CA1046174A - Pressure-sensitive adhesive compositions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A pressure-sensitive adhesive composition is dis-closed which comprises synthetic and/or natural rubber in combination with a synthetic resin. This resin is an aromatic hydrocarbon resin resulting from the polymeriza-tion of a selected fraction of thermally cracked petroleum oil, which fraction has a boiling point in the range of 140° to 220°C and contains such contents of conjugated diolefins and indene and its derivatives and such rates of conjugated diolefin content and indene content that are severely restricted to provide highly satisfactory tackiness, adhesive and cohesive strength and other important properties of the resulting pressure-sensitive adhesive compounds.

Description

:~04~174 This invention relates to improvements in and relating to adhesive compositions and more particularly to a pressure-sensiti~e adhesive composition comprising a blend of a rubber component and an aromatic hydrocarbon resin.
Generally, pressure-sensitive adhecive compo~itions are considered satisfactory if they have a proper balance of tackiness, adhesive stren~th, cohesive stren~hh and weather-resistance. Resinous materials which serve as the adhesion-and tack-imparting component must be highly compatible with rubbers and soluble in solvents.-Heretofore, pressure-sensitive adhesive compositions which are useful as adhesive coatings on tapes, sheets of paper, fabric and other backing materials have been proposed which are mixtures of natural rubber and/or synthetic rubber with a terpene resin. This resin is alp~a-pinene, beta-pinene or mixtures thereof which are-present in refined pine resins.
The~e naturally occuring substances are limited in their origin, and their resources are growing more and more scarce with con-siderable yield and price fluctuations.
As the-tac~$i~r~-f r E~essure-sensitive adh~sive com-positions there are also known rosin esters, aliphatic hydro-carbons and cumaDQne~-indenQ resin. These resins however are inferior to terpene resins in the balance of cohesive stre~gth, adhesive strength, tackiness and other important properties, and are furthermore not-ver~-compatibl~ with rubbers or not well soluble in solvents.
Therefore, it is the primary object of this invention to provide improved pressure-sensitive adhesive compositions ~.~

- 2 - ~

~046~74 ~ ~which contain synthetic or natural rubbers in combination with aromatic hydrocarbon resins which are less costly, more abundantly available and comparable to or even better in ~uality than terpene resins.
In accordance with the invention, there is provided a pressure-sensitive adhesive composition which comprises 100 parts by weight of a rubber component including styrene-butadiene copolymers or rubbery mixtures chiefly consisting of styrene-butadiene copolymers, in combination with from 20 to 140 parts by weight of a resin component consisting of an aromatic hydrocarbon resin resulting from the polymerization of a thermally cracked petroleum fraction at temperatures in the range of -30 to +60~. in the presence of a ~riedel-Crafts catalyst added in amounts ~f 0.01 to 5 weight percent of said fraction, said fraction boiling in the range of 140 to 220C
and having a conjugated diolefin content of 0.7 weight percent or less, a rate of conjugated idiolefin content of 3 percent or less, a total content of indene and its alkyl derivatives of 2 weight percent of less and a rate of indene content of 8 percent or less.
The term rubber component as used herein includes $tyrene-butadiene copolymer rubbers commonly known as SBR and rubbery mixtures chiefly consisting of SBR. Illustrative of these rubber components are cold rubber type SBR or hot rubber type SBR prepared by an emulsifying polymerization ~-process, and random copolymer type or block rubber type SBR
prepared by a solution polymerization process. These SBRs may be mixed ~ith other tvpes of rubber such as for example natural rubber, isoprene rubber, butyl rubber, polyisobutylene, ~ 3 .~ . - . . . .

~046~'74 butadiene rubber, ethylen0-propylene rubber, ethylene-propylene d:Lene rubber, chloroprene rubber, nitrile rubber and the like.
Preferred among these rubbers are natural rubber and isoprene rubber. They may be used in amounts of 0 - 100 parts by weight, preferably 0 - 80 parts by weight, more preferably 0 - 60 parts by weight per 100 parts by weight of SBR.
The term resin component includes aromatic hydrocarbon resins resulting from the polymerization of a thermally cracked petroleum fraction having a boiling point in the range of 140 to 220C.
Generally, petroleum hydrocarbon resins are prepared by polymerizing thermally cracked, normally liquid petroleum oil fractions and have boiling points ranging between 20 and 280C, between 20 and 170C and between 140 and 280C. When a petroleum fraction boiling in the range of 20 to 140C is used for polymerization, the resulting resin will be non-aromatic with no aromatic ring. Since such fraction contains large amounts of conjugated diolefins and non-conjugated diolefins, the resin has a high degree of unsaturation and hence a very low weather-resistance. With petroleum fractions boiling in the range of 140 to 280C, the resulting resin will be aromatic but still not quite satisfactory in its resistance to weather.
A close investigation of the characteristic properties of each of the various components in the starting petroleum fractions has now indicated that it is possible to obtain a highly satisfactory tack-imparting resin by precise separa-tion of certain selected components in the starting oil.

The resin component of the pressure-sensitive adhesive composition according to the invention is an aromatic hydro-carbon resin prepared from a starting petroleum fraction boiling in the range of 140Q to 220C and containing unsaturated com-pounds which are substantially styrene and its derivatives, and indene and its derivatives. This starting material is regulated to satisfy a condition such that the content of con-jugated diolefins i8 0.7 weight percent of less, the rate of conjugated diolefin content is 3 percent of less, the total content of indene and its alkyl derivatives is 2 weight per-cent or less and the rate of indene content is 8 percent or less.
The starting material is subjected to polymerization in the presence of a Friedel-Crafts catalyst. The catalyst is removed, ;
and thereafter unreacted petroleum fraction and low molecular polymers are removed by evaporation or distillation, whereby an aromatic hydrocarbon resin having the desired properties is obtained.
The starting material for the resin employed in accord- ~
ance with the invention is a thermally cracked petroleum fracr ~ -tion boiling in the range of 140 to 220OC which is present in the by-products obtained when ethylene, propylene, butenes and butadienes are produced by thermal cracking as by for example steam cracking of petroleum fractions such as naphtha, kero-sene and light oii fractions.
A gas chromatographical analysis was made of the petro- ;
leum fraction boiling in the above range, with the results tabulated below.

,, - 5 - ~

;,.~. .. .. . . .
, ~: - , . .
: . , FRACTION

Boiling Component Point C Content _ Hg abs) Percent) Styrene ------------------------------ 145.8 13-20 Allylbenzene ------------------------- 156-157 0.1-1 ~-Methylstyrene ----------~ ---- 165.4 0.5-6 ~-Methylstyrene ---------------------- 175 0.5-6 p-Vinyltoluene ----------------------- 168~
m-Vinyltoluene ----------------------- 169~ 10-20 o-Vinyltoluene ----------------------- 171J
Indene ------------------------------- 182.2 2-11 Methylindene homologs ---------------- 184-206~
Dimethylindene and ethylindene~ 1-3 homologs ------------------------ 4~212J
Xylene (o-, m-, and p-isomers) ------- 138-142~
Ethylbenzene ------------------------- 136.2~ 17-10 Isopropylbenzene --------------------- 152.5J
Ethyltoluene (o-, m-, and p~-isomers) - 158-164.6 18-7 n-Propylbenzene ---------------------- 159.6 1-0.1 Trimethylbenzene (1,3,5-, 1,2,4-, and 1,2,3,-isomers) ------------- 164.6-176.5 25-6 Indane ------------------------------- 177 9-1 Methylindane homologs ---------------- 182-203 Dimethyl and ethylindane homologs -----------------~ 200~ 2-0.5 Naphthalene -------------------------- 218J
Dic~yclopentadiene (1) ---------------- 170 0.2-3 Undetected component (2) -------------140- 220 0.7-5.4 .

- ~0461'74 Note ~ A part or whole of the dicyclopentadiene may in some cases be depolymerized with heat into cyclo-pentadiene.
~2): A part of the undetected component contains cyclo-pentadiene-methylcyclopentadiene co-dimer and methylcyclopentadiene dimer. A part o~ whole there- - ' of may in some cases be depolymerized with heat into cyclopentadiene and methylcyclopentadiene. It is possible to analyze these monomers by gas chroma- ;
tography.
The total of styrene and its derivatives, indene and ~ ;~
its derivatives is considered as the polymerizable component.
In case cyclopentadiene and methylcyclopentadiene are produced -~-by heating and contained in the starting oil as described in Notes (1) and (2) of Table I, these monomers are also considered as polymerizable components.
In order to produce a hydrocarbon resin suitable for the purpose of the invention, it is essential that a thermally cracked petroleum oil fraction boiling in the range of 140 to ~-220C be precisely distilled to obtain a particular fraction , which satisfies the following conditions. The former fraction is conveniently referred to as "starting cracked oil", and the latter fraction as "starting fraction".

STARTING FRACTI ON ;
(a) The total content of cyclopentadiene and methyl~
cyclopentadiene, that is, the content of conjugated diolefin in the starting fraction separated from the starting cracked ~V461'74 oil is adjusted to a value of 0.7 wt. percent or less and the '~
rate of content of the conjugated di~efin defined in the following equation (1) is adjusted to 3% or less.

Rate of con~ugated diolein content (%) Conjugated diolefin content in the _ starting fraction (wt. ~) x 100 --- (1) Polymerizable component in the starting fraction twt. %) (b) The total content of indene and its alkyl deriv-atives in the starting fraction is adjusted to a value of 2 wt.
percent or less and the rate of content of the indene defined in the following equation (2) is adjusted to 8% or less.
.
Rate of indene content (%) Content of indene and its alkyl derivatives in the starting fraction (wt. %) ' ' x 100 --- (2) =

Polymerizakle componea~ in the starting fraction (wt ~) Each component of the starting cracked oil and of the ~ , starting fraction is ana~yzed by gas chromatography under the following conditions.
(1) Styrene, allybenzene, 1,3,5-trimethylbenzene, , and o-ethyltoluene are analyzed at 100C with a flow rate of ' ,helium at 60 cc/min. by empl ~ g a co~umn 3 meters long in which UCelite''* (manufactured by Johns-Manville Corp.) con-taining 20% by w~ight of "Apiezon L"** grease (manufactured('by Associated Electri~al,Industries Ltd.) is filled.

*Trademark for a 325-mesh uncalcined, amorphous diatomaceous earth.
**Trademark for a hydrocarbon grease having a very low vapor pressure and good thermal stability produced by a molecular distillation.

~0461~4 (ii) Other components than those listed in (i) is analyzed at 125C with helium flowing at a rate of 60 cc/min.
by employing a similar column in which "Celite" containing 20% by weight of polyethylene glycol 4,000 is filled.
The total content of styrene, its alkyl derivatives, indene, its alkyl derivatives, cyclopentadiene, and methyl- ;
cyclopentadiene analyzed as above is considered as a poly-merizable component.
For the separation of the starting fraction from the starting cracked oil, there may be employed any convenient and suitable process such as for example atmospheric dis- ;
tillation, vacuum distillation and extractive distillation.
Ac previously stated, it is one of the requisite conditions in the preparation of the starting fraction from the starting cracked oil that the total content of cyclo-pentadiene and methylcyclopentadiene, namely, the content of conjugated diolefin should be held at a value of 0.7 weight percent or 12ss and the rate of conjugated diolefin content at 3 percent or less. This condition may be conveniently ;~
met with by distilling either the starting cracked oil or the fraction which contains the required total content of indene and alkyl indene and the required rate of indene content, thereby selectively removing conjugated diolefins.
This operation is facilitated by the fact that the boiling points of cyclopentadiene and methyl cyclopentadiene are 42C and 70C, respectively, which are lower than the initial boiling point of the starting cracked oil.

If these conjugated diolefins are in the form of Diels-~lder dimers as found in the starting cracked oil, there may be conveniently employed an atmospheric distilla-tion to obtain the adjusted values of total indene content and rate of indene content, in which distillation the con-jugated diolefin dimers can be depolymerized into conjugated diolefins which may be thereafter removed from the starting fraction by distillation.
However, if such conjugated diolefin dimers are found only in a minor proportion in the starting fraction, it is not always necessary to remove them because the dimers as compared to conjugated diolefins are less harmful to the resulting resin with respect to its resistance to weather and heat.
In order to satisfy the second requisite condition that the total content of indene and alkyl indene is 2 weight percent or less and the rate of indene content is 8 percent or less, the starting cracked oil may be conveniently dis-tilled to remove conjugated diolefins, with the distillate further subjected to precise fractionation. Since o-vinyltoluene and indene normally boil at 171C and 182~2C, respectively, this boiling difference may be utilized so that the starting fraction satisfying the requirements of the resin of the invention can be taken overhead from the column.
In the art of petroleum resins it is an entirely new concept to take a selected component in a thermally cracked petroleum oil and subject it to a precise fractionation to obtain a fraction having highly restricted characteristics.

-104t;174 Particularly, as disclosed herein, this concept is directed to restricting the content and rate of content of c~jugated diolefins and indenes;to certain values a~ above listed. This operation can not be performed by ordinary known distillation columns but it requires an atmospheric or vacuum fractionator equiE~ped with a greater number of trays.
To the starting fraction prepared as above is added 0.01 - 5 wt. percent of a Friedel-Crafts type catalyst such as boron trifluoride, aluminum chloride, and a complex compound of boron trifluoride and phenol, preferably, boron trifluoride, boron trifluoride etherate, and boron trifluoride phenolate. -The resulting mixture is polymerized at a temperature ranging between -30 and +60C for a period of 10 minutes to 15 hours. ~
Then, the catalyst is decomposed and removed with alkalis such ~ ;
as caustic soda and sodium carbonate. If necessary, the thus treated reaction product is washed with water, and unreacted oil and low molecular weight polymers are separated from the reaction product by evaporation or distillation. The resulting product is an aromatic hydrocarbon resin having a softening point of 60 - 120C and a bromine value of 15 or less. It has excellent resistance to weather and heat. The preferred resin here has a softening point of 80 - 100C.
It has now been found that if any of the four Lmportant criteria for the starting fraction; namely, 1) 0.7 wt.% con-jugated diolefin contene, ~i) 3~ conjugated diolefin content rate, iii) 2 wt.% indene and its alkyl derivative content, and iv~ 8% indene content rate, should be neglected, the hydro-carbon resin resulting from the polymerization of such defective starting fraction will exhibit very poor resistance to weather and heat, will become yellowish and when used in a pressure-sensitive adhesive composition, will be unsatisfactory in respect of the weather-resistance, co-hesive strength, adhesive streng~h, tackiness and tackiness life.
The pressure-sensitive adhesive compositions according to the invention are prepared by blending the above-specified aromatic hydrocarbon resin with styrene-butadiene rubber (SBR) or rubbery mixtures chiefly consisting of this SBR. Blending ratios may vary widely. Generally, the resin may be 20 to 140 parts by weight, preferably 30 to 120 parts by weight per 100 parts rubber. If desired, there may be added various addi-tives including for example about 0 to 60 parts of a softening agent, 0 to 60 parts of a plasticizer, 0 to 100 parts of a filler and 0 to 50 parts of an ageing inhibitor. These parts may depend upon the type of rubber component used but may usually be in the range of 0 to 100 parts per 100 parts rubber.
The invention will be further described with reference to the following examples presented only for purposes of illustration but not in the limiting sense.

Example 1 The resin component for use in the pressure-sensitive adhesive compositions of the invention is prepared in the manner following.
The starting cracked oil previously defined was a by-product of the steam cracking of naphtha and had a boiling , 1046~74 point in the range of 140C to 220C. It was analyzed by gaq chromatography to reveal the following composition:

Composition of Starting Cracked Oil Polymerizable components (wt. %) --------------- 49.0 Total content of cyclopentadiene and methyl cyclopentadiene (wt. %) ----------------- 1.6 Total content of indene and its ~- -alkyl derivatives (wt. %) ---------------------- 8.4 Content of dicyclopentadiene (wt. %) ----------- 0.4 Rate of conjugated diolefin content (%) -------- 4.0 Rate of indene content (~)---------------------- 18.5 The above identified starting cracked oil was charged via a heater into a first fractionator A-l and thence to a second fractionator B-l, both fractionators being specified in the following table.

TABLE II-SPECIFICATIONS AND OPERATING CONDITIONS
OF FRACTIONATORS

Fractionators ------------------------------ A-l B-l Type of tray ------------------------------- (1) (2) Number of trays ---------------------------- 30 7 Feed tray (from the bottom) ---------------- 18 4 Feed temperature (C) ---------------------- 108 55 Bottom preS~ure (mm. Hg. abs.) ------------- 120 110 Bottom temperature (C) ------------------- 145 120 Top temperature (C) ----------------------- 93 25 , Top pressure (mm. Hg. abs) --------------- 68 95 Residence time at bottom (hr.) ----------- 1.0 0.5 Reflux ratio ----------------------------- 5.0 2.0 (1) ----- Sieve (2) ----- Bubble cap.

The operating conditions of the fractionator A-l had been chosen so that the overhead fraction of this fractionator contained a total content of indene and its alkyl derivatives of 2 weight percent or less and a rate of indene content of 8 percent or less. The overhead product of the first fraction-ator A-l was thereafter introduced into the second frationator B-l which was operated also under the above tabulated conditions so that there was obtained a desired starting fraction from the bottom of the fractionator B-l in which the total content of cyclopentadiene and methyl cyclopentadiene was 0.7 weight percent or less and the rate of diolefin content was 3 per-cent or less. Con~ugated diolefins were removed from the top of the fractionator B-l. This opeEatiOn produced 58 parts of the starting fraction against 100 parts of the starting cracked oil. The resulting starting fraction consisted of the follow-ing composition:

Composition of Starting Fraction Polymerizable components (wt. %) ------------------ 42.60 Total content of cyclopentadiene and methyl cyclopentadiene (wt. %) -----~ ----------- 0.40 Total content of indene and its alkyl ~ ~-derivatives (wt. %) ------------------------------- 1.00 ~-Rate of conjugated diolefin content (%) ----------- 0.84 Rate of indene content (%) ------------------------ 2.51 ;

To the starting fraction thus obtained was added 0.5 weight percent of boron trifluoride phenol complex as catalyst, and polymerization was carried out for 3 hours at 20C. The -product was washed with aqueous solution of ~odium hydroxide to remove the catalyst and then washed with water. Unreacted oil and low polymers were removed from the product by distil-lation. The resulting resin had a softening poin~ by Ring and Ball method of 95C, a bromine value of 7 (according to ASTM
.:
D-1158-57T) and a Gardner color of 1 (according to ASTM D~
1544-58T). The resin was blended in amounts of 30 parts, 50 parts, 80 parts and 100 parts by wèight, respectively, per 100 parts by weight of a commercially available styrene-buta-diene rubber ~SBR). The blend was dissolved in toluene to make up 20 weight percent concentration.
:,, Example 2 50 parts by weight of the resin prepared in Example 1 was blended with 70 parts by weight of SBR and 30 parts by weight of natural rubber, and the whole was dissolved in 600 parts by weight of toluene.

Comparative Examples 1 and 2 The starting cracked oil was subjected to polymeriza-tlon under the same conditions as in Example 1. A similar .... . . . . . .

operation was also carried out with the starting cracked oil but at a polymeriza~on temperature of 60C. There were obtained two different resins, one having a softening point of 120C, a bromine value of 12 and a color of 2 and the other havlng a softening point of 80C, a bromine value of 25 and a color of 5. These resins were blended each in amounts of 30, 50, 80 and 100 parts by weight per 100 parts by weight of SBR.

Comparative Examples 3 and 4 The procedure of Comparative Example 1 was followed except that the following resins were used.
Comparative Example 3: "Picolite A"* (softening point 115C), a terpene resin, manu- ~ ;
factured by Esso Chemicals Co.
Comparative Example 4: "YS resin PX1150"** (softening 15` point 115C), a terpene resin, manufactured by Yasuhara Resin Industries Ltd.

Comparative Examples 5 - 8 The procedure of Example 2 was followed except that 50 parts by weight of each of the resins used in Comparative Examples 1 - 4 was blended with the rubber components.
The various pressure-sensitive~adhesive compositions obtained in the foregoing Examples and Comparative Examples were subjected to the following tests and the results of these tests are shown in Tables III and IV.
*Trademark **Trademark 1046174 ~ ~:

1. Test of Tackiness:
Each of the various adhesives obtained as above was applied to a polyester film (38 microns thick) to a thickness of about 30 microns. The coated film was disposed for 25 hours at room temperature of 23+1C thereby making an ad-hesive tape. This tape was tested for its tackiness by the J. Dow Ball Rolling ~ethod in which steel balls measuring in the range of 32/32 inch to 1/32 inch diameter were rolled on the adhesive tape tilted at an angle of 30 with an approach run of 10 cm. Largest diameter ball that stopped within an adhesive area of 10 cm square of the tape was taken as a measure of tackiness of each particular adhesive composition.
The larger the ball number, the greater the tack, as shown in Tables III and IV.
~ -2. Test of Adhesive Strength:
This was conducted in accordance with the provisions of Japanese Industrial Standards (JIS) Z-1523. The adhesive tapes prepared as above were cut to 25 mm wide strips and stuck on a stainless steel panel polished by a water-proof polishing paper. The force was measured which was required to peel the strips 180 at a rate of 300 mm per minute.

3. Test of Cohesive Strength:
This test was in accordance with JIS Z-1524 in which strips of the adhesive tapes measuring 25 cm by 25 cm were attached to a stainless steel panel fixed in position. The distance was measured by which the test strip was shifted under the influence of a 1 kg load applied to the film part - 104~174 of the tape after a lapse of 24 hours.

4 Test of Tack Life:
The test strips that had been subjected to Test 1 above were further disposed at room temperature of 23+1C for a period of 7 consecutive days and thereafter again tested by the procedure of Test 1.

5. Test of Weather-Resistance:
Each test adhesive was coated on a "Cellophane"*
paper to a thickness of 30 microns and disposed at room temp-erature of 23+1C for 24 hours. To the thus prepared ad-hesive "Cellophane" was stuck a white paper which was then radiated by a 15 W. sterilization lamp located 30 cm apart.
Changes of color of the adhesive compositions over a period of 15 hours were observed with the naked eyes. This color evaluation was indicated in Table III by the following marks:

-------- Excellent (substantially colorless, transparent) O -------- Good (slightly yellowish) X -------- Bad (extremely yellowish) It has thus now been found that the pressure-sensi-tive adhesive compositions provided in accordance with the pre-sent invention exhibit an excellent balance of adhesive strength, cohesive strength, tackiness and weather resistance as com-pared to those prepared in Comparative Examples.

*Trademark for a brand of regenerated cellulose film produced from viscose by treatment with sulfuric acid and/or ammonium salts.

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104~174 TABLE IV: TEST RESULTS

A & esive Cohesive A &esive Tackiness Strength Strength Compound (Ball No.) (g/25 mm wide) (distance of tape shift) - (mm) Example 2 13 1,400 0.0 Comparative Example 5 0 1,150 0.0 Comparative Example 6 5 1,100 0.5 Comparative Example 7 19 1,050 1.0 Comparative - .
Example 8 7 1,250 1.0 -.

...
.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pressure-sensitive adhesive composition which comprises 100 parts by weight of a rubber component including styrene-butadiene copolymers or rubbery mixtures chiefly consisting of styrene-butadiene copolymers, in combination with from 20 to 140 parts by weight of a resin component consisting of an aromatic hydrocarbon resin resulting from the polymerization of a thermally cracked petroleum fraction at temperatures in the range of -30° to +60°C. in the presence of a Friedel-Crafts catalyst added in amounts of 0.01 to 5 weight percent of said fraction, said fraction boiling in the range of 140° to 220°C. and having a conjugated diolefin content of 0.7 weight percent or less, a rate of conjugated diolefin content of 3 percent or less, a total content of indene and its alkyl derivatives of 2 weight percent or less and a rate of indene content of 8 percent or less.

2. The composition of claim 1 wherein said rubber component is natural rubber.

3. The composition of claim 1 wherein said resin component has a softening point in the range of 60° to 120°C. and a bromine value of 15 or less.

4. The composition of claim 1 wherein said resin component is blended in amounts of 30 to 120 parts by weight per 100 parts by weight of said rubber component.

5. The composition of claim 3 wherein said resin component is blended in an amount of 50 parts by weight per 100 parts of the rubber component, said rubber component consisting essentially of 70 parts by weight of styrene-butadiene copolymer rubber and 30 parts by weight of natural rubber.