(12) United States Patent
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`Sheppard et al.
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`(10) Patent N0.:
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`(45) Date of Patent:
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`US 6,455,150 B1
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`*Sep. 24, 2002
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`US006455l50Bl
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`............. .. 428/349
`9/1987 Keung et al.
`4,692,379 A
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`. . . .. 428/216
`1/1988 Crass et al.
`. . . . . .
`4,720,420 A
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`: 212:: 6‘ 1,1111111111A 2:22;
`:‘:ZZ1‘€:Z:
`amanoe a.
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`E/I".H°m ettali ““““““
`2
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`4,961,992 A * 10/1990 Ballzlldrrlii) :t
`........ 5 428/332
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`4,966,933 A * 10/1990 Kawakami et 51:55.22... 524/310
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`5,057,177 A
`10/1991 Ballonietal.
`....... .. 156/244.11
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`5,110,671 A *
`5/1992 Balloni et al.
`............ .. 428/218
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`5,169,714 A * 12/1992 Kondo et al.
`............. .. 428/331
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`E13
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`W0
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`FOREIGN PATENT DOCUMENTS
`0 242 055
`10/1937
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`W0 95/15256
`6/1995
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`OTHER PUBLICATIONS
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`Schmitz, Peter et al., “Films.” Ullmann’s Encyclopedia of
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`Industrial Chemistry, 5th Ed., Vol. A11, pp. 85-110, Jan.,
`1988.*
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`* cited by examiner
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`Przmary Exam;/1er—ViVian. Chen
`(74) Attorney, Agent, or Fzrm—Dennis P. Santini; Rick F.
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`James
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`ABSTRACT
`(57)
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`(*9 a“ “PP”
`A hemealable multilayer. film ‘’°mP‘iSi“g:
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`heat-sealable layer comprising (I) an ethylene polymer,
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`t
`1. k d
`t.
`1
`t
`1
`d
`1
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`f1°§‘r’0Z$:r’legugggfufefier0j‘“Sik:(a:ep§:;f;1 aaiilggissalfiicfle
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`P Y
`P
`g
`.
`Y
`Y
`size of from about 0.5 pm to about 20.0 /tm, as a combined
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`slip agent and antiblocking agent: (b) an intermediate core
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`layer comprising a propylene polymer; and (c) a lower
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`heat_Sea1ab1e layer Consisting essentially of
`an ethylene
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`polymer copolymer or
`terpolymer
`(ii) a particulate
`crosslinkied hydrocarbyl-substituted polysiloxane having ei
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`mean particle size of from about 0.5 pm to about 20.0 /tm
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`as a combined slip agent and antiblocking agent; and (iii)
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`from about 0.15 wt% to about 1.5 wt% of a liquid,
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`hydrocarbyl-substituted polysiloxane. The upper heat-
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`1'
`'d
`I bl
`l bl
`l
`d
`t
`t
`'
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`;::y:,,,:,;:’,:,;,;g,:;,:§:,,,::;,,;:;;,g1;,,;,,,;:1;;,
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`transferred from the lower heat-sealable la er
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`‘
`5’
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`17 Claims, N0 Drawings
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`(54) MULTI-LAYER ORIENTED HEAT
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`SEALABLE FILM STRUCTURE OF
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`(76)
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`Inventors: Karen A. Sheppard, 67 Edendery Cir.,
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`Fairpert’ NY (US) 14450’ Jay Ki“
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`K°““g> 6011 A119“ Padgham Rd->
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`MaC€d0H>NY(US)14502;FF311°iS
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`Tran The-Dzuy, 1349 Ayrau1tRd.,
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`Fairport, NY (US) 14450; Joseph E.
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`Brew, 801 East AVe., Newark, NY (US)
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`14513; Benoit Ambroise, Rue de la
`Barriere, 50, B-6792 Halanzy (BE)
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`This patent issued on a continued pros-
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`ecution application filed under 37 CFR
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`155(d)’ and is Subjeet to the twenty year
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`term provlslons of 35 U'S'C'
`patent
`154(a)(2)~
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`(*) Notice:
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`Subject to any disclaimer, the term of this
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`patent is extended or adjusted under 35
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`USC. 154(b) by 0 days.
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`(21) Appl. No.: 08/164,598
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`(22)
`Filed:
`Dec. 9, 1993
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`Int. Cl.7 ....................... .. B32B 27/08, B32B 27/18,
`(51)
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`.
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`B32B 27/32, B32B 31/30
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`(52) U.s. Cl.
`..................... .. 428/327, 428/323, 428/343,
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`428/346, 428/347, 428/349; 428/354, 428/355 EN;
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`428/515; 428/516; 428/523; 156/24411;
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`264/17316
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`Fleld Of Search ............................... ..
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`428/527’ 405’ 515’ 516’ 525’ 557’ 545’
`546’ 547’ 549’ 554’ 555 EN’ 156/24411’
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`264/17516
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`(56)
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`,
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`References Clted
`
`
`Us. PATENT DOCUMENTS
`
`
`
`8/1985 Gust ., ,1.
`..................
`4,533,509 A
`
`
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`
`
`428/215
`6/1986 Crass ct 41‘
`4’595’625 A *
`
`
`10/1986 Doyen ...................... .. 428/213
`4,618,527 A
`3/1987 Crass et al.
`............... .. 428/337
`4,652,489 A
`
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`4/1987 Balloni et al.
`............ .. 428/213
`4,659,612 A
`
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`PAGE 1 OF 8
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`BOREALIS EXHIBIT 1008
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`BOREALIS EXHIBIT 1008
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`PAGE 1 OF 8
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`

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`US 6,455,150 B1
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`2
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`slip characteristics without the adverse appearance, wetting
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`and adhesion effects typically experienced with amide-
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`modified films. However, when laminated to other films,
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`such structures exhibit significantly higher coefficient of
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`friction values and cannot be used in conventional form, fill
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`and seal machines.
`
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`
`U.S. Pat. No. 4,618,527, discloses a biaxially oriented
`
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`film structure comprising (I) a comparatively thick base
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`layer of a thermoplastic resin containing: an antistatic com-
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`bination of (a) a compound of the formula RN(R1)2 wherein
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`R is a C5—C24 alkyl group R1 is H(OCH2CH2)n; n=1—25; and
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`(b) a monoester of an aliphatic C2—C24 fatty acid; and a slip
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`improving proportion of (c) a C12—C24 fatty amide; and (II)
`a comparatively thin surface layer on at least one surface of
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`(I), the surface layer comprising a thermoplastic resin con-
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`taining an anti-block and COF reducing proportion of a
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`finely divided inorganic material. This structure can be
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`laminated to another film such as a polymeric film or a paper
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`film.
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`In U.S. Pat. No. 4,652,489, a sealable, opaque poly-
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`olefinic multilayer film composed of a polypropylene base
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`layer, a non-sealable surface layer, and a sealable surface
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`layer, is disclosed. The. sealable surface layer has a low
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`minimum sealing temperature and is made from a copoly-
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`mer of propylene and ethylene or butene-1 units and/or a
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`terpolymer of ethylene, propylene and butene-1 units. The
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`non-sealable layer
`is a combination of a propylene
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`homopolymer and a slip agent. The base layer contains an
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`additive which is incompatible with polypropylene. The
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`process includes stretching of the film, and during the
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`stretching step, the polymer matrix is torn open around the
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`additive particles to form vacuoles which give the base layer
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`a degree of opacity
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`U.S. Pat. No. 4,659,612 discloses an oriented, polymer
`
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`film laminate possessing a low coefficient of friction, good
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`receptivity for water-based coatings and good optical char-
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`acteristics.
`
`U.S. Pat. No. 4,692,379 discloses an oriented, heat seal-
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`able polymer film laminate possessing a low coefficient of
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`friction, good receptivity for water-based coatings and good
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`optical clarity and a method for manufacturing such a
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`laminate.
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`U.S. Pat. No. 4,720,420 discloses a sealable, transparent
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`polyolefinic multilayer film composed of a polypropylene
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`base layer, a non-sealable surface layer, and a sealable
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`surface layer. The sealable surface layer has a low minimum
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`sealing temperature and is made from a copolymer of
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`propylene and ethylene or butene-1 units and/or a terpoly-
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`mer of ethylene, propylene and butene-1 units. The non-
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`sealable layer
`is a combination of
`a propylene
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`homopolymer, a slip agent, and an anti-blocking agent. The
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`process provided includes coextruding the three layers,
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`biaxially stretching the coextruded film, and subjecting the
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`non-sealable layer to a corona-discharge treatment.
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`U.S. Pat. No. 4,734,317 relates to a polyolefin film having
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`a base layer composed essentially of propylene polymers
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`and having sealing layers present on both sides, composed
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`essentially of sealable olefin polymers. Polydialkylsiloxane
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`is incorporated in a first of the two sealing layers, and this
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`layer is not subjected to corona treatment. The second
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`sealing layer is subjected to corona treatment and has
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`polydialkylsiloxane, not
`incorporated, but present on its
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`the polydialkylsiloxane having been trans-
`outer surface,
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`ferred to this layer by contact with the sealing layer in which
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`polydialkylsiloxane is incorporated. The relative polydi-
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`alkylsiloxane occupancy on the second layer, which is
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`1
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`MULTI-LAYER ORIENTED HEAT
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`SEALABLE FILM STRUCTURE OF
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`IMPROVED MACHINABILITY
`
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`FIELD OF THE INVENTION
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`This invention relates to the field of composite polymer
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`films of reduced surface frictional characteristics and to a
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`method of making such films. It more particularly refers to
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`a biaxially oriented composite film structure having
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`improved properties,
`including heat sealability, good
`machinability and reduced coefficient of friction.
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`BACKGROUND OF THE INVENTION
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`In the packaging of certain types of foods, such as snack
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`foods including candies, potato chips, cookies and the like,
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`it is common practice to employ a multi-layer film. Polypro-
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`pylene films are widely used in the packaging industry due
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`to their superior physical properties, such as, transparency,
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`stiffness, moisture barrier characteristics and others. Despite
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`these highly desirable properties, unmodified polypropylene
`film has the disadvantageous property of having a high
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`inherent coefficient of friction and film-to-film destructive
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`blocking on storage. This high film-to-film coefficient of
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`friction makes polypropylene films difficult to be success-
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`fully employed in automatic packaging equipment in their
`unmodified form.
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`In the past, coefficient of friction characteristics of
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`polypropylene and other thermoplastic films have been
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`beneficially modified by the inclusion in the polymer of fatty
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`acid amides, such as, erucamide and oleamide. The effec-
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`tiveness of this type of material depends upon its ability to
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`migrate to the surface of the film in order to reduce the
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`coefficient of friction. Both of the aforementioned amides
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`are commonly used for reducing coefficient of friction. The
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`development of the desired low coefficient of friction value
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`is strongly dependent upon the type and amounts of amides,
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`and time and temperature aging effects. Even the heat
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`history of the film while in storage and shipping and during
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`subsequent converter processes, significantly affects the
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`coefficient of friction. In addition,
`the presence of these
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`types of fatty acid amides on the film surface results in
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`visible adverse appearance effects, manifested by an
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`increase in haze, a decrease in gloss and the presence of
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`streaks. These materials also adversely effect the wettability
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`and adhesion of solvent and water-based inks, coatings and
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`adhesives.
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`In the case of oriented polypropylene films which are
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`widely used in the food packaging industry, it is common to
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`laminate this film with itself or with other thermoplastic
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`films or with paper films. When oleamide or erucamide are
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`used in the polypropylene films a significant increase in
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`coefficient of friction has been observed after lamination to
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`such films. It
`is theorized that this is due either to the
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`migration of the amide back into the polypropylene film or
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`to the loss of the additive layer at the film surface. Therefore,
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`these types of oriented laminated polypropylene films have
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`limited usage for particular converting processes. Attempts
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`to replace these amides to provide a consistent coefficient of
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`friction have not been successful.
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`In U.S. Pat. No. 4,533,509, there is described a multi-
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`layer structure comprising a comparatively thick base layer
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`of an optically clear thermoplastic resin and a comparatively
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`thin surface layer containing a finely divided inorganic
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`material in a proportion sufficient to thereby impart anti-
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`block characteristics and decrease film-to-film coefficient of
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`friction. The resulting film has non-blocking and improved
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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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`PAGE 2 OF 8
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`PAGE 2 OF 8
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`US 6,455,150 B1
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`3
`determined by means of ESCA spectroscopy, is not more
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`than 15. The three-layer polyolefin film is prepared by a
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`coextrusion process. It is particularly suitable for use as a
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`packaging film on high-speed packaging machines.
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`U.S. Pat. No. 4,764,425 discloses an oriented, heat-
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`sealable polypropylene film which possesses a low coeffi-
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`cient of friction, excellent anti-static behavior and good
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`optical clarity.
`U.S. Pat. No. 4,961,992 relates to a polymer film laminate
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`having improved machinability on modern high speed belt
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`drive machines, particularly when these machines are set up
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`to form lap seals. Amethod of assembling such a film is also
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`provided. The film includes an outside web having-an upper
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`surface layer containing a silicone oil. This laminating web
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`can be used with virtually any co-laminate, metallized or
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`not, which is bonded thereto with an adhesive. Upon wind-
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`ing the composite film laminate upon a core, silicone oil is
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`transferred to the inside surface of the laminates thus pro-
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`viding an inside coefficient friction which is about equal to
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`or less than the outside coefficient of friction. Hot slip
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`properties are also improved upon such transfer. The outside
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`and inside webs are independently formed, which allows the
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`inside web to include coatings or film layers which are not
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`ordinarily usable in a silicone oil-containing film.
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`U.S. Pat. No. 5,110,671 discloses an oriented, multi-layer
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`polymer
`film laminate having a core of isotactic
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`polypropylene, an outside skin layer of isotactic polypropy-
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`lene containing an anti-blocking agent and an inside heat
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`sealable skin layer containing an anti-blocking agent and a
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`coefficient of friction reducing amount of a silicone oil.
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`Despite these advances in the art, a need still exists for a
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`film structure of improved machinability which also pro-
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`vides excellent sealability, strength and stiffness.
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`SUMMARY OF THE INVENTION
`
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`In accordance with the present invention, there is pro-
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`vided a film structure which includes at least one layer of an
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`olefin homo-, co- or ter-polymer having a surface-treated
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`external surface which is printable, sealable and machinable,
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`the layer containing, as combined slip agent and antiblock,
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`a particulate cross-linked hydrocarbyl-substituted polysilox-
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`ane. Particularly preferred particulate cross-linked
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`hydrocarbyl-substituted polysiloxane include the poly-
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`monoalkylsiloxanes.
`Also, a heat sealable multilayer film structure of improved
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`machinability is provided. The film structure comprises an
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`upper heat sealable layer comprising an olefinic homopoly-
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`mer copolymer or terpolymer having a surface-treated exter-
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`nal surface which is printable, sealable and machinable, the
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`layer containing, as combined slip agent and antiblock, a
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`particulate cross-linked hydrocarbyl-substituted
`polysiloxane, an intermediate layer comprising an olefinic
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`polymer, and a lower heat sealable layer comprising an
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`olefinic homopolymer, copolymer or terpolymer having an
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`external surface which is sealable and machinable, the layer
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`containing, as combined slip agent and antiblock, a particu-
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`late cross-linked hydrocarbyl-substituted polysiloxane.
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`A method of producing a-heat sealable multilayer film
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`structure of improved machinability is also provided. The
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`method includes the-step of coextruding a film structure, the
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`film structure including an upper heat sealable layer com-
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`prising an olefinic homopolymer, copolymer or terpolymer
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`having a surface-treated external surface which is printable,
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`sealable and machinable, the layer containing, as combined
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`slip agent and antiblock,
`a particulate cross-linked
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`hydrocarbyl-substituted polysiloxane, an intermediate layer
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`10
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`15
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`25
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`65
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`PAGE 3 OF 8
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`4
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`comprising an olefinic polymer, and a lower heat sealable
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`layer comprising an olefinic homopolymer, copolymer or
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`terpolymer having an external surface which is sealable and
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`machinable, the layer containing, as combined slip agent and
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`antiblock, a particulate cross-linked hydrocarbyl-substituted
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`polysiloxane.
`In practicing the method of the present
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`is particularly preferred to employ as the
`it
`invention,
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`particulate dross-linked hydrocarbyl-substituted polysilox-
`ane a polymonoalkylsiloxane.
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`By improved machinability is meant that the film exhibits
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`a consistently low coefficient of friction and has improved
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`anti-slip and non-blocking characteristics.
`Accordingly, it is an object of the present invention to
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`provide a film structure of excellent sealability.
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`It is another object of the present invention to provide a
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`film structure with improved machinability.
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`It is a further object of the present invention to provide a
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`film structure having an improved range of process oper-
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`ability.
`It is yet another object of the present invention to provide
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`a film which may be bonded to a wide variety of substrates
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`and coatings.
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`It is a yet further object of the present invention to provide
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`a film .structure in which a conventional treatment testing
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`method can be used.
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`Other and additional objects, and the several advantages
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`of the present invention, will become apparent to those of
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`ordinary skill in this art upon a reading of the specification
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`and the claims appended thereto.
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`DETAILED DESCRIPTION OF THE
`
`
`INVENTION
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`In general, the present invention can be practiced with any
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`thermoplastic film, for example, the polyolefins in general,
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`and specifically, polymers, copolymers and blends of
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`ethylene, propylene, butylene, etc., polyesters, such as,
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`polyethylene terephthalate acrylic polymers and copolymers
`and the like. The basic film structures of the present inven-
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`tion find utility when supported or laminated to another film
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`in order to accommodate a particular end use. Thus, polymer
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`film layers different from the intermediate layer can be
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`laminated to the intermediate layer of the structure for
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`particular purposes. Such polymeric films include any ther-
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`moplastic film different from the intermediate layer of the
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`film.
`
`Particularly preferred polymers employed as the interme-
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`diate layer of the film herein are the polypropylenes which
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`are highly isotactic. The preferred polypropylenes are well
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`known in the art and are formed by polymerizing propylene
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`in the presence of stereospecific catalysts system. They can
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`have a melt index at 230° C. ranging from about 0.1—25. The
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`crystalline melting point
`is about 160° C. The number
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`average molecular weight ranges from about 25,000 to
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`100,000. The density ranges from about 0.90-0.91.
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`For descriptive purpose only, the film structures of the
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`present invention will be described as having an upper skin
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`layer (a), an intermediate layer (b) and a lower skin layer
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`As may be appreciated by those skilled in the art, the use of
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`the terms upper and lower to refer to particular skin layers
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`is merely relative. Moreover, although referred to as skin
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`layers,
`the upper and lower layers may have additional
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`structures bonded thereto, based on the functional require-
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`ments of the overall structure.
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`The polymer materials which are contemplated as the
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`material for use in forming skin layers (a) and (c) are
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`PAGE 3 OF 8
`
`

`
`
`
`US 6,455,150 B1
`
`5
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`suitably exemplified by polyolefinic homopolymers, copoly-
`mers and terpolymers. Where homopolymers are to be used,
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`they may be formed by polymerizing the respective mono-
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`mer. This can be accomplished in a conventional manner by
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`bulk or solution polymerization, as those of ordinary skill in
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`this art will plainly understand. The copolymers are exem-
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`plified by and include block copolymers, for example of
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`ethylene and propylene, random copolymers, for example of
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`ethylene and propylene, and other ethylene homopolymers,
`copolymers, terpolymers, or blends thereof.
`
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`Preferred for use in forming upper skin layer (a) and lower
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`skin layer (c) are heat sealable polymeric materials selected
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`from the group consisting of ethylene-propylene-butene-1
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`(EPB)
`terpolymer, ethylene -propylene (EP)
`random
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`copolymer, linear low density polyethylene (LLDPE), low
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`density polyethylene (LDPE), medium density polyethylene
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`(MDPE), high density polyethylene (HDPE) or blends
`thereof.
`
`Suitable EPB terpolymers are those obtained from the
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`random inter-polymerization of from about 1 to about 8
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`weight percent ethylene, preferably from about 3 to about 6
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`weight percent ethylene with from about 65 to about 95
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`weight percent propylene, preferably from about 86 to about
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`93 weight percent propylene, butene-1 representing the
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`balance. The foregoing EPB terpolymers are for the most
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`part characterized by a melt index at 230° C. of from about
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`2 to about 16 and advantageously from about 3 to about 7,
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`a crystalline melting point of from about 100° C. to about
`
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`140° C., an average molecular weight of from about 25,000
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`to about 100,000 and a density within the range of from
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`about 0.89 to about 0.92 gm/cm3.
`The EP random copolymers generally contain from about
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`2 to about 7 weight percent ethylene, the balance being made
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`up of propylene. The copolymers can have a melt index at
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`230° C. generally ranging from about 2 to about 15 and
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`preferably from about 3 to about 8. The crystalline melting
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`point is usually from about 125° C. to about 150° C. and the
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`number average molecular weight range is from about
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`25,000 to 100,000. The density will usually range from
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`about 0.89 to about 0.92 gm/cm3.
`
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`
`In general, where blends of EPB terpolymer and EP
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`random copolymer are used, such blends will contain from
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`about 10 to about 90 weight percent EPB terpolymer and
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`preferably from about 40 to about 60 weight percent EPB
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`terpolymer,
`the balance being made up of EP random
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`copolymer.
`Heat sealable blends of homopolymer which can be
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`utilized in providing layers (a) and/or (c) include about 1 to
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`about 99 weight percent polypropylene homopolymer, e.g.
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`one which is the same as, or different from, the polypropy-
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`lene homopolymer constituting intermediate layer (a)
`blended with about 99 to about 1 weight percent of a linear
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`low density polyethylene (LDPE).
`Prior to extrusion,
`in accordance with the present
`
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`
`
`
`
`
`
`invention, one or both skin layers (a) and/or (c) is com-
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`pounded with an effective amount of a combined antiblock-
`
`
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`
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`ing and slip agent. Preferred combined antiblocking and slip
`
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`
`
`
`
`
`agents are selected from the group of particulate cross-
`
`
`
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`
`
`
`
`
`
`
`
`
`linked hydrocarbyl-substituted polysiloxanes. Particularly
`preferred are the particulate cross-linked polymonoalkylsi-
`
`
`
`
`
`
`loxanes. Most particularly preferred are non-meltable poly-
`
`
`
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`
`
`
`monoalkylsiloxanes characterized as having a mean particle
`
`
`
`
`
`size of about 0.5 to about 20.0 um and a three dimensional
`
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`
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`structure of siloxane linkages. Such materials are commer-
`
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`cially available from Toshiba Silicone Co., Ltd., worldwide,
`
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`
`
`and in the United States from General Electric Co., and are
`
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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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`PAGE 4 OF 8
`
`
`6
`marketed under the tradename Tospearl. Other commercial
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`sources of similar suitable materials are also known to exist.
`
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`
`Although the polymer from which skin layer (a) is formed
`is not compounded with a silicone oil,
`this layer may
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`
`
`
`ultimately acquire a machinability-improving and coeffi-
`
`
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`
`
`cient of friction-reducing amount of silicone oil. Thus, when
`
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`
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`the finished film laminate containing silicone oil on the
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`exposed surface of skin layer (c) is taken up on a winding
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`coil, some of the silicone oil will be transferred from this
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`surface to the exposed surface of skin layer (a), primarily to
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`the exposed surfaces of the combined antiblocking and slip
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`agent particles which protrude from layer (a). However,
`since the interior of layer (a) contains no amount of silicone
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`oil which could interfere with the heat sealing properties of
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`this layer (and ordinarily contains no-silicone oil at all), the
`presence thereon of the transferred silicone oil serves to
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`
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`further enhance the coefficient of friction of the layer,
`
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`improves its machinability, without significantly impairing
`its heat sealability.
`
`
`
`Either or both layers (a) and (c) can also contain pigments,
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`fillers, stabilizers, light protective agents or other suitable
`
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`modifying ingredients if desired. Further, skin layers (a)
`and/or (c) can optionally contain a minor amount of an
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`additional antiblock material, such as silica, clays,
`talc,
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`glass, and the like. These antiblock materials can be-used
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`alone, or different sizes and shapes can be blended to
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`optimize machinability. The major proportion of these
`particles, for example, anywhere from more than half to as
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`high as 90 weight percent or more, will be of such a size that
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`a significant portion of their surface area, will extend beyond
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`the exposed surface of such skin layer.
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`In order to enhance its receptivity for water-based
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`coatings, the upper skin layer can be advantageously treated
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`by flame treating.
`Lower skin layer (c) of the film laminate can be of
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`substantially the same composition as that of upper surface
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`layer (a). In a preferred embodiment, the polymer consti-
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`tuting layer (c) is compounded with a silicone oil. The
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`silicone oil advantageously possesses a viscosity of from
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`about 350 to about 100,000 centistokes with 10,000 to about
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`60,000 centistokes being especially preferred. Examples of
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`suitable silicone oils are polydialkylsiloxanes,
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`polyalkylphenylsiloxanes, olefin-modified siloxane oils,
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`polyether-modified silicone oils, olefin/-polyether-modified
`silicone oils, epoxy-modified silicone oils and alcohol modi-
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`fied silicone oils, polydialkylsiloxanes which preferably
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`have from about 1 to about 4 carbon atoms in the alkyl
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`group,
`in particular polydimethyl-siloxanes. Of the
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`foregoing,
`the polydialkylsiloxanes,
`in particular,
`a
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`polydimethylsiloxane, are preferred for use herein.
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`The silicone oil is added to layer (c) generally in the form
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`of a dispersion or emulsion,
`the silicone being present
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`within, as well as on the exposed surface of this layer as
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`discrete microglobules, frequently of an average size of from
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`about 1 to about 2 microns. The silicone oil, which is
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`generally substantially uniformly distributed on the exposed
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`surface of layer (c), is responsible for improving machin-
`ability and imparting a further reduction in the coefficient of
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`friction to this surface as well as the exposed surface of layer
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`(a) when some of the oil is transferred thereto after these
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`surfaces have been placed in mutual contact, e.g., as will
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`occur when the laminate film has been wound on a winding
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`coil.
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`Polydimethylsiloxane or other silicone oils can be present
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`at from about 0.15 to about 1.5 weight percent, preferably
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`less than 0.5 weight percent, of lower layer Some of this
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`PAGE 4 OF 8
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`US 6,455,150 B1
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`7
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`silicone oil will, of course, be present on the exposed surface
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`of layer
`The amount selected should in any event be
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`sufficient to provide a coefficient of friction of layers (a) and
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`(c) (following transfer of silicone oil microglobules to the
`latter) of about 0.4 or less, preferably between about 0.25 to
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`about 0.3 up to at le