CA1059695A - Hot melt pressure-sensitive adhesive polymers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Hot melt pressure-sensitive adhesive polymers are made by copolymerizing certain alkyl acrylates with polar monomers, the homopolymers of which have a glass transition temperature (Tg) greater than -5°C.

Description

~ C~59695 This invention relates to hot melt pressure-sensitive adhesive polymers, and to flexible sheet material coated with polymers including pressure-sensitive adhesive tape.
It has previously been proposed to provide hot melt pressure-sensitive adhesive polymers o~ Yarious types as ~ for example, in U.S. Patents 3,342,902, M.E. Peterkln, dated Sept. 19, 1967; 3,630~980, T.E.Russell, dated Dec. 28, 1971; 3,635~861, T.E.
Russell, dated Jan. 18, 1972, and 3,725gll5, R.M.Christenson et al, dated Apr. 3, 1973. It has also been proposed to prepare con-lG ventional pressure-sensitive adhesives from acrylate esters as ln U.S. Patents ?,601, 016, , dated 3,008,850, E. W. Ulrich, dated Nov. 14, 1961, and 3,299,010, C. M.
Samour, dated Jan. 17, 1967.
Now it has been found ln accordance with this invention that pressure-sensitive adhesive polymers derived from acrylate ;
e~ters can be prepared and that these adhesives can be hot melt coated, resulting in adhesives having good physical properties.
More in detall, the polymer of monomers of this invention comprises (A~ at least one ester monomer selected from the group consistlng of monomers, the molecules of which have the structure H2C=CH-C=O
OR

wherein the R groups are selected from alkyl -~
groups containing up to and including about 18 carbon atoms, the average number of carbon atoms of the selected alkyl groups being ~rom about 2 to about 14, at least about 50% of the ester ;~

monomer molecules having the R groups attached 3o at non-tertiary carbon atoms to the oxygen atoms, (B) at least one polar monomer whose homopolymer has a T greater than -5 C, the amount of ~-,,i 1 ~

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polar monomer being between about lO and about 40~ by weight of the total of monomer (A) and monomer (B);

said polymer of monomers having an intrinsic viscosity between about 0.05 and about 0.5.

Preferably, the polymer of monomers has a Brookfield viscosity of between about lO0 cps and about 300,000 cps at a temperature between about 100C and about 300 C.
The~ es~er m~omers tA) used in the polymers of the present invention are well known and can be made by esterifying acrylic acid with at least one alcohol. Where only one alcohol is em-ployed, it must have from about ~ to about 14 carbon atoms; where mixtures of alcohols are used for the esterification, the individual .
alcohols can contain from l up to and including 18 carbon atoms providing the average number of carbon atoms in the mixture of alcohols is from about 2 to about 14. In preferred embodiments 1:
of the invention, the average number of carbon atoms in the alkyl )-groups of the alkyl acrylates is from about 2 to about lO.
The polar monomers (B) are also well known and include any monomer copolymerizable with monomer ~A) provided the homopolymer .
of monomer (B) has a glass transition temperature (Tg) greater ~:
than -5C. Exemplificative polar monomers ~B) include acrylo-nitrile, acrylic acid, methacrylic acid, acrylamide, methacryl-amide, itaconic acid, methyl methacrylate, diacetone acrylamide and N,N'-dimethylacrylamide. :~
- It is to be understood that mixtures of ester monomers (~) .
and polar monomers (B) can be used in this invention. ...
- The polymers of the present invention may be prepared by :
polymerizing together two essential types of monomers described .

abovs in any of the usual emulsion or so1ution oolymerization

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p edures. Various types of catalysts or initiators useful in the polymerization of acrylate and methacrylate monomers may be employed in the production of th~ polymers of this invention. Examples of peroxide-type, free radical polymeri-zation initiators are inorganic peroxides, such as hydrogen peroxide and barium peroxide; organic peroxides such as dicumyl peroxide, di-~tertiary butyl) peroxide, cumyl hydrogen peroxide, -~
diacetyl peroxide, and dibenzoyl peroxide; azo-bis-~aliphatic nitriles); and inorganic per-acids, such as ammonium persulfate, potassium persulfate and potassium percarbonate. The initiators can be used alone or in the presence of reducing agents such as ferrous salts, cuprous salts, bisulfite, thiosulfate, hydro-sulfite and tetrathionate salts, dimethylaniline, triethanolamine, and alkylene polyamines. Other types of initiating systems may be used for the preparation of these polymers, for example, ultra- `
violet light in the presence of organic peroxides or photosensi-tizers such as benzophenone. The choice of catalysts depends upon a variety of factors well known to the art. The type of monomers to be polymerized and the type of polymerization, whether solution or emulsion polymerization, the pH of the emulsion, the type of ~he emulsifier and the temperature of the emulsion are also fac-tors. In general, the amounts of the i~itiators used in the pre- ;
ferred aqueous emulsion polymeri~ation system may vary from as little as 0.1 or lower to about 2 parts per 100 parts of total - monomers. ;, Many different types~of emulsifiers can be used in a~ueous emulsion polymerization as is well known to the art including anionic, nonionic and cationic emulsifiers. Emulsifiers of these types commonly used in acrylate aqueous emulsion polymeriza-tion systems can in general be used with success in preparing ~lepolymers of the pFesent inventLon. The polymer can be separated ~. ~;

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P~-492 J ~5~95 f~m the polymeri2ation medium by coàgulation with acids, salts, or by freezing, and the resulting crumb may be washed and/or dried before use if desired.
In order to achieve the desired intrinsic viscosity, a chain transfer agent is generally employed in the preparation of the polymers of this invention. Illustrative chain txansfer agents include bromotrichloromethane, hexachlorocyclopentadiene~
dodecyl mercaptan, carbon tetrabromide, methylene bromide and dibromodichloromethane.
While it is possible in formulating pressure--sensitive adhesive products embodying the polymers of the present inven-tion, to mix with the polymer other materials for reasons in-cidental to or for the puxpose of supplementing its inherent adhesive properties, the presence of such additional or supple-mental materiais is usually unnecessary. For example, anti- ;
oxidants can be employed. Where the Brookfield viscosity of the polymer is too high, appropriate tackifier resins, oils etc. can ~`
be used to bring the viscosity within the defined limita.
Ater completion of the polymerization, the polymer is applied to a fle~ible backing by the hot melt technique. Polymers accord-ing to this invention melt and are stable at temperatures up to about 300C.
Suitable flexible backings include polyester films, e~g.
polyethylene terephthalate and tensilized polyethylene terephthalate; ;
vinyl films; polyethylene films; polyethylene-polypropylene films;
aluminum foil; cloth: laminates of vinyl film and cloth; glass cloth; etc., provided such backings are stable at the melt tempera-ture of the system.
The following examples will serve to illustrate the practice of th~s invention. The monomer "N-t-C12 maleamic acid" is a ,, , PF-49~ ' S96gS 1.
m. .ure o~ maleamic acid monomers prepared by the amidation of maleic anhydride with a complex mixture of t-al~yl primary amines marketed by The Rohm and Haas Company The t-alkyl groups are highly `
branched alkyl groups. Primene 81-R~tsR~oJ~e~o~a series o~ t-alkyl amines marketed by this company containing such amines as t-butyi amine; 1,1,3,3-tetramethylbutyl amine; 1,1,3,3,5,5-hexame~hyl-hexyl amine; 1,1,3,3,5,5,7,7-octamethyloctyl amine; L,1,3,3,5,5~-7,7,9,9-decamethyldecyl amine; and 1,1,3,3,5,5,7,7,9,9,11,11-dodecamethyldodecyl amine. Primene 8:L-R consists principally ~90~) of Cll to C14 branched alkyl amines. The neutral equivalent of Primene 81-R is 191 corresponding to an alkyl amine having an a~erage alkyl group of about 1~ carbon atoms.

- Ammonium hydroxide 27Be' (20 ml.~ and water (950 ml.) were placed in a 5-liter round-bottom flask fitted with an overhead stirrer, condenser, thermometer and gas inlet tube. Then a mix-ture of N-t-C12 maleamic acid (140 g. of a 44.5~ by weight solu- I
.- .
tion in 2-ethyl hexyl acrylate), 2-ethylhexyl acrylate (517 g.), ethyl acrylate (113 g.), acrylonitrile ~85 g.) and bromotrichloro-methane (3.0 g.) was added, with vigorous stirring, to the ammonium hydroxide solutionO The resulting mixture was sparged with nitrocJen and stirred for one hour to insure good emulsi~ication. Then hydrogen peroxide 3.5% aqueous solution ~171 ml.) was added f followed five minutes later by a solution of thiourea (3.0 g.) in water (100 ml.)~ Initiation of polymerization was indicated by an exothermic reaction. After polymerization had ceased, the latex was coagulated with isopropanol and the polymer dried to constant weight in a circulating air oven at about 140C. The resulting polymer hacl an intrinsic viscosity of 0,63, and a ~ookfield viscosity (Spindle 6, 10 rpm) of 75,000 cps at 180C
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and 136,000 cps at 130 C.

Following the emulsion polymerization procedure described in Example 1, a series of pressure-sensitive adhesive polymers were prepared employing the ingredients and amounts reported ~ -in Table I. Where a starting temperature is reported, the initial emulsion was cooled to the indicated temperature prior .
to the addition of the hydrogen peroxide solu ion. Peak tempera-ture is the highe~t temperature reached after addition of the ~.
initiator system, and peak time is the time after addition of the initiator system that the polymerization mixture took to reach the peak temperature. .

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~., EXAMPLES 7-16 - , Pre sure-sensitive adhesive po:Lymers were prepared follow~
ing the procedure described in the preceding examples but using different monomers. The ingredients, amounts, conditions and properties are reported in Table II.

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Pressure-sensitive adhesive polymers were prepared accord-ing to the following solution polymerization technique employing the ingredients, amounts and conditions set forth in Table III.
To a 2 liter flask fitted with overhead stirrer, thermometer, nitrogen inlet tube, addition funnel and condenser is added the indicated solvent mixture. The polar monomer was then added to the solvent mixture and the resulting mixture heated to the polymerization temperature. Then the monomer mixture~ the peroxide and the bromotrichloromethane were added gradually from th~ funnel over a period of two hours. The mixture was held at the polymerization temperature from 2-3 hours after all monomer had been added, and the mixture was sparged with nitro-gen throughout the reaction. After polymerization, the adhesive was obtained in the form suitable for hot melt application by flashing off solvent at 140C in a circulating air oven. Dry-ing was continued until the material attained constant weight.
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TABLE III
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Exam le 17 18 ;
P , . . `':
Polar Monomer Acrylamide 126 g.
Methacrylamide 60 g. ~ i ~onomer Mixture 2-Ethylhexyl Acrylate614 g.614 g.
Butyl Acrylate 113 g. 113 g.
Bromotrichloromethane2 g. 4 g.
Lauroyl Peroxide 34 g~ 34 g.
Solvent Mixture Toluene 200 g.
Methanol 300 g.
Methyl Ethyl Ketone390 g.
Water 170 g.

Po~ymerization Temp. 60C 60C
Intrinsic Viscosity .37 .28 Brookfield Viscosity6,000cps1,500cps -~
at 175C; at 190C;
12,000cps 7,000cps at 125C; at 140C;
26,000cp~21,000cps at 115C. at 110C.

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EX~PLES 19-21 These examples illustrate the practice of compounding a polymer of monomers having a Brookfield viscositY greater than 200,000 cps, at 300C in order to reduce the viscosity to a level appropriate for hot melt applications. Eirst, polymers A and B were prepared follow~ng the emulsion polymeri~
zation procedure described in ~xample 1 and employing ingre-dients and techniques as described below.
- . ' A B

Water 5) 1800 ml. 1800ml.
Surfactant~ - 140 g. 140 g. -Igepal CO 630 25 g. 25 g.
N-t-C12 Maleamic Acid158 g. 158 g.
~44.5% by weight solu-tion in 2-Ethylhexyl Acrylate) 2-Ethylhexyl Acrylate607 g. 607 g. , N-t-octyl Acrylamide250 g. 250 g.
Methacrylic Acid 50 g. 50 g.
Bromotrichloromethane1 g. 2 g. ~-Hydrogen Peroxide (3.5~) 128 ml. 128 ml. ~-Water 100 ml. 100 ml. ~-;
Thiourea 2.4 g. 2.4 g.
Brookfield Viscositymuch ~ 200,000cps ~200,000cps (Spindle 6, 10 rpm)at 200C at 200C

':
~5) The surfactant is an aqueous mixture containing 25% by weight of the quaternary ammonium reaction product of KEMAMINE T 9902D and epichlorohydrin; KE~MINE T 9902D
is distilled dimethyl stearyl amine as marketed by 33Humko Products, Chemical Division~

In Examples 19 Lmd 20, polymer A was admixed with 10 Jnd A ~ e /~ ~ :
20 parts per hundred respectively of oil (A~OCO~No.~ 35 ~hi'te Oil, a product of The American Oil Company), reducing the vis-cosity to 95,000 cps and 90,000 cps respectively at 140C. In Example 21, polymer B was admixed with 60 parts per hundred of ( rr~ e ~kJ ;
tackifier resin, Permalyn~XA-115, reducing the Brookield ~iscosity of the polymer to 90,000 cps at 140C. Permalyn XA-115 ,' , ' :, ' , ' '. ' ' . ' . '' ' ' "'' ' ." ' ' ~ '' ' ' '" ' ' ' ' ' r~ , ~i96~5 i, is a cycloaliphatic hydrocarbon resin sold by Pine &
Paper Chemicals Department, Hercules Incorporated, Wilmington, Delaware. (In both examples, .l pphr of butylated hydroxy-toluene antioxidant was also added.) The polymers of the foregoing examples were applied to backings in the following manner to provide pressure-sensitive adhesive tapes. The polymer of Example 14 was heated at 170C for three hours under nitrogen and hot melt coated onto releas~ paper and transferred to bleached rayon acetate cloth. The polymers of the remaining examples were individually dissolved in heptane and spread separately on one mil polyethylene terephthalate film and dried. Then the adhesive properties of the tapes were determined with the results set forth in Table IV.
The probe tack was determined by means of a Polyken probe tack tester as described in U.S. Patent 3,214,971 F. H. Hammond, Jr. - Nov. 2/65 having the following 4 functional parts: (1) a cylindrical steel probe attached -to the compression loaded spring of (2) a series L Hunter Mechanical Force Gauge (Hunter Spring Company, Brochure 750/FG, revised February, 1961), (3) an annulus having an opening slightly larger than the diameter of the probe and (4) a carrier for the annulus which moves down to bring the annulus around the probe and then up to remove the annulus therefrom. The carrier movesat a speed of 0.1 inch per second. At the beginning of the test, the carrier is at its uppermost point of travel and thea~nulus rests upon the carrier so that the opening in the annulus is in line with the probe positioned beneath it. In carrying out the test, a strip of -tape is placecl upon the annulus, adhesive side down, and spanning the annulus opening. As the carrier is driven downwardly by the ',' ~:

~ 5 s synchronous motor, the a~hesive surfac exposed through the opening is brought into contact with the flat surface of the probe so that the tape and the annulus attached thereto are suspended on the probe as the carrier continues farther on i~s 3 ~ i`
downward path. The carrier then reverses its movement return-ing to pick up the annulus, thereby separating the tape from the probe surface. Separation begins after one second contact between the probe and the adhesive. The force required to separate the tape from the probe is recorded on a g~uge. The recorded value is the probe tack value. Measurements were made employing loadings of 10, 100 and 500 grams/cm as indicated. -The adhesion values represent the forces in ounces re-quired to remove a one-inch wide adhesive tape from a stainless steel surface or from the backing applied to a steel surface i~
after contact therewith for 2 minutes at a temperature of about 75F. The tape is stripped from the surface at an angle of 180 at a rate of 12 inches per minute.
The creep resistance values are determined by applying to a cylindrical steel rod a strip of the adhesive tape 1 inch wide and then heating the surface to a temperature of about 160F., after which a 1 kilogram weight is hung from the tape. The ;
reported value is ~he length of time in hours required for the tape to fallO In all instances, cohesive failure was ob- -;
served when the tape fell.
Rolli~g ball tack was determined by securing a pieee of the adhesive tape, adhesive side up, to a horizontal surface.
A steel ball 1/2 inch in diameter is placed on a track, inclined 60 to the horizontal test surface; the vertical height in inches from which the ball is released is the first reported value. The ;;
ball is released, and a7lowed to roll to a stop on the adhesive.
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The distance in inches traveled on the. adhesive is reported :-as the second measurement.
Although specific embodiments of the invention have been described herein, it is not intended to limit the invention~solely thereto bu~ to include all of the varia- :
tions and modifications which suggest themselves to one skilled in the art within the spirit and scope of the appended claims.

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Claims (12)

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

1. A pressure-sensitive hot melt adhesive polymer of monomers comprising (A) at least one ester monomer selected from the group consisting of monomers, the molecules of which have the structure wherein the R groups are selected from alkyl groups containing up to and including about 18 carbon atoms, the average number of carbon atoms of the selected alkyl groups being from about 2 to about 14, at least about 50% of the ester monomer molecules having the R groups attached at non-tertiary carbon atoms to the oxygen atoms;
(B) at least one polar monomer whose homopolymer has a Tg greater than -5°C, the amount of polar monomer being between above 12 and about 40%
by weight of the total of monomer (A) and monomer (B);
said polymer of monomers having an intrinsic viscosity between about 0.05 and about 0.5, and a Brookfield viscosity of between about 100 cps and about 300,000 cps at a temperature between about 100°C and about 300°C.

2. The polymer of monomers of Claim 1 wherein said polar monomer is acrylonitrile, acrylic acid, methacrylic acid, acrylamide, methacrylamide, itaconic acid, methyl methacrylate, diacetone acrylamide or N,N'-dimethyl acrylamide.

3. The polymer of monomers of Claim 1 wherein the R groups of said monomer (A) have an average number of carbon atoms from about 2 to about 10 and said monomer (B) is acrylonitrile.

4. The polymer of monomers of Claim 1 wherein the R groups of said monomer (A) have an average number of carbon atoms from about 2 to about 10 and said monomer (B) is methyl methacrylate.

5. The polymer of monomers of Claim 1 wherein the R groups of said monomer (A) have an average number of carbon atoms from about 2 to about 10 and said monomer (B) is diacetone acrylamide.

6. The polymer of monomers of Claim 1 wherein the R groups of said monomer (A) have an average number of carbon atoms from about 2 to about 10 and said monomer (B) is acrylic acid.

7. The polymer of monomers of Claim 1 wherein the R groups of said monomer (A) have an average number of carbon atoms from about 2 to about 10 and said monomer (B) is methacrylic acid.

8. The polymer of monomers of Claim 1 wherein the R groups of said monomer (A) have an average number of carbon atoms from about 2 to about 10 and said monomer (B) is acrylamide.

9. The polymer of monomers of Claim 1 wherein the R groups of said monomer (A) have an average number of carbon atoms from about 2 to about 10 and said monomer (B) is methacrylamide.

10. An adhesive tape comprising a flexible backing and supported thereon a hot melt coated pressure-sensitive adhesive polymer of monomers according to Claim 1, 2 or 3.

11. An adhesive tape comprising a flexible backing and supported thereon a hot melt coated pressure-sensitive adhesive polymer of monomers according to Claim 4, 5 or 6.

12. An adhesive tape comprising a flexible backing and supported thereon a hot melt coated pressure-sensitive adhesive polymer of monomer according to Claim 7, 8 or 9.