EP1097180A1

EP1097180A1 - Low noise unwind pressure-sensitive adhesive tape

Info

Publication number: EP1097180A1
Application number: EP98935948A
Authority: EP
Inventors: John L. Thiele; Raymond R. Rivera; Dieter Jung; Maria Margareta Luca
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1998-07-21
Filing date: 1998-07-21
Publication date: 2001-05-09
Also published as: WO2000005291A1; JP2002521513A; AU8509398A

Abstract

A low noise pressure-sensitive adhesive tape is disclosed that includes a release coating that includes the reaction product of: (i) from 15-35 wt.-% silicone MQ-resins bearing one or more (meth)acrylate functional groups; (ii) from 50-85 wt.-% long chain radiation curable organopolysiloxane where at least one (meth)acrylate group is present on the organopolysiloxane; (iii) less than 25 wt.-% short chain radiation curable organopolysiloxane where at least one (meth)acrylate group is present on the organopolysiloxane; and (iv) an effective amount of photoinitiator, the weight percentage given for component (i, ii and iii), respectively, referring to the sum of the masses of components (i, ii and iii) which add up to 100 wt.-%.

Description

LOW NOISE UNWIND PRESSURE-SENSITIVE ADHESIVE TAPE Background of the Invention

The present invention relates to preparing pressure-sensitive adhesive tape.

Pressure-sensitive adhesive tape often includes a backing, a release coating, and an adhesive composition. Release coatings such as, for example, silicone-based release coatings, are used in conjunction with pressure-sensitive adhesive compositions, such as, for example, (meth)acrylate-based pressure-sensitive adhesive compositions and natural rubber-based pressure-sensitive adhesive compositions, to decrease the unwind force of a roll of tape. It is, however, often difficult to provide a controlled unwind force with silicone-based release coatings. If the unwind force is too low, the pressure-sensitive adhesive of the roll of tape may release or slide from the backside of the underlying lap causing the roll of tape to telescope. If the unwind force is too high, the release coating may be fully or partly transferred to the pressure-sensitive adhesive layer upon unwinding of the roll, resulting in a partial detackifying of the adhesive and/or decrease of the peel adhesion of the tape to a substrate.

Transfer of the release coating to the adhesive layer can be reduced or avoided when using a release coating that includes the reaction product of an MQ silicone resin and an organopolysiloxane bearing one or more reactive (meth)acrylate groups as described in U.S. Patent No. 5,494,979.

Pressure-sensitive adhesive tapes are used in a wide variety of technical fields. When applied by end-users such tapes are often adhered at relatively low unwinding forces such as, for example, 0.1 - 30 m min^"1, whereas in some industrial applications such as, for example, packaging and diaper manufacturing, adhesive tapes are applied semi-automatically or automatically at high unwind speeds of, for example, 100 - 150 m/min^"1 or more. One of the problems encountered with adhesive tapes is that unwinding the tape from the roll both at low and high unwinding speeds frequently results in an unacceptably high level of noise which causes discomfort and, in industrial applications, potential hearing damage to the workers in the taping area. The noise at unwind is influenced by the unwind force.

Adhesive tapes that include a silicone-based release coating may exhibit low noise at unwind. The noise level is influenced by both the release coating and the type of pressure-sensitive adhesive of the tape. One example of a tape system that can be prepared to produce low noise is a tape system that includes an epoxy-organopolysiloxane release composition and a synthetic rubber-based pressure-sensitive adhesive composition, as described in WO 94/28,080. One example of an ultraviolet (UN) radiation curable epoxyfunctional silicone composition that can be cured to form a release coating includes a UN-radiation curable epoxyfunctional diorganopolysiloxane, an MQ resin, a photoinitiator, and, optionally, a halogenated hydrocarbon solvent, as described in EP 0,473,995. Pressure-sensitive adhesive compositions based on, e.g., acrylate or natural rubber, are typically coated onto a backing using organic solvent- based and dispersion coating processes. Organic solvent-based coating operations are undesirable from an environmental point of view and are often characterized by low coating speeds relative to hot melt coating processes. Dispersion coating processes are also often characterized by low coating speeds relative to hot melt processes. Hot melt coating processes, which can be used for coating hot melt coatable synthetic rubber pressure-sensitive adhesive compositions, in general, do not require the use of solvents. Summary of the Invention In one aspect, the invention features a pressure-sensitive adhesive tape that includes a backing having a first major surface and a second major surface, a pressure-sensitive adhesive provided on the first major surface, and a release coating provided on the second major surface. The release coating includes the reaction product of:

(i) from 15 - 35 wt.% of one or more silicone MQ-resins bearing one or more (meth) acrylate functional groups;

(ii) from 50- 85 wt.% of one or more radiation curable organopolysiloxanes of formula (I)

R¹R¹R²SiO(R¹R¹SiO)_x(R'R²SiO)_y(R^,R¹SiO)_zSiR¹R¹R² (I) wherein

R¹ independently from each other is an alkyl group having 1-3 carbon atoms, R² independently from each other is an optionally branched alkyl group with

1-20 carbon atoms wherein one or more CH₂ groups may be replaced with

OH X O

I I II

— C C — , — O — , — C — ,

H H

R⁶ R⁶ O H

1 1 II

C = C — or — O — C C = C

R⁶ and wherein one or more CH₃ groups may be replaced with

R⁵C =C — C — O — , CHY, — , CH₂Y — , or HCO

I I II

R⁴ R⁴ O with the proviso that two oxygen atoms are not directly linked, R independently from each other is H or CH 3'

R⁵ independently from each other is H or an optionally branched alkyl group having 1-5 carbon atoms,

R⁶ independently from each other is H or R¹, X independently from each other is F or Cl,

Y independently from each other is F, Cl or OH, x is 0 or a number of up to 200, y is 0 or a number of up to 40, z is 0 or a number of up to 200, with the provisos that

• 60 < x + y + z < 300,

• at least one (meth)acrylate group is present, and

• the average (meth)acrylate, vinyl and/or ethenylene functionality of the compounds of formula I is > 2; (iii) less than 25 wt.%> of one or more radiation curable organopolysiloxanes of formula (II)

R¹ R¹ R²SiO(R'R¹SiO)_a(R¹R²SiO)_b(R¹R¹SiO)_c Si R¹ R¹ R² (II) wherein a is 0 or a number up to 30, b is 0 or a number up to 20, c is 0 or a number up to 30, and wherein the other variables have the meaning indicated above for formula I, with the provisos that

• 5< a + b + c < 60, • at least one (meth)acrylate group is present, and

• the average (meth)acrylate, vinyl and/or ethenylene functionality of the compounds of formula II is > 2; and

(iv) an effective amount of one or more photoinitiators, the weight percentages given for components (i), (ii) and (iii), respectively, referring to the sum of the masses of components (i), (ii) and (iii) which add up to 100. wt.%.

In preferred embodiments, the amount of the radiation-curable organopolysiloxane of formula (II) is no greater than about 15 wt %

(preferably no greater than about 10 wt %, more preferably no greater than about 5 wt %).

In some embodiments, the pressure-sensitive adhesive tape, when in the form of a roll, exhibits no greater than about 80 dB(A), upon unwind at unwind speeds of up to about 110 m/min, when measured according to the

"Noise Level at Free-Standing Unwind Stand" test. In preferred embodiments, the pressure sensitive adhesive tape, when in the form of a roll, exhibits less than 75 dB(A), upon unwind at unwind speeds of up to about 100 m/min, when measured according to the "Noise Level at Free-Standing Unwind Stand" test. The pressure-sensitive adhesive tape, when in the form of a roll, also preferably exhibits an unwind force of at least about 0.5 N/cm, at an unwind speed of about 0.3 m/min.

In one embodiment, the backing includes an oriented polymeric film selected from the group consisting of polyester, polyolefin, and combinations thereof. In some embodiments, the backing layer has a thickness of about 20

- 100 μm. In other embodiments, the pressure-sensitive adhesive is a hot- melt coatable pressure-sensitive adhesive. The adhesive is selected from the group consisting of ABA-type, and AB-type synthetic resin block copolymers, where A is a thermoplastic block and B is a rubber block. In other embodiments, the pressure-sensitive adhesive includes a block copolymer selected from the group consisting of styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene-butylene-styrene, and combinations thereof. In another embodiment, the pressure-sensitive adhesive further includes one or more tackifiers. The pressure-sensitive adhesive has a thickness of about 10-50 μm.

In another aspect, the invention features the use of the above- described tape as a packaging or box-sealing tape. In one embodiment, the method features uwinding a roll of the above-described pressure-sensitive adhesive tape and adhering the tape to a cardboard substrate (e.g., a box).

In another aspect, the invention features the use of the above- described pressure-sensitive adhesive tape as low-noise packaging and box- sealing tapes.

The invention provides pressure-sensitive adhesive tapes that have a relatively low noise-level at unwind, and an unwind force that is sufficiently high to allow for stable rolls of tape and that is sufficiently low to allow for smooth unwinding. The adhesive tapes can also be formulated to have a relatively low shockiness index. The invention also provides hot-melt coatable pressure-sensitive adhesive tapes that are particularly useful as packaging tapes and box sealing tapes.

The pressure-sensitive adhesive tapes of the invention can be selectively prepared to exhibit a noise upon unwinding of preferably no greater than about 80 dB(A), at unwind speeds of about 110 m/min, as measured according to the test method "Noise Level at Free-Standing Unwind Stand" described below. The composition of the precursor of the release coating can be selected so that the unwind force is at least about 0.5 N/cm, at a low unwind speed of about 0.3 m/min. Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims. Detailed description of the invention The pressure-sensitive adhesive tapes of the invention include a backing, a pressure-sensitive adhesive on a first major surface of the backing, and a release coating on a second major surface of the backing. Useful backing materials for the pressure-sensitive adhesive tape include films and layers of various stiffness. Preferred backings are flexible. Suitable backing materials include, e.g., polymeric films and layers, paper (e.g., treated paper) films and layers, layers of non-wovens, laminates (such as, for example, polyacrylate foams laminated on both sides with polyolefin films, and papers laminated or jig-welded with polyethylene terephthalate), metals, and combinations thereof. Useful polymeric films and layers include, for example, polyolefin polymers, monoaxially oriented polypropylene (MOPP), biaxially oriented polypropylene (BOPP), simultaneously biaxially oriented polypropylene (SBOPP), polyethylene, copolymers of polypropylene and polyethylene, polyester polymers, polycarbonate polymers, polymethacrylate polymers, cellulose acetate, polyester (e.g., biaxially oriented polyethylene terephthalate), vinyl acetates, and combinations thereof. Useful backings also include surface modified backings modified by, e.g., flame treatment, corona treatment, and roughening.

Preferred backings have a thicknesses between 20μm and 3,000μm, preferably between 20μm and l,000μm, more preferably between 25 μm and lOOμm.

Suitable pressure-sensitive adhesive (PSA) compositions include hot-melt coatable, solvent coatable, transfer-coatable, and latex coatable PSA compositions. Pressure-sensitive adhesive compositions are normally tacky at room temperature and can be adhered to a surface by application of, at most, light finger pressure. Examples of useful adhesive compositions include thermoplastic elastomer, polyacrylate, polyvinyl ether, diene- containing rubber such as natural rubber, polyisoprene, and polybutadiene- acrylonitrile polymer; amorphous polyolefin; silicone; ethylene containing copolymers such as, e.g., ethylene vinyl acetate, ethylacrylate, and ethyl methacrylate; polyurethane; polyamide; epoxy; polyvinylpyrrolidone and vinylpyrrolidone copolymer; polyester; and mixtures of the above. A general description of useful pressure sensitive adhesive compositions can be found in Encyclopedia of Polymer Science and Engineering, vol. 13, Wiley-Interscience Publishers (New York, 1988). Additional description of useful pressure sensitive adhesives can be found in Encyclopedia of Polymer Science and Technology, vol. 1, Interscience Publishers (New York, 1964).

Preferred pressure-sensitive adhesive compositions are hot-melt coatable and include one or more synthetic rubber block copolymers that preferably are of the ABA- or AB-block type, where A is a thermoplastic block and B is a rubbery block. The block copolymers can be linear, branched, radial, and combinations thereof. Examples of suitable block copolymers include styrene-isoprene-styrene (SIS), styrene-butadiene- styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS), styrene-butadiene (SB), ethylene-propylene-diene, and hydrogenation products thereof. Preferred A-B-A block copolymers are described in some detail in D. Satas (ed.), Handbook of Pressure-sensitive Adhesive Technology, 2nd edition,

Van Nostrand Reinhold, New York 1989, pp. 317-373.

Suitable commercially available block copolymers include, e.g., those block copolymers available under product numbers 1107, 1101, 1111, 1112, and 1117 from Shell Chemical Company under the Kraton™ trademark. Other useful block copolymers include Vector™ 4100 series block copolymers, available from Dexco Polymers.

Hot-melt coatable, pressure-sensitive adhesive compositions preferably additionally include tackifiers, which can be solid, liquid, and combinations thereof. Suitable solid tackifiers include, e.g., rosin, rosin derivatives, hydrocarbon resins, polyterpenes, coumarone indenes, and combinations thereof. Suitable liquid tackifiers include, e.g., liquid hydrocarbon resins, hydrogenated liquid polystyrene resins, liquid polyterpenes, liquid rosin esters, and combinations thereof. Suitable tackifier resins are described in D. Satas, Handbook of Pressure-sensitive Adhesive, loc. cit, and pp. 527-544. Preferred commercially available tackifier resins include Escorez 2203 and 1310 from Exxon Chemicals, Wingtack™ 95 and Wingtack™Plus from the Goodyear Tire & Rubber Company, and Regalrez™ 1018 and 1078 from Hercules, Inc. The hot-melt coatable, pressure-sensitive adhesive compositions can also include one or more additives such as, for example, bonding agents, plasticizers, antioxidants, stabilizers, fillers, oils, polymer additives such as, for example, poly (ethylene vinyl acetate), dyes, pigments and combinations thereof. The hot-melt coatable, synthetic rubber based pressure-sensitive adhesive is preferably prepared using a compounder, for example, a twin screw extruder to mix the components of the adhesive. A suitable twin screw extruder is described, for example, in the Short Course Notes of the Technical Association of the Pulp and Paper Industry, 1981, Hot Melt Coatings, "Liquid Resin Injection System for Continuous Mixing of

HMPSA", W. H. Korez. The extruder described includes a port valve for injecting liquid resins.

The preferred release coating of the pressure-sensitive adhesive tape includes the reaction product of: (i) 15-35 wt.% (preferably 20-35 wt.%, more preferably 25-35 wt.%) of one or more silicone MQ resins bearing one or more (meth)acrylic functional groups and, optionally, one or more vinyl and/or ethenylene functional groups; (ii) 50-85 wt.% (preferably 60-80 wt.%, more preferably 65-80 wt.%) of one or more radiation curable (preferably UV-curable) organopolysiloxanes of formula I described below;

(iii) less than 25 wt.% (preferably no greater than 15 wt. %, more preferably no greater than 10 wt. %) of one or more radiation curable (preferably UV-curable) organopolysiloxanes of formula II described below; and

(iv) an effective amount (preferably between 0.1 and 5 wt.%, more preferably between 0.5 and 4 wt.%) of one or more photoinitiators.

The weight percentages given above refer to the sum of the masses of components (i), (ii) and (iii), which add up to 100% wt.

Preferred silicone MQ resins are three-dimensional silicone resin that include quadrofunctional silicate groups Q, and monofunctional end-capping groups M

— O,, — O — M

"2 "₂

and, optionally, trifunctional groups T and/or difunctional groups D

O 1/2 O 1/2

X² — Si — O_1/2— T X¹ — Si— O_1/2 — D.

O_1/2 X²

wherein X¹ and X² are end groups.

In the above formulae for Q, M, T and D, X¹ and X² preferably have the following meanings: X¹ independently from each other is an optionally branched alkyl group having

1-6 carbon atoms, preferably 1-4 carbon atoms, more preferably methyl or ethyl; and X² independently from each other is an optionally branched alkyl group having 1 to 8 carbon atoms, wherein 1 or 2 - CH₂ - groups may be replaced by

OH halogen _ l _ _ l _ __ _ _

, C , C or C _C

H H X⁴ X⁴ and wherein one or two CH₃ groups may be replaced with H₂C=CX⁴-, HOCH₂- or halogen-CH₂- with X⁴ being independently from each other H, CH₃, C₂H₅ or

OH.

Preferred MQ resins have an M/Q ratio between 0.1 and 10, preferably between 0.2 and 8, (more preferably between 0.25 and 7.5), an average molecular weight M„ of between 500 and 100,000 g/mol (preferably between 500 and 80,000 g/mol, more preferably between 600 and 60,000 g/mol), and an OH-content of between 0.0001 and 4 wt.% (more preferably of between 0.005 and 2.5 wt.%) with respect to the mass of the MQ resin.

Suitable MQ resins are described, for example, in EP 0,464,706 incorporated herein. Preferred MQ resins include the MQ resins defined in claim 1 of US 5,494,979 and designated there as siloxane resin A. Particularly preferred MQ resins are those resins disclosed, for example, in US 5,494,979 at col. 11, 11. 12-15. MQ resins are commercially available, for example, from the silicone division of General Electric Co.

One method for preparing (meth) acrylate, vinyl and/or ethenylene modified siloxane MQ resins of component (i) includes reacting one or more

MQ resins with one or more organopolysiloxane compounds of formulae I and II, described below. One preferred method for preparing acrylate-modified MQ resins includes reacting an MQ resin with one or more (meth)acrylate substituted organopolysiloxanes in the presence of an acidic equilibration catalyst at a temperature of about 0 to 140°C as described in US 5,494,979, which is incorporated herein. Preferred meth(acrylate) substituted organopolysiloxane compounds include, e.g., the compounds of formulae I and II described below and the organopolysiloxane compounds described in U.S. Patent No. 5,494,979, col. 11, 1. 16 - col. 13, 1. 15, and that are designated therein as organopolysiloxanes B. Suitable equilibrating catalysts are described in U.S.

Patent No. 5,494,979, col. 13, 11. 22-26.

The preferred radiation curable organopolysiloxanes of formula (I) are

R^,R¹R²SiO(R¹R¹SiO)_x(R¹R SiO)_y(R'R¹SiO)_zSiR¹R¹R² (I) wherein

R¹ independently from each other is an alkyl group having 1-3 carbon atoms,

R² independently from each other is an optionally branched alkyl group with

1-20 carbon atoms wherein one or more CH₂ groups

OH X O

I I II may be replaced with — C — , - — C — , — O — , — C — ,

H H

R⁶ R⁶ O H

1 1 II 1

C = C — or - — O — C — C = C —

R° and wherein one or more CH₃ groups may be replaced with

R⁵c =C — C — O — , CHY₂ — , CH₂Y — , or HCO —

I I II

R⁴ R⁴ O with the proviso that two oxygen atoms are not directly linked, R⁴ independently from each other is H or CH₃,

R⁵ independently from each other is H or an optionally branched alkyl group having 1-5 carbon atoms, R⁶ independently from each other is H or R¹, X independently from each other is F or Cl, Y independently from each other is F, Cl or OH, x is 0 or a number of up to 200, y is 0 or a number of up to 40, z is 0 or a number of up to 200, with the provisos that

♦ 60 < x + y + z < 300,

• at least one (meth)acrylate group is present, and • the average (meth)acrylate, vinyl and/or ethenylene functionality of the compounds of formula I is > 2 . The organopolysiloxanes of formula I are long-chain organopolysiloxanes where 60<x+y+z<300, preferably 80<x+y+z<250. In the organopolysiloxanes of formula I, at least one of R² exhibits one or more (meth)acrylate groups and, optionally one or more vinyl and/or ethenylene groups. R² and/or y are selected so that the acrylate, vinyl and/or ethenylene functionality of the organopolysiloxane compounds on average is at least 2 and more preferably at least 2.1 in order to obtain upon curing (e.g., UV or electron (E)-beam curing) a crosslinked, 3-dimensional release coating. Organopolysiloxane compounds of formula I having an average acrylate, vinyl and/or ethylene functionality of at least 2.2, preferably at least 2.3, more preferably about 2.3-6, are preferred.

Useful examples of group R² include • H₃C —

• H₃C — (CH₂)_t —

• H₂C =C — C — O — (CHX —

I II

H O

CH₃

I

(CH₂)_r

I

. H₂C =CH — C — O — CH₂ — C — CH₂ — O — (CH₂)_r —

II I

O (CH₂)_r

O

I

C = O

I

CH

II

CH,

. H₃C — (CH₂)₅C— O — (CH₂)_t—

II O wherein p is 1-8, r is 0-5, and t is 1-9.

The organopolysiloxanes of formula I can be prepared using the methods described in DE 38 10 140 and incorporated herein.

One example of a useful (meth)acrylate modified organopolysiloxane of formula I is Tego^® RC 726, which is commercially available from Th. Goldschmidt AG, Essen, Germany. Tego^® RC 726 was analytically determined by the present inventors, by nuclear magnetic resonance (NMR) spectroscopy ('H, ¹³C, ²⁹Si), and gel permeation chromatography (GPC), to be

(CH₃)₃Si[OSi(CH₃)₂]₁₀₄[OSiCH₃]₆OSi(CH₃)3

(CH₂)₆

O

I

O =C

CH

II

CH₂

Another useful example of a (meth)acrylate modified organopolysiloxane of formula I is disclosed in DE 38 10 140 as

CH₃

I

(A'_m,A² _n,A³ ₀) — [SiO(CH₃)₂]₁₆₀[SiO]₂Si(CH₃)₂ _(A ,A² _n ³ ₀)

A ¹ A² A³

A¹ is — (CH₂)₄ OCC= CH₂ ,

II

O

A² is — (CH₂)₄OC (CH₂)₉ CH₃ ,

O

A³ is — (CH₂)₅ — CH₃ , m is 0.7, n is 0.1, and o is 0.2.

A particularly useful example of a mixture of components (i) and (ii) is Tego^® RC 708, which is commercially available from Th. Goldschmidt. Tego^®RC 708 was determined by the present inventors to include about 25-30% MQ resins and about 70% RC 726. The MQ resin component of Tego^®RC 708 is an acrylate-modified MQ-resin. The MQ resin was determined by the present inventors, using NMR and GPC analysis, to have approximately the following properties: a polystyrene equivalent number-average molecular weight of about 3000 with a heterodispersity index of about 2.8, indicating a very broad molecular weight distribution; and a ratio of M units over Q units of about 48-56%: 44-52%) where the

M units: (CH₃)₃SiO — and

(CH₃)₂[CH₂ =CHCO₂(CH₂)_6.8 ]SiO—

are present in a ratio of about 10:1.

The preferred radiation curable (e.g., UV or E-beam curable) organopolysiloxanes of formula (II) are:

R¹ R¹ R²SiO(R¹R¹SiO)_a(R¹R²SiO)_b(R¹R¹SiO)_c Si R¹ R¹ R² (II) wherein a is 0 or a number up to 30, b is 0 or a number up to 20, c is 0 or a number up to 30, and wherein the other variables have the meaning indicated above for formula I, with the provisos that

• 5< a + b + c < 60, • at least one (meth)acrylate group is present, and

• the average (meth)acrylate, vinyl and/or ethenylene functionality of the compounds of formula I is > 2.

The organopolysiloxanes of formula II are short-chain compounds where 5< a+b+c<60, preferably 10< a+b+c<40, more preferably 10< a+b+c<30. The organopolysiloxanes of formula II are preferably added to the precursor of the release coating to improve the dissolvability of the (meth)acrylate-modified MQ resins of component (i) in the (meth)acrylate- modified organopolysiloxane compounds. R² and/or y in the organopolysiloxanes of formula II are selected such that the average acrylate, vinyl and/or ethenylene functionality is at least 2, more preferably at least 2.1.

The organopolysiloxanes of formula II can be prepared using the methods described in DE 38 10 140. A useful example of a organopolysiloxane of formula II is Tego^®

RC 711, commercially available from Th. Goldschmidt AG, Essen, Germany. Tego^® RC 711 was analytically determined by the present inventors, using NMR spectroscopy ('H, ¹³C, ²⁹Si) and GPC, to be

(CH₃)₃Si[OSi(CH₃)₂]₁₆₂[OSiCH₃]_5.8OSi(CFi)₃

(CH₂)₃

O CH₂

HC OH

CH₂

O

C= O

CH

CH₂

Another example of an organopolysiloxane of formula II is Tego^® RC 715, which is commercially available from Th. Goldschmidt AG. Tego^® RC 715 was analytically determined by the present inventors, by NMR spectroscopy (Η, ¹³C, ²⁹Si) and GPC, to be

(D\D²)— [(CH₃)₂SiO]₂₆Si(CH₃)₂ — (D\D²)

where

D¹ is H₂C =CHCOOCH₂CH(OH)CH₂O(CH₂)₃

D² is HOCH₂C[(OOCCH= CH₂)H]CH₂O(CH₂)₃ — where D¹ and D² are present approximately in a ratio of about 4: 1.

Other useful organopolysiloxanes of formula II include, e.g.,

^^CHCCX CH^ (CH₃)₂SiO[Si(CH₃)₂O]₆₂ S CH^CH^ OOC CH =CH₂ and

(CH₃)₃SiO[Si(CH₃)₂O]₁₆₂ [(CH₂=CH COO(CH₂)₃Si(CH₃) O]_{7 8} Si(CH₃)₃ the preparations of which are described in DE 38 10 140.

The amount of the short-chain organopolysiloxanes of formula II is selected to allow the acrylate modified MQ resin of component (i) to dissolve in the release coating composition, and to allow sufficient anchoring of the release coating to the backing. It was found to be essential that the amount of such components be less than 25 wt. %, preferably no greater than about 15 wt. %), and more preferably about 10 wt %> or less. If the concentration of the short-chain organopolysiloxane components in the release coating of the present invention is more than 15 wt %>, the noise level upon unwinding of the adhesive tape tends to become unacceptably high. This finding was surprising because Tego^®RC 708, which, as indicated above, is a mixture of 30 wt. % of an acrylate modified MQ resin and 70 wt. % Tego^®RC726, is recommended by the preliminary data sheet of Tego^® RC 708 published by Goldschmidt AG in November 1993, to be blended with at least 30 wt. % of Tego^®RC 711. A minimum of 30 wt. % of Tego^®RC 711 in combination with Tego^®RC 708 is also mentioned, for example, in T. Ebbrecht et al., Silicone Acrylate Systems, lecture on the COWISE Conference, Chicago, U.S.A., March 2-3, 1992, p. 7, charts 10 and 11.

Examples of suitable photoinitiators include benzyl ketals, benzoin ethers, acetophenone derivatives, ketoxime ethers, benzophenone, benzo- or thioxanthones, etc.. Specific examples of photoinitiators include: 2,2- diethoxyacetophenone; 2- or 3- or 4- bromoacetophenone; benzoin; benzophenone; 4- chlorobenzophenone; 4- phenylbenzophenone; benzoquinone; 1- chloroanthroquinone; p- diacetyl-benzene; 9, 10 dibromoanthracene; l,3-diphenyl-2-propanone; 1,4-naphtyl-phenyl ketone;

2,3-pentenedione; propiophenone; chlorthioxanthone; xanthone; and fluorene; and mixtures thereof. An example of a suitable photoinitiator is Darocure 1173, which is commercially available from Ciba Geigy, Switzerland. The concentration of the components of the radiation curable release coating composition are preferably selected within the ranges as given above so that the precursor of the release coating forms a coatable mixture or solution. If necessary a small amount of solvent such as, for example, heptane may be added.

The precursor of the release coating composition may also include additives such as, for example, stabilizers, dyes, pigments, antioxidants, fillers and combinations thereof. The amount of such additives preferably is no greater than 25 wt.%>, more preferably no greater than 20 wt.%, of components (i), (ii) and (iii).

The pressure-sensitive adhesive tape can be made by coating the precursor of the release coating onto a major surface of the backing and subsequently radiation-curing the release coating. The adhesive can then be applied to the other major surface of the backing. The processes may be carried out separately, in-line sequentially, and simultaneously. Both the precursor of the release coating and the adhesive coating are preferably selected to allow for solvent-less coating.

Prior to either or both coating steps, the backing may be treated to enhance adhesion of the composition to the backing. Such treatments include chemical priming, flame treatment, corona treatment, and combinations thereof.

Pressure-sensitive adhesive tapes according to the present invention wherein the (meth)acrylate modified silicone MQ resins of component (i) are present in an amount of 25-35 wt.%>, the long-chain organopolysiloxane compounds of formula I (component (ii)) are present in an amount of 55-75 wt.% and the short-chain organopolysiloxane compounds of formula II (component (iii)) are present in an amount of 0-10 wt.%>, are especially preferred for use as packaging and box-sealing tapes. The objectives and advantages of this invention are further illustrated by the following examples but the particular materials and the amounts thereof recited in these examples should not be construed to unduly limit the invention. Several test methods which are utilized in the examples, are also described. Parts given herein are parts by weight.

EXAMPLES

Test Procedures I

Test procedures used in Examples 1-6 and Comparative Examples

1-5 include the following. Noise Level at a Free-Standing Unwind Stand Test I

A 50 mm wide roll of adhesive tape is unwound in a tangential direction at 25 m/min or 110 m/min, respectively, using HSU- 1000 High

Speed Unwind Machine (Chemsultants International Network, Cincinnati,

Ohio). A Test 815 sound probe (Testo, Lenkirch, Germany) is placed 1 m from the unwinding in the direction of the rotation axis around which the tape roll is unwound. The sound level in dB(A) is read from the meter and recorded.

Noise Level at an Unwind Stand Placed in a Box Test I A 50 mm wide roll of adhesive tape is placed horizontally in the middle of a wooden box having the dimensions of 60 cm x 60 cm x 60 cm. The roll is unwound in a tangential direction at a speed of 20 m/min whereby the tape is travelling through a vertical slit (2 cm x 8 cm) in the front wall of the wooden box. One of the side walls of the box next to the front wall of the box has a second vertical slit (2cm x 8 cm) facing the horizontally placed roll and oriented parallel to the rotation axis of the tape roll. A Test 815 sound probe is placed in the plane of the slit so that the sound probe is in the direction of the middle axis of the tape roll (=axis vertical to the rotation axis and intersecting such rotation axis). The sound level in dB(A) is read from the meter and recorded.

Unwind Force at High Speed Test I

The force required to unwind a 50 mm wide roll of tape at high speed (110 m/min) is measured using the HSU- 1000 Unwind Machine having an unwind motor, a winder station, and the capability of electronically evaluating the unwind behavior of the adhesive tape. The output is then printed out in the form of a graph showing the actual unwind force in N/cm as a function of distance along the tape. The shockiness index (SI) is calculated from such graph as the ratio (maximum unwind force-minimum unwind force)/ average unwind force.

Unwind force at Low Speed Test I

The unwind force at a low speed of 0.3 m / min is measured according to Association Des Fabricants Europeens De Rubans Auto- Adhesifs (AFERA) 4013. The unwind force is recorded in N/cm and the average unwind force and the shockiness index is obtained as described above.

180° Peel Adhesion Test I Peel adhesion is measured according to AFERA 4001 from stainless steel at 0.3 m/min. Results are recorded in N/cm.

Static Shear from Fiberboard Test I

Static shear to fiberboard is measured according to AFERA 4012 with the exception that instead of the stainless steel substrate required by this method, a substrate of Mosinee C696 virgin fiberboard (Mosinee Paper Corp, Wisconsin) is used. The adhered sample area is 1.27 x 1.27 cm and a weight of 1 kg is used. Time to bond failure is recorded in minutes.

Rolling Ball Tack Test I

Rolling ball tack of the adhesive surface is measured according to PSTC 6 (Pressure-Sensitive Tape Council, Chicago, Illinois). The results were recorded in mm.

All tests of Test Procedures I were repeated three times and the results averaged. Results were measured on tape rolls which had been freshly prepared and stored at 23°C and a relative humidity of 50% for approximately one week, and on aged tape rolls. The aging procedure included storing of the above mentioned rolls at 50°C in a forced air oven for 11 days. The tape rolls were reconditioned to 23 °C and 50% relative humidity for at least 24 hrs before testing

Test Procedures II

Test procedures used in Example 7 include the following.

Noise Level at a Free-Standing Unwind Stand Test II

The noise level at free-standing unwind is determined by unwinding a 48 mm wide roll of adhesive tape in a tangential direction at 5, 25, 60 and 100 m/min, respectively, using a HSU- 1000 High Speed Unwind Machine (Chemsultants International Network, Cincinnati, Ohio). A Real-Time Frequency analyzer Type 2144 with microphone type 4185 sound probe

(Bruel & Kjaer, Naerum, Denmark) is placed 1 m from the unwinding in the direction of the rotation axis around which the tape roll is unwound. The sound level in dB(A) is read from the meter and recorded.

Unwind Force at High Speed Test II

The force required to unwind a 48 mm wide roll of tape at 5, 25, 60 and 100 m/min is measured using a HSU- 1000 Unwind Machine having an unwind motor, a winder station, and the capability of electronically evaluating the unwind properties of the adhesive tape. The output is printed in the form of a graph showing the actual unwind force in N/cm as a function of distance along the tape. The shockiness index (SI) is calculated form such graph as the ratio (maximum unwind force-minimum unwind force)/average unwind force. Unwind Force at Low Speed Test II

The unwind force at a speed of 12 in/min (0.3 m/min) is measured according to PSTC 8 (Pressure-Sensitive Tape Council, Chicago, Illinois, U.S.A.). The unwind force is recorded in N/cm and the average unwind force and the shockiness index are obtained as described above.

180° Peel Adhesion Test II

Peel adhesion is measured according to PSTC 1 from a stainless steel substrate at 12 in/min (0.3 m/min). Results are recorded in oz/in.

Static Shear from FiberBoard Test II

Hanging shear failure times are measured according to PSTC 2. The adhered sample area is 1.27 x 1.27 cm and a weight of 1 kg is used. Time to bond failure is recorded in minutes.

Rolling Ball Tack Test II

Rolling ball tack of the adhesive surface is measured according to PSTC 6. The results are recorded in mm.

All tests of Test Procedures II were repeated three times and the results averaged. Results were measured on tape rolls which had been freshly prepared and stored at 23°C and a relative humidity of 50% for approximately, one week, and on aged tape rolls. The aging procedure included storing of the above mentioned rolls at 120°F (50°C) in a forced air oven for 11 days. The tape rolls were reconditioned to 23 °C and 50% relative humidity for at least 24 hrs before testing.

Example 1

A 35μm thick, biaxially-oriented polypropylene (BOPP) film was corona-treated on one side and then coated with a UV-curable precursor of a release coating composition that included 100 parts Tego^® RC 708 (Th. Goldschmidt AG, Essen, Germany), and 3 parts of Darocur 1173 UV photoinitiator (Ciba-Geigy, Basel, Switzerland ) based on 100 parts of Tego^® RC 708. The release coating was prepared using a five-roll coater at a coating weight of the precursor of 0.6 g/m² (thickness of the cured release coating about 0.6 μm), and then cured by UV radiation (120 W/cm) using lamps Model F-450 (Fusion UV Systems, Inc., Gaithersberg, Maryland) in a nitrogen atmosphere.

The opposite side of the BOPP was flame-treated and then coated with a synthetic rubber resin pressure-sensitive adhesive that included Vector

4511 pure triblock styrene-isoprene-styrene synthetic block copolymer (Dexco Polymers), Escorez 2203 LC hydrocarbon tackifier resin (Exxon Chemicals), and Milsol 100 naphthenic oil (Oleotecnica S.p.A., Milan, Italy) in a ratio 100:100:10 parts by weight using standard hot-melt extrusion coating techniques. The adhesive composition also included 1.5 parts Irganox

1076 antioxidant and 1.5 parts PS 800 antioxidant (Ciba Geigy, Basel, Switzerland). The adhesive composition was applied at a coating weight of 18 g/m² corresponding to a thickness of about 18 μm. The tape was rolled up onto itself, slit into 50 mm rolls and stored as described above to give freshly prepared or aged, respectively, tape rolls.

Examples 2 and 3

Example 1 was repeated with the exception that the coating weight of the precursor was reduced to 0.42 and 0.30 g/m², respectively.

Examples 4 and 5

Example 1 was repeated with the exception that the precursor of the release coating composition included a mixture of Tego^® RC 708 (Th. Goldschmidt AG) and Tego^® RC 711 (Th. Goldschmidt AG) instead of 100 parts of Tego^®RC 708. In Example 4, the weight ratio of Tego^® RC 708 to RC 711 was 95 parts/5 parts and in Example 5, the weight ratio was 90 parts/10 parts.

Example 6

Example 1 was repeated with the exception that the precursor of the release coating composition included instead of 100 parts of Tego^® RC 708, a mixture of Tego^® RC 726 and the same acrylate modified MQ silicone resin contained in Tego^®RC 708, in a weight ratio of 80 parts/20 parts.

Properties of the adhesive tape of Examples 1-6 were evaluated according to the Test Procedures I given above. All bond failures that occurred in the Static Shear from Fiberboard Test I were of the adhesive failure type. The results of the Unwind Force at Low Speed Test I, the Unwind

Force at High Speed Test I, and the shockiness index (SI) are recorded in Table 2. The results of the Noise Level at an Unwind Stand Placed in a Box Test I are recorded in Table 3. The results of the Noise Level at a Free- Standing Unwind in Stand Test I are recorded in Tables 3 and 4. The results of the 180° Peel Adhesion Test I, Static Shear from Fiberboard Test I, and rolling Ball Tack Test I are recorded in Table 5.

Example 7

A 35μm thick, biaxially-oriented polypropylene (BOPP) film was corona-treated on one side and then coated with a UV-curable precursor of a release coating composition that included 100 parts Tego RC 708 and 3 parts of Darocur 1173 UV photoinitiator (Ciba-Geigy, Basel, Switzerland) based on 100 parts of RC 708. The release coating was prepared using a five-roll coater at a coating weight of the precursor of 0.6 g/m² (thickness of the cured release coating about 0.6 μm), and then cured by UV radiation using lamps (Fusion UV Systems, Inc., Gaithersberg, Maryland) in a nitrogen atmosphere.

The opposite side of the BOPP was flame-treated and then coated with a synthetic rubber resin pressure-sensitive adhesive that included Kraton

1107 pure triblock styrene-isoprene-styrene synthetic block copolymer (Shell Chemical Company) and Wingtack Plus hydrocarbon tackifier resin (Hercules, Inc.) in a ratio of 100:85 parts by weight using standard hot-melt extrusion coating techniques. The adhesive composition also included 1.5 parts of Irganox 1076 antioxidant (Ciba Geigy) and 1.5 parts Cyanox LTDP antioxidant (Ciba Geigy). The adhesive composition was applied at a coating weight of 23 g/m² corresponding to a thickness of about 23 μm. The tape was rolled up onto itself, slit into 48 mm rolls, and stored as described above to give freshly prepared or aged, respectively, tape rolls. Properties of the adhesive tape of Example 7 were evaluated according to the Test Procedures II given above. All bond failures that occurred in the Static Shear from Fiberboard Test II were of the adhesive failure type. The results of the 180° Peel Adhesion Test II, Static Shear from Fiberboard Test II, and rolling Ball Tack Test II are recorded in Table 5. The results of the Unwind Force at Low Speed Test II are recorded in Table 6.

The results of the Unwind Force at High Speed Test II and Noise Level at a Free-Standing Unwind Stand Test II are recorded in Table 7.

Comparative Example 1 Example 1 was repeated with the exception that the precursor of the release coating composition included a mixture of Tego^® RC 708 and Tego^® RC 711 in a ratio of 70 parts/30 parts instead of 100 parts Tego^®RC 708. Comparative Example 2

Example 1 was repeated with the exception that the precursor of the release coating composition included 100 parts of Tego^® RC 726 instead of 100 parts of Tego^® RC 708.

Comparative Example 3

Example 6 was repeated with the exception that the precursor of the release coating composition included a mixture of Tego^® RC 726 and the acrylate-modified MQ silicone resin contained in Tego^®RC 708 in a weight ratio of 60 parts/40 parts.

Comparative Example 4 and 5

Example 1 was repeated with the exception that the precursor of the release coating composition included a mixture of Tego^® RC 902 (Th. Goldschmidt AG) and the same acrylate-modified MQ silicone resin contained in Tego^®RC 708 in a weight ratio of 70 parts/30 parts instead of

100 parts of Tego^® RC 708. The coating weight of the precursor composition was 0.50 g/m² in Comparative Example 4 and reduced to 0.36 g/m² in

Comparative Example 5. Tego^® RC 902 was analytically determined by the present inventors, by NMR spectroscopy and GPC, to be

(B B² ) -KCH ₃)₂SiO— ]₅₆ Si(CH₃)₂ — (B',B²) where βⁱ is — (CH₂)₃OCH₂C[(C₂H₅)(CH₂OOCCH =CH₂)]CH₂OOCCH =CH₂ β2 is — (CH₂)₃ OCH₂C[(C₂H₅)(CH₂OOCCH=CH₂)]CH₂OOCCH₂CH₂OOCCH=CH₂

where B¹ is the major end group, and B² is present to a minor degree. Properties of the adhesive tape of Comparative Examples 1-5 were evaluated according to the Test Procedures I given above. All bond failures that occurred in the Static Shear from Fiberboard Test I were of the adhesive failure type. The results of the Unwind Force at Low Speed Test I, the Unwind Force at High Speed Test I, and the shockiness index (SI) are recorded in Table 2. The results of the Noise Level at an Unwind Stand Placed in a Box Test I, and the results of the Noise Level at a Free-Standing Unwind in Stand Test I are recorded in Table 3. The results of the 180° Peel Adhesion Test I, Static Shear from Fiberboard Test I, and rolling Ball Tack Test I are recorded in Table 5.

Table 1 Overview of Tape Constructions

PSA Pressure-sensitive adhesive

(*) percentages are percentages by weight related to the mass of the precursor of the release coating

SR Synthetic rubber (as specified in Example 1)

BOPP Biaxially-oriented polypropylene

HM Hot-melt

SFC Solvent-free coated

Table 2 Unwind Force and Shockiness Index (SI)

Table 3 Noise at low unwind speeds

Table 4 Noise at high unwind speed

Table 5 Adhesive-related Properties

Table 6

Table 7

Other embodiments are within the claims.

What is claimed is:

SUBSTITUTE SHEET (RULE 28)

Claims

1. A pressure-sensitive adhesive tape comprising a backing having a first major surface and a second major surface, a pressure-sensitive adhesive provided on said first major surface, and a release coating provided on said second major surface, said release coating comprising the reaction product of:

(i) from 15 - 35 wt.% of one or more silicone MQ-resins bearing one or more (meth) acrylate functional groups,

(ii) from 50- 85 wt.% of one or more radiation-curable organopolysiloxanes of formula (I) R¹R¹R²SiO(R¹R¹SiO)_x(R¹R²SiO)_y(R¹R¹SiO)_zSiR¹R¹R² (I) wherein

R¹ independently from each other is an alkyl group having 1-3 carbon atoms,

R² independently from each other is an optionally branched alkyl group with 1-20 carbon atoms wherein one or more CH₂ groups

OH X O

I I II may be replaced with ΓÇö C ΓÇö , ΓÇö C ΓÇö , ΓÇö O ΓÇö , ΓÇö C ΓÇö ,

I I

H H

R⁶ R⁶ O H

I I II I

ΓÇö C = C ΓÇö or ΓÇö O ΓÇö C ΓÇö C = C ΓÇö

and wherein one or more CH₃ groups may be replaced with R⁵C =C ΓÇö C ΓÇö O ΓÇö , CHY₂ ΓÇö , CH₂Y ΓÇö , or HCO

I I II

R⁴ R⁴ O with the proviso that two oxygen atoms are not directly linked,

R >4 independently from each other is H or CH₃, R⁵ independently from each other is H or an optionally branched alkyl group having 1-5 carbon atoms,

R⁶ independently from each other is H or R¹,

X independently from each other is F or Cl, Y independently from each other is F, Cl or OH, x is 0 or a number of up to 200, y is 0 or a number of up to 40, z is 0 or a number of up to 200, with the provisos that ΓÇó 60 < x + y + z < 300,

ΓÇó at least one (meth)acrylate group is present, and

ΓÇó the average (meth)acrylate, vinyl and/or ethenylene functionality of the compounds of formula I is > 2 ,

(iii) less than 25 wt.% of one or more radiation-curable organopolysiloxane of formula (II)

R¹ R¹ R²SiO(R^,R^,SiO)_a(R¹R²SiO)_b(R¹R¹SiO)_c Si R¹ R¹ R² (II) wherein a is 0 or a number up to 30, b is 0 or a number up to 20, c is 0 or a number up to 30, and wherein the other variables have the meaning indicated above for formula I, with the provisos that

ΓÇó 5< a + b + c < 60,

ΓÇó at least one (meth)acrylate group is present, and the average (meth)acrylate, vinyl and/or ethenylene functionality of the compounds of formula II is > 2; and (iv) an effective amount of one or more photoinitiators, the weight percentages given for component (i), (ii) and (iii), respectively, referring to the sum of the masses of components (i), (ii) and (iii), which add up to 100 wt.%.

2. The pressure sensitive adhesive tape of claim 1, wherein said tape, when in the form of a roll, upon unwind exhibits no greater than about 80 dB(A), at unwind speeds of up to about 110 m/min, when measured according to the "Noise Level at Free-Standing Unwind Stand" test.

3. The pressure sensitive adhesive tape of claim 1, wherein said tape, when in the form of a roll, upon unwind exhibits less than 75 dB(A), at unwind speeds of up to about 100 m/min, when measured according to the "Noise Level at Free-Standing Unwind Stand" test.

4. The pressure-sensitive adhesive tape of claim 2, wherein said tape, when in the form of a roll, exhibits an unwind force of at least about 0.5 N/cm, at an unwind speed of about 0.3 m/min.

5. The pressure-sensitive adhesive tape of claim 3, wherein said tape, when in the form of a roll, exhibits an unwind force of at least about 0.5 N/cm, at an unwind speed of about 0.3 m/min.

6. The pressure-sensitive adhesive tape of claim 1, wherein the amount of said radiation-curable organopolysiloxane of formula (II) is no greater than about 15 wt. %.

7. The pressure-sensitive adhesive tape of claim 1, wherein the amount of said radiation-curable organopolysiloxane of formula (II) is no greater than about 10 wt. %.

8. The pressure-sensitive adhesive tape of claim 1, wherein the amount of said radiation-curable organopolysiloxane of formula (II) is no greater than about 5 wt. %.

9. The pressure-sensitive adhesive tape of claim 1 , wherein the backing comprises an oriented polymeric film selected from the group consisting of polyester, polyolefin, or a combination thereof.

10. The pressure-sensitive adhesive tape of claim 1, wherein the backing has a thickness of about 20 - 100 ╬╝m.

11. The pressure-sensitive adhesive tape of claim 1 , wherein the pressure-sensitive adhesive comprises a hot-melt coatable pressure-sensitive adhesive.

12. The pressure-sensitive adhesive tape of claim 1, wherein the adhesive comprises ABA-type or AB-type synthetic resin block copolymers where A is a thermoplastic block and B is a rubber block.

13. The pressure-sensitive adhesive tape of claim 1 , wherein the pressure-sensitive adhesive comprises a block copolymer selected from the group consisting of styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene- butylene-styrene, or a combination thereof.

14. The pressure-sensitive adhesive tape of claim 12, wherein the pressure-sensitive adhesive further comprises one or more tackifiers.

15. The pressure-sensitive adhesive tape of claim 1 , wherein the pressure-sensitive adhesive has a thickness of about 10-50 ╬╝m.

16. The pressure-sensitive adhesive tape of claim 1, wherein said pressure-sensitive adhesive tape is in the form of a roll of tape.

17. Use of the tape of claim 1 as a packaging or box-sealing tape.

18. A method of using a roll of the pressure-sensitive adhesive tape of claim 1, said method comprising: unwinding said roll of pressure-sensitive adhesive tape; and adhering said pressure-sensitive adhesive tape to a cardboard substrate.

19. The method of claim 18, wherein said cardboard substrate comprises a box.