US007883769B2
`
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`(12) United States Patent
`Seth et al.
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`
`(10) Patent No.:
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`(45) Date of Patent:
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`US 7,883,769 B2
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`
`*Feb. 8,2011
`
`(54)
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`INTEGRALLY FOAMED
`
`
`MICROSTRUCTURED ARTICLE
`
`
`
`
`(75)
`
`
`
`
`
`
`Inventors: Jayshree Seth, Woodbury, MN (US);
`Christopher K. Haas, Cottage Grove,
`
`
`
`
`MN (US); Ravi K. Sura, Woodbury, MN
`
`
`
`
`
`
`
`(US); Katherine A_ S_ Graham,
`
`
`
`Roseville, MN (US); Janet A. Venne,
`Roseville, MN (US)
`
`
`
`
`4,940,736 A
`
`
`7/1990 Alteepping et al.
`
`
`
`
`
`(Continued)
`
`
`
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`
`FOREIGN PATENT DOCUMENTS
`
`
`
`0830930 A1
`3/1998
`
`
`
`EP
`
`
`
`
`
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`
`
`(73) Assignee: 3M Innovative Properties Company,
`
`
`St. Paul, MN (US)
`Subject to any disclaimer, the term of this
`
`
`
`
`
`
`patent is extended or adjusted under 35
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`
`
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`USC. 15403) by 0 days.
`
`( * ) Notice:
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`This patent is subject to a terminal dis-
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`C1aimer.
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`(21) Appl. No.: 10/464,215
`.
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`Filed:
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`(22)
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`
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`Jun. 18, 2003
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`(65)
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`Prior Publication Data
`
`
`
`US 2004/0258902 A1
`Dec. 23, 2004
`
`
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`
`
`(51)
`
`
`II1t- CL
`
`
`B323 3/26
`(200601)
`
`
`
`3323 3/06
`(2006.01)
`
`
`
`(52) U.S. Cl.
`............ .. 428/314.8; 428/314.4; 428/316.6;
`
`
`
`
`
`
`428/99; 428/100
`
`
`(58) Field of Classification Search ............ .. 428/316.6,
`
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`
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`428/99, 100, 315,7, 314,4, 3148
`
`
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`
`
`See application file for complete Search history,
`
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`
`
`_
`
`References Clted
`
`
`US. pATENT DOCUMENTS
`
`
`
`
`(56)
`
`
`
`4390348 A
`
`:
`,
`,
`
`4,753,838 A
`
`4,761,256 A
`
`4,916,198 A
`
`
`
`
`
`9/1981 Kemf3Tf3T et 31~
`
`
`
`
`g/Ia1:“n1'VVeden5kY et 31'
`lg;
`at
`
`
`6/1988 Kimura
`
`
`8/1988 Hardenbrook et al.
`
`
`4/1990 Scheve et al.
`
`
`
`
`
`
`
`
`(Continued)
`OTHER PUBLICATIONS
`
`
`
`
`
`
`
`
`
`
`
`Ainslie T. Young, “Microcellular Foams Via Phase Separation”, J.
`Vac. Sci. Technol. A 4(3), p. 1128-1133, May/Jun. 1986*
`
`
`
`
`
`
`
`,
`
`(Continued)
`Primary Examiner—Hai V0
`
`
`
`
`
`(57)
`
`
`
`ABSTRACT
`
`
`
`The invention is directed in part to an article that includes a
`
`
`
`
`
`
`
`polymer foam having a surface with surface microstructures,
`
`
`
`
`
`
`
`the surface microstructures have at least one extent or dimen-
`
`
`
`
`
`
`
`
`sion of about 10 microns or more, preferably 50 microns or
`
`
`
`
`
`
`more. A maximum extent (unless it is a continuous rib-like
`
`
`
`
`
`
`
`structure) the microstructure is about 300 microns or less,
`
`
`
`
`
`
`
`preferably 200 microns or less, and generally a maximum
`
`
`
`
`
`
`
`height of 1000 microns or less, preferably 750 microns or less
`
`
`
`
`
`
`
`
`and a minimum height of 200 microns or more, preferably
`
`
`
`
`
`
`
`300 microns or more. The foamed article may be provided in
`
`
`
`
`
`
`
`
`a variety of shapes, including a rod, a cylinder, a sheet, etc. In
`
`
`
`
`
`
`
`
`a preferred embodiment where the foam is provided in the
`
`
`
`
`
`
`
`
`form of a sheet, the foam has a pair of major surfaces, one or
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`both of which can be provided with surface microstructures.
`The foam backing and microstructures include a plurality of
`
`
`
`
`
`
`
`voids, which voids are preferably of a mean size substantially
`
`
`
`
`
`
`
`
`less than the smallest cross-sectional dimension or extent of
`
`
`
`
`
`
`
`~
`
`
`the mlcrostmcmres
`
`21 Claims, 6 Drawing Sheets
`
`
`
`
`
`
`/ so
`
`
`
`81
`
`
`
`
`
`
`V ff ff
`amvmm mmagampmi
`‘£4.84”~'\ J'|'l'|’ ‘$305.
`'§\ 5- ac‘); - ‘.2,’
`
`85
`
`82
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`
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`PAGE 1 OF 18
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`BOREALIS EXHIBIT 10 18
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`BOREALIS EXHIBIT 1018
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`PAGE 1 OF 18
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`

`
`U.S. PATENT DOCUMENTS
`
`
`Masutomi et al.
`8/1994
`
`
`
`Reeves et al.
`............. .. 428/167
`2/1996
`....... .. 604/385.23
`Menard et al.
`9/1996
`
`
`
`
`
`
`
`
`Leonard et al.
`2/1997
`
`
`
`2/1997
`DeNicola, Jr. et al.
`
`
`
`
`Petrakis et al.
`10/1998
`
`
`
`................. .. 264/2.7
`Ulsh et al.
`8/2000
`
`
`
`
`8/2000
`Cejka et al.
`
`
`
`1/2001
`Kennedy et al.
`
`
`
`1/2001
`........... .. 521/134
`Agarwal et al.
`
`
`
`
`
`8/2001
`Insley et al.
`..... ..
`428/172
`
`
`
`
`
`........... .. 521/64
`Thunhorst et al.
`3/2002
`
`
`
`
`6/2002
`Pozniak
`
`
`7/2002
`Chun et al.
`................. .. 264/28
`
`
`
`
`
`
`
`
`
`
`12/2002
`Kretrnan et al.
`........ .. 428/317.9
`
`
`
`
`4/2003
`Fuda et al.
`
`
`
`5/2005
`...... .. 428/319.3
`Kaminsky et al.
`2/2006
`
`
`
`
`
`Cheng et al.
`........... .. 430/109.3
`3/2007
`Ausen et al.
`................ .. 24/451
`
`
`
`
`
`
`
`
`
`11/2002
`Romar1ko et al.
`
`
`
`.................... .. 264/51
`1/2003
`Tan et al.
`
`
`
`
`
`5,334,359
`
`5,491,015
`46*
`
`5,558,658
`
`5,599,602
`
`5,605,936
`
`5,824,400
`
`6,096,247
`
`6,106,922
`
`6,174,476
`
`
`6,174,930
`
`
`6,280,824
`
`
`6,353,037 B1*
`
`
`6,406,466 B1
`
`
`
`
`
`6,423,252 B1*
`
`
`6,497,946 B1*
`
`6,540,497 B1
`
`
`6,890,642 B2*
`
`
`7,001,702 B2*
`
`
`7,185,401 B2*
`
`
`2002/0162197 A1
`
`
`2003/0011092 A1*
`
`
`
`
`
`US 7,883,769 B2
`Page 2
`
`
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`
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`
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`
`
`
`
`
`Hester et al.
`6/2003
`2003/0104192 A1*
`
`
`
`
`
`Haas et al.
`6/2003
`2003/0105176 A1*
`
`
`
`
`Fontana et al.
`11/2003
`....... .. 248/231.91
`2003/0209642 A1*
`
`
`
`
`
`
`Dotson ..................... .. 428/119
`12/2004
`2004/0253412 A1*
`
`
`
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`
`0892320 A2
`1/1999
`
`98/39759
`9/1998
`99/17630
`4/1999
`
`99/17631
`4/1999
`
`
`WO 99/36466
`7/1999
`WO 99/61520
`12/1999
`
`
`
`WO 00/00520
`1/2000
`
`
`
`00/06974
`10/2000
`WO 02/00412 A2
`1/2002
`
`
`
`
`
`WO 2004/093591
`11/2004
`
`
`
`OTHER PUBLICATIONS
`
`
`Seymour S. Schwartz & Sidney H. Goodman, Plastics Materials and
`
`
`
`
`
`
`Processes, p. 9, Van Nostrand Reinhold Publishing Company, Copy-
`
`
`
`
`
`
`
`
`
`right 1982.
`
`
`
`* cited by examiner
`
`
`
`EP
`W0
`
`W0
`
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`
`
`
`
`
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`
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`
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`
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`EEE>>>>D>D>D>>
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`46**
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`PAGE 2 OF 18
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`PAGE 2 OF 18
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`U.S. Patent
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`Feb. 8, 2011
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`Sheet 1 of6
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`US 7,883,769 B2
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`PAGE 3 OF 18
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`PAGE 3 OF 18
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`U.S. Patent
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`Feb. 8, 2011
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`Sheet 2 of6
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`US 7,883,769 B2
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`PAGE 4 OF 18
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`PAGE 4 OF 18
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`U.S. Patent
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`Feb. 8, 2011
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`Sheet 3 of6
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`US 7,883,769 B2
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`PAGE 5 OF 18
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`PAGE 5 OF 18
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`U.S. Patent
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`Feb. 8, 2011
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`Sheet 4 of6
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`US 7,883,769 B2
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`7
`
`,.«.-Absuasllfifiw-u- -M-pus. - -:gr3'-my
`
`;
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`lfifivm MC
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`IMA(}El6()F‘18
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`PAGE 6 OF 18
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`U.S. Patent
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`Feb. 8, 2011
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`Sheet 5 of6
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`US 7,883,769 B2
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`PAGE 7 OF 18
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`U.S. Patent
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`Feb. 8, 2011
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`Sheet 6 of6
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`US 7,883,769 B2
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`
` V&J4z&4
`
`3:“ 82
`
`
`\\‘..3."*s‘\4A‘»-«'L'»!~-‘$3’.-~'¢.JJ)
`
`
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`85
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`Fig. 15
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`PAGE 8 OF 18
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`PAGE 8 OF 18
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`US 7,883,769 B2
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`2
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`FIG. 6 is a counterexample photomicrograph of a foamed
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`hook formed by a method in FIGS. 1 and 2.
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`FIG. 7 is a photomicrograph of a foamed hook formed by
`
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`a method such as shown in FIG. 3.
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`FIG. 8 is a photomicrograph of a foamed hook formed by
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`a method such as shown in FIG. 3.
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`FIG. 9 is a perspective view of a disposable garment using
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`a breathable hook fastener member according to the present
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`invention.
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`FIG. 10 is a perspective view ofa disposable garment using
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`a hook member according to the present invention.
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`FIG. 11 is a perspective view ofa disposable garment using
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`a hook member according to the present invention.
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`FIG. 12 is a perspective view of a feminine hygiene article
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`using a hook member according to the present invention.
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`FIG. 13 is a breathable hook fastener of the present inven-
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`tion as a self-engaging structure.
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`FIG. 14 is a breathable hook fastener of the present inven-
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`tion used as a body wrap.
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`FIG. 15 is a breathable hook fastener of the present inven-
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`tion used as a body wrap.
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`SUMMARY OF THE INVENTION
`
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`In a first aspect, the invention is directed to an article that
`
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`includes a polymer foam having a surface with surface micro-
`
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`
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`structures. The surface microstructures have at least one
`
`
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`
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`
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`extent or dimension of about 10 microns or more, preferably
`
`
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`
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`50 microns or more, and preferably a maximum extent (un-
`
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`
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`
`
`less it is a continuous rib-like structure) of about 300 microns
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`or less, preferably 200 microns or less, and generally a maxi-
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`mum height of 1000 microns or less, preferably 750 microns
`
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`
`or less and a minimum height of 200 microns or more, pref-
`
`
`
`
`
`
`
`
`
`erably 300 microns or more. The foamed article may be
`
`
`
`
`
`
`
`
`provided in a variety of shapes, including a rod, a cylinder, a
`
`
`
`
`
`
`sheet, etc. In a preferred embodiment where the foam is
`
`
`
`
`
`
`
`
`provided in the form of a sheet, the foam has a pair of major
`
`
`
`
`
`
`
`
`
`surfaces, one or both of which can be provided with surface
`
`
`
`
`
`
`
`
`microstructures. The foam backing and microstructures
`
`
`
`
`
`
`include a plurality of discrete foam cells, which foam cells are
`
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`
`
`
`
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`of a mean size substantially less than the smallest cross-
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`sectional dimension or extent of the microstructures. The
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`foam can be formed by known blowing agents.
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`DETAILED DESCRIPTION OF THE PREFERRED
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`EMBODIMENT
`
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`The shape ofthe foam is dictated by the shape of die and/or
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`the mold surface ifused. Although a variety of shapes may be
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`produced, the foam is typically produced in the form of a
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`continuous or discontinuous sheet having surface microstruc-
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`tures.
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`An extrusion process using a single-screw, double-screw or
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`tandem extrusion system may also be used to form the foam
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`using a blowing agent, e.g., a physical or chemical blowing
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`agent. The temperature and pressure conditions in the extru-
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`sion are preferably sufficient to maintain the polymeric mate-
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`rial and blowing agent as a homogeneous solution or disper-
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`sion. Preferably, the polymeric materials exit the extruder and
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`are foamed at no more than 30° C. above the melting tem-
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`perature of the neat polymer thereby producing desirable
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`properties such as uniform and/or small cell sizes. When a
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`physical blowing agent, such as C02 is used, the polymer is
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`generally initially maintained above the melting temperature.
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`The physical blowing agent (preferably in the supercritical
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`state) is then injected (or otherwise mixed) with the molten
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`polymer and the melt mixture is cooled in the extruder pref-
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`1
`
`INTEGRALLY FOAMED
`
`
`MICROSTRUCTURED ARTICLE
`
`
`
`BACKGROUND OF THE INVENTION
`
`
`
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`This invention relates to preparing extruded articles having
`
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`surface microstructures formed with a microcellular polymer
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`foam. Generally, a polymer foam includes a polymer matrix
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`and is characterized by a density that is lower than the density
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`of the polymer matrix itself. Density reduction is achieved in
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`a number of ways, including through creation of gas-filled
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`voids in the matrix (e.g., by means of a blowing agent). The
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`foam void is of a size less than that of the microstructures.
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`In order to improve the mechanical properties of standard
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`cellular foamed materials, a microcellular process was devel-
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`oped for manufacturing foamed plastics having greater cell
`densities and smaller cell sizes. Such a process is described,
`
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`
`
`for example, in U.S. Pat. No. 4,473,665. The process presatu-
`
`
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`rates the plastic material with a uniform concentration ofa gas
`
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`under pres sure. A sudden induction of thermodynamic insta-
`
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`bility then nucleates a large number of cells. For example, the
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`material is presaturated with the gas and maintained under
`
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`pressure at its glass transition temperature. The material is
`
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`suddenly exposed to a low pressure to nucleate cells and
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`promote cell growth to a desired size, depending on the
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`desired final density, thereby producing a foamed material
`
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`having microcellular voids, or cells, therein. The material is
`
`
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`then quickly further cooled, or quenched, to maintain the
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`microcellular structure. Such a technique tends to increase the
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`cell density, i.e., the number of cells per unit volume of the
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`parent material, and to produce much smaller cell sizes than
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`those in standard cellular structures. The resulting microcel-
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`lular foamed materials that are produced, using various ther-
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`moplastics and thermosetting plastics, tend to have average
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`cell sizes in the range of 3 to 10 microns, with void fractions
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`of up to 50% of the total volume and maximum cell densities
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`of about one billion voids per cubic centimeter of the parent
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`material.
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`Microcellular foamed plastic materials are also described
`
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`in U.S. Pat. No. 4,761,256 which describes a web of plastic
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`material impregnated with an inert gas. The web is reheated at
`
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`a foaming station to induce foaming, the temperature and
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`duration of the foaming process being controlled prior to the
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`generation of the web to produce the desired characteristics.
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`The process is designed to provide for production of foamed
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`plastic web materials in a continuous manner. The cell sizes in
`
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`the foamed material is stated to be within a range of from 2 to
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`9 microns in diameter.
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`U.S. Pat. No. 5,334,359 describes foamed materials which
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`can be of smaller cell sizes, e.g., 1.0 micron or less. The
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`materials also allegedly have a wide range of void fraction
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`percentages from very high void fractions (low material den-
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`sities) up to 90%, or more, to very low void fractions (high
`
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`material densities) down to 20%, or less.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
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`FIG. 1 is a schematic view of a first method for forming an
`
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`extruded foamed hook strip in accordance with the invention.
`
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`FIG. 2 is a schematic view of a further method used in
`
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`forming hook strip in accordance with the present invention.
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`FIG. 3 is a schematic view of a second method for forming
`
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`an extruded hook strip in accordance with the invention.
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`FIG. 4 is an enlarged perspective view of a hook fastener
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`formed by the method of FIG. 3.
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`
`FIG. 5 is a cross-section photomicrograph of a foamed
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`hook formed by a method such as shown in FIGS. 1 and 2.
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`10
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`15
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`20
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`25
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`65
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`PAGE 9 OF 18
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`PAGE 9 OF 18
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`

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`US 7,883,769 B2
`
`3
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`erably to an exit temperature that is less than 50° C. above the
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`melting temperature or Tg of the polymer T<Tm (or Tg)+50°
`C. while the pressure is maintained at or above 1000 psi (13.8
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`MPa), preferably 30° C. while the pressure is maintained at or
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`above 2000 psi. Under these conditions the polymer/blowing
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`agent generally remains in a single phase. As the melt mixture
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`passes through the die the melt foams and expands, generat-
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`
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`ing foams with preferably small, uniform cell sizes. When a
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`chemical blowing agent is used, the blowing agent is added to
`
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`the polymer, mixed, heated to a temperature above the Tm of
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`the polymer to ensure intimate mixing and further heated to
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`an activation temperature of the chemical blowing agent,
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`resulting in generation of gasses. The melt mixture is cooled
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`in the extruder preferably in a manner similar to that used for
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`physical blowing agents. A liquid or solid chemical foaming
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`agent is generally added to the polymer prior to its reaching its
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`molten (Tm) state.
`
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`
`A supercritical fluid foaming agent can be defined as a
`
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`material which is maintained at a temperature which exceeds
`
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`a critical temperature and at a pressure which exceeds a
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`critical pressure so as to place the material in a supercritical
`
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`fluid state. In such state, the supercritical fluid has properties
`
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`which cause it to act, in effect, as both a gas and a liquid. Thus,
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`in the supercritical state, such a fluid has the solvent charac-
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`teristics of a liquid, but the surface tension thereof is substan-
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`tially less than that of a liquid so that the fluid can diffuse
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`much more readily into a solute material, as in the nature of a
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`gas. For example, it is known that carbon dioxide (CO2) can
`
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`be placed in a supercritical state when its temperature exceeds
`
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`31° C. and its pressure exceeds 1100 psi.
`
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`
`When the foam is formed into a microstructured article
`
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`
`
`directly from the extrusion die, the polymer matrices of the
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`invention foams can comprise one or more amorphous poly-
`
`
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`
`
`mers or polymer blends as well as semicrystalline polymer.
`
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`
`
`The polymers may be homopolymers or copolymers, includ-
`
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`
`
`ing random and block copolymers. The amorphous polymers
`
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`have a Tg with the Tg typically an average, (based on the
`weight percent of each polymer in the mixture), of the glass
`
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`
`
`transition temperatures of the component polymers. Suitable
`
`
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`
`
`
`
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`
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`amorphous polymers include, e.g., polystyrenes, polycarbon-
`ates, polyacrylics, polymethacrylics, elastomers, such as sty-
`
`
`
`
`
`
`renic block copolymers, e.g., styrene-isoprene-styrene (SIS),
`
`
`
`
`
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`
`
`
`styrene-ethylene/butylene-styrene
`copolymers
`block
`(SEBS), polybutadiene, polyisoprene, polychloroprene, ran-
`
`
`
`
`
`dom and block copolymers of styrene and dienes (e.g., sty-
`
`
`
`
`
`
`
`
`rene-butadiene rubber
`(SBR)), ethylene-propylene-diene
`
`
`
`
`monomer rubber, natural rubber, ethylene propylene rubber,
`
`
`
`
`
`
`
`polyethylene-terephthalate (PETG). Other examples of
`
`
`
`
`
`
`
`
`
`
`amorphous polymers include, e.g., polystyrene-polyethylene
`
`
`
`
`copolymers, polyvinylcyclohexane, polyacrylonitrile, poly-
`
`
`
`
`
`chloride,
`thermoplastic polyurethanes,
`aromatic
`vinyl
`
`
`
`
`
`epoxies, amorphous polyesters, amorphous polyamides,
`
`
`
`
`acrylonitrile-butadiene-styrene (ABS) copolymers, polyphe-
`
`
`
`
`
`
`
`nylene oxide alloys, high impact polystyrene, polystyrene
`
`
`
`
`copolymers, polymethylmethacrylate (PMMA), fluorinated
`elastomers, polydimethyl siloxane, polyetherimides, amor-
`
`
`
`
`
`
`
`
`
`
`phous fluoropolymers, amorphous polyolefins, polyphe-
`
`
`
`
`
`nylene oxide, polyphenylene oxide-polystyrene alloys,
`copolymers containing at least one amorphous component,
`
`
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`
`
`and mixtures thereof.
`
`
`
`When the microstructured article is formed by contact with
`
`
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`
`
`a mold surface having the microstructures therein the poly-
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`
`mer must be maintained in a molten state following extrusion
`
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`
`
`from the die. Amorphous polymers generally freeze immedi-
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`
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`
`
`
`ately and are not preferred for this process. Semicrystalline
`
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`
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`polymers are preferred. For example, high, medium, low and
`
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`linear low density polyethylene, fluoropolymers, poly(l -
`
`5
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`65
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`PAGE 10 OF 18
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`4
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`butene), ethylene/acrylic acid copolymer, ethylene/vinyl
`
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`acetate copolymer, ethylene/propylene copolymer, styrene/
`
`
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`
`
`butadiene copolymer, ethylene/styrene copolymer, ethylene/
`
`
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`
`
`
`ethyl acrylate copolymer, ionomers and thermoplastic elas-
`tomers such as styrene/ethylene-butylene/styrene (SEBS),
`
`
`
`
`
`
`and ethylene/propylene/diene copolymer (EPDM). Preferred
`
`
`
`
`
`are polyolefins such as polypropylenes or polyethylenes and
`
`
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`
`
`most preferably high melt strength polyolefins, such as
`
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`
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`branched polyolefins. These high melt strength polymers help
`control the growth of the multiple discrete foam cells within
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`
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`the desired range necessary for creating the discrete micro-
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`structures and prevent collapse of the cells during surface
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`microstructure formation ifneeded. Suitable semi-crystalline
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`
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`
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`materials include polyethylene, polypropylene, polymethyl-
`
`
`
`
`
`pentene, polyisobutylene, polyolefin copolymers, Nylon 6,
`
`
`
`
`
`Nylon 66, polyester, polyester copolymers, fluoropolymers,
`
`
`
`
`
`
`
`
`
`poly vinyl acetate, poly vinyl alcohol, poly ethylene oxide,
`
`
`
`
`
`
`functionalized polyolefins, ethylene vinyl acetate copoly-
`mers, metal neutralized polyolefin ionomers available under
`
`
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`
`
`
`
`the trade designation SURLYN (E.l. DuPont de Nemours,
`
`
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`
`
`
`
`
`
`
`
`
`Wilmington, Del.), polyvinylidene fluoride, polytetrafluoro-
`
`
`
`
`
`
`ethylene, polyformaldehyde, polyvinyl butyral, and copoly-
`mers having at least one semi-crystalline compound. Pre-
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`
`
`
`
`
`
`ferred high melt strength polymers are high melt strength
`
`
`
`
`
`
`
`
`
`polypropylenes which include homo- and copolymers con-
`
`
`
`
`
`
`
`taining 50 weight percent or more propylene monomer units,
`
`
`
`
`
`
`
`preferably at least 70 weight percent, and have a melt strength
`
`
`
`
`
`
`
`
`in the range of 25 to 60 cN at 190° C. Melt strength may be
`
`
`
`
`
`
`
`
`conveniently measured using an extensional rheometer by
`
`
`
`
`
`
`extruding the polymer through a 2.1 mm diameter capillary
`
`
`
`
`
`
`
`
`having a length of 41 .9 mm at 190° C. and at a rate of 0.030
`
`
`
`
`
`
`cc/sec; the strand is then stretched at a constant rate while
`
`
`
`
`
`
`
`
`
`measuring the force to stretch at a particular elongation. Pref-
`
`
`
`
`
`
`
`erably the melt strength ofthe polypropylene is in the range of
`
`
`
`
`
`
`
`30 to 55 cN, as described in WO 99/61520.
`
`
`
`
`Such high melt strength polypropylenes may be prepared
`
`
`
`
`
`
`
`by methods generally known in the art. Reference may be
`
`
`
`
`
`
`
`
`made to U.S. Pat. No. 4,916,198 which describes a high melt
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`strength polypropylene having a chain-hardemng elonga-
`tional viscosity prepared by irradiation of linear propylene in
`
`
`
`
`
`
`a controlled oxygen environment. Other useful methods
`
`
`
`
`
`
`
`include those in which compounds are added to the molten
`
`
`
`
`
`
`
`
`polypropylene to introduce branching and/or crosslinking
`
`
`
`
`
`such as those methods described in U.S. Pat. No. 4,714,716,
`
`
`
`
`
`
`
`
`WO 99/36466 and WO 00/00520. High melt strength
`
`
`
`
`
`
`
`
`polypropylene may also be prepared by irradiation of the
`
`
`
`
`
`
`
`
`resin as described in U.S. Pat. No. 5,605,936. Still other
`
`
`
`
`
`
`
`
`
`useful methods include forming a bipolar molecular weight
`
`
`
`
`
`
`
`distribution as described in J1 Raukola, “A New Technology
`
`
`
`
`
`To Manufacture Polypropylene Foam Sheet And Biaxial Ori-
`
`
`
`
`
`
`
`
`ented Foam Film”, VTT Publications 361, Technical
`
`
`
`
`
`
`
`Research Center of Finland, 1998 and in U.S. Pat. No. 4,940,
`
`
`
`
`
`
`
`
`736.
`
`Generally,
`the foamable polypropylenes may comprise
`
`
`
`
`
`
`solely propylene homopolymer or may comprise a copolymer
`
`
`
`
`
`
`having 50 wt % or more propylene monomer content. Further,
`
`
`
`
`
`
`the foamable propylenes may comprise a mixture or blend of
`
`
`
`
`
`
`
`propylene homopolymers or copolymers with a homo- or
`
`
`
`
`
`copolymer other than propylene homo- or copolymers. Par-
`
`
`
`
`
`
`
`ticularly useful propylene copolymers are those of propylene
`
`
`
`
`
`
`
`and one or more non-propylenic monomers. Propylene
`
`
`
`
`
`
`
`copolymers include random, block, and grafted copolymers
`
`
`
`
`
`
`
`of propylene and olefin monomers selected from the group
`
`
`
`
`
`
`
`
`
`consisting of ethylene, C3-C8 ot-olefins and C4-C10 dienes.
`
`
`
`
`
`
`
`Propylene copolymers may also include terpolymers of pro-
`
`
`
`
`
`
`
`pylene and ot-olefins selected from the group consisting of
`
`
`
`
`
`
`
`
`C3-C8 ot-olefins, wherein the ot-olefin content of such terpoly-
`
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`
`PAGE 10 OF 18
`
`

`
`
`
`US 7,883,769 B2
`
`5
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`mers is preferably less than 45 wt %. The C3-C8 ot-olefins
`
`
`
`
`
`
`
`include 1 -butene, isobutylene, l -pentene, 3 -methyl- 1 -butene,
`
`
`
`
`
`
`
`
`
`
`l-hexene, 3,4-dimethyl-l-butene,
`l-heptene, 3-methyl-l-
`hexene, and the like. Examples of C4-C10 dienes include
`
`
`
`
`
`
`
`
`
`
`
`
`
`1,3-butadiene, 1,4-pentadiene, isoprene, 1,5-hexadiene, 2,3
`dimethyl hexadiene and the like.
`
`
`
`
`
`If high melt strength polymers are used, minor amounts
`
`
`
`
`
`
`
`
`
`(less than 50 percent by weight) of amorphous polymers may
`
`
`
`
`
`
`
`be added to the high melt strength polymer. Suitable amor-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`phous polymers include, e.g., polystyrenes, polycarbonates,
`polyacrylics, polymethacrylics, elastomers, such as styrenic
`
`
`
`
`
`block copolymers, e.g., styrene-isoprene-styrene (SIS), sty-
`
`
`
`
`
`
`
`
`
`
`rene-ethylene/butylene-styrene block copolymers (SEBS),
`
`
`
`
`
`polybutadiene, polyisoprene, polychloroprene, random and
`block copolymers of styrene and dienes (e.g., styrene-buta-
`
`
`
`
`
`
`
`diene rubber (SBR)), ethylene-propylene-diene monomer
`
`
`
`
`
`
`
`
`
`
`
`
`rubber, natural rubber, ethylene propylene rubber, polyethyl-
`
`
`
`
`
`
`ene-terephthalate (PETG). Other examples of amorphous
`
`
`
`
`
`polymers include, e.g., polystyrene-polyethylene copoly-
`
`
`
`
`mers, polyvinylcyclohexane, polyacrylonitrile, polyvinyl
`
`
`
`
`
`chloride,
`thermoplastic polyurethanes, aromatic epoxies,
`
`
`
`
`
`amorphous polyesters, amorphous polyarnides, acrylonitrile-
`
`
`
`
`
`butadiene-styrene (ABS) copolymers, polyphenylene oxide
`
`
`
`
`
`
`alloys, high impact polystyrene, polystyrene copolymers,
`polymethylmethacrylate (PMMA), fluorinated elastomers,
`
`
`
`
`
`
`
`
`
`polydimethyl siloxane, polyetherimides, amorphous fluo-
`
`
`
`
`
`ropolymers, amorphous polyolefins, polyphenylene oxide,
`
`
`
`
`
`polyphenylene oxide—polystyrene alloys, copolymers con-
`taining at least one amorphous component, and mixtures
`
`
`
`
`
`
`
`thereof.
`
`In addition to the high melt strength polypropylene, the
`
`
`
`
`
`
`
`
`foam layer may contain other added components such as
`
`
`
`
`
`
`
`
`dyes, particulate materials, a colorant, an ultraviolet absorb-
`
`
`
`
`
`
`ing material, inorganic additives, and the like. Useful inor-
`
`
`
`
`
`
`
`
`
`ganic additives include glass fibers, TiO2, CaCO3, mica or
`
`
`
`
`
`
`
`
`high aspect ratio clays such as wollastonite
`
`
`
`
`
`
`Either a physical or chemical blowing agent may plasti-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`cize, i.e., lower the Tm and Tg of, the polymeric material. With
`the addition of a blowing agent, the melt mixture may be
`
`
`
`
`
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`
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`processed and foamed at temperatures considerably lower
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`than otherwise might be required, and in some cases may be
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`processed below the melt temperature of the polypropylene.
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`The lower temperature can allow the foam to cool and stabi-
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`lize (i.e., reach a point of sufiicient solidification to arrest
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`further cell growth and produce smaller and more uniform
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`cell sizes).
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`Physical blowing agents useful in the present invention
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`may be any materials that are a vapor at the temperature and
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`pressure at which the foam exits the die. A physical blowing
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`agent may be introduced, i.e., injected into the polymeric
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`material as a gas or supercritical fluid. Flammable blowing
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`agents such as pentane, butane and other organic materials
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`may be used, but non-flamrnable, non-toxic, non-ozone
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`depleting blowing agents such as carbon dioxide, nitrogen,
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`water, SF6, nitrous oxide, argon, helium, noble gases, such as
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`xenon, air (nitrogen and oxygen blend), and blends of these
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`materials are preferred because they are easier to use, e.g.,
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`fewer environmental and safety concerns. Other suitable
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`physical blowing agents include, e.g., hydrofluorocarbons
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`(HFC), hydrochlorofluorocarbons (HCFC), and fully- or par-
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`tially fluorinated ethers.
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`Chemical blowing agents are added to the polymer at a
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`temperature below that of the activation temperature of the
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`blowing agent, and are typically added to the polymer feed at
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`room temperature prior to introduction to the extruder. The
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`blowing agent is then mixed to distribute it throughout the
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`polymer in unactivated form, above the melt temperature of
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
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`6
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`the polypropylene, but below the activation temperature of
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`the chemical blowing agent. Once dispersed, the chemical
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`blowing agent may be activated by heating the mixture to a
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`temperature above the activation temperature of the agent.
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`Activation of the blowing agent liberates gas either through
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`decomposition (e.g., exothermic chemical blowing agents
`such as azodicarbonamide) or reaction (e.g., endothermic
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`chemical blowing agents such as sodium bicarbonate-citric
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`acidmixtures), such as N2, C02 and/or H20, yet cell formation
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`is restrained by the temperature and pressure of the system.
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`Useful chemical blowing agents typically activate at a tem-
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`perature of 140° C. or above.
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`Examples of chemical blowing agents include synthetic
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`azo-, carbonate-, and hydrazide based molecules, including
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`azodicarbonarnide, azodiisobutyronitrile, benzenesulfonhy-
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`drazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene
`sulfonyl semi-carbazide, barium azodicarboxylate, N,N'-
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`dimethyl-N,N'-dinitrosoterephthalarnide and trihydrazino
`triazine. Specific examples ofthese materials are Celogen OT
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`(4,4' oxybis(benzenesulfonylhydrazide)). Other chemical
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`blowing agents include endothermic reactive materials such
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`as sodium bicarbonate/citric acid bends that release carbon
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`dioxide. Specific examples include Reedy International Corp
`SAFOAM products.
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`With either a chemical or physical blowing agent, as the
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`melt mixture exits the extruder through a shaping die, it is
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`exposed to the much lower atmospheric pressure causing the
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`blowing agent (or its decomposition products) to expand.
`This causes cell formation resulting in foaming of the melt
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`mixture. When the melt mixture exit temperature is at or
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`below 50° C. above the Tm ofthe neat polymer, the increase in
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`Tm of the polymer as the blowing agent comes out of the
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`solution causes crystallization ofthe polypropylene, which in
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`turn arr