WO2013055446A1

WO2013055446A1 - Composition and method for packaging polyolefin-based hot melt adhesives

Info

Publication number: WO2013055446A1
Application number: PCT/US2012/051715
Authority: WO
Inventors: James N. FOWLER; Enrico L. Buenacosa; James Haselman; John Joseph Decair
Original assignee: Rextac Llc
Priority date: 2011-10-14
Filing date: 2012-08-21
Publication date: 2013-04-18

Abstract

A polyolefin-based hot melt adhesive that may be packaged in an easy-to-use form comprises a non-tacky film layer having certain physical properties that surrounds the outside of the polyolefin-based adhesive to prevent the individual packages from sticking together or blocking in a carton. The film layer is specifically designed to melt in-process along with the polyolefin-based adhesive and not have any deleterious effects on the process or the adhesive. Suitable polyolefins include but are not limited to APAO, Metallocene catalyzed polyolefin polymers, Ziegler-Natta catalyzed olefin polymers, polypropylene, polybutene-1, and co-polymers of the aforementioned polymers.

Description

COMPOSITION AND METHOD FOR PACKAGING POLYOLEFIN-BASED HOT MELT ADHESIVES

CROSS-REFERENCE TO RELATED APPLICATIONS:

[0001] This application claims the benefit of U.S. Provisional Application

No. 61 /547,488, filed on October 14, 201 1 .

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT: Not Applicable

BACKGROUND OF THE INVENTION

1 . Field of the Invention.

[0002] This invention relates to packaging adhesives. More particularly, it relates to polyolefin-based hot melt adhesives.

2. Description of the Related Art including information disclosed under 37 CFR 1 .97 and 1 .98.

[0003] Hot melt adhesive (HMA), also known as "hot glue," is a form of thermoplastic adhesive. In industrial use, hot melt adhesives provide several advantages over solvent-based adhesives. Volatile organic compounds are reduced or eliminated, and the drying or curing step is eliminated. Hot melt adhesives have a long shelf life and can usually be disposed of without special precautions. Some of the disadvantages of HMAs involve thermal load of the substrate, limiting use to substrates not sensitive to higher temperatures, and loss of bond strength at higher temperatures (up to complete melting of the adhesive). This can be reduced by using a reactive adhesive that, after solidifying, undergoes further curing e.g. by moisture (e.g. reactive urethanes and silicones), or is cured by ultraviolet radiation. HMAs do not lose thickness during solidifying whereas solvent-based adhesives may lose up to 50-70% of layer thickness during drying. [0004] Some of the possible base materials for HMAs include the following:

• Ethylene-vinyl acetate (EVA) copolymers,

• Polyolefins (PO) (polyethylene (usually LDPE but also HDPE; HDPE has higher melting point and better temperature resistance), atactic polypropylene (PP or APP), polybutene-1 , oxidized polyethylene, etc. These polymers provide very good adhesion to polypropylene, form a good moisture barrier, and exhibit chemical resistance against polar solvents and solutions of acids, bases, and alcohols. They have a longer open time in comparison with ethylene vinyl acetate (EVA) and polyamides. Polyolefins have low surface energy and provide good wetting of most metals and polymers. Polyolefins made by metallocene catalyzed synthesis have a narrow distribution of molecular weight and a correspondingly narrow melting temperature range. Due to their relatively high crystallinity, polyethylene-based glues tend to be opaque and, depending on additives, white or yellowish in color.

Polyethylene hot melts have high pot life stability, are not prone to charring, and are suitable for moderate temperature ranges and on porous non-flexible substrates. Nitrogen or carbon dioxide can be introduced into the melt, forming a foam which increases spreading and open time and decreases transfer of heat to the substrate, allowing use of more heat-sensitive substrates. Polyethylene-based HMAs are usually used in such applications. Amorphous

polypropylene HMAs have good dielectric properties, making them suitable for use at high frequencies. PE and APP are usually used on their own or with a small amount of tackifiers (usually hydrocarbons) and waxes (usually paraffins or microcrystalline waxes, for lower cost, improved anti-blocking, and altered open time and softening temperature). The molecular weight of the polymer is usually lower. Lower molecular weights provide better low-temperature performance and higher flexibility, higher molecular weights increase the seal strength, hot tack, and melt viscosity.

o Polybutene-1 and its copolymers are soft and flexible, tough,

partially crystalline, and slowly crystallizing with long open times. The low temperature of recrystallization allows for stress release during formation of the bond.

o Amorphous polyolefin (APO/APAO) polymers are compatible with many solvents, tackifiers, waxes, and polymers and find wide use in many adhesive applications. APO hot melts have good fuel and acid resistance, moderate heat resistance, are tacky, soft and flexible, have good adhesion and longer open times than crystalline polyolefins. APOs tend to have lower melt viscosity, better adhesion, longer open times and slow set times than comparable EVAs. Some APOs can be used alone, but often they are compounded with tackifiers, waxes, and plasticizers (e.g. mineral oil, poly-butene oil). Examples of APOs are amorphous (atactic) propylene (APP), amorphous propylene/ethylene (APE), amorphous propylene/butene (APB), amorphous propylene/hexene (APH), amorphous propylene/ethylene/butene. APP is harder than APE, which is harder than APB, which is harder than APH, in accordance with decreasing crystallinity. APOs show relatively low cohesion, the entangled polymer chains having a fairly high degree of freedom of movement. Under mechanical load, most of the strain is dissipated by elongation and disentanglement of polymer chains and only a small fraction reaches the adhesive-substrate interface. Cohesive failure is therefore a more common failure mode of APOs. Amorphous Poly-alpha-olefins (APAO) may be produced by (co-) polymerization of a-olefins, e.g. propylene or 1 -butene with Ziegler-Natta catalysts. The (co-)polymers have an amorphous structure which makes them useful for the production of hot melt adhesives. • Polyamides and polyesters

• Polyurethanes

• Styrene block copolymers (SBC), also called styrene copolymer

adhesives and rubber-based adhesives,

• Polycaprolactone with soy protein, using coconut oil as plasticizer

• Polycarbonates

• Fluoropolymers, with tackifiers and ethylene copolymer with polar groups

• Silicone rubbers

• Thermoplastic elastomers

• Polypyrrole (PPY), a conductive polymer, for intrinsically conducting hot melt adhesives (ICHMAs), used for EMI shielding.

• various other copolymers

[0005] Common additives in H MA formulations include:

• tackifying resins (e.g. rosins and their derivates, terpenes and modified terpenes, aliphatic, cycloaliphatic and aromatic resins (C₅ aliphatic resins, Cg aromatic resins, and C5/C9 aliphatic/aromatic resins), hydrogenated hydrocarbon resins, and their mixtures, terpene-phenol resins (TPR, used often with EVAs)), up to about 40%. Tackifiers tend to have low molecular weight and glass transition and softening temperatures above room temperature providing them with suitable viscoelastic properties. Tackifiers frequently represent most of the weight and cost of hot-melt adhesive.

• waxes, e.g. microcrystalline waxes, fatty amide waxes or oxidized Fischer-Tropsch waxes; to increase the setting rate. Waxes lower the melt viscosity and can improve bond strength and temperature resistance. • plasticizers (e.g. benzoates, e.g. 1 ,4-cyclohexane dimethanol dibenzoate, glyceryl tribenzoate, or pentaerythritol tetrabenzoate, phthalates, paraffin oils, polyisobutylene, chlorinated paraffins, etc.)

• antioxidants and stabilizers (e.g. hindered phenols, BHT, phosphites, phosphates, hindered aromatic amines); added in small amounts (<1 %), not influencing physical properties. These compounds protect the material from degradation during the service life, compounding and while in the molten state during application.

• UV stabilizers that protect the material against degradation by

ultraviolet radiation

• pigments and dyes

• biocides (where hindering bacterial growth is desired)

• flame retardants

• antistatic agents

• fillers, for reducing cost, adding bulk, improving cohesive strength (forming an aggregate-matrix composite material) and altering properties; e.g. calcium carbonate, barium sulfate, talc, silica, carbon black, clays (e.g. kaolin).

[0006] Melt flow index or MFI is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative prescribed temperatures. The method is described in the similar standards ASTM D1238 and ISO 1 133. Synonyms of Melt Flow Index are Melt Flow Rate and Melt Index. More commonly used are their abbreviations: MFI, MFR and Ml.

[0007] Melt flow rate is an indirect measure of molecular weight, with high melt flow rate corresponding to low molecular weight. At the same time, melt flow rate is a measure of the ability of the material's melt to flow under pressure. Melt flow rate is inversely proportional to viscosity of the melt at the conditions of the test, although the viscosity for any such material depends on the applied force. Ratios between two melt flow rate values for one material at different gravimetric weights are often used as a measure of the broadness of the molecular weight distribution.

[0008] Melt flow rate is very commonly used for polyolefins,

polyethylene being measured at 190°C and polypropylene at 230°C. A plastics converter will typically choose a material with a melt index sufficiently high to easily form the polymer in the molten state into the article intended, but low enough that the mechanical strength of the final article is sufficient for its intended use.

[0009] Typical hot melt adhesives that use a polyolefin polymer are commonly used for a variety of applications. The conventional method of packaging the polyolefin-based hot melt is by cutting the polyolefin adhesive into individual pieces - anywhere from 20 grams to 1000 grams. When the polyolefin adhesive has residual surface tack after cooling, an additional step may be employed wherein the individual pieces are either placed in a film pouch or otherwise surrounded with a non-tacky film. The problem has been that the particular films available for this secondary type of packaging are not ideally compatible with the polyolefin hot melt and this can result in process failures due to the film not blending adequately with the polyolefin hot melt in process. Currently, polyolefin-based adhesives must be packaged in silicone-lined containers or, in some cases, co-extruded with a non-tacky coating in order to prevent them from sticking together.

[0010] U.S. Patent No. 7,350,644 to Harwell et al. describes Multi-layer films are used to package hot melt adhesives. The packaging film does not require removal prior to use of the adhesive. Multi-layer films used to package low application temperature hot melt adhesives have at least one layer with a melting point below about 100°C. [001 1] U.S. Patent No. 6,155,029 to Jain describes the packaging of a hot melt adhesive in a plastic film to prevent the adhesive from blocking during shipping and storage. The hot melt adhesives may be thermoplastic or thermosetting in nature. The films used to wrap the adhesive are flexible in nature and are made of polymer composition, which become part of the adhesive once the adhesive is melted.

[0012] U.S. Patent No. 5,373,682 to Hatfield et al. describes a method for tackless packaging of hot melt adhesives wherein a non-blocking hot melt adhesive mass is packaged by directly pouring or pumping the molten adhesive into a cylindrical plastic tube, the cylindrical tube being in contact with a heat sink. The resultant adhesive package is provided in cartridge form which may be produced in a continuous line operation.

[0013] U.S. Patent No. RE36,177 to Rouyer et al. describes a method of packaging an adhesive composition, especially a thermoplastic or thermosetting hot melt adhesive. The method comprises the steps of providing one substantially uniform separate portion of the adhesive composition; sufficiently solidifying the portion for packaging; and, surrounding the solidified portion with a plastics packaging material. The packaging material is meltable together with the adhesive composition and blendable into the molten adhesive composition, the kind and amount of the packaging material being chosen so as not to disadvantageously affect the properties of the adhesive composition when blended into it. The packaging material may be a net, a wrap, a sack or a bag. Packagings made of plastic film are voided of air, to prevent problems in melting.

[0014] U.S. Patent No. 7,137,235 to Burriez et al. describes a method for packaging a sheathed hot-melt adhesive product in block form that comprises the steps of: (a) continuously supplying a sheathed hot-melt adhesive product, (b) immersing the sheathed hot-melt adhesive product in a liquid refrigerant, (c) pressing the sheathed adhesive product at a portion thereof, (d) ultrasonically welding the sheathed adhesive product at the pressed portion; and (e) cutting the sheathed adhesive product into a block at the pressed portion.

[0015] U.S. Patent No. 5,401 ,455 to Hatfield et al. describes a method for packaging hot melt adhesives wherein a non-blocking hot melt adhesive mass is prepared by (a) lining a rigid mold with a plastic film, the film being meltable together with the adhesive composition and blendable into the molten adhesive composition, and the mold being a heat sink or being in contact with a heat sink; (b) pouring molten hot melt adhesive into the lined mold; and (c) allowing the molten hot melt adhesive to solidify.

[0016] U.S. Patent No. 6,430,898 to Remmers et al. describes a method of packaging a thermoplastic composition with a film having a low complex viscosity. It is reported that complex viscosity directly relates to physical film compatibility and identifies a class of polyolefin materials which are said to be particularly amenable to exhibiting such properties if the film material is first chemically compatible with the thermoplastic composition to be packaged. The method is said to be particularly useful for low viscosity thermoplastic compositions having a Brookfield viscosity of less than about 10,000 cPs at 350° F., such as pressure sensitive hot melt adhesive compositions which are typically applied by melting the packaged adhesive composition in a melt tank wherein the melt tank lacks an active mixing means.

[0017] U.S. Pub. No. 2003/0155261 by Paul et al. describes films having a melting point below about 100°C. that may be used to package low temperature hot melt adhesives. It is said that the packaging film does not require removal prior to use of the adhesive.

[0018] This invention relates to a film that has specific properties that permits its use with polyolefin-based hot melt adhesives. When the film falls within a specific range of properties, there is no negative effect on either the hot melt process or the properties of the adhesive. BRIEF SUMMARY OF THE INVENTION

[0019] A polyolefin-based hot melt adhesive that may be packaged in an easy-to-use form comprises a non-tacky film layer that surrounds the outside of the polyolefin-based adhesive to prevent the individual packages from sticking together or blocking in a carton. The film layer is specifically designed to melt in process along with the polyolefin-based adhesive and not adversely affect the process or the adhesive. Suitable polyolefins include but are not limited to APAO, metallocene catalyzed polyolefin polymers, Ziegler-Natta catalyzed olefin polymers,

polypropylene, polybutene-1 , or any co-polymers of the aforementioned polymers, etc. In one particular preferred embodiment, the packaging film has a Melt Index of at least about 30 and a differential scanning calorimeter melt point below about 150°C.

DETAILED DESCRIPTION OF THE INVENTION

[0020] In one preferred embodiment, the invention comprises a non- tacky film layer surrounding a polyolefin-based hot melt adhesive wherein the film is highly compatible with the polyolefin HMA. The result is that the film layer melts in process along with the polyolefin HMA when used and does not cause negative effects on the process or properties of the hot melt adhesive.

[0021] The film layer keeps the individual polyolefin-based hot melt pieces from sticking or blocking together when packaged in a carton or sack. The film may completely enclose the individual pieces of the polyolefin hot melt and may be designed to be included (not removed) when the polyolefin hot melt pieces are added to a melt tank for processing. The film is very compatible and combines with the hot melt adhesive in process without the need for mixing.

[0022] For the film to blend well into the polyolefin-based hot melt adhesive, it is preferable that it have a Melt Index (per ASTM method D- 1238 run at 190°C 2.16Kg) of 30 or higher and a DSC melt point that is below 150°C. Additionally, the resin is preferably able to be processed into a film that can then be wound and un-wound. In particular, films made from polybutene homopolymers, copolymers or terpolymers have been found to show superior performance over polyethylene- or polypropylene- based films.

[0023] One way to achieve the needed properties is to start with a base resin that is lower in Melt Index (Ml) and vis-break the resin so as to obtain a higher Ml. Alternatively, the base resin can be blended with certain additives to further increase the Ml and/or to enhance the processibility of the resin for making a film. Other additives may include process aids such as slip agents and anti-blocking agents which are commonly used in such processes. Other additives may also include hydrocarbon waxes, oils, tackifying resins and similar materials that are compatible with the olefin film. Hydrocarbon waxes may also be used to enhance some of the desirable properties for film processing and also help to lower the Ml.

[0024] In one particular preferred embodiment, the film comprises a vis- broken propylene-based terpolymer - with ethylene and 1 -butene - from Basell. Resins of similar chemistry and Ml can be expected to perform equivalently.

[0025] Representative Example

[0026] The starting resin was Polybutene-1 (DP-8220M from Basell).

[0027] Polybutene-1 grade DP 8220M is a random copolymer of butene- 1 with medium ethylene content. This grade is highly compatible with polypropylene due to its similar molecular structure, and it is used to modify the sealing behavior of polypropylene-based films - a typical example is its use to reduce the seal initiation temperature of bi-axially oriented polypropylene (BOPP) sealing layers.

[0028] The relatively slow kinetics of crystallization of this resin allow for an excellent wetting behavior. Its highly shear-sensitive flow behavior allows it to remain easily dispersible also in even less compatible polymers such as thermoplastic elastomers.

[0029] TABLE 1 - Product Characteristics

Typical Properties Method Value Unit

Physical

Density ISO 1183 0.901 g/cm³

Melt flow rate (MFR) ISO 1133

(190°C/2.16kg) 2.5 g/lO min

(190°C/10kg) 46 g/lO min

Mechanical

Flexural modulus ISO 178 140 MPa

Tensile Strength at Yield ISO 8986-2 10 MPa

Tensile Strength at Break ISO 8986-2 32 MPa

Tensile Elongation at Break ISO 8986-2 300 %

Note: Measured on specimens conditioned for 10 days at 20°C

Thermal Melting temperature DSC

97 °C

T_ml

85 °C

T_m2

[0030] This resin was then further processed by vis-breaking in a twin screw extruder to a melt flow of about 85 to 95 (190°C/2.16kg). The process for vis-breaking an olefin polymer is generally known by those skilled in the art. A typical process includes a twin screw extruder run between 350 and 400°F. The low M l polymer was fed to the feed throat and a corresponding amount of peroxide was added in order to achieve the desired Ml.

[0031] Alternatively, a wax may be blended along with the vis-broken resin to achieve a higher melt flow. One particular wax found to be suitable when used in this blend is available from Sasol and designated Sasolwax® C-80. C-80 is a linear structure Fischer-Tropsch wax having a congealing point between 78 and 83°C (per ASTM D-938), an oil content of no more than 0.75% (per ASTM D-721 ) and a needle penetration at 25°C of no more than 0.7mm (per ASTM D-1321 ). This wax is said to give a HMA the unique characteristics of low viscosity combined with high crystallinity.

[0032] The resulting resin may then be cast into a film by existing cast film processes. The resulting film may then be used to enclose a block of the APAO based hot melt adhesive. The resulting packaged blocks can then be safely stored at normal warehouse and shipping conditions with no danger of the blocks sticking together or sticking to the corrugated box in which they are packaged. Once ready to use, the blocks of adhesive may be placed in the hot melt tank with the film attached and the film will melt together with the hot melt adhesive with no negative effects on the adhesive's performance. [0033] Films as low as 80MI and as high as 150M I have been tested. It has been found that some high-M I resins do not cast easily into a film, but otherwise work in the process of the invention. Poly 1 -butene resins vis- broken to 80M I have also been found to work well in the present invention. In general, any film that is compatible with the polyolefin-based adhesive and has a Ml of 30 or higher and a DSC melt point of 150°C or lower is suitable for use in connection with this invention.

[0034] Differential scanning calorimetry or DSC is a thermo-analytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. It is widely used in industrial settings as a quality control instrument due to its applicability in evaluating sample purity and for studying polymer curing.

[0035] DSC is used widely for examining polymers to check their composition. Melting points and glass transition temperatures for most polymers are available from standard compilations, and the method can show possible polymer degradation by, for example, the lowering of the expected melting point (T_m). T_m depends on the molecular weight of the polymer, so lower grades will have lower melting points than expected. The percentage crystallinity of a polymer can be found from the

crystallization peak of the DSC graph since the heat of fusion can be calculated from the area under an absorption peak. DSC can also be used to study thermal degradation of polymers. Impurities in polymers can be determined by examining thermograms for anomalous peaks, and plasticizers can be detected at their characteristic boiling points.

[0036] One particular film according to the invention comprises an alpha-olefin polymer of 1 -propene (CAS# 25895-47-0) and has a film thickness of 1 .6 - 1 .8 mils (+ 0.10 mil). The properties of the resin are: a Melt Index of 100 (grams/10 minutes at 190°C/2.16Kg); a melting point of 130°C; and, a density of 0.920 g/cm³. [0037] Although particular embodiments of the present invention have been shown and described, they are not intended to limit what this patent covers. One skilled in the art will understand that various changes and modifications may be made without departing from the scope of the present invention as literally and equivalently covered by the following claims.

Claims

CLAIMS What is claimed is:

1 . A polymer film prepared by the process comprising the steps of: vis-breaking a polyolefin polymer to a Melt Index of at least about 30 and a melting point below about 150°C; casting the vis-broken polymer into a film.

2. A polymer film as recited in claim 1 wherein the polyolefin polymer is selected from the group consisting of polybutene homopolymers, polybutene copolymers and polybutene terpolymers.

3. A polymer film as recited in claim 1 wherein the polyolefin polymer is selected from the group consisting of polyethylene and polypropylene.

4. A polymer film as recited in claim 1 wherein the polyolefin polymer is a propylene-based terpolymer with ethylene and 1 -butene.

5. A polymer film as recited in claim 1 wherein the vis-breaking is performed in a twin screw extruder.

6. A polymer film as recited in claim 5 wherein the temperature of the extruder is between about 350°F and about 400°F.

7. A polymer film as recited in claim 5 further comprising the addition of a peroxide to the extruder during the vis-breaking.

8. A polymer film as recited in claim 1 wherein the vis-breaking comprises blending the polyolefin polymer with one or more additives.

9. A polymer film as recited in claim 8 wherein the additive comprises a linear structure Fischer-Tropsch wax.

10. A polymer film as recited in claim 9 wherein the wax has a congealing point between 78°C and 83°C.

1 1 . A method for packaging a polyolefin-based holt melt adhesive comprising: forming a polyolefin-based hot melt adhesive into individual pieces; enclosing the individual pieces in a polymer film having a Melt Index of at least about 30 and a differential scanning calorimeter melt point below about 150°C.

12. A method as recited in claim 1 1 wherein the polymer film comprises a vis-broken propylene-based terpolymer with ethylene and 1 -butene.

13. A method as recited in claim 12 wherein the polymer film comprises a polybutene-1 -based polymer vis-broken to a Melt Index between 85 and 95.

14. A method as recited in claim 1 1 wherein the polymer film comprises a resin selected from the group consisting of polybutene homopolymers, polybutene copolymers and polybutene terpolymers.

15. A polymer film as recited in claim 1 1 wherein the polymer film comprises a resin selected from the group consisting of polyethylene and polypropylene.

16. A hot melt adhesive composition prepared by: wrapping a polyolefin-based hot melt adhesive in a polymer film

having a Melt Index of at least about 30 and a differential scanning calorimeter melt point below about 150°C; and, melting the wrapped hot melt adhesive together with the film.

17. A hot melt adhesive composition as recited in claim 16 wherein the polymer film comprises a vis-broken propylene-based terpolymer with ethylene and 1 -butene.

18. A hot melt adhesive composition as recited in claim 16 wherein the polymer film comprises a vis-broken polymer selected from the group consisting of polybutene homopolymers, polybutene copolymers and polybutene terpolymers.

19. A hot melt adhesive composition as recited in claim 16 wherein the polymer film comprises a hydrocarbon wax.

20. A hot melt adhesive composition wherein the polymer film has a Melt Index of about 85 to 95 at 190°C with a 2.16kg weight per ASTM D-1238.