Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-11-15
2004-10-19
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S221000, C525S301000, C525S075000, C525S078000, C525S080000, C525S085000, C525S191000, C525S222000, C525S227000, C525S299000
Reexamination Certificate
active
06806320
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to block copolymer melt-processable compositions such as adhesives, pressure sensitive adhesives, sealants, elastomers, other hot melt processable compositions, to methods of their preparation, and to articles having a coating of such a composition applied thereto.
BACKGROUND
Among adhesive chemistries, poly(meth)acrylates (e.g., polymers derived at least in part from one or more methacrylate monomer or acrylate monomer) are one of the most prominent. (Meth)acrylates have evolved as a preferred class of adhesives due to their durability, permanence of properties over time, and versatility of adhesion, to name just a few of their benefits.
Traditionally, adhesives such as (meth)acrylates have been provided in organic solvent for processing, application, or other incorporation into a larger product. Solvent based adhesives can be applied to a substrate and the solvent can be removed, leaving behind the adhesive.
Hot-melt adhesives advantageously reduce or eliminate the use of organic solvents in adhesives and their processing. Hot-melt adhesive systems are essentially 100% solid systems. Usually, such systems contain no more than about 5% organic solvent or water, more typically no more than about 3% organic solvent or water. Most preferably, such systems are free of organic solvent and water. Advantageously, by reducing the use of organic solvents, special handling concerns associated with the use of organic solvents are also reduced.
Melt-processable block copolymer materials have been prepared, as described in PCT International Publication Number WO 00/39233. These block copolymers are described as generally contemplated to include homopolymer or copolymer blocks. According to this publication and other prior art techniques, to provide a block copolymer with melt-processing capability, the molecular weight of homopolymer end blocks may be relatively low. The relatively low molecular weight of the end blocks can still allow for useful and acceptable cohesive strength, but the ability to use relatively higher molecular weight end blocks, without losing melt-processing capabilities, could be advantageous by further improving other properties of a block copolymer composition such as cohesive strength.
SUMMARY
Block copolymers contain at least two different polymeric “blocks” that cause the bulk block copolymer to exhibit desired properties. (The term “block copolymer” is used herein to describe a block copolymer on a molecular scale, and also for convenience to reference a block copolymer-containing composition or “bulk” block copolymer). Typically, one block, the end block or “A” block, is a relatively high glass transition temperature polymeric block that provides structural and cohesive strength within use temperature ranges. The “B” block or blocks, which may typically constitute the middle or core of the block copolymer, have a relatively lower glass transition temperature and provide elastomeric properties. The chemistry of the B block can also affect properties of the block copolymer composition including glass transition temperature and modulus, which relate to tackiness of the composition.
The polymeric blocks interact with each other in a bulk composition differently at different temperatures, providing useful temperature-controlled properties. At low temperatures, e.g., use temperatures, e.g., temperatures below the glass transition temperature of the end A blocks and above the glass transition temperature of the B blocks (e.g., for pressure sensitive adhesive and elastomer compositions, typically below 100° C. and above −50° C.), the different blocks organize into ordered A and B phases, or “phase separate,” within the bulk block copolymer composition. For compositions containing less than about 50 weight % of the A block, typically microdomains of discontinuous A block are formed within a continuous phase of B block. The A domains provide rigidity and strength within the lower modulus continuous B phase, for a desirable combination of properties. At higher temperatures, e.g., at a temperature greater than the Tg of an A block, e.g., greater than 100° C. to about 200° C., the bulk block copolymer can be melt processed. In a favorably designed block copolymer, the thermal energy imparted to the bulk block copolymer at these temperatures is sufficient to disrupt the ordered multiphase morphology and create disorder within the block copolymer composition. The disordered composition does not retain the strength of the ordered microdomains and as a result can flow and be “melt processed” relatively easily—melt-processable block copolymer compositions have a viscosity upon melting that allows the compositions to be melt-processed (e.g., applied to a substrate). Upon cooling, the composition returns to the ordered, strengthened, multi-phase morphology.
FIG. 2
illustrates thermal behavior of a block copolymer of Example 1 over a range of temperatures such that the different regions of block copolymer viscoelastic behavior could be accessed. G′ (storage modulus), G″ (loss modulus), and tan ∫ (the ratio G″/G′) are plotted in the figure as a function of temperature. These dynamic mechanical measurements were conducted using a rheometer in a shear geometry. At very low temperatures (<−50° C.), the entire block copolymer is in a glassy state and the material is predominantly elastic (G′>>G″). A precipitous drop is observed in G′ over a temperature range (ca. −50° C. to ca. −10° C.) and a peak in tan ∂ is observed which is associated with the Tg of the B block. A plateau in G′ is observed from ca. 0° C. to ca. 100° C. and is attributed to the entanglements of the B block polymer chains. Above ca. 100° C., G′ starts dropping sharply due to the onset of flow in the system and as the Tg of the A block is exceeded. Accordingly, the viscoelastic response is dominated by G″ in this flow region (G″>G′) and a steep increase in tan ∂ (=G′/G′) is observed. It is in this “flow region” of the viscoelastic curve that melt processing is often conducted.
The temperature at which meltflow occurs is referred to herein as the meltflow temperature. One convenient measurement of meltflow temperature that can be used for purposes of this description is that the meltflow temperature of a block copolymer is the temperature at the intersection of G′ and G″ in the flow region of the viscoelastic curve.
FIG. 1
shows a plot of G′ versus temperature for a variety of block copolymers. The meltflow temperature progressively increases in this case for copolymers identified herein as Examples 1, 2, 3, and 4. The flow region could not be accessed for Example 5, even when heated to 240° C., and so it would be difficult to hot melt process this material without causing thermal degradation or without the use of other processing aids.
Different features of the molecular structures of the A and B polymers have been found to affect properties of bulk block copolymers such as tackiness (or non-tackiness), meltflow temperature, modulus, Tg, and cohesive strength. These features include the molecular weight of an A block polymer or a B block polymer and the ratio of the molecular weight of the A block polymer to the molecular weight of the B block polymer (MW
A
:MW
B
). In general, higher molecular weight A blocks increase cohesive strength of a bulk block copolymer, but will also increase meltflow temperature (for a given MW
B
), which may not be desired. The ratio of MW
A
to MW
B
can have a significant effect on which phase is the continuous phase, the A block or the B block. This in turn can alter the properties of the block composition. Preferred block compositions have a continuous B block, and it can therefore be preferred to keep the ratio of MW
A
to MW
B
in a range to maintain the continuous B block.
Often, it is desirable to control (e.g., increase or decrease) the meltflow temperature of a block co
D'Haese Francois C.
Everaerts Albert I.
Khandpur Ashish K.
Ma JingJing
Nguyen Lang N.
3M Innovative Properties Company
Asinovsky Olga
Fulton Lisa P.
Seidleck James J.
LandOfFree
Block copolymer melt-processable compositions, methods of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Block copolymer melt-processable compositions, methods of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Block copolymer melt-processable compositions, methods of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3273906