Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/40—Adhesives in the form of films or foils characterised by release liners
  • C09J7/401—Adhesives in the form of films or foils characterised by release liners characterised by the release coating composition
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2483/00—Presence of polysiloxane
  • C09J2483/005—Presence of polysiloxane in the release coating

Definitions

• Pressure-sensitive release and adhesive materials are well known and in wide commercial use to secure tapes, labels, or other articles to receiving surfaces. Such adhesives can be attached to a variety of materials by the simple application of pressure. Thus tapes coated with adhesive on opposite sides are used to Join two articles together.
• Pressure-sensitive adhesives are generally based on elastomeric polymers including natural and synthetic rubbers. They can be compounded with extenders, plasticizers, tackifiers and other materials to provide specifically desired properties. Examples of such materials and their use are provided in numerous prior art U.S. patents, including 3,085,903; 3,246 ,049 ; 3,356,635; 3,501,365; and 3,532,652.
• a release layer typically a nontacky silicone polymer. This facilitates handling, storage and dispensing.
• the resulting products include label stock in which a base or support is bonded to the adhesive and the exposed adhesive surface is covered with a siliconerelease paper or film.
• a spirally wound tape with a film or paper support having one surface bonded to an adhesive. The exposed adhesive surface is in contact with a release layer that is carried by the opposite side of the support, or by a separate interleaving support.
• Still another example is a spirally wound transfer tape in which the support is coated on both sides with release layers, and one of the release layers is overcoated with adhesive
• the adhesive initially can be formed directly on the support surface, or on the Felease surface. The latter is necessary for transfer tapes with release coatings on both sides of the support. Consistently low uniform release forces between the adhesive and release layer are more difficult to obtain when the adhesive is solidified from a liquid in contact with the release layer surface.
• laminates which are composite structures having at least one support, temporary or permanent, a pressure-sensitive adhesive layer, and at least one release layer in surface contact with the adhesive. Other layers such as a second release layer or a second support may also be present.
• Elastomeric, pressure-sensitive silicone adhesives are widely known and have a number of attractive properties. They are useful over a wide range of temperatures, both high and low; they are chemically stable, and have good adhesion to a variety of materials.
• silicone pressure-sensitive adhesives adhere with such tenacity to conventional release surfaces, that the materials often tear before releasing. The consequence is that the use of silicone adhesive has been limited generally to direct application without a release layer, or to use with plastic films strong enough to withstand the considerable release forces required in unwinding spiral tapes. Release surfaces with ridges which tend to reduce contact area have also been employed with limited success, but at increased expense.
• an object of the invention is to realize a silicone pressure-sensitive release laminate that is practical for use, both immediately after preparation and after extended periods of storage. Another object is to realize silicone adhesive laminate structures which can be releasably separated with stripping or release forces comparable with known, nonsilicone pressure-sensitive adhesive laminates.
• Still another object is to realize silicone pressuresensitive laminate structures which permit the use of existing pressure-sensitive application techniques and equipment.
• a further object of the invention is to facilitate the use of silicone adhesives.
• a related object is to provide release materials, for such adhesives which expedite their use.
• Still another object is to achieve release and adhesive combinations which are readily produced and are usable over a wide range of temperature conditions.
• a related object is to achieve a silicone release and adhesive laminate which is operable under frigid Arctic conditions, as well as humid and high temperature tropical conditions.
• the invention provides for the employment of one or more releasable dimethylpolysiloxanes which, before curing, have viscosities in the range from about 60 centipoises to about 100 centipoises, and from about 100 centipoises to about 600 centipoises.
• a less preferred range of viscosities is from above about 600 centipoises to below 1000 centipoises.
• a similarly suitable viscosity range extends below about 60 centipoises.
• Silicone release resins for the practice of the invention are sold essentially as linear polymers or prepolymers in liquid form, with or without solvents. They are coated onto paper, film or other supports and then cured, typically by heat and/or surface catalytic action,to form solid, nontacky, cross-linked polymers in situ.
• release resins are formed from halosilanes and consist predominantly of repeating units of the structure
• R - O - Si - R where R is hydrogen or a hydrocarbon radical, principally a lower alkyl or aryl, typically methyl; O is oxygen; and Si is silicon.
• the degree of polymerization is such as to produce a liquid linear prepolymer material with no significant cross-linkage. While liquids are preferred, high molecular weight wax-like solids can be substituted where sufficient solvent or can be employed to provide fluidity for coating without premature curing. It is believed that presently known silicone linear release prepolymers consist of at least 95 per cent repeating units of the above structure with reactive end groups, but that small quantities of other modifying units may be present, if desired. Such release materials are described, for example, in an article by Alvin E. Bey, titled "New Developments in Silicone Release Coatings for
• silicone pressure-sensitive adhesives can be contacted with release layers formed from selected silicone release polymers, stored for extended periods, and removed for use when needed.
• the equipment and forces are generally comparable to those heretofore employed with rubber and acrylic-based adhesives.
• These results are obtained by employing one or more silicone release polymers with a net viscosity below 1000 centipoises, which subsequently are highly cross-linked.
• the degree of cross-linking can be conveniently measured by the absorption of solvent. The greater the degree of crosslinking, the less is the absorption of solvent.
• Silicone release polymers are sufficiently cross-linked for use with the laminates of the present invention if they absorb less than about 200 per cent of their cured weight of the solvent heptane.
• the absorption of heptane is measures as follows: A sample of liquid coating material, catalyzed for curing, is placed in a container from which it can be removed after curing.
• the container may be a small laboratory weighing dish of aluminum foil.
• Inert solvent if present, is then removed and the liquid fully cured.
• a sufficient sample should be used to provide a cured thickness of about one fourth inch.
• the cured sample is then removed, weighed, and immersed in heptane until the sample reaches substantially constant weight.
• the sample is removed from the heptane, the surface dried by blotting and the sample is reweighed. The increase in weight represents the amount of absorbed heptane.
• the release mechanism has been previously theorized, for example,in Bey, cited above, as involving a low polarity surface of low surface tension, highly flexible polymer chains, incompatibility of the release surface with dissimilar contacting adhesive polymers.
• the degree of cross-linking affects the release forces.
• such theories have not led to successful release laminates for silicone pressure-sensitive adhesives.
• a high degree of functionality can be provided on a polysiloxane prepolymer, as by silicon-bonded hydrogen or vinyl substituents, which are polymerized and cross-linked with polyfunctional cross-linking agents. Additive reactions between unsaturated hydrocarbon groups, such as vinyls or the like, and silicon-bonded hydrogens are preferred.
• the unsaturated hydrocarbon groups may be provided as reactive groups in a hydrocarbon molecule, preferably of low molecular weight, as in Example I, or on a polysiloxane prepolymer, as in Example VI, below.
• all or a majority of the polysiloxane prepolymers be of low molecular weight, preferably having a Brookfield viscosity at 25°C. below 1000 centipoises, corresponding to a molecular weight below about 25,000. Such lower molecular weight prepolymers are believed to minimize sterlc effects in the attainment of a highly cross-linked structure.
• the total liquid coating prepolymer composition absent inert solvent, preferably has a viscosity below about 600 centipoises and most preferably less.
• Particularly suitable materials have a net viscosity in the range extending from 300 to between 60 and 100 centipoises. Less suitable but usable are materials having a viscosity range above 600 centipoises and below 60 centipoises.
• the silicone release layers of the present invention be formed from reactive polysiloxane prepolymer compositions having a substantial content of silicon-bonded hydrogen substltuents sufficient to provide an infra-red (IR) absorption ratio above about 0.4 for the ratio of (a) silicon-hydrogen (Si-H) absorption, in the range from about 4.5 to 4.8 microns, to (b) for carbon-hydrogen (C-H) absorption in the range from about 3.4 to 3.5 microns.
• IR infra-red
• Si-H silicon-hydrogen
• C-H carbon-hydrogen
• Prepolymers containing silicon-bonded hydrogen can comprise the major component, as in Examples I-V, below, which can be highly cross-linked with co-reactive silanes,multivinyl containing cross-linking agents, or similar reactive unsaturated compounds such as dicyclopentadiene, or, as illustrated in Example VI, the silicon-bonded, hydrogen-containing prepolymer can be employed to cross-link other co-reactive polysiloxane prepolymers having sufficient co-reactive substituents, preferably vinyl groups, to provide a siloxane copolymer with a high degree of cross-linking. Catalysts for the above reactions are known and are exemplified in the
• Figure 1 is an infrared (IR) spectrographic absorption chart for silicone release resin prepolymer No. 4280 of the General Electric Company;
• Figure 2 is an IR spectrographic absorption chart for silicone release resin prepolymer No. SS4281C of the General Electric Company;
• Figure 3 is an IR spectrographic absorption chart for silicone release resin prepolymer No. 4191 of the General Electric Company
• Figure 4 is an IR spectrographic absorption chart for silicone release resin prepolymer No. X2-7018 of the Dow Corning Corporation;
• Figure 5 is an IR spectrographic absorption chart for silicone release resin prepolymer No. X2-7016 of the Dow Corning Corporation;
• Figure 6 is an IR spectrographic absorption chart for silicone release resin prepolymer No. 23/30 of the Dow Corning Corporation;
• Figure 7 is an IR spectrographic absorption chart for silicone release resin prepolymer No. EP 6396 of the imperial Chemical Industries, Ltd., Stevenston, Ayrshire, Scotland;
• Figure 8A is an IR spectograph absorption chart for Dow-Corning Q-2-7044/7045;
• Figure 8B is a reduced portion of Figure 8A to permit determination of the IR ratio
• Figure 9A is a schematic diagram of a laminate in accordance with the invention.
• Figure 9B is a schematic diagram of another laminate in accordance with the invention.
• FIG. 9C is a schematic diagram of a furtherlaminate in accordance with the invention.
• DETAILED DESCRIPTION Detailed considerations applicable to the practice of the invention are set forth below
• the runs were performed on an INFRACORD prism IR spectrophotometer.
• the cast film was of a thickness such that both absorption peaks of interest, when present, fell within about the absorption region extending from above
• the first absorption peak is 0.72 at 3.4 microns.
• the estimated base line at 3.4 microns is about 0.05 (by straight line extrapolation across the absorption interval indicated by the broken line).
• the prepolymers of Figures 1 and 2, and also of Figures 4 and 5 are mixed in the proportion of 10 parts by weight of the first material to 1 part by weight of the second material and coated with or without solvent, and cured. They form release layers, but not for silicone adhesives.
• the materials of Figures 3 and 6 are conventional solvent coating release materials, cured with catalyst and small quantities of reactive silanes as recommeneded by the suppliers.
• the material of Figure 7 is a solventless coating material cured with added platinic acid catalyst containing dicyclopentadiene, as recommended by the supplier.
• the coatings applied without solvents generally give about one-half these values.
• conventional release sheets often tear before release is obtained.
• the tack or adhesion of the silicone adhesives is sometimes diminished, believed to be due to retention of release polymer on the surface of the adhesive.
• a carrier was provided by a conventional 42-pound per ream (250,000 square inches) super calendered and densified Kraft release paper and coated as follows:
• EP 6396 from imperial Chemical Industries Limited (ICI), Ayrshire, Scotland was mixed with ICI catalyst EP 6439 (platinic acid type containing dicyclopentadiene) in the weight ratio of 1.5 parts catalyst to 100 parts resin and placed in the pan of an offset gravure coating apparatus.
• EP 6396 is believed to be predominantly silanol terminated polydimethylsiloxane having a viscosity of 60 to 100 centipoises at 25°C, in combination with a minor proportion of polymethylhydrogensiloxane having a viscosity of about 25 centipoises at 25°C.
• the net viscosity is about 70 centipoises and is verifiable from the IR spectrographic absorption chart of Figure 7.
• Figure 7 and Table I show that the material has a sufficient amount of hydrogen-bonded silcicon (IR ratio of 0.45) to provide an adequate release.
• a gravure roll, partially immersed in the pan, with 150 lines per inch engraved on steel was employed with a rubber transfer roll operated at a roll speed ratio of 1:1.
• the release carrier paper was fed over the transfer roll by a steel drive roll, with the paper fed between the nip formed by the rubber transfer roll and the steel drive roll, at a speed six times as great as the linear speed of the surface of the transfer roll surface. This provided a smooth, uniform coating of about 0.3 pounds coating per ream.
• the coating was then passed into a hot air oven and cured for 7 seconds at 395°F (202°C).
• the second or reverse side was then similarly coated and cured, with the first side again heated for 7 seconds at 395°F
• the release paper was then further coated on the first, twice heated side, by drawing the paper under a shimmed steel bar with 1.0 to 1.5 mils thickness of silicone pressure-sensitive adhesive (after drying and curing).
• the adhesive employed was SR 574 .obtained from the General Electric Company and catalyzed as recommended with 1.5 per cent by weight of equal weight parts of dichlorobenzoyl peroxide and silicone oil or dibutyl phthalate.
• the coating was cured at 300°F. for 2 minutes.
• the cured adhesive was covered with a 0.002 inch thick strip of Mylar polyester film and a compressive force of about 400 pounds per inch applied for eight minutes.
• composition for SR 574 adhesive is disclosed by William J. O'Malley in an article titled "Silicone Pressure Sensitive Adhesives for Flexible
• SR 574 The specific composition of SR 574 is discussed, for example, on page 1 at line 8 and in Figures 1 and 2. It is Indicated that pressure sensitive adhesives of the SR 574 type are based on the combination of a gum and an "MQ" resin.
• the gum component as shown by Figure 1 of the article, is a polysiloxane gum such as methylphenylpolysiloxane.
• Figure 2 of the article discloses the MQ resin to be an organopolysiloxane resin.
• organopolysiloxane pressure sensitive adhesives is specifically set forth in
• the test was conducted on a TLMI tester, and samples 1 inch by 6 inches were stripped at 180° and 600 inches per minute, following TLMI release test method VIII-LD270.
• the measured stripping or release forces were as follows, for various periods of storage time at standard conditions of temperature and pressure following preparation of the laminate:
• the resulting release mixture was coated using a Number 4 Mayer rod onto a support film of Mylar polyester, dried and cured in an oven for 20 seconds at 275°F.
• overcoated with General Electric SR 574 silicone pressure-sensitive adhesive laminated and tested, all as set forth in Example I, low release values immediately and after storage for one week were obtained.
• the prepolymer of Figure 2 having a comparatively high IR absorption ratio (of 1.51 as shown in Table I) and a viscosity of 600 centipoises, is used after being suitably cured with catalyst such as that of Example I.
• the prepolymer of Figure V also having a comparatively high IR absorption ratio (of 1.03 as shown by Table I) and a viscosity believed to be below 1000 centipoises is used when suitably cured with a catalyst such as that of Example I.
• the low viscosity below about 1000 centipoises is supported by the suitability of the material for reverse roll coating. Improved release properties for silicone adhesives are obtained.
• a mixture of one part by weight Q-2-7045 was mixed with ten parts Q-2-7044, obtained from the Dow Corning Corporation. The mixture was substituted for the ICI material specified in example I.
• Q-2-7044 is understood to be a polysiloxane having a plurality of reactive vinyl substltuents attached to its silicone atoms, a viscosity of about 300 centipoises, and a molecular weight of about 15,000, corresponding to a degree of polymerization of about 200. It also contains rhodium, or platinum-based catalyst.
• Q-2-7045 is understood to be approximately 60 per cent by weight Q-2-7044 and 40 per cent by weight polymethylhydrogensiloxane of low molecular weight. This material is understood to have a degree of polymerization of about 40 units and an IR ratio substantially greater than 0.4.
• the reactive hydrogen substituents of the Q-2- 7045 cross-link with the vinyl groups of the Q-2-7044 prepolymer.
• the material was coated, cured, and tested in accordance with Example I, except that the rubber transfer roll and the steel drive roll were driven at the same speed. This was greater than the surface speed of the gravure roll by 10 per cent or more. A coating weight of between one and two pounds per ream was applied.
• Example I Similar results were obtained as for Example I. In addition this release material was employed on the Alaska pipeline and found to be the only material, of those tested, that could be used successfully under Arctic conditions.
• Examples I, III, IV and VI are preferred.
• Assurance of the suitability of the material is made by choosing relatively low viscosity material below 1000 centipoises at 25°C, and preferably lower, with a sufficient number of reactive groups, either at or intermediate terminal positions.
• an indicator of suitability is given by a relatively high IR ratio (above 0.4).
• Other indices of active sites are employed for vinyls, alkoxys, esters and the like.
• Such groups may be provided, for example, by incorporating phenyl-methyl siloxane in the polymer monomer units.
• Inclusion of "M” and “Q” units as described in the above patents is also preferred. The amount of such "M” and “Q units can be " varied to vary the tack of the resulting adhesives.
• each such laminate 10 consisted of a support layer 11 of Mylar film or tape; a silicone pressure-sensitive adhesive layer 12 adhered to one surface of the film 11; a cured, highly cross-linked silicone release polymer layer 3 removably adhered upon the adhesive layer; and a release paper carrier 14 adhered to the release layer on the side opposite the adhesive.
• the adhesive can be readily stored, handled, dispensed and applied in this form.
• the silicone release layer 12 is applied to the side of the Mylar film 11 opposite the adhesive 13 and no separate carrier sheet is needed.
• both sides of the Mylar 11 or other support are coated with respective release layers 12 and 12'. It should be noted that low release values were obtained even though the adhesive was applied and cured directly on the releasesurface.
• R X where R' is an alkyl, preferably methyl, radical
• R is partially or entirely hydrogen and the balance if any, is an alkyl, preferably lower carbon chain radical
• O oxygen
• Si is silicon
• X is below about 350 and preferably lees. Such low molecular weight material provide a Brookfleld viscosity at 25°C. below 1000 centipoises, and/or preferably less.
• These prepolymers are believed to be substantially homopolymers of methylhydrogenpolysiloxane when X is about 40; or are copolymers with dimethylpolysiloxane when X is greater than 40 and below about 350 and preferably below about 300.
• R" Y where R' is an alkyl, principally methyl radical
• R" is a mixture of vinyl and lower alkyl groups
• Si is silicon
• Organosiloxanes should comprise the major portion of the coating composition. Where hydrocarbon cross-linking agents such as dicyclopentadiene are used, they preferably have small structures and are used in limited amounts sufficient to provide highly cross-linked organosillcone.
• Example VI a minor portion of a silicon-bonded hydrogen- containing prepolymer is employed with a substantial number of reactive hydrogen substituents. Undue stoichiometric excess of unreacted silicon-bonded hydrogen substituents is preferably avoided.
• Cure of the release coatings should be carried substantially to completion, so that low release values are obtained.
• a minimum of free reactive groups at the surface is considered desirable.
• Substantially complete cure can be achieved using sufficient heat and time, e.g. from about 7 to about 20 seconds at 395°F. or higher.
• Infra-red heaters can be employed usefully at the end of the cure cycle, for example to raise the coating temperature momentarily to about 500°F.
• free surface Si-H groups may be treated with hydrogen free, reactive silanes such as by a gas phase exposure to a mixture of trichloromethylsilane and dichlorodimethyl silane for 5 seconds at 225°F., or a liquid treatment with a 3 per cent by weight solution of trimethoxymethyl silane in heptane, with di-N-butyl tin diacetate as catalyst, followed by drying. Curing with sufficient heat is desirable Control of moisture during cure may also be important in obtaining low release values, especially for low coating weights.
• Ambient moisture in the drying and curing air has not been a problem and reasonable care in excluding contamination or condensation of water in the coating prepolymer mixture is sufficient.
• excess moisture in the carrier paper, where used can be troublesome, and it is preferred that the paper have a moisture content by weight of about 4 per cent or less. Pre-drying can be employed, if necessary.
• Coating weights between about 1.0 and 2.0 pounds per ream are preferred. These coating weights are used for normal support having good hold-out surfaces. Higher amounts may be required when the liquid release materials are applied to more porous surfaces to compensate for absorption into the support.
• High speed release forces are often more important than low speed release because of the common use of high speed applicatlng equipment. High speed release forces less than about 100 grams (3.3 ozs.) per inch of width are preferred, forces less than about 50 grams (1.7 ozs.) are more preferred, and about 25 grams (0.8 oz.) or less per inch of width are most preferred. Such low values have not been obtainable previously in consistent commercial practice prior to the present invention, especially where the adhesive coating is formed directly on the release surface. Low release values are particularly important amounts may be required when the liquid release materials are applied to more porous surfaces to compensate for absorption into the support.
• High speed release forces are often more important than low speed release because of the common use of high speed applicating equipment. High speed release forces less than about 200 grams per Inch of width are preferred, forces less than about 100 grams are more preferred, and about 50 grams or less per Inch of width are most preferred. Such low values have not been obtainable previously in consistent commercial practice prior to the present invention, especially where the adhesive coating is formed directly on the release surface. Low release values are particularly important where paper is used as a carrier due to its limited strength, and where high speed applicating equipment is used.
• release polymers used in the Examples were obtained from the commercial sources indicated.
• Other release polymers of suitable viscosity and absorbance can be produced by hydrolysis of organo substituted halosilanes. This results in a hydrolyzate of linear and cyclic polysiloxanes.
• the hydrolyzate is treated with a catalyst, such as potassium hydroxide, to bring about depolymerization.
• the desired polymers are separated by distillation.
• Suitable organopolysiloxane can also be produced by hydration of high order organopolysiloxanes and heating.
• an organopolysiloxane with a viscosity of 1,000,000 centipoises at 25°C may be heated at 160°C with 1.0 per cent by weight water for 2 hours to reduce the material to chains having viscosities below 1000 centipoises.

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• 1985
  • 1985-12-12 WO PCT/US1985/002424 patent/WO1987003537A1/en not_active Application Discontinuation
  • 1985-12-12 JP JP61500419A patent/JP2619633B2/ja not_active Expired - Lifetime
  • 1985-12-12 EP EP86900458A patent/EP0250400A1/de active Pending

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