WO2018184198A1

WO2018184198A1 - Ultra removable hotmelt and label containing same

Info

Publication number: WO2018184198A1
Application number: PCT/CN2017/079697
Authority: WO
Inventors: Xiaoming Pan; Shaohua Wang; Xinyu Xing; Harry WANG
Original assignee: Avery Dennison Corporation
Priority date: 2017-04-07
Filing date: 2017-04-07
Publication date: 2018-10-11
Also published as: AR111147A1; CN108690540A; CN108690540B; TW201900820A

Abstract

A hotmelt adhesive comprising from 15 wt％ to 65 wt％ of a styrene-isoprene-styrene copolymer, a tackifier having a softening point below 150℃, from 1 wt％ to 15 wt％ of a wax having a high needle point penetration greater than 8 dmm, as measured by ASTM D5 (2016), and a plasticizer. The adhesive demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 20 N/inch, as measured by FINAT Test Method 2 (2016).

Description

ULTRA REMOVABLE HOTMELT AND LABEL CONTAINING SAME

FIELD OF THE INVENTION

The present application relates generally to hotmelt adhesives and, in particular, to improved hotmelt adhesives that provide high levels of removability. The application also relates to labels containing the improved hotmelt adhesives.

BACKGROUND OF THE INVENTION

Hotmelt pressure-sensitive adhesives (PSAs or HMPSAs) are known to provide adhesiveness or tack to various substrates (when applied at room temperature) . This adhesiveness provides for instantaneous adhesion to the substrate when pressurized. PSAs are easy to handle in solid form, quickly form adhesive bonds without significant supplementary processing. And PSAs generally have a long shelf life. PSAs are generally known to provide a convenient and economical way to label articles of commerce such as glass, metal, and plastic containers for consumer and industrial products. Specifically, PSAs are widely used for the manufacture of self-adhesive labels, which are fastened to articles for the purpose of presenting information (such as a barcode, description, price) and/or for decorative purposes.

In some applications, it is desirable to remove and/or reposition items attached using PSAs. For example, labelled packages and/or containers are subjected, after removal of their contents, to cleaning (or recycling) treatments either for the purpose of reusing them or, after destruction, for the purpose of recovering their constituent material. Such treatments often require the label to be completely separated from the article to which it is fastened, without leaving adhesive residues on the surface of said article, so as to make the recycling process easier. In other cases, a container may utilize a repositionable or reattachable closure device to open and close the container multiple times, e.g., tissue box closure labels. In other applications, removable PSAs may be employed to attach loose items to appliances, e.g., refrigerators, during transportation. As another example, children’s books may utilize reattachable adhesives to associate pictures with the respective words, thus enhancing the learning experience. In these applications a PSA having a particular combination of tack, adhesive strength, removability, and/or repositionability are desirable.

US Publication No. 2005/0013996 discloses a hot melt pressure sensitive adhesive (HMPSA) obtained by combining a linear A-B-A block copolymer, wherein the B component is polyisoprene and the A component is polystyrene (S-I-S) , at least one compatible tackifying resin, at least one plasticizer, antioxidant (s) and stabilizer (s) and optionally a wax The A-B-A block copolymer contains 0 to 10％by weight residual A-B diblock. The HMPSA is suitable as a positioning adhesive for disposable articles like plasters, bandages, sanitary napkins, e.g. feminine napkins, adult incontinent pads or diapers. The HMPSA has a viscosity from 3,500 mPas to 25,000 mPas at 140 ℃. and exhibits adhesion values from 1.0 to 3.0 N/cm at coat weights of 10 to 25 grams per square meter.

US Publication No. 2010/0193127 discloses a hot-melt pressure-sensitive adhesive (HMPSA) composition comprising 25 to 50％of a styrene block copolymer chosen from the group comprising SIS, SIBS, SEBS and SEPS block copolymers； 35 to 75％of a compatible tackifying resin having a softening temperature of between 80 and 150 ℃. and an acid number of less than 20； and 0.5 to 20％of one or more carboxylic acids, the hydrocarbon chain of which comprises 6 to 54 carbon atoms.

US Patent No. 9,242,437 discloses a hot-melt pressure-sensitive adhesive (HMPSA) composition comprising (a) 25 to 50％of one or more styrene block copolymers SBS, SIS, SIBS, SEBS or SEPS； (b) 35 to 75％of one or more compatible tackifying resins that are liquid or have a softening temperature below 150 ℃. ； and (c) 1 to 20％of one or more supramolecular polymers obtained by reaction between 1- (2-aminoethyl) -2-imidazolidone and a fatty acid composition comprising 51 to 100％of one or more dimers and/or trimers of fatty acids and 0 to 49％of one or more monomers of fatty acids. A multilayer system including the HMPSA, an adjacent printable support layer, made of paper or a polymer film, and a protective layer adjacent is also provided. The multilayer system may be used in a self-adhesive label.

Chinese Application No. 103849100A discloses preparation of a carrier styrene-isoprene block copolymer composition and adhesive for plaster or patch. The composition comprises the following ingredients in percentage by weight: 80％-90％of styrene-isoprene-styrene tri-block, i.e., S-I-S, and 10％-20％of styrene-isoprene di-block, i.e., S-I. A block ratio S: I of the styrene-isoprene-styrene tri-block is (14-17) : (83-86) . Molecular weight is 0.11 million to 0.14 million. The block ratio S: I of the styrene-isoprene di-block is (8-12) : (88-92) . The molecular weight is 0.055 million-0.075 million. The preparation adopts 100 parts of SIS composition, 70-80 parts of plasticizer and 140-150 parts of tackifying resin to prepare plaster or patch carrier hot-melt pressure-sensitive adhesive which is high in drug loading capacity, low in drug adding temperature, lower in release force and good in holding power.

Chinese Application No. 104694047A discloses a hot-melt pressure-sensitive adhesive and a preparation method of the hot-melt pressure-sensitive adhesive. The hot-melt pressure-sensitive adhesive belongs to the technical field of waterproof rolls. The problem to be solved is that the waterproof roll is unsuitable to be used in winter or tundra because the conventional pre-paving anti-adhesion construction only can be performed in a climatic environment of over 4℃ below zero. The hot-melt pressure-sensitive adhesive disclosed by the invention is prepared from raw materials comprising an elastomer, polyisobutene, a first C5 petroleum resin and a second C5 petroleum resin, wherein the first C5 petroleum resin refers to a solid alicyclic hydrocarbon type hydrogenated petroleum resin and has the softening point of 80-127℃； and the second C5 petroleum resin refers to a liquid petroleum resin and has the softening point of less than or equal to 1℃. According to the hot-melt pressure-sensitive adhesive disclosed by the invention, a high density polyethylene self-adhered film waterproof roll can be firmly overlapped under the condition of 10℃ below zero, and the hot-melt pressure-sensitive adhesive can be applied to sealing tapes, double sided tapes and the like.

Chinese Application No. 103602295A discloses a high resilience force resisting hot-melt type pressure sensitive adhesive and a preparation method thereof. The high resilience force resisting hot-melt type pressure sensitive adhesive is characterized by comprising 25-40wt％of elastomer SIS (styrene isoprene styrene block copolymer) , 50-65wt％of synthetic resin, 4-10wt％of synthetic wax, 5-10wt％of rubber plasticizer and 0.3-1wt％of antioxidant. The preparation method comprises the following steps: adding the elastomer SIS, the rubber plasticizer and the antioxidant to a stainless steel reactor in proportion； slowly heating to 140-175℃, stirring till all materials are molten, and stably reacting for 5-20 minutes； adding the rest of other materials in proportion under a stirring condition, and constantly stirring for 5-30 minutes and cooling, and carrying out molding treatment so as to obtain the required hot-melt type pressure sensitive adhesive. The high resilience force resisting hot-melt type pressure sensitive adhesive prepared by the method has the advantages of high instant bonding strength, high hot bonding strength, large release force, firm and rapid bonding, convenience to use, and no bouncing. It is very suitable for the manufacturing of mattresses, sofas or cushions.

Chinese Application No. 102660219A discloses a method for preparing a low temperature-resistant hot-melt pressure-sensitive adhesive. The low temperature-resistant hot-melt pressure-sensitive adhesive is characterized by comprising the following components in percentage by weight: 12-25 percent of an elastomer SIS, 30-50 percent of tackifying resin, 10-25 percent of synthetic liquid rubber, 2-12 percent of synthetic wax, 25-35 percent of a rubber plasticizing agent and 0.2-0.5 percent of an antioxidant. The method comprises the following steps of: during preparation, putting the elastomer SIS, synthetic liquid rubber, synthetic wax, plasticizing agent and antioxidant into a stainless steel reactor according to a certain proportion； slowly heating to 130-160℃； stirring till all materials are molten； reacting stably for 5-20 minutes； adding other remaining raw material while stirring； continuously stirring for 5-30 minutes； and cooling and molding to obtain a needed low temperature-resistant hot-melt pressure-sensitive adhesive product. An adhesive product produced with the method has the advantages of low temperature resistance, high peeling strength and firm adhesion, and is very suitable for sealing LDPE (Low-Density Polyethylene) film plastic bags.

Even in view of these references, the need exists for hotmelt PSAs that provide improvements in performance characteristics, in particular, removability and repositionability.

SUMMARY OF THE INVENTION

In one embodiment, the invention relates to a hotmelt adhesive, comprising from 15 wt％to 65 wt％of a styrene-isoprene-styrene copolymer, a tackifier having a softening point below 150℃, from 1 wt％to 15 wt％of a wax having a high needle point penetration greater than 8 dmm, and a plasticizer. The adhesive demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 20 N/inch, as measured by FINAT Test Method 2 (2016) , preferably ranging from 0.5 N/inch to 5 N/inch. The styrene-isoprene-styrene copolymer comprises less than 35 wt％polymerized styrene monomers and/or less than 60 weight ％SI diblock, optionally the styrene-isoprene-styrene copolymer comprising less than 60 weight ％SI diblock is present in an amount ranging from 15 wt％to 65 wt％. The tackifier may have a molecular weight less than 1180 and/or may comprise a hydrogenated (cycloaliphatic) hydrocarbon resin. The wax may have a melting point above 60℃ and/or may have a dynamic viscosity at 140 ℃ ranging from 150 to 500 cps, as measured by a Brookfield viscometer. Preferably, the wax has a melting point above 60℃ and the tackifier has a molecular weight less than 1180. The plasticizer may have a molecular weight of at least 200 and/or may have a viscosity of at least 175mm²/second, at 40 ℃, as measured by Chinese Standard BG/T 265 (1988) . The plasticizer may be selected from the group consisting of polyisobutene, naphthenic oil, paraffin oil, liquid polyisoprene, liquid white mineral oil, and combinations thereof. The weight ratio of plasticizer to tackifier may be at least 0.05: 1, and/or may range from 0.05: 1 to 2: 1. The weight ratio of wax and plasticizer, combined, to tackifier may be at least 0.05: 1 and/or the weight ratio of wax to tackifier may be at least 0.05: 1. The hotmelt adhesive may comprise from 15 wt％to 45 wt％tackifier； and/or from 5 wt％to 35 wt％plasticizer. The invention also relates to a label comprising a facestock suitable for printing indicia and the hot melt adhesive. The invention also relates to a process for producing a hotmelt adhesive, the method comprising the steps of providing the styrene-isoprene-styrene copolymer； the tackifier； the wax； and the plasticizer； determining a desired peel strength range； determining a weight ratio of plasticizer to tackifier based on the desired peel strength； and combining the styrene-isoprene-styrene copolymer； the tackifier, the wax, and the plasticizer to form the hotmelt adhesive. The plasticizer and the tackifier are present at the determined weight ratio of plasticizer to tackifier, and wherein the stainless steel peel strength of the hotmelt adhesive is within the desired peel strength range.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to hotmelt pressure sensitive adhesives (PSAs) that provide advantageous performance characteristics, specifically improved removability and repositionability without leaving significant adhesive residue on the bottle or other container from which the label is removed. This characteristic can be particularly important when the PSAs are utilized for repositionable or reattachable closure devices or to attach labels to containers that are to be reused or recycled.

As noted herein, several conventional hotmelt PSAs are known. Many of these hotmelts, however, were developed for applications where high adhesive strength is preferred. In these cases, removability and repositionability are not desirable features. In fact, components used to contribute to improved adhesion often have detrimental effects on removability/repositionability. In other applications, conventional (non-permanent) hotmelt PSAs fail to provide sufficient removability/repositionability without forming or leaving significant amounts of residue on the substrate.

The inventors have now discovered that particular combinations of components, optionally utilized in specific amounts, surprisingly provide for high performance PSAs that demonstrate highly desirable combinations of performance characteristics, e.g., sufficient adhesion/tack strength in conjunction with high levels of removability and/or repositionability, and optionally low levels of (if any) cohesive failure and low adhesive transfer (strong substrate anchorage) . Beneficially, these PSAs also show improvements in processability during adhesive and label manufacture and application, and good adhesive and label quality in a finished end user product.

In particular, it has been found that a hotmelt adhesive, e.g., a hotmelt PSA, comprising a (low diblock content) styrene-isoprene-styrene (SIS) copolymer, a tackifier, a (soft) wax, and a plasticizer unexpectedly provides for a hotmelt PSA having the aforementioned combination of performance characteristics. For example when a low diblock content SIS copolymer, e.g., having a diblock content less than 60 wt％, a soft wax, e.g., a wax having high needle point penetration greater than 8 dmm, a tackifier optionally having a softening point below 150℃, and/or a high viscosity plasticizer, e.g., at least 175 mm²/second, at 40 ℃, are utilized, the resultant hotmelt PSA surprisingly demonstrates a stainless steel peel strength ranging from 0.5 N/inch to 20 N/inch, as measured by FINAT Test Method 2 (FTM 2) (2016) . In some cases, this range of peel strength represents a hotmelt PSA that provides for a desired combination of adhesive strength and removability/repositionability. The hotmelt PSAs thus prepared exhibit other beneficial performance characteristics, e.g., lack of cohesive failure, low adhesive transfer, and/or improved oil migration properties. In some cases, the hotmelt PSA can be used to produce a label that has good removability, repositionability, and oil migration, while still being easy to use in standard compounding and coating applications. If not mentioned otherwise, all test methods are presumed to be the 2016 version.

Also, without being bound by theory, it is believed that many typical hotmelt formulations comprise of the smaller molecule components, which detrimentally become rigid after only minimal aging. In addition, these small molecule components have been found to have a tendency to migrate from the hotmelt and onto the substrate where these molecules form undesirable residue on the respective substrate. The hotmelt PSAs described herein contain a specific combination of components that has a limited amount of these smaller molecules. As a result, the inventive hotmelt PSAs are able to provide the aforementioned combination of performance characteristics. In addition, the internal interactions of the components of the hotmelt adhesive can act to, for example, limit or minimize oil migration if indeed it does begin to occur. Additionally, in preferred embodiments, the tackifiers comprise a hydrogenated (cycloaliphatic) resin. The hydrogenated resin has lower polarity and lower adhesion, as compared to a non-hydrogenated resin. The use of such hydrogenated resins and the resultant adhesion inhibition advantageously allows the hotmelt PSA to utilize a lower amount of oils, which may be employed to keep down adhesion for removability and repositionability purposes. Further, it is believed that the use of lower molecular weight (and/or low viscosity) tackifiers allows for the use of higher molecular weight plasticizers which provides for a synergistic balance of larger molecule components.

In particular, the inventors have found that the weight ratio of the plasticizer to the tackifier and the weight ratio of the combination of wax and plasticizer to tackifier each have a surprising relationship with, inter alia, peel strength and adhesive failure mode. Ranges and limits for these ratios and other component ratios are discussed herein. In particular, when the weight ratio of the plasticizer to the tackifiers is at least 0.05: 1 and/or optionally when the weight ratio of wax and plasticizer (combined) to tackifiers is at least 0.05: 1, e.g., desirable peel strength, elimination or reduction of cohesive failure mode, and/or elimination or reduction of anchorage failure are achieved. Anchorage failure may refer to a situation where there is adhesive competition between the facestock and the substrate； if the adhesive has stronger adhesion to the substrate than to the facestock, the adhesive detrimentally transfers from facestock to substrate. This phenomenon may also be referred to as adhesive transfer. Preferably, the hotmelt PSA has stronger adhesion (anchorage) to the facestock than to the substrate, and the substrate remains clean when the label or tape (with the hotmelt PSA) is peeled from the substrate.

In one embodiment, the SIS copolymer has less than 60 wt％diblock content, the tackifier has a softening point below 150℃, the wax is a soft wax, e.g., a wax having high needle point penetration greater than 20 dmm, and the plasticizer has a high viscosity, e.g., at least 175 mm²/second, at 40 ℃, as measured by Chinese Standard BG/T 265 (1988) , and/or a high molecular weight, e.g., at least 200. As a result of the combination of these components, the resultant hotmelt PSA demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 20 N/inch, as measured by FTM 2, e.g., from 0.5 N/inch to 15 N/inch； from 0.5 N/inch to 10 N/inch, 0.5 N/inch to 5 N/inch, 1.0 N/inch to 10 N/inch, 1 N/inch to 7 N/inch, 1 N/inch to 5 N/inch.

In terms of lower limits, the hotmelt PSA demonstrates a stainless steel peel strength of at least 0.5 N/inch, e.g., at least 1.0 N/inch, at least 1.5 N/inch, at least 2.0 N/inch, at least 2.5 N/inch, at least 3.0 N/inch, at least 3.5 N/inch, at least 4.0 N/inch, at least 4.5 N/inch, or at least 5.0 N/inch. In terms of upper limits, the hotmelt PSA demonstrates a stainless steel peel strength of less than 20 N/inch, e.g., less than 15 N/inch, less than 10 N/inch, less than 7 N/inch, less than 5 N/inch, less than 4.5 N/inch, less than 4.0 N/inch, less than 3.5 N/inch, less than 3.0 N/inch, less than 2.5 N/inch, less than 2.0 N/inch, less than 1.5 N/inch, or less than 1.0 N/inch. These particular peel strength ranges/limits represent a highly desirable degree of removability and repositionability. A lower peel strength would not provide sufficient tack or adhesion, while a higher peel strength would make removal or repositioning difficult if not impossible without facestock tear, substrate tear, or adhesion failure.

In one embodiment, the peel strength focuses on lower ranges ( “ultra low tack version” ) . For example, the hotmelt PSA demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 2.0 N/inch, e.g., from 0.5 N/inch to 1.5 N/inch, from 0.5 N/inch to 1.0 N/inch, or from 0.5 N/inch to 0.75 N/inch

In one embodiment, the peel strength focuses on low-medium ranges ( “low tack version” ) . For example, the hotmelt PSA demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 3.0 N/inch, e.g., from 0.5 N/inch to 2.5 N/inch, from 1.0 N/inch to 3.0 N/inch, from 1.0 N/inch to 2.5 N/inch, from 1.0 N/inch to 2.0 N/inch, or from 1.2 N/inch to 2.3 N/inch. The low tack applications involving washi paper.

In one embodiment, the peel strength focuses on medium ranges ( “medium tack version” ) . For example, the hotmelt PSA demonstrates a stainless steel peel strength of ranging from 1.5 N/inch to 4.5 N/inch, e.g., from 1.5 N/inch to 4.0 N/inch, from 2.0 N/inch to 4.0 N/inch, or from 2.5 N/inch to 3.5 N/inch. The medium versions may be suitable, for example, for containers that utilize a repositionable or reattachable closure device to open and close the container multiple times, e.g., tissue box closure labels, and also for some washi paper applications.

In one embodiment, the peel strength focuses on higher ranges ( “high tack version” ) . For example, the hotmelt PSA demonstrates a stainless steel peel strength of ranging from 4.5 N/inch to 20.0 N/inch, e.g., from 5.0 N/inch to 15.0 N/inch, from 5.0 N/inch to 10.0 N/inch, from 4.5 N/inch to 10.0 N/inch, or from 7.0 N/inch to 9.0 N/inch. The high tack version may be suitable, for example attaching loose items to appliances, e.g., refrigerators, during transportation.

Compositional make-ups for these versions are further discussed herein. Also, the upper and lower limits mentioned above may be applied to these versions, as appropriate. For example, the low tack hotmelt PSA demonstrates a stainless steel peel strength of at least 0.5 N/inch, e.g., at least 1.0 N/inch.

Polymer

The polymer of the hotmelt PSA comprises a styrene-isoprene-styrene copolymer (SIS block copolymer) , where "S" denotes a polymerized segment or "block" of styrene monomers, and "I" denotes a polymerized segment or "block" of isoprene monomers. SIS block copolymers can be a pure triblock copolymer containing no SI diblock, or can contain a certain percentage of SI diblock. In some cases, a single SIS block copolymer may be employed, while in other cases, a combination of SIS block copolymers may be used. The SIS copolymer may comprise a mixture of multiple copolymer products. The architecture of the SIS copolymer may vary widely, e.g., linear, branched, radial, asymmetric radial, or combinations thereof. Preferably the SIS copolymer has a linear or radial structure.

In addition to the SIS blocks, the copolymer may, in some embodiments, also include other blocks. Different types of polymer may be blended with the SIS blocks. Examples include, but are not limited to SBS, SIBS, SEBS, and mixtures thereof.

It has been found that higher diblock content (SI, SB, or combinations thereof) (in the SIS copolymer) may be associated with an excessive increase in tack of the SIS block copolymer. Beneficially, a lower SI diblock content has been found to be associated with an increase in elasticity of the copolymer and an improvement in removability and repositionability. The SI diblock content of the SIS copolymer can be within the range from 0 wt％to 60 wt％, e.g., from 1 wt％to 60 wt％, from 1 wt％to 55 wt％, from 3 wt％to 55 wt％, from 15 wt％to 53 wt％, from 20 wt％to 53 wt％, from 10 wt％to 30 wt％, from 22 wt％to 53 wt％, or from 25 wt％to 50 wt％. In terms of upper limits, the SI diblock content of the SIS copolymer can be less than 60 wt％, e.g., less than 55 wt％, less than 53 wt％, less than 50 wt％, less than 35 wt％less than 30 wt％, less than 25 wt％, or less than 20 wt％. In terms of lower limits, the SI diblock content of the SIS copolymer can be at least 5 wt％, at least 10 wt％, at least 15 wt％, at least 20 wt％, at least 22 wt％, at least 25 wt％, or at least 30 wt％％. In some embodiments, the base polymer is substantially free, e.g., less than 10 wt％, less than 5 wt％, less than 3 wt％, or less than 1 wt％, of SI diblock, e.g., free of SI diblock. In some cases, the SIS block copolymer may have a lower SB diblock (and/or a low SB and SI diblock) content. The weight percentages mentioned herein with respect to SI diblock are applicable to SB diblock content and total diblock (for example SB and SI) content as well.

The styrene content of the SIS copolymer can also impact the performance characteristics of the base polymer. It has been found that specific styrene content, along with a particular diblock content, can give a base polymer the desired properties of a high melt flow index (greater than 20 g per 10 minutes at 190 ℃) and a low viscosity. Together these properties make the polymer more suitable for compounding and coating processes. The styrene content of the base polymer can within the range from 0 to 35 wt％, e.g., from 5 to 30 wt％, from 10 to 30 wt％, from 10 to 25 wt％, from 15 to 30 wt％, from 15 to 25 wt％, 15 to 20 wt％, or from 25 to 30 wt％. In terms of upper limits, the styrene content can be less than 35 weight ％, e.g., less than 30 wt％, less than 25 wt％, less than 20 wt％, less than 15 wt％, less than 10 wt％, or less than 5 wt％. In terms of lower limits, the styrene content can be at least 5 wt％, e.g., at least 10 wt％, at least 15 wt％, at least 20 wt％, at least 25 wt％, at least 30 wt％, or at least 35 wt％.

The amount of the (solid) SIS copolymer within the hotmelt PSA composition can be within the range from 15％to 65％, e.g., from 15％to 45％, from 20％to 50％, from 25％to 55％, from 30％to 60％, or from 35％to 65％. The amount of the SIS copolymer within the hotmelt PSA composition can be within the range from 30％to 50％, e.g., from 30％to 42％, from 32％to 44％, from 34％to 46％, from 36％to 48％, or from 38％to 50％. In terms of upper limits, the amount of the SIS copolymer within the hotmelt PSA composition can be less than 70％, less than 65％, less than 60％, less than 55％, less than 50％, less than 45％, or less than 40％. In terms of lower limits, the amount of the SIS block copolymer within the hotmelt PSA composition can be at least 10％, at least 15％, at least 20％, at least 25％, at least 30％, at least 35％, or at least 40％.

In some cases, the copolymer may have a lower molecular weight. As one example with linear copolymers, the molecular weight of the copolymer may range from 50000 to 300000, e.g., from 65000 to 275000, from 80000 to 250000, or from 100000 to 200000. In terms of lower limits, the linear copolymer may have a molecular weight of at least 50000, e.g., at least 65000, at least 80000, or at least 100000. In terms of upper limits, the linear copolymer may have a molecular weight of less than 300000, e.g., less than 275000, less than 250000, or less than 200000. Molecular weight of radial copolymers will depend on the number of branches. For instance the molecular weight of the copolymer may range from 200000 to 1200000, e.g., from 300000 to 1000000, or from 350000 to 800000. In terms of lower limits, the radial copolymer may have a molecular weight of at least 200000, e.g., at least 300000, at least 400000, or at least 500000. In terms of upper limits, the radial copolymer may have a molecular weight of less than 1200000, e.g., less than 1000000, less than 900000, or less than 800000.

Suitable commercial SIS copolymers include (but are not limited to) , for example, SIS 1220, SIS 1100, SIS 1300, SIS 1250, available from Shandong Jusage Technology Company, Ltd. (Shandong, China) ； SIS 4019, from Balin Yueyang Sinopec； Quintac 3421, available from Nippon Zeon Company, Ltd. (US sales office –Louisville, Ky. ) ； Vector 4293, Vector 4230 and Vector 4111 available from Dexco/TSRC, and Kraton ^TM rubbers, available from Kraton Polymers (Houston, Texas) .

Tackifier

The tackifiers employed in the hotmelt formulation may vary widely. In some embodiments, a tackifier having a low softening point is preferred. For example, the tackifier may have a softening point below 150℃, e.g., below 140℃, below 130℃, below 120℃, below 110℃, below 105℃, below 100℃, below 95℃, below 90℃, below 85℃, or below 80℃. In terms of ranges, the tackifier may have a softening point ranging from 60℃ to 140℃, e.g., from 80℃ to 150℃, from 90℃ to 130℃ or from 90℃ to 110℃.

In some cases, the tackifier may comprise a single tackifier. In other cases the tackifier may comprise a mixture of multiple tackifier products.

In some embodiments, the tackifier has a low molecular weight (number average molecular weight may apply to molecular weights discussed herein) . For example, the tackifier may have a molecular weight less than 1700, e.g., less than 1500, less than 1200, less than 1180, less than 1000, less than 900, less than 800, less than 700, or less than 650. The tackifier may have a molecular weight greater than 300, e.g., greater than 400, greater than 500, greater than 550, greater than 600, greater than 650, greater than 700, greater than 750, or greater than 800. In terms of ranges the tackifier may have a molecular weight ranging from 500 to 1700, e.g., from 500 to 1000, from 300 to 1180, from 500 to 1180, from 500 to 900, from 600 to 800, or from 600 to 700. Without being bound by theory, it is believed that the use of lower molecular weight (and/or low viscosity) tackifiers allows for the use of specific higher molecular weight plasticizers which provides for a synergistic improvement in oil migration properties.

In preferred embodiments, the tackifier comprises a hydrogenated (hydrocarbon) resin. In some (but not all) cases, hydrogenated resins may often have lower polarity than non-hydrogenated resins. The lower polarity leads to lower adhesion in the hotmelt PSA, which is advantageous for applications that require removability and/or repositionability. In some cases, the tackifier comprises a (hydrogenated) cycloaliphatic hydrocarbon resin. Oils are often employed in hotmelt formulations to keep down adhesion. The use of hydrogenated resins and the resultant adhesion inhibition advantageously allows the hotmelt PSA to utilize a lower amount of oils.

As an additional benefit, hydrogenation of the resin results in an adhesive layer and label that has reduced color, odor, and char particles.

Suitable commercial tackifiers include (but are not limited to) , for example, hydrogenated DCPD resins such as HD1100, HD1120 from Luhua, or E5400 from Exxon Mobil. Other suitable hydrogenated resins include fully hydrogenated resins such as Regalite S1100, R1090, R1100, C100R, and C100W from Eastman, and fully hydrogenated C9 resins QM-100A and QM-115A from Hebei Qiming. E5400 and HD1100 are hydrogenated cycloaliphatic DCPD resins.

In one embodiment, the hotmelt PSA composition comprises (solid) tackifiers in an amount ranging from 15 wt％to 45wt％, from 15wt％to 40 wt％, from 20wt％to 40wt％, from 20 wt％to 35wt％, or from 25wt％to 35wt％. In terms of upper limits, the amount of tackifier in the hotmelt PSA composition may be less than 45wt％, e.g., less than 40wt％, less than 35wt％, less than 30wt％, less than 25wt％, less than 20wt％, or less than 15wt％. In terms of lower limits, the amount of tackifier in the hotmelt PSA composition may be at least 10 wt％, at least 15 wt％, at least 20 wt％, at least 25 wt％, at least 30 wt％, at least 35 wt％, at least 40 wt％, or at least 45 wt％.

Wax

The hotmelt PSA may utilize a soft wax. In some embodiments the soft wax has a high needle point penetration, e.g., a needle point penetration greater than 8 dmm, as measured by ASTM D5 (2016) , e.g., greater than 10, greater than 12, greater than 15, greater than 17, greater than 20, or greater than 25 dmm, greater than 30 dmm, or greater than 35 dmm. In terms of ranges, the soft was has a needle penetration ranging from 8 dmm to 40 dmm, e.g., from 10 dmm to 40 dmm, from 10 dmm to 35 dmm, from 10 dmm to 30 dmm, from 15 dmm to 40 dmm, from 15 dmm to 30 dmm or from 15 dmm to 25 dmm. The inventors have discovered that the use of harder waxes leads to high stiffness, which results in very low initial tack, as well as a high degree of “zippiness” when peeled away from the substrate. Zippiness is associated with rapid removal of the hotmelt (or the label comprising the hotmelt) from a substrate. A label that peels away rapidly and results in a loud peeling sound is said to have a high degree of zippiness. And zippiness is a negative quality, especially from the viewpoint of the end user. It has been found that the soft waxes advantageously provide prolonged softness to the hotmelt PSA, which results in the benefits of improved tack (vs. harder waxes) and a smooth, non-zippy peel.

In some cases, the wax may comprise a single wax. In other cases the wax may comprise a mixture of multiple wax products.

The wax may have a higher molecular weight. The inventors have found that higher molecular weight waxes may advantageously improve oil migration.

In some preferred embodiments, exemplary waxes include microcrystalline waxes paraffin waxes, hydrocarbon waxes, and combinations thereof.

In some cases, the wax is a polyethylene wax. The polyethylene wax can function to increases the hydrophobicity of the adhesive. This increased hydrophobicity can assist in improving the resistance of the adhesive to water whitening, and the ability of the adhesive to be cleanly removed or repositioned. The particular polyethylene wax can also be selected to further reduce the overall viscosity of the hotmelt PSA, and to have minimal impact on the transparency of the adhesive.

In some embodiments, the wax has a high melting point. For example the wax may have a melting point above 60℃, e.g., above 65℃, above 70℃, above 75℃, above 80℃, or above 85℃. In terms of ranges, the wax may have a melting point ranging from 60℃ to 125℃, e.g., from 65℃ to 115℃, from 65℃ to 100℃, from 70℃ to 90℃, or from 75℃ to 85℃. The wax may have a melting point below 150℃, e.g., below 125℃, below 100℃, below 95℃, below 90℃, or below 85℃. The use of these waxes has been found to surprisingly reduce oil migration, especially during storage and transportation. In addition, the use of waxes having a higher melting point has unexpectedly been found to provide better aging performance at a higher temperature. Without being bound by theory, it is believed that the use of the higher melting point waxes contributes to the resultant adhesive softening at much higher temperatures. Thus, better cohesive strength is demonstrated for a much broader (higher) temperature range.

The wax can have a relatively low viscosity, such as a dynamic viscosity as measured by a Brookfield viscometer. The polyethylene wax can have a dynamic viscosity at 140 ℃ within the range from 150 centipoise cps to 500 cps, e.g., from 150 to 300 cps, from 250 to 400 cps, from 350 to 500 cps, from 150 to 200 cps, from 200 to 250 cps, from 250 to 300 cps, from 300 to 350 cps, or from 350 to 400 cps. In terms of upper limits, the polyethylene wax can have a dynamic viscosity at 140 ℃ that is less than 500 cps, less than 450 cps, less than 400 cps, less than 350 cps, less than 300 cps, less than 250 cps, or less than 200 cps. In terms of lower limits, the polyethylene wax can have a dynamic viscosity at 140 ℃ that is at least 150 cps, e.g., at least 200 cps, at least 250 cps, at least 300 cps, at least 350 cps, at least 400 cps, or at least 450 cps.

The wax can also be selected to have a particular pour point as measured by the standard procedure ASTM D5949. The pour point is defined as the temperature at which a liquid becomes semi-solid and loses its flow characteristics. The polyethylene wax can have a pour point that is greater than 90 ℃, greater than 91 ℃, greater than 92 ℃, greater than 93 ℃, greater than 94 ℃, greater than 95 ℃, greater than 96 ℃, greater than 97 ℃, greater than 98 ℃, greater than 99 ℃, greater than 100 ℃, greater than 101 ℃, greater than 102 ℃, greater than 103 ℃, greater than 104 ℃, greater than 105 ℃, greater than 106 ℃, greater than 107 ℃, greater than 108 ℃, greater than 109 ℃, or greater than 110 ℃. In some embodiments, the polyethylene wax has a pour point that is greater than 100℃.

The amount of the wax in the hotmelt ranges from 1 wt％to 15 wt％, e.g., from 1wt％to 12 wt％, from 2 wt％to 12 wt％, from 2 wt％to 10 wt％, from 3 wt％to 9 wt％, from 2 wt％to 8 wt％, or from 3 wt％to 8 wt％. In terms of upper limits, the amount of the wax in the hotmelt may be less than 15 wt％, less than 13 wt％, less than 12 wt％, less than 10 wt％, less than 9 wt％, less than 8 wt％, less than 7 wt％, or less than 5wt％. In terms of lower limits, the amount of the polyethylene wax within the hotmelt PSA composition can be zero or at least 1wt％, at least 2 wt％, at least 3 wt％, at least 4 wt％, at least 5 wt％, at least 7 wt％, at least 10 wt％, or at least 12 wt％.

Suitable commercial waxes include (but are not limited to) , for example, Sasol wax 3971, 7835, 6403, 6805, and 1800 from Sasol； A-C1702, A-C 6702, A-C 5180 from Honeywell； Microwax FG 7730 and Microwax FG 8113 from Paramelt Specialty Materials (Suzhou) Co. Ltd.

Plasticizer

The hotmelt PSA comprises a plasticizer. The plasticizer may vary widely. In some embodiments, the plasticizer has a high molecular weight and/or a high viscosity. The use of a high molecular weight plasticizer has been found to provide many advantages to the hotmelt, which have not been observed with conventional hotmelt PSA compositions. Without being bound by theory, the high molecular weight plasticizer (especially in combination with a low molecular weight tackifier) inhibits or eliminates oil migration in the hotmelt PSA, which contributes to the beneficial performance characteristics discussed herein.

In some cases, the plasticizer may comprise a single plasticizer. In other cases the plasticizer may comprise a mixture of multiple plasticizer products.

In some embodiments, the plasticizer has a molecular weight of at least 200, e.g., at least 300, at least 400, at least 500, at least 700, at least 1000, at least 1200, or at least 1500. In terms of ranges, the plasticizer may have a molecular weight that ranges from 200 to 1500, e.g., from 200 to 1000, from 250 to 900, from 400 to 900, from 400 to 800, from 500 to 700, or from 550 to 650. In terms of upper limits, the plasticizer may have a molecular weight that is less than 3000, e.g., less than 2000, less than 1000, less 800, less than 650, or less than 600. The use of these plasticizers has been found to surprisingly reduce oil migration and/or film facestock swelling.

The plasticizer, in some embodiments, may have a high viscosity. The kinematic viscosity can be measured, for example, using the procedures of Chinese Standard BG/T 265-1988. The plasticizer can have a kinematic viscosity at 40 ℃ that is within the range from 175 mm²/second to 1000 mm²/second, e.g., from 300 mm²/second to 1000 mm²/second, from 300 to 800 mm²/second, from 400 to 800 mm²/second, from 400 to 700 mm²/second, from 450 to 650 mm²/second, from 475 to 625 mm²/second, or from 500 to 600 mm²/second. In terms of upper limits, the plasticizer can have a kinematic viscosity that is less than 1000 mm²/second, e.g., less than 900 mm²/second, less than 800 mm²/second, less than 700 mm²/second, less than 650 mm²/second, less than 625 mm²/second, less than 600 mm²/second, or less than 500 mm²/second. In terms of lower limits, the plasticizer can have a kinematic viscosity that is at least 175 mm²/second, e.g., at least 200 mm²/second, at least 300 mm²/second, at least 400 mm²/second, at least 450 mm²/second, at least 475 mm²/second, at least 500 mm²/second, at least 600 mm²/second, at least 700 mm²/second, at least 800 mm²/second, or at least 900 mm²/second.

In some cases, the use of plasticizers having lower molecular weights or viscosities is also contemplated, although higher molecular weights and viscosities are preferred.

In some embodiments, the plasticizer is a compound selected from the group consisting of polyisobutene, naphthenic oil, paraffin oil, liquid polyisoprene, liquid white mineral oil, and combinations thereof.

Suitable commercial plasticizers include (but are not limited to) , for example, 300# white oil, KN 4010 and KP 6030 from Sinopec, Claire F55 from Tianjin, F550 from Formosa Petrochemical Corp., and various polyisobutene products.

Another advantage of the high molecular weight plasticizer is that the hotmelt PSA can be used to create labels with greater structural integrity. For example, labels that include the hotmelt PSA can exhibit reduced wrinkling and swelling. Reduced swelling can indicate a change in size of less than 5％, less than 4％, less than 3％, less than 2％, or less than 1％over a predetermined measurement period. The swelling and wrinkling measurement period can be greater than 3 days, greater than 4 days, greater than 5 days, greater than 6 days, greater than 7 days, greater than 8 days, greater than 9 days, or greater than 10 days. The reduced swelling and wrinkling can be observed during storage at a temperature greater than 45 ℃, greater than 50 ℃, greater than 55 ℃, greater than 60 ℃, greater than 65 ℃, or greater than 70℃. The reduced swelling and wrinkling can be observed during storage at a relative humidity greater than 80％, greater than 82％, greater than 84％, greater than 86％, greater than 88％, or greater than 90％. In some embodiments, the label that includes the hotmelt PSA has either no change in size, or changes in each dimension that are less than 2％, upon storage at 85％relative humidity for either 4 days at greater than 65 ℃, or 7 days at greater than 50 ℃.

In cases where the plasticizer comprises a paraffin oil, these paraffin oils have surprisingly been found to enhance the stability of labels, with lower migration of oils within and among the layers of a label, and less leakage of adhesion beyond the original footprint of the adhered label. These improvements not only increase the effectiveness of the label in adhering to items and anchoring and retaining printed indices, but also increase the visual presentation of the label from the perspective of an end user. As labels are often used to present important information, or to increase the visibility or appeal of consumer products, these improvements can enhance the value of the labels significantly.

The amount of the plasticizer in the hotmelt PSA composition may range from 5 wt％to 35 wt％, e.g., 10 wt％to 30 wt％, from 12 wt％to 28 wt％, from 10 wt％to 25 wt％, from 15 wt％to 25 wt％, or from 18 wt％to 25 wt％. In terms of upper limits, the amount of the plasticizer within the hotmelt PSA composition can be less than 3 5wt％, less than 30 wt％, less than 28 wt％, or less than 25 wt％. In terms of lower limits, the amount of the plasticizer within the hotmelt PSA composition can be at least 5 wt％, at least 10 wt％, at least 12 wt％, at least 15 wt％, or at least 18 wt％.

Component Weight Ratios/Tack-related Versions

In some embodiment, the weight ratio of soft wax to plasticizer is at least 0.05: 1, e.g., at least 0.1: 1, at least 0.15: 1, at least 0.17: 1, or at least 0.2: 1. In terms of ranges, the weight ratio of soft wax to plasticizer may range from 0.05: 1 to 2: 1, e.g., from 0.05: 1 to 1.5: 1, from 0.05: 1 to 1: 1, from 0.1: 1 to 0.8: 1 or from 0.1: 1 to 0.6: 1. The weight ratio of soft wax to plasticizer may be less than 2: 1, e.g., less than 1.5: 1, less than 1: 1, less than 0.8: 1, less than 0.6: 1, or less than 0.5: 1.

In some cases, the weight ratio of soft wax to tackifier in the hotmelt is high. The inventors have found that a specific balance of high molecular weight to low molecular weight tackifier may balance the overall molecular weight of the hotmelt composition, which has been found to inhibit oil migration. In some cases, the weight ratio of soft wax to tackifier is at least 0.05: 1, e.g., at least 0.1: 1, at least 0.15: 1, at least 0.2: 1, at least 0.3: 1, at least 0.4: 1, at least 0.5: 1, or at least 1: 1. In terms of ranges, the weight ratio of soft wax to tackifiers may range from 0.05: 1 to 2: 1, e.g., from 0.05: 1 to 1.5: 1, from 0.05: 1 to 1: 1, from 0.1: 1 to 0.8: 1 or from 0.1: 1 to 0.5: 1. The weight ratio of soft wax to tackifier may be less than 2: 1, e.g., less than 1.5: 1, less than 1: 1, less than 0.8: 1, less than 0.6: 1, or less than 0.5: 1.

It has been found that the use of the tackifier (having a low molecular weight and viscosity) advantageously (partially) offsets or allows for the use of higher molecular weight and viscosity of the plasticizer. This combination provides for significant improvements in aged staining, which is a measure of oil migration. In some cases, the weight ratio of plasticizer to tackifier is at least 0.05: 1, e.g., at least 0.1: 1, at least 0.15: 1, at least 0.2: 1, at least 0.3: 1, at least 0.4: 1, at least 0.5: 1, or at least 1: 1. In terms of ranges, the weight ratio of soft wax to tackifiers may range from 0.05: 1 to 2: 1, e.g., from 0.05: 1 to 1.5: 1, from 0.2: 1 to 2: 1, from 0.2: 1 to 1: 1, from 0.2: 1 to 1: 1.1, or from 0.2: 1 to 0.9: 1. The weight ratio of plasticizer to tackifier may be less than 2: 1, e.g., less than 1.5: 1, less than 1.1: 1, less than 1: 1, or less than 0.8: 1.

In some cases, the weight ratio of soft wax and plasticizer, combined, to tackifier in the hotmelt is high. In some cases, the weight ratio of soft wax and plasticizer, combined, to tackifier is at least 0.05: 1, e.g., at least 0.1: 1, at least 0.15: 1, at least 0.2: 1, at least 0.3: 1, at least 0.5: 1, at least 0.7: 1, or at least 1: 1. In terms of ranges, the weight ratio of soft wax and plasticizer, combined, to tackifier may range from 0.05: 1 to 3: 1, e.g., from 0.1: 1 to 3: 1, from 0.2: 1 to 2: 1, from 0.3: 1 to 1.5: 1 or from 0.5: 1 to 1.5: 1. The weight ratio of soft wax and plasticizer, combined, to tackifier may be less than 3: 1, e.g., less than 2: 1, less than 1.5: 1, less than 1: 1.4, less than 1.3: 1, or less than 1: 1.

In one embodiment, a high tack hotmelt PSA comprises the styrene-isoprene-styrene copolymer, the tackifier, and the plasticizer, (and optionally the wax) in the weight percentages discussed herein. In some embodiments, the high tack hotmelt PSA does not comprise a wax component.

When a wax is not employed, the weight ratios may be similar to those discussed above, e.g., the weight ratios may vary by less than 20％, e.g., less than 15％, less than 10％or less than 5％. In cases where a wax is not employed, the weight percentages for the components (the copolymer, the tackifier, and the plasticizer) may be slightly higher, e.g., less than 20％, less than 10％, or less than 5％, than the weight percentages that are utilized when a wax is employed.

The overall viscosity of the hotmelt PSA can be such that the dynamic viscosity of the adhesive at 170 ℃ as measured by a Brookfield viscometer is within the range from 10,000 cps to 35,000 cps, e.g., from 10,000 cps to 30,000 cps, from 12,000 cps to 28,000 cps, from 12,000 cps to 16,000 cps, from 14,000 cps to 18,000 cps, from 16,000 cps to 20,000 cps, from 10,000 cps to 12,000 cps, from 12,000 cps to 14,000 cps, from 14,000 cps to 16,000 cps, from 16,000 cps to 18,000 cps, or from 18,000 cps to 20,000 cps. In terms of upper limits, the hotmelt PSA can have a dynamic viscosity at 170 ℃ that is less than 35,000 cps, e.g., less than 33,000 cps, less than 30,000 cps, less than 28,000 cps, less than 25,000 cps, less than 20,000 cps, less than 18,000 cps, less than 16,000 cps, less than 14,000 cps, or less than 12,000 cps. In terms of lower limits, the hotmelt PSA can have a dynamic viscosity at 170 ℃ that at least 10,000, e.g., at least 12,000 cps, at least 14,000 cps, at least 16,000 cps, at least 18,000 cps, at least 20,000 cps, at least 22,000 cps, or at least 25,000.

The overall viscosity of the hotmelt PSA can be such that the dynamic viscosity of the adhesive at 160 ℃ as measured by a Brookfield viscometer is within the range from 15,000 cps to 50,000 cps, e.g., from 15,000 cps to 48,000 cps, from 20,000 cps to 48,000 cps, from 22,000 cps to 48,000 cps, from 25,000 cps to 46,000 cps, from 25,000 cps to 40,000 cps, from 30,000 cps to 40,000 cps, or from 32,000 to 38,000 cps. In terms of upper limits, the hotmelt PSA can have a dynamic viscosity at 160 ℃ that is less than 50,000 cps, e.g., less than 48,000 cps, less than 46,000 cps, less than 40,000 cps, or less than 38,000 cps. In terms of lower limits, the hotmelt PSA can have a dynamic viscosity at 160 ℃ that at least 15,000, e.g., at least 20,000 cps, at least 22,000 cps, at least 30,000 cps, or at least 32,000 cps.

Tunability

As noted above, the inventors have found that the weight ratio of the plasticizer to the tackifier and the weight ratio of the combination of wax and plasticizer to tackifier each have a surprising relationship with, inter alia, stainless steel peel strength. The invention further relates to a process for producing a hotmelt adhesive based on a desired stainless steel peel strength. In one embodiment, the process comprises the steps of providing the styrene-isoprene-styrene copolymer； the tackifier, the wax, and the plasticizer and determining a desired peel strength or peel strength range. Based on the desired peel strength range, the proper weight ratio of plasticizer to tackifier can be determined. The process further comprises the step of combining the components to form the hotmelt adhesive. Importantly the plasticizer and the tackifier are combined such that these components are present at the determined weight ratio of plasticizer to tackifier. The resultant hotmelt adhesive will have a stainless steel peel strength within the desired peel strength range. In some preferred embodiments, the process further comprises the step of determining a weight ratio of plasticizer and was, combined, to tackifier based on the desired peel strength, and combining the components such that the plasticizer, the wax, and the tackifier combined such that these components are present at the determined weight ratio of plasticizer and wax, combined, to tackifier.

In some embodiments, other component relationship may be utilized to arrive at the desired peel strength range. The process may further include the step of determining a weight ratio of one or more components to another. For example, the various weight ratios of components for the ultra low-, low-, medium-, and high-tack versions may be utilized along with the respective performance characteristic ranges.

In one embodiment, the process may further include the step of determining a weight ratio of wax to tackifier based on the desired peel strength range. This determination can be made using the weight ratio ranges and peel strength ranges discussed herein.

In one embodiment, the process may further include the step of determining a weight ratio of wax and plasticizer, combined, to tackifier based on the desired peel strength range. This determination can be made using the weight ratio ranges and peel strength ranges discussed herein.

In one embodiment, the process may further include the step of determining a weight ratio of wax to plasticizer based on the desired peel strength range. This determination can be made using the weight ratio ranges and peel strength ranges discussed herein.

Labels

The invention also relates to labels comprising the aforementioned hotmelt PSAs and a facestock (suitable for printing indicia) . The facestock can include, for example, paper facestock, cardboard facestock, plastic facestock, a multilayer laminated facestock including both paper and plastic layers, or any other materials that are commonly used in the industry. The multilayer laminate facestock can include a paper layer overlying a plastic layer. The plastic layer of the multilayer laminate facestock can be extruded or otherwise coated onto the paper layer. The paper layer can include, for example, high gloss paper, semi-gloss paper, lithographic paper, or electronic data processing (EDP) paper； and can be configured for use in, for example, multi-color printing, typewriter printing, or inkjet printing. The plastic layer can include, for example, polyesters, such as PET； polyolefins, such as polypropylene (PP) , ethylene-propylene copolymers, polyethylene (PE) ； and other materials. Other polymeric film materials include urethane based polymers such as polyether urethane and polyester urethane； amide based polymers including polyether polyamide copolymers； acrylic based polymers including a polyacrylate, and ethylene/vinyl acetate copolymer； polyester based polymers including a polyether polyester； a vinyl chloride； a vinylidene chloride； a polystyrene； a polyacrylonitrile； a polycarbonate； a polyimide； or the like. The facestock can include a flexible facestock. The facestock can include a transparent polymeric film. In certain applications, it can be useful to utilize "shrink" films or oriented films as a facestock layer. The present subject matter includes, for example, biaxially oriented films such as PET as a facestock layer.

In some embodiments, the label further includes print disposed on the layer of facestock. The print can include layers or regions of ink, dyes, pigments, or like materials. As will be understood, "dye" and like terms mean a visible light absorbing compound present in a molecularly dispersed or dissolved form. "Pigment" and like terms mean a visible light absorbing material or compound that is present in a non-molecularly dispersed or particulate form. "Ink" and like terms means a coatable or printable formulation containing a dye and/or pigment. Although the present subject matter is largely directed toward labels including visually perceptible print, it is contemplated that the labels may include print that is exclusively or primarily indicative under UV light or other conditions.

The hotmelt PSA layer can be applied directly adjacent to, and in contact with, the facestock. There can be intervening layers between the hotmelt PSA layer and the facestock. The label can include two or more layers of hotmelt PSA and/or facestock. The hotmelt PSA layer of the label can be coated onto the facestock with a coat weight of, for example, from 5 grams per square meter (gsm) to 30 gsm. The adhesive layer coat weight can befrom 6 gsm to 20 gsm, from 8 gsm to 20 gsm, from 22 gsm to 30 gsm, from 16 gsm to 40 gsm. In some embodiments, the adhesive layer coat weight is within the range from 5 gsm to 40 gsm. In terms of upper limits, the adhesive layer coat weight can be less than 40 gsm, e.g., less than 35 gsm, less than 30 gsm, less than 25 gsm, less than 20 gsm, less than 15 gsm, or less than 10 gsm. In terms of lower limits, the adhesive layer coat weight can be at least 5 gsm, e.g., at least 10 gsm, at least 15 gsm, at least 20 gsm, at least 25 gsm, at least 30 gsm, or at least 35 gsm.

The present subject matter can include the incorporation of one or more clear or transparent layers in any of the label constructions described herein. The present subject matter can also include the incorporation of one or more metallic layers or metal foils in any of the label constructions described herein. It is also contemplated that the label constructions can also include combinations of one or more transparent layers and one or more metallic layers. In some embodiments, the label is a clear on clear label having a laminate composition that includes a transparent biaxially oriented polypropylene (BOPP) film, a transparent hotmelt PSA layer, and a transparent PET liner.

In some embodiments, the label further includes a liner disposed on the layer of hotmelt PSA. A releasable liner can be positioned adjacent to the adhesive layer such that the adhesive layer is disposed, or sandwiched, directly or indirectly between the bottom surface of the facestock and the releasable liner. The releasable liner may function as a protective cover such that the release liner remains in place until the label is ready for attachment to an object. If a liner or release liner is included in the label, a wide array of materials and configurations can be used for the liner. In many embodiments, the liner is a paper or paper-based material. In many other embodiments, the liner is a polymeric film of one or more polymeric materials. Typically, at least one face of the liner is coated with a release material such as a silicone or silicone-based material. As will be appreciated, the release coated face of the liner is placed in contact with the otherwise exposed face of the adhesive layer. Prior to application of the label to a surface of interest, the liner is removed to thereby expose the adhesive face of the label. The liner can be in the form of a single sheet. Alternatively, the liner can be in the form of multiple sections or panels.

Other additives can be added to one or more of the hotmelt PSA, facestock, or liner layers to obtain a certain desired characteristics. These additives can include, for example, one or more waxes, surfactants, talc, powdered silicates, filler agents, defoamers, colorants, antioxidants, UV stabilizers, luminescents, crosslinkers, buffer agents, anti-blocking agents, wetting agents, matting agents, antistatic agents, acid scavengers, flame retardants, processing aids, extrusion aids, and others.

The present invention also relates to labeled containers that include a hotmelt pressure sensitive adhesive of the present invention. The labeled containers include a container defining an outer surface, and a label as described above that is adhered to the outer face of the container. In some embodiments, the container is a bottle. The outer surface to which the hotmelt PSA is adhered can include a wide range of substrates. The outer surface can include glass, plastic, wood, metal, combination of these and other materials. In some embodiments, the outer surface of the container includes glass.

In some embodiments, the outer surface of the container includes plastic. The outer surface can include or be formed from any suitable polymer or mixture of polymers. The polymer or mixture of polymers can include, for example, PET, recycled polyethylene terephthalate (rPET) , high density polyethylene (HDPE) , polyvinyl chloride (PVC) , poly lactic acid (PLA) , cellulose, biopolymer films, low density polyethylene (LDPE) , PP, polystyrene (PS) , polyesters, or other types of polymers or plastics. In some embodiments, the plastic includes PET.

Although labels can generally be removed from containers, the outer surface of the container can retain a portion of the adhesive used to adhere the label to the container. This adhesive residue can contaminate or interfere with subsequent container operations such as later washings, relabeling, or container recycling. In some embodiments, the provided label can be removed from the outer surface while substantially all of the adhesive remains disposed and/or retained with the label rather than remaining with the outer surface.

The present invention also relates to methods of applying a label to a container. The methods include providing a container defining an outer surface, and a label in accordance with an embodiment. The methods further include adhering the label to the outer surface of the container, thereby applying the label to the container.

The labels can be adhered to one or more containers or articles in a batch, continuous, or semi-continuous fashion. Prior to application, one or more liners can be removed from the labels to thereby expose the adhesive face of the labels. The adhesive face and label is then contacted with the container (s) or article (s) and the labels applied thereto. Adhering may also include one or more operations of pressing or otherwise applying a pressing force against the label to promote contact and/or adhesion with the container； activating and/or curing of the adhesive such as by heating and/or exposure to UV light； and/or drying operations.

Other applications for the hotmelt PSA are contemplated. For example, one application relates to an adhesive sheet that does not include a facestock. Another application relates to an adhesive sheet that uses this composition on both sides of a facestock, e.g., a double coated tape. Another application relates to a self-wound adhesive having the hotmelt PSA on one side of a facestock and any other adhesive composition on the other side. Such a construction may optionally include a liner or may be linerless.

The hotmelt PSA may be useful in many markets. For example, in the electronics market, the hotmelt PSA may be employed in applications where good adhesion to glass and/or to a variety of engineering plastics is desired. The aforementioned removability and/or repositionability characteristics of the hotmelt PSA may provide sufficient adhesion to electronics substrates as well as the ability to rework products as issues in production arise. In particular, the ability to be cleanly removable may allow the substrate from which the hotmelt PSA is removed to be recycled after use.

In building and construction markets, the hotmelt PSA may be useful in situations where removability and/or repositionability characteristics are desired. Some examples include a self-would product, as discussed above, or a masking tape, e.g., a painter’s tape.

In other markets, e.g., automotive, the hotmelt PSA may be employed as an adhesive skin for foam compositions, in particular, applications where one side removability is desired. In other cases, the ability to adhere to low surface energy materials, e.g., engineered plastics, oleophobic coated glass, or painted metals, since it is a low polarity designed composition, may be advantageous.

Among others, the following embodiments are contemplated. All combinations of features and embodiments are contemplated.

Embodiment 1: A hotmelt adhesive, comprising: a styrene-isoprene-styrene copolymer, optionally present in an amount ranging from 15 wt％to 65 wt％； a tackifier having a softening point below 150℃； from 1 wt％to 15 wt％of a wax having a needle point penetration greater than 8 dmm, as measured by ASTM D5 (2016) , optionally present in an amount ranging from 1 wt％to 15 wt％；； a plasticizer, wherein the adhesive demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 20 N/inch, as measured by FINAT Test Method 2 (2016) .

Embodiment 2: An embodiment of embodiment 1 wherein the adhesive demonstrates a stainless steel peel strength ranging from 0.5 N/inch to 5 N/inch, as measured by FINAT Test Method 2 (2016) .

Embodiment 3: An embodiment of any one of embodiments 1 and 2, wherein the styrene-isoprene-styrene copolymer comprises less than 60 weight ％SI diblock.

Embodiment 4: An embodiment of any one of embodiments 1–3, wherein the adhesive comprises from 15 wt％to 65 wt％of a styrene-isoprene-styrene copolymer comprising less than 60 weight ％SI diblock.

Embodiment 5: An embodiment of any one of embodiments 1–4, wherein the styrene-isoprene-styrene copolymer comprises less than 35 wt％polymerized styrene monomers and less than 60 weight ％SI diblock.

Embodiment 6: An embodiment of any one of embodiments 1–5, wherein the weight ratio of plasticizer to tackifier is at least 0.05: 1.

Embodiment 7: An embodiment of any one of embodiments 1–6, wherein the weight ratio of plasticizer to tackifier ranges from 0.05: 1 to 2: 1.

Embodiment 8: An embodiment of any one of embodiments 1–7, wherein the weight ratio of wax and plasticizer, combined, to tackifier is at least 0.05: 1.

Embodiment 9: An embodiment of any one of embodiments 1–8, wherein the weight ratio of wax to tackifier is at least 0.05: 1.

Embodiment 10: An embodiment of any one of embodiments 1–9, wherein the tackifier has a molecular weight less than 1180.

Embodiment 11: An embodiment of any one of embodiments 1–10, wherein the tackifier comprises a hydrogenated hydrocarbon resin.

Embodiment 12: An embodiment of any one of embodiments 1–11, wherein the wax has a melting point above 60℃.

Embodiment 13: An embodiment of any one of embodiments 1–12, wherein the wax has a melting point above 60℃ and the tackifier has a molecular weight less than 1180.

Embodiment 14: An embodiment of any one of embodiments 1–13, wherein the wax has a dynamic viscosity at 140 ℃ ranging from 150 to 500 cps, as measured by a Brookfield viscometer.

Embodiment 15: An embodiment of any one of embodiments 1–14, wherein the plasticizer has a molecular weight of at least 200.

Embodiment 16: An embodiment of any one of embodiments 1–15, wherein the plasticizer has a viscosity of at least 175mm²/second, at 40 ℃, as measured by Chinese Standard BG/T 265 (1988) .

Embodiment 17: An embodiment of any one of embodiments 1–16, wherein the plasticizer is a compound selected from the group consisting of polyisobutene, naphthenic oil, paraffin oil, liquid polyisoprene, liquid white mineral oil, and combinations thereof.

Embodiment 18: An embodiment of any one of embodiments 1–17, wherein the hotmelt adhesive comprises: from 15 wt％to 45 wt％tackifier； and from 5 wt％to 35 wt％plasticizer.

Embodiment 19: A label comprising a facestock suitable for printing indicia； and a hot melt adhesive of any one of embodiments 1–18.

Embodiment 20: A process for producing a hotmelt adhesive, the method comprising: providing a styrene-isoprene-styrene copolymer； a tackifier having a softening point below 150℃； a wax having a high needle point penetration greater than 8 dmm, as measured by ASTM D5 (2016) ； and a plasticizer； determining a desired peel strength range； determining a weight ratio of plasticizer to tackifier based on the desired peel strength； combining the styrene-isoprene-styrene copolymer； the tackifier, the wax, and the plasticizer to form the hotmelt adhesive, wherein the plasticizer and the tackifier are present at the determined weight ratio of plasticizer to tackifier, and wherein the stainless steel peel strength of the hotmelt adhesive is within the desired peel strength range.

Examples

Three removable hotmelt PSAs were prepared according to the formulations listed below in Table 1.

*Minor amounts of additional additives include antioxidants.

As shown in Table 1, hotmelt PSA Examples 1–3 demonstrated peel strengths ranging from 1–5 N/inch. These samples demonstrated sufficient tack, high removability/repositionability, elimination or reduction of cohesive failure mode, low adhesive transfer, and little, if any, oil migration. The weight ratio of plasticizer to tackifiers ranged from 0.6 to 1. The weight ratio of wax and oil, combined, to tackifier ranged from 0.7 to 1.4. Examples 1–3 (and the other examples) demonstrate the importance of the specific components, e.g., the (low diblock content) polymer, the (soft) wax, plasticizer, and tackifiers, used in the particular ratios/weight percentages.

Tables 2a and 2b show two formulations prepared using different waxes and the related performance characteristics.

As shown in Table 2b, the use of a soft was improves release, G’, and zippiness, thus demonstrating the importance of the utilization of a high needle penetration wax (even when a higher molecular weight tackifier is employed) .

Table 3 shows hotmelt PSA formulations utilizing plasticizers having various viscosities.

Example 5 demonstrated slight staining, but not as much as Example 6, which demonstrated some staining. These examples show that these formulations provide hotmelt PSAs having beneficial tack, removability and repositionability. The examples also show the particular benefits of utilizing higher viscosity plasticizers, e.g., improvements in oil migration.

Table 4 shows hotmelt PSA formulations utilizing plasticizers having various viscosities, as well as the viscosities of the resultant hotmelt PSA.

These examples show formulations that provide, inter alia, hotmelt PSAs having beneficial tack, removability and repositionability. In addition, the use of the low molecular weight tackifiers allows the use of a higher molecular weight plasticizer, e.g., KP6030 or KN 4010, which provides for the aforementioned improvements. In addition to the oil migration-related benefits, the higher viscosity plasticizers, when employed with the aforementioned wax and tackifiers, provide a hotmelt PSA having a viscosity that provides for ease of processing as well as other benefits. This example demonstrates the importance of the plasticizer to tackifier weight ratio and the plasticizer and wax (combined) to tackifier weight ratio.

Examples 7 and 8 demonstrated a lower peel value, which is particularly beneficial in applications where more removability and repositionability are desired, e.g., for label applications. The risk of adhesive transfer and/or facestock tear is advantageously improved. Example 7 does not utilize a low molecular weight tackifier. Also, the examples show the benefit of using a cycloaliphatic hydrocarbon tackifier, e.g., HD1100, as compared to a linear hydrocarbon resin, e.g., C100R.

Table 5 shows hotmelt PSA formulations utilizing polymers having varying amounts of diblock content. These hotmelt PSAs were applied to various substrates, aged at 60℃ for 1 day, and tested for removability. Table 5 shows the results.

**SIS 1250 contains 50％SI diblock； SIS 1220 contains 25％diblock； Solprene 1205 is essentially a pure SB diblock copolymer.

These examples show formulations that provide, inter alia, hotmelt PSAs having beneficial tack, removability and repositionability. In particular, when SI diblock content (based on the total weight of the polymer) or total SB and SI diblock content is decreased, the failure mode beneficially improves as compared to instances where higher SI diblock or higher total SB and SI diblock content is used. Example 9’s SI diblock content (in the total polymer) was approximately 50％. Example 10’s diblock content (in the total polymer) was approximately 25％ (in the total polymer) . In terms of SI and SB diblock, Example 9 contained ～10％SI diblock and ～20％SB diblock (based on the total weight of all components, while Example 10 contained only ～10％SI diblock.

While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited below and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention.

Claims

A hotmelt adhesive, comprising:

from 15 wt％to 65 wt％of a styrene-isoprene-styrene copolymer；

a tackifier having a softening point below 150℃；

from 1 wt％to 15 wt％of a wax having a needle point penetration greater than 8 dmm, as measured by ASTM D5 (2016) ；

a plasticizer；

wherein the adhesive demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 20 N/inch, as measured by FINAT Test Method 2 (2016) .
The hotmelt adhesive of claim 1, wherein the adhesive demonstrates a stainless steel peel strength ranging from 0.5 N/inch to 5 N/inch, as measured by FINAT Test Method 2 (2016) .
The hotmelt adhesive of any of the preceding claims, wherein the styrene-isoprene-styrene copolymer comprises less than 60 weight ％SI diblock.
The hotmelt adhesive of any of the preceding claims, wherein the adhesive comprises from 15 wt％to 65 wt％of a styrene-isoprene-styrene copolymer comprising less than 60 weight ％SI diblock.
The hotmelt adhesive of any of the preceding claims, wherein the styrene-isoprene-styrene copolymer comprises less than 35 wt％polymerized styrene monomers and less than 60 weight ％SI diblock.
The hotmelt adhesive of any of the preceding claims, wherein the weight ratio of plasticizer to tackifier is at least 0.05: 1.
The hotmelt adhesive of any of the preceding claims, wherein the weight ratio of plasticizer to tackifier ranges from 0.05: 1 to 2: 1.
The hotmelt adhesive of any of the preceding claims, wherein the weight ratio of wax and plasticizer, combined, to tackifier is at least 0.05: 1.
The hotmelt adhesive of any of the preceding claims, wherein the weight ratio of wax to tackifier is at least 0.05: 1.
The hotmelt adhesive of any of the preceding claims, wherein the tackifier has a molecular weight less than 1180.
The hotmelt adhesive of any of the preceding claims, wherein the tackifier comprises a hydrogenated hydrocarbon resin.
The hotmelt adhesive of any of the preceding claims, wherein the wax has a melting point above 60℃.
The hotmelt adhesive of any of the preceding claims, wherein the wax has a melting point above 60℃ and the tackifier has a molecular weight less than 1180.
The hotmelt adhesive of any of the preceding claims, wherein the wax has a dynamic viscosity at 140℃ ranging from 150 to 500 cps, as measured by a Brookfield viscometer.
The hotmelt adhesive of any of the preceding claims, wherein the plasticizer has a molecular weight of at least 200.
The hotmelt adhesive of any of the preceding claims, wherein the plasticizer has a viscosity of at least 175mm²/second, at 40℃, as measured by Chinese Standard BG/T 265 (1988) .
The hotmelt adhesive of any of the preceding claims, wherein the plasticizer is a compound selected from the group consisting of polyisobutene, naphthenic oil, paraffin oil, liquid polyisoprene, liquid white mineral oil, and combinations thereof.
The hotmelt adhesive of any of the preceding claims, comprising:

from 15 wt％to 45 wt％tackifier； and

from 5 wt％to 35 wt％plasticizer.
A label comprising:

a facestock suitable for printing indicia； and

a hot melt adhesive, comprising:

from 15 wt％to 65 wt％of a styrene-isoprene-styrene copolymer；

a tackifier having a softening point below 150℃；

from 1 wt％to 15 wt％of a wax having a high needle point penetration greater than 8 dmm, as measured by ASTM D5 (2016) ；

a plasticizer；

wherein the adhesive demonstrates a stainless steel peel strength of ranging from 0.5 N/inch to 20 N/inch, as measured by FINAT Test Method 2 (2016) .
A process for producing a hotmelt adhesive, the method comprising:

providing a styrene-isoprene-styrene copolymer； a tackifier having a softening point below 150℃； a wax having a high needle point penetration greater than 8 dmm, as measured by ASTM D5 (2016) ； and a plasticizer；

determining a desired peel strength range；

determining a weight ratio of plasticizer to tackifier based on the desired peel strength；

combining the styrene-isoprene-styrene copolymer； the tackifier, the wax, and the plasticizer to form the hotmelt adhesive,

wherein the plasticizer and the tackifier are present at the determined weight ratio of plasticizer to tackifier, and wherein the stainless steel peel strength of the hotmelt adhesive is within the desired peel strength range.