylenically unsatured comonomers used herein, with given glass transition temperatures and polar groups, allow the corresponding acrylic esters to be rendered more suitable for the particular application intended. Specific examples of comonomers include carboxyl group-containing monomers such as acrylic 1 1 i, k.

114 acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, maleic anhydride, and ethyl maleate, hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate, amide-group- containing monomers such as acrylamide, methacrylamide, N-methylacrylamide and N-methylmethacrylamide, monomers containing amide groups and methylol groups, such as N-methylolacrylamide and N-methylolmethacrylamide, and amino group-containing monomers such as aminoethyl acrylate, aminoethyl methacrylate, dimethyl-aminoethyl acrylate, and dimethylaminoethyl methacrylate.

Other ethylenically unsaturated comonomers may also be employed which include, for example, monomers containing single unsaturated bonds such as vinyl acetate, vinyl ether, styrene, alpha-methylstyrene, and vinyl toluene, and monomers containing double or multiple unsaturated bonds such as divinyl benzene, diallyl maleate, diallyl fumarate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate.

The base polymers may be obtained by bulk, solution, emulsion or suspension polymerization or copolymerization. The number-average molecular weight of the polymer should usually be larger than 01 5,000, preferably larger than 10,000 with cohesion in view, but smaller than 200,000 having regard to workability.

There may be used numerous additives other such as other tackifiers, antioxidants, pigments, fillers, 5 plasticizers and cross-linking agents, including polyvalent metal oxides and hydroxides, epoxy resins, polyisocyanates, methylol condensates, polyamines and polyamides.

The invention will be further described by way of the following examples which are not to be regarded as limiting the invention. In these examples, all hydroxyl numbers are as determined by the acetic anhydride method (IEC, Anal. Ed., vol. 17, p. 394, is 1945), and all parts and percentages are by weight unless otherwise stated.

Preparation of Hydrocarbon Resins Example 1 Into 100 parts of a petroleum fraction derived from steam-cracked naphtha and having a boiling point of 1450 - 1900C and an unsaturated components content of 43% were incorporated 8 parts of phenol and 0.6 part of a boron trifluoride-phenol complex catalyst. The mixture was polymerized at 300C for 3 hours after which aqueous sodium hydroxide was added to decompose the catalyst. The polymerizate was washed with water and then vacuum-distilled to remove unreacted oils and low fi A- -Q t 7 polymers. There was thus obtained 47% of a hydrocarbon resin according to the invention, i.e. Resin I having a hydroxyl number of 54 and a softening point of 113 0 C.

Examples 2 and 3 Coal tar-derived gas oil was distilled to collect a fraction boiling at from 176 0 to 190 0 C. he resulting oil contained unsaturated components such as indene-methyl indene and coumarone, in amounts of 54% and 6.8% respectively, and other similar components in an amount of 7.6%. To 100 parts of the oil were added as two samples, 12 parts and 25 parts respectively of commercially available cresylic acid composed of 300% of phenol, 10% of o-cresol, 25% of m- cresol, 15% of p-cresol and 10% of xylenol, and then in each case a boron trifluoride-ether complex. The mixtures were polymerized at 60 0 C for 2 hours, followed by treatment-as in Example 1, thereby obtaining two resins according to the invention, 62% of Resin II and 69% of Resin III. Resin II had a hydroxyl number of 75 and a softening point of 132 0 C, and Resin III corresponding values of 116 and 93 0 C.

Comparative Example 1 The procedure of Example 1 was followed except that the amount of the phenol was changed to 1.5 parts and that polymerization was effected at 60 0 C for 2 hours, whereby 43% of Resin IV was obtained. This resin had a hydroxyl number of 15 and a softening point of 115 0 C.

Comparative Example 2 The procedure of Examples 2 and 3 was followed except that 6 parts of phenol was used in place of the cresylic acid. There was obtained 58% of Resin V having a hydroxyl number of 41 and a softening point of 156 0 C.

Comparative Examples 3 - 5 Two commercially available resins were used, one being a terpene phenol resin having a softening point of 100 0 C and designated as Resin VI, and the other being a pentaerythritol rosin ester having a softening point of 1200C and designated as Resin VII. An additional control was devoid of hydrocarbon resin.

Production of Adhesives Different adhesives were produced by blending 100 parts of a commercially available acrylic polymer solution having a non-volatiles content of 40% with 2.5 parts of an isocyanate hardener having a solids content of 37.5% and also with each of Resins I to VII in amounts Of 10 parts and 15 parts, respectively, based on the weight of the solid acrylic polymer.

The adhesives were each coated with an applicator onto a polyester film in a dry thickness of 25 - 30 microns, followed by crosslinkage at 100 0 C for 5 minutes. The resulting tapes were examined for tackiness, adhesion and cohesion under the conditions V 1 z W t given below and with the results as tabulated.

Testinq Procedures 1. Tackiness Test The ball tolling method of J. Dow was followed. A 25 mm x 250 mm coated tape was contact-laminated onto a kraft tape with coated face projecting 100 mm from the latter tape. The laminate was placed obliquely at an angle of 300 and at an ambient temperature of 200C. From a distance of 100 mm, steel balls of varying diameters were rolled on to the coated side. Tackiness was determined by the maximum diameter of a ball held still on the coated side.

2. Adhesion Test A 25 mm wide coated tape was contact-laminated onto a 125 mm long polyethylene plate. The tape was released from the fixed polyethylene plate at a temperature of 2'OOC, at an angle of 1800 and at a speed of 300 mm/min using an Instron type tester (Tensilon UTM- III-100, Toyo Baldwin Co., Ltd.).

Adhesive force was adjudged by the load required for this releasing.

3. Cohesion Test A 25 mm wide coated tape was contact-laminated onto a stainless steel plate at an adhesion area of 25 mm x 25 mm. The laminate was suspended perpendicularly at a temperature of.60.oC and at a load of 1,000 g on a creep tester (Toyo Seiki Co., Ltd. ). Cohesion was measured by the length of time required for the tape to drop or by the length of displacement after a lapse of 24 hours.

As appears clear from the test results, the adhesives representing Resins 1 to 3 are all satisfactory in respect of tackiness, adhesion and cohesion. Resins IV and V outside the specified ranges of hydroxyl numbers or softening points were inadequate in tackiness and adhesion as evidenced by Comparative Examples 1 and 2 and even inferior to the control devoid of hydrocarbon resin. Cohesion was insufficient in conventional Resins VI and VII.

1 11 U a 11 - T a b 1 e resinous tackifier tackiness adhesion cohesion (ball no.) (g) (mm) Example 1 (resin 1) 18 630 less than 1 2 (resin 11) 15 550 less than 1 3 (resin 111) 18 650 less than 1 Comparative Example 1 (resin IV) 15 200 less than 1 2 (resin V) 12 350 less than 1 3 (resin VI) is 500 1 4 (resin VII) 17 640 dropped after 7 hrs (not added) 19 400 less than 1 1

Claims (10)

1. A pressure-sensitive adhesive comprising an acrylic polymer and a hydrocarbon resin having a hydroxyl number of 40 - 130 0 0 and a softening point of 60 - 150 C.

2. A pressure-sensitive adhesive according to claim 1 wherein said hydrocarbon resin is present in an amount of 3 - 70 parts by weight based on 100 parts by weight of said acrylic polymer.

3. A pressure-sensitive adhesive according to claim 1 or claim 2 wherein said hydrocarbon resin is derived from polymerization of at least one of either or both aromatic petroleum and coal tar 0 0 fractions having a boiling point of 140 - 240 C with at least one phenol in the presence of a Friedel-Crafts type catalyst.

4. A pressure-sensitive adhesive according to claim 3 wherein said one phenol is phenol, cresol, xylenol, t-butyl phenol or nonyl phenol.

5. A pressure-sensitive adhesive according to claim 3 or claim 4 wherein said catalyst is boron trifluoride, aluminium chloride, a boron trifluoride-phenol complex, or a boron trifluoride-dialkyl ether complex.

6. A pressure-sensitive adhesive according to any one of claims 3 to 5 wherein said catalyst is present in an amount of 0.05 - 5 percent by weight of said fraction.

7. A pressure-sensitive adhesive according to any one of the preceding claims wherein said acrylic polymer is an acrylic 1 I.

4 _P ester homopolymer or copolymer having a number-average molecular weight of 5,000 - 200,000.

8. A pressure-sensitive adhesive according claim 7 wherein said homopolymer is a polymer Of methyl acrylate, ethyl acrylate, n-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, hexylethyl acrylate, octyl acrylate or 2-ethylhexyl acrylate.

9. A pressure-sensitive adhesive according to claim 7 wherein said copolymer is a polymer of at least one acrylic ester having an alkyl group of 1 - 8 carbon atoms with at least one ethylenically unsaturated comonomer.

10. A pressure-sensitive adhesive according to claim 9 wherein said comonomer is acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, maleic anhydride, ethyl maleate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylamide, methacrylamide, N-methylacrylamide, N- methylmethacrylamider N-methylol-acrylamide, N-methylolmethacrylamide, aminoethyl acrylate, aminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, vinyl acetate, vinyl ether, styrene, alpha-methylstyrene, vinyl toluene, divinyl benzene, diallyl maleate, diallyl fumarate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,6- hexanediol diacrylate, 1,6-hexanediol -dimethacrylate, trimethylolpropane triacrylate or k_ trimethylolpropane trimethaerylate.

1 Pubilshed 1988 at The Patent Office. State House. 66'71 Hig.'l Holborn, London WClR 4TP FVrther copies may be obtained from The Patent office, SaJes Branch, St Mary Cray, Orpington, Kent BR5 3RD. PrInted by Multiplex techniques ltd. St Mary Cray, Kent. Con. 1/87.