WO1989001002A1

WO1989001002A1 - Copolymer of propylene and hexene as a positioning adhesive

Info

Publication number: WO1989001002A1
Application number: PCT/US1988/002446
Authority: WO
Inventors: Richard Kingsley Stuart, Jr.; Bruce William Foster
Original assignee: Eastman Kodak Company
Priority date: 1987-07-24
Filing date: 1988-07-20
Publication date: 1989-02-09
Also published as: KR890701647A

Abstract

Disclosed is a pressure-sensitive positioning adhesive for use on items used for absorbing and retaining fluids such as feminine care products. The positioning adhesives is a substantially amorphous copolymer of propylene-hexene having a viscosity at 190°C of between about 1.500 and 8.500 centipoise and a hexene content of between about 35 to about 51 percent by weight.

Description

DESCRIPTION

COPOLYMER OF PROPYLENE AND HEXENE AS A POSITIONING ADHESIVE

Field of Invention

The present invention concerns a pressure- sensitive adhesive comprising a copolymer of propylene and 1-hexene. This pressure-sensitive adhesive is useful as a positioning adhesive for items such as disposable feminine care products.

Background of the Invention Positioning adhesives are used in products such as disposable feminine care products, diapers, wound dressings and incontinence briefs. Currently, the most widely used positioning adhesives are rubber based adhesives wherein the rubber is a styrene butadiene styrene block copolymer or a styrene butadiene rubber material. These rubber materials are blended with tackifiers and plasticizers to achieve the proper balance of properties. Problems associated with these mυlticomponent adhesives include adhesive residue left on the undergarments of a user of a product containing the adhesive and the potential for skin irritation.

U.S. Patent 3,954,697 discloses certain polypropylene-hexene copoly ers useful as pressure- sensitive adhesives. The copolymers disclosed in this patent have viscosities greater than 10,000 centipoises at 190°C and have a 1-hexene content of 55 to 75 weight percent (40 to 60 mole percent). However, the adhesives disclosed in the prior art patent do not have the necessary physical and adhesive properties suitable for use as a positioning adhesive.

The use of a propylene-hexene copolymer for use as a positioning adhesive has heretofore been unknown. The adhesives of the present invention are single component adhesives that avoid prior art problems while maintaining excellent adhesive and physical properties for use as positioning adhesives.

Summary of the Invention

The present invention is directed to a pressure- sensitive positioning adhesive of a substantially amorphous polypropylene-hexene random copolymer having a specific viscosity and hexene content. More specifically, the present invention is directed to a substantially amorphous propylene-hexene random copolymer having permanent tack, shear strength of greater than 300 minutes when tested with a one kg load, tensile strength between about 8 and about 50 pounds per square inch (psi), a viscosity at 190°C of between about 1,500 and about 8,500 centipoiεes (cp) and an amount of 1-hexene of from about 35 to about 54 percent by weight. The present invention is also directed to an article in which it is desirable to have adhesive properties comprising an item used for retaining fluids having thereon, on its surface, an effective amount of the copolymer of the present invention. As used herein the term "positioning adhesive" refers to an adhesive applied to the surface of items used for absorbing and retaining fluids such as sanitary napkins; bandages, and diapers; and the term "effective amount" refers to that amount of copolymer that will result in a desired degree of adhesiveness when applied to the surface of an item used for retaining fluids such as a sanitary napkin, diaper, or bandage. The desired degree of adhesiveness is at least 100 grams/inch adhesion to cotton or nylon using methodology described herein.

Detailed Description of the Invention

Multicomponent adhesives known in the art contain plasticizerε and tackifiers which leave residues on undergarments. In addition, since the positioning adhesive of the invention is a single component (rather than multicomponent), the chances for potential allergeric reactions (skin irritation or skin sensitization), caused by the adhesive in close proximity to skin, are lessened.

The positioning adhesive of the present invention is a single component polyolefin copolymer which has permanent tack yet has sufficient cohesive strength that it does not leave an adhesive residue when peeled from cotton or other cloth garments.

Permanent tack refers to a probe tack value measured on a Polyken Probe Tack tester at a dwell time of 2 seconds and a carrier speed of 2 centimeters per second (cm/sec). Under these conditions typical probe tack values of about 130 to about 600 grams are obtained. Sufficient cohesive strength or static shear resistance refers to providing shear adhesion or strength (holding power; static shear resistance) of greater than 300 minutes when tested with a one kilogram load using PSTC Test-7.

The copolymers of this invention must also have sufficiently high tensile strength. Sufficiently high tensile, strength is typically between about 8 and about 50 psi, preferred is between about 10 and about 40 psi. The tensile strength can be determined by the methodology disclosed in American Society for Testing and Materials (ASTM) method D-638-72. The percent elongation using the same methodology is typically greater than about 400%. The unusual combination of intrinsic physical and adhesive properties make the copolymer of this inven¬ tion an ideal choice for use as a positioning adhesive. The high cohesive and tensile strength of the propylene-hexene copolymer allows an article attached with this adhesive to be removed cleanly and completely without leaving an adhesive residue. The permanent tack properties of the copolymer allow the coated article to adhere firmly to a surface. The copolymer's static shear resistance property prevents it from shifting positions. Thus these attributes make the copolymer of the present invention an excellent positioning adhesive.

The melt stability of the copolymer of this invention (100 hours at 350°C) is typically good with less than 25% viscosity loss. The melt stability can be determined by placing 200 grams of polymer in a 400 ml beaker and placing it in a forced draft oven set at 350°F. After 100 hours in the oven the color and viscosity of the polymer is determined and compared to the original values. The change in viscosity under such conditions is typically between about 5 and about 15 percent.

The number average molecular weight of the copolymer of the invention is typically between about 4500 and about 9200. The weight average molecular weight of the copolymer of the invention is typically between about 19,000 and about 40,000.

The color of the copolymer of this invention is typically a Gardner Color of between 1 and 3 in the melt. When the polymer is subjected to heat (e.g.. 350°C for 100 hours), the Gardner Color will vary between about 5 and about 8. Gardner Color can be determined by ASTM method D-1544.

The copolymer of this invention preferably has a viscosity at 190°C of between about 2,800 and about 5,800 cp, and a hexene content between about 40 and about 49 percent by weight. Viscosity can be measured using a Brookfield Thermosel Viscometer according to the methodology described in ASTM method

D-1824-66. Hexene content of the polymer can be determined by either C 13 nuclear magnetic resonance

(NMR) or Fourier Transfer infrared spectroscopy

(FTIR). In the FTIR method the peak ratio of the 727 and 972 wavenumber peaks are determined. The percent hexene is then obtained from a calibration curve.

It is preferred that the softening point at the copolymer is between about 106°C and about 129°C. The softening point can be determined using the Ring and Ball method described in ASTM method E-28.

The glass transition temperature (Tg) is sometimes useful for characterizing the copolymer of this invention. One suitable method for measuring Tg of polymers is by Differential Scanning Calorimetry [John Mitchell and Jen Chin, Anal. Chem. Annual Reviews, 43. 267R (1971); M. J. O'Neill and R. L. Fyans. "Design of Differential Scanning Calorimeters and the Performance of a New System", paper presented at the Eastern Analytical Symposium, New York City. November. 1971]. The Tg of the copolymer of this invention is typically between about -20 and about -35°.

Cone penetration using a micrometer Adjustment Penetrometer according to the methodology described in ASTM method D-1321-76 is also sometimes useful for characterizing the copolymer of this invention. Typically, cone penetration is between about 25 and about 45 decimillimeters (dmm) .

The propylene-hexene copolymer of this invention can be prepared by the copolymerization of propylene and hexene by anionic coordination catalysts such as Lynx 900 (a commercially available catalyst from Catalyst Resources. Inc.. Houston. Texas), or aluminum-activated titanium trichloride ("AA-TiCl ") . An aluminum alkyl such as triethyl- aluminum ("Et Al")'or the like is used as a cocatalyst. The temperature of the reaction is typically between about 150°C and about 180°C and the pressure is typically between about 600 and about 1.200 pounds per square inch gauge (psig).

It is preferred that the process is run continuously with agitation, e.g., stirring. Optionally, a solvent can be used for the reaction such as mineral spirits, hexane. benzene, and the like. The reaction also must proceed in the presence of a chain transfer agent such as hydrogen gas to obtain the proper viscosity.

This invention is further illustrated by the following examples, however, these examples should not be interpreted as a limitation on the scope thereon.

EXAMPLE 1

A 6.7-gallon stirred loop reactor was fed continuously with propylene. 1-hexene, and catalyst slurry in mineral spirits (solvent). The copolymer, monomers, and solvent mixture containing catalyst was renoved from the reactor continuously to a letdown tank. Unreacted monomers and some solvent were flashed overhead. The copolymer and remaining solvent mixture was treated with steam, air, and nitrogen to deactivate the catalyst and remove solvent. The copolymer was then alumina bed treated. Reactor conditions and monomer conversions were as shown below:

Propylene Charge, Pound/Hour 5.0

Hexene Charge. Pound/Hour 4.9

H- Charge. Pound/Hour 9.6 x 10~

Catalyst Type LYNX 900 Catalyst Charge, Pound/Hour 0.004

Cocatalyst Et Al

Cocatalyst/Catalyst Mole Ratio 0.5/1

Copolymer Produced, Pound/Hour 7.4

Propylene Conversion, % 85 1-Hexene Conversion, % 63

Reactor Temperature, °C 178

Reactor Jacket Temperature, °C 166

Reactor Pressure, psig 1,040

Stirrer Speed, Revolutions 750 Per Minute (rp )

Off Gas, Standard Cubic Feet 8.1 Per Hour (εcfh)

The propylene-hexene copolymer had a viscosity at 190°C of 3,250 cp and a softening point of 116°C. It contained 42 weight percent 1-hexene as determined by both infrared spectral analysis and material balances. The glass transition temperature was -27°C.

Example 2

The system of Example 1 was used with the following feeds: Propylene Charge, Pound/Hour 5.28

Hexene Charge, Pound/Hour 5.73

H_ Charge, Pound/Hour 1.1 x 10 -5

Catalyst Type LYNX 900

Catalyst Charge, Pound/Hour 0.002

Cocatalyst ^Ets^A1

Cocatalyst/Catalyst Mole Ratio 0.5/1

Copolymer Produced, Pound/Hour 8.1

Propylene Conversion, % 85

1-Hexene Conversion, % 62.9

Reactor Temperature. °C 178

Reactor Jacket Temperature. °C 166

Reactor Pressure, psig 1.040

Stirrer Speed. Revolutions 750

Per Minute (rp )

Off Gas. Standard Cubic Feet 7.1

Per Hour (scfh)

The propylene-hexene copolymer had a viscosity at 190°C of 2,750 cp and a softening point of 113°C. It contained 44 weight percent 1-hexene as determined by infrared spectral analysis.

EXAMPLES 3 to 6 Four propylene-hexene copolymer samples made according to the teachings of Examples 1 and 2 were coated as a continuous web on release paper at 25 mg per square inch coating weight. The four samples differ from each other in viscosity and softening point as shown in Table I. The adhesive coating was transferred via passage through a nip roller to polyethylene film backed with an embossed absorbent pad suitable for use as a panty liner.

The adhesion to cotton peel value was obtained by removing half the release liner from one end of a 6-inch strip of coated polyethylene/absorbent pad. The coated polyethylene film side was placed on a 2-inch by 5-inch piece of cotton and placed under a 250-gram weight in an oven at 105°F for 1 hour. The samples were cooled and tested on an Instron tensile tester at a crosεhead speed of 20 inches per minute. The adhesion to nylon peel value was determined by the same general method except the sample condi¬ tioning procesε used a 1,600-gram weight in an oven set to 120°F for 15 minutes.

Adheεive reεidue transferred to cotton or nylon was tested by applying the coated polyethylene to the cotton or nylon with a minimum of pressure. The sample is aged at 105°F for 6 hoυrε under a load of 1,600-gramε. After the samples are cooled to room temperature the cloth is peeled away and the residue level is determined. The resultε of theεe tests are shown in the Table I:

TABLE I

Performance of Positioning Adhesives Examples

Sample ID

1. Adhesion to 172 105 96 180 Cotton, Grams (g)/inch (in)

Adhesion to 502 306 230 240 Nylon, g/in

Residue Level

On Cotton Fabric - None None None On Nylon Fabric Slight None None None TABLE I (Continued)

Performance of Positioning Adhesives Examples

Sample ID 4

4. Viscosity at 4.200 4,500 4.500 7,300

350°F. cp Viscosity at 2,750 3.250 3.300 5.200 190^βC, cp

5. Ring and Ball 112 117 114 113 Softening Point, *C

6. Hexene Content, 44 42 43 48 Weight %

7. Gardner Color 2 2 2 2 (Clear) (Clear) (Clear) (Clear)

8. Melt Stability Slats Block (100 Hours at 350°F)

% Change in -11 -26 Viscosity

Color

9. Cone Penetration, 44 32 28 38 Decimillimeter (dmm) TABLE I (Continued)

Performance of Positioning Adhesiveε

Sample ID

10. Tensile Strength, 11 42 20 15 Pounds Per Square Inch (psi) % Elongation 400 550 >600 670

Claims

CLAIMSWe claim:

1. A substantially amorphous propylene-hexene random copolymer having permanent tack, shear strength of greater than 300 minutes when tested with a one kg load, tensile strength between about 10 and about 50 psi. a viscosity at 190°C of between about 1.500 and about 8,500 cp and an amount of 1-hexene of from about 35 to about 54 percent by weight.

2. The copolymer of Claim 1 having a viscosity at 190°C of between about 2,800 and about 5,800 cp and an amount of hexene of from about 40 to about 49 percent by weight.

3. The copolymer of Claim 1 having a softening point at between about 106°C and about 129°C.

4. An article in which it is deεirable to have adhesive properties comprising an item used for retaining fluids having thereon on its surface an effective amount of a subεtantially amorphouε propylene-hexene random copolymer having permanent tack, shear strength of greater than 300 minutes when tested with a one kg load, tensile strength between about 10 and about 50 psi. a viscosity at 190°C of between about 1,500 and about 8,500 cp and an amount of hexene of from about 35 to about 51 percent by weight.

5. The article of Claim 4 wherein the copolymer has a viscoεity at 190°C of between about 2,800 and about 5,800 cp and an amount of hexene of from about 40 to about 49 percent by weight.

6. The article of Claim 4 wherein the copolymer has a softening point at between about 106°C and about 129°C.

7. The article of Claim 4 wherein said item is selected from the group consisting of a feminine care product, a diaper, and a bandage.

8. The article of Claim 5 wherein said item is selected from the group consisting of a feminine care product, a diaper, and a bandage.

The article of Claim 6 wherein said item is selected from the group consisting of a feminine care product, a diaper, and a bandage.